Influence of synthesis conditions on growth of Ni-doped chrysotile

Ni-doped chrysotile fibers were synthesized in hydrothermal conditions at 300–350 °C, 15–200 MPa, 160–312 h treatment times and pH 5–10. The starting materials and run products were characterized by X-ray powder diffraction (XRPD) and by scanning and transmission electron microscopy, both with annexed energy-dispersive spectrometry (SEM/EDS and TEM/EDS, respectively). The growth of Ni-doped chrysotile fibers depends greatly on the starting materials: they are observed as run products only starting from synthetic Ni-doped forsterite. When oxides are used as starting phases, even in the same hydrothermal conditions, the growth of Ni-doped talc is observed. As regards the morphology of synthesized chrysotile fibers, under the conditions of the present work, cone-in-cone crystals were prevalent, but other morphologies were also detected, all showing well-defined crystallinity, as revealed by electron diffraction patterns of selected areas (SAED). Fibers with cylindrical shape showed outer diameters ranging from 37 to 52 nm and a central hollow (empty core) ranging from 6 to 10 nm. The average concentrations of nickel oxide in chrysotile fibers varied from 4 to 11 (wt%). Further characterization by differential scanning calorimetry (DSC)/thermogravimetric (TG) and by μ-Raman spectroscopy allowed to study the effect of Ni doping on the chemical/physical characteristics of the chrysotile fibers.