High-Temperature Oxidation and Corrosion of Engineering Ceramics

Abstract

The problems of high-temperature oxidation and corrosion of Si3N4 and SiC are discussed. Other ceramics usually do not meet the requirements of structural applications at high temperatures. If the application has to meet very defined limits of size change, it is necessary to specify the exact material composition, as well as the atmosphere composition and physical environment to be able to specify the limits. This is in any case true for extremely reducing conditions or very high temperatures. Under oxidizing conditions, the region between ≈850 and 1100°C should be avoided when salty, sulfurous, and wet fuel conditions are expected. High temperature limits for long-time applications of Si3N4 in oxidizing environments are between 1200 and 1400°C, corresponding to eutectic temperatures of the glass phase. The ultimate limit for long-time use of SiC is likely to be between 1700 and 1800°C, where bubble formation and spallation may become inevitable.

Silicon Nitride for High‐Temperature Applications

“…Especially during long-term exposure at elevated temperatures, compositional and microstructural changes in the upper surface and bulk region of these materials were observed. [119][120][121][122][123][124][125][126] These processes generate a new defect population in the materials consequently leading to degradation of the properties of the ceramics in spite of the optimal combination of properties originally designed during fabrication. Additionally, significant evidence to the consequences of the oxidation processes were provided in studies dealing with life-time behavior of Si 3 N 4 at elevated temperatures 49,54,125 The influence of these processes on microstructure and the mechanical properties was described in 127 The HIPed material exhibited a very low weight gain with 0.7 mg/cm 2 after 2500 h as a clean protective layer of pure SiO 2 with the low-diffusion coefficient of oxygen 119 was formed.…”

Degradation of Silicon Nitride Glow Plugs in Various Environments. Part 2: Gas Burner Rig

“…partial crystallization) will result in a logarithmic law. 5 In real applications often a model forcing data to yield parabolic rate constants is used to compare different materials performance.…”

Silicon Nitride/Molybdenum Disilicide Composite with Superior Long‐Term Oxidation Resistance at 1500°C

“…4 -7 Advanced Si 3 N 4 materials with Y 2 O 3 or rare-earth oxides as sintering aids exhibit quite stable oxidation behavior up to temperatures of 1500°C (⌬m between 1 and 2 mg/cm 2 after 10 3 h and K ox between 10 Ϫ7 and 10 Ϫ6 mg 2 /(cm 4 ⅐s)). 8,9 Despite this small weight gain, the mechanical properties of the Si 3 N 4 materials are strongly degraded, especially after long-term oxidation treatment. Studies show that oxidation occurs on the surface and in the bulk of Si 3 N 4 materials.…”