Advanced Materials Research Vols. 328-330

Abstract: Nano materials have made a revelation in all fields of engineering and technology. Materials of size less than 100 nm are termed as nano materials. The excellent properties of nano materials have attracted the scientists and engineers more towards nano technology. Solid nano particles dispersed in the base fluids such as water or ethylene glycol are called nanofluids, especially used to increase the heat transfer capability of base fluids. In this work we have synthesized Al₂O₃-Cu nano composite powder in a thermo chemical route that involves the preparation of precursor powder from metal nitrates and hydrogen reduction technique. Two different proportions of precursors were used to obtain the nano composites of two different proportions. The prepared powder was characterised using XRD, SEM and EDS. Water based hybrid nanofluids were prepared and their stability have been studied for different volume concentrations.

Abstract: In the whole process of micro-forging regulation laser cladding layer, the microstructure structure of cladding layer would change. In order to establish the microstructure evolution of the whole process, firstly re-crystallization model was set up based on Avrami equation and experimental data, and various material constants were gained with regress; secondly calculation for the model was carried out on DEFORM-2D,then the results were compared with experimental data, which showed that calculation results of this model kept good consistency with experimental data, and proved that the model could be applied in a full size finite element simulation of the micro forging process.

Abstract: In this research, the B₄C/BN nanocomposite powders were fabricated by chemical reaction and heat treatment process, then the B₄C/BN nanocomposites bulks were fabricated by hot-pressing process. The B₄C/BN nanocomposite powders were fabricated by chemical reaction at 550°C for 15h and heat treatment at 850°C for 6h. The B₄C/BN nanocomposites bulks were fabricated by hot-pressing process at 1850°C for 1h under the pressure of 30MPa. In this research, the phase composition and microstructure of the B₄C/BN nanocomposite powders produced by chemical reaction and heat treatment process were investigated. The phase composition and microstructure of the B₄C/BN nanocomposites produced by hot-pressing process were investigated. The XRD patterns results showed that there existed the B₄C phase and amorphous BN phase in the composite powders produced by chemical reaction and heat treatment, and the amorphous BN phase completely transformed into the h-BN phase by hot-pressing process. The XRD patterns results showed that there existed the B₄C phase and h-BN phase in the composites sintered bulks. The microstructure of the synthesized B₄C/BN composite powders showed that the B₄C particles were surrounded with the amorphous BN nano-sized particles, the thickness of amorphous BN coated layer was about 300-500nm. The B₄C/BN nanocomposites exhibited the homogenous and compact microstructure, and the nano-sized h-BN particles were homogenously distributed in the B₄C matrix. The mean particles size of B₄C matrix was about 2-3μm, the length of nano-sized h-BN particles was about 1-2μm and width of nano-sized h-BN particles was about 100-200nm. The B₄C/BN nanocomposites bulks exhibited more homogenous and compact microstructure with the increase of h-BN content.

Abstract: Polyaniline (PANI) and polypyrrole (PPy) doping with hydrochloric acid (HCl), p-toluenesulfonate (pTSA) were successfully synthesized by chemical oxidation polymerization. Ammonium peroxydisulfate was used as an oxidizing agent at room temperature. Microstructure of PPy and PANI was studied by scanning electron microscopy (SEM). Discussed the acid concentration how influenced on the electrical conductivity properties of PANI and PPy, and also compared their resistivity and thermal stability. The results showed that HCl effectively improved conductive properties of PANI in a wide range concentrations, and pTSA in narrow range concentrations. When doping with HCl, the minimum volume resistivity of PANI was 0.24 Ω • cm, and PPy was about 10.5 Ω • cm. When doping with pTSA, the volume resistivity minimum of PANI was 1.3 Ω • cm, and PPy was 15.8 Ω • cm. The conductivity of PPy was weaker than PANI. The thermal stability of conducting polymers which doping with pTSA was better than which doping with HCl.

