Papers by Keyword: Porous Structures

Abstract: Ti₂AlC is one of the most promising MAX phase materials due to its combination of properties at high temperatures (> 800 °C) such as high strength, good oxidation and corrosion resistances, low thermal expansion, readily machinable, high thermal conductivity and nonsusceptibility to thermal shock. Porous structures based on Ti₂AlC are excellent candidates for diverse applications such as heat exchangers and filters, although more systematic studies are required to implement this material. In this work, porous Ti₂AlC material was obtained using a low cost and eco-friendly process, the space holder technique. Commercial Ti₂AlC powder was mixed with different contents (30, 50 and 70 vol.%) of ammonium hydrogen bicarbonate (NH₄HCO₃) as space holder. Afterwards, the obtained powder was uniaxially pressed, followed by elimination of space holder by a heat treatment at low temperature. Finally, porous Ti₂AlC structures were consolidated at 1350 °C under argon atmosphere. Processing, final microstructure and pore characterization of the consolidated materials are described in detail.

Abstract: This paper presents a novel process for fabricating micro-porous Aluminium (Al) alloy structures with possible application in antimicrobial filtration of drinking water which is contaminated with pathogenic micro-organisms responsible for water-borne diseases. This process is an integration of cold spray (CS) with the alloy-de-alloy phenomenon. In this process, the Al, Aluminium oxide () and Copper (Cu) powders with antimicrobial capabilities were mixed and deposited directly onto to a substrate using CS. To create porosity in the Al-Alumina-Cu coating, pores were innovatively engineered by alloying the Al--Cu with pore forming agents followed by preferential de-alloyed of these agents. The resulting structures have promising microstructural composition and porosity which make them favourable for antimicrobial filtration of contaminated drinking water. Consequently, this research demonstrates that via CS, a novel process was developed for fabricating porous Al-Alumina-Cu alloy metal foam for application in decontamination of drinking water.

Abstract: Studies show that, for viable product realisation and maintenance, a spectrum of novel processing technologies and materials to improve performance and reduce costs and environmental impact must constantly be addressed. One of these technologies, namely the cold spray process has enabled a broad range of coatings and applications, including many that have not been previously possible or commercially practical, hence its potential for new light metal applications. Therefore, the purpose of this paper is to highlight some advantages of this technology and explore how the cold spray process could be used to repair light metal unserviceable components and develop new light metals including light metal porous structures.

Abstract: The potential of laser assisted Direct Metal Deposition (DMD) process, for creating structures from high strength steel alloys that can be used in engineering applications requiring high strength and greater ductility in combination with high hardness is investigated. Due to increasing interest in metallic honeycomb and sandwiched structures, solid and porous specimens are prepared and examined in similar conditions. Specimen using two different powders of 316L stainless steel and H13 tool steel alloy are generated by DMD cladding on mild steel plates as substrates. The parts are tested under quasi static compressive loading and curves plotted and analysed for stress vs. strain behaviour. The results indicate that at low laser power, solid and porous steel structures with yield strength and ductility comparable to commercial grades can be produced. Porous structures show excellent characteristics suitable for applications in newly developing field of metallic honeycombs and sandwiched structures. Low modulus of elasticity is a matter of concern, but it can be improved by heat treatment.

Abstract: Porous structures of carbon nanotube (CNT) composites with highly accessible surface areas have numerous potential applications such as heterogeneous catalysts and adsorbents. In this study sodium alginate was added to CNTs dispersions as gelling agent. Before being dried, the hydrogels were shaped into bead, disk, and sheet forms. The alginate in the composites was then decomposed by heating up the samples under an inert gas. The morphology of the as-prepared composite was studied by scanning and transmission electron microscopy and the pore size distribution was measured by BJH method. The MWCNT composite showed a density of around 0.08 g/cm³ and a specific surface area of 164 m²/g. The as-synthesized porous composite was examined as an adsorbent to remove methylene blue (MB) from aqueous solutions. Complete removal of MB was observed. The adsorption isotherm and kinetics were also evaluated.

Abstract: This paper reports the results of a study aimed to deposit a biomimetic apatitic coating on the porous surface of Ti alloy acetabular cups, produced with AM techniques. To this purpose, we utilized a slight supersaturated Ca/P solution at physiological values of pH and temperature. The results of the XRD, SEM and EDS investigation indicate the 6 h immersion in the calcifying solution are sufficient to provoke the deposition of a uniform coating of poor crystalline apatite on the surface and inside the porous structure of the substrates.

Abstract: The present paper deals with the application of the transient techniques for thermophysical analysis of the structural changes in materials. The technique has been applied for study of equilibrium transitions as well as for kinetic transitions. A special methodology has been developed to study kinetic transitions like crystallization, melting, etc. in a “pseudo-equilibrium states” by the help of porous structures. The paper includes three different issues: the transient methods for measuring thermodynamic and transport parameters, data analysis and application of the pulse transient method for measurements of materials in thermodynamic equilibrium, pseudoequilibrium and in non-equilibrium (quasi-equilibrium) states. Equilibrium transitions in CsPbCl3 and CsPbBr3 single crystals, kinetic transitions of freezing and thawing water in porous stones and non-equilibriums states in E-glass and Al2O3 ceramics during sintering have been studied.

Abstract: Hydroxyapatite (HA) is the calcium-phosphate material with composition closest to that of human bone, what makes it suitable for osseous implant purposes, namely as fillers, spacers and bone grafts substitutes. This study is aimed at the development of a method to produce porous spherical hydroxyapatite granules. The process involves the spraying of a suspension with different amounts of a setting agent to a setting media. The tailor and the control of the morphology, size and porosity of the granules were attained by adjusting the nozzle diameter, the pressure of air flow and the distance between the nozzle and the setting media.