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Influence of lithium oxide as auxiliary flux on the properties of triaxial porcelain bodies
Abstract
The influence of Li2O-content on the properties of standard triaxial porcelains was investigated. Two series of porcelain formulations were produced. The first one comprised seven model formulations with increasing amount of Li2CO3 (1–7wt.%), with respect to the standard triaxial porcelain formulation. The experimental results showed that desirable properties for tableware porcelains can be attained if the Li2O-content does not exceed ∼1.5wt.%. In the light of this conclusion, the second series of formulations aimed at producing new porcelains using Li-bearing natural rocks. Under an industrial perspective, the most important finding is that these compositions matured at temperatures 100–120°C lower than the standard triaxial porcelain formulation and exhibited remarkable resistance at over-firing conditions. The role of increasing Li2O-content at the different stages of firing is interpreted in the light of its influence on densification, the evolution of crystalline phases and microstructure.
... They revealed that spodumene has a lighter atomic weight than Na + and K + , and therefore, it can be used as an alternative fluxing agent [8]. Tulyaganov et al. [9] revealed that Li 2 O addition for tableware porcelain composition should not exceed 1.5 wt% [9]. Because the high Li 2 O content results in industrial problems such as pink colouring and lower bulk density. ...
... They revealed that spodumene has a lighter atomic weight than Na + and K + , and therefore, it can be used as an alternative fluxing agent [8]. Tulyaganov et al. [9] revealed that Li 2 O addition for tableware porcelain composition should not exceed 1.5 wt% [9]. Because the high Li 2 O content results in industrial problems such as pink colouring and lower bulk density. ...
... In this case, large problems arise in the properties of the final product. Tulyaganov et al. [9] showed that Li 2 O addition for tableware porcelain composition should not exceed 1.5 wt% due to the pink colouring of the final product [9]. Since ceramic sanitaryware is white fired products, Li 2 O content was used as a maximum of 0.049 by considering this value stated by Tulyaganov. ...
Raw materials and energy are among the most important costs in ceramic sanitaryware production. With the decrease in raw material sources and increasing costs of energy in recent years, researches on alternative raw materials and energy have started to gain importance. In this study, blast furnace slag and spodumene were used to reduce both energy and raw material costs. In standard vitreous china ceramic sanitaryware, a maximum of 15% blast furnace slag and 4% spodumene was used instead of sodium feldspar. In this study, the effects of CaO, MgO, and Li2O on microstructure, technological properties such as flexure strength, water absorption, porosity, bulk density; and also, thermal properties such as sintering analysis were investigated by using a non-contact optical dilatometer and thermal expansion. The dry strength and flexure strength of fired samples increased. The increase in dry strength was approximately 47%. The increase in flexure strength was approximately 67%. The reduction in the thermal expansion coefficient values was approximately 17%, which is also important in terms of stability of the final product. As a result, the use of blast furnace slag and spodumene will result in a reduction in both energy and raw material costs. The spodumene and BFS provided a reduction in sintering temperature at a rate of approximately 60 °C. The flue gas emissions may also reduce because flue gas emissions are higher as the temperature inside the furnace is higher. The spodumene and blast furnace slag addition provide a decrease in the peak of sintering temperatures so that flue gas emissions will reduce.
Graphic Abstract
... The development of needle-shaped long mullite crystals in all directions forms three-dimensional interlocking networks, strengthens the porcelain, and reduces plastic deformation [6,7]. Spodumene as a lithium aluminosilicate source can be added porcelain compositions to enhance mullite formation [8]. Sodium and potassium feldspars are the main sources of fluxing agents in the porcelain compositions [9]. ...
... Spodumene mineral as a source of Li which has a lighter atomic weight than Na and K can be an alternative fluxing agent for porcelain compositions. There are many studies in the literature reporting the use of spodumene in porcelain compositions [8,[10][11][12][13]. Cowen et al. 1950 reported that the ratio of feldspar to spodumene of 70:30 reduces firing temperature of sanitaryware porcelain. ...
... Cowen et al. 1950 reported that the ratio of feldspar to spodumene of 70:30 reduces firing temperature of sanitaryware porcelain. Tulyaganov et al. (2006) worked on tableware porcelain and reported that Li 2 O addition to composition should not exceed 1.5 wt%. Also, they observed that the recipes including Li 2 O matured 100-120°C earlier than standard recipe. ...
Pyroplastic deformation tendency of vitreous body compositions is a major production problem. In this work, a vitreous sanitaryware body composition (ST) which was developed in a previous work was taken as standard, and the sodium feldspar content of this recipe was changed with spodumene as a source of Li2O. Six different compositions were formulated by applying two different approaches: weight percent formulation and Seger formulation. Bodies were fired at 1250 °C and after firing deformation, firing shrinkage, and water absorption values were measured. Pyroplastic deformation behavior of bodies was determined by using fleximeter with a peak temperature of 1250 °C. According to the results, it was observed that spodumene addition with Seger formulation gives better results than weight percent formulation. The body which contains 0.1 mol% of Li2O (L2 body) has deformation value which is 11% lower than that of standard body due to its different phase composition and microstructure than ST body.
... Porcelain tiles are sintered by fast single firing up to 60 minutes cold-to-cold, 1200-1250 o C of peak firing temperature and 5-10 minutes of soaking time [4]. As a result of sintering process phase final composition consist of crystalline phases, both new formed (mullite) and residual ones (quartz and feldspars) embedded in an abundant glassy matrix [5]. ...
... The main standard requirement for porcelain stoneware is a very low water absorption (0.5% according to TS EN 13006) that is largely fulfilled, being < 0.1% in the products. In industrial firing process, a residual closed porosity cannot be completely removed-ranging usually from 2 to 8%-consisting of both small <10 μm and spherical, gas-filled pores and irregularly shaped, coarser pores probably due to coalescence of smaller ones [5]. ...
... In general, the Li 2 O-Al 2 O 3 -SiO 2 systems are well known for their low or even negative thermal expansion coefficients. As a result, much more effort has been directed at producing ceramics which contain eucryptite (LiAlSiO 4 ) and spodumene (LiAlSi 2 O 6 ) with relatively high content of Li 2 O. Tulyagonav et al have investigated influence of Li 2 O doping on non-isothermal evolution of phases in K-Na-containing aluminosilicate matrix and influence of lithium oxide as auxiliary flux on the properties of triaxial porcelain bodies [5,7] In the light of this conclusion, the second series of formulations aimed at producing new porcelains using Li-bearing natural rocks. Under an industrial perspective, the most important finding was that these compositions matured at temperatures 100 o -120 o C lower than the standard triaxial porcelain formulation and exhibited remarkable resistance at over-firing conditions. ...
Lithium aluminosilicates, such as spodumene, have been used as raw materials in the production of thermal shock resistant whiteware and sanitaryware. The presence of spodumene causes enhancement of mullitization and imparts better physical and mechanical properties to ceramics. In this study, the influence of Li2O-content on the properties of a standard porcelain stoneware body was investigated. Sodium feldspar was replaced by the spodumene in varying amounts (up to 4 wt. %). The results showed a significant microstructural improvement, the presence of spodumene which, during firing, allows the development of a low viscosity liquid phase with a decrease of closed porosity, also with increasing bulk density and bending strength.
... The use of lithium-bearing minerals as a liquid-phase sintering aid has been investigated in various ceramics, to reduce the firing temperature or to improve the thermal-shock resistance of the ceramics [10][11][12][13][14][15]. The effects of CaO-Li 2 O-K 2 O-Na 2 O as fluxing agents in porcelain ceramic tiles was discussed by Zhou et al. [16], who showed that a multicomponent eutectic system can produce a liquid phase at a lower temperature. ...
... This study performed two series of experiments. In the first series, the LO was added to the mixtures as a replacement for feldspar, and these samples were designated S10, S20, S30, S40, and S50, which represent the percentage of feldspar that was replaced, i.e., 10,20,30,40, and 50 wt.%, respectively. ...
... Consequently, the use of new alternative sources as fluxing agents needs to be investigated in detail. Relevant studies have already been reported in the literature regarding to this problem [6][7][8][9][10][11][12][13][14][15]. Besides the use of natural resources as feldspar source in the body formulations, the use of waste materials as flux-forming additives has also been extensively investigated [16][17][18][19][20][21][22][23][24][25]. ...
... Obtained slips were first allowed to dry, then sieved down to 1 mm and humidified (5)(6) wt. % moisture content) in order to obtain suitable powders for pressing. ...
