Komposit La1-xSrxCo1-yFeyO3-d (LSCF) sebagai bahan katod tahan lama bagi sel fuel oksida pejal bersuhu sederhana-rendah: ulasan kajian

Solid oxide fuel cell (SOFC) is the most efficient fuel cell with the ability to directly convert chemical energy into electrical energy. Although there are numerous advantages offered by SOFCs, such as high energy conversion efficiency, low noise, less emission of pollutants and flexibility of hydrocarbon fuels, the processing cost and the performance improvement of SOFCs are hindered due to the higher operational temperatures. Therefore, the tendency to reduce the operational temperature of SOFC has brought about the development of research in materials and fabrication technology of fuel cells. Recently, among the many types of cathode materials that have been studied, lanthanum strontium cobalt ferrite, La1-xSrxCo1-yFeyO3-d (LSCF) has been discovered to offer the most potential for use as cathode material in intermediate to low temperature SOFCs. The use of LSCF composite cathode has significantly reduced the cathode polarisation resistance and expanded the triple phase boundary (TPB) area available for oxygen reduction. The overall performance of cathodes and fuel cells are also influenced by the method of powder preparation and fabrication of the composite cathodes. As such, the present article focuses on the LSCF composites for use as durable cathode material in SOFCs from the aspects of materials development, powder preparation and fabrication technique

Kesan suhu pensinteran terhadap sifat mekanik dan mikrostruktur alumina-zirkonia yang difabrikasi dengan kaedah pengacuan suntikan seramik

Kesan suhu pensinteran terhadap sifat mekanik dan mikrostruktur bahan komposit alumina-zirkonia telah dikaji. Jasad hijau alumina-zirkonia difabrikasi dengan menggunakan kaedah pengacuan suntikan seramik menggunakan sistem bahan pengikat pelbagai komponen. Jasad perang yang terhasil selepas proses penyahikatan disinter pada suhu 1400, 1450, 1500, 1550, 1600 dan 1650°C selama 2 jam. Selanjutnya nilai ketumpatan, kekerasan dan keliatan patah bagi jasad tersinter diukur. Mikrostruktur jasad tersinter ditentukan dengan menggunakan mikroskop imbasan elektron (SEM). Kajian menunjukkan nilai ketumpatan, kekerasan dan keliatan patah bagi jasad tersinter meningkat sejajar dengan peningkatan suhu pensinteran. Hasil uji kaji juga mendapati pada suhu pensinteran 1650°C sifat mekanik bahan mencapai keadaan maksimum. Penumpatan jasad tersinter 98% menghampiri ketumpatan teori dengan nilai kekerasan 16.9 GPa dan keliatan patah mencecah 3.95 MPa.m1/2. Keputusan tersebut dapat dikaitkan dengan mikrostruktur bahan yang padat didorong oleh tumbesaran ira yang lengkap

Kajian pengoptimuman penyahikatan larutan menggunakan kaedah permukaan sambutan

Proses penyingkiran bahan pengikat polietilena glikol (PEG) dari padatan pengacuan suntikan logam dikaji pada pelbagai nilai beban serbuk, suhu larutan dan juga masa rendaman, atau pembolehubah tak bersandar. Rekabentuk gubahan memusat berputar digunakan untuk mengkaji kesan pembolehubah tersebut terhadap kekuatan jasad perang, atau pembolehubah bersandar. Kertas kerja ini membincangkan penggunaan Kaedah Permukaan Sambutan(RSM) dalam mengoptimumkan parameter pemprosesan penyahikatan larutan bagi padatan serbuk keluli tahan karat SS316L (saiz purata 19.6 µm) untuk mencapai kekuatan jasad perang yang maksimum. Berdasarkan nilai optimum yang diperolehi (beban serbuk 64% isipadu, suhu larutan sebanyak 59oC dan masa rendaman selama 3 jam), kekuatan jasad perang maksimum yang dicapai adalah 5 MPa. Beban serbuk memiliki kesan paling signifikan terhadap kekuatan jasad perang, diikuti masa rendaman dan suhu larutan. Kaedah ini memberi kemudahan dalam penyelidikan penyahikatan larutan pada masa akan datang terutamanya untuk menyingkirkan PEG dari jasad anum dengan hanya menggunakan persamaan matematik tanpa perlu melakukan ujikaji

An influence of a binder system to the rheological behavior of the SS316l Metal Injection Molding (MIM) feedstock

The influence of a binder system to the rheological behavior of a metal injection molding (MIM) feedstock is presented in the paper. The binder systems used are: a) PEG & PMMA b) Palm stearin & LLDPE and, c) Tapioca starch & LLDPE. The viscosity and shear rate of the feedstocks were measured at various range of temperature and shear rate across the L/D = 10 capillary rheometer. The flow behavior index, n and activation energy, E of each feedstock were measured to show its significance as MIM feedstock. Generally, the result indicates all feedstock exhibits a shear thinning behavior and the binders are suitable as MIM binder. Additionally, the present paper has discovered that the binder system does not have much influence to the activation energy. In order to show the relevance of the rheological bahavior to the actual injection molding performance, green parts has been injection molded and the results shows an agreement with the rheological behavior result

Rheological Analysis of Zirconia-Hydroxyapatite with Bi-Modal System of Binders; Low-Density Polyethylene and Palm Stearin

