Advanced Materials Research Vol. 748

Abstract: Fe-W based composite have successfully been prepared using natural resource. The ferberite (Fe (Mn, Sn)WO₄) tailings mixed with aluminum, carbon and boron oxide powder were used as reactants. The reactants were pressed and followed by oxy-acetylene flame ignition. The products from the self-propagating high-temperature synthesis (SHS) reaction were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) couple with dispersive X-ray (EDS).

Abstract: An investigation on the electrochromic performance of NiO films in 1M KOH was carried out using cyclic voltammetric technique. The NiO films were deposited on ITO glass substrate using bath solution containing nickel sulfate, sodium acetate and sodium sulfate at pH 6.7 by applying constant current of 0.2 mA cm^-2 for 300 s at different deposition temperatures (ie: 25 °C, 40 °C and 80 °C). The as-deposited films were undergone post treatment through annealing process at 300 °C for 900 s. The surface morphology of the NiO thin films was characterized by field-emission scanning electron microscopy (FESEM) and the electrochemical properties of both NiO films were measured in 1M KOH electrolyte by cyclic voltammetry (CV). Deposition at 25 °C produced a smooth and compact thin film on the ITO surface. However, when higher temperatures were used (ie: 40 °C and 80 °C), porous structure of NiO formed. The electrochromic performance of the smooth film prepared at 25 ° C showed is better than the porous films. The annealing process has enhanced the stability of NiO film for intercalation and de-intercalation of OH^- ions during cycling in 1M KOH. These results show that the temperature (heating and annealing process) has significantly influenced the formation of NiO films on ITO substrates which affected the performance of the electrochromic material.

Abstract: In recent years, the energy efficiency improvement has become significant due to rapid consumption of world's energy resources. Particularly in manufacturing industry, hard turning process is one of the most fundamental metal removal processes that require huge power consumption and it could be improved in term of energy usage by many alternatives. At the same time, the improvement in term of machined surface quality is become a need since it would reflect appearance, performance and reliability of the products. As for example in the CNC machining field, one of the solution for this issue is by increasing the effectiveness of the existing lubrication systems as it could improve the machined surface quality, reduce the power required to overcome the friction component in batch production of machining process and reduce the oil consumption. The effectiveness of the lubrication system could be improved by introducing the nanobase lubrication system for much less power consumption as the rolling action of billions units of nanoparticle in the tool chip interface could reduce the cutting forces significantly. In this research work, the possibility of using SiO₂ nanobase lubrication system is investigated to reduce the machining power consumption as well as improving surface quality in hard turning process of AISI4140.

Abstract: Extrusion is one of established methods of polymer processing with fibre and consequently disperses fibre inside polymer. Different speed shows different behaviour of fibre dispersion. This study was conducted to produce composites from polylactic acid and kenaf by extrusion method. Kenaf bast and core was undergone chemical treatment with sodium hydroxide (6% w/w) followed by hydrochloric acid. Then, kenaf bast and core was mechanically beaten to reduce the fibre size. PLA and kenaf fibre (bast and core) was mixed by extrusion process with 3 different rotation speeds (60, 70 and 80 rpm). Kenaf bast composite and kenaf core composite was referred as KBC and KCC respectively. Flexural and impact strength was done to investigate the effect of different screw rotation speed on KBC and KCC. KBC and KCC processed with 60 rpm rotation speed shows better performance on flexural strength. For impact strength, KBC with 70 rpm and KCC with 60 rpm rotation speed have higher impact values.

Abstract: Chemically derived auto-combustion technique is employed to synthesize the Zn_0.95-xFe_0.05 Al_xO (x=00.07 in 0.02 increment) nanocrystallites. X-ray diffraction studies of all compositions revealed the phase pure wurtzite crystal structure with space group P63mc. The lattice parameters and crystallite size is changed with doping of Al attributed to the diversity in size of ionic radii. Temperature dependent electrical resistivity shows a decreased trend with the rise of temperature, confirming the semiconductor nature of compositions. The lower resistivity and enhanced saturation magnetization values in Al doped compositions correspond to the increase in density of carriers. Carriers mediated RKKY interactions are found to observe for enhancement of magnetization.

