Abstract: The experimental results indicated that the WC-12wt% Co specimens showed excellent mechanical properties and microstructure by the optimal sintering process. The G5 specimen sintered at 1400°C/1 h achieved a relative density of 98% and a hardness of HRA 88.5. Meanwhile, the TRS increased to 2400 MPa. F12 specimens that sintered at 1350°C/1 h achieved a relative density of 99% and a hardness of HRA 92.5. The TRS was also enhanced to 2170 MPa. In this study, the η phase (Co3W3C) precipitated at a high sintering temperature. The precipitations generated by liquid phase sintering gathered in some specific regions of the specimens and reacted with the WC particles. In addition, Co3W3C was a hard and brittle phase that resulted in a low TRS for the specimens; and a large amount of η phases were detrimental to the fracture toughness of the specimens.
Abstract: Organic fibres (Kevlar/ Arbocel / Acrylic) have good thermal stability, higher surface area and bulk density. The optimization of organic fibres percentage for thermal behaviour is considered using TGA. The temperature raise during brake application will be between 150-4000 C and this temperature zone is very critical to determine the fade characteristics during friction testing. Hence, three different friction composites are developed with the same formulation varying only the Kevlar, Arbocel and Acrylic fibres which are compensated by the inert filler namely the barites and are designated as NA01, NA02 and NA03 respectively. After the fabrication, the TGA test reveals that the composite NA03 has minimum weight loss. The friction coefficient test rig is then used to test the friction material as per SAE J661a standards. The results prove that the brake pad with minimum weight loss during TGA has higher friction stability. Thus, we can correlate the thermal stability with the stability of friction.
Abstract: Investigated the fragmented substructure of steel 30CrMnSiA after heat treatment and deformation. Found that after heat treatment of steel is the main component of α-phase (~ 96%), γ- phase (~ 3%) is present in the material in the form of residual austenite. Batch martensite is 0.7 on the volume of α- phase plate - 0.3. Most of the residual martensite (1.5%) is located in the plate martensite, the lowest - in a fragmented packet martensite component (~ 0.5%). In unfragmented batch martensite of residual austenite is present in an amount of 1%. Found that in the process of deformation martensite structure formed after heat treatment is completely destroyed and the volume fraction of anisotropic fragments is 25%, 75%-isotropic. Electron microscopic studies have shown that originated fragmented structure is stabilized by tertiary carbides formed during deformation. These carbides are cementite particles and special carbide M6C. These particles are located mainly along the boundaries and junctions of the fragments.
Abstract: A poly(ether imide) (PEI) composite membrane was prepared by dip coating a PEI membrane pretreated with 2-aminoethanole (AEOH) into an aqueous solution of poly(vinyl alcohol) PVA and glutaraldehyde (GA). PEI membrane support was firstly prepared via phase inversion technique by casting a solution of PEI in N-methylpyrrolidone (NMP), using water as non-solvent. The hydrophilicity, permeability, anti-fouling and mechanical properties of unmodified PEI and PEI/PVA composite membranes were investigated. By comparison with the unmodified PEI membrane, the PEI/PVA composite membrane exhibited a higher pure water flux and an increase in its hydrophilicity. In addition, the flux recovery of the pure water flux of the composite PEI membrane was higher than that of the unmodified PEI membrane. This indicated that the obtained composite membrane could reduce the membrane fouling and improve its use for ultrafiltration.
Abstract: BaGd2ZnO5:Eu3+ phosphors were synthesized at sintering temperatures of 800, 900, 1000, 1100 and 1200 °C by high-energy ball milling method. The crystallinity, surface morphology and photoluminescence properties of phosphors were investigated by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and luminescence spectrophotometry, respectively. The XRD results indicate that the crystallinity of the powder was improved and the powder shows a orthorhombic structure as the sintering temperature increased. The emission spectra of BaGd2ZnO5 phosphors excited at 280 nm exhibit a series of shaped peaks assigned to the 5D0→7FJ (J=0, 1, 2, 3) transitions, and luminescence intensity was increased with increasing sintering temperature. The FE-SEM images indicate that the size and shape of particles are regular.
Abstract: Superplastic behaviors of a Ti-48Al-2.3Cr-0.2Mo alloy with the initial grain size of 0.6m, resulting from 3-steps forging, have been investigated at temperatures ranging from 950°C to 1100°C and at strain rates ranging from 810-5 s-1 to 210-4s-1. The elongations above 500% were obtained at 1050°C-1100°C. An maximum elongation of 566% was obtained at 1050°Cand at a strain rate of 810-5s-1. The flow softening and continuous strain hardening were observed in the curves of true stress-true strain, it is suggested dynamic recrystallization and high-density dislocation caused by pre-deformation are the reasons. By OA, TEM, microstructure evolutions during the deformation were observed. It is found that after superplastic deformation, the grain size become smaller, and the distribution of grain size become more uniform, the densities of dislocations become lower and the dislocations mainly distributed in the areas near grain triple junction. Grain boundary sliding accommodated by dislocation slip is the predominant deformation mechanism.
Abstract: Series of star-shaped molecules based on 1,3,5-triazine core have been synthesized via CF3SO3H-mediated cyclotrimerization reaction, and then characterized by 1H-NMR, 13C-NMR, MALDI-TOF-MS, and elemental analysis. The effects of different factors, such as the steric hindrance and electronegativity on the reaction efficiency, are systematically studied. The results indicate that the steric hindrance plays an important role in the reaction, while electronegativity has little impact on this reaction. In addition, the bridges including ethylene group and carbon atom between 1,3,5-triazine core and peripherals are firstly studied in this work, which expands the application of CF3SO3H-mediated cyclotrimerization reaction. Moreover, we have successfully broadened the cyclotrimerization reaction to the preparation of 1,3,5-triazine derivatives with different substituents as the peripheral, which is promising for preparation of single-layer multi-functional optoelectronic materials.
Abstract: NiFe2O4 ferrite was synthesized by sol-gel method. Its structural characteristics, morphology, electromagnetic and microwave absorption properties were analyzed by X-ray diffraction, scanning electron microscope and network analyzer, and analyzed the influence of the combustion temperature and citric acid. The results indicated that the particle size be enlarged with an increased combustion temperature and be diminished first, then increased with the increased of citric acid, and the best ratio of citric acid with metal ions for nCA: nFe: nNi = 4:2:1. Its microwave absorbing property is increased with the increased combustion temperature. Its complex permittivity imaginary part first decreases with temperature increases and then increases, the imaginary part of complex permeability with increasing temperature increases, indicating that the increase of calcination temperature, help to improve the sample microwave absorbing properties.
Abstract: Hybrid solar cell based on copper-phthalocyanine (CuPc) and textured Si has been fabricated. Influence of silicon texturization on the photovoltaic properties of CuPc/n-Si hybrid solar cell was studied by current-voltage characteristic curves in the dark and under illumination conditions. As a result, it is found that textured Si can improve significantly the performance of hybrid solar cell. It exhibits a three times increase in the short-circuit current density with respect to that of the standard hybrid solar cell, and the short-circuit current density reaches up to 5.4 mA/cm2. In addition, the open-voltage and fill factor are almost constant. The solar-energy conversion efficiency is increased by about three times by the textured Si and achieved about 0.8% under “one Sun” illumination. Furthermore, the possible reasons for this result have been discussed.