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

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

Influence of sintering parameters on the compressive yield strength of stainless steel foams produced by the space holder method

Metallic foams are a new class of materials that have a great potential to be used in various functional and structural applications. Due to their competitive price compared to aluminium, metallic foams are anticipated to become an alternative material for light-weight structures. In this study, stainless steel foams are fabricated using a powder space holder method. The materials used include stainless steel powder, a novel space holder glycine and binders consisting of palm stearin and of polyethylene (PE). The stainless steel foams are sintered at 1100oC, 1200oC and 1300oC with sintering times of 1, 2 and 3 h, respectively, to investigate the effects of the sintering parameters on the compressive yield strength of the stainless steel foams. The results showed that all of the stainless steel foams produced exhibit the general behaviours of metal foams. The sintering time is the most significant parameter that influences the compressive yield strength of stainless steel foams. Increasing the sintering temperature and sintering time will increase the compressive yield strength. The interaction between the sintering temperature and sintering time is found to be not statistically significant

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

Parameter Optimization of Sintering Ti-6Al-7Nb Powder and Palm Stearin Binder System for the Highest Sintered Density using the Taguchi Method / Rozie Nani Ahmad...[et al.]

The application of titanium (Ti) based biomedical materials such as Ti-6Al-7Nb is widely being used at present. Due to the toxicity of vanadium to the human body, the Ti-6Al-7Nb alloy has been developed as a more suitable biomaterial to replace the Ti-6Al-4V alloy. The sample was prepared by a metal injection moulding process, which is a net-shaped powder metallurgy forming process using palm stearin as a binder system. Meanwhile, the Taguchi method was used in conducting the experiment of the sintering process to investigate the effects of sintering factors on the density of the sintered parts. The density measurement was carried out by the Archimedes method using distilled water as a medium. The results showed that the sintering temperatures and dwell times were the most significant parameters that contribute to the highest sintered part density

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

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