FUNDAMENTAL PROPERTIES OF SOLUBLE SALTS IN ENAMEL MILL LIQUORS *

This paper is a summary of the present basic information concerning the individual chemical, physical, and pyrochemical characteristics of the possible, more common soluble constituents present in porcelain enamel slips. The data were chosen with particular regard to their importance in the study of the nature and effect of the various soluble salts on properties of enamel slips and on their drying behavior.     

PROPERTIES OF ENAMEL SLIPS: II,SOLUBLE SALTS IN ENAMEL SLIPS*

This paper contains data on the soluble salts to be found in mill liquors obtained on milling a number of different commercial porcelain-enamel frits. The change in soluble salts on aging the enamel slips and the variation in pickup was also investigated. The mill liquors were found to contain chiefly Na₂O, B₂O₃, and NaF. The effect of various proportions of these salts was studied by adding NaOH, Na₂B₄O₇. 10H₂O, and NaF to a slip composed of clay, water, and fine-ground quartz. The correlation of the various data is discussed     

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.     

OPACIFYING EFFECT OF SOME FLUORIDES IN ENAMEL MILL ADDITIONS1

This paper describes the results of a study of the effect of barium fluoride and zinc fluoride on enamels when added in the mill. These fluorides were used with high silica, high borax, high lead oxide, and high antimony oxide enamels. The effect of these fluorides upon opacity and the creation of such defects as crawling and crazing are shown by triaxial diagrams and photographs.     

EFFECT OF ENAMEL ON THE STRENGTH OF ENAMELING IRON*

Ground-coat enamel was first applied on one side and then on each side of 26-, 20-, 18-, 10-, and 6-gauge enameling stock, and the strengths of the pieces were determined in cross bending. The results show a decided increase in strength for the enameled specimens over that of the stock before enameling. An increase in the thickness of the enamel also increases the strength within limits. The effect on the lighter gauges is greater than on the heavy gauges, and the strength is greater when the enamel is under compression than under tension.     

DETERMINATION OF COMPRESSIVE STRESS PRESENT IN PORCELAIN ENAMEL ON SHEET IRON*

A method for determining comparative compressive stress produced in porcelain enamel on sheet iron is described. The method consists of preparation of laboratory samples under carefully selected and controlled conditions and measurement of the warpage produced in the sample due to application of enamel on one side. Data obtained by the above method are compared with expansion curves. Several methods of analyzing the curves fail to produce correlation between expansion as determined on frit samples and compression in the porcelain enamel as indicated by the warp of sample plates. It is concluded that expansion curves on frit samples are not a satisfactory means of evaluating compressive stress in the porcelain enamel coating on sheet iron.     

NOTE ON THE SOLUBILITY OF ENAMEL FRIT IN MILL WATER1

Methods of determining the solubility of enamel frit in mill water are outlined. Various tests tried show that (1) solution increases as fineness increases, (2) mixing has little or no effect upon solubility, (3) variation of smelter treatment has little or no effect upon solubility, and (4) Na₂O and B₂O₃ will dissolve from dry ground frit proportionately to the fineness thereof.     

SOLUBLE SALTS AND CLAY WARES*

A résumé of the present knowledge of the causes and the prevention of “Scum” and “Efflorescence.” It is proposed that the term “Efflorescence” be restricted to designate the surface deposits appearing because of the presence of soluble salts in the clays or burned wares and that the term “Scum” be used to describe the salts formed by the action of gases upon the wares during the drying or burning operations. Mention is made of the formation of a surface coating upon the ware soon after the kiln is opened, sometimes not appearing until some days after the ware is removed from the kiln. This scum is readily and permanently removed by the application of water. Such a residue was found to consist of sodium sulfate and sodium chloride. It is suggested that its formation was due to the presence of sodium chloride in the fuel and its subsequent deposition on the burned ware where it was changed in part to the sulfate by the action of the oxides of sulfur evolved from the fuel.     

EFFECTS OF VARIOUS CLAYS USED IN MILL ADDITIONS ON PROPERTIES OF A TITANIA-OPACIFIED ENAMEL*

In the course of investigations made in connection with the development of titania-opacified enamels, it was observed that color, reflectance, and acid resistance were influenced by the clay used in the mill additions. In a subsequent search for a clay which would produce the best over-all enamel properties, a study of the effects of twenty clays of different types was made under standardized conditions of milling, spraying, and firing. Coatings sprayed at 30 gm. per sq. ft. were examined for bisque strength, brushing behavior, and tearing. After firing for 3 minutes at 1540°F., and at 1640°F., the reflectance, color, gloss, and acid resistance of the enamels were observed. It has been concluded that the success or failure of an enamel is determined to an important degree by the clay used in the mill addition.     

THE RELATION OF DEFECTS IN ENAMEL COATINGS TO HYDROGEN IN STEEL*

The effects of hydrogen as functions of time, temperature, and impurities in steel are described and experimentally demonstrated. Experimental evidence is presented to show that the blistering and boiling action over carbide areas in steel are due principally to hydrogen that associates with the carbon. Steel enameling stock contains quantities of hydrogen which may effuse during firing to cause or aggravate such phenomena as “boiling,”“primary boiling,”“rebelling,”“blistering,” and “bubbling.” Low-temperature effusion of hydrogen contributes to other defects, including “fishscaling,”“delayed fishscaling,” and possibly “pop-offs,”“jumping,”“shiners,” and some cases of “chipping” and, perhaps, “bursting” of enamel on cooking utensils. These defects have seldom been identified with hydrogen evolution. An indirect effect of hydrogen on “copperheads” and “black specks” is also identified. An exhaustive review of both English and German literature on enameling defects is included. Many observations recorded in the literature are shown to agree with the hydrogen theory. Certain types of inclusions in steel are shown to react with occluded hydrogen to form compounds that will not dissociate appreciably at some enamel-firing temperatures, and critical quantities of the hydrogen are therefore prevented from reaching the enamel coating during firing to cause blistering and related defects.     

