N. Ikram

X-ray diffraction analysis of silicon prepared from rice husk ash

Polycrystalline silicon has been prepared by metallothermal reduction of rice husk ash, which contains a considerable amount of amorphous silica. Acid-leached rice husk was burnt at a temperature of 620° C to obtain rice husk ash (RHA). RHA was then reduced with magnesium and major impurities were minimized or removed by an acid leaching process. The end-product was analysed using X-ray diffraction and mass spectrometric techniques. It was found that the powdered silicon obtained from magnesium reduction of RHA had a very low impurity concentration indicating that rice husk, which is an agricultural waste, is a potential source of metallurgical and solar-grade silicon.

Spin-Polarized Structural, Electronic, and Magnetic Properties of Diluted Magnetic Semiconductors Cd1-xMnxS and Cd1-xMnxSe in Zinc Blende Phase

We studied the structural, spin-polarized electronic band structures, density of states, and magnetic properties of the diluted magnetic semiconductors (DMSs) Cd(1-x)Mn(x)S and Cd(1-x)Mn(x)Se in zinc blende phase (B3) with 25% Mn by using the ab initio method. The calculations were performed by using the full potential linearized augmented plane wave plus local orbitals (FP-L/APW+lo) method within the spin-polarized density functional theory and the local spin density approximation (LSDA). Calculated electronic band structures and the density of states of these DMSs are discussed in terms of the contribution of Mn 3d(5)4s(2), Cd 4d(10)5s(2), S 3s(2)3p(4), and Se 4s(2)4p(4) partial density of states and we also compute the local magnetic moments. We estimated the spin-exchange splitting energies, Delta(x)(d) and Delta(x)(p-d), produced by the Mn 3d states, and we found that the effective potential for the minority spin is more attractive than that for the majority spin. We determine the s-d exchange constant N(0)alpha and p-d exchange constant N(0)beta, which resembles a typical magneto-optical experiment. The calculated total magnetic moment is found to be 5.0020 and 5.00013 mu(B) for Cd(1-x)Mn(x)S and Cd(1-x)Mn(x)Se, respectively. These values indicate that every Mn impurity adds no hole carriers to the perfect CdS and CdSe crystals. Moreover, we found that p-d hybridization reduces the local magnetic moment of Mn from its free space charge value of 5.0micro(B) and produces small local magnetic moments on the nonmagnetic Cd and S sites.

Microstructure studies in Al-6% Si-1.9% Cu-x% Mg alloys

The nature of precipitates formed in the aged Al-6% Si-1.9%Cu-x%Mg alloys (where x varies from 0.2 to 1.13) was investigated using scanning and transmission electron microscopy. Vickers hardness and grain size were measured. Results showed peak hardness around 4 and 10 h ageing time for 0.54% Mg and 1.13% Mg alloy, respectively. Hardness was found to increase with increasing magnesium content except for the 1.13% Mg alloy aged for 10 h. Q-phase particles have been observed and these are most probably responsible for the variation of hardness.

The effect of boron addition on the tensile properties of control-rolled and normalized C-Mn steels

Control-rolled and normalized C-Mn steels with and without boron alloying at two finish rolling temperatures of 800 °C and 1000°C were studied with respect to their tensile properties in order to investigate the role of boron in enhancing the strength of these materials. It was found that in boron steels ultimate tensile strength increased and impact transition temperature decreased owing to a decrease in grain size and an increase in pearlite fraction at both the finish rolling temperatures.

Resistivity change due to short-range order and size-effect correction in Ni-Al alloys

Abstract The influence of short-range ordering in Ni-Al solid solutions on electrical resistivity has been calculated. The atomic potential for nickel and aluminium were obtained in the Pseudopotential formalism. It is found that short-range order in Ni 100− x Al x decreases the electrical resistivity by about 3–7 per cent of its value for random configuration. The size-effect correction causes a further decrease of about 2–5 per cent. It is further noticed that at a given composition, the resistivity for Ni-Al alloys due to short-range order increases with decreasing temperature in accordance with the experimental results.