Kinetic studies have been made of the oxidation of zirconium diboride at 945~176 and of zirconium carbide at 554~176 The ZrB2-O2 reaction is parabolic throughout the temperature range studied, whereas the ZrC-O2 reaction is linear. In the former case ZrO2, together with a molten layer of boron oxide, is formed which protects against further direct attack of oxygen on the ZrB2, while in the latter, a rather porous film of zirconium oxide is formed which is not protective. The rate of oxidation of ZrB2 is directly proportional to the oxygen partial pressure between 102 and 744 ram.

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The preparation and characterization of Hong and von Alpen types of Nasicons are described. When highly reactive gelprocessed powders are heated at about lOOO"C, Nasicons are formed in a finely divided state. Sintering of compacts requires 1125" to 1325"C, depending on the composition. Observed sintering kinetics suggest a liquid-phase mechanism; SEM reveals the Hong Nasicons to contain two (when zirconia-free) or three phases. The von Alpen materials are zirconia-free, but consist of two phases. A glass phase is common to both materials, and its presence is attributed to the liquid-phase sintering mechanism.

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