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Precipitation and characterization of Precipitation and characterization of

Ca(II)Ca(II)--Cu(II)Cu(II)--Fe(III)Fe(III)--AsO AsO44--SOSO44 phases phases

Mario Alberto Gomez

PhD Oral Defense

Department of Mining and Materials Engineering,McGill University, Montreal, QC, Canada

January 6th, 2011



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OutlineOutline

This talk will be broken into three This talk will be broken into threesections:sections:

1.1. Fe(III)Fe(III)--AsO AsO44--SOSO44 system (150system (150--225225 °°C)C)

2.2. Cu(II)Cu(II)--Fe(III)Fe(III)--AsO AsO44--SOSO44 system (150system (150 °°C)C)

3.3. Ca(II)Ca(II)--Fe(III)Fe(III)--AsO AsO44 system (95system (95 °°C)C)

Contributions to Original KnowledgeContributions to Original Knowledge Future Work Future Work

Acknowledgments Acknowledgments



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In our studyIn our study three distinct phasesthree distinct phases were found : were found :ScoroditeScorodite,, Ferric Arsenate subFerric Arsenate sub--Hydrate (Hydrate (FAsHFAsH)) andand

Basic Ferric Arsenate Sulphate (BFAS)Basic Ferric Arsenate Sulphate (BFAS)

ScoroditeScorodite : FeAsO: FeAsO44 Ã 2HÃ 2H22OO

Ferric Arsenate subFerric Arsenate sub--Hydrate (Hydrate (FAsHFAsH) :) : FeAsOFeAsO44 Ã 3/4HÃ 3/4H22OO

NOTNOT (Fe(Fe22(HAsO(HAsO44))33 zH2O by Swash) confirmed via vibrational spectroscopyzH2O by Swash) confirmed via vibrational spectroscopy

Basic Ferric ArsenateBasic Ferric Arsenate--SulphateSulphate (BFAS):(BFAS):

Fe(AsOFe(AsO44))xx (SO(SO44)) y y (OH)(OH)zz Ã wHÃ wH22OO

The Fe (III)The Fe (III) ² ² AsO AsO44 ² ² SOSO44 System System



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Phase Diagram for the High TemperaturePhase Diagram for the High TemperatureFe(III)Fe(III)--AsO AsO44--SOSO44 System (1994)System (1994)

P.M. Swash and A.J. Monhemius, Hydrometallurgy 94, Published by Chapman & Hall, 1994.



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Phase Diagram for the High TemperaturePhase Diagram for the High TemperatureFe(III)Fe(III)--AsO AsO44--SOSO44 System (2010)System (2010)



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10 20 30 40 50 60 70 80

R l a t i v e I n t e n s i t y

2 U

Scorodite

Ferric Arsenate sub-Hydrate

Basic Ferric Arsenate Sulphate

Orthorhombic ± Pbca

Triclinic- P1

Monoclinic(P21/c)-Orthorhombic(Pnma)?

FeFe

AsAs

HHFeAsOFeAsO44 · 2H· 2H22OO

FeAsOFeAsO44 · 3/4H· 3/4H22OO

Fe(AsOFe(AsO44

))xx

(SO(SO44

))yy

(OH)(OH)zz

· wH· wH22

OOJakeman et al., Inorg. Chem. 30, 2806 (1991)


Ventruti and Gomez et al. (2011) unpublished



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Scorodite : Orthorhombic FAsH : Triclinic BFAS : Monoclinic?Monoclinic?

Aggregates of

crystallites.On average, thesize of individualcrystallites is < 1m.

Aggregates of

crystallites.

On average, thesize of individualcrystallites is � 1 m.

Aggregates of two

distinct particles.

On average, thesize of individualcrystallites is � 2 m.




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E vidence of well grownE vidence of well grownmonoclinic type of monoclinic type of crystals.crystals.

