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FIRST YEAR ANNUAL REPORT – DELIVERABLE N. 13
Annual Report
on
JRA2 Task 1- Application of NMR techniques to the study of
ceramics (UNI-PG)
Eu-ARTECH
Access, Research and Technology for the conservation of
the European Cultural Heritage
Integrating Activity
implemented as
Integrated Infrastructure Initiative
Contract number: RII3-CT-2004-506171
Project Co-ordinator: Prof. Brunetto Giovanni Brunetti
Reporting period: from June 1st 2004 to May 31st 2005
Project funded by the European Community
under the “Structuring the European Research Area”
Specific ProgrammeResearch Infrastructures action
1
First Year Annual Report on
JRA2 Task 1- Application of NMR techniques to the study of
ceramics
(Responsible: UNI-PG)
According to Annex I of the contract, the main aim of this study is to explain the structural changes with the
temperature of an iron-rich clay, as preliminary step to clarify the firing processes of the ancient ceramic
technology. To this purpose, illite-rich clay samples were characterized using a multi-techniques approach,
i.e. EPR, SEM-EDS, XRPD, MAS and MQ-MAS NMR. During the firing in the temperature range 6001100 °C, four main reaction processes occur: dehydration, de-hydroxylation, structural breakdown and recrystallization.
Dehydration of water interlayers, located close to the aluminium octahedral sites occurs at temperatures
lower than 600 °C, while the de-hydroxylation occur in the 600-700 °C temperature range. At higher
temperatures (800-900 °C), the structural breakdown of the illite is observed with the full iron oxidation to
Fe3+, while in the temperature range of 1000-1100 °C an iron clustering occurs, with the appearance of ferro
or ferri magnetic effects, due to the presence of large iron single crystals.
Furthermore, the appearance of octahedral and tetrahedral sites of aluminium is discussed as function of the
investigated temperatures.
Introduction
Clays form a class of technologically important materials having widespread industrial applications,
including catalyst support in petrochemical industries. Clays are the major components of white-ware
products, bricks, roof tiles and cements. Firing involves breaking down some phases and forming new ones.
Consequently clay artefacts are considered as artificial rocks formed in a kiln.1 The thermal decomposition of
clays is one of the most studied ceramic reactions. Moreover clays is an important constituent of new
synthetic materials such as nano-composites for advanced applications.
The growth of new phases, during and after firing, is related both to the firing temperature and to the
composition of the micro-sites in which the phases grow. To optimize the processing of clays, the thermal
decomposition mechanisms must be fully understood. In particular, as the clay structure breaks down, details
on the structure and on the distribution of atomic species in the intermediate amorphous states should be
obtained.
To study the modification induced by firing an illite-rich clay from Deruta, a town in the region of Umbria
(Italy), was chosen. In fact, Deruta has been for many centuries one of the most important centers for the
production of ceramics in Italy. The quality of these ceramics is well known, being historical wares from
Deruta, especially those belonging to the Renaissance period, exhibited in the most relevant museums of the
world. Several factors encouraged Deruta to become a major producer of ceramics, one of these is the
availability of suitable earth from which to form clay. In fact, the hills around Deruta are particularly rich in
a pure strain of clay which also washes up along the shores of the close Tiber river. Therefore the aim of this
study is to clarify the structure of this clay and to explain the structural changes involved in its firing, as a
preliminary step to obtain information about the firing processes of the ancient ceramic technology. To this
purpose illite-rich clay samples fired at different temperatures were characterized using a multi-techniques
approach, i.e. by EPR, SEM-EDS, XRPD, MAS and MQ-MAS NMR.
Previous studies on illite-rich clays2 using various techniques3 showed that four main reaction processes
occur during firing: dehydration, dehydroxylation, structural breakdown and recrystallization. In the 350-400
°C temperature range, the interlayer water is driven off; dehydroxylation occurs between 450 and 700 °C; the
irreversible structural breakdown occurs between 800 and 900 °C, with the formation of new phases at about
900 °C. For the sake of clarity the results obtained from each technique will be discussed separately.
2
Experimental
Firing Procedure. The samples were prepared using the following procedure. To easily model the clay, it
was plunged in water and then dried at room temperature for one day. Samples were fired in oxidant
atmosphere at different temperatures: 600, 700, 800, 900, 1000 and 1100 °C, in a kiln of a ceramist’s
workshop. After an 8-hour heating cycle, the temperature was kept constant for 2 hours at the final value.
Finally, the samples were slowly cooled down to room temperature inside the kiln.
Analytical investigations were performed using Atomic Absorption spectroscopy, scanning electron
microscopy with energy dispersion X-ray spectrometry (SEM-EDS) and X-ray fluorescence spectrometry
(XRF).
Compositional Analysis. The chemical composition of the samples was determined by X-ray
fluorescence spectrometry using a Philips, PW 1400 with a RhK radiation. The measurements were carried
out on compressed powder pellets. The loss on ignition (L.o.I) was determined by heating at 1000 °C for 12
hours. Intensities were processed according to methods previously reported by Franzini, Leoni & Saitta.
A quantitative determination of the clay iron content was also carried out by a Perkin Elmer Atomic
Absorption spectrophotometer mod. 1100B. Acid digestion was performed using mixtures of HClO4/HF. The
composition was 5.4 0.6 % of iron for all the samples.
SEM-EDS. Samples were cut to obtain thin cross-sections which were coated with carbon at high pressure
to make the surface conductive. Scanning Electron Microscopy investigation was performed using a Philips
XL 30 operating at 20 kV and equipped with an EDAX DX4 energy dispersive spectrometer (EDS).
Elements with atomic number higher than 10 were identified. The counting rate was kept close to 1500-1800
counts per second over the whole energy range. After peak acquisition, the intensity values were used for
quantification, according to the ZAF procedure and to the “standardless” approach (namely, using computed
pure element intensity factors). Analytical accuracy was checked using secondary standards, i.e. samples
with known composition; an agreement better than 10 % was achieved. The analytical precision was better
than 0.5 % for major elements, and better than 20 % for minor elements (with a concentration ranging from
0.3 up to 3-5 wt %).
To study the morphology of the samples, back-scattered images (BSE) were collected.
EDS compositional studies have been carried out on bulk and on grains of the samples. For the
characterization of the bulk ten measurements, taking care to avoid the iron-rich grains, were performed
scanning different areas with dimensions about 800x800 m2. Then the results were obtained using the
arithmetic average. Instead, the areas used for the compositional studies of the grains were related to the
dimensions of the grains.
