PREPARATION, PROPERTIES APPLICATIONS HIGHLY DISPERSED METALLIC PARTICLES. Dan Goia Clarkson University

Transcription

1 PREPARATION, PROPERTIES AND APPLICATIONS OF HIGHLY DISPERSED METALLIC PARTICLES Dan Goia Clarkson University

2 PREPARATION OF METALLIC PARTICLES Phase break down - Milling/grinding -Atomization Phase transformation - Thermolysis/Pyrolysis -Reduction Phase build-up - Condensation in gas phase (Me 0 ) g - Condensation in liquid phase (Me 0 ) l

3 PHASE BREAK DOWN / MILLING Size reduction of coarse/agglomerated metallic powders - Mechanical energy (shear, collision) - Dispersion media (liquid or gas) - Dispersing agents - Controlled atmosphere and temperature frequently required Suitable for some applications (mechanical alloying) Rarely yields highly monodispersed, spherical particles

4 PHASE BREAK DOWN / ATOMIZATION Spraying/pulverization of molten metals Large particles, broad size distributions - Monodispersed particles - Sub-micrometer size Capable to produce a large variety of alloy powders Low manufacturing costs Inert carrier gases may be required

5 PHASE TRANSFORMATION AEROSOL THERMOLYSYS AEROSOL REDUCTION MeX 2 T Metallic particle +2 e - MeX 2-2X - Difficult to control the size distribution of precursor droplets - Agglomeration of droplets/particles due to collisions Wide particle size distribution

6 PHASE TRANSFORMATION T, ne - +n e - -n X Metallic compounds Metallic particles

7 SPRAY PYROLYSIS/AEROSOL THERMOLYSIS Decomposition of liquid precursors in gas phase >120 0 C >850 0 C >1,000 0 C Pd(NO 3 ) 2 droplet Pd(NO 3 ) 2 crystal Polycrystalline Highly crystalline Pd particle Pd particle Size, uniformity, and degree of agglomeration of Me particles depends on: a) Size and size distribution of droplets - Droplet generation pneumatic/spraying ultrasonic - Size control pressure transducers frequency, size ~ ν - Size distribution various approaches (momentum, gravitation force) b) Stability of the aerosols (droplets, intermediates, and final particles) - Laminar flow during the process - Working below the critical concentration)

8 PHASE BUILD UP / CONDENSATION Condensation from gas phase Condensation from liquids (Chemical Precipitation) CVD Plasma (Me n+ ) l (MeX) g -X T T (Me 0 ) s + ne - (Me 0 ) g (Me 0 ) l Nucleation and Growth (Me 0 n) gas (Me 0 n) liquid

9 CHEMICAL PRECIPITATION Metal atoms generated via redox reactions: Me n+ + Red Me 0 + Ox Driving force: E 0 = E 0 1 -E0 2 ln K e = nf E 0 /RT E 0 critical supersaturation nucleation rate

10 MnO H e - MnO 2 + 2H 2 O Au e - Au 0 Pt e - Pt 0 Pd e - Pd 0 Ag + + e - Ag 0 C 6 H 8 O 6 C 6 H 8 O e- + 2H + R-CH 2 OH R-COH + 2e - + 2H + N 2 H 4 + 4OH- N e - + H 2 O Cu e - Cu 0 H + + e - ½H 2 Co e - Co 0 Fe e - Fe 0 Zn e - Zn 0 V e - V Ti e - Ti 0 Al e - Al 0

11 TAILORING E 0 Ag + + 1e - Ag 0 E 0 = V Precipitation Ag + + Cl - AgCl K sp = 1.82 x AgCl + 1e - Ag 0 + Cl - E 0 AgCl = E0 Ag /1 log[cl- ]/K sp = (log[Cl - ] logk sp ) = 0.222V AgI K sp = 3.0 x E 0 = V Ag 2 S K sp = 6.3 x E 0 = V Complexation Ag + + 2NH 3 Ag[NH 3 ] 2 + pk f = Ag[NH 3 ] e - Ag 0 + 2NH 3 E 0 Ag[NH3]2 = E0 Ag /1 log[ag+ ][NH3] 2 /[Ag(NH3)2] + = (pK f ) = 0.373V Concentration Ag(SO 3 ) e - Ag + + 2SO 2-3 pk f = 8.68 E 0 = 0.430V Ag(S 2 O 3 ) e - Ag + + 2S 2 O 2-3 pk f = E 0 = 0.010V Ag(CN) e - Ag + + 2CN - pk f = E 0 = V E = E log [Ag 0 ]/[Ag + ] = log[ag + ] [Ag + ] = 10 3 M E 0 = 0.777V

