After the thermal treatments a large amount of nano- and
microstructures such as rods, needles and wires appears on the surface
of all the samples (Fig. 1). The observed morphologies depend
neither on the initial MnCO3 content nor on the temperature of
the treatment. However, differences are observed depending on
the position relative to gas inlet so that this parameter enables a
control of the obtained morphologies. In areas close to Ar intake,
wires with several microns length and diameters of a few hundred
nanometres are observed [Fig. 1(a)]