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HE data presented by these authors are valuable in showing the formation of certain compounds, in identifiable amounts, during the reactions of the cement minerals with water in pastes. The writer42 has pointed out that the reactions of the cement minerals with water are almost certainly solid-liquid reactions in which the solids react with water, without first going into solution, to form solid reaction products; i.e., product solids. These product solids tend to dissolve in water to form solutions from which either stable or metastable products crystallize. For example, the product solids formed by the solid-liquid reaction of CaA and CIS with water tend to dissolve and yield a solution containing the equivalent of CaO, Algol, and SiO2. It is readily understandable that the compound C3AHs containing some silica could crystallize from such a solution. A similar solution would

Dense compacts of mixtures of Tic, Sic, and B,C were prepared by sintering in an argon atmosphere and by hot pressing. Titanium carbide and B4C reacted during heating to form TiB2. The oxidation resistances of these ternary compacts were determined by the weight gained at 2000OF. in air. Compacts containing 10% B4C, 70 to 50% Tic, and the remainder Sic had superior oxidation resistances. The oxide coating on these compositions consisted of rutile, silica, and a n amorphous third phase. A compact composed of 73.5% Tic, 17% silicon, a n d 9.5% boronwas hot-pressed. It had zero porosity and better oxidation resistance than any other composition tested.

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