Papers by Keyword: Porosity

Abstract: Peat is superficial deposit or soil with high organic content. The soil is highly compressible and acidic. The organic acidic water in swampy peat soil consists humic acid that is potentially corrosive to concrete and metal structures. Geopolymer is a material using waste from agro-industry such as fly ash (FA) and palm oil fuel ash (POFA) that is activated with alkaline solution. In this research, the acid resistance of geopolymer mortars from fly ash and palm oil fuel ash was measured by change in compressive strength and porosity. The samples were subjected to distilled water and acidic peat water. The OPC mortars showed a considerable decrease in compressive strength after subjected in peat water for up to 180 days. There was a fluctuated trend of geopolymer FA and a high decrease in compressive strength of geopolymer POFA after subjected to the peat water. The porosity of the geopolymer specimens was higher than the control mortars. However, it was observed that the geopolymer FA is more resistant to the acidic peat water than the geopolymer POFA due to stable aluminosilicate bonding.

Abstract: This paper describes the result of investigating volcanic ash of Mount Kelud as fly ash substitute material to produce geopolymer concrete. The test was held on geopolymer concrete blended with 0%, 25%, 50% and 100% fly ash replacement with volcanic ash. Natrium Hidroxide (NaOH) with concentration of 12 molar and Natrium Silicate (Na₂SiO₃) were used as alkaline activator. While alkali-activator ratio of 2 was used in this research. The physical properties was tested by porosity and setting time test, while split tensile strength presented to measure brittle caracteristic of geopolymer concrete. The result shown that increasing volcanic ash content in the mixture will increase setting time of geopolymer paste. On the other hand increasing volcanic ash content will reduce split tensile strength and porosity of geopolymer concrete. After all replacing fly ash with volcanic ash was suitable from 25% to 50% due to its optimum physical and mechanical properties.

Abstract: In this study, the effect of holding time on the microwave sintered 84Fe-11Cr-5Al₂O₃ metal matrix composite (MMC) was investigated. Sintering was carried out in a tubular microwave furnace HAMiLab-V3 under N₂ atmosphere. The holding time was selected between 0 to 75 minutes with increment of 15 minutes respectively. A study of microstructure and physical properties was carried out on sintered samples. It was discovered that, when the samples sintered at 1400oC with 20oC/min heating rate, the hardness was significantly increased from 110Hv to 160 Hv for holding time ranging from 30 to 45oC/min. Further increment until 75 minutes of holding time, no significant changes were obtained and hardness values were at steady state. The enhancement of bulk density and reduction of porosity were observed commences at 30 minutes until 45 minutes holding time. However, the results showed that the optimum holding time was at 45 minutes where the micro hardness is at the highest point which is about 160Hv.

Abstract: Underwater attachment is a significant challenge, for which we have no good general solutions in our technology. Yet, a number of biological organisms have evolved solutions to this problem. One intriguing approach to underwater attachment is that of the marine bivalve mussel Anomia simplex that uses a biomineralized byssus to permanently anchor itself to substrates. The byssus has a highly complex hierarchical structure and contains over 90 wt% CaCO₃. The byssus features a complex set of porosities, presumed to be highly important for the function of the attachment system. The pore space is the main focus of the present work. We characterize the three dimensional distribution of pore spaces in the byssus using micro-computed tomography (µCT) through a combination of in house mCT and high resolution synchrotron µCT. The pore structures are observed to fall into distinct categories in various parts of the byssus. We discuss the branching of one set of pores that reach the byssus substrate interface in particular. They form a network reaching the byssus surface that we now visualize in three dimensions.

Abstract: The liquid hot isostatic pressure in superplastic conditions was applied to eliminate macroporosity in a die cast Al-12%Si eutectic alloy. The removing of macroporosity provides the yield stress increase of 56%, the ultimate tensile strength increase of 46%, the total elongation increase of 21%, the fracture toughness increase of 340% and the fatigue strength increase of 58%. Remarkable improvement of mechanical properties is caused by suppression of crack initiation on internal coarse pores.

Abstract: Cobalt Chromium Molybdenum (CoCrMo) is a metal that are widely used in the biomedical field of orthopedic applications. CoCrMo foam was developed in the form of a porous structure where it has a high porosity on the surface with the different pore sizes and shapes. This research is intended to produce CoCrMo foam by using slurry method and to study the effect of composition and sintering temperature on the metal foams. The slurry of CoCrMo was prepared by mixing the binder materials of Methylcellulose (CMC), Polyethylene Glycol (PEG) and distilled water for an hour. Followed by mixing and stirring the CoCrMo powder for another 1 hour until it becomes slurries. Polyurethane (PU) foam was then impregnated into the slurry and dried for a day in the oven with 60 °C. Sintering process is carried out at temperature of 1000 °C, 1100 °C and 1200 °C using a tube furnace. Then sample of CoCrMo foam was going through a shrinkage measurement, microstructure analysis by using Scanning Electron Microscope (SEM), analysis of element by using Energy Diffraction X-ray (EDX) and also the density and porosity test by using Archimedes method. The sample with the composition of 65wt% was the best result in this experiment. While sintering temperature of 1200 °C produced the highest number of porosities. The shrinkage percentage is from 2.67% to 14.13%. The density obtained is in between 1.538 g/cm3 and 2.706 g/cm3 while the percentage of porosity is from 50.284% to 78.934%. The average pore size is in the range of 249.63μm to 445.38μm. The best sintering temperature and composition to produced high porosity were on 1200 °C and 65wt%.

