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Constitution of Bone China: II, Reactions in Bone China Bodies
Journal of The American Ceramic Society
Abstract
The reactions which occur on firing bone china are described and discussed with reference to the phase data for the system lime-alumina-phosphorus pentoxide-silica. X-ray examination of variously fired china bodies indicates that up to approximately 1000°C. the mineralogical interactions are similar to those that occur in earthenware; above this temperature the nature of the reactions is characteristic of the bone china body alone. Intimate mixing, high firing temperature, and fluidity of phosphatic melts combine to promote rapid reactions in bone china bodies. Thus, phase data may be applied profitably to problems involving the properties and behavior of bone china bodies at high temperatures. The failure of differential thermal analysis to yield satisfactory information is noted.
... In general, the reactions that occurred in the bone china body in the sintering process include dehydrations of hygroscopic, bound, and structural water of kaolin, decomposition of hydroxyapatite into β-tricalcium phosphate and lime, formation of anorthite from lime and metakaolin, and fusing of fluxing agents. 30 Among them, sintering after the fusing of fluxing agents is the most important stage in which the bone china body undergoes rapid densification due to the diffusion of the liquid phase into the pores between the particles. 31 After the sintering in the presence of the liquid phase, a relatively loose mass of compacted particles transforms into a denser body. ...
... The endothermic reaction taking place at 400−600°C with a dramatic mass loss of 3.67% is ascribed to the decomposition of carbonate and the dehydroxylation of kaolin to form metakaolin. 37 The endothermic peak ranging from 860 to 1000°C with a mass loss of 0.44% is caused by the decomposition of hydroxyapatite into β-tricalcium phosphate, lime, and water. Simultaneously, the released lime reacts with metakaolin to form anorthite. 30 The last endothermic change above 1100°C is due to the appearance of the liquid phase. An abnormal mass gain of about 0.6% occurs above 1000°C. ...
... and water. 30 This process can be distinguished on DSC and TG curves as well (Figure 3a). The second shrinkage stage that occurs in a temperature interval from 1165 to 1250°C with a shrinkage of 7.00% is caused by the liquid-phase sintering of bone china. ...
The sintering process of bone china bodies containing 0, 2, 4, and 6 wt % palygorskite was studied by X-ray diffraction (XRD), differential scanning calorimetry and thermogravimetry (DSC/TG), and dilatometric tests. According to the XRD and DSC/TG results, the increment of palygorskite increased the content of the amorphous phase and reduced the formation temperature of the early liquid phase in the bone china bodies. The shrinkage data showed that the starting sintering temperature and maximum shrinkage temperature of bone china bodies in the stage of liquid-phase sintering decreased by 20 and 15 °C via adding 6 wt % palygorskite, respectively. Also, the maximum shrinkage rose with increasing amount of palygorskite. Moreover, the kinetic analysis of shrinkage data was conducted by the Salem model. The value of the mechanism-characteristic exponent, m, rose from 0.62 to 0.91 by adding 6 wt % palygorskite. In addition, with increasing palygorskite, the value of activation energy, Ea, linearly reduced, and the value of rate constant A increased.
... Full mixing, adequate synthesis temperature, and phosphate melt fluidity are very effective in accelerating bone china body reactions. Generally, the following reactions occur with increasing temperature during bone china synthesis [3,[10][11][12][13][14][15]: ...
... C.I.E colour curve[13] ...
Beta-tricalcium phosphate (ꞵ-TCP) and anorthite are the main crystalline components in bone china bodies. The difference in their thermal expansion coefficients causes a decrease in the thermal shock resistance of the body. In this study, anorthite was replaced with bone ash in the bone china body, and the effect of this new composition on different properties of bone china after sintering at 1260 C for 3 h was investigated. The results showed that the physical and mechanical properties of the sample containing 50 wt% anorthite compared to the typical bone china improved and only 8.7% of the whiteness index diminished. Also, the microstructure of anorthite samples, studied with SEM, was observed without thermal crack and with uniform distribution of crystalline phase in the heterogeneous glass matrix.
