Abstract: Nanofluids have great attention in the world due to big potential to replace conventional fluids that have been used in some systems such as automotive, nuclear reactors, solar heating, building heating, and industry. Utilization of indigenous raw material in production of nanoparticles is a key to reach real application of the nanofluids. The aim of this study is to know the effect of combination of organic agent in solgel synthesis on characteristic of Al2O3 nanoparticles and nanofluids made of them. In this study, Al2O3 nanoparticles have been synthesized from local bauxite using solgel method with citric acid and PEG 4000 as chelating and capping agent. Nanofluids with pH 10 were prepared from the nanoparticles. Raw material of Al (OH)3 was extracted from the bauxite. Powder of Al (OH)3 was diluted in water, and citric acid and PEG 4000 was added into the solution to form a sol. The sol was heated to form a xerogel, and then calcined at 900°C for 3 hours to get the Al2O3 nanoparticles. From the synthesis we got gamma-Al2O3 nanoparticles with crystallite size of 4.0-4.6 nm. From the characterization data of the nanofluids it was known that the nanofluids with concentration of Al2O3 nanoparticles of 0.025 vol % to 0.1 vol% possessed relatively high zeta potential of-39.2 mV to-40 mV, and good critical heat flux (CHF) enhancement of 13% to 74%. The nanofluids had large potential to be applied as coolant for External Reactor Core Cooling System (ERVCS), ECCS (Emergency Core Cooling System), electronics, automotive, metal forming and solar heating system.
Abstract: Cooling rate plays an important role in the formation of thin wall ductile iron microstructure due to their thickness, which is 3 mm below based on Stefanescu. Cooling rate is closely related to casting design and determines the microstructure. This paper discusses the effect of casting design modification to casting yield and microstructures. Modification was made on a patented design used previously to produce thin wall ductile iron plates. The design was minimized and casting simulation was used to analyze castability of the design. After that, the design were casted in several pouring temperatures. Improvement was made to casting design based on the failure during the experiment. Casting process took place after simulation analysis. The casting product was fully casted as shown by the simulation. The casting yield has improved to 28%. When all plates were examined for microstructure, the result showed that all the microstructure of the plates was not graphite in ferrite matrix as occurred in the patented design but it was graphite in pearlite matrix.
Abstract: Lampung is one of provinces with wide area of palm oil plantations and processing industries in Indonesia. Each palm oil mill produces 0.7-1 m3 of POME per ton of fresh palm bunches and pollutes the environment when untreated. Furthermore, Lampung is also a region with abundant Natural Zeolites (ZAL) availability. This research was performed to study the influences of modified ZAL as the microorganisms immobilization media (Biocarrier) in biogas production of POME. Hereafter, ZAL as Biocarrier will be applied on Anaerobic Fluidized Bed Reactor (AFBR). AFBR with biocarrier will have higher efficiency than conventional biogas reactor. Furthermore the vertical design of the AFBR does not require excessive land. Modification of ZAL was conducted to provide appropriate place for microorganisms, especially methanogen. This research was started by physical modification of ZAL (CV. Minatama, Lampung), followed by impregnation of ZAL by Fe2+ and Mg2+. Each of the modified ZAL was analyzed by XRF, then characterized by XRD and FTIR before used. Based on XRF analysis, SiO2/Al2O3 mol ratio of physical activated ZAL was 8.913, while ZAL-Fe2+, and ZAL-Mg2+ were 9.957 and 8.8, respectively. The anaerobic process took place in a 2.8 L batch anaerobic digester by adding POME and an active digester effluent of cattle manure as microbial inoculum and 280 grams of each type of the modified ZALs to each digester. Result showed that that impregnated ZAL decreased the organic content of POME more rapidly than the physically treated ZAL. Besides, impregnated zeolite also resulted in higher methane concentration than the digester using physical activated.
Abstract: MgB2 superconductor with relatively high critical temperature (Tc=40 K) has been developed for possibilities utilization in various practical applications such as Magnetic Resonance Imaging. In order to enhance the process, the material was prepared by Powder-In-Tube (PIT) method, while the superconducting properties was improved by incorporating 0 wt.%, 10 wt.% and 20 wt.% SiC nanoparticles into MgB2 structure. This study aimed at analyzing the effect of sintering temperature on the microstructure, resistivity and phase of Fe-sheathed MgB2 superconducting wires. Three different compositions of MgB2 powders were inserted into Fe tube with inner ø of 4 mm and outer ø of 6 mm. This tube was then rolled and drawn into a ø 2.5 mm wire. Wire samples with three different compositions of SiC were heat treated at 600°C and 800°C respectively. All samples were characterized to analyze the morphology, resistivity and crystal structure. X-ray diffraction (XRD) analysis showed that some Mg may react with SiC to form MgSi and with oxygen to form MgO. Scanning electron microscope (SEM) images revealed that with no addition of SiC, MgB2 was formed and dispersed uniformly in wire, but with 10 wt.% and 20 wt.% SiC nanoparticles, the whisker morphology was observed resulting in degradation of the superconducting properties.
