SONOCHEMICAL SYNTHESIS OF NANOCRYSTALLINE MOLYBDENUM DISILICIDE (MOSI2)

Sonochemical co-reduction of MoCl5 and SiCl4 with NaK alloy in a hexan e dispersion using 600 W, 20 kHz irradiation, followed by annealing at 900 degrees C produces nanocrystalline MoSi2 powders with approximate to 90% yield. Consolidation by hot pressing at 1170 degrees C, 140 MP a for 4 h gives a 78%-dense compact with 31 nm average grain sizes and a Vickers microhardness of 1484 (10% kg/mm(2). Consolidation by hot p ressing at 1200 degrees C, 100 MPa for 10 min. followed by hot isostat ic pressing at 1100 degrees C, 200 MPa for 4 h gives a 83%-dense compa ct with 41 nm average grain sizes and a Vickers microhardness of 1587 +/- 10% kg mm(-2). The second compact exhibits a compressive yield str ength of 2875 MPa, and fractures without significant plastic deformati on. The microhardness values and compression strengths are 50-70% high er in nanocrystalline MoSi2 than in conventional, coarse-grained MoSi2 .