Small Spot and Mapping Analysis of Gold and Silver Alloys 2019/S2 Bonvin.pdf · •Standard-less analysis program have improved and provide good quantitative data for difficult alloys

The world leader in serving scienceProprietary & Confidential

18 March 2019

Didier Bonvin, Chris Shaffer, Kaizen Li & Jean-Marc Bohlen

Small Spot and Mapping Analysis of Gold and Silver Alloys

2 Proprietary & Confidential

Wavelength Dispersive X-ray Fluorescence Spectrometer: Goniometer

Sample cassette

X-ray Tube

Digital

high speed

crystal

1theta drive

Digital

high speed

detector

2theta drive

Detectors

Crystal changer

7 primary

beam

filters

4 collimators

ARL PERFORM’X 1500W-2500W-4200W

High Performance sequential XRF


X-ray

Generator

X-ray Source

(X-ray Tube or

Radioactive

Isotope)

Elec-

tronics Computer

Micro

Processor

Read-

Out

Secondary Collimator

Detected element: Ca at 113.08°2

Crystal

DetectorSample

PrimaryCollimator

Wavelength dispersive X-ray spectrometer: Role of the goniometer

n = 2 d sinwhere is the wavelength of the radiation

2d is the interplanar spacing of the crystal

is the angle between the incident beam and crystal


X-ray

Generator

X-ray Source

(X-ray Tube or

Radioactive

Isotope)

Elec-

tronics Computer

Micro

Processor

Read-

Out

Crystal

DetectorSample

PrimaryCollimator

Secondary Collimator

Detected element: V at 76.93°



X-ray

Generator

X-ray Source

(X-ray Tube or

Radioactive

Isotope)

Elec-

tronics Computer

Micro

Processor

Read-

Out

CrystalDetector

Sample

PrimaryCollimator

Detected element: Mo at 20.33°

• WDXRF provides superior resolution compared to EDXRF system

• 15 eV vs 130 eV at Mn Kα

• Excellent repeatability and stability

• Low limits of detection

• Simultaneous analysis of low and high concentrations



• One the most useful development in XRF technique

of recent years

• Tremendous help when no standard samples exist to

create a calibration

• UniQuant calibration is based on 64 pure element