【東京ダイレック】TSI Webinar Scanning Mobility Particle Sizing … · If the aerosol is highly charged & poorly neutralized (left hand side) ... →Works best if impactor

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© 2007, TSI Incorporated© 2009, TSI Incorporated

Scanning Mobility Particle Sizing (SMPS) Key Factors for Accuracy

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This webinar will begin at:Greenwich Mean Time (GMT) Thursday, 1:00amBeijing, China 8:00am Tokyo, Japan 9:00amUS CST 7:00pm (Wednesday Evening)

Kathy EricksonProduct Specialist

Particle InstrumentsApril 20, 2011

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This webinar will begin at:Greenwich Mean Time (GMT) Thursday, 5:00pmUS PST 9:00amUS CST 11:00amUS EST 12:00pm (just after noon)Germany, Berlin 6:00pm




Interactive Webinar Format

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included with e-mail login information– Visual: via internet - link information included login information

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3. Multi-media - Interactive chat: Please send questions via chat during and after the presentation.

4. Follow-up: e-mail including Adobe pdf file of presentation will be sent to registered attendees.

Electrical Mobility Sizing: Outline

– Introduction & Theory

– Key Factors for Accuracy

1. DMA voltage, flows & design2. Charge Distribution3. Efficiency curve of the CPC4. DMA transfer function


4. DMA transfer function5. Scan time6. Parameters of working gas7. Diffusion losses8. Aggregate correction

– ISO 15900

– ES + SMPS

– Closing Comments

Applications for Nanoparticle SizingParticle Size: Critical Metric

Nanomaterial R&D

Inhalation Toxicology Indoor Air

Quality


Atmospheric Research

Manufacturing Process Control

Filter Efficiency Testing

Emission Characterization

Engine/Fuel Development

Milestones in Electrical Mobility Particle Sizing

~1900 Electrostatic classification of atmospheric aerosols1921 Erickson first Differential Mobility Analyzer (DMA)1957 Hewitt co-axial cylindrical ‘DMA’ with unipolar charging1966 Whitby & Clark ‘Whitby Aerosol Analyzer’ (TSI 1967 – first commercial system)1983 TSI ‘DMPS’ voltage stepping system 1990 Scanning concept devised by Wang & Flagan


1991 Used by NIST to size 60nm (Mulholland et al 1991) 1993 First commercial scanning sizing system

Scanning Mobility Particle Sizer Spectrometer (SMPS)2005 Duke Scientific (Vasilou) evaluated scanning SMPS to size 20 to 100nm PSL

“In all cases, the SMPS mean diameter fell within the uncertainty of the reference standard [TEM].Note: surface techniques designed to image nanoparticles—not designed for sizing accuracy.

2006 Used by NIST to size 60nm & 100nm SRM (Mulholland et al 2006) 2009 ISO Standard 15900:2009 ‘Determination of particle size distribution –

Differential electrical mobility analysis for aerosol particles’2010 NIST Test Protocol ‘Analysis of Gold Nanoparticles by Electrospray Differential

Mobility Analysis (ES-DMA)’ [nanoparticle liquid colloids (sol)]

Reasons for Increased Interest in Electrical Mobility-based Sizing

– Discreet method: individual particles are counted and sized

– Large sample size

– No assumptions regarding size distribution

– Independent of optical properties of material (& liquid)

– 1st principle technique: no size calibration necessary


– 1st principle technique: no size calibration necessary

– High resolution: ~±10% of particle size (or better at higher flow ratios)

“it affords an opportunity to monitor the quality of product particles in real time with size resolution that is unattainable in most other particle characterization technologies” (Flagan 2008)

– Low uncertainty: ±3.5% (Mullholand et al 1991)

– Real-time: 16-300s

– Easy to use; does not require a trained technician

Colloids Suitable for Electrical Mobility Particle Sizing

Dispersed Phase

Gas Liquid Solid

Colloids - a substance microscopically dispersed evenly throughout another substance


Gas NoneAll gases are miscible

Liquid aerosol Solid aerosol

Liquid Foam Emulsion Sol

Solid Solid Foam Gel Solid sol

substance

Con

tinuo

us M

ediu

m

Electrical Mobility Analysis

Where:np = number of charges per particlee = elementary unit of chargeE = electric field strengthµ = viscosity of gasD = particle diameter

F n eEelectric p=�

FD v

Cviscousdragp

=3πµ

�

Zp ≡ electrical mobility; ability of a charged particle to traverse an electric field


