DIELECTRIC PROPERTIES OF GLASSES AT ULTRA-HIGH FREQUENCIES AND THEIR RELATION TO COMPOSITION *

The dielectric constants and dielectric losses of 104 glasses of a wide range of compositions have been measured at 10-cm. and 3-cm. wave lengths by the resonating cavity method (3000 and 10,000 megacycles, respectively). By correlating the power-factor data with the compositions of these glasses, the authors propose a qualitative explanation of the mechanisms producing energy absorption and dielectric losses in the microwave range. These mechanisms are determined by the nature of the bonds joining atoms and ions in the randomly oriented atomic networks of glasses. The rigid and continuous networks of SiO₂ and B₂O₃ glasses are relatively transparent to centimeter wave lengths. Energy absorption and dielectric losses are low. Addition of network-modifying oxides yields glasses of greater energy absorption owing to the oscillation of the interstitial ions thus introduced. Increasing the content of any one of these ions in a glass results in higher losses while the coexistence of a variety of these ions generally results in lower losses. Alkali ions in glasses give rise to high losses, which increase as the number of ions present increases. Glasses containing a combination of alkalis show lower losses than the equivalent compositions with only one alkali. Divalent ions do not contribute as much to losses as alkalis, but high power factors are shown by glasses with high BaO or PbO contents. Using combinations of these oxides instead of only one, slight reductions in power factor are effected. Dissimilar interstitial ions interact in ultra-high frequency fields with the result that energy absorption is reduced. The losses of high-lead glasses are thus reduced by alkalis and, on the other hand, the presence of RO lowers the losses of glasses containing R₂O. Alumina increases the dielectric losses of glasses in much the same manner as other network modifiers.     

APPLICATION OF GARDNER MOBILOMETER TO ENAMEL SLIP CONSISTENCY STUDIES AND CONTROLS*

A brief review of the type of instrument used by previous investigators is given. The Gardner mobilometer is described and its application to enamel-slip consistency problems and control is discussed.     

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.     

NICKEL FLASHING AND ITS RELATION TO ENAMEL ADHERENCE*

Nickel flashing as applied to enameling stock is shown to be primarily metallic nickel. The role of nickel in developing enamel adherence is apparently bound up with the retardation of oxidation which the nickel flash imparts in the enameling cycle. The problem of adherence may be considered to be a corrosion phenomenon of the base iron developed by the action of gases and other agents which may be present at enameling temperatures. As such, the degree of adherence is a function of oxygen pressure at the interface when the glass is fused. The equilibria developed are strongly affected by the presence of nickel. Using cover coats directly on iron, the amount of nickel required will vary with each particular enamel composition. Şome evidence as to the nature of the adherence-promoting oxide is presented.     

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.     

RELATION OF THICKNESS TO IMPACT RESISTANCE OF PORCELAIN ENAMEL*

Chipping of porcelain enamel on the flanges of table tops as a result of impact was studied and compared with the results obtained from the Porcelain Enamel Institute tentative standard impact test. A correlation was found to exist between the results using the P.E.I, test on standard 1-in. tubes and those obtained on the corner of a table-top flange. The impact resistance of enamels applied over a radius also increased as the thickness of the enamel was increased.     

RELATION OF METAL THICKNESS,ENAMEL THICKNESS,AND BOTTOM RADIUS TO IMPACT RESISTANCE OF PORCELAIN ENAMELED UTENSILS*

Three series of standard two-quart pudding pans of different metal thicknesses, coated with one, two, and three coats, respectively, of enamel were tested for impact resistance, using the Enameled Utensil Manufacturers' Council standard impact test. The impact resistance of the pans was increased with increase (1) in metal thickness of the pans, (2) of the enamel thickness, and (3) in the size of the bottom radius. The size of the chip formed on impact also increased with increase in enamel thickness. The literature dealing with the fracture of glass and enamels is reviewed, and the factors influencing spontaneous chipping and chipping caused by bending and impact are discussed.     

RELATION OF ELECTRICAL CONDUCTIVITY TO CHEMICAL COMPOSITION OF GLASS*

The electrical conductivity of some glasses in the soda-lime-silica system was measured at 400 °C. with an apparatus which is described. The specific resistance at this temperature ranged from 0.06 to 5.0 × 10⁵ ohms per cc. Measurements were made on other glasses containing equivalent amounts of various oxides incorporated in a parent soda-lime-silica glass. It was found that an increase in resistance was produced by additions of MnO, ZnO, B₂O₃, Fe₂O₃, BaO, PbO, TiO₂, and K₂O, the resistances increasing in this order. A decreased resistance was produced by Na₂O, CaO, and Al₂O₃. Previously published data on the power factors of these glasses are reviewed.     

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.     