The possible use of trachyte as an alternative fluxing agent in a commercial floor tile body was investigated. The experiments were carried out in two parts: In the first part, standard tests were applied to the products obtained from the experimental tile bodies modified with varying amounts (0-40 wt. %) of non-magnetic trachyte following single fast-firing under industrial conditions. The results indicated that 20 wt. % of trachyte (TRA2 formulation) as a substitute of albite completely and pegmatite partially in the standard formulation (STD) was satisfactory to carry out further experiments. In the second part, both STD and TRA2 formulations were further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. Consideration was also given to the phase and microstructural evolution of the tile bodies using x-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with energy dispersive x-ray spectroscopy (EDS), respectively. The preliminary results showed that it was possible to incorporate trachyte into a floor tile formulation as a fluxing agent and to obtain meaningful technological properties.
... Consequently, the use of new alternative sources as fluxing agents needs to be investigated in detail. Relevant studies have already been reported in the literature regarding to this problem [6][7][8][9][10][11][12][13][14][15]. Besides the use of natural resources as feldspar source in the body formulations, the use of waste materials as flux-forming additives has also been extensively investigated [16][17][18][19][20][21][22][23][24][25]. ...
... Obtained slips were first allowed to dry, then sieved down to 1 mm and humidified (5)(6) wt. % moisture content) in order to obtain suitable powders for pressing. ...
The possible use of trachyte as an alternative fluxing agent in a commercial floor tile body was investigated. The experiments were carried out two parts: In the first part, standard tests were applied to the products obtained from the experimental tile bodies modified with varying amounts (0-40 wt. %) of non-magnetic trachyte following single fast-firing under industrial conditions. The results indicated that 20 wt. % of trayte (TRA2 formulation) as a substitute of albite completely and pegmatite partially in the standard formulation (STD) was satisfactory to carry out further experiments. In the second part, both STD and TRA2 formulations were further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. Consideration was also given to the phase and microstructural evolution of the tile bodies using x-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with energy dispersive x-ray spectroscopy (EDS), respectively. The preliminary results showed that it was possible to incorporate trachyte into a floor tile formulation as a fluxing agent and to obtain meaningful technological properties.
... Such fluxes give rise to a viscous liquid phase, which plays a key role in the consolidation of ceramic bodies. Because of their low water absorption and good mechanical resistance [2][3][4][5], vitreous ceramic bodies are extensively used as table wares and sanitary objects, and have been the subject of numerous studies [6][7][8][9][10][11][12][13]. ...
... Considering the acceptable values for water absorption (≤ 1.5%) and firing shrinkage (≤ 13%) for whiteware bodies [2,3,5,6,8] and using the desirability function [30], the acceptable domains for both properties relevant to different combinations of the operating parameters were established (white domains in Fig. 5). Globally, it can be deduced that for: ...
Microstructure of vitreous ceramic samples manufactured from kaolinitic-clay and feldspars raw materials from Cameroon was investigated in the range 1150–1250 °C by X-ray diffraction and scanning electron microscopy and by measuring some technological properties. Moreover, the simultaneous influence of feldspars content, heating temperature and soaking time on water absorption and firing shrinkage was evaluated by adopting the response surface methodology (Doehlert matrix), using the New Efficient Methodology for Research using Optimal Design (NEMROD) software. The results show that a spinel phase, mullite, glassy phase and some amount of hematite were formed. However, the spinel phase and potassic feldspar, as compared to the sodic one, disappeared at moderate firing temperature and soaking time. Apparently, mullite developed from spinel phase, which is formed from the demixion of metakaolin. On the other hand, it is found that the effects of fluxing content and firing temperature on the measured properties were almost similar and more influent than soaking time. Antagonistic and synergetic interactions existed between the considered parameters, and their importance differed for the considered properties. By using this mathematical tool, suitable operating conditions for manufacturing vitreous bodies were determined.
... This may be achieved by adopting fast firing cycles and using fluxes. Many studies on the use of fluxing agents in the production of ceramic products for reducing the firing temperature have been reported [6][7][8][9][10]. For the firing cycle, there is also much literature on the effect of temperature and soaking time on the ceramic properties [11][12][13][14]. ...
Four mixtures of kaolinite clay and feldspar (Western-Cameroon) were prepared and sintered at 1200 • C for 2 h at the heating rate of 5 • C/min, 10 • C/min, 15 • C/min and 20 • C/min. The main new crystalline phase was mullite associated with quartz, anatase and cristobalite for all heating rates. By increasing the feldspar content, both the amounts of mullite and of glassy phase increase which promotes the densification of the samples. Heating rate has less influence on the formation of new mineral phases, while this process is sensitive to flux content. Both heating rate and flux content have an effect on the microstructure of the fired bodies as well as technological properties. The specimens with 30% feldspar content sintered at 1200 • C from 5 • C/min to 20 • C/min exhibited water absorption values <10% and bending strength >12 MPa. These materials are suitable as wall tiles. Thus, these samples can be sintered at a heating rate of 20 • C/min instead of 5 • C/min which leads to a saving in firing time and in energy
... The occluded pores contain gases from the release of product reactions or even from the firing atmosphere, which exerts pressure on the pore walls, opposing densification [1,9,16]. In the industrial firing process, closed pores cannot be eliminated entirely (remain between 2 and 8%), and both small spherical pores (< 10 μm) and irregularly shaped coarse pores (> 10 μm) remain in the microstructure [17]. Nevertheless, at the high temperatures (> 1200 °C), the gas pressure of the occluded pores is high and counteracts capillary pressure, causing the bloating of the tile body. ...
In this study, the possibility of using calcined-colemanite as an alternative fluxing agent in a body mixture used for porcelain tile was investigated. For this aim, a part of industrial spray-dried powders was replaced with the colemanite calcined by microwave-assisted heating (MACC) in varying amounts (up to 3 wt. %). The tile compositions prepared with different proportions of MACC addition were pressed uniaxially at 15 MPa, and the shaped tiles were then fired at 1220 °C for 50 min in an industrial roller kiln. Physical and mechanical tests, X-ray diffractometer (XRD), and scanning electron microscopy (SEM) analyses were performed to examine the effects of MACC addition on porcelain tile’s technical properties and phase development. The results revealed that the porcelain tiles having 0.5 wt. % of MACC had better technical properties, i.e., lower water absorption (0.09%) and porosity (0.22% for apparent porosity and 7.25% for closed porosity), and higher bending strength (66.04 MPa) than that of others. Consequently, the MACC addition promoted a low-viscosity liquid phase during firing, resulting in a significant microstructural improvement by decreasing the closed porosity and increasing the bulk density and flexural strength.
... In some ceramic recipes, fluxes other than feldspar are used such as: frit, alkali, alkaline earths, ZnO, TiO 2 , MnO, Li 2 O, B 2 O 3 and zirconium compounds. These co-fluxing materials lower the maturing temperature and increase the glassy phase content that play a role in improving the optical properties of the fired bodies [1][2][3][4][5][6][7][8][9][10][11]. K.Spirov et al. [7] reported that improved properties, such as density, whiteness, and translucency etc. of the porcelain were achieved by addition of boric-zirconium compounds. ...
The influence of adding 2 mass % LiF or B 2 O 3 as co-flux on phase composition and optical properties of ceramic batches to the system: clay, quartz sand and K-feldspar was investigated. The content of clay was kept constant at 40 mass %, while quartz was added in the range between 10...40 mass % at the expense of K-feldspar. The main phases detected in the fired bodies were mullite,ß-eucryptite, quartz with traces of cristobalite and microcline. The results indicate that the light absorption coefficient in the visible range depends mainly on the type of co-flux added. The borate bodies with increasing quartz content showed a reduction in the absorption coefficient at short and long wavelengths. The scattering coefficient on the other hand increases with the wavelength in the same range. This may be attributed to the amount, size and shape of mullite crystals formed in the borate bodies. The degree of whiteness was slightly improved by LiF addition. The hue for all samples was light blue, except for Li-bodies containing 10 mass % quartz which showed light yellow.
... Although total porosity increased, bulk density and bending strength increased. The decrease in the viscosity of liquid phase due to the addition of spodumene resulted in a rising up in densification rate [7][8][9][10]. The decrease in the viscosity also resulted in an increase in the amount of mullite crystals [11]. ...
New production systems developed in recent years made it possible to improve
different aesthetic appearance and large sizes for porcelain stonewares. In
order to produce these tiles, optical and mechanical properties of the
porcelain stonewares should be improved. Optical and mechanical properties
also related with microstructure. In this study, spodumene, alumina and
zircon were used to improve the microstructure of the porcelain stonewares
and consequently their optical and mechanical properties. The wear
resistance of porcelain stonewares is the one of the most important
mechanical properties. In this study, a different test method was used
because the existing wear test methods on the tiles were insufficient. The
solid particle impingement method using alumina particles was used to
determine wear resistance of the porcelain stoneware bodies.
