The effects of the kinetics of reactions of the type solid -» solid + gas on the corresponding differential thermal analysis pattern are explored.

In differential thermal analysis, the temperature at which the maximum deflection is observed varies with heating rate for certain types of reactions. An expression can be derived relating this variation with the kinetics of the reaction. By making a number of differential thermal patterns at different heating rates, the kinetic constants can be obtained directly from the differential thermal data.Measurements of the variation of peak temperature with heating rate have been made for several minerals of the kaolin group, the values of the kinetic constants determined, and these values compared with corresponding values obtained for both the same samples and similar material by conventional isothermal techniques. Some factors affecting the results are discussed.

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strengths were determined on 276 brick. Exposure of 271 brick to natural weather for 5 years resulted in 214 brick passing (unaffected or slight spalls not exceeding 1 sq. in.) and 52 failing (larger spalls through partial to complete disintegration),The following conclusions appear to be justified from the analysis of the data:(1) Of the 14 samples of deaired shale and fire-clay brick considered in this paper, 12 samples did not significantly differ in their relations among water absorptions by 5-hour boiling, saturation coefficients, and compressive strengths from nondeaired shale and fire-clay brick in the Same range of maturity. The data on two samples were anomalous in that very low absorptions were associated in whole or in part with high saturation coefficients. (3) Of 148 brick habing absorptions by 5-hour boiling not exceeding S.O%, 2 failed. The proportion of failures increased with increasing absorptions. Of 57 brick with absorptions exceeding l2.0%, 35 failed.With the exception of the two samples teferred to in the statement above, high saturation coefficients were, in (2) (4) general, associated with poor weathering resistance and low saturation coefficients with good weathering resistance.(5) In general, the higher the associated compressive strength, the better was the resistance to weathering. The minimum compressive strength indicating satisfactory resistance to weathering varied, however, from sample to sample.For some brick, intermediate weathering durability (between "no effect" and complete disintegration) appeared to be associated with excessive lamination or nonhomogeneous structure.The durability gradings given in A.S.T.M. Specification C G2 for building brick and C 216 for facing brick, when used with a modified waiver clause (acceptance into the top (SW) grade for brick not exceeding 8.0% in absorption by 5-hour boiling irrespective of saturation coefficients), reasonably predicted the durability of the deaired brick considered in this investigation.For samples of deaired brick reported in this paper, no significant differences in properties or behavior were observed in comparison with those described earlier for nondeaired brick made from similar raw materials and by the stiff-mud method of manufacture.The mechanism of decomposition of manganous sad ferrous carbonates has been explored by high-temperature X-ray diffraction in controlled atmospheres, by differential thermal analysis, and by thermogravimetric analysis. The heat effects of the series of reactions which occur are calculated from thermochemical data. The heat effects observed in merentid thermal analysis agree reasonably well with the calculated heats of the proposed reactions. The manner in which the techniques used in obtaining differential thermal andpis patterns may af€ect the results is discussed.

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