Effect of excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction

• Published in: Ceramics international 2014-11, Vol.40 (9), p.14235-14246
• Main Authors: Nasiri-Tabrizi, Bahman, Ebrahimi-Kahrizsangi, Reza, Bahrami-Karkevandi, Mojtaba
• Format: Article
• Language: English
• Subjects: Activated; B. Nanocomposite; Borides; Boron oxide; Excess boron oxide; Formations; Leaching; Magnesium; Magnesium oxide; MSR; Nanocomposites; Thermodynamic assessment; Tungsten; WO3–B2O3–X (C, Mg)
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2014.06.013

The influence of the type of reducing agent, milling time and excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction was studied. The powder mixtures were mechanically activated using a high-energy planetary ball mill under two distinct experimental conditions. In the first manner, a mixture of tungsten trioxide, boron oxide and graphite with the stoichiometric composition was milled for different times. In the second approach, a mixture of tungsten trioxide, boron oxide and elemental magnesium with a molar ratio of 2:x:y (with x=2.5–6.25 and y=13.5–24.75) was activated for 1 and 30h. In the presence of 30–50wt% excess boron oxide, WB was formed during milling. Further increasing the boron oxide content to 150wt% led to a significant change in the mechanochemical behavior of the system so that WB and W2B5 became more dominant after 1h of milling. During leaching in 18% HCl aqueous solution, MgO was completely removed and consequently tungsten boride nanocomposites with high phase purity were obtained. According to microscopic observations, the 30h milled sample showed an average particle size of about 95nm after the leaching process.