An experimental study on the hydrothermal preparation of tochilinite nanotubes and tochilinite–serpentine-intergrowth nanotubes from metal particles

Tochilinite and tochilinite–serpentine-intergrowth (TSI) phases, including their nanotubes, are major components of CM carbonaceous chondrites. The laboratory synthesis of tochilinite and TSI phases, particularly their nanotubular forms, has rarely been reported. In this article, we show that FeMgAl tochilinite nanotubes and TSI nanotubes can be hydrothermally prepared from heat-treated metal particle mixtures below 200°C under reducing and basic conditions. The metal particles used in the preparation of FeMgAl tochilinite were Fe, Mg and Al and those used for the preparation of TSI were Fe, Mg, Al, Si, Cr and Ni. FE-SEM, TEM, HRTEM, ED, EDX and XRD were used to characterize the reaction products. The yield of FeMgAl tochilinite and TSI was generally low and the FeMgAl tochilinite and TSI samples were very heterogeneous. Both the FeMgAl tochilinite and TSI crystallites existed in two forms, i.e. flakes and nanotubes. They generally had micrometer to sub-micrometer sizes and low crystallinity, and they were extremely sensitive to the electron beam. The FeMgAl tochilinite showed various structural modifications; however, the chemical compositions of these structural modifications were similar. The same phenomenon existed for TSI. The structural modifications of FeMgAl tochilinite and TSI may originate mainly from their mixed-layer structures, two-dimensional incommensurability of their sub-structures and the synthetic conditions. Some of the FeMgAl tochilinite nanotubes and the TSI nanotubes were likely to have been formed by curling of the corresponding flakes. The curling process appears to be delicate, requiring a quiet reaction environment with stable temperature and pressure and without vibrations. Our synthetic FeMgAl tochilinite and TSI showed remarkable similarities to natural tochilinite and TSI, respectively. Therefore, meteoritic tochilinite and TSI probably formed by reaction of metal particles with S2− bearing water at temperatures of around 50–100°C.