Article

Effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to different cooling rates

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Porcelain tile is a high-performance ceramic tile, in which quartz is a major compositional component. After the firing cycle, macroscopic residual stresses develop in the product as a result of rapid cooling. Further, during cooling, the presence of quartz particles also increases natural flaw size. Both phenomena significantly affect the product's mechanical behaviour. This study examines the effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to two very different cooling rates: a rapid or a slow cooling rate. A series of porcelain tile compositions were designed for this purpose, in which quartz particle size was varied. The mechanical behaviour of the sintered pieces was evaluated on the basis of linear elastic fracture mechanics. It was verified that, in the slowly cooled material, the modulus of elasticity and fracture energy increased, and natural flaw size decreased as quartz particle size decreased. However, fracture energy also diminished in pieces that contained excessively small particles, with an advanced state of dissolution. For the rapidly cooled material, though the larger sized quartz particles debonded at higher temperatures owing to thermal stress, their presence, even in small quantities, contributed to natural flaw growth. The lower fracture energy associated with this last type of piece also favours this phenomenon.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Despite all these factors apparently affecting the mechanical strength of high-performance ceramic tiles, the fracture toughness varies within quite a narrow range of 1-2 MPa m 1/2 [10]. In fact, recent studies carried out at ITC (forthcoming) have revealed that adding 20 vol.% of inclusions of quartz, alumina or zircon does not result in reinforcement of a glass matrix made of sodium feldspar. ...
... Using two pyrometers, the top and bottom surface temperatures of the specimen were recorded. This rapid cooling gives rise to macroscopic mechanical stresses [10]. As a control test, we prepared an additional set of specimens but under slow cooling. ...
... In particular, let us suppose that v quantifies the fraction of uncracked inclusions, namely those that were able to withstand the tensile microscopic residual stresses and, as a consequence, retained their integrity. Therefore, D v would be a critical diameter above which particles are cracked [10,42]. Let us assume that residual stress in unbroken particles is given by r res;0 and the broken particles have no residual stress. ...
Article
The aim of this work is to clarify the influence of quartz inclusions added to a vitreous matrix on the macroscopic fracture toughness (KICKIC). We use numerical simulations to model a silicate-based ceramic material as a heterogeneous region composed of an isotropic brittle matrix and a distribution of embedded quartz inclusions. Using the material point method (MPM), we present a two-dimensional study, that albeit an approximation, sheds light on the role of the material composition in the fracture behavior observed in these ceramic materials. The value of KICKIC is calculated from the maximum strength obtained via computational analysis of a single-edge-notch tension specimen. The model test allows us to study in detail the effects occurring in a region close to the main notch. Additionally, to validate and understand our numerical findings, we fabricated and characterized experimentally a representative set of specimens with the same features as the numerical ones. We focus our attention on the effect of both the size and volume fraction of the dispersed phase, as well as the initial state of microcracking of the material and its influence on the macroscopic mechanical performance. The simulations have shown the decisive role played simultaneously by the volume fraction and typical size of the inclusions that are cracked during the cooling process.
... Even being smaller than 40 μm, cracks in quartz particles with sizes of the order of 7 μm up to 18 μm are clearly observable. Quartz grains should be smaller than ~40 μm to avoid the formation of critical peripheral and radial cracks [5,7,65]. Some of the cracks might have been created on gridding. ...
... The present observations agree with references [23,65,67], where it is stated that finer quartz grains are more prone to dissolution, exhibiting advanced dissolution states than coarser grains. Additionally, coarser grains are more prone to crack and even to detach from the ceramic body than finer grains due to residual stresses created due to the difference between the thermal expansion coefficients of the vitreous and of the crystalline (quartz and mullite) phases [5,68]. ...
Article
Microwave heating technology is presented as an alternative to conventional stoneware firing, with focus on the crystallochemical transformations. Scanning electron micrographs of microwave fast-fired samples show similar features as those of conventionally fired in a natural gas kiln, taken as reference samples. Electrically fast-fired samples present incipient mullite type-II crystals, while in the microwave and conventionally (gas) fired samples it is fully formed. X-ray diffraction pattern show that the crystallochemical transformations occur at lower temperatures when samples are microwave fired, particularly for temperatures lower than the vitrification temperature. Kaolinite dehydroxylation is fully accomplished at 500 °C when the samples are microwave fired, being still incomplete at 800 °C in electrically fired samples. Stoneware crystallochemical and microstructural transformations point to lower microwave firing temperatures (up to 100 °C lower) than that required by electric firing. These observations are in good agreement with what is reported in the literature, explaining at the microscopic level what happens at the macroscopic level.
... De acordo com as análises mineralógicas, o quartzo é o mineral mais abundante nas matérias-primas, com exceção do rejeito do Ponto B (41,4%), e proporciona melhorias quanto às propriedades mecânicas de resistência [33,34]. Nas amostras de solo e dos Pontos A, B e C foi encontrado 36,6%, 0,0%, 50,3% e 3,6% de caulinita, respectivamente, segundo constituinte mais expressivo, com exceção do Ponto A. Esse teor de caulinita contribui para a melhoria das propriedades térmicas e mecânicas das cerâmicas [35], por outro lado, contribui significativamente para o encolhimento linear de queima das composições [36], como visto na Figura 4, na qual B10 e B20 apresentam os maiores valores de Rlq. ...
... Os corpos de prova com a adição de 5% do rejeito do Ponto A apresentaram resistência à compressão menor que o corpo de prova sem rejeito, mas apresentaram aumento da resistência em teores de 10 e 20%. De maneira análoga, os corpos de prova com adição dos rejeitos dos Pontos B e C apresentaram aumento da resistência à compressão, fato que pode ser explicado pelo aumento do teor de quartzo nos Pontos A e C (Tabela 2) [33,34] e, no Ponto B, pela maior densificação provocada pelo aumento do teor de fundentes e caulinita na mistura [30,31,32,35]. ...
Article
Full-text available
The mineral extractive industry is responsible for the production of large-scale waste which, when discarded incorrectly, can cause damage to nature and public health. Knowing this, the feasibility of the addition of tailings was studied in the production of red ceramics, seeking a sustainable alternative for the use and disposal of these wastes. The residue used for the work was extracted from three holding basins in the region of the Areinha gold mining, in Diamantina-MG, and is a mud composed of silicates and some heavy metals. The objective of this study was to manufacture structural test specimens with addition of these tailings and to evaluate their technological properties, such as: linear retraction, loss on ignition, color study, water absorption, apparent porosity and compressive strength. In comparison to the test specimens produced with pure soil, the results pointed out important improvements in these properties with addition of the tailings, reducing the water absorption and increasing the compressive strength, pointing out the viability of its use for the incorporation of the mining tailings and stabilization of heavy metals.
... For the red lines, where the processing head only shifts for the application of the next green line, v is defined as 3000 mm.min -1 . This parameter is important, as it influences the substrate cooling rate and, consequently, the allotropic quartz transformation [25,26]. ...
... Table 4 and Making use of these parameters, for P ≥ 900 W, microcracks were observed on the ceramic substrate surface. Furthermore, in some cases, the cracks caused rupture of the specimen due to the high difference temperature between the surface and the bulk of the ceramic substrate that causes the fast volume changes of the quartz (polymorphism) [25,26]. ...
Article
This study aims to develop a new approach for the permanent sealing of surface pores on polished porcelain stoneware tiles, using ceramic frits for the filling pores, followed by laser-sealing to ensure the fixation of the applied material. The laser-sealing parameters compatible with the ceramic substrate were focus height (z) of 105 mm, scan speed (v) of 2640 mm.min⁻¹, and power values of 750, 800, and 850 W. In order to define the working parameters, three ceramic frits with 30, 50, and 70 wt.% solid contents were tested by sealing at the mentioned powers. High stain resistant polished stoneware tiles were obtained using frit 1 and frit 3 with 50 and 70 wt.% solid contents, respectively, and the proposed procedure. High ease of cleaning is obtained related to the current treatment, demonstrating its suitability for improving the stain resistance for meeting the ISO 13006:2012 requirements.
... At higher magnifications (Fig. 3(b) and (d)) it is possible to see microcracks located in the interlayer formed between the unsolved quartz particles and matrix, and also through the quartz particles as reported in the literature. 19 The microcracks display very frequently a circumferential orientation because in the cooling stage quartz shrinks more than the glassy phase. Consequently, the mechanical behavior of quartz porcelains may be unstable and not easily predictable. ...
Article
A focused research was conducted on samples prepared from an industrial porcelain tile composition containing quartz, used to produce ceramic floor tiles, with the aim of evaluating the variation of fired specimens’ Young's modulus with temperature. These samples were fired in controlled laboratory conditions so that specimens with pre-existing cracks were obtained and subject to non-destructive in situ thermo-mechanical measurements (impulse excitation technique) in the 22–700°C temperature range during heating and cooling processes in order to find evidences to explain the hysteresis phenomenon in the Young's modulus versus temperature curve. The observed irreversible Young's modulus may be directly related to the pre-existent cracks that on heating and cooling are closed and opened up respectively, changing thus the Young's modulus which is well characterized by a hysteresis cycle.
