in vapor pressure of the reactant sets, as well as the relative kinetic stability of the carbonyl-substituted species. Both W(CO)6 and triphenylphosphine are solids, and have relatively low vapor pressures, even in solution [97]. Fe(CO)5 and P(CH2CH3)2, on the other hand, are both liquids with high vapor pressures, and are expected to be the principal components of the gas-phase composition of the cavities.

Buhro et al. [98] used coreduction of MoCl5 and SiCl4 with an NaK alloy in a hexane dispersion using 600 W, 20 kHz irradiation, followed by annealing at 900 ° C to produce 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). The microhardness values and compression strengths are 50-70% higher in nanocrystalline MoSi2 than in conventional, coarse-grained MoSi2.

Recently, Suslick et al. [99] developed a new synthetic technique, that is, sonochemical synthesis of nanostructured inorganic materials, to produce Mo2N with a face-centered cubic structure [hereafter designated as Mo2N (fcc)]; a stream of NH3 (Matheson, 99.99%) was passed through the reaction cell at a flow rate of 135 mmol • s-1. Following rapid heating to 500 K, the sample was further heated to 973 K with a linear ramping rate of 30 K, and then maintained at a final temperature for 1 h. Once the reaction was complete, the gas flow was switched to a flow of helium (25 mmol • s-1) prior to quenching the catalysts.

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