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The rheology of suspensions and mechanical properties of green bodies with cordierite composition (raw materials 37 wt% kaolin, 41 wt% talc, 22 wt% alumina, resulting in 46.6 wt% SiO2, 38.1 wt% Al2O3, 13.6 wt% MgO) and two types of starch (corn or potato) are investigated. Rotational viscometry of suspensions with solids loading 50, 60, and 70 wt% without starch showed that all tend to be shear-thinning with a small degree of thixotropy. Suspensions with a total solids loading of 60 wt% with 25 wt% replaced by starch exhibited higher viscosity and thixotropy, but the viscometric behavior is almost identical for the two starch types (apparent viscosities 130–50 mPa·s). Oscillatory rheometry shows that for suspensions with potato starch the onset temperature for gelatinization is 61°C–63°C, that is, lower than for corn starch (72°C–73°C). Maximum storage moduli and phase shift values after gelatinization are similar for both systems. The mechanical properties of green disks, measured via diametral compression tests, reveal clear differences between materials prepared with corn and potato starch, with the latter showing higher elastic modulus, higher strength, and higher deformation at fracture, obviously because of incompletely gelatinized starch granules in the green bodies prepared with corn starch.

A cordierite precursor mixture of talc, boehmite, and kaolin was studied with respect to the influence of dry milling intensity per unit time on phase transformation pathways and microstructural development. Three milling methods (ball, ring, and planetary) were used, and the effects of mechanical action and milling times were investigated at different temperatures. Sintering at 1000°C for 2 h resulted in the development of significant mechanically assisted phase transformations specifically related to formation of mullite in the most highly activated materials. Mullite transformation to precordierite mineralogy and the formation of magnesium aluminum silicate were also found to be dependent on the degrees and methods of mechanical processing. Planetary milling resulted in the highest densification of the material, which when sintered at 1300°C for 2 h produced a ceramic body rich in cordierite composition.

Densification and crystallization behaviors of nonstoichiometric cordierite synthesized from minerals through the glass route are reported in this paper. DTA of glass powder was conducted under isothermal and nonisothermal conditions. The activation energy was calculated from the dilatometry test at constant heating rate by using Arrhenius equation to observe their densification behavior. The densification and crystallization of composition with MgO mole ratio of 3.4 and 4.0 below 900°C were confirmed using nonisothermal DTA and dilatometry. However, samples below 2.6 mol MgO were not fully densified and crystallized when isothermally heated for 2 h. When MgO content was increased 2.0–3.0 mole ratio, the activation energy for densification decreased, but it increased for MgO mole ratio≥3.4.

A method to control the number of layers of dispersed silicate platelets was investigated. In order to achieve control over the number of layers, a layered silicate with two antagonistic properties, swelling and nonswelling, was prepared in each particle. A new regularly interstratified layer silicate composed of talc/talc/ smectite (TTS) in an ordered sequence was synthesized using a hydrothermal technique. A novel layered silicate-polymer nanocomposite was then prepared through exfoliation of the regularly interstratified TTS. The controlled morphology of the nanocomposite indicates that silicate nanolayers consisting of three layers/group are uniformly dispersed in the polymer matrix, which suggests a method for the control of the number of dispersed layers in polymer nanocomposite technology. More importantly, this new composite system could extend the field of high-performance materials beyond traditional applications to encompass new unexpected functionality.

A study was made relative to the dry pressing of wall tile having a thickness of 3/16 in. Three bodies, a high talc, a high pyrophyllite, and a regular body were studied. The water content was kept constant and the forming pressures were varied from 1000 to 3000 lb. per sq. in. The bodies were fired to cones 4, 6, and 8. The bisque tile were tested for thermal expansion, warpage, absorption, shrinkage, impact strength, transverse strength, and moisture expansion. The glazed tile were tested for warpage, impact resistance, and moisture expansion. The results showed that satisfactory thin wall tile could be made from all bodies, the high-pyrophyllite body indicating the greatest promise. It was found that pressing pressures had definite effects on impact strength, warpage, shrinkage, and thermal expansion.