Abstract: Used of carbon pyrolyzed from table sugar in the synthesis of LiFe(1-x)VxPO4/C for lithium ion battery cathode has been examined. The process was begun by synthesizing LiFePO4 through a hydrothermal method with the precursors of LiOH, NH4H2PO4 and FeSO4.7H2O. The as-synthesized LiFePO4 was then mixed with various H4NO3V concentrations and fixed 3 wt.% of carbon pyrolyzed from table sugar and calcined for 2 hours at 400 °C. The result was ball-milled and was then characterized using a thermal analyzer to determine the transition temperature at which sintering temperature of 700 °C for 4 hours was obtained. X-ray diffraction (XRD) was performed to analyze the crystal structure whereas scanning electron microscope (SEM) was used to examine the microstructure and surface morphology. XRD results show that LiFe(1-x)VxPO4/C phase has been formed with an olivine-based structure. SEM results showed an even distribution of LiFe(1-x)VxPO4/C particles. The batteries were prepared from the as-synthesized materials and were tested using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge and discharge (CD) tests. The EIS results showed that carbon improved the conductivity. The performance test showed that the addition of vanadium resulted in a capacity of about 51.06 mAh/g with a potential of 3.581 V at charging and 49.42 mAh/g with a potential of 3.319 V at discharging. These results are promising in terms of using table sugar as a cheap carbon source for lithium ion battery cathode development.
Abstract: Beta type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) is one of the titanium alloys which have gained much attention in dental applications. Dental precision casting is predominant for fabricating dental prostheses. However, there is a possibility for the mechanical properties of its casting to be degraded because of a α case, shrinkages and pores and a dendrite structure. One of the ways to enhance their mechanical properties is heat treatment process. Therefore, the aim of this study is to investigate the effect of aging treatment on mechanical properties and microstructure of TNTZ cast into magnesia based mold in order to improve its mechanical properties. As results, the Vickers hardness of the cast TNTZ after solution treatment is larger than that of the wrought TNTZ. The aging curve of the cast and the wrought TNTZ at an aging temperature of 673 K and 723 K exhibit almost similar pattern. For each aging time, the higher the aging temperature, the smaller the Vickers hardness for both alloys. Microstructures of cast TNTZ at various aging conditions consist of a dendritic structure and the average diameters of their grain size are around 40 μm. The diffraction peaks of precipitation of α and β phase s are detected in under aging (UA), peak aging (PA) and over aging (OA) conditions for both aging temperatures. However, the diffraction peak of ω phase is observed only in OA condition for cast TNTZ at aging temperature of 673 K. The highest tensile strength of the cast TNTZ and the wrought TNTZ at both aging temperatures are in PA condition and the elongation decrease continuously by increasing aging time. The tensile strengths of cast TNTZ in UA, PA and OA conditions at an aging temperature of 723 K are lower and their elongations are higher in comparison with those of 673 K. The high oxygen content seems to contribute to the poor elongation. SEM fractographs of the cast TNTZ at aging temperatures of 673 and 723 K in UA, PA and OA conditions show the brittle morphology with intergranular fracture that increases with increasing of aging time.
Abstract: Activated carbon has been successfully prepared from coconut shell charcoal using novel dry mechano-chemical activation with KOH and planetary ball mill. The combination of chemical activation and mechanical activation on coconut shell charcoal is found to increase its micopore volume and surface size. These increase yielded to a high adsorption capacity which was measured at 298 K and 268 K found to be 0.6 wt. % for activated carbon. The adsorption experiments were conducted using constant-volume-variable-pressure (CVVP) test. Adsorption parameters were calculated using adsorption isotherm models: Langmuir and Dubini-Asthakov models and were found in good agreement for type II adsorption phenomenon. It is also found that the adsorption capacity of activated carbon was suitable for hydrogen storage application.
Abstract: In this experiment, the influence of non-treated (NT), natural aging (T4) and artificial aging (T6) heat-treatments was investigated on the tensile strength of Al-5.9Cu-1.9Mg at different casting temperatures. Three levels of casting temperatures were used: 688, 738, 788 °C while the mold temperature was kept constant at 220 °C. The cast sample was heat-treated by natural aging and artificial aging techniques. The results show that the tensile strength in the non-treated sample decreases initially and then rises slightly with increasing casting temperature. The effect of casting temperature on T4 involved first an increase in tensile strength and then a decrease when elevating the casting temperature, but with no significant effect. In the T6 treatment, the tensile strength first decreases followed by a slight increase with increasing casting temperature. The heat treatment process improved the tensile strength in the three different samples, except at a casting temperature of 768 °C.
Abstract: Aluminium 6061 composites have been succesfully produced by stirr casting method. The process involved melting aluminium at 800°C and mixed with AlSr, TiB and Mg to produce master alloy of matrix phase, then degassing to remove all of gas entrapped in molten aluminium by argon. There are two types of particles reinforced added into aluminium to produce aluminium composite such as SiC and Al2O3. The particles reinforced addition for both SiC and Al2O3 are started from 2vf-% to 10vf-% to obtain the optimum compostion which have good mechanial propperties. The addition of 10wt-% Mg is to promote wetting between matrix and reinforced while the addition of AlSr and TiB are to improve mechanical properties by modifying the eutectic structure as well as grain refinement of the matrix phases. The two composites are compaired both mechanical properties and microstructure analysis. The mechanical properties of Al/SiC composites such as tensile strength, elongation, and hardness have a maximum value at addition of 10 Vf-% SiC with the value up to 230 MPa, 6.5%, and 62 HRB respectively. While for Al/Al2O3 composites have the highest tensile strength and elongation at 6 Vf-% Al2O3 with the value of 224 MPa and 7% respectively, but the highest hardness is obtained at addition of 10 Vf-% Al2O3 reaches to 55 HRB. The percentages of porosity were increased for both composites along with the increase of particles reinforced. The microstrutures for both composites are similar since they have the same matrix and Sr clearly changed primary Mg2Si become finer chinese scripts, while TiB as grain refiner worked efficiently for higher reinforced particles addition because the grain size reduced for both composites.