High surface area and interconnected nanoporosity of clay-rich astromaterials: N2 BET and TG-DSC-MSEGA data

Description

Whereas the bulk porosity of clay-rich meteorites is well established, the magnitude of their surface area and nano-scale porosity is poorly known. Here we apply the N2 BET gas adsorption method to measure the scale-distribution and net surface area of porosity in a range of clay-rich carbonaceous chondrite (CC) meteorites: Tarda (C2-ung), Ivuna (CI1), Orgueil (CI1), Aguas Zarcas (CM2), and Murchison (CM2). For comparison, N2 BET data was also acquired from the anhydrous CC Allende (CV3). Tarda (C2-ung) has high surface area, up to 82 m2/g, dominated by an interconnected network of ~3-nm-sized pores. In comparison, Ivuna and Orgueil (CI1) and Aguas Zarcas and Murchison (CM2) have bimodal nanopore-size distributions with a lower density of ~3-nm pores and broader size distributions around 40 nm, and corresponding lower surface areas ~14-19 m2/g. A summary of the data is shown in Table 1 (file 2Table1 N2BET data CC meteorites.docx). Two data sets are included that accompany the paper entitled "High surface area and interconnected nanoporosity of clay-rich astromaterials": the raw N2 BET data files including the derivation of the pore size and pore-size distribution; and the TG, DSC, and MSEGA data for the unweathered and artificially weathered Tarda meteorite. Prior to the N2 BET measurements, it is necessary to remove these physisorbed species through outgassing. The N2 BET measurements were acquired after several outgassing pretreatment - the pretreatment is listed after the meteorite name: Tarda-100 refers to the sample outgassed at 100 °C under flowing N2 for 24 hr; after prolonged storage under a dry N2 atmosphere (-NH); after being held under a vacuum for 24 hr at room temperature (-VRT); and, after heating in the presence of flowing dry nitrogen at 250 °C for 24 hr (-250) (Table 1). The N2 BET measurements are made by exposing the degassed sample to N2 at a series of controlled pressures while maintaining the sample at a constant cryogenic temperature of -195.8 °C, which corresponds to the boiling point of N2. The volume of adsorbed or desorbed gas is measured over a relative equilibrium adsorption pressure (p/p0) from near 0 to 1, where p is the absolute equilibrium pressure and p0 the saturation pressure of the gas. The Tarda N2 BET data shows the ease with which atmospheric moisture can adsorb onto its high surface area. This magnitude of the adsorption under laboratory conditions is measured by TG-DSC-MSEGA. Further information on the data acquisition and the samples is provided in the attached file 1Materials and Methods - N2BET, TG, DSC, MSEGA.doc

Steps to reproduce

The N2 BET were acquired under the conditions outlined in the file 1Materials and Methods - N2 BET, TG, DSC, MSEGA.doc. It is Important to note that the surface area measurements are sensitive to the curatorial history of the individual meteorites and the outgassing conditions. The Tarda and Aguas Zarcas meteorites studied here were collected soon after they fell, acquired by the Buseck Center for Meteorite Studies (BCMS) at Arizona State University (ASU), and are curated under a dry nitrogen atmosphere. As our research shows, even relatively brief periods of high relative humidity can dramatically alter the surface area data.

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