Abstract: This study investigated the bulk crystallization of 54B2O3-19SiO2-17Al2O3-5BaO-5MgO (mol%) glass. Melting was carried out at 1500°C for 1 h using a bottom-load electric furnace. The glass melt was cast into a block and annealed at 500°C for 2 h. Isothermal heat treatment was carried out at 1100°C for 2, 4, 8, 16, 32 h to form bulk crystallized glass-ceramics using a heating and cooling rate of 5°C/min. Phases present in the glass-ceramic samples were studied by x-ray diffraction. Crystalline Al4B2O9 and Al18B4O33 were the main phases and the phase stability depended on the isothermal time. Microstructures were observed by a scanning electron microscope. The size of aluminum borate whiskers/rods tend to increase with longer isothermal holding period. The whisker/ rod-like crystals uniformly oriented throughout the microstructure in all heat treated samples. This led to interlocking microstructure and hence an increase in hardness and fracture toughness. Glass-ceramics synthesized at longer heat treatment times resulted in an increase in the surface hardness and shorter path length at the corner of the diamond pyramid-shaped indenter. Glass-ceramics synthesized in this study can be applied as high temperature resistant machinable materials because their microstructures can resist micro-cracking upon indentation.
Abstract: Grain growth in ZnO with Bi2O3 addition of up to 1 mol% was examined in great detail for sintering in air. The results are analyzed and compared with previous reports in the context of the simplified phenomenological grain growth kinetics equation along with the physical properties of the sintered ceramics. In spite of the eutectic temperature at 735 °C, high density (> 90%) was not achieved at all Bi2O3 contents; this finding was contradictory to the well-known liquid-phase sintering. At 800 °C, rapid improvement in sintering occurred when increasing the content of Bi2O3 from 0.125mol% to 0.25mol%. Schematic study on weight loss also demonstrated an insignificant level of Bi2O3 volatilization under certain content. Analysis of the grain growth kinetics from isothermal sintering (900 °C - 1,000 °C) revealed strikingly different results in both grain growth exponent (n) and activation energy previously reported in literature. The n values ranged from 3.2 to 5.6 whereas the activation energy from 335 to 598 kJ/mol. Such large disparities were believed to be associated with various mass transport processes. The grain sizes in this study were much smaller than those published in literature (> 10 μm). This size difference, along with other microstructural features, was discussed and correlated in order to explain such anomalies and new findings obtained from the grain growth kinetics results.
Abstract: Alumina (Al2O3) is one of the most successful advanced ceramics due to its high hardness, chemical resistance as well as thermal stability under various severe operating conditions. Therefore, the Al2O3 and Al2O3 matrix composites were generally employed as cutting tool materials. The present work investigates an improvement in fracture toughness of the Al2O3-based composites reinforced by tungsten carbide (WC) particles. A change in toughness of the Al2O3/WC composites according to the additions of cobalt (Co) or partially stabilized zirconia (PSZ) is also of interest. The 90 wt% of Al2O3 and 10 wt% of WC powders, containing various amounts of Co or MgO-doped PSZ (Mg-PSZ), were formed by a conventional uniaxial pressing. The percentages of Co and Mg-PSZ were varied up to 3 and 4.5 wt%, respectively. The specimens were sintered in argon atmosphere at 1600 °C for 2 hours. The sintered specimens were subjected to testing and characterisation. The density was measured by water immersion method. Microstructure and phase analysis were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. Vickers indentation technique was used to determine hardness and fracture toughness. Density of higher than 95% of the theoretical values could be achieved in all cases. The hardness values of the WC reinforced Al2O3 composites were higher than those of the monolithic Al2O3. The hardness of the composites did not change significantly with the Co addition but it gradually decreased with PSZ additions. However, the presence of both Co and PSZ led to slightly higher fracture toughness. The hardness and fracture toughness of the fabricated composites were in the range of 16-18 GPa and 5-8 MPa.m1/2, respectively, which were in the same ranges as commercial cutting tools currently used in the market.
