Vazquez et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-018-0229-y(2018) 5:75

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open AccessInfluence of substrate and temperature on
the crystallization of KNO3 droplets studied
by infrared thermography
Patricia Vazquez* , Lucas Sartor and Céline Thomachot-Schneider

Abstract
Salt crystallization is a major agent of deterioration in buildings, especially important when belonging to a city’s
cultural heritage. The study of this process is therefore essential to understand the decay evolution and to establish
a correct preservation protocol to avoid future interventions. KNO3 is a salt found commonly associated to othersalts in weathered areas of buildings. In order to recognize the presence of this salt without sampling, thecrystallization of KNO3 was assessed by means of a new non-destructive tool, the infrared thermography. The
supersaturation necessary for the nucleation of crystals was obtained by evaporation of solution droplets thatallowed the recording of all the processes with an infrared thermography camera. The droplets were tested at
different temperatures by placing them on an electric plate at 20 °C and 50 °C to simulate real conditions ofbuilding stones placed outdoors and also at 75 °C to emulate extreme situations of stones in arid environments.
The droplets evaporated from four different substrates all of them with different interstitial properties: a black 3M
tape frequently used as a reference substrate in similar works, a glass slide, and a marble plate with two different
artificial finishes, polished and sawed. Thus, the contact angle was around 30° on the glass substrate, over 60° on
the 3M tape and the polished marble, and close to 90° in the case of the sawed marble. Results highlighted theusefulness of the infrared thermography in the study of crystallization processes. The exothermic reaction
associated to crystallization was too low to be observed, and only punctual heat release spots were recorded.
However, a creeping process that creates efflorescence crystallization was clearly observed as an intermittent
decrease in the thermographic signal preferentially at high temperatures. The contact angle of the droplet with thesurface played an important role in the crystallization type (crystal shape, location, spreading length) whencomparing different substrates (i.e., glass and black tape). The different test temperatures revealed different
behaviors related to the substrate. The solution spread more at 20 °C on the black tape creating efflorescences
while at 50 °C this kind of crystals formed on the stone with both finishes. At 75 °C, the solution spread uniformly
over the surface of the glass slide while crystals grew on the top of preexisting ones for the three other substrates
with higher contact angle.
Keywords: Infrared thermography, Salt crystallization, Potassium nitrate, Creeping, Efflorescence, Evaporation* Correspondence: patricia.vazquez@univ-reims.fr
GEGENAA EA 3795, University of Reims Champagne – Ardenne, 2, Esplanade
Roland Garros, 51100 Reims, France© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.

