Advanced Materials Research Vol. 789

Abstract: Savonius windmill having advantages high starting torque and simple construction is applicable for Indonesia as a developing country with annual average wind speed 4,5 5,0 m/s. The purpose of the experiment is to identify characteristics of an electric machine used for low speed electric generator. The electric machine for the experiment is a permanent magnet electric motor usually used for electric bicycle. The electric motor is tested as an electric generator and rotated with variations of speed. Outputs of the generator are torque, voltage and current with 1) variation of lamps-load, 2) constant voltage-load for 12 volt and 24 volt battery charging and 3) combination of 12 volt battery charging and variation of lamps-load. The average efficiency of the generator is 59,8% and 65,4% for 12 volt and 24 volt battery charging. Battery charging starts at 95 rpm and maximum electric generating current is 20 Ampere at generator speed about 175 rpm.

Abstract: One of the components of the vehicle are of particular interest is the brake system , because its main function is to stop the rotation axis, set the axis of rotation and to prevent unwanted rotation. One classification system is the brake drum that has been widely made of cast iron, cast iron and cast steel special. This study makes brake drum of composite materials aluminum-based, with reinforcement is silicon carbide (SiC), obtained optimum composition of 15%, so it is written (Al-Si)-SiC/15%. Physics testing includes testing of thermal conductivity and thermal expansion coefficient, and Chemistry testing the corrosion penetration rate when the test material was coating with regular polish, with chrome, with nickel and with nickel + chrome. The final results showed that the value of conductivity and thermal expansion coefficient of the composite material is lower than cast iron, aluminum and other alloys. That is pretty good heat resistance when applied to brake drum material. The lowest of corrosion penetration rate on coating material with a layer of Ni-Cr.

Abstract: The present works concerns in developing alternative interconnect material for solid oxide fuel cell (SOFC) application. For this purpose, ferritic stainless steel is used as the substrate material while various nickel composite layers were coated on the substrate in order to improve its oxidation resistance at SOFC application temperature. Nickel layers were deposited on ferritic stainless steel by high velocity oxy-fuel (HVOF) method. In order to create nickel-oxide layer, the coated samples is then heated at temperature of 950°C for 1 hour, wherease sol-gel coating was performed on the coated samples in order to create nickel manganese oxide spinnel composite layers. All samples were then oxidized at temperature 800°C for 8 hours, in order to evaluate their oxidation characteristics at SOFC service temperature. Before and after oxidation, x-ray diffraction (XRD) and scanning electron microscope (SEM) were performed to all samples. It was observed that coated samples effectively inhibit the formation of chromium oxide that normally occurs on stainless steel surface at SOFC service temperature.

Abstract: The oxidation of hot-dip aluminized AISI 1020 steel coated with NaCl in static air at 700°C for a duration of time 49 h was studied by employing thermogravimetry, Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. It was found that NaCl deposits markedly accelerated the oxidation of the AISI 1020 steel. The aluminide coating on the bare steel gives the best oxidation protection by forming continuous alumina scale (Al₂O₃). The degradation of aluminide layer and alumina scale on the steel are associated by chloridation/oxidation cyclic reactions. In addition, the released chlorine will be as catalytic actions and leads to the formation of loose Al₂O₃ during corrosion.

Abstract: So far, application of RRA (Retrogression and Re-aging) heat treatment in improving SSC (stress corrosion cracking) resistance of aluminum alloy 7075 is limited to thin samples as it is constrained by short retrogression time at high temperature. The aim of this research is to obtain thick aluminum alloy 7075 plate with good SCC resistance through RRA modification. In RRA modification, the retrogressed alloy samples were rolled at three different temperatures (27^o C, 120^o C, and 180^o C) and at three different thickness reductions (10%, 15%, and 20%) followed by re-aging at 120^o C for 16 hours. SCC resistance was determined from time to failure (t_f) at fixed loading at 0.8 yield strength of material in test solution of 3 wt -% NaCl at pH 4. The sample with longest time to failure is referred to as the most SCC-resistant. Generally, modified RRA alloy has better SCC resistance compared to T6 alloy and conventional RRA alloy. Highest SSC resistance was found at three conditions, namely 27^o C-20% reduction, 27^o C-15% reduction, and 180^o C-20% reduction). Micro-structurally, these conditions produce large precipitates with wider space in grain boundaries. Around grain boundaries, they also produce smaller intermetallic particles with broader distribution.

Abstract: The presence of carbon dioxide (CO₂) and water in the fluid can cause severe internal corrosion in the pipelines. This study aims to observe corrosion behavior during the changes in flow rate and acidity conditions in order to obtain the relationship between the parameters by the measured corrosion rate. Corrosion rate measurements were performed for API 5L X52 steel material by using polarization method in 3.5% NaCl solution with saturated CO₂ injection. Solution with different acidity were applied which has pH 4, 5, and 6 respectively. To simulate the flow rate, a Rotating Cylinder Electrode RCE was used at various rotation rates 0, 375, 750, 1500, and 3000 rpm, at room temperature (25°C) and atmospheric pressure. Based on testing results, the changes in rotation converted to flow rate showed that the corrosion mechanism of API 5L X52 steel in NaCl solution with saturated CO₂ content was mainly controlled by mass transport at pH=4 whereas chemically controlled involved both at pH=5 and pH=6 conditions.

Abstract: The main objective of this research is to investigate the effectiveness of Myrmecodia Pendans (MP) wood extract as Eco friendly Corrosion Inhibitor on corrosion of material API 5L Grade B in 3,5% NaCl solution using potentiodynamic polarization curve, Gas Chromatography-Mass Spectrometer (GC-MS) and Electrochemical Impedance spectroscopy (EIS). MP usually called as sarang semut in Indonesia. We analyzed MP in different concentration of extract. By 500, 1000, 1500, 2000 and 2500 ppm. The experiment was started by extraction of the MP. According to the polarization potensiodynamic data, the rate corrosion could be decrease about 90,36% by concentration 500 ppm. In accordance with the data of the EIS, the same concentration of inhibitor produced 92.3% with charge transfer resistance of 595.6 Ω.cm². It means MP extract could serve as an effective inhibitor for the corrosion. This is consistent with the initial hypothesis that MP contains antioxidant compounds that can inhibit oxidation thereby reducing the corrosion rate.

Abstract: 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.

Abstract: Cobalt based oxide are promising as coating material for solid oxide fuel cell interconnect due to their high oxidation resistance and conductivity. In this report, Co-based coating layer was deposited on AISI 430 ferritic stainless steel substrate using thermal spray methods. The high temperature oxidation behavior of Co-based coating was studied in air atmosphere at 800 °C. Optical and SEM observation shows that the total thickness of Co-based layer was about 100-120 μm. The coatings were mainly growth by the melted particles impacting on the substrate that flatten to form splats which later on piled on top of the others. Phase identification by XRD showed that the coating layer contained Co₃O₄, and NiO oxides. EDS analysis indicated that the coating layer were sufficient to prevents the formation and the growth of Cr₂O₃ scale. The Co-based coating shows relatively a large mass gain during oxidation compared to the uncoated steel, with parabolic rate constant, K_p = 4x10^-15 gr².mm^-4.ks^-1.

Abstract: 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.