April 21, 2023 1

Study of Ni3Si-type core-shell nanoparticles by contrast variation

in SANS experimentP. Strunz1,2, D. Mukherji3, G. Pigozzi4, R. Gilles5, T. Geue6, K. Pranzas7

1Nuclear Physics Institute, CZ-25068 Řež near Prague (strunz@ujf.cas.cz)2Research Centre Řež, CZ-25068 Řež near Prague, Czech Republic

3TU Braunschweig, IfW, Langer Kamp 8, D-38106 Braunschweig, Germany4ETH Zurich, Laboratory for Nanometallurgy, CH-8093 Zürich, Switzerland5TU München, ZWE FRM-II, Lichtenbergstr. 1, D-85747 Garching, Germany

6PSI & ETH Zurich, Laboratory for Neutron Scattering, CH-5232 Villigen PSI, Switzerland7GKSS Research Centre, Institute of Materials Research, D-21494 Geesthacht, Germany

Project supported by the European Commission under the 6th Framework Programme through the Key Action: Strengthening the European Research Area, Research Infrastructures. Contract n°: RII3-CT-2003-505925 '

Outline Metallic nanoparticles

• production by ESPD• core-shell nanoparticles

SANS experiment• motivation• bulk alloy• extracted nanoparticles

(contrast variation)

April 21, 2023 2

Nano-size particles – productionNano-size particles – production

Synthesis of nano-size particles: sputtering, laser ablation, inert gas condensation, mechanical alloying or other means of severe plastic deformation, chemical methods …

Synthesis of nano-size particles: sputtering, laser ablation, inert gas condensation, mechanical alloying or other means of severe plastic deformation, chemical methods …

extractionmesoscale or nanoscale structural

entities present in many bulk materials

ETH Zurich and TU Braunschwieg: electrochemical selective phase dissolution technique

=> production of different nano-structures, including nano-particles with a core-shell structure

extraction of nano-sized precipitates from simple two phase metallic alloys

extractionmesoscale or nanoscale structural

entities present in many bulk materials

ETH Zurich and TU Braunschwieg: electrochemical selective phase dissolution technique

=> production of different nano-structures, including nano-particles with a core-shell structure

extraction of nano-sized precipitates from simple two phase metallic alloys

April 21, 2023 3

Extraction processExtraction process

the technique not new TU Braunschweig and

ETH Zurich: significant modifications

the technique not new TU Braunschweig and

ETH Zurich: significant modifications

particle size tailoring diverse compositions (various intermetallic phases) each nano-particle: single crystal

particle size tailoring diverse compositions (various intermetallic phases) each nano-particle: single crystal

1. Formation of nano-sized precipitates structure in bulk alloy by heat treatment

1. Formation of nano-sized precipitates structure in bulk alloy by heat treatment

2. Separating the nano-structure from the bulk: selective phase dissolution

2. Separating the nano-structure from the bulk: selective phase dissolution

3. Collection of nano-particles (ultrasound vibrations)

3. Collection of nano-particles (ultrasound vibrations)

flexibility: flexibility:

April 21, 2023 4

Potential applicationsPotential applications

intermetallic particles: production of exotic/unconventional composites thin coatings

Hyperthermia for magnetic particles

Catalytic and photonic applications for suitable particles

intermetallic particles: production of exotic/unconventional composites thin coatings

Hyperthermia for magnetic particles

Catalytic and photonic applications for suitable particles

Nanoparticles covered by shellNanoparticles covered by shell

potential applications in diverse fields: optical devices, magnetic storage media, health

potential applications in diverse fields: optical devices, magnetic storage media, health

April 21, 2023 5

matrix dissolution process tested on two-phase Ni–Si or Ni–Si–Al alloys: Ni3Si particles covered by amorphous shell made of SiOx (ETH Zurich, Institute of Applied Physics)

Core-shell particles only in Si containing alloys

amorphous Si-O shell is bio-resistant => particles may be suitable for medical applications

matrix dissolution process tested on two-phase Ni–Si or Ni–Si–Al alloys: Ni3Si particles covered by amorphous shell made of SiOx (ETH Zurich, Institute of Applied Physics)

Core-shell particles only in Si containing alloys

amorphous Si-O shell is bio-resistant => particles may be suitable for medical applications

Nanoparticles covered by shellNanoparticles covered by shell

April 21, 2023 6

Studied material: alloy Ni - 13.3Si - 2Al (at %)

