Papers by Author: Tawee Tunkasiri

Abstract: The fabrication of lead-free (1-x)Bi_0.5Na_0.5TiO₃ - xKNbO₃ or (1-x)BNT-xKN ceramics where x = 0.00, 0.05, 0.10, and 0.15 was carried out by the modified two-step mixed oxide method. The effects of KNbO₃ on structure, piezoelectric and ferroelectric properties were systematically investigated. XRD results revealed that the (1-x)BNT-xKN ceramics with low KN content of x less than 0.05 contained ferroelectric phase with a rhombohedral symmetry while the ceramics with x = 0.05 possessed pseudocubic structure. The higher KN content (x ≥ 0.10) ceramics had symmetries rhombohedral structure. At room temperature, the highest P_r and low E_c were obtained when the composition of x = 0.05. Moreover, the results showed the moderate KN addition could enhance the piezoelectric response. The d₃₃ of 0.95BNT-0.05KN reached as high as 125 pC/N.

Abstract: In this work, the effects of crystalline morphology on the mechanical properties of polycaprolactone/polyvinyl alcohol/ butterfly pea extract (PPB) nanofiber composite were investigated. Biopolymer nanofiber composite of PPB was fabricated by electrospinning technique using polycaprolactone concentration and distance of nozzle to ground collector of 7 wt% and 20 cm, respectively. The influence of applied voltage (vary from 15-25 kV) on the stress-strain curves was also observed. The structure and morphology of electrospun PPB nanofibers were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that, the degree of crystallinity increased with applied voltage and the mechanical properties was affected by the morphology of PPB nanofiber.

Abstract: Recent years, propolis has plenty of biological and pharmacological properties and its mechanisms of action have been widely investigated. There is a substantive database on the biological activity and toxicity of propolis indicating it may have many antibiotic, antifungal, antiviral and antitumor properties, among other attributes. The one-step incorporation of propolis into nanofibrous mats of polycaprolactone (PCL) by electrospinning was demonstrated. In this research, the preparation of the PCL nanofibers films added ethanolic extract propolis (EEP) by electrospinning technique was studied. The EEP content was varied from 0, 2, 4, 6, 8 and 10%. The morphology was observed by a scanning electron microscope (SEM). The functional group was investigated by FT-IR

Abstract: In this research, the two-step sintering method was employed to develop the physical properties of Hydroxyapatite (HA) ceramics. HA powder was extracted from bovine bone and vibro-milling method was used to make the fine particles. For the two-step sintering process, the samples were heated up to the first step temperature (T₁=1200^°C) for 6 min then the temperature was lowered down to second step temperatures (T₂=1150^°C and 1100^°C) for 5, 10 and 15 h. Another set of samples were heated up to the first step temperature (T₁=1250^°C) for 6 min then the temperature was lowered down to second step temperature (T₂=1150^°C) for 5, 10 and 15 h. X-ray diffraction (XRD) was carried out for investigating the phase formation in the prepared ceramics. Physical properties of the prepared ceramics were studied such as porosity, density by Archimedess principle. It is found that most of the samples exhibit Ca₅(PO₄)₃(OH) phase with JCPDS number 09-0432. The first step temperature plays the most roles on controlling the density of HA ceramics than T₂ and dwell times. Microstructures of the HA powder and ceramics were characterized using scanning electron microscope (SEM).The feasibility in using the prepared ceramics for bone replacement applications was discussed.

Abstract: Hydroxyapatite (HA) is classified as one of the important bioceramics, which has been used in orthopedics, medical and dental applications. It has bioactivity and good biocompatibility with the human organism, which is suitable in medical applications as an implant or coating on prostheses such as metal. In this study, the effects of calcinations temperatures on phase formation and physical properties of HA particles were investigated. The HA particles synthesized from bovine bone were cleaned and fired at 800°C and subsequently ball milled for 24 h. Then received HA particles were divided into two parts. The first one was calcined at various temperatures from 900 to 1400°C and the second one was vibratory milled for 4 h and subsequently calcined at various temperatures from 900 to 1400°C. The calcined HA particles were characterized by X-ray diffraction (XRD) for their crystal structure and particle size analysis. Scanning electron microscope (SEM) was used for microstructural.

Abstract: The antimicrobial activities of propolis against some bacterial strains have been studied. However, there are few reports on biopolymers from propolis. Polycaprolactone (PCL) is a biodegradable polymer that has a long history of use in the biomedical field. In this work, the polymer nanofiber was grown from a Brazillian propolis extract solution on PCL using an electrospinning technique. Antimicrobial activities were investigated by the disc diffusion method. The propolis extract and polymer nanofiber could inhibit some human pathogenic bacteria. In addition, the inhibitory effects on tested microorganism depended on the concentration of propolis extract mixed with the polymer nanofiber. Such properties of the propolis/PCL nanofiners can be further developed for biomedical applications.

Abstract: The purpose of this work was to study the effect of ZnO on properties of P₂O₅-CaO-Na₂O glass system for bone substituting applications. The glass formula used in this study is 45P₂O₅ - (30-x)CaO - 25Na₂O - xZnO where x = 0, 1 , 3, and 5 mol%. The corresponding glasses were prepared by conventional glass melting technique at 1000 °C for 1 h. Thermal parameters of each glass were studied by differential thermal analysis (DTA). These glasses were investigated in terms of infrared spectra and in vitro bioactivity. DTA results gave the glass transition temperatures in a range 227-280°C and crystallization temperatures in the range 521-529°C. Form FTIR results, the infrared spectra of all glass samples showed vibrations of phosphate network and the transmittance intensity of glass systems decreased with increasing ZnO content. All glass samples were exhibited the growth of apatite cells at the surface after immersed in SBF for 7 days. The optimum composition was found for the glass samples containing 5 mol% ZnO which contained the most apatite layer formation.

Abstract: During recent years, there have been efforts in developing nanocrystalline bioceramics, to enhance their mechanical and biological properties for use in hard tissue engineering applications. In this work, we study the effects of some sintering additive nanopowders dopants on the properties of the sintered HA structures. Calculated quantities of silica nanopowders are incorporate as dopants into dried HA nanopowder. The mixing powders are uniaxially compacted and then sintered at 1200°C by rate-controlled sintering method in air. Compositional, microstructural, morphological and mechanical characterizations are carried out on sintered HA samples.

Abstract: In this work, preparation conditions and effect of ZrO2 doped BaFe0.5Nb0.5O3 ceramics were studied. Relationship between structure and dielectric properties was investigated. Single-phase cubic BFN powder was synthesized by solid-state reaction at 1200°C for 4 hours with heating and cooling rate of 5°C/min. Various amount of ZrO2 doped from 0.1 to 0.5 %weight were used for doping. After that BFN ceramics were formed via uniaxial pressing and sintered at 1300°C for 4 hours with heating and cooling rate of 5°C/min. Physical properties, microstructure, phase evolution and dielectric properties were studied to find out the optimum conditions for high voltage capacitor applications.