Asep Ridwan Setiawan

Effect of Ti Addition on Oxidation Behavior and Area Specific Resistance of Fe-20Cr Alloys for SOFC Interconnects

In this work, the oxidation behavior of Fe-20wt.%Cr alloys with different titanium contents: 0, 0.5, and 1 wt.% are studied as a function of time in air atmosphere. The samples were isothermally oxidized at 700°C for 24, 48, and 96 h in a box furnace. The area specific resistance of oxides formed at the alloys surface during oxidation is measured by four-point probe methods at 700°C for 24 h. For Ti containing alloys, surface morphology observation by SEM shows that a few of TiO2 particles formed on the top of Cr2O3 scales. Continous TiO2 layer was not formed at the alloys surface after oxidation. XRD analysis on the oxide scales of Fe-20Cr-Ti alloys confirms that Cr2O3 and TiO2 oxide formed on the alloys. Ti addition into the alloys increases the oxidation rates of alloys at the initial stages. Oxidation behavior of Fe-20Cr-0.5Ti and Fe-20Cr-1Ti alloys showed two regimes. The parabolic rate constant, kp (in gr2/cm4s) were 1.57 x 10-13 and 3.08 x 10-13 respectively for initial stage of oxidation then changed to-9 x 10-15 and-3 x 10-14 respectively for the remainder of the test. ASR measurement shows that the presence of Ti in the alloys decreases the electrical resistance up to 60%. Ti addition into Fe-Cr alloys affect the oxide growth rate and increase the conductivity of Cr2O3 scales.

Effect of Pulse Frequency on the Deposition of Cu-Fe Alloy via Pulsed Current Electrodeposition Method

In an attempt to reduce the oxidation and Cr evaporation rates of solid oxide fuel cells (SOFCs) interconnect, Cu-Fe coating was developed on the AISI 430 ferritic stainless steel substrate by a pulsed current electrodeposition method. Effects of pulse frequency on properties and performance of the fabricated coating were investigated. Results show that Cu-Fe alloy was sucessfully fabricated using pulse deposition methods. The variation of pulsed frequency during pulse current deposition strongly influence the coating morphology and its composition. The increase of pulse frequency tend to increase the Cu-Fe grain size. Moreover, the amount of Cu particles decreases with the increase of pulse frequency.

Preparation of Zn-ZrO2 Nanocomposite Coating by DC and Pulsed Current Electrodeposition Technique with Low Current Density

In the present work, Zn-ZrO2 nanocomposite coatings were deposited on the copper substrate through DC and pulse electrodeposition technique with low current density (10 mA/cm2). The effect addition of ZrO2 nanoparticles and pulse current were studied. The surface morphology, microhardness and erosion resistance of Zn-ZrO2 nanocomposite coating were evaluated. The result shows that, with the addition of ZrO2 particles, the surface morphology of Zn-ZrO2 nanocomposite coating was smoother. Phase identification by XRD confirm that Zn layer had been sucessfully deposited. The presence of ZrO2 nanoparticles was not detected. Compared to DC, pulsed current electrodeposition technique showed higher cathodic efficiency, better microhardness and good erosion resistance.

Oxidation Characteristics of Cr2O3-La2O3 and NiAl-La2O3 Coated on Ferritic Stainless Steel by Thermal Spray Method

The present works concerns in evaluating thermal oxidation characteristic of composite coating on ferritic stainless steel at high temperature application. SUS430 ferritic stainless steel was used as the substrate material whereas Cr2O3-La2O3 and NiAl-La2O3 were used as the coating material. Thermal spray has been used as the deposition method, whereas thermal oxidation at temperature of 750°C for 24, 48 and 96 hours has been employed on the coated material in the atmosphere environment. From the weight meausurement before and after thermal oxidation, it was observed insignificant weight losses, whereas this condition is stable for all the applied oxidation period. However weight losses is more on the NiAl-La2O3 as compared with Cr2O3-La2O3 samples, which is due to the morphological characteristic of the former layer as observed by scanning electron microscope (SEM) characterization. From X-ray diffraction (XRD) characterization, it was observed the formation of stable layer Cr2O3 for Cr2O3-La2O3 coated samples, whereas formation of NiO observed for the case of NiAl-La2O3 sample.

Protective CuO Coating Synthesis via Electrodeposition of Copper on AISI 430 Ferritic Steel for SOFC Interconnect Applications

In this work, electrodeposition of copper on AISI 430 steels substrate with relatively low current density followed by oxidation of Cu to form protective and conductive oxide layer is examined. Result shows that the activation by Ni strike plating on AISI 430 steels substrate prior to electroplating improves the coating ability of copper. Phase identification by XRD on the oxidized sample confirms that as coated Cu layer was transformed into CuO. The growth of CuO scales was relatively low and effectively prevents Cr outward diffusion from the ferritic steels.

Oxidation Characteristics of Various Nickel Composite Coated on Ferritic Stainless Steel

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.

Liquid Phase Epitaxy of Si-Doped AIN at 1300 °C in Ga-Al Melt

In the present study, we have successfully grown Si-doped AlN developed by solution growth technique using Ga-Al melt as a solvent under nitrogen atmosphere at 1300 °C. Si doping was introduced to the Ga-Al melt by adding pure Si metal. To allow homoepitaxial growth during solution growth experiment, sapphire substrate were nitrided with precise control to produce hiqh quality single crystalline AlN films with low dislocation density. With the help of AlN film template from above methods, we have successfully grown Si-doped AlN single crystalline layer with a flat surface and almost free from cracks. The full width at half maximum (FWHM) of x-ray rocking curve values for (0002) and (10-12) diffraction from the Si-doped AlN film were 43,2 and 594 arcsec, respectively.

High Temperature Oxidation Behavior of Co-Based Coating at 800o C as Alternative Coating Material for SOFC Interconnect

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, Kp = 4x10-15 gr2.mm-4.ks-1.

Enhancement of Carbothermic Reduction of Al2O3 via Mechanical Milling

The mixture of Al2O3 and graphite with a molar ratio (1:3) were mechanically milled in a planetary ball mill at room temperature using zirconia ball. The mixture was milled for 0.5, 1, 2, 4 and 8 h in air atmosphere. Unmilled and milled mixtures were characterized using a combination of X‐ray diffraction (XRD) analysis, scanning electron microscopy (SEM), specific surface area analysis (SSA), and thermogravimetry analysis (TGA). TG analysis indicated that the reduction reaction of milled sample occurs at lower temperature compared to the unmilled sample. Mechanical milling of Al2O3‐graphite mixtures has led to the following results; size reduction of the Al2O3 crystallite up to ∼20nm, formation of amorphous graphite and the increase in the surface area of Al2O3 particles.