Abstract: Iron oxide (α-Fe2O3) as adsorbent was no longer new in CO2 adsorption studies. However, its contributions in the industry still in limited wherein lack of convincing results of quantifying of adsorbed CO2. This work presents an analysis for α-Fe2O3 was prepared by simple mixing method with identified the adsorption capacity that applied in CO2 capture. The synthesized α-Fe2O3 from different concentrations of precursor were analyzed using XRD, N2 adsorption-desorption isotherms with BET and BJH method, TEM, FTIR, CO2 adsorption at 298 K, CO2-TPD and TGA-DTG. It was noted that 2M concentration of precursor (s2M) with highest crystallite peaks shows highest surface area among all samples which indicative of well generated pores. The different concentration of precursor was found generated more porosity rather than particle size according to TEM micrograph. The sphere shape crystallite particle with high surface area (50.5 m2/g) and porosity were desirable properties in CO2 adsorption. Consequently, physically adsorbed CO2 with adsorption at 298 K was highest with adsorption capacity of at 17.0 mgCO2/gadsorbent. Finally, chemically adsorbed CO2 was successfully identified from CO2–TPD analysis with adsorption capacity of 0.19 mgCO2/gadsorbent and 1.31 mgCO2/gadsorbent at maximum desorption temperature of 375 °C and 749 °C respectively.

Abstract: Slurry dipping is a simple and popular method of producing porous and interconnected foams using a metallic slurry. The advantage of the network-like metal foams is it exhibits a natural bone-like structure which enables ingrowth of bone cells and blood vessels. The aim of the present study was to investigate the effect of using difference composition and scaffold to produce Cobalt Chromium Molybdenum (CoCrMo) foams. The CoCrMo slurry was prepared by using different composition of CoCrMo powder which was 60wt%, 65wt% and 70wt%. Also two different types of scaffold were used in this study. The CoCrMo slurry was produced by mixing CoCrMo powder with Polyethylene Glycol (PEG), Carboxyl Methyl Cellulose (CMC) and distilled water. Then, polyurathane foam template was dipped in CoCrMo slurry and dried at room temperature. Sintering process was running by vacuum furnace at high temperature, 1200°C. The CoCrMo foam was characterized by using a Scanning Electron Microscopy (SEM) analysis. The physical properties of CoCrMo foam was analyzed by porosity and bulk density test that was Archimedes method. From the study it was expected that the composition of metallic slurry play important roles to produce a CoCrMo foam. In order to orthopaedics application to apply in cancellous bone, highest value of porosity from PU foams type (a) was most suitable result to use. This is due to the value of porosity that generate that was 65.2%.

Abstract: Nowadays, the 316L stainless steel metal foams (SS316L) have acknowledged important attention in various fields and are required to be used as engineering materials including heat exchange, sound absorption, filtration and others. So, in this study the production of SS316L foams using different composition through compaction method by using a starch powder as space holder was studied. The range of selected composition of SS316L that obtained is between 50 wt% to 60 wt% while the remaining percentages are space holder and binder. The SS316L compact is prepared by mixing SS316L alloy powder, starch powder, and Polyethylene Glycol (PEG). Then, the mixture is compact into a mould under 8 tonnes of controlled pressure using hydraulic press machine. This is later sintered in a vacuum furnace. The sintered SS316L foams were characterised using a Scanning Electron Microscopy (SEM) analysis. Then, the physical properties of SS316L foam was also analysed by Archimedes method that includes porosity and bulk density test. As a result, the sample with 60 wt% were produced a good and finer pores and struts. Meanwhile, for that sample the percentage of porosity and bulk density are 0.19% and 7.44 g/cm³, respectively.

Abstract: Sintering involves several interactions as particles bond and enable microstructure evolution toward a minimized energy condition, resulting in a complex interplay of measurement parameters. Overriding the evolution is energy minimization, and from that perspective some simple relations emerge. The natural progression is determined by energy reduction, measured by surface area, density, and grain boundary area (grain size). Contrary to the usual sintering analysis that starts with atomic level mass transport mechanisms, presented here is an approach that links to global energy reduction during sintering to simple monitors. Initially sintering converts surface area into lower energy grain boundary area. Subsequently grain growth annihilates grain boundary area. Thus, grain boundary area peaks at intermediate sintered densities, while surface area continuously declines. The trajectory follows a straightforward dependence on density as illustrated using data for a wide variety of materials and consolidation conditions.