IR and Raman spectroscopies, a way to understand how the Roamn

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IR and Raman spectroscopies, a way to understand how the Roman
window glasses were made?
L. Raffaëlly a,*, B. Champagnon a, N. Ollierb, D. Foyc
a Université de Lyon; Université Lyon 1; CNRS; Laboratoire de Physico-Chimie des Matériaux Luminescents, Domaine scientifique de la
Doua, Bât. Kastler, 10 rue Ampère, Villeurbanne, F-69622, France.
b Laboratoire des Solides Irradiés, Ecole Polytechnique, CEA/DSM, CNRS 91128 Palaiseau, France
c Laboratoire d’Archéologie Médiévale Méditerranéenne, UMR6572, MMSH, Aix en Provence, France
Abstract
Two processes are known to make panes in West Europe during the Roman period: they may be cast on
a flat surface or manufactured by the cylinder-blown process. The aim of our research is to give physicochemical arguments to distinguish between both methods by using IR and Raman spectroscopies to determine
the fictive temperature Tf of the archaeological samples. The position of the 1050 cm-1 band in the IR reflection
spectra of annealed samples versus T f has been studied, giving a calibration curve to determine the T f of the
archaeological sample. The position of the 1100 cm-1 Raman band and the ratio of the Q2/Q3 Raman bands
intensities are also studied versus T f for annealed samples. The Tf of both sides are found to be different, which
is an argument in favor of the cast method.
PACS : 61.43.Fs, 78.30.-j
Keywords: Archaeological glass, Raman scattering, IR reflection, Soda-lime silicate, Fictive
temperature
1.
Introduction
The present study is focused on Roman window glasses. In West Europe two processes are known to
make panes: they can be cast in a frame on a flat support or manufactured by the cylinder-blown method or muff
process. This last process consists in blowing a cylinder of glass, both ends are opened and the cylinder cut
longitudinally. Then after a small reheating, it is opened out flat[1-3]. Actually, it is difficult to distinguish easily
the two methods even if, by observing the samples, one could sometimes determine which process is used. The
clues can be for example differences in the roughness of the sides, shape of bubbles and of the edges. However,
some characteristics are common to both techniques [1], that is why it could be very interesting to determine
distinguishing properties. The aim of our research is thus to give physico-chemical arguments to distinguish the
two processes.
1
Depending on the process, the sides of the pane are not cooled in the same way: for a cylinder-blown
pane both sides are cooled with the same velocity and have therefore the same thermal history, but for a cast
pane, one side is cooled faster than the other. In this last case, the cooling velocity depends on theside position:
on the support or in contact with the atmosphere. So the two sides don’t have the same thermal history[4]. The
fictive temperature Tf of a glass is defined as the highest temperature at which the glass has reached an
equilibrium state before a rapid quenching to room temperature [5]. This parameter characterizes the thermal
history of glass, which has a great influence on the glass structure and properties. Structural changes induced by
different fictive temperature Tf can be investigated by the study of position and intensity of some bands in IR and
Raman spectroscopies. Successful studies on silica [5-12], doped silica [13] and silicate [14, 15] can be found in
literature. So we propose to use these spectroscopic signatures to determine the T f of the archaeological samples.
For this purpose, calibration curves, such as peak position versus fictive temperature, are necessary to obtain the
Tf of the sample. That’s why the samples are annealed in order to achieve different fictive temperatures.
2.
Experimental procedure
2.1 Sample preparation
Two samples types are used: an archaeological one, named “Embiez” and a modern synthetic analogue,
named “GuilB”. The studied antic sample is a piece of flat quadrangular pane from the freight of the Roman
wreck of “les Embiez”, dated from the beginning of the III rd century AD (France) [16]. One of the sides seems to
be smooth and the other grainier, what can be an argument in favor of a cast method. The modern analogue was
synthesized by Allain Guillot, (glassmaker, Boisse, France) with a chemical composition similar to that of the
archaeological sample for the major components: SiO2 ~ 70%, Na2O ~ 18%, Al2O3 ~ 2.5%, CaO ~ 8% (Table 1).
