Effects of functional additives on the self propagating high temperature synthesis (SHS) of nano ZrB₂ and B₄C powders

There are many production methods for the synthesis of boride based advanced nano ceramics such as carbothermic reduction, synthesis from elements, gas phase reactions and self-propagating high-temperature synthesis (SHS). Self-propagating high-temperature synthesis is one of the important methods to synthesize advanced materials such as ceramics (e.g. ZrB₂, TiB₂, B₄C, Si₃N₄); abrasives, cutting tools and polishing powders (e.g. TiC, cemented carbides); resistive heating elements (e.g. MoSi₂), shape-memory alloys (e.g. TiNi); high-temperature structural alloys (e.g. nickel aluminides); master alloys (e.g. AlTiB); neutron attenuators (e.g. refractory metal hydrides) as well as conventional metals and their alloys. The advanced thermochemical simulations of the reactions were investigated in detail including different ratios of initial mixtures, as well as different initial temperatures in order to reduce the number of experiments. The X-ray diffraction analysis (XRD) analysis showed that main phases of the SHS product were MgO and ZrB₂. After the SHS process, ZrB₂ was separated from byproducts MgO, Mg₃B₂O₆ and Mg₂B₂O₅ by HCl acid leaching. KCL₄ and NaCl additives effected negatively to leach parameter. Mg₃B₂O₆ and MgB₄O₇ phases could not be removed on 1.88 M HCl solution at 1 / 20 S / L ratio for 60 min at 80 ℃ leach conditions. On the other hand Brunauer-Emmett-Teller (BET) analyses revealed that the products has higher surface area with KCL₄ and NaCl additives. Similar effects detected in B₄C experiments and surface area increased from 15.4 m²/g to 30 m²/g. (author)