Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Integration of iron in natural and synthetic Al-pyrophyllites: an
  infrared spectroscopic study   Numerous studies focus on the relationships between chemical composition and
OHband positions in the infrared (IR) spectra of micaceous minerals. These
studies are based on the coexistence, in dioctahedral micas or smectites, of
several cationic pairs around the hydroxyl group which each produce a
characteristic band in the IR spectrum. The aim of this work is to obtain the
wavenumber values of the IR OH vibration bands of the (Al-Fe3+)-OH and
(Fe3+-Fe3+)-OH local cationic environments of 'pyrophyllite type' in order to
prove, disprove or modify a model of dioctahedral phyllosilicate OH-stretching
band decomposition. Natural samples are characterized by powder X-ray
diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies
and electron microprobe; the hydrothermal synthesis products are also analysed
by powder XRD and FTIR after inductively coupled plasma measurements to obtain
the chemical compositions of nascent gel phases. Natural samples contain some
impurities which were eliminated after acid treatment; nevertheless, a small Fe
content is found in the pyrophyllite structure. The amount of Fe which is
incorporated within the pyrophyllite structure is much more important for the
synthetic samples than for the natural ones. The IR OH bands were clearly
observed in both natural and synthetic pyrophyllites and assigned to hydroxides
bonded to (Al-Al), (Al-Fe) and (Fe-Fe) cationic pairs. During this study, three
samples were analysed by DTG to check the cis- or trans-vacant character of the
layers and to determine the influence of this structural character on the
OH-stretching band position in IR spectroscopy.

9
The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org