Heat treatment:

solution treatment - 1100°C 48 h WQ

ageing - 600°C 24 h WQ

electrochemical selective phase dissolution (ESPD): electrolyte: aqueous solution, 1% citric acid, 1% ammonium

sulfate

extraction voltages between 1.25 and 1.45 V

Studied material: alloy Ni - 13.3Si - 2Al (at %)

Heat treatment:

solution treatment - 1100°C 48 h WQ

ageing - 600°C 24 h WQ

electrochemical selective phase dissolution (ESPD): electrolyte: aqueous solution, 1% citric acid, 1% ammonium

sulfate

extraction voltages between 1.25 and 1.45 V

Processing parameters for core-shell particleProcessing parameters for core-shell particle

April 21, 2023 7

Characterization by XRD, TEM, EDSCharacterization by XRD, TEM, EDS

Shell amorphous no precise composition, estimation: Si 15%, O 85%

core structure and composition: = precipitates in the bulk alloy apparently: the nanoparticles retain also the shape and size

But: these methods alone insufficient

Shell amorphous no precise composition, estimation: Si 15%, O 85%

core structure and composition: = precipitates in the bulk alloy apparently: the nanoparticles retain also the shape and size

But: these methods alone insufficient

Shell formation, possibilities : 1. Depletion of Ni from Ni-Si solid

solution matrix and re-deposition of Si on particle surface;

2. Depletion of Ni from Ni3Si precipitate surface;

3. Depletion of Ni from Ni-Si solid solution matrix and local diffusion of Si on particle surface.

Shell formation, possibilities : 1. Depletion of Ni from Ni-Si solid

solution matrix and re-deposition of Si on particle surface;

2. Depletion of Ni from Ni3Si precipitate surface;

3. Depletion of Ni from Ni-Si solid solution matrix and local diffusion of Si on particle surface.

April 21, 2023 8

SANS: motivationSANS: motivation

confirm core-shell structure by an independent method

confirm core-shell structure by an independent method

comparison: precipitates in the bulk alloy and nanoparticles

contrast variation (masking the shell)

=> core and core+shell size, shell SLD

comparison: precipitates in the bulk alloy and nanoparticles

contrast variation (masking the shell)

=> core and core+shell size, shell SLD

indicate the shell composition indicate the shell composition

indicate which mechanism of shell formation takes place

indicate which mechanism of shell formation takes place

methodmethod

April 21, 2023 9

Experimental (SANS-II, SINQ, PSI)Experimental (SANS-II, SINQ, PSI)

1. solid sample from the bulk alloy

2. about 20 mg of nanoparticles dispersed in H2O/D2O mixture

(extracted from the same alloy as the bulk sample)

ultrasonic vibration for 30 min: to obtain a cluster free dispersion

possible to measure within 30 minutes, then decrease of intensity due to sedimentation

used D2O volume fractions in H2O/D2O: 100% (SLD of the mixture 63.3×109 cm-2), 80% (49.7×109 cm-2), 67% (40.7×109 cm-2) 32% (16.3×109 cm-2)

1. solid sample from the bulk alloy

2. about 20 mg of nanoparticles dispersed in H2O/D2O mixture

(extracted from the same alloy as the bulk sample)

ultrasonic vibration for 30 min: to obtain a cluster free dispersion

possible to measure within 30 minutes, then decrease of intensity due to sedimentation

used D2O volume fractions in H2O/D2O: 100% (SLD of the mixture 63.3×109 cm-2), 80% (49.7×109 cm-2), 67% (40.7×109 cm-2) 32% (16.3×109 cm-2)

April 21, 2023 10

Solid sample of Ni-13.3Si-2Al alloySolid sample of Ni-13.3Si-2Al alloy

The inter-particle interference peak at low Q magnitudes: dense population of precipitates

four precipitate populations necessary to describe the data

The inter-particle interference peak at low Q magnitudes: dense population of precipitates

four precipitate populations necessary to describe the data

model: polydisperse 3D system of particles

2nd population: an extension of the 1st one

3rd and 4th populations in the channels between the larger precipitates

model: polydisperse 3D system of particles

2nd population: an extension of the 1st one

3rd and 4th populations in the channels between the larger precipitates

Polycrystalline alloy => isotropic => 3D cross section averaged

Polycrystalline alloy => isotropic => 3D cross section averaged

gray: precipitate white: matrix

1st population

2nd population

3rd population 4th population

April 21, 2023 11

solid sample, parameterssolid sample, parameters

Volume distributionsVolume distributions

total volume fraction of all populations ~44%

total volume fraction of all populations ~44%

April 21, 2023 12

nanopowder sample extracted from bulk alloynanopowder sample extracted from bulk alloy

