Nanoparticles from the Gasphase: Formation, Structure, Properties

424 Pages·2012·16.133 MB·English

by  Hartmut Wiggers, Mustapha Fikri, Irenaeus Wlokas, Paul Roth, Christof Schulz (auth.), Axel Lorke, Markus Winterer, Roland Schmechel, Christof Schulz (eds.)

NanoScience and Technology
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Editors
Nanoparticles from
the Gas Phase
Formation, Structure, Properties
123
Editors
Axel Lorke Roland Schmechel
Department of Physicsand CENIDE Faculty ofEngineering, and CENIDE
Universityof Duisburg-Essen Universityof Duisburg-Essen
Lotharstraße 1 Bismarckstraße 81
47057Duisburg 47057Duisburg
Germany Germany
MarkusWinterer Christof Schulz
Nanoparticle ProcessTechnology, InstituteforCombustion and Gasdynamics
and CENIDE (IVG), andCENIDE
Universityof Duisburg-Essen Universityof Duisburg-Essen
Lotharstraße 1 Lotharstraße 1
47057Duisburg 47057Duisburg
Germany Germany
ISSN 1434-4904
ISBN 978-3-642-28545-5 ISBN 978-3-642-28546-2 (eBook)
DOI 10.1007/978-3-642-28546-2
SpringerHeidelbergNewYorkDordrechtLondon
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(cid:2)Springer-VerlagBerlinHeidelberg2012
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Foreword
Duringthelastdecadesnoareainnaturalsciencesandengineeringhasdeveloped
more rapidly than nanostructured materials. The reason is that in the size regime
between a few atoms and the bulk limit, many properties vary in a dramatic way
such as melting temperature, band gap, or magnetic and optical properties. This
rich variety of size effects by nanoparticles has inspired many practical applica-
tions and is considered to be one of the driving forces behind future technical
solutions.Theimportanceofthenanometersizeregimewasalreadymentionedby
W. Ostwald in his famous book ‘‘Die Welt der vernachlässigten Dimensionen’’
published in 1915. But only at the end of the twentieth century, a systematic
preparation of nanoparticles in colloidal and gaseous systems and their charac-
terization by a variety of physical and chemical tools started. New theoretical
concepts exploring the measured size effects were accompanying the starting
nano-age.Thedevelopingnanoscienceisahighlyinterdisciplinaryfieldthatsheds
light on many fundamental issues but must also show its practical relevance by
inspiring new or improved processes and products.
Nanoparticles from the gas phase have their special properties because the
formationandtransportspaceisinthiscaserestricted.Typicalbirthprocessesare
nucleation from supersaturated vapor and/or reactive formation due to a chain of
gaseous decomposition and synthesis reactions. Laser or plasma ablation from
solid surfaces and subsequent nucleation and surface growth is a kind of rear-
rangement of material in the form of nanoparticles. A reactive formation of
nanostructures normally proceeds in a fluid flow containing the gaseous or liquid
dissolved precursors. The partly endothermic reactions must be initiated by
increasingthetemperaturebyvarious energysources.Typicaldevicesused inthe
science community are hot wall reactors, plasma and laser reactors, or different
types of flames. They all open the possibility of staged reaction processes for
coated or mixed particles.
In industry, gas-phase combustion synthesis of carbonaceous and inorganic
particles is used routinely today to make a variety of commodities like various
kinds of soot or the oxides SiO , TiO , Al O , etc. amounting to millions of tons
2 2 2 3
v
vi Foreword
annually. They are industrially used in particular for tires and as pigments,
opacities, catalysts, flowing aids, for optical fibers, and telecommunication. The
flame reactor is today the workhorse of this technology. It is cost-effective and
offers advantages over other material synthesis processes, e.g., wet-phase chem-
istry. The characteristic of gas-phase-made particles is self-purification with the
final powder product as a consequence of normally high synthesis temperature.
The detailed knowledge of the gas-phase synthesis of nanoparticles is still
limited. The kinetics of e.g. precursor reactions is not understood in all details.
Radicals, intermediates, and product molecules are formed, which polymerise or
nucleate to first clusters. Their thermal stability determines in many cases the
furtherparticlesevolutionprocess.Theclusterscangrowbygaskineticcollisions
between each other or by the addition of monomers to the cluster surface. The
coalescenceofcluster–clusterensemblesisnormallyveryfastresultingincompact
nearly spherical structures, which could be called ‘‘particle’’. The further particle
dynamics is determined by surface growth and by the interdependence of coag-
ulation and coalescence. Depending on their typical time scales, either ‘‘soft’’ or
‘‘hard’’ fractal aggregates are formed.