With the aid of FEGWith the aid of FEG--SEMSEMandand TEMTEM--SA ED, aSA ED, a snapsnapshot of the roundedshot of the rounded

particle particle rere--crystallizingcrystallizing totoform the well definedform the well definedmonoclinic likemonoclinic like crystal wascrystal wascaptured.captured.




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FAsH contains arsenate in

2 distinct crystallographic sites.

AsO43-

OH-/H2O

Scorodite contains arsenate in

1 distinct crystallographic site.

1000 900 800 700 600

280032003600

2004006008001000

Wavenumber (/cm-1)Wavenumber (/cm-1)

Wavenumber (/cm-1) Wavenumber (/cm-1)

R a m a n I n t e n s i t y )

T r a s m i s s i o n I n t e n s i t y

R a m a n I n

t e n s i t y )


280032003600

06

07

08

09

010

0

2

00290033003700

2004006008001000



R a m a n I n t e

n s i t y )


R a m a n I n t e n s i t y )

T r a s m i s s i o n I n t e

n s i t y

2

00290033003700

OH-/H2O AsO43-




10

1400 1200 1000 800 600

2500290033003700

200400600800100012001400



R a m a n I n

t e n s i t y )


R a m a n I n

t e n s i t y )


2500290033003700

Basic Ferric Arsenate Sulphate


AsO4

3-

SO42-

OH-

/H2O

Fe-O

AsO43-



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Basic Ferric Arsenate Sulphate (molecular solid solution)

SO4

SO4

AsO4

AsO4

C2v

~Td

C2v~Td

�� In general, the AsOIn general, the AsO44 (SO(SO44) group symmetry is reduced from a T) group symmetry is reduced from a TddCC2, 2v 2, 2v while that while thatof the AsOof the AsO44 (SO(SO44) group remains ~ T) group remains ~ Tdd (equivalent).(equivalent).

�� This demonstrated that each sulfate and arsenate can occupy similar molecularThis demonstrated that each sulfate and arsenate can occupy similar molecularsites in the crystal structure. This was later confirmed upon solution of the crystalsites in the crystal structure. This was later confirmed upon solution of the crystalstructure (unpublishedstructure (unpublished --Ventruti Ventruti andGomez 2011).and Gomez 2011).




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Comparis on of ou r Comparis on of ou r FAsH FAsH a nd BFAS t o previ ou sly reporte d ´ n ewµ a nd a nd BFAS t o previ ou sly reporte d ´ n ewµ a nd

´ ol d µ phases (1994 & 2007)´ ol d µ phases (1994 & 2007)

BFAS = Phase 3 = Type 2BFAS = Phase 3 = Type 2FAsH = Phase 4 = Type 1FAsH = Phase 4 = Type 1

McGill

2007

1994

McGill

2008

2007

1994

McGill

2008

2007

1994




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As-O As-Fe

X ANES/EX AFSX ANES/EX AFSdetermines average localdetermines average localcoordination up to 4coordination up to 4 Å Å..

For Scorodite andFor Scorodite and FAsHFAsHcrystallographiccrystallographicinformationinformation existexist toto fitfit thetheEX AFS.EX AFS.

However,However, forfor BFAS noBFAS nocrystallographiccrystallographic

information exist for now.information exist for now.

FAsHFAsH

BFASBFAS

FAsHFAsH

BFASBFAS


ScoroditeScorodite

FAsHFAsH



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�� Short term stability tests showed that all phases yielded < 1ppm As.Short term stability tests showed that all phases yielded < 1ppm As.

�� At lower pH (3 and 5), the At lower pH (3 and 5), the FAsHFAsH phase was found to yield higher amounts of phase was found to yield higher amounts of

arsenic then the corresponding low and high sulphate BFAS phases.arsenic then the corresponding low and high sulphate BFAS phases.��However at lower pH (3), the BFAS with lower sulphate content gave slightlyHowever at lower pH (3), the BFAS with lower sulphate content gave slightlyhigher arsenic release in comparison to the higher sulphate containing BFAS.higher arsenic release in comparison to the higher sulphate containing BFAS.

