Andanastuti Muchtar

Microstructural characteristics on the surface and subsurface of semimetallic automotive friction materials during braking process

Abstract In this study, a series of friction tests on semimetallic automotive friction materials were conducted on a friction test machine by pressing test samples against a rotating cast iron brake disc, thus simulating actual braking. After each friction test, the morphological changes of the wear surface and subsurface were investigated using scanning electron microscopy. Microstructural examinations showed that the major wear mechanisms in operation during braking are comprised of the following: (i) abrasive, (ii) adhesive, (iii) fatigue, (iv) delamination, and (v) thermal. The wear mechanism and wear transition are found to be influenced by the applied loads and braking times. In the study of the subsurface morphology, microcracks generated in the subsurface are thought to be due to the following phenomena; (i) growth of microvoids, (ii) coalescence of microvoids, (iii) coalescence of second phase particles, and (iv) coalescence of microvoids and second phase particles. The microcracks generated in the subsurface grew and propagated parallel to the sliding surface as the braking times as well as applied loads are increased. Finally, the microcracks grew and joined each other producing wear particles on subsequent braking. These mechanical and thermal failures manifested a complex wear mechanism, causing plastic collapse in the local region which subsequently produced wear particles in different shapes depending on the modes of failure.

Correlation of filler loading and silane coupling agent on the physical characteristics of epoxidized natural rubber-alumina nanoparticles composites

Studies were conducted on the effects of filler loading and 3-aminopropyltriethoxysilane (SCA) on the physical characteristics of epoxidized natural rubber (ENR)-alumina nanoparticles composites (ENRAN). The filler loading varied from 10, 20, 30, 40, 50, and 60 phr in the absence and presence of 2 phr SCA in every formulation. The alumina nanoparticles have a positive interaction with the ENR matrix since they increase the glass transition temperature of the composites [Mohamad, N., Muchtar, A., Ghazali, M.J., Dahlan, H.M. and Azhari, C.H. (2008). The Effect of Filler on Epoxidized Natural Rubber-Alumina Nanoparticles Composites, Eur. J. Sci. Res., 24: 538—547]. The addition of SCA decreased the maximum torque (MH) and the torque difference (MH-ML) of ENRANs compound as well as causing the curing process to occur at a very fast rate. The spherical alumina particles were dispersed in ENR matrix and a uniform particle distribution was observed under scanning electron microscope enabling the increase of the torque values in the composites.

Durability and Stability of LSCF Composite Cathode for Intermediate-Low Temperature of Solid Oxide Fuel Cell (IT-LT SOFC): Short Review

Solid oxide fuel cell (SOFC) is well known as power and heat generation device which converts chemical energy directly from fuel into electricity. SOFC operate at high temperature becomes obstacle for SOFC which reducing ionic conductivity material of current electrolyte, reduce lifetime of cell components, high fabrication cost, limited durability and performance issues. This introduce to environment pollution and decrease the SOFC lifetime. The fabrication of durability and stability composite cathode are comprised from mixing of perovskite La0.6Sr0.4CO0.2Fe0.8 (LSCF) powders with nanoscale ionically conducting ceramic electrolyte materials, SDC-carbonate (SDCc) was overcome this problems. Powder preparation and composite cathode fabrication must consider which as main factors in the development of durability and stability of LSCF-SDCc composite cathode. Powders must in nanoscale to enhance the conductivity and decrease the interfacial polarization resistance and the composite cathode should in nanoporous morphology for achieve high power density over than 500 h and remarkable durability. Calcination also plays in important role and its operations will effects to the SOFC durability and performance. The necessary to prolong the lifetime and increase the SOFC performance has lead to development of durability and stability of SOFC. This paper reviews the durability and stability of the composite cathode and focus on the challenges in material technology.

