Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd

Suzuki, Masanori

Tanaka, Toshihiro

Journal of Physics : Conference Series

Thermodynamic analyses were performed to evaluate the composition ranges for metastable immiscibility including spinodal decomposition in multi-component silicate systems, where glass was regarded as a super-cooled liquid phase. Experimental studies on two-phase separation in glass were carried out, and the phase separation was observed in those silicate glasses corresponding to calculated metastable miscibility gaps. The authors also attempted the fabrication of porous glass using phase separation in oxide glasses containing B2O3. A multi-component borosilicate glass composition was prepared based on the silicate glass composition where spinodal decomposition had been confirmed. One of the glass phases formed by the spinodal decomposition in the boro-silicate glass was selectively removed by acid leaching and porous glass was successfully obtained.Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd

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Osaka UniversityTitle Prediction of phase separation in multi-component oxide glassfor the fabrication of porous glass materials from waste slagAuthor(s)Suzuki, Masanori; Tanaka, ToshihiroCitationJournal of Physics: Conference Series. 165(1) P.012078Issue Date2009Text VersionpublisherURL http://hdl.handle.net/11094/25987DOI info.doi/10.1088/1742-6596/165/1/012078Rights©2009 IOP Publishing LtdPrediction of phase separation in multi-component oxide glass for the fabrication of porousglass materials from waste slagThis content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 133.1.91.151This content was downloaded on 26/09/2013 at 05:38Please note that terms and conditions apply.2009 J. Phys.: Conf. Ser. 165 012078(http://iopscience.iop.org/1742-6596/165/1/012078)View the table of contents for this issue, or go to the journal homepage for moreHome Search Collections Journals About Contact us My IOPscience      Prediction of phase separation in multi-component oxide glass for the fabrication of porous glass materials from waste slag Masanori Suzuki1,2 and Toshihiro Tanaka1 1 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, 565-0871 Osaka, Japan. 2 Research fellow of the Japan Society for the Promotion of Science.  E-mail: masanori.suzuki@mat.eng.osaka-u.ac.jp Abstract.  Thermodynamic analyses were performed to evaluate the composition ranges for metastable immiscibility including spinodal decomposition in multi-component silicate systems, where glass was regarded as a super-cooled liquid phase.  Experimental studies on two-phase separation in glass were carried out, and the phase separation was observed in those silicate glasses corresponding to calculated metastable miscibility gaps.       The authors also attempted the fabrication of porous glass using phase separation in oxide glasses containing B2O3.  A multi-component borosilicate glass composition was prepared based on the silicate glass composition where spinodal decomposition had been confirmed.  One of the glass phases formed by the spinodal decomposition in the boro-silicate glass was selectively removed by acid leaching and porous glass was successfully obtained.   1.  Introduction Phase separation in glass represents a phenomenon in which a single glass phase separates into two glass phases with different compositions during the heat-treatment of the glass at a given temperature.   To create functional glass materials using waste glass and slag from metallurgical processes or waste melting processes, the authors have investigated phase separation in multi-component oxide glass.  For instance, spinodal decomposition as one of phenomena of the phase separation forms three-dimensionally interconnected microstructure, and porous glass is obtained by leaching one of those phases with acid solution.  This porous glass can be expected in many applications such as a filter to remove impurities from polluted water or air.  Thus, slag can be transformed into value-added functional glass materials using phase separation in oxide glass.   To obtain phase separation in glass from slag, the composition ranges for metastable immiscibility for multi-component oxide systems should be evaluated.  In this study, the metastable immiscibility regions including spinodal decomposition were evaluated in several multi-component silicate systems by thermodynamic analyses, where glass was regarded as super-cooled liquid phase.  Experimental studies were performed to confirm the phase separation in heat-treated glasses in the predicted miscibility gap.  The fabrication of porous glass has been attempted using the phase separation in a multi-component oxide glass containing B2O3.   2. Estimation of the Composition Ranges for Phase Separation and Spinodal Decomposition [1,2] Liquid-liquid phase separation can be generally predicted from the Gibbs energy curve of the liquid phase. For instance, the miscibility gap in a binary system is obtained from two points of contact on the Gibbs energy curve with a common tangent.  