XRPD. X-ray powder diffraction patterns were collected in the 3-100° 2 range according to the step
scanning procedure with CuK radiation on a Philips X’PERT APD diffractometer; a PW3020 goniometer
equipped with a bent graphite monochromator on the diffracted beam, 0.5° for divergence and scatter slits
and a 0.1 mm for receiving slit were used. The LFF tube operated at 40 kV and 30 mA. To minimize
preferred orientations, the sample was carefully side loaded into an aluminium sample holder with an
oriented quartz mono-crystal underneath. The diffraction patterns for quantitative analysis were collected in
the 3–100° 2θ range with a 13 s/step data collection time. The diffraction patterns for qualitative analysis
were collected in the 3-60° 2θ range with a 3 s/step data collection time. Microcrystalline silicon powder
(200 mesh) was used as a reference standard and it was added to the samples in a Si / sample = 1/10 weight
fraction ratio.
EPR Spectroscopy. Electron paramagnetic resonance spectra were recorded at the X-band frequency,
9.1 GHz, at 297 K using a Bruker EMX EPR spectrometer, equipped with the EMX High Sensitivity
Probehead. Samples were finely powdered, weighted, 124 mg, and inserted into 4 mm EPR quartz tubes.
In order to perform the Fe3+ quantitative analysis, six samples were prepared containing alum
(KAl(SO4)2*12H2O)/ferric-alum (Fe(NH4)(SO4)2*12H2O) mixtures with known amounts of Fe3+, namely :
9.65%, 7.72%, 5.79%, 3.86%, 1.93% and 0.37%.
NMR spectroscopy. Samples, 130 mg, were inserted in 4 mm zirconia rotors sealed with Kel-F caps.
All spectra were recorded on a Bruker ASX200 NMR spectrometer. The spinning rate was always 12 KHz.
27
Al NMR. 27Al MAS spectra were recorded at 52.15 MHz. The /2 pulse width was 3 s; number of
scans (ns) = 800, time domain (td)=512 data points, recycle delay 60 sec.. The choice of this long recycle
delay is by no means casual, but due to the presence of a long relaxing component. Before the relaxation
measurement a careful match of the magic angle was performed. T 1 spin-lattice relaxation time was
3
measured using the Saturation Recovery sequence. These measurements were repeated twice at two different
spin-rates, 5 and 12 KHz. The longest T1 component is  12 sec., while the other component is  0.05 sec..
27
Al 1H CP MAS NMR spectra. The cross-polarization was performed applying the variable spinlock sequence “RAMP” 4. The ramp can be applied on the X or on the 1H channel. The ramp causes one of
the channels to be spin-locked slightly off the Hartmann-Hahn condition, except in the middle of the ramp
where the spin-lock is exactly matched at the Hartmann-Hahn condition. This method allows to overcome
the motional modulation of the aluminium and proton coupling caused by spinning the sample at high rate.
The ramp was applied on the 1H channel and, during the contact time , the amplitude of the spin-lock
increased from 50% up to 100% of its maximum value. All spectra were recorded using the TPPM15 1H
decoupling sequence, with a decoupling field strength of 75 KHz 5. CP-MAS spectra were recorded at
different contact times , with  ranging from 0.2 up to 20 ms. The signal in the cross-polarized spectra
showed a maximum at
 = 0.5 ms, therefore this contact time was used in all spectra.
27
Al 3Q MAS NMR spectra6 - 9 were obtained with a two pulses sequence: p1 – t1 – p2 – aq; the phase
cycling was composed of six phases for the selection of triple-quantum coherences. The pulse durations p1
and p2 were optimised to 3 s and 7 s respectively. The delay t1 between the two pulses was incremented
regularly, t1= 6 s, in the 3Q dimension (f1), with a total of 100 increments, td1 = 100, and according to a
TPPI acquisition scheme; 256 data points were used in the f2 dimension; 732 transients were recorded for
each t1 increment.
The ppm scale was referenced to 0 frequency in the f2 dimension and to 30 in the f1 dimension, using
Al(H2O)63+ as an external reference.
The 3Q MAS spectra were zero filled and Fourier transformed using 512 x 512 data points.
The centres of gravity G1 and G2 of the 2D spectral ridges in the f1 and f2 dimension respectively can
be used for estimating the isotropic chemical shift iso and the second order quadrupolar effect Pq while  is
the
slope
PQ  ν 0
of
the
quadrupolar

axis
QIS:
δ iso 
ξδ G2  p δ CG1
ξ p
being
δ CG1 
δ G1
p
and

2
9 4I2I  1 δ CG1  δ G2
;
10 p 2  1
10 6
in the case reported here: p=3, I=5/2 and 0 =52.15 MHz and =3/4
 19 
 3
 ν 2 ; the QIS axis is defined by ν 1    ν 2
 12 
 4
In the 3Q MAS spectra, the A axis is defined by ν 1  
and the CS axis is defined by ν1  3ν 2 10.
Spectral deconvolution. The deconvolution of 27Al MAS and 3Q MAS NMR spectra was performed
using the dm2004 program 11 .
Deconvolution of 27Al 1D MAS spectra. In the dm2004 program the Q-MAS ½ model was selected to
model the central transition under infinitely fast MAS spinning. Each resonance was characterized by the
following parameters: the isotropic chemical shift iso, the amplitude, the quadrupolar coupling constant Cq,
the asymmetry parameter q and EM, a parameter used to apodize the theoretical lineshape. The starting
values of iso and Cq were extracted from the 3Q-MAS spectra; then the best fit procedure was applied,
obtaining the best fit values for all parameters and the integral of the resonances.
The test version of dm2004 allowed us to fit the resonance due to the octahedral site. In fact, using the
test version of dm2004 it was possible to take into account the presence of a chemical shift distribution using
the Czjzeck model 12. According to this model the line to be fit was characterized by the following
parameters: iso, Cq, q, EM, the amplitude, the width of the isotropic chemical shift distribution CS, and
the parameter d; this parameter d, ranging between 1 and 5, for a Gaussian isotropic distribution of EFG is an
exponent equal to 5 13.
Deconvolution of 27Al 3Q- MAS spectra. The deconvolution of 3Q-MAS spectra was applied for
deconvoluting the spectral ridges due to Al in tetrahedral sites.
Before performing the deconvolution of the spectra, a shearing transformation was applied to align the
anisotropic lines parallel to the f2 axis14.
In modelling multi-dimensional experiments some problem arises from the large number of variable
parameters to be taken into account. Therefore we started fitting the corresponding 1D MAS spectrum and
4
then we used the obtained parameters as starting parameters in the deconvolution of the 3Q MAS spectrum.
