The microstructure and optical transmittance thermal analysis of sodium borosilicate bio-glasses |
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Authors: | Mojumdar S C Kozánková J Chocholou?ek J Majling J Nemecek V |
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Institution: | (1) Institute for Research in Construction, National Research Council of Canada M-20, 1200 Montreal Rd., Ottawa, ON, K1A 0R6, Canada E-mail;(2) Department of Ceramics, Glass and Cement, Slovak University of Technology Radlinskeho-9, SK-81237, Bratislava, Slovakia;(3) Technické sklo (Technical Glass) 844 03, Bratislava, Slovakia;(4) Department of Ceramics, Glass and Cement, Slovak University of Technology Radlinskeho-9, SK-81237, Bratislava, Slovakia |
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Abstract: | The conditions to fabricate the bulk porous specimens have been studied on account of sodium borosilicate (NBS) glasses. Glass
composition, heat treatment at phase separation and TiO2 addition have been considered in this study. Original glass samples of composition in mol%: sample A: 9.19 Na2O - 23.58 B2O3 - 67.23 SiO2, sample B: 9.29 Na2O - 3.17 TiO2 - 23.82 B2O3 - 63.72 SiO2 were prepared by melting reagent grade chemicals (Na2CO3, HBO3, SiO2 and AgNO3) in platinum crucibles at 1480°C for 1 h in air. The melts were poured onto stainless steel plates and were annealed at 500°C
for 0.5 h after cooling. Thus, obtained samples were phase separated at 700°C for 2, 15, 25 and 50 h to study their microstructure
by scanning electron microscope (SEM). Besides the direct study of the microstructure by SEM, information on glass structural
changes of samples are provided by measuring in situ changes by the optical transmittance thermal analysis. The isothermal
measurements were carried out at 700, 720 and 740°C. The temperature of phase separation, the leaching and nucleator addition
(TiO2), significantly influence the microstructure of the resulting leached product. TiO2 additive seems to suppress crystallization of cristobalite: especially at the extended above heat treatment phase separation
runs. The phase-separated domains of glasses containing above 80 moles of SiO2 are so small that it is very hard to observe them by SEM. The glass composition in our case was selected in a way to have
relatively large phase separated areas easily observed by SEM at magnification 20 000·. The influence of TiO2 is not too pronounced. It seems to suppress the cristobalite crystallization, especially of longer heating runs. The image
analysis of leached glasses shows the prevailing content of the skeletal phase in a comparison to pores. The TiO2 content diminishes the content of the skeletal phase.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | microstructure SEM optical transmittance thermal analysis optical microscopy sodium borosilicate bio-glasses |
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