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Sol–Gel Synthesis and Formation Mechanism of Ultrahigh Temperature Ceramic: HfB 2
Author(s) -
Venugopal Saranya,
Boakye Emmanuel E.,
Paul Anish,
Keller Kristin,
Mogilevsky Pavel,
Vaidhyanathan Bala,
Binner Jon G. P.,
Katz Allan,
Brown Peter M.
Publication year - 2014
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12654
Subject(s) - hafnium , boron , boric acid , materials science , carbothermic reaction , carbon fibers , amorphous solid , equiaxed crystals , inorganic chemistry , chemical engineering , chemistry , zirconium , crystallography , metallurgy , organic chemistry , composite material , carbide , alloy , composite number , engineering
Hafnium diboride (HfB 2 ) powder has been synthesized via a sol–gel‐based route using phenolic resin, hafnium chloride, and boric acid as the source of carbon, hafnium, and boron, respectively, though a small number of comparative experiments involved amorphous boron as boron source. The effects of heat‐treatment dwell time and hafnium:carbon (Hf:C) and hafnium:boron (Hf:B) molar ratio on the purity and morphology of the final powder have been studied and the mechanism of HfB 2 formation investigated using several techniques. The results showed that while temperatures as low as 1300°C could be used to produce HfB 2 particles, the heat treatment needed to last for about 25 h. This in turn resulted in anisotropic particle growth along the c ‐axis of the HfB 2 crystals yielding tube‐like structures of about 10 μm long. Equiaxed particles 1–2 μm in size were obtained when the precursor was heat treated at 1600°C for 2 h. The reaction mechanism involved boro/carbothermal reduction and the indications were that the formation of HfB 2 at 1300°C is through the intermediate formation of an amorphous B or boron suboxides, although at higher temperatures more than one reaction mechanism may be active.