... Small quartz particles as well as crystal edges favour silica enrichment of the glassy phase during the sintering process. The silica dissolution produces strong interphases between the glass matrix and the crystalline particles [17]. However the complexity of stoneware requires new analytical tools to evidence stress distribution in order to clarify the responsible mechanism of its strengthening. ...
Article
Differences in thermal expansion during the sintering process promote the appearance of stresses in a glassy matrix having crystalline particles. The stress distribution is critical in the performance of materials as porcelains that are widely used and produced in large volume by the industry. A controversy still exists on how crystalline phases as quartz strengthen the glass matrix. In this work, the existence of stress into quartz grains and into glassy phase in porcelain is evidenced by using Confocal Raman Microscopy. Surface and depth profile images of Raman shift show an anisotropic stress distribution in crystalline particles. Quartz grains are under tensile stress into the glassy phase and the stress is accommodated through the rotation of the rigid tetrahedrons around the (001) axes and the decreasing of the bonding constant forces for the Si-O bonds. The appearance of cracks into the crystalline particles is due to the stress asymmetry exceeding the tensile limit. The proposed mechanism is relevant for the design of new glassy-matrix based composites.
... One is to improve the preparation process, such as prolonging ball grinding time and raising firing temperature. 4 The other is to introduce the strengthening phase, such as the addition of corundum, 5 quartz, 6 and mullite. 7 Through the previous methods, the strength of the porcelain can be improved to a certain extent. ...
Article
Flexural strength is an important parameter of domestic ceramics to meet the criteria for mechanized washing, filling and sealing process in the automatic production line. In this work, the anorthite coating was prepared using calcite, silica, and alumina as raw materials. Taking the temperature with the highest matrix strength as the optimal temperature, the influences of chemical formulation on the phase composition and coefficient of thermal expansion (CTE) of coatings were investigated. The enhancement effect of the coating with different formulations and surface number and thickness was compared. As a result, the flexural strength of the ordinary domestic ceramic body was improved due to the residual compressive stress in the coating caused by mismatch of CTE between the coating and the matrix. At the optimal sintering temperature (1280°C), the coating with 20 mass% alumina addition has the best strengthening effect on the body, in which the thickness of the anorthite coating is approximately 50 μm and the flexural strength has increased by 64.6%, from 88 ± 4 to 144 ± 6 MPa. This article is protected by copyright. All rights reserved
... Porcelain stoneware tile composition is mainly based on a triaxial mixture similar to that of porcelain, the mixture typically containing a plastic material (generally clay), an inert or filler material (usually quartz or feldspathic sand), and a fluxing material (commonly sodium feldspar (SF)) [6][7][8]. A typical porcelain stoneware tile composition contains 40-50 wt% illite-kaolinite clay, 10-15 wt% quartz or feldspathic sand, and 35-45 wt% SF [9,10]. ...
Article
This study examines the effects of replacing fluxing and filler materials with rice straw ash (RSA) in manufacturing porcelain stoneware tile, using the design of experiments (DOE) methodology. The results of the characterization were used to obtain statistically significant, valid regression equations, relating the technological properties of the dried and fired test pieces to the raw materials content in the unfired mixtures. The regression models were analysed in relation to the X-ray diffraction and scanning electron microscopy results and used to determine the most appropriate combinations of traditional raw materials and RSA to produce porcelain stoneware tiles with specific technological properties. The studied range of tile body compositions: clay (40 wt%), feldspar (20–50 wt%), feldspathic sand (5–20 wt%), and RSA (0–25 wt%) was shown to be appropriate for porcelain stoneware tile manufacture.
... Os dados de composição química das matérias-primas das massas As argilas utilizadas foram identificadas como: argila 1 (A1), argila 2 (A2), argila 3 (A3), caulim 1 (K1), caulim 2 (K2), caulim 3 (K3) em que a composição química é mostrada na tabela 5. Algumas argilas e caulins adicionados a massa como a A2 com 73,08 % de sílica e a K3 com 65,66% de sílica proporcionam um aumento na composição de sílica na massa, o que é `prejudicial com relação a resistência mecânica (DE NONI, 2009 Tabela 5: Composição química das matérias-primas plásticas presentes nas massas C1, C2 e C3 em % de massa. (Bonetti, 2009 O experimento foi composto por um forno elétrico para aquecimento do tubo de alumina onde três corpos de prova (peças cerâmicas) à verde foram dispostos para as experiências de sinterização (Figura 7). ...
Research
Full-text available
In this work porcelain with triaxial composition, which is used as high voltage insulators, was developed with appropriate mechanical and microstructural characteristics, mainly by increasing its strength. In particular, we investigated the replacement of the quartz based porcelains for the alumina based porcelains, with the additions of bauxite as alternative raw material. We also employed oxide compounds, which are reactive in the reducing atmosphere of the sintering furnace. In particular, two of the three compositions presented better mechanical strength when an alternative thermal treatment was used.
... As indicated above, the mechanical strength for rapidly cooled porcelain stoneware tiles increases due to the development of compressive macroscopic residual stress at the surface of the pieces. However, this increase is lower than is to be expected on the basis of the measured residual stresses (89). After the allotropic transformation of quartz (573 °C), the particles undergo pronounced shrinkage, which increases microscopic stresses. ...
Article
Full-text available
Porcelain stoneware is a strongly sintered ceramic material fabricated from ball clays-quartz-feldspar mixtures. Porcelain stoneware is characterized by its excellent technical and functional properties (low water absorption, high mechanical properties, resistant to chemical substances and cleaning agents, aesthetic possibilities …). These characteristic and technical features make that among the different types of ceramic tile, porcelain stoneware is the ceramic product that in the last years has best withstood the economic crisis in the construction sector. These properties are related to the microstructure of porcelain stoneware, which is a grain and bond type with large particles of filler (quartz), mullite crystals, a silica-rich amorphous phase and porosity. The understanding of the relationship between the microstructure and the properties of porcelain stoneware is hardly important for the development and design of these materials whose tendency is the manufacture of thinner tiles with higher dimensions but must continue to comply the specific technical requirements.
... As indicated above, the mechanical strength for rapidly cooled porcelain stoneware tiles increases due to the development of compressive macroscopic residual stress at the surface of the pieces. However, this increase is lower than is to be expected on the basis of the measured residual stresses (89). After the allotropic transformation of quartz (573 °C), the particles undergo pronounced shrinkage, which increases microscopic stresses. ...
Article
Full-text available
Porcelain stoneware is a strongly sintered ceramic material fabricated from ball clays-quartz-feldspar mixtures. Porcelain stoneware is characterized by its excellent technical and functional properties (low water absorption, high mechanical properties, resistant to chemical substances and cleaning agents, aesthetic possibilities …). These characteristic and technical features make that among the different types of ceramic tile, porcelain stoneware is the ceramic product that in the last years has best withstood the economic crisis in the construction sector. These properties are related to the microstructure of porcelain stoneware, which is a grain and bond type with large particles of filler (quartz), mullite crystals, a silica-rich amorphous phase and porosity. The understanding of the relationship between the microstructure and the properties of porcelain stoneware is hardly important for the development and design of these materials whose tendency is the manufacture of thinner tiles with higher dimensions but must continue to comply the specific technical requirements.
... During cooling, different ramps and/or holds may also be necessary, in this case owing to the presence of phases that are subject to transformation and may cause residual stresses. 22 In addition to common ramp and hold schedules, numerous pressureless sintering methods using conventional furnaces have been mentioned in the literature. One of the earliest attempts to optimise firing schedules was the Rate-Controlled Sintering (RCS), 23 which uses the monitoring of densification to establish the heating schedules. ...
Article
Full-text available
For technological applications, zirconia is commonly blended with other oxides to stabilise the tetragonal and/or cubic phases at low temperature, being yttria the most frequently added dopant. It is generally desirable to obtain highly dense ceramics while maintaining grain sizes in the nanoscale (<100 nm). Small grains contribute to stabilise the tetragonal phase and to improve the toughness and flexural strength. Moreover, a higher ionic conductivity for cubic zirconia electrolytes is achieved with smaller grain size and lower thickness of the intergranular regions. The sintering onset temperatures required for nanometric particles are significantly reduced when compared to conventional micrometric powders. However, densification is generally accompanied by an undesirable grain coarsening. A Ramp and Hold Sintering (RHS) is the simplest densification schedule, consisting of heating up to the peak temperature followed by a holding time at that temperature. Another approach, called Two-Step Sintering (TSS) is based on the principle that the activation energy for grain growth is lower than the activation energy of densification. The key elements in this method are heating up to a high temperature to achieve a density >75% Theoretical Density (TD) to render the pores unstable, and then cooling down rapidly to a lower temperature to finish sintering and hinder grain growth. Alternatively, considerable efforts have been made in increasing the heating rate and/or reducing the hold time at the peak temperature during sintering cycles in processes that are generally referred to as 'Fast Firing' (FF) or 'rapid sintering'. This review summarises the attempts in the literature for obtaining dense monolithic nanocrystalline Yttria-Stabilized Zirconia (YSZ) ceramics by pressureless sintering schedules carried out in conventional furnaces. RHS, FF and TSS schedules are reported only from YSZ as starting powders, i.e. without the aid of any additional dopant or grain growth inhibitor. For the sake of comparison, the discussion is focused mainly on YSZ nanoceramics with final densities >99% TD and average grain size <100 nm. Powder and shaping effects on microstructure and properties of bulk nanoceramics are discussed. A comparison among sintering approaches is then made taking into account the microstructural development of the nanostructures and some key properties of the products. © 2015 Institute of Materials, Minerals and Mining and ASM International.
