Advanced Materials Research Vols. 55-57

Abstract: Ni-Ti alloy wires have been widely used in clinical orthodontics because of their properties of superelasticity (SE) and shape memory effect (SME). The purpose of this study was to assess the mechanical properties and phase transformation of 50.7Ni-49.3 Ti (at%) alloy (NT) and 45.2Ni-49.8Ti-5.0Cu (at%) alloy (NTC), cold-rolled with various percent reductions. To investigate SE and SME, heat-treatment was performed at 400°C and 600°C for 1 h. The specimens were examined using an Energy-Dispersive X-ray Spectroscope (EDS), Differential Scanning Calorimeter (DSC), Universal Testing Machine (Instron), Vickers Hardness Tester and Optical Microscope (OM). On the three-point bending test, the superelastic load-deflection curve was seen in NTC heat-treated at 400°C. Furthermore, NT heat-treated at 400°C with 30% reduction produced a partial superelastic curve. For SME, no conditions revealed superelasticity at the oral temperature. Micro-hardness value increased with greater percentage reduction. The average grain size for all specimens was typically 55-80 µm. The results showed that locally-made Ni-Ti alloys have various transformation behaviors and mechanical properties depending on three principal factors: chemical composition, work-hardening (the percent reduction) and heat-treatment temperature.

Abstract: Two types of rectangular orthodontic archwires; NiTiTM and 40oCuNiTi, were heat treated by Direct Electric Resistance Heat Treatment (DERHT) using different electric currents for 4 s. Their mechanical properties were then evaluated by micro hardness and three-point bending tests. After applying 4.5-5.5 A current, the hardness of NiTiTM increased with the increased current, whereas the change in hardness of 40oCuNiTi was slight. When 6 A current was applied, the hardness of the midspan of both wires significantly decreased. From the three-point bending test, unloading forces of NiTiTM increased after treating with 5.5 A current, while those of 40oCuNiTi decreased. However, both specimens lost their superelasticity when applied with 6 A current. In conclusion, after DERHT, various changes in mechanical properties can be noted in the different types of nickel titanium archwire.

Abstract: The nanocrystalline Strontium Barium Bismuth Titanate (SBBT) thin films with structure of Al/TiO2/SBBT/TiO2/RuO2/SiO2/Si were fabricated using sol-gel technique. The source materials are bismuth acetate Bi(CH3COO)2, barium acetate Bi(CH3COO)2, strontium acetate Sr(CH3COO)2 and titanium butoxide (Ti(OC4H9 )4). Different nanostructures of the films were prepared with un-annealed condition as well as after annealing at three different temperatures of 400, 500 and 6000C, in air for 2 minutes. The structure of SBBT thin films have been systematically studied by XRD, AFM, SEM and dielectric constant measurement. For the sensor device measurement, the SBBT thin film pressure sensors were tested by pneumatic loading method at pressure range between 0 to 450 kPa. It was found that the sensing properties of the films were affected by the crystalline nature of the films. It is shown that there is a linear relationship between the crystallization, grains size and dielectric properties with the sensing response of the film towards pressure.

Abstract: Conducting polyacrylonitrile (PAN) nanofiber mats were prepared by dipping non-woven nanofiber mats of PAN in the solution of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS). PAN nanofiber mats were fabricated via the electrospinning process. The solvent used for PEDOT/PSS was ethylene glycol and isopropanol. The morphology of the resulting PAN nanofibers and the coating layers was investigated using SEM analysis. The electrical conductivity of PEDOT/PSS coated PAN nanofiber mats was measured by the four-point probe method, for different concentrations of solvent in the PEDOT/PSS solution. An addition of ethylene glycol resulted in higher electrical conductivity of the coated mats than that of isopropanol. The resistive humidity sensing properties were also investigated. The device reproducibility was presented by vapor adsorption/desorption dynamic cycles. The reproducibility of the PEDOT/PSS coated mats was superior to that of neat PEDOT/PSS films. The response sensitivity of coated mats using isopropanol as solvent was higher than that using ethylene glycol.

