EFFECT OF COMPOSITION ON PROPERTIES OF TITANIUM ENAMELS*

The development of a superopaque, acid-resistant titanium enamel is described. Different components of the batch were varied systematically and the properties, such as reflectance, color, flow, gloss, and acid resistance, were determined. Variations in composition, reflectance curves, and spectrophotometer curves are given for all of the enamels investigated. The stability of this type of enamel during firing and smelting was also studied. Spectrophotometric analyses of this type of enamel show a characteristic low reflectance in the short-wave length region of the visible spectrum, differing in this respect from superopaque antimony and zirconia enamels. Additions of as much as 0.5% Fe₂O₃ and 0.2% V₂O₅ to the titanium enamel did not cause any appreciable variations in color. Although some differences in the spectrophotometer curves were noted over the field of enamels investigated, the only major change in color occurred when minute amounts of Cr₂O₃ were present. X-ray diffraction patterns of enamels show that rutile crystals in most cases, or sometimes anatase, are the crystals causing opacity.     

EFFECT OF FIRING TREATMENT ON PHYSICAL PROPERTIES OF DRY-PROCESS ENAMELS *

The relations between the firing treatment and physical properties of some commercial, antimony-bearing dry-process enamels for cast iron were studied. These properties include opacity and resistance to surface abrasion for both acid-resistant and regular enamels and acid resistance of the acid-resistant types. In contrast to wetprocess enamels for sheet steel, these dry-process enamels were found to be little affected by the extreme variations in firing which might be encountered in ordinary practice.     

EFFECT OF SET OF ENAMELS ON HYDROMETER READINGS OF THE SLIP *

The operation in enameling that is the most difficult to control is the setting up of enamels for dipping. The difficulty occurs because there has been no practical accurate method for measuring the set of the enamel. Practical experience shows that viscosity is not an indication of the set or of the dipping weight. The method presented consists in determining the apparent specific gravity of the enamel slip with true value for the specific gravity. Calculations give a numerical value for the value of the set or yield point. The measurements are accurately reproducible, and dipping weights have been found to correlate quite well with the results given of tests in laboratory and plants.     

EFFECT OF PARTICLE SIZE AND INDEX OF REFRACTION ON REFLECTANCE*

The effect of particle size on the reflectance of thin semitransparent layers, such as enamels, was studied by using mixtures containing opacifying particles of definite sizes in an oil of known index of refraction. The mixtures were applied on a black glass plate, and the reflectance was measured. The coefficient of scatter per unit surface of the particles was calculated and was found to decrease slowly as the particle size decreased. On the other hand, for the range of sizes studied, the reflectance of the semitransparent layer increased rapidly as the particle size decreased.     

A PECULIARITY OF SHEET-IRON ACID RESISTING COVER COAT ENAMELS*

It has been demonstrated that the small bare spots evident in the first coat of acid-resisting enamel applied directly upon the ground coat are not necessarily the result of a process fishscaling in the ground coat during the firing operation, but are more often the result of reboiling of the ground-coat enamel and lack of film strength in the yet unfused layer of acid-resisting enamel. Reboiling, or other mechanical movements of the ground coat, may promote defects in acid-resisting enamels which would not be visible in those of the nonacid-resisting type, particularly when these enamels are applied directly upon the ground coat. The electrolytes used with acid-resisting enamels are directly connected with the popping condition noted. A choice of the proper kinds and amounts of electrolytes for “setting-up” the enamel can, in some cases, eliminate or minimize this trouble. The use of a nonacid-resisting enamel, properly set up as an intermediate layer between the ground coat and the finish coat of acid-resisting enamel, will also prevent troubles of this kind. The tendency for this peculiar defect to occur depends also upon the type of enameling base metal used and its tendency to reboil.     

EFFECT OF SODIUM ALUMINATE ON CONSISTENCY AND ACID RESISTANCE OF SOME ACID-RESISTANT ENAMELS*

This paper includes consistency studies and shows variations in acid resistance occurring with concentration and the method of using sodium aluminate as a setting-up agent.     

X-RAY INVESTIGATION OF THE OPACIFYING COMPOUNDS PRESENT IN SHEET-IRON COVER ENAMELS*

By the use of X-ray methods, sheet-iron cover-enamel frits and fired enamels were investigated. The results obtained show that tin oxide exists as tin dioxide in the enamel, antimony as antimony pentoxide, fluorspar as calcium fluoride, and cryolite as sodium fluoride. Zirconium oxide does not exist as the crystalline zirconium oxide even when present as a mill addition. Variations in the compositions of the ordinary sheet-iron cover enamels do not affect the identity of the crystals.     

