Key Engineering Materials Vols. 675-676

Abstract: The optical and scintillation properties of Ce³⁺-doped YGd₂(Al,Ga)₅O₁₂ single crystal scintillators were investigated. The Ce³⁺ 5d-4f emission was blue-shifted with increasing Ga content due to the decrease of the crystal field strength. Temperature dependence of the photoluminescence decay times was measured and the thermal activation energy for the luminescence quenching was calculated. Light yield (LY) and its dependence on an integration time were measured under γ-ray excitation. The fast component content in the scintillation response increases with increasing Ga content. The YGd₂Al₂Ga₃O₁₂:Ce sample showed a high LY of 38,000 photons/MeV. The decrease of LY value observed for a YGd₂Al₁Ga₄O₁₂:Ce sample is mainly due to the thermal ionization of the 5d₁ excited state of the Ce³⁺ emission center to the conduction band.

Abstract: In this work, Pd metal layer was deposited on in-house prepared macro-porous disc alumina support by electroless plating. The in-house prepared support were repeatedly seeded for 4 cycles to obtain Pd nuclei before repeatedly electroless plated for 4 cycles. The 4-cycle Pd plating was to obtain the full layer of Pd metal observing from changing support surface from black to light grey. The plated membrane samples were annealed at 550 and 600oC for using in high-temperature H₂ separation. The annealed samples were observed morphology by SEM and confirm the occurrence of Pd layer with EDS. The SEM images revealed incomplete Pd layer. The over 4 cycles of plating were needed to form complete Pd layer since the numerous Pd ions diffused into macro-pores alumina support instead of depositing on the surface of macro-porous support. The higher annealing temperature of 600oC led to denser layer of Pd with the presence of small cracks due to the contraction of Pd particles.

Abstract: The prepared TiO₂ and commercial grade of TiO₂ with anatase and rutile phase combined with bulk and powder of activated carbon (TiO₂/AC) observed the photocatalytic activity under weak UV. The surface fluorination was applied for all photocatalysts (F-TiO₂/AC) to enhance photocatalytic activity. The decolorization of methylene blue (MB) was used to indicate the efficiency of adsorption and degradation of the samples. The prepared TiO₂ was prepared by Sol-Gel method under condition of the titanium tetraisopropoxide (TTIP) to 2-propanol (2-PP) ratio of 1:30 and adjusts pH of 2 by HCl acid. Under surface fluorination, the samples of TiO₂/AC were immersed of 2 hours under NaF solution of 30 mmol. Surface morphology was observed by field-emission scanning electron microscopy (FE-SEM). MB absorption was recorded by UV-VIS spectrophotometer to indicate MB decolorization. The results showed that, MB were under photocatalytic test of the rich porosities of AC and prepared TiO₂/AC were the highest decolorization due to AC showed high adsorption and prepared TiO₂/AC showed high decomposition of MB. Both of TiO₂/AC and F-TiO₂/AC, pure anatase phase showed higher photocatalytic activity than pure rutile phase. Under the same crystalline phase, F-TiO₂/AC showed higher photocatalytic activity than TiO₂/AC. Prepared TiO₂ showed higher photocatalytic activity than TiO₂ of commercial grade. Moreover, under the same TiO_2, AC powder showed higher adsorption than AC bulk due to AC powder has surface area greater than AC bulk. The best sample for MB-decolorization was F-prepared TiO₂/AC powder. Under the sample to MB solution (0.05 mmol) ratio of 0.15g: 400 ml, the MB solution changed to be the colorless solution after treatment of 5 min.

Abstract: Rice husk is an agricultural residue from a rice-mill known as a rich source of silica. In this study, the rice husk was extracted for the contained silica by pretreatment with hydrochloric and calcination at 700 °C, and the white rice husk ash (WRA) mainly consisting of the silica was finally obtained. WRA was then investigated for its composition and structure with X-ray fluorescence (XRF) and X-ray diffractometer (XRD). The results showed that WRA contained a large amount of silica (90%) with amorphous structure. After that, WRA was used as filler for the preparation of natural rubber products. Two kinds of the natural rubber products were prepared here: 1) the pure natural rubber (PNR) product and 2) the deproteinized natural rubber (DNR) product. DNR was a protein removal natural rubber which is suitable for use as a dental material with the low allergenic properties caused from the proteins. Additionally, DNR used in this study could be provided by removing proteins from the natural rubber latex with 0.1 % urea in the presence of surfactant at room temperature. It was found that the nitrogen content (main element of proteins) of DNR was lower than PNR under the test condition. For the preparation of natural rubber products, WRA was mixed into the PNR and DNR latexes comparing with the commercial silica (Hisil-233). All finished latexes were compounded to obtain the natural rubber products. The viscoelastic properties and the cure characteristics of the entire products were investigated. It can be observed that WRA can be comparable with the commercial silica for use as filler for the natural rubber products. This is an attractive option to produce dental materials from the agricultural residues, which will reduce the cost of the production and also add value to the agricultural residues.

