Study On Preparation And Injection Molding Of Aluminum Nitride Powder

Aluminum nitride ceramics have excellent thermal conductivity,high insulation and good mechanical properties,similar thermal expansion coefficient to silcon,resistance to plasma erosion,etc.,and have been considered as the key materials of semiconductor chip packaging,precision electronic instrument parts and optical devices for consumer electronics.Research on raw material powder preparation,ceramic forming and sintering,and subsequent metallization and packaging are also in progress.The high price of raw materials for manufacturing high-purity aluminum nitride powder,long synthesis time and high energy consumption,would result in high price of aluminum nitride powder.In addition,its fine particle size and easy hydrolysis also make the high price of storage and using environment.Due to the high hardness,brittleness and poor processing performance of aluminum nitride,it is difficult to produce parts with complex shapes and high precision by traditional processing methods,which greatly limits the application of aluminum nitride ceramics.All these restrict the wide application of aluminum nitride materials.Aiming at the above problems,the following research is carried out in this paper:(1)A mixed precursor of ammonium hydrogencarbonate and carbon black is synthesized by a precipitation method,and a carbothermal reduction reaction is carried out under heating with nitrogen to synthesize a mixture of aluminum nitride and carbon,and excess carbon is removed in the air.When the reverse titration method is adopted and the pH value is controlled between 8.5 and 10,the synthetic phase of precursor can be ammonium aluminum carbonate.The initial nitridation temperature of the precursor is between 1200? and 1300?.By adjusting the ratio of carbon to aluminum and the reaction temperature,aluminum nitridation powder with different particle sizes can be prepared.When the molar ratio of carbon to aluminum is 8:1,the reaction temperature is 1450?,the primary particle size of the synthesized aluminum nitride powder is 80nm,and the specific surface area is i7m2/g.The molar ratio of carbon to aluminum is 1.8:1.When the reaction temperature is 1650?,the primary particle size of aluminum nitride powder is about 700nm,the specific surface area is 2.1m2/g.(2)The surface of the synthesized aluminum nitride powder was modified with phosphoric acid and aluminum dihydrogen phosphate,and the modified powder was subjected to a hydration resistance test.It was found that the untreated powder quickly hydrolyzed and the pH value in the water rose to 10,XRD analysis showed that the phase was aluminum hydroxide,and the morphology was found to be rod-shaped or columnar by SEM.The surface-modified aluminum nitride powder could be stably hydrolyzed in water at 70? for more than 72 hours.The treated powder was ball-milled with the Y2O3 powder.It was found that after the grinding time exceeded 16 hours,the oxygen content of the calcined powder at 600? increased significantly,and the aluminum nitride surface protective layer was destroyed.The mixed slurry of aluminum nitride and cerium oxide grinded for 4 hours was subjected to spray granulation to obtain an average particle size of 52.1um,bulk density of 0.93g/cm3 and tap density of 1.05g/cm3,and the powder at a pressure of 200MPa.The relative density is 58%.The aluminum nitride ceramic obtained by degreasing and sintering has a thermal conductivity of 171.2W/m·k and bending strength is 340MPa.(3)The wax-based binder was mixed with the self-made carbothermal reduction aluminum nitride powder and the purchased direct nitriding powder to prepare aluminum nitride ceramic feedstocks.The effect of powder morphology and particle size on the critical solid loading of the feedstock was studied.The carbothermal reduction powder has a higher critical solid loading than the direct nitridation powder.The critical solid loadings of the two are 60 vol.%and 58 vol.%,respectively.The relationship between viscosities of the feedstock and e of shear rate and temperature were studied.It was found that the comprehensive factor aSTV of the two feeds was between 0.6 and 0.75.The thermal conductivity of the sintered aluminum nitride ceramic parts was 186 W-m-1·K-1 and 130 W·m-1.K-1,respectively,and the flexural strengths were 363 MPa and 320 MPa,respectively.By adding 1wt.%of the thermoplastic phenolic resin to the binder during the mixing process,it was found that the carbon content in the brown part was 0.4 wt.%,and the brown part was heated to 1500? for 4 hours.The carbon content was changed to 0.04 wt.%,and the oxygen content was decreased from 1.89 wt%to 1.32 wt.%.The second phase composition of the sintered sample is composed of Y4Al2O9 and YAlO3.The ratio of the two phases is 1:2,the thermal conductivity is 248 W·m-1·k-1,the second phase is island-like distribution.