An investigation of the fundamentals of the adherence of porcelain enamels to metals indicated that good adherence is the result of metal-tometal bonds between the atoms in the base metal and 'the proper metallic ions in the enamel. To accomplish this type of bond, the enamel must meet certain chemical and thermodynamic requirements: (1) The enamel at the inteuface must be saturated with an oxide of the metal and (2) this oxide must be one which, when in solution in the glass, will not be reduced by the metal. In the case of iron, the oxide is FeO. Many of the phenomena observed in commercial enameling were investigated and found to be related to adherence, but not essential for its development. An example is the precipitation of metallic particles in the enamel. Much of the complexity in commercial enameling arises from the limitations imposed by practical considerations. For example, because enamels usually are &ed in air, the heavy scale developed during the early stages of firing must be removed before adherence can be developed.Likewise, as the conditions of the enamel-metal interface change rapidly during flring, "adherence-promoting oxides" are used to help maintain the necessary conditions for the time required in commercial enameling. Surface roughness, although not necfor excellent adherence, was found to improve the apparent adherence when the bond between the enamel and the metal was relatively weak.

An extensive compilation of data on the free energy of formation of oxides is presented in graphic form. From these curves it is possible to obtain the free energy of most ceramic oxides in the temperature range 0' to 24OOOC. Methods for Estimating the Entropies of Oxides, Silicates, and Titanates, and the Prediction of Reaction Equilibria and Yields," J. A m . Ceram. SOC., 34 [12] 384-87 (1951).

Titanium Alloy Manufacturing Company for their helpful suggestions throughout the course of this work. They also wish to thank B. D. Bruce, ceramic engineering student the enamels. This investigation was financed by the Titanium Alloy Manufacturing Company of Niagara Falls, N. Y., and was conducted as a cooperative project in the Department of Ceramic Engineering under the auspices of the Engineering Experiment Station at the University of Illinois. ~~~~~~~~~o RNGINEERINC IJRBANA, ILLINOISType I1 enamels should dissolve a large quantity of 0pacifyin.g material during smelting, but at ,firing solubility so that the opacifier which has been dissolved will crystallize.The blue color of type I1 enamels is often caused by the presence of very fine particles. ABSTRACTThe solubility of zirconia at 1500" and at 2200°F. was determined for glasses containing NaZO, BzOa, A1208, and SiO,. The solubility at these same temperatures was also determined for glasses containing equal parts of boric oxide and silica and one or more of the following constituents in quantities of 10, 20, or 3070'0: ABSTRACT Phosphorus pentoxide, which was used first to improve the color of heavy flint glasses, was later recognized as a valuable constituent of optical glasses, and the excellent ultraviolet transmission and low softening points of phosphate glasses have been found recently. Glasses that have a high content of PSOS have poor chemical resistivity, but this drawback is largely overcome by the addition of alumina. A possible picture of the constitution of phosphate glasses is presented, and the effect of alumina is explained. Some of the properties of the phosphate glasses have been investigated and correlated with their chemical composition and structure.

It may be noted that the change in coordination number of boron from 3 to 4 indicated from an X-ray study of the borate glasses24 would predict the more rapid decrease in compressibility with increasing alkali content observed at low concentrations of alkalis. However, no crossing of compressibilitycomposition curves would be apparent from such an explanation. (5) Comparison of Expansivity and Compressibility DataExpansivity data and compressibility data are usually considered to yield similar information on interatomic forces. This interrelationship is open to question except for ideal gases.26 The fallacies encountered by assuming such a relationship for glasses are clearly shown by a comparison of the behavior of expansivities and compressibilities of the glasses. The alkali borates exhibit an expansivity with a well-defined minimum in the composition range 0 to 30The compressibilities on the other hand uniformly decrease with increasing RzO content and a t the maximum concentration have dropped by at least one half. For the alkali silicates a uniform twofold increase in expansivity occurs with increased alkali ont tent.^(^) The compressibility, however, exhibits a very minor uniform decrease over the same range of compositions. The compressibility data on the silicates may involve a maximum for at least one alkali and some curvatures at low composition, but the expansivity data appear to extrapolate smoothly to the L4 (a) J. Biscoe and B. E. Warren, "X-Ray Diffraction Study of Soda-Boric Oxide Glass," J . A m . Cerum. SOC., 21 [8] 287-93 (1938). (b) R. L. Green, "X-Ray Diffraction and Physical Properties of Potassium Borate Glasses," ibid., 25 [3] 83-89 (February 1, 1942). 16 P. W. Bridgman, Physics of High Pressure, Chapter V. G. Bell and Sons, Ltd., London, 1949. 445 pp.value for vitreous SiOz. One apparent explanation for the discrepancies between dependence of compressibility and expansivity data on alkali content lies in the fact that in isobaric expansion the thermal energy introduced may be distributed among many degrees of freedom.*& A glass will possess many different types of degrees of freedom and it is a very questionable assumption that all degrees of freedom, even granting equipartition of energy, affect the volume in a uniform m p n e r . On isothermal compression, however, the molecules are forcibly displaced to new positions, potential energies are directly involved, and the thermal energy is not varied from external causes. On isothermal compression, the internal energy initially decreases, since more heat is liberated than required by the PAV work performed, but ultimately it increases on continued compression. This apparent anomaly can be accounted for on the basis of potential energie~.~5 Bridgman25 discusses this question in some detail in considering the pressure coefficient and concludes, in essence, that when pressure does not arise from purely kinetic sources (as in all condensed phases), expansivity and compressibility are not, in general, manifestations of equivalent phenomena, It ...

large portion of the nickel consumed by the ceramic industry is supplied in the form of oxides or sulfates. The utility of these compounds is based on a relatively small number of their inherent properties. One of the first of these is the ability of nickel oxide to absorb light selectively, as, for example, when the oxide is used to produce a colored glass or a colored pigment. A second use of nickel depends upon the ease with which nickel can be replaced by iron, as in a plating solution. The use of nickel in porcelain enamel ground coat compositions is dependent upon the ability of nickel to promote the adherence of the enamel to iron and upon the effect of nickel on the viscous properties of. the enamel. Nickel oxide is used in ferrite-type compositions as a means of improving the magnetic and electrical properties of these materials. The use of metallic nickel in the ceramic industry is due mostly to the properties obtained in nickel-bearing alloys. Such materials owe their utility to such qualities as good oxidation resistance, high fusion temperature, and good corrosion resistance. Their use in thermocouples is dependent upon their high thermoelectric power, which is also proportional to the temperature to which the couple is exposed. The various uses in the ceramic industry of nickel and nickel compounds are discussed in some detail. Most of the discussion concerns ceramic products in which nickel compounds form some part of the composition. In addition, a brief review is given of the use of nickel in equipment for the production of ceramic products.