In-situ High-pressure Transmission Electron Microscopy (TEM) Measurement

Project: Research project

Description

Intellectual merit We plan high-pressure measurements within a transmission electron microscope (TEM), the first within the earth sciences. We will apply the results to problems that potentially span the width of the globe, from the development of Earths core to water on Earths surface. These rather ambitious and far-reaching claims arise from the ideas that a) high pressures can be produced within miniscule pressure vessels and b) the early Earth contained both large amounts of hydrogen trapped within accreting minerals plus significant amounts of magnesiowstite. We hypothesize that the latter, when pressurized during burial, released small amounts of iron metal, leaving increased amounts of ferric iron in the magnesiowstite. The metal slowly migrated to the core, whereas the ferric iron reacted with the trapped hydrogen to form water that then fluxed the normal convective overturn of Earths mantle, in the process carrying water to the surface where it contributed to forming the oceans. We propose to test this idea by focusing on wstite, the Fe-rich, non-stoichiometric component of magnesiowstite. We will use carbon nanotubes as pressure containers within a TEM. Such nanotubes contract upon electron radiation, pressurizing materials enclosed within them. We will a) experiment with ways of loading different types of materials into the nanotube containers, b) test their responses to temperature increases using a standard TEM heating stage, c) calibrate the nanotube containers with materials with known pressure responses, and d) finally do experiments on standard materials in a TEM with an environmental stage in which we can expose the samples to hydrogen (loading hydrogen into a conventional high-pressure cell is difficult). After having gained sufficient experience with the technique, we will study wstite, searching for the release of iron metal in response to pressure at a suitably elevated temperature. The high spatial resolution afforded by a TEM combined with its capabilities for chemical analysis will permit in-situ measurements of the reaction products. The results will expand available experimental methods for high-pressure capabilities and provide fundamental new mineralogical information of interest to geophysics and geodynamics. Broader impacts of the proposed research Education of future researchers and promotion of diversity are major goals of my research group. Five nationalities are currently represented, as are members of underrepresented groups. As in the past, outreach will include science talks to school groups (including grade schools), presentations during annual Earth Day events, interviews with U.S. and overseas television stations about scientific activities, and periodic interviews with the radio and press. Thus, our research results will promptly be brought to the attention of the non-scientific community in ways intended to be educational. Also, my son is on the faculty of the Tohono Oodham Community College (a Native American college in Sells, AZ), and I hope to recruit one or more TOCC students as undergraduate interns to work with us on this project, perhaps to help develop ways of loading the nanotubes with various materials of interest. The proposed research will develop and refine new ways of doing high-pressure experiments, producing results that cut across several fields of study, thereby contributing to cross-disciplinary interactions and ideas. In keeping with prior practice, the results will be published in leading professional journals and disseminated through seminars and other talks at professional meetings and universities. The requested support will contribute to training of a graduate student and postdoctoral researcher, including extensive mentoring activities and presentations at professional meetings.
StatusFinished
Effective start/end date4/1/103/31/13

Funding

  • National Science Foundation (NSF): $300,206.00

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transmission electron microscopy
hydrogen
iron
metal
student
electron
early Earth
overturn
experiment
television
Earth science
geophysics
water
in situ measurement
chemical analysis
geodynamics
spatial resolution
vessel
temperature
material