automated particle analysis of aerosols formed during...

© ZFE / FELMI TU Graz

Automated particle analysis of aerosols Automated particle analysis of aerosols formed during biomass combustion by formed during biomass combustion by

SEM/EDXSEM/EDXSS

DI Stefan Mitsche

Austrian Centre Austrian Centre for Electron Microscopyfor Electron Microscopyand and NanoanalysisNanoanalysis


OverviewOverview

General information about SEM

Fundamentals of particle analysis

Principles of the automated particle analysis (APA)

APA of aerosols from biomass plants


The Scanning electron microscopeThe Scanning electron microscopePrimary electrons (up to 30keV)

Augerelectrons (AE) Cathodoluminescence (CL)

SEM images:• Secondary electrons (SE)• Backscattered electrons (BSE)

Characteristic x-rays (EDXS)

Specimen current

Electron-specimen interaction and generated signals


Monte Carlo simulations of electron scattering of an 100 nm particle of:left K2SO4 and right PbCl2E0 = 7 keV

Monte Carlo simulations of electron scattering of an 100 nm particle of PbCl2:left E0 = 20 keV and right E0 = 7 keV

The Scanning electron microscopeThe Scanning electron microscope


Fundamentals of particle analysis Fundamentals of particle analysis

pure chemicals (K2SO4, PbSO4 and PbCl2) were ground in a ball mill

suspended in pure sec-butanolfiltered through a 3 µm Nucleopore filterthe filtrate was filtered through a 0.05 µm (C-

coated) Isopore poly-carbonate filter

Experimental

top: in-lens image (SEI); bottom: BSE image (BSE) PbSO4-particles

1 µm


EDX-detector

x-ray yield

in-lens detector

BSE detector

objective lens

The Scanning electron microscopeThe Scanning electron microscope

primary electrons

Instrumentation:

Zeiss DSM 982 Gemini

Noran Voyager EDX-detector, 30 mm2 Si(Li), ultrathin window



Size measurement

Influence of the coating of the particles on the measured particle size



Size measurement

yellow: SEI-signalgreen: BSE-signalparticle: PbCl2no coatingacc. voltage: 7 keV

yellow: SI-signalgreen: BSE-signalparticle: PbCl2carbon coatingacc. voltage: 7 keV



Size measurement

Influence of mean atomic number of the particles on the measured particle size


0

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

SEI-C-coated

BSE-C-coated

SEI-uncoated

BSE-uncoated

0

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

SEI-uncoated

average SEI-BSEC-coated


Size measurement

average diameter / µm

freq

uenc

y


a)

1 µm

a)

b)

X-ray analysis of biomass fly ash particle (E0 = 7 keV, Ip = 0.7 nA);a) image of particles with the analysis spot marked by a cross (SE – image)b) x-ray spectra


Chemical composition


K2SO4 particles: measured ratio of K (at%) / S (at%), in dependence on both the type of the substrate and the coating (spot analysis, E0 = 7 keV, Ip = 0.7 nA; spectra at 10s and 60s stored without any interruption; mean particle diameter: 400 nm)






Automated analysis of standard particles: K2SO4 , PbSO4 and PbCl2


Principles of Automated Particle AnalysisPrinciples of Automated Particle Analysis

binary imagesBSE image

image width 3.8 µm

SEI-image


field1,1 beam control

stage control

field1,2

field1,n

stage control

field2,1

field2,2

field2,n

fieldi,1

fieldi,n

fieldi,2

Principles of Automated Particle AnalysisPrinciples of Automated Particle Analysis

Scheme auf the automated particle analysis procedure


Automated Particle Analysis of aerosolsAutomated Particle Analysis of aerosols

waste wood bark

Size distribution of aerosols (fuel: waste wood, bark)



waste wood bark

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

10

20

30

40

50

60


wt% Pb

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

20

40

60

80


wt% K

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

10

20

30

40

50

60

wt% Pb


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

20

40

60

80

wt% K


Concentrations of Pb and K in dependence on the diameter of the aerosols (fuel: waste wood, bark)



waste wood bark

0 10 20 30 40 50 600

10

20

30

40

50

60

wt% Cl

wt% Pb

0 10 20 30 40 50 600

10

20

30

40

50

60

wt% S

wt% Pb

0 10 20 30 40 50 600

10

20

30

40

50

60

wt% Pb

wt% Cl

0 10 20 30 40 50 600

10

20

30

40

50

60

wt% Pb

wt% S

Correlations between various elements for aerosols (fuel: waste wood, bark)



waste wood bark

Correlations between various elements for aerosols (fuel: waste wood, bark)

0 20 40 60 800

20

40

60

80

wt% S

wt% K

0 20 40 60 800

20

40

60

80

wt% Cl

wt% K

0 20 40 60 800

20

40

60

80

wt% K

wt% S

0 20 40 60 800

20

40

60

80

wt% K

wt% Cl



0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

100

200

300

400

500spot 1spot 2

C O

NaZn

SPb

ClK

energy / keV

counts

SE-image (image width: 0.29 µm) of an aerosol particle (left) and the EDXS – spectra (right) at the 2 spots marked in the image


SummarySummary

If only the particle size is of interest, uncoated particles and the use of the in-lens detector is recommended.

In case of carbon coated particles the average of the sizes obtained from images of the in-lens and the BSE-detector have to be used

Automated analysis of aerosols with SEM/EDXS is possible down to particle diameters of about 50 -100 nm depending on the chemical composition


Institute for Electron Microscopy:Prof. Ferdinand Hofer

Dr. Peter PoeltDr. Mario Schmied

Institute for Resource Efficient and Sustainable Systems:Prof. Ingwald Obernberger

DI Thomas Brunner DI Markus Jöller

AcknowledgementAcknowledgement

automated particle analysis of aerosols formed during...

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