Synthesis of bulk nanocrystalline HfB2 from HfCl4–NaBH4–Mg ternary system
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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 °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 °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 °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.
This study was financially supported by “The Scientific and Technological Research Council of Turkey (TÜBİTAK)” with the Project Number of 112M470 and by “Istanbul Technical University Scientific Research Projects” with the Project Number of 37544. The authors also wish to express their appreciations to Prof. Dr. Servet Turan for his help with the SPS experiments and Prof. Dr. Hüseyin Çimenoğlu and M.Sc. Faiz Muhaffel for their supports in wear tests.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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