Papers by Author: Hekmat Razavizadeh

Abstract: In this research Cu-Ni nanostructure powders were prepared by using a chemical procedure including initial precipitating, calcining the precipitates and reducing the calcined powders. The influence of nickel contents on the characteristics of the synthesized powders was investigated. Copper and nickel sulfate and sodium hydroxide were used as raw materials. CuSO4.3Cu(OH)2, NiOOH and Ni(OH)2 precipitates were obtained by addition of sodium hydroxide into aqueous copper and nickel sulfate solution. Oxide powders were produced by calcinations of precipitates. Considering the information obtained from the TGA test, calcination was done on precipitates. Copper-nickel nanostructure powders were synthesized by reduction of calcined powders in a hydrogen atmosphere. Eventually powders were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallite size of final synthesized powders was in the range of 30 to 33 nm.

Abstract: With the rising cost of zinc reaching historic levels, more emphasis is being placed on technologies to increase the efficient utilization of zinc. One area targeted for increased efficiency is in-house recycling of metallic zinc industrial wastes. The largest consumer of zinc is the hot-dip galvanizing of steel. Large amount of zinc slag containing more than 50% zinc, are accumulated during galvanization processes at the surface of molten zinc bath and is usually skimmed manually. At First, The pyrometallurgical recovery of zinc from slag samples was carried out, and parameters affecting recovery processes such as time, temperature, and flux percentage were studied. The results obtained revealed that zinc metal is successfully recovered from these secondary resources. The recovery efficiency is 70% for zinc waste materials having a particle size diameter of + 1.25 mm. An optimum percentage of 25% weight of ammonium chloride fluxing agent was obtained. The optimum temperature for the recovery process was 700°C.

Abstract: A homogeneous precipitation process was employed to prepare nanosized W-10%wtCu-10%wtAg powders using ammonium meta tungstate, copper nitrate and silver nitrate as precursors. The initial precipitates were obtained by reacting ammonium meta tungstate, copper nitrate and silver nitrate solutions under certain PH and temperature. In order to synthesis W-Cu-Ag composite powders, the initial precipitates washed, dried, and then calcined in air in order to prepare CuWO4-x, Ag2W4O13 and WO3 oxide powders for the next step reduction. The reduction was carried out in a hydrogen atmosphere to form the final W-Cu-Ag nanocomposite powders. The powders were characterized by X-ray diffraction (XRD) technique. The morphologies of the powders were observed by scanning electron microscopy (SEM).

Abstract: W-25%Cu nanocomposite was produced via a thermochemical co-precipitation procedure. Copper nitrate and sodium tungstate salts were used as Cu and W containing precursors respectively. Aqueous solutions of these salts were reacted under controlled pH condition prepared by ammonia addition and the resulting precipitates were then calcined at 450oC and hydrogen reduced at 800oC. The products of each step were characterized by XRD and Electron Microscope. Using a basic medium with a pH of 13 which caused the formation of complex Cu(NH3)42+ was found to provide suitable condition for precipitation of nanosized composite powders. Cu2WO4(OH)2 and CuWO4.2H2O as raw precipitates, CuWO4-x , CuO, and WO3 as calcined powders, and W-Cu reduced composite powders, all were seen to keep nanosize dimensions through high temperature treatments of fabrication. Sintering of the reduced powders at the temperature of 1150oC led in a density of about 98% theoretical density.

Abstract: Titanium Aluminide-based composites with Al2O3 reinforcement can be produced via reaction of Al with TiO2. These composites are considered as low-cost materials for high temperature applications. Addition of KClO4 to the TiO2/Al system was investigated in this research. On the basis of the results obtained, addition of KClO4 to the mixture of TiO2/Al and subsequent heating, results in titanium aluminide/alumina nanometric particle formation with dimensions of about 30 nm. Densification of this composite powder leads to production of a titanium aluminide-alumina nanocomposite body. Dimensions of the alumina phase are in the range of 100-150nm.