... ions). Owen (2001bOwen ( , 2002 notes that animal bones 'burned' below 1000°C give rise to low-fired bone ash with CaO 58.37 wt%, P 2 O 5 36.94 wt%, and H 2 O 4.69 wt% (CaO/P 2 O 5 = 4.00 (molecular proportions). When added to ceramic pastes and fired to temperatures >1000°C bones progressively dehydrate and over a temperature range of 1000-1400°C (St. Pierre, 1955) the anhydrous mineral β-tricalcium phosphate more commonly referred to as whitlockite Ca 3 (PO 4 ) 2 develops through dehydration (loss of water) and partial volatile-loss of calcium. Consequently on progressing from animal bones to high-fired calcined bones or whitlockite the CaO/P 2 O 5 ratio changes from 4.0 to 3.0 (molecular proport ...
A detailed survey of Bow porcelains from first patent to second patent wares is presented. In addition a compositional stratigraphy of the factory production is given. This is the first account of the Bow porcelain manufactory to integrate the entire Bow output in an holistic manner. Numerous fallacies in English thinking on ceramics is pointed to.
... ions). Owen (2001bOwen ( , 2002 notes that animal bones 'burned' below 1000°C give rise to low-fired bone ash with CaO 58.37 wt%, P 2 O 5 36.94 wt%, and H 2 O 4.69 wt% (CaO/P 2 O 5 = 4.00 (molecular proportions). When added to ceramic pastes and fired to temperatures >1000°C bones progressively dehydrate and over a temperature range of 1000-1400°C (St. Pierre, 1955) the anhydrous mineral β-tricalcium phosphate more commonly referred to as whitlockite Ca 3 (PO 4 ) 2 develops through dehydration (loss of water) and partial volatile-loss of calcium. Consequently on progressing from animal bones to high-fired calcined bones or whitlockite the CaO/P 2 O 5 ratio changes from 4.0 to 3.0 (molecular proport ...
Approximately 50 items of Bow porcelain, some of documentary origin, from private and major public collections were subjected to micro-analytical techniques and from these analyses the theoretical recipe used in each case was calculated. Three published recipes pertaining to Bow paste compositions are also noted (the 1744 and 1749 patents and the Josiah Wedgwood formulation of 1759) and all three are examined in the light of these analyses. Based on the calculated paste compositions derived from analysis, three major groups of Bow wares are recognised, namely a hard-paste Si-Al-Ca body with an associated Si-Al-Ca glaze (Bow first patent wares or 'A'-marked period c. 1743-1745), a soft-paste, bone ash body with a Si-Pb glaze (Bow second patent bone ash wares c. 1746-1774), and a magnesian (steatitic) body (c. mid 1740s). Five recipe classes and a high-lead subgroup are recognised for Bow second patent wares and these changes in paste types are placed in a chronological order and linked to physical attributes of these porcelain wares (body, glaze, weight, hardness, and translucency). A comprehensive classification from the collector's and museum curator's viewpoint is presented and it is proposed that the contribution to porcelain development in the English-speaking world by the Bow proprietors has been significantly underestimated.
... While the amorphous phase is rich in SiO 2 and Al 2 O 3, but also contains K 2 O and CaO, the crystalline phase is mainly calcium phosphate [2]. CBB could therefore be used to change the liquidus temperature [23][24][25], promote liquid phase formation, and reduce the sintering temperature via liquid phase sintering. ...
Calcined bovine bone (CBB) is generally used to manufacture high-quality porcelain known as bone china. In these products, the amount of bone ash is about 50%. However, it is known that CBB, in small quantities added to raw materials such as feldspars, can reduce the liquidus temperature and thus promote liquid-phase sintering. The purpose of this study was to evaluate the potential use of bone ash as a sintering promoter of porcelain made by a classical triaxial system. Hard porcelain was prepared with 0, 1, 2, and 5 wt% CBB and sintered at temperatures ranging from 1100 to 1400 °C. For the sample containing 2% CBB, the sintering temperature was reduced by 50 °C relative to 0% CBB, while the sample’s tensile strength was the highest among all samples. Two mechanisms could be observed during porcelain sintering depending on CBB quantities: for 1 and 2% of CBB, the mullite formation determined the final shrinkage without changes on initial sintering temperatures; for 5% the initial sintering temperature was decreased by liquid formation.