... After their allotropic transformation (573ºC), quartz particles undergo pronounced shrinkage, increasing microscopic stresses. As the piece cools, the particles begin to debond from the matrix, giving rise to peripheral cracks [23]. MUD has a positive effect on the sinterization process, open porosity decreases in 97/3 and 95/5. ...
Article
Full-text available
The main objective of this paper is focused in the use of a waste generated by the TiO2 pigment industry, ilmenite mud (MUD), on the production of ceramic bodies. These ceramic bodies were produced from mixtures of a commercial red stoneware mixture (RSM) with different concentrations of mud (3, 5, 7, 10, 30 and 50 wt.%). The samples were sintered to simulate a fastfiring process. The sintering behaviour of the fired samples was evaluated by linear shrinkage, means of water absorption, apparent porosity and bulk density. Both green powder and fired samples were characterised by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC/TG), field emission scanning electron microscopy (FESEM) and bending strength measurements. Moreover, the activity concentrations of radionuclides were measured by highresolution low-background gamma spectrometry, because this mud is a NORM (Naturally Occurring Radioactive Material) waste. Finally, the TCLP leaching test (Toxicity Characteristic Leaching Procedure, USEPA) was performed to assess the risks of use tiles from an environmental perspective. The results demonstrated that MUD can be successfully valorised in the manufacture of red stoneware ceramic bodies with similar or even better technological properties than commercial materials used currently.
... Thus, as verified by the authors, along with the increase in the flexural strength the microstructures could be degraded. For the same condition of fast cooling, the degree of microstructural degradation decreased with an increase in the flexural strength [2,18]. ...
... There was an increase in fracture toughness by reducing the particle size of quartz. The effect of the crystalline quartz particles on mechanical strength was also investigated by De Noni et al. [25], who found a relationship between the compression caused by the quartz crystal in a glassy phase and microstructural defects caused by cracks around (or inside) quartz particles. Moreover, Gilabert et al. [26] modelled the fracture patterns of quartz particles added to a glassy (albite) matrix. ...
Article
The influence of quartz particle size, weight content and firing temperature on the Young's modulus of porcelain tiles was studied. To simulate a porcelain tile microstructure, an albite glass matrix with added crystalline quartz particles was developed. Average particle size of quartz (3.4 and 31 μm) and volume content (18.5 and 37.6 vol%) were varied. An acoustic impulse excitation technique was used to measure the elastic modulus from room temperature up to 700 °C. Results showed that quartz has a major influence on the elastic modulus of porcelain tiles. At temperatures below 573 °C, a hysteresis area between the Young's modulus curves during heating and cooling was closely related to quartz particle size. Between 573 and 700 °C, the variation of the Young's modulus was related to the quartz volume fraction. By using those correlations, a prediction of quartz content and quartz particle size in commercial porcelain materials can be carried out from Young´s modulus data.
... La baldosa de gres porcelánico se compone de una mezcla triaxial similar a la de la porcelana, compuesta de arcilla, un material de relleno y un material fundente [9], [10], [11]. La arcilla confiere plasticidad a la mezcla, permitiendo el fácil conformado, actúa como aglomerante para los otros componentes en la pieza cruda y contribuye a la formación de mullita después de la cocción. ...
Article
Full-text available
In this research are presented the results of using rice straw ash (RSA) in low proportions as substitute of feldspar for manufacturing stoneware tiles. Specimens of semidry triaxial mixtures, where feldspar was substituted for different percentages (25 % and 50 %) of RSA, were prepared by uniaxial pressing, followed by drying and sintering. Physical and mechanical properties of sintered bodies were evaluated. Porcelain stoneware tile specimens C0 and CF25 reached bending strength and water absorption values were in accordance with standard ISO 13006 (Annex G, BIa) ( ≥ 35 MPa and ≤ 0.5 %, respectively). However, in porcelain stoneware tile specimens CF50 due to bloating phenomenon was not possible obtain commercial tiles in accordance with standard ISO 13006. By using Scanning Electron Microscopy (SEM) needles of primary and secondary mullite were identified in a vitreous phase; and by using X-Ray Diffraction (XRD) mullite and quartz phases were identified. It was concluded that feldspar can be substituted positively by RSA in stoneware tile pastes.
... At higher magnifications (Fig. 3(b) and (d)) it is possible to see microcracks located in the interlayer formed between the unsolved quartz particles and matrix, and also through the quartz particles as reported in the literature. 19 The microcracks display very frequently a circumferential orientation because in the cooling stage quartz shrinks more than the glassy phase. Consequently, the mechanical behavior of quartz porcelains may be unstable and not easily predictable. ...
Data
Full-text available
A focused research was conducted on samples prepared from an industrial porcelain tile composition containing quartz, used to produce ceramic floor tiles, with the aim of evaluating the variation of fired specimens' Young's modulus with temperature. These samples were fired in controlled laboratory conditions so that specimens with pre-existing cracks were obtained and subject to non-destructive in situ thermo-mechanical measurements (impulse excitation technique) in the 22–700 • C temperature range during heating and cooling processes in order to find evidences to explain the hysteresis phenomenon in the Young's modulus versus temperature curve. The observed irreversible Young's modulus may be directly related to the pre-existent cracks that on heating and cooling are closed and opened up respectively, changing thus the Young's modulus which is well characterized by a hysteresis cycle.
... Concerning quartz sands, many papers document their use as component for the production of some ceramic wares [12,13], conversely, the use of Mg containing silicates such as forsterite or cordierite is widely documented [14][15][16][17], but that of olivine or olivine containing powders is presently confined to the production of some special refractory bricks [18,19] or particular glazes for tiles [20]. ...
Article
Full-text available
The present basic research aims to evaluate the possible recycling of olivine, a by-product of a foundry process, into the ceramic industry. With this goal in mind, olivine powders (O) were milled alone or blended with 20, 40, 60 and 80 wt% of a high grade kaolin (K) by attrition milling to obtain powders of different composition. Samples made with K alone were also prepared as blank composition. All mixtures were dried, sieved, uniaxially pressed into specimens and air sintered for 1 h at temperatures ranging from 1100 to 1400 °C. The resulting materials were characterized by water absorption, shrinkage and phase composition in order to test their sintering behaviour. It was observed that all compositions, sintered below 1100 °C display high open porosity, but enter into the final sintering stages between 1150 and 1200 °C as a function of their compositions, when their water absorption lowers below 5%.
... The presence of cracks caused by the b-quartz to a-quartz transition was not observed probably due to the small size of quartz grains (see Fig. 2) and to the relatively low cooling rate during the sintering process [37,38]. Table 3 reports apparent density of green and fired materials, flexural rupture strength and Vickers hardness of the samples fired at 1040 8C for 1 h. ...
Article
Two different types of clay (a yellow and a red clay) were used to prepare two sets of materials containing spent foundry olivine sand. They were blended by attrition milling in varying proportions to obtain powders of different composition.All mixtures were dried, sieved, uniaxially pressed into specimens and air sintered for 1 h at temperatures ranging from 900 to 1140 °C. The resulting materials were characterized by density, water absorption, shrinkage, crystallographic composition, microstructure and physico-mechanical properties. Mechanical and crystallographic properties were determined on samples fired at 1040 °C in order to compare materials with similar characteristics. It was observed that, after sintering, all compositions show the presence of the glassy phase which surrounds the crystalline grains and the set of materials prepared using the red clay displayed best overall behavior. XRD analysis performed on the free surface of the fired samples did not show the presence of compounds containing heavy metals present in the starting materials.
... It is important to note the existence of both open (<5 µm) and closed (<10 µm) pores in the samples. Once the allotropic transformation is carried out at 573°C, quartz particles produce shrinkage giving rise to cracks when the piece cools [65]. The addition of the moderate percentages of ilmenite mud has a benefit, decreasing the open porosity as we can see in 97/3 and 95/5 samples. ...
Chapter
Full-text available
The recycling of waste generated by industrial production processes is a topic of considerable environmental and economic interest. The minimization of waste disposal, avoiding its direct release into the environment, generates environmental benefits for industries in addition to the manufacture of the main product. Some of these wastes, measured by their radioactive element content, may be considered as naturally occurring radioactive material (NORM). Two of these NORMs are phosphogypsum (PG) and ilmenite mud (IM) come from the fertilizer industry and TiO2 pigment industry, respectively. This chapter discusses the viability of valorization and/or recycling of PG and IM in the manufacture of sulfur polymer cement/concrete, Portland cement, and ceramic materials.
