Magnetic properties in neutron irradiated graphites
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Magnetic properties in neutron irradiated graphites. D. Pontiroli , A. Goffredi, M. Belli, F. Giaferrari, M. Mazzani, M. Riccò Università degli Studi di Parma and CNISM, Via G. Usberti 7/a, 43100 Parma (Italy). Aim of the work.

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Magnetic properties in neutron irradiated graphites

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Magnetic properties in neutron irradiated graphites

Magnetic properties in neutron irradiated graphites

D. Pontiroli, A. Goffredi, M. Belli, F. Giaferrari, M. Mazzani, M. Riccò

Università degli Studi di Parma and CNISM, Via G. Usberti 7/a, 43100 Parma (Italy)

Daniele Pontiroli –Università degli Studi di Parma


Aim of the work

Aim of the work

If magnetism in graphite is induced by defects, neutrons could represent a good alternative way to protons

B. T. Kelly, IAEA, Wien 2000

Two different strategies:

  • Direct neutron bombardment of graphite compounds (powders) at high energy (~1 MeV)

  • Indirect irradiation by fission of atoms (Boron) incorporated into graphite (powder) with neutrons

Daniele Pontiroli –Università degli Studi di Parma


Direct irradiation with neutrons

99% if Eneutr = 1 MeV!

Direct irradiation with neutrons

  • If Eneutr < 60 eV, neutrons do not produce any defect in graphite

  • If 60 eV <Eneutr< 120 eV, neutrons produce only primary defects

  • If Eneutr> 120 eV, neutrons produce also secondary defects

Daniele Pontiroli –Università degli Studi di Parma


Irradiation of boron enriched graphite

Irradiation of boron enriched graphite

Two different typologies of compounds:

  • Molecules containing boron intercalated in graphite

  • Boron compounds and graphite composites (NaBH4)

The defect generation is due to the breaking of 10B nuclei induced by epithermal neutrons (~1eV)

Daniele Pontiroli –Università degli Studi di Parma


The l e n a laboratory pavia it

The L.E.N.A. Laboratory (Pavia, IT)

T.R.I.G.A. MARK II nuclear reactor, 250 KW (central channel)

Bi-modal spectrum: peaks at:

  • 1.71012 n/cm2 sec at 1 eV

  • 0.81012 n/cm2 sec at 1 MeV

Daniele Pontiroli –Università degli Studi di Parma


Intercalated and exfoliated graphites

Intercalated and exfoliated graphites

  • Exfoliation of K-EtOH intercalated graphite:

    KC8 + CH3CH2OH  8C + KOCH2CH3 + ½ H2

If the planes of graphite are well outdistanced the approximation of graphene-like compound could be maintained even in the bulk phase

heating at 1050° C

  • Production of other intercalated graphite (KCx exposed to NH3 vapours, RW-A graphite exposed to SO3 vapours)

Daniele Pontiroli –Università degli Studi di Parma


Sample preparation

Sample Preparation

Pristine:

  • RW-A pristine graphite

    Intercalated graphites:

  • KC24 + NH3

  • RW-A graphite + SO3

    Exfoliated graphite:

  • KC8/KC24 + EtOH, then exfoliated

    With boron:

  • KC24 + borazine

  • KC24 + BCl3

  • Boron composites: RW-A + NaBH4 at 1, 20, 50%

We prepared the following samples (powder):

Daniele Pontiroli –Università degli Studi di Parma


Sample preparation1

Sample Preparation

Two different sample holders:

  • Quartz vial (the sample always remained in the same vessel)

  • Aluminium cylinder (better than Teflon®)

    Irradiation time: 6 h (central channel)

I ) Defects induced directly by n

Eneutr = 1 MeV

Thomson-Wright formula

Doseneutr = 1.73e16 n/cm2

1 Cdis every  44100 at. (3 1018 def/cm3)

1 def. in a cube of 35 at. edge (~5 nm)

Daniele Pontiroli –Università degli Studi di Parma


Sample preparation2

Sample Preparation

Two different sample holders:

  • Quartz vial (the sample always remained in the same vessel)

  • Aluminium cylinder (better than Teflon®)

    Irradiation time: 6 h (central channel)

II ) Defects induced by B fission

Eneutr = 1 eV

Optimal doping:5 – 20%B in weight, in order to maximise the penetration depth (lambda) and the reaction rate

Daniele Pontiroli –Università degli Studi di Parma


Pristine rw a graphite

0

Before n irrad.

After n irrad.

Magnetic Moment (emu/g)

-0.1

-0.2

0

50

100

150

200

250

300

Temperature (K)

Pristine RW-A graphite

After irradiation, a clear onset of Pauli paramagnetism was observed. No FM was detected down to 10 K

Before n irradiation

0.1

After n irradiation

0

Magnetic Moment (emu/g)

-0.1

-0.2

-40

-20

0

20

40

Applied Field (kOe)

Daniele Pontiroli –Università degli Studi di Parma


Magnetic results

Magnetic Results

Daniele Pontiroli –Università degli Studi di Parma


Magnetic results1

20

10

Ms (emu)

0

-10

-20

-10

-5

0

5

10

Applied field (KOe)

Magnetic Results

Magnetic SQUID measurements (Quantum Design MPMS)

Graphite + SO3

  • Background subtraction

  • Measure of the same vial before and after the treatment

  • Ms = [M(after)-M(before)]s

  • Sensitivity:  5 emu

Data

Fit

Ms = 2(1)10-5 emu

Daniele Pontiroli –Università degli Studi di Parma


Magnetic results2

0

B 1%

B 20%

0.02

-0.05

B 50%

B 1%

0

B 20%

B 50%

-0.02

-0.1

FIT

 (emu/g)

-0.04

Magnetic Moment (emu/g)

-0.06

-0.15

-0.08

-0.1

-0.2

0

100

200

300

-0.12

Temperature (K)

-0.14

0

10

20

30

40

50

Applied Field (kOe)

Magnetic Results

Magnetic SQUID measurements (Quantum Design MPMS)

Boron composites

  • Presence of Curie (and Pauli?) paramagnetism

  • Extrapolated FM signal:

    1% = -3.310-4 emu/g

    20% = 8.110-4 emu/g

    50% = 5.4 10-4 emu/g

  • No clear onset of FM signal

Daniele Pontiroli –Università degli Studi di Parma


Conclusions

Conclusions

  • Irradiated pristine RW-A graphite (powder) displays the onset of Pauli paramagnetism

  • In-plane defects produced by neutrons does not induce clear FM

Future developements

  • New investigations on the still not clear presence of FM magnetism into intercalated precursors (intrinsic effect?)

  • New irradiation of boron composites with smaller grain size

Daniele Pontiroli –Università degli Studi di Parma


Magnetic properties in neutron irradiated graphites

Thanks for your attention!

Daniele Pontiroli –Università degli Studi di Parma


Magnetic properties in neutron irradiated graphites

Daniele Pontiroli –Università degli Studi di Parma


Magnetic properties in neutron irradiated graphites

Daniele Pontiroli –Università degli Studi di Parma


Montecarlo calculation for boron composites

Montecarlo Calculation for Boron Composites

The particle range and the number of event for 7Li and 4He in graphite and NaBH4 was symulated with SRIM2003

Daniele Pontiroli –Università degli Studi di Parma


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