... The relative clay to stone contents would have been higher for the Staffordshire body than for the Nantgarw bodies since the former contains higher alumina and lower alkali. When bone-ash porcelain or bone chira bodies are fired (St-Pierre 1955;Dinsdale 1986, 47-9). the bulk of the hydroxy-apatite iCa,(OH) (PO,),) associated with the bone-ash converts to B-tricalcium phosphate (Ca,(PU,)2). ...
... While the amorphous phase is rich in SiO 2 and Al 2 O 3, but also contains K 2 O and CaO, the crystalline phase is mainly calcium phosphate [2]. CBB could therefore be used to change the liquidus temperature [23][24][25], promote liquid phase formation, and reduce the sintering temperature via liquid phase sintering. ...
Bovine bone ash is the main raw material for fabrication of bone china, a special kind of porcelain that has visual and mechanical advantages when compared to usual porcelains. The properties of bone china are highly dependent on the characteristics of the bone ash. However, despite a relatively common product, the science behind formulations and accepted fabrication procedures for bone china is not completely understood and deserves attention for future processing optimizations. In this paper, the influence of the preparation steps (firing, milling, and washing of the bones) on the physicochemical properties of bone ash particles was investigated. Bone powders heat-treated at temperatures varying from 700 to 1000 °C were washed and milled. The obtained materials were analyzed in terms of particle size distribution, chemical composition, density, specific surface area, FTIR spectroscopy, dynamic electrophoretic mobility, crystalline phases and scanning electron microscopy. The results indicated that bone ash does not significantly change in terms of chemistry and physical features at calcination temperatures above 700 °C. After washing in special conditions, one could only observe hydroxyapatite in the diffraction pattern. By FTIR it was observed that carbonate seems to be mainly concentrated on the surface of the powders. Since this compound can influence in the dispersion stability, and consequently in the quality of the final bone china product, and considering optimal washing parameters based on the dynamic electrophoretic mobility results, we describe a procedure for surface cleaning.
The mineralogy of the raw materials and of the fired ceramics used in the production of artificial stone and the species that are formed form their fusion at high temperatures in the kiln are discussed along with details given of the chemical changes that occur during the firing process at several temperature ranges. The sourcing of the raw materials and of their chemical composition are presented and considered for primary and secondary clays sand, flint, alkaline flux, glass frit, grog and feldspar are outlined. The analytical interrogation of the minerals formed in ceramics at high temperatures in the kiln are described.
The Pendock Barry dessert service was a completely unknown Derby porcelain service until its appearance in the Thomas Neale auction of 1894. This chapter examines the origins and history of the Derby Old China Works from its foundation, closure and the establishment and closure of the King Street Factory. Then goes on to considers the likely date of manufacture of the Pendock Barry service using information acquired from new research regarding the commissioning patron, Pendock Neale Barry, relating to his early and illicit acquisition and use of the Pendock Barry Arms from the College of Arms around 1805. This suggests a date of manufacture of around 1805–1806. Further evidence that the service was manufactured prior to the Bloor period is provided by indications that the service was gilded by Thomas Soar and that the service does not show the craquelure typical of Bloor Derby porcelain. Analyses of the plate shape to indicate a date of manufacture after 1800, and an examination paste translucency to demonstrate that paste of the Pendock Barry service dates to before the late Kean period. Chapter 5 also discusses the chemistry of Derby porcelain and proposes future work involving the characterisation of the Derby paste via the chemical analysis of Derby sherds acquired from Derby Museum and Art Gallery and complete dated pieces of porcelain available to the authors for inspection.KeywordsDerby Old China WorksWilliam DuesburyChelsea China WorksBow China WorksLongton HallWilliam BillingsleyMichael KeanRobert BloorPendock Barry ServiceNealesTollertonCollege of ArmsThomas SoarPlate shapesTranslucencyGlaze craquelureCeramic paste analysisChemical analysisCeramic constituents
Some 53 Nantgarw porcelain services have been categorised as “named” services, wherein either their original provenance or later possession by a purchaser or inheritor is known. A detailed analysis reveals that half of these have been decorated in London ateliers through the agency of John MortlockMortlock, John , Oxford Street , London of Oxford Street and the rest locally at the Nantgarw China Works by William BillingsleyBillingsley , William, Thomas PardoePardoe, Thomasand William WestonYoung , William Weston Young. Few ceramic artists in the London ateliers of Robins & RandallRobins & Randall , atelier and John Sims have been identified. Some criteria for identifying a London sourced decoration on Nantgarw porcelain are advanced.
