Sirirat Rattanachan

Fabrication of piezoelectric laminate for smart material and crack sensing capability

Abstract Piezoelectric laminate composite has been successfully fabricated as a smart material by a spark plasma sintering process. Fully or nearly fully dense BaTiO3/MgO (pre-sintered)/BaTiO3, BaTiO3/MgO with 10 vol% BaTiO3/BaTiO3 laminates were sintered at 1300 8C with a holding time of 5 min under a pressure of 35 MPa. From EDS analysis, no reaction between BaTiO3 and MgO layers was observed along the interface. Effects of cycle stress and stress intensity factor on the voltage response of the proposed laminates were investigated for confirmation of a crack detecting capability. The resultant relationship between crack length and voltage response range clearly showed that the proposed laminates have a crack sensing capacity.

The pH-Dependent Properties of the Biphasic Calcium Phosphate for Bone Cements

Self-setting calcium phosphate cement (CPC) has been used in bone repair and substitution due to their excellent biocompatibility, bioactive as well as simplicity of preparation and use. The inherent brittleness and slow degradation are the major disadvantages for the use of calcium phosphate cements. To improve the degradation for the traditional CPC, the apatite cement formula incorporated with β-tricalcium phosphate (β-TCP) with varying concentration were studied and the effect of the pH value of liquid phase on the properties of this new calcium phosphate cement formula was evaluated. The apatite cements containing β-TCP for 10 and 40 wt.% were mixed into the aqueous solution with different pH values and then aging in absolute humidity at 37°C for 7 days. The setting time and phase analysis of the biphasic calcium phosphate were determined as compared to the apatite cement. For proper medical application, the compressive strength, the phase analysis and the degradation of the CPC samples at pH 7.0 and 7.4 were evaluated after soaking in the simulated body fluid (SBF) at 37°C for 7 days. The results indicated that the properties of the samples such as the setting time, the compressive strength related to the phase analysis of the set cements. The high degradation of the CPC was found in the cement with increasing β-TCP addition due to the phase after setting. Apatite formation with oriented plate-like morphology was also found to be denser on the surface of the biphasic bone cements after soaking in SBF for 7 days. The obtained results indicated that the cement containing β-TCP mixed with the liquid phase at pH 7.4 could be considered as a highly biodegradable and bioactive bone cement, as compared to the traditional CPC.

Effect of Apatite Wollastonite Glass Ceramic Addition on Brushite Bone Cement Containing Chitosan

Apatite wollastonite glass ceramic (AW-GC) (34.2% SiO2, 44.9% CaO, 16.3%P2O5, 4.6% MgO, 0.5% CaF2) was added into a brushite bone cement, which composed of β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP) and monocalcium phosphate monohydrate (Ca (H2PO4)2H2O, MCPM) in powder phases. Cement was prepared using a 3 β-TCP:2 MCPM in weight ratio. To evaluate the effect of AW-GC on the mechanical strength and degradability of brushite bone cement, the powder phases and 1 wt.% of chitosan dissolved in 5 wt.% of citric acid solution were mixed and soaked in simulated body fluid solution at 37 °C for 1, 3, 5,7 and 14 days, respectively. The compressive strength and setting time of AW-GC added in brushite bone cement were studied and compared with pure brushite cement. The pH values increased with addition of AW-GC. Additionally, the obtained brushite bone cements were characterized by XRD, SEM techniques.

Structural and optical characterizations of n-type doped ZnO by sol-gel method for photovoltaic

This paper presents the effect of Bi doping concentration and annealing temperature on structural and optical properties of zinc oxide thin films. The samples in this study were prepared by sol-gel technique. These thin films were characterized by X-ray diffractometer technique. XRD analysis revealed that the Bi-doped thin films after annealing indicated good preferential orientation along c-axis perpendicular to the substrate, in particular very low concentration of Bi dopant. As a result, it indicated that Bi atoms acting as donor impurities can be in phase of ZnO. The surface morphology was characterized by using SEM (Scanning Electron Microscope). The visible region was measured by UV-VIS spectrophotometer. Finally, the optical band gap of undoped and Bi-doped ZnO thin films were obtained by the Tauc plot. Varying the Bi doped in the range of 0.2–0.6 at.% under annealing temperature at 600 °C caused a no significant change in optical band gap. In contrast, the annealing procedure produced significant changes from 3.27eV to 3.32eV in the optical band gap in order to higher blue responsibility for photovoltaic.

Polarization Switching of PZT under Electrical Field via in-situ Synchrotron X-ray Absorption Spectroscopy

Lead zirconate titanate (PZT) ceramics have been extensively used for electronic applications due to their ability to couple mechanical and electrical energy, a so-called piezoelectric effect. This effect is caused by the shift of Ti4+ or Zr4+ ion relative to neighbouring atoms. The movement of the ions due to an external load causes reorientation of the ferroelectric polarization. Microscopically, the detail of the shift of Ti ion, reflecting polarization switching behaviour, can be analyzed by X-ray absorption near-edge structure (XANES) technique. The aim of this project is to investigate the shift of Ti4+ ion in PZT under the application of electric field by in-situ X-ray absorption technique. For this project, the special custom-built high voltage sample chamber installed at synchrotron XANES beam line at Synchrotron Light Research Institute, Thailand, was employed to conduct the experiment. XANES spectrum of bulk PZT was collected under the different amplitudes of an applied electric field. Ti K-edge X-ray absorption spectra were analyzed by IFEFFIT software package. The results showed that the pattern of XANES changed with the alternation of the applied field amplitude. The change of XANES spectrum was caused by the movement of Ti4+ ion reflecting the change of ferroelectric polarization. From the analysis, it was found that this technique could be used to investigate the Ti4+ ion shifting of PZT bulk ceramics.

