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New Results in H 2 Treatments of Ball-Milled Graphite

New Results in H 2 Treatments of Ball-Milled Graphite. D. Pontiroli, M. Belli, A. Goffredi, M. Mazzani, M. Riccò, T. Makarova . 1 – Dipartimento di Fisica and INFM, Università di Parma, Parma, Italy 2 – Umeå University, Umeå, Sweden. Outline. Introduction.

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New Results in H 2 Treatments of Ball-Milled Graphite

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  1. New Results in H2 Treatments of Ball-Milled Graphite D. Pontiroli, M. Belli, A. Goffredi, M. Mazzani, M. Riccò, T. Makarova 1 – Dipartimento di Fisica and INFM, Università di Parma, Parma, Italy 2 – Umeå University, Umeå, Sweden Daniele Pontiroli - CNISM Parma

  2. Outline • Introduction • Experimental apparatus and optimisation of the parameters • Magnetic results • Conclusions Daniele Pontiroli - CNISM Parma

  3. Effect of Hydrogen • Hydrogen revealed to play a crucial role in magnetism of graphene and graphite (both from theory and experiments): • P. O. Lehtinen et. al., Phys. Rev. Lett.93 (2004) 187202 • L. Pisani et al., Phys. Rev. B75 (2007) 064418 • P. Esquinazi et al., Phys. Rev. Lett.91 (22) (2003) 227201 • Y. Kopelevich et. al., Carbon Based Materials, ed. T. Makarova, F. Palacio, Elsevier (2006) • The two main ingredients seems to be hydrogen + defects in graphene sheets • Interest in developing a technique to produce magnetic carbon in bulk Daniele Pontiroli - CNISM Parma

  4. in-plane vacancies edges ball milling Turbostratic disorder reaction with H2 Magnetism? Effect of Ball Milling Presence of paramagnetichighly reactive centres Daniele Pontiroli - CNISM Parma

  5. Sealed quartz working tube Quartz vessel and sample Ceramic filter Overall view of the tube Experimental Environment • Thermal treatments were performed both at high (up to 800°C) and low temperature (-196°C), by avoiding air-moisture contamination Daniele Pontiroli - CNISM Parma

  6. Our Preliminary Results • Preliminary results on H2 treated VSP-C ball-milled graphite (1 ppm Fe impurities) • Strong increase of Ms for some of the samples not clearly related to the T of treatment 20 Starting VSP-C H2 @ 100°C 10 M-Mdia (10-3 emu/g) 0 -10 Measurement at 30°C -20 -10 -5 0 5 10 Applied Field (Oe) Daniele Pontiroli - CNISM Parma

  7. Optimisation of the Experimental Technique • Use of powder graphite RW-A (SGL Carbon)instead of VSP-C: mesh 240, content of Fe <0.2 ppm, previously treated in vacuum 1 night at 700°C • Use of an agate grinding bowl, instead of zirconium oxide bowl, in order to minimise the introduction of impurities • Optimisation of the ball-milling parameters (time, frequency, mass amount of the sample) • Ageing effectswere taken into account • Study of H2 treatments at low temperature (-196°C) Daniele Pontiroli - CNISM Parma

  8. Grinding Bowls Daniele Pontiroli - CNISM Parma

  9. 10 min @ 35 Hz 60 min @ 50 Hz 60 min @ 35 Hz 40 min @ 35 Hz 30 min @ 35 Hz 15 min @ 35 Hz XRD Results • Effect of ball-milling on graphite RW-A crystal structure • Progressive increase of turbostratic disorder CuK • Increase of the amorphous phase Intensity (a. u.) • Reduction to the mean grain size down to ~10 nm, confirmed by Raman (HE-4) 25 30 35 40 45 50 55 2 (degrees) Daniele Pontiroli - CNISM Parma

