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High Pressure-High Temperature Studies on Boron Nitride in a Diamond Anvil Cell

Uses of Boron Nitride. Because of its:High heat capacityGood thermal conductivityContainment of most molten metalsLubricityBN is used for coatings of tools and mold release in the commercial world. Most of all, Boron Nitride is useful in machining Ferrous Alloys: cast iron, steel, etc.. Nove

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High Pressure-High Temperature Studies on Boron Nitride in a Diamond Anvil Cell

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    1. High Pressure-High Temperature Studies on Boron Nitride in a Diamond Anvil Cell Research Experience for Undergraduates 2004 Melissa Glaser University of the South, Sewanee, TN Wei Qiu and Yogesh K. Vohra University of Alabama at Birmingham, Birmingham, AL

    2. Uses of Boron Nitride Because of its: High heat capacity Good thermal conductivity Containment of most molten metals Lubricity BN is used for coatings of tools and mold release in the commercial world. Most of all, Boron Nitride is useful in machining Ferrous Alloys: cast iron, steel, etc.

    3. Novelty of the Present Approach Use high pressure high temperature without catalyst (direct conversion) Exploring high pressure regions in the phase diagrams

    4. Motivation Investigate formation of new superhard phases in Boron Nitride at high pressures and high temperatures. Can synthesized phases be better than the known cubic Boron Nitride phase?

    5. BN Phase Structures

    6. Diamond Anvil Cell

    7. Pressure measurement Ruby is an optical pressure marker Ruby at zero pressure wavelength=694.041nm

    8. High Temperature Nd:YAG laser, Wavelength 1064 nm Laser power is 13 Watts at Q-Switch mode (pulse rate 10-50 Hz, pulse width 50 ns) Heats sample in the DAC to 2000-3000 Kelvin

    9. Temperature measurement: Blackbody Radiation

    10. Experiment procedure 30 GPa loaded on sample 30 mins of YAG heating at 1500 k Release pressure (new phase should be stable) Use Raman spectroscopy to find phase transition Use X-Ray Diffraction to determine the crystal structure.

    11. Raman Spectroscopy Ar laser wavelength = 514.35 nm Laser beam excites sample, which emits Raman signal which can reflect the material’s structure

    12. Initial

    13. Final

    14. X-Ray Diffraction Because our sample size is so small, the XRD here at UAB will not detect the lattice structures of BN in order to observe any transformation. Brookhaven National Lab has an intense X-Ray source which allows for us to study crystal structures at high pressures.

    15. Diffraction Geometry

    16. Setup of Bragg’s Law

    17. X-Ray diffraction of laser heated sample

    18. Conclusions Able to laser heat Boron Nitride at 30 GPa to temperature of 2500-3000 K. Raman measurement shows partial conversion of hBN and appearance of new peaks X-Ray diffraction measurement shows appearance of a new crystal structure with characteristic interplanar spacing

    19. Further queries Determine new structure Measure the hardness and toughness of the new material.

    20. Acknowledgements We acknowledge the use of X-17C beamline, National Synchrotron Light Source, Brookhaven National Labs, Long Island, New York. We acknowledge support from the National Science Foundation (NSF)- Research Experiences for Undergraduates (REU)-site award to the University of Alabama at Birmingham (UAB) under Grant No. DMR-0243640

    21. Bibliography Solozhenko, Vladimir L. and Vladimir Z Turkevich and Wilfried B. Holzapfel. “Refined Phase Diagram of Boron Nitride.” J. Phys. Chem. B (1999):103, 2903-2905. http://www.physik.uni-paderborn.de/ag/ag-holz/ldvholz/ldv-208.pdf http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/bragg.html http://carbon.cudenver.edu/public/chemistry/classes/chem4538/raman.htm

    22. Questions?

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