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.     

INVESTIGATION OF FELDSPAR AND ITS EFFECT IN POTTERY BODIES*

The history and purpose of the investigation are outlined and reports are made on (1) fineness determinations, chemical analyses, softening range, softening points, “true” specific gravity, thermal expansion, and petrographic analyses of the individual feldspars; (2) the results of porosity, volume shrinkage during firing, color and translucency, mechanical strength, petrographic analyses, effect of feldspar used on relative “glaze fit,” thermal expansion, and elasticity determinations on vitreous and semivitreous bodies in which feldspar is the only variable component.     

COMPUTATION OF HEAT TREATMENTS FOR WHITEWARE BODIES *

The constant in Arrhenius’equation, when applied to the vitrification process of feldspathic whiteware bodies was calculated, using known data. Proceeding from this point, a mathematical expression for the amount of reaction taking place in a normal whiteware mixture, heated according to a given schedule, was obtained. Formulas were also derived for calculating heating schedules of various rates of temperature rise and lengths of soaking period productive of a given amount of reaction. The calculated amounts of reaction necessary to vitrify feldspathic whiteware bodies were correlated with the RO contents of the bodies. Data on the physical properties of variously heat-treated bodies are given to substantiate the validity of the formulas. A chart is given by means of which many heat-treatment problems can be solved without using the mathematical formulas.     

TRANSLUCENCY METER FOR USE IN WHITEWARE RESEARCH*

A photoelectric light meter, based on a design by RCA, was developed for a research tool in investigations on whiteware, particularly chinaware. Since its development, it has also found use in work on enamels and on glass. The meter is described in this paper and results obtained with it on both laboratory-prepared and commercially prepared chinaware are given. In addition to use in research, it may be of interest to chinaware manufacturers as a control instrument. The chinaware bodies investigated followed Lambert's exponential law of light absorption. The necessity for obtaining translucency data on pieces of the same thickness, even for relative values, is indicated.     

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.     

CORRELATION OF GLAZE-BODY STRESSES WITH THERMAL PROPERTIES OF WHITEWARE BODIES*

Several lead borosilicate glazes with high to low thermal expansion were applied to a bisque whiteware body having porosities ranging from 20 to 30%, and the thermal properties were studied. Test pieces were subjected to an autoclave test at 50, 150, and 300 lb. per sq. in. and to a thermal-shock test by quenching from 400° to 600°F. into cold water. The thermal-expansion curves for the various glazes and for the body at each porosity were determined on the interferometer. The glaze-fit ring test was used to determine the degree of tensile and compressive stress, and these stresses were plotted graphically with the body porosity. The resistance to crazing was increased in both the autoclave and thermal-shock tests as the thermal expansion of the glazes, as measured on the interferometer, decreased. The 10% porosity body gave the best results in the thermal-shock test. A close correlation was found between the thermal-expansion curves for the glazes and bodies of varying porosity and the stress characteristics shown by the glaze-fit ring test.     

USE OF NEPHELINE SYENITE IN FLOOR-TILE AND WALL-TILE BODIES*

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.     

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.     

THE USE OF TALC AND PYROPHYLLITE IN SEMIVITREOUS DINNERWARE BODIES *

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.     

ALUMINA IN WHITEWARE *

A brief résumé on an extensive investigation of the use of calcined alumina in white-ware bodies is presented. Its use in vitreous chinaware, semivitreous dinnerware, electrical porcelain, cooking ware, and sanitary ware is discussed. Data are given also on special alumina bodies of unusual strength.     

USE OF THE PHOTRONIC CELL AND SPECTROPHOTOMETER FOR MEASURING TRANSLUCENCY OF WHITEWARE*

A method has been developed for measuring the translucency of whiteware by means of the photronic cell, and a modified formula has been derived to express the relationship between translucency and thickness of ware. Bodies containing mixtures of feldspar and lepidolite were translucent over a greater range of temperatures than those which contained feldspar or lepidolite alone, although the translucency of the feldspar bodies was greater than that of the lepidolite bodies having equivalent absorptions. The spec-trophotometer gives a more complete record of the translucency of porcelain because it may be used to measure the transmittance of ultraviolet, visible, and infrared light.     

