Oxidation resistance of ZrB₂‐based monoliths using polymer‐derived Si(Zr,B)CN as sintering aid

Abstract

The focus of the present work is the investigation of the influence of polymer‐derived ceramics, used as sintering aids for preparing ZrB2‐based monoliths, on their high‐temperature oxidation behavior. For the preparation of the monoliths, ZrB2 powder was coated with polymer‐derived SiCN, SiZrCN, or SiZrBCN and subsequently densified via hot‐pressing at temperatures as low as 1800°C. To investigate the oxidation kinetics, thermogravimetric analysis (TGA) was performed at 1300°C in synthetic air with exposure times of 50 and 100 h. A detailed study of the materials oxide scale and subsurface microstructure was conducted using optical microscopy, electron probe microanalysis, scanning electron microscopy, and X‐ray diffraction. The experimental findings were compared to thermodynamic equilibrium calculations using the CALPHAD method, which led to a better understanding of the oxidation mechanism. In comparison to the literature data of ZrB2–SiC, the results show improved oxidation resistance for all three investigated materials. The formation of gaseous species during oxidation, in particular CO, CO2, B2O3, and SiO, within the oxide scale of the monoliths was rationalized via CALPHAD calculations and used to explain the oxidation behavior and kinetics and also the formation of bubbles in the subsurface region of the oxidized specimens.

Energetics and structure of SiC(N)(O) polymer‐derived ceramics

“…Thus, much systematic work still remains to be done. Future investigations require more thermodynamic measurements and perhaps the use of softwares like CALPHAD to compare with experimental data and predict thermodynamic properties of multicomponent PDC systems 100,101 …”

Oxidation Behaviors of ZrB2–SiC Ceramics with Different Porosity

“…By adding the second‐phase SiC, the oxidation resistance of ZrB 2 ‐based ceramics will be further improved beyond 1200 °C, due to that the borosilicate glassy layer formed by the SiO 2 –B 2 O 3 mixture can flow and fill the pores and cracks, which can effectively prevent the ceramic substrate from oxidizing oxidation. [ 14,15,20,21 ] In detail, the oxidation of ZrB 2 ‐SiC ceramics can be negligible below 800 °C which can be confirmed by thermogravimetric analysis of SiC and ZrB 2 powders, and ZrB 2 –SiC ceramics. [ 22–24 ] When the oxidation temperature is between 800 and 1200 °C, the oxidation rate of ZrB 2 is more rapid than that of SiC.…”

Oxidation response of ZrB2–SiC–ZrC composites prepared by spark plasma sintering

“…For example, ZrB 2 transforms into ZrO 2 and B 2 O 3 at temperatures above 800 °C [21,22], SiC into SiO 2 and CO at temperatures above 900 °C [23,24], and ZrC into ZrO 2 and CO at temperatures above 450 °C [13,25]. Therefore, by placing the ZrB 2 -SiC-ZrC composites in oxidation conditions at 1400 °C, the following chemical reactions are expected: The formation of the SiO 2 oxide layer causes the consumption of silicon in the lower layer and hence a Si-depleted zone appears [26][27][28]. The formed SiO 2 oxide phase creates a sticky glass layer that increases the oxidation resistance [29][30][31].…”