High-temperature oxidation of ZrB₂–SiC–La₂O₃ ceramic material produced via spark plasma sintering

Abstract

The study investigated the influence of La2O3 addition on the oxidation properties of composite ceramics with a composition of 80 vol. % ZrB2 and 20 vol. % SiC. The source materials utilized in this study included zirconium diboride (DPTP Vega LLC., Russia), grade 63C silicon carbide (Volzhsky Abrasive Works JSC, Russia), and lanthanum hydroxide concentrate (Solikamsk Magnesium Plant JSC, Russia), with the following elemental content (wt. %): La – 54.2, Nd – 4.3, Pr – 2.8, and trace amounts of other elements (<0.1). The La2O3 content in the charge varied between 0, 2 and 5 vol. %. The powders were mixed in a planetary mill with ethyl alcohol as the medium for 2 h, using a grinding media to powder ratio of 3:1. Consolidation of the powders was achieved through spark plasma sintering at 1700 °С, applying a pressing pressure of 30 MPa. The heating rate was 50 °С/min, and the isothermal holding time was 5 min. Oxidation was carried out in air at 1200 °С and the total oxidation time was 20 h. Oxidation experiments were conducted in air at 1200 °С, with a total oxidation time of 20 h. It was observed that the most significant weight gain occurred within the first 2–4 h of testing. Specimens containing 5 vol. % La2O3 exhibited the smallest weight gain after 20 h of exposure. Regardless of the presence of La2O3 , silicon carbide was found to be the first material to undergo oxidation. In specimens without La2O3 addition, the oxidized layer mainly consisted of silicon monoxide and dioxide. In contrast, specimens with La2O3 exhibited a predominantly oxidized layer composed of ZrSiO4 and ZrO2 . The study revealed that the introduction of La2O3 intensified the formation of zircon, which subsequently slowed down the oxidation processes in the material.