The samples glass transition temperature is around 540°C. Both samples types are first cut in squares (~5mm x
5mm) and annealed, in order to achieve the desired T f, in a vertical furnace, at the temperature TA, during the
necessary time for relaxation (T A=Tf): during 3 hours at 441 and 487°C and 30 minutes at 533, 557, 580, 627,
675 and 721°C. It was checked at 533°C that this annealing time is long enough to have T A=Tf. The samples are
then quenched to room temperature. Fujita [15] mentions that alumino-silicate glasses are very sensitive to the
water vapor in the atmosphere which acts as a catalyst for relaxational process. As a consequence, the samples
are first annealed, then the surface layer affected by the atmosphere is removed by polishing before the IR
spectra monitoring. The polishing quality is very important to improve the reproducibility of the IR reflection
2
spectra. One part of the Embiez archaeological sample is not annealed but just slightly polished and its reflection
spectra collected on both sides.
2.2 Experimental setup
IR spectra are obtained using a Perkin Elmer GX II FTIR with a microscope attachment, taking 1000
scans at a data spacing of 0.5 cm-1 with a beam size approximately of 100 µm x 100 µm for the reflection under
microscope, and with KBr pellets for the macroscopic absorption. In order to compare absorption and reflection
spectra it is usually proposed to make a Kramers-Krönig transformation. However we choose to avoid this
transformation to study our reflection spectra. This transformation is valid for pure specular reflection and
should be done over the full the spectral domain including wavelengths outside our experimental range. A
comparison between the absorption and the Kramers-Krönig transformed reflection spectra has demonstrated us
that in our case this treatment introduces a strong error. As in this work only the main peak position is
considered, reflection spectra are directly compared. The main peak position around 1060 cm -1 is determined by
derivation with the software Grams (Thermo Electron Corporation). Several measurements for the same sample
allowed us to estimate the error in the peak position around 0.26 cm-1.
Raman spectra are obtained using a Raman Renishaw RM1000 spectrometer with a microscopic
attachment (objective X100); a 1800 grooves per mm grating, associated with a “notch” filter for rejection of the
Rayleigh line. An Ar+ ion laser is used for the excitation: (514 nm and 50mW, 6.25mW on the sample). The
signal is collected with a cooled CCD, from 1400 to 300 cm-1, accumulation time 600s. The maxima and
intensities of the peaks are determined by a curve fitting with Gaussians. For the Embiez sample, Raman spectra
are collected at high temperature (250°C), using a Linkam TS1500 stage. The peak position is estimated by
using curve fitting. The error in the Raman peak position can be estimated around 0.27 cm -1.
Raman spectra with an excitation at 325 nm (laser He/Cd, 2mW on the sample) are obtained at room
temperature, by using a LabRAM HR UV (Jobin-Yvon Horiba),with a 600 grooves per mm grating with a
microscopic attachment (objective X40, numerical aperture NA=0.45), associated with Edge filter for rejection
of the Rayleigh line. The signal is collected with a Back Thinned detector, for 2 accumulations, with an
accumulation time of 20s.
3.
Results
3.1 IR spectroscopy
3
An example of IR reflection spectra of the non-annealed Embiez archaeological sample and its synthetic
analogue “GuilB” is given in Fig.1. The main band around 1060 cm-1 can be attributed to asymmetric stretching
vibrations of Si-O bonds in [SiO4] network [14, 17]. The shoulder around 960 cm-1 can be attributed to
symmetric stretching vibrations of Si-O bonds in [SiO4] network [14, 17]. The band at 750 cm-1 can be attributed
to the bending vibrations of the Si-O-Si or Si-O-Al bonds [17]. The peak position evolution near 1060 cm-1 is
plotted versus the fictive temperature in Fig. 2 for the Embiez archaeological sample (squares) and for the
modern analogue GuilB (triangles). Linear regressions fit can be extracted and the equations are respectively:
 cm 1   1052.36  0.00969 * T f C  with a regression coefficient R2 = 0.831 for Embiez
 cm 1   1052.50  0.0186 * T f (C)
with a regression coefficient R2 = 0.9446 for GuilB
For the not-annealed Embiez sample, the grainy side shows a maximum in the reflection peak at
1058.83 cm-1 and the smooth side at 1058.37 cm-1.