12 TAILORING E 0 Effect of the ph Whenever H + or OH - species are involved in the reaction Examples a) C 6 H 6 O + 6 2e - + 2H + C 6 H 8 O 6 E 0 = V E 0 = E /2 log[c 6 H 8 O 6 ]/[H + ] 2 [C 6 H 6 O 6 ] = (ph) [H + ], ph C 6 H 8 O 6 less strong reductant b) N 2 + 4e - + 4H 2 O N 2 H 4 + 4OH - E 0 = V E 0 = E /4 log1/[oh - ] 4 = (14 - ph) [H + ], ph Hydrazine becomes a less strong reductant

13 REDOX DIAGRAMS E (V) + Pd e - Pd 0 Ag + + e - Ag 0 Ag[NH 3 ] e - Ag 0 + 2NH 3 0 ph Pd[NH 3 ] e - Pd NH 3 C 6 H 6 O 6 + 2e - + 2H + C 6 H 8 O 6 - N 2 + 4e - + 4H 2 O N 2 H 4 + 4OH -

14 CONDENSATION FROM LIQUID PHASE METAL IONS/COMPLEXES Reduction METAL ATOMS (~3Å) CLUSTERS NUCLEI (~8-10Å) Diffusional growth NANOSIZE PRIMARY PARTICLES (1-30 nm) Diffusional growth/ Coagulation Effective Stabilization Aggregation LARGE PARTICLES (Crystalline / Polycrystalline) TRUE NANOSYSTEMS AGGREGATED NANOSIZE SYSTEMS

15 EXPERIMENTAL DIRECT ADDITION REVERSED ADDITION DOUBLE-JET ADDITION Red Me n+ /MeX m n Red Me n+ /MeX m n MeX n+ m Me n+ Disp. Red Disp. Disp. C C Red C Me n+ Me n+ Red Me n+ Red T n T f Time T n T f Time T n T f Time

16 CRITICAL PROPERTIES Particle size and size distribution Internal structure Particle morphology Internal composition Surface properties

17 PREPARATION OF NANOSIZE METALLIC PARTICLES a) Generate a large number of nuclei b) Involve a large fraction (f) of atoms in the nucleation step Final size in the nanosize range R p = r n (100/f ) 1/3 Provide high supersaturation (large E) Use suitable dispersion media Work in dilute systems Use surfactants c) Prevent the aggregation of primary particles Maximize electrostatic repulsive forces (dilute systems) Minimize/screen attractive forces (dispersing agents)

18 Platinum Particles (~ 2.0 nm)

19 Nanosize Silver Particles (~90 nm)

20 PREPARATION OF LARGE PARTICLES A. CRYSTALLINE diffusion growth - Slow nucleation (small E, strong metallic complexes) - Slow addition of precursors in the system - Use of seeds - Very effective stabilization B. POLYCRYSTALLINE PARTICLES aggregation - Control the attractive/repulsive forces by adjusting: - Ionic strength -ph - Activity of the dispersant/protective colloid - More versatile in controlling the size of the particles

21 CRYSTALLINE GOLD POWDER

22

23 0.15 µm 0.30 µm 0.5 µm 1.0 µm AgPd Spherical Alloy Particles

24 INTERNAL PARTICLE STRUCTURE Diffusional Growth Effective colloid stabilization Small E, supersaturation Crystalline Particles Nanosize Primary Particles Coagulation/Aggregation Poor colloid stabilization Large E, supersaturation Polycrystalline Particles

25 INTERNAL METAL PARTICLES FORMATION STRUCTURE Crystalline Monodispersed Gold Polycrystalline Monodispersed Gold 2 µm 2 µm

26 IMPORTANCE OF PARTICLE STRUCTURE A. Electronics/Thick film Due to the absence of internal grain boundaries, highly crystalline particles of PM yield dense, continuous, thinner, and more conductive fired films. B. Electronics/Oxidation of base metals Highly crystalline base metals (Cu, Ni) are more resistant against oxidation when used as precursors for thick film conductors. C. Medicine/Biology Highly crystalline, dense gold particles are more effective as carriers of drugs/vaccines through biological tissues.

