Example 2
Mixtures of molybdenum, silicon and chromium powders were prepared and heated in Ar to form MoSi2 and Mo0.85Cr0.15Si2, respectively. The reaction products were milled to an average particle diameter of 5 μm. Silicide powder was subsequently mixed with 5 wt. % bentonite (bentolite L) and water to form a paste for extrusion. Respective composition was extruded into 9 mm diameter rods, which were subsequently dried and pre-sintered in hydrogen for 1 h at 1375° C. Final sintering to achieve full density was then performed by resistance heating in air to 1500° C. for 5 minutes.
Samples of each composition were ground to remove the protective SiO2 scale that was formed during final sintering. Samples were placed individually on alumina sample holders to collect potential oxidation products and include them in the weight measurements. The samples were placed in laboratory air in an electrical furnace heated to 450° C. employing FeCrAl heating elements and utilized with ceramic fiber insulation. Sample and holder were weighted to monitor individual weight changes as function of exposure time.
The combination (Mo,Cr)Si2-based terminal portions on MoSi2-based portions together with MoSi2-based heating zone material displayed significantly improved resistance.
