WASHING TESTS OF GEORGIA CLAYS1

The Whirlpool Classifier .—A device is described by which the impurity in a clay can be separated more efficiently than is possible by simple elutriation processes. Washing Plants .—A semi-commercial plant used to wash 1000-lb. samples is described, together with a suggested plan for a commercial plant. Beneficiation of Georgia Clays .—Results obtained on several Georgia sedimentary clays are given. The washed clays are reported free from grit and material producing specks in burned ware as well as improved in color, both in the raw and burned state.     

THE MECHANICAL MOVEMENT OF WATER THROUGH CERTAIN CLAYS AND ITS CONTROL12

Introduction .—Ceramic bodies containing Georgia clay cast and release from the molds slower and have a greater tendency to crack in drying and burning than similar bodies containing English china clay. Experiments were conducted to improve these properties of Georgia clays by studying the movement of water through them and its control. Permeability .—It was found that the permeability of the clays to water was independent of the time between 2 and 10 days; that is, P is nearly constant in the formula P = W/T, in which W is the total water which has passed through and T is the time in days. This factor for North Carolina kaolin was 1.55≠.05; for English china clay 1.45≠.06; for Georgia clay 0.938≠.07; for South Carolina clay 0.673≠.07; and for Tennessee ball clay 0.64≠.08. Capillarity .—The investigation showed that the capillary rise of water through these clays may be expressed by the formula H=C_h (log T - 1.041) in which H is the height attained by the water in time T, and C_h is approximately constant for each clay between 10 and 250 minutes, that is, it represents the movement of water through clay when it contains a certain amount of water below that required for saturation. This factor for North Carolina kaolin is 6.67≠ 0.30; for English china clay 7.30≠ 0.70; and for Georgia clay 4.66≠ 0.80. The great capillary conductivity of water through primary kaolins explains why bodies containing these get drier and release from the molds quicker than those containing secondary clays. Methods for Improving Georgia Clay .—The Permeability factor of Tennessee ball clay was increased from 0.64 to 1.20 by adding 0.7% NaOH, and that of kaolin from Dry Branch, Georgia increased from 0.938 to 1.72 by calcining to 450°C. By either, or a combination of the above treatments, it was possible to improve the properties of many Georgia clays, making them more like the English china clay in regard to permeability to water.     

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.     

EFFECTS OF AUTOCLAVE TREATMENTS ON CERAMIC BODIES AND CLAYS1

It has been found that porous ceramic bodies increase in volume and weight due to an autoclave treatment in which the ware is subjected to steam at a pressure of 150 pounds per square inch. The change is rapid at first but decreases as the time of treatment is increased. Typical American and English china clays also increase in volume but ball clays when fired to the same temperature as the china clays do not increase in volume. The effect of prolonged drying treatments after the autoclave treatment is also studied. Data given indicate that the changes in volume are not necessarily caused by rehydration of the clay within the body. Bodies containing clay, feldspar, and flint show a greater increase in volume than do the pure clay constituents. It is shown that the composition is a more important factor than absorption in determining the reaction of ceramic products to the autoclave treatments.     

THE USE OF GEORGIA AND NORTH CAROLINA KAOLINS IN A SEMIPORCELAIN BODY

Tables are given, comparing properties and analyses of Georgia and North Carolina kaolins and two English china clays. These two domestic clays are found to be very adaptable to this type of body. North Carolina kaolin reduced warping of ware in the glost kiln, but made the body less plastic. Georgia kaolin enabled a higher flint content to be used, also imparted greater dry strength to the body. Since using these domestic kaolins, crazing has been reduced.     

THE EARLY STAGES OF THE SCIENCE OF CERAMICS IN AMERICA1

Metallurgical operations and growth of white pottery and tile manufacture stimulated search and analyses of desired clays, by state and national departments, after the Civil War. A chemical relation between composition of pottery bodies and glazes was not surmised in English-speaking countries, until projected by the writer. Finding the idea in operation in current work of Seger, his methods of investigation were applied to American raw materials and ceramic processes during ten years, without followers in any other country but Germany. Native clay resources, white vitreous ware, standardization of production and control were developed independently, and introduced commercially. Growth of the large body of ceramic engineers, obligated by immediate demands for technical results, has prevented true scientific study, of common ceramic phenomena, under known laws of modern physical chemistry. Research is entirely empirical, and hand-books of constants, available to engineers in other fields, are still impossible. To this need of the profession all should now make systematic contribution.     

TESTS ON SOME SAGGER CLAYS AND BODIES1

Tests on the Sagger Clays.—Bars were made from three typical sagger clays without the addition of grog. After burning at cone 101/2 these bars were tested for linear shrinkage, transverse strength, dry and fired, absorption of moisture, and dye penetration. Tests on Fire Clay-Grog Sagger Bodies.—Two series of bodies were made up into bars. After being burned at cone 101/2 the bars were tested for linear shrinkage, transverse strength, dry and fired, and resistance to heat changes. The best body of this type tested was No. 5 which had the composition: No. 8 buff clay, 29.870; No. 1 fine clay, 18.2%; grog, 6-to 20-mesh, 42.0%; grog, 20-mesh and finer, 10.0%. As a plant test 100 saggers were made from this body. At the end of five fires, three were broken, and fifteen were slightly cracked. Tests on Some Refractory Bodies not Commonly Used for Saggers–Three bodies were made into bars, fired to cone 101/2 and tested as before. Two proved much superior to those of the fire clay-grog type. Their compositions are: These bodies, especially No. 14, are of types ordinarily considered too expensive (their first cost) for general use. Are such bodies actually more expensive, when the cost is figured on the basis of the lives of the saggers? They can be determined only by making plant trials of a large number of saggers, determining the relative “cost per fire.”     

