Advanced Materials Research Vol. 795

Abstract: Shielding concretes of different iron filling contents were assessed for their anti radiation attenuation properties. The measurements have been performed by using gamma spectrometer of NaI (Tl) detector, the sources were Cs¹³⁷ and Co⁶⁰ radioactive elements with photon energies of o.662 MeV, for Cs¹³⁷ and the two 1.17MeV, 1.33 MeV energy levels for the Co⁶⁰. Likewise, the mean free path of the tested samples was obtained as well. From the measurement of the linear attenuation coefficients for these different shielding materials, it was found that as the iron filings within the concrete are increased the linear attenuation coefficient is increased also. It can be concluded from this work that the Iron filings content in concrete is very effective in augmentation of the anti-radiation shielding capability. It can be used as shelters material for secure storing of the nuclear wastes.

Abstract: This paper represents the mechanical and microstructure changes in geopolymeric material synthesized by the alkali activation of locally source fly ash at high temperatures of 400, 600 and 800 °C. The high compressive strength of geopolymer cured at 70 °C underwent thermal shrinkage and substantial strength losing at temperatures of 400, 600 °C caused by the high dehydration of the structural water. Exposure to temperature of 800 °C, the geopolymer lost its strength due to extremely densification and expansion processes of the high unreacted silicate phase in the structure. The SEM results showed that the high activator content generated large quantities of unreacted silicate crystals at high temperatures which sintered at range of temperatures of 700-800 °C causing system failure.

Abstract: The study was undertaken to determine the extraction of proteins from chicken meat. The effect of buffer (phosphate, citrate and glycine) and four pH values (6.0, 7.0, 8.0 and 9.0) were investigated. The protein extractability of phosphate, citrate and glycine buffer with in the pH range (pH 6.0 to 9.0) was assessed to determine the best protein extractant for chicken meat. The maximum protein extractabilities at pH 8.0 for phosphate and citrate buffer, and at pH 9.0 for glycine buffer were observed. ANOVA analysis showed that there was no significant difference in protein extractabilities for citrate from phosphate and glycine buffer. Whereas, a significant difference was observed for phosphate buffer from glycine. However, no significant effects of pH were observed.

Abstract: The effect of retrogression and reaging heat treatment on microstructure evolution andmechanical properties of 7075 Al alloy in direct chilling casting process was investigated. The subsequent heat treatment process comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then reaging at 120°C for 24 h. By this three-step process, the mechanical properties of the chilled casted samples were substantially improved. The samples retain their high strength at T6 level. They gave yield strength up to 290 MPa, ultimate tensile strength of 386 MPa and elongation of 5.9%. The average value of multiple Vickers hardness tests results were in the range of 210 Hv. The direct chilling process followed by retrogression and reaging heat treatment yielded casts of fine and uniform microstructure as opposed to the microstructure of samples casted by the conventional process.

Abstract: Porous silicon structures have been fabricated by electrochemical etching using different current density. From field emission scanning electron microscope images (FE-SEM) it was observed that more uniform distribution of pores is obtained when the current density was increased from 20mA/cm² to30 mA/cm2. The porosity is estimated based on the analysis of FE-SEM and gravimetric analysis, the results were confirmed by reflectivity measurements which show that the high current density and porous samples have low reflection for wide spectrum. Results show good improvement in the solar cell efficiency.

Abstract: The formation of anodic aluminium oxide (AAO) membrane in anodising process has been studied. The anodising process was done in two different type of electrolyte which are single phosphoric acid and a mixture of phosphoric acid and acetic acid. This study was done to determine the influence of this mixed electrolyte toward the formation of AAO membrane. The anodising voltage was control from 90V to 130V while concentration, time, and temperature were kept constant at 1M, 60 minute and 15°C respectively. The characterisation of the AAO membrane was done by using scanning electron microscopy (SEM). The results of this study confirm that the addition of organic acid in the acidic based electrolyte resulted to the larger pores size of AAO membrane.

Abstract: Cadmium sulfide (CdS) nanostructures were prepared with different spin coating speed 1000 and 3000 rpm and molarities of Cd:S to be 1.2 to 0.01 mol/L using sol-gel spin coating technique. It is found that the average grain size of CdS nanostructures deposited on glass substrates at 1000 and 3000 rpm is 43 to 4 nm respectively. The effect of grain size on the semiconductor properties are in agreement with experimental and theoretical data.

Abstract: Silicon carbide reinforced copper matrix (Cu-SiC_p) composites fabricated via the conventional powder metallurgy methods have inferior thermophysical properties due to the weak bonding between the copper matrix and the SiC_p reinforcement. In order to improve the bonding between the two constituents, the SiC_p were copper coated via electroless coating process. Based on the experimental results and findings, a continuous copper deposition on the SiC_p was obtained via the electroless plating process. The copper film was found to be high in purity and homogeneously deposited on the SiC_p surfaces. The thickness of the coated copper layer was roughly estimated to be around 1μm.

Abstract: The demand for advanced thermal management materials such as silicon carbide reinforced copper matrix (Cu-SiC_p) composites is increasing due to their high thermal conductivity and low CTE properties. However, the weak bonding between the copper matrix and the SiC_p reinforcement degrades the thermophysical properties of the composites. In order to improve the bonding between the two constituents, the SiC_p were copper coated (Cu-Coated) via electroless coating process. Based on the experimental results, the CTE values of the Cu-Coated Cu-SiC_p composites were found significantly lower than those of the non-Coated Cu-SiC_p composites. The CTEs of the Cu-Coated Cu-SiC_p composites were in agreement with Kernels model which accounts for both the shear and isostatic stresses developed in the component phases.

Abstract: The widespread use of metal matrix composites as the packaging materials is due to their tailorable thermal conductivity and coefficient of thermal expansion (CTE). For the same reason, silicon carbide reinforced copper matrix (Cu-SiC_p) composites are highly rated as thermal management materials in the electronic packaging applications. However, the Cu-SiC_p composites fabricated via the conventional powder metallurgy methods have inferior thermophysical properties due to the presence of porosity in the interface of copper matrix and the SiC_p reinforcement. In order to improve the bonding between the two constituents, the SiC_p were coated with copper via electroless coating process. Based on the experimental results, the CTE values of the copper coated Cu-SiC_p composites were found significantly lower than those of the non-Coated Cu-SiC_p composites. The CTEs of the composites tend to decrease as the porosity increases. The significant difference in the CTE values was related to the presence of sub-micron gap between the copper matrix and the SiC_p reinforcement.