Advanced Materials Research Vols. 488-489

Abstract: The true stress-strain curves of AZ31B magnesium alloy sheet were obtained by using the uniaxial tensile tests at the temperature ranging from 50°Cto 300°C and the initial strain rate ranging from 0.001/s to 0.1/s. The influence of temperature and strain rate on the flow stress was analyzed. The results show that the flow stress decreases and the elongation in fracture increases with increasing temperature and decreasing strain rate，and the plastic performance is improved obviously. Through the analysis of the true stress-strain curves，a mathematical model of the flow stress was established based on an exponential form whose power is a quadratic function. All the coefficients in the model were fitted as functions of temperature and strain rate. The comparison of the calculated results with experimental data shows that the model established in this study can accurately reflect work hardening and strain softening effect of AZ31B magnesium alloys during the hot deformation. It can be used for the prediction of flow stress for AZ31B magnesium alloys under hot work conditions and numerical simulation of forming processes.

Abstract: The blend of poly(butylene adipate-co-terephthalate) (PBAT) and thermoplastic starch (TPS) are a promising way to get a new class of bio-compostible plastic, balance the cost effective issue and good mechanical properties. Blends of both polymers are immiscible in nature. Therefore, to make the blend to be more compatible, some block-copolymer compatibilizer can be introduced. Reactive blend is one of effective ways to create such compatibilization at the interface. The objective of this work was to study the reactive blends of PBAT/TPS in comparison to the physical blend. The reactive blends were prepared in both an internal mixer and a twin-screw extruder. For reactive blends in twin-screw extruder, PBAT, starch, glycerol and reactive agent were all pre-mixed and blended in an extruder on one step process. The weight ratio of PBAT:TPS (starch + glycerol) was fixed at 60:40. The reactive agent maleic anhydride (MA) and peroxide (Luperox® 101) were used at very low level 0-0.1 phr. The mechanical properties, morphology and flows property of blends were characterized using tensile machine, scanning electron microscope (SEM) and melt flow indexer (MFI). The internal mixer torque showed a decrease in a final torque value of TPS when MA being added, confirming the chain scsision reaction of TPS. The finer morphogy and better mechanical properties were obtained in the reactive blend with 0.1 phr of MA and 0.1 phr of peroxide.

Abstract: The blend of poly(styrene-co-acrylonitrile) (SAN) and natural rubber (NR) is immiscible and incompatible which lead to poor mechanical properties. Many methods can be carried out to improve the compatibility. In this work, the potential of various reactive compatibilizers in SAN and NR blend was explored. The morphological and mechanical properties were compared. The melt blending of SAN and NR were prepared in an internal mixer with various types of reactive agent such as styrene-co-maleic anhydride (SMA), maleic anhydride (MA), peroxide and mixed reactive agents. The morphological textures of the blends were investigated by scanning electron microscope. Mechanical properties including tensile strength, impact strength and elongation at break were measured. The results of morphological observations revealed that SAN/NR blend with reactive agent, the mixture of SMA and MA show the smallest and the most uniform dispersed NR particles, where the size of NR particle is about 1 µm. The mechanical properties of the blends revealed impact strength and elongation at break were increased with addition of reactive agents. SAN/NR blend with the mixture of SMA and MA showed the highest elongation at break but it had lower impact strength than the blend with SMA.

Abstract: Chromium zirconium nitride (Cr-Zr-N) thin films have been prepared by reactive dc closed field unbalanced magnetron co-sputtering on Si (100) wafers without external heating and voltage biasing. Heating effect on chemical composition, microstructure, and adhesion of the films by increasing in Zr sputtering current was investigated by using field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). The results suggested that heating in the film and substrate during the deposition with high Zr target current was caused by bombarding the growing film with high energetic particles. From EDX analysis, the decrease of N content could be an effect of nitrogen desorption caused by heating and bombarding of high energetic particles. FE-SEM cross-sectional morphology revealed that grain refinement by Zr addition and high atomic diffusivity on both surface and bulk by heating and bombarding of high energetic particles resulted in denser fibrous grain microstructure. However, the increase of Zr target current leaded to the film with high compressive stress and could affect the film adhesion.

Abstract: Conventional fibre size has large surface area for binding site while nanocellulose posses higher surface area thus making more available binding site for fibre-matrix interaction. Kenaf has poor surface properties before treated. Treatment was applied to overcome this problem with alkali followed by acidic treatment. The nanocellulose has been produced from kenaf core (hibiscus cannabinus) by chemi-mechanical method. The fibre was treated with alkali followed by acidic treatment (HCl). Treated fibres were mechanically process by using pulverisette & cryocrushing to reduce the fibre size. The nanocellulose fibres were observed under Scanning Electron Microscope (SEM). The result convinced that chemi-mechanical method is a new technique for producing high yield kenaf nanocellulose.

