Papers by Keyword: Porous Alumina

Abstract: Recently, demand for this Anodic Alumina Oxide (AAO) has been raised throughout the year due to its unique and special properties that will bring many benefits to the nanotechnology industry. AAO is the self-organized porous alumina produced by anodizing aluminum and can also be seen as nanotube arrays with honeycomb-like structures. Throughout these centuries, many research has been done in order to study the optimum parameter to produce high-quality AAO. This paper is specifically to investigate the effect of anodization voltage on the structural formation of AAO by using anodization of the aluminum process. A porous alumina template was prepared by using a difference voltage range of 20 V – 30 V in 0.3 M of oxalic acid; a copper wire was used as the cathode electrode and an aluminum template was used as an anode. It is observed that after the anodization process, there is a significant increase in current density at every voltage increment, as well as an increase in the size of the nanopores in AAO. The morphology and phase composition were characterized by using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDX) and Fourier Transform Infrared Spectroscopy (FTIR).

Abstract: A comparative analysis of the thermal conductivity for porous alumina using Taguchi method has been reported in the current research. Porous alumina is one of the most critical ceramics amongst those that are widely used in the thermal insulator industry; this is because of their physical properties. Thus, the investigation of these properties is highly desirable. Test variables were performed for the thermal conductivity studies-weight per cent of a pore-forming agent (yeast), sintering temperature, and soaking time. Through implementing the experimental design using the Taguchi method for thermal conductivity of porous alumina was statistically analyzed. The Signal-to-noise ratio and variance analysis investigated the influence of different parameters on the porous media's thermal conductivity. The result of research determines that the addition of the pore-forming agent obtained a higher thermal insulator. Based on the optimum conditions obtained from the Taguchi method factor was 20wt.% weight of yeast cell , sintering temperature at 1200 C , and the holding time 1.5 h. that give higher value of the S/N ratio.

Abstract: The effect of slurry solids content was studied for a novel direct foaming method based on slurry boiling to produce porous alumina ceramics. Slurries with solids contents of 30 to 45 wt. % were produced by conventional processing methods. The physical properties of slurry density and surface tension were measured, as well as thermal properties such as specific heat and latent heat, which were obtained using differential scanning calorimetry (DSC). Samples were fabricated by boiling the slurries on a hot plate until the liquid was completely evaporated. The resultant porous samples were presintered at 1000 °C and were examined to determine the pore size and structure. The measured pore diameter of samples obtained from this experiment were compared with theoretical calculations of departing bubble diameter from a heated surface proposed by Fritz, and Cole & Rohsenow. It was found that the pore size had a relationship with slurry solids content depending on the thermal gradient. The pore size, at a position away from the heated surface, increased as the solids content increased. However, the pore size at the heated surface did not vary significantly with solids content. The results showed that a direct foaming method based on slurry boiling is capable of producing porous alumina and that solids content of the slurry may be utilized to somewhat control pore size and structure.

Abstract: The porous scaffold has a weakness in terms of compressive strength. This is due to the porosity that is inversely proportional to the strength of the porous scaffold. Greater the percentage of porosity will decreasing the compressive strength. However, this compressive strength can be improve by controlling several factors (i.e., number of PU pores, composition ratio of slurry, percentage of binder and number of coating process). In general, fabrication porous alumina by conventional process was takes a longer time and consuming high cost. In addition, the conventional process could not explain the interaction relationship between all factors. Therefore, experimental design using Minitab 16 is applied to investigate the factors’ interaction. From the analysis, a combination of composition ratio and number of coating were found to have a significant impact to increase the compressive strength (> 2MPa) while others are less significant.

Abstract: The porous alumina templates were synthesized by anodization process. For preparation, the aluminum foils were cleaned by acetone acid and ethanol. After that, cleaned foils were firstly anodized by oxalic acid with direct current (DC) voltage source. When the first anodization process was complete, the aluminum foils were etched by chromic and phosphoric acid for an hour and then they were secondarily anodized for 15 min to increase the pore depth. For characterization, the surface morphology of porous alumina on aluminum surface was evaluated by scanning electron microscope. The results show that the pore diameter increases with increasing DC voltage and concentration of oxalic acid. The lowest pore diameter is 57.19 nm at DC voltage of 20 V for concentration of 0.2 M that it has highest pores density of 157 Gpores/in².

