THERMAL AND MOISTURE EXPANSION OF BALL CLAYS AND BODIES FIRED TO DIFFERENT TEMPERATURES*

Thermal and moisture expansion determinations were made on ten ball clays of the Kentucky, Tennessee, and English types alone and on typical semivitreous and vitreous bodies in which each of these ball clays was incorporated. The clays and bodies were fired at cones 6, 9, and 11. The data indicate that the ball clays fall into five distinct groups. Although none of the clays showed a direct relation between its expansion and that of the bodies in which it was incorporated, a majority possessed characteristics sufficiently similar to permit their classification into groups in which the behavior of the clays alone is indicative of their influence on the bodies. When several ball clays were jointly incorporated into bodies, they showed additive thermal and moisture expansion values.     

THE SHALES AND BRICK CLAYS OF GEORGIA*

A résumé is given of the geology, general ceramic properties, and uses of the shales and alluvial clays of Georgia, based on a study by the Georgia Geological Survey. The conclusions were derived from seven months of field work and from ceramic tests on 115 samples from private properties and active plants.¹     

MINERALOGY AND PROPERTIES OF TYPICAL TEXAS CLAYS*

Powder diffraction, chemical, and thermal studies were made of four kaolins, two volcanic ashes, and eleven clays and, in addition, particle size, plastograph, electrodialysis, and soluble salt studies were made on five of the clays. The impurities present in the kaolins were quartz, calcite, and montmorillonite. The preponderate mineral in nine clays was either kaolinite or halloysite and that in two clays was illite: A correlation of all the studies made on the five clays which were used in Texas brick plants indicated that the gelatinous nature of the clays which caused increased power consumption during the extruding operation and large loss in the drier was due to organic matter, soluble salts, and montmorillonite.     

PLASTICITY OF CLAYS*

A theoretical discussion is presented on the plasticity of clays from a colloid-physical standpoint and based on modern concepts of the nature and source of the charges associated with the colloidal system.     

AN IMPROVED METHOD FOR DETERMINING THE TENSILE STRENGTH OF UNFIRED CLAYS1

It is thought that knowledge of the tensile strengths of unfired clays is valuable and in view of this fact the present unsatisfactory method for its determination has been improved upon. A new apparatus and method for tensile strength determinations is described, in which the cast or pressed cylindrical test piece has a collar of low-melting alloy cast around each end, thus eliminating gripping difficulties and greatly increasing the accuracy. The apparatus is also adaptable to determinations of bond and transverse strengths of clays.     

MINERALOGY OF TYPICAL NORTH CAROLINA CLAYS AND SHALES*

A microscopic examination was made on those clays and shales of North Carolina which gave most promise of future development in the structural day products industry. The more common minerals were determined rather than the rare ones which did not occur in sufficient quantity to affect the quality of the clay. The work showed clay substance to be the most abundant material present, followed by quartz, red and yellow iron oxides, muscovite through sericite to hydromica, and epidote, with smaller amounts of rutile, biotite, titanite, tourmaline, and zircon. Diatoms were found in two cases and kaolinite in one.     

TESTING AND IMPROVING THE DRYING BEHAVIOR OF CLAYS*

A simple test has been developed to measure the drying behavior of clays by noting the relative rate of flow of water through the clays as compared with the rate of evaporation from the surface. The addition of 0.2% of various chemicals to clays improved their drying properties. No one chemical was best for all of the clays, but the most effective chemicals varied in their reaction on different clays. Iron chloride exerted beneficial effect on most of the clays. A wetting agent, such as sodium chloride, hydrochloric acid, or soda ash, also improved the drying properties of certain clays.     

REHYDRATION STUDY OF CLAYS*

The rehydration characteristics of a group of twenty clays were studied by dehydrating at 300°C. and then rehydrating by exposure to a water-saturated atmosphere at 30°C. for periods extending from approximately 28 to 80 days. A sharp differentiation was obtained between the montmorillonite and the kaolinite-illite types of clays. A simple, rapid rehydration-dehydration test and the results on ninety-five clay samples are presented as an aid in the evaluation of clays. The test can be completed within five hours and permits a limited but useful classification of clays.     

HIGH-ALUMINA CLAYS OF PULASKI AND SALINE COUNTIES,ARKANSAS*

Extensive deposits of kaolinitic clay and closely associated bauxite occur in Pulaski and Saline counties, Arkansas, as products of early Cenozoic weathering of nepheline syenite. The clays of the bauxite-kaolin deposits normally contain more than 35% of alumina. Siderite is the principal impurity. The deposits for the most part are buried beneath sediments of Wilcox age or younger, but the overburden is thin or absent near outcrops of syenite. Deposits beneath overburden that does not exceed 50 feet in thickness probably total more than 100 million tons.     

ORIGINAL PAPERS THE BONDING EFFECT OF BALL CLAYS IN FIRED BODIES1

Seven American and fourteen English ball clays were compared in regard to bonding effect, (a) after burning, in a composition containing no fluxes, at cones 5, 8, 10 and 12; (b) in a semi-porcelain body burned to cone 8; and (c) in a vitreous china body burned to cone 11. The English clays developed greater strength in the absence of fluxes. The semi-porcelain and vitreous china bodies containing the imported clays were in general of greater strength than those bodies in which the domestic clays were used, but most of the bodies containing American clays were of good transverse strength.     