3.2 Raman spectroscopy
The Raman spectrum of the analogue GuilB shown in Fig. 3a, is very similar to that obtained for silicates by
other authors [18, 19]. The broad band near 560 cm-1 can be attributed to the vibration of bridging oxygen in
inter-tetrahedral Si-O-Si linkages [18, 20]. The band at 785 cm-1 is assigned to Si–O stretching vibration with a
dominant Si motion [21]. The other bands are related to Si-O stretching vibrations within the tetrahedral network
with a variable number of non-bridging oxygen (NBO): 950 cm-1 for two NBO (Q2) and 1100 cm-1 for one NBO
(Q3) with probably a contribution of the unit with no NBO, fully polymerized (Q 4) [12, 19, 20, 22].
The Raman band at 1100 cm-1 shifts to lower frequencies when the fictive temperature increases (Fig. 4,
triangles). The linear regression fitting the data points is given by the following equation:
 cm 1   1101.55  0.00524 * T f C  with a regression coefficient R² = 0.8075.
The intensity ratio between the Q2 and the Q3 Raman mode, I(Q2)/I(Q3), increases with increasing T f
(Fig. 5). This evolution can be linearly fitted by the equation:
I (Q 2 )
I (Q 3 )
 9.351  0.0109 * T f (C ) with a regression coefficient : R²=0.9505
A direct application of this method to our Embiez archeological sample is not possible. Indeed the
Embiez sample exhibits a strong luminescence, with a maximum at 642 nm under the 514 nm laser excitation.
This luminescence hides the Raman scattering as shown in the inset in fig 3b. Two ways are possible to decrease
the luminescence intensity: with the same excitation wavelength, to work at higher temperature or at room
4
temperature, to change the excitation wavelength [23]. A Linkham TMS1500 heating stage is used to obtain the
Raman spectra at a higher temperature (250°C) in order to decrease the luminescence intensity (Fig 3b).
Although a moderate luminescence still exists under these conditions, the same bands as for the sample GuilB
are observed: the Q3 stretching mode at 1100 cm-1, the Q2 stretching mode at 960 cm-1, the Si-O stretching mode
at 800 cm-1 and the Si-O-Si bending mode at 580 cm-1. The frequency of the Raman band around 1100 cm-1
decreases when Tf increases (Fig. 4, squares). This evolution can be linearly fitted by the equation:
 (cm 1 )  1124.10  0.0263 * T f (C) , with a regression coefficient R² = 0.7342.
In order to decrease the influence of the luminescence, Raman spectra with an excitation at 325 nm, in
UV are monitored. As one can see in Fig3c the luminescence is strongly reducing and Raman bands are
observable even at room temperature. The 1090 cm-1 peak frequency decreases when T f increases (Fig. 6). This
evolution can be linearly fitted by the equation :
ν (cm-1) = 1103.82 – 0.01565 * Tf (°C)
with a regression coefficient R² = 0.7663
Both faces of the non annealed Embiez sample are also studied: the peak position for the smooth side is
1094.88 cm-1 and for the grainy side 1094.54 cm-1.
4.
Discussion
4.1 IR spectroscopy
The vibration centered at 1100 cm-1 for and 1070 cm-1 for different silicate glasses is known to depend
on the average Si-O-Si bond angle θSi-O-Si [24]. An increase in the frequency of the peak reflects an increase of
this angle θSi-O-Si. For SiO2 glass, a decrease of the wave number of the band around 1100 cm-1 is observed when
the fictive temperature increases. Equations obtained in literature are summarized in Table 2. More complex
silicates compositions were also studied: Agarwal and Tomozawa (1995) [14] worked on a soda-lime silicate
glass (SiO2: 71-73%, Na2O: 12-14%, CaO: 10-12%, MgO: 1-4%, Al2O3: 0.5-1.5%) and Fujita, Sakamoto et al.
