Papers by Keyword: Microporosity

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Authors: J. Chojcan, M. Sachanbiński
Authors: Nelson H.A. Camargo, Priscila F. Franczak, Enori Gemelli, Bruna Ditzel da Costa, Aury Nunes de Moraes
Abstract: The calcium phosphate microporous bioceramics, and hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) biphasic compositions, in the granular form of microporous biomaterials, are research themes and present potential biomedical applications in rebuilding and repairing maxillofacial bone and tooth structure and in orthopedic applications. This is associated with microstructural characteristics of biocompatibility and bioactivity and osteoconductivity properties that these biomaterials offer when applied in vivo or in simulated environment. Another differential point of these biomaterials is the solubilization capacity that they present when applied in the biological environment. These compositions of calcium phosphates (hydroxyapatite matrix and/or β-tricalcium phosphate) allow for the gradual release of calcium and phosphate ions for the biological environment, which are absorbed and promote the formation of new bone tissue. These materials are also promising in applications in the field of traumatology as in the repair of traumatized bone tissue and drugs controlled release and bone structure treatments. The favorable results of these biomaterials as bone reconstruction matrix and drugs controlled release are associated with crystallographic characteristics, morphology, surface and solubility that these biomaterials present when in contact with body fluids. This work aimed to describe three types of calcium phosphate microporous granulated biomaterials. The biomaterials used were provided by the Biomaterials Group from Universidade do Estado de Santa Catarina - UDESC and are: hydroxyapatite, β-tricalcium phosphate and biphasic composition 60% hydroxyapatite/40% β-tricalcium phosphate. The Scanning Electron Microscopy technique (SEM) was used for carrying out the morphological characterization and microstructure studies of granulated biomaterials. The X-Ray Diffractometry (XRD) served for characterization of crystalline phases. Arthur Method was used for determining open porosity and hydrostatic density of biomaterials. The BET technique served to support determination of the surface area of microporous granulated biomaterials. The results are encouraging and show that these biomaterials present promising morphological characteristics and microporous microstructure as wettability and capillarity. These characteristics may contribute to biomaterial osteointegration by new tissue, bone formation and mineralization process.
Authors: Kristine Salma, Zilgma Irbe, Dmitrijs Jakovlevs, Natalija Borodajenko, Liga Berzina-Cimdina
Abstract: In this work three different preparation techniques of biphasic calcium phosphate (BCP) bioceramics (consisting of both hydroxyapatite (HAp) and β-tricalcium phosphate (TCP)) are compared: sintering of synthetic calcium-deficient apatites (CDAs) (intimate mixture of HAp and TCP - SBCP), sintering of mechanical mixture of synthetic HAp and apatitic tricalcium phosphate (Ap-TCP) - MBCP and sintering of mechanical mixture of synthetic HAp and calcium metaphosphate glass (CMG) - GBCP. Two different HAp/TCP phase ratios were investigated: 20/80 and 60/40. Phase composition, microstructure, sintering properties and microporosity of obtained BCP bioceramics were investigated. The open porosity of prepared BCP bioceramics is strongly influenced by phase composition and preparation technique. BCP bioceramics SBCP and MBCP have homogeneous microstructure, whereas GBCP has inhomogeneous inclusions of dense TCP. High content of hydroxyapatite (HAp) phase in MBCP and SBCP correlates with high microporosity.
Authors: Conor T. Buckley, K.U. O’Kelly
Abstract: Tissue-engineering scaffold-based strategies have suffered from limited cell depth viability when cultured in vitro, with viable cells existing within the outer 250-500μm from the fluid-scaffold interface. This is primarily believed to be due to the lack of nutrient delivery into and waste removal from the inner regions of the scaffold construct. Other issues associated with porous scaffolds involve poor seeding efficiencies and limited cell penetration resulting in heterogeneous cellular distributions. This work focuses on the development a novel hydroxyapatite multi-domain porous scaffold architecture (i.e. a scaffold providing a discrete domain for cell occupancy and a separate domain for nutrient delivery) with the specific objectives of embodying in one scaffold the structures required to optimise cell seeding, cell proliferation and migration and potentially to facilitate vascularisation once implanted in vivo. This paper presents the development of the multidomain architecture and preliminary results on cell viability which show a significant improvement in cell viability in the scaffold interiors.
