Pore structures in shungites as revealed by small-angle neutron scattering T.V.Tropin 1, M.V.Avdeev 1, V.L.Aksenov 1,2, L.Rosta 2, V.M.Garamus 3, N.N.Rozhkova.

Pore structures in shungites as revealedPore structures in shungites as revealedby small-angle neutron scatteringby small-angle neutron scattering

T.V.Tropin1, M.V.Avdeev1, V.L.Aksenov1,2,

L.Rosta2, V.M.Garamus3, N.N.Rozhkova4

1Joint Institute for Nuclear Research, Dubna, Russia

2Russian Research Center “Kurchatov Institute”, Moscow, Russia

3Research Institute for Solid State Physics and Optics HAS, Budapest, Hungary

4GKSS Research Centre, Geesthacht , Germany

5Institute of Geology Karelian Research Centre RAS, Petrozavodsk, Russia

“Stress and Textures Investigation by Means of Neutron Diffraction”, STI-2011, FLNP, JINR, Dubna, Russia

OutlineOutline

• Introduction: Introduction: shungite spreading, properties, shungite spreading, properties, applications and microstructure.applications and microstructure.

• ExperimentsExperiments• Method: small-angle neutron scattering

(SANS)• Samples description• SANS: characteristics of levels• SANS: open/close porosity study

• ConclusionsConclusions

Shungite spreadingShungite spreading

Shungites are carbon-rich rocks of Precambrian age widespread over Russian Karelia.There are four types of shungite different in carbon content.

Buseck PR, et al. Canadian Mineralogist (1997)

Shungite depositsShungite deposits

Shunga Maksovo

Shungite depositsShungite deposits

Negozero

Characterization of shungitesCharacterization of shungites

Elastic modulus 24 GPa (shungite I)Tensile strength ~110 MPa Compression strength >200 MPaDensity 1.9 g/cm3

Resistance ~0.1 Ω·cm (shungite I, semiconductor)

Glassy carbon

Mixture of properties

Coal Graphite Coke

Shungite carbon applicationsShungite carbon applications

•low-temperature catalysts of hydrogenation

•adsorbents and filters in water purification

•multi-functional fillers of polymeric and inorganic binders

•radiation screening construction materials

•alternative material for coke and quartzite

•natural source of fullerenes (?) Buseck PR, Tsipursky SJ, Hettich R. Fullerenes from Geological Environment. Science (1992)

A general task of the study of shungites is to find out the most A general task of the study of shungites is to find out the most effective technologies of their treatment and application!effective technologies of their treatment and application!

……In this connection, the knowledge about the structure of this rock and its modifications In this connection, the knowledge about the structure of this rock and its modifications is of great importance.is of great importance.

Shungite microstructure: HRTEMShungite microstructure: HRTEM

Shungite carbon contains Shungite carbon contains packed globular or ellipsoidal multi-packed globular or ellipsoidal multi-layered graphene units (size < 10 nm) forming aggregates with layered graphene units (size < 10 nm) forming aggregates with

chaotic (Shunga) or preferable (Maksovo) orientation.chaotic (Shunga) or preferable (Maksovo) orientation.

Shunga Maksovo

Additional study by: chemical analysis, chromatography, electron and X-ray diffraction, HRTEM, Additional study by: chemical analysis, chromatography, electron and X-ray diffraction, HRTEM, AFM, SAXS.AFM, SAXS.

Research motivationResearch motivation

• To use SANS method to reveal structural features of To use SANS method to reveal structural features of shungite powders at the scale of 1-100 nm shungite powders at the scale of 1-100 nm complementary to previous investigations;complementary to previous investigations;

• Compare SANS signals from shungites at different Compare SANS signals from shungites at different deposits and to determine characteristic parameters of deposits and to determine characteristic parameters of various types of the structural organization of shungites;various types of the structural organization of shungites;

• Use the SANS contrast variation technique to separate Use the SANS contrast variation technique to separate effects of the closed and open porosity on the scattering effects of the closed and open porosity on the scattering and conclude about the pore structures of shungite.and conclude about the pore structures of shungite.

