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Influence of grinding on the structure and colour properties of talc, bentonite and calcite white fillers

Christidis Georgios, Pagona Makri , Vassilis Perdikatsis

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Περίληψη

The influence of grinding on colour and particle-size properties of talc and smectitefrom a white bentonite were studied and compared with a fine-grained calcite from a chalk. Grindingdecreased the grain size of all three minerals. The crystallite size and structure of smectite was notaffected but the crystallite size of talc decreased. The Si–O–Mg and MgO bonds of talc weredisrupted and cation exchange capacity increased with increasing grinding. Delamination of talccrystallites was observed in the initial stages of grinding, whereas with more intense treatment,amorphous material was formed. Comminution improved the colour properties of all three minerals,namely brightness, L* (lightness) and DE*ab (deviation from perfect white diffuser). Grinding timeexerts greater influence on the reflectance from calcite surfaces than from clay minerals. Thisdifference is attributed to continuous formation of progressively smaller diffuse reflection unitsforming a smoother calcite surface. Decrease of grain size does not form considerably smaller diffusereflection units in clay minerals unless delamination takes place. With prolonged grinding,amorphization forms additional diffuse reflection units and a smoother surface due to comminution.

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