Key Engineering Materials Vol. 751

Abstract: Nowadays, increase in numbers of automotive results in a large amount of used engine oil, which is a waste and has a tremendous effect on the environment. Used engine oil, however, has a relatively high calorific value so that it is interesting to be used this waste as a renewable fuel for heat generation. The present experimental study on used engine oil combustion in a vertical tube burner, therefore, had been conducted. The two-stage combustion was divided by the air supply to the burner into two levels and the air flow rate of both levels can be adjusted. The fuel in the first stage was heated and vaporized by the incompletes combustion. The exhaust gases and residual fuel vapor from the first stage were then flow to the second combustion stage and the complete combustion was achieved. The combustion temperatures along the length of the burner in both of the single and the two stage combustion had been measured and compared. Amount of exhaust gases at the exit of the burner was also monitored. The results revealed that the temperature profile along the length of the burner in the combustion zone of the two-stage burner was higher than those in the single-stage type as a result of a better mixing of air and fuel. In addition, it also found that an increase in a distance of air supply location between two stages resulted in an increase of the emission.

Abstract: Biogas derived from anaerobic digestion of biological wastes has been extensively used for heating purposes and/or electricity generation. Presence of hydrogen sulfide (H₂S) in biogas affects engine performance adversely, thus reducing H₂S content is a valuable part in practical application before utilizing biogas. Adsorptive separation is very appealing due to being an economical and effective method including the use of iron oxide based adsorbents. Pelletization of iron oxide adsorbents has never been reported among the adsorbents described to date. Therefore, H₂S capture in two iron oxides (ferric oxide (Fe₂O₃) and magnetite (Fe₃O₄)) was experimentally investigated to determine technical feasibility of shaping pellets based on active iron oxide sorbent in removing H₂S from a simulated gas stream (0.35 vol.% H₂S balanced in N₂). Many factors affecting the behavior of gas adsorption such as gas in-flow rate, adsorption temperature, binder loadings and textural characteristics were considered. The pellet strengths were also undertaken using a bulk crushing strength analyzer. The results indicated that higher temperature favors the diffusion of H₂S molecules from the surface into the bulk of iron oxides. The H₂S-sorption capacity of Fe₃O₄ sorbent was higher than that of Fe₂O₃ sorbent corresponding with the different pore volume and surface area in each adsorbent. With the same active Fe₃O₄, the extruded pellet produced with starch binder showed the excellent H₂S uptake and crushing resistance. The higher gas in-flow rate had positive impact to contacting efficiency and mass transfer of solid and gas phase. The adsorbed H₂S gas can be readily desorbed from the pellets with the desorption temperature below 60°C and the H₂S-sorption capacity was consistent over repeated cycles. The pellets can be reused several times for consecutive adsorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial absorbers.

Abstract: The crystallization of planar solid oxide fuel cells (SOFCs) sealant glasses in the systems BaO-Al₂O₃-SiO₂-B₂O₃ (BaBS) and BaO-Al₂O₃-SiO₂-B₂O₃-ZnO (BaBS-Zn) was investigated via both X-ray diffractometer and scanning electron microscopy with energy dispersive spectroscopy. The effect of nucleation heat-treatment of the BaBS glass at different temperature for 5 hours, i.e. 550 and 590 °C, on the crystallization behavior was also studied. Thermal expansion profiles of the glasses indicate that both glasses have a low sealing temperature. XRD patterns of all BaBS glass-ceramics, devitrified at 800 °C for 30 hours, show that Ba₂Si₃O₈, BaAl₂Si₂O₈, Ba₃B₂O₆ and some unknown crystalline phases were found. It was also found that crystalline size of unknown barium aluminosilicate with low silicon content depends on the nucleation heat-treatment temperature. For the ZnO-containing glass, ZnO reduces the coefficient of thermal expansion value of glass and causes the devitrification of large needle-like barium zinc silicate phases. The crack at the YSZ/BaBS-Zn glass-ceramic interface was also observed. Two barium silicate phases, which are BaZnSiO₄ and BaZn₂Si₂O₇ were devitrified in ZnO-containing glass-ceramic.