Abstract: Measurements of basic materials properties of building materials with pozzolanic waste admixture originated from grinding of thermally insulating bricks were performed by means of pycnometry method. Besides, the thermal conductivity dependence on the moisture content measurements were carried out by using a non-stationary pulse method. Obtained data were subsequently analyzed by simple Wiener’s bounds and sophisticated homogenization formula taking into account the shape of ellipsoidal pore inclusions. Validity of applied homogenization models were assessed by comparison of the measured and the calculated data. On the basis of experimental data and homogenization analysis, the shape effect on the thermal conductivity is discussed.

Abstract: Ammonium dihydrogen phosphate (ADP) crystals is very interesting due to its nonlinear optical property. This study investigated on improving of material for academic use by adding boric acid to modify ADP crystals. Slow evaporation method in aqueous solutions of pure ADP and ADP doped with three concentrations of H₃BO₃ as 0.1, 1.0, 5.0 %wt were studied. The grown crystals were confirmed tetragonal structure by powder X-ray diffraction studies. The FTIR spectrum analysis presented various functional groups of boron in three conditions of doped ADP. TGA study was comfirned the temperature stability at 220 °C for both pure and doped ADP crytals. The machanical stress was analyzed by Vicker’s hardness measurement. The results of this analysis showed boric acid doped 1.0 %wt had superior machanical stress from 10 to 75 grams. ADP doped with boric acid at 1.0 %wt was accepted in all test properties.

Abstract: ZnO films were deposited on fluorine doped tin oxide glass substrate and chemically treated by KOH solutions. The films were immersed into 2 M KOH solution with various immersing time of 0-6 min at room temperature, rinsed and thermally treated. Small pore size was observed for treated films by scanning electron microscopy indicated that dense ZnO particles were removed. Eosin-Y sensitizer was loaded into treated photoanode using re-adsorption technique. The photovoltaic characteristics were investigated under standard light illumination (AM1.5). Short circuit current densities are not much changed for 0-4 min treatment. After then, it is rapidly decreased for 6 min treatment. Open-circuit voltage, fill factor and shunt resistance are increased after treatment. In addition, increased charge transfer resistance indicated that recombination is reduced by KOH solution treatment. The reduced recombination contributes efficient electrons transport through external circuit. These improvements resulting efficiency reached maximum value of 0.72% at 4 min treatment, compared with pristine cell efficiency of 0.64%.

Abstract: This work focuses on the oxidation behavior of 2.4wt.%C-30wt.%Cr-3.75wt.%V cast iron in air at 1000 °C for 1-48 h with weight gain measurements taken at different times. The oxidized surfaces and cross sections were characterized by XRD, OM, SEM and EDS. It was found that the as-cast microstructure consisted of a ferritic matrix and M₇C₃ carbide. The surface oxide scale consisted of multi-oxides and the grain size of the oxides increased with increasing holding times. XRD and SEM-EDS results revealed that the multi-oxide layer can be Cr₂O₃, (Fe,Cr,V)₂O₃ and SiO₂. After about 48 h, a continuous SiO₂ inner-layer was observed and the oxide scale tended to swell, contained pores, and became detached from the surface because of its poor adherence.

Abstract: Light green pigments based on Cr₂O₃, TiO₂, Al₂O₃ and SiO₂were prepared for reflective heat from solar radiation. The prepared pigment powders were mixed with ceramic glaze and sprayed onto ceramic substrates and then calcining accordance with ceramic processing for the reflectance measurement. The results show that the ceramic glaze 100 g mixed with the prepared pigment 5 g gives a maximum near infrared solar reflective of 70.94 %. The comparisons of performance test between prepared pigment and commercial green pigment that use for ceramic coating tile roof were covered two test boxes for temperature measurement. The results shown that the prepared pigment using make decrease the middle – room temperature less than commercial pigment using about 0.8 °C. It can be concluded that the prepared pigment is suitable to be used as a coating ceramic-based roofs for reducing the heat penetrating into the building.

Abstract: In this research, the effects of bismuth zinc zirconate (BZZ) additive on phase formation, microstructural and mechanical properties of bismuth sodium potassium titanate (BNKT) ceramics were investigated. The BZZ-doped BNKT ceramics were prepared using solid state reaction technique. The pure phase of BZZ-doped BNKT powders were achieved for a calcinations temperature of 850 °C for 4h. The obtained powders were pressed into small pellets and sintered at optimum temperature to from dense ceramics. The XRD analysis of the ceramics shows that all ceramic samples exhibited a pure phase perovskite structure. The bulk densities of samples were about 5.82-6.03 g/cm³ which measured using the Archimedes method. The mechanical properties were measured using micro hardness tester. The microstructural of sintered surface was investigated using scanning electron microscopy (SEM). Average grain size increased with increasing BZZ content. The relations of these results were discussed and compared to the previous works.