The adsorption behavior of a hydroxypropyl methyl cellulose (HPMC) polymer in aqueous suspensions of alumina, silica, kaolin, and talc powders, two-component combinations, and one three-component combination was determined. Powders were well characterized by chemical analysis, XRD, DRIFT, SEM, particle size, surface area, and density analyses. The zeta-potential of each powder in aqueous suspension was determined over a range of pH to determine particle charging and the isoelectric point for each material. Alumina and silica powders having heavily hydroxylated surfaces were observed not to adsorb the HPMC polymer over a range of pH. The layer-type minerals talc, which was noticeably hydrophobic, and kaolin, which had differently hydrated basal planes, adsorbed the HPMC polymer but in different amounts per unit of surface area. In the two-component systems, HPMC polymer adsorption for systems of dispersed particles of like electrical charge (kaolin + silica, talc + silica or alumina, and kaolin + talc) was proportionate to the sum of the fraction x specific surface area x adsorption capacity for each particle type. In systems where particles had an opposite electrical charge (kaolin + alumina, kaolin + talc + alumina), the HPMC polymer adsorption was significantly lower than that calculated for a dispersed system. SEM analysis showed very fine, nonadsorbing alumina particles predominantly on the faces of the adsorbing kaolin particles that apparently masked polymer adsorption. Results suggested a hydrophobic mechanism for the HPMC polymer adsorption and adsorption on only one face of the kaolin particles.

The densification behavior of fine alumina (mean particle size of ∼0.31 μm) and coarse alumina (mean particle size of ∼4.49 μm) during liquid-phase sintering with additions of talc have been studied, as well as the microstructural evolution. Small amounts (0, 5, and 10 wt%) of talc were added to the fine alumina and coarse alumina, which were sintered at various temperatures for 2 h. When 5 wt% of talc was added to the coarse alumina, densification proceeded rapidly above the liquid-formation temperature in alumina–talc compacts, because of the promotion of a rearrangement process of the solid grains by the liquid phase. The addition of 10 wt% of talc greatly accelerated densification by increasing the volume fraction of liquid. On the other hand, in the fine alumina, which has a higher activity and a greater driving force for sintering, appreciable densification started below the liquid-formation temperature, which prevented further densification after liquid formation. Moreover, the densification was suppressed as the talc content increased. The rigid skeleton of solid grains that was formed by densification below the liquid-formation temperature is believed to have suppressed the rearrangement process of the solid grains, and further densification of the compacts was retarded, even after the formation of a liquid phase above the liquid-formation temperature.

To investigate the transformation process from talc to expandable micas, mixtures of talc and Na{sub 2}SiF{sub 6} were heated from 600 to 900 C and air-quenched at 50 C intervals. The air-quenched product at 800 C mainly consisted of expandable micas with a basal spacing of 1.25 nm, nonexpandable materials with a basal spacing of 0.96 nm, and a small amount of talc used as the starting material. A lattice fringe image by HRTEM of the product shows that the layer spacing at the edges surfaces is about 1.2 nm, but the layer spacing inside of the particles is close to that of talc. Such a nanostructure indicates a topotactic reaction from talc to expandable micas and confirms that Na{sup +} ions intercalate into the structure from the edge to the core.

The use of talc and pyrophyllite in semivitreous dinnerware bodies is discussed. The effect of these materials on shrinkage, absorption, modulus of rupture, and moisture expansion are shown. The advantages obtained are better drying and firing properties, higher mechanical strength, and greater resistance to delayed crazing.

