Advanced Materials Research Vol. 789

Abstract: Atomic layer deposition (ALD) technique shows superior application in the fabrication of TiO₂ inverse opals (IO), compared with conventional infiltration methods. In the present report, TiO₂ IO structures were infiltrated by ALD method in a continuous-flow and internally developed stop-flow process, respectively. The corresponding optical and optoelectrical properties of TiO₂ IO structures were investigated. The prepared uniform IO structure of 288 nm was used as a photoanode for dye-sensitized solar cells. An efficiency of 2.22% was achieved, which was much higher than that of prepared by conventional solution-infiltration method. It is indicated that ALD method is an effective approach for fabricating TiO₂ IO photoanode.

Abstract: Aluminum composite reinforced ceramic particles can be created through stirring process (Stir Casting) so that the molten aluminum to form a vortex as a space for the reinforced of Al₂O₃ particles well distributed on the aluminum melt. Engineering ceramic particles and vortex formation process will determine the distribution of particles in molten aluminum metal. Mg was added during the melting and argon was flushed to improve wetting system and protect oxidation. In this study, billet Al.6061 was combined with various percentage of Al₂O₃ from 5Vf % to 20Vf%. The results showed that the optimum tensile strength obtained at 10Vf % Al₂O₃ with the value of 190 MPa.

Abstract: A novel functional material has been synthesized by modification of multi-walled carbon nanotubes (MWNTs) with nanostructured zinc oxide (ZnO). Multi-walled carbon nanotubes have unique electronic and photonic properties, as well as nanostructured zinc oxide [. Both have advantages when combined as to provide a material with extremely high surface area-to-volume ratio, which is required for the sensor structure. So far, CNT-based gas sensors have been investigated for the detection of H₂, N₂, NO₂, and NH₃ [. In this study, modification of multi-walled carbon nanotubes with nanostructured zinc oxide is conducted by simple screen printing and ultrasonic spray pyrolysis (USP) methods, which consists of the fabrication of MWNTs paste, the formation of ZnO sol, and calcination. The deposited thin films are then characterized using several characterization techniques, such as X-ray diffraction and SEM. The performance testing of the sample as a CO gas sensitive layer has also been investigated and the measurement results on 100 ppm CO gas exposure at 250°C showed the sample had a sensitivity of 85%, response time of 5 minutes and recovery time of 20 minutes.

Abstract: We have investigated of composite (1-x)Ba_0.5Sr_0.5Fe_11.7Mn_0.15Ti_0.15 / xLa_0.7Ba_0.3MnO₃ by conventional ceramic method. The sturcture of composite and complex impedance are carried out by XRD, SEM and Impedance Spectroscopy. With changing the weight ratio from x=0; 0.3; 0.5 and x=1 the phase exhibit the composite behavior. Very interestingly, for the case of the case of weight ratio x=0.5 and 0.7 showed the complex impedance with xemicircle pattern in frequency range from 1 KHz to 1 MHz.

Abstract: Anode active material Li₄Ti₅O₁₂/C has an advantage to increase the life time and the ability to charge and discharge lithium batteries. An experiment was carried out to make Li₄Ti₅O₁₂/C more cheaper and simple process. Preparation of Li₄Ti₅O₁₂/C was carried out with stoichiometric composition of raw materials TiO₂ (Merck) and LiOH.H₂O (Germany) under powder metallurgy method. After mixing and calcinations cassava starch as a source of carbon black coating could be mixed under comparison 1:1 with calcinations powders. Pyrolisis process was done in - situ by the sintering process at temperature variation, i.e. 800, 850 and 900°C for 1 hour. XRD test results indicated the presence of anatase TiO₂ entire sample. The best results of powder Li₄Ti₅O₁₂/C with in situ process under 850°C for 1 hour had conductivity in the order of 10^-4S/cm and capacity round 5mAh/g. Carbon coating of cassava starch that is well identify in the black color of sample powder and EDX analysis, gave influence on electrochemical graphics of oxidation and reduction by cyclic voltammeter. The working voltage of Li₄Ti₅O₁₂/C is in general 1.55V.