Effect of Temperature on Ferroelectric and Piezoelectric Behaviour of Mn-Doped 0.75BF-0.25BT Multiferroic Ceramics

The effect of temperature on ferroelectric and piezoelectric behaviour of multiferroic ceramics (1 mol% Mn-doped 0.75BF-0.2BT) was investigated under an electric field at various temperatures (30 to 200°C). The polarization hysteresis loop and strain loop of ceramics were investigated at various temperatures. The effect of temperature was represented by the change of polarization hysteresis loop, strain loop and dielectric properties with various temperatures. The results showed that the remanant polarization and remanant strain of ceramics were improved with increasing temperature. The improving of these properties could be attributed to the greater domain switch ability at high temperature.

Boron Doping Effects on the Structural and Optical Properties of Sol-Gel Transparent ZnO Films

In this study, undoped and B-doped ZnO thin films were successfully deposited on the glass substrates by a sol-gel spin coating method. The influence of doping concentrations and the annealing temperature effects on the structural and optical properties of ZnO thin films were investigated. All of films exhibited polycrystalline structure, with a preferential growth along the c-axis plane and the optical transparency with visible transmittance was higher than 90%. The crystallite size was calculated using a well-known Scherrer’s formula and found to be in the range of 11-18 nm. The optical band gap of these films were determined and compared with those obtained for undoped ZnO thin film.

Optical Band Gaps and Electrical Conductance of Si Nanocrystals in SiO2 Matrix for Optoelectronic Applications

In this study, silicon nanocrystal (Si-nc) films were synthesized by compositing of Si-nc powder embedded in silicon oxide phase. The Si-nc film produced by the spin-coating methode using Tetraethylorthosilicate, ethanol, phosphoric acid, and Si-nc powder as suspension precursors. The variation in structural and optical properties of Si-nc sol films with the amounts of Si-nc powder have been characterized. Atomic force microscopy (AFM) shows that low density level of Si-nc power can result in the amount of porosity in the Si-nc films. It is found that when the Si-nc films have the higher Si-nc density, the small pores in the SiO2 phase were removed. In addition, optical energy gap (Eg) of Si-nc samples was evaluated by the Tauc plot method. It is a crucial attribute for a promising photonic device. The obtained optical bang gap values were extended from 1.10 eV to 1.40 eV as compared with the typical Si bulk. In addition, density of Si-nc clusters has a considerable effect on the electrical conductance of the Si-nc films measured at room temperature.

Original article. Development of chitosan/nanosized apatite composites for bone cements

Abstract Background: Calcium phosphate cements (CPC) is a promising materials for bone defect repair. Nanosized apatite or calcium orthophosphate has a better bioactivity than coarser crystals. Chitosan is produced commercially from chitin that is the structural element in the exoskeleton of crustaceans such as crabs and shrimp. The mixing of nanosized apatite and chitosan may provide the consistency cement, improving mechanical properties of the set bone cement. Objective: Develop nanosized apatite powder with chitosan for bone composite cement. Materials and method: Nanosized apatite was synthesized by chemical method at low temperature and used as the single-component for bone cement. The nanosized apatite powder was characterized using X-ray diffraction method, Fourier transform infrared spectroscopy, and transmission electron microscopy. CPCs were developed based on chitosan/nanosized apatite and calcium sulfate hemihydrate. The compressive strength of the set cement was measured after one to four weeks. The phase composition and the morphology of the set cements were investigated. Results: Calcium sulfate hemihydrate was effective in increasing the compressive strength after setting in a simulated body fluid for seven days. The compressive strength of chitosan/nanosized apatite composite was about 18 MPa after soaking. Conclusion: The workability and setting time of this composite were suitable to handling for bone cement. These composite cements had a significant clinical advantage for substitution of the regenerated bone.

Chitosan-Crystallized Apatite Composites for Bone Cements: Mechanical Strength and Setting Behavior

Crystallized apatite behaved to plaster of Paris was prepared by the chemical method. Apatite powder was mixed with chitosan. In this study, it was also studied the effect of HA seed and sodium hydrogen phosphate as an additive on their mechanical strength, compared with the normal calcium phosphate cements. Setting time of paste cements was determined using Gillmore method. Phases of cement obtained from a crushed cylinder were analyzed using XRD analysis. From the results, chitosan was effective both in increasing mechanical properties and accelerating hardening of the normal bone cements. Nevertheless, the compressive strength of chitosan-crystallized apatite composites was not significantly improved as compared to the controlled one. In addition, it was found that the mechanical strength of the cements decreased when increasing the concentration of HA seed and an additive.