(2018) 5:75

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Introduction
The understanding of salt behavior is an essential topic
in the past and current research due to their contribution in several phenomena affecting everyday life. Thus,
the knowledge of salt crystallization and phase change
are essential for many fields such as catalysis, energy
storage, food research, building stability, and durability
and artwork conservation (Telkes 1980; Barta et al.
1986; Graber et al. 1999; Benavente et al. 2004; Aquilano
et al. 2016). Several salts such as sodium chloride, sodium sulfate, magnesium sulfate, or gypsum are the center of current researches due to their interest for thesociety in the mentioned fields. Nevertheless, the intricate processes associated to their formation make necessary the use of complex and high-resolution techniques
to achieve further knowledge (Hamilton and Menzies
2010; Saidov et al. 2012; Derluyn et al. 2014; Vázquez etal. 2015). Nitrates are associated to the damage observedin cultural heritage although their studies are less spread(Maguregui et al. 2008). Regarding the current environment and the salt distribution in stone buildings and artworks, nitrate sources are related to pollution(Maguregui et al. 2008; Gibeaux et al. 2018) as industry
and diesel shoots affecting mainly areas of high traffic
concentration (Lebret et al. 2000). Another nitratesource in buildings is the capillary rising water, especiallyin an agricultural environment, with fertilizers and animal fecal rests rich in this substance (Curt et al. 2004).
Due to the high solubility of nitrates and the fact that
KNO3 crystallizes in high relative humidity (up to 95%
at 20 °C and up to 75% at 75 °C), this salt can be found
not only in the surface but also within the porous network, independently of the total porosity, the pore size,and distribution in the rocks. Even very compact stones
can be affected by the damage caused by nitrate
crystallization, as the case of basalt, granite, or marble(Dei et al. 1999).
The thermodynamic conditions vary in relation to theporous media. Crystallization of potassium nitrate inporous stones results in an exothermic reaction, whilethermal reaction was not observed in calcareous compacted stones such as marble (Dei et al. 1999). Even
within porous stones, the thermal behavior differs fromthe porous network. The study on cooling solutions also
reported temperature variations during crystallization(Barta et al. 1986). Therefore, the study of single droplets
becomes necessary in order to understand the
crystallization processes without medium constraints
and in stable conditions.
The use of infrared thermography (IRT) has been widelyadopted over the last several years in many fields such as
medicine, chemistry, and security, and it is a basic tool incivil engineering which works even for those requiring
special attention as in the case of cultural heritage due toits non-destructive character (Avdelidis and Moropoulou
2004; Bodnar et al. 2013; Bagavathiappan et al. 2013). Oneof the last applications of this technique was laboratory
detection of moisture and salts (Gomez-Heras et al. 2013;
Thomachot-Schneider et al. 2016; Lelarge et al. 2017) andthe study of salt crystallization from evaporation droplets(Parsa et al. 2015; Vázquez et al. 2014; Vázquez et al.
2015; Vazquez et al. 2018; Sartor et al. 2017) and also inbuildings of cultural heritage (Lerma et al. 2014).
Vázquez et al. (2015) presented the study by IRT of sodium chloride from an evaporating droplet, with the differentiation of three phases in relation to thethermosignal variation. Some chemical processes trigger
heat exchange reactions such as water evaporation(endothermic reaction) or crystallization (exothermic reaction). Nevertheless, this energy is not always strong
enough to be detected by the IRT camera. The
crystallization from a droplet entails a variation in shapeand consequently in emissivity which allows observing
other phenomena of the crystallization process (Vázquez
et al. 2014; Vázquez et al. 2015; Vazquez et al. 2018).
The variation in shape during evaporation is strongly related to the interface droplet substrate and may condition the evaporation and crystallization process(Shahidzadeh-Bonn et al. 2008).
The aim of this research is to deepen the understanding of the crystallization process of KNO3, which conducts material deterioration of cultural heritages
preferentially in urban areas. For this purpose, the evaporation of single droplets was assessed by IRT at different temperatures and on different substrates.

Vazquez et al. Progress in Earth and Planetary Science

Methods/experimental
The experimental setup is shown in Fig. 1. In this study,
the crystallization of KNO3 droplets was analyzed bymeans of a FLIR SC655 long-wave infrared thermography camera operating in the wavelengths 7.5–14 μm
and with a detection temperature ranging from − 40 to
150 °C with a sensitivity of 0.1 °C. The detector is an uncooled array of microbolometers. The image size is
640 × 480 pixels, and the noise signal is approximately
40 mK. As in previous works (Vázquez et al. 2015), therecorded signal is called thermosignal (TS). The TS depends on the temperature and emissivity and isexpressed in isothermal units (IU). All measurements
were undertaken using the passive IRT mode, i.e.,
without external changing stimulus. All the processes
experimented by the droplets were recorded at constant temperature. Prior tests concluded that the optimal recording speed (frame rate) was one image persecond throughout the test for the conditions used.
The images were treated and analyzed with the
ResearchIR software (FLIR).

Vazquez et al. Progress in Earth and Planetary Science(2018) 5:75

Fig. 1 Experimental setup

The supersaturation needed for the crystallization was
obtained by the evaporation of the solvent. Six droplets
were dropped in a determinate substrate with a micropipette (5 μL) in each test. KNO3 solutions were prepared with distilled water at saturations of 80% at threedifferent temperatures of 20 °C, 50 °C, and 75 °C (purityof > 99%, Sigma Aldrich). These solutions were preparedat the same temperature than the substrates, and the
80% saturation was chosen to avoid the possible nucleation by cooling during the process of placing the droplet on the support.
Twelve different tests were conducted combining threetemperatures of 20 °C, 50 °C, and 75 °C and four substrates: industrial black tape (3M), microscopy glass
slide, polished Amarillo Triana marble, and sawed Amarillo Triana marble. The black adhesive tape was stuck
on a microscopy glass slide, and the droplets were
dropped on it. This material served as a reference (Vázquez et al. 2015) since its emissivity was determined tobe 0.96 in the wavelength analyzed by the camera. On
the other three substrates, a small piece of this 3M tape
was also stuck to serve as reference point. The glass
slide was the one used to make microscope thin sections. The Amarillo Triana marble is a yellow marble
with < 1% porosity (Vázquez et al. 2013). Samples were2 × 2 × 0.1 mm, with the same thickness than the glass
slide for glass and 3M tests and showed two artificial