In addition to the parameters which characterize a resonance in a 27Al 1D MAS spectrum, a parameter was
added to compute the two dimensional spectrum, that is the line-width in the f1 dimension.
29
Si NMR. MAS NMR spectra were recorded at 39.76 MHz. The /2 pulse width was 4 s, number of
scans (ns) =4000, recycle delay = 60s, time domain (td)=512 data points.
CP-MAS spectra were obtained using the following parameters: /2 pulse width 3.5s, contact time 1
ms, recycle delay 3s.
The ppm scale was referenced to tetramethylsilane (TMS).
To model each resonance, the deconvolution of 29Si MAS spectra was performed using the dm2004
program11. The Gaussian/Lorentzian model was selected. Each resonance was characterized by the following
parameters: amplitude, position, the width at half height and a function (xG/(1-x)L) of the
Gaussian/Lorentzian ratio (1 for a Gaussian lineshape and 0 for a Lorentzian lineshape); we used only
Lorentzian lineshapes, fixing this ratio to 0.
23
Na NMR. MAS NMR spectra were recorded at 52.94 MHz. The /2 pulse width was 4.5 s, number of
scans (ns) = 12000, recycle delay = 1 s, time domain (td) = 512 data points.
Results
XRF. The chemical composition of the samples was obtained by X-ray fluorescence analyses. The
samples composition of the main components ranges as follow: Na2O = 2.8 - 3.1%, MgO = 3.3 – 3.5%,
Al2O3 = 15.9 – 16.7%, SiO2 = 56.7 – 58.4%, P2O5 = 0.1 - 0.2%, K2O = 2.2 – 2.4%, CaO = 5.2 – 5.4%, TiO2 =
0.6 – 0.7%, MnO = 0.1 – 0.2%, Fe2O3 = 5.5 – 5.7% L.o.I = 3.8 –6.8%. The composition of all samples is
practically constant apart, as expected, the loss on ignition.
SEM-EDS. The SEM-EDS was used to determine micro-textural and micro-chemical features of the
samples. All samples show the same micro-texture which consists of grains (from 10 to several hundreds
micrometers) within a fine-grained porous matrix. The pore size is variable and can reach up to 100 m.
EDS analysis of the grains shows different compositions. Many grains are quartz-grains15, others are
aluminum-silicate of alkaline metals (Na, K, Ca, and Mg); these minerals belong to the unfired clay or are
formed after the structural breakdown of the phyllosilicates. Other grains are rich of Ba and S, or of Mn, or
P, or Fe (Table 1) 16.
A more detailed treatment is required for the description of the iron content observed both in the grains
and in the matrix of the samples. The dimension of the iron rich grains ranges from 50 m2 up to several
hundreds of m2. In the samples fired at T < 900 °C the iron content is lower than 60 wt % (Table 2),
whereas in the samples fired at T  900 °C it can be as high as 90 wt % (Table 3). In the sample fired at 1100
°C a particular grain made up both octahedral and tetrahedral crystals with dimension of about 150 x 200
m2 and an iron content of about 90 wt % is observed (figure 1a and 1b).
The iron content of the matrix of the samples was studied considering the average composition of ten
areas of about (800 x 800 m2); the chosen areas did not contain iron grains. The iron content in the samples
matrix decreases as the firing temperature increases (see figure 2).
This observation suggests that the iron migrates from the matrix toward preferential sites of
crystallization. In fact the amount of iron in grains increases from 60% up to 90%.
XRPD: Qualitative phases analysis. The mineralogical phases in all samples were identified with a
search/match on the PDF database on the basisof the characteristic reflections.
The unfired clay contained Quartz, (Qz, SiO2, PDF n. 46-1045), K-feldspar (Kfs, (K,Na)(Si,Al)4O8, PDF
n. 84-0710), Na-rich plagioclase (Napg, NaAlSi3O8, PDF n. 18-1202), Illite 2M (Ill,
(K)(Al,Mg,Fe)2(Si,Al)4O10(OH)2 n(H2O), PDF n. 26-0911), Calcite (Cc, CaCO3, PDF n. 13-0198) and
ordered Anorthite (An, Ca2Al(AlSi)O7, PDF n. 71-0788); the basal reflections of Montmorillonite 15A (Mm,
(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O),
PDF
n.
29-1498)
and
chlorites
(Chl,
Na0,5(Al,Mg)6(Si,Al)8O18(OH)12·5(H2O), PDF n. 40–0744) were also identified. The reflections of the last
two phases are beyond doubt less intense than the others. Therefore Montmorillonite and Chlorites can be
neglected in the further considerations.
The pattern of the sample fired at 800°C showed the disappearance of the calcite peak, due to the
breakdown of the carbonates, while the illite basal reflections were still present.
The Hematite (Hem, Fe2O3, PDF n. 33-0664), Gehlenite (Geh, Ca2Al(AlSi)O7, PDF n. 35-0755) and
Diopside (Di, CaMgSi2O6, PDF n. 24-0203) peaks were identified as new-formation phases, and the intensity
of their reflections is more enhanced in the samples fired at 1000°C and 1100°C.
5
The illite peaks disappear above 900 °C, whereas the peaks of Na-Ca plagioclase (27-29° 2θ region)
increase and they are well defined in the samples heated at 1000 and 1100 °C (see figure 3a).
XRPD:Quantitative phases analysis. The quantitative mineralogical phase composition of the samples
fired at 800, 900, 1000 and 1100 °C, was estimated using the Rietveld method implemented in the program
GSAS 17. The weight fraction of the phases present in the bulk was calculated according to the Bish &
Howard formula 18. Its generalized form can be written as
m
Wm = amSm/
a S
k 1
k
k
, where Wm is the weight fraction of the mth component in the sample and ak is its
calculated density, expressed as ak = ZkMkUk (Zk is the number of chemical formula units in a unit cell, Mk is
the molecular weight and Uk is the unit-cell volume).
The amorphous content was estimated with the internal standard method 19.
The amount of the amorphous phase Wa was calculated directly from the weight of the internal standard
according to the following equation: Wa =
1 
Ws 
where Ws is the weight fraction of the
1

1  Ws  Ws, c 
internal standard added to the mixture and Ws, c is its calculated weight fraction after the Rietveld
refinement.
The structural data (cell edges and atomic parameters) of these phases were downloaded from the
American Mineralogist Crystal Structures Database 20 and they were used for the Rietveld refinement of the
diffraction patterns. The structure of illite was derived from that of muscovite, decreasing the K/Si ratio to a
value of 0.25. The Rietveld procedure was performed refining the profile shape, the background and the
scale factor for each phase. The profile was modelled using a pseudo-Voigt profile function for each phase,
in which the Gaussian, the Lorentzian and the sample displacement term were refined.
