Synthesis of Metal Nanoparticles by Transferred Arc Discharge

179 Pages·2015·2.88 MB·English

Synthesis of Metal Nanoparticles
by Transferred Arc Discharge
Von der Fakult(cid:228)t f(cid:252)r Ingenieurwissenschaften,
Abteilung Elektrotechnik und Informationstechnik
der Universit(cid:228)t Duisburg-Essen
zur Erlangung des akademischen Grades
Doktor der Ingenieurwissenschaften
genehmigte Dissertation
von
Matthias Stein
aus
M(cid:252)lheim an der Ruhr
1. Gutachter: Prof. Dr.-Ing. Einar Kruis
2. Gutachter: Prof. Dr. Andreas Schmidt-Ott
Tag der m(cid:252)ndlichen Pr(cid:252)fung: 21.09.2015

(cid:16)What I want to talk about is the problem of manipu-
lating and controlling things on a small scale. As soon
as I mention this, people tell me about miniaturization,
andhowfarithasprogressedtoday. Theytellmeabout
electricmotorsthatarethesizeofthenailonyoursmall
(cid:28)nger. Andthereisadeviceonthemarket,theytellme,
by which you can write the Lord’s Prayer on the head
of a pin. But that’s nothing; that’s the most primitive,
halting step in the direction I intend to discuss. It is a
staggeringlysmallworldthatisbelow. Intheyear2000,
when they look back at this age, they will wonder why
it was not until the year 1960 that anybody began se-
riously to move in this direction. Why cannot we write
theentire24volumesoftheEncyclopediaBrittanicaon
the head of a pin? (cid:16)
Richard P. Feynman

i
Preface
This thesis is the result of an amazing and very instructive research time I
hadduringtheperiodbetween2011and2015attheInstituteofTechnologyfor
Nanostructures(NST)oftheUniversityofDuisburg-Essen. Myworkduringthis
timehasbeenpartoftheEuropeanproject(cid:16)BUONAPART-E(cid:17) .Ithasreceived
funding from the European Union’s Seventh Framework Program under grant
agreementNo: 280765. Igreatlyenjoyedthechallengeandtasksofthisproject,
thecollaborationwithresearchersalloverEuropeondi(cid:27)erenttopics,thefruitful
discussions with all the partners and the interesting and instructive journeys to
conferences as well as research visits.
The very (cid:28)rst I want to express my deepest gratitude to professor Einar
Kruis,whogavemetheopportunitytoworkinhisgroup. Hispersistentsupport
and broad scienti(cid:28)c experience made my research work possible. He highly
contributedtotheoutcomeofthiswork. Thankyouforthefruitfuldiscussions,
the trust and the scienti(cid:28)c freedom you showed me.
I want to thank professor Roland Schmechel for the help in experimental or
theoretical questions, chapter corrections, discussions and for his support in his
function as head of the institute.
I thank Anssi Ar(cid:27)man from the University of Tampere for the CFD model
of the OSU, on which my particle formation model bases and Maria Messing
from the University of Lund for all the high resolution TEM images.
I wish to thank all the people of the NST, who made the time here highly
enjoyable and supported me during this work. Especially Dennis Kiesler, who
gave me essential support with his expertize in all kinds of technical questions.
This thesis would not have been possible without Felix Bensel and Christoph
Kleinert, who helped me setting up the production facility and assembling an
apparently endless number of vacuum clamps.
I appreciated the collaboration with the group of Hartmut Wiggers, who
welcomed me and the production facility in their lab. I also want to thank the
workshops of the university for manufacturing the technical devices, even on
short notice.
Furthermore,Iappreciatedworkingwithmanystudents,whoallcontributed
to this work: Jeremias Geiss, Mohammed Bishady, Janis Heldmann, Matthias
Masuhr, Yannick Beckmann, David Pawlak and Mustafa Demir.
Finally I want to express my heartiest gratitude to my parents Ute and
Wolfgang Stein, my family, friends and of course Tanja, who always support
me.
ii
Abstract
Metal nanoparticles are already used in various applications and products,
with rising tendency. Scaled-up production facilities are needed to answer the
demand of the industry, but are very challenging to realize. A production pro-
cess should generally be energy e(cid:30)cient and sustainable, however the produc-
tionofmetalnanoparticlesrequiresfurtherattributes. Inordertoproducepure
metalnanoparticles,theprocessneedstobefreefromoxygen. Also,ithastobe
ensured that the mass output of nanoparticles is scaled up without increasing
the particle size. Detailed information about particle formation and dedicated
measurement systems are of importance.
