EFFECT OF OPACIFIERS ON FUSED VISCOSITY OF FELDSPATHIC GLAZES*

A study has been made of the fusion characteristics of feldspar, flint, kaolin, and whiting used in glaze compositions with zine oxide and various opacifiers. The fusion characteristics of tin oxide, Opax, Zircopax, and various combinations of opacifiers are given. All heat-treatments mentioned are at cone 12. Isoviscosity triaxial diagrams show the fields of good glazes in each series, and the rclative effects of composition changes on the physical properties are outlined.     

EFFECT OF ZIRCOPAX ADDITIONS ON ABRASION RESISTANCE AND VARIOUS PROPERTIES OF SEVERAL GLAZES*

A test method is described and the results of four series of experiments are given for the empirical evaluation of the effect of Zircopax in improving the resistance to abrasion of glazes. Simultaneous resistance to crazing and the effect on gloss, color, and opacity are noted.     

EFFECT OF VARIOUS GASEOUS ATMOSPHERES ON THE VITRIFICATION OF CERAMIC BODIES*

Various types of ceramic bodies were fired in atmospheres of O₂, N₂, CO₂, H₂, and H₂. A marked increase in the rate of vitrification occurred when bodies containing feldspar were fired in an atmosphere of H₂O. This effcct was explained on the basis of a feldspar-water eutectic.     

EFFECT OF REPEATED WETTING AND DRYING ON PHYSICAL PROPERTIES OF A CLAY BODY*

Specimens of fine-grained, red-firing clay, which had been fired to temperatures corresponding to various stages of vitrification, were subjected to 200 cycles each of wetting at 100°F. and drying at 100°F. and 60% of relative humidity. This treatment, simulating weathering in mild climates, caused (1) a permanent gain in weight which was greater for the softer specimens; (2) a moisture expansion for the softer specimens but none for those near vitrification; (3) a fairly uniform decrease in modulus of elasticity for all specimens; and (4) a decrease in modulus of rupture for the softer specimens but an increase in strength for those that were completely vitrified. The data indicate that moisture expansion and a decrease in strength of soft-fired clay bodies, caused by repeated wetting and drying, may be eliminated by proper vitrification.     

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.     

THE EFFECT OF BORIC ACID IN RAW MILLED GLAZES*

A study of the reactions between boric acid and typical ceramic raw materials in slips was made to determine the cause of raw glazes thickening upon standing. Raw zinc oxide, precipitated barium carhonate, and light magnesium carbonate were found to react deleteriously with boric acid in milled slips with thickening or “setting” occurring. This thickening does not occur in many instances when large amounts of white lead are present in the mill batch. Remedies are given which were used to overcome this increase in viscosity in commercial raw glazes by using calcined mixtures and insoluble frits.     

EARTHENWARE BODIES AND GLAZES1

Effect of body composition on crazing .—-Six bodies of each of 2 standard clay compositions were prepared with variable clay and flint content and after biscuiting at cone 8 were glazed with 21 earthenware glazes and glost fired at cones 4 and 6. The results indicated that the variability of the silica content of clays would not be great enough to produce crazing in a well-balanced glaze. Effect of proportion and composition of frit .—-A standard whiteware glaze was compounded in 6 different ways and several other glazes in 2 ways. It was found that the method of compounding had no effect on crazing but it affected the gloss and fusibility. Increase in the percentage of material fritted increased the gloss and fusibility. With the same percentage of frit the best glost and highest fusibility were obtained when the flint and part of the clay were included in the frit. Effect of some variations in glaze composition .—-Substitution of CaO by Na₂O, pound for pound, as well as direct addition of Na₂O, increased crazing, improved gloss and increased the fusibility. Direct addition of feldspar increased crazing slightly and diminished gloss, but did not noticeably affect the fusibility. Substitution of 1½1/2 parts of feldspar for one part of flint to maintain the same fusibility increased crazing and diminished gloss. Direct addition of CaO improved gloss, increased fusibility and slightly reduced crazing.     

EFFECT OF EXCHANGEABLE BASES ON ABSORPTION AND TRANSVERSE STRENGTH OF CLAY BODIES*

The absorption and transverse strength of clay bodies, both in the fired and unfired state, are influenced greatly by the nature of the exchangeable bases present on the surface of the clay particles. Plastic clays with high exchange capacity are more affected than nonplastic clays, such as flint clays. Of the various common base forms studied, sodium-type clays in general require less water to give the same degree of stiffness, and their fired and unfired transverse strengths are high. Hydrogen clays require higher water content and have greater porosity and lower transverse strength. Data are given on a plastic fire clay, a ball clay, a bentonite, and two flint fire clays. All experiments made were on stiff-mud bodies.     

THE EFFECT OF HEAT-TREATMENT AND COMPOSITION OF SEMI-PORCELAIN BODIES ON CRAZING

Limits of Investigation.—The investigation was confined to practical semi-porcelain bodies and glazes, therefore, the results may be applicable only to this branch of the whitewares industry. Effect of Thickness of Glaze.—The thicker the glaze the greater the tendency to craze. The glaze on several pieces of dinner ware may appear to the eye to be of uniform thickness, but still have sufficient variation in thickness as to show difference in crazing behavior. It being impossible to obtain a uniform thickness of glaze by hand dipping there is a need for a mechanical dipper. An improved type of biscuit kiln which will produce ware with a uniform absorption is another need. Effect of Glaze Composition.—When sufficient change was made in the composition of a typical semi-porcelain glaze to cause a marked decrease in its crazing tendency, it was at the expense of other desirable properties. Effect of Body Composition.—The addition of 10.0% to 20.0% of “Hercules” clay to a general ware body greatly decreased its tendency to craze. No other change in body composition was found feasible, for when the change was sufficient to cause a decrease in the crazing it was at the sacrifice of other essential properties. Effect of Variation in Absorption.—Contrary to the general opinion among potters, the tendency to craze was not increased by every increase in absorption. An absorption of about 7.0% to 12.0% showed the most resistance to crazing. Effect of the Time-temperature of the Gloss Burn.—Tendency to craze is decreased by increasing the maturing time-temperature portion of the gloss burn.     

