Papers by Keyword: Porous

Abstract: Indonesia is a tropical country with high rainfall, which necessitates pavement with higher void content and good drainage conditions. The quality of road pavement depends on the materials used. One type of asphalt mixture with high void content and permeability but low stability is porous asphalt. This is due to the composition of porous asphalt, which consists predominantly of coarse aggregates compared to fine aggregates. This study utilizes waste tires, Low-Density Polyethylene (LDPE), gilsonite, and 60/70 penetration asphalt as binders, referred to as modified asphalt, in porous asphalt mixtures. The objective of this study is to determine the Optimum Asphalt Content (OAC) using waste tires, LDPE, gilsonite, and 60/70 penetration asphalt as binders in porous asphalt mixtures and to compare it with the OAC of conventional asphalt. The method used in this research is based on the Australian Asphalt Pavement Association (AAPA) (2004) method, employing open-graded porous asphalt with a maximum aggregate size of 14 mm. According to AAPA (2004), OAC determination requires three parameters: Cantabro Loss (CL), Asphalt Flow Down (AFD), and Voids in Mix (VIM). The study began with testing the physical properties of aggregates and asphalt, both conventional and modified. After testing the physical properties, the next step was determining the optimum asphalt content. The OAC obtained for porous asphalt mixtures using modified asphalt as a binder was 5.3%, while the OAC for conventional asphalt was 5.75%, serving as a comparison.

Abstract: The analysis of unsteady MHD flow over a porous stretching plate is critical for various engineering applications, particularly in systems involving chemical reactions and thermal radiation. This study explores the novel effects of heat and mass transfer in a two-dimensional unsteady magnetohydrodynamic (MHD) flow. This present work examines the effects of radiation and a transverse magnetic field on a chemically reacting fluid flowing over a stretched plate. The unsteady nature of the flow is associated with the time-dependent variations in stretching/extending velocity, temperature, and fluid concentration. The nonlinear governing boundary layer partial differential equations (PDEs) are transformed into a set of nonlinear ordinary differential equations (ODEs) using a similarity transformation, which are then numerically solved using the MATLAB bvp4c method. The flow, heat, and concentration profiles are quantitatively analysed through graphs for various problem parameters, including the unsteadiness parameter (A), Hartmann number (M), porosity parameter (Sp), radiation parameter (N), chemical reaction parameter (K), Soret number (Sr), Eckert number (Ec), Schmidt number (Sc), and Prandtl number (Pr). Additionally, the skin friction coefficient, Nusselt number (Nu), and Sherwood number (Sh) are numerically addressed and illustrated using graphs.

Abstract: Due to its low density, high strength to weight ratio, and been unreactive to the human body, titanium is commonly used in human bone implants. Titanium in bone implants can be used in its porous form because the porosity reduces the elastic modulus of the implant, near to that of human cortical or trabecular bone, which prevents the effects of stress-shielding. To date, majority of the published studies using the space holder (SH) method to produce porous titanium, utilized-45 μm titanium hydride dehydride (Ti-HDH) powder, or similar titanium powder. However, there is limited research conducted on the use of coarse titanium powder particles, such as-150 μm Ti-HDH powder to produce porous titanium. Fine Ti-HDH powders are known to have higher oxygen content than coarse Ti-HDH powders, thus the specimens produced from fine powders are harder, require higher compaction pressures and are expected to have lower impact resistance. The following study thus investigated the use of-150 μm Ti-HDH powder to produce porous titanium specimens, by the SH method. The porous specimens of 45 mm diameter were produced by uniaxially compacting mixtures of sodium chloride (NaCl) powder and Ti-HDH powder at 500 MPa. The NaCl powder utilized was hand sieved to a range of-500 μm. The specimens were sintered at 1150 for 4 hours in a high-vacuum tube furnace. Three porosity levels were investigated i.e. 40%, 50% and 60%. The sintered compacts were assessed for density, porosity and elastic moduli. It was found that the sintered porosity of the specimens ranged from 42.7-59.1%, and the sintered density ranged from 1.84-2.58 g/cm³. The elastic moduli of the specimens were found to reduce as the porosity increased, and ranged from 0.59-1.3 GPa, which is similar to the elastic moduli of human trabecular bone. The use of-150 μm Ti-HDH powder is thus potentially a lower cost alternative, than the use of-45 μm Ti-HDH powder, to produce porous titanium for human bone implants.

Abstract: In this study, the activation of natural diatomite was done with alkaline solution. The diatomite powder was sieved and purified prior to activation at room temperature (Alk-DA RT) and 85 °C (Alk-DA 85 °C). The effect of activation time of Alk-DA 85 °C samples was observed for 1 h, 2 h and 5 h. At temperature interval from room temperature to 530 °C, the weight loss for all of Alk-DA are less than R-DA. The reduction of particle aggregation was found in Alk-DA at both RT and 85 °C as shown in SEM images, indicating the activation by NaOH that effectively breaks down the bulky structure. The formation of silanol group (Si-OH) were obtained on the surface of Alk-DA. However, BET result revealed there is no increment of surface area and porosity in case of RT. In addition, Alk-DA 85 °C samples at 1 h and 2 h provided the spongy surfaces with obvious improvement of surface area, and reduction in porosity and pore size. In contrast, Alk-DA 85 °C 5 h showed more cluster of particle aggregation. Moreover, it can be observed that Alk-DA 85 °C 1 h is the most interesting for further study since it potentially provides high gas adsorption but only requires a shorter activation time.