ILLITE,MONTMORILLONITE, HALLOYSITE,AND VOLCANIC ASH AS WHITEWARE BODY INGREDIENTS*

Plasticity of whiteware bodies can be increased by additions of montmorillonitic, illitic, or halloysitic clays. Montmorillonite gives the highest plasticity, illite slightly less, and halloysite the least. The use of montmorillonite may cause poor casting properties owing to its thixotropic quality. Both montmorillonite and halloysite increase the shrinkage of cast or jollied ware. The former, however, may be used successfully in dry-pressed bodies to increase the plasticity. Illite increases the plasticity without increasing the shrinkage or damaging the casting properties of slips, and small additions of illite to kaolins give a workability similar to that of ball clays. Illite, a flux with a wide vitrification range, also yields a true translucent porcelain at maturing temperatures as low as cone 8 and vitreous floor tile at cone la. Although the rhyolite ashes are not plastic, they increase the shrinkage of vitrified ware without increasing the plasticity. They are, however, good raw material for porous ware, especially wall tile, permitting a rapid firing schedule.     

THE MANUFACTURE OF AN INSULATING BRICK FROM DIATOMACEOUS EARTH

Development of an Insulating Brick. —Pulverized diatomaceous earth was blended with each of the four clays, Tennessee ball, Bedford shale, Rock Hill, Tionesta, in percentages of 0, 5, 10, 15, 20, 30, 50 clay. Dry pressed briquettes were made using 50 to 60% water, and were burned at cones 06, 02 and 2. Heat conductivity tests were made upon the best bodies of the series.     

X-RAY INVESTIGATION OF THE EFFECT OF HEAT ON CHINA CLAYS1

X-ray diffraction patterns were obtained from an English china clay and a Georgia sedimentary kaolin, both raw and fired to various temperatures. The chief crystalline constituent of the raw clays was found to be kaolinite. Upon dehydration the kaolinite lattice was destroyed and the clays gave no diffraction pattern. Mullite was formed in both clays at 950°C and the amount increased with increase of firing temperature. In addition to the mullite, free alumina was present in the Georgia clay from 950 to 1100°C and cristobalite at temperatures above 1200°C.     

THE BEHAVIOR OF FIRE BRICK IN MALLEABLE-IRON FURNACE BUNGS1

Purpose. —An investigation was conducted to study the requirements of fire clay and bodies used for fire brick in malleable-iron furnace bungs. Tests were made on complete bungs holding forty sample brick in malleable-iron furnace bungs with twenty different fire brick. Laboratory tests were also made in conjunction with them. Results. —The spalling tests bear the closest relation to the service test; those brick losing less than 10% withstand more than fifteen heats. There is also a relation between the porosities and densities of fire brick, which lie between 15 and 28% and 1.5 and 2.6%, respectively, for the best brick. There is no close relation between the load test and softening-points of fire brick and their lifetime in malleable furnace bungs, so these tests are no criterions in judging the serviceability of brick, provided the brick are sufficiently refractory to support the arch at furnace temperatures. Methods for Improving Fire Brick. —The resistance of a brick to spalling may be governed by: (1) the selection of the proper clays, (2) the size of grain and the proportioning of the non-plastic ingredients, (3) the fineness of grain of the bond clay, (4) the manner of molding, and (5) the temperature of firing.     

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.     

AN INVESTIGATION OF TWENTY-ONE SASKATCHEWAN BALL CLAYS1

Twenty-one Saskatchewan ball clays have been investigated; the study covers in a general way their chemical, raw, and fired properties. The information presented will no doubt prove of immediate interest to the ball clay trade and especially to the Saskatchewan shippers and exporters. In general, the more outstanding properties of the clays studied are raw strength, fired color, craze resistance, and rate of vitrification. Their raw strength is remarkably high, greater than that of any similar clay on the market at the present time. One clay developed the exceptional raw strength, though diluted with 50% potters’ flint, of over 1000 lbs. per square inch, a second one 938 lbs., while the average of the eleven highest is 812.8 lbs.; clays of such high strength should prove of interest to the trade where it is desirable to reduce losses in the raw and bisque state. A number of the clays tested are outstanding as ball clays in that they fire white or nearly so up to and including cone 12, the purity of whiteness being equal to that of white firing china clays. The porosity and fired volume shrinkage of the Saskatchewan clays correspond more nearly to those of the English ball clays than do the Tennessee-Kentucky clays as studied by Sortwell.     

