Andrei V. Ragulya

Liquidus surface in the HfO2-Y2O3-La2O3 system

The liquidus surface in the HfO2-Y2O3-La2O3 system was studied by differential thermal analysis in helium at temperatures of up to 2500°C, derivative thermal analysis in air at temperatures of up to 3000°C, x-ray diffraction, optical microscopy, and electron microscopy. The liquidus surface was found to comprise five primary crystallization fields-those of theH-Y2O3-,C-Y2O3-,F-HfO2-, andX-La2O3-based solid solutions and the pyrochlore phase La2Hf2O7. Three invariant equilibria were identified in the system studied-two peritectics and one eutectic.

Fe-catalyzed synthesis of SiC nanofibers from methyltrichlorosilane

We have studied Fe-catalyzed chemical vapor deposition of silicon carbide nanofibers via thermal decomposition of methyltrichlorosilane, CH3SiCl3, in hydrogen at temperatures from 1100 to 1350°C and the effects of synthesis temperature and time and gas (CH3SiCl3 + H2) flow rate on the growth rate of SiC nanofibers. In the temperature range 1100–1350°C, the activation energy for nanofiber growth is 120 kJ/mol. The SiC nanofibers have the stoichiometric composition and consist of single-crystal β-SiC (cubic structure).

Laser Sintering of SiO2 Powder Compacts

Regularities of sintering compacted SiO2 powder under the action of a CO2-laser are studied by experiment. Features are considered for rebuilding the structure of a powder body (particle regrouping, formation of interparticle contacts, joining of particles into conglomerates, evolution of the porous structure) in different stages of sintering (with different laser irradiation duration). Sintering is accomplished by a liquid-phase mechanism (by melting particles and joining solid unmelted cores by the liquid phase formed). The results obtained may be used for developing laser sintering methods for ceramic powders.