SANS from nanoparticles in D2O (100%)

compared to the precipitates in the bulk alloy from which the nanoparticles are extracted

SANS from nanoparticles in D2O (100%)

compared to the precipitates in the bulk alloy from which the nanoparticles are extracted

volume fraction lower, scattering contrast higher => magnitude of scattering similar

Shape changed (no influence of interparticle interference) the slope of the scattering curve from the powder in the asymptotic

region deviates from Porod law (dΣ/dΩ ~ Q-4)

volume fraction lower, scattering contrast higher => magnitude of scattering similar

Shape changed (no influence of interparticle interference) the slope of the scattering curve from the powder in the asymptotic

region deviates from Porod law (dΣ/dΩ ~ Q-4)

April 21, 2023 13

nanopowder sample, contrast variationnanopowder sample, contrast variation

extracted nanoparticles dispersed in various mixtures of H2O/D2O

all mixtures except 80% D2O: the slope at medium-to-large Q deviates from Porod law

evolution with changing SLD cannot be explained without the presence of a shell

extracted nanoparticles dispersed in various mixtures of H2O/D2O

all mixtures except 80% D2O: the slope at medium-to-large Q deviates from Porod law

evolution with changing SLD cannot be explained without the presence of a shell

nanoparticles represented by a cuboid model, core-shell form

core SLD 80.7×109 cm−2

distribution of sizes

two populations

nanoparticles represented by a cuboid model, core-shell form

core SLD 80.7×109 cm−2

distribution of sizes

two populations1st population

2nd population

detail

model model

April 21, 2023 14

contrast variation, SLD of the shellcontrast variation, SLD of the shell

SANS measurement:

H2O/D2O mixture with 80% D2O: the shell masked

Q-4 scattering at medium-to-large Q magnitudes

=> SLD of the shell: around 49×109 cm-2

Calculation:

Input (EDS): Oxygen content 85 at%

Input: mass density of amorphous silicon oxide 2.20 g/cm3

=> theoretical SLD around 41×109 cm-2.

Difference: cannot be explained by experimental errors

Possible explanations

presence of OH ions in the shell

density of amorphous SiOx layer higher than assumed

SANS measurement:

H2O/D2O mixture with 80% D2O: the shell masked

Q-4 scattering at medium-to-large Q magnitudes

=> SLD of the shell: around 49×109 cm-2

Calculation:

Input (EDS): Oxygen content 85 at%

Input: mass density of amorphous silicon oxide 2.20 g/cm3

=> theoretical SLD around 41×109 cm-2.

Difference: cannot be explained by experimental errors

Possible explanations

presence of OH ions in the shell

density of amorphous SiOx layer higher than assumed

80% D2O80% D2O

100% D2O100% D2O

April 21, 2023 15

contrast variation, nanopowder parameterscontrast variation, nanopowder parameters

volume-weighted size distribution of extracted core-shell nanoparticles (all mixtures)

volume-weighted size distribution of extracted core-shell nanoparticles (all mixtures)

Sample preparation results of SANS evaluation 1st population (large particles) 2nd population (medium-size

particles) Sum

D2O content (%)

SLD of H2O/D2O mixture (cm-2)

Vol.fr. of particles1 (%)

Vol. fr. of core (%)

Total2 mean size (nm)

Shell thickness (nm)

Vol. fr. of core (%)

Total2 mean size (nm)

Shell thickness (nm)

Core vol. fr. (%)

100 63.3×109 3.22 1.02 205 16.5 1.30 82.5 5.1 2.32 80.2 49.8×109 2.59 0.73 201 (3) 17.0 1.24 82.5 (3) 5.4 1.97 67.0 40.7×109 2.18 0.62 202 16.9 1.13 76.6 5.1 1.75 31.7 16.3×109 1.27 0.24 194 14.3 0.60 82.6 5.5 0.84

April 21, 2023 16

comparison: precipitates vs.

nanopowder

comparison: precipitates vs.