��Interestingly at higher pH (7.5) bothInterestingly at higher pH (7.5) both FAsHFAsH and the lower sulphate containing BFASand the lower sulphate containing BFAS yielded similar arsenic release, while the higher containing sulphate BFAS gave the yielded similar arsenic release, while the higher containing sulphate BFAS gave thehighest arsenic release.highest arsenic release.



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The Cu (II)The Cu (II) ² ² Fe (III)Fe (III) ² ² AsO AsO44 ² ² SOSO44 System System

Case1 Case 2

Case 3 Case 5



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TestTest Fe %Fe % As %As % Cu %Cu % Mg %Mg % S %S % RamanRaman

Case 1Case 1 24.124.1 28.828.8 00 00 1.61.6 **SDSD--SOSO44

Case 2Case 223.923.9 31.631.6 00 00 0.20.2 **SDSD--SOSO44

Case 3Case 3 21.121.1 35.135.1 0.40.4 00 0.60.6 **SDSD--SOSO44

Case 4Case 4 23.923.9 31.931.9 0.300.30 00 0.10.1 **SDSD--SOSO44

Case 5Case 5 21.221.2 29.529.5 0.800.80 0.600.60 1.21.2 **SDSD--SOSO44

R esults: Solid CompositionR esults: Solid Composition

* SD* SD--SOSO44 : sulphate containing scorodite: sulphate containing scorodite

Theoretical:Theoretical: 24.224.2 32.532.5 SDSD



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�� XRD and IR of all trials at 0 hrs (i.e. 2.5hrs) and after 10hrs (i.e.12.5hrs) reactionXRD and IR of all trials at 0 hrs (i.e. 2.5hrs) and after 10hrs (i.e.12.5hrs) reactiontime determined:time determined: sulphate-containing scorodite: (Fe(AsO4)1-x(SO4)x(OH)x· 2H2O.

�Interestingly, the H-bonding environment in case 1 was not fully ordered.




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�In case 1 (Fe/As � 1.5) at 2.5 hrs and 150 C, the H-bonding environment was foundnot to be well ordered in comparison to other cases (Fe/As � 1.5 ) under the same

reaction times. Similar results were also observed for tests at 175 C.�Extension of reaction time (3.5 hrs) in case 1, allows the structure to fully developthe H-bonding environment similar to longer times or lower Fe/As ratio (� 1.5 ) andindependent of the presence of copper.

��Powder XRD indicated that in all cases the product was crystalline scorodite but wasPowder XRD indicated that in all cases the product was crystalline scorodite but was

not able to detect the disorder in the Hnot able to detect the disorder in the H--bonding environment. bonding environment.




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�� Evidence of Evidence of metastablemetastable phase formationphase formation during the heat up periodduring the heat up period

(150C ~ 2.5 hrs) of Case 4 was observed.(150C ~ 2.5 hrs) of Case 4 was observed.

�� AA precipitate was seen to form before 150 C, this was unlikeprecipitate was seen to form before 150 C, this was unlike

scorodite and unlike any of the other casesscorodite and unlike any of the other cases..

��Solid samples were collected and analyzed by various techniques.Solid samples were collected and analyzed by various techniques.

101 C and40 min

150 C and750 min




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�The intermediate phase throughout the reaction was found to contain variousamounts Fe, As, Cu, S and O (ICP-A ES, EDS and XPS).

�The gel-like product was made up of smaller particles which exhibitedordered and unordered domains.




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�The unknown gel-like precipitate was further analyzed via XR D and

cross polarized microscopy.

�XR D showed that indeed this gel-like precipitate was composed of anX-ray (= 1.78897 Å) amorphous phase but also some domains existed

where longer range order exist.

�This is in agreement with cross polarized microscope results.

40 min (101 C)

Cross Polarized Microscope




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�The unknown intermediate phase was further analyzed via

ATR -IR and Micro-R aman to determine its molecular structure

IR IR R amanR aman

�Both BFAS and this intermediate phase were found to havesimilar molecular groups, symmetry and bonding in both IR andR

aman analysis.