REVIEW OF THE RELATION OF DENSITY AND REFRACTIVE INDEX TO THE COMPOSITION OF GLASS: I *

The density, refractive index, and specific refractivity and their relationship to the composition of glass are discussed. The subject is treated from the standpoint of additive properties based on composition both as to linear and collective or complex functions. Not only are these applied in the rapid checking of constancy of composition in practice but also from the standpoint of possible changes in properties through partial changes of individual components. There is the further possibility of tying up constitution with composition so that a structural analysis may result. The article serves as a review of existing literature and elaborates the possibility of expansion of published data.     

RELATION OF THE PARTICLE SIZES OF THE FRIT AND COLOR OXIDES TO THE COLOR PROPERTIES OF PORCELAIN ENAMELS*

The effect of variations in the particle size of typical green and blue color stains in sized fractions of a representative clear frit was studied. Microscopic examinations were made of the sized fractions, and photomicrographs of the respective fields are presented. The color characteristics of the enameled panels were determined on a continuously recording spectrophotometer. Frit particles of 45 to 75 μ, combined with color particles of less than 5μ, were found to give the optimum or most efficient color characteristics, and color particles larger than 5 μ, seriously impaired the resulting color.     

SOLUBILITY OF A ZIRCONIUM OXIDE OPACIFIER IN ENAMEL GLASSES*

The solubility of a zirconium oxide opacifier was determined by fusion in enamel glasses and then by heat-treating at enameling temperatures and noting the amount of crystallization. An increase in the alumina, zinc oxide, and calcium oxide content in the glasses caused a decided decrease in the solubility of the zirconium oxide opacifier. The fusion temperatures of the enamels were raised by solution of zirconium oxide.     

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     

PROPERTIES OF ENAMEL SLIPS: I,GENERAL PROPERTIES OF CLAYS AND ENAMEL SLIPS*

Five clays used to suspend porcelain enamels and their properties were studied. Fundamental data were first obtained on the clays, which were then milled in different proportions with several types of porcelain enamel frits. The properties of the resulting slips were studied. The pickup weight, that is, the amount of enamel retained on a ground-coated plaque which had been dipped in the slip and allowed to drain, was used as a basis of comparison.     

RELATION OF PARTICLE SIZE AND CHARACTERISTICS OF LIGHT REFLECTED FROM PORCELAIN ENAMEL SURFACES*

Various opacifiers were added in increasing percentages to clear, regular white, very opaque white, and acid-resisting enamels. These were ground to various degrees of fineness from coarse down to a few microns or finer; they were applied to sample plates and their reflectances were measured. Increased opacity is obtained by extremely fine milling because of the excellent dispersion of the opacifiers.     

SOME RELATIONS OF COMPOSITION TO SOLUBILITY OF ENAMELS IN ACIDES1

Review of literature.—The literature on acid resisting enamels and glasses is reviewed. Acid resisting powers produced by different oxides.—When substituted one for another, in each case in equal percentage amounts, various oxides and minerals increased the resistance of various enamels to the action of boiling 20 per cent hydrochloric acid in the following order of effectiveness: Al₂O₃, cryolite, Na₂O, PbO, BaO, Li₂O, MgO, CaF₂, ZnO, SrO, CaO, B₂O₃. The first five mentioned were especially effective. The remainder are undesirable materials from the standpoint of acid resistance. Effect of the enamel base.—The relative effects of the materials were the same for various base enamel compositions. Effect of ZrO₂ and TiO₂. —ZrO₂ and TiO₂, when substituted for small amounts of SiO₂, increased the resistance of various enamels to attack by acids, ZrO₂ being most effective in this respect. The favorable action of ZrO₂, is offset by a tendency to produce excessive chipping. Rutile gives less chipping than either zirconia or silica and greater acid resistance than silica. Best compositions.—Enamels 2,17,19,26,27, and 33 of table 1 showed resistance to action of the acid equivalent to that of the original competitions based on the analysis of a French acid-resisting enamel. By use of the data developed in this investigation other highly acid-resisting compositions can readily be formulated.     

RELATION OF SURFACE OXIDATION TO CERTAIN DEFECTS IN ENAMEL COATINGS ON STEEL, III

Oxide on the surface of enameling stock is found to play an important part in controlling the occurrence of hydrogen-caused defects. Actually, steel with a preformed oxide coating of certain characteristics may be fired directly with a white cover coat without incurring fish scaling, copperheading, blistering, or reboiling. The oxidizing treatment probably removes some of the inherent hydrogen from the stock and then prevents subsequent absorption during firing from the reaction of iron with moisture which remains in the dried enamel coating. The advantages of preoxidation are discussed. All other gases that may evolve from the enamels pass through the enamel without causing defacement. The primary boil simultaneously oxidizes and hydrogenizes the steel; and the pickup of hydrogen, which occurs during firing, is often the portion responsible for subsequent fish scaling and reboiling.     

MECHANICS OF ENAMEL ADHERENCE,IV-VII*

Sheet-steel enamels with varying amounts of cobalt, nickel, and manganese oxides were applied to cast iron. Their impact resistance was determined and a study of contact zones was made.