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Thermal and Evolved Gas Analysis of "Nanophase" Carbonates: Implications for Thermal and Evolved Gas Analysis on Mars Missions
| Content Provider | Semantic Scholar |
|---|---|
| Author | Lauer, Howard V. Archer, Paul Douglas Sutter, Brad Niles, Paul B. Ming, Douglas W. |
| Copyright Year | 2012 |
| Abstract | Introduction: Data collected by the Mars Phoenix Lander’s Thermal and Evolved Gas Analyzer (TEGA) suggested the presence of calcium-rich carbonates as indicated by a high temperature CO2 release while a low temperature (~400-680 o C) CO2 release suggested possible Mgand/or Fecarbonates [1,2]. Interpertations of the data collected by Mars remote instruments is done by comparing the mission data to a database on the thermal properties of well-characterized Martian analog materials collected under reduced and Earth ambient pressures [3,4]. We are proposing that “nanophase” carbonates may also be contributing to the low temperature CO2 release. The objectives of this paper is to (1) characterize the thermal and evolved gas properties of carbonates of varying particle size, (2) evaluate the CO2 releases from CO2 treated CaO samples and (3) examine the secondary CO2 release from reheated calcite of varying particle size. Materials and Methods: The following well characterized carbonates were analyzed in a laboratory thermal analyzer (TA) intergrated with a quadrupole mass spectrometer (QMS) that mimicked the operating conditions for the MSL Sample Analysis at Mars (SAM) and the Phoenix TEGA instruments: Iceland Spar calcite (CaCO3, Chihauhau, Mexico); Winchester Magnesite (MgCO3, Winchester, WI); Ledge dolomite [(CaMg(CO3)2, W. York, PA] and Copper Lake siderite[(Fe0.65Mg0.35CO3), Copper Lake Nova Scotia, Canada]. The calcite experiments were performed using samples ground and sieved in ethanol to produce a starting material of known particle size, whereas the other experiments were conducted on unsieved finely ground starting material. The analyses were performed with He carrier gas at 3sccm at 30 mb pressure (Samlike operating conditions) or N2 carrier gas at 1 sccm and 12 mb system pressure (TEGA-like operating conditions). The calcite experiments were done using different grain size starting material (<50 m, 50-125 m, 125250 m, 250-500 m and a single crystal ~2-3 mm/side) to quantify the affect of particle size on the temperature of the CO2 release. Samples were weighed in previously baked out (1000 o C in air ) aluminia crucibles and then placed in the sample holder of the TA. The instrument was evacuated and back filled with the specified carrier gas (He or N2) three times. The system was then allowed to equilibrate until all of the gas masses to be measured with the QMS have reached their steady state level. The TA instrument was heated to 1200 o C at 20 o C/min and then cooled back to ambient. The instrument was reheated to 1200 o C and allowed to cool to ambient. During both heatings and cooling cycles, the net heat flow in the sample and the evolved gases from the sample were recorded as a function to the sample temperature. The purpose of the second heating was to measure the thermal heat flow background signal for the sample being analyzed. The results from experiments using SAM-like or TEGA-like operating conditions are very similar. Since a much larger set of experiments dealing with grain-size effects have been completed using SAM-like conditions, only these experiments will be presented. In addition because of space limitations, detailed results will only be presented for the calcite portion of this study. In addition to reporting the evolved CO2 gas results as a function of grain size, an experiment was done to show the ability of fine grain carbonates to form from oxides at reduced pressure with an elevated partial pressure of CO2. In this experiment ~30 mg of <50 calcite was analyzed in the TA instrument using the He carrier gas at 30 mb and 3sccm. The sample was heated to 1250 o C as previously described. The cool down process was halted and the sample temperature held at 400 o C at which point the carrier gas was switched to CO2. The sample was held at 400 o C in flowing CO2 for 6 hrs. The sample was then allowed to cool down to ambient.The system/sample was then treated as though it was a new sample. Results: Figure 1 presents the evolved CO2 from calcite as a function of temperature for several different particle sizes using SAM-like conditions. The results obtained for TEGA-like conditions were similar. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120001840.pdf |
| Alternate Webpage(s) | https://www.lpi.usra.edu/meetings/lpsc2012/pdf/2299.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