Meat and bone meal (MBM) ash is a type of waste generated by the incineration of inorganics sourced from industrial livestock production. MBM ash contains 50–55 wt% calcium oxide (CaO) and 35–45 wt% phosphorus pentoxide (P2O5). It has the potential to be used as a raw material in the inorganic coating industry due to its chemical composition. In this study, the use of MBM ash as an environmentally friendly and cost-effective source of CaO and P2O5 is investigated in the production of inorganic coating raw material, i.e., frit on an industrial scale. Frits containing 3.5 wt% MBM ash are prepared. A commercially available frit is compared to the frit produced using MBM ash. The sintering behavior of frits is characterized by using heating microscope. An XRD analysis is carried out to verify the glassy structure of frits. The frits are applied on steel substrates using electrostatic powder method and subsequently fired at 830 °C for minutes. The surface properties, esthetic appearances, and chemical resistance of enamel coatings were comparatively analyzed. Analyses yield that MBM ash can be used as a source of CaO and P2O5 in inorganic coating raw material production and thus can be recycled for use in the economy.
A history of industrial archaeology and the excavation of the Nantgarw China Works site, including the kilns and discovery of the waste pit and the acquisition of porcelain shards.
A comparative research between the technical properties of a typical porcelain composition manufactured from bone ash according to English traditional composition and a hard porcelain was made. The influence of quartz addition on final strength was also studied. Chemical and mineralogical composition of the glass and crystalline phase were analyzed by SEM and XRD. The results revealed that compared to traditional porcelains it is more difficult to sinter bone china in fast firing cycle, due to its shorter firing range. The higher mechanical strength of bone china is dependent on the presence of quartz and its particle size.
A comparative research between the technical properties of a typical porcelain composition manufactured from bone ash according to English traditional composition and a hard porcelain was made. The influence of quartz addition on final strength was also studied. Chemical and mineralogical composition of the glass and crystalline phase were analyzed by SEM and XRD. The results revealed that compared to traditional porcelains it is more difficult to sinter bone china in fast firing cycle, due to its shorter firing range. The higher mechanical strength of bone china is dependent on the presence of quartz and its particle size.
In this study, hydroxyapatite powders with different Ca/P ratio (1,40, 1,45,
1,50, 1,67, 1,80, 2,07) were synthesized, thermal characteristic of these powders
were analyzed and it was investigated using of these powders in a standard bone
china body replacing of bone ash. Bone china bodies were prepared according to
the developed model recipe (25 % Na-feldspar, 25 % Kaolin, 50 %
Hydroxyapatite). With the tests applying onto bodies, the water absorption,
density, firing shrinkage, colour of the standard and HA powder containing bodies
sintered different temperatures between 1230 oC and 1290 oC were determined
and its effect on their microstructure was tried to be found. In the light of these
results, it was concluded that synthesized hydroxyapatite powders indicate a using
capacity in the bone china body and that the bone china body prepared by using
HA powder with Ca/P: 1.50 mol ratio has the same properties with commercial
one.