To get insights into the structure and properties of gas phase synthesized par-
ticles, modern diagnostics have been developed in the last decades. In situ size
measurements during the birth period of the particles are confronted with the
problemofsizingstructuresformnearlymoleculardimensionstoabout50nmand
more. Sampling techniques with online characterization of nanoparticles, which
have been developed for some time, are calibrated only with spheres. But syn-
thesized nanoparticles are often occurring as agglomerates, which need a detailed
description of their structure. As the smallest particles have a very high mobility
andreactivity,alsoexsituprobingonsurfaces,e.g.TEMgrids,mustbeperformed
very carefully. A representative particle sampling, which does not falsify or
changetheparticlepropertiesduringthecollectionitself,isnecessary.Thefurther
analysis of deposited particles depends on the available instrumentation or better
on the structural or morphological information which is of interest.
Applications of nanoparticles collected from the gas phase are still under
debate. Obviously, flame-made powders produced in industrial scales are needed
and the respective technologies will be improved. On the other hand, gas-phase
synthesiswillcontributetothedevelopmentofnewmaterialsandproducts,which
previouslyhavenotbeenmadebyothertechniques.Insitudopedparticles,mixed
metals, and mixed oxides will find technical and medical applications. Unusual
combinations of materials in segregated, dissolved, or core–shell structures wait
for practical usage. The question of bringing such functional particles into
respective matrixes or on surfaces will be a scientific and technical challenge for
the future.
This book summarizes scientific results, obtained from the ‘‘Sonderfor-
schungsbereich ‘Nanopartikel aus der Gasphase’ ’’, which was over many years
financiallysupportedbytheDeutscheForschungsgemeinschaft.Itwasinitiatedin
1998 by scientists from mechanical and electrical engineering and from physics.
Foreword vii
The different experiences of the participants in reactive flow phenomena, aerosol
technology, semiconducting, magnetic, and optoelectronic materials was suc-
cessfully bundled and was the interdisciplinary basis of the resulting research
program.
Duisburg, Germany Paul Roth
Heinz Fissan
Eberhard Wassermann
Contents
Part I Formation
1 Synthesis of Tailored Nanoparticles in Flames:
Chemical Kinetics, In Situ Diagnostics, Numerical
Simulation, and Process Development . . . . . . . . . . . . . . . . . . . . . 3
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 State of the Art in Flame-Based Synthesis
of Nanoparticles. . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Principles of Particle Formation and Growth
in the Gas Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Shock-Tube Studies of Precursor Reactions. . . . . . . . . . . . . . 8
1.3.1 Formation of Iron Clusters From Fe(CO) . . . . . . . . . 9
5
1.3.2 Reaction of Gallium Atoms
with Nitrogen and Oxygen. . . . . . . . . . . . . . . . . . . . 11
1.4 Flame Reactor Studies of Particle Formation and Growth . . . . 13
1.4.1 Molecular-Beam Sampling. . . . . . . . . . . . . . . . . . . . 15
1.4.2 Thermophoretic Sampling with Ex Situ Analysis . . . . 16
1.5 Laser-Based Diagnostics in Particle Synthesis Reactors. . . . . . 16
1.5.1 Diagnostics for Temperature . . . . . . . . . . . . . . . . . . 17
1.5.2 Diagnostics for Species Concentration. . . . . . . . . . . . 19
1.5.3 Optical Diagnostics for Particle Sizes. . . . . . . . . . . . 22
1.6 Chemistry Modeling and Simulation of Reactive Flows . . . . . 23
1.6.1 Modeling and Validation of the Fe
Chemistry in Flames. . . . . . . . . . . . . . . . . . . . . . . . 25
1.6.2 CFD Simulation of Reactive Flows
in Nanoparticle Synthesis . . . . . . . . . . . . . . . . . . . . 30
1.7 Examples of Flame-Synthesized Particles . . . . . . . . . . . . . . . 32
1.7.1 Semi-Conducting Single Oxide Particles. . . . . . . . . . 34
1.7.2 Mixed Oxide and Composite Nanoparticles. . . . . . . . 37
1.8 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
ix
x Contents
2 Chemical Vapor Synthesis of Nanocrystalline Oxides. . . . . . . . . . 49
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.2 Influence of Pulsed Precursor Delivery on Particle
Size and Size Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.2.1 Experimental Methodology . . . . . . . . . . . . . . . . . . . 51
2.2.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 53
2.3 Influence of the Time-Temperature Profiles
