Multiphase analysis - combining EDS and EBSD · Automated phase recognition (PCA) 1 - The spectra...

Multiphase analysis - combining EDS and

EBSD

Review:

Conventional materials characterisation:

Analysing polyphase materials using EDS

Analysing polyphase materials using EBSD

Combined EDS and EBSD measurements

Phase identification

Phase discrimination during mapping

Simultaneous EBSD and EDS scanning

Chemistry assisted Indexing ChI scan

Outline

Plot showing drift path during map acquisition

EDS (live) spectral mapping

EDS area analysis: Spectral mapping

(live) Spectral mapping procedure:

• With a short dwell time a spectrum is collected for each pixel

in the entire image. This is repeated while adding all additional

counts to the spectrum for each pixel.

• Drift correction is often needed to ensure continuous

alignment of subsequent maps. At fixed intervals a reference

image is collected and matched to the original location.

Sulfide ore - example

Application example:

Spectral mapping, phase identification, and phase

differentiation on a polyphase sulfide ore rock

Spot mode in NiAs grain.

Acquisition parameters:

HT = 25 kV

Mag = 190 x

Matrix = 512 x 400 pixels

Scan area = 695 x 542 micrometer

Nr frames = 183

Acquisition time = 2.8 hrs

Spectral mapping data review

Spot mode in FeNiS grain.


Area mode in NiAs grain.


Area mode in NiFeS grain.


Freedraw mode in biotite grain.


Freedraw mode in (NiCoFe)AsS grain.


Full area spectrum.


As Ni

Cu

Sb SSi

Co

Fe

X-Ray maps are

constructed for all

elements as identified by

the auto peak ID routines

How many phases are

present ?

Collected X-Ray maps

A method of statistical analysis of spectral mapping data:

Phase cluster analysis

Allows the user to automatically find phases in the

recorded data without prior knowledge

Clusters spectra at each pixel based on similarity in the

channels counts

With PCA the user can automatically

• Find Clusters

• Review the phases

• Build Maps

• Match Spectra

Step 1 - The spectra from the first 4x4 block

of measurement points is assumed to be

from the first phase.

An automated routine has been

developed to automatically determine the

chemical fingerprint of each phase –

phase cluster analysis (PCA).

Phase 1


Step 2 - The spectra from the second 4x4

block is compared to the first phase.

Phase 1 Phase 2


Step 3 - If the second block matches the

first phase within a specified tolerance,

this second spectrum is added to the

first to refine the phase spectrum.

+

Phase 1 Phase 1


Step 4 - If the second block does not

match, this second spectra then defines

a second phase.

Phase 1 Phase 2


Step 5 - This comparative process is

continues until each 4x4 block has been

matched to a phase.

Phase 1 Phase 2 Phase 3


Step 6 - The spectrum of each individual

measurement pixel is then compared

with and matched to one of the

determined phases.



Automatic phase map of sulfide ore

PCA – phase distribution

Using the stored spectral data, a maximum

intensity spectrum can be extracted using the

maximum intensity found in a map data cube

for each individual channel in the spectrum.

Max Channel spectrum

As Ni

Cu

Sb SSi

C

o

FeZn

Reconstructed X-Ray maps

Add the Zn component to the

phase cluster analysis

Corrected phase distribution

AsNiFe and

NiZnS

composite RGB

maps

AsCoFe X-Ray

overlay

Combined X-Ray maps

Combined X-Ray maps

Phase identification

The chemistry was determined using EDS analysis

Combining EDS with EBSD crystal information provides the mineral phase

Example: grain containing Zn, Fe, and S

Zn Fe S phase EBSD pattern

(Zn,Fe) S Sphalerite

Cubic (Oh) [m3m]

a = 5.41 Å

EDS - EBSD phase identification

sphaleritepentlandite pyrrhotite

chalcopyrite NickelineCobaltitebiotite

EBSD patterns of all phases

OIM scan area on SE

image

EBSD mapping results

EBSD Image Quality map

Grain boundaries and polishing

scratches are clearly visible in

the darker phases.