INFLUENCE OF FLUXES OF SPODUMENE AND FELDSPAR MIXTURES ON PROPERTIES OF CHINAWARE BODIES*

The most fusible spodumene-feldspar mixture used in these studies was composed of 30% of spodumene, 10% of potash feldspar, and 60% of soda feldspar. In semi-vitreous bodies and vitreous hotel chinaware bodies, however, the most effective fluxes were made up of 30 to 40% of spodumene, 40 to 60% of potash feldspar, and 10 to 20% of soda feldspar. Such fluxes lowered the maturing temperature of these bodies and improved their strength at lower temperatures. When they were fired at cones 6 to 9, their resistance to impact was equal to or higher than that of the feldspar bodies.     

DIFFICULTIES IN FIRING DECORATED WHITEWARE*

Some of the problems encountered in firing decorated whiteware are discussed. Both commercial and laboratory tests were conducted to show the cause of difficulties and their prevention. The subjects discussed are (1) “spit-out” or blistered glaze, (3) prevention of crazed or dunted glaze, (3) firing of selenium red overglaze, and (4) prevention of specks in decorating or overglazing one-fired whiteware.     

THE MELTING RELATIONS OF POTASH FELDSPAR,SODA FELDSPAR,AND FLINT MIXTURES1

P.C.E. values of ternary mixtures of potash feldspar, soda feldspar, and flint were determined and results shown on a solid phase diagram. No eutectics were developed with either of the binary series of feldspar and flint. The soda feldspar-flint mixtures were more refractory than were those of the potash feldspar series. At least 20% flint variation with potash feldspar will show no change in P.C.E. values and at least 10% with the soda feldspar showing the unreliability of P.C.E. to indicate the amount of the quartz content.     

USE OF SPECIAL OXIDES IN PORCELAIN BODIES1

Substitution of special oxides for flint.—The oxides of thorium, titanium and zirconium and the silicate of zirconium were used. Variations in composition were based on batch weights, the percentage of oxide (or silicate) increasing from 27 to 49% with a corresponding decrease in feldspar content. A similar series using flint was also made a basis for comparison. Effect of special oxides on drying and burning behavior, dielectric strength and resistance to spang.—(1) Rutile causes high drying and burning shrinkage. The burning range is long but softening in every case results above cone 12. Resistance to spalling is above normal. (2) Thoria produces a body with a long burning range and great refractoriness. Drying shrinkage is normal, burning shrinkage very high, resistance to spalling very low, and the bodies warp badly. (3) Zirconia bodies have a normal drying shrinkage and a high burning shrinkage, no warping, long firing range, and the highest resistance to spalling. (4) Zircon.—The zirconium silicate bodies soften at temperatures below cone 18 and the firing range is short. Drying and burning shrinkage are similar to flint bodies but resistance to spalling is above normal. Effect of oxides on dielectric resistance.—No effect on dielectric resistance is obtained through the use of the special oxides mentioned.     

EFFECTS OF LITHIA SUBSTITUTION FOR SODA IN VITREOUS ENAMEL*

Lithia, as lithium carbonate, was substituted progressively for soda in the composition of a white cover frit. Substitutions were made on both weight and mol bases. Mol replacement of soda by lithia has resulted in improved fusibility, gloss, and opacity; higher gouge, surface abrasion, and acid resistance; and lower thermal expansion coefficient. Weight replacement has caused increased fusibility and gloss; a small decrease in surface abrasion resistance; marked decreases in opacity and in gouge and acid resistance; little change in thermal expansion coefficient, and a noticeable lowering of the transformation temperature.     

NOTE ON MOISTURE EXPANSION OF CERAMIC WHITEWARE IN STORAGE AND IN SERVICE*

Eighteen samples of wall tile and 15 samples of tableware, which had been in service or in storage for periods of time ranging from 23 years to less than 1 year, were tested to determine how much moisture expansion had taken placc. Selected samples were also autoclaved, and the resultant moisture expansions were compared.     

THE ADAPTABILITY OF VARIOUS METHODS TO THE COLOR- DETERMINATION OF WHITEWARE BODIES1

A reliable and convenient instrument is needed to measure the absolute color of nearly white ceramic bodies. Various instruments and methods for color measurement are here described and criticized. Nearly all of them neglect the importance of the source of illumination. A method of color measurement is given, and although the Klett-Ritchic spectro-colorimeter was found to be unsatisfactory for this work, it is believed that the modification of the Pfund colorimeter suggested here would be a reliable and conveuient instrument for plant use.