Abstract: In this study, production processes for porous alumina, and the characteristics of the material, were investigated. Porous alumina was produced by a wet-shaping process in which air bubbles were introduced into the slurry. The feature of this production process is that many pores are produced by slip casting carried out using whipped slurry, where only the conditions of the slurry are adjusted. The advantage of this process is its simplicity. From the results, it is made clear that a green compact of porous alumina can be produced by changing the amount of solvent and binder, and also that a sintered compact of porous alumina can be produced by a low sintering temperature, such as 1473 K. The four point bending strength of porous alumina is about 515 MPa when the porosity is about 30 %. The excellent characteristics of the sintered compact of porous alumina are shown by the observation results of the fracture surface in this production process. The dense alumina body is sintered while maintaining the fine grains, and with the micro pores remaining in the grain boundary.

Abstract: Porous alumina films are widely used as templates for fabricating one-dimensional (1-D) nanostructures such as nanowires or nanotubes. Using a two-step anodisation process, we have successfully optimized the growth conditions for fabricating highly ordered porous alumina films with pore diameters ranging from 20 to 150 nm, to be used as templates for 1-D nanostructure synthesis. The effects of the anodisation conditions on pore structure and the formation rate of the films were systematically studied. It was found that low electrolyte temperatures and agitations decreased the growth rate of the films but favored the process of pore ordering. Removal of oxide layer formed from first anodisation process and removal of barrier oxide at pore ends had an important bearing on pore morphology. Besides the stand-alone porous alumina films, we have also fabricated porous alumina films on rod-shaped Al substrates.

Abstract: In this study, porous alumina was fabricated by using polymeric sponge method. The slurries were prepared by mixing alumina (Al₂O₃) and polyvinyl alcohol (PVA) powder in distilled water. Slurries with two different compositions (60 and 70 wt. %.) of solid concentration were prepared. Samples were dried in an oven at 80 °C for 24 hours and sintered at temperature of 1500 °C. The effect of solids concentration was studied. Characterizations such as density and porosity tests, compressive strength as well as microstructure morphology were then used to analyze the sintered porous alumina samples. Specimens with 60 wt. % of solid loadings showed the higher porosity (88.06%) and pores structure more clearly interconnected. However, specimens with higher strength, 0.55 MPa, were obtained by using slurry with solid loadings of 70 wt. %.

Abstract: The traditional method of preparation alumina insulation material includes the addition of pore-forming agent, direct foaming, foam impregnation and gel-casting. In this experiment, α-alumina as raw material, silica fume as an additive, Combination freeze-drying method, add pore-forming agent and direct foaming successfully prepared low-density, high strength, low thermal conductivity of alumina insulation material. Change the particle size of pore-forming agent can be get different properties of the sample. The SEM photograph was clearly observed that the hole wall dense uniform, α-alumina particles sufficient contact, no significant ice sublimation hole left. There are also the reasons of the sample with higher value of bending strength and compressive strength. This can make a control of porosity, as well as pore size, pore shape and pores space topology of alumina insulation material.

Abstract: Porous alumina (Al₂O₃) ceramics were fabricated by powder injection moulding process. The feedstocks, composed of 44 50 vol% of Al₂O₃ powder, could be prepared using a composite binder, consisting of polyethylene glycol (PEG) and polyvinyl butyral (PVB). Debindings were carried out using a combination of water leaching of the PEG and thermal debinding of the PVB. It was observed that the removal of the PEG was fast at the initial stage and more than 90 wt% of the PEG could be removed within 4 hours. Sintering was performed in argon atmosphere at 1600 °C. The sintered specimens had apparent porosity in range of 26-32 %, depending on the feedstock compositions. The flexural strength values were in range of 90-140 MPa while the hardness values were in range of 5-9 GPa. It was found that both the strength and hardness of the specimens were increased with increasing powder loading.