(2003) [15] on an alumino-silicate glass (SiO2: 70 mol%, Al2O3: 15mol%, Li2O: 10mol%, TiO2, ZrO2: 2-3 mol%
and 2-3 mol% of other alkali and alkaline earth oxide components). The evolution of the 1080 cm -1 band is given
in Table 3.
According to Table 2, for silica glasses, an increase in T f involves a decrease of θSi-O-Si, so a
densification. This phenomena correspond to the anomalous behaviour of silica [24-26]. The alumino-silicate
glass studied by Fujita et al.[15] has the same behaviour as silica. But the soda-lime silicate glass studied by
Agarwal and Tomozawa [14] shows a “normal” behaviour. For our samples, whose composition is very close to
5
the composition of Agarwal and Tomozawa samples [14], a “normal” behaviour is also observed: when Tf
increases, the peak frequency increases, indicating a θSi-O-Si increases and consequently a density decrease. This
difference between normal and anomalous behaviour is observed on different physical properties and is
attributed to structural effects linked to the composition difference [27].
One can note in Tables 2 and 3 that the slopes are small for all the experiments. It means that important
variations in Tf induce small variations in the band position. Small slopes for Embiez and GuilB are also
observed.
The IR reflection results show difference in the peak position at 1060 cm-1 between both sides of the
Embiez archaeological pane. With the calibration curve – position of the 1060 cm-1 peak versus Tf – the value of
the fictive temperature of both sides can be estimated: 668 °C (±27°C) for the grainy side and 620 °C (±27°C)
for the smooth side (stars in the Fig. 2). This difference is small compared to the uncertainty but the same
variation is observed on five different points. This difference of T f is the result of two different thermal histories.
It is an argument in favour of the cast method, with different cooling rate for each side. This physico-chemical
argument is in agreement with the sample observations: two different sides, one smooth, in contact with the
atmosphere, cooled “gently” by convection and one grainy, on the support, more quickly quenched by
conduction.
4.2 Raman spectroscopy
There are fewer articles about the Raman spectra evolution as a function of the sample fictive
temperature than for the IR spectra. Geissberger and Galeener [5] studied the frequency variations with T f for
silica : the ωi frequencies (around 440, 790, 1060 and 1190 cm-1) vary with Tf, in the way of a densification of
the network with increasing Tf. In pure SiO2 and SiO2-GeO2 glasses different slopes with Tf were observed with
the same anomalous behaviour [6, 7, 10, 13]. A decrease in the 1100 cm-1 band position is observed. This band is
a complex one with a main contribution of Q3 , but also with contribution of Q2 for low frequency and of Q4 for
high frequency [12]. So a decrease of the peak position could be interpreted as a decrease of Q 3 tetrahedra and an
increase of Q2 tetrahedra, as observed by Levelut and al. [12] for soda-silicate glass. The population evolution
between Q2 and Q3 tetrahedra could explain the evolution of the complex band at 1100 cm-1: Q2 contribution
increase could induce a shift in the maximum of the 1100 cm-1 complex band. This interpretation is coherent
with the intensity ratio increase, I(Q2)/I(Q3) with increasing Tf (Fig. 5). There are more non-bridging oxygens at
6
high Tf. This result shows a local depolymerisation with the T f increase. This is also coherent with an NMR
study of a soda-lime silicate glass [28].
For the archaeological Embiez sample, due to the strong luminescence excitation at 514 nm at room
temperature, the spectra obtained at high temperature are not precise enough to distinguish a difference in the
1100 cm-1 band position between the two pane faces. Due to those spectra poor quality of those spectra the
intensity ratio could not be estimated as it was done for the GuilB sample. But with the excitation at 325nm, a
calibration curve can be drawn (peak position versus T f (Fig. 6)) and used to determine both sides fictive
temperature on the non-annealed Embiez pane : 592 °C ±17 °C for the grainy side and 571 °C ± 17°C for the
smooth side.
