December 11, Study of Ni 3 Si-type core-shell nanoparticles by contrast variation in SANS experiment P. Strunz 1,2, D. Mukherji 3, G. Pigozzi 4, R. Gilles 5, T. Geue 6, K. Pranzas 7 1 Nuclear Physics Institute, CZ Řež near Prague 2 Research Centre Řež, CZ Řež near Prague, Czech Republic 3 TU Braunschweig, IfW, Langer Kamp 8, D Braunschweig, Germany 4 ETH Zurich, Laboratory for Nanometallurgy, CH-8093 Zürich, Switzerland 5 TU München, ZWE FRM-II, Lichtenbergstr. 1, D Garching, Germany 6 PSI & ETH Zurich, Laboratory for Neutron Scattering, CH-5232 Villigen PSI, Switzerland 7 GKSS Research Centre, Institute of Materials Research, D 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 ' Outline  Metallic nanoparticles production by ESPD core-shell nanoparticles  SANS experiment motivation bulk alloy extracted nanoparticles (contrast variation)

December 11, Nano-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 …  extraction  mesoscale 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  extraction  mesoscale 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

December 11, Extraction 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  2. Separating the nano- structure from the bulk: selective phase dissolution  3. Collection of nano-particles (ultrasound vibrations) flexibility:

December 11, Potential 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 shell  potential applications in diverse fields: optical devices, magnetic storage media, health

December 11,  matrix dissolution process tested on two-phase Ni–Si or Ni–Si– Al alloys: Ni 3 Si particles covered by amorphous shell made of SiO x (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: Ni 3 Si particles covered by amorphous shell made of SiO x (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 shell

December 11,  Studied material: alloy Ni Si - 2Al (at %)  Heat treatment:  solution treatment °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 Si - 2Al (at %)  Heat treatment:  solution treatment °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 particle

December 11, Characterization 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 Ni 3 Si 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 Ni 3 Si precipitate surface;  3. Depletion of Ni from Ni-Si solid solution matrix and local diffusion of Si on particle surface.

December 11, SANS: motivation  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 which mechanism of shell formation takes place method

December 11, Experimental (SANS-II, SINQ, PSI)  1. solid sample from the bulk alloy  2. about 20 mg of nanoparticles dispersed in H 2 O/D 2 O 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 D 2 O volume fractions in H 2 O/D 2 O:  100% (SLD of the mixture 63.3×10 9 cm -2 ),  80% (49.7×10 9 cm -2 ),  67% (40.7×10 9 cm -2 )  32% (16.3×10 9 cm -2 )  1. solid sample from the bulk alloy  2. about 20 mg of nanoparticles dispersed in H 2 O/D 2 O 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 D 2 O volume fractions in H 2 O/D 2 O:  100% (SLD of the mixture 63.3×10 9 cm -2 ),  80% (49.7×10 9 cm -2 ),  67% (40.7×10 9 cm -2 )  32% (16.3×10 9 cm -2 )

December 11, Solid 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 gray: precipitate white: matrix 1 st population 2 nd population 3 rd population4 th population

December 11, solid sample, parameters  Volume distributions  total volume fraction of all populations ~44%

December 11, nanopowder sample extracted from bulk alloy  SANS from nanoparticles in D 2 O (100%)  compared to the precipitates in the bulk alloy from which the nanoparticles are extracted  SANS from nanoparticles in D 2 O (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 )

December 11, nanopowder sample, contrast variation  extracted nanoparticles dispersed in various mixtures of H 2 O/D 2 O  all mixtures except 80% D 2 O: 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 H 2 O/D 2 O  all mixtures except 80% D 2 O: 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 80.7×10 9 cm −2  distribution of sizes  two populations  nanoparticles represented by a cuboid model, core-shell form  core SLD 80.7×10 9 cm −2  distribution of sizes  two populations 1 st population 2 nd population detail  model

December 11, contrast variation, SLD of the shell  SANS measurement:  H 2 O/D 2 O mixture with 80% D 2 O: the shell masked  Q -4 scattering at medium-to-large Q magnitudes  => SLD of the shell: around 49×10 9 cm -2  Calculation:  Input (EDS): Oxygen content 85 at%  Input: mass density of amorphous silicon oxide 2.20 g/cm 3  => theoretical SLD around 41×10 9 cm -2.  Difference: cannot be explained by experimental errors  Possible explanations  presence of OH ions in the shell  density of amorphous SiO x layer higher than assumed  SANS measurement:  H 2 O/D 2 O mixture with 80% D 2 O: the shell masked  Q -4 scattering at medium-to-large Q magnitudes  => SLD of the shell: around 49×10 9 cm -2  Calculation:  Input (EDS): Oxygen content 85 at%  Input: mass density of amorphous silicon oxide 2.20 g/cm 3  => theoretical SLD around 41×10 9 cm -2.  Difference: cannot be explained by experimental errors  Possible explanations  presence of OH ions in the shell  density of amorphous SiO x layer higher than assumed 80% D 2 O 100% D 2 O

December 11, contrast variation, nanopowder parameters  volume-weighted size distribution of extracted core-shell nanoparticles (all mixtures)

December 11, 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

December 11,  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 Summary

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December 11, Next slides left here only for possible discussion

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December 11, Potential 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  (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

December 11, volume 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