Porous ceramic monoliths based on diatomite

Abstract

Porous silica ceramics were obtained at low forming pressure and low sintering temperature by using diatomaceous earth as a silica source and boric acid as an inexpensive additive. The starting raw material, diatomite from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid up to 2wt%. Powder was compacted by using different pressures of 40, 60 and 80MPa. The pressed samples were sintered at 850, 1000, 1150, and 1300°C for 4h in air. A relatively high porosity in the range of 60–70% is obtained for the samples pressed at 40, 60 and 80MPa and sintered at 1000°C. Median pore size diameters are in the range of macroporous up to 2μm in the samples sintered at 1150 and 1300°C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scaning electron microscopy (SEM) and mercury porosimetry measurements were employed to characterize the phases, functional groups, microstructure and pore size distribution of the obtained samples. In addition, measurements of densities and open porosities by immersion technique, according to Archimedes principle, were used. The relations between mechanical properties (Young modulus, Poisson ratio, and compressive strength) versus content of boric acid in the investigated samples were studied and disscussed.