Comparison of Various TEM Sample Preparation Techniques of Nuclear Graphite

TITLE: Comparison of Various TEM Sample Preparation Techniques of Nuclear Graphite The mechanical behavior and microstructure of nuclear graphite can dictate the lifetime of nuclear reactors. Nuclear reactors cause fast moving particles to collide with the graphite, thus introducing irradiation damage and lattice defects to the microstructure. Through transmission electron microscopy, one can ‘simulate’ and monitor the irradiation effects of nuclear graphite that would occur in a nuclear reactor. Different TEM sample preparation techniques produce varying effects within samples; in turn, all techniques possess strengths and weaknesses in terms of difficulty, time consumption, and induced damage. This presentation identifies and describes the strengths and weaknesses associated with powder, ion mill, and oxidation (synthetic, nuclear grade graphite) TEM sample preparation techniques. Additionally, this research attempts to illuminate the benefits of using oxidation techniques[1] to prepare TEM samples of synthetic, nuclear grade graphite. By implementing oxidation techniques, the samples are theoretically artifact free; and by utilizing artifact free samples, all irradiation damage within the samples is a result of transmission electron microscopy. FUNDING ACKNOWLEDGEMENT: **This project is based upon work supported by the U.S Department of Energy’s EPSCoR-State/National Laboratory Partnership Program (Award # DE-SC0016427). All TEM use and sample preparation was conducted at the Boise State Center for Materials Characterization (BSCMC). MENTORS: Dr. Karthik Chinnathambi & Dr. Rick Ubic Additional advising: Steve Johns [1] Johns, S.; Shin, W.; Kane, J. J.; Windes, W. E.; Ubic, R.; Karthik, C. A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite. Journal of Nuclear Materials 2018, 505, 62–68 DOI: 10.1016/j.jnucmat.2018.03.058

P2/P3 Heterostructured Layered Transition Metal Oxide Cathode Materials in Sodium-Ion Batteries

Lithium-ion batteries (LIBs) have been a popular option for many applications in electrical energy storage. However, concerns over the availability of lithium and cobalt, the two most common elements used in LIBs, have led to the renewed interest in more sustainable alternatives, especially in large-scale energy storage applications. Sodium-ion batteries (SIBs) have gained an interest as an alternative due to the large abundance of sodium and relatively low cost. In particular, layered transition metal oxides (LTMOs) have been the main focus of positive electrode materials research due to their high capacities, and high operating voltage. The P3-type Na0.5Ni0.25Mn0.75O2 material is a promising manganese-rich positive electrode for future SIBs due to its high working voltage and capacity. However, fast capacity fading due to the high voltage P3-O3 phase transition has been the bottleneck for commercialization of such materials. To combat this limitation, we attempted to synthesize a heterostructured P2-Na2/3MnO2-coated P3-Na0.5Ni0.25Mn0.75O2 cathode material. The created material exhibited an increased capacity of 119.3 mA h g-1 at 1C rate and improved cycling stability of 64.7% retention after 80 cycles at 1C. However, characterization techniques, including HR-TEM, SEM, and XRD, have not shown that the hypothesized layer has grown. Future research should be done into realizing the effect that our synthesis had upon the P3 material, and how to implement it towards the improvement of manganese-rich P3-type sodium LTMO cathode materials for future applications