The composition range for spinodal decomposition, referred to as the “spinodal region,” is determined from two inflexion points in the Gibbs energy curve. In our study, the composition ranges for phase separation and spinodal decomposition were estimated by calculating Gibbs energies in the metastable liquid phase, where glass in silicate systems International Conference on Advanced Structural and Functional Materials Design 2008 IOP PublishingJournal of Physics: Conference Series 165 (2009) 012078 doi:10.1088/1742-6596/165/1/012078c© 2009 IOP Publishing Ltd 1      was regarded as a super-cooled liquid phase.  The Gibbs energies were calculated with the FactSage thermodynamic computing program and the F*A*C*T oxide databases for molten oxide systems [3]. To definitively determine the spinodal region, the activity of SiO2 was calculated from the Gibbs energy in the super-cooled liquid phase.  In an A-B binary system, the spinodal region is evaluated with the derivative of the activity with respect to composition derived by the following Equation (1): BBBBBXRTRTXa∂∂=∂∂ µµ?)exp(,)1( 22BMixBB XGRTaX ∂∂−= ? ?                                (1) where MixG  denotes the Gibbs energy for mixing in the liquid phase.  Bµ  and Ba  are the chemical potential and activity of component B and described by Eq. (2) under the pure liquid standard state:  .)1(lnBMixBMixBB XGXGaRT ∂∂−+==µ                                             (2) Equation (1) indicates that the spinodal region is determined from the extremum points in the activity curve, because the second derivative of the Gibbs energy should be zero at its inflexion points. The above estimation procedure for the spinodal region can be extended to ternary and multi-component systems as follows: if pure component A constitutes one of the separated phases, the spinodal region in an A-B-C ternary system is determined by calculating activity of component A across straight lines with constant composition ratios of components B and C that correspond to tie-lines of the miscibility gap.  The spinodal region in a quaternary system is derived, similarly, by calculating activities of A in A-B1-xCx-D quasi-ternary systems (here x varies from 0 to 1). 3. Experimental Procedure 3.1 Preparation of Two-phase Glass Materials Phase separation in glass was investigated experimentally to verify the calculated results of the metastable miscibility gaps.  SiO2-CaO-MgO-Na2O and SiO2-CaO-Al2O3-Na2O glasses were prepared from silica, magnesia, alumina, sodium carbonate and calcium carbonate.  These raw materials were melted in air for 5 h at 1873 K, and glass samples were obtained by quenching the melts in water.  The glasses were then heat-treated at 948 K or 993 K.  X-ray diffraction analysis was conducted on annealed glasses to confirm that they were glassy.  Microstructures in these glasses were observed by a transmission electron microscopy. 3.2 Fabrication of Porous Glass Materials using Phase Separation in Glass Porous glass was fabricated using two-phase glasses obtained from spinodal decomposition by leaching one of decomposed phases with acid solution.  In the leaching process, glass sample was immersed in a HCl solution for 14 h, where bulk size of the sample was less than 2 mm in diameter.  Microstructure on the surface of the porous glass was observed by field emission scanning electron microscopy. Composition of the glass dissolved in acid was examined with ICP emission spectrometry. 4. Results and Discussion 4.1 Prediction of Phase Separation in Multi-component Silicate Glasses [1,2] Figure 1 shows the calculated metastable miscibility gap and the spinodal region of SiO2-CaO-MgO- 5 mol% Na2O system, where molar fractions of each component are divided by the sum of the molar concentrations of all components except Na2O.  The occurrence of phase separation was investigated for the glasses A-C, having compositions indicated by square marks in Fig. 1.  The selected chemical compositions are shown in Table 1.   Electron micrographs of the heat-treated glasses A-C are shown in Figure 2, and they depict the occurrence of a phase separation.  An interconnected microstructure is observed in glass A, and it corresponds to the spinodal decomposition.  In glass B, a particle structure indicating the binodal decomposition was observed.  As the composition of glass C is outside the miscibility gap, no specific microstructure was observed after annealing for 192 h.  Since electron diffraction patterns for each specimen showed no evidence for the presence of crystalline phases, the heat-treated specimens were International Conference on Advanced Structural and Functional Materials Design 2008 IOP PublishingJournal of Physics: Conference Series 165 (2009) 012078 doi:10.1088/1742-6596/165/1/0120782      glassy in microscopic observation area.  The above experimental results indicated that the phase separation occurs in SiO2-CaO-MgO-Na2O glasses according to the predicted miscibility gap.              200 nmFigure 2. Electron micrographs of SiO2-CaO-MgO-Na2O glasses after annealing for 192 h at 948 K. The metastable miscibility gap and the spinodal region in the SiO2-CaO-Al2O3-5 mol% Na2O system was calculated and is shown in Figure 3.  Molar fractions of each component are divided by the sum of the molar concentrations of all components except Na2O.  The occurrence of spinodal de-composition in this system was investigated for glass D, whose composition is described by a square mark in Fig. 3.  An interconnected microstructure indicating the spinodal decomposition was observed in the annealed glass D, as shown in Figure 4.  