SOME EXPERIMENTS ON THE FIRECRACKING OF TERRA COTTA1

Firecracking .—occurs on terra cotta under certain conditions and is characterized by the appearance of sharp, hair-line cracks extending into the body. The experiments were made by firing large typical pieces of terra cotta made from various clays and grogs and cooling them at different rates. The tendency to firecrack was observed after weathering. The absorption, porosity and transverse strength of the various bodies were determined. Rate of Cooling .—All bodies similar to those used in practice showed a tendency to firecrack when cooled rapidly and all were free from cracks when cooled slowly. The rate of cooling has a much greater effect on the tendency to firecrack than the composition or physical properties of the body. Effect of Clay .—Three of the four sandy clays showed a decided tendency to firecrack, due to the difference in the expansion and contraction behavior of sand and clay in heating and cooling. The sandy clays showed more tendency to firecrack than the non-sandy, vitrifying clays. The tendency of a clay to develop firecracks in a body depends to a very large extent upon the character of the clay itself, regardless of the impurities it contains. The presence of sandy material and the character of the clay appear to have a much greater effect on the tendency to firecrack than the absorption, porosity or transverse strength of the body. No relation was found to exist in these experiments between the porosity and transverse strength of a body and its tendency to firecrack. Effect of Grog .—The greatest tendency to firecrack was found on a body with all grog finer than 40-mesh, but a body with all grog coarser than 40-mesh did not appear to have much less tendency to firecrack than the average. Increase of grog reduced the tendency to firecrack. The kind or source of the grog used does not have as much effect on the tendency to frecrack as the size and amount. The kind of grog is of much less importance in this respect than the kind of clay.     

THE EFFECT OF VARIATION IN FIRING ON THE PHYSICAL PROPERTIES OF VITREOUS CHINA BODIES1

The porosity, transverse strength, compressive strength and impact strength of ten commercial china bodies were determined on sets of specimens fired in three positions in a kiln in each of ten potteries. The results showed that while there was considerable difference in the maximum strength of the bodies, nearly all of them developed high strength when fired most advantageously. The maximum strength existed over a narrower range in heat treatment than that of complete vitrification. Underfiring and overfiring of this type of body caused serious loss in strength. Specimens of eleven bodies fired at cones 6, 8, 10, 12 and 14 in a laboratory kiln showed about the same differences in maximum strength as specimens of the same bodies fired in the pottery kilns. In one body only was as high strength. developed in the small kiln as in the factory. In most instances the highest strength developed was coincident with complete vitrification and in all the bodies it occurred near or prior to cone 12. There was considerable difference in the range in temperature over which the different bodies were vitrified and were of high strength. While two of the bodies were excellent in this respect, the remainder were vitrified and of high strength through only a narrow temperature range.     

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.     

THE DEFLOCCULATION OF CLAY SLIPS AND RELATED PROPERTIES1

In an earlier paper² the authors have given the particle analysis and other tests of a number of English china clays, one English ball clay and several domestic kaolins. In this paper are presented the following additional data for the same clays: the carbon content as a measure of organic matter; the change in state of dispersion with pH for 20% slips as determined by settling tests; the change in viscosity with pH as determined with 40% slips; the alkali absorption for 20% and 40% slips. The more plastic clays are characterized by high organic content, high alkali absorption, and dispersion at low pH. Casting slips made up with the different china clays and two ball clays in varying proportions show that ball clay causes fluidity and that the plastic china clays produce more viscous slips than the less plastic.     

Traditional and new applications for kaolin, smectite, and palygorskite: a general overview

Clays have been and continue to be one of the more important industrial minerals. Clays and clay minerals are widely utilized in many facets of our society. They are important in geology, agriculture, construction, engineering, process industries, and environmental applications. Traditional applications are many. Some of the more important include ceramics, paper, paint, plastics, drilling fluids, foundry bondants, chemical carriers, liquid barriers, decolorization, and catalysis.Research and development activities by clay scientists in academia, government, and industry are continually resulting in new and innovative clay products Many of these new applications are the result of improved processing, which provides clays of higher purity, more precise particle size and distribution, whiter and brighter color, modified surface chemistry, and other physical and chemical modifications. Some new and improved clay products include tailored or engineered paper coating kaolins, enhanced paint thickeners, nanocomposites for plastics, pillared clays as special absorbents and catalysts, clays for liquid fertilizer suspensions, clays for absorption of animal wastes, calcined kaolins with high brightness and low abrasion, faster casting clays, and clays with a very high modulus of rupture.Improvement of mining and processing techniques will lead to the continued growth of traditional clay applications and to the development of new and innovative clay products. Value added products are the wave of the future for the traditional industrial clay minerals.     

USE OF A HIGH SERICITE PYROPHYLLITE IN VITREOUS BODIES*

A pyrophyllite containing approximately 15% of sericite is being produced at Hemp, North Carolina. When it is substituted in vitreous bodies for all of the flint or all of the flint and some feldspar, a marked increase in fired strength results, and the shrinkage and absorption properties are not affected by this substitution. The types of bodies studied include electrical porcelain, made by the dry and plastic processes, sanitary ware, vitreous floor tile, and hotel china ware.