The cell parameters for the plagioclase structures (albite and anorthite solid solutions) were also refined;
at the end of the refinement the shifts of all parameters were minor than their standard deviations.
Figure 3b shows the Rietveld plot of the sample fired at 800 °C. Table 4 shows the relative amount of the
phases present in the samples fired at 800, 900, 1000 and 1100 °C; the amorphous content is also shown in
the same Table.
The statistical uncertainty of the weight fractions is strongly dependent on some factors, these are the
crystallinity degree, the presence of strong scatterers, the variability in stoichometry and mainly the
overlapping degree of the most intense reflections of each phase 21.
In our case the estimated standard deviations of the weight fractions of Quartz, Calcite and Hematite fell
in the range 0.001 ÷ 0.01 because their reflections had a low overlapping degree.
The estimated standard deviation of the weight fraction of plagioclases/feldspars phases ranges between
0.01 ÷ 0.1 because of the higher overlapping degree of the reflections of these phases and their high chemical
variability.
Figure 3c shows the percentage of the weight fraction of each phase after the Rietveld refinements for
the samples fired at 800, 900, 1000 and 1100 °C.
In all samples quartz is the predominant phase and its weight fraction shows a maximum at 1000 °C
(37%) and then a decrease.
In the sample fired at 900 °C the amorphous content markedly increases, at the same time, a decrease of
the illite weight fraction and the breakdown of the calcite structure are observed. Then, in the samples fired
at 1000 and 1100 °C (22%), the amorphous content progressively decreases.
The feldspars/plagioclases phase increases with the firing temperature; in the sample fired at 1100 °C, up
to 10-15% weight fraction has been found. These values must be taken with caution because they are only
indicative of a general trend. The high chemical variability and the strong overlapping degree of the
characteristic reflections of these phases, do not allow a good repartition of the weight fraction of each phase.
The simultaneous increase of the weight fractions of these phases with the temperature is indicative of
the reaction of the alumino-silicatic amorphous matrix, with K+ and Na+ ions. This reaction gives rise to the
neo-formation of Na-rich K-feldspatic phases.
The formation of new phases such as Gehlenite and Diopside is due to the reaction of Ca 2+ with the
phyllosilicate matrix, while Anhortite formation probably occurs at the Quartz crystals grain boundaries 22.
The general increase of the amorphous matrix up to 900 °C is mainly due to the clay minerals
decomposition, whereas, above this temperature, a general re-crystallization of new phases is observed, as
shown by the decrease of the amorphous content observed in the samples fired at 1000 and 1100 °C.
6
EPR spectra. In clays Fe can be present as Fe2+ and as Fe3+. Traces of Mn2+ may be also present and
eventually other paramagnetic compounds in trace. Therefore, to perform a characterization of paramagnetic
centers present in the clay, a quantitative EPR study was performed. The EPR spectra of the fired clays are
shown in figure 4. In all samples EPR spectra show the presence of Fe 3+ and, in the sample fired at low
temperature also of Mn2+.
EPR spectra allow the distinction of samples in two sets, i.e. samples fired at 600, 700 and 800 °C ,
named set S1, and the ones fired at 900, 1000 and 1100 °C, named set S2.
The EPR linewidth of Fe3+ is about 100 mT for the first group of samples whereas it is about 50 mT for
the second group.
In the set S1, where iron is present mostly as Fe2+, the quantity of Fe3+ is smaller; the spectra show an
intense resonance absorption at g = 2.4 and a shoulder in the region of g = 4.2 (rhombic site). Spectral line
widths are dominated by dipolar broadening 23. In the set S2, the Fe2+ in the clay is fully oxidized to Fe3+. An
intense resonance at g = 2.1 (octahedral site) is observable 24, 25. The spectral line-widths are dominated by
exchange narrowing 23.
The intense resonance at g = 2.1 begins to appear in the sample fired at 800 °C.
The spectrum of the clay fired at 900 °C is intermediate between the two sets; the shape of the Fe 3+
resonance is similar to that one of the S2 set, its intensity however is intermediate. The presence of Mn 2+ is
observable only in samples fired at T  800 °C, whereas at higher temperature, Mn2+ is oxidized to Mn3+,
therefore no more observable by EPR. Note that, in the unfired sample, the Mn2+ resonance is the stronger
one, data not shown.
Quantitative analyses were performed using ferric-alum dispersed in alum. In figure 5a the straight line
represents the result of the titration; the dashed horizontal line represents the intensity of an hypothetical clay
sample containing un-clustered 5.4 % Fe3+ i.e. the value corresponding to the total amount of Fe3+ as given
by elemental analysis. It can be easily seen that in clays fired at the higher temperatures, the EPR spectrum
shows an anomalously high intensity, see figure 5b. Therefore the presence of ferromagnetic or ferrimagnetic
domains of Fe3+ contained in clusters is strongly suggested. A decrease of the EPR intensity in the sample
fired at 1100 °C on respect to the one fired at 1000 °C might be due to coupled Fe3+ ions in clusters.
27
Al NMR MAS spectra. 27Al MAS NMR characterization of many different clay minerals allows a
useful comparison of the Al MAS spectral characters to the structural and compositional parameters of the
clay 26. Many naturally occurring clays contain substantial amount of iron which affects the NMR spectra.
The extent of the influence of paramagnetic iron on the NMR spectra provides information on the
distribution of the iron in the clay.
As shown by elemental analysis and X-rays fluorescence techniques, our samples contain a considerable
amount of iron, about 5.4 %. As the firing temperature increases, Fe2+ oxidizes to paramagnetic Fe3+. As
previously observed 27 a considerable amount of paramagnetic iron does not impair an NMR study. In fact, it
has been previously shown that the observation of a 27Al NMR signal in an iron containing clay strongly
depends upon the distance between Fe3+ and Al. As reported in the literature 28 the extent of Fe3+ segregation
can be assessed by the effect of 27Al NMR signal loss caused by the presence of Fe3+. It is possible to select a
“wipeout” radius (R  6 Å) around Fe nuclei, within which the 27Al NMR signal is lost. Accordingly, in the
NMR spectrum of an iron containing clay, resonances due to some Al atoms are not observable. It is also
known that any Fe atom absorbed in the clay matrix is highly favoured to be incorporated into the Oh
(octahedral) layer, with Fe3+ replacing Al3+ into the Oh layer 29. As a consequence in iron rich clays, the
Al(Td)/Al(Oh) signals obtained by NMR may appear larger than expected, affecting a quantitative evaluation.