... The amorphous phase has a very low linear thermal expansion coefficient compared with that of mineral phases (Kingery et al., 1976). The presence of 53.8% of amorphous phase, combined with a moderate amount of quartz (15.1%), makes these ceramics less sensible to thermal gradients than other materials, such as BAR1 and BAR2 ceramics, where the consistent amount of quartz can cause some problems due to differential expansion or shrinkage (De Noni Jr et al., 2009. The high sintering level, favored by the complex chemical composition of the clayey matrix, improves both the fracture strength and the Young's modulus of the ceramic body (Allegretta et al., 2015). ...
... Quartz is a filler material which remains stable in the normal firing range and reduces distortions and shrinkage [3]. Many studies on triaxial porcelains report that quartz significantly affects triaxial porcelain properties [4][5][6] . Recently, researchers were tried to replace those natural raw materials with a variety of industrial waste materials. ...
Article
Full-text available
In the preparation of triaxial porcelain from Palm Oil Fuel Ash (POFA), a new parameter variable must be determined. The parameters involved are the particle size of POFA, percentage of POFA in triaxial porcelain composition, moulding pressure, sintering temperature and soaking time. Meanwhile, the shrinkage is the dependent variable. The optimization process was investigated using a hybrid Taguchi design and flower pollination algorithm (FPA). The interaction model of shrinkage was derived from regression analysis and found that the shrinkage is highly dependent on the sintering temperature followed by POFA composition, moulding pressure, POFA particle size and soaking time. The interaction between sintering temperature and soaking time highly affects the shrinkage. From the FPA process, targeted shrinkage approaching zero values were predicted for 142 μm particle sizes of POFA, 22.5 wt% of POFA, 3.4 tonne moulding pressure, 948.5 °C sintering temperature and 264 minutes soaking time.
... A presença de quartzo e de caulinita no resíduo sólido contribuem para o seu uso em revestimentos cerâmicos devido à melhoria das propriedades físicas que proporcionará à cerâmica. De acordo com SOLER et al. [18], o quartzo proporciona melhoria das propriedades mecânicas do material cerâmico, como a resistência mecânica à flexão. A caulinita contribui para a melhoria das propriedades mecânicas e térmicas do material cerâmico [19]. ...
Article
Full-text available
The current paper had as main aim characterize and assess the use viability of a solid waste from sand beneficiation process in the production of ceramic tiles. To determine the main components the solid waste was characterized by X-ray fluorescence and the main crystalline phases were determined by X-ray diffraction. To evaluate the addition effects of the solid waste over the solid waste was introduced into a ceramic composition in proportions of 5% and 10%. The ceramics materials obtained were subjected to the linear retraction, water absorption and flexural strength analysis according to the Brazilian standard NBR 13818 (1997). Additionally, the solid waste and the ceramic materials obtained in this study were classified according to the Brazilian standard NBR 10004 (2004) to assess the potential environmental impact. The main solid waste constituents identified were silicon dioxide and aluminum oxide, respectively 50.2% e 19.2%, distributed in the crystal forms of quartz and kaolinite. The ceramic materials obtained after firing at 1100oC, without and with 10% of solid waste presented respectively flexural strength of 13.86 MPa and 14,52Mpa. The results of water absorption without and with addition of 10% of solid waste were respectively 16.96% and 16.63%, both appropriate performances for use in ceramic tiles according to the Brazilian standard NBR 13818 (1997). On the other hand, the ceramic materials obtained with the addition of 10% of solid waste were classified as inert materials according to Brazilian standard NBR 10004 (2004), showing the capability of incorporating solid waste in ceramic materials.
... [3][4] Especially for the largesized tiles (e.g., 1200 × 3600 mm 2 or 1800 × 3600 mm 2 ), the requirement of mechanical strength is even higher than that of the medium-or small-sized products (up to 600 × 900 mm 2 ). The well-known strengthening mechanisms or processes, such as eliminating surface defects, 5-8 minimizing grain size, [9][10] improving densification or reducing porosity, [11][12][13][14] dispersion strengthening, [15][16] fiber reinforcing, [17][18] applying low expansion glaze, 19 have obtained great achievements in enhancing the mechanical properties of ceramic tiles. However, a more efficient and economical strengthening technique for large-scale application still needs to be pursued in building ceramic industry. ...
Article
To improve the flexural strength of ceramic tiles, a surface strengthening method is presented in this work. By co‐firing coating and substrate, residual compressive stress is introduced in the coating. The phase composition and morphological characteristics of coating materials, and the influences of coefficient of thermal expansion (CTE) and coating thickness on the flexural strength have been investigated. The pre‐stressed ceramic tile is prepared by pressureless sintering a green body coated with a low CTE coating at 1200 °C. The CTE of green body and optimal coating is 7.85 × 10−6 °C−1 and 5.69 × 10−6 °C−1, respectively. The flexural strength of pre‐stressed porcelain tiles (89 ± 3 MP) has been increased by 102% when the coating thickness is 67 µm compared to their uncoated counterpart (44 ± 3 MPa). This simple surface strengthening method of ceramic tiles is cost‐efficient and economical for large‐scale industrial applications.
... This hypothesis was first suggested by Zoellner [13]. Some researchers have also stated this opinion (mechanically strengthening is related to the amount and size of crystals rather than quartz) [14,15]. According to these researchers, mullite amount increases both hardness value and deep abrasion property of porcelain tile. ...
Article
In this study, it is aimed to design porcelain tile composition with high impact strength. In the composition developed, according to the composition failed in impact strength test, amount of mullite crystals is aimed to be increased and amount of vitreous phase is aimed to be decreased. Technical properties of the composition developed were compared with the standard composition. SEM and XRD analyses were conducted. Porcelain tiles prepared with the newly developed composition and standard porcelain tiles were tested with the method stated in -CSTB-NF UPEC (French Quality Certificate)-Specification No: 2898 (resistance of the tiles against the impact strength and 510 g mass) standard and the results were compared. It was stated that the newly developed composition (D1) has passed the impact strength test and has been taken to production.
... The liquid phase sintering which eliminates the pores and the feldspar react with amorphous silica to interlock the particles for the development of strength behavior (Ritwik Sarkar et al., 2007). The bioceramic tiles are higher strength than the standard tile and it is concluded that the nano sized biosilica exhibits greater mechanical strength when compared to quartz (Agenor De Noni Junior et al., 2009). The mechanical strength of the ceramic tiles depends on its elastic properties, surface and internal defects and the character of the force to which it is subjected. ...
Article
Full-text available
Vitrified bioceramic tiles were subjected by the incorporation of synthesized biosilica from bioresidue of Rice straw ash. The partially and fully substitution of biosilica for quartz in porcelain formulation enhances the physico-mechanical parameters. The ultrasonic pulse velocity was correlated with the compressive strength. The result which confirms that the biosilica act as a filler in porcelain tiles thus improves the mechanical behaviour of bioceramic tiles than reference tile. This synthesized biosilica has a highly substantial for quartz and it is environmental pollutant control in a sustainable way. Thus, biosilica is a suitable material for the production of vitrified bioceramic tiles.
... GPOFA was presented by the best bulk density specimen to improve compaction and forming process in sintering process because GPOFA was made by lower particle size than UGPOFA. Theoretically, a smaller particle size powder would be more reactive [46][47][48]. Fig. 1(e) shows optimal parameters of the best flexural strength, where it was recorded by a condition of 5 wt.% of GPOFA composition, pressed at 4 t, sintered at 1200 °C, and 180 min of soaking times. It was absolutely like optimal bulk density specimen, but composition of POFA 5 wt.% was reported by optimal flexural strength specimen. ...
... The role of the β ↔ α quartz transition is amply recognised, not only for possible ruptures during cooling [60][61][62][63][64] but also for its effect on elastic properties and residual stresses [61,[64][65][66]. ...
Article
A silicate ceramic that is similar to porcelain and exhibits a maximum toughness of 4.6 MPa m1/2 was obtained by tape casting from kaolin and 3 vol% of alumina fibers. Improved toughness and strength are achieved with the organized micro-composite microstructure that results from preferential orientation during the shaping of kaolinite particles and fibers in-plane of layers. During sintering, typical nucleation and growth processes of mullite produce specific microstructural characteristics, such as bulk zones, oriented fibers and large interfacial zones between the fibers and the bulk. Toughening is attributed to the decreased crack energy in the bulk ceramic, in which a dense and organized network of short mullite occurs, and in interfacial zones containing a superimposed network of large mullite. The silicate ceramic that is reinforced by only 3 vol% of the alumina fibers is strong (95 MPa) and tough (4.6 MPa m1/2); although these properties are often mutually exclusive.