Dp = particle diameterC = Cunningham slip correctionv = Velocity

Cviscousdrag �

F Felectric viscous= drag�

ZvE

n eC

Dpp

p

= =3πµ� Electrical mobility: inversely

proportional to particle size

Second order function of particle size

Assumptions� Stoke’s Regime (Re<1)� Drag based on rigid sphere

Differential Mobility Analyzer (DMA)

– Classical Knutson & Whitby cylindrical DMA design (1975)

– Applied voltage


determines electric field

– Laminar flow

– Particle free sheath air

– 4 balanced flows

– Monodisperse aerosol exiting DMA

Mobility Particle Sizing

Aerosol Conditioner

Differential Mobility Analyzer

Classifier

ParticleCounter

ZvE

n eC

Dpp

p

= =3πµ


Control hardware & software

Counts size selected

particlesto build

distribution

Selects particles according to

electrical mobility→ particle size

Produces a known charge

distribution

Laminar Flow CPCs


– Fast– Precise temperature control– Low particle losses

S = Supersaturation RatioPv = Vapor PressurePsaturation(T) = Saturation Vapor Pressure

Dkelvin = Kelvin DiameterdS = Surface Tension of Working FluidM = Molecular Weight of Working FluidrL = Density of Working FluidR = Gas ConstantT = TemperatureS = Supersaturation Ratio

DM

RT SkelvinS

L

= 4δρ log

SP

P Tv

saturation

≡( )

Assumption: particle material is readily wetted by but insoluble in the condensing vapor

Scanning Mobility Particle SizerSMPS

Polydisperse Aerosol

Scanning Voltage DMA– 1990 Wang & Flagan– If voltage is exponentially ramped, all particles follow the same trajectory in the DMA– The resolution (transfer function of the DMA) is identical to that of stepping systems– 16 to 300s (or below?)


DMA

SelectsSingleSize

Counter

Monodisperse Aerosol

Voltage/Diameter

Concentration

Size Distribution

SMPS: Key Factors for Accuracy

1. DMA voltage, flows & design2. Charge distribution

6. Scan time7. Parameters of working gas

True: 1st Principle Device: No calibration required

Also True: Data Inversion - Electrical Mobility to Particle Size


2. Charge distribution3. Efficiency curve of the CPC4. DMA transfer function

7. Parameters of working gas8. Diffusion losses9. Aggregate correction

DMA Voltage & Flowrates

)r

rln()]qq(2/1q[

Z 1

2mpt +−

=

ZvE

n eC

Dpp

p

= =3πµ


VL2Z 1

p π=

Where:qt = total flowrate (sheath + poly)qm = monodisperse flowrateqp = polydisperse flowrater2 = outer electrode radiusr1 = inner electrode radius V = voltage on center electrodeL = length between sample exit and aerosol inlet

‘Nano’ Differential Mobility Analyzer

– Designed in collaboration with the University of Duisburg and the University of MN

– Aim to improve nanometer size resolution• Shortening effective length• Eliminate flow and electric field non-uniformities• Minimize diffusion broadening


• Minimize diffusion broadening• Increase transmission efficiency

1. Reduce particle losses due to diffusion 2. Reduce losses due to electrostatic forces

– DMA design governs• Size range • Ideal resolution (increased resolution <10nm

results in decreased size range)• Electric field & flow uniformities (manufacturing

non-conformities can also affect this).

DMA Voltage & Flowrates

Voltage1) Reliable high voltage supply &

electronics2) Calibrated using NIST Traceable

meters

Flow1) Laminar flow element


1) Laminar flow element2) Re-circulating flow scheme to

minimizes flow disturbances (decreased resolution)

3) NIST Traceable flow meters4) Volumetric flow rate: atmospheric

temperature & pressure adjustment. 5) Periodically check flow accuracy with

independent volumetric flow meter.

Charges Per Particle

Must know number of charges per particle

Particle VelocityElectric Field Strength 3πµDp

neC===Zp

VE

Equilibrium Charge Distribution

Need to Generate Bi -polar Ions


Need to Generate Bi -polar Ions

Note: Poor charging leads predominately to concentration inaccuracies. However, since charging is size dependent it leads to sizing inaccuracies as well.