THERMAL AND MOISTURE EXPANSION OF KAOLINS AND BODIES FIRED TO DIFFERENT TEMPERATURES*

Thermal-expansion and moisture-expansion determinations were made on four kaolins of the Georgia, Florida, North Carolina, and English types alone and on typical semivitreous, hotel china, and electrical porcelain bodies embodying each of these kaolins after being fired at cones 6, 9, and 11. The Georgia and Florida kaolins and bodies showed surprisingly similar expansion characteristics. The general order of decreasing thermal expansion and increasing moisture expansion of the kaolins at all three firing treatments was Georgia, Florida, North Carolina, and English china. The semivitreous bodies at cones 6 and 9 showed the same order of expansion as the kaolins alone, but at cone 11 the thermal expansion of the English china clay body was the highest and the North Carolina kaolin body next in order. Moisture expansion of the bodies at cone 11 was found to be a function of the absorption, regardless of the kaolin used with no expansion obtaining at zero absorption. Mixtures of clay, flint, and feldspar, given an autoclave treatment after being fired to cones 6 and 9, showed that feldspar additions increased moisture expansion. When these mixtures were dehydrated at different temperatures, the data obtained were insufficient to confirm any theory on the nature of moisture expansion in a porous ceramic body.     

QUANTITATIVE DETERMINATION OF THE DEVELOPMENT OF MULLITE IN FIRED CLAYS BY AN X-RAY METHOD1

Firing clays alone or with fluxes to high temperatures results in the formation of mullite crystals in a highly siliceous vitreous mass. Quantitatively, the extent to which mullite in clays is developed by firing to cone 10 has been determined for Ivory Fat English ball clay, Great Beam ball clay, Jernigan Tennessee ball clay, M. & M. English ball clay and A-1 English china clay. The method consisted in procuring X-ray patterns by the powder method of the clays fired with feldspar as a flux, using mullite as a reference material. The intensities of the lines in these photographic films were then compared with the intensities of lines obtained from a series of mullite and feldspar mixtures, fired to vitrify the flux. The results given in Table II indicate that each clay develops the maximum quantity of mullite in crystalline form, which the chemical composition of the clay allows.     

SOME PROPERTIES OF ENGLISH CHINA CLAYS*

A study is presented of some of the properties of fifteen English china clays in common use commercially in the United States. Data are presented which may be useful in making substitutions for these clays, as well as furnishing a basis of correlation of some of the properties. A study of the base exchange capacities shows a general relationship to the transverse strengths of the clays in the unfired state.     

ZINC-VAPOR GLAZING OF CLAYS: II,EFFECT OF VARIABLE LIME AND ALKALIS IN CLAYS ON ZINC-VAPOR GLAZE COLORS*

A study was made of the influence of the lime content of brick on their ability to take zinc-green, yellow, tan, and brown glazes. Desirable greens were obtained with clays containing as much as 3% lime; those with a higher percentage of lime generally produced yellow-greens. The probability of obtaining good greens was best on clays with more than 6% of alkalis when their absorptions after firing were below 2%. Desirable greens were not obtained on bodies which had absorptions greater than 6.7%. Firing under oxidizing conditions before flashing and slow cooling tended to promote the formation of desirable brown, tan, and straw-colored zinc-vapor glazes.     

DIFFERENTIAL THERMAL ANALYSIS OF CLAYS AND SHALES,A CONTROL AND PROSPECTING METHOD*

The differential thermal method, by determining the thermal reactions undergone by a clay or shale, is a rapid means of identifying the mineral components of such materials, and because the properties of clays and shales depend largely on their mineral composition, it is at the same time a rapid method of evaluating the properties of such materials. Differential thermal analyses are presented for the pure forms and synthetic mixtures of the common components of clays and shales, namely, kaolinite, halloysite, illite, montmorillonite, quartz, gibbsite, boehmite, diaspore, dolomite, calcite, gypsum, organic material, pyrite, marcasite, goethite, and limonite. Differential thermal analyses are presented also for a variety of well-known types of clays, and on the basis of the thermal data for the pure components, the mineral composition is indicated. The correlation of mineral composition of clays and shales (as reflected in the differential thermal curves) with the ceramic properties is discussed as a basis for using this thermal method to indicate the properties of such materials. Finally, differential thermal analyses are presented for sequences of samples from the pits of several operating clay products plants in order to illustrate the way in which the method can be applied in prospecting and in plant control.     

SOME EFFECTS OF GRAIN SIZE OF CHINA CLAYS*

Measurements of grain size of a series of china clays were made, and a preliminary investigation of the relation between particle size and some properties was undertaken.     

PLASTIC AND DRYING PROPERTIES OF CERTAIN CLAYS AS INFLUENCED BY ELECTROLYTE CONTENT*

Electrodialyzed samples of several clays were saturated at pH 7 with various cations, and measurements were made to determine the effect of these cations on the workability and drying behavior of the clays. Excellent correlations were noted between the influence of these ions on clays in the plastic state and their behavior in causing flocculation or denocculation of dilute suspensions of clay. The results should be valuable for such industrial forming processes as throwing, jiggering, hot pressing, and extruding.     

IMPROVEMENT OF STIFF-MUD CLAYS THROUGH PH CONTROL *

Clays, when given a correct alkali treatment, show a marked improvement in working qualities. They become more plastic, require less power to extrude the clay through the die, and, when dried, have greater strength and are less pervious to water. The tendency of clays to laminate is reduced. The fired ware is stronger and has a lower moisture absorption. Both acid and calcareous clays are susceptible to improvement by this process. The amount of reagents must be carefully controlled by p_H measurement for best results. The method of testing for p_H. and the limits within which the two type clays must be held are described.     

EXPANSION,CONTRACTION, AND STRENGTH CHANGES OF SOME CLAYS DURING FIRING*

The objective of these experiments was to determine (1) the linear changes in expansion arid shrinkage during firing, (2) the effect of compressive loading on these changes, and (3) the variations in strength at furnace temperatures during the firing of some typical shales and fire clays used for the manufacture of structural clay product.