Article
Full-text available
Su damlasının üzerinde 90o’den büyük açı yaptığı yüzeyler hidrofobik yüzeyler olarak adlandırılır. Hidrofobik yüzeyler özellikle hijyen gerektiren ortamlarda yaygın olarak kullanılmaktadır. Yapılan çalışmada endüstriyel porselen karo yüzeyinde hidrofobik yüzey özelliğinin alkol ve su bazlı iki farklı türde polimer kaplama yapılması ve kendinden hidrofobik özelliğe sahip çinko oksit tozu ile ticari porselen karo sırının modifiye edilmesiyle eldesi amaçlanmıştır. Yüzeylerin morfolojik gelişimi taramalı elektron mikroskobu ile incelenmiş ve faz gelişimi X-ışınları difraksiyon cihazı ile belirlenmiştir. Temas açısı gonyometresi kullanılarak polimer kaplanmamış ve alkol ve su bazlı polimer ile kaplanmış yüzeylerin temas açıları ölçülüp, kıyaslanmıştır. Sonuç olarak alkol bazlı polimer ile kaplanmış yüzeylerin su bazlı polimer ile kaplanmış yüzeylere göre daha iyi hidrofobik etki gösterdiği tespit edilmiştir. Mikron boyutunda çinko oksit ilavesi yapılan sır kompozisyonlarının endüstriyel fırında pişirim sonrasında willemit (Zn2SiO4) fazı gelişimi gözlenirken, nano boyutta çinko oksit kullanımı zinsit fazı (ZnO) gelişimini sağlamıştır. Nano çinko oksit modifiyeli sırlarda yüzeyde çatlak oluşumu yüzeyin su emmesini sağladığından kaplanmamış yüzeylerin temas açısı ölçümü gerçekleştirilememiştir. Polimer kaplama sonrası en yüksek temas açısı 139o olarak N2 kodlu sır kompozisyonunda elde edilmiştir.
Article
Full-text available
Recently ion exchange, also known as chemical tempering, has been applied to strengthening of porcelain tiles based on the substitution of ions present in the material by larger ones. This paper investigates the chemical tempering in industrial porcelain tiles by the variation of process parameters such as temperature, immersion time and chemical composition of the porcelain tile. Furthermore, a numerical simulation of the ionic diffusion process was applied. Using a design of experiments approach, the results show that the temperature and the chemical composition primarily affected the flexural strength of the tile. The largest increment obtained was 37% resulting in a porcelain tile with flexural strength of 73 MPa after chemical tempering. Through numerical simulation it was possible to estimate a diffusion coefficient of potassium ions equal to 1.25×10‐14 m2·s‐1 into the porcelain tile microstructure. This value is about 10 times higher than the diffusion coefficient in glasses.
Article
Full-text available
Ceramics are semi vitreous materials that are made of kaolin clay, feldspar and quartz. These materials are fired at a temperature greater than 1000°C. Due to low sinterability during firing, quartz remains embedded in a glassy matrix. During cooling, a mismatch in the thermal expansion coefficient of quartz and its surrounding creates cracks as a result of residual stress. This study therefore explores the effect of quartz particle size on the magnitude of residual stress. The results are later compared with the mechanical behavior of the samples. Test samples were pressed at 40 MPa and then fired at a peak temperature of 1300°C at a rate of 60°C/min. Their microstructure was studied using a scanning electron microscope (SEM). The X-ray diffraction method was used to measure residual stress, calculation was based on [101] and [110] quartz planes. In addition, the measurement of flexural strength and hardness was limited to three point loading and Vickers indentation, respectively. The study revealed that the residual stress on quartz decreases with particle size over a range of 45–200 µm. The decrease was attributed to cracks formed in the microstructure of fired samples. The SEM micrograph of bodies with 45 µm showed a crack free glassy phase. As a result, a high value of flexural strength (33±1 MPa) and hardness (5.8±0.2 GPa) was exhibited by these samples. These results further point out that flexural strength is comparable to ISO 13006 standards of ≥ 35±2 MPa. The samples with 90 µm particle size exhibited strength of 25±1 MPa and hardness of 5.4 ± 0.1 GPa. Due to severe cracks triggered by residual stress effect, samples with 200 µm exhibited strength of 15±1 MPa and hardness of 4.6±0.1 GPa. Therefore, to minimize cracks due to stress effect, quartz size milling of less than 90 µm is encouraged.
Article
The characterization of the ceramic materials integrity without damage has become a major issue for many industrial sectors. In this context, a research study has been initiated to assess the influence of the firing conditions on mechanical strength behaviors of Porcelain stoneware and Terracottas specimens. A focus is made on a non-destructive characterization method to evaluate the residual mechanical stresses, based on the Impulse Excitation Techniques. The influence of the cooling rate (≈200 °C/min by air ventilation vs. controlled cooling at 50 °C/h) and the heating temperature (1160 °C vs. 1185 °C for Porcelain stoneware; 1100 °C vs. 1150 °C for Terracotta) have been highlighted. The effect of samples annealing at 700 °C with a heating and cooling rate of 50 °C/h was also evaluated. A significant variation of the internal friction (2.5 times less important with a controlled cooling) and a small variation of 2.0% of the Young and shear moduli of porcelain stoneware samples caused by the cooling rate variation was shown. The negative effect of the fast-cooling was also discussed on terracotta samples by a small decrease (2.7%) of the Young and shear moduli. This decrease caused by a fast-cooling is led to micro-cracks formation induced by the quartz allotropic transformation during the cooling. In the case of terracotta, the 50 °C increase of the heating temperature induces a significant increase of mechanical strength properties linked to the open porosity decrease. The internal friction calculation from Impulse Excitation Techniques are able to efficiently evaluate the heat treatment quality of a porcelain stoneware ceramic material which allows the detection of mechanical performance decrease generated by micro-cracks in ceramic products.
Article
Influence of typical ceramic deflocculant – sodium hexametaphosphate – on the rheological properties (viscosity) of calcium aluminate cement paste, porcelain raw materials mixture (casting slip), and fired porcelain body respectively, was determined. It was used two different typed of calcium aluminate cements (from two sources – producers - Istra, Almatis) with different content of Al2O3 (40 % and 70 %). Sodium hexametaphosphate decreases of water content needed to prepare slip casting with constant viscosity. Deflocculant increases the modulus of rupture MOR of dried green body and its bulk density. Sodium hexametaphosphate admixture is very suitable for the creation of porcelain body with low porosity after firing.
Article
Porcelain is a traditional ceramic material, which is manufactured for centuries from a mixture of kaolin - quartz - feldspar. Replacement of kaolin for calcium aluminate cement can be achieved primarily increases strength of fired body, reduces the coefficient of linear thermal expansion, increases the whiteness of the fired body and increases of sintering activity.
Article
The fast firing technique is one of the most important ways to save energy consumption and improve production efficiency in the porcelain tile industry. In the actual production, excessively short firing cycle time easily causes the cutting edge defects. This work examines the effect of microstructure on cutting processability of a representative composition of a commercial porcelain tile fired at 1200 °C with two different firing cycles as follows: 40 min and 60 min. The phase composition and microstructure were investigated by using a combination of techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result indicated that it was beneficial to extend firing cycle (from 40 min to 60 min) for the cutting processability of porcelain tiles, which was due to the formation of positive microstructures such as secondary mullite needles and small-volume residual quartz.
Article
Crushed alumina powder heterocoagulated with 1 or 2 wt.% carbon nanotube (CNT) was used to produce plasma-sprayed coatings with improved tribological properties. Heterocoagulation is a colloidal processing technique, and it was used to produce a homogenous mixture of CNT in alumina. These coatings were compared with a pristine alumina coating using a pin-on-disk setup under various speed–load conditions. A 6-mm-diameter WC–Co ball was used as counterbody. The wear resistance of the coatings increased in the following order: pristine alumina, alumina with 1 wt.% CNT, and alumina with 2 wt.% CNT. Wear progressed by low cycle fatigue, microfracture, and finally pulverization of the already dislodged wear debris on repeated rubbing by the counterbody. The higher wear resistance of the reinforced coatings is attributed to their higher hardness and fracture toughness. The pristine alumina coating was found to crumble owing to diffuse intergranular fracture beneath the surface during rubbing under higher speed and load. Upon crumbling, the pulverized debris assumed a paste-like form and was ejected at the top under the compressive action exerted by the counterbody at its leading edge. The high wear of the pristine alumina coating is attributed to this effect.
Article
Full-text available
This work compares values of Young's modulus and fracture toughness of amorphous albite measured from different experimental techniques. Sodium feldspar powder was used to synthesize the albite glass. After quenching, the microstructure of the amorphous solid was analyzed via scanning electron microscopy and X-ray diffraction. Several nanoindentations on albite samples were carried out with two purposes: determination of Young's modulus by continuous stiffness measurement, and critical stress intensity factor by crack size evaluation. Concurrently, impulse excitation technique and three point bending single-edge notched test were adopted for providing the comparison of elasticity and toughness, respectively. Young's modulus measured by continuous stiffness yielded a value of 71.8 +/- 0.9 GPa, which was in agreement with the value obtained by impulse excitation (72.5 +/- 1.3 GPa). The fracture toughness determined by nanoindentation was slightly higher (0.86 +/- 0.06 MPa m(1/2)) than that (0.78 +/- 0.06 MPa m(1/2)) obtained by single-edge notched beam.