on Powder Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.3.1 Experimental Methodology . . . . . . . . . . . . . . . . . . . 60
2.3.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 61
2.4 Control of Composition by Laser Flash Evaporation:
Crystal and Local Structure of Cobalt Doped Zinc
Oxide Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.4.1 Experimental Methodology . . . . . . . . . . . . . . . . . . . 65
2.4.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 67
2.5 Summary and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . 74
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3 Nucleation, Structure and Magnetism of Transition Metal
Clusters from First Principles. . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2 Magnetism and Structural Transformations
in Nanoparticles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.3 Structure and Magnetism in Binary Nanoparticles . . . . . . . . . 85
3.4 MAE of Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
3.4.1 MAE for Perfect Clusters . . . . . . . . . . . . . . . . . . . . 91
3.4.2 MAE for Relaxed Clusters. . . . . . . . . . . . . . . . . . . . 93
3.5 Summary and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4 Synthesis and Film Formation of Monodisperse
Nanoparticles and Nanoparticle Pairs . . . . . . . . . . . . . . . . . . . . . 99
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.2 Synthesizing Monodisperse Nanoparticles by Means
of Spark Discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.2.1 Spark Discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.2.2 Synthesis of Monodisperse Au Nanoparticles. . . . . . . 105
4.2.3 Synthesis of Ge Nanoparticles . . . . . . . . . . . . . . . . . 108
4.3 Formation of Alloy and Pair Nanoparticles . . . . . . . . . . . . . . 110
4.3.1 Motivation and Synthesis Approach . . . . . . . . . . . . . 110
4.3.2 Synthesis of Au-Ge Pair Nanoparticles . . . . . . . . . . . 111
4.3.3 Synthesis of AuGe Alloyed Nanoparticles
by Co-Sparking . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.4 Film Formation by Electrostatic Means. . . . . . . . . . . . . . . . . 116
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Contents xi
Part II Structure and Dynamics
5 Diffusion Enhancement in FePt Nanoparticles
for L1 Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
0
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.2 Gas-Phase Preparation of FePt Nanoparticles. . . . . . . . . . . . . 125
5.3 Diffusion Enhancement in FePt . . . . . . . . . . . . . . . . . . . . . . 129
5.3.1 Oxygen Mediated Destabilization of Twinned
Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.3.2 L1 Stabilization by Interstitial
0
Nitriding–Denitriding . . . . . . . . . . . . . . . . . . . . . . . 132
5.3.3 L1 Stabilization by the Mobility Enhancement
0
of a Substitutional Element . . . . . . . . . . . . . . . . . . . 135
5.4 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
6 Simulation of Cluster Sintering, Dipolar Chain Formation,
and Ferroelectric Nanoparticulate Systems . . . . . . . . . . . . . . . . . 139
6.1 General Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.1.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
6.2 Molecular-Dynamics Simulations of the Dipolar-Induced
Formation of Magnetic Nanochains and Nanorings. . . . . . . . . 142
6.3 Molecular-Dynamics Simulations of Metal Cluster
Agglomeration and Sintering . . . . . . . . . . . . . . . . . . . . . . . . 146
6.3.1 Sintering of Nickel Nanoparticles. . . . . . . . . . . . . . . 146
6.3.2 Agglomeration of Icosahedral Iron Nanoparticles. . . . 150
6.4 Density Functional Simulations of Dielectric Nanoparticles:
Agglomeration and Ferroelectric Trends . . . . . . . . . . . . . . . . 152
6.5 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
7 Nanopowder Sintering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7.2 Particle Coalescence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
7.2.1 Phenomenological Theory. . . . . . . . . . . . . . . . . . . . 164
7.2.2 Atomistic Modeling . . . . . . . . . . . . . . . . . . . . . . . . 167
7.2.3 Coalescence of Agglomerates. . . . . . . . . . . . . . . . . . 168
7.2.4 Coalescence of Two Particles of Different Size . . . . . 169
7.3 The Effect of Grain Boundaries . . . . . . . . . . . . . . . . . . . . . . 171
7.3.1 Rigid Body Dynamics Combined with KMC. . . . . . . 173
7.3.2 Competition Between Reorientation and Neck
Growth for Two Particles . . . . . . . . . . . . . . . . . . . . 174
7.3.3 Reorientation Effects in Porous Agglomerates . . . . . . 178