In figure 6, the 27Al MAS NMR spectra of the starting clay sample (a) and of samples fired at different
temperatures, T=600 (b), 700 (c), 800 (d), 900 (e), 1000 (f), 1100 (g) °C, are shown; in the figure the
deconvoluted spectra have been overlapped to the experimental ones, along with the components obtained
from the deconvolution. 27Al spectra allow to separate samples in two sets referred as S1 and S2 respectively,
i.e samples fired at temperatures lower than 900 °C and samples fired at temperature equal or higher than
900 °C; S1 also includes the unfired clay sample. All samples belonging to S1 show at least two main, broad
resonances: the low frequency resonance apparently centred at about 50 ppm is characteristic of Al in a
tetrahedral environment (Td), whereas the resonance apparently centred at about 0 ppm is characteristic of Al
in an octahedral environment (Oh). This finding is in agreement with the large amount of illite found using
XRPD. In fact illite has a 2:1 layer structure with a plane of octahedral coordinated cations sandwiched
between two inward pointing sheets of tetrahedral 30. In the illite structure one out of four Si4+ ions are
replaced by Al3+ in the tetrahedral sheet; besides some octahedral Al3+ may be replaced by Fe2+ and Mg2+.
7
These replacements give raise to a negative charge which is neutralized by large cations in the interlayers
spaces. Therefore the resonances of Al both in Td and in Oh environments are observed. As the firing
temperature increases, the signal of Al in Oh environment decreases, fully disappearing at temperature higher
than 800 °C. This observation may be rationalized by two effects. In fact, as the firing temperature increases,
Fe2+, which preferentially replaces Al in Oh environment, oxidizes to paramagnetic Fe3+ which affects the
intensity of the signal of Al in Oh environment. Moreover, as the firing temperature increases, the illite
structure breaks down and the signal due to Al in Oh environment does not exist any more. According to
XRPD data, as the illite structure breaks down, new phases are observed; all these new phases contain Al
only in the Td environment 31, 32.
As previously shown, in the 27Al MAS NMR spectra significant differences exist among different clays,
including dehydroxylated fired clays 32. For instance in the case of Kaolinite and Hallosyte, besides the
resonances due to Al in Td and Oh environment, a resonance at about 26 ppm has been reported. This
resonance has been ascribed to Al in a penta-coordinated environment. AlO5 has been also found in the 2:1
system Pyrophyllite 33 whereas, in other clay minerals, no signal due to AlO5 has been reported 34.
In the 27Al spectra, see figure 6, no evidence of resonances due to Al in a penta-coordinated environment
(20 – 30 ppm) is observed. However the spectra are too broad for definitely ruling out the presence of Al in a
penta-coordinated environment, which however may be present in a small amount. Therefore for obtaining
more information, the spectral resolution must be improved.
27
Al 3Q MAS NMR spectra. To obtain 27Al NMR spectra with improved resolution, we performed
triple-quantum MAS NMR experiments. This 2D method 6, 9 involving multiple-quantum excitation in
combination with the magic angle spinning, is able of refocusing the second order quadrupolar effects which
broaden the 27Al signals. The 3Q-MAS spectra are shown in figure 7: unfired clay (a), and clays fired at T =
600 (b), T = 700 (c), T = 800 (d), T = 900 (e), T = 1000 (f) and T = 1100 °C (g).
In the 2D map, in the multi-quantum dimension, the lines are three times more separated by their
isotropic chemical shift than in MAS single quantum dimension, moreover they are free of second order
quadrupolar effects. In the 2D spectra, figure 7, the dotted lines represent the different orientation of signals
in an 3Q-MAS spectrum: “A” denotes the anisotropic axis, “QIS” is the axis giving the direction of the
induced quadrupolar shift and “CIS” axis gives the direction of the isotropic chemical shifts. 3Q-MAS
spectra of samples belonging to S1 show two main well separated spectral ridges, respectively due to Al in
Td and in Oh environment. It must be noted that the spectral ridges of Al in T d environment are rather well
aligned along the CS axis, whereas the spectral ridge of Al in Oh environment appears out of the CS
alignment, thus showing the presence of a chemical shift distribution. Note also that the cross-peak due to the
Td site lies along the A axis, whereas the cross-peak due to the Oh site appears not well aligned along this
axis. According to this observation we infer that the quadrupolar coupling constant of Al in T d site is larger
than that one of Al in Oh site. It is worth noticing that the QIS axis is the axis along which the mass centres
of the ridges from different species with the same isotropic chemical shift but different quadrupolar constants
are located. In the 3Q-MAS spectrum of the unfired clay, at least two spectral ridges due to Al in tetrahedral
sites, Td1 and Td2 aligned along the QIS axis, are clearly observable, see figure 7a, furthermore also the
isotropic projection along the F1 dimension shows a clear multiplicity. The 3Q-MAS spectra of samples
fired at 600, 700, and 800 °C show again the presence of spectral ridges due to Al into two different
tetrahedral environments, however as the firing temperature increases the chemical shifts of these two
tetrahedral sites, Td1 and Td2, become very close to each other, making the observation of their separation
increasingly difficult, see figures 7 b,c,d.
The 3Q-MAS spectra of samples belonging to S2 show only the spectral ridges due to Al in T d
environment, see figures 7e,f,g. Two spectral ridges, T d1 and T2d, due to Al in two slightly different Td
environments, both aligned along the QIS axis, are observed: T d1 and Td2 have chemical shifts close to each
other, whereas their quadrupolar coupling constants are rather different.
According to the literature 35, 36 using the centres of gravity G1 and G2 (in the f1 and f2 dimension
respectively) of the 3Q-MAS spectra, it is possible to estimate the isotropic chemical shift iso and the second
order quadrupolar effect Pq of each spectral ridge. The obtained parameters were used as starting parameters
in a best fit procedure applied for deconvoluting the 1D MAS spectra.
The isotropic chemical shifts isoTd1 and isoTd2, the quadrupolar coupling constants CqTd1 and CqTd2, the
asymmetry parameters qTd1 and qTd2 of Al in Td sites, and isoOh and CqOh of Al in the Oh site are reported in
Table 5. The Czjzeck model 12 used for the simulation of the resonance of Al in Oh site accounts for a
chemical shift distribution 13, the width of the chemical shift distribution CS is also reported in Table 5. The
used program, dm2004, gives also the area of each 27Al resonance. It is then possible to obtain the percentage
8
of Al in Oh site and the percentage of Al in Td site, data not shown. However, it must be pointed out, that,
due to presence of Fe3+, this percentage is not quantitative. In fact, the resonances due to 27Al atoms within
the wipe out sphere of Fe3+, are fully lost; therefore the obtained values refer only to those sites outside the
Fe3+ wipe out sphere 27. In the unfired clay Al is present in an almost equal amount in Oh and Td sites. As the
firing temperature increases, the amount of Al in Oh progressively decreases; in samples fired at temperature
higher than 800 °C, the resonance at about 4.5 ppm fully disappears, reflecting the structural breakdown of
the illite structure; this observation fully agrees with the XRPD data previously shown.