Article
Porcelain stoneware tile is the best class of ceramic tiles regarding technical performance. Low porosity and high glass content are some of its highlighted characteristics. The manufacturing cost is highly dependent on the feldspar content and the processing flow rate. Certain technical bottlenecks in the manufacturing steps, such as milling, forming and firing, are intrinsically associated with limitations in the processing properties, such as the dry strength, bulk density and pyroplastic deformation. In this work, improvements in these properties were achieved using high energy milling after conventional milling. This study was carried out on a pilot industrial scale in the milling stage. Six experimental runs were evaluated. Slurries were spray‐dried. The powders were humidified with 6.5% moisture. Specimens were conformed under a specific pressure of 45 MPa. The firing was performed using temperature ranging from 1150 to 1230 °C. The use of high energy milling, in comparison to traditional milling for the similar particle size distributions, has increased the dry density, +0.2 g.cm‐3, dry bending strength, +1.0 MPa, and decreased the pyroplastic deformation index, ‐1.10‐5 cm‐1. These results allow an estimated thickness reduction of 10%.
Article
In recent years, an innovative system for a rainscreen façade system with low thickness and large tiles of porcelain stoneware has been patented. This paper presents the results of a large experimental campaign investigating mechanical performance of a ceramic tile in 3different configurations: tile without net, with fiberglass net glued on the back, and the entire cladding system (slab/net/frame). The main objective is to determine material mechanical characteristics (e.g. modulus of rupture and Young's modulus) considering a protocol of artificial ageing (fatigue test, freeze-thaw, heat-rain, H2O Saturation, heat treatment, accelerated corrosion SO2 and NaCl, irradiation UVB and condensation) in order to understand the possible decay during the service life and consequently to design the technological solution of a rainscreen façade system. The results showed that on the modulus of rupture the most influences ageing effects are fatigue test and freeze-thaw while the influence on young's modulus is negligible. Furthermore, it is necessary to consider second-order effects for the evaluation of the resistance and, finally, that the fiberglass net does not lead to a significant increase in resistance.
Book
Full-text available
Rapid trend of industry and high technological progress are the main sources of the accumulation of hazardous wastes. Nuclear applications have been rapidly developed recently, and several nuclear power plants have been started to work throughout the world. The potential impact of released hazardous contaminants into the environment has received growing attention due to its serious problems to the biological systems. A book "Management of Hazardous Wastes" contains 9 chapters covering 2 main topics of hazardous waste management and microbial bioremediation. This book will be useful for many scientists, researchers and students in the scope of development in waste management program including sources of the hazardous waste, the government policies on waste generation and treatment with particular emphasis on bioremediation technology.
Article
En este documento se presentan los resultados de una investigación basada en el uso de un material alternativo como lo es la ceniza de tamo de arroz (CTA), en sustitución del material de relleno (cuarzo) utilizado para la manufactura de gres porcelánico. Para ello, fue preparada una mezcla estándar (RS_0) (15 % cuarzo, 45 % feldespato, 25 % arcilla caolinítica y 15 % caolín), y dos mezclas más donde la CTA sustituyó al cuarzo en porcentajes del 25 % y 50 % (RS_25 y RS_50, respectivamente). Especímenes de las pastas obtenidas fueron moldeados, secados, y cocidos. A partir de los valores de absorción de agua y resistencia a la flexión, los especímenes cocidos de las mezclas estándar (RS_0) y aquellas con adición de CTA RS_25 y RS_50, fueron clasificados como baldosas de gres porcelánico prensadas en seco pertenecientes al grupo BIa, conforme a la normativa ISO 13006 (resistencia a flexión > 35 MPa y absorción de agua ≤ 0,5 %); sin embargo, en aquellos especímenes cocidos RS_50 el intervalo óptimo de cocción más estrecho y el fenómeno de hinchamiento deben ser tenidos en cuenta a la hora de establecer la temperatura óptima de cocción; lo que indica que debe tenerse un mayor control del proceso de cocción de estas mezclas. Los resultados permitieron concluir que la CTA bajo las condiciones de obtención, sí reemplaza parcialmente el material de relleno utilizado en la elaboración de gres porcelánico.
Article
Due to low water absorption, high bending strength and abrasion resistance, and excellent chemical and frost resistance, porcelain building ceramic tiles are the highest increase in production and sales over all other kind of building ceramic tiles materials. In this paper, porcelain building ceramic tiles was prepared by a fast firing process of rare earth tailings as the main raw material, low fused sand and Zhuji porcelain sand et al mixture. Effects of firing temperature and forming pressure on the sintering behavior and mechanical property of porcelain building ceramic tiles were studied. The sintering behavior of the fired samples was evaluated by linear shrinkage and water absorption. The fired samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and bending strength measurements. The sample is pressured at 15 MPa and sintered at 1180 °C and endowed with 0.04% of the water absorption and 51 MPa of the bending strength, due to denser microstructure. The obtained results would contribute to save natural resources and protect environment.
Article
Calcium aluminate cement CAC is able to increase strength of green body distintly. Influence of typical ceramic dispersants – sodium hexametaphosphate SHMP, sodium carbonate SC and sodium silicate (water glass) SWG – on the rheological properties (viscosity) of calcium aluminate cement – kaolin slurries with different ratio between CAC and kaolin was determined. In all cases sodium carbonate is the most effective dispersant but deflocculation is not very intensive – decrease of torque during the rotational viscometer test was not higher than 15 % (from 68,8 N.mm to 58.3 N.mm for ratio 1:1 of CAC:kaolin suspension when 0,06 %-wt of sodium carbonate was used).
Article
In this article, the effects of sintering on the mechanical and electrical properties of ceramic porcelain insulator reinforced by zirconia (ZrO2) particles are studied for the low frequencies (20 Hz-1 MHz). The samples were prepared for varying contents of zirconia by replacing alumina content in the base porcelain composition. The samples are sintered at 1250 °C and 1350 °C with a heating rate of 5 °C min⁻¹ and the soaking period is 2 h. The β-cristobalite phase of base porcelain decreases and the crystalline phase of zircon increases with the increasing sintering temperature. This improvement in crystallite phase of zircon improves the mechanical strength of the reported samples. The sample with zirconia content of 20 wt% sintered at 1350 °C shows the best mechanical properties with minimum water absorption of 0.89%. The highest measured value for modulus of rupture (MOR), compressive strength, and linear shrinkage are 138 ± 5 MPa, 221 ± 10 MPa, and 10.6%, respectively. The sample with zirconia content of 30 wt% sintered at 1350 °C shows the best electrical properties among all samples. Maximum observed value for AC dielectric strength of the sintered sample is 22.85 ± 0.5 KV mm⁻¹. The measured AC conductivities of samples are 3.88 × 10⁻¹² S cm⁻¹ and 1.41 × 10⁻⁹ S cm⁻¹ at 500 Hz and 1 MHz respectively. The complex permittivity's of the sintered samples are found to be dependent on contents of ZrO2 and also exhibit a frequency dependent characteristics for a range of frequency (20 Hz to 1 MHz). The result indicates that variation in ZrO2 composition leads to significant improvements in mechanical and electrical properties of porcelain ceramic.
Article
Whiteware is a traditional ceramic material that has been manufactured for centuries from a mixture of kaolin + quartz + feldspar. Replacement of kaolin by calcium aluminate cement can increase the strength of green bodies, reduce the coefficient of linear thermal expansion and enhance the whiteness of fired products. A negative aspect of using calcium aluminate cement in ceramic bodies is reduced sintering activity and therefore, need for a higher firing temperature. Sodium hexametaphosphate admixture was also found to be very suitable for creation of calcium aluminate cement-based whiteware bodies with low porosity after firing. Use of this deflocculant increased the modulus of rupture (IWOR) and bulk density of dried green bodies. Sodium hexametaphosphate also decreases the water content needed to achieve optimal viscosity for slip casting.
Article
In this research are presented the results of using rice straw ash (RSA) as substitute of filler material for manufacturing stoneware tiles. Specimens of standard porcelain stoneware tile (RS_0) were compared to porcelain stoneware tiles where quartz was replaced by RSA in the formulation in percentages of 25% and 50%, respectively (RS_25 and RS_50). Specimens of semidry triaxial mixtures were prepared by uniaxial pressing, followed by drying and sintering. Porcelain stoneware tile specimens RS_0, RS_25 and RS_50 reached bending strength and water absorption values were in accordance with standard ISO 13006 (Annex G, BIa) (≥ 35 MPa and
Article
The article introduces the differences in the properties of whiteware (porosity, strength, thermal expansion coefficient) when a non-traditional binder is used. Pure calcium aluminate cement and a mixture of kaolin and calcium aluminate cement compared with traditional plastic raw material for whiteware - kaolin - are used for the preparation of whiteware bodies with a constant content of non-plastic raw materials: K-Na feldspar and quartz sand. The results are discussed in connection with the microstructure of the fired body of prepared whitewares (mineralogical composition). Calcium aluminate cement (CAC) in whiteware raw-material mixtures is an interesting alternative to kaolin for a higher strength of the green and fired bodies. Using calcium aluminate cement reduces the sintering temperature of the fired body and significantly changes its mineralogical composition: anorthite is the main mineralogical phase instead of mullite, which is typical for standard porcelain bodies made from raw-material mixtures based on kaolin. The coefficient of thermal expansion increases with an increasing content of CAC in the raw-materials mixture.