Abstract: Porous NiTi shape memory alloy is of special interest for biomedical purposes especially for human bones application due to its attractive features such as lower stiffness to minimize the effect of stress shielding and good strength to prevent deformation and fracture apart from its shape memory effect and superelastic behavior. With all these great benefits, however, the challenge is to produce porous NiTi which resembles cancellous bone. Therefore, in this research, pore forming agent such as calcium hydride, CaH₂, is added to the equiatomic of Ni and TiH₂ powder mixture to produce porous NiTi with higher porosity level using powder metallurgy technique. Here, the effect of composition of pore forming agent on porosity level, phase formation and transformation behaviour of porous NiTi were investigated. From the observation, the pores formation exhibits small closed pores instead of interconnected pores. The result also shows that by adding 3wt% composition of pore forming agent, the porosity level of sample sintered can reach up to 32%. For phase transformation behavior, there are martensitic transformation peaks observed both upon cooling and heating for all samples, however the overall enthalpy changes are significantly lower (<2 J/g). This due to undesirable phase such NiTi₂, Ni-rich phase and also Ni₃Ti that co-exist with NiTi formation, thus jeopardize the transformation enthalpy for porous NiTi.

Abstract: Microstructure-tailored TiO₂ nanoarrays with adjustive wall-hole morphology have been designed to improve electrochemical properties. Tubular, porous and flow-through TiO₂ nanoarrays are fabricated by one-stepped, two-stepped and three-stepped anodization process under the controlled reaction condition. Tubular nanoarray with the opened-mouth and closed-bottom has a tube diameter of 120-130nm, a length of 8.12μm, and wall thickness of 15nm. Similarly, porous TiO₂ nanoarray with the opened-mouth and closed-bottom has a pore diameter of 60-70nm, a length of 8.25μm, neighboring wall distance of 70-80nm. Comparatively, flow-through TiO₂ nanoarray with the opened-mouth and opened-bottom has a pore diameter of 110-120nm, a length of 8.56μm, neighboring wall distance of 40nm. In comparison with tubular and porous TiO₂ nanoarrays, flow-through TiO₂ nanoarray indicates the deceased charge transfer resistance and diffusion-related Warburg impedance, presenting the enhanced current response at the same electrode potential. Accordingly, bottom-opened flow-through TiO₂ nanoarray achieves the specific capacitance of 6.35 mF cm^-2, which is higher than the bottom-closed tubular and porous TiO₂ nanoarrays (2.94 and 3.78 mF cm^-2). The flow-through TiO₂ nanoarray presents the improved electrochemical performance for the electrochemical energy-storage.

Abstract: Porous Co/C composite nanofibers were fabricated by combination of electrospinning method and polymer blend. The phase composition, microstructure and electromagnetic characteristics of them were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vector network analyzer (VNA), and their microwave absorption performances were studied. The results indicate that nanofibers were composited by amorphous carbon and face-centered cubic structured Co nanoparticle after sintering. The addition of PMMA is a key factor of nanofibers morphology and the aperture was improved with the increase of PMMA. When the thickness is 2.0 mm, the samples exhibit the best microwave absorption performance. Their effective absorpt ion bandwidths (RL < 10 dB) are 6.3 GHz, 6.2 GHz and 6.1 GHz, and it’s obviously superior to ordinary morphology nanofibers.

Abstract: Calcium sulfate dihydrate (CSD) has been clinically used as bone filler for decades. CSD bone graft is cheap, biocompatible and can be transformed to other osteoconductive ceramics such as hydroxyapatite and carbonate apatite. In addition, porous ceramic bone grafts is desired clinically. Development of porous ceramics bone graft with simple and cost-effective method is preferred. Thus, in this study, porous CSD was developed. Porous CSD can be used both as bone filler or precursor for porous hydroxyapatite and carbonate apatite. Porous CSD was prepared by mixing calcium sulfate hemihydrate (CSH) containing sucrose granules with distilled water. After setting, the sucrose granules were removed by immersion in distilled water. Porous CSD was obtained after sucrose leaching. It was observed that more pore formed in the specimen with 50% sucrose granule compared with that of 25% sucrose granule. The sucrose was completely removed from the porous CSD evident from ATR-FTIR analysis. The diametral tensile strength of the porous CSD tend to decrease with the increase of sucrose granule. Finally, sucrose granule was feasible to be used as pore maker in preparation of porous CSD.

Abstract: In this paper, melamine was used as porogen to prepare porous polyimide film by in-situ polymerization. The mechanical properties, thermal properties, dielectric properties, oil content and friction and wear properties of polyimide films with different porosity were investigated. The tensile strength of porous films decreases obviously with increase of melamine content. It shows the lower thermal decomposition temperature and the faster decomposition speed compared with the non-porous film, indicating higher heat exchange rate due to holes in porous films. As the porogen content increases, the dielectric constant decreases significantly, and the film with melamine content of 20 wt.% has the lowest dielectric constant of 2.43. The holes lead to good oil storage performance and the wear rate and the friction coefficient decrease with the increase of porosity. Keywords: polyimide; porous; melamine; dielectric; friction

Abstract: Porous, phosphate-silicate glass with high-conductivity and nano-size pores was synthesized through a xero-gel route, using non-ionic surfactant polyethylene glycol monocetyl ether (Brij 56) to control pore size. The influences of Brij 56 concentration on pore size and conductivity under different humidity were studied by measuring conductivity and calculating the volume ratio of adsorbed-water to pore volume. Samples prepared with 0.1 wt% Brij 56 had 5.2 nm pore size, 0.91 volume ratio, and narrower pore size distribution than other samples. The nano-size pores were filled with water, which in pores of 5.2 nm is mostly chemically bonded with the hydroxyl groups on the pore surfaces, resulting in higher conductivity than other samples in high relative humidity (over 55%).