Abstract: Sb layered Te/Cd thin films have been prepared by using Stacked Elemental Layer (SEL) method. The presence of mixed phases (CdTe and Sb2Te3) in the films was confirmed by the x-ray diffraction technique. The calculated structural parameters demonstrated the feasibility of Sb doping via SEL method. The topographical and electrical studies of the synthesized thin films depicted the influence of Sb on both surface morphology and conductivity. The values of conductivity of the annealed films were in between 2 x 10-3 and 175 x 10-2 Scm-2. A desired chemical composition of films was confirmed from spectrum shape analysis using energy dispersive x-ray.

Abstract: This work investigated the effect of montmorillonite clay surface modified with 25-30 wt% trimethyl stearyl ammonium (clay) on mechanical, thermal and morphological properties of polyoxymethylene (POM)/clay nanocomposites were investigated. The results showed that POM/clay nanocomposites could maintain or decrease their tensile strength for a certain clay loading range. The Young’s modulus of the nanocomposites increased by adding clay in a range of 0.5-4 wt% while the impact strength showed an increase in a range of 0.5-2 wt%. The percent strain at break of the nanocomposites decreased with increasing filler content. The thermal degradation temperature decreased with an increase of clay content thus the addition of clay did not improve the thermal stability of POM. The microstructure of neat POM and POM/clay nanocomposites was observed that the dispersion of clay was a good in POM matrix at low clay content. The nanocomposites formed the intercalated structure with clay, and the intercalated clay stacks were distributed uniformly in the nanocomposite. The increase of clay content observed increasing of brittleness in POM/clay nanocomposites.

Abstract: Compared to traditional hot-stamping process, partial pressing hardening (PPH) can alter mechanical properties of metal components in any desired regions by controlling its bainite and martensite distribution. The mechanical property of the structure that is produced by PPH process is quite different from traditional hot-stamping steels (Martensitic steels) and has never been evaluated. Based on the merit of PPH process, this paper investigated the effect of bainite-martensite distribution on the deformation pattern and energy absorption capacity of PPH structures. The FE material models of martensitic and bainitic steel were set up and verified. After that, the deformation pattern and energy absorption capacity of PPH structures with different distribution patterns was investigated and discussed by three-point bending and tensile bending FE simulation.

Abstract: The effects of epoxidized natural rubber as a compatibilizer in modified-montmorillonite filled natural rubber were studied. Natural rubber was compounded with 2, 5 and 10 parts per hundred rubber (phr) of organomodified montmorillonite as a reinforcing filler and cured by using a conventional sulfuric system. Epoxidized natural rubber with 25 and 50 mol% epoxidic units (ENR25 and ENR50, respectively) was used as compatibilizer at the amount of 5, 10 and 15 phr. Rubber compounds were then tested for their curing properties. Test specimens for mechanical testing were prepared by compression molding. The use of montmorillonite as a filler in natural rubber efficiently improved mechanical properties that are tensile strength, modulus, elongation at break, tear strength and hardness, especially with the small amount of montmorillonite. This is supposed to be related to intercalation and exfoliation process. The increasing amount of montmorillonite caused the filler to be agglomerated thus the reinforcing efficiency was reduced and some mechanical properties were dropped. It was further founded that epoxidized natural rubber compatibilized montmorillonite filled natural rubber effectively. As the amount of epoxidized natural rubber increased, the mechanical properties tended to increase. The presence of epoxidized natural rubber improved filler-rubber interaction and filler dispersion. The compatibilizing efficiency of ENR25 was slightly superior to that of ENR50. This is because ENR 25 contains more double bonds than ENR 50 hence higher strain-induced crystallinity is occurred

Abstract: A low temperature solvothermal method was employed to synthesize nitrogen-fluorine doped TiO₂ materials (N/F -TiO₂) at various mole ratio of Ti:F; 10:1, 10:0.3 and 10:0.1, for photocatalytic applications. Doping fluorine and nitrogen in the TiO₂ structure extend the spectra response of the materials toward a visible region resulting in the high efficiency to oxidize methyl orange (MO) under UV-Vis irradiation. The microstructure and photocatalytic activity of the materials appeared to depend on titanium precursors, titanium isopropoxide (TTIP) or tetrabutyl orthotitanate (TBOT), and the concentration of dopant (NH4F). The highest MO decolorization efficiency under UV-Vis irradiation for 30 minutes is about 86 % by using N-F-TiO₂ (TTIP precursor) with Ti: F of 10: 3 as catalyst. The decolorization efficiencies of MO over N-F-TiO₂ materials (TTIP precursor) are twice higher than that of the undoped catalyst.