Mixtures of magnesia and silicic acid ranging in composition from 0.5 to 2.0 M/S were treated hydrothermally at temperatures of 75° to 350°C. for various periods of time. The reaction solids were examined by differential thermal analysis, X ray, and electron microscopy and analyzed chemically. The intermediate products of reaction ranging in composition between that of talc (0.75 M/S) and chrysotile (1.5 M/S) comprised a continuous series of cryptocrystalline needle-like crystaIs matted tightly together and showing the same X-ray pattern. The initial reaction product of the 0.75 to 1.50 M/S raw mixtures was a cryptocrystalline solid having a 1.5 M/S ratio. This phase subsequently reacted with the residual silica, so long as any was available, to form a solid having the composition of the raw mix, but only at relatively moderate temperatures(100°to175°C.). As the temperature was increased the crystals of the 0.75 and 1.50 M/S compositions increased in size, but all remained submicroscopic. The compositions intermediate between 0.75 and 1.5 M/S crystallized as mixtures of talc and chrysotilelike products. The chrysotilelike product appeared as minute needles which did not possess any apparent flexibility.

This paper describes the use of a specific type of tale in wall-tile bodies and explains the effect of various percentages on shrinkage, absorption, modulus of rupture, moisture expansion, and resistance to delayed crazing. The data indicate the effects of talc with various combinations of wall-tile body ingredients and the compositions and heat treatment of greatest potential resistance to crazing.

The fundamental properties of nepheline syenite, such as thermal expansion and fusion characteristics, are given. Test specimens of twelve bodies, comprising various flux combinations of nepheline syenites and potash feldspars with talc, whiting, magnesium carbonate, and pyrophyllite, were fired to seven different cones. The firing linear shrinkage curves of combinations of nepheline syenite with the. various materials are somewhat similar to such combinations with potash feldspar except that the syenite combinations are active at lower temperatures. That the sintering ranges of nepheline syenites are longer than those of potash feldspar is explained thermochemically.

This investigation covered three systematic fields of composition of leadless, opaque, fritted glazes for cone 04. Studies were made of the effect of variations in the RO fluxes (calcium, barium, and zinc oxides), and in the alumina and the silica-alumina ratio. Leadless glazes of low boric oxide content with either desirable mat textures or good gloss were obtained on both low and medium talc tile bodies. These glazes applied to tile of medium talc content withstood an autoclave test for crazing, but all glazes except those high in zinc oxide crazed on tile of low talc content. Zinc oxide improved the resistance to crazing. It also produced the most opaque glazes and those with the best gloss. Typical compositions for bright and mat glazes at cone 04 are recommended.

Three talcs, representative of low, medium, and high CaO content, were used in preparing twenty-four bodies which were heated at four temperatures. The products ranged from the highly porous earthenware type to porcelain, and test results indicate some possibilities and limitations which the white-ware industry may expect of white-ware bodies made with 14 to 40% talc.

Several iron-bearing tales were fired alone and in body form and were measured for shrinkage and absorption. Their colors were also noted. Electrical measurements of dielectric constant and loss characteristics were made on the bodies and compared with white-firing tales. The effect of small additions of Fe2O3 on a white-firing talc is also described.

The suitability of various California talcs for use in a wall-tile body was investigated. The nature of the talcs and their associated minerals was studied using the petrographic microscope, chemical and differential thermal analysis, and heavy liquid separation techniques. The characteristics of the various talc ores were related to some of the properties of the fired wall tile.

The quantitative determination of the amount of quartz, mullite, and glass resulting from varying grinding and firing treatments was correlated with the physical properties of a whiteware body. The body composition selected contained 20% potash feldspar, 30% flint, 7.5%, ball clays, and 42.5% kaolins. The body mix was ground for 8−, 25−, and 100−hour periods, and, in addition, the flint and feldspar were preground for 25 and 100 hours. Special fluxes such as talc and nepheline syenite were also tried. All bodies were heated to cones 5, 7, and 9, and the fired porosity, modulus of rupture, and volume shrinkage after firing were determined. The amounts of quartz, mullite, and glass (by difference) were determined quantitatively with a Geiger-counter X-ray spectrometer, using a powdered sample with an internal standard. The results showed that the finer grinding of the body, flint, or the potash feldspar reduced the quartz content, increased slightly the mullite formation, and increased the amount of glass. The combination of finely ground feldspar and flint gave a much higher mullite formation and a lower quartz content. The results showed that an increase of talc is unfavorable to mullite formation. The transverse strength of the bodies investigated was proportional to the total mullite and glass content.

