Chakraborty, Shirshendu and Das, Probal Kumar and Ghosh, Dinabandhu
(2019)
Thermodynamics of the oxidation of ZrB2-TiB2, ZrB2-SiC and ZrB2-B4C ceramics.
Bulletin of Materials Science, 42 (5).
Art No-UNSP 245.
ISSN 0250-4707
Abstract
The thermodynamics of the oxidation of three-high temperature ZrB2-based ceramics (ZrB2-TiB2, ZrB2-SiC and ZrB2-B4C) has been studied in order to find the stability domain of zirconium diboride, in terms of temperature, partial pressure of oxygen and composition, in which it is protected against oxidation. In the case of the ZrB2-TiB2 binary system, a plot of log pO2vs. 1/T in the temperature range of 500-2000 K and another plot of pO2 (x1014) vs.xTiB2 for T=2000 K are made taking into account the two-extreme possibilities of no solubility and 100% solid solubility between ZrB2 and TiB2, respectively. A plot of log pCOvs. log pO2 is made for 1773 K for the systems ZrB2-SiC and ZrB2-B4C. It was found that the ZrB2-TiB2 ceramics does not have sufficient oxidation resistance in the temperature range of 500-2000 K. ZrB2 of ZrB2-SiC ceramics can be protected under 1 atmosphere oxygen or in air if the liquid borosilicate (with the chosen composition, 70% B2O3-30% SiO2), which is an intermediate product, provides a kinetic barrier to the continuation of oxidation by forming an impervious layer on the exposed surfaces. In contrast, the ZrB2-B4C ceramics does not produce the borosilicate upon oxidation. In view of the volatility of pure liquid B2O3, it is recommended that the ZrB2-B4C ceramics can be used at a lower temperature, perhaps below 1373 K, when the vapour pressure of B2O3 is significantly small.
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