  10. H2 treated sample after 13 days • Small ageing effect in H2 treated sample Magnetic Results • Ageing effects on the reactivity of RW-A ball-milled graphite • Msdecreases if the delay between milling and treatment increases 30°C H2 treated graphite 80 Starting milled graphite 60 • Relation between number of PM active centres and magnetism Ms (10-3 emu/g) 40 20 100°C 500°C 250°C 0 0 50 100 150 200 250 Time (hours) Daniele Pontiroli - CNISM Parma

  11. Magnetic Results • M(H) measurement on a magnetic H2 treated compoundat RT • Hysteresis is practically absent Ms = 0.086(2) emu/g Hc = 20(2) Oe 100 Starting RW-A milled graphite H2 @ 30°C 50 • This result was obtained once! 0 M-Mdia (10-3 emu/g) -50 Measurement at 30°C -100 -10 -5 0 5 10 Applied Field (KOe) Daniele Pontiroli - CNISM Parma

  12. 12 H2 treated graphite 10 RW-A graphite 2nd measurement 8 6 Ms (10-3 emu/g) • Not homogeneous magnetic behaviour of the samples! 4 2 0 0 100 200 300 400 500 600 700 800 Temperature of the treatment (°C) Magnetic Results • Production of large amount of H2 treated samples ( 600 mg) • The samples were treated just after the ball milling: minimisation ofthe ageing effects Daniele Pontiroli - CNISM Parma

  13. Treatments in H2 at low T • Treatments in H2 at low T (-196°C) – preliminary results! • The sample is kept in liquid N2during the treatment with H2 • Different treatment periods were considered (from 3 h to 3 days) Daniele Pontiroli - CNISM Parma

  14. By heating the SQUID sample for 1 night at 300°C, the magnetic response slightly increases Treatment at 300°C 2nd measurement Magnetic Results • Treatments in H2 at low T (-196°C) – preliminary results! 25 H2-D2 treated graphite Starting milled graphite 20 15 Ms (10-3 emu/g) • Magnetic response seems to be homogeneous 10 5 • Work in progress… 0 0 10 20 30 40 50 60 70 80 Duration of the treatment (hours) Daniele Pontiroli - CNISM Parma

  15. Conclusions • New efforts were made in investigating magnetism in H2 treated ball-milled graphite, by improving the preparation of the samples • Increase in the magnetic signal was found in some samples, but reproducibility is still missing • A clear ageing effect was found in the reactivity of ball-milled graphite, while less ageing effect is present in the hydrogenated samples • Preliminary hydrogenation tests at low T (-196°C) were made, but work is still in progress Thank you for your attention! Daniele Pontiroli - CNISM Parma

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  19. 6 Before H2 After H2 4 2 Mmol/H (10-5 emu/mol  Oe) 0 -2 -4 0 50 100 150 200 250 300 Temperature (K) Paramagnetism in H2 Treated Ball-Milled Graphite • M(T) on ball-milled graphite before and after the hydrogenation • Paramagnetic signal clearly decreases after idrogenation Before H2 treatment: 1 spin ½ every 2400 u.f. After H2 treatment: 1 spin ½ every 4800 u.f. Daniele Pontiroli - CNISM Parma

  20. 0.06 Before n irrad. After n irrad. 0.05 0.04 M (emu/g) 0.03 0.02 0.01 0 0 50 100 150 200 250 300 T (K) Graphite Irradiated with Neutrons • Several samples of pristine, exfoliated and intercalated graphite were irradiated for 6 hours with neutron (LENA reactor) • M(T) measurements show the onset of paramagnetism (Curie law) in the irradiated sample • No presence of ferromagnetic transition down to 10 K H = 5 T Daniele Pontiroli - CNISM Parma

  21. 1 0.8 Ms (10-3 emu/g) 0.6 0.4 0.2 0 0 50 100 150 200 250 Time (hours) Magnetic Results • Ageing effects on the reactivity of RW-A milled graphite • All the samples were treated in H2 at the same temperature of 250°C • Smallest magnetic signal: Wigner energy release? Daniele Pontiroli - CNISM Parma

  22. Paramagnetism of Ball Milled Graphite Daniele Pontiroli - CNISM Parma

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