Phase change materials integrated into glass scraps-based tiles for ventilated façades applications: a laboratory scale-up case study

Ceramic foams represent an interesting class of materials for applications as insulator, thanks to their low flammability, which makes them a safer alternative to polymeric insulation products. Ceramic foams are characterized by peculiar microstructures with a porous texture, which formation can be induced by the introduction of foaming agent. Its activation within the ceramic batch is achieved during the firing process. The integration of Phase Change Materials (PCM) into the pores of the ceramic matrix represents a challenging goal to significantly improve the thermal insulating performances and comfort of buildings. The possibility to embody PCM into porous fired tiles is strictly related to the size and number of pores formed during the process. For this purpose, the capability to control and predict the bloating phenomena as a function of the tile size is a key point to define the thermal performances of final device. Starting from a typical porcelain stoneware tile formulation, silicon carbide (SiC) powder was added as foaming agent. Furthermore, the bulk composition was optimized by addition of glass scraps aiming to reduce the carbide stability in order to observe bloating phenomena in a temperature range typical of the industrial ceramic tiles production. To evaluate how the tile size can influence microstructure, in terms of amount, shape and size of pores, a laboratory scale up process was carried out. It was done passing from small specimen (30 mm of diameter) to a demonstrator device (150x150 mm). The samples were characterized by bulk density, linear expansion, water absorption and pores distribution. The effects of the firing process parameters on physical properties were studied. The increase of temperature led to an initial decrease of the bulk density, given by gas formation due to SiC oxidation, followed by a progressive densification regardless the increased expansion potential. The amount, size and shape of pores are dependent on both the efficiency of SiC decomposition and glass viscosity. The changes in terms of density are consistent with the porosity, affecting the potential amount of PCM that could be incorporated. Linear bloating and pores size showed an evident relationship to the specimens size, emphasized by the reduction of the heating rate.