Papers by Keyword: Zirconia

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Authors: Frank Kern, Rainer Gadow
Abstract: Zirconia-alumina composites are structural ceramics which due to their high strength and toughness are interesting in biomedical and engineering applications. Reinforcement of such materials with in situ formed platelets can improve fracture toughness and reliability, the mechanisms are however not yet fully understood. In this study alumina and zirconia based composites (ZTA and ATZ) reinforced with various hexaaluminates were investigated. In ZTA materials the main effect of platelets is the improvement of toughness as the the grain size distribution of the microstructure is broadened and transformability of the zirconia dispersion is improved. Crack deflection by platelets is unimportant, toughening is commonly achieved at the expense of strength and hardness. In case of zirconia based composites results are strongly depending on the type of stabilizer (Y-TZP or Ce-TZP) used and the type of hexaaluminates formed in situ. Here platelets can cause crack deflection and crack bridging. By variation of the composite recipes a multitude of compositions can be produced which have mechanical properties tailored for individual applications.
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Authors: Meor Yusoff Meor Sulaiman, Khaironie Mohamed Takip, Ahmad Khairulikram Zahari
Abstract: The high temperature phase transition of zirconia produced from commercial zirconyl chloride chemical was compared with that produced from a Malaysian zircon mineral. Zirconyl chloride was produced from zircon by using the hydrothermal fusion method. Initial XRD diffractogram of these samples at room temperature show that they are of amorphous structure. High temperature XRD studies was then performed on these samples; heated up to 1500°C. The XRD diffractograms shows that the crystalline structure of tetragonal zirconia was first observed and the monoclinic zirconia becomes more visible at higher heating temperature.
375
Authors: You Tao Xie, Xue Bin Zheng, Chuan Xian Ding, Xuan Yong Liu, Yi Zeng, Soo Wohn Lee
Abstract: The in vitro attachment, spread, and proliferation behavior of osteoblast cells on the plasma-sprayed composite coating with 70wt% zirconia and 30wt% dicalcium silicate were studied. The composite coating shows good cytocompatibility. The human osteoblast cells attached, spread and proliferate well on the surface. The cytocompatibility of the coating was attributed to the incongruent dissolution of dicalcium silicate and the large amount of Si-OH functional groups produced on the surface. The released calcium and silicon ions are also positive to the proliferation of cells. All our results show that the composite coating possesses good cytocompatibility.
563
Authors: Daisuke Yamashita, Makoto Noda, Miho Machigashira, Motoharu Miyamoto, Hironobu Takeuchi, Naoshi Takeuchi, Hiroshi Kono, Kazuyuki Noguchi, Seiji Ban
Abstract: The aim of this study was to investigate the response of osteoblast-like cells (MC3T3-E1) to the surface of hydroxyapatite-containing glass coating on zirconia (HA-G-Zr) in comparison to yttria stabilized zirconia (Y-TZP). The MC3T3-E1 cells were cultured on HA-G-Zr and Y-TZP specimens in 24-well tissue culture plates. Surface properties were evaluated by X-ray diffractometry, Fourier tranfer infrared microscopy (FT-IR) and scanning electron microscopy (SEM). Cell proliferation in each well was measured by MTT assay. Cell morphology was observed by SEM. Cell differentiation was evaluated by alkaline phosphatase (ALP) activity and osteocalcin levels. After the glass coating on Y-TZP, X-ray diffraction peaks due to hydroxyapatite (HA) were observed clearly. HA-G-Zr appeared on surface of uneven and roughened state, wherein microcracks on the microns in width and many voids of several microns in size were present. Time-dependent proliferation and differentiation of MC3T3-E1 cells were found in all the specimens. MC3T3-E1 cells on HA-G-Zr plates showed higher differentiation than Y-TZP. These results demonstrated that HA-G-Zr showed better cellular biocompatibility than Y-TZP.