Ossos bovinos calcinados (OBC) são geralmente utilizados para a fabricação de uma porcelana de alta qualidade conhecida como bone china. Nesses produtos a quantidade de OBC é cerca de 50% do produto. Apesar de o rebanho bovino brasileiro ser um dos maiores do mundo com cerca de 200 milhões de cabeças, grande parte dos resíduos de ossos ainda não é aproveitada. Contudo, é conhecido que o OBC em pequenas quantidades e associado com materiais-primas fundentes, como feldspatos, pode reduzir a temperatura de liquidus e com isso promover a sinterização via fase líquida. A finalidade deste trabalho foi de verificar a potencialidade do uso de OBC como promotor da sinterização de porcelanas fabricadas com o sistema triaxial clássico: caulim, feldspato e quartzo. Foram introduzidas quantidades de 1, 2 e 5% em massa e sinterizadas entre 1100 e 1350 ºC. As amostras foram comparadas com a formulação sem adição de OBC com respeito à limite de resistência e absorção de água, formação de fases por difração de raios X e observações no microscópio eletrônico de varredura. A temperatura de sinterização foi reduzida em 50 ºC para a quantidade de 2% de OBC, porém grande quantidade de porosidade residual pode ser gerada se houver aquecimento demasiado das porcelanas.
A porcelana de cinza de ossos é amplamente aceita e alcança alto valor de mercado, entretanto, sua produção ainda é pouco difundida, de modo que sua fabricação e pesquisa são restritas a poucos países. Sendo o Brasil grande produtor de gado, apresenta grande potencial para a reciclagem de ossos, podendo-se encontrar aplicação destes em materiais cerâmicos. Neste trabalho foi feita uma análise comparativa das características técnicas entre uma formulação de porcelana obtida com cinzas de ossos conforme a receita tradicional inglesa e uma formulação de porcelana tradicional. Os resultados mostraram que a sinterização de porcelana de cinzas de ossos requer cuidados extras em ciclos rápidos de queima quando comparada à porcelana tradicional, devido a um menor intervalo de gresificação. No entanto, a maior resistência mecânica e as qualidades estéticas, destacando-se a elevada alvura, fazem desta porcelana bastante atrativa em termos de potencial de aplicações industriais.
Compositional data determined for excavated porcelain sherds suggest that both silicious and phosphatic wares were produced at the Nantgarw and Swansea manufactories. The silicious Swansea sherds are virtually phosphate-free, and have lower MgO (<0·5%) and higher Al2O3(21–25%) contents than magnesian (“soapstone”) porcelains that characterize part of the production history of this manufactory. Together with the silicious Nantgarw samples, they appear to represent a new class of Welsh porcelains. Although visually similar, the silicious porcelains can easily be distinguished from phosphatic samples by their appearance under a black (UV) light. The silicious paste might represent a technological improvement on the phosphatic recipes used at both manufactories. This hypothesis can be tested using phase diagrams.
Bulk and phase compositional characteristics of 18th century glassy (frit) and phosphatic Derby porcelains constrain aspects of production methods before and after the acquisition of the Chelsea works in 1770. Based on sherds excavated adjacent to the Derby manufactory site, glassy wares were derived from a recipe containing quartz (30–55 wt.%), flint glass frit (34–56%), kaolinite (6–10%), calcite (≤16%), and subordinate bone ash (0–6%) and gypsum (0–1%). The recipe for phosphatic wares contained bone ash (31–43 wt.%), kaolinite (21–24%), quartz (31–39%), and lesser amounts of calcite (1–6%). Although both recipes contained calcite and quartz, wollastonite is restricted to glassy sherds because in phosphatic samples, all calcite was consumed by a bytownite-forming reaction (calcite+kaolinite=plagioclase+2H2O +CO2) initiated at a relatively low temperature (≥200°C versus ≥350°C) dictated by the composition of the pore fluid. Due to resorption by a melt phase at peak firing conditions, however, most if not all of the wollastonite in the glassy wares is interpreted as a liquidus phase.
