Pierre Micoud

Evaluation of talc morphology using FTIR and H/D substitution

Abstract Deuteration (H/D substitution at 200ºC) was performed on powders of two ground talcs of different particle shapes (different basal/lateral surface ratios). Results indicate that the deuteration process is only efficient on lateral talc surfaces, and suggest that the hydrogens located in the hexagonal ring of the talc basal surfaces are not exchanged. The FTIR spectra collected from the two talc samples show that it is possible to discriminate between particles with the same specific surface area but with different basal/lateral surface ratios using the deuteration process.

Cation site distribution in clinochlores: a NIR approach

Abstract A near infrared (NIR) spectroscopy approach was undertaken to collect information on the Al cationic distribution in tetrahedral and octahedral sites in natural chlorite (clinochlore) samples. Structural formulae were established using electron microprobe and Mossbauer spectroscopy. A band located near 7115 cm-1 was attributed to the overtone of OH fundamental stretching mode of Mg2AlOH and increases with the total Al amount. Good correlation was obtained between the (SiAl)O-OH vibration band area and tetrahedral Al content, making it easy to partition Al (and thus Fe3+) between octahedral and tetrahedral sites.

Fast-Geomimicking using Chemistry in Supercritical Water

Herein we introduce a powerful and fast method to produce nanominerals using a bottom up approach. The supercritical hydrothermal flow synthesis is exploited to produce model nanominerals by mimicking natural environments at high temperatures under pressure. This innovative concept is demonstrated with the talc synthesis; this represents a major technical breakthrough since it allows decreasing the mineral-synthesis time from tens of hours to tens of seconds. Through this example, we show these nanominerals exhibit new crystal-chemistry signals and new properties. This approach provides a means to reproduce the early stages of formation of minerals in different natural environments from sedimentary environments (low temperature and pressure) to hydrothermal/metamorphic environments (high temperature and high pressure).

Synthetic talc and talc-like structures: preparation, features and applications

This contribution gives a comprehensive review about the progress in preparation methods, properties and applications of the different synthetic talc types: i) crystalline nanotalc synthesized by hydrothermal treatment; ii) amorphous and/or short-range order nanotalc obtained by precipitation, and iii) organic-inorganic hybrid talc-like structures obtained through a sol-gel process or a chemical grafting. Several advantages of nanotalc such as high chemical purity, high surface area, tunable submicronic size, high thermal stability, and hydrophilic character (leading to be the first fluid mineral) are emphasized. Synthetic nanotalc applications are also considered including its use as nanofiller in composite materials, as absorbers of organic compounds, as anticorrosion coatings and as agents for cosmetic applications. Regarding their high industrial application potential, intensive research has been carried out to better understand their behavior and develop processes to produce them. To facilitate further research and development, scientific and technical challenges are discussed in this Review article.

The crystal-chemistry of Vietnamese talcs from the Thanh Son district (Phu Tho province, Vietnam)

Abstract The mineralogy and crystal chemistry of a new talc ore deposit situated at Thu Ngac commune, Thanh Son district, Phu Tho province, Vietnam, was investigated using X-ray fluorescence, electron microprobe, X-ray diffraction, Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance (29Si and 1H) and colorimetry. Both chemical and crystal-chemical analyses showed that the talcs from the Phu Tho province are very pure because they contain few accessory minerals (chlorite, amphibole and goethite) and few substitutions of Si by Fe and Al in their crystal structure. The talc ore may well meet the standards required for a wide range of industrial applications.