A. Zakeri,, M. Sh. Bafghi, Sh. Shahriari,
Volume 4, Issue 3 (12-2007)
Abstract
Abstract: In this paper, kinetics of reductive leaching of manganese dioxide ore by ferrous ion in
sulfuric acid media has been examined. Experimental results show that increasing temperature
from 20 to 60 °C and decreasing ore particle size from −16+20 to −60+100 mesh considerably
enhance both the dissolution rate and efficiency. Molar ratios of Fe2+/MnO2 and H2SO4/MnO2 in
excess to the stoichiometric amounts were needed for successful manganese dissolution. Under the
optimum condition (ore particle size of −60+100 mesh, Fe2+/MnO2 molar ratio of 3.0,
H2SO4/MnO2 molar ratio of 2.0) manganese could be extracted with over 95% efficiency by 20
minutes leaching at room temperature. A kinetic analysis based on dimensionless time method
showed that shrinking core – ash diffusion control model fits the experimental results reasonably
well. Value of activation energy was found to be 28.1 kJ/mole for the proposed mechanism.
N. Khatami , Sh. Mirdamadi,
Volume 11, Issue 1 (3-2014)
Abstract
The presence of alloying elements, sometimes in a very small amount, affects mechanical properties one of these elements is Boron. In Aluminum industries, Boron master alloy is widely used as a grain refiner In this research, the production process of Aluminum –Boron master alloy was studied at first then, it was concurrently added to 2024 Aluminum alloy. After rolling and homogenizing the resulting alloy, the optimal temperature and time of aging were determined during the precipitation hardening heat treatment by controlled quenching (T6C). Then, in order to find the effect of controlled quenching, different cycles of heat treatment including precipitation heat treatment by controlled quenching (T6C) and conventional quenching (T6) were applied on the alloy at the aging temperature of 110°C. Mechanical properties of the resulting alloy were evaluated after aging at optimum temperature of 110°C by performing mechanical tests including hardness and tensile tests. The results of hardness test showed that applying the controlled quenching instead of conventional quenching in precipitation heat treatment caused reduction in the time of reaching the maximum hardness and also increase in hardness rate due to the generated thermo-elastic stresses rather than hydrostatic stresses and increased atomic diffusion coefficient as well. Tensile test results demonstrated that, due to the presence of boride particles in the microstructure of the present alloy, the ultimate tensile strength in the specimens containing Boron additive increased by 3.40% in comparison with the specimens without such an additive and elongation (percentage of relative length increase) which approximately increased by 38.80% due to the role of Boron in the increase of alloy ductility