4.3 Comparison between the results obtained by IR and Raman spectroscopy
IR and Raman spectroscopie allow us to determine glasses Tf using calibration curves (peak position
versus Tf). We find that both faces of the archaeological pane don’t have the same T f: the grainy side has a
fictive temperature greater than the smooth one. This is probably the proof of the use of the cast method for
manufacturing this pane. Moreover the absolute value of the fictive temperature of both sides are close with
both spectroscopic methods :
grainy side : 668°C (±27°C) by IR spectroscopy and 592 °C(±17°C) by Raman spectroscopy
smooth side : 620°C (±27°C) by IR spectroscopy and 571 °C(±17°C) by Raman spectroscopy
Both spectroscopies are in a excellent agreement.
5.
Conclusion
We have shown that our silicate glasses have a “normal” behaviour: their density decreases with T f. It
has been demonstrated that IR and Raman spectroscopies can provide information about the fictive temperature
of silicate glasses and calibration curves have been established: IR and Raman bands position versus T f. Through
spectroscopic properties, we demonstrate that the archaeological panes thermal history can be shown. Therefore
it is possible to distinguish between the two antic processes. This method was applied to a piece of Embiez
Roman window glass from the beginning of the III rd century AD and has shown that it was not blown but cast on
a flat surface. It will be soon extended to other archaeological samples, in particular to glasses likely made by the
cylinder-blown method. It will be then possible to establish a chronological evolution of the antic processes.
Acknowledgements
7
We want to acknowledge Allain Guillot (Le Bourg, 24560 Boisse, France) for the elaboration of
modern synthetic analogue of Roman glasses, CECOMO (University Lyon 1) for IR and Raman experimental
facilities, and application laboratory of Jobin Yvon Horiba for the Raman analysis with an excitation at 325 nm.
References
[1] S. Wolf, C. M. Kessler, W. B. Stern and Y. Gerber, Archaeometry 47 (2005) 361
[2] S. D. Fontaine and D. Foy, in: Id'antique, Bavay (France), 2005, p.15
[3] F. Dell'Acqua, in: Les fenêtres vitrées dans l'Antiquité romaine, Florence-Milan, 2006, p.111
[4] L. Raffaëlly, B. Champagnon and F. Lesage, to be published (2007)
[5] A. E. Geissberger and F. L. Galeener, Phys. Rev. B 28 (1983) 3266
[6] B. Champagnon, C. Chemarin, E. Duval and R. L. Parc, J. Non-Cryst. Solids 274 (2000) 81
[7] R. LeParc, B. Champagnon, P. Guenot and S. Dubois, J. Non-Cryst. Solids 293-295 (2001) 366
[8] M. Tomozawa, J.-W. Hong and S.-R. Ryu, J. Non-Cryst. Solids 351 (2005) 1054
[9] A. Agarwal, K. M. Davis and M. Tomozawa, J. Non-Cryst. Solids 185 (1995) 191
[10] R. LeParc, PhD thesis, 2002, Université Claude Bernard, Université de Lyon (France)
[11] Y. L. Peng, A. Agarwal, M. Tomozawa and T. A. Blanchet, J. Non-Cryst. Solids 217 (1997) 272
[12] C. Levelut, R. L. Parc, A. Faivre and B. Champagnon, J. Non-Cryst. Solids 352 (2006) 4495
[13] V. Martinez, R. L. Parc, C. Martinet and B. Champagnon, Opt. Mater. 24 (2003) 59
[14] A. Agarwal and M. Tomozawa, J. Am. Ceram. Soc. 78 (1995) 827
[15] S. Fujita, A. Sakamoto and M. Tomozawa, J. Non-Cryst. Solids 330 (2003) 252
[16] S. A. Fontaine and D. Foy, in: Une cargaison fragile : les vitres de l'épave ouest Embiez 1, 2005, p.38
