Thermomechanical behavior of mica implanted with noble gases

Gary Alan Hishmeh, Marquette University


Some phlogopite micas exhibit anomalous reversible expansions of several hundred percent perpendicular to the basal (cleavage) planes. This is due to water-containing lenticular cavities within the silicate layers, which expand from the liquid-vapor phase change above 100$\sp\circ$C. In muscovite and synthetic micas, this behavior is not observed due to the lack of extra non-structural water in their structures. The objective of this research is to control the thermomechanical properties of mica by introducing a known amount of noble gas into the structure by ion implantation, creating a mica-gas composite. The focus is on how ion beam implantation with noble gases effects the mica structure, whether or not the noble gases are retained in the structure and the effect on thermal expansion. Muscovite and synthetic fluorophlogopite was implanted with helium, neon, argon, krypton and xenon. The thermal expansion of helium implanted mica, as measured by thermal mechanical analysis, increased greater than an order of magnitude, however some of the helium was found to escape over time. The quantity of xenon and krypton in mica is constant over time and after repeated annealing, as determined by Rutherford backscattering and cavity counting. Gas cavities, 5-150 nm in diameter characterize the xenon, krypton, and argon implanted mica, in contrast to larger (a few $\mu$m in diameter) lenticular cavities found in helium implanted mica and phlogopite. Low-temperature transmission electron microscopy shows xenon and krypton to be located within cavities. Electron diffraction reveals polycrystalline rings from solidified xenon and krypton indicating an FCC structure with lattice parameter, a$\sb{\rm oXe}$ = 0.630 $\pm$ 0.015 nm, and a$\sb{\rm oKr}$ = 0.565 $\pm$ 0.005 nm. Observations of mica after implantation with xenon, krypton, and argon at fluences greater than 10$\sp{14}$ ions/cm$\sp2$, revealed an amorphous state; Helium implanted mica remained crystalline. Virgin and implanted micas became amorphous from electron beam exposure. The technique of capacitance dilatometry was developed to measure the thermal expansion of thin, micron-thick mica specimens. Initial measurements on thin (5 $\mu$m) phlogopite specimens gave thermal expansions in agreement with measurements performed on thicker (200 $\mu$m) specimens by thermal mechanical analysis.

Recommended Citation

Hishmeh, Gary Alan, "Thermomechanical behavior of mica implanted with noble gases" (1993). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI9411519.