The effect of the temperature of heat treatment process and the concentration and duration of acid leaching on the size and crystallinity of nano-silica powders formed by the dissociation of natural diatom frustule

Author:

Ülker Sevkan1,Güden Mustafa2

Affiliation:

1. Department of Material Science and Engineering, Izmir Institute of Technology, a, Izmir, 35430, Turkey

2. Mechanical Engineering, Izmir Institute of Technology, a, Izmir, 35430, Turkey

Abstract

The present study focused on the processing of nano-silica powders in varying sizes and crystallinities through heat treatment (900–1200 °C), hydrofluoric acid leaching (1–7 N), and ball milling (1 h, 500 rpm) of natural diatom frustules. The starting natural frustules were determined to be composed of amorphous silica (88%) and quartz. The partially ordered crystalline low-quartz and or precursor to low-cristobalite started to form at ~900 °C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 °C to 46% at 1200 °C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6–13.7 μm to 7.2–6.7 μm, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, a ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774–547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling.

Publisher

American Scientific Publishers

Subject

General Materials Science

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