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finishes (saw and polish). All the supports were cleaned
with alcohol before each test to minimize the presenceof impurities.
The use of four different substrates, among them alsostone, had the purpose of determining the differences insolution spreading and crystallization processes between
reference materials (black tape and glass) and real stone
used in buildings (marble). The different surface roughness and the character more or less hydrophilic orhydrophobic of the materials lead to a different contact
angle between the droplet and the substrate. This angle
seems to condition the crystallization process and the
crystal patterns (Shahidzadeh-Bonn et al. 2008). For thatreason, the contact angle between the droplets and thefour substrates was measured at room conditions (20 °C)
on 10 droplets for each substrate.
Test temperatures were set constant with the help ofcooling plate Tetech CP-061 with a precision of 0.01 °C.
The substrates were placed on the cooling plate until
they reached the equilibrium with the environment at
the set temperature (20 °C, 50 °C, and 75 °C). The sample temperature was measured with thermocouples witha precision of 0.05 °C. In the experimental setup, therisks associated to environmental variations were minimized (control of temperature, humidity, and light).
Nevertheless, some variables were introduced due to thehuman factor of some tasks such as the deposition of
the droplets.
Once the droplets crystallized, the crystal morphology
and distribution were assessed by optical microscopy
with the aid of an Olympus SZH-ILLB stereomicroscopewith a digital Tri-CCD camera (Sony, DXP 930) andimage analysis software Saisam from Microvision
Instruments.

Results
Contact angle measurements

Average and standard deviation of 10 contact angle measurements are shown in Table 1.
The lowest value corresponded to the glass support,i.e., the most hydrophilic, with a wide difference with therest of materials. The black tape, used as reference insome related studies (Vázquez et al. 2014, Vázquez et al.
2015), showed higher values but slightly lower than themarble whatever its surface finish. Dei et al. (1999)
Table 1 Average and standard deviation of contact angle of
KNO3 droplets in four different supports. N = 10
SupportAverage

St. Dev.

Black tape

68

3

Glass

33

3

Saw marble

89

9

Polished marble

74

5

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measured contact angles of 30° for sandstones and 50°
for calcareous stones. That can be interpreted as theblack tape having similar values to a slightly porous
stone. The sawed sample showed an almost verticalangle with the support while the polished marble withsofter and flatter surface presented lower values.

edge, zone B appeared deformed and its dimension was
difficult to observe and measure. The efflorescences
spread through the support at low temperatures while
they grew preferentially in height at high temperatures
except for the glass. Evaporation was faster at 50 °C and
75 °C and produced the crystallization of efflorescenceson the top of pre-existent crystals (zone B). The halo
was hardly visible at low temperatures as the residual solution precipitated as efflorescences while at high temperatures the evaporation was too fast to produce visible
crystals.
Regarding the substrate, the black tape showed themost homogeneous precipitations while in the glass support the solution spread considerably through the surface, which made difficult to recognize the crystallization
pattern, even impossible at 75 °C. The two stone finishes
showed similar precipitation shapes, slightly more spreadin the polished finish. In both cases, the center ring
looked deformed with respect to the black tape and thestone color made it difficult in some occasions to observe and measure the halo.

Vazquez et al. Progress in Earth and Planetary Science

Droplet shape

After crystallization, four different zones were detected.
Figure 2 shows the thermal image of the droplet and thevisible photograph with the different zones. From the inside to outside, the first one was the inner circle (A), in
which the crystals were well-formed due to the longer
permanence of the solution. They showed mainly acicular or needle shape. This habitus is typical when salt
crystallizes in a non-porous system (Dei et al. 1999) andis known as the stable phase of KNO3 which in this casewere all the supports. The second visible zone corresponded to the liquid droplet edge, and in this area (B),the crystals precipitated as a crown of higher relief thatsurrounds the crystals. The third area was the efflorescence area (C) that exhibited visible crystals with variable shape formed by the solution spreading out of thedroplet edge. The last zone, not always observable, corresponded to the halo (D), in which no crystals were visible through a binocular microscope but show a shadowthat indicated crystal formation. The halo spread further
than the efflorescences.
The dimensions of these four zones have been measured to compare the droplet behavior related to the different substrates and temperatures (Fig. 3). The numberof measurements was variable in relation to the droplet
though a minimum of three values was required for eachzone in each of the six droplets. The results are shownin Table 2.
The tests at different temperatures revealed variations
in crystal shape and spreading. As observed in Figure 3
and corroborated by the results in Table 2, at low temperatures, the crystals in the droplet center (A) werelonger. Due to the big size of these crystals and the factthat the rest of the solution tended to flow out of theabThermal response

