Modification of matrix for magnesia material by in situ nitridation

Mg-alpha-SiAlON bonded periclase composites were prepared at 1550 degrees C in a nitrogen atmosphere using sintered magnesia particles, Al metal powder, Si powder, magnesia, and alpha-Al203 powder as raw materials and were bonded with a phenolic resin. The modification mechanism was investigated. Tabular-shaped Mg-alpha-SiAlON can be obtained through the diffusion-reaction-dissolution-precipitation mass transfer mechanism. It was found that modification of the matrix for the magnesia material led to a direct bonding mode and a card structure. The optimal percentage of powder material was determined to be 40 wt%, by which a well-developed card structure was obtained. The sintered Mg-alpha-SiAlON bonded periclase composites exhibited excellent cold modulus of rupture (12.5 MPa), and the residual strength retention rate was 3 times higher than that of a magnesia specimen after the third thermal shock. The enhanced thermal shock resistance was attributed to a lower thermal expansion coefficient and the "crack deflection" mechanism of tabular-shaped Mg-alpha-SiAlON.