Article
Full-text available
The goal of this research was to improve the ion exchange mechanism in porcelain tiles by modifying the tile surface chemically. Ion exchange, also known as chemical tempering, is a procedure for improving the mechanical qualities of porcelain tiles. So, solutions comprising alkaline and alkaline earth metals with a low ionic radius were sprayed on the surfaces of pressed unfired porcelain tiles (lithium, calcium, and magnesium). Subsequently, the porcelain tiles were sintered at the maximum densification temperature (1200ºC). The ion exchange process was carried out at 480ºC for 25 min in a eutectic mixture of molten salts with 73 wt.% KNO3 and 27 wt.% Ba(NO3)2. The results show that the flexural strength of the Li+/Mg+2 surface-enriched samples was 75 ± 4 MPa, representing an increase of 32% in relation to non-treated porcelain tiles and an increase of 17% in relation to the chemically tempered samples without prior modification. A significantly larger Weibull modulus (1520) were found for the chemically modified tiles in comparison with the value for the unmodified porcelain tiles (78). These findings demonstrated that chemical modification of the porcelain surface can optimize the ion exchange process, resulting in increased breaking force and, as a result, flexural strength and Young's modulus. This approach can help reduce the thickness of ceramic tiles while maintaining mechanical properties. This would result in lower raw material usage and energy expenditure during production, as well as lower carbon emissions associated with the production of porcelain tiles.
Article
Full-text available
The effect of the quartz component on strength, σf, and fracture toughness, KIc, of a triaxial porcelain was studied by varying the size distribution of the quartz particles. Both σf and KIc were found to increase and then to pass over a maximum as the quartz distribution became finer. Improvements in σf and KIc of more than a factor of 2 were achieved. The flaw size that controlled failure was shown to equal the maximum quartz particle size in the material containing the coarsest quartz component and to be a constant independent of the quartz size in the other materials. The toughness increase was attributed to microcrack toughening of the glass matrix, the microcracks being formed by thermal mismatch stresses between the quartz particles and the glass matrix on cooling from the sintering temperature.
Article
Full-text available
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.
Article
Full-text available
This study was undertaken to determine the influence of post-fire cooling on generation of residual stress and mechanical properties in porcelain tile. The test pieces were prepared and subjected to different types of cooling. Macroscopic stresses were determined by the strain relaxation method with incremental cutting. Microscopic stresses on the quartz particles were analysed by X-ray diffraction (XRD). During fast cooling, a macroscopic residual stress profile, characteristic of tempering processes in glasses, was observed to develop with the ensuing increase in mechanical strength. XRD analysis showed that the quartz particles were subjected to tension, additionally strengthening the material. However, the quartz also gave rise to microstructural deterioration owing to crack generation and growth. Such microstructural deterioration limits the increase in mechanical strength, in particular for the high cooling rates used after the allotropic transformation of quartz. El presente estudio ha sido planteado con el objeto de determinar la influencia del enfriamiento de la etapa de cocción sobre el desarrollo de tensiones residuales y las propiedades mecánicas del gres porcelánico. Para ello se prepararon probetas que fueron sometidas a diferentes tipos de enfriamiento. Las tensiones macroscópicas fueron determinadas con el método de relajación de deformaciones por corte incremental. Las tensiones microscópicas sobre las partículas de cuarzo fueron analizadas por DRX. Se observó que durante el enfriamiento rápido el material desarrolla un perfil de tensiones residuales macroscópicas característico de procesos de templado de vidrios, con el consecuente incremento en la resistencia mecánica. La difracción de rayos X ha puesto de manifiesto que las partículas de cuarzo se encuentran sometidas a tracción, reforzando también el material. Sin embargo, el cuarzo provoca un deterioro microestructural por la generación y crecimiento de grietas. Este último hecho limita el incremento de la resistencia mecánica, lo cual es especialmente notorio para las elevadas velocidades de enfriamiento que tienen lugar después de la transformación alotrópica del cuarzo.
Article
This study was undertaken to determine the influence of post-fire cooling on generation of residual stress and mechanical properties in porcelain tile. The test pieces were prepared and subjected to different types of cooling. Macroscopic stresses were determined by the strain relaxation method with incremental cutting. Microscopic stresses on the quartz particles were analysed by X-ray diffraction (XRD). During fast cooling, a macroscopic residual stress profile, characteristic of tempering processes in glasses, was observed to develop with the ensuing increase in mechanical strength. XRD analysis showed that the quartz particles were subjected to tension, additionally strengthening the material. However, the quartz also gave rise to microstructural deterioration owing to crack generation and growth. Such microstructural deterioration limits the increase in mechanical strength, in particular for the high cooling rates used after the allotropic transformation of quartz.
Article
A study was performed to determine how the nature and proportion of each raw material in the starting mixture affects fired tile phases to end-product whiteness and mechanical strength. High-plasticity kaolin, quartz, potassium feldspar and sodium feldspar were used as raw materials. On firing the porcelain tile, quartz partially dissolved in the liquid phase and a new crystalline phase, mullite formed. Most of the starting quartz remained undissoled, as a result of the fast-firing cycle usually used in firing porcelain tile.
Article
The structure analysis of a natural transparent quartz crystal was carried out using X-ray diffraction amplitudes at temperatures ranging from 298K to 1126 K. The temperature dependence of the atomic probability density function (PDF), the mean-square displacement (MSD) and the orientation of thermal-motion ellipsoids was analysed in detail and shown to be useful for discussing the β-quartz structure. There is no obvious X-ray diffraction evidence supporting a disordered model for β-quartz as previously suggested by neutron diffraction work. Instead, a more weakly disordered or even ordered model seems to be in better agreement with the observations. -from Author
Article
Residual microstructural stresses in ceramics and ceramic composites are shown to influence the fracture toughness by modifying the stress-displacement relation for stretching of crack-bridging ligaments. Modified toughnesses are calculated using a J-integral analysis for several typical stress-displacement laws. The magnitude and sign of the toughening are found to be strongly dependent upon the details of the bridging mechanism and the criterion for ligament rupture. The analysis is also used to derive the condition for spontaneous matrix cracking due to residual tensile stress in the matrix.
Article
The effect of coarse quartz grains on mechanical properties of triaxial porcelain body was examined. Bodies composed of 50 kaolin, 25 potash feldspar and 25% fine quartz, which was replaced in turn with 74-149μm coarse ones, were fired at 1400°C for 1h. Their bulk density was about 2.38g/cm3 and hardly changed with the amount of coarse quartz. Bending strength of the fired specimens was markedly decreased from 1350kgf/cm2 for the body free from the coarse quartz grains to about 900kgf/cm2 by addition of only 0.03% of the coarse grains, and further decreased with an increase in the amount of the coarse quartz grains. Scattering in the bending strength values and also mean deviation of starting point of failure from the maximum stressed point decreased with increase in the content of the coarse quartz grains. From these relations, it was inferred that most failures of the specimens were started at the origin associated with the coarse quartz grains. The results clearly show that not only the control of the quartz grain size within an appropriate range but also the prevention of the contamination by coarse quantz grains are indispensable for the increase in the mechanical strength of a porcelain body.
Article
The effect of grain size of quartz on mechanical strength of poreclain body was examined. The bending strength of the fired body increased with an increase in interplanar spacing of quartz in the fired body, which indicates that the quartz is under a tensile stress. Consequently, the glassy matrix surrounding the quartz grains is a compressive stress which acts as prestress, improving mechanical properties. The strength of the body depends on the grain size of quartz, and maximum strengths were obtained at 10 to 20, 5 to 10 and 5μm, respectively, fired at 1400, 1350 to 1250 and 1200°C. Smaller and larger quartz grains gave lower strength, probably because of extensive dissolution and crack generation, respectively.
Article
The science governing the strength and fracture of structural ceramics has developed from a mostly empirical topic in 1965 into a mature discipline that now sets the standards in the field of mechanical behavior. The intent of this review is to provide a perspective regarding this evolution, followed by succinct descriptions of current understanding. The rapid developments in the field are considered to have commenced upon the first concerted attempt to apply fracture mechanics concepts to ceramics, beginning in the middle 1960s. This allowed a distinction between the separate contributions to strength from the flaws in the material and from the microstructure, as manifest in the fracture toughness. Another contribution that accelerated the learning process was the development of indentation techniques, which allowed trends in the damage resistance of new ceramics to be assessed on a routine basis. However, the most important development, which originated at about the same time, was the discovery of toughened zirconia alloys. The ensuing research on these alloys established two vital precedents.