The expanded tetrahedral region of all spectra, after applying the shearing procedure 14 is shown in figure
8, with the experimental spectra shown on the left side, and the simulated spectra shown on the right side. It
is worth to note that the set of parameters obtained for the Td sites from the simulation of 1D-MAS spectra is
very similar to the corresponding set obtained from the best fit of the 3Q-MAS spectra. On samples fired at a
temperature lower than 900 °C, two tetrahedral sites have been always found. As previously observed, these
two sites give rise to NMR signals with very similar chemical shift values whereas the quadrupolar coupling
constant values are different 37. A possible interpretation of the structural difference of these two
environments is that slightly different distortions may change the Electric Field Gradient (EFG) distribution,
and, as a consequence, the value of the quadrupolar coupling constant. In fact the quadrupolar coupling
constant Cq is proportional to the largest of the three principal axes of the EFG tensor at the
nucleus 34. It has been previously shown that, in some cases, either the distortion of the local environment or
long range lattice effects may affect the magnitude of the Electric Field Gradient (EFG) and, therefore, the
magnitude of Cq 38. Therefore two Td sites may show resonances with isotropic shifts very similar to each
other, but with different Cq values.
In samples fired at temperature higher than 800 °C, Al spectra show only two tetrahedral environments.
The parameters obtained for the two Al resonances are very close in chemical shifts whereas again they show
different Cq values .
Dehydration and dehydroxylation of fired clays. Many factors may affect the efficiency of the crosspolarization process of the resonances of quadrupolar nuclei under MAS conditions. Thus resonances of two
distinct sites may display markedly different cross-polarization properties, exhibiting matching conditions at
very different field strength. Carefully taking into account these points, we may asses that the efficiency of
the transfer of the magnetization from proton nuclei to Al nuclei is closely related to the total proton
concentration in the sample. According to the literature39, in hydrous aluminates such as Gibbsite, the
interlayer water is associated to Al in Oh environment. Moreover, earlier studies on Illite-rich clays 31,40
showed that, in the 350 – 400 °C range of firing, the interlayer water is driven off, therefore only the protons
of the hydroxyl groups participate to the CP-process. The dehydroxylation takes place between 450 – 700
°C.
In figure 9, the 27Al MAS (a) and CP MAS (b) spectra of the unfired clay are shown. According to the
literature 39 the CP-MAS NMR spectra show that the available protons are closely associated with Al in Oh
site, as this site provides a considerable CP-MAS signal intensity whereas no CP-MAS intensity is observed
for the resonance of Al in Td sites.
The intensity of the CP-MAS signal decreases in the sample fired at 600 °C and, due to the
dehydroxylation, the signal fully disappears in the sample fired at 700 °C (data not shown).
29
Si MAS spectra. In figure 10, the 29Si MAS NMR spectra of the unfired and fired clays are shown. The
corresponding deconvoluted spectra have been superimposed to the experimental ones, along with the single
components obtained from the deconvolution procedure.
In all spectra a resonance centred at –107  -108 ppm due to quartz is observed; this resonance is much
sharper in the spectra of clays fired at T= 600, 700 and 800 °C, thus showing a certain amount of short range
disorder in the clays fired at the higher temperatures.
The resonance centred at about –93 ppm can be easily ascribed to the Q3 units of Illite; this resonance is
observed in the spectra of samples fired at temperatures lower than 900 °C; at higher temperatures, when the
structural breakdown of illite occurs, this resonance is no more observable.
In agreement with XRPD data, the resonances centred at about –96 and –101 may be safely attributed to
the presence of K-Feldspars41.
The peak broadening and the extra intensity in the –86  -100 ppm range may be tentatively attributed to
the resonances of a range of silicon environments in strained regions between Albite and Anorthite-rich
domains 41, 42.
In some sample a shoulder centred at –113  -115 ppm is also observable, see Table 6; this shoulder
might be possibly due to silica polymorphs or to silica glass with a broad distribution of the SiOSi bond
9
angles. In fact, according to the literature41, the resonances of silica polymorphs appear at the highest field of
the 29Si chemical shift range of silicates, from -107 (quartz) to to –121 ppm, whereas silica glass may show a
broad resonance centred at about –110  -111 ppm
Note that no evidence of Gehlenite , observed with XRPD, was found neither in the 29Si NMR spectra.
It is important to point out that, even if a considerable amount of paramagnetic iron is found in the
sample, in order to avoid saturation of the signal from the crystalline quartz, a recycle delay of at least 60 s
must be used. Therefore, in the crystalline quartz domain, no paramagnetic iron is present and the observed
line broadening is possibly due to disorder.
The 29Si MAS (bottom) and CP-MAS (top) spectra of the unfired clay are shown in figure 11. As
expected, the quartz spectral resonance fully disappears in the CP spectrum of the unfired clay, as compared
to the simple MAS spectrum of the same clay, see figure 11.
23
Na MAS NMR spectra. 23Na MAS NMR spectra of all clays are shown in figure 12. In clays fired at the
higher temperatures the spectrum shows a single broad line, rather symmetric and unstructured, centred at
about –27 ppm from NaCl. This line well corresponds to literature data and it is due to Albite glasses 43
and/or Na-rich Plagioclase 34.
Spectra of clays fired at lower temperatures appear complex and poorly resolved. A comparison with
literature data does not allow a significant assignment. A further study at higher field and higher spin rate
will be performed.
Conclusion
The use of a large number of chemical physical techniques allowed a clear description of the effect of firing
on a complex material such as an Fe rich clay. Taken all together these characterization methods have shown
the following items:
-Interlayer water is driven off at temperatures lower than 600 ºC. As shown by 27Al CP-MAS NMR spectra,
interlayer H2O is located close to octahedral sites.
-Dehydroxilation occurs in the temperature range 600-700 ºC.
-In the 800-900 ºC temperature range, due to a full breakdown of the Illite structure, Al in octahedral sites
disappears; in the same temperature range all Fe is oxidized to Fe 3+ .
-In samples fired at 1000 and 1100 ºC a clustering of the iron has been observed accompanied by the
presence of large iron single crystals with the appearance of ferro or ferri magnetic effects.
-The Al in octahedral site present at temperatures lower than 900 ºC presents a continuous chemical shift
distribution pointing to the presence of slightly distorted sites.
