Cyril Szopa

Caroline Freissinet

A Buch

Maëva Millan

B Sutter

Michel Cabane

P Glavin

R Navarro-Gonzalez

P M Mahaffy

Gale Crater C Szopa1

C Freissinet1

A Buch3

M Millan4

B Sutter6

M Cabane1

D P Glavin4

R Navarro-Gonzalez7

P Mahaffy4

Analysis of Organic Molecules with Pyrolysis Gas Chromatography Mass Spectrometry in the Presence of Chlorides: Possible Implications for Measurements Performed with the SAM Experiment in Gale Crater

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Introduction: Results from Checam, SAM, and APXS instruments onboard the Curiosity rover indicate that chlorides are present on Mars at Gale Crater, [1,2]. Even if no evaporitic layer of chlorides was found, these chemical species could represent a non-negligible fraction of chlorine bearing inorganic molecules present at the near surface of the crater floor. Laboratory analog studies have demonstrated that oxychlorine phases in Gale Crater material could serve as an O2 and HCl source that causes the oxidation and chlorination of organic molecules present in samples analyzed by pyrolysis. SAM analysis detected chlorine bearing organic molecules in the Cumberland sample pyrolyzed at low temperatures (<400°C) [3,4]. This demonstrated that salts can interact with organic molecules present in a sample analyzed by pyrolysis. Total Cl from APXS analysis is always greater than SAM detected total Cl from oxychlorine phases indicating that chlorides likely dominate Cl in the Gale Crate4r materials. The goal of this work was to evaluate Mars analog chloride reactions with organic molecules to determine if the SAM detected chlorinated organics would form.

Moreover, other studies showed that other salts, as sulfates, can play a role of protection against the effect of oxychlorines during the pyrolysis [5,6,4]. Indeed, those salts start decomposing at higher temperatures than oxychlorines. Thus, organic molecules embedded in the salt matrix can be isolated from the gases released at low temperatures, preventing their reaction and alteration. Then, their protective role toward the effect of oxychlorine can be a key for detecting organic molecules indigenous to Mars.

The understanding of those reaction could also be a key to understand the organic molecule detected by SAM.

For these reasons, our team performed a systematic study in the laboratory of the possible influence of different chlorides on the analysis and detection of organic molecules. Then we performed pyrolysis gas chromatography mass spectrometry analysis, in order to assess their possible role in the analyses performed with the SAM experiment in Gale crater, and potentially future in situ experiments that would use such an analytical technique.

Experimental procedure: NaCl and MgCl2 were used as the reference chlorides. Their thermal behavior was studied using thermal gravimetry (TG) and evolved gas analysis (EGA). More particularly their thermal decomposition was characterized as a function of the temperature up to about 900°C. Both chloride was then mixed with different organic molecules of interest for study of the Mars surface, i.e. polyaromatic hydrocarbons, amino acids, and carboxylic acids. Each mixture was submitted to two different pyrolytic treatments : i. a SAM like pyrolysis heating the sample from the ambient temperature up to 850°C at a 35°C.min-1 rate; ii. a flash pyrolysis at 850°C. The products of pyrolysis were analyzed using gas chromatography mass spectrometry (GCMS) and compared.

Implications: The products of pyrolysis identified are compared to those detected with the SAM experiment. In particular, an emphasis will be done on the chlorinated organic molecules identified with SAM when analyzing the Cumberland sample collected in the Yellow Knife bay area early in the mission. Conclusions about the possible influence of chlorides on GCMS analyses of Mars surface samples will be done.

2219.pdf 51st Lunar and Planetary Science Conference (2020)

Acknowledgments: NASA Mars Exploration Program supported for the development and operations of SAM. The French National Space Agency, the Centre National d'Etudes Spatiales (CNES), supported the development and operations of the SAM gas chromatograph.


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Inverse problem identification of thickness and viscoelastic properties of a film deposit by scanning acoustic microscopy

Pooyan Manoochehrnia, Pierre Maréchal, Damien Leduc, Ech-Cherif

El-Kettani Mounsif

To cite this version:

Pooyan Inverse problem identification of thickness and viscoelastic properties of a film deposit by scanning acoustic microscopy

Pooyan Manoochehrnia 1 , Pierre Marechal 1 , Damien Leduc 1 , Mounsif Ech-Cherif El-Kettani 1 1 University of Le Havre Normandie -LOMC, UMR 6294 CNRS, France Afternoon Session III, January 18, 2024, 14:30 -15:30

Solving an inverse problem has been always a matter of importance. In this study, the question focuses on finding acoustic parameters of the structure and the transducer thanks to a numerical implementation of a physical model matching with the experimental ultrasonic response. In this paper, it has been tried to apply a step-by-step matching methodology, that isolates important characteristics of the ultrasonic signal and matches the model parameters (individually or as linked coefficients) with experimental signal.

A 85 µm thick layer of epoxy resin has been deposited on a glass plate of 1.66 mm thick to form a twolayered structure. The structure is characterized using scanning acoustic microscope (SAM) equipped with a plane wave transducer with a central frequency of 50 MHz. The Debye series model (DSM) has been chosen for its efficiency to calculate the reflection coefficient of the structure as a function of the frequency. This reflection spectrum is then multiplied by the Gaussian envelope of the transducer's response. Therefore, the DSM is run with 11 different parameters and its result is then compared to experimental signal.

A step-by-step, reproducible and physically consistent method has been carried out to match parameters of DSM model with experimental signal. The first set of parameters includes the central frequency (f0), the relative bandwidth, as well as the phase-shift of the Transducer Gaussian envelope. The second set of parameters includes material acoustic parameters notably thickness (Th), longitudinal velocity (CL), density and attenuation, both for deposit layer and substrate layer. Varying these 11 parameters, results in a quantifiable mismatch between the model and the experiment. The visual form of the resulting signal, as well as the physical consistency of parameters and the value of mismatch error, are indicators of the way ahead.

The identification consists in isolating the first reflection echo on the substrate, then identifying each surrounding echoes and fitting each of those methodically. The first step of the inverse problem concerns the transducer's response, which is modelled by the central frequency (f0) and relative bandwidth ( ), corresponding (in a first approach in the time domain) to the pseudo-period and echo duration. In addition, the phase shift ( ) of the transducer's response is updated to match to the local minima and maxima. The second step consists in the syncing of Time of Flight (ToF) inside the deposit layer, using the (Th/C)d ratio. The third step focuses on the amplitude mismatch adjustment through the mismatch between the acoustic impedance of the deposit (.C)d and that of the substrate (.C)s layers. The amplitudes of the subsequent echoes are related to attenuation of deposit layer (Alpha)d.

Varying the model parameters as described earlier, results in a very good match between the model and experimental signal. Notably, a very good agreement between form of signals is achieved, since the time shift between echoes has been corrected, and the amplitudes have been matched.

  Manoochehrnia, Pierre Maréchal, Damien Leduc, Ech-Cherif El-Kettani Mounsif. Inverse problem identification of thickness and viscoelastic properties of a film deposit by scanning acoustic microscopy. Anglo-French Physical Acoustics Conference 2024 (AFPAC), IOP Physical Acoustics Group; Groupe d'Acoustique Physique, Sous-marine et UltraSonore (GAPSUS) of the Société Française d'Acoustique (SFA), Jan 2024, Loch Lomond, United Kingdom. hal-04460624