A number of steatite ceramics were prepared under carefully controlled conditions, and their dielectric losses and direct-current resistances were measured at elevated temperatures. It was found that variations of the ratio of talc to kaolin within certain limits had little effect on the dielectric properties. These properties, however, were changed to a considerable extent by varying the amounts, proportions, and kinds of alkaline earth oxides added as fluxes. The data indicate also that the conditions in a ceramic favorable to a high specific resistance are not necessarily those favorable to a low dielectric loss.

Four groups of body compositions involving partial replacement of feldspar by spodumene were investigated. In the first group the firing temperature was maintained constant and the clay content was increased at the expense of the flux. In the second group the flint, clay, and total flux (flux was 20y0 of the body) contents were held constant and spodumene replaced 19, 30, and 40y0 of the total flux. In the third group the flux content containing varying proportions of spodumene was increased from 20 to approximately 40% of the body at the expense of flint and the firing temperature was lowered. In the fourth group miscellaneous bodies containing a variety of fluxes, including flotation soda feldspar, nepheline syenite, talc, and whiting in addition to the potash feldspar and spodumene, were tested. The spodumene appeared to have little advantage in lowering the maturing temperature of the 20% flux bodies; however, a spodumene: feldspar ratio of 30:70 appeared to lengthen the firing range. The effectiveness of the spodumene increased as the total flux was increased. A body containing 27% of flux matured at cone 11–12 when potash feldspar alone was used and at cone 8 when 8% of the feldspar was replaced by spodumene. A body containing spodumene, talc, and nepheline syenite matured at cone 3–4 and had a fired modulus of rupture in excess of 10,000 lb. per sq. in. The small amounts of spodumene (up to 8% of the body) had no apparent effect on the stability of the casting slips or similar properties.

The effect of introducing talc in amounts not exceeding 25% on some of the properties of a sagger body was investigated. The results obtained show improved working properties of the body in the plastic state, increased dry and fired mechanical strength, decreased absorption, lower thermal expansion, increased heat-shock resistance, decreased total shrinkage, decreased sag tendency, smoother fired surface, and darkening of fired color. Talc in amounts greater than 15% shows no appreciable increased benefits, indicating this content to be the practical limit for a commercial cone 10 sagger composition.

It has been the purpose of this study to determine the effect of the substitution of calcined ball clay for flint in certain type bodies. Complete data on the physical properties of these bodies has been obtained, including electrical resistivity up to 980°C. A substitution of calcined ball clay for a portion of the talc in a type talc body has also been made.

Talcs exhibit considerable variation in texture and in chemical analyses. These variations are explored on the basis of phase, field, and atomic structure considerations with the aid of chemical, X-ray, and dserential thermal analyses. It is proposed that this complexity is accounted for primarily on the basis of the existence of solid solutions of the layer or group type.

The physical properties of wall-tile bodies and floor-tile bodies are described. The wall-tile bodies are fluxed respectively with nepheline syenite; feldspar; talc and feldspar; talc and syenite; talc, pyrophyllite, and syenite; and talc, pyrophyllite, and feldspar. Floor-tile bodies, developing at lower temperatures, may be formulated with nepheline syenite. The greater refractoriness of American clays used in these bodies, as compared to English clays, is compensated for by the increased fluxing action of nepheline syenite.

A discussion is given of the characteristics of vitrified steatite bodies containing more than 70% talc. Several typical compositions have been selected from a series of experimental bodies and their firing range and other ceramic and physical properties are described.

This paper is an attempt to explain the firing behavior of pure talc as well as talc-clay, talc-lime, talc-clay lime, and some other high magnesia mixtures. Phase rule equilibrium diagrams are used. The study applies only to those mixtures where talc is present in amounts greater than 50% of the total composition.