... Quartz is partially added to reduce pyroplastic deformation [2]. Due to the high firing temperature (>1,200 o C for soft porcelain and 1,400 o C for hard porcelain), flux-forming additives were generally employed in order to reduce the energy consumption without compromising productivity and product [3][4][5][6]. Some of the reported works are exemplified here. ...
... Based on the literature [7][8][9][10][11][12], wollastonite and spodumene were chosen as the energetic fluxes that were introduced in a standard composition (STD). The effects of these additions were estimated through the Fluegel's model [1] and the predictions were compared with the experimental results. ...
Reducing the firing temperature and accelerating the densification process bring economic and environmental benefits. This study used Fluegel’s viscosity model, developed for glasses, to estimate the decrease of the firing temperature produced by the introduction of energetic fluxes in a porcelain body. The experimental results confirmed the prediction of the model, a 30 ºC reduction in the temperature, for the addition of wollastonite. However, for the addition of spodumene, the reduction was slightly higher than the predicted. These results suggested that Fluegel’s model may be used to estimate the effects of the introduction of energetic fluxes in porcelain tile compositions. However, the predictions should be seen as a general orientation. Among the limitations of the model were the extrapolation of limit values established by the model for the composition and, above all, the initial hypothesis that the chemical composition of the vitreous phase in porcelain tiles is constant.
... The use of lithium-bearing minerals as a liquid-phase sintering aid has been investigated in various ceramics, to reduce the firing temperature or to improve the thermal-shock resistance of the ceramics [10][11][12][13][14][15]. The effects of CaO-Li2O-K2O-Na2O as fluxing agents in porcelain ceramic tiles was discussed by Zhou et al. [16], who showed that a multicomponent eutectic system can produce a liquid phase at a lower temperature. ...
Porcelain tiles are a building material that has been widely used in recent years and that consumes substantial resources during the sintering process. This study reports on the production of low-temperature porcelain tiles by using low-grade lithium ore (LO) and silica crucible waste (SCW) in a new SiO2–Al2O3–Na2O–K2O–Li2O system. The firing temperature of the porcelain tiles was reduced from 1260 °C to 1070 °C by adding 30% LO instead of feldspar in a modified triaxial ceramic body, and SCW was recycled and used as a raw material. These actions help to reduce the carbon emissions produced during sintering and achieve sustainable development. The effect of phase transitions on the sintering and technological properties of the porcelain tiles was studied by quantitative phase analysis, using X-ray diffraction (XRD). Secondary mullite (0–19%) can be formed at 1040–1100 °C, where more quartz and cristobalite will be retained, which increases the rupture modulus of the porcelain tiles. While the vitreous phase increases rapidly at 1100–1160 °C, the closed pores (0.1–33.1%) will simultaneously expand, causing a decrease in compactness. The results show that low-grade LO (with a cost similar to that of feldspar) allows for the production of porcelain tiles with better process performance at lower temperatures (≤1100 °C).
... Their structures are listed in Table I. In our calculations, the ordinary ambient-pressure phases, Pnnm LiO 2 , P6 3 /mmc Li 2 O 2 , and F m-3m Li 2 O are successfully reproduced and their crystal structures are consistent with previous experimental and theoretical works [10,12,14,[30][31][32][33][34][35]. For other theoretically predicted phases, such as P-6m2 Li 3 O 4 , our calculations (taking great care for the precision and quality of the PAW potential) indicate metastabilty. ...
We study the stability of Li-O compounds as a function of pressure, with rich phase diagram, diverse properties, and fundamental chemical interest in mind. Using the ab initio evolutionary algorithm USPEX, we predict the stability of compounds LiO4, Li5O3, and Li6O under pressure. Unexpectedly, LiO2 will decompose to Li2O2+LiO4 in the pressure range 6–18 GPa. LiO4, formed at the pressure of just 6 GPa, can be seen as ɛ−O8 accepting two electrons from two Li atoms. This phase is superconducting, with Tc up to 12.2 K at 10 GPa. This is remarkable, because elemental oxygen becomes superconducting at much higher pressure (96 GPa) and has much lower Tc (<0.6 K), and suggests that chemical alloying with other elements has the potential of not only decreasing metallization pressure, but also of increasing Tc. Since ɛ−O8 is called red oxygen, LiO4 can be identified as “lithium red-oxide”, and is distinct from superoxide. Additionally, Li5O3 is stable at pressures above 70 GPa and can be represented as a hybrid structure 4Li2O·Li2O2, and electride suboxide Li6O is stable above 62 GPa.
... It was found that the use of 0.5-2% boric acid added samples as a fast single firing wall tile is suitable [2]. The addition of 0.4-0.5% ulexite was found to shorten the grinding time, increase dry strength and reduce the firing temperature [3].In the porcelain tiles with boric acid addition, the amount of B2O3 increased to 0.5-1%, the firing temperature of 15 0 C and 28 0 C was observed respectively [4].It was observed that the desired results were obtained in the conditions where the addition of lithium oxide to the porcelain body did not exceed 1.5% [5].According to Yet & Kara [6] and Cigdemir et al. [7], rheological problems caused by boric acid addition in slip can be solved by electrolyte addition. ...
The aim of this study was to determine the effect of boric acid and lithium carbonate on microstructure and sintering characteristics of wall tile after firing. Amount of Li2 (CO3) (0.1-0.3-0.6- 0.9-1.2-4 wt.%) were added in wall tile corresponding to each constant amount of added of H3BO3 (0.1-0.3-0.6-0.9-1.2-2 wt.%). All samples were fired in 1135 0C 35 minutes in an industrial fast firing kiln. Dry strength, fired strength, water absorption and colorimeter values of all samples were determined after firing. Scanning electron microscope (SEM), x-ray diffraction (XRD) analysis, optical dilatometer measurements were performed in order to determine the microstructure and melting temperature for prescribed purpose (1-2-7-8-11-32-37). Standard (1) and alternative (8) receipe’s thermogravimetric and diferantial thermal analyses were performed. 37 (2% H3BO3 + 4% Li2 (CO3) recipe’s sintering starting temperature was 984 0C. In the recipe 8 (0.3% H3BO3 + 0.1% Li2(CO3) is an alternative to the standard wall tile, which can be used with higher strength values.
... Porcelains are vitrified product consisting of ternary mixture of clay (generally kaolin) for plasticity, feldspar (generally) for fluxing, and quartz (generally) as a filler raw material [1][2][3][4][5][6][7]. Porcelains are generally classified according to the firing temperature. ...
This investigation is reported the effects of perlite addition on the properties of hard porcelain glazes. Five compositions were prepared containing 10, 25, 50, and 90% perlite addition. The glaze compositions were formulated using the Seger method and prepared by conventional porcelain processing. Chemical and microstructural characterization of materials prepared from representative samples were carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques, respectively. The melting test, color measurement test, thermal shock resistance test (Harkort test), autoclave test, and chemical resistance tests were done to all of the glazed samples. As a result of this study, it has been shown that addition of 10% perlite mineral can be utilized as an alternative fluxing raw material for production of the hard porcelain glaze.
... This may be achieved by adopting fast firing cycles and using fluxes. Many studies on the use of fluxing agents in the production of ceramic products for reducing the firing temperature have been reported [6][7][8][9][10]. For the firing cycle, there is also much literature on the effect of temperature and soaking time on the ceramic properties [11][12][13][14]. ...
Four mixtures of kaolinite clay and feldspar (Western-Cameroon) were prepared and sintered at 1200 °C for 2 h at the heating rate of 5 °C/min, 10 °C/min, 15 °C/min and 20 °C/min. The main new crystalline phase was mullite associated with quartz, anatase and cristobalite for all heating rates. By increasing the feldspar content, both the amounts of mullite and of glassy phase increase which promotes the densification of the samples. Heating rate has less influence on the formation of new mineral phases, while this process is sensitive to flux content. Both heating rate and flux content have an effect on the microstructure of the fired bodies as well as technological properties. The specimens with 30% feldspar content sintered at 1200 °C from 5 °C/min to 20 °C/min exhibited water absorption values <10% and bending strength >12 MPa. These materials are suitable as wall tiles. Thus, these samples can be sintered at a heating rate of 20 °C/min instead of 5 °C/min which leads to a saving in firing time and in energy.
... The bands in the region 775-1150 cm −1 were attributed to B-O vibrations in the [BO 4 ] tetrahedral [17], the bands in the region 1150-1600 cm −1 may be related to vibrations of B-O in the [BO 3 ] triangle [18] and the bands at ∼630-775 cm −1 were attributed to bending vibrations of bridging oxygen between trigonal boron atoms [19]. The two small bands at 475 and 555 cm −1 may be attributed to the vibrations of some type of borate segments and to the bending vibrations of Si-O-Si linkages [20]. ...
