Synthesis of bulk nanocrystalline HfB2 from HfCl4-NaBH4-Mg ternary system


AKCAMLI N., Ağaoğulları D. , Balci O., Öveçoğlu M. L. , Duman I.

JOURNAL OF MATERIALS SCIENCE, vol.52, no.21, pp.12689-12705, 2017 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 52 Issue: 21
  • Publication Date: 2017
  • Doi Number: 10.1007/s10853-017-1382-1
  • Title of Journal : JOURNAL OF MATERIALS SCIENCE
  • Page Numbers: pp.12689-12705

Abstract

This study reports on the synthesis and consolidation of pure HfB2 powders starting from HfCl4-NaBH4-Mg blends via autoclave processing, annealing and purification followed by pressureless sintering (PS, with 2 wt% Co aid) or spark plasma sintering (SPS). During autoclave reactions conducted at 500 A degrees C for 12 h under autogenic pressure, excess amounts of NaBH4 were utilized to investigate its effects on the reaction products and mechanism. A subsequent washing (with distilled water), annealing (at 750, 1000 and 1700 A degrees C) and acid leaching (HCl) were applied on the as-synthesized products. Pure HfB2 powders with an average particle size of 145 nm were obtained after autoclave synthesis in the presence of 200 wt% excess NaBH4, washing, annealing at 1000 A degrees C for 3 h and 6 M HCl leaching. SPS sample has higher relative density and microhardness values (94.18% and 20.99 GPa, respectively) than those of PS sample (90.14% and 14.85 GPa). Relative wear resistance was improved considerably (8.2 times) by employing SPS technique.