This work reports about the development of a scaled-up production facility
ofpuremetalnanoparticles. Thescale-upapproachistheparallelizationofmul-
tiple transferred arcs. The basic idea is thereby, to (cid:28)rst optimize the particle
formation of a single transferred arc process (lab-scale) in terms of production
rate,particlesizeandelectricityconsumptionandthenuseitinparallel(produc-
tion facility), in order to multiply the production rate and minimize the energy
consumption. Optimizationofthelab-scaleprocessisachievedbyadjustingthe
electrode and gas (cid:29)ow adjustment or by varying the carrier gas composition.
The in(cid:29)uence of the carrier gas composition on production rate, speci(cid:28)c elec-
tricityconsumptionandparticlesizeisinvestigated. Furthermore,thein(cid:29)uence
of gas (cid:29)ow and power input are investigated. Optimal process parameters for
metal nanoparticle synthesis by transferred arc discharge are found. Long-term
production is achieved by the development and adaption of a suitable feeding
mechanism. The optimization of the lab-scale process results in an optimal sin-
gleunit(OSU)formetalnanoparticleproduction,whichisusedforthescale-up
approach.
A dedicated measurement system based on parallel aerodynamic and mo-
bility diameter measurement with a novel analysis method is applied in order
to determine the primary particle size of the synthesized particles online. An
equation is found, which allows calculating the mass mobility exponent directly
on the basis of the e(cid:27)ective density of a particle, hence allowing the direct de-
termination of primary particle size. Also, a thermophoretic proximity sampler
is used to determine the particle size evolution during formation. It is found
that a thermophoretic proximity sampler can be used to determine particle size
evolution in arc discharge synthesis. Particles are successfully sampled at three
di(cid:27)erent characteristic moments during primary particle growth; shortly after
nucleation, during common growth processes and when growth of primary par-
ticles has already been (cid:28)nished.
In order to understand the particle formation and the in(cid:29)uence of di(cid:27)erent
process parameters on the particle size, a simple particle formation model in-
cludingnucleation,coagulationandsinteringisintroduced. Toincludesintering
iii
in the model, speci(cid:28)c sintering parameters of the modeled material system are
needed. The sintering parameters are determined experimentally by a tandem
di(cid:27)erential mobility analyzer setup including a sintering furnace. The sintering
parametersareobtainedbya(cid:28)ttingprocedureoftheexperimentaldatatoasin-
tering model. The particle formation model including the sintering parameters
describes the particle formation accurately.
The production facility applying the scale-up approach is assembled consid-
eringintensesafetyrequirements. Itcontains16OSUsintworeactorchambers,
eachconsistingof8electrodepairs(mOSU),agasrecirculationsystemanda(cid:28)l-
trationunit. The(cid:28)ltrationunitisbuiltwithanovel, valve-lessbaggingsystem.
Also, a particle passivation system is added. It is shown that the production
rateoftheprocessscalessuccessfullywiththenumberoftransferredarcs,while
the primary particle size stays constant on the nanoscale. It appears however
that the scaled-up process favors the formation of larger agglomerates, which is
found not be a result of the residence time, but apparently the increased heat
development of the mOSU.
Inordertoshowanapplicationoftheproducedparticles,acoppernanopow-
der is used to produce a copper ink. The ink is printed on glass substrate by
spin or hand coating. It is found that the electrical resistivity is dependent of
theprinted(cid:28)lmthickness, whichmightbeconsequenceof(cid:28)lminhomogeneities.
Applied sintering to the printed (cid:28)lms improved the conductivity signi(cid:28)cantly.
