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Thermal and acid treatment of diatom frustules
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Purpose: Diatoms, belonging to Bacilariophyta family, are single-celled microscopic (1-100 micron) plants living in aquatic environment. The diatom cell is protected inside a shell (frustule) constructed from amorphous nano-silica particles. It is proposed that the frustules and purified silica powders obtained from frustules can be used to reinforce composites. In this study, microstructural properties of two diatom frustules were determined and different methods were investigated for silica powder processing from diatom frustules. Design/methodology/approach: Natural (ND) and calcined (CD) diatom frustules were used in this study. The chemical and microscopic properties of the diatom frustules were determined using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR) and energy dispersive X-Ray Florescence spectrometer (XRF). Two different processing routes were applied to process silica powder from diatom frustules. These included (i) leaching the frustules directly in HF, (ii) incorporating thermally treated frustules in to the liquid nitrogen. Findings: At increasing HF concentrations, the variety of shapes, nanopores and open voids were seen on the surface of frustules as silica particles were removed from the surface. SEM micrograph results showed that HF significantly etched inside the existing pore structure of the diatom frustules. HF concentration was found more effective in mass loss than the leaching time. Thermal treatment induced several cracks propagated between macro pores and nanopores of the frustules. Practical implications: Results show that thermal and acid treatments were not effective for obtaining silica powder from frustules. Ball milling can be used for silica powder processing from frustules in the further study. Originality/value: In this paper, the microstructural properties of ND and CD frustules were determined. The effect of thermal and acid treatment on frustules was investigated with SEM.