Papers by Author: R. Ivănuş

Abstract: An experiment of lively biohydrometallurgical leaching of worn-out hydrogenation catalysts in an aerobic batch system with Thiobacillus ferrooxidans is carried out for process parameters optimization. The maximum bioleaching of worn-out catalysts is noticed at 74.85% (w/w) and 71.50% (w/w) for 25 kg Cu/m3 and 30 kg Cu/m3 initial concentration of 200 to 240 μm waste mesh size in 192 h with pH 2.5 and temperature 35°C, respectively. The optimum shaking speed is noticed as 60 rpm. All results are noted after subtraction of leaching in control conditions. Seven days age-old and 20% (v/v) innoculum culture is used in the present study. The dissolved copper was precipitated by the precipitation using metallic iron splinter. The copper powder obtained was characterized by chemical and physical methods.

Abstract: The powder metallurgy technique was adopted to prepare SiCp copper alloy matrix composites. The mechanical properties of the composites were measured to investigate the influence of processing parameters, SiC particle characteristics and metallic coating (copper) of the SiC particles. It was found that the mechanical properties of the composites prepared by pressing, sintering, re-pressing, and resintering are superior to those of composites prepared by the pressing and sintering route, and that sintering temperature was an important factor in controlling composite properties. Changes in hardness, theoretical density, ultimate tensile strength, and wear resistance of composites containing SiC of varying silicon carbide content were observed. In all cases, composites made from copper coated SiCp exhibited better properties than those from uncoated particles.

Abstract: Powders-based on the Fe-Cu-Ni-Mo system are well known in the P/M industry for combining good compressibility and dimensional stability with a potential for high strength. The typical heterogeneous microstructure of these materials has proven to provide favourable mechanical properties. However, in applications where strength and hardness become critical variables, faster cooling rates after sintering are required to meet application requirements. Test specimens containing various graphite contents to achieve 0.20, 0.35 and 0.55% combined carbon were pressed to 7.0 and 7.2 g/cm3, sintered in a furnace at 1150°C and cooled directly from sintering temperature with either normal or rapid cooling. Test results are discussed in terms of tensile properties, apparent hardness and microstructure. The formation of bainite and martensite by raising carbon content and cooling rate increased tensile strength and apparent hardness, while a higher green density maintained satisfactory ductility. It was possible to achieve ultimate tensile and yield strengths as 920 and 660 MPa respectively with apparent hardness 30 HRC.