Papers by Keyword: Porosity

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Authors: Sofiane Terzi, Luc Salvo, Michel Suéry, Jérôme Adrien, Éric Maire, Elodie Boller
Abstract: This paper is concerned with an investigation of the deformation behaviour of an Al-Cu alloy during tensile testing in the semi-solid state. It was carried out by fast in-situ X-Ray microtomography at ESRF, Grenoble. Deformation was performed at constant velocity, which was chosen to be small enough so as not to affect the acquisition of the images. It is observed that deformation is accompanied, initially, by some liquid flow from the adjacent regions towards the deformed zone. Then pores form in the liquid films and grow until they occupy a significant part of the cross section of the specimen. Quantification of this phenomenon was carried out thus leading to a better understanding of pore formation in semi-solid mixtures.
Authors: Anke Bernstein, Renate Gildenhaar, Georg Berger, Hermann O. Mayr
Abstract: Bioactive ceramics such as β-tricalcium phosphate (β-TCP) promote and enhance biological fixation. Ceramics with a porous interconnected structure are suited for facilitation of bony ingrowth. An interconnected pore system with pore diameters in excess of 100 µm is required for cell penetration, tissue ingrowth, vascularization and nutrient delivery to the centre of the regenerating tissue. Human osteoblasts were cultured on the surface of a ceramic. In an in-vivo study, β-TCP samples with a porous interconnected structure were implanted into the femur of sheep and then investigated 6 weeks after operation. Histological analysis was performed on the area surrounding the implant. An indentation test was performed to complete failure of the bone/ceramic compound. Linear load, peak load and stiffness were recorded. All cylinders were found to be biocompatible and osteoconductive. Bone was more abundant in the outer ring than in the rest of the cylinder. The ceramic/bone compound was of low mechanical grade.
Authors: Ana Cristina P. Machado, Marize Varella de Oliveira, Robson Pacheco Pereira, Yasmin R. Carvalho, Carlos Alberto Alves Cairo
Abstract: The osseointegration of porous titanium implants was evaluated in the present work. Implants were fabricated from ASTM grade 2 titanium by a powder metallurgy method. Part of these implants were submitted to chemical and thermal treatment in order to deposit a biomimetic coating, aiming to evaluate its influence on the osseointegration of the implants. The implants were characterized by Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy. Three coated and three control (uncoated) implants were surgically inserted into thirty albino rabbits’ left and right tibiae, respectively. Tibiae samples were submitted to histological and histomorphometric analyses, utilizing SEM, optical microscopy and mechanical tests. EDS results indicated calcium (Ca) and phosphorous (P) at the surface and Raman spectra exhibited an intense peak, characteristic of hydroxyapatite (HA). Bone neoformation was detected at the bone-implant interface and inside the pores, including the central ones. The mean bone neoformation percentage in the coated implants was statistically higher at 15 days, compared to 30 and 45 days. The mechanical tests showed that coated implants presented higher resistance to displacement, especially after 30 and 45 days.
Authors: F. Dombrowski, P.W. Garcia Caso, M.W. Laschke, M. Klein, J. Günster, Georg Berger
Abstract: The paper presented here deals with the investigations of orthophosphates (Q0) containing none or differing amounts of meta-(Q2) and diphosphate phases (Q1) for the use of 3-dimensional printing process in order to create porous, bioactive, nonloadbearing bone replacement scaffolds. The main ceramic phase in all cases is Ca10[K/N(PO4)7 hereinafter called 401545(100) consisting of 99,9% Q0 and 0,1% Q1-phase. The other phosphate ceramics i) 401545(40) consists of 75% Q0-phase, 22% Q1-phase and 4% Q2-phase ii) 401545(15) consists of 65% Q0-phase, 33% Q1-phase and 2% Q2-phase iii) 401545consists of 56% Q0-phase, 40% Q1-phase and 4% Q2-phase. The in-house produced ceramics where crushed and sieved to achieve particles of irregular shape in the range of 45-90µm. These powders show a quite good flowability and were used to generate cylindrical samples with a diameter of 5,5mm and a height of 11mm via 3-dimensional printing using a R1 printer from ProMetal company (USA). After drying the samples at T=125°C for 48 hours they were sintered at temperatures according to the thermal analysis results in the range of 900°C up to 1300°C. Afterwards the porosity, the linear shrinkage and the compressive strength were determined.
