Synthesis of zirconium, hafnium and their ternary borides by a polymer complex route

Abstract

Submicrometer (100-500 nm) zirconium diboride powders were synthesized by a polymer complex route using simple and mainly nontoxic starting reagents. In this aqueous process, chitosan was used as a coordinating polymer to immobilize the metal ion and boric acid in the molecular so as to inhibit the segregation of various components in the dried gel. This zirconium-based precursor (4 B/metal molar ratios) was thus completely transformed into ZrB 2 after 1400°C heat treatments. As a comparison, synthesis of zirconium diboride using phenolic resin with poor complexation ability was also conducted, and the results showed that the final products comprised of a mixture of boride and a considerable amount of carbide phase in spite of the excess of boron source. Moreover, HfB 2 and the ternary boride powders were also synthesized by the polymer complex method and had a submicrometer size; moreover, the ternary boride showed a single phase AlB 2 -type products. Thus, the polymer complex method was demonstrated to be a more effective method to synthesize boride particles. Graphical AbstractKeywords Submicrometer metal diboride powder Á Preceramic precursor Á Polymer complex route Á Intimate mixing Á Chitosan

Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics

“…322−326 For example, a polymer system acting as a precursor for both ZrB 2 and HfB 2 ceramics was synthesized through the reaction of MOCl 2 with chitosan and boric acid, B(OH) 3 . 327 Chitosan is a commercially available polysaccharide, containing numerous alcohol groups that can be used as linkers in condensation reactions. A complex product is formed in a reaction between the metal oxychloride, chitosan, and boric acid.…”

“…Further heating to 1800 °C resulted in the conversion to crystalline ZrB 2 /ZrC/C composites . ZrOCl 2 has been demonstrated to be a reliable zirconium source for preceramic polymer formation by several groups. − For example, a polymer system acting as a precursor for both ZrB 2 and HfB 2 ceramics was synthesized through the reaction of MOCl 2 with chitosan and boric acid, B­(OH) 3 . Chitosan is a commercially available polysaccharide, containing numerous alcohol groups that can be used as linkers in condensation reactions.…”

The effects of partially or fully linked boron with a cross-linking structure of an organic precursor on the purity and morphology of ZrB2 powder

“…33 However, organic boron sources are expensive and difficult to store. Subsequently, researchers used polyols or polysaccharides as ligands and carbon sources to chelate with H 3 BO 3 promoting the uniformity of boron in precursors, such as D-fructose, 38 sorbitol, 32,39,40 glycerol, 34,41 chitosan, 42 and mannitol. 26,43 The purities and morphologies of ZrB 2 particles using different ligands were different.…”