Abstract: In this research, sodium silicate (Na₂SiO₃) was prepared by rice husk ash reacted with 10 M sodium hydroxide. The mixtures were heated by microwave at 400, 600, and 800 watt for 5 and 10 minutes. The formation of sodium silicate was characterized by Fourier transform infrared spectrophotometer. The vibrations of (Na)O–Si–O(Na) and O–Si–O were observed at 595 and 1023-986 cm^-1, respectively, except at 800 watt disappeared those vibrations. The results of flame atomic absorption spectrophotometer provided the mole ratio of sodium and silicon was 2:1 as heating the product at 600 watt for 5 and 10 minutes. The phase of sodium silicate was characterized by X-ray diffraction. Sodium silicate could be used as catalyst as in biodiesel production from palm oil. The percentage of yield was 81 by volume.

Abstract: Ceramic injection moulding (CIM) has advantages for a cost effective fabrication of large-scale, near-net-shape products. In this work, CIM is carried out to prepare porous anode-support for solid oxide fuel cells (SOFC) applications. The CIM process started with a preparation of feedstocks by mixing powder with binder. The feedstock is then injected into the mould of desired shapes. The mouldings were subsequently undergo the removal of the binder (debinding) and, finally, sintering. It is shown that porous nickel oxide-yttria stabilized zirconia (NiO-YSZ) anode-support for SOFC were successfully prepared by CIM technique. In addition, a water-soluble based binder system, consisted mainly of polyethylene glycol (PEG), has been used in this work. This is to avoid the use of organic solvents when wax-based binder was used. Therefore, it can promote more environmentally friendly process. The removal of binder was carried out using water debinding technique. The porous anode for SOFC was subjected to systematic characterisation. The effect of processing parameters, such as powder characteristics and powder/binder ratio has been investigated. Rate of binder removal was also studied. The porous anode specimens were characterised for their properties and microstructure. It was also found that the porosity of the specimens can be controlled by adjusting the sintering temperatures and holding times.

Abstract: Thin film electrolyte made of 8-mol% yttria stabilized zirconia (8YSZ) was fabricated on porous NiO-8YSZ anode substrates using electrophoretic deposition (EPD). The porous NiO-8YSZ anode substrates were prepared by powder injection molding technique. The electrolyte suspensions containing 8YSZ nanoparticles and polyethylene glycol (PEG) as a dispersant (1-19 wt%) were formed in ethanol. The maximum zeta potential value was obtained from the 8YSZ suspension with 5 wt% PEG considered as an optimal content of PEG dispersant. The electrophoretic deposition of 8YSZ film was performed on the porous anode substrate using a constant voltage of 30 V for 150 sec prior to co-sintering at different temperatures in order to obtain dense 8YSZ electrolyte film on the porous anode substrate. Co-sintering at 1250°C for 1 h resulted in a formation of a dense 8YSZ thin-film electrolyte with a thickness of 6.35 mm. An open circuit voltage at 800°C of a single cell having 8YSZ thin-film electrolyte on porous NiO-8YSZ anode substrate was 1.09 V, indicating a gas-tightness of 8YSZ thin-film electrolyte fabricated by using EPD.

Abstract: Corncob represents a great potential as a raw material for the production of high-value added chemicals, fuels and other industrial products. Thus, corncob is suitable residue for study molecular structure through the pretreatment method. In this study, the effect of calcium-based salts on the hydrothermal carbonization (HTC) of corncob were studied at 160, 180, and 200 °C for 2 h. CaSO₄ and Ca₃(PO₄)₂ were used as a reaction medium. Hydrochar was characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and ATR-Fourier transform infrared spectroscopy (ATR-FTIR). Characteristics of the hydrochar varied with calcium-based salt. Cellulose crystallinity in hydrochar decreased dramatically and carbon content in hydrochar obviously increased when Ca₃(PO₄)₂ and CaSO₄ were added, respectively. In case of hydrothermal at 180°C with Ca₃(PO₄)₂ and CaSO₄, the carbon microsphere was occurred.

