1 / 22

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.

tyler
Télécharger la présentation

New Results in H 2 Treatments of Ball-Milled Graphite

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

  16. Daniele Pontiroli - CNISM Parma

  17. Daniele Pontiroli - CNISM Parma

  18. Daniele Pontiroli - CNISM Parma

  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

More Related