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(1) Teck Metals

� The residue was produced under bench scale pressure oxidation CESL

processing conditions (150C and 60 min).

��From the literature,From the literature, the general view is that under thesethe general view is that under these

conditions arsenic should precipitate asconditions arsenic should precipitate as ¸ ScoroditeScorodite ¸ in additionto having hematite, and elemental sulfur in the residue.

Element

Assay

(%)

As 0.54Fe 29.3

S Total 36.3

S elemental 32.1

Pb (ppm) 4290

C haracterizati on of I ndu strial Resi du es C haracterizati on of I ndu strial Resi du es



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(1) Teck Cominco R esidue (XR D via Database Search Analysis)

Match to HematiteMatch to Hematite Match to SMatch to S°°

Match to ArsenopyriteMatch to Arsenopyrite Match to ScoroditeMatch to Scorodite



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(1) Teck Cominco (Vibrational: R aman Analysis)

Teck R esidue

Hematite (STD)

Teck R esidue

Elemental S° (STD)



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(1) Teck Cominco (Vibrational: ATR -IR Analysis)

600 700 800 900 1000 600 700 800 900 1000

600 700 800 900 1000 700 750 800 850 900

Scorodite

(FeAsO4*2H

2O)

AsO4 region

BIAS

(FeAsO4SO

4OH)

AsO4 region

IAsH

FeAsO4*3/4H

2O

AsO4region

Teck Cominco

Industrial Residue

AsO4

region

Wave numbers(cm-1)



2727

During the synthesis work an unknown amorphous phase was firstobserved, followed by some scorodite impurities and finally the

yukonite [Ca2Fe3-5(AsO4)3(OH)4-10·xH2O where x = 2-11].

Single crystal and synchrotron analysis ( = 0.71 and 0.41 Å) of thenatural Tagish Lake sample was conducted to observe if anycrystallographic information could be extracted(space group and lattice parameters).

The C a (II)The C a (II) ² ² Fe (III)Fe (III) ² ² AsO AsO44 ² ² SOSO44 System System



2828

Lab based PXRD indicated that the synthetic yukonite material was in

excellent agreement with that of the natural Tagish Lake sample and unlikethat of arseniosiderite.

The Grotta della Monaca yukonite was found to have scorodite impurities(PXRD) and sulfate impurities in the form of K 2SO4

(ATR-IR and SEM-EDS).

= 1.54 Å

TL yukonite




2929

TEM and SAED of the Tagish Lake yukonite showed that at 100 nm it was essentiallyamorphous. However, at 5nm nano-crystalline domains ranging from 1-15 nm in sizewere observed and all exhibited lattice fringes of 0.32nm.

This is in contrast to arseniosiderite which is composed of micro-size single crystaldomains and exhibits lattice fringes of 0.54 nm. In addition an hexagonal symmetry

lattice was observed and no monoclinic domains were observed.

TL yukonite

Tagish

Lake

Yukonite

RomanechArseniosiderite




3030

To probe the local As and Fe structure (and oxidation states) of yukonite and

arseniosiderite XAS analysis was conducted.The oxidation states for the Tagish Lake yukonite and Romanech arseniosideritewere found to be in the As5+ and Fe3+ states, in agreement with that of the syntheticsamples where pure As5+ and Fe3+ sources were used.More importantly, the local structure and order of arsenate and ferric octahedralstates in yukonite and arseniosiderite were found to be similar in both minerals.

TL yukonite

As K-edge XANES As K-edge EXAFS

Fe 2p-edge XANES




3131

Therefore, we decided to conduct Ca L-edge XANES analysis on yukonite andarseniosiderite to investigate if the local structure was the same in arseniosiderite and

yukonite.

