Comparison of two β-SiAlON ceramics prepared from synthetic and natural raw materials

Two types of β-SiALON ceramics (denoted SiALON-S and SiAlON -N) were synthesized by carbothermal reduction and nitridati on. The starting raw materials used were commercial synthetic powders (AlN, Al 2O3 and Si 3N4) for SiAlON-S and natural aluminosilicate raw materials (pyrophilite) for SiA lON-N. Sintering of materials has been achieved by hot- isostatical pressing procedure at 1730 °C using Y 2O3 as a sintering additive. In this study XRD and SEM methods were used. XRD method showed that SiAlON-S is pure aluminum silicon nitride oxide, while sample from n atural pyrophilite is composed of two aluminum silicon nitride oxides and corundum. Hardness and fracture toughness values were measured for all samples, the average values (means of 10 measurements) of SiAlON-S and SiAlON -N were HV = 12.28 GPa and 12.34 GPa, KIC = 4.11 MPa m 1/2 and 3.77 MPa m 1/2 respectively. A new testing method was used to asse ss the resistance of SiAlON samples to repeated thermal shocks. Samples with initiated cra cks by Vickers’s indentor were cyclically heated to 1000˚C and cooled to 500˚C. Apart from phase composition, the source of raw materials has a little influence on the properties of ceramic samples. Therefore, pyrophilite could be a potential natural source to synthesize S iAlON ceramics.