Advanced Materials Research Vols. 239-242

Abstract: To study the removal mechanism of materials during nano cutting, molecular dynamics method is adopted to simulate single crystal copper nanomachining processes, and subsurface defects evolvements and chip forming regulation are analyzed by revised centro-symmetry parameter method and the ratios of the tangential cutting force and the normal cutting force. The results show that there are different defects under different cutting depths. When cutting depths is shallower, there are dislocation loop nucleation in the subsurface of the workpiece beneath the tool; however, when the cutting depths is deeper, there are dislocations nucleation and slipping along {101} plane and (111) plane. In addition, both tangential cutting force and the normal cutting force decrease as the cutting depths decreasing. When the ratios of the normal cutting force and the tangential cutting force is below 0.9, the chip will be formed.

Abstract: A series of sulfonated polyimides (SPIs) were synthesized by 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 2,2′-benzidinedisulfonic acid (BDSA) and 4,4′- diaminodiphenyl ether (ODA) in m-cresol. The sulfonation degree of SPI was controlled through the ratio of sulfonated diamine to the non-sulfonated diamine, and the SPI membranes were prepared by a casting method. The chemical structures of SPI membranes were characterized by FT-IR. The properties of obtained SPI membranes were investigated, such as water uptake, ion exchange capacity, proton conductivity and permeability of vanadium ion. The proton conductivities of SPI membranes are ranged from 0.012 to 0.051 S/cm, and the permeabilities of vanadium ion are one or two orders of magnitude less than that of Nafion^® 117 (1.80×10^-6cm²/min ). Experimental results showed that SPI membranes are potential candidates for vanadium redox flow battery.

Abstract: The effects of SiC fiber shape, aspect ratio and loading direction on the deformation behavior of SiC fiber reinforced Al matrix composites were studied by finite element method using axisymmetric unit cell model. The results showed that the addition of reinforcements will cause constraint on the plastic flow of ductile matrix, and thus result in no-uniform stress distribution. The reinforcement shape has a pronounced effect on the overall plastic deformation of the metal matrix composites. The loading condition will cause different failure mechanisms of composites. Under tensile loading, the stress-bearing ability in the plastic region is increased with the fiber aspect ratio due to the increase in the interface between the reinforcement and matrix and the decrease in the inter-particle space.

Abstract: 3 mol% yttric(Y₂O₃)-stabilized tetragonal zirconia ( denoted as: 3Y-TZP) powders were synthesized by the reaction of Zr(CO₃)₂·nH₂O,Y₂(C₂O₄)₃·nH₂O,H₂C₂O₄·2H₂Oand H₄C₂O₂-C₂H₅OH mixed via stirring ball milling. The curve of decomposition of precursors was studied according to differential thermal analysis and thermogravimetry (DTA-TG). The 3Y-TZP powders were confirmed by characterization of XRD, TEM and BET. These results shown that the size of the 3Y-TZP powders were in the range of about 18nm-28nm with good dispersion and the main phase of target production was tetragonal phase. When calcining temperature and holding time was higher, the size of particles grown up and the tetragonal phase volume fraction decrease gradually. And the calcining temperature has more significant effect.

Abstract: Microstructure and low-frequency noise test were measured for N80 steel casing drilling, through SEM analyzed their morphology. Results showed that: (1) power spectral density of 1/f noise increases two orders of magnitude after fatigue crack growth. (2) 1/f noise parameters of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, which were proved by microstructure morphology. From the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which can serve as a viable tool to study the defects and the characterization of defects.

Abstract: Taken the pore structure effects into account, a mathematical model to describe the interaction of mass transfers, the chemical reaction and the pore structure in the gas sensitive porous medium is presented and solved. The properties of the mass transfers and the reaction characteristics of the gas-sensitive porous system are analyzed. The effects of pore size distribution and porosity on the concentration field of detected gas and the effective utilization degree of the porous matrix are provided. The results indicate that the Thiele number, which can reflect the relative magnitude of chemical reaction rate and gas diffusion velocity in nature, is the main basis for judging the effects of various parameters. It usefully reproduces the observed effects of pore structure and reaction temperature on diffusion and chemical reaction response, showing that the gas sensitivity and the effective utilization coefficient of the gas sensitive porous medium can be controlled by adjusting key parameters.

Abstract: In this paper, the problem of ZrAl₃ compound obtained by self-propagating reaction as the only and favorable formation phase was considered. It shows that the ZrAl₃ phase could be synthesized by self-propagating reaction in Zr-Al system and was especially identified as the only phase by XRD, which was further confirmed by DTA. Using the theories of structural lattice of ZrAl₃, Modified Effective Heat of Formation (MEHF) model, coupled with the First Nucleation Rule (FNR), the only formation of ZrAl₃ phase in Zr-Al system could be reasonably interpreted.

Abstract: Polypropylene specimens were made by the injection molding experiments under different processing conditions. The crystallinity of each polypropylene specimen was obtained using the X-ray diffraction method. The effects of the injection molding processes on the crystallinity of polypropylene were revealed: (1) the crystallinity decreases as the melt temperature increases, and the higher the melt temperature, the slower the crystallinity decreases, (2) the crystallinity decreases as the mould temperature increases, and the higher the mould temperature, the faster the crystallinity decreases, (3) the crystallinity increases as the injection speed increases, and the larger the injection speed, the faster the crystallinity increases. By the tensile experiments of the injection molded specimens, it is also found that the crystallinity has a major impact on the mechanical properties of polypropylene. The yield strength and tensile strength of polypropylene specimens increase as the crystallinity increases.

Abstract: The electrochemical behavior of Nitroso-R-salt (NRS) in aqueous solutions and the influence of pH are investigated. In alkaline solution, the electrode reaction of NRS exhibits stagnant electrode kinetics. With rising acid concentration, it exhibits more and more fast electrode kinetics and a diffusion-controlled process. Thus, acidic aqueous solutions are favorable for the NRS as active species of a redox flow battery (RFB). Average coulombic and energy efficiencies of the NRS/Zn RFB are 93.2 and 80.6%, respectively, showing that self-discharge is small. The preliminary exploration shows that the NRS is electrochemically promising for RFB application.

Abstract: In this paper, a kind of titanium-doped silicone prepolymer(TDS) was modified by hydroxyl-terminated saturated polyester (HTSP) by condensation polymerization. By Fourier Transform Infrared Spectroscopy (FTIR) the reaction of ethoxy groups of the TDS prepolymer with hydroxyl groups of the HTSP during condensation polymerization process was confirmed. The resins were cured with blocked polymeric isocyanate. The influence of the HTSP content on the properties of the modified resins such as thermal stability, corrosion resistance, as well as mechanical and other properties, were discussed in detail. The results showed that the properties of the resins were improved greatly after modification, and the optimal mass ratio of TDS to HTSP in the modified resins was 1:1. Thermogravimetry analysis (TGA) studies indicated that the weight loss of this sample（wTDS : wHTSP =1:1） was not obviously below 400°Cand the impedance value of this coating was significantly higher than that of the others.