Abstract: Different Zinc tungstate (ZnWO₄) nanostructures were controllably synthesized via facile hydrothermal method in the presence of surfactant polyethylene glycol 20000 (PEG-20000). During the synthesis, cheap and simple inorganic salts were used as precursors. The shape and size of ZnWO₄ nano/microstructures can be well controlled by the dosage of surfactant, the pH value of reaction system and other hydrothermal parameters. Apart from structural and morphological characterizations of the ZnWO₄ nano/microstructures, the composition and the photoluminescent (PL) properties of typical samples have also been investigated by powder X-ray diffraction pattern and fluorescence spectrophotometer, respectively. The results indicated that all the products of ZnWO₄ with different morphologies exhibited the only blue peak at 506 nm with an excitation wavelength at 253 nm.

Abstract: Silicon is the most attractive anode material of all known host materials for lithium ion batteries because of its high theoretical lithium-insertion capacity up to 4200 mAh g-1, but it is difficult to be applied for its poor cyclability caused by the mechanical invalidation for the insertion of lithium ions. Nanosilicon/CMC/AB composite electrodes doped with WC were prepared by ball milling. The effect of the structure transformation of the doped electrode on the electrochemical behavior was systematically analyzed by X-ray diffraction. The mechanical properties of doped silicon electrode play an important role on its long-term electrochemical stability. The capacity retention could be maintained about 90% after 40 cycles. It was demonstrated that the cycling stability of the nanosilicon composite electrode could get a great promotion by WC doping. The intensification of the mechanical properties is critical to enhance the performance of the composite electrode.

Abstract: A novel superabsorbent hydrogel was obtained by graft coplolymerization of cottonseed protein (CP), acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA). This composite was synthesized by free radical copolymerization in aqueous solution in the presence of redox initiators, potassium persulphate and sodium sulfite, and N, N-Methylene bisacrylamide (NMBA) as cross-linking agent. The effects of the certain variables of the copolymerization on the swelling capacity of the hydrogel were measured and its swelling properties in different solutions were investigated. This approach shows a promising method in utilizing cottonseed protein to synthesis superabsorbent polymer with excellent water absorbency and potential in various applications.

Abstract: Different doses of electron beam was imposed on polyacrylonitrile(PAN) precursor fibers before the fibers were stabilized. The effect of electron beam irradiation on the chemical structure, orientation degree, surface morphology and tensile properties of PAN precursor fibers were characterized by use of fourier transform infrared spectroscopy (FTIR), tensile test and scanning electron microscope (SEM), respectively. The results showed that the extent of cyclization and orientation degree was increased firstly and decreased later. The surface morphology of PAN precursor fibers was smoother when the irradiation doses 150kGy and 200kGy. Tensile strength of the fibers was increased first and decreased later. The change of tensile strength might be in correlation with the changes of extent of cylization, orientation factor and surface morphology.

Abstract: In this paper, the hot deformation behavior of GH4169 superalloy were investigated at temperature of 900-1020°C and at strain rate of 0.001-0.1up to a 60% height reduction of the sample using isothermal constant strain rate compression tests on process annealed material. The high temperature deformation behaviour of pure titanium was characterized based on an analysis of the stress–strain curves The proposed constitutive equation and the stress-strain curves were implanted into DEFORM2D, a hot forging process for the disc of GH4169 was simulated, and the micro-variable, recrystallized volume fraction, average grain size, recrystallized grain size and etc., were plotted with a contoured figure. According to the comparision between the experimental and predicted result, the absolute error between them is acceptable. The method for microstructure prediction will be significant to the engineering.

Abstract: Hot deformation tests were carried out on Al5083 – 2 %(vol) TiC nanocomposite in a temperature range of 250 – 450°C at varying strain rate of 0.01 – 1.0 sec^-1. Constitutive models were developed for the prediction of peak flow stress relating strain rate, true stress, temperature and activation energy. The percentage error between measured flow stress and constitutive model values were calculated to analyse the efficacy of the model in the prediction of peak stress. Finally, a window of working of the selected nanocomposite is established for finding out the safer region of working.