As it can be seen from the Figure above, the Ca L-edge XANES of both mineralsare exactly the same indicating that crystal field splitting, coordination and sitesymmetry around the Ca atoms should be the same. This is in contrast to the previousEXAFS findings.




3232

Structural and molecular analysis of yukonite

In the case of yukonite, the IR analysis showed that the arsenate molecules werefound in an ~Td environment, and its hydroxyl (as well as its arsenate) environmentwas quite diffuse in nature typical of a semi-crystalline phase. Raman analysis further

confirmed this behavior.

For arseniosiderite the arsenate molecules were found to be in an ~Td environment but in addition HAsO4

2- molecules were observed in both the IR and Raman spectra.More importantly the hydroxyl environment is indicative of two distinct H-bondingenvironments and this was postulated to cause the higher degree of order.

HAsO42-



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Ex pecte d Con trib u ti on s T o Origi n al K nowle d ge Ex pecte d Con trib u ti on s T o Origi n al K nowle d ge

Unequivocal and systematic identification of the type of phases producedUnequivocal and systematic identification of the type of phases producedunder high temperature autoclave conditions in the Fe(III)under high temperature autoclave conditions in the Fe(III)--AsO AsO44--SOSO44system.system.

Correction and determination of a new phase diagram, name andCorrection and determination of a new phase diagram, name andmolecular formulae for the phases produced in the Fe(III)molecular formulae for the phases produced in the Fe(III)--AsO AsO44--SOSO44system.system.

The first time the importance of reaction time (kinetics) was shown to The first time the importance of reaction time (kinetics) was shown toaffect the stability of these phases viaaffect the stability of these phases via metastablemetastable phases.phases.

Clarification of the discrepancies in previous works (Swash andClarification of the discrepancies in previous works (Swash and DutrizacDutrizac) )and unification of the ideas (including our own studies) and theories forand unification of the ideas (including our own studies) and theories forthe Fe(III)the Fe(III)--AsO AsO44--SOSO44 system.system.

New vibrational (IR and Raman) and group analysis data for the phasesNew vibrational (IR and Raman) and group analysis data for the phasesproduced in the Fe(III)produced in the Fe(III)--AsO AsO44--SOSO44 system as well as new XAS data (As K system as well as new XAS data (As K--edge and Fe Ledge and Fe L--edge) presented.edge) presented.

Analysis of industrial residues indicated that scorodite was not the main Analysis of industrial residues indicated that scorodite was not the mainarsenic form found but rather a BFAS like phase was observed.arsenic form found but rather a BFAS like phase was observed.

Long term arsenic release data for the non scorodite phases ( Long term arsenic release data for the non scorodite phases (FAsHFAsH andand

BFAS).BFAS).




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The first time the effect of copper on the Fe(III) The first time the effect of copper on the Fe(III)--AsO AsO44--SOSO44 system wassystem wasinvestigated at 150 C (CESL temperatures).investigated at 150 C (CESL temperatures).

Copper (or Mg) was found not to interfere with scorodite formation at 150Copper (or Mg) was found not to interfere with scorodite formation at 150C and 2.5 hrs.C and 2.5 hrs.

Excess ferric iron in starting solutions (Fe/As ~ 2 and � 2.5 hrs) wasExcess ferric iron in starting solutions (Fe/As ~ 2 and � 2.5 hrs) wasfound to affect the Hfound to affect the H--bonding (IR) in the produced scorodite withoutbonding (IR) in the produced scorodite without

affecting its crystallinity (XRD).affecting its crystallinity (XRD). Existence of a never before observedExistence of a never before observed metastablemetastable CuCu--FeFe--AsO AsO44--SOSO44 phasephase

at lower temperature (< 150 C), time (< 60 min) andat lower temperature (< 150 C), time (< 60 min) and equimolarequimolar Fe, Cu, AsFe, Cu, As was discovered. was discovered.

