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The combined additions of Ca 2+ and PO 3À 4 to the SiO 2 -ZrO 2 system were attempted through in situ sol-gel technique. Six different combinations were synthesized and the results were compared with pure SiO 2 -ZrO 2 system. The synthesized materials were subjected to accelerated leaching tests to evaluate their phase degradation behavior, nanoindentation for mechanical analysis, and immersion tests in simulated body fluids (SBF) to test their apatite forming ability. The results confirmed the phase stability of t-ZrO 2 till 1100°C and the presence of SiO 2 , Ca 2+ , and PO 3À 4 in t-ZrO 2 matrix exhibited good apatite forming ability during SBF immersion and their reluctance in phase degradation during accelerated leaching tests. However, the values of hardness and Young's modulus were found inferior in comparison with the commercial t-ZrO 2 products.A. Bandyopadhyay-contributing editor Manuscript No. 37167.

Partially stabilized tetragonal zirconia (t-ZrO2) is of particular interest for hard tissue replacements. Ageing related failures of the ceramic associated with the gradual transformation from t-ZrO2 to m-ZrO2 (monoclinic zirconia) can lead to its premature removal from the implant site. In addition, monitoring the satisfactory performance of the implant throughout its life span without invasive techniques is a challenging task. The magnetic resonance imaging (MRI) contrast ability of dysprosium (Dy 3+ ) is well established. To this aim, varied levels of Dy 3+ additions in the ZrO2-SiO2 binary oxide system have been explored. The results indicate the effective role of Dy 3+ in the formation of thermally and mechanically stable c-ZrO2 (cubic zirconia) phase at higher temperatures. The presence of SiO2 influenced the t-ZrO2 stabilization whereas Dy 3+ tends to occupy the ZrO2 lattice sites to induce c-ZrO2 transition. Magnetic and magnetic resonance imaging (MRI) tests displayed the commendable contrast ability of Dy 3+ stabilized ZrO2-SiO2 binary systems. Nanoindentation results demonstrate a remarkable enhancement on the mechanical properties.Keywords: Silica; Zirconia; Dysprosium; Stabilization; Mechanical. 3 IntroductionThe demand for bone implants is growing rapidly due to the increasing incidents of trauma and age related defects caused by osteoporosis. In view of the above potential advantages of Dy 3+ as an addition to ZrO2-SiO2 binary oxides in terms of increased t-ZrO2 stability and enhance MRI image contrast, we present a study of the influence of Dy 3+ on the ZrO2-SiO2 binary oxide system through in-situ sol-gel synthesis, followed by a systematic analysis of the resulting phase composition and structure, mechanical strength and imaging contrast features. Materials and Methods Powder synthesisThe synthesis of Dy 3+ doped ZrO2-SiO2 (DZS) binary oxides was achieved through the sol-gel method. Analytical grade Dy(NO3)3.H2O, ZrOCl2·8H2O and (C2H5)4OSi (TEOS), all procured from Sigma-Aldrich, India, were taken as precursors for the synthesis. The molar concentrations of ZrOCl2·8H2O and (C2H5)4OSi were maintained at a constant ratio of 1: 1 throughout the 5 synthesis whereas the Dy(NO3)3 additions were adjusted to obtain a wide range of compositions.Additionally, a pure ZrO2-SiO2 binary with 1:1 molar ratio was prepared for comparative purposes. The molar concentrations of the different precursors and the respective sample codes are reported in Table 1; the same codes will be used throughout the manuscript. The synthetic procedure is briefly explained as follows. Previously prepared Dy(NO3)3 stock solution as detailed in Table 1 was added to the ZrOCl2 solution under vigorous stirring. The required amount of ethanol was added to this continuously stirred mixture at an operating temperature of 80 °C for 30 minutes. This was followed by the addition of 1 M TEOS to the solution under constant stirring conditions and finally 0.1 M of HNO3 was added to this mixture as a catalyst. The homogeneous solut...

The salient features of bioinert, chemical resistance, and high mechanical strength of synthetic ZrO 2 and the bioactivity characteristics of SiO 2 has been well-known in biomedical applications. This study has been aimed at the synthesis and quantitative structural analysis of SiO 2 -stabilized tetragonal ZrO 2 . The synthesis has been performed through sol-gel technique and the resultant characterization of the powders has been done through X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. Quantitative analysis on the ZrO 2 -SiO 2 binary oxide systems has been performed by Rietveld Refinement using GSAS-EXPUGI software package. The results from this study have confirmed that SiO 2 concentration has played a major role in the stabilization of tetragonal ZrO 2 . Lower SiO 2 concentration has resulted in the formation of mixture of any two different phases comprising of monoclinic ZrO 2 (P2 1 /c symmetry) or cubic ZrO 2 (Fm-3 m symmetry) or tetragonal ZrO 2 (P4 2 /nmc symmetry), whereas higher SiO 2 concentration has resulted in the stabilization of single phase tetragonal ZrO 2 (P4 2 /nmc symmetry).

The present study investigates the formation of zircon (ZrSiO4) and hematite (α-Fe2O3) biphasic composites targeted for biomedical applications. The main aim of this study is to understand the role of α-Fe2O3 in controlling the ZrSiO4 crystallization followed by their mechanical evaluation. The results from the investigation confirmed the essential role of both the heat treatment conditions and α-Fe2O3 content in the elimination of t-ZrO2, c-SiO2, and m-ZrO2 phases to yield composite mixtures of ZrSiO4 and α-Fe2O3. The occupancy of Fe3+ at the Zr4+ sites of ZrSiO4 lattice has stimulated the interfacial reaction between amorphous SiO2 and t-ZrO2 to yield crystallized ZrSiO4. α-Fe2O3 content in the concentration range of 50–100 wt % was sufficient enough to achieve the formation of biocompatible ZrSiO4/α-Fe2O3 composite at 1300 °C with the yield of better mechanical properties.

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This study has been aimed at the phase stabilization of tetragonal Zirconia (t-ZrO 2 ) by the additions of Ca 2+ and PO 4 3 -through an in situ synthetic approach. A wide range of variations have been attempted in which the precursor concentrations of Ca 2+ and PO 4 3 -have been maintained constant for every synthesis. The characterization results from XRD, Raman spectra, FT-IR spectra, XRF, and the quantitative analysis have confirmed the t-ZrO 2 stabilization for the selected concentrations ranging from 5% to 20% of Ca 2+ and PO 4 3 -in the ZrO 2 system at 900°C. Pure ZrO 2 system without the additions of Ca 2+ and PO 4 3 -have yielded the mixture of c-ZrO 2 and m-ZrO 2 at the investigated temperatures ranging between 800°C and 1000°C with no identified traces of t-ZrO 2 . Thus, the stabilization of t-ZrO 2 has been mainly attributed to the combined influence of Ca 2+ and PO 4 3 -presence in the ZrO 2 matrix creating oxygen vacancies that has been confirmed from impedance measurements. Heat treatment beyond 900°C had resulted in the phase degradation leading to the formation of mixture of phases comprising of major amount of m-ZrO 2 and minor amount of t-ZrO 2 .