[1] With the prevalence of glass and molten silicates in volcanic environments, and the important role of surface emissivity in thermal infrared (TIR) measurements, it is imperative to characterize accurately the spectral features associated with silicate glasses and melts. A microfurnace has been developed specifically for use with a laboratory Fourier transform infrared (FTIR) spectrometer to collect the first in situ TIR emission spectra of actively melting and cooling silicate glasses. The construction, implementation, and calibration of the microfurnace spectrometer system are presented here. Initial testing of the microfurnace is also discussed, which includes acquisition of thermal emission spectra of a quartz powder (unmelted), a melted and cooled oligoclase feldspar, and glassy melt of rhyolitic composition. Unlike a solid material, which may only have bending and stretching vibrations within its molecular structure, a fully molten material will exhibit several more degrees of freedom in structural movement, thus changing its spectral character. Differences in spectral behavior and morphology are observed between a glass in a solid state and its molten counterpart, confirming previous field measurements of lower emissivity upon melting. This laboratory microfurnace system has been designed to quantify the TIR emission spectral behavior of glassy materials in various physical states. Ultimately, it is hoped that the microfurnace data will help improve the ability of field-based, airborne, and spaceborne TIR data to characterize glassy volcanic terranes.Citation: Lee, R. J., M. S. Ramsey, and P. L. King (2013), Development of a new laboratory technique for hightemperature thermal emission spectroscopy of silicate melts,
This investigation seeks to better understand the thermal infrared (TIR) spectral characteristics of naturally‐occurring amorphous materials through laboratory synthesis and analysis of glasses. Because spectra of glass phases differ markedly from their mineral counterparts, examination of glasses is important to accurately determine the composition of amorphous surface materials using remote sensing datasets. Quantitatively characterizing TIR (5–25 μm) spectral changes that accompany structural changes between glasses and mineral crystals provides the means to understand natural glasses on Earth and Mars. A suite of glasses with compositions analogous to common terrestrial volcanic glasses was created and analyzed using TIR reflectance and emission techniques. Documented spectral characteristics provide a basis for comparison with TIR spectra of other amorphous materials (glasses, clays, etc.). Our results provide the means to better detect and characterize glasses associated with terrestrial volcanoes, as well as contribute toward understanding the nature of amorphous silicates detected on Mars.
[1] Si-O-Si bond vibrations within silicate materials produce a prominent absorption feature in the 8-12 mm region of thermal infrared (TIR) spectra. The wavelength position of this absorption varies with SiO 2 content and may be used to determine rock composition. However, the presence of glass greatly affects the measurement of emitted and reflected TIR energy from the surface, a phenomenon which is not currently well understood. This study examines the TIR spectral characteristics of a suite of synthetic high-SiO 2 quartzofeldspathic glasses that vary systematically in composition. Glasses were synthesized in the albite-quartz, oligoclase-quartz, and andesine-quartz systems. Microreflectance (∼1000 mm 2 ) and TIR emission spectra (bulk sample) were collected, and the spectral band maxima and minima were determined for each. Reflectance band maximum positions show a strong correlation with emissivity band minimum positions, indicating that the two types of spectra are comparable for this study. Excellent correlations are obtained between weight percent SiO 2 and reflectance maxima position, emission minima position, and spectral shoulder position. Molar Al/[Al+Si] and [Na+Ca]/ Si are all well-correlated with reflectance maxima and shoulder positions but slightly less correlated with emission minima. Results of this study will contribute to a better understanding of spectral properties of quartzofeldspathic glasses and will provide a means to more accurately detect and map glassy surfaces (e.g., volcanoes and impact craters) remotely from the ground and from orbit.Citation: Lee, R. J., P. L. King, and M. S. Ramsey (2010), Spectral analysis of synthetic quartzofeldspathic glasses using laboratory thermal infrared spectroscopy,
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