This This metastablemetastable phase was found to consist of ordered and disorderedphase was found to consist of ordered and disordereddomains (XRD, TEM and Polarized Microscoscopy) but its moleculardomains (XRD, TEM and Polarized Microscoscopy) but its molecularstructure was found to be similar to BFAS and unlike scorodite.structure was found to be similar to BFAS and unlike scorodite.

Analysis of an industrial residue produced under CESL conditions found Analysis of an industrial residue produced under CESL conditions foundthe arsenic to be in a BFAS like form (or arsenate adsorbed onto hematite)the arsenic to be in a BFAS like form (or arsenate adsorbed onto hematite)and not scorodite.and not scorodite.

The Cu (II)The Cu (II)- -Fe (III)Fe (III) ² ² AsO AsO44 ² ² SOSO44 System System



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First timeFirst time Yukonite Yukonite was successfully synthesized (Dr. L. was successfully synthesized (Dr. L. BeczeBecze). ). Comparison with the natural specimens from distinct locations inComparison with the natural specimens from distinct locations in

the world (Italy and Canada) showed the synthetic product tothe world (Italy and Canada) showed the synthetic product to bebeequivalentequivalent at the elemental, molecular and structural level.at the elemental, molecular and structural level.

First time vibrational (IR and Raman) and XANES (Fe and Ca LFirst time vibrational (IR and Raman) and XANES (Fe and Ca L--

edge) data was presented for bothedge) data was presented for both yukoniteyukonite (synthetic and natural)(synthetic and natural)andand arseniosideritearseniosiderite..

First time a molecular (IR, Raman, XANES) and structural (XRD,First time a molecular (IR, Raman, XANES) and structural (XRD, TEM TEM--ED) link was given between these two otherwise similarED) link was given between these two otherwise similarminerals.minerals.

Yukonite Yukonite was found to consist of was found to consist of nanonano--crystalline ordered domainscrystalline ordered domains while while arseniosideritearseniosiderite was found to was found to consisitconsisit of micro size orderedof micro size ordereddomains and the link between the order of these structures wasdomains and the link between the order of these structures wasfound to arise from the difference in their Hfound to arise from the difference in their H--bonding.bonding.

The C a(II)The C a(II)- -Fe (III)Fe (III) ² ² AsO AsO44 System System



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F u t u re W orkF u t u re W ork

Determine the crystal structure of BFAS and how it relatesDetermine the crystal structure of BFAS and how it relates

crystallographically with BFS.crystallographically with BFS.

Does varying the [FeDoes varying the [Fe3+3+ ] and fixing the [As ] and fixing the [As5+5+ ] produce ] producedifferent phases.different phases.

How does precipitation viaHow does precipitation via i n i n - -sit u sit u oxidation (Ooxidation (O22 or air) of or air) of FeFe2+2+ and Asand As5+5+ affect the arsenic phases produced. Theseaffect the arsenic phases produced. Thesephases must be thoroughly analyzed via elemental,phases must be thoroughly analyzed via elemental,electronic, molecular and structural analysis.electronic, molecular and structural analysis.

No phase transformation toNo phase transformation to ferrihydriteferrihydrite of the ferricof the ferricarsenate phases produced herein was observed at 25 C;arsenate phases produced herein was observed at 25 C;is this idea a real experimental occurrence or just ais this idea a real experimental occurrence or just acomputational thermodynamic calculation ?computational thermodynamic calculation ?



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Acknowledgements Acknowledgements

Dr. Demopoulos and Dr. CutlerDr. Demopoulos and Dr. Cutler

Dr. Becze and Dr. Le BerreDr. Becze and Dr. Le Berre

Dr. AssaaoudiDr. Assaaoudi Laboratoire de Caractérisation des MatériauxLaboratoire de Caractérisation des Matériaux

(Dr. Eluatik)(Dr. Eluatik)

Centre for Self Assembled Chemical StructuresCentre for Self Assembled Chemical Structures Canadian Light Source (Dr. Warner and HXMA,Canadian Light Source (Dr. Warner and HXMA,

SGM team)SGM team)

phd presentation 2 2

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