A study of slip solids content and wall thickness on thermal shock behavior of a slip cast reaction bonded silicon nitride ladle

The mechanical and thermal properties, before and after thermal shock testing, of reaction bonded silicon nitride (RBSN) produced by slip casting, were studied. Slips with solids contents of 27 wt% and 50 wt% silicon powder were used to produce bend bars. Metals casting ladles, with wall thicknesses of 8 mm and 24 mm, were cast from the 50 wt% slip. Nitridation was conducted at 1500 °C for 4 h. X-ray diffraction (XRD) showed α and β phases of Si3N4 were formed. It was found that increasing the solids content increased the density and flexural strength of the bars. After thermal shock testing the flexural strength decreased. The 24 mm ladle which was exposed to 700 °C aluminum fractured after one exposure, while the 8 mm ladle withstood five exposures before failure. This was attributed to the difference in thermal strain.