Abstract: Solid oxide fuel cell (SOFC) is an electrochemical energy conversion device which is considered as clean energy source generator with reliability and relatively inexpensive production cost. One of the most important components for planar design SOFC is the hermetic seal that prevents fuel from leaking out of between the stack of fuel cells. Glass-ceramics are attractive materials as sealing materials for this device. The expected coefficient of thermal expansion (CTE) of the glass-ceramic sealants should be between 9 and 12 x 10⁻⁶ K⁻¹. Glass – ceramics based on åkermanite (Ca₂MgSi₂O₇) crystalline phase were reported their high CTE value from about 10 to 11.3 x 10⁻⁶ K⁻¹. In this study, glass compositions in the CaO-MgO-B₂O₃-Al₂O₃-SiO₂ system with varying amounts of Bi₂O₃ from 0 to 10 wt. % were prepared by conventional melting and investigated their properties. The selected compositions were derived from ternary åkermanite–forsterite–anorthite phase diagram. Phase composition and quantitative phase analysis of glass–ceramics were examined by X-ray diffractometer. The onset of crystallization (T_x) and crystallization temperature (T_c) were measured by DTA. The thermal properties of bulk glass samples and heat treated samples at 900 oC for 2 h which were glass transition temperature (T_g), dilatometric softening temperature (T_s), and coefficient of thermal expansion (CTE) were determined by dilatometer. Furthermore, the long-term stability of their CTE was investigated. The samples were continued to soak at 800 °C for 100 h and observed their change in CTE value. The results found that the åkermanite phase tended to increase with increasing amount of Bi₂O₃ content.

Abstract: In this study, the synthesis of the ternary semiconductor sensitized silver bismuth telluride (AgBiTe₂: SBT) particles was produced in the solution of AgNO₃, Bi (NO₃)₃×5H₂O and Na₂O₃Te by using a chemical bath deposition (CBD) method and annealing at 200°C for 1 h. According to scanning electron microscopy (SEM), the particle size of SBT after annealing was bigger than before annealing. Based on X-ray diffraction, the SBT after annealing for 1h became more crystalline. In addition, the XRF data also demonstrated that the SBT powder consists of Ag, Bi, and Te as dominant elements. The XRD result confirms a successful growth of the SBT particles with rhombohedral crystal structure. Based on the obtaining results, the SBT particles were successfully synthesized and potentially applied for solar cell application.

Abstract: Two transition metals were loaded on H-ZSM-5 zeolite to produce bimetallic zeolite supported catalysts for catalytic pyrolysis reaction. Ni and Co metal were loaded on H-ZSM-5 via wet impregnation method. The loading sequence was applied using one-step and two-step loading method. The different loading sequence affect surface properties of catalyst and catalytic activity in pyrolysis reaction. The bimetallic catalysts were prepared at Ni+Co metal loading content of 10+10 wt% (Ni:Co=1:1) to 10+20 wt% (Ni:Co=1:2 or 2:1). All bimetallic catalysts supported on H-ZSM-5 were calcined and characterized by X-ray Diffraction (XRD), Surface area analysis (BET) and Temperature Programmed Desorption of ammonia (NH₃-TPD). The XRD patterns of bimetallic zeolite supported catalysts revealed that loading of two metals at high content affect crystalline structural of ZSM-5 support. All XRD patterns illustrated peaks characteristic of ZSM-5, cobalt oxide and nickel oxide. The NH₃-TPD results showed number of acid sites of the catalyst which revealed that the acid sites of ZSM-5 support was weakened with transition metal added. The two-step loading of 10+20 wt% metals on ZSM-5 reduced the peak intensities of NH₃ desorption due to the metal particles aggregate on acid sites of ZSM-5. The two-step 10+20 wt% bimetallic catalysts has the lowest surface acidity, followed by the one-step 10+20 wt%, the two-step 10+10 wt% and the one-step 10+10 wt% bimetallic catalysts, respectively. Jatropha residue was used for catalytic pyrolysis study. Jatropha residue and bimetallic catalyst was pyrolyzed at 500 °C in a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The product vapor was analyzed by GC/MS for the different groups of organic products such as fatty acid, aldehydes, ketones, aliphatic hydrocarbons, aromatic hydrocarbons and nitrogen compounds. The product from catalytic pyrolysis of jatropha residue with bimetallic zeolite supported catalysts enhance deoxygenation reaction that resulted in high aliphatic and aromatic hydrocarbons product. The one-step loading at ratio Ni:Co = 1:1 (10+10 wt%) gave the highest hydrocarbons product yield at 57.81%.