Salt-Assisted SHS Synthesis of Aluminium Nitride Powders for Refractory Applications

Powders of aluminum nitride can be prepared by self-sustain high-temperature synthesis (SHS) between aluminum and nitrogen but its high exothermic effect causes melting and evaporation of aluminum and low efficiency of such reaction. A presence of inorganic salt in the starting powder mixture can decrease a heat evolved in the SHS reaction, hinders melting and coalescence of aluminum, and facilitates penetration of nitrogen into interior of a powder bed. Mixtures of alumina powders with different grain sizes and different amounts of aluminum carbonate were subjected to the SHS reaction under 0.05, 0.1 or 1 MPa nitrogen. The powders were composed of aluminum nitride, unreacted aluminum, aluminum oxynitride and in some cases corundum and aluminum oxycarbonate. The finale effects are strongly dependent on the amount of the salt, a grain size of aluminum and a nitrogen pressure.

Tuning electron delocalization and surface area in COFs derived N,B co-doped carbon materials for efficient selective hydrogenation of nitroarenes

Metal-free carbon catalysts with excellent conduction performance have drawn much research attention in reduction reactions.Herein,a N,B co-doped carbon catalyst with high pyrrolic N proportion(35.75%)and excellent surface area(1409 m^(2)/g)was successfully prepared via carbonizing covalent organic framework materials(COFs)containing N and B atoms assisted by ZnCl_(2)molten salt.The presence of ZnCl_(2)maintains the micropore structure of COFs to provide high specific surface areas and abundant lattice defects for carbon materials.In addition,electron-withdrawing B heteroatom further facilitates the formation of pyrrolic N at defect sites by modifying the electronic structure of carbon network.The tuning of surface areas and active N species in carbon catalysts successfully improve the selective hydrogenation of nitrobenzene to aniline.The optimized carbon material exhibits excellent nitrobenzene conversion(99.9%)and aniline selectivity(>99%)within 15 min,as well as excellent substrate suitability.This work provides a certain guiding for the design and application of metal-free catalysis.