材料科学与工程杂志

Experiments were conducted on several alloys representing the Al-Cu-Ag-Mg system to determine the applicability of using these alloys for AM. Alloys were formulated and prepared utilizing a powder blending technique using a pre-alloyed master alloy powder containing Al, Mg, Ti, and Zr with elemental powders of pure Cu and Ag. These powder were processed using laser-based directed energy deposition to produce specimens that were treated to represent the post-process aged only and post-process solution heat treated and aged conditions. Microhardness and microstructural characterization was then conducted. Results of this investigation showed that an aluminum alloy containing between 6 and 8% Cu and 1 to 4% Ag, while also containing 0.3% Mg, Ti, and Zr, displayed excellent response to precipitation strengthening for both post-process treatments. Alloys that were completely solutionized and aged after processing where able to achieve microhardness values exceeding 180 VHN, which are significantly higher than the commonly used Al-10Si-0.5 Mg alloy for AM processes. The high microhardness achieved with the experimental alloy could be attributed to a uniformly distributed network of fine θ’ and Ω precipitates, which was confirmed through TEM. Depending upon the desired post processing treatment (aging only or solutionizing and aging), the results indicate that an alloy composition within this system may be defined to provide optimal strength.

Recycling is the process of making or bringing out new products from a product that has originally served its purpose. The use of non-woven for noise reduction is based on two major advantages of these materials, namely low production costs and small specific gravity. Through this thesis, an attempt was made and implemented an innovative technique of developing stitch bonded non-woven by using recycled fiber. Knitted wastes were collected from cut and sew knitwear factories and recycled by using fabric opening machine in Adey abeba textile factory. The opened fibers are carded by mechanical carding machine by varying the number of layers. Six nonwoven samples are manufactured by stitching the web structure with core spun yarn. The manufactured reclaimed fiber stitch bonded nonwoven sound absorption coefficients were measured according to ASTM E 1050 standard by an impedance tube. The results revealed that the sound absorption coefficient increased with increasing frequency level of 500 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz and 3000 Hz. Factors influencing sound absorption of nonwoven materials such as fabric thickness, areal density, air permeability and thermal conductivity were tested. The results revealed that while thickness increases the sound absorbing performance also increases. Low frequency sound absorption has direct relationship with thickness. However, at higher frequencies thickness has insignificant effect on sound absorption. Less dense and more open structure absorbs sound of low frequencies. Denser structure performs better for frequencies above 2000 Hz. Air permeability of the stitch bonded nonwoven decreases the sound absorption performance increases. The mechanism of sound absorption was conversion of sound energy in to heat but the effect of thermal conductivity of stitch bonded nonwoven structure was very small.

The paper shows that the presence of aluminium oxide is conditioned by the residual air content in the chamber, which deteriorates the coating quality. In this connection, the residual pressure and content of aluminium oxide were calculated in the chamber of the circulation setup.

The discovery of a steel nail in the concrete wall of a cistern of possible high-imperial Roman origin (1st century BC and 1st century AD) has made it possible to date this construction chronologically. Until now, no method of dating concrete has been possible; however, the metallographic study of this nail gives clues for chronological dating. The existence on the nail of microstructures that reveal the existence of old perlite can be a clear fact in the chronology of the steel nail and the wall where it was found inside.

A kinetic study evaluating heterogeneous transesterification of soybean oil was performed using zeolite from coal fly ash as a catalyst, under reaction conditions with different temperatures and reaction times. The catalyst characterization revealed that zeolite type hydro-sodalite was synthesized and consists of mesoporous agglomerates particles with a specific surface area of 7.53 m² g-1 and a basic catalytic character. The conversion rate of soybean oil to its methyl esters was found to increase with an increase in temperature. An ester yield of 92.5% was the highest methyl ester achieved at 65°C and at a 12:1 methanol-to-oil molar ratio. The reaction followed pseudo-first order kinetics with a calculated activation energy (Ea) of 27.23 kJ mol-1.

For targeting the cancer cells, a low pressure ICP reactor was utilised to fabricate a drug delivery system. On the surface of biocompatible collagen membranes, thin plasma polymer coatings were deposited to encapsulate an anticancer drug carboplatin and impart different biologically active functionalities. The characteristics of the deposited films were analysed by FTIR and XPS and the overall functionalities were tested by in vitro and in vivo experiments on the cancer cells lines on the cancer nodules respectively. Preliminary results of fabricated drug delivery systems showed the inhibition of cancer cell proliferation in vitro as well as tumour growth in mice models by 2.8 folds in mass compared to the control case