The image of the droplets just after their deposition revealed a lower TS than the support (Fig. 2a). These differences were due to two factors: temperature andemissivity. Since the laboratory room was set at 20 °C, inthe test at 20 °C, no temperature variations existed between the substrates, the droplet edge, and the droplet
top. Thus, the lower signal emitted by the droplet wasdue to emissivity variations. These variations could be
due to the shape effect, for which emissions with angles
higher than 45 °C were not received by the camera, andthus, the total signal was lower than a flat shape solution. During the test at 50 °C and 75 °C, the substrate
was hotter than the environment and this introduced atemperature gradient within the droplet in which the
top had lower temperature than the bottom and theedges.
During the process of crystallization from a droplet,different phases could be determined as observed bycFig. 2 Droplets observed by IRT and binocular microscope. (a) Infrared image of a droplet at the beginning of the test. (b) Infrared image of thesame droplet after complete evaporation. (c) Visual image of the evaporated droplet with the four studied zones

Vazquez et al. Progress in Earth and Planetary Science(2018) 5:75

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Fig. 3 Evaporated droplets. Pictures of a representative evaporated droplet for each substrate and temperature

IRT. As explained in Vázquez et al. 2015, the thermosignal
differences between the droplet and the reference black
tape profiles (ΔTS) could be divided into three phases:
Phase I: Homogeneous evaporation of the droplet. The
difference of TS between the droplet and the substrate
reduced homogeneously and was more evident in thedroplet center (Fig. 4a). The droplet became flatter,
reducing the emissivity losses, and also thinner, reducing
the temperature gradient and approaching the support

temperatures. During this phase, some nucleation in thecenter of the droplet could occur, although the TS
emitted was too low to be observed by the IRT.
Phase II: Crystallization. The crystals’ shape became
visible with or without visible thermal reactions. The
TS was still slightly lower than the support due mainly
to the relief (Fig. 4) and allows to observe the shapeoccasionally.
Phase III: Creeping. This phase corresponded toefflorescence growth, and it was easily identified by an

Table 2 Measurements carried out in the four zones of the droplets. Average values from six droplets with at least threemeasurements for zone and droplet
Black tape (mm)Glass (mm)Sawed marble (mm)Polished marble (mm)

Zone

20 °C

50 °C

75 °C

20 °C

50 °C

75 °C

20 °C

50 °C

75 °C

20 °C

50 °C

75 °C

A

2.2

1.2

0.6

3.3

1.0

/

1.6

0.8

/

2.1

1.1

/

B

3.7

3.9

3.6

6.6

2.8*

/

5.8

3.2

2.8

4.8

4.1*

2.6

C

1.6

0.8

1.1

2.2*

1.7

11.4*

/

0.9

0.8

2.4

2.1

0.6

D

0.1*

1.0

0.8

0.2*

0.4*

1.2*

/

/

/

0.5*

/

1.6

A, average of acicular crystals; B, circle diameter; C, average of efflorescence ratio; D, average of halo ratio; * not visible in all the dropletsVazquez et al. Progress in Earth and Planetary Science(2018) 5:75

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abFig. 4 Representative profiles of a droplet evaporation measured with IRT. a IRT profile measured in the droplet center (zone A). b IRT profile
measured out of the droplet edge (zone C)intermittent decrease of the TS. Depending on the salt
and the temperature, this process may vary in intensityand duration.
Depending on where the TS was recorded, the orderof phases may be different from the succession of phase
described above for the center of the droplet. For example, in the edge of efflorescence area (zone B), phase I
could be missing or creeping (phase III) could occur before crystallization (phase II) (Fig. 4b).
Regarding the zones corresponding to the efflorescence (zone C) and halo area (zone D), at the beginningof the evaporation, the measurement point was placedoutside the droplet, on the substrate, and ΔTS was equal
or close to zero. When the solution reached the measurement point, the TS became negative since the signal
was lower than the black tape. Then, the thermosignal
varied. It could show creeping (phase III), an evaporation of the solution ΔTS = 0, a crystallization ΔTS < 0,or even the three processes.

