Sonochemical synthesis of nanocrystalline molybdenum disilicide (MoSi2)

Sonochemical co-reduction of MoCl5 and SiCl4 with NaK alloy in a hexane dispersion using 600 W, 20 kHz irradiation, followed by annealing at 900 °C produces nanocrystalline MoSi2 powders with ≈90% yield. Consolidation by hot pressing at 1170 °C, 140 MPa for 4 h gives a 78%-dense compact with 31 nm average grain sizes and a Vickers microhardness of 1484 (10% kg/mm2. Consolidation by hot pressing at 1200 °C, 100 MPa for 10 min. followed by hot isostatic pressing at 1100 °C, 200 MPa for 4 h gives a 83%-dense compact with 41 nm average grain sizes and a Vickers microhardness of 1587 ± 10% kg mm−2. The second compact exhibits a compressive yield strength of 2875 MPa, and fractures without significant plastic deformation. The microhardness values and compression strengths are 50–70% higher in nanocrystalline MoSi2 than in conventional, coarse-grained MoSi2.