EFFECT OF REFRACTORY MILL ADDITIONS ON MOLTEN APPARENT VISCOSITIES OF STEEL GROUND-COAT ENAMELS*

A viscosimeter of the rotating-cylinder type was used to determine the effect of refractory mill additions on the molten apparent viscosity of steel ground-coat enamel. A blend of three commercial frits was used as the base enamel to study the effect on molten viscosity of various amounts of silica, feldspar; and nepheline syenite. Results indicated that silica imparted the greatest increase in molten viscosity. Additions of feldspar and nepheline syenite of 9% or less increased the molten viscosity about the Same amount. With, however, a 12% addition of refractory, feldspar was more effective for increasing molten viscosity than nepheline syenite.     

EFFECT OF COEFFICIENT OF EXPANSION OF GROUND- AND COVER-COAT ENAMELS ON THERMAL-SHOCK AND IMPACT RESISTANCE *

Four antimony cover-coat enamels, four fluoride cover-coat enamels, and four ground-coat enamels were formulated to give varying coefficients of expansion. The calculated values were 250, 275, 300, and 325 × 10^–7. The observed coefficients of expansion are included in the paper. The enamels were applied to standard 2-quart pudding pans and were tested for thermal shock and impact resistance using the standard methods of the Enameled Utensil Manufacturers’Council. The results show that thermal-shock resistance is controlled chiefly by the coefficient of expansion of the ground-coat and cover-coat enamels. The best results were obtained by using a cover-coat enamel with a low coefficient of expansion and a ground coat with a high coefficient of expansion. No conclusive evidence was found to indicate any effect of the coefficient of expansion of the ground- and cover-coat enamels on impact resistance. The solubility resistance and reflectance curves for the enamels are also included.     

EFFECT OF SIZE AND SHAPE OF TITANIUM OXIDE CRYSTALS ON SPECTROPHOTOMETRIC PROPERTIES OF TITANIUM-BEARING PORCELAIN ENAMELS*

Color changes of three titanium enamels given varied firing treatment were investigated. The size and shape of titanium oxide particles were studied with the electron microscope, the relative amounts of anatase and rutile were determined from X-ray analyses, and spectrophotometric curves of the fired panels were made. Electron micrographs showed that rutile particles recrystallized as needles or “sticks,” whereas anatase appeared as ill-defined, irregularly shaped, rounded particles. With increasing firing temperature or firing time (1) rutile particles showed a greater increase in size than anatase particles, (2) the amount (by weight or volume) of anatase crystals decreased and the amount of rutile crystals increased, and (3) a color change from blue-white to cream-white was observed. The change in color seemed to be related to the scattering of blue light by small particles at lower temperatures or shorter periods of firing. As the size of opacifying particles increased, the scattering of blue light decreased, and the characteristic absorption of visible light in the shorter wave lengths was more apparent. In enamels containing both anatase and rutile, the smaller anatase crystals were predominant at lower and the larger rutile crystals at higher temperatures, so that sharp changes of color were observed as the firing temperature was increased.     

EFFECT OF VARIATIONS IN COLOR STAINS AND FRITS ON COLORS PRODUCED IN PORCELAIN ENAMELS*

A representative series of colors, blue, brown, green, red, and yellow, was selected for this investigation. Variations of the constituents for these five stains were made and the resulting colors produced in the enamels were measured by means of spectrophotometric curves. The influence of additions of barium oxide, lead oxide, and zinc oxide to the frit was also studied. The addition of lead oxide to the frit tended to give greater solution of the blue stains. The barium oxide additions dissolved the lead antimonate yellow the most, while the lead oxide had the least effect on the yellow stains. Variations in calcination temperatures of the red stains produced decided changes in color. The additions of lead oxide darkened the color produced with the red stains.     

A SYSTEMATIC STUDY OF SHEET-IRON COVER ENAMELS1

Based on the limits of composition for sheet-iron cover enamels as commercially used, a systematic field of compositions was plotted and studied. The results show the relation between composition and properties of these enamels. The acid-resisting properties were studied and a treatment developed for improving it.     

