Preparation And Performance Research Of High Thermal Conductivity AlN Ceramics Under Low Temperature Sintering

Abstract: AlN and Y-doped nano-sized powders were synthesized by CarbothermalReduction Nitride （CRN） route from sol-gel low temperature precursors by usingaluminum nitrate, glucose and calcium nitrate or yttrium nitrate as raw materials.With those nano-sized powders as additives, AlN ceramics were prepared at lowsintering temperature. The influences of nano-sized powders to the sinteringbehavior and thermal conductivity of AlN ceramics were investigated. The resultsare as follows.A proper addition of nano-sized AlN powders to the micro-sized AlN powderscan promote the sintering of micro-sized AlN ceramics at a certain extent. The AlNceramics were sintered at1800℃. But there were some stomas in the ceramics, andits density was just about3.12g·cm^-3, as a result gotten the low thermal conductivityof66.74W/（m·K） of the highest.Compared with single addition of Y₂O₃to the micro-sized AlN powders, theadditions of nano-sized AlN powders and Y₂O₃simultaneously can improve thedisputation of second phase by increasing the contact of Y₂O₃and AlN. The AlNceramics can also be sintered at1800℃, but gotten a higher thermal conductivityof125.29W/（m·K）.The calcium and yttrium compounds can react with alumina and result in somealuminates. Those aluminates formed liquid during the nitradation process, whichpromoted the transformation of Al₂O₃to AlN and the growth of AlN particles byincreasing the dispersion of Al₂O₃and AlN powders. Yttrium compounds remainingin the products, and then gotten Y-doped nano-sized AlN powders.A proper addition of Y-doped nano-sized AlN powders to the micro-sized AlNceramics lowered the sintering temperature to1750℃, and gotten a density to itstheoretical density. But when the addition of Y₂O₃were lower than1wt%, theparticles of AlN were smaller with larger grain boundaries and looser boundarycontact, which caused the low thermal conductivity of92.42W/（m·K） of the highest. When the sintering temperature increased to1850℃, the grain boundaries weredecreased with the growth of AlN particles, and gotten a higher thermal conductivityof130.99W/（m·K）。With the40-60wt%Y-doped nano AlN powders as the addition, increasing theY₂O₃content to2-3wt%, AlN grains grew completely with less grain boundaries andcloser boundary contact, and the second phases distributed at the triangle area ofAlN boundary. As a result, the thermal conductivity of AlN ceramics reached191.82W/（m·K） of the highest at sintering temperature of1750℃.AlN ceramics with higher density, no pores, bigger grain, less boundaries andsecond phases distributing at triangle area of AlN boundary have high thermalconductivity.