In this work, new glasses were synthesized from wastes of limestone and phosphate rocks besides commercial borax. The glasses were characterized by FTIR, DTA, ultrasonic techniques and UV spectroscopy. It was found that the concentration of both CaO and P2O5 increases and the concentrations of B2O3 and Na2O decrease as the content of phosphate rocks increases. Variation of the contents of the different oxides affects the concentration of the structural units constituting the glass, which was indicated by the behaviour of the fraction N4 of BO4 units in the borate matrix. The density and the refractive index of the glasses decrease as the CaO and P2O5 contents increase, which was attributed to the increase of [BO3] structural units. On the other hand, the physical parameters such as the ultrasonic velocity, the elastic moduli, the optical bandgap and the optical polarizability increased, which was attributed to the higher coordination number of CaO6 compared with the coordination of borate structural units and to the former effect of P2O5. As a result, a polymerization of the total co-ordination number of the glass, crosslink density and connectivity within the glass network will occur.
... The major energy consumption during manufacturer of porcelains and other ceramics occurs during the firing process [14]. Hence, efforts have been made to lower the total energy consumption by modifying the heating ramps and chemical compositions [5,[15][16][17][18]. The term " fast firing " was introduced to ceramic production in 1965 [19]. ...
Most of the energy consumed during the processing of porcelains is accounted by the heating rate, dwell time and cooling rate employed. Efforts are made in this study to lower the total energy consumption, and thereby total emissions, by optimizing the porcelain processing parameters. Porcelain samples processed at 5, 15 and 30 °C/min heating rates were compared with samples processed under direct sintering. X-ray diffraction and microstructural characterisation confirmed that the phase evolution, such as mullite formation in the porcelain, is heating rate independent while glass formation is heating rate dependent, and directly sintered porcelain had physical and mechanical properties comparable to conventionally heat-treated samples. Direct sintering reduced total processing time by ∼50% and also lowered the sintering temperature from 1200 °C to 1175 °C, suggesting that the direct sintering method provides benefits meaning it may in future replace conventional porcelain processing.
... Thus, ceramic industry is continuously searching for more economical raw materials in order to replace the traditional fluxes without altering the process and product characteristics. Relevant studies have already been reported extensively in the literature [3][4][5][6][7][8] . Densification process of triaxial bodies proceeds by viscous phase sintering, with the development of a liquid phase that flow by capillary pressure, in interconnected voids amongst the particles, causing the development of a ceramic bonding, constituted by new crystalline phases and part of the residual crystals such as quartz in a glassy matrix. ...
The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. ln addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
... Commercially, lithium oxide is used as an auxiliary flux to decrease the processing temperature of ceramics such as porcelains [26]. It was thus expected that the sintering temperature for lithium-containing bioactive glasses would be lower than that of 45S5 Bioglass®. ...
Incorporation of therapeutic ions into the structure of bioactive glasses for direct stimulation of cells is a very attractive approach for tissue engineering strategies. Lithium has recently been identified as a biologically active ion which can stimulate osteoblast cell activity. In this study, lithium-containing bioactive glasses (Li-BGs) where Li2O substitutes Na2O in different amounts (2.5, 5 and 10 wt.% Li2O) in 45S5 bioactive glass (BG) were produced and made into 3D scaffolds by the foam replica method. The structural changes that occur after heat treatment, the effect of lithium-content on the bioactivity of the glasses and their lithium ion release profiles were investigated. The results show that the novel Li-BG formulations exhibit the formation of an apatite-like layer on their surface after immersion in SBF for 1 day thus confirming their high surface reactivity, similar to undoped 45S5 BG. XRD results showed that the Li-doped BGs crystallize mainly to combeite (Na2Ca2Si3O9) and silicorhenanite (SiO4(PO4)2Ca5) but also Li6P6O18 and Li3PO4 phases were detected. In terms of lithium ion release, the formulations at 2.5 wt.% and 5 wt.% Li2O content were the only ones to be within the therapeutic range (< 8.3 ppm).
... Commercially, lithium oxide is used as an auxiliary flux to decrease the processing temperature of ceramics such as porcelains [26]. It was thus expected that the sintering temperature for lithium-containing bioactive glasses would be lower than that of 45S5 Bioglass®. ...
Bioactive glasses were invented 45 years ago and have been in clinical use since the 1980s in otology, orthopaedics and dentistry. Initially born as bioactive materials to fill bone defects, bioactive glasses expanded their biomedical suitability towards a broad spectrum of tissue engineering and therapeutic applications, and research evolution seems to witness that their potential is far from being fully exploited. Classical applications of bioactive glasses involve bone filling materials and dental implants; however, the fascinating question to be answered in the next few years is: how can bioactive glasses be useful in soft tissue regeneration and to treat diseases, such as tumours, that may affect internal organs? This review paper focuses on research that demonstrates the suitability of bioactive glasses in contact with tissues outside the skeletal system, including muscle and nerve tissue regeneration, treatment of diseases affecting sense organs (eye and ear), embolization of neoplastic tissues, cancer radiotherapy via injectable microspheres, and wound dressing. A prospect for future research is also provided, highlighting the potential associated to targeted therapy via local ion release, angiogenesis stimulation and in situ drug release, as well as the promise of biofabrication for the development of bioactive glass-containing composite constructs for organ regeneration.
... Porcelain, the foundation of the ceramic industry, is composed mainly of fine-grained clay (commonly plastic kaolin), fluxes (normally feldspar) and a filler (usually quartz) which is heat-treated to form crystalline and glassy phases [1][2][3][4][5][6][7]. Researchers have found that porcelain matrix results in a remarkable increase in mechanical strength with partial or complete substitution of silica by alumina and these types of porcelains can be used for engineering aspects [8,9]. ...
A mullite-reinforced porcelain composite with antibacterial properties has been developed using transition metal oxides by solid state sintering. The composite has been characterized in terms of mullite content, hardness, color and antibacterial properties. The physico-chemical properties of the porcelain were substantially increased in the presence of V2O5 and CuO. Well-crystallized needle shaped mullite of average length ∼ 3 μm was observed in the porcelain body at 1300 °C and 1500 °C after the addition of V2O5 and CuO. Vickers hardness of the composite increased 4.2 times for 2% V2O5 at 1500 °C. The porcelain composites showed satisfactory antibacterial activity on gram negative bacteria Escherichia coli with mortality rates of 45% and 22% for V2O5 and CuO doped porcelain respectively.
... Porcelanas triaxias foram analisadas, empregando-se, primeiramente, carbonato de lítio e, num segundo momento, rochas contendo espodumênio. Os autores conseguiram uma redução de 100-120 ºC na temperatura de gresificação e concluíram que os teores de Li 2 O não devem exceder ~1,5%, para não se perder em densificação das peças [14]. O uso de espodumênio, com aporte de 1 a 1,6% de Li 2 O à massa, mostrou-se benéfico para produção de porcelanas de alta alumina, com ganho de densificação, resistência mecânica e diminuição da temperatura de queima [15]. ...
A spodumene rock was used as a flux in ceramic bodies, analyzing its reactivity to other raw materials such as quartz and kaolin. The petrology properties of the pegmatite (parent rock) from which the flux is extracted was characterized. The grindability, fluxing strength and pyroplastic deformation of the spodumene rock were investigated. The influence on technological properties of the final pieces, mainly in relation to the firing temperature, phases formation and microstructure were also further analyzed. The firing behavior to other commercial flux such as albite and feldspar were then compared. The spodumene rock was considered an effective flux, capable of reducing the firing temperatures of the tested bodies by viscous flow.
... Thus, ceramic industry is continuously searching for more economical raw materials in order to replace the traditional fluxes without altering the process and product characteristics. Relevant studies have already been reported extensively in the literature [3][4][5][6][7][8] . Densification process of triaxial bodies proceeds by viscous phase sintering, with the development of a liquid phase that flow by capillary pressure, in interconnected voids amongst the particles, causing the development of a ceramic bonding, constituted by new crystalline phases and part of the residual crystals such as quartz in a glassy matrix. ...
Use of rhyolite as flux in porcelain tile production The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. In addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
... Several works has been published using raw materials containing spodumene in ceramic formulations. Tulyaganov et al. 7 showed a reduction of 100-120 °C in the sintering temperature of porcelains and concluded that the levels of Li 2 O should not exceed 1.5% to avoid bloating and the correspond decreasing of parts densification. ...
The use of a waste from mineral processing, a spodumene-bearing rock, was investigated as a flux for bone china composition, partially replacing feldspar. The effect of lithium oxide in bone china body was favorable for reducing firing temperature. The presence of Li2O reacting with other oxides and silicates formed a liquid phase of lower viscosity, which was favorable for densification through viscous flow sintering, and to a higher mechanical strength. It was obtained a large plateau for firing, without deformation on firing (pyroplastic deformation) of parts; which is not an easy task to be achieved in bone china processing. Rheological and casting properties were also investigated. Microstructures of the fired bodies were discussed. They correlated well with the final properties of the parts.
