The Role of Additives in the Densification of Nitrogen Ceramics.

Abstract

Densification of silicon nitride by either hot-pressing or pressureless sintering requires an additive which reacts with the surface silica and some of the nitride to give an oxynitride liquid that promotes shrinkage and, at the same time, the phase transformation from alpha to beta. Silicon nitride is densified by hot-pressing with scandia additive but theoretical density is not achieved by pressureless sintering. The kinetics of densification are interpreted in terms of a Kingery model with a slope of one-third for the solution-precipitation stage indicating that solution of alpha or precipitation of beta is rate-controlling. Sintering with equal weights of scandia and alumina gives improved densities. An important advantage over beta yttrium sialon is that the quaternary scandium oxynitride and glassy grain boundary phases do not undergo catastrophic oxidation at 1000 C.

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Document Details

Document Type
Technical Report
Publication Date
Oct 01, 1979
Accession Number
ADA116581

Entities

People

  • K. H. Jack

Organizations

  • Newcastle University

Tags

Communities of Interest

  • Advanced Electronics
  • Air Platforms

DTIC Thesaurus Topics

  • Body Weight
  • Ceramic Materials
  • Chemical Analysis
  • Chemistry
  • Crystal Structure
  • Crystallography
  • Crystals
  • Diffraction
  • Electron Microscopy
  • Glass Transition Temperature
  • Heat Treatment
  • Materials
  • Materials Engineering
  • Materials Processing
  • Materials Science
  • Phase Transformations
  • Transition Temperature

Fields of Study

  • Materials science

Readers

  • Powder metallurgy of Titanium alloys.