Abstract: In this work, the photoluminescence properties of bismuth borate glass doped with Dy³⁺ have been studied. Glasses were prepared using the glass composition formula 30Bi₂O₃ : (70-x)B₂O₃ : xDy₂O₃, where x is 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%. Glass samples were fabricated by the use of the normal melt-quenching technique at the melting temperature of 1,100 °C at 3 hour time intervals. Glass samples were annealed at the temperature of 500 °C at 3 hour time intervals to remove thermal strain. From photoluminescence study, the emission spectra (excited at 451 nm) were observed three emission peaks, which are assigned to ⁴F_9/2⁶H_15/2 (484 nm), ⁴F_9/2⁶H_13/2 (574 nm), and ⁴F_9/2⁶H_11/2 (661 nm) transitions, respectively. The luminescence intensities of all glasses are comparable and the strongest intensity peak at 574 nm was obtained.

Abstract: Straight carbon nanotubes (CNTs) with radially-growing morphologies and long length were grafted on carbon fibers by catalytic chemical vapor deposition and they were used to reinforce carbon/carbon composites (C/Cs). Mechanical tests indicate that CNTs can increase the interlaminar shearing strength of C/Cs by about 200 %. The reinforcement mechanism was concretely discussed with emphasis placed on the change of the cohesion of pyrocarbon matrix.

Abstract: In this study, an Al_0.3CrFe_1.5MnNi_0.5 high entropy alloy was synthesized by arc-melting in Ar. The as-cast alloy ingot was heat treated for 8 h at 650-750°C and then cooled in furnace to investigate the effects of age treatment on the microstructure, hardness and corrosion behaviour. The microstructure of as-cast sample has a typical rich-Cr BCC structure of dendrites, rich-Ni FCC interdendrite phases and a small fraction of cross-like rich-Ni FCC phase within the majority dendritic structure. During annealing treatment at 650°C, the cross-like FCC phase (β-FCC) gradually decreased, dendritic rich-Cr BCC phase transfers to Cr₅Fe₆Mn₈ phase, and the AlNi phase precipitated within the matrix dendrites. The interdendritic β₁-FCC phases gradually decomposed and transfers to second-phase (β₂ FCC), and the AlNi precipitated phase coarsen during annealing at 750°C. In addition, Cr₅Fe₆Mn₈ phase gradually transfers to rich-Cr BCC phase during slow-cooling process. These precipitation phases in the grain matrix are the main age hardening mechanism. The potentiodynamic polarization of the Al_0.3CrFe_1.5MnNi_0.5 high entropy alloys, obtained in 3.5% NaCl solutions, clearly revealed that the corrosion resistance increases and the passive region decreases as annealing temperature increasing.

Abstract: Oxidation tests of 18%Cr-oxide dispersion strengthened (ODS) steels with and without 5%Al were carried out in air at 700900 °C for time period up to 540 h. No minor alloying elements affect the oxidation behavior and the Al concentration between these ODS steels is a main difference. Cr₂O₃ and (Fe,Cr)₃O₄ spinel oxides exist on the surface of 18Cr-ODS steel; however, the surface oxide of 18Cr5Al-ODS steel is comprised of only Al₂O₃. Oxidation resistance of the ODS steels exposed at 700 °C is much better than Incoloy800 of which the Cr content is larger and their oxidation behavior doesnt follow the aluminum content. These results suggest that oxide particles dispersion and grain refinement play a more critical role than alloy composition in the high-temperature oxidation resistance.

Abstract: Si₃N₄/SiBCN composite ceramics were prepared by infiltrating and pyrolyzing liquid polyborosilazane in porous Si₃N₄ ceramics. To increase their wave-absorbing ability, SiC nanoparticles and SiC film obtained by chemical vapor infiltration were separately introduced into the composite ceramics. The surface morphology, element and phase composition of ceramics were analyzed by means of scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. Dielectric and electromagnetic wave absorbing property researches show that the permittivity and dielectric loss of the ceramics were effectively improved and the electromagnetic reflection coefficient was visibly decreased when SiC was loaded. It is indicated that SiC is an effective dielectric lossy absorbent, and the Si₃N₄/SiBCN composite ceramics containing SiC possess the great potential in the application of wave-absorbing material.