... Thus, ceramic industry is continuously searching for more economical raw materials in order to replace the traditional fluxes without altering the process and product characteristics. Relevant studies have already been reported extensively in the literature [3][4][5][6][7][8] . Densification process of triaxial bodies proceeds by viscous phase sintering, with the development of a liquid phase that flow by capillary pressure, in interconnected voids amongst the particles, causing the development of a ceramic bonding, constituted by new crystalline phases and part of the residual crystals such as quartz in a glassy matrix. ...
The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in thestandard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies wasevaluated using adouble-beam optical non-contact dilatometer. In addition, XRD was used toanalyse the phases formed after firing. SEM was also employed in order toobserve the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into aporcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
... Taking into consideration the technical requirements for whiteware ceramics (floor and wall tiles): WA ≤ 1.5%; λ ≤ 13%; d: 2.2-2.4 g/cm 3 and σ ≥ 35 MPa (e.g. Bragança and Bergmann, 2004;Munier, 1957;Tulyaganov et al., 2006) the desirability functions, which show the smallest and the highest suitable values as well as the most desired ones (targets) of the responses, were plotted (Fig. 5) by the NEMROD program, and were used to define the desirability domains for manufacturing whiteware bodies. The bidimensional and tridimensional representations of the desirability domains, i.e. the suitable sets of factors for floor and wall tiles manufacturing, are shown in Fig. 6. ...
The effects of firing temperature, flux content and soaking time on shrinkage, bending strength, water absorption and density of a clay-based ceramic material were evaluated using response surface methodology (RSM) and were investigated by X-ray diffraction and scanning electron microscopy. The results of the regression models showed that the weights of the factors increased in the following order: temperature > flux content > soaking time. The interactions between the factors were relatively less important, and they had different (antagonistic/synergetic) influences on the properties. An increase of these factors resulted in the formation of mullite and melt and had positive effects on the properties. However, their vigorous increase had adverse effects, most likely because of the melt abundance and/or coalescence of pores. The RSM results showed that white floor and wall tiles could be manufactured by the use of a body consisting of 38 wt.% feldspar and selected firing temperatures and soaking times. The ceramic suitability of the body was discussed in relation to some ceramic diagrams.
... 7 On the whole, the magnitude of the foregoing physicochemical transformations can vary considerably, depending on the characteristics of the raw materials employed and the complex interplay between them. According to available studies in the literature, it is the current trend to employ flux-forming additives, both natural (feldspars, nepheline syenite, zeolites, spodumene, etc.) [8][9][10][11][12] and synthetic (including industrial wastes such as waste glass and fly ash) in order to reduce the peak firing temperature and soaking time of triaxial whiteware bodies and thereby reducing the cost of energy without compromising productivity and product quality. [13][14][15][16][17] These additives may, however, produce a rapid rise in the amount of liquid phase in a short time-temperature interval during sintering, thus providing a narrow firing range and a risk of pyroplastic deformation to the ware unless a careful control of formulations is achieved. ...
In this study, an attempt was made in order to develop a multipurpose tile body using a single formulation. In order to achieve this, several body recipes were prepared using mainly local raw materials with clearly defined physical and chemical properties at different sieve residues and single fast fired under industrial conditions in the first part of the study. In the second part, the most suitable formulations with the corresponding sieve residues were determined and further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. The tested peak firing temperatures were varied at 20 °C intervals from 1120 to 1200 °C for multipurpose wall tile body and from 1140 to 1220 °C for multipurpose floor tile body. The physical and thermal properties of the fired bodies such as water absorption, linear firing shrinkage, bulk density and linear thermal expansion coefficient were measured. The vitrification behaviour of the multipurpose bodies was also evaluated using a double-beam optical non-contact dilatometer. Furthermore, the fired bodies were subjected to colour measurements. Particular consideration was given to the phase and microstructural evolution of the developed tile bodies. X-ray diffraction (XRD) was used to analyse the phases formed before and after firing. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS) was further employed in order to observe the microstructural and microchemical characteristics of the fired bodies with respect to peak firing temperature. The preliminary experimental results showed that it was possible to obtain a multipurpose body with the properties in accordance with ISO-EN 10545.
The stoneware tiles were prepared from graphite tailings, kaolin, shale, potash feldspar and albite, and the firing temperature range was broadened by adding talc as an additive. The effects of talc on the phase compositions, microstructures and properties of the stoneware tiles were analyzed, and the mechanism for broadening firing temperature range of the stoneware tiles was studied. The results showed that sample B3 (60.87 wt% graphite tailings, 8.7 wt% kaolin, 8.7 wt% shale, 8.7 wt% potash feldspar, 13.04 wt% talc) fired from 1080 °C to 1100 °C exhibited better properties than other samples with the water absorption and the bending strength of 0.22% ∼ 0.48% and 88.04 MPa ∼ 93.54 MPa respectively. The performance meets the requirements of Chinese national standard “Ceramic Tiles” (GB/T 4100-2015). Based on the results of XRD, the phase compositions of the samples are quartz, anorthite, enstatite and hematite. Enstatite is a new phase compared with our previous study, due to the transformation of talc to enstatite. Talc can not only promote densification by reducing the high temperature liquid viscosity, but also broaden the firing temperature range of stoneware tiles by promoting the crystallization and growth of enstatite grains.
Strong fluxes are needed to fire vitrified ceramics at temperatures significantly lower than those usually reached in industrial firing cycles. This work is aimed at understanding the role of strong fluxes in the microstructural evolution during sintering. Six fluxes (colemanite, ulexite, wollastonite, diopside, spodumene and phonolite) were individually added to a porcelain stoneware batch and processed in standard conditions. Compacts and fired bodies were characterized by optical dilatometry, XRD-Rietveld, SEM and measuring technological properties. Strong fluxes change the firing behaviour with a complex interplay of sintering kinetics, microstructural features, and phase composition. Every flux has its own repercussion on the properties of the liquid phase (chemical composition, degree of polymerization, viscosity and surface tension) which are key points to explain the observed microstructure, densification rates, and stability at high temperature. Batches with phonolite, wollastonite or diopside exhibit characteristics closer to standard porcelain stoneware, while spodumene and borates suffer from unsatisfactory microstructures and lower densification efficiency.
In granite body, 1-3-5 wt% ZnO was replaced instead of feldspar and fired in an industrial continuous production kiln. Physical properties of the tiles were determined including dried strength, fired strength, water absorption, fired loss, and colorimeter values. X-Ray Diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-Ray (EDX) measurements for distinctive microstructural changes and phases formed were done. The fired strength values of the standard and 3% ZnO added body are 399.94kg/cm2, 510.50 kg / cm2, respectively. Water absorption and firing shrinkage values are close to each other. In the analysis of the sample with 3% added ZnO with XRD, it was observed that the solubility of quartz was increased, mullite formation was prevented; besides 27.4 wt.% spinel phase and 13.8 wt.% albite formation was observed.
Chemical and thermal etching techniques are commonly used to enhance microstructural features. While thermal etching works well for high purity ceramic systems, thermal etching may not be appropriate where glass is present. Porcelain and industrial alumina both contain a glass phase, typically 40-60 vol% and 4-30 vol%, respectively and these glass chemistries are similar. Chemical etching of porcelain is common, but the images published in the literature are frequently over-etched. When glass is present in the grain boundaries of alumina, thermal etching can cause the glass to disappear or to recrystallize obscuring the microstructure. Because of this, it is proposed that both chemical and thermal etching are necessary to prepare an industrial alumina microstructure for grain size measurements. In addition, it was observed that chemical etching is sensitive to the residual stress in the glass phase, becoming more aggressive when there is residual tension in the glass.
The pyroplastic deformation of porcelain is a key issue for reducing production loss. In this study, material design to realize both low a water absorption and low pyroplastic deformation in alumina‐strengthened porcelain, which have a trade‐off relationship, was proposed. In this porcelain material design, a rigid microstructure composed of entangled needle‐like mullite crystals is formed by the addition of Gairome clay, which has the positive effect of suppressing pyroplastic deformation but negatively affects densification. This was balanced by the controlling the amount and viscosity of the liquid phase in the porcelain fired at elevated temperatures with optimized quantities of added petalite and Gairome clay to obtain a low water absorption and low pyroplastic deformation. As a result, a water absorption below 0.5 % and pyroplastic deformation index below 1.5×10‐6 mm‐1 in a wide firing temperature range from 1194 to 1384 °C were obtained for porcelain containing Amakusa clay at 37.8 mass%, Gairome clay at 17.0 mass%, petalite at 13.7 mass%, and alumina at 31.5 mass%.
