Study On Preparation Technology Of Lanthanum Hexaboride Nanoparticles

Lanthanum hexaboride has many excellent performances,such as high electric conductivity,low rate of evaporation at high temperature,high emission current density and good chemical stability.In this paper we aimed to study the preparation process of La B6 nanopowder of high-purity, small particle size distribution and the good performance, to provide a reference for the development and application of its performance. After a demonstration by comparing different scenarios, we used solid-phase synthesis method to prepare La B6 nanopowder, and did a research and analysis on the solid phase synthesis reaction mechanism on the raw material of KBH4 and La Cl3, and did an optimization of the synthesis process parameters. In addition, we also studied the cleaning and dispersion technology of the products, and did performance test and microstructure characterization on it.Stability of La B6 nanopowder dispersion was observed and analyzed by means of natural sedimentation and scanning electron microscopy,and effective dispersion method and particle size analysis method of La B6 nanopowder was explored.Natural sedimentation method and scanning electron microscopy were used to analyze the stability of La B6 nanopowder dispersion system. We found that different dispersants and dispersion methods have significantly different effects on the dispersion of La B6 nanopowder.The dispersing effect of cationic surfactant PEI is not obviously, and the effect of nonionic surfactant PEG2000 is not ideal, the dispersion effect of anionic surfactant DBS is good, but still serious agglomeration after drying.Effect of phosphoric acid on the dispersion of La B6 nanopowder is the best, and more stable than DBS, dispersion liquid is still stable even the powder was dried again.Reaction Mechanism was explored through the analysis of the reaction products’ component at different temperatures.It showed that, in addition to the main product of La B6, there were a large number of KCl and small amounts of La BO3 and La3BO6. The chemical reaction started at the temperature of 600 ℃,and reacted more fully at the temperature of 700 ℃,as the reaction temperature increased, La B6 particles gradually increased,and the content of La BO3 and La3BO6 increased.Process parameters were studied with the help of XRD diffraction analysis, scanning electron microscopy and sedimentation analysis. The results show that, the higher the reaction temperature, the bigger crystallite size of La B6 nanopowder; the longer the holding time, the more conducive to the formation of La B6 to grain coarsening,;improve the B element proportion were contributed to the formation of La B6, but the products agglomerated seriously;by adding the reaction agent of Mg could effectively avoid the combination of B and La elements and O element.The structure and performance of La B6 nanopowder was fine characterized and tested.La B6 nanopowder prepared by solid phase synthesis crystallized well, grain size was in the range of 10~50nm. After the optimization of the process parameters was optimized,La B6 nanopowder was prepared with high purity of 97.52%,the average grain size was D=19.53 nm,and the lattice constant was a=4.153?. Work function was 2.45 e V that calculated by the Richardson straight line method.