A Comparison of Oxidation Kinetics of O′‐SiAlON and β‐SiAlON Powders Synthesized from Bauxite

Abstract

The oxidation mechanism and kinetics of β‐SiAlON and O′‐SiAlON powders synthesized from bauxite have been investigated using thermogravimetric analysis, X‐ray diffraction (XRD), and scanning electron microscopy. Oxidation experiments were carried out in both isothermal and nonisothermal modes in oxygen atmosphere. β‐SiAlON begins to oxidize at above 1000 K, and the rate increases significantly after 1200 K, forming SiO2 and Al2O3 at low temperature and mullite at high temperature. By comparison, the oxidation of O′‐SiAlON powder starts at about 1250 K and after 1300 K the rate increases significantly. The O′‐SiAlON phase remains dominant up to 1623 K, as demonstrated by XRD analysis, and the oxidation products are SiO2 as well as a small amount of mullite. At higher temperature, liquid phase resulting from the fusion of SiO2 and the impurities in O′‐SiAlON powder hinders the progress of oxidation, which causes O′‐SiAlON to have more oxidation resistance. Diffusion is the controlling step during both the oxidation processes. Based on the experimental data, a new model for predicting the oxidation process is developed. The application of this new model to the two systems demonstrates the validity of this new model. The activation energy of the oxidation of O′‐SiAlON and β‐SiAlON has been calculated to be 224.1 and 175.7 kJ/mol, respectively.

Thermal oxidation of SiAlON powders synthesized from coal gangue

“…In this work, the value of ΔE for the oxidation of β-SiAlON synthesized from coal gangue with ferric oxide is 184.5 kJ/mol, which is similar to that (175.7 kJ/mol) synthesized from bauxite [18]. While the value is lower than the result (250 kJ/mol) obtained by MacKenzie et al [13].…”

“…Thus, the morphology of the oxide products would differ at different temperatures and in turn affect the value of Δm max . This has been proven in dealing with the oxidation of SiAlON powders synthesized from bauxite [18].…”

“…This is in accordance with the previous results in Refs. [7][8][9][10][11][12][13][14][15][16][17][18].…”

“…The reliability of Chou's model has been verified by many systems such as AlN, Si 3 N 4 and SiAlON synthesized from oxide or bauxite etc. [16][17][18]. In order to extend its application range, more experimental results are required, especially the data involving the oxidation of SiAlON synthesized from natural aluminosilicate minerals.…”

Morphological development and oxidation mechanisms of aluminum nitride whiskers

“…From the above analysis, the oxidation behavior of AlN whiskers belongs to gas-solid reaction [12]. In our previous work, a series of formulae have been developed explicitly expressing the reacted fraction x as a function of time ''t'', cylinder diameter ''R 0 '' and other related physical parameters.…”