Sol–Gel Synthesis and Formation Mechanism of Ultrahigh Temperature Ceramic: HfB2. Issue 1 (28th November 2013)

• Record Type: Journal Article
• Authors: Venugopal, Saranya; Boakye, Emmanuel E.; Paul, Anish; Keller, Kristin; Mogilevsky, Pavel; Vaidhyanathan, Bala; Binner, Jon G. P.; Katz, Allan; Brown, Peter M.; Fahrenholtz, W.
• Is Part Of: Journal of the American Ceramic Society. Volume 97:Issue 1(2014)
• Page Start: 92
• Page End: 99
• Publication Date: 2013-11-28
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12654
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" id="jace12654-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Hafnium diboride (HfB₂) 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 HfB₂ formation investigated using several techniques. The results showed that while temperatures as low as 1300°C could be used to produce HfB₂ particles, the heat treatment needed to last for about 25 h. This in turn resulted in anisotropic particle growth along the <italic>c</italic>‐axis of the HfB₂ 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 HfB₂ 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.</p> </abstract>