Effect of Oxygen Content of Furnace Atmosphere on Adherence of Vitreous Coatings to Iron

Abstract

A series of porcelain enamel ground coats of the same basic composition but with various amounts of cobalt oxide was fired on enameling iron in atmospheres consisting of various oxygen‐nitrogen mixtures. The effect of the oxygen content of the atmosphere on adherence was determined and the effect on interface roughness was estimated from an examination of metallographic cross sections. A decrease in the amount of oxygen in the firing atmosphere necessitated an increase in the amount of cobalt oxide in the enamel if optimum adherence was to be secured. Ground coats containing 3.2% cobalt oxide or more developed a weak but definite bond in oxygen concentrations as low as 0.02 mole %. A qualitative correlation was found between adherence and surface roughness regardless of the oxygen content of the firing atmosphere.