Structural and dielectric properties of barium strontium, titanate (Ba(ÿ)SrxTiO$) ceramics with x—
0.25, 0.5 and 0.75 were investigated. The Ba(i-xjSrxTiOs ceramics were synthesised by solid state
reaction method. Microstructure, surface morphology and dielectric properties of the synthesised
ceramics were examined using XRD, SEM and Impedance Spectroscopy respectively. XRD results
revealed that all samples contained BaTiOg as primary phase with tetragonal perovskite crystal
structure. The crystallite size slightly increased with the increasing of Sr contents. SEM micrographs
showed that the microstructure become denser when Sr contents increased. Impedance spectroscopy
showed dielectric constant for all samples were decreased with increasing temperature up to 200°C.
Al/B4C composites with 0 wt.%, 5 wt.% and 10 wt.% of B4C were prepared by powder metallurgy and their properties were characterised successfully. Investigation of the effect of milling times (4, 8, 12, 16 hours) on microstructure, phase identification, hardness and neutron attenuation coefficient of composites has been studied. The results showed that hardness increased with increased of milling time, with maximum hardness obtained at 16 hours milling time. The increment is slower as the composition of B4C increased. The hardness of Al/10%B4C, Al/5%B4C and Al/0%B4C were 81.7, 78.7 and 61.2 HRB respectively. Morphology of scanning electron microscopy (SEM) showed that microstructures play important role in controlling the hardness. Meanwhile, x-ray diffraction (XRD) analysis showed the phases and crystalline present in composites with an indication that crystalline of the grain increased as the milling time increased. Neutron absorption of Al/10%B4C composites showed that this composite has the highest attenuation coefficient, thus indicating that it is the best composites for neutron shielding.
The preparation, physical and mechanical properties of Al/B4C composites with 5 and 10 wt.% reinforcement content were investigated. In order to obtain the feedstock with a low powder loading, B4C mixtures containing fine powders were investigated to obtain the optimal particle packing. The experimental results indicated that the fine containing 5 and 10 wt.% particles are able to prepare the feedstock with a good flowability. The composites fabricated by powder metallurgy have low densities and homogeneous microstructures. Additionally there is no interface reaction observed between the reinforcement and matrix by XRD analysis. The hardness of Al/B4C composites prepared by powder metallurgy was high.