EFFECT OF SOLUBLE SALTS ON THE PROPERTIES OF ENAMELS1

Enamels, in common with other types of glasses, are more or less soluble in water, depending on their compositions. The nature and quantity of salts dissolved from the enamel glass during milling have a very definite bearing on the suspension, work ability, and other properties of the enamel, such as pitting and crawling. Those enamels which produce mill liquors which are excessively alkaline have very poor floating qualities. The ratio of free alkali to boric oxide dissolved from the enamel frit is an important factor in the flotation properties of the enamel. The poor floating powers of certain enamels can be corrected by the addition of suitable electrolytes. The kind and quantity of salts dissolved from the frit will determine the selection of the proper electrolyte. Enamel compositions having minimum solubility for good suspension and other properties are given. The value of an enamel clay cannot be determined by floating the clay in water. Tests must be made with the clay in the type of enamel with which it is to be used. Any studies on the effect of aging of enamels on their working properties must give consideration to the constitution and quantity of the individual salts dissolved from the enamel frit, and to the action of carbon dioxide in neutralizing part of the free alkali.     

EFFECTS OF COMPOSITION ON THE PROPERTIES OF GROUND COAT ENAMELS FOR SHEET STEEL1

A series of ground coats was developed about each of three refractory bases, one of which consisted of flint and feldspar in a ratio frequently used commercially, another consisting of feldspar only, and the third of flint only. In each case the refractory portion was 58.5 parts of the whole. Besides the refractory, a “fixed addition” of 11.5 parts, comprised of 0.5 cobalt oxide, 1.0 manganese oxide, 5.0 boric oxide and 5.0 sodium oxide, was used in every enamel, bringing the basic constant portion for each series to 70 parts of the whole. The variable portion in each series was made up of equal parts of three constituents commonly used in enameling, chosen from a total of six in such a way that every possible combination was employed, making a total of twenty enamels in each series. All were given two cover coats of a standard white and tested for resistance to mechanical and thermal shock. In general the ingredients which were most conducive to resistance to the test treatments were flint in the refractory portion, and sodium oxide in the variable portion, constituted of fluxes. Also, boric oxide favorably influenced resistance to mechanical shock in the series containing both flint and feldspar. Resistance to mechanical and thermal shock in ground coats was considerably less affected by variations in expansivity than is the case in cover coats, the influence of that factor appearing to be partially obscured by other factors.     

ELECTROSTATIC SPRAYING OF PORCELAIN ENAMELS *

The application of the process of electrostatic spraying to the porcelain enamel industry is described. The equipment which is used and the method of using it are discussed in detail. Particular emphasis is placed on the preparation of enamel for electrostatic spraying and on theoretical considerations which have a direct bearing on the spraying process. The applicability and limitations on the use of the equipment in the porcelain enamel industry are considered.     

PROGRESS REPORT ON THE EFFECT OF FURNACE GASES ON THE QUALITY OF ENAMELS1

The appearance of sheet-steel enamels fired in atmopheres of nitrogen, carbon dioxide, sulphur dioxide, and Urbana city gas has been determined. A study of the effect of variations in the composition of sheet-steel ground coats and sheet-steel cover coats on their resistance to attack by sulphur gases has been made. Plans for future work on the problem are outlined.     

THE TEARING OF VITREOUS ENAMELS*

Similar to other enamel shop problems, tearing has not been reproducible under controlled conditions in the laboratory. Experiments show that tearing is caused by a cracking of the bisque before enamel fusion. To produce bisque cracking experimentally in the laboratory, a ground-coated cross-bend strip, 2 by 12 inches, was covered on one side with a coating of the test enamel. The enamel was dried, and before firing it was flexed to a predetermined degree in a Danielson-Lindemann cross-bending machine. The strip was fired, and the degree of tearing was studied. The effect of various factors, such as grinding fineness, application, clay, and other mill additions, in overcoming tearing difficulties was determined by this method. Certain materials which overcome tearing do not prevent bisque cracking but cause the cracked bisque to heal rather than break away during the firing process. Experimental results are given.     

ABRASION RESISTANCE OF PORCELAIN ENAMELS*

The abrasion resistances of enamels, differing in composition and properties, were determined by the test for resistance of porcelain enamels to surface abrasion (a standard of the Porcelain Enamel Institute, March, 1942). Four to five classes of abrasion resistance were obtained, but for the most part, the results fell within relatively narrow limits. Differences in abrasion index, in general, were not distinguishable by visual inspection. No one class or kind of enamel was superior. While changes in abrasion index were affected by changes in frit formula, it seems that many compositions will give comparable results.