THE USE OF AUXILIARY FLUXES IN DINNERWARE BODIES*

A plant and laboratory study was made of the use of frits as auxiliary fluxes in dinnerware bodies. The frits were added to a commercial earthenware body. Seven-inch plates of these bodies were jiggered, fired, and glazed at the pottery. Some practical difficulties encountered were as follows: (1) Due to the progressive solubility of the frits, even when this solubility was slight and only 2 to 4% of the frit was used, the slip was deflocculated and the plasticity of the body was destroyed. This trouble apparently was overcome by using a slight excess of hydrochloric acid in the body slip. (2) The ware of the bodies containing frit warped more than the normal body, especially in the glost fire. Results of tests of the slips, bodies, and ware are presented.     

SYNTHETIC SILLIMANITE IN CERAMIC BODIES1

The manufacture, characteristics, and use of a new ceramic product in which the stable form of sillimanite, having a composition of 3A1₂O₃–2SiO₂, is the chief constituent. An interesting feature of the product is the fusible matrix of definite composition, in which sillimanite needles are held, and which permits of recrystallization at commercial temperatures when the product is added to porcelain or whiteware body mixes. Introduction of sillimanite apparently greatly toughens and strengthens the body in which it is introduced.     

INCREASE IN REFRACTORINESS IN CERAMIC BODIES IN INTERRUPTED HEAT TREATMENT1

The increase in refractoriness referred to here is usually termed freezing. The study was undertaken to overcome the tendency of pyrometric cones to set or freeze when subjected to prolonged heat treatment when the temperature is more or less fluctuating. The work includes a study of the freezing tendency of some natural clays, of several pottery bodies, and of pyrometric cones. A body was developed that does not freeze under the treatment that produces the phenomenon in the other materials tested but the cause is not established.     

TALC AS THE PRINCIPAL BODY INGREDIENT IN VITRIFIED CERAMIC BODIES1

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.     

EFFECT OF WATER IN EXPANDING CERAMIC BODIES OF DIFFERENT COMPOSITIONS1

The effects of the composition of some ceramic bodies on their moisture expansions were investigated. With the exception of mixtures containing blast-furnace slag or magnesite, most bodies with high absorptions developed considerable expansion. Bodies with low absorptions composed of pure clay and feldspar developed practically no moisture expansion while those composed of clay, feldspar, and more than 20% silica developed considerable moisture expansion. By adding magnesite, the resistance of a ceramic body to moisture expansion was improved. Additions of whiting, iron oxide, and titanium oxide were not as beneficial as magnesite. It was found that crazing caused by moisture expansion of bodies can usually be prevented by proper manufacturing control.     

THE HEAT REQUIRED TO FIRE CERAMIC BODIES1

A differential thermal method for determining interval specific heats of ceramic materials is described. The specific heat of the unknown is determined by comparing its temperature to that of quartz after each sample has been subjected to a definite heat treatment. This method shows the number of calories required to heat one gram of the material in question from 0 to t°C, accounting for all thermal processes which the material may undergo during the heating process. It shows the temperatures at which the various thermal processes begin and end as well as the quantitative figures for the more pronounced of these thermal processes. The kaolin, ball, flint, and diaspore clays undergo an endothermic reaction at about 575°C which amounts to “60 to 130” calories per gram of the air dried material. They undergo an exothermic reaction at about 960°C which amounts to about 25 calories per gram of the air dried material. About 510 calories are required to heat one gram of any firebrick body from 25 to 1200°C, the specific heat over this interval being about 43. About 500 calories are required to heat one gram of any kaolin or ball clay from 0–1000°C, the specific heat over this interval being about 5. About 290 calories are required to heat one gram of flint or feldspar from 0–1050°C, the specific heat over this interval being about 28. Instead of the kiln efficiencies being about 22% as was previously believed, this work proved them to be about 35%.     

STUDY OF EUTECTIC FLUXES IN SEMIVITREOUS AND VITREOUS WHITEWARE BODIES*

Frits of oxides of lithium, barium, calcium, and magnesium combined with calcined alumina and pulverized flint were substituted for feldspar in a dry-press whiteware body. Three series of bodies were studied which contained (1) about one half the normal RO content, (2) the normal RO content, and (3) about three times the normal RO content. Firing behavior and mechanical properties of the various bodies in the vitreous and semi-vitreous range were determined, and the results are reported in this paper.     