The effect of composition on the ability of glazed dishes to withstand thermal-shock treatments ordinarily received in cooking was studied. Bodies which gave best results contained approximately 10% of New York talc and also a small amount of calcined clay substituted for potters' flint. Bodies which had sufficiently high thermal expansion to throw the glaze into moderate or strong compression gave the best results. A terra sigillata finish applied to talc-free bodies was found to withstand autoclave treatment without crazing, and ware so made stood up very well in service tests.

An attempt has been made to correlate the differential shrinkage of fired steatite pieces with the particle shape of the raw talc used in their manufacture. Various talcs of widely varying particle shape were used in making the steatite test pieces. It was found that the more irregular in shape the talc particles, the greater the differential shrinkage. A method is given for assigning arithmetical values to various particle shapes depending on their deviation from sphericity, this arithmetical value being known as specific shape factor. A direct relationship was found to exist between the differential shrinkage of a talc and its specific shape factor. As the talc particles became more irregular in shape, the “specific shape factor” value increased and the differential shrinkage was found to increase. The proper selection of the talc td be used and blends of various talcs were found to be helpful in the control of differential shrinkage.

The electrical resistivities of flint fire clay, kaolin, magnesite, sillimanite, silica, diaspore, Maryland, Italian and Indian talcs were determined at temperatures up to 1500°C. Tests were made in an atmosphere of nitrogen, by the Wheatstone bridge method, using 45-volt 1000 cycle alternating current. With the exception of magnesite, the rate of decrease of resistivity decreases with an increase in temperature. The investigation indicates that the resistivity of a complex ceramic body, especially if it is open and porous, is not constant for a given temperature above the temperature at which its most fusible mixture melts. Resistivity is affected by the amount of impurities present, decreasing with an increase of impurities. As was shown in the tests of Italian talc, the resistivity is not only dependent upon the amount of impurities, but also upon their distribution. Within the limits of the voltage used, the resistivity is independent of the potential applied.

Phosphate-bonded talc shows advantages over block talc, which indicates that it is a superior substitute for this strategically important raw material. A satisfactory product has been made using talc from domestic sources. It has been formed by various methods, such as dry pressing, hydrostatic pressing, or hot pressing. Some factors that control the properties of the end product have been investigated, and the mechanical and dielectric properties are compared with those of natural block talc.

Experiments were made to determine which degree of fineness of ground talc would be most suitable for steatite-type ceramics. A laboratory-type air separator, Andreasen pipette, and the Casagrande hydrometer methods were used to measure the particle-size distribution of commercial steatite talcs. The results indicate that, although wide variations in the particle-size distribution of steatite talcs have a bearing on the firing shrinkage when the talc is incorporated in a body, the differences in grinding obtained in commercial talcs are not of great importance when proper milling practice is employed.

About forty specimens of talc have been examined by X-ray powder methods. Variations in the degree of crystallinity of the mineral have been observed, but no evidence has been obtained for polymorphic structural varieties. Single-crystal data have confirmed the two-layer mono-clinic cell. Little evidence has been obtained of talcs containing mixed-layer sequences. Electron micrographs have revealed a variety of platy and fibrous forms, and in the latter a close structural relation between talc and tremolite has been established. Talcs prepared synthetically in the presence of aluminum showed small lattice parameter differences from talcs prepared in the absence of aluminum, and the results are consistent with the substitution of small percentages of A1 ions in the talc structure. New X-ray powder data and unit-cell parameters for talc and tremolite are listed.

Arstract Samples of soapstone from a deposit in the Cascade Mountains of Washington were heated to various temperatures, draw trials were made, and the effect of temperature on the structure and texture was studied microscopically. The results obtained indicate a change of the talc to enstatite at about 1000°C. with a further change to clinoenstatite at about 1200°C. At the higher temperatures iron impurities have united with silica, probably to form fayalitc along the original impure schistosic planes of the soapstone.