This experimental result corresponds to the calculated miscibility gap as shown in Fig. 3. 0.2(A(mol%CaO(%) (mol%SiO2 )/Z(%)060801001.00.80.6(Mole fraction of CaO) (Mole fraction of SiO2 )O)(%)4020)/Z(SiO2)   Figure 3. Calculated metastable immiscibility regions including spinodal decomposition in the SiO2-CaO-Al2O3-5 mol% Na2O system at 973 K. (Z= mol% (SiO2+CaO+Al2O3)) Figure 4. Electron micrograph of glass D (80.8SiO2-11.7CaO-2.5Al2O3-5.0 mol%  Na2O) annealed for 96 h at 993 K.  100????40 60 80 100406080020406080100?????????(mol%CaO)/Z  (%) (mol%SiO2 )/Z  (%)(mol%MgO) /Z (%)20020033 Figure 1.  Calculated composition ranges for spinodal decomposition and binodal decom-position for the SiO2-CaO-MgO-5 mol% Na2O system at 948 K. (Z= mol% (SiO2+CaO+MgO)) Table 1. Compositions of SiO2-CaO-MgO-Na2O glass samples used in the experiment.  Composition [mol%]  SiO2 CaO MgO Na2OA 80.8 9.5 4.7 5.0 B 66.5 19.0 9.5 5.0 C 47.5 31.7 15.8 5.0 (CaO) Binodal decomposition (SiO2) (MgO)Spinodal decomposition A B C A B CD (Al2O3)(CaO) ( 2) 100 nm D(5 mol% Na2O)(5 mol% Na2O)Spinodal decomposition Miscibility gap International Conference on Advanced Structural and Functional Materials Design 2008 IOP PublishingJournal of Physics: Conference Series 165 (2009) 012078 doi:10.1088/1742-6596/165/1/0120783      4.2 Fabricating Porous Glass using  Spinodal Decomposition in Multi-component Borosilicate Glass The fabrication of porous glass was attempted using two-phase glasses with spinodal decomposition by leaching one of the decomposed glass phases with an acid solution.   It should be noted that in the spinodal decomposition in glasses containing B2O3, one of separated phases contains plenty of B2O3 and can be leached out with acid solutions [4,5].  In this study, a multi-component borosilicate glass composition D-2 was designed by partially substituting SiO2 with B2O3 in the SiO2-CaO-Al2O3-Na2O glass D.  Its composition is included in the spinodal region of the silicate system, and it was used to remove one of the separated phases in the leaching process. Figure 5 shows microstructures of the borosilicate glass D-2 after heat-treatment and acid leaching.  Morphology with interconnectivity was observed in the heat-treated glass, and an inter-connected porous structure was obtained after leaching.  These microstructures indicate that one of the glass phases formed by spinodal decomposition was removed selectively with acid leaching.  The chemical composition analysis for the glass phase dissolved into the acid solution revealed that a high proportion of B2O3 was dissolved in acid, and the porous glass contains a high concentration of SiO2.                 Figure 5. Microstructures in glass D-2 (59.7SiO2-13.8CaO-2.9Al2O3-5.9Na2O-17.7 mol% B2O3), (a) after annealing for 96 h at 993 K; (b) after leaching one of separated phases with acid solution.5. Conclusions Immiscibility regions in multi-component silicate glasses were determined by calculating Gibbs energies in the metastable liquid phase, where glass was regarded as a super-cooled liquid phase.  The occurrence of phase separation in those silicate glasses was verified by observing microstructures in heat-treated glasses, and these experimental results corresponded to the predicted miscibility gaps. For the fabrication of porous glass, a multi-component borosilicate glass was prepared by partially replacing SiO2 with B2O3 in the silicate glass composition where spinodal decomposition had been confirmed.  One of the glass phases formed by the spinodal decomposition in the borosilicate glass was leached out with an acid solution, and porous glass with a three-dimensional interconnected structure was obtained. Acknowledgements This study was supported by Priority Assistance for the Formation of Worldwide Renowned Centres of Research - The Global COE Program (Project: Center of Excellence for Advanced Structural and Functional Materials Design) from the Ministry of Education, Culture, Sports, Science and Tech-nology (MEXT), Japan.  Observation of the microstructures in the samples by transmission electron microscopy was supported by professor Hirotaro Mori and technical official Eiji Taguchi (Research Center for Ultra-High Voltage Electron Microscopy, Osaka University), and carried out in a facility in the Research Centre for Ultra-High Voltage Electron Microscopy, Osaka University. References [1] M.Suzuki and T.Tanaka, ISIJ Int., 46 (10), 1391 (2006). [2] M.Suzuki and T.Tanaka, ISIJ Int., 48 (4), 405 (2008). [3] A.D.Pelton and M.Blander, Metall. Trans., 17B, 805 (1986). [4] T.H.Elmer, M.E.Nordberg, G.B.Carrier, E.J Korda: J. Am. Ceram. Soc., 53 (4), 171 (1970). [5] T.Nakashima and Y.Kuroki, Nippon Kagaku-kaishi, (10), 1231 (1981). 500 nm 500 nm (a) (b)International Conference on Advanced Structural and Functional Materials Design 2008 IOP PublishingJournal of Physics: Conference Series 165 (2009) 012078 doi:10.1088/1742-6596/165/1/0120784

Prediction of phase separation in multi-component oxide glass for the fabrication of porous glass materials from waste slag

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Prediction of phase separation in multi-component oxide glass for the fabrication of porous glass materials from waste slag

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