Note that these are not visible in

the SEM image.

EBSD mapping results

EBSD maps:

Left: Image Quality map

Middle: Phase map 3 phases with similar

crystal structure

Right: Inverse Pole Figure crystal direction map

EBSD mapping results: conventional

Sphalerite EBSD pattern

Cu

bic

(O

h)

[m3

m]

sphalerite a=5.41 Å chalcopyrite a=5.60 Å cobaltite a=5.66 Å

ZnS pattern indexed as …

cobalt iron zinc

sulphur antimony arsenic copper

nickel

X-ray maps collected together with the EBSD map indicate the phase distribution.

Chemical information is used to select the proper EBSD crystal structure file.

Corresponding EBSD patterns are forced to be indexed with the correct phase.

EBSD mapping results: ChI-Scan

EBSD maps:

Left: Image Quality map

Middle: Phase map

Right: Inverse Pole Figure crystal direction map

EBSD mapping results: ChI-Scan

Issues with phase selection based on chemistry:

• Variation in EDS intensity over the scan area

-1- Because of the high-tilts required for EBSD,

there is often a change in the EDS signal with WD

-2- Beam instabilites may cause variations in

countrates during long scans

• Difference in spatial resolution of EDS and EBSD

The spatial resolutions of the two techniques are approximately 50 nm and

1 micron for EBSD and EDS respectively.

Thus, there will be some “smearing” at the boundaries where the EBSD

must be used exclusively for the phase differentiation.

These issues can be minimised with Automated Phase Recognition

Automated phase recognition (PCA)

1 - The spectra from the first 2x2 block of measurement points is

assumed to be from the first phase.

2 - The spectra from the second 2x2 block is compared to the

first phase.

3 - If the second block matches the first phase within a specified

tolerance, this second spectrum is added to the first to refine

the phase spectrum.

4 - If the second block does not match, this second spectra then

defines a second phase.

5 - This comparative process continues until each 2x2 block has

been matched to a phase.


PCA - Phase Cluster Analysis

PCA - Phase Cluster Analysis


6 - The spectrum of each individual measurement pixel is then

compared with and matched to one of the determined phases.

SE image BSE image

The dark phase is dolomite (Ca,Mg)CO3

The lighter phase is calcite CaCO3

Example: marble

CaCO3 (Ca,Mg)CO3

Possible phases are:

Calcite: CaCO3 Trigonal (D3d) [-3m] a = 4.94Å c = 16.85Å

Mg-rich Calcite: (Mg,Ca)CO3 Trigonal (S6, C3i) [-3] a = 4.99Å c = 17.06Å

Dolomite: (Mg,Ca)CO3 Trigonal (D3d) [-3m] a = 4.83Å c = 15.94Å

Marble: chemistry

calcite

calcite

dolomite

Marble: EBSD patterns

dolomite

calcite

dolomite

Marble: EBSD patterns

Red is calcite

Green is dolomite

Conventionally indexed

X-ray maps acquired during scanning - 16 points/second - 63 msec dwell time

X-Ray maps

The automated component analysis

found three components:

Green is dolomite, red is calcite, and

blue is a (Ca) Al K Si O phase

(probably feldspar).

Results from automated analysis

IPF on IQ map, yellow

boundaries are calcite

twins

Phase map, orange is

dolomite, yellow is

calcite

Calcite IPF map Dolomite IPF map

ChI-scan results

2 Phases3 Phases

4 Phases

5 Phases 7 Phases

9 Phases

With ChiScan it no longer matters how many phases

are in your material.

ChI-scan = multi-phase EBSD mapping

Thank you for your attention

Multiphase analysis - combining EDS and EBSD · Automated phase recognition (PCA) 1 - The spectra...

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Transcript of Multiphase analysis - combining EDS and EBSD · Automated phase recognition (PCA) 1 - The spectra...