THE HEAT REQUIRED TO FIRE CERAMIC BODIES1

The interval specific heats of twenty-three refractory clays of various types from Pennsylvania, Ohio, Maryland, Kentucky, Missouri, Colorado, and New Jersey were calculated as well as ten clays used in the Bureau of Mines investigation “The Burning Problems of Industrial Kilns.” This group included fire clay, shales, and surface clays. The results showed that there was very little difference in the interval specific heats at 1000 °C between the various types of fire clay, shales, and surface clay. The values ranged from .425–440. In the Bureau of Mines investigation the average kiln efficiencies were calculated to be about 18%; using the corrected figures obtained for interval specific heats, the average kiln efficiencies were found to be about 29%.     

METHOD OF MEASURING STRAINS BETWEEN GLAZES AND CERAMIC BODIES1

A new test was developed for comparing the strains existing between different glazes or other ceramic finishes and the bodies to which they are applied. By its use these strains may be so adjusted that the finishes will be in suflicient compression to prevent crazing from subsequent expansion of the body without causing initial shivering. The new test is particularly valuable because the measuremen & are made on combinations of glaze and body prepared and treated almost exactly like those intended for regular use and because of the simplicity and cheapness of the apparatus required. A modification of the test provides a comparison of the moisture expansions of different bodies.     

METHODS FOR TESTING CRAZING OF GLAZES CAUSED BY INCREASES IN SIZE OF CERAMIC BODIES1

Investigations to determine the causes of a type of crazing which develops on certain glazed ceramic wares, some time after firing, revealed the fact that in many cases such crazing is caused by an expansion of the body. This is probably due to the combination of water with the body, while the glaze remains practically constant in size. A body may be tested for this type of crazing by placing the glazed specimens in an autoclave and subjecting them to a steam pressure of 150 to 175 pounds per square inch for one hour. Bodies showing the least tendency to develop this type of crazing are those which have a low porosity, are not very soluble in sulphuric acid, and have a low ignition loss above 110°C.     

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.     

FITTING GLAZES TO CERAMIC BODIES*

In fitting glazes to bodies, conditions of manufacture and service must be considered. Crazing tests for glazed ware to be used under different types of service are described, and new data are given pertaining to fitting glazes to ceramic bodies.     

CONTINUITY IN PLASTIC BODIES1

Extended experiments have shown that the plasticity of a clay increases with the growth of algae in it and the presence of hydrogel of alumina caused by a biochemical reaction. Air included in a clay body causes shortness. Experiments were run in evacuating the air in a clay and then by suddenly breaking the vacuum, collapsing the evacuated clay. The clay thus treated shows greatly increased plasticity, reduced warpage, elimination of blistering and resistance to rupture on distortion. The physics and chemistry of making clay plastic are discussed.     

COLOR FORMATION IN VITREOUS BODIES1

A simple vitreous body of the Parian type was made up and the coloring produced by adding varying amounts of cobalt, chromium, iron, uranium, nickel, and copper oxide was determined. The color was measured by the Hardy recording spectrophotometer, and the resulting curves were analyzed for the three attributes of color. The hue, brilliancy, and saturation were all proportional to the logarithm of the coloring oxide. It was found that the color was mainly due to the particles of the practically undissolved oxide, and not to a colored glass. This makes it possible to color a body for use in reflected light, but not for transmitted light. Some excellent magenta red bodies were produced by reducing the copper oxide, but the results could not be consistently reproduced.     

PROGRESS OF FLUIDITY IN PORCELAIN BODIES1

Firing characteristics of a group of thirteen clay-flint-feldspar porcelain bodies were studied. Firing shrinkage, porosity, and rate of deformation were determined on specimens of all bodies fired at a series of temperatures, thus observing the rate of vitrification and subsequent fluidity of each of the bodies in question. Cross-breaking strength tests were made in order to ascertain the relation of composition and firing temperature to mechanical strength.     

INSULATION IN THE CERAMIC INDUSTRY1

The following subjects are discussed: (1) heat losses in ceramic kilns, (2) early attempts at reducing heat losses from kilns, (3) properties of an ideal insulation for kilns, (4) advantages of kiln insulation, and (5) various applications of heat-insulating material in the glass plant.