Key Engineering Materials Vol. 608

Abstract: Carbon and amorphous silica from rice husk charcoal was prepared by carbonization of rice husk in an incineration furnace around 700 °C. The rice husk charcoal was taken as a precursor in the synthesis of carbon and zeolite NaA composites by hydrothermal method at various synthesis temperatures of 80-110 °C and for 2-8 hour. The composite powder was formed into rectangular shape of 10 mm width, 60 mm length and 10 mm thickness by hydraulic pressing at 60 MPa with 1% of carboxy methyl cellulose mixed with 5-20% of phenolic resin as binders. Samples were fired in a tubular furnace with 5% CO₂+N₂ gas flow at 300-700 °C for 1 hour as the thermal activation of carbon and sintering of the composite samples. Activated carbon and zeolite NaA composites were characterized in terms of phase analysis, morphology, thermal stability, mechanical strength, calcium ions absorbtivity and specific surface area by x-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), three points bending, inductive coupled plasma-optical emission spectroscopy (ICP-OES) and brunauer-emmett-teller technique (BET), respectively.

Abstract: The main focus of the research was to correlate the composition and sintering parameters with the microstructure and dielectric properties of Ta₂O₅ (Tantalum Oxide) doped BaTiO₃ (Barium Titanate) ceramics. Ta₂O₅ was doped at three different percentages viz. 0.5, 1.0 and 1.5 mole%. The doped samples were then sintered using both single and double stage sintering techniques. Thereafter field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) techniques were used to examine the structure of the samples with particular focus on the incorporation of Ta⁵⁺ions into the BaTiO₃ crystal lattice. Finally, the dielectric properties were analyzed using impedence analyzer and the relationship between the properties and structure of doped BaTiO₃ was established. From the research, it can be stated that double stage sintering yielded best dielectric properties. The best stable value of room temperature dielectric constant (k) of 19000 was obtained for 1.5mole % Ta₂O₅ doped BaTiO₃ sample, sintered at 1320°C for 0 hour and 1280°C for 6 hours due to the combination of high percent theoretical density (%TD) and optimum grain size. At a temperature range of 30°C to 60°C, this combination of composition and sintering parameters yielded dielectric constant in the range of 18000-19000.

Abstract: The ballistic performance of transparent armors has been continuously developed for an application on security purposes. Generally, ballistic performance of the laminated glass increases with its thickness and weight while the user requirement prefers high level of ballistic protection with thin and light weight body. In this study, fabrication of light weight glass-PVB transparent armors with the level-3 protection according to the National Institute of Justice (NIJ) standard was attempted. The ballistic performances of various configurations of glass-PVB laminates were determined against 7.62 mm ammunitions. Results from fragmentation analysis indicated the influence of glass-sheet-arrangement in the armor structures on the ballistic damages. The minimum requirement on the thickness of front-face layer was also discussed. To verify the experimental results, finite element analysis was performed on all laminated systems. It was found that the results from computational analysis were in reasonable agreement with the experimental results.

Abstract: Tricalcium phosphate (TCP) and hydroxyapatite (HA) are materials widely used to repair and reconstruct damaged parts of bone. They have been interesting for applying in human skeleton because of their excellent properties of biocompatibility, bioactivity and osteoconduction. Combining TCP and HA as composite material could improve their biological properties for artificial bone. In this work, phase, microstructure, and pore size of TCP/HA composite were observed at the various weight ratio of TCP:HA (7:3, 1:1, 1:4). The mixtures were formed in granule and then sintered at 1200, 1250, and 1300°C. The sintered granules of TCP/HA composite presented the porosity and pore size of 27-45% and 10-17 micron, respectively. The maximum porous sample was observed from TCP/HA composite at the weight ratio of 7:3 and it was selected to test for biocompatible prediction in vitro cytotoxicity by MTT assay.

Abstract: La_4-xSr_xNi₃O_10±δ (x = 0, 0.05, 0.1, 0.2, 0.3, 0.5 and 1) compositions synthesized via citrate gel method have been investigated as a candidate cathode for intermediate temperature SOFC. The n = 3 RP single phase of La_4-xSr_xNi₃O_10±δ (x = 0, 0.05, 0.1 and 0.2) can be achieved after calcined at 1000°C for 4 hrs in air. The further addition of Sr with x 0.3 leads to obtain La_2-xSr_xNiO_4±δ and NiO as the second phase. La₄Ni₃O_10±δ based material shows the highest electrical conductivity with a value of 124 S/cm at room temperature. With Sr dopant, both of transition temperature and the electrical conductivity of La₄Ni₃O_10±δ decrease and further decrease with increasing the amount of Sr. The electrical conductivity at 250°C of La_4-xSr_xNi₃O_10±δ (x = 0, 0.05 and 0.1) is 100, 94 and 75 S/cm respectively. For x = 0.3, 0.5 and 1, it reduces to the values of 28, 7 and 4 S/cm, respectively because of the lower conductivity phase of La_2-xSr_xNiO_4±δ.

