Effect of the Machining Method on the Catalycity and Emissivity of ZrB ₂ and ZrB ₂ –HfB ₂ ‐Based Ceramics

Abstract

The emissivity and the catalytic efficiency related to atomic oxygen recombination were investigated experimentally in the range 1000–2000 K for ZrB 2 and ZrB 2 –HfB 2 ‐based ceramics. In order to evaluate the effect of the machining method, two series of samples, one prepared by electrical discharge machining and the other machined by diamond‐loaded tools, were tested. High emissivity (about 0.7 at 1700 K) and low recombination coefficients (on average 0.08 at 1800 K) were found for all the materials. The experimental data showed an effect of the surface machining on the catalytic behavior only on the ZrB 2 ‐based composite; conversely, small variations were found in the recombination coefficients of ZrB 2 –HfB 2 ‐based samples for the different machining processes. The surface finish affected the emissivity at lower temperatures in both compositions, with the effect becoming negligible at temperatures above 1500 K.