Preparation And Study Of High-purity Chromium Nitride Powders

Chromium nitride powder, which has a lot of excellent properties, such as highrigidity, outstanding resistant causticity of acid and alkali, high chemical stability,good resistant attrition and high melting point, is widely applicated in magnetics,electron industry and fire-resistant ceramic et al. At present, chromium nitride powderis produced by carbon thermal reduction, which has some shortcomings, for example,the chromium nitride powder has low purity. In this paper, high-pure chromiumnitride have been synthesized by ammonolysis of ultra-fine chromium oxide which isobtained by ammonia precipitation method.The ultra-fine chromium oxides have been prepared by ammonia precipitationmethod and homogeneous precipitation method. The results show that the specificsurface area and granularity of chromium oxide synthesized by homogeneousprecipitation method were were better than chromium oxide synthesized by ammoniaprecipitation method. The synthesis conditions, such as concentration of chromiumion, temperature, methods of droping ammonia, pH value in end point, surfactantsand methods of drying was studied. SEM, BET and laser diffraction granularityanalyzer were adopted for the characterization of the powders obtained under differentconditions. According to experimental results, the optimized condition weredetermined: precursor was precipitated with ammonia, temperature was set at 60℃,concentration of chromium ion was 0.1mol/L, ammonia was dropped slowly, 2wt% of PEG2000 was added as surfactant, pH value in end point was 8 , obtainedprecursor was aging for some time and then washed with alcohol, and dried byazeotropic distillation method. The specific surface area of the precursor was morethan 61.47 m²/g, and the particle size of the precursor was around 50nm.The effect of different precursors such as commercial Cr₂O₃, Cr₂O₃ synthesizedby ammonia precipitation method and homogeneous precipitation method wasstudied. The results show that in the same ammonolysis conditions, the purity of CrNis highest by ammonolysis Cr₂O₃ synthesized by ammonia precipitation method. Thesynthesis conditions, such as ammonolysis temperature, the holding time, flow fluxof NH₃, thickness of materiel, press of hearth, configuration of hearth, additive ofurea, NH₄Cl and CrN crystal seeds were studied. X-ray diffraction, SEM andnitrogen/oxygen analyzer were adopted for the characterization of the powders obtained under different ammonolysis conditions. The results show that whenultra-fine chromium oxide was mixed with 5wt% CrN and 10wt% urea, ultra-fine andhigh-pure CrN powders with purity more than 99.5wt% and size of 0.2μm weresynthesized at 800℃for 12h by ammonolysis of ultra-fine chromium oxide whichwas synthesized by ammonia precipitation method.