d lt 150 micrometers u03bcm compacted at 20 kilonewtons kn over 13 millimeters mm and then sintered 1450 u00b0 c for 3 hours h in air grain corrosion by slag was evaluated with an optical microscope after calcining a grain slay mixture at 1450 u00b0 c the slag was essentially constituted by sio 2 40 cao 40 na 2 o 10 and al 2 o 3 5 it presented a basicity index cao mgo sio 2 of 1 although the grains were not intended to come into contact with slag corrosion in slag serves to impose particularly severe conditions making it possible to measure corrosion that is significant a score u201c r u201d for resistance to corrosion was given in the range 0 to 4 with the resistance being better for higher r scores the allotropic transformation temperature u201c t u201d of the tested grains needs to be as close as possible to that of reference 2 alumina zirconia grains so that microcracking is effective in improving the ability of the composite material made from a mixture of these two types of grain to absorb energy during thermal shocks as explained in the introduction in contrast and for the same reason the coefficient of expansion at 1000 u00b0 c u201c a.