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Aluminium nitride ceramics containing 15-30 w/o of SiC whiskers can be sintered tofull density(by hot pressing at 1800℃)using2-3 w/o of Y_2O_3,additions.The whiskersincrease the toughness and strength of thecomposite,K_(10) increasing from 2.8 to about5.0 and flexural strength increasing by 30-50%.However,the whiskers must be welldispersed and if the dispersion is notsatisfactory,toughness may increase but thestrength decreases.The hot-pressingtemperature can be reduced by up to 100℃ ifY(NO_3)_3 .5H_20 is used as the sinteringadditive instead of Y_2O_3,but some oxidation ofthe AIN occurs during heating.Isopropan-2-01 is a better dispersing agent thancyclohexane,but again some oxidation of theAIN does occur.The best sample prepared during this work contained 20 w/o of SiC whiskers and 2 w/oY_2O_3 added as Y(NO_3)_3. 5H_2O and mixed inisopropanol.This exhibited a mean strength of453MPa(maximum 522MPa,measured bydisc flexure)and a fracture toughness of5.5MPam~(1/2).
Aluminium nitride containing 15-30 w / o of SiC whiskers can be sintered tofull density (by hot pressing at 1800 ° C.) using 2-3 w / o of Y 2 O 3, additions. Whiskers increase the toughness and strength of the composites, K_ (10) increasing from 2.8 to about 5.0 and flexural strength increasing by 30-50% .However, the whiskers must be welldispersed and if the dispersion is notsatisfactory, toughness may increase but the strength decreases.The hot-pressing temperature can be reduced up to 100 ° C. ifY (NO_3) _3 .5H_20 is used as the sintering additive instead of Y_2O_3, but some oxidation of the AIN occurs during heating. Isopropan-2-01 is a better dispersing agent thancyclohexane, but again some oxidation of theAIN does occur. The best sample prepared during this work contained 20 w / o of SiC whiskers and 2 w / o Y_2O_3 added as Y (NO_3) _3. 5H_2O and mixed in isopropanol.This exhibited a mean strength of 453 MPa (maximum 522 MPa, measured by disc flexure) and a fracture toughness of 5.5 MPam ~ (1/2).