Characterization of Al2O3 composites with fine Mo particulates, I. Microstructural development
Journal
Nanostructured Materials
Journal Volume
10
Journal Issue
6
Pages
965-981
Date Issued
1998
Author(s)
Abstract
Alumina based composites containing nano- or submicron-meter Mo grains in the amounts of 20 vol% or less were prepared through a dissolution of molybdenum oxide in ammonium solution, followed by spray-drying, hydrogen reduction and sintering with or without hot-pressing. The properties of alumina/molybdate solutions and the ζ-potential of alumina particles in the solution were measured. By using electron microscopic and quantified X-ray diffraction techniques, the microstructural features and the evolution of Mo particulate in spray-dried powder and sintered bodies were analyzed. The time dependent exponent and activation energy of grain growth of Mo between 600 to 900 °C were determined. There is no glassy phase or reaction at the interfaces between Mo/Al2O3 of dense composites. Only one coherent interface was found, and the others are incoherent. The results reveal that submicrometric Mo grains may grow by surface diffusion in reduction stage (≤900 °C) and greatly retard the densification and reduce the grain size of alumina matrix in sintering stage.
Type
journal article