Small-angle neutron scatteringSmall-angle neutron scattering

k 0

k

q co s

q s in

0kkq

2sin

4

q

k

0kq

YuMO time-of-flight setup, IBR-2 Reactor, FLNP, JINR, Dubna

Instruments

Yellow Submarine steady-state setup, Budapest Neutron Center

)(qfd

d

SANS-1 steady-state setup, GKSS Research Centre, Geesthacht

size ~1-100 nm

~ 0.001-1

Contrast variationContrast variation

s

s

s

the shell is matched

the core is matched

2 s 1 s

2222 )()()0( VnVnI s

SamplesSamples

Deposite

Average

interlayer

spacing,

d 002 ,nm

Volatile

matter,

%/ pH

Open/

closed

porosity,

%

Surface

area

(BET),

m2/g

Average

pore size

(SAXS),

nm

Micro-

porosity

%

Shunga 0.350 4.15/6.8 4.7/ 8.1 2-5 2-4 67

Maksovo 0.349 2.65/2.8 18.8/6.6 180-240 3 96

Chebolaksha 0.346 1.95/6.4 1.6/12.4 5-10 6 -

Shungite carbon-rich rocks type-I, dry grinding down to granule size ~ 40 m

Small-angle neutron scatteringSmall-angle neutron scattering

Level II (small q-values). Mass fractal (dimension DM).

Level I (large q-values). Surface fractal (dimension DS).

qqI

1~)(

SD6

qqI

1~)(

MD0.1 1

0.1

1

10

100

1000

10000

100000

~q-2.7

~q-3.6

~q-2.2

~q-2.7

I(q

)/ m

,g-1 c

m2

q, nm-1

~q-4 Maksovo, 100 Shunga, 10 Chebolaksha

~ 2 / Dmax

d / d

q

SANS fitting models: single levelSANS fitting models: single level

.4,2

,

,

6

,1

)(

2

22

3*

*3

22

PSnB

nVG

qkRerf

qq

Cq

BeGqIPRq

CC – is the background remaining after corrections;PP – characterizes the type of mass or surface organization of the scattering units;nn, VV, ρρ – particle number density, volume and scattering length density of the scattering units; - mean scattering length density of the bulk medium;kk – an empirical constant;RR – radius of gyration of the particles;S – surface area of the scattering units;

This model was used to fit a single level and obtain the parameters.This model was used to fit a single level and obtain the parameters.

SANS fitting models: generalization for two levelsSANS fitting models: generalization for two levels

Cq

BeGq

eBeGqIIIIIIIIIP

IIII

Rq

II

P

I

Rq

I

Rq

I

*3

*33 11

)(

222222

The proposed model describes the two-level structure of shungites. The proposed model describes the two-level structure of shungites. It allows to obtain structure parameters after the fit.It allows to obtain structure parameters after the fit.

Impact of scattering from level-II units on the scattering from level-I units.

level Ilevel I level IIlevel II

Comparison: SANS and SAXS resultsComparison: SANS and SAXS results

0.1 10.01

0.1

1

10

100

1000

10000

Maksovo

SANS SAXS models

I(q

)/ m

,g-1 c

m2

q, nm-1

• The results of SANS and SAXS experiments are in a good The results of SANS and SAXS experiments are in a good agreement;agreement;

• The fit of SANS results by the proposed models of two-level The fit of SANS results by the proposed models of two-level structure has been successful;structure has been successful;

Characteristics of the levelsCharacteristics of the levels

Level I Level II Sample Surface

fractal dimension Size of

subunits Mass

fractal dimension Size of

subunits

Maksovo 2 > 100 nm 2.7 6 nm

Chebolaksha 2 > 100 nm 2.2 12 nm

Shunga 2.4 > 100 nm 2.7 > 20 nm

4,2

/2)(

:

