A.V. Shishkin

Formation of ZnO at zinc oxidation by near- and supercritical water under the constant electric field

The work has detected an influence of a constant electric field (up to E = 300 kV/m) on the structure of a nanocrystalline layer of zinc oxide, formed on the surface of a planar zinc anode in water under supercritical (673 K and 23 MPa) and near-critical (673 K and 17. 5 MPa) conditions. The effect of an increase of zinc oxidation rate with an increase in E is observed under supercritical conditions and is absent at near-critical ones. Increase in the field strength leads to the formation of a looser structure in the inner part of the zinc oxide layer.

Synthesis of MoO2 particles during oxidation of bulk molybdenum samples by supercritical water

It was found that bulk samples of molybdenum 〈Mo〉 are oxidized by supercritical water forming nanoparticles of monocline MoO2. The average size of nanoparticles obtained at uniform heating of 〈Mo〉 with supercritical water was about 27 nm, and the size of agglomerates of nanoparticles was ≤ 1 μm. From time dependence of the amount of formed H2nH2(t), we have determined kinetic parameters of 〈Mo〉 transition to MoO2 particles. The dependence dnH2/dt is characterized by the presence of two pronounced maxima. This is explained by the change of mutual diffusion of H2 and H2O molecules along with the growth of thickness of the layer of MoO2 nanoparticles.

Synthesis of nanostructured ZnO at oxidation of liquid Zn by supercritical CO 2

The synthesis of nanoparticles (ZnO)_n was found out at study of liquid zinc (Zn)_L oxidizing by supercritical CO₂. This process called as chemical recondensation (CR). It was determined that depending on CR conditions the nanoparticles with size of 5-50 nm and the nanoneedles with diameter of 25.100 nm, length of up to 50 mum are synthesized. For CR of (Zn)_L in CO₂ the cluster mechanism is suggested and kinetic parameters are estimated. Besides (ZnO)_n at zinc CR in CO₂ carbon and CO are formed.

Mechanism and kinetics of zinc oxidation by sub- and supercritical water

Bulk solid (Zn)_S and liquid zinc (Zn)_L samples are oxidized by water with the formation of nanodimensional ZnO. The rate of this process, called chemical recondensation (CR) by water, increases with temperature and water density rise. The CR process begins with the formation of (ZnO)_n clusters via the reaction (Zn)_S,L + nH₂O = [(Zn)_S,Lmiddot(ZnO)_n] + nH₂, followed by their growth at n > 4. The CR of solid Zn leads predominantly to the formation of nanowires and nanorods, while the CR of liquid Zn practically always proceeds with the formation of nanoparticles. The complete CR of solid Zn cylinders results in the formation of highly porous nanostructural ceramics.

Zinc oxidation by H 2 O/CO 2 mixture under sub- and supercritical parameters

At oxidizing of liquid zinc by H₂O/CO₂ mixture at supercritical parameters it is found the formation of nanoparticles (ZnO)_n with size from 1.5 to 100 nm and combustible substances: H₂, CO, lower paraffin and aromatic hydrocarbons, alcohols and formaldehyde. Composition of combustible products depends on H₂O/CO₂ ratio in mixture. Synthesized ZnO samples were studied by methods of scanning and transmission electron microscopy, thermal analysis.