Synthesis of Volcanic Ash‐based Porous Inorganic Polymers Using Biomass as Pore Inducing Agent: Phase Evolution and Descriptive Microstructure

In the present study, multi-scale sized porous inorganic polymers were produced by alkaline activation of volcanic ash. Rice husk ash, an agricultural biomass, was used both in the synthesis of the alkaline activator and as pore inducing agent. Hardened porous geopolymers underwent mineralogical analysis, compressive strength and apparent density tests. Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy coupled with X-rays Energy Dispersive Spectrometry (SEM/EDS), Stereo Optical Microscope and Mercury Intrusion Porosimetry (MIP) measurements were also conducted on hardened porous specimens. The obtained porous matrices showed modified microstructures, with a heterogenous distribution of more capillary pores of various sizes. It was found that the total pore volume increased from 24.1 to 73.7 vol.% with the addition of rice husk ash. The decrease of apparent density as well as that of compressive strength were in perfect correlation with the increase of the pore network. The pore framework of porous geopolymers consisted of larger capillary pores, interconnected macropores and mesopores. Based on the pore structure, the elaborated porous inorganic polymers could be promising candidates in a wide range of applications such as acoustic and thermal insulation, thermal comfort, catalysis, adsorption and filtration.