A complete investigation on the sintering behaviour, involving ceramic transformation, of volcanic ash is reported. Sintering and softening points, vitrification and fusion of finely ground powders of volcanic ash were obtained by hot stage microscope observation. Then, a suitable thermal cycle, which matches the better microstructure and mechanical properties, has been performed. The low quartz content of the final product, the relative high density together with the particular structural complexity of the matrix consequence of the interlocking of various crystalline phases conferred to fired volcanic ash relevant ceramic characteristics. Nucleation and microcrystallisation of pyroxene together with oxidation and cation enrichment are indicated as the main sintering mechanism of fired volcanic ash. Differently from conventional vitrified ceramics, i.e. quartz and mullite in vitreous matrix, the microstructure of the fired products presents spinel, anorthite, diopside, enstatite, pyroferrite, fayalite and hedenbergite crystals embedded in the high viscous liquid phase resulting in dense and resistant materials.
The primary-phase fields of the system tricalcium phosphate-anorthite-silica are delineated, and the distribution of isotherms is related to the firing of bone china. The system is a true ternary with a eutectic at 11% tricalcium phosphate, 51% anorthite, 38% silica that melts at 1290°± 5°C.
The character of porcelain wares made by Nicholas Crisp early and late in his career was assessed using microchemical and petrographic data for sherds excavated from the sites of the factories he operated at Vauxhall and Bovey Tracey. The results indicate that, over time, Crisp increasingly made use of diverse types of pastes as he struggled to produce a commercially viable line of porcelain. Based on the analysis of a limited number of samples, he appears to have largely restricted himself at Vauxhall to using soapstone (Mg-rich)- and flint-glass (Pb-rich) frit-bearing pastes that varied in the amount of calcite they contained. He also experimented with Mg+Pb-rich pastes at Bovey Tracey, but included a novel ingredient (barite) and varied the proportion of other minor constituents (e.g., bone ash), apparently in an effort to resolve some of the firing problems that plagued him at Vauxhall. In addition, Crisp appears to have produced bone ash (phosphatic) porcelain at Bovey Tracey, and, in collaboration with William Cookworthy, the proprietor of the Plymouth factory, fired a range of true porcelain (Si+Al-rich) pastes. Bulk compositional data indicate that Crisp's diopside-bearing Mg+Pb-rich wares were derived from pastes containing talc and calcite rather than dolomite. The mineralogy of these and some contemporary magnesian/plombian porcelains are interpreted using the SiO2-CaO-MgO phase diagram. This diagram shows that these wares can form and preserve diopside (Ca-Mg silicate) given suitable bulk CaO contents and kiln-firing temperatures. Phosphatic sherds from Bovey Tracey are compositionally distinct (lower SiO2 and higher Al2O3 and bone-ash components) from a single bone-ash sample from Vauxhall, indicating that Crisp experimented with novel bone-ash pastes, and was not positively influenced by the Vauxhall phosphatic recipe, if indeed one existed. True porcelains from Bovey Tracey have more extreme SiO2/Al2O3 ratios (= 2.0 [two sherds]; 4.5 [one sherd]) than their Plymouth/Bristol counterparts (SiO2/Al2O3 = 2.3–3.0). Collectively, the analytical data underscore the experimental—and ultimately unsuccessful—character of the diverse wares produced by Nicholas Crisp. © 2000 John Wiley & Sons, Inc.
New ZnO-containing glazes were developed, characterized and incorporated (5–8 wt.%) in conventional hard porcelain formulation for producing tableware porcelains. The experimental results showed that glaze additives enhancement the densification of porcelains. Maturing temperature range was widened due to the dissolution of quartz crystals. The modified porcelains featured better mechanical properties and whiteness and lower shrinkage than conventional hard porcelains. Good matching of thermal properties between porcelain body and glaze resulted in successful glazing.
