Nano- and Microcrystals of Molybdenum Trioxide and Metal-Matrix Composites on their Basis (pp. 147-179)
Authors: (Tatyana V. Sviridova, Larysa I. Stepanova, Dmitry V. Sviridov, Institute for Physico-Chemical Problems, Belarusian State University, Minsk, Belarus, and others)
Abstract: The chapter is concerned with the morphology-controllable solvothermal synthesis of nano- and microcrystals of molybdenum trioxide (including the hexagonal h-MoO3) in the form of spherical nanoparticles, fibers and prisms using the molybdic acid as the starting material. The mechanism of crystal growth and the major factors controlling the structure and habitus of the resultant crystals are discussed in detail. The synthesis employing thermoinduced polycondensation of oxo-anions in solution can be readily combined with chemical dispergation of grown oxide phases that opens novel degrees of freedom in preparation of MoO3 morphologies. On the basis of solvothermal technique, the synthetic routes yielding spherolites of different size and rod-like particles with different aspect ratio can be developed.
Particular attention is paid to practical applications of the molybdenum trioxide phases obtained by solvothermal method, with special emphasis on their employment as the reinforcing phases for metal-matrix composites. Thus, the layered structure inherent in h-MoO3 makes it a promising high-temperature lubrication material. The incorporation of h-MoO3 microcrystals in the deposit of galvanic nickel yields metal-matrix composite
that retains its antifriction properties under heating. By contrast, co-deposition of nickel with MoO3 nanoparticles leads to the metal-matrix composites with extra-high wear resistance resulting from the dispersion hardening. The redox properties exhibited by molybdenum trioxide facilitate the overgrowing trapped MoO3 particles with a metal layer that results in their rapid and efficient encapsulation with matrix metal and strong bonding in the composite coating.