# Glass-Ceramic Foams from Alkali-Activated Vitrified Bottom Ash and Waste Glasses
## 2 Materials and Methods  
The starting materials consisted of vitrified bottom ash (VBA; mean particle size \(<\)75 \(\upmu\)m), soda-time glass (SLG; courtesy of SASIL SrI, Biella, Italy; mean particle size \(<\)30 \(\upmu\)m) and borosilicate glass (BSG, courtesy of Nuova OMPI, Padova, Italy; mean particle size \(<\)75 \(\upmu\)m). VBA was derived from the processing of incinater bottom ash by means of DC plasma reactor [22] at 1400 \({}^{\circ}\)C (courtesy of SAV Bratislava, Slovakia). The chemical compositions, obtained via XRF, are provided in Table 1. VBA was also subjected to thermal analysis (differential scanning calorimetry (DSC), Mettler Toledo TGA/DSC 3+, STARe System, Columbus, OH, USA), in order to determine the glass transition temperature (T\({}_{\rm g}\)) and the crystallization temperature (T\({}_{\rm c}\)).  
Powdered VBA, the main component, was suspended in 2.5 M NaOH aqueous solution, either pure or mixed with SLG or BSG in a 70/30 weight ratio, under constant mechanical stirring (500 rpm), for 2 h. The overall solid content of the suspensions was kept constant at 70 wt %. Afterwards, 4 wt % of surfactant (Triton X-100, (polyoxyethylene octyl phenyl ether, C\({}_{14}\)H\({}_{22}\)O(C\({}_{2}\)H\({}_{4}\)O)\({}_{n}\), n = 9-10), Sigma-Aldrich, Gillingham, UK) was added to the suspensions. The suspensions were finally foamed by means of intensive mechanical stirring (2200 rpm), poured into polystyrene molds, and left at 40 \({}^{\circ}\)C for 48 h [14].  
The foams that developed at nearly room temperature were fired at 850-1000 \({}^{\circ}\)C; the heating rate was 10 \({}^{\circ}\)C min\({}^{-1}\), whereas the holding time at the maximum temperature was 1 h. The cooling rate was restricted to 5 \({}^{\circ}\)C min\({}^{-1}\) to avoid cracking of samples. The glass-ceramic samples before and after firing were subjected to: phase analysis via X-ray diffraction (XRD; Bruker D8 Advance, Cu K\({}_{\alpha}\) radiation 0.15418 nm, Karlsruhe, Germany); pycnometry (Micromerities AccuPyc 1330, Norcross, GA, USA); optical microscopy (AxioCam ERc 5 second microscope camera, Carl Zeiss Microscopy, Thornwood, NY, USA); and scanning electron microscopy (SEM FEI Quanta 200 ESEM, Eindhoven, The Netherlands). The phase identification from X-ray diffraction patterns was performed through High Score Plus (PANanalytical B.V, Almelo, The Netherlands).  
Representative samples of approximately 10 mm \(\times\) 10 mm \(\times\) 10 mm were cut from the main specimens and subjected to compression tests (Quasar 25, Galdabini, Cardano, Italy), operating with a crosshead speed of 1 mm min\({}^{-1}\). Each data point represents an average value obtained by testing ten specimens.  
In order to assess the chemical stability of prepared samples, 1 g of crushed sample (pieces smaller than 10 mm) was placed into a polypropylene test-tube with 10 g of deionized water, in order to obtain a solid/liquid ratio of 1/10 w/w. The suspensions were stirred for 24 h, after which, clear solutions were obtained via decantation, centrifugation, and filtering. Leachates were analyzed via optical emission spectroscopy with induction plasma (ICP-OES, Agilent 7500 cx, Santa Clara, CA, USA).