-In the full temperature range the presence of at least two tetrahedral Al sites has been revealed,
characterized by different values of the quadrupolar coupling.
-In some samples silica polymorphs or silica glasses with a broad distribution of the SiOSi bond angles have
been also found.
Few other observations can be obtained comparing XRPD and NMR data. In fact both set of data show a
maximum quartz content in the sample fired at 1000ºC. Both techniques confirm the presence of K-Feldspars
34
, observed by XRPD and by NMR. Albite which, according to XRPD data, increases in the samples fired at
the higher temperature was also observed in the 23Na NMR. However Gehlenite , observed with XRPD, was
not found neither in the Al and in the Si NMR spectra. The same for anhortite not observed neither in the Al
and in the Si NMR spectra. However, some extra intensity observed in the Si spectra, may be tentatively
attributed to a range of silicon sites in strained regions between Albite and Anorthite-rich domains 41, 42.
Even if the set of parameters obtained from 3Q MAS experiments and from the deconvolution procedure
makes sense, the accuracy in determining the isotropic chemical shift and quadrupolar coupling constant may
be improved by the combined evaluation of MAS and 3Q MAS spectra measured over a range of different
Larmor frequencies. Measurement at different H0 fields will allow the assessment of the relative importance
of second order quadrupole parameters vs. line broadening mechanisms in determining the shape and the line
width characteristic of an observed NMR resonance composed of overlapping resonances from different
sites44. Moreover, the resolution of the observed Td and Oh Al sites, might be improved at higher field and
higher spin rate. Moreover Si spectra obtained at higher field will surely be more informative.
Acknowledgements
Thanks are due to Prof. D. Massiot for the  version of the program dm2004.Thanks are due to Dr. M. Liberi
and Dr. R. Melzi , Bruker Biospin Milano for the use of the Bruker EMX EPR spectrometer. We thank Dr. F.
10
Ziarelli for the stimulating and useful discussions.Thanks are due to Dr. A. De Stefanis and to Mrs P.
Cafarelli for elemental analysys. This work was performed as part of the Eu-ARTECH project within the VI
Framework Program.
11
Table 1: Composition W(%) of different grains typically found in the samples.
Aluminium
Silicate
Other
crystals
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
Na2O
0.6
13.6
1.6
0.6
2.2
1.7
0.9
1.4
MgO
1.3
1.7
0.9
3.3
6.8
1.9
0.6
4.4
Al2O3
4.4
19.9
20.9
1.8
20.0
4.0
3.0
3.4
SiO2
89.7
63.8
59.1.
24.8
35.5
40.0
7.0
7.7
P2O5
n.d.
n.d.
n.d.
0.9
n.d.
46.5
n.d.
n.d.
SO3
0.2
0.5
0.5
12.7
0.5
2.6
26.2
0.8
K2O
0.6
0.1
15.8
0.2
2.7
0.5
0.3
0.4
CaO
0.9
0.1
1.0
53.8
5.0
1.4
1.5
23.3
BaO
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.-
59.5
n.d.
TiO2
0.4
n.d.
n.d.
0.5
n.d.
0.4
n.d.
n.d.
MnO
n.d.
n.d.
n.d.
n.d.
24.0
0.2
n.d.
53.6
FeO
1.8
n.d., not detected
0.3
0.4
1.6
3.4
1.0
1.0
4.9
Table 2: Composition of some iron-rich grains of the sample fired at temperature lower than 900°C.
600°C
700°C
800°C
50x10m 20x20m 20x10m 60x100m 70x130m 40x60m 30x20m 20x15m 20x10m
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
Na2O
2.4
2.5
0.9
2.1
1.6
1.5
2.4
1.8
1.6
MgO
5.5
12.8
2.9
6.5
2.6
2.9
5.0
2.4
4.9
Al2O3
9.7
20.2
5.8
16.3
7.1
8.3
10.9
17.5
12.1
SiO2
18.7
36.1
12.5
31.9
14.0
19.4
23.5
24.6
17.0
P2O5
0.8
0.8
1.7
n.d.
n.d.
n.d.
n.d
n.d.
n.d.
SO3
0.2
1.0
12.0
0.7
1.0
1.2
1.3
0.8
0.8
K2O
0.9
1.1
1.2
1.9
0.5
0.9
0.7
1.0
1.4
CaO
3.0
2.0
11.0
2.0
14.1
10.4
12.0
1.4
2.1
TiO2
n.d.
n.d.
n.d.
0.7
0.4
0.4
0.1
0.7
0.9
MnO
1.6
n.d.
0.6
n.d.
n.d.
10.2
n.d.
n.d.
n.d.
FeO
57.3
23.6
51.3
38.0
58.7
44.8
44.1
49.9
59.3
n.d., not detected
12
Table 3: Composition of some iron-rich grains of the sample fired at temperature higher than 800°C.
900°C
1000°C
1100°C
20x50m 80x120m60x120m 30x30m 100x30m 100x60m 150x200m 60x40m 80x80m
Elements W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
W(%)
Na2O
3.4
2.8
2.2
n.d.
2.2
2.2
0.8
1.1
1.9
MgO
4.9
4.2
4.1
4.9
3.8
2.6
1.1
1.2
3.9
Al2O3
7.4
3.8
7.2
7.5
5.5
4.9
2.1
3.6
6.0
SiO2
12.2
5.2
17.2
9.4
13.2
14.4
3.1
9.7
18.0
P2O5
n.d.
2.7
n.d.
3.7
2.0
0.5
0.4
n.d.
0.7
SO3
1.7
2.1
2.0
0.4
1.2
0.5
0.7
0.7
n.d.
K2O
0.7
0.1
0.4
0.5
0.2
0.4
0.4
0.4
0.2
CaO
3.3
6.6
5.4
2.9
5.4
2.5
0.4
1.0
8.5
TiO2
0.7
0.5
0.2
0.4
0.5
0.3
0.8
0.5
0.4
MnO
n.d.
0.7
2.4
n.d.
1.2
0.7
n.d.
n.d.
n.d.
FeO
65.8
71.4
58.9
70.4
64.8
71.2
90.3
81.8
60.4
Table 4: Percentage of different phases in samples fired at 800, 900, 1000 and 1100°C as obtained by
Rietveld method.
Phases (%)
800°C
900°C
1000°C
1100°C
Qz (%)
26.9
26.9
37.6
27.5
Hem (%)
1.0
1.3
1.0
1.5
NaPg (%)
5.7
5.8
7.2
10.5
Geh (%)
n.d.
1.7
2.0
4.2
Di/Augite (%)
n.d.
