Preparation of hierarchically porous phase separated foam glasses
SEDLACIK M. 1, BARTONÍCKOVÁ E. 1, PALOV?ÍK J. 1, CÁBA V. 1, MÁSILKO J. 1
1 Brno University of Technology, Brno, Czechia
Porous glasses are well established materials finding use mainly as inert catalyst support, membranes or in photocatalytic application. They are generally obtained via thermally inducing phase separation in alkali borosilicate glasses with subsequent leaching of the soluble alkali borate rich phase. This process is often also used in combination with other manufacturing and shaping methods to obtain hierarchically porous glasses. Very few studies however dealt with the combination of conventional glass foaming process and phase separation. Carbonaceous foaming agents conventionally utilized in foam glass production carry a significant drawback in form of solid residues remaining in the foam structure, making the foam opaque which could limit the possible application as a catalyst support in photocatalytic processes. Possible solution to this problem could be foaming of sodium borosilicate glasses via hydrate route, with NaOH as a foaming agent, previously described for soda-lime-silicate glass systems.
In this study we prepared hierarchically porous glass foams via combination of powder glass foaming method and subsequent phase separation and acid leaching to introduce additional porosity. Sodium borosilicate glass of controlled composition was synthesised, glass powder was prepared and NaOH was used as a foaming agent. Mixtures of glass and foaming agent were heat treated to induce foaming and phase separation and acid soluble phase was leached out, using HCl, to introduce additional porosity into the material. Effects of the foaming temperature and phase separation temperature on the structure of prepared glasses was studied. Prepared foams were characterized using multiple analytical methods. Specific surface area and pore size were analysed using nitrogen adsorption and mercury intrusion porosimetry, respectively. Microstructure of prepared foams was assessed using scanning electron microscopy. Effects of the NaOH foaming agent on the glass structure and crystallization was studied using Infrared spectroscopy and X-ray diffraction analysis. Highly porous samples with porosities ranging over multiple scales were prepared from sodium borosilicate glass using NaOH foaming agent.