Materials Science Forum Vols. 561-565

Abstract: Large-scale silicon carbide nanowires are prepared by pure silicon powder and phenolic resin, which are mixed, molded, carbonizated, and then subjected to the microwave heating with a rate of 10oC/min between 1300 and 1400oC in the static argon atmosphere for 0.5~2h. The patterns of the SiC nanowires are characterized by means of SEM, the composition of the samples are determined through EDX. The prepared nanowires have the diameters between 20 to 100nm. The current results imply that liquid silicon can act as a catalyzer during the formation of SiC nanowires.Introduction Since the discovery of carbon nanotubes by Iijima[1], there has been great interest in the synthesis and characterization of other one-dimensional (1D) structures. Nanowires, nanorods and nanobelts constitute an important class of 1D nanostructures, which provide models to study the relationship between electrical transport, optical and other properties with dimensionality and size confinemen[2~7]. The 1D nanowires can also act as active components in devices as revealed by recent investigations[8,9]. Up to now, several techniques for preparing SiC nanowires have been developed. Dai et al.[5] synthesized SiC nanorods via the reaction of carbon nanotubes with SiO. Zhou et al. [6] synthesized SiC nanowires by hot filament chemical vapor deposition (CVD). Liang et al.[9] grew SiC nanowires by carbothermal reduction of silica xerogels embedded with Fe nanoparticles, etc. However, many of these routes involved complex processes and high cost. The usage of metal catalyst for the vapor–liquid–solid (VLS) growth mechanism makes it difficult to remove the resident catalyst after the synthetic process. In this paper, it is reported that a simple and low cost synthetic route is developed for the preparation of SiC nanowires by microwave heating technique without any catalyst. The prepared nanowires have core-shell structure with the diameters between 20 to 100nm. The growth of these SiC nanowires is considered to involve a VLS process.

Abstract: This research carries out an inexpensive, rapid and novel exercise, which is applied to perform the photocatalyst decomposition effectiveness of Methanol and Ethanol in gaseous form. The major devices of this applicable measurement developed by this practice are only utilizing ultraviolet-visible spectrophotometer and quartz cuvette, and the experimental procedures are straightforward and speedy. In the conduct experiments, Methanol and Ethanol with a specific concentration is initially injected into an enclosed quartz cuvette. Then the cuvette is put in ultraviolet- visible spectrophotometer to measure the Methanol and Ethanol concentration, so as to obtain an unique UV absorbance spectrum at its particular concentration. In the conduct experiments of measuring photocatalyst decomposition efficiency, the self-made (SANSS) nanocatalyst TiO2 is initially coated in the quartz plate, and put into the quartz. Then a specific concentration of methanol alcohol and ethanol is injected into the quartz cuvette under the UV irradiation exposure, so as to carry out photodecomposition of Methanol and Ethanol experiment. After that, the cuvettes are then put into the ultraviolet-visible spectrophotometer for measuring the absorbance intensity of UV spectrums in order to produce degradation chart. The preliminary results point out that the self-made nanocatalyst TiO2 has exceptionally outstanding decomposition efficiency which further points out the fact that, when UV irradiation for 60minutes, the gaseous Methanol can be reduced to 3.8% of the original sample, and the gaseous Ethanol can be reduced to 6% of the original sample. But when exercising with commercial nanocatalyst TiO2 to undergo the same process exactly under the same circumstances, the residue gaseous concentration can only be reduced to 17% and 16% of the gaseous Methanol and Ethanol original sample.

Abstract: The addition of Ti and Zr to Ni-Ta binary alloys is effective for the increase in stabilization of supercooled liquid and glass-forming ability (GFA). As the Ti content increases, the supercooled liquid region
Tx and reduced glass transition temperature (Tg/Tl) of Ni60Ta40-xTix glassy alloys increase, show maximum values of 63 K at 20 at.%Ti and 0.589 at 25 at.%Ti, respectively, and then gradually decrease. The addition of 5 at.% Zr to Ni-Ta-Ti alloys lowers liquidus temperature (Tl), resulting in the higher Tg/Tl values of 0.600. The best GFA were obtained for Ni60Ta15Ti20Zr5 and Ni60Ta20Ti15Zr5 alloys and the glassy alloy samples with a diameter of 1.0 mm were fabricated. The new Ni-Ta-based bulk glassy alloys exhibit high Tg of ~897 K, large ΔTx of ~74 K, high strength of over 3180 MPa with plastic strains of ~0.4% and excellent corrosion resistance in 1 N HCl solution.

