Papers by Keyword: Surface Reaction

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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.
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Authors: Hiroki Yamaguchi, Yukinori Sakiyama, Emi Makino, Shoichi Onda, Yoichiro Matsumoto
Abstract: The origin of the polytypes of SiC has been investigated from the viewpoint of surface reactions by the density functional theory (DFT) within the Projector Augmented Wave-Generalized Gradient Approximation. Three radicals were considered here as the major species in the crystal growth process: Si, Si2C and SiC2. We supposed that these radicals contribute to the crystal growth directly through the adsorption on the 4H-SiC (000-1) C-face surface. The DFT calculations showed that the Si2C, which relatively has a similar structure with the SiC crystal, had no activation barrier to be adsorbed chemically to the 4H-SiC C-face surface. On the other hand, SiC2 with Si showed an activation barrier of 0.79eV to form the 4H-SiC crystal. In order to investigate the arrangements to decide polytypism in SiC, we compared the adsorption energies between the different sites, which correspond to the 4H-SiC crystal and a disordered arrangement. The activation energies had almost no difference. Our calculations indicated that these radicals do not contribute to the origin of the polytypes of SiC.
235
Authors: Norimitsu Murayama, Noriya Izu, Woosuck Shin, Ichiro Matsubara
Abstract: For resistive oxygen sensor elements of Ce1-xZrxO2 (x = 0.0, 0.05, 0.1, 0.2), grain diameter was varied in the range of 86 – 300 nm by changing sintering temperature or changing Zr content. The grain diameter decreased with increasing Zr content. The response time was approximately proportional to the square of the grain diameter. In the relationship between the amplitude of sensor output, An and the frequency, f of sine wave of variation in oxygen partial pressure, the gradient in the high-frequency region of a plot of log An vs. log f in was approximately –0.5. From these results, it was concluded that the sensor response was determined by the oxygen vacancy diffusion rate. The grain diameter of Ce0.8Zr0.2O2 element was 86 nm and the response time at 1073 K was 9 ms, which result opens the door to the technological development of independent control of engine cylinders.
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Authors: Yoshio Furuya, Akito Takasaki, Masao Koga, Takao Kino
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Authors: Anke Bernstein, Doreen Nöbel, Hermann O. Mayr, Renate Gildenhaar, Georg Berger, Ute Ploska, Joerg Brandt
Abstract: Bioactive ceramics such as hydroxypatite (HA) promote and enhance biological fixation. There is still a discussion on the desired longevity of the coating. Stable coatings require an optimum between resorption rate, flexural strength and adhesive strength of the coating. Ceramic coatings containing fluorapatite (FA, Ca5(PO4)3F) and calcium zirconium phosphate (CZP, CaZr4(PO4)6) promise lower resorption rates than conventional HA coatings in the biological milieu. It is hoped that they can improve the long-term stability of implants by eliminating the detrimental resorption of coating material. For the in vivo studies plasma sprayed coatings were generated. The materials were implanted into the distal femur epiphysis of rabbits and investigated after 2, 4, 6, 12, and 24 weeks postoperatively. Histological analysis was preformed on the areas surrounding the implant. The amount of osseointegration was determined by using the automatically image analysis. The bonding strengths were compared with HA coating and uncoated titanium alloy. According to available data, there is inhibition of mineralization of bone at the interface of calcium zirconium phosphate ceramics of the described composition.
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Authors: Anke Bernstein, Norbert Suedkamp, Hermann Otto Mayr, R. Gadow, A. Killinger, N. Stiegler
Abstract: Bioceramics used as coatings show different biocompatibility and bioactive behavior in relation to their chemical and morphological behavior. Bioactive ceramics such as β-tricalcium phosphate (β-TCP) promote and enhance biological fixation. Stable coatings require an optimum between resorption rate, flexural strength and adhesive strength of the coating. Therefore new bioceramic coating materials that ensure the balance between loss of substances and osteointegration need to be designed and investigated. By modifying the high velocity suspension flame spraying (HVSFS) process parameters, five coatings with different materials were obtained. The in vitro cytotoxicity was determined by the microculture tetrazolium (WST) assay after 24, 48 and 72 h. Cells were grown on the materials for 3, 7, 14, and 21 days and counted. Cell morphology, cell attachment, and cell spreading were investigated using fluorescence microscopy and raster scanning electron microscopy. All substrates supported sufficient cellular growth for 19 days and showed no cytotoxicity. On each material an identical cell colonisation of well communicating, polygonal, vital cells was verified.
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Authors: Renate Gildenhaar, Anke Bernstein, Georg Berger, W. Hein
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