MICROSCOPIC AND X-RAY INVESTIGATION OF SOME STEATITE BODIES*

Microscopic, and X-ray examinations of a series of steatite compositions reveal that the body having the best dielectric properties Also has the simplest and most homogeneous physical structure. It is believed that the attainment of similar physical structures in other ceramic bodies will lead to improvements in dielectric properties. This empirical finding is in accordance with present theories of conduction in crystals. It depends on the contribution to conductivity and dielectric loss made by imperfections of crystal structure. However, even in homogeneous materials, alkaline earth ions tend to cause less conduction under like conditions than alkali ions, and there are high-dielectric constant materials like the titanates which, though homogeneous and pure, have a high loss.     

EFFECT OF FIRING ATMOSPHERE ON DEVELOPMENT OF COLORS IN CERAMIC GLAZES*

The effect of systematic variations in atmosphere between 100% oxidizing and 100% neutral was noted. The principles and definitions of color designation are given and possible physicochemical changes which result in color variation are considered. Experimental data indicate the relative stability of typical colors under atmospheric variations.     

EFFECT OF COMPOSITION ON PROPERTIES OF CONE 11 ZIRCONIUM SILICATE-OPACIFIED GLAZES *

Studies were made of the effects of magnesium, calcium, barium, strontium, and zinc oxides on the gloss, texture, and opacity of one-fire, zirconium silicate-opacified glazes at cone 11. The opacity was determined with a Hunter multipurpose reflectometer and the gloss was observed visually. Limits for the various fluxes were determined and a practical base glaze formula was developed.     

THE EFFECT OF PROCESS CONDITIONS ON THE DRYING KINETICS AND REHYDRATION CHARACTERISTICS OF SOME MW-VACUUM DEHYDRATED FRUITS

ABSTRACT

The effect of drying conditions, namely, microwave power, vacuum pressure, as well as sample geometry, on the drying kinetics and rehydration characteristics of five microwave vacuum dehydrated fruits (apple, avocado, mushroom, pear and strawberry) was studied. The investigation involved a wide range of microwave power, vacuum pressure and sample size levels. The drying rate and the rehydration ratio, a measure of rehydration characteristics, were found to depend on the drying conditions. An empirical mass transfer model, involving a characteristic parameter for each process (drying and rehydration( as a function of process variables, namely, microwave power, vacuum pressure and sample size, was also tested with the data obtained in a microwave oven equipped with vacuum apparatus. Furthermore, a comparison of rehydration properties of microwave vacuum and conventionally dehydrated products, was conducted.     

THE EFFECT OF PROCESS CONDITIONS ON THE DRYING KINETICS AND REHYDRATION CHARACTERISTICS OF SOME MW-VACUUM DEHYDRATED FRUITS

The effect of drying conditions, namely, microwave power, vacuum pressure, as well as sample geometry, on the drying kinetics and rehydration characteristics of five microwave vacuum dehydrated fruits (apple, avocado, mushroom, pear and strawberry) was studied. The investigation involved a wide range of microwave power, vacuum pressure and sample size levels. The drying rate and the rehydration ratio, a measure of rehydration characteristics, were found to depend on the drying conditions. An empirical mass transfer model, involving a characteristic parameter for each process (drying and rehydration( as a function of process variables, namely, microwave power, vacuum pressure and sample size, was also tested with the data obtained in a microwave oven equipped with vacuum apparatus. Furthermore, a comparison of rehydration properties of microwave vacuum and conventionally dehydrated products, was conducted.     

THE INFLUENCE OF CHEMICAL COMPOSITION ON THE PHYSICAL PROPERTIES OF GLAZES*

This paper presents some preliminary work on the study of the factors affecting fit of ceramic bodies and glazes. From the experimental work on 118 glazes and glasses, a method is outlined for calculating from the chemical composition of the glaze, approximate values of the tensile strength, Young's modulus of elasticity, and the mean linear coefficient of expansion of the glaze in the temperature range from 25°C to the lower limit of the critical range.     

组成对分相-析晶乳浊釉显微结构及表面性质的影响

采用X射线衍射、透射电镜和扫描电镜等测试手段,研究了不同组成对分相-析晶乳浊釉显微结构及釉面性状的影响.研究表明:B2O3和P2O5能促进分相形成,并且由于分相具有很小的表面张力而使其液滴易于长大.适量引入CaO能使液滴尺寸增大,体积分数提高,但过量引入会由于析晶而使体积分数降低.控制分相液滴尺寸接近可见光波长以及使釉中析出适量钙钠长石晶体可获得最佳的乳浊效果,而液滴过大或过小都难以获得较佳的乳浊效果.     

EFFECT OF STEAM AND HOT WATER WITH SODA ASH AND A WETTING AGENT ON PROPERTIES OF CLAY*

The use of combined treatments was found to Ix more efficient in improving the properties of clays than individual treatments, and the best results were obtained when the clay was pugged with steam and hot water with an addition of 0.2% of soda ash. This process lowered the water of plasticity 26%, the drying shrinkage 58%, arid the absorption 46.5%. The dry and fired strengths were increased 123% and 144%, respectively.