THE BLISTERING OF CAST IRON ENAMEL*

This Progress Report II is a continuation of the report presented before the Enamel Division in 1932. The subjects discussed are (1) gases from metal, (2) possible reaction between enamel and iron, and (3) gases from the enamel itself. The author concludes in this report that nothing has developed which is inconsistent with the facts summarized in the 1932 report.     

EFFECT OF COMPOSITION AND TEMPERATURE ON SOLUBILITY OF IRON OXIDE IN GROUND-COAT ENAMEL GLASS*

The solubility of iron oxide in ground-coat enamel glasses at various temperatures was studied by adding varying amounts of ferric oxide to the milled enamel and giving the mixture a heat-treatment to acquire uniformity without devitrification at the desired temperature. The iron oxide solubility was obtained by finding the breaking point in the curve for iron oxide versus index of refraction. The frit solubilities were obtained at 1400°, 1600°, 1800°, and 2000°F. with variations in Na₂O, B₂O₃, A1₂O₃, CaF₂, CaO, F₂, SiO₂, COO, NiO, MnO₂, BaO, and MoO₃. Data are given on a number of commercial frits.     

MICROSCOPIC TECHNIQUE IN THE INVESTIGATION OF ENAMEL COATING AND SOME OBSERVATIONS*

The polishing equipment and the technique of polishing specimens of vitreous enameled metal are described. A discussion is given of the characteristics of various enamel defects which are illustrated by photomicrographs.     

THE EFFECT OF FURNACE ATMOSPHERE ON THE FIRING OF ENAMEL1

It is shown that in firing ground coat and other one coat enamels, the atmosphere of the furnace plays an important part. Oxygen in the muffle penetrates the enamel during the early stages of the firing forming a film of iron oxide on the surface of the steel. This film, whether applied before enameling or formed incidentally to firing, partially dissolves in the fused enamel giving the intimate bond between metal and enamel. Ground coat enamel fired in an atmosphere of nitrogen was found not to adhere to the steel. Approximate values are given for the proportion of furnace space to enameled surface to insure sufficient oxidation when residual air is depended upon to supply the oxygen.     

EFFECT OF RESIDUAL COLOR ON CONSUMER ACCEPTANCE OF PORCELAIN ENAMEL WHITES*

Reflectometers are widely used to give a numerical rating for the comparative whiteness of porcelain enamels, but these instruments occasionally show values in disagreement with a careful visual comparison. To find the reason for this disagreement, a survey was made to determine the effect of residual color on the consumer rating of porcelain enamel whites. A series of 12 white plaques was made ranging from 67 to 75% in reflectance, from 478 to 485 m/x in dominant wave length, and from 1.6 to 5.6% in residual color. These specifications were determined from curves run on a Hardy G. E. recording spectrophotometer. The 12 plaques were submitted to 36 persons who arranged them in order of whiteness. The order of arrangement was compared statistically, and the whites were rated in their order of acceptance. Residual color was found to have an important effect on apparent whiteness, and of these typical porcelain enamel whites, those most highly colored (blue) were preferred.     

STUDY OF THE PROPERTIES OF SIMPLE ENAMEL GLASSES1

Three component glasses of the systems Na₂–B₂O₃–SiO₂ and Na₂O–PbO–SiO₂ were investigated as to acid-resisting properties. An increase in silica in general improves the acid resistance. The effect of Na₂O, B₂O₃, and PbO on the acid resistance of an enamel is dependent on the composition to which these oxides are added. Some of these enamels showed considerable promise as acid-proof enamels.     

乙醇-水-盐体系汽液平衡

用改进的Ｏｔｈｍｅｒ汽液平衡釜在０．１０１３ＭＰａ下测定了乙醇水氯化钙、醋酸钾体系在恒盐摩尔分率下的汽液平衡数据。用Ｆｕｒｔｅｒ方程、修正的Ｆｕｒｔｅｒ方程、拟二元模型及溶剂化模型对实验数据进行关联，取得良好结果，其中乙醇水氯化钙体系实验数据用修正的Ｆｕｒｔｅｒ方程关联，所得汽相平均偏差为０．０１２４。     

EFFECT OF CONDUCTING WALLS ON THE DISPERSION OF SOLUBLE MATTER IN MHD CHANNEL FLOW

An exact analysis of the dispersion of a solute in an incompressible electrically conducting fluid flowing between two electrically conducting parallel plates permeated by a transverse magnetic field is presented in this paper. A generalized dispersion model which is valid for all time has been used. It is found that for fixed Hartmann number M, the time dependent dispersion co-efficient K₂(τ) decreases with increase in the wall conductivity parameter φ. It is also found that the dispersion co-efficient remains unaltered if the two walls are interchanged.     

A MECHANISM OF BLACK SPECK FORMATION IN ENAMEL RESULTING FROM REBOILING OF THE GROUND COAT*

Experimental and microscopic evidence is given to show that rebolling of a ground coat results from a fracture when refiring the ground-coat enamel. Air fills the cracks and connected bubbles. The cracks are sealed over and there is an expansion of the bubbles downward toward the base metal into the oxide layer. No evidence has been found which indicates that reboiling is caused by evolution of gas from the metal.