Abstract: The nano-porous Al2O3 layer was performed onto inner surface of micro- porous Al2O3 tube by using electrophoretic deposition (EPD). Initially, Polypyrrole (Ppy) was applied on inner wall of tube to make conductive surface. The Al2O3 deposition was carried out in Al2O3 suspension with 5 wt % solid content in ethanol medium system using various applied voltages. Thickness of the deposited layer depends on applied voltages, after sintering at 1400oC the morphology of the deposited layer was investigated by FE-SEM. The good deposited surface without cracks and peeling has been prepared under applied voltage condition of 10 V.
Abstract: Soda-lime glass is produced by melting sand (SiO2), soda ash (Na2CO3), lime stone (CaCO3) together with effective additives such as dolomite (CaMg(CO3)2) and an important structural modification, alumina (Al2O3) in which the melting temperature is very high around 1500°C. With this reason, to dissolve alumina, high amount of energy is needed. Consequently, one of possibilities to reduce the melting energy is replacing alumina by the raw material with a lower enthalpy of melting. The heat required for melting the batch of raw materials from atmosphere temperature to melting temperature is called exploited heat (Hex), which can be calculated from chemical enthalpy (H°chem) and heat content (Hmelt) at reference temperature (Tex). From thermodynamic approach, chemical enthalpy of alumina is higher than feldspar (KAlSiO3) or pyrophyllite (Al2Si4O10(OH)2). For the glass batch with alumina, the calculated exploited heat is 540 kWh/ton while the batch with feldspar or pyrophyllite is lower, namely 534 and 484 kWh/ton, respectively. This means that the melting process can be emerged easier than the batch with alumina because the melting point of feldspar is around 1200°C and pyrophyllite dehydroxylates around 900°C. The kinetic properties of batch melting were investigated by Batch-Free Time method, which defines the melting ability of the modified batch. According to thermodynamic calculation, it was found that both alternative batches were melted easier. The study showed that feldspar or pyrophyllite could be used instead of alumina without significant changes in glass chemical composition and physical properties. The concern of using feldspar or pyrophyllite is the quantity of minor impurities which affect to the color appearance especially in clear glass products.
Abstract: Magnetic fluid is a special class of materials which possesses the advantages of a liquid state of the carrier and a magnetic state of the particles. In addition to the conventional uses in mechanical engineering, magnetic fluids containing magnetite (Fe3O4) superparamagnetic nanoparticles are under research and development for drug delivery, hyperthermia and MRI contrast agents. On the other hand, iron-platinum (FePt) is investigated as materials for ultrahigh density recording. Before their assembly into patterned media, the as-synthesized FePt nanoparticles in superparamagnetic state are commonly stored in forms of magnetic fluids. In this work, iron-platinum (FePt) nanoparticles with their surface modified by oleic acid and oleyleamine were synthesized from the polyol process. The starting material was an environmental friendly iron(III) acetylacetonate and the products were dispersed in n-hexane. In small-angle X-ray scattering (SAXS) measurements at the Synchrotron Light Research Institute, Thailand, each magnetic fluid was injected into a sample cell with aluminum foil windows and the X-ray of wavelength 1.55 Å from BL2.2 was used. The measured SAXS intensity profiles as a function of the scattering vector from 0.27 to 2.30 nm-1 were fitted and compared between two different reactions. Nanoparticles synthesized by using a higher amount of Fe(acac)3 were matched with monodisperse spheres of radius 2.4±0.3 nm. The other reaction with a reducing agent gave rise to smaller nanoparticles of two size distributions. From this work, the potential of synchrotron radiation to complement conventional characterization techniques in the investigation of nanoparticles for high density recording and biomedical applications is underlined.
Abstract: Herbal compress ball has been traditionally used in Thai spa industry. The major limitations of the product are microbial contamination and a short reuse-cycle. Thus, this work attempts to develop the ceramics in the form of compress ball. The porosity of the prepared porcelain ceramics, which affects the different absorption and vaporization of essential oils, was studied by the variation of Al2O3 quantities and firing temperatures. The absorption and vaporization on water and essential oils of the developed ceramics were studied at ambient temperature (24-27 °C), 50 °C and 100 °C. The ceramic product fried at 1150 °C possessed a higher absorption and evaporation than that fired at 1230 °C in all evaporated temperatures. Moreover, in term of the absorption property, water absorption raised as the Al2O3 content increased however; at 1150 °C of firing temperature, water absorption increased to maximum at 4% Al2O3 content but decreased at higher content. In addition, ceramic compress ball with the optimal properties (fired at 1150 °C, 4% Al2O3) was prepared and 60 mg of mixture of Plai oil, Lemongrass oil and Kaffir lime oil were added into the compress ball. The product was then tested by 10 volunteers and it showed that 80% of volunteers were highly satisfied with the product. Even though, the ceramic compress ball product tends to have volunteer’s positive satisfaction, there are some issues for further improvement such as rough and hard feeling, shape and usability of the product.
Abstract: The biocompatibility of orthopaedic or dental metallic implants can be significantly enhanced by the coatings of bioceramic materials. Currently, various deposition techniques such as plasma spraying, magnetron sputtering and pulsed laser deposition can be used for the metallic implant coating. Nevertheless, these methods are addressed as a high temperature processing and manufacturing cost. Electrostatic spray deposition (ESD) has gained interest due to its simple and economical process involving a room temperature processing. Hence, the objectives of this study have focused on preparation and characterisation of cattle bone based hydroxyapatite (cHA) stainless steel implant coatings using ESD. Process parameters including electrode-substrate distance, applied electrical voltage, powder feed rate and current were optimised. The chemical composition of cattle bone powder was investigated both before and after coating by X-ray diffractometry (XRD). The XRD pattern of cattle bone powder demonstrated that all significant peaks matched with HA both before and after coatings. The morphological characteristic of the coatings was examined by scanning electron microscope (SEM). The surface morphology of the coatings showed a homogeneous and dense layer. The average thickness was about 40 µm. The in vitro bioactivity of cHA coatings was investigated by an acellular simulated body fluid soaking experiment. The accelerated apatite precipitation process occurred on the cHA-coated stainless steel surfaces compared to the uncoated stainless steel surfaces. Thus, the use of ESD is a promising technique in producing cHA coatings for biomedical applications.
Abstract: Virgin coconut oil (VCO) has been utilized as traditional medicine and herbal vehicle especially in tropical countries. The wax formation dispersed in this oil during storage at cool environment makes it not homogenous and opaque. The utilization of this oil is limited for the cool climate countries and also this is difficult for using it as injectable oil vehicle in pharmaceuticals. Therefore the decrease of wax formation temperature will possibly diminish this problematic behavior. The purpose of this study is to investigate the wax inhibitor capability of other injectable vehicles and controlled drug release characteristic of VCO without or containing these vehicles. Ibuprofen (IB) which is non steroidal anti-inflammatory drugs (NSAIDs) was used as a model drug because it can be soluble in VCO. N-methyl-2-pyrrolidone (NMP), benzyl benzoate (BB), benzyl alcohol (BA), isopropyl myristate (IM) and ethyl oleate (EO) were employed as injectable vehicles. Viscosity, pour point, cloud point and polarized light microscope examinations were conducted to characterize the change of VCO physical properties. In vitro drug release experiment was performed using dialysis method at 50 rpm and 37 °C, in phosphate buffer pH 7.4. Then least square fitting in vitro release data to the different mathematical expressions (power law, first order, Higuchi’s and zero order) was carried out using Scientist 2.1 Programme. Because injectable vehicles decreased viscosity of VCO, they improved the efficiency for measuring the VCO viscosity at lower temperature. BB and NMP were chosen as representative of the injectable vehicles because they showed many proper properties for injectable formula. Both pour point and cloud point were apparently reduced by BB greater than NMP, because BB could disturb the wax crystal formation as seen under polarized light microscope. The release rates of IB without or containing injectable vehicles were not different. From curve fitting, drug release profiles were first order kinetic therefore the drug release depended on the drug concentration in dialysis tube. From the results indicated that the injectable vehicles especially, BB and NMP could inhibit the VCO wax formation but not affected the drug release kinetic from VCO.