Fabrication of Porous LSCF-SDC Carbonates Composite Cathode for Solid Oxide Fuel Cell (SOFC) Applications

Composite cathodes made of perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and SDC carbonates (SDC-(Li/Na)2CO3) were investigated in relation to their structure, morphology, thermal expansion coefficient and porosity. As a first step, the LSCF powder was prepared by sol-gel technique. This was followed by the preparation of the LSCF-SDC carbonates composite cathode by mixing the LSCF with SDC-(Li/Na)2CO3 electrolyte via solid state reaction in various compositions, i.e. 30, 40 and 50 wt.%, namely 70LSCF-30SDC7030, 60LSCF-40SDC7030 and 50LSCF-50SDC7030, respectively. The powder mixtures were then calcined at 680oC. The resultant powder was fine with surface area of about 3.39-7.42 m2/g and particle size of 0.56-0.66µm. The powder consists of two distinct phases, i.e. LSCF and SDC-(Li/Na)2CO3 as confirmed with x-ray diffraction. The microstructures were observed under scanning electron microscopy (SEM). Increasing the amount of the SDC-(Li/Na)2CO3 electrolyte in the composite cathode was found to bring the thermal expansion of the cathode closer to that of the electrolyte. The cathode pellets were later compacted at different pressures (27, 32 and 37 MPa) and sintered at 600oC. The optimum porosity (20.99-24.98%) was achieved for samples with SDC-(Li/Na)2CO3 content of 30-50% sintered at 600oC and cold pressed at 37 MPa.

Optical, morphology and electrical properties of In2O3 incorporating acid-treated single-walled carbon nanotubes based DSSC

This study focuses on the influence of an acid treatment process of single-walled carbon nanotubes (SWCNTs) in In2O3-based dye-sensitized solar cells (DSSCs). Pure In2O3, In2O3-SWCNTs with acid treatment and In2O3-SWCNTs without acid treatment were prepared using the sol–gel method via a spin coating technique annealed at 450 °C. The optical, morphology and electrical properties of the photoanodes were characterized by means of UV–Vis analysis, atomic force microscopy and field-emission scanning electron microscopy, and J–V curve measurements, respectively. The optical band gap obtained through UV–Vis analysis showed that the acid treatment process modified the band gap of the photoanode, which enhances the V oc of the DSSCs. In addition, In2O3-SWCNTs with acid treatment possess a porous structure that improves the power conversion efficiency (PCE) of the DSSCs. In addition, the diameter of acid-treated SWCNTs was reduced compared to pristine SWCNTs. In2O3-SWCNTs with acid treatment exhibited the highest PCE of 1.40% with J sc of 7.6 mA cm−2, V oc of 0.51 V, and fill factor of 0.36. The increment in V oc is due to the higher band gap obtained through the UV–Vis absorption spectrum. Moreover, In2O3-SWCNTs with acid treatment has a higher electron lifetime with a higher effective diffusion coefficient that slows down the recombination rate and speeds up the electron transport process.

Perspectives for Titanium-Derived Fillers Usage on Denture Base Composite Construction: A Review Article

Poly(methyl methacrylate) (PMMA) is an extensively used material in dentistry because of its aesthetics, processability, and reparability. However, PMMA is still far from being ideal in fulfilling the mechanical requirements of prosthesis. PMMA-based denture base polymers exhibit low fracture resistance and radiopacity behavior. Efforts to improve the mechanical and radiopacity properties of denture base materials through inclusion of silica-based fillers are ongoing. Although silane-treated siliceous fillers are commonly used, they are not sufficiently strong. They also exhibit cracks, which either cut through the glass fillers or propagate around the filler particles. This defect occurs when the dental composites are placed in aqueous oral environment because of the hydrolytic degradation of silica-based fillers and silane-coupling agents. The clinical problem of using silanes in adhesion promotion is bond degradation over time in oral environment. In addition, silanes do not bond effectively to nonsilica-based dental restorative materials. This review presents titanium-derived fillers as alternatives to siliceous fillers. Titanate-coupling agents are found to be effective couplers in treating Ti-based fillers because of their chemical compatibility and relatively high stability in aqueous environment.