Porcelain stoneware is a product produced from kaolinite clay, quartz, and feldspar. This paper studies the potential of POFA layers as a secondary raw material in the porcelain stoneware application. POFA was separated to four layers. Each layer was investigated by using scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX) in order to analyse the microstructure images and elemental analysis of POFA layers. The result was compared to all basic raw materials of porcelain stoneware for a benchmark. The result shows that the fourth layer has the largest silica content. It is the layer that has a characteristic close to the real porcelain stoneware. The microstructure and elemental analysis of POFA layers are compared with previous finding of POFA. There is little published information on POFA layers but certain POFA layers have approached the result of published POFA.
Alumina porcelain electrical insulators were prepared using Li2O-bearing spodumene flux as a partial substitute for feldspar. The effects of spodumene on microstructure, crystalline phases, physical properties, modulus of rupture, dielectric breakdown strength and volume resistivity were investigated. The samples with spodumene content >5 mass-% sintered at 1350 °C showed both zero percent water absorption (WA) and apparent porosity (AP). Density was found to decrease with increasing spodumene content from 2.39 g/cm3 (at 5 mass-% spodumene) to 2.37 g/cm3 (10 mass-%) to 2.33 g/cm3 (15 mass-%). This may be due to the irreversible phase transformation of α-spodumene to β-spodumene, which accompanies a change in density of spodumene from α-phase (3.20 g/cm3) to β-phase (2.35 g/cm3). The crystalline phases were characterised by X-ray diffraction and scanning electron microscope. They showed that spodumene favours crystallisation of elongated needle-like mullite and spodumene solid solution that coexist with alumina particles embedded in the glassy matrix of bodies sintered at 1350 °C. This resulted in an increase in modulus of rupture and enhanced the electrical properties of the porcelain bodies. The maximum 71 N/mm² modulus of rupture (MOR), dielectric strength of 21 KV/mm and electrical resistivity equal to 10×10¹² Ω•cm were recorded with 10 mass-% spodumene.
The influence of talc addition on the pyroplastic deformation of alumina-strengthened porcelain was investigated in this study. Along with the lower content of feldspar, the addition of talc contributed to the crystallization of the cordierite during the firing process, and the resulting cordierite crystals formed complicated filler structures. The porcelain samples made with the addition of talc showed an unprecedented pyroplastic deformation characteristic with almost no changes in the pyroplastic deformation index value during further firing at over 100°C after the water absorption reached almost zero. This improvement of pyroplastic deformation was thought to synchronize with the crystallization of cordierite.
We study the stability of Li-O compounds as a function of pressure, with Li ion battery applications and fundamental chemical interest in mind. Using the ab initio evolutionary algorithm, we predict stability of novel compounds LiO4, Li5O3 and Li6O under pressure. LiO4, formed at the pressure of just 6 GPa, can be seen as {\epsilon}-O8 accepting two electrons from two Li atoms. This phase is superconducting, with Tc up to 12.2 K at 10 GPa. This is remarkable, because elemental oxygen becomes superconducting at much higher pressure (96 GPa) and has much lower Tc (<0.6 K), and suggests that chemical alloying with other elements has the potential of not only decreasing metallization pressure, but also of increasing Tc. Since {\epsilon}-O8 is called red oxygen, LiO4 can be identified "lithium red-oxid", and is distinct from superoxide. Additionally, Li5O3 is stable at pressures above 70 GPa and can be represented as a hybrid structure 4Li2O {\cdot} Li2O2, and electride suboxide Li6O is stable above 62 GPa.
In this study, the effect of glassy phase viscosity and chemical composition of sanitaryware body was investigated. Additionally, the effects of these parameters on the sintering temperature were researched. The amount of mullite, quartz and glassy phases were estimated by slope ratio method, as 18.8 %, 22.1 % and 59.1 %, respectively. The alternative glassy phase compositions which are enhanced at low temperatures were calculated starting from glassy phase chemical composition, determined in body of sanitaryware. In this section, different Na2O/K2O, Al2O3/Si 2O and sum of them, different CaO/MgO ratios were researched to determine the best composition. The melting behaviors of prepared compositions were analyzed by heat microscope. The glassy phase compositions (S0.3-1, S2T0.8, S2T0.8-1 and S2T2) which are showed that melting behavior at low temperature, were used in preparation of body recipe. As a result, the composition (S2T2) with the ratio of Na2O/K2O (2.5-3.0), Al2O 3/SiO2 (6.0-6.5), Na2O+K2O (0.6-0.7) and Al2O3+SiO2 (5.0-6.0) was sintered at 80°C lower temperature than that of standard composition (STD).
The influence of adding 2 mass % LiF or B2O3 as coflux on phase composition and optical properties of ceramic batches to the system: clay, quartz sand and K-feldspar was investigated. The content of clay was kept constant at 40 mass %, while quartz was added in the range between 10...40 mass % at the expense of K-feldspar. The main phases detected in the fired bodies were mullite,β-eucryptite, quartz with traces of cristobalite and microcline. The results indicate that the light absorption coefficient in the visible range depends mainly on the type of co-flux added. The borate bodies with increasing quartz content showed a reduction in the absorption coefficient at short and long wavelengths. The scattering coefficient on the other hand increases with the wavelength in the same range. This may be attributed to the amount, size and shape of mullite crystals formed in the borate bodies. The degree of whiteness was slightly improved by LiF addition. The hue for all samples was light blue, except for Li-bodies containing 10 mass % quartz which showed light yellow.
The effects of varying the quartz-feldspar ratio and adding 2 mass-% LiF or B2O3 as co-flux on the densification, crystalline phases, microstructure, and the mechanical and chemical properties of porcelain stoneware tiles have been studied. The results show that the addition of 2 mass % LiF to stoneware bodies reduces the maturing temperature by about 100°C. However, with increasing quartz-feldspar ratios the addition of 2 mass-% B 2O3 raises the vitrification temperature and improves the densification properties, as well as increasing the modulus of rupture (MOR) to 58 MPa. The major crystalline phases are β-eucryptite and mullite for lithia bodies and borate bodies, respectively, together with quartz residues and traces of cristobalite and microcline. Also, LiF or B2O3 additions to ceramic bodies significantly improves the material's resistance to deep abrasion and chemical attack, especially by household chemicals and highly concentrated HCl and lactic acid.
Glass-Ceramic monoliths of the SiO2-CaO-MgO-Al2O3 system are obtained in this research. Due to its potential dual role as a flux and as a nucleating agent, two CaF2 levels (X = 3 and X = 6 mol.%) are investigated in the parent glass composition. Due to its good mechanical properties, we intend to obtain Diopside-type pyroxene [(Ca)(Mg,Al)(Al,Si)2O6] as the main crystalline phase in the synthesized glass-ceramics. Vickers microhardness (HV), density and type of crystallization are determined in the latter materials. The morphology and size of the Diopside crystals, as well as the crystallized fraction, are determined with the help of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Both materials exhibit surface crystallization with Diopside-type pyroxene phase with acicular morphology homogeneously distributed in the glassy matrix. The specimen with the least amount of added fluorine shows the highest microhardness value, as well as the largest and thickest acicular crystals of Diopside-type pyroxene, the lowest apparent density and the largest crystallized fraction. Our results indicate that CaF2 added in the amounts used by us does not act as nucleating agent, but it does affect the growth of the acicular crystals of the Diopside-type pyroxene phase. This is attributed mainly to the effect of fluorine on the glass structure and properties. The materials developed in this study may be considered as viable alternatives for applications in abrasive and corrosive environments, as well as for substrates for metallic coatings, and for abrasion-resistant floor tiles and other structural applications.
Four formulas of the stoneware bodies were formulated with and without an increasing amount of lithium oxide. The bodies were designed to vitrify at the temperature lower than 1150°C. A comparison on the physical properties and the phase formation of the bodies after firing at the temperature of 1100°C, 1150°C, and 1200°C was studied. The experiment results showed that the bodies containing lithium oxide vitrified at lower temperature and showed less variation in water absorption, density, and shrinkage values in the firing range 1100-1200°C. The XRD results showed that, at 1100°C, all the bodies composed of mullite, albite, and quartz. A reduction in the amount of albite and quartz associated with mullite formation was observed when increasing the amount of lithium oxide or the temperature. Furthermore, the body with lithium oxide tended to have higher value of the Modulus of Rupture.
