Sol–gel synthesis, structure, sintering and properties of bioactive and inert nano-apatite–zirconia glass–ceramics. Issue 9 (November 2015)

• Record Type: Journal Article
• Authors: Montazerian, Maziar; Schneider, José Fabián; Yekta, Bijan Eftekhari; Marghussian, Vahak Kaspari; Rodrigues, Alisson Mendes; Zanotto, Edgar Dutra
• Is Part Of: Ceramics international. Volume 41:Issue 9(2015)Part A
• Page Start: 11024
• Page End: 11045
• Publication Date: 2015-11
• Subjects: A. Sintering -- D. Glass–ceramic -- D. Apatite -- Sol–gel -- Bioactive -- Crystallization -- Zirconia; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2015.05.047
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: We synthesized four glasses of the system 61.2SiO2 –(24.3– x )CaO–4.5P2 O5 –10ZrO2 – x K2 O ( x =0, 2, 4, 6 mol%=Ca replaced by K) using a sol–gel route and compared their properties with a 68SiO2 –27CaO–5P2 O5 (mol%) Zr-free base glass. Their structure, sintering and crystallization behavior were investigated with the aim of converting the gel-glasses into dense glass–ceramics. Then, the in vitro bioactivity and mechanical properties of the optimized sintered samples were characterized. The structure of the gel-glasses was investigated by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and high-resolution transmission electron microscopy (HR-TEM). The sintering and crystallization kinetics of the glasses were studied by hot stage microscopy (HSM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microstructures of the resulting glass–ceramics were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with energy dispersive spectroscopy (EDS). The apatite-forming ability of the sintered glass–ceramics in simulated body fluid (SBF) was investigated using FTIR spectroscopy and SEM. The three-point bending strength, Vickers microhardness and fracture toughness were also measured. Structural analysis by NMR and FTIR revealed that Zr acts as a glass former and K is a modifier, as expected. The K2 O addition strongly improved the material׳s sinterability, e.g., 2 mol% K2 O decreased the optimum sintering temperature from 1300 °C to 1050 °C. Uniformly dispersed ZrO2 nano-crystals, with particle sizes of 25–55 nm, were precipitated in the glass–ceramics. In vitro bioactivity tests confirmed that the K2 O-free glass–ceramics (partially sintered at 1000 °C) were bioactive and hydroxycarbonate apatite (HCA) grew on their surface after 24 h in SBF. However, the >90% dense glass–ceramics with various contents of K2 O exhibited low solubility and a much smaller tendency toward HCA formation. Improvement of some mechanical properties was observed for the sample containing 2 mol% K2 O, in which apatite and zirconia crystallized. The 3p-bending strength and fracture toughness of the 94% dense sample were approximately 140 MPa and 2 MPa m 1/2, respectively. We propose that crack deflection by the ZrO2 crystals and the presence of Zr ions in the residual glass network are prevalent for improving the materials׳ mechanical properties. Some potential applications, such as bioactive scaffolds, are suggested for these glass–ceramics.