2

42

PSnB

qSnqI

lawPorod

Level I:Level I:•nn<10<1013 13 cmcm-3-3;;•Volume fraction - ~4%;Volume fraction - ~4%;•Inner surface ~0.3 mInner surface ~0.3 m22/g;/g;

Level II:Level II:•nn<10<1017 17 cmcm-3-3;;•Volume fraction - <10%;Volume fraction - <10%;

Two-level organization of shungitesTwo-level organization of shungites

AFMHRTEM

Arrow shows large globule unit

Arrows showbasic structural units (BSUs)

Arrow showspore between BSU filled with non-structured fractal carbon

Maksovo:

Kovalevski V.V., Prikhodko A.V., Buseck P.R., Carbon 2005;Rozhkova N.N., Golubev E.A., V.I.Siklitski, M.V.Baidakova In: Fullerenes and fullerene containing materials, Eds. Vityaz’ P.A., et al., Minsk: UP”Tehnoprint”, 2002;

Matching of open pores in shungitesMatching of open pores in shungites

= – C ~ –71010 cm-2

+ D2O

open pores: = D2O – C ~ 0.71010 cm-2

closed pores: = – C ~ – 71010 cm-2

• Comparison of the scattering curves for initial sample (Maksovo, Shunga) Comparison of the scattering curves for initial sample (Maksovo, Shunga) and the same sample after absorption of Dand the same sample after absorption of D22O during one week before O during one week before

experiments. experiments. • Changes in the scattering are due to matching of open porosity. Changes in the scattering are due to matching of open porosity.

Matching of open poresMatching of open pores

Contrast variation in shungitesContrast variation in shungites

0.1 1

0.1

1

10

100

1000

10000

~q-4

~q-4

~q-2.7

~q-1

Maksovo powderMaksovo powder + D2O

I(q

), c

m-1

q, nm-1

Pores at level I. Size > 200 nm, fraction < 10 vol. %, fully open;

Open pores at level II.Size 5-10 nm, posses inner fractal structure of units less than 1 nm in size.

Closed pores at level II Repeat sample elongation texture, L > 60 nm, R < 2 nm

Main contribution into inner surface comes from open poresat level II: S ~ 130 m2 g-1 (SANS) S ~ 200 m2 g-1 (BET)

Level I Level II

Two-level organization of shungitesTwo-level organization of shungites

AFMHRTEM

Arrow shows large globule unit

Arrows showbasic structural units (BSUs)

Arrow showspore between BSU filled with non-structured fractal carbon

Maksovo:

Kovalevski V.V., Prikhodko A.V., Buseck P.R., Carbon 2005;Rozhkova N.N., Golubev E.A., V.I.Siklitski, M.V.Baidakova In: Fullerenes and fullerene containing materials, Eds. Vityaz’ P.A., et al., Minsk: UP”Tehnoprint”, 2002;

•Complex structural organization of shungites is detected in Complex structural organization of shungites is detected in SANS, SAXS and EM experiments;SANS, SAXS and EM experiments;

•All samples from different deposits are characterized by two All samples from different deposits are characterized by two scattering levels corresponding to fractal structures at the scales scattering levels corresponding to fractal structures at the scales of ~10 and > 100 nm, respectively;of ~10 and > 100 nm, respectively;

•Despite the structural similarity a significant difference in bulk Despite the structural similarity a significant difference in bulk morphology for shungites from different deposits is observed;morphology for shungites from different deposits is observed;

•Open porosity determines the fractal organization of the first Open porosity determines the fractal organization of the first scattering level (size ~10 nm), while the close pores at this level scattering level (size ~10 nm), while the close pores at this level are polydisperse elongated globules, which is in agreement with are polydisperse elongated globules, which is in agreement with the present model of shungite basic structural units.the present model of shungite basic structural units.

Conclusions