The two component micro-powder injection molding (2C-μPIM) process has evolved from μPIM process because of the increasing demand for multi-functional micro-components applications. In this research work, the selected materials to fabricate micro-sized bi-material parts are zirconia (ZrO2) and hydroxyapatite (HA). ZrO2 is chosen for structural integrity and bio-inert, while HA is mainly chosen for bio-active properties. The reason of employing the multi-component binders is to ensure the flowability of the feedstock. Feedstock rheological characteristics needs to be carefully investigated to avoid any undesirable and inhomogeneous mixture between powder and binder. A common binder system which is comprised of palm stearin and low-density polyethylene (LDPE) were mixed with individual ZrO2 and HA powder particles to prepare for ZrO2 and HA feedstocks. Typically, the feedstocks were obtained ZrO2 and HA powders independently with a binder ratio of 60 wt.% of palm stearin and 40wt.% low-density polyethylene (LDPE). The mixing was carried out in Brabender mixer. Before mixing, critical powder volume percentage (CPVP) analysis was carried out to determine the optimal powder loadings required to prepare the ZrO2 and HA feedstocks. In this research work, the obtained CPVP of ZrO2 and HA powders were 47.0 and 59.0 vol.%, respectively. Based on CPVP analysis, six feedstocks with optimal powder loadings of 43, 44 and 45 vol.% for ZrO2 and 54, 55 and 56 vol.% for HA were prepared. The rheological analysis involving viscosity, shear rate, flow behavior index, activation energy and moldability index was investigated using capillary rheometer. Based on the obtained rheology result, it shows that the overall shear rate and viscosity are within the 2C-μPIM process recommended range. All tested composition shows pseudoplastic behavior. The results of the study found that ZrO2 and HA with optimal powder loadings of 55 vol.% and 44 vol.% have good rheological properties compared to feedstocks with other powder loadings. This is because both materials meet the criteria of good rheological properties which are low viscosity, high shear rate, flow behavior index less than one, low activation energy and high moldability index

Identifying Student-Focused Intervention Programmes through Discrimination Index

AbstractDiscrimination index is one of the quantitative methods that seek to differentiate between students of high and low achievement by analysing their answers to examination questions at the end of their learning process. This assessment is done based on specific objectives such as identifying the level of students understanding on what they had learnt. Through discrimination index, various intervention programmes that students focused on can be proposed. Intervention programme must be designed according to the level of achievement of the students in the different groups and not based on the overall students’ achievements of the particular cohort. This paper reports a study on discrimination index using index ratings on a final year design-based course at the Department of Mechanical and Material Engineering of Universiti Kebangsaan Malaysia. The calculated indices have been successful in identifying appropriate intervention programmes to suit students of low achievers in the course

Effects of debinding and sintering atmosphere on properties and corrosion resistance of powder injection molded 316 L - stainless steel

316L stainless steel is a common biomedical material. Currently, biomedical parts are produced through powder injection molding (PIM). Carbon control is the most critical in PIM. Improper debinding can significantly change the properties of the final product. In this work, thermal debinding and sintering were performed in two different furnaces (i.e. laboratory and commercially available furnaces) to study the mechanical properties and corrosion resistance. Debounded samples were sintered in different atmospheres. The samples sintered in inert gas showed enhanced mechanical properties compared with wrought 316L stainless steel and higher corrosion rate than those sintered in the vacuum furnace. The densification and tensile strength of the hydrogen sintered samples increased up to 3% and 51%, respectively, compared with those of the vacuum-sintered samples. However, the samples sintered in inert gas also exhibited reduced ductility and corrosion resistance. This finding is attributed to the presence of residual carbon in debonded samples during debinding

The Characterization and Rheological Investigation of Materials for Powder Injection Moulding / Ukwueze Bonaventure Emeka...[et al.]

Stainless steel and Zirconia have become an attractive choice of powder injection moulding (PIM) materials because of their respective excellent mechanical and thermal properties. These are often combined deliberately to produce functional graded components. The characterization and rheological investigations of the materials are thus indispensable for successful implementation of subsequent stages to the PIM process. In this investigation, the powder materials were characterized. Two feedstock with solid loadings of 68% for stainless steel (17-4PH) and 50% for 3mol% yttria stabilized zirconia (3YSZ), were prepared based on optimal loading of 3% lower than the critical value. A common binder was employed comprising of 60% palm stearin and 40% polyethylene. The rheological results for the two materials exhibited pseudo-plastic and shear thinning behaviour indicated by decrease in velocity with increasing shear rate. The results also show that a temperature of 1300C is considered appropriate for injection moulding of both feedstock

Pengoptimuman parameter pengacuan bagi mengurangkan kecacatan jasad anum proses pengacuan suntikan logam (MIM)

Injection molding parameters of the metal powder mixture has been optimized using L27 (313) orthogonal array. Parameters optimized were injection pressure, injection temperature, powder loading, mold temperature, holding pressure and injection speed. Metal powder mixture used is a bimodal SS316L, and polyethylene glycol (PEG), polymethyl methacrylate (PMMA) and stearic acid as binder. Beside those, interactions of the injection pressure, injection temperature and powder loading were studied. Pareto-Anova analysis for the smallest the best signal to noise ratio (S/N) presents the significance of each parameters and interactions. Results shows that the interaction between injection pressure and temperature has highest significant percentage (19.39 %) followed by interactions between injection pressure and power loading (17.77 %) and, injection temperature and powder loading (14.41 %). Beside those, injection rate was the single parameter that greatly influences the green part defects of 14.41 %, while injection pressure and holding pressure were less significant of about 0.27 % and 0.58 % respectively. Results shows that the optimum injection parameter was as follows: 350 bar (injection pressure); 150 oC (injection temperature); 64 % volume (powder loading); 51 oC (mold temperature); 700 bar (holding pressure); and 15 ccm/s (injection rate). Signal noise ratio at the optimum condition was -2.46 dB 2.05 at 90 % confidence interval. The optimum parameter has been confirmed by the confirmation experiment to ten samples and its signal noise ratio obtained was -255 dB which was within the optimal range