Authors: Anton du Plessis, Stephan Gerhard le Roux, Herman van Rooyen
Abstract: This paper describes a typical 3D X-ray micro computed tomography (microCT) analysis of light metal parts, from a radio controlled airplane engine. This case study shows the power of 3D X-ray inspection and analysis for this type of material, including information about the size and location of casting defects, the location of turbine blade balancing weights and dimensional measurements indicating the axle was not perfectly centre. Advantages and limitations of the method for light metals are described in general
Authors: Nor Bahiyah Baba, Mohamad Amir Harunsyam Lamshah, Mohamad Asyraf Mohd Amin
Abstract: The paper discussed on a 3-dimensional porosity network in electroless nickel (Ni) - yttria stabilized zirconia (YSZ) composite coating. The important characteristics of Ni-YSZ composite such as high ceramic YSZ incorporation and adequate porosity up to 40 vol.% are used as the main parameters. The arrangement of the porosity that give a 3-dimensional porosity network within the composite was design in Pro-Engineer Wildfire 3.0 software. Three structures of 3-dimensional porosity network were used namely honeycomb, atomic sphere and rhombic dodecahedra. The calculated area and volume of one unit porosity, consequently the number of porosity were compared between the three structures. These were supported by the porosity in the electroless Ni-YSZ composite coating obtained experimentally. Two batches were produced, EN-YSZ and EN-YSZ-G representing samples without and with pore former respectively. The two batch samples were investigated and compared. The addition of graphite pore former was burnt out completely and left porosity in the coating.
Authors: Hans Eckart Exner, Günter Petzow
Abstract: Understanding porosity coarsening is essential for controlling the properties of sintered materials and for producing high density or near net shape parts. As porosity is interconnected up to relative densities in excess of 80% or even 95%, measuring, monitoring and modelling of the growth of individual pores is relevant only at very high relative densities. This paper tries to convey two essentials of porosity coarsening: (i) characterization of the geometry of the pore space in the lower range of densities is possible by using stereological parameters, and (ii) coarsening of porosity takes place during all sintering stages by various mechanisms. Porosity coarsening has been reported in metals, ceramics and glasses. Recent and classical approaches, experimental results with two dimensional model arrangements as well as computer simulations of formation and opening of particle contacts are discussed. The effect of porosity dimensions on the properties of sintered materials and measures for preventing and provoking porosity coarsening are briefly addressed.
Authors: Divya Jyoti, Devendra Mohan, Amrik Singh, Dharamvir Singh Ahlawat
Abstract: Until breakthrough in 1991, commercialization of dye-sensitized solar cell (DSSC) has been a gradual process leading to a scarce production. A thorough study of dilemmas is needed to overcome the shortcomings of DSSC to make it stand against traditional silicon based solar cells. A DSSC is composed of important components including photoanode, dye, electrolyte and counter electrode. Among these photoanode is the focussed area of the presented article. The photoanode is a thin porous film of metal oxide semiconductor supported on to a transparent conducting oxide (TCO) glass. Extensive research in this field has revealed the photophysics of semiconducting electrodes like TiO2, ZnO and SnO2 etc. Selection of metal oxide for this purpose relies on crystallinity, particle size, and thickness of the film, surface area, dye affinity and porosity. These parameters related to the candidature of a particular metal oxide film as photoanode in DSSC have been discussed and optimized values have been quoted. The present study aims at emphasizing the history of DSSC as well as recent developments in electrodes, dyes and electrolytes in this specific area.
Authors: M.Madhu Vamsi, V. Pradeep Kumar, S.H. Shariff
Abstract: The use of aluminum castings in the automotive industry has increased dramatically over the past two decades. The Al-Si system forms the basis of many important casting alloys, LM 0, LM 2, LM 4, LM 5, LM 6, LM 12, LM 13, LM 24 and LM 26 are the major cast alloys used in aerospace casting (e.g., fuel pump connectors) and premium automotive castings (e.g., suspension arms). The driving force for this increased use is vehicle weight reduction for improved performance, particularly fuel efficiency. In many cases the mechanical properties of the cast aluminum parts are superior to those of the cast iron or wrought steel parts being replaced; however, in some applications, defects in the cast microstructure undermine performance characteristics.
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