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Authors: Sandrine Coste, Ghislaine Bertrand, Christian Coddet, Eric Gaffet, Horst Hahn, H. Sieger, M.A. Rodriguez, Cathy Meunier, Serge Vives
Abstract: Superior properties of nanostructured Al2O3 based materials, such as higher hardness and fracture toughness, have been evidenced. In order to optimize their manufacturing, the mechanical activation of the starting powders (Al2O3-TiO2 and Al2O3-ZrO2) was studied. In the present work, Al2O3 powders blended with 13wt% and 44wt% of titania or 20wt% and 80wt% of yttria partially stabilized zirconia have been high-energy ball-milled using a planetary mill, P4 (Fritsch) with steel vials and balls. The effect of the milling time and operating parameters, such as shock energy and friction to total energy ratio, on the powder structural and microstructural evolutions has been determined by SEM, XRD and BET. The transformation of the metastable anatase TiO2 phase into the high pressure TiO2 II phase and rutile phase was evidenced, simultaneously to the decrease of the alumina crystallite size, in the Al2O3-TiO2 system. In the Al2O3-ZrO2 system, the transformation of the monoclinic phase and the decrease of the alumina and tetragonal zirconia crystallite size have been observed.
303
Authors: Carlos A. Xavier Santos, Motozo Hayakawa, José Carlos Bressiani
Abstract: Y-TZP presents excellent properties at room temperature but these properties decrease as the temperature increases. This paper studies the behavior 20vol%Si3N4-SiC when added in YTZP matrix and heated under no pressure system. Al2O3 and Y2O3 were used to maintain the stability of the matrix and as sintering aids. The addition of Si3N4 and SiC in a Y-TZP matrix leads to formation of silicon oxynitride and it increases the mechanical properties like toughness and hardness. The mixture was milled and molded by CIP. Samples were heated at 1500°C, 1600°C and 1700°C for 2h without pressure under atmospheric conditions in bed-powders of Si3N4. Samples were characterized by XRD. Density, hardness, toughness, bending strength were measured. The structure of the material was observed in SEM/EPMA to verify the distribution of the materials in the composite. The formation of Si2N2O was observed in the sintered material and it showed an increment of both hardness and toughness as temperature increases. The samples presented considerable resistance of oxidation at 1000°C.
415
Authors: Verônica Moreno, J.L. Aguilar, Dachamir Hotza
Abstract: In the last years many efforts have been spent to develop colloidal processes that use water instead of organic solvents. The aim of this study was to develop aqueous tape casting systems to produce zirconia tapes. Different types of binder were tested. Rheological properties of the slurries were measured at room temperature. The slurries were cast on a PET carrier with/without a silicone-based coating. Interactions between the slurry and the polymeric substrate were evaluated. It was found that an acrylic binder is more appropriate for colloidal processing. The acrylic-based suspensions showed a pseudoplastic behavior and remained stable after hours. Tapes with thicknesses between 90 and 200 µm were produced. Optimized tapes showed smooth and homogeneous surfaces and adequate plasticity.
752
Authors: Mei Ling Zhang, Yang Huang, Rong Jian Lu, Bin Deng
Abstract: Purpose: Compared relative translucency of IPS e.max CAD,Vita Suprinity,Lava Zirconia,Cercon Zirconia,Zenostar and upcera Zirconia, to provide a reference for the clinical aesthetic choice. Method: Relative translucency were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white backing (Yw) to give Yb/Yw with Minolta CR-321.One-way analysis of variance and Tukey’s multiple comparison test were used to analyze the data (P<0.05). Results: Relative translucency of control group was 0.577-0.843,while experimental group was from 0.798(IPS e.max CAD) to 0.947(upcera Zirconia),there were significantly different between the groups. The relative translucency of the six systems are as follows: IPS e.max CAD >Vita Suprinity >Lava Zirconia >Cercon Zirconia >Zenostar >upcera Zirconia. Conclusion: There were significantly different between the six groups, for patients with anterior tooth areas restoration and high aesthetic requirements, IPS e.max CAD and Vita Suprinity are recommended; For patients with poor transmittance of adjacent teeth, and the abutments are dark which need to be covered can choose Lava Zirconia and Cercon Zirconia; For low transparency like posterior areas and severe tetracycline teeth, upcera Zirconia and Zenostar ceramic blocks may be considered.
729
Authors: H. Ogawa, N. Sawaguchi, Fumihiro Wakai
571
Authors: Takashi Nakamura, Masao Akagi, Tadashi Yasuda, Yasuaki Nakagawa, Makoto Shimizu
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