Multiphase analysis - combining EDS and EBSD

Transcription

1 Multiphase analysis - combining EDS and EBSD

2 Outline 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

3 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. Plot showing drift path during map acquisition

4 Sulfide ore - example Application example: Spectral mapping, phase identification, and phase differentiation on a polyphase sulfide ore rock

5 Spectral mapping data review 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

6 Spectral mapping data review Spot mode in FeNiS grain.

7 Spectral mapping data review Area mode in NiAs grain.

8 Spectral mapping data review Area mode in NiFeS grain.

9 Spectral mapping data review Freedraw mode in biotite grain.

10 Spectral mapping data review Freedraw mode in (NiCoFe)AsS grain.

11 Spectral mapping data review Full area spectrum.

12 Collected X-Ray maps X-Ray maps are constructed for all elements as identified by the auto peak ID routines How many phases are present? Cu Fe As Ni Co Sb Si S

13 Phase cluster analysis A method of statistical analysis of spectral mapping data: 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

14 Phase cluster analysis Step 1 - The spectra from the first 4x4 block of measurement points is assumed to be from the first phase. Phase 1 An automated routine has been developed to automatically determine the chemical fingerprint of each phase phase cluster analysis (PCA).

15 Phase cluster analysis Step 2 - The spectra from the second 4x4 block is compared to the first phase. Phase 1 Phase 2

16 Phase cluster analysis 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 +

17 Phase cluster analysis Step 4 - If the second block does not match, this second spectra then defines a second phase. Phase 1 Phase 2

18 Phase cluster analysis Step 5 - This comparative process is continues until each 4x4 block has been matched to a phase. Phase 1 Phase 2 Phase 3

19 Phase cluster analysis Step 6 - The spectrum of each individual measurement pixel is then compared with and matched to one of the determined phases. Phase 1 Phase 2 Phase 3

20 PCA phase distribution Automatic phase map of sulfide ore

21 Max Channel spectrum 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.

22 Reconstructed X-Ray maps Zn Cu Fe As Ni C o Sb Si S

23 Corrected phase distribution Add the Zn component to the phase cluster analysis

24 Combined X-Ray maps AsCoFe X-Ray overlay AsNiFe and NiZnS composite RGB maps

25 Combined X-Ray maps

26 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

27 EDS - EBSD phase identification Zn Fe S phase EBSD pattern (Zn,Fe) S Sphalerite Cubic (Oh) [m3m] a = 5.41 Å

28 EBSD patterns of all phases biotite chalcopyrite Cobaltite Nickeline pentlandite pyrrhotite sphalerite

29 EBSD mapping results OIM scan area on SE image

30 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.

31 EBSD mapping results: conventional EBSD maps: Left: Image Quality map Middle: Phase map 3 phases with similar crystal structure Right: Inverse Pole Figure crystal direction map

32 Cubic (Oh) [m3m] ZnS pattern indexed as Sphalerite EBSD pattern sphalerite a=5.41 Å chalcopyrite a=5.60 Å cobaltite a=5.66 Å

33 EBSD mapping results: ChI-Scan cobalt iron zinc nickel sulphur antimony arsenic copper 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.

34 EBSD mapping results: ChI-Scan EBSD maps: Left: Image Quality map Middle: Phase map Right: Inverse Pole Figure crystal direction map

35 Automated phase recognition (PCA) 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

36 PCA - Phase Cluster Analysis 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. Phase 1 Phase 2 Phase 3

37 PCA - Phase Cluster Analysis 6 - The spectrum of each individual measurement pixel is then compared with and matched to one of the determined phases. Phase 1 Phase 2 Phase 3

38 Example: marble SE image BSE image The dark phase is dolomite (Ca,Mg)CO 3 The lighter phase is calcite CaCO 3

39 Marble: chemistry CaCO 3 (Ca,Mg)CO 3 Possible phases are: Calcite: CaCO 3 Trigonal (D3d) [-3m] a = 4.94Å c = 16.85Å Mg-rich Calcite: (Mg,Ca)CO 3 Trigonal (S6, C3i) [-3] a = 4.99Å c = 17.06Å Dolomite: (Mg,Ca)CO 3 Trigonal (D3d) [-3m] a = 4.83Å c = 15.94Å

40 Marble: EBSD patterns calcite calcite dolomite

41 Marble: EBSD patterns calcite dolomite dolomite

42 Conventionally indexed Red is calcite Green is dolomite

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

44 Results from automated analysis 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).

45 ChI-scan results IPF on IQ map, yellow boundaries are calcite twins Phase map, orange is dolomite, yellow is calcite Calcite IPF map Dolomite IPF map

46 ChI-scan = multi-phase EBSD mapping 2 Phases 3 Phases 4 Phases 5 Phases 7 Phases With ChiScan it no longer matters how many phases are in your material. 9 Phases

47 Thank you for your attention