Abstract: The gas sensors are fabricated from multiwalled carbon nanotube-based. The electrode is constructed from platinum (Pt) and titanium (Ti). The gas sensors are used for detecting oxygen (O2), ethyl alcohol (C2H5OH) and ammonia (NH3) by measuring the charge of their electrical capacitance. In the ratio silicon dioxide (SiO2) : carbon nanotube (MWCNTs) = 100:1 by weight, the electrical capacitance of the film layer has changed at the highest rate. The response of oxygen with concentration of 10,000 ppm, 20% of ethyl alcohol and 20% of ammonia, it is found that the electrical capacitance of thin layer has change about 34%, 60% and 70%.

Abstract: Stable silk fibroin (SF) membranes were prepared by modifying SF with polyethylene glycol diglycidyl ether (PEGDE) for use as enzyme immobilizing matrix. Morphology, structure, and water solubility of the modified silk fibroin (MSF) membrane were investigated. SEM images revealed greater porosity in the MSF membranes. IR spectra confirmed the predominant β-sheet conformation when the PEGDE was greater than 4%. In addition, the MSF membranes were highly insoluble within the pH range 4 10. An amperometric glucose biosensor was initially constructed using glucose oxidase (GOx) immobilized on the MSF membrane, coupled to a Prussian Blue (PB) deposited Au electrode. The response characteristics of the biosensors based on the GOx immobilized onto the 4% and 8% PEGDE modified SF membranes (4P-MSF and 8P-MSF) and the methanol treated SF membrane (MT-SF) were investigated. Amperometric measurements at the applied potential of 0.0 V demonstrated that the glucose biosensor based on the GOx immobilized onto the 4P-MSF membrane exhibited high sensitivity to glucose with a short response time, less than 3 s. Moreover, the stability of the biosensors based on the 4P-MSF membranes was better than those based on the MT-SF membrane after 2 weeks of storage in a phosphate buffer of pH 7.0 at 4 °C. These fundamental electroanalytical features of the sensor are therefore expected to be useful in biosensor application

Abstract: Fluorescence gas sensor was developed to identify the presence of volatile organic compounds by using porphyrin dye thin film. The porphyrin dye used was iron (III) meso-tetraphenylporphine chloride. The porphyrin thin film was deposited on quartz substrate using self-assembly through dip coating technique. The sensing properties of the thin films toward volatile organic compounds; ethanol, acetone and 2-propanol were studied using luminescence spectrometer. In presence of air and volatile organic compounds, thin films produced different emission spectra and ease for chemical identification process. To improved the sensing performance, TiO2 nanoparticles colloid were prepared, coated with porphyrin dye and deposited as thin film. It was found that the thin film of TiO2 nanoparticles coated with porphyrin dye has more intensive interaction toward volatile organic compounds than porphyrin thin film, and improved the selective property. This may be due to the nanostructured thin film provided more surface area for dye molecules to react with VOCs.

Abstract: In this work, an experimental X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure of Mn in BaTiO3. Synchrotron X-ray absorption near-edge structure (XANES) experiments were performed on Mn-doped BaTiO3 samples. The BaTi0.8Mn0.2O3 powders were used for the XAS experiment. XAS spectra at the Mn K-edge were recorded in transmission mode. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Mn K-edge XANES were consistent with Mn on the Ti site and inconsistent with Mn on other sites. The clear agreement was the strongest evidence of Mn substituting for Ti in BaTiO3.

Abstract: In this work, effects of compressive stress on the ferroelectric properties of 0.7PMN–0.3PT ceramics were investigated. The ceramics with the formula (0.7)Pb(Mg1/3Nb2/3)O3-(0.3)PbTiO were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress were observed at stress up to 80 MPa using a compressometer in conjunction with a modified Sawyer-Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of 0.7PMN–0.3PT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P-E) loop, the saturation polarization (Psat), the remanent polarization (Pr) and loop squareness (Rsq), decreased with increasing compressive stress, while the coercive field (Ec) remained relatively constant. Stress-induced domain wall motion suppression and non-180oC ferroelectric domain switching processes are responsible for the changes observed.

Abstract: Effects of electric field-amplitude and mechanical stress on hysteresis area were investigated in partially depoled hard PZT bulk ceramic. At any compressive stress, the hysteresis area was found to depend on the field-amplitude with a same set of exponents to the power-law scaling. Consequently, inclusion of compressive stresses into the power-law was also obtained in the form of < A – Aσ=0 > α E05.1σ1.19 which indicated the difference of the energy dissipation between the under-stress and stress-free conditions.