Microprobe Analysis Parameters for Hydrous Aluminosilicate Glass (2011)

Undergraduates: Zachary Vance, Ryan D. Mill Dr. R. C. Tacker

Faculty Advisor: Allen Glazner
Department: Geology

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Dissolved water in synthetic and natural glasses can be bonded as both OH and molecular H2O and can have an impactful result on melt viscosity, density and crystallization rates. The most common method for determining the dissolved water content of aluminosilicate glasses is infrared (IR) spectroscopy because it is sensitive to OH and H2O. However, IR spectroscopy does not provide sufficient spatial precision to determine crystal-glass boundary gradients which can be as small as 5 µm. An alternative method for determining water content of aluminosilicate glass is electron probe microanalysis (EPMA). Problems incurred during EPMA include light element migration and heavier elemental "grow-in." The hypothesis tested was: if the spatial area analyzed could be minimized and the analytical precision could be maintained then boundaries between crystals and glass could be analyzed accurately. EPMA was performed on an experimentally derived hydrous aluminosilicate glass of known composition at Fayettville State University. I found that a probe current of 10nA, an accelerating voltage of 15kV, a counting time of 15 seconds optimized the accuracy of the probe at the smallest spot size of 5µm.