nanopowder

3rd and 4th populations (small precipitates) observed in the bulk sample not present in the nanopowder sample

1st and 2nd distributions (core) correspond well in size scale with the original populations in the solid sample

=> indication that the particle core was not attacked by the electrolyte during extraction process

3rd and 4th populations (small precipitates) observed in the bulk sample not present in the nanopowder sample

1st and 2nd distributions (core) correspond well in size scale with the original populations in the solid sample

=> indication that the particle core was not attacked by the electrolyte during extraction process

distributions in solid sample compared to extracted nanoparticles

displayed distributions: the core and the core + shell

distributions in solid sample compared to extracted nanoparticles

displayed distributions: the core and the core + shell

April 21, 2023 17

1. The existence of a core-shell structure in the extracted nanoparticles is confirmed by SANS measurements.

2. SANS provided quantitative information on the size distribution and volume fraction of nanoparticles.

3. SANS indicates that the selective phase dissolution is very effective for the manufacturing of the core-shell nanoparticles (the matrix dissolved, precipitate unaffected)

4. Dealloying of matrix Ni(Si) provides Si for shell formation; Si deposits on top of extracted nanoparticle core in conjunction with oxidation

1. The existence of a core-shell structure in the extracted nanoparticles is confirmed by SANS measurements.

2. SANS provided quantitative information on the size distribution and volume fraction of nanoparticles.

3. SANS indicates that the selective phase dissolution is very effective for the manufacturing of the core-shell nanoparticles (the matrix dissolved, precipitate unaffected)

4. Dealloying of matrix Ni(Si) provides Si for shell formation; Si deposits on top of extracted nanoparticle core in conjunction with oxidation

SummarySummary

April 21, 2023 18

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April 21, 2023 20

Next slides left here only for possible discussion

April 21, 2023 21

April 21, 2023 22

1E-3 0.01 0.10.01

0.1

1

10

100

1000

10000

azimuthal average

Qx (Å-1)

d/d

(c

m-1sr

-1)

GKSS-SANS-2 21m, 11.6A GKSS-SANS-2 21m, 5.8A GKSS-SANS-2 9m, 5.8A GKSS-SANS-2 3m, 5.8A GKSS-SANS-2 1m, 5.8A

April 21, 2023 23

Potential applicationsPotential applications

intermetallic particles: production of exotic/unconventional composites thin coatings.

Hyperthermia for magnetic particlesCatalytic and photonic applications for suitable particles

intermetallic particles: production of exotic/unconventional composites thin coatings.

Hyperthermia for magnetic particlesCatalytic and photonic applications for suitable particles

74.0 74.2 74.4 74.6 74.8 75.0 75.2 75.4 75.6 75.8 76.00

1000

2000

3000

4000Sample II, 220 reflection:estimated particle size: 84nm.

Experimental Data

Fitted curve (peak broadening including instrumental curve)

Fitted curve (peak broadening without instrumental curve)

Instrumental curve (taken from 450nm powder, reflection 220)

Mea

sure

d a

nd

fit

ted

inte

nsi

ty

(cou

nts/

100s

)

2 (°)

(by product) application can be also for development of evaluation methods for diffraction (profile analysis):

no strain, no texture, small size => test of size-broadening formulas

(by product) application can be also for development of evaluation methods for diffraction (profile analysis):

no strain, no texture, small size => test of size-broadening formulas

uniaxial load => directional coarsening (rafting)

interconnected lamelae through the sample

metallic nanoporous membrane: filtering, separation processes

uniaxial load => directional coarsening (rafting)

interconnected lamelae through the sample

metallic nanoporous membrane: filtering, separation processes

April 21, 2023 24

volume fraction, scattering contrastvolume fraction, scattering contrast

A. absolute magnitude of the cross-section can be used

scattering contrast has to be known

frequently unknown in multicomponent solids (uncertainties in composition)

A. absolute magnitude of the cross-section can be used

scattering contrast has to be known

frequently unknown in multicomponent solids (uncertainties in composition)

B. dense system: interparticle distance determined

=> geometrical volume fraction => real volume fraction (if

homogeneous distribution) contrast back-calculated using

the absolute dΣ/dΩ

B. dense system: interparticle distance determined

=> geometrical volume fraction => real volume fraction (if

homogeneous distribution) contrast back-calculated using

the absolute dΣ/dΩ

gray: precipitate white: matrix