27 PARTICLE MORPHOLOGY Hexagonal Gold platelets

28 PARTICLE MORPHOLOGY Crystalline Pd Particles

29 INTERNAL COMPOSITION Bimetallic particles electronics (wide range of properties attainable) catalysis (enhanced catalytic activity) Core/Shell structure E 0 1 E 0 2 the most electropositive element will form the core the most electronegative element will form the shell Precipitation order can be tailored by appropriate complex formation Solid solutions /Alloys E 0 1 E 0 2 similar reduction rates E 0 1, E0 2 >> fast reactions Uniformly mixed crystalline lattices

30 SURFACE PROPERTIES IMPACT Dispersibility in liquids Self assembly properties Sintering characteristics Catalytic activity Adhesion properties Corrosion TAILORING SURFACE BEHAVIOR Selection of precipitation environment (reductant, dispersant, solvent) Subsequent surface treatment (performed on either wet or dry powders) - Coating with organic compounds - Coating with inorganic compounds - Coating with metals

31 ELECTROLESS PLATING Nucleation Growth Homogeneous Heterogeneous Ox Ox Ox Ox Red e - Ag + Ag + e - Red Red Red e - Ag + Ag + e - Ag n 0 e - e - Ag + Ag 0 Ag + Ag + n e - e- Ag + Ag + Ag n 0 e - Metal cluster Red: C 6 H 8 O 6, N 2 H 4 Substrate

32 ELECTRODISPLACEMENT Ag + Ag+ Cu 2+ e - e - Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Cu 0 Copper Cu 2+ e - e - e - e - Ag + Ag+ Ag + Ag+ Cu 2+ e - Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Cu 0 e -

33 APPLICATIONS OF MONODISPERSED METALLIC PARTICLES Electronics Catalysis Biology and medicine Pigments Obscurant smokes Nonlinear optics Transparent conductive coatings Ferromagnetic fluids High density magnetic storage

34 Conductive layers a) Fired /Sintered films THICK FILM TECHNOLOGY Metal paste Drying Green layer Sintering Metallic layer substrate b) Non-Fired films Metal paste Drying/Curing Metal-filled polymer film substrate

35 ULTRATHIN METALLIC LAYERS Dielectric Tape 1.0 µm Electrode film

36 SECTION THROUGH A MLCC (Up to 800 alternative layers) dielectric layers (~ 6 µm) metallic layers (~ 1 µm) Human hair (~ 60 µm)

37 HIGH PERFORMANCE METAL POWDERS Spherical Monodispersed Size : µm Non-agglomerated particles Easily dispersible Controlled composition (metals ratio, impurities) Highly crystalline Controlled sintering behavior

38 Ag/Pd Ni Cu 2.0 µm 1.0 µm 2.0 µm

39 ULTRATHIN METALLIC FILMS % = 131 nm 50% = 153 nm 90% = 179 nm 100% = 240 nm 100 Φ SEM = 130 nm Intensity I A = Particle Diameter (nm) Monodispersed AgPd Particles

40 Monodispersed Co particles

41 Monodispersed Ag Particles Applications Antimicrobial activity - Antimicrobial coatings - Water purification SPR Biosensing Transparent conductive coatings - Coating of CRT screens - Potential replacement for ATO 50 nm

42 Monodispersed Nanosize Gold Particles Applications: Medicine and Biology - Delivery of anti-tumor drugs - Vaccine delivery - Biosensing and bioassays (SPR) Pigments for functional glasses 50 nm

43 NANOSIZE METALS IN CATALYSIS Decreasing particle size larger specific surface area larger fraction of surface atoms Benefits : Increased catalytic activity Significant cost reduction Difficulties : Separation of reaction products Propensity for sintering Supported metal catalysts

44 SUPPORTED METALLIC CATALYSTS Adhesion technique On-support precipitation Support Dispersant Metallic particle

45 Pt/Ru/C Catalyst For PEM Fuel Cells

46 PEM FUEL CELLS Electrodes: nm Pt and Pt/Ru particles supported on carbon - Up to 60% metal loading Pt, PtRu/Carbon H 2 / H 2 O Anode 2 e - PEM 2 H + Cathode 2 O 2-2 e - Pt/Carbon H 2 O O 2 /Air

47 CONCLUSIONS Chemical precipitation is a versatile technique capable to yield non-agglomerated monodispersed metallic particles with: - wide range of modal diameters (1 nm to several microns) - controlled internal structure and morphology - controlled composition - controlled surface characteristics Materials for many existing and emerging fields of high technology CHALLENGE: Assembly of fine particles (nanoparticles) into ordered mono, bi, and three-dimensional complex structures structures