Article
Samples made from a mixture of 50% kaolin and clay, 25% quartz and 25% feldspar were tested by non-destructive sonic resonant method, which is sensitive to the structure defects. Sound velocity and Young's modulus of the green samples were measured during a cooling stage of the firing from temperature 1250°C. Fired samples were also measured in temperature cycles 20–800–20°C to reveal a role of the quartz grains in porcelain structure. A microcracking was begun in the cooling stage at the glass phase transformation point (∼760°C) and continued to room temperature as a consequence of different thermal expansions of phases. A sharp drop of the mechanical strength (∼25%) measured during cooling between 600 and 500°C confirms an important function of the β→α transformation of quartz. Unsolved quartz grains decrease their volume and generate tensile stress in their close surroundings, which causes the microcracks. Sound velocity and Young's modulus of the fired samples evidenced hysteresis on heating and cooling, attributed to microcracking during cooling and healing the microcracks during heating in the region of the α–β transformation of quartz. Given those conditions, there follows a rapid change of the sound velocity (∼21%) and Young's modulus (∼46%).
Article
Now in its seventh edition, this accessible book provides readers with clear and concise discussions of key concepts while also incorporating familiar terminology. The author treats the important properties of the three primary types of materials (metals, ceramics, and polymers) and composites, as well as the relationships that exist between the structural elements of materials and their properties. Throughout, the emphasis is placed on mechanical behavior and failure, including techniques that are employed to improve performance.
Article
In the last years polished white porcelain stoneware tiles, coupling the smooth and glossy surface with the increased body whiteness, get a prominent role on the market. The bright white colour is obtained by adding noteworthy quantity of opacifiers, such as zircon, corundum and spinel. To better understand the complex relationships among the microstructure and the mechanical, tribological and functional behaviour of this class of products, four polished white porcelain stoneware tiles were selected and thoroughly characterized by a wide spectrum of chemico-physical and microstructural analyses. Products exhibit excellent mechanical properties (flexural strength, Young modulus, fracture toughness) with a clear dependence of these properties on porosity and phase composition. Mullite and zircon tend to increase the mechanical performances, through a predominant mechanism of matrix reinforcement, while quartz plays an opposite role.
Article
This paper examines the development of microscopic residual stresses on quartz particles in porcelain tile using the XRD technique. The study was conducted with a typical porcelain tile composition consisting of sodium feldspar, kaolin, and quartz, using quartzes with different particle sizes. The methodology used, based on determining the volume strain of the quartz unit cell, allowed a residual stress value equivalent to the entire particle and not just to a given crystalline plane to be obtained. The linear thermal expansion measurements indicated that, for all test compositions, the quartz in the mixture contributes to a thermal expansion coefficient comparable to the expansion of its c-lattice parameter. When this information was taken into account in the theoretical estimation of microscopic residual stress, the results were verified to be consistent with the experimental measurements.
Article
The development of macroscopic residual stress, as in glass-tempering processes, was studied for porcelain tile. Mechanical strength was observed to increase less than might be theoretically expected, owing to deterioration of the sintered tile microstructure. A model has been developed, using linear elastic fracture mechanics, to estimate the natural flaw size in the tempered material. The study shows that as the cooling rate raises, the macroscopic residual stress and flaw size increase. This microstructural deterioration is mainly attributed to the allotropic transformation of quartz in the presence of thermal tensile stress at the porcelain tile surface.
Article
Stable crack growth can be produced on residually stressed surfaces, provided that the residual-stress profile is carefully chosen. Once identified, these conditions will lead to strengthening and an insensitivity of strength to the size of the initial surface flaw. Theoretical calculations are performed that involve choosing idealized forms of either the required toughness curve or the residual-stress profile. The results of this analysis allow the range of stable growth and the strengthening to be determined. Thus, in the material-design process, if the range of surface flaws in the stress-free surface are known, then the required stress profile or toughness curve for optimum performance can be selected.
Article
The types of fractures in a whiteware body containing quartz vary as a function of quartz grain size. The transition from one type of fracture to another is illustrated by strength, thermal expansion, and water absorption, as well as microstructural observations. The thermal expansion behavior of compositions containing alumina does not vary as a function of grain size, thus showing the absence of fracture in white-ware bodies containing alumina.
Chapter
The uses of tempered glass for architectural, automotive, and commercial applications are enumerated. The importance of tempered glass as a “safety” glazing is discussed. The glass tempering process is described. The physics of the tempering process is outlined. The strength and break pattern characteristics of tempered glass are delineated.
Article
The present study was undertaken to determine the influence of sintered porcelain tile microstructure on mechanical properties (fracture strength, modulus of elasticity and fracture toughness) and surface properties (gloss and stain resistance). To obtain sintered specimens with different microstructures the peak firing temperature was varied for bodies made with industrial spray-dried powder, and sets of test compositions were also made in which quartz content and quartz particle size were varied. Liquid-phase sintering is the typical densification mechanism involved in the achievement of minimum porosity, which is characterised by isolated round pores. Bloating occurred above the firing temperature for minimum porosity. Increases in quartz content and quartz particle size in the starting composition led to reduced body sinterability, and thus gave rise to higher porosity in the fired tile. Mechanical properties were adversely affected by an increase in fired tile porosity. For the same variation in porosity, mechanical properties were more sensitive to the change in quartz content than to changes in particle size. No toughening effect was observed with a rise in quartz content or a decrease in particle size: mechanical properties depended primarily on sintered specimen porosity. Gloss and stain resistance (which characterise polished surface quality) varied with surface porosity, both showing the highest values for lowest porosity. The relationship between porosity and gloss was close to linear.
Article
The science governing the strength and fracture of structural ceramics has developed from a mostly empirical topic in 1965 into a mature discipline that now sets the standards in the field of mechanical behavior. The intent of this review is to provide a perspective regarding this evolution, followed by succinct descriptions of current understanding. The rapid developments in the field are considered to have commenced upon the first concerted attempt to apply fracture mechanics concepts to ceramics, beginning in the middle 1960s. This allowed a distinction between the separate contributions to strength from the flaws in the material and from the microstructure, as manifest in the fracture toughness. Another contribution that accelerated the learning process was the development of indentation techniques, which allowed trends in the damage resistance of new ceramics to be assessed on a routine basis. However, the most important development, which originated at about the same time, was the discovery of toughened zirconia alloys. The ensuing research on these alloys established two vital precedents.
Article
Numerical computations of the strain energy release rate for cracks propagating around the interface between a spherical particle and a matrix have been used to determine the strain energy release rate function for the case where stresses arise due to differential thermal contraction. The strain-energy release rate function was found to exhibit a maximum as a function of crack length consistent with the theoretical conditions for crack extension and arrest proposed by Lange. The calculations show that a critical particle size exists below which crack extention does not occur for a given thermalmechanical stress. The predicted critical particle size correlates well with experimental results.Des calculs numriques de la relaxation d'nergie de dformation dans le cas de fissure se propageant au voisinage de l'interface entre une particule sphrique et une matrice ont t utiliss en vue de dterminer la fonction de relaxation de vitesse d'nergie de dformation dans le cas o les contraintes sont cres par une contraction thermique diffrentielle. Cette fonction a t trouve telle qu'elle prsente un maximum suivant la longueur de fissure et que ce maximum est compatible avec les conditions thoriques d'extension de fissure et d'arrt de fissure proposes par Lange. Les calculs montrent qu'il existe une dimension critique de particule en-dessous de laquelle l'extension de fissure ne se produit pas pour en systme donn de contrainte thermomcanique. La dimension critique de particule que l'on peut prdire est en bonne corrlation avec les rsultats exprimentaux.
Article
The effect of filler grain size, quartz content in the filler and firing conditions (sintering temperature, firing time) on the physical and mechanical properties of a sanitary-ware porcelain has been studied in the narrow range of values used by industrial practice. The investigation has been carried out using the Taguchi method for experimental design. Quartz grain size is the most important factor regarding the physical properties and dominates bending strength in two ways, directly by inducing compressive stresses to the vitreous phase and indirectly through the development of a favorable microstructure. The characteristics of the last are discussed in detail. The optimum grain size of quartz was found to be 5–20 μm. This results in 20–30% increase of bending strength compared to the reference porcelain. The results confirm the “Matrix Reinforcement” theory, however, the positive effect of mullite content on bending strength was not observed.
Advanced Techniques for Assessment Surface Topography
  • Liam Blunt
  • Xiangqian Jian
Liam Blunt and Xiangqian Jian, ed., Advanced Techniques for Assessment Surface Topography. Kogan Page Science, London and Sterling, 2003.
El vidrio, constitución, fabricación y propiedades
  • J M F Navarro
Navarro, J. M. F., El vidrio, constitución, fabricación y propiedades. CSIC, Madrid, 2003.
Mecánica de fractura en materiales cerámicos frágiles: Principios fundamentales
  • Torrecillas
Torrecillas, R. and Moya, J. S., Mecánica de fractura en materiales cerámicos frágiles: Principios fundamentales. Bol. Soc. Esp. Ceram. Vidr., 1988, 27(3), 123-134.