Islam S. Humail

Morphology and microstructure characterization of 95W-3.5Ni-1.5Fe powder prepared by mechanical alloying

Abstract The mechanism of mechanical solid-state reactions for formation of tungsten heavy alloy powder was discussed. A high-energy ball mill operating at room temperature was used for preparing tungsten heavy alloy powders, starting from elemental tungsten (W), nickel (Ni), and iron (Fe) powders. X-ray diffraction (XRD), particle size analyzer, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to follow the progress of the mechanical solid-state reaction of W, Ni, and Fe powders. These morphological studies revealed three stages in the milling process. In the first stage, the particle deformation changes the irregular structure of the as-received powder particles to flattened morphology, and the average particle size increases. In the second stage, the powder is sufficiently deformed and the tendency to fracture predominates over welding, and the particle size decreases. With continuous milling, the system reaches steady state, and relatively small and uniform particle size distribution is obtained after 20 h of milling.

Influence of binder composition on the rheological behavior of injection-molded microsized SiC suspensions

The influence of four kinds of binders consisting of paraffin wax (PW), random-polypropylene (RPP), high-density polyethylene (HDPE), and stearic acid (SA) on the rheological behavior of injection-molded SiC feedstocks was investigated over a temperature range of 150°C to 180°C and a shear rate range of 4 s−1 to 1259 s−1. The results showed that all the feedstocks exhibited pseudoplastic flow behavior. The wax-based binder of multipolymer components (PW-RPP-HDPE) exhibited better comprehensive rheological properties compared with the binder of monopolymer components (PW-RPP or PW-HDPE). The addition of 5wt% SA to the binder could reduce the viscosity of the feedstock but enhance the rheological stability by improving the wettability between the binder and the SiC powder. The binder of 65wt% PW + 15wt% HDPE + 15wt% RPP + 5wt% SA was found to be a better binder for microsized SiC injection molding.

Effect of different additives on the properties of lithium alanate

LiAlH4 doped with Ni and Ce(SO4)2 additives and the effect of doping on temperature and hydrogen release were studied by pressure-content-temperature (PCT) experiment and X-ray diffraction (XRD) analysis. It is indicated that doping with Ni induces a significant decrease in temperature in the first step and LiAlH4 doped with 1mol% Ni presents the most absorption of hydrogen. Doping with Ce(SO4)2 also causes a marked decrease, while the amount of hydrogen release changes only slightly. The results from X-ray diffraction analysis show that doping does not cause any structural change; Ni and Ce-containing phases are not observed at room temperature or even at 250°C.

Effects of Different Debinding Atmosphere on the Properties of Powder Injection Molded AlN Ceramics

In the present work the influence of two different thermal debinding atmosphere, vacuum and air, on the properties of 5wt% Y2O3-doped aluminum nitride (AlN) ceramics was investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compact was fabricated by employing powder injection molding technique. The polymer-wax binder consists of 60wt% paraffin wax (PW), 35wt% polypropylene (PP) and 5wt% stearic acid (SA). The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. After the removal of binder, specimens were sintered at 1850˚С in nitrogen atmosphere at atmospheric pressure. The result reveals that debinding atmosphere has significant effect on the thermal conductivity and densification of AlN ceramics. The microstructure and secondary phase identification was determined by scanning electron microscopy and X-ray diffraction. The thermal conductivity and density of injection molded AlN ceramics are 177.3W·m-1·K-1 and 3.31g·cm-3 in the air and 200.8W·m-1·K-1 and 3.28g·cm-3 in the vacuum.