P. Zarrabian, M. Kalantar, M. Mosallaeepour, A. Mashreghi,
Volume 33, Issue 3 (3-2015)
Abstract
Nickel ferrite based cermets and their relevant composites have been widely used as inert anodes for aluminum electrolysis due to their good combination of chemical resistance, thermal stability and mechanical properties. In this study, various NiO/NiFe2O4 composites consisting of 5, 10 and 15% NiO in conjunction with Cu/NiFe2O4 cermets containing 0.5, 10 and 15% Cu were prepared by powder metallurgy method. The degradation resistance of the developed inert composites was examined under hot corrosion condition by plunging samples in to the molten electrolyte at 1000ºC. The strength, toughness, hardness, relative density, microstructural observation, phase analysis and electrical resistivity were evaluated by 3-points bending tests, Vickers method, Archimedes method, scanning electron microscope, x-ray diffraction and conventional direct current four-probe techniques, respectively. The experimental results for NiO/NiFe2O4 composites showed that a significant improvement of toughness and degradation resistance continuously occurred with a moderate decrease in strength by increasing NiO content, while the relative density was increased only up to 5%NiO content. By increasing the Cu content in the cermet samples, all the properties such as strength, toughness and electrical conductivity were improved considerably but the degradation resistance decreased.
A. Amiri Moghaddam, M. Kalantar,
Volume 36, Issue 1 (6-2017)
Abstract
The aim of this investigation is obtaining WC-Co composite powder from WO3 and Co3O4 by in-situ and carbothermic reduction method using activated carbon as a reducing agent. In this study, cobalt and tungsten oxide powders with 17% carbon (30% more than stoichiometric value) were mixed by ball-milling under atmosphere of argon for 20 hours. Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA) results on powder mixture show complete reducing of oxides at 1050°C and forming cobalt carbide and tungsten carbide. Compact samples underwent carbothermic reduction at 1050 °C for different times of 1, 2 and 4 hours with protective layer of alumina and carbon powder mixture with ratio of 1:1. Based on X-Ray Diffraction (XRD) analyses, the best holding time in furnace is 4 hours, in which tungsten reduction and carbonization is completed. XRD evaluation of reduced compacted samples in three conditions of atmosphere protective layer of alumina and carbon powder mixture with ratio of 1:1, protective foil of refractory steel and argon, shows that unreduced oxides and extra phases are present in argon atmosphere and protective foil of steel but not in alumina and carbon mixture layer. The measurement results of physical and mechanical properties on the sintered composite sample in heating rate of 5 °C /min to temperature 1500 °C and the holding time of 2 hours under a shielding layer of alumina and carbon shows obtaining the optimal properties (Pr=80%, KIC=8.1 MPa , MHV=15.67GPa) comparable to that of advanced and costly methods.
