Badrul Munir

Synthesis of Highly-Ordered TiO2 through CO2 Supercritical Extraction for Dye-Sensitized Solar Cell Application

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 (Rw) 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 (Voc) measurement reveals that the DSSC fabricated with aerogel provided a higher voltage (21,40 mV) than xerogel (1,10 mV).

Growth of Porous Alumina Layer and Cerium Sealing of Al7xxx/SiC Composite for Structural Lightweight Alloy Corrosion Resistant Application

AMC (Aluminum Matrix Composite) as a main material for automotive and aircraft applications has the keyadvantage that islighter thanaluminumalloys. So, it can be ascertained that fuel comsumption forthoseapplicationswill be reduced. However, AMC materials are generally suceptible to galvanic corrosion due to galvanic reaction between aluminum matrix and reinforcement, and the formation of microstructure at matrix/reinforcement interface as well. Anodizing is the most effective surface modification method in order to protect AMCs surfaces. This process produces porous anodic coating which has the characteristics of high corrosion resistance and hardness layer. However, the presence of reinforcement particles in AMC hinders the initiation and growth of the protective oxide layer by forming cavities and micro crack. Therefore cerium sealing has been done to remedy the poor anodic film in order to further enhance the corrosion resistance in aggressive circumstances. The material studied in this research was AMC Al7xxx/SiC. Anodizing process were conducted in H2SO4 solution at current densities 15, 20, and 25 mA/cm2 at 0°C for 30 minutes. Subsequently, continuedwithelectro lesssealinginCeCl3.6H2O+H2O2 solutionat room temperature atpH9 for 30 minutes. The morphologies of anodic coating and sealing layer were examined by means of FE-SEM, the corrosion resistance of composites was estimated in a 3.5 wt.% NaCl solution by potentiodynamic polarization test. Coating process conducted by anodizing and cerium sealing in various of anodizing current densities at 0°C results in protective layers which lead to the decreasing of corrosion rate and current density up to four orders magnifications than that of bare and anodizedAl7xxx/SiCcomposite.

Utilization of Albizia Wood (Albizia falcata) and Ramie Fibers as Wind Turbine Propeller Modification of NACA 4415 Standard Airfoil

Ramie fibers and albizia wood, which are abundantly available in Indonesia, were used in fabricating hybrid sandwich composite for wind turbine propeller. A prototype was fabricated by modification of NACA 4415 standard airfoil, intended for low speed wind and environmental friendly operations. Hand lay-up method was applied for fabrication of this hybrid composite with one and two layers of ramie fiber. Mean volume fiber fraction (vf) of one-layer and two-layer composite are 47,12% and 44,82%, respectively. The highest measured bending stress is 30.88 MPa for two-layer composite with modulus of elasticity 2.02 GPa and bending strain 1,795%. Microstructure of this hybrid composite is unchanged significantly after 5.5 months operation. With ultimate simplicity and low manufacturing cost, hand lay-up method is suitable for small scale production.

Influence of Intermetallic Inclusion to Brittle Fracture of Electric Motor Shaft AISI 1045 under Torsion Loading

A shaft of electric motor fin-fan cooler failed after two years operation. The inspection revealed that the v-belt attached on the electric motor loosed before the failure occurred. Visual investigation results showed the brittle fracture with less plastic deformation. Multiple crack origins observed on the edge of the shaft indicates that the more than one stress concentration generated within the shaft. Microstructure observation revealed fine grain on the edge and become coarse into the center of the shaft. The hardness test results were in good agreement to the microstructure observation where the edge are is harder than the center. Fractography using SEM revealed inclusions located within the shaft and some inclusions are clustered on the area where the cracks initiate to propagate. The presence of intermetallic inclusions was identified by microanalysis using EDS. Inclusions that are brittle in nature become stress concentrations for the operating load since its properties is close to ceramic. The presence of fine grain and inclusions on the edge of the shaft become detrimental to the shaft properties and the presence of fine grain aggravate the failure for its effect according to Hall-Petch theory.

Contribution of Galvanizing Layer to Hydrogen Induced Cracking Failure of AISI 4140 Bolt for Padeye Fixing in Marine Environment

A high strength bolt with hot dip galvanizing treatment failed shortly after being installed for two days on a padeye of mooring dolphin. The bolt was installed with increasing stress on the second day in which the value was nearly twice. Investigation results showed the bolt fractured with the nut head separated from the pin. Corroded fracture surface with brittle characteristic and no plastic deformation observed dominating the failed area. Characterization of hardness and chemical composition followed with microstructure and fractography observation on the fracture surface then conducted in order to analyze the reason for this brittle fracture occurrence. Results indicate that, while the bolt conforms to the material specification in term of chemical composition, the hardness value was high. The microstructure observation reveals a transgranular crack propagation and cleavage failure occurred. The cleavage failure was clearly observed under fractography observation using scanning electron microscope. Failed galvanize layer due to mechanical failure becomes preferential site for hydrogen evolution in marine environment, which leads to hydrogen diffusion into the matrix, thus results in hardness increase. The increasing stress during installation become detrimental to the bolt and facilitate the hydrogen induce cracking. Detrimental effect of hot dip galvanize layer is pointed out in the application of high strength material in marine environment.

Band Gap Optimization by Ga and S Additions in CuInSe2 for Solar Cell Absorber Applications

Gallium or sulphur additions in CuInSe2 were prepared using RF magnetron sputtering and pulsed laser deposition respectively. All of the observed thin films show a chalcopyrite structure with the S addition increases the favourable (112) peak. The optical absorption coefficients were slightly decreased. The films energy band gap could be shifted from 1.04 to 1.68eV by adjusting the mole ratio of S/(S+Se) and In/(In+Ga). It is possible to obtain the optimum energy band gap by adding S solute or Ga at a certain ratio in favour of Se and In respectively. It is also necessary to control the ratio of Ga and S additions and to retain a certain portion of In to provide better properties of CIS films.