Effect of sintering temperature on the microstructure and ionic conductivity of Ce0.8Sm0.1Ba0.1O2-δ electrolyte

This study investigated the effects of sintering temperature on the microstructure and ionic conductivity of codoped ceria electrolyte with barium and samarium as dopants. The electrolyte (Ce0.8Sm0.1Ba0.1O2-δ) powder was synthesized using the citric acid-nitrate combustion method and calcined at 900°C for 5 h. The calcined electrolyte exhibited a cubic fluorite crystal structure with some impurity phases. The calcined powder was then pressed into cylindrical pellets using uniaxial die-pressing. The pellets were sintered at three different temperatures, i.e., 1200, 1300 and 1400°C for 5 h. Microstructural analysis of the pellets showed that the average grain size increased with the increase in sintering temperature. The sintered densities of the pellets were measured by Archimedes’ method, and the relative density values were within the range of 78%TD to 87%TD as the sintering temperature increased from 1200 to 1400°C. Electrochemical impedance spectroscopy analysis showed that conductivity increased with the increase in sintering temperature, but no considerable change in conductivity was observed for the pellets sintered at 1300 and 1400°C. The results revealed that the electrolyte pellet sintered at 1300°C exhibited the ionic conductivity of 0.005 S/cm with lowest activation energy of 0.7275 eV.

Nanostructured and Nonsymmetrical NiO–SDC/SDC Composite Anode Performance via a Microwave-Assisted Route for Intermediate-Temperature Solid Oxide Fuel Cells

This work investigates the electrical properties of NiO–SDC/SDC anode sintered at approximately 1200°C for 1 h via the microwave method. Nanopowders Sm0.2Ce0.8O1.9 (SDC—samaria-doped ceria) and NiO were mixed using a high-energy ball mill and subsequently co-pressed at three different compaction pressures of 200, 300, and 400 MPa. This study determines the effect of compaction pressure on the electrochemical performance of Ni–SDC/SDC anode, with no binder used between layers. The electrical behavior of the prepared anode was studied via electrochemical impedance spectroscopy in controlled atmospheres, operating at high temperatures (600–800°C). The results indicate that decreasing the compaction pressure and increasing the operating temperature lead to a high electrochemical performance of the nonsymmetrical NiO–SDC/SDC anode. The mechanism for manufacturing NiO–SDC/SDC involves ball milling, dry pressing, and microwave furnace sintering processes.

Fabrication and Characterisation of La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC Composite Cathode

Composite cathode is a promising material to be used as electrodes in fuel cells. The fabricated composite cathode materials in this study are comprised of a mixture of submicron La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428) powders with two types of nanoscale ionically conducting ceramic electrolyte materials, samarium-doped ceria (SDC) and SDC-carbonate (SDCc). 30 – 50 wt% of electrolyte materials are added to the LSCF6428 cathode via the solid state method. The composite powders were ball-milled in ethanol and calcined at the temperature range of 800°C to 900°C for 2 hours in air. The composite cathode powders are characterised in terms of morphology and crystal structure. It is found that after calcining, the LSCF and the electrolyte materials retained their original structures as there was no chemical reaction between the two components. In addition, the LSCF-SDC composite cathode powders were found to exhibit a narrower distribution in size compared to the LSCF-SDC carbonate powders.

Fabrication of Dense Composite Ceramic Electrolyte SDC-(Li/Na)2CO3

Composite electrolytes made of samarium-doped cerium (SDC, Ce0.8Sm0.2O1.9) and (67 mol% Li/ 33mol% Na)2CO3 carbonate salts were investigated in relation to their structure, morphology and porosity of the electrolyte. The fabrication of the SDC–(Li/Na)2CO3 composite electrolytes were achieved in two steps: step (1) preparation of the samarium-doped cerium powders by sol-gel; step (2) mixing of the samarium-doped cerium with carbonates in various compositions by solid state reaction. The electrolyte pellets were compacted at different pressures (25 and 50 MPa) and sintered at 600oC, 700oC and 800oC. The XRD results demonstrated that the introduction of carbonates did not change the SDC phase structure. FESEM images showed that the carbonate component was amorphous and well distributed in the SDC. The lowest porosity (2.92%) was achieved for samples with carbonate content of 30% (SDC7030) sintered at 800oC and cold pressed at 50MPa.