Discussion
The differences in the final shape of the crystallized
droplets in relation to the temperature and the support
indicated that the formation processes were also different (Gomez-Heras and Fort 2007; Shahidzadeh-Bonn etal. 2008). The thermal response probed these behaviors.

The thermal response was similar for the six dropletsof each test. The representative profiles obtained fromeach temperature, on each support, and for three zones(center, edge, and halo) were drawn in Figs. 5, 6, and 7.
Concerning the profiles measured in the droplet center,the first remark was focused on the starting point. As mentioned above, the top of the droplet had a lower TS than
the reference material. This difference was higher with hotter temperature due mainly to the temperature gradient inside the droplet. In all the cases, two stages could beobserved in the homogeneous evaporation part (phase I)
that corresponded to the slope from the initial point to thestabilization. Within this line, there was a first part in which
the ΔTS decreased uniformly (slope ascendant) that corresponded to the homogeneous evaporation of the solution
with time. This was followed by the second stage expressed
as a sudden decrease (slope ascended almost vertically)followed by a horizontal stabilization, which indicated a
final evaporation leading to a crystal (ΔTS < 0) or the substrate (ΔTS = 0). In some of the cases, the ΔTS increased
again after a great time interval (slope descendant in Fig. 5,
polished). That could be due to the intrusion of a growing
crystal in the measuring point in which the solution evaporated and the measurement was done on the support until
the intrusion. This phenomenon was not observed at 20 °C
due to the long duration of the test in these conditions but
it was clearly observed in the 50 °C and 75 °C tests.

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Fig. 5 IRT profiles of each droplet zone at 20 °C for each substrate

The efflorescence and halo areas were sometimes easier to observe on the IRT images than on the visible
light ones as in the case of marbles. However, in the IRT
image, when the halo was very thin, it could be confounded with the efflorescence area due to energy irradiance of the signal. The thermosignal profiles for theedge and halo measurement points varied in relation totemperature. At 20 °C, the profiles were more or lessstable with small irregularities that indicated the arrivalof the solution and the crystallization of a layer of crystals that did not interfere too much in the TS. At 50 °C
and 75 °C, the signals’ amplitude was wider and gave
place to interpretation. As in the droplet center, thedifferences of ΔTS were higher at 75 °C due to thetemperature change from the environment to the support. The TS could start in the substrate or in the edgeof the droplet since the heat emission close to theedge made it difficult to delimitate the real threshold.
If the measurement point was placed on the support(ΔTS = 0), a descent of the profile line was measured
due to the arrival of the solution. Then, a fast increase
with or without previous creeping was observed until
stabilization below ΔTS = 0, which indicated crystal
formation.

Regarding temperature, at 20 °C, the TS amplitude
was very small and the different phases were less evident. However, phases I and II were recognizable. No
creeping was observed at this temperature.
At 50 °C, the droplets tested on the black tape showed
clearly all the phases described above, and both stones
showed similar behavior despite their different finish
and contact angle. The droplets tested on the glass
had an erratic behavior explained by the low contact
angle and the wide spread of the solution. A flash
that corresponded to crystallization energy release
was observed punctually at 50 °C; however, due thelack of repeatability in this study, no information wasprovided.
For all the droplet measured points at 75 °C, thestabilization was not the final stage. The reactions continued in the whole droplet due to the ascension of thesolution and the precipitation on the top of preexistent
crystals (Vázquez et al. 2015). Due to that, the measuring point can be stable on a crystal during a time interval followed by a new decrease when a new crystal
precipitated on it. Thus, in the black tape and the glass,more than one phenomenon of crystallization was measured as confirmed by three steps in the descendingVazquez et al. Progress in Earth and Planetary Science(2018) 5:75