Abstract: Nano sized Co-20wt%Ni composite powder was synthesized by electroless chemical reduction method using metallic salt precursors and hypophosphite as a reducing agent in alkaline tartarate bath as a complexing agent. The synthesized powder provide better sinterability, mechanical, electrical and magnetic properties with homogeneous microstructure. The nano-sized powder could be obtained, which have the average particle size of 40 nm, with a saturation magnetization (Bs ) of 97.95 which was increased by heat treatments of powder in hydrogen to 127 emu/g due to the exclusion of the precipitated phosphrous in the composite powder. The powder underwent cold compaction at 600 Mpa and sintering at 1050 oC for 30 min. The saturation induction for the sintered material of 149.3 emu/g higher than the synthesized powder and has electrical resistivity value of 7.6 μcm.

Abstract: Present investigation was focused on to synthesize TiAl-Nb2Al nanocomposite powders by high energy ball milling from a mixture of prealloyed TiAl, niobium, aluminium and SiC powders. Systems chosen with different Nb and Al concentrations were processed at optimized ball milling parameters. The synthesized powders were characterized with the help of X-ray diffraction (XRD), electron microscopy, differential thermal analysis (DTA) to understand the milling behaviour of TiAl / TiAl-Nb-Al-SiC systems. High energy ball milling of prealloyed TiAl powder resulted nanocrystalline structure at early time intervals (10hrs) and sustained up to 50hrs. TiAl-Nb-Al-SiC systems exhibited amorphous structure in lower Nb content and formation of Nb2Al nanocrystalline compound with increasing Nb and Al additions. Stability of TiAl covalent bonded intermetallic compound was weakened by dissolution of Nb in the matrix and resulted amorphous structure. The final product contained nanocrystalline TiAl, amorphous structure and TiAl-Nb2Al intermetallic nanocomposite powders with varying Nb and Al concentrations.

Abstract: Phase constitution in the solution-treated and quenched state and the heat treatment behavior were investigated by electrical resistivity, hardness, and elastic modulus measurements, X-ray diffraction, and optical microscopy. Hexagonal martensite and the β phase were identified in the Zr-5mass%Nb alloy. β and ω phases were identified in the Zr-10 and 15mass%Nb alloys, and only the β phase was identified in the Ti-20Nb alloy. Resistivity at RT, Vickers hardness and elastic modulus increased up to 10Nb and then decreased dramatically at 15Nb. Above 15Nb, these values slightly decreased. The elastic moduli for 15Nb and 20Nb were 59.5 and 55.5 GPa, respectively. On isochronal heat treatment, the isothermal ω phase precipitated between 473 and 623 K and then the α phase precipitated in the 10Nb, 15Nb and 20Nb alloys.

Abstract: The production of natural hydroxyapatite (HAp) specifically from cortical bovine bones and natural calcite was studied in this paper. Bovine hydroxyapatite (BHA) was produced from bovine bone in bulk form by de-fatting continued with calcination at 900°C. Natural calcite hydroxyapatite (CHA) was produced by hydrothermal method. It was confirmed from XRD, FTIR, and SEM results that HA have been successfully produced from natural sources like bulk bovine bone and natural calcite. The results also show that the crystallinity of BHA is higher than CHA, matching with the hardness test results of sintered BHA and CHA.

Abstract: The effect of cold rolling on two-way shape memory was investigated by x-ray diffraction technique and TEM in a Cu-18Al-10.5Mn (at.%) alloy. Cold rolling leads to a preferred orientation distribution on the stress-induced martensite with 6M-structure, which leads to the dependence of two-way shape memory on the specimen directions. The relationship of stress state and anisotropy of 6M-structured martensite lattice inside cold rolling deforming region is elucidated through analyzing the deformation process-related variant selection according to original grain orientation.

Abstract: Bone mechanical function is given as a result of the material and structural parameters of bone tissue. We previously reported that the material parameter of regenerated bone can be evaluated dominantly using two indices of the density and the preferred orientation degree of biological apatite (BAp). In addition, bone morphology remarkably changes during bone regeneration, which may lead to a dynamic change in the mechanical function of whole bone. In this study, therefore, material and structural parameters of regenerated bone are analyzed separately. A 5-mm-long defect was introduced in rabbit ulna and spontaneously regenerated, and then a three-point bending test was conducted at the regenerated portion. The important parameter which dominantly controls the whole bone mechanical function shifts from a structural to material parameter during bone regeneration. Moreover, it was statistically demonstrated that the increase in the material parameter is strongly determined by recovery of the orientation degree of the BAp c-axis.