In a survey of magnesium silicates for use as refractories, experimental studies with talc, serpentine, and olivine, and also with mixtures of these minerals and magnesia (MgO) are reported. Since forsterite (2MgO°SiO2) is the only magnesium silicate which has a stable existence above 1562°C, the development of a commercial magnesium silicate refractory required that the ultimate product should be mainly forsterite. Such a refractory was developed by enriching a low iron magnesian olivine with MgO. The magnesia served to convert certain accessory minerals found in the olivine rocks, including the hydrated minerals (talc and serpentine), to forsterite. Talc and serpentine are so universally present in olivine that, in the absence of the magnesia treatment, they provide a low melting bond which would cause the refractory to fail at relatively low temperatures under load and to exhibit other unsatisfactory properties. On the other hand, the forsterite refractory withstood an exceptionally high temperature before failure under load. The general characteristics of the refractory are discussed. The data include refractoriness, strength hot and cold, volume stability when reheated, spalling, thermal expansion, chemical behavior, resistance to various slags, thermal conductivity, etc.

Reactions in the ternary system MgO-SiO2-H2O were studied over the temperature range 100° to 300° C. and were found to produce only two phases. Under conditions of 100° to 200° C. and atmospheric pressure up to 20,000 lb. per sq. in., and regardless of the initial MgO/SiO2 ratio, the predominant magnesium silicate product was found to have a MgO/SiO2 ratio of 1.5. In the range 200° to 300°C. at 210 to 20,000 lb. per sq. in. two stable phases, 3MgO.2SiO2.2H2O (I) and 3MgO.4SiO2.H2O (II), were observed. In this case the phase that was favored was determined by the molar ratio of MgO/SiO2 of the reaction mixture at the start of the run. The physical and chemical properties of phases (I) and (II) resembled those of the natural minerals serpentine and talc respectively. Two different morphologies were observed in electron micrographs of phase (I). From 100° to 160°C. it occurred as crumpled foils, and at 170°C. fibrous crystallites, which resembled the natural asbestos mineral chrysotile, appeared at the expense of some of the foils.

By using phosphoric acid as the binding agent for powdered synthetic mica, it was possible to produce by dry-pressing a glass-free machinable low-shrinkage dielectric whose properties were controllable by varying the mica com- position, the forming pressure, the firing temperature, and the phosphate content. The total shrinkage was easily maintained at less than 3%, with the transverse strength in excess of 6000 lb. per sq. in. A zero-shrinkage composition was also developed and its properties are discussed. A dense, impervious ceramic was not produced by this method; the water absorption seldom was less than 4% with forming pressures of 10,000 lb. per sq. in. or less. The dielectric characteristics of this ceramic approached those reported for hot-pressed phosphate-free synthetic mica when it had similar porosity. The dielectric loss factor was of the order of 1 to 2% at room temperature and 4 to 8% at 300°c. and 1 mc. This material is suggested as a replace- ment for natural block talc.

Effects of MgO and of CaO, introduced as a lime-free talc and as a lime-bearing “tremolite” talc, in whiteware heated at four temperatures were investigated. The results indicate that (1) in earthenware bodies, 40% or less of talc may be expected to increase porosity slightly and materially decrease shrinkage, (2) thermal expansion may be greatly affected by small variations in the amount of talc used, the temperature of heating, and the percentage of CaO, and (3) talc has a beneficial effect on resistance to moisture crazing.

Ceramic bodies approaching the theoretical composition of cordierite were prepared from mixtures of talc and clay; talc, clay, and varying amounts of MgCO3; talc, clay, and alumina; and prochlorite and clay. Additions of BaCO3 and PbSiO, were made. Differential thermal analysis and X-ray diffraction methods were used in reaction studies of each composition. Bodies had thermal expansions from 0.344 to 0.109% (25° to 900°C.). BaCO3 and PbSiO3 affected thermal expansion. Dielectric properties were improved by additions of BaCO3 and were markedly improved by additions of both BaCO3 and PbSiOl. Cordierite started to crystallize at about 1250°. Additions of PbSiO3 lowered this temperature about 50°C. With sufficient BaCO3, the Ba-C phase, as described by Wisely, crystallized in place of cordierite. The crystallization temperature for the Ba-C phase was about 1200°C. With insufficient BaCO3, both cordierite and Ba-C formed. Additions of PbSiO3 reduced the crystallization temperature of the Ba-C phase by 50°C. and increased the glassy phase. Several of the compositions should haw considerable practical value.

