Study of the milling parameters optimization in the direct carburization of WO3 by mechanical alloying

Abstract The mechanical alloying method allows obtaining tungsten carbide by direct carburization of tungsten trioxide. The parameters that have a determining role on the kinetic reactions are the temperature and the pressure of the process. The milling installation must maintain a low pressure by removing the carbon dioxide released during the carburizing reaction. In a planetary balls mill, the energy developed during a ball impact was determined via a simplified computational modeling and depends on the mass of balls and on the speed of balls reached during the milling process. The energy dissipated during impact increases exponentially with the speed rotation of the mill and with the balls diameter. Tests were carried out in a planetary balls mill equipped with bowls lined with tungsten carbide and filled with tungsten carbide balls of 10- and 12-mm diameter. Two levels of filling of the bowls, 150 g and 200 g of balls were also tested. The balls/milled powder ratio was kept at 10:1 in all tests. To monitor the carburizing reaction, samples were taken every 3 h of grinding. They have been investigated by X-ray diffraction to determine the phases in presence. The morphology of the particles was studied by scanning electron microscopy and the particle size was investigated by laser granulometry in liquid medium. To determine the effect of various milling parameters on the temperature during a milling cycle, a temperature-monitoring device was created and installed on the grinding bowl. The obtained values demonstrate that the diameter of the balls and the filling degree of the bowl have an important role in the evolution of the temperature during milling.