The phenomenon of moisture expansion as related to structural clay products was studied to obtain information on the magnitude of expansion in commercial brick and to determine the phases in the &ed body which are responsible for the expansion. Many commercial brick were tested and analyzed, and the results were expanded by laboratory tests on specimens prepared from the crude clays. Pure kaolin specimens, with and without controlled additions of impurities, were employed to study the mechanism and causes of moisture expansion. Information was gathered to substantiate the theory of moisture expansion proposed by Smith in 1955. The results produced considerable doubt about the reliability of an accelerated autoclave test as a measure of moisture expansion under service conditions. At the end of this study, several factors came to light which would assist the brick manufacturer in producing a more stable product with respect to moisture expansion.

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in-weight determinations made in this study, if it was assumed that the same degree of volatilization took place on enameled iron. However, volatilization apparently did affect the gain-in-weight values of the coated stainless steel specimens that exhibited a small amount of oxidation.In the limited effort spent on studying the edge effect influence on gain-in-weight determinations a t high temperatures, no significant correlation was found between the area-to-perimeter ratio of the specimen and the gain in weight due to oxidation. The amount of the edge effect was not known quantitatively, but it was felt that it should be about the same on all 2-by 44x1. specimens that had the same enamel thickness.The difference in the oxidation rates of enameled and unenameled iron specimens was large a t 1600°F., less pronounced at 1700°F., and quite small a t 1850°F. This means that an enamel coating is appreciably more effective in preventing the oxidation of the iron a t 1600°F. than a t 1850°F. All bare or nickel-plated specimens oxidized quite rapidly a t the temperatures tested. I n general, the nickel-plated specimens oxidized more slowly than the bare specimens a t 1600"F., 1700"F., and 1850°F.The parabolic oxidation rate was investigated for enameled and unenameled specimens at 1850"F., 1700°F., and 1600°F. All specimens oxidized in a manner approaching the parabolic rate after each specimen had an initial oxidation period corresponding to approximately 0.20 gm. per sq. in. gain in weight. The oxidation of the specimens proceeded quite close to this parabolic relation until the limit of oxidation of the iron was apparently approached, or at about 0.75 gm. per sq. in. The oxidation of specimens approached a linear rate below 0.20 gm. per sq. in. Therefore, it has been indicated that between 1600" and 1850°F. enameled and unenameled specimens oxidized up to a weight gain of 0.20 gm. per sq. in. a t a linear rate and above this amount a t a parabolic rate. The oxidation rate, as the specimens approached the limit of oxidation, appeared to be an exponential relation between weight gain and time, owing to slower diffusion and to the conversion of the iron oxides present to higher oxides.The temperature dependence of the oxidation rate was shown for all specimens of bare and enameled iron and tompared with bare and mated stainless steel. The oxidation rate for enameled iron and coated stainless steel was affected more by a temperature change than were the bare metal specimens.Sandblasting before enameling slightly reduced the oxidation of iron a t 1700°F. and did not appreciably affect the amount of oxidation a t 1600°F. when compared with mechanical abrasion and chemical cleaning.The nickel plate under the porcelain enamel acted to decrease the amount of oxidation of the iron, at a selected time, as the amount of nickel plate increased up to 0.70 gm. per sq. ft. This reduction, however, was not very great when compared with the effect of the porcelain enamel and the variation in enamel thickness. Two coats of enamel, c3m...

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