A study was made of the use of nepheline syenite-talc combinations as a flux for producing vitrified bodies at low temperatures. It was found that a mixture of 85% nepheline syenite and 15% talc had a lower deformation temperature than either of these materials alone, indicating a eutectic in the system. Bodies were compounded by adding nepheline syenite and talc, in the ratio found to be the most fusible, to clays and flint. Bodies were developed that had less than 0.3% absorption in the firing range cone 02 to cone 2. These bodies had good color. Their modulus of rupture values ranged from 7000 to 10,000 lb. per sq. in.

A mechanism for crack propagation is presented to explain the production of thin foils when a brittle material fractures. A general technique for continuing this process and collecting the foils for electron microscopy is described. This method has been successful with every material examined, although there was considerable variation in the number and sizes of foils produced. The materials studied include single-crystal MgO, LiF, twinned KAlSi3O8 (microcline), CaCO3, Ge, Si, Zn, MgAl2O4, Al2O3, and glasses, and the polycrystalline materials SiC, talc, MgO, and Al2O3 all in order of relative success. A brief review of other electron transmission sample preparation methods is included with special reference to those most similar to the method described herein.

The preparation of test specimens is described as well as methods employed in testing approximately seventy different talcs, including materials for commercial use and-samples from new sources. Correlations are noted between chemical analysis and the measured physical properties, if they are present to any degree.

Dehydroxylation and enstatite development during the decomposition of talc were investigated by transmission electron microscopy using in situ heating. Bubbles and voids are produced during dehydroxylation, and enstatite then precipitates near the voids. Evidence of preferential bubble nucleation at dislocations was obtained. Enstatite crystallites of random orientation were observed initially but on further heating the product phase was formed topotactically.

Cordierite bodies having virtually zero porosity when fired between 1285° and 1325°C. were obtained by using calcined blends of MgCO3, talc, and clay; the calcine was combined with raw clay to form the body. These bodies were characterized by low thermal expansion, good mechanical strength, and excellent thermal-shock resistance.

New York State diopside and wollastonite as well as a high tremolite material obtained as a by-product of the electrostatic separation of talc were fired at a series of temperatures. Petrographic examination of the fired materials, absorptions, shrinkages, and P.C.E. values are reported, and observations on color and hardness are also given. Summary Diopside and wollastonite resemble talc in having short firing ranges, but they develop a dark color at higher temperatures due to a brown, glassy phase that separates from solid solution at temperatures of 1200°C. and higher. The tremolite-talc-quartz mixture is highly refractory; its color at 1435°C. is still white and complete reaction of the constituents has taken place to produce cristobalite and a solid solution of diopside in enstatite. Low absorption was not obtained even with the complete reaction and no glassy phase was evident.

Fluxing agents used in most steatite bodies contain alkalis which lower the electrical resistivity of these insulators. Attempts were made to obtain a vitreous steatite composition by additions of oxides containing no alkalis. The effect of grain size, liquids, and varying pressures was determined to obtain the best mixture which would produce the lowest absorption when fired to cone 14, and to this mixture the various oxides were added. The absorption and shrinkages were obtained after firing to cones 13 and 14.

Several bodies capable of being processed by thc usual manufacturing methods, with varying talc, clay, and mullite content, were studied to determine their relative resistance to thermal shock. These bodies were fired a t various temperatures and submitted to quenching and transverse strength tests.

Diopside was substituted for both talc and feldspar in a typical wall-tile body. It was found to lower the fusion temperature and to lower thermal expansion when compared with talc and to raise thermal expansion when compared with feldspar. Its effects on firing shrinkage, fired absorption, and moisture expansion were somewhat similar to those of talc.

An optical study of talc-tremolite from Fullerville, St. Lawrence County, New York, confirmed the crystallographic orientation determined by Stemple and Brindley. Both minerals exhibit normal optic properties. The optic orientation of talc given in standard references appears to be in error.