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Fig. 6 IRT profiles of each droplet zone at 50 °C for each substrateslope. The halo TS followed the same pattern than theefflorescence, also with some associated creeping.
Regarding the substrate, the glass and the polishedmarble had a hydrophilic surface that entailed a higher
spreading of the solution. Due to that, creeping was observed even in the droplet center, with crystallization ofa very thin film of solution.
The most important observation in the crystallization of
KNO3 was the presence of a large and fast evaporation
stage in most of the droplets, independent of the zones
and the temperatures. Before stabilization, with or without
previous creeping, a final decrease in the slope followed
by a rapid increase preceded the crystal formation. Thisevaporation was not localized punctually but experimented by the whole droplet. This phenomenon was not observed in other salts (Vázquez et al. 2015, Sartor et al.
2017, Vazquez et al. 2018) and requires further research.
Another difference regarding other salts was thevisualization of the creeping in the outer efflorescences
and the halo. In other salts such as NaCl (Vázquez et al.
2015), the creeping phenomenon was observed only athigh temperatures, when efflorescences grow on the topof preexistent crystals on the droplet edge. In KNO3
droplets, the creeping was clearly observed and strong
TS was measured on the spread solution out of thedroplet and also in the halo zone, which may indicatethat the energy absorption for the evaporation needed toform the crystals is bigger than for other salts.

Conclusions
IRT probed to be an efficient tool to study salt
crystallization. The study of KNO3 evaporation at different temperatures and substrates revealed essential information to understand this salt behavior. Thus, thethermal response of salt crystallization could be studiedin situ and, thus, according to the substrate type (porosity, artificial finish, treatments), to determine the type ofsalt that appeared on the stone.
For KNO3, the thermosignal and thermal phenomena
were more intense with higher temperatures. The different phases of crystallization, i.e., homogeneous evaporation, crystal formation, and creeping, were clearlyobserved. The latter was measured from the solutionthat spread out from the droplet edge. In addition, a big
evaporation before signal stabilization was observed in
the whole droplet for a representative number of samples and for all temperatures and substrates. This evaporation phenomenon can be considered as a special
thermal signature of KNO3 that will allow to recognize
this salt crystallization in situ. Efflorescences were foundout of the edge for all the droplets but also on the top of
preexistent crystals for the high-temperature tests. The

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Fig. 7 IRT profiles of each droplet zone at 75 °C for each substrateheat release due to crystallization was punctually observed though it was not repeatable.
The contact angle of the droplet with the surface
played an important role especially if data are compared
to contrasted substrates (i.e., glass and black tape).
Among narrow contact angles (i.e., black tape and marble), the crystallization was more dependent on the substrate properties than on the angle values.
Temperature revealed different behaviors related tothe substrate. The solution spread more at 20 °C in theblack tape that led to efflorescence apparition while at
50 °C they were visible on the stone surfaces. At 75 °C,
crystals grew on the top of preexistent ones for the three
supports with a higher contact angle, while for the glass
the solution spread uniformly through the surface.
The study of the KNO3 thermal response revealed thatthe crystallization as efflorescence and the crystal
spreading through the surface, one of the main problems
related to this salt in stone building decay, depends on
the specific surface, the stone properties, and thetemperature. Low temperature entails a wider spreadingof the efflorescences while higher temperature leads tothicker and concentrated ones.

Authors’ information
PV PhD is an associate Professor at the University of Reims Champagne –Ardenne (France) since 2012. Her research topic is the understanding of thestone deterioration processes at a grain scale, and one of the main decay
agents is salt crystallization. In 2013, she got a project to develop IRT in thedetection of salt crystallization processes and the consequent stone
deterioration. She already published and submitted works about sodium
chloride and sodium sulfate.

Abbreviations
IRT: Infrared thermography; TS: Thermosignal

Competing interests
The authors declare that they have no competing interests.

Acknowledgements
PV and CS gratefully acknowledge the grant from PEPS to attend the JpGU
symposium 2017 held at Tokyo, Japan. LS gratefully acknowledges the travel
grant from American Geoscience Union to attend the JpGU symposium2017 held at Tokyo, Japan.
Funding
This work was supported by the University of Reims Champagne – Ardenne.
Availability of data and materials
Data sharing is not applicable to this article as no datasets were generated
or analyzed during the current study.
Authors’ contributions
PV proposed the topic and conceived and designed the study. LS carriedout the experimental study. PV and LS analyzed the data and helped in theirinterpretation. CS collaborated with the corresponding author in theconstruction of the manuscript. All authors read and approved the final
manuscript.

Vazquez et al. Progress in Earth and Planetary Science(2018) 5:75

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.
Received: 9 January 2018 Accepted: 10 October 2018

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