Plasma spraying of Al2O3–WO3 composite coatings

• Published in: Surface & coatings technology Vol. 206; no. 14; pp. 3323 - 3331
• Main Author: Matthews, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.03.2012; Elsevier
• Subjects: Al2O3–WO3 composite; Alumina; Aluminum oxide; Applied sciences; Composite coatings; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Heat treatment; Materials science; Metals. Metallurgy; Oxides; Physics; Plasma spraying; Production techniques; Scanning electron microscopy; Surface treatment; Surface treatments; Thermal dissociative reduction; Transformations; Tungsten; Tungsten oxides; X-ray diffraction; X-ray diffraction; Scanning electron microscopy; Plasma spraying; Al2O3–WO3 composite; Alumina; Thermal dissociative reduction; Plasma; Hot spraying; Surface treatments; XRD; Al; O; Tungsten oxide; Composite materials; Composite coating; composite; Plasma arc spraying; WO
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2012.01.043

Al2O3–WO3 oxide composites are of considerable interest as solid acid catalysts in the petrochemical industry. Typically they consist of a monolayer of WO3 dispersed over a high surface area alumina support. The aim of this work was to form a single layer Al2O3–WO3 composite coating by plasma spraying. Ammonium metatungstate was dispersed through porous alumina particles and transformed to WO3 by heat treatment. WO3 doped powders were plasma sprayed using “low” and “high” enthalpy plasma systems. Plasma spraying led to dramatic changes in the WO3 oxide to form metallic tungsten, a metastable Al2O3–W solid solution and the mixed oxide Al2(WO4)3. The mechanisms accounting for these transformations are discussed. ► Al2O3–WO3 composite powders were produced using an incipient wetness method. ► The composite powders were sprayed by plasma spraying to form non-equilibrium, metastable composite compositions. ► Plasma spraying led to the formation of metallic W, a Al2O3–W solid solution and Al2(WO4)3. ► The mechanisms accounting for these compositional transformations are discussed.