Two Neutralizers

Aerosol Out

+++

+

+

++

+ ++ --- --

--

--

-Aerosol In

Kr-85 gas

TraditionalKr-85 gas

Advanced Aerosol NeutralizerSoft X-ray

– Nonradioactive– Comparable SMPS


sealed stainless-steel tube

Kr-85 facts– Kr-85 inert gas sealed in air-tight stainless steel – Never absorbed by the body– In US classified as a “non-biological health hazard”– In US no handling limitations for amount used in SMPS– 10.4 year half life– Beta-emitter

sizing– No transportation

restrictions– Does not decay

over time

Poor Charging: Soot Aerosol

Generated aerosol is very highly charged


High soot aerosol concentration and 1 neutralizer TSI model 3077: SMPS measurement shows that charge equilibrium was not reached

Diluted soot aerosol and neutralizers TSI models 3077 and 3012 in series:Charge equilibrium was reached

If the aerosol is highly charged & poorly neutralize d (left hand side) large errors in size distribution and concentration.

Multiple ChargesFuch’s Equilibrium Charge Distribution

Dp (nm) -2 -1 0 +1 +2

10 0 5.03 90.96 4.02 0

Percent of particles carrying np elementary charge units


10 0 5.03 90.96 4.02 020 0.02 11.14 80.29 8.54 0.0150 1.13 22.94 58.10 17.20 0.6370 2.80 26.02 49.99 19.53 1.57100 5.67 27.42 42.36 20.75 3.24130 8.21 27.30 37.32 20.85 4.77200 12.18 25.54 29.96 19.65 7.21300 14.56 22.71 24.16 17.51 8.65500 15.09 18.60 18.28 14.33 8.95700 14.29 15.94 15.15 12.27 8.46

1000 12.86 13.33 12.36 10.24 7.59

FromA. Wiedensohler: “An Approximation of the Bipolar Charge Distribution for Particles in the Submicron Size Range”, Journal of Aerosol Science, Vol. 19, No. 3, pp. 387-389, 1988.

Multiple Charge Correction→ Useful for larger aerosols

→ Must use impactor (physical size cut ≅ no larger multiple particles)

→ Works best if impactor cut point is just to the right of complete distribution

• Too far to the right—no effect

• Cut into size


• Cut into size distribution—will see notch in distribution

→ Best to view distribution, and use if makes sense

Efficiency Curve of CPCCPC Efficiency Curve

Cou

ntin

g E

ffici

ency

%

50% cut point ~ 2.5 nm


Particle Diameter (nm)

Cou

ntin

g E

ffici

ency

%

50% cut point ~ 2.5 nm

CPC Efficiency curves affected by:1) Instrument to instrument

variation2) Working fluid3) Carrier gas (Niida et al 1988)

Sizing Accuracy:1) Most applications, small CPC efficiency curve

differences have very little effect on accuracy.2) Nanoparticle applications can be sensitive to

efficiency curves: large numbers of particles close to the lower detection limit.

3) Can generate custom efficiency curve to use in data inversion (Liu et al 2006).

Zp∆∆∆∆Zp = qs

qa

DMA Transfer FunctionTransfer Function ≡ probability that an entering particle with a specific electrical mobility will have the correct trajectory to exit through the exit slit with the classified aerosol. (Knutson & Whitby 1975) Ideal Transfer Function

Con

cent

ratio

n

Where:qa = aerosol flowrate


Con

cent

ratio

n

Particle Diameter Dp (nm)

9nm

NDMA Transfer Function

qa = aerosol flowrateqs = sheath flowrateZp = set mobility

(Knutson & Whitby 1975)

Electrical Mobility

Effect of sheath:Sample Flow Ratio on SMPS Transfer Function

Electrospray Aerosol: No TDMA 10:1 sheath:Sample Flow rate on DMA 1 2:1 Sheath:Sample Flow rate on DMA 1

Tandom DMA Experimental Setup: Adjust flow ratio on DMA 1

+ElectroSpray

Aerosol Generator

MODEL

3480 + DMA 1 DMA 2


Effect of Sheath:Sample Flow Ratio on Electrostatic Classifier

10:1 sheath:Sample Flow rate on DMA 2 5:1 sheath:Sample Flow rate on DMA 2 2:1 sheath:Sample Flow rate on DMA 2

+ElectroSpray

Aerosol Generator

MODEL

3480 + DMA 1 DMA 2

Tandom DMA Experimental Setup: Adjust flow ratio on DMA 2


Diffusion Broadening

– Widens the transfer function for nanoparticles <100nm

– Reduces peak transmission efficiency

– More severe at lower voltages


– More severe at lower voltages

– Significant for particles <20nm

– Stolzenberg (1998) created a model for the diffusion-broadened transfer function