Abstract: Dye-sensitized solar cell (DSSC) is one of the very promising alternative renewable energy sources to anticipate the diminishing in the fossil fuel reserves in the next few decades and to make use of the abundance of intensive sunlight energy in tropical countries like Indonesia. TiO₂ nanoparticles have been used as the photo electrode in DSSC because of its high surface area and allow the adsorption of a large number of dye molecules. In the present study, TiO₂ aerogel have been synthesized via sol-gel process with water to inorganic precursor ratio (R_w) of 2.00, followed with subsequent drying by CO₂ supercritical extraction (SCE). As comparison, the TiO₂ xerogel was also prepared by conventional drying and annealing. Both types of gels were subjected to conventional and multi-step annealing. The resulting nanoparticles in aerogel and xerogel have a band-gap energy of 3.10 and 3.04 eV, respectively. The open circuit voltage (V_oc) measurement reveals that the DSSC fabricated with aerogel provided a higher voltage (21,40 mV) than xerogel (1,10 mV).

Abstract: The deformation after ballistic impact loading of silicon carbide reinforced aluminium alloy composite is investigated in this research. The composite consists of 10 % volume fraction of silicon carbide particulate in a matrix of Al-7Si-Mg-Zn alloy and were produced through the squeeze casting process with a pressure of 1 MPa at semi-solid melting temperatures of 590-610 °C. The mechanical property of the composite was examined with hardness test. The ballistic tests were performed with two types of projectiles, 9 mm and 5.56 mm calibre of projectiles. Furthermore the deformed surfaces were studied with optical microscopy. During ballistic testing, the 9 mm projectile did not pierce the composite plate although the test resulted in significant cracks on the backside of the plate. The cross section observation of the plate showed ductile deformation in the matrix and silicon carbide particulates give significant rule in withstanding the penetration of the projectile. By contrast, the 5.56 mm projectile pierced through the composite and caused a brittle fracture of the matrix.

Abstract: Mg, in the form of MgH_2, is one kinds of materials widely used as hydrogen storage materials. Absorption and desorption properties of hydrogen which comes from metal hydride depend on materials itself, addition of elements, as well as manufacturing method. In this research, Mg as hydrogen storage were prepared by mechanical alloying with Ni, Cu, and Al as element addition and variation milling time for 10, 20 and 30 hours. Some morphological analyses (XRD, SEM) were done to observe phase transformation. Absorption and desorption properties characterization were employed by DSC and hydrogenation tests. The improvement in milling time decreased particle size, therefore enhanced wt% of absorbed hydrogen and decrease onset desorption temperature. However, the excessive of agglomeration and cold welding on mechanical alloying process resulted in bigger particle size. Alloying elements, Al and Cu, served as catalyst, while Ni acted as alloying which reacted with hydrogen. Mg10wt%Al with 20 hours milling time at hydrogenation temperature 250°C, 3 atm pressure, and 1 hour holding time resulted in the highest weight percent of H₂ (0.38%wt). However, Mg10wt%Al with 30 hours milling time had the lowest onset temperature, 341.49°C

Abstract: Barium hexaferrite and strontium titanate are respectively well established permanent magnet and piezoelectric materials which are technologically and scientifically attractive due to their potential for various applications in the field of magnetic electronics functional materials. However, the material properties for both require a careful control of grain structure as well as microstructure design to meet specific applications. In this work, we report some results of materials characterization especially particles and crystallites in a BaFe₁₂O₁₉/SrTiO₃ composite which were promoted during mechanical milling. The composite was synthesized using a planetary ball mill with a ball to powder ratio 10:1. Changing in the particle and crystallite-sizes at various milling time up to 60 hours are studied with the aid of particle-size analyzer and X-ray diffraction. It was found that the particle size of composite powders initially increased due to laminated layers formation of a composite and then decreased to an asymptotic value of ~8 μm as the milling time extended even to a relatively longer time. However, based on results of line broadening analysis the mean crystallite size of the particles was found in the nanometer scale. We thus believed that mechanical blending and milling of mixture components for the composite materials has promoted heterogeneous nucleation and only after successive sintering at 1100 °C the millled powder transformed into particles of nanograin. The crystallite growth kinetics at isothermal temperatures follow the relaxation equation with the activation energy value for BHF (Q_BHF) and STO (Q_STO) are respectively 73.63 kJ/mol and 122.69 kJ/mol.