Use of rhyolite as flux in porcelain tile production The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. In addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
Ceramic stoneware body has been modified with ceramic and glass industrial wastes by replacing 25–100% as flux in the formula. The effects of solid wastes added to the bodies were studied after firing in the temperature range 950–1280 °C. The physical properties of linear shrinkage, bulk density, apparent porosity, water absorption and 3-point bending strength were determined. A composition which related to the general stoneware properties was found when using soda-lime cullet and glaze sludge. It had a firing range lowered to 1050–1100 °C. SEM results demonstrated the sintered microstructure increased in density with increase in solid waste in the modified body. XRD results after firing showed the crystalline phases comprised of mullite, albite calcian and quartz. Thermal expansion was measured in the range 6.53–6.67 × 10−6 K−1 at 30–500 °C. The modified bodies were capable of forming prototype products by slip casting and jiggering.
We have studied the influence of increasing the amount of β-spodumene (LiAlSi2O6), as a Li2O-containing flux, on the phase composition, the microstructure evolution and the physical properties of high-alumina porcelain. Quartz reacts with β-spodumene in the temperature range 1150–1250°C, forming lithium aluminium silicates with a larger amount of SiO2. The presence of lithium minerals contributes to a lower CTE for the fired bodies. At 1300°C an improved flexural strength is achieved with compositions containing 1.0 or 1.2wt.% of Li2O, as a result of a more uniform microstructure. With increasing amounts of Li2O the overfiring effect is greatly enhanced. The most favourable characteristics from an industrial perspective with regard to flexural strength and deformation during firing were attained by using a high-alumina porcelain composition containing 1.0wt.% Li2O.
In this work, spodumene-bearing rock, a waste from mineral processing, was used as a flux in ceramic bodies, and its reactivity to other raw materials such as quartz and kaolin was analysed. The petrology properties of the pegmatite (parent rock) from which the flux is extracted were characterised. The grindability, fluxing strength and pyroplastic deformation of the spodumene-bearing rock were investigated. In addition, the influence of spodumene-bearing rock on technological properties of the final pieces, mainly in relation to the firing temperature, phases formation and microstructure was also analysed. Then, the firing behaviour to other commercial fluxes such as albite and feldspar was compared. The spodumene-bearing rock was considered an effective flux, capable of reducing the firing temperatures of the tested bodies by viscous flow.
The co-occurrence, at the thin section scale, of the three anhydrous Li-aluminosilicates spodumene, petalite and eucryptite, is not a common feature. Such an association occurs in some aplite-pegmatite dykes of the Covas de Barroso district, northern Portugal. We describe their mutual relationships: where spodumene is an early magmatic phase, petalite precipitates directly fr om a late orthomagmatic fluid, the spodumene remaining metastably, whereas eucryptite is obviously hydrothermal and secondary. Replacement of the primary Li-minerals is the rule, but is diversified and selective: spodumene is mainly replaced by albite an d muscovite, petalite by K-feldspar and eucryptite. Muscovite is widespread, and the late hydrothermal paragenesis is dominated by quartz associated with various mixtures of phosphates. The assemblage eucryptite, K-feldspar and albite is obviously in chemical disequilibrium with the early phases. The compositional evolution of the hydrothermal fluids (Na, K, Li) is tentativel y bracketed. There is disequilibrium among thermodynamically conflicting mineral phases in terms of pressure, temperature and fluid:rock ratio, in a mobile and partly open system. A genetic affiliation of the Li-enriched pegmatites with the nearby two-m ica granites is difficult to prove. The tectonically controled intrusion of biotite granites to the east of the pegmatite belt woul d seem to be responsible of the drop in pressure that accounts for the spodumene-petalite transition and the development of the wide- spread replacement by feldspars, not present in the western part of the belt.
Porcelain represents the foundation of the ceramics discipline and one of the most complex ceramic materials. Composed primarily of clay, feldspar, and quartz, porcelains are heat-treated to form a mixture of glass and crystalline phases. This review focuses on raw materials, processing, heat treatment, and mechanical behavior. Because of the complexities of the porcelain system and despite the substantial amount of research already conducted within the field, there remain significant opportunities for research and study, particularly in the areas of raw material understanding, processing science, and phase and microstructure evolution.
The use of β-spodumene (Li2O·Al2O3·4SiO2) has been investigated as a liquid-phase sintering aid for the densification of mullite processed from fumed silica and ESP
(alumina) dust. XRD, DTA, SEM and Vickers indentation were used to characterize the effect of spodumene on the phase relations,
sintering behaviour, microstructure and mechanical properties of mullite. The results show that the presence of spodumene
significantly reduces the porosity, improves the sintering behaviour and enhances the formation of mullite at 1550 °C. Spodumene-modified
mullite ceramics also have better physical and mechanical properties.
An efficient firing curve can be designed using data from differential thermal analysis, thermal expansion, and irreversible thermal dilatometry of an unfired body. A sequence of events that occurs during the firing of porcelains is also presented.
In most of the currently used porcelain body compositions, rapid firing schedules are used to achieve substantial reductions in both capital and operating costs. Ceramic bodies shrink more under rapid heating conditions, since the fluxes become less saturated with clay and quartz, and the surface tension of the low viscosity melt has time to exert its maximum effect. Glaze additions were used to decrease shrinkage values and to increase mechanical properties and whiteness of the porcelain.
Technical porcelains in the clay-felspar-sillimanite system were investigated to study the effect of firing temperature on the physical properties and flexural strength. The effect of felspar replacement with sillimanite sand on the mechanical properties were also discussed. Replacing felspar by sillimanite sand resulted in significant improvements in the mechanical properties. These were dominated by bulk density, which in turn was determined by fired porosity and body composition. Maximum strength (119.36 MPa), toughness (1.21 MPa · m 1/2) and hardness (670.38 GPa) were found in the body containing the highest amount of sillimanite sand (30 mass-%). Improved mechanical properties in the bodies containing sillimanite sand was due to the decrease in Griffith's flaws and the formation of a dispersion-strengthened matrix reinforced by the insoluble residual sillimanite particles.
The influence of the particle size fraction of the quartz and the choice of feldspar added to a conventional triaxial porcelain composition was studied with respect to the physical properties obtained in a fast-firing schedule - increasing (to 1400 degree C) and decreasing within 3h. The results indicate that by a careful choice of commercially available raw materials it is possible to produce a body that compares favorably with a composition produced under more conventional circumstances.
Range curves present the changes in properties of a ceramic material as a function of firing temperature. This paper describes the methods used to determine the firing range curves and their application to determine the vitrification temperature. The effect of heating rate and soak time on range curves is illustrated. The uses of range curves in research and development and in process control are outlined with cautionary remarks on test specimens and the interpretation of results.
This book appears in the authoritative series reporting the international research and development activities conducted by the Schott group of companies. This series provides an overview of Schott's activities for scientists, engineers, and managers from all branches of industry worldwide in which glasses and glass ceramics are of interest. Each volume begins with a chapter providing a general idea of the current problems, results, and trends relating to the subjects treated. This new extended edition describes the fundamental principles, the manufacturing process, and applications of low thermal expansion glass ceramics.
This work describes a study conducted on the processing of a spodumene ore occurring as aplite —pegmatitic lodes in granites located in Northern Portugal, in order to obtain lithium concentrates for addition to glass and ceramic bodies.Besides spodumene, the ore contained mainly K feldspar, quartz and mica, mainly muscovite. Its beneficiation was carried out by flotation and heavy media separation (HMS).The flotation testwork was carried out with 300/75μm deslimed feeds assaying from 1.9 to 3%Li20. Rougher concentrates assaying 6.1 %Li20 and recleaner concentrates assaying 7.75%Li20 were obtained at stage recoveries of respectively 67% and 31%.The HMS tests were done with bromoform, on classified feed samples containing (2.3–2.7) %Li20. Sink products assaying c.a. 5%Li20, which comply with the specifications for the glass grade spodumene, were obtained. The lithium distributions in these products, varied from 39 to 61%.From the treatment of this ore, by flotation and HMS, it was possible to obtain concentrates with Lithia grades capable of being used by the glass and ceramics industries.
Traditional porcelain bodies used for tableware, electrical insulators, and sanitaryware can be formulated with a small fraction of synthetic zinc or calcium borate, resulting in a substantial reduction in firing temperature and a broadening of the useful firing range. The relationship to temperature was explored with a gradient firing technique where samples were examined for shrinkage, porosity, density, and microstructure over a broad temperature range (about 200°C). A designed formulation experiment was used to help create a model describing temperature efects. Strength testing was also carried out on rods fired at discrete temperatures. Benefits to reformulating include reduced energy consumption, reduced production of combustion gases, longer kiln and refractory service life. and potential increased capacity and yield.
