Formation and stability of tungsten boride nanocomposites in WO3–B2O3–Mg ternary system: Mechanochemical effects

Abstract

Mechanochemical behavior of WO3–B2O3–Mg ternary system to produce tungsten boride-based nanocomposites was investigated in terms of milling duration. To provide essential conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR), a mixture of tungsten trioxide, boron oxide and elemental magnesium with the stoichiometric composition was activated using a high-energy planetary ball mill. Based on the obtained data, the adiabatic temperature was around 3659K which confirmed that the reaction mode was MSR. Due to the occurrence of a combustion reaction at the beginning of milling, the phase compositions were W, WB, W2B, and MgO. After 60min of milling, WB disappeared completely and a ternary nanocomposite with the phase constituents of W2B, W and MgO was obtained. With increasing the milling time to 1800min, no phase transformation was observed and thus a nanocomposite powder with similar phase compositions was produced. However, the percentage of the detected phases fluctuated in terms of milling time. During the leaching process, MgO (unwanted phase) was completely removed and consequently a nanocomposite powder with the phase compositions of W2B and W was formed. From the microscopic observations, the size of the composite particles was varied from 38 to 500nm.