Chapter 58. Hafnium Reactivity Below 1500°C in Search of Better Processing of HfB2/SIC UHTC Composites

  1. Rajan Tandon,
  2. Andrew Wereszczak and
  3. Edgar Lara-Curzio
  1. Yigal D. Blum,
  2. Steven Young,
  3. David Hui and
  4. Esperanza Alvarez

Published Online: 27 MAR 2008

DOI: 10.1002/9780470291313.ch58

Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 2

Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 2

How to Cite

Blum, Y. D., Young, S., Hui, D. and Alvarez, E. (2006) Hafnium Reactivity Below 1500°C in Search of Better Processing of HfB2/SIC UHTC Composites, in Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 2 (eds R. Tandon, A. Wereszczak and E. Lara-Curzio), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291313.ch58

Author Information

  1. SRI International 333 Ravens wood Ave. Menlo Park, CA 94025

Publication History

  1. Published Online: 27 MAR 2008
  2. Published Print: 1 JAN 2006

ISBN Information

Print ISBN: 9780470080528

Online ISBN: 9780470291313

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Keywords:

  • hafnium;
  • ultra-high-temperature ceramics (UHTC);
  • hafnium;
  • XRD;
  • boronitride

Summary

Ultra–high–temperature ceramics (UHTC) have regained significant interest as materials of choice for aerospace and energy applications. UHTCs are based on composites consisting of borides, carbides and nitrides of hafnium and zirconium combined with a silicon carbide phase. The current hot–press processing of UHTCs is a major obstacle in incorporating such composites into component designs and ultra–high–temperature protective coatings. This article further explores exothermic chemical reactions and behavior of Hf metal that may lead to processes that are performed under pressureless conditions or below 1500°C. Such reactions have rarely been studied outside the context of self–propagating high–temperature synthesis (SHS). This article reports a local micro–melting phenomenon at the surface of Hf strips after interacting with powders containing B and/or C powders. The melting is observed at temperatures more than 1000°C below the actual melting point of Hf (2227°C), due to confined energy release derived from the very exothermic reactions Intriguing displacement reactions between the Hf surface and boron–containing compounds (B4C and BN) are also reported, which demonstrate the powerful reactivity of the metal even in the presence of minimal contact area between the reactants. The presence of distinct large crystallites after the reactions with the boron compounds means long–range diffusivities of the elements in the molten and solid phases of the Hf.