Papers by Author: Viorica Muşat

Abstract: Lead hardened through oxide scattering is investigated as raw materials for the fabrication of the support gratings of lead accumulators in order to increase their life service. For the preparation of lead powder hardened through oxide scattering we used air jet pulverisation, a technique specific to powder metallurgy. Two research approaches are presented in the paper: one in which the oxide was introduced through oxidised lead powder, and the other in which additional lead oxide was introduced. Oxide dispersion into metallic matrix was achieved by pronounced deformation through extrusion of the powder. During extrusion, the particles are compelled to pass through the mould calibration zone and consequently they are considerably deformed. As an effect of this deformation, the particles of fragile oxide which cover the lead powder particles are crashed and carried away to the material flowing through the matrix longitudinally on the extruded semiproduct. The content of oxide introduced in matrix by the oxidised lead powder depends on the powder particle size. This paper presents the effect of the powder particle size and oxide phase dispersion in the metallic matrix on the mechanical, chemical and electrical properties of the extruded semi-products. The semi-products made from lead powder belonging to the grain size class of < 40 µm and oxide particles allowance have the highest mechanical resistance and the best corrosion behaviour. Using controlled oxidised lead powder better extruded semi-products are obtained in terms of mechanical resistance, corrosion behaviour and electrical conductivity as compared with lead and Pb-Sb alloy. A higher electrical conductivity represents an important advantage especially for the starting accumulators where the voltage fall should be as low as possible.

Abstract: The thermoreactivity of a zinc acetate non-alkoxide solution used for the preparation of ZnO-based thin films was investigated in the temperature range 20-600°C by TG-DTA, XRD and SEM data. We found that the formation in air of ZnO crystallites from the sol-gel precursor occurs above 150°C simultaneously with the decomposition of an intermediary compound, most probably carbonate hydroxide (sclarite and/or hydrozincite). At 200 °C, the crystalline structure is well defined in terms of ZnO hexagonal lattice parameters, although residual organic compounds and water were not yet fully removed and an amorphous phase coexists. A kinetic investigation on the thermal decomposition of sol-gel precursor from DTA data using Kissinger differential equation is also presented. Apparent activation energy values of about. 100 kJ mol-1 corresponding to the nonisothermal decomposition of solid precursors in the temperature range 170-250oC have been found.