– Shortening the effective length of the DMA & increasing the flowrate through the DMA:

1. reduces diffusion broadening

2. reduces the size range

Scan Time

a) 300 s b) 16 s

Electrospray Sucrose Aerosol


Scan Time

a) 300 s b) 16 s c) 16 s scan range 6.98 – 12 nm

Fast Scanning - CPC features1) Laminar flow2) Fast response3) High aerosol flow rate/high concentration aerosol

Electrospray Sucrose Aerosol


Russell et al (1995) noted ‘scan time effect’: for very short scans, tails toward larger distributions; theorized result of turbulent mixing in plumbing between DMA & CPC & internal to CPC - primarily notable on older 3071A classifier platforms & CPCs.

Cunningham Slip Coefficient

Parameters of Working GasWorking gas ≅ sheath gas in the DMA.

Note: If using a recirculating flow scheme, the sample carrier gas will eventually become the sheath gas.

Particle VelocityElectric Field Strength 3πµDp

neC===Zp

VE

µ and C both affected by working gas properties


→ C = ƒ(λλλλ, Dp); λλλλ = mean free path of working gas → Empirical formula dependent on gas T & P→ In free molecular regime Kn>>1 (<10nm); C→1.7

Software Calculates µ & λλλλ• Classifier measures T&P of

air

• Software calculates gas viscosity (µ) and mean free path (λλλλ) for every sample (based on air)

Other Working Gases

– Flowmeters are calibrated with Air (must manually measure

Gas Property Air N 2 Ar CO 2 He

µ (10-4g/cm-s) 1.82 1.75 2.2 1.47 1.95

λ (10-6 cm) 6.64 6.41 6.75 4.69 18.7


– Flowmeters are calibrated with Air (must manually measure and control flow)

– Noble gases have breakdown voltages much lower than air: this will effectively reduce the upper end size range (Meek & Craggs 1978)

– Bipolar charge distribution differs—can use extended Fuchs model (Wiedensohler 1991)

– CPC efficiencies differ in gases other than air (Ahn 1990)– Karg et al (1992), Schmid (2002) investigated DMA accuracy

in N2, Ar, CO2 & He and generally concluded no fundamental effect of gas type

Diffusion LossesDiffusion is a stronger than gravitational forces for particle <100nm

Circular Tube Penetration Efficiency

0.8

0.9

1.0Diffusion losses are size dependent.


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.00001 0.0001 0.001 0.01 0.1 1DLQ

Pen

etra

tion

Gormley and Kennedy (1949) derived an equation for circular tube penetration efficiency.

D = Diffusion coefficient; D = ƒ(T, Gas type, d p))L = Length of tubeQ = Volumetric flow rate

Diffusion LossesSMPS Diffusion loss:

1) Sampling scheme

2) System losses through• Controller platform• DMA• CPC

Diffusion losses �� with:

1) Increasing tubing length

2) Decreasing particle diameter

3) Increasing temperature


• CPC• Connection tubing

– Software option for diffusion loss correction

– Uses hardware settings to estimate diffusion loss and apply correction

– Empirical and calculated contributions.

– Can apply diffusion loss correction to previously collected data

Diffusion Loss AlgorithmExample – Ambient Air


Without correction With correction

Aggregates– Zp derivation assumes spherical model for drag force– Equilibrium charge distribution based on spheres– Nanoparticle aggregate correction option– Input

• estimated primary particle size• estimated agglomerate orientation (typically parallel)


• estimated agglomerate orientation (typically parallel)– Can apply to previously collected data– Lall & Friedlander (2006)

Aggregate Correction - Example

dV

/dlo

g(d m

), #

/cc

50x109

100x109

150x109

200x109

250x109

), n

m2 /c

m3

10x109

12x109

14x109

16x109

18x109

Surface Area

MassSpherical assumption: redAggregate correction: greenPrimary particle diameter = 17nmParallel orientation

© 2007, TSI Incorporated© 2009, TSI IncorporatedMobility Diameter (dm), nm

10 100 1000

dN/d

logd

m,

#/cc

0

100x103

200x103

300x103

400x103

500x103

Mobility Diameter (dm), nm

10 100 10000

Mobility Diameter (dm), nm

10 100 1000

dA/d

log(

d m),

nm

0

2x109

4x109

6x109

8x109

10x10

Number

– Aggregate drag model (Chan & Dahneke 1981)