Contents
1 Introduction 1
1.1 General introduction . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Nanometals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Arc discharge synthesis. . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 This work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 State of the art in arc discharge synthesis 9
3 Fundamentals of transferred arc nanoparticle synthesis and
nanoparticle characterization 15
3.1 Synthesis of metal nanopowder by arc discharge . . . . . . . . . . 15
3.1.1 Nanoparticle formation by arc discharge . . . . . . . . . . 15
3.1.2 Collection of nanoparticles. . . . . . . . . . . . . . . . . . 19
3.2 Nanoparticle characterization . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Particle diameter and size statistics . . . . . . . . . . . . 20
3.2.2 O(cid:31)ine characterization . . . . . . . . . . . . . . . . . . . 23
3.2.2.1 X-ray Di(cid:27)raction . . . . . . . . . . . . . . . . . . 23
3.2.2.2 Brunauer-Emmett-Teller measurement . . . . . 24
3.2.3 Online characterization . . . . . . . . . . . . . . . . . . . 25
3.2.3.1 Dilution system . . . . . . . . . . . . . . . . . . 25
3.2.3.2 Tapered Element Oscillating Microbalance . . . 26
3.2.3.3 Scanning Mobility Particle Sizer . . . . . . . . . 28
3.2.3.4 Electrical Low Pressure Impactor . . . . . . . . 29
4 Optimizedsinglearcdischargeunit(OSU)formetalnanopar-
ticle production 33
4.1 Setup of the OSU . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.1.1 General setup of the OSU . . . . . . . . . . . . . . . . . . 34
4.1.2 Particle synthesis setup of the OSU (inner setup) . . . . . 37
iv
Contents v
4.1.3 Particle characterization setup . . . . . . . . . . . . . . . 38
4.1.4 Safety requirements . . . . . . . . . . . . . . . . . . . . . 40
4.2 Crucible design and electrode arrangement. . . . . . . . . . . . . 40
4.3 E(cid:27)ect of carrier gas composition on nanoparticle synthesis . . . . 46
4.4 In(cid:29)uence of power input and gas (cid:29)ow on production rate and
particle size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.5 Long term process stability including crucible feeding . . . . . . 65
5 Online and ex-situ determination of primary particle size in
transferred arc synthesis 69
5.1 Online determination of primary particle size . . . . . . . . . . . 69
5.1.1 Experimental setup and procedure of the online measure-
ment technique . . . . . . . . . . . . . . . . . . . . . . . . 70
5.1.2 Results of the online size determination . . . . . . . . . . 73
5.2 Thermophoretic proximity sampling . . . . . . . . . . . . . . . . 78
5.2.1 Experimental setup & method for thermophoretic prox-
imity sampling . . . . . . . . . . . . . . . . . . . . . . . . 79
5.2.2 Results of thermophoretic proximity sampling . . . . . . . 82
6 Onlinedeterminationofsinteringparametersformetalnanopar-
ticles and their application in a simple model for particle size
estimation 87
6.1 Determination of sintering parameters . . . . . . . . . . . . . . . 87
6.1.1 Sintering parameters . . . . . . . . . . . . . . . . . . . . . 88
6.1.2 Experimental procedure & model to determine sintering
parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.1.3 Experimentally obtained sintering parameters of metal
nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.2 A simple model for particle size estimation . . . . . . . . . . . . 97
6.2.1 Nucleation . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.2.2 Coagulation and Sintering . . . . . . . . . . . . . . . . . . 100
7 Nanoparticle synthesis by multiple transferred arcs (mOSU) 105
7.1 Setup of the pilot plant for nanoparticle production. . . . . . . . 107
7.1.1 Gas supply & reconditioning . . . . . . . . . . . . . . . . 108
7.1.2 multiple Optimal Single Unit (mOSU) for nanoparticle
synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.1.3 Filtration unit for particle collection . . . . . . . . . . . . 112
7.2 Nanoparticle production by the mOSU . . . . . . . . . . . . . . . 118
Contents vi
8 Coppernanoparticleinkpreparedfromgas-phasesynthesized
nanoparticles 125
8.1 Copper nanoparticle ink preparation . . . . . . . . . . . . . . . . 126
8.2 Performance of the printed conductive (cid:28)lms prepared from the
copper nanoparticle ink . . . . . . . . . . . . . . . . . . . . . . . 127
9 Conclusions 131
Bibliography vii
List of Figures xxii
List of Tables xxvii
A Abbreviations xxviii
B Technical drawings xxxiii
C Curriculum Vitae xxxix
D Publications xl