Authors: Qun Gong He, Jun Liu, Lin Xu Li, Zhen Huan Gao, Xiao Yan Shi, Gong Xian Yang
Abstract: The microstructures and mechanical properties of IN738LC superalloy made by investment castings followed by Hot Isostatic Pressing (HIP) treatment have been investigated. The results revealed that after HIP treatment, the microporosities have been almost removed and the density rose by 0.21%. The eutectic size became smaller and the fraction decreased. The γ' phase was more regular and also increased in size, while a large number of secondary γ' phase appeared. With HIP treatment, the impact toughness increased from 5.0J ~ 7.0J to 8J ~ 9J and tensile strength at 200°C ~ 800°C was improved by approximately 3.2%~19.7%. In addition, the ductility and the stress rupture life have also been greatly improved as well.
Authors: X. Sun, Zhan Yi Cao, Hai Feng Liu, W. Jiang, L.P. Liu
Abstract: Cast Magnesium alloys often exhibit large variability in fracture related properties such as ductility. In this study, the characteristics of micro-voids in high-pressure die-cast (HPDC) AM50 alloy were investigated by microstructural detecting. Specimen-to-specimen fractographic analysis of tensile fractured surface was executed to summarize the relation between microporosity and tensile properties. The results indicated that the variability in tensile properties is quantitatively correlated to the areal fraction of porosity in the corresponding fracture surface, which could be expressed by a power law equation. All the results proved that the most highly localized cluster of micro-voids is most preferentially to be the origin of fracture, and then, fracture crack will preferentially propagate through the adjacent regions that with large porosity.
Authors: E. Foglio, Marcello Gelfi, Annalisa Pola, D. Lusuardi
Abstract: Heavy-section ductile iron castings solidify under low cooling rates, giving the risk to form defects like non-metallic inclusions, microporosities and degenerated shapes of graphite that have a negative effect on fatigue resistance, favoring the crack nucleation. The aim of this work is to precisely identify the defects that most affect the fatigue behavior in heavy-section castings, in order to guide the foundry to take the proper countermeasures. For this purpose, fatigue rotating bending tests were carried out on specimens machined from small-scale samples opportunely cast to reproduce long solidification times. The fracture surface of broken samples were investigated by means of Scanning Electron Microscopy in order to identify crack initiation points and fracture mechanisms. Shrinkage porosities and spiky graphite were found to play the most important effect on crack nucleation, lowering the fatigue resistance of the castings, while chunky graphite just behaved as a preferential path for crack propagation.
Authors: Xie Hua Li, Li Zi He, Yi Heng Cao, Pei Zhu, Ya Ping Guo, Jian Zhong Cui
Abstract: The influences of cooling rate, hydrogen inflating time, degassing time, inclusion content on the distribution of pores within the ingot , hydrogen content and the mechanical properties of 1050 aluminum alloy were investigated by tensile test, optical microscope(OM), scanning electron microscope(SEM). With the increasing inflating hydrogen time, the hydrogen content increases, while, the strengths and elongation decrease. With the increasing degassing time, the hydrogen content decreases, while, the strengths and the elongation increase. With increasing cast temperature, the hydrogen content remains constant at first and increases obviously from 7200C to 7600C, while the strengths and the elongation decrease gradually. The crack is mainly originated at outcrop of slip step, inclusion and porosity.
Authors: Yong Zhi Zou, Zheng Bin Xu, Jian Min Zeng
Abstract: Microporosity in cast aluminum alloys formed during solidification of castings can be due to the evolution of dissolved hydrogen gas from the liquid metal, the inability of liquid metal to feed through interdendritic channels, or a combination of both. The secondary dendrite arm spacing (SDAS) of the casting may affect either the evolution of hydrogen gas or the ability of feeding. In this investigation, a method based on the Nearest-Neighbor-Distance (NND for short) cluster analysis of image analysis data was used for distinguishing the gas and shrinkage pores in A357 alloy, in order to study the effects of SDAS on the microporosity formation. It shows that the shrinkage pores are prone to form in the specimens with small SDAS. The discrete, isolated gas microporosity is prone to form in the specimens with large SDAS.
Authors: Ibrahim Yakub, Masita Mohammad, Zahira Yaakob
Abstract: Activated carbon was developed from physic nut seed hull through chemical activation using zinc chloride. The characteristics of raw physic nut seed hull as well as char and activated carbon from physic nut seed hull were obtained to study the effects of ZnCl2 impregnation. The comparisons of the characteristics that included elemental composition, surface morphology, surface area, surface functional groups and zeta potential were made on the three samples. The study found that ZnCl2 had positive effects towards developing activated carbon including increasing the carbon content, surface area and pore volume besides improving the microporosity and surface charge distribution of the carbon.
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