– Aggregate charge distribution (Wen et al 1984)

ISO 15900:2009

– Aimed at user; not developers– Describes differential electrical mobility

ISO 15900:2009Determination of particle size distribution — Differe ntial electrical mobility analysis for aerosol particlesDétermination de la distribution granulométrique —Analyse de mobilité électrique différentielle pour les particules d'aérosol

Table 1 – Values of Parameters Recommended for the Calculation of the Electrical Mobility From the Particle Size in Air


– Describes differential electrical mobility analysis

– Raises awareness– Gives guidance on important issues

• Slip correction factor• Size dependent charge distribution• Methods for data inversion

ISO 10808:2010 Characterization of nanoparticles in inhalation exposure chambers for inhalation toxicity testing

ISO 28439:2011 Workplace atmospheres -- Characterization of ultrafine aerosols/nanoaerosols -- Determination of the size distribution and number concentration using differential electrical mobility analysing systems

Nanoparticle Colloids (Sols)ES + SMPS

Sizing Nanoparticles In LiquidsElectrospray + SMPS = ES+SMPS

– Increased interest in the last decade for high resolution liquid nanoparticle sizing

– Wide array of peer reviewed publications


– Wide array of peer reviewed publications• Gold (Au) [Bottinger et al 2007, Tsai et al

2008] • Carbon Nanotubes (CNT), [Pease et al

2009]• Protein-coated Quantum Dots (QD), [Pease

et al 2010]• Copper (Cu), [Elzey et al 2010]• Silver (Ag), [Elzey et al 2010]• Iron Oxide (FexOy) ,[Hildebrandt et al 2010]

Closing CommentsScanning Mobility Particle Sizing– Rapid, high resolution size nanoparticle size distribution measurements– Discreet technique with large sample size– No assumptions regarding size distribution– Low uncertainty– Easy to use– Useful for:

1. liquid aerosols

Ovalbumin (AG501-X8)

6.38

(#/c

m3)

[e7]


1. liquid aerosols2. solid aerosols3. nanoparticles suspended in liquids (sols)

3.22

3.72

4.61

8.20

Mobility Diameter (nm)

dN/d

logD

p(#

/cm

3) [e

7]

Considerations– Measures mobility � particle size is calculated– Limits to particle size range; <1µm– Proper neutralization is fundamental– Size resolution can be degraded by

1. Design defects: imperfect flow fields or electric fields

2. Low voltages: increases diffusion broadening � decreases resolution

3. Too short of scans

Thank You For


Thank You For Your Attention

Any Questions?Any Questions?Kathy Erickson ([email protected])Kathy Erickson ([email protected])

Webinar ScheduleMay 5 th Using TDMAs to Measure Haze

by Tim Johnson

May 19 th Electrospray with SMPS (ES+SMPS) for Size Measureme nts of Nanoparticles Suspended in Liquids by Dr. Stan K aufman

June 23 rd Indoor Exposure to Ultrafine Particles: Sources and Measurements by Dr. Lance Wallace

July 21st Toxicological Evidence that Inhalation of Nanoscale

TSITSITSITSI PARTICLE NEWSPARTICLE NEWSPARTICLE NEWSPARTICLE NEWS

www.tsi.com/webinars


July 21st Toxicological Evidence that Inhalation of NanoscaleParticulates in Urban Air Pollution is Associated w ith Cognitive Impairment by Dr. David Davis (USC)

• Size resolution <5% at 0.5 µµµµm • User adjustable size channels• Size range: 0.3 – 10 µµµµm in up to

16 channels• Wide concentration range

from 0 to 3000 particles/cm 3

• Fully compliant with ISO 21501-01/04

Optical Particle Sizer Model 3330

US +1 651-490-2811 EURO +49 241-52303-0 ASIA + 86 10 8251 6588 [email protected]

New WCPC’s Models 3787 & 3788

• 2.5nm detection • Single particle counting to

4x105 particles/cm3• <100 ms rise-time response

w/ 42 ms time constant (fastest CPC available)

• Convenient, eco-friendly water as working fluid Model 3788

Documents

【東京ダイレック】TSI Webinar Scanning Mobility Particle Sizing … · If the aerosol is highly charged & poorly neutralized (left hand side) ... →Works best if impactor