The composition of the glass phase in a fired porcelain sample can be calculated exactly by taking the diference of the bulk chemical analysis and the quantitative crystalline phase composition obtained from powder X-ray difraction. Data indicates that all of the glass phase compositions are similar at any given heat treatment temperature. The ratio of alkali (R2O) to alumina (Al2O3) is essentially constant over the firing temperature range of 1150–1400°C. It is therefore proposed that the glass phase composition oftri-axial porcelains lies on the glass formation boundary within the R2O-Al2O3-SiO2 system. This observation has important implications for fast-firing pyroplastic deformation, and fired strength of porcelains, and can be used to explain many of the inconsistencies in the published literature.
Four groups of body compositions involving partial replacement of feldspar by spodumene were investigated. In the first group the firing temperature was maintained constant and the clay content was increased at the expense of the flux. In the second group the flint, clay, and total flux (flux was 20y0 of the body) contents were held constant and spodumene replaced 19, 30, and 40y0 of the total flux. In the third group the flux content containing varying proportions of spodumene was increased from 20 to approximately 40% of the body at the expense of flint and the firing temperature was lowered. In the fourth group miscellaneous bodies containing a variety of fluxes, including flotation soda feldspar, nepheline syenite, talc, and whiting in addition to the potash feldspar and spodumene, were tested. The spodumene appeared to have little advantage in lowering the maturing temperature of the 20% flux bodies; however, a spodumene: feldspar ratio of 30:70 appeared to lengthen the firing range. The effectiveness of the spodumene increased as the total flux was increased. A body containing 27% of flux matured at cone 11–12 when potash feldspar alone was used and at cone 8 when 8% of the feldspar was replaced by spodumene. A body containing spodumene, talc, and nepheline syenite matured at cone 3–4 and had a fired modulus of rupture in excess of 10,000 lb. per sq. in. The small amounts of spodumene (up to 8% of the body) had no apparent effect on the stability of the casting slips or similar properties.
The spinel phase formed on the thermal reaction of kaolin group minerals was characterized by X-ray quantitative analysis, lattice constant determination, and chemical analysis by analytical TEM. The spinel phase was determined to be nearly γ-Al2O3 with ∼8 wt% of SiO2, significantly less than previously reported.
X-ray diffraction data for the high-temperature phases show that a spinel-type structure develops with marked orientation at about 925°C. This phase is considered to be an aluminum silicon spinel with vacant cation sites. Mullite is thought to be formed by the decomposition of the spinel. Silica is eliminated progressively as metakaolin transforms to the spinel phase and thence to mullite. The X-ray data show variation in the mullite parameters between 1200° and 1400°C.; at 1400°C., the composition probably approximates 3A12O3·2SiO2. The nature of the intermediate spinel-type phase is discussed in relation to the crystal chemistry of spinels.
Compositions having negative linear thermal expansions ranging from 0 to –0.38% have been obtained in two areas of the system lithia-alumina-silica. Petrographic and X-ray examinations indicate the presence of three principal crystalline phases, each of which is a solid solution: β-eucryptite, β-spodumene, and an unidentified quartzlike phase. All compositions were prepared from lithium carbonate, clay, flint, and alumina. Some compositions have been prepared which, for all practical purposes, exhibit no change in length when heated from room temperature to as high as 600°C. Some of these compositions have excellent thermal endurance, withstanding repeated quenchings from a temperature of 1100°C. into water at room temperature.
Sintering studies were conducted using kaolin, metakaolin, zeolite 4A, and various synthetic mixtures of Al2O3 and SiO2 in the presence of Li2CO3 and LiCl as fluxing agents. Various compositions of the above were prepared, and conventional sintering studies were conducted at temperatures of 900°–1450°C with soaking periods of 1–3 h. Kaolin, metakaolin, and amorphized kaolin in the presence of Li2CO3 showed nucleation centers of β-spodumene as pink specks, whereas synthetic mixtures of Al2O3 and SiO2 failed to behave in the same manner. To determine whether the pink specks formed were color centers or F centers, the samples were subjected to UV, IR, and X-ray irradiation; however, the samples showed no tenebrescence properties. External addition of iron as an impurity in a nonlayered system also resulted in pink speck formation. This observation indicated that impurities present in the natural kaolin were the cause of this phenomenon. Moreover, the LiCl-based samples did not result in pink specks, even though the kaolinitic samples contained iron as an impurity. Therefore, although β-spodumene was formed in aluminosilicates in the presence of Li2CO3 and LiCl, the pink variety of β-spodumene (kunzite) formation occurred only in the presence of lithium-rich aluminosilicates and in the presence of iron as an impurity. The phase identification and microstructure were explained based on XRD, DTA, and SEM studies.
Microstructural evolution in a model triaxial porcelain was studied by X-ray diffractometry and electron microscopy of quenched samples after firing for 3 h at 600°–1500°C. The clay component dehydroxylated to metakaolin at ∼550°C. Metastable sanidine formed from decomposition of the feldspar at >600°C and dissolved at >900°C. Liquid formation at ∼1000°C was associated with melting of feldspar and silica discarded from metakaolin formation via the K2O–Al2O3–SiO2 eutectic. Liquid content increased at 1000°–1200°C with further feldspar melting and additionally at >1200°C because of quartz dissolution. Small (≤7 nm) mullite and -alumina crystals precipitated in pure clay relicts and larger (≤30 nm) mullite crystals in mixed clay-feldspar relicts at 1000°C. In the evolving microstructures, three regions were observed. These regions were derived from pure clay relicts containing primary (type-I) mullite; feldspar-penetrated clay relicts, also containing secondary (granular type-II) mullite; and the matrix of fine clay, feldspar, and quartz, containing secondary (granular type-II and elongated type-III) mullite. In addition to shape, the mullite size changed, increasing from regions containing type-I to type-III mullite, because the increasingly fluid liquid enhanced crystal growth. Below 1300°C, primary mullite was richer in Al2O3 than the secondary mullite, and the glass composition was inhomogeneous, with the K2O and Al2O3 contents varying throughout the microstructure. Above 1400°C, mullite began to dissolve.
β-Eucryptite, β-spodeumene and solid-solution porcelain were prepared by the conventional ceramic technique with three lithia:alumina:silica (LAS) ratios, 1:1:2, 1:1:3 and 1:1:4. The optimization of the ceramic parameters was assessed through measuring their vitrification parameters with firing temperatures in the range 1000–1350 °C. Structural characterization of the bodies obtained at optimum conditions were followed through X-ray diffraction (XRD) and infrared (IR) spectral analyses. Thermal dilation up to 1000 °C was measured. Morphological variations were examined through scanning electron microscopy (SEM) of fractured surfaces, as well as selected area electron diffraction (SAED).Results proved that the change from β-eucryptite with 1:1:2 LAS through its solid solution to β-spodumene with 1:1:4 LAS, i.e. from hexagonal to tetragonal structures, need a firing temperature of 1320 °C. Shifts in XRD lattice planes were complemented by parallel shifts in IR bands specific for silicates around 1100 cm−1. Unique negative thermal expansion up to 1000 °C for β-eucryptite changed to the positive value only after 600 °C for β-spodumene. Characteristic large grains were detected in both β-eucryptite and β-spodumene micrographs parallel with the polycrystalline rings of the SAED figures. On the other hand, the β-eucryptite solid-solution body has smaller grain size with higher glassy phase shown by the larger SAED halo. The present results illuminate the importance of assessing the detailed structural features for future radiation damage studies.
The effect of sillimanite sand as a replacement for quartz and alumina/cordierite glass-ceramic for feldspar was studied. Compositional variations were due to the gradual incorporation of alumina in place of cordierite glass-ceramic. Increased replacement of cordierite glass-ceramic by alumina (20%) increased the flexural strength by 100%, giving a value of 195 MPa. Elastic modulus, microhardness and fracture toughness also showed sharp increases compared with values for conventional triaxial whiteware compositions. Improvement in mechanical properties was attributed to the presence of sillimanite and alumina particles present as fracture-resistant dispersoids in a viscous glassy matrix. Increased fracture behaviour is due to minimization of the glassy phase and limiting the size of Griffith's flaws.
The microstructure of standard commercial porcelain consists of alpha-quartz grains held in a complex matrix. Quartz grains are surrounded by amorphous silica-rich solution rims while the matrix contains clay relicts of small (~200 nm × 40 nm × 40 nm) primary (2Al2O3:1SiO2) mullite crystals in aluminosilicate glass and feldspar relicts of acicular (>1 µm long) secondary (3Al2O3:2SiO2) mullite in potassium aluminosilicate glass. A continuous increase in mullite crystal size from the clay-feldspar relict interface to the feldspar relict center and their compositions indicate a transformation from primary to secondary mullite. In aluminous porcelain, corundum grains are observed in addition to alpha-quartz and regions of clay and feldspar relicts. Small (~50 nm × 10 nm × 10 nm) tertiary mullite crystals (formed by precipitation from Al2O3-rich glass) were detected adjacent to these corundum grains.
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