Investigation On Preparation Of AlN Powder By Plasma-assisted High Energy Ball Milling

AlN is a widely used functional materials, it also has broad application prospects in the fieldof naval architecture and Ocean Engineering, nowadays the fabrication and synthesis mechanismof AlN is still a hot topic. Al2O3carbon thermal reduction method of AlN is one of the mostwidely used method now, but it has the shortcomings of high reaction temperature, and needslong reaction time. Plasma-assisted milling is a new method for preparations of nano-materials.Due to its rapid thinning effects of ball milling on the powder and its high activation, using thisto activated Al2O3is expected to reduce the subsequent reaction temperature, promoting reactioninto entire. This paper uses the following three types of reaction scheme, by contrasting withthose normal ball mill process and found that plasma-assisted milling has a significant effect onpromoting synthesis of AlN.1）Mixing Al2O3+C3H6N6powder as raw materials, we find that the use of plasma-assistedmilling and general milling were unable to synthesis AlN directly. But by plasma-assisted milled,the X-ray through C3H6N6’s diffraction peaks have tended to disappear, while the X-raydiffraction peaks of C3H6N6ordinary milled still very evident. This shows that the latticedistortion plasma assisted milling of powders is larger. After milling the powder was subjected todifferential thermal analysis, heat the temperature to1400℃, the two methods of mixed powderstill cannot synthesis nitrogen. Because at280℃, when C3H6N6nitrogen gas escapes with thelost pyrolysis, at that time Al2O3reduction reaction never happen yet.2）The Al2O3powder was milled to separate activation, and C powder mixed evenly asreaction raw materials. The plasma assisted milling for40h, in N2atmosphere at1400℃for4h,Al2O3can be converted to AlN to complete the reduction reaction of carbon heat. The ratio ofAl2O3to conventional carbon thermal reduction reaction required1680℃decreased. Calculatedusing Kissinger differential method, down to371.5kJ/mol can activate the plasma assistedmilling40h synthesis of AlN. While the ordinary milling40h Al2O3, under the same conditions,the yield of AlN is about47%. Analysis shows that, the milling caused by grain refinement andlattice distortion of Al2O3is the main reason for promoting carbon thermal reduction reaction.Synergistic effect of plasma increased the formation of Al2O3crystal defects and latticedistortion, improves the internal energy of powder storage, thereby reducing the thermodynamicreaction energy barrier. 3）Mix the milling together as Al2O3+C reaction material, we will that plasma-assistedmilling only need for30h, reaction insulation materials under1400℃in N2atmosphere for4h,Al2O3will completely converted to AlN. While ordinary milling of the mixed raw material for30h, under the same conditions the yield of AlN only about83%. Analysis showed that theplasma-assisted milling making alumina particles embedded on the graphite substrate in a moreuniform way, so that it can form a fine structure layer composite sheet and the effective contactarea of the reaction will be increased, the average diffusion path reaction can be shorter. Thisgreatly facilitated the carbon thermal reduction reaction on kinetics, thus shorten the milling timemore than10h, compared with Option II.Through the research above, we believe that when separate ball milled Al2O3, subsequentcarbothermal reduction reaction in the gas phase reaction model-driven. Mixed milled Al2O3+C,the carbon thermal reduction reaction in solid-solid reaction model-driven.