As demonstrated in Figs. 3(c) and 6(c) and discussed above, when 20 mol % excessive Mg was used with CaCl2, phase-pure CaB6 could be prepared after either 4 h firing at 1000°C or 6 h at 800°C. SEM images and EDS of product powders synthesized under these two conditions in the sample resultant from 6 h firing at 800°C. As mentioned earlier, the overall synthesis process of CaB6 can be indicated by Reaction (1).
Nevertheless, the actual formation process should be involved several individual steps based on reaction extents and phase formations in different samples fired under different conditions (Figs. 18) and previous MSS studies on other borides,27)29), the main reactions involved in each step can be detailed as follows. At testing temperatures (8001000°C), CaCl2 initially melted, forming a desirable molten salt medium in which both Mg and CaO partially dissolved,30),31) and subsequently reacted, forming a CaMg binary liquid [Ca in this liquid is indicated by (Ca)] and MgO. On the other hand, the dissolved Mg also diffused through the molten salt medium to the liquid (dissolved or undissolved in CaCl2) B2O3 and then reduced to B. Before all of the B2O3 was consumed, the unreduced B2O3 would react with the MgO from Reactions (2) and (3) forming the intermediate Mg3B2O6. Improving/optimizing the synthesis conditions, e.g., increasing firing temperature or time and using excessive Mg (Figs. 16), the formed Mg3B2O6 would be further reduced by Mg dissolved in CaCl2, producing more B and releasing MgO. If you are looking for high quality, high purity, and cost-effective Calcium hexaboride, or if you require the latest price of Calcium hexaboride, please feel free to email contact mis-asia.
