XRD pattern of the sample which was just ball milled for 7.5 h (but not ignited) is presented in Fig. 3(a). It can be seen that no reaction took place. The mixture was composed of unreacted Mg and ZrO2. The XRD pattern of the VCS products of this mixture is shown in Fig. 3(b). As can be easily realized from this figure, expected phases ZrB2 and MgO were formed successfully and formation of Zr2ON2 was prevented due to the absence of N2 gas, however; formation of Mg3B2O6 could not be prevented. Furthermore, complete reduction of ZrO2 could not be achieved.