In our present work we are studying the effect of heat on the constituents of bone porcelain. We have formulated three compositions, in which we varied the type of melting. We placed these compositions in the phases diagram Ca3(PO4)2-Al2O3-SiO2,; with which we intend deduce the presents crystalline or vitrious phases. We are studying the influence of the type of melting on the properties of the obtained product.
En el presente trabajo se estudia la acción del calor sobre los constituyentes de la porcelana de huesos. Se formulan tres composiciones, en las que variamos el tipo de fundente. Se sitúan dichas composiciones en el diagrama de fases Ca3(PO4)2-Al2O3-SiO2,; a la luz del cual se intenta deducir las fases cristalinas o vítreas presentes. Se estudia la influencia del fundente en las propiedades del producto obtenido.
In this investigation quantitative relations have been established between the time and temperature effects in the maturing of whiteware bodies. Six typical commercial whiteware bodies were used. Similar shrinkage and porosity curves were obtained for different firing times but the longer the time the lower the curve was shifted on the temperature scale. It was found that in all cases the usual logarithmic law relating temperature with the rate of reaction applied. The constant, however, was not the same for all bodies. The microstructure of these bodies will be dealt with in Part II of this paper.
This investigation deals with the microscopic examination of three of the whiteware bodies which were described in Part I of this paper. With respect to the influence of time of firing upon the crystalline texture, it was found that with samples which showed the same degree of maturity by physical test, the long-fired, low-temperature samples showed more quartz solution as well as more mullite development than the samples fired more quickly at higher temperatures.
A bstract
The present knowledge concerning reactions which take place during the heat treatment of clay, feldspar, and silica is discussed as well as the relations of these three to the ternary system K 2 O‐Al 2 O 3 ‐SiO 2 . The manner of growth of mullite crystals in feldspar has been studied. Additional experimental data as evidenced by the thermal‐expansion curves of day‐feldspar and clay‐silica mixtures previously fired at high temperatures are presented.
A bstract
A rapid and sensitive method for the quantitative determination of the crystalline constituents in kaolin‐flint‐feldspar blends has been developed with the Geiger‐counter X‐ray spectrometer. Two variations of this method were the use of (1) a powdered sample with a reference‐material addition and (2) a polished normal body surface. The powdered‐sample technique with a reference‐material addition showed the greater accuracy and consistency of results. The polished‐surface technique was slightly less accurate, but the preparation and nature of the test specimen make it very adaptable to control methods. With this technique the complete preparation and testing of the fired surface can be carried out in approximately 10 minutes. Standardization curves for the X‐ray spectrometer technique were used to obtain quantitative information concerning the crystalline constituents in the following blends: (1) kaolin‐flint, (2) kaolin‐feldspar, (3) flint‐feldspar, and (4) kaolin‐flint‐feldspar, as well as with additions of 1.2 and 2.8% lime and magnesia, and direct substitution of nepheline syenite for feldspar. Pressed 1 1/2‐in. pellets of each body were subjected to 3‐ and 12‐hour soaking periods at 1200° and 1400°C. Quartz, mullite, cristobalite, and wollastonite were identified as the crystalline constituents in the kaolin, flint, and feldspar blends studied. Quantitative X‐ray information concerning the reduction of the free‐quartz content, formation of cristobalite and mullite, and the amount of the total crystalline content was used to determine the effects of variations in composition and heat‐treatment for the different blends.
This investigation represents a first attempt to interpret the thermal behavior and constitution of bone china by means of a phase diagram of an idealized system. A consideration of the Tricalcium phosphate-alumina-sica phase diagram in relation to the quaternary system lime-alumina-phosphorus pentoxide-silica indicates that the composition of a normally tired commercial bone china body is β-tricalcium phosphate and anorthite in a siliceous glassy matrix. X-ray examinations of many such bodies confirm this interpretation. This preliminary investigation indicates the most profitable fields for further research.
Some Observations on the Microstructure of Fired Earthenware
- Weymouth J. H.
Biscuit‐Firing Schedule for Ceramic Goods
- Dale A. J.
Physics and Chemistry of Firing Ceramic Ware
- Austin J. B.