1.4
7.0
6.5
Kfs (%)
5.6
5.4
5.1
13.9
An (%)
10.3
4.7
9.1
13.9
Ill (%)
21.1
8.3
n.d.
n.d.
Mont (%)
<1
n.d.
n.d.
n.d.
Cc (%)
1.3
n.d.
n.d.
n.d.
Amorphous (%)
27.1
44.5
31.0
22.0
Agreement
Rwp=
Rwp=0.120 Rwp=0.120 Rwp=0.142
indices
0.124
Rp=0.09
Rp=0.09
Rp=0.107
Rp= 0.09 GOF=2.9
GOF=4.9
GOF=3.9
GOF=3.5
Rwp = ( w(Io-Ic)2 /  wIo2)1/2
Rp =  |Io-Ic| /  Io
GOF = ( w(Io-Ic)2 / (No - Nvar))1/2
n.d., not detected
13
Table 5. 27Al NMR parameters as obtained from the deconvolution procedure applied to 1D MAS NMR
spectra as well as 3Q MAS NMR spectra.
iso = isotropic chemical shift; Cq = quadrupolar coupling constant; q = asymmetry parameter; CS= width
of the chemical shift distribution.
T(K) isoT1(ppm) CqT1(KHz)
unfired
72
2065
600
71
2683
700
66
2373
800
66
2373
900
63
2160
1000
64
3266
1100
64
3298
qOh was fixed at 0.61
qT1 isoT2(ppm) CqT2(KHz)
0.1
62
3099
0.9
64
3371
0.8
61
3227
0.8
61
3227
0.0
60
3096
0.0
61
2431
0.0
57
1992
qT2 isoOh(ppm) CqOh(KHz) CS(ppm)
0.5
4.7
2451
37
0.6
4.6
1711
18
0.6
4.6
1841
19
0.6
4.5
1708
17
0.0
0.0
0.0
Table 6. 29Si Chemical shifts and relative integrals as obtained applying the deconvolution procedure to 1D
MAS spectra.
Sample (ppm)
unfired
600C
700C
800C
900C
1000C
1100C
-110.1
-107.6
-107.3
-108.1
-108.0
-108.4
-108.2
%
A
49
16
15
21
33
46
42
(ppm)
-100.8
-100.5
-101.0
-101.8
-100.8
-100.7
%
A
(ppm) % A (ppm)
14
2
5
12
22
28
-97.4
-96.6
-96.9
-97.3
-96.8
-95.0
-95.0
27
21
13
28
21
15
13
-87.3
-87.2
-86.7
-89.1
-91.0
-89.7
-88.9
%
A
13
17
35
9
33
8
8
(ppm) % A (ppm) % A
-92.4
-92.7
-92.6
-93.2
11
32
35
16
-112.9
20
-115.6
-113.3
10
10
The peak broadening and the extra intensity in the -90-100 ppm range is tentatively attributed to a range of
silicon site environments in strained regions between albite and anhortite-rich domains in the modulated
structure (Ripmeester,J.A.; Davidson,D.W. J.Mol.Structure 1981, 75, 67 ).
Glass of aluminosilicate G.Engelhardt and T.Michel, J.Wiley and Sons Norwich, G.B. 1987 page 97.
Si
O
SiOSiOSi
O
Si
14
Figure 1 a) Grain formed by octahedral and tetrahedral crystals with dimension of about 150 x 200 m and a
content of iron of about 90 wt %. It was found in sample fired at 1100°C. b) Magnification of the same grain,
nice octahedral crystal is observable.
15
Figure 2 Iron content in the bulk of the samples fired at different temperatures.
16
Figure 3 a) XRD patterns collected at different temperatures along with labelling of the main phases. b)
Rietveld plot of the sample fired at 800°C: experimental, calculated and difference spectra are shown, the
sticks represent the calculated Bragg positions for all the phases. c) weight fractions of the main
mineralogical phases in samples fired at 800, 900, 1000 and 1100°C.
17
Figure 4. EPR spectra of fired clays.
18
Figure 5 a)Titration line used for the quantitative analysis of Fe 3+, the dashed vertical line corresponds to
the amount of Fe 3+ present in fired clays as obtained by elemental analysis, the horizontal line represents the
corresponding EPR integral ; b) amount of Fe 3+ in clays fired at the temperatures shown in the
abscissa axis. The dashed horizontal line represents the theoretical amount of Fe 3+ .
19
Figure 6. 27Al MAS NMR spectra of clays and their deconvolution; a) unfired; b) fired at 600 ºC; c) fired at
700 ºC; d) fired at 800 ºC; e) fired at 900 ºC; f) fired at 1000 ºC; g) fired at 1100ºC.
20
Figure 7 Un-sheared 27Al 3Q MAS NMR spectra of clays; a) unfired; b) fired at 600 ºC; c) fired at 700 ºC;
d) fired at 800 ºC; e) fired at 900 ºC; f) fired at 1000 ºC; g) fired at 1100 ºC. In f2 the MAS spectrum is
shown, whereas in f1 the isotropic projection is shown The CS, QIS and A axes have been defined in the
experimental section.
21
Figure 8 (continue)
22
Figure 8 Sheared 27Al 3Q MAS NMR spectra of clays, only the Td region is shown. On the left experimental
spectra, on the right simulations. a) unfired; b) fired at 600 ºC; c) fired at 700 ºC; d) fired at 800 ºC; e) fired
at 900 ºC; f) fired at 1000 ºC; g) fired at 1100ºC.
23
Figure 9.
27
Al NMR spectra of the unfired clay: a) CP-MAS, b) MAS
24
Figure 10 29Si MAS NMR spectra and their deconvolution of clays; a) unfired; b) fired at 600 ºC; c) fired at
700 ºC; d) fired at 800 ºC; e) fired at 900 ºC; f) fired at 1000 ºC; g) fired at 1100 ºC.
25
Figure 11 29Si NMR spectra of the unfired clay: a) CP-MAS, b) MAS
26
Figure 12 23Na MAS NMR spectra of clay: a) unfired clay; b) fired at 600ºC; c) fired at 700ºC; d) fired at
800 ºC; e) fired at 900ºC; f) fired at 1000ºC; g) fired at 1100ºC.
27
References
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(2) Altaner, S.P.; Weiss, JrC.A.; Kirkparick, R.J. Nature 1988, 331, 699.
(3) de Araújo, J.H.; da Silva, N.F.; Acchar, W.; Gomes, U.U. Materials Research 2004, 7, 359.
(4) Metz, G.; Wu Z.; Smith, S.O. J. Magn. Res. A 1994, 110, 219.
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