[17] L.-G. Hwa, S.-L. Hwang and L.-C. Liu, J. Non-Cryst. Solids 238 (1998) 193
[18] P. McMillan and B. Piriou, Bull. Minéral. 106 (1983) 57
[19] T. Furukawa, K. E. Fox and W. B. White, J. Chem. Phys. 75 (1981) 3226
[20] C. I. Merzbacher and W. B. White, J. Non-Cryst. Solids 130 (1991) 18
[21] D. W. Matson, S. K. Sharma and J. A. Philpotts, J. Non-Cryst. Solids 58 (1983) 323
[22] P. Colomban, J. Non-Cryst. Solids 323 (2003) 180
[23] L. Raffaëlly and B. Champagnon, to be published, J. Raman Spec. (2007)
[24] A. Agarwal and M. Tomozawa, J. Non-Cryst. Solids 209 (1997) 166
[25] S. Sen, R. L. Andrus, D. E. Backer and M. T. Murtagh, Phys. Rev. Lett. 93 (2004) 125902
[26] B. Champagnon, V. Martinez, C. Martinet, R. LeParc and C. Levelut, Philos. Mag. 87 (2007) 691
[27] V. Bogdanov, Golovnev, Smerdin, Solovyev, Ananev and Champagnon, NCM10 Congress Prague (2006)
[28] T. J. Kiczenski, L.-S. Du and J. Stebbins, J. Non-Cryst. Solids 351 (2005) 3571
[29] V. Martinez, PhD thesis, 2004, Université Claude Bernard, Université de Lyon (France)
Figure captions
Fig. 1 : IR reflection spectra of the non-annealed Embiez archaeological sample (solid line) and its modern nonannealed analogue “GuilB” (dotted line)
Fig. 2 : 1060 cm-1 peak position versus fictive temperature for Embiez (squares) and GuilB (triangles) annealed
samples and for the two sides of the non-annealed Embiez sample (stars)
Fig. 3 : Raman spectra of (a) the non-annealed modern synthetic analogue GuilB, (b) the non-annealed Embiez
archaeological sample at 250°C and room temperature (inset) (excitation: 514 nm) and (c) the non-annealed
Embiez sample at room temperature (excitation: 325 nm)
Fig. 4 : Raman band position around 1100 cm-1 as a function of Tf, for Embiez at 250°C (squares) and GuilB
(triangle) samples
Fig. 5 : Evolution of the intensity ratio of the Q 2/ Q3 bands in the Raman spectrum of GuilB versus Tf
8
Fig. 6 : Raman band position around 1100 cm-1 as a function of Tf, for Embiez annealed samples (squares) and
for the two sides of the non-annealed Embiez sample (stars), with the 325 nm excitation
Wt %
Samples
Embiez
(X-Ray Fluorescence
measurements)
Synthetic glass GuilB
(Nominal composition)
SiO2
Na2O
Al2O3
CaO
Fe2O3
K2O
MgO
P2O5
MnO
69.4
16.8
2.5
7.8
0.5
0.6
0.6
0.1
0.7
70.6
19.4
2.6
7.4
Table 1 : Glass compositions of the Embiez archaeological sample and a modern synthetic analogue
References
Tomozawa et al
[8]
Agarwal et al
[9]
LeParc [10]
Martinez [29]
Peng et al [11]
Equations
ν (cm-1), Tf (°C)
Tested domain Tf
(°C)
Wave number domain
(cm-1)
ν = 1130.69 – 0.00653 * Tf
1000-1250
1098.5 - 1100.1
ν = 1129.38-0.00567 *Tf
950-1400
1121.4-1124
ν = 1131-0.0069 *Tf
ν = 1131.7 – 0.011 *Tf
ν = 1129.47 – 0.00565 *Tf
1100-1400
950-1300
1100-1300
1121.3-1123.4
1117.4-1121.2
1122.1-1123.3
Table 2 : Evolution of the position of the IR reflection band around 1100 cm-1 with Tf for silica glasses
References
Agarwal and
Tomozawa [14]
Fujita et al
[15]
this study
Embiez
this study
GuilB
Equations
ν (cm-1), Tf (°C)
Tested domain
Tf (°C)
Wave number domain
(cm-1)
ν = 1044 + 0.0263 * Tf
425-575
1055.2-1059.1
ν = 1089.39-0.0105 * Tf
600-750
1081.5-1082.6
ν = 1052.36 + 0.00969 * Tf
440-720
1057.1 – 1059.9
ν = 1052.5 + 0 .0186 * Tf
530-720
1062.8 – 1066.2
-1
Table 3 : Evolution of the position of the IR reflection band around 1100 cm with Tf for silicate glasses
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