Abstract: Hydrophilicity of the as-anodized films is an important factor for improving the osseointegration of Ti implants and bone tissues. This study investigated the surface characteristics and the hydrophilicity of the as-anodized films formed on Ti-6Al-4V. The as-anodized films on Ti-6Al-4V were prepared using galvanostatic method in 1M H₃PO₄ or 1M MCPM as an electrolyte with different current densities (5, 20, 80 mA/cm²) and using potentiostatic method with different voltages (5, 100 and 150 V) for 30 minute at room temperature. The as-anodized films shows a significantly lower water contact angle compared to the untreated Ti-6Al-4V. The porous oxide films were fabricated on Ti-6Al-4V. Ti 2p spectra show that the as anodized films consist of TiO₂ and O 1s present hydroxide (OH^-) and adsorbed water (H₂O) that effect to the hydrophilicity on the as-anodized film surface. These results demonstrate that the galvanostatic method at a high current density of 20 mA/cm² and the potentiostatic at a high voltage of 150 V in MCPM could enhance both of the high surface roughness and appropriate surface species which is leading to good hydrophilicity on the as-anodized films.

Abstract: Calcium phosphate cement has been widely used as a bone substitute because of its chemical similarity to natural bone. In this study, calcium phosphate cement was prepared using dicalcium phosphate dihydrate (CaHPO₄.2H₂O) and calcium carbonate (CaCO₃) as starting raw materials. The cement pastes were mixed and the chemistry adjusted with two different aqueous solutions of sodium hydroxide (NaOH) and disodium hydrogen phosphate (Na₂HPO₄). Concentrations of the solution were varied in the range 0.5 to 5.0 mol/L with the ratio of solid/liquid = 2 g/ml. The cement paste was then poured into a silicone mold having a diameter of 10 mm and a height 15 mm. Setting times for the cement were measured using a Vicat apparatus. XRD, FT-IR, and SEM techniques were used to characterize properties and microstructure of the cement. From the experimental results, it is clear that different concentrations of Na₂HPO₄ and NaOH have affected the setting times of the cement. The relationship between concentration of NaOH and Na₂HPO₄ and setting time, including final properties of the cement, is discussed.

Abstract: This research aimed to develop a cementing material from synthetic geopolymers using water treatment residue (WTR) from a water treatment plant in Bangkaen as an aluminosilicate starting material, with the addition of rice husk ash (BHA) from a paddy factory in Thailand as a source of crystalline silica, to achieve Si/Al ratios of 2.00, 3.00, 4.00 and 5.00. The geopolymers were prepared by NaOH activation of the five compositions of WTR and BHA mixtures, followed by curing at ambient temperature (29±2°C). The compressive strengths of the geopolymers were determined after 3, 7, 28 and 60 days. The samples cured for 28 days were examined by XRD, FTIR and SEM. The Si/ Al ratio of 2.00 was found to produce the greatest strength at all curing times. After 7 days, all samples were 30% stronger than the 3 day-samples. XRD revealed the presence of sodium aluminium silicate hydrate, while an FTIR vibration band related to the geopolymer product shifted to 1000 cm^-1. SEM revealed a homogeneous non-crytalline and dense microstructure in the sample with the highest Si/Al ratio of 5.00, suggesting that a transformation to sodium silicate had occurred in this sample.

Abstract: Soda-lime-silica glasses were prepared by the composition range of SiO₂ 67-72, Na₂O+K₂O 15-18, CaO+MgO 5-8, BaO 2-4 and ZnO 2 in wt% for producing low melting glass billets. The billet properties were similar to commercial glasses, but higher melting ability. Respecting to thermodynamic calculation approach, the exploited heat (H_ex), which was the required heat for melting the batch from atmosphere temperature to the melting temperature, was calculated in order to compare the melting ability. The results represented that glass batches with lower silica content which possessed lower H_ex than batch with higher silica and consequently higher melting ability. Therefore, to reduce melting energy, silica content in batches should be as low as possible. H_ex of batch with SiO₂ 67 wt% was 480 kWh/t, while the batch with SiO₂ 72 wt% was higher, namely 495 kWh/t. In addition, the glass batch with SiO₂ 67 wt% was completely melted at 1350 °C only. Properties of billets were determined, and the coefficient of thermal expansion was 9.6 x 10^-6 °C^-1. The glass transition point was 535 °C, and the refractive index was approximately 1.52. The study succeeded in producing glass billets with good quality and with melting temperatures lower than 1400 °C.

Abstract: Slumping molds or sagging molds are utilized for shaping glassware containers and many kinds of slumped glass products from glass plates. In Thailand, a large number of slumped glass factories use such molds in their production because slumping process is easy and cheap; however, the major cost of this process is slumping molds. They are imported from other countries and are expensive. In this research, slumping molds are created from local raw materials using the basic method to reduce the cost of the production. One of proper materials for making slumping mold is refractory mortar which can be easily formed into various shapes and sizes. Consequently, it is interesting to prepare slumping molds from refractory mortar. In this study, the effect of different sources of alumina (calcined alumina and aluminum sludge) and soaking time on the properties of the refractory mortar were investigated. Dolomite clay, milled sand and white portland cement were mixed with sources of alumina in distilled water to form pastes. Super plasticizer was added to the pastes to adjust flow ability. Plastic containers were used as molds for specimen forming. Specimens were cured at room temperature for 24 hours and dried in air for 24 hours. After that specimens were dried in an oven at 110 °C for 24 hours and then fired at 1100 °C. The result showed that the suitable condition for making slumping mold is to use calcined alumina as a source of alumina with soaking temperature of 1100 °C for 4 hours. The physical properties, chemical properties and thermal properties were discussed.