Abstract
Two commercial vermiculites from China and Libby were treated with different alcohols (methanol, ethanol, propanol and butanol) at room temperature for up to one month and afterwards irradiated with microwaves. The exfoliated and non-exfoliated particles were characterized by X-ray diffraction, high-resolution transmission microscopy, thermal gravimetric analyses and infrared spectroscopy to explain the inconsistencies in relation to potassium distribution and the exfoliation observed in previous investigations. The percentages of the exfoliated and non-exfoliated particles of the investigated vermiculites greatly varied, with no indication of a relationship between the resultant exfoliation and alcohol treatment. The crystallinity and structural order of the phases composing the particles are independent of the success of their exfoliation. The existence of a mosaic structure, the intra-particle mosaic-like intergrowth of the different mineral phases, in the treated and pristine commercial vermiculites could be attributed to the heterogeneous distribution on the nanoscale of interlayer cations as potassium and iron.
Highlights
Commercial vermiculite [1] is a micaceous mineral that exfoliates quickly when rapidly heated to elevated temperatures, chemically treated [2,3] or irradiated with microwaves [4,5]
Hillier et al related the exfoliation with the mosaic distribution of the different mineral phases within the vermiculite particles [2]
There is a wide variation in the percentages of exfoliated and non-exfoliated particles, independent of alcohol and treatment time
Summary
Commercial vermiculite [1] is a micaceous mineral that exfoliates quickly when rapidly heated to elevated temperatures, chemically treated [2,3] or irradiated with microwaves [4,5]. It was found that the greatest exfoliation is achieved in the presence of interstratified mica-vermiculite [1,8]. The lateral phase boundaries between vermiculite and other phases (mica, or vermiculite and chlorite) could prevent the escape of gas from a particle, resulting in exfoliation when the pressure exceeds the bonding forces that hold the layers together. This type of thermal delamination is the oldest, and it is still used today to a greater extent in industry. The water content, type of cations of the interlayer and the interstratifications of a vermiculite are factors that greatly influence its exfoliation [7,9,10]
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