Fabrication of ceramic monoliths from diatomaceous earth: effects of calcination temperature on silica phase transformation

Abstract

The raw diatomaceous earth from the vicinity of Bitola (North Macedonia) showed low bulk density (0.61-0.69 g/cm3), high-water absorption (75-81%) and porosity (66- 72%). The chemical composition was determined with ICP-MS, revealing the following results for the diatomaceous earth: SiO2 (63.69 wt%), Al2O3 (11.79 wt%), Fe2O3 (5.95 wt%), MnO (0.15 wt%), TiO2 (0.65 wt%), CaO (1.51 wt%), MgO (2.24 wt%), P2O5 (0.13 wt%), K2O (1.64 wt%), Na2O (0.93 wt%), LOI (11.21 wt%). XRPD data of the examined sample of clayey diatomite mainly depicted crystalline behavior with a small presence of amorphous phase. The crystalline mineral phases mainly comprise: silica (quartz), feldspars (plagioclase), mica (muscovite), chlorites and dolomite. SEM and TEM results show cased presence of micro- and nanostructures with pores ranging from 250 to 600 nm. The clayey diatomite was sintered at three temperatures (900, 1000 and 1100?C) for a period of 1 h. XRPD of the sintered samples at 1100?C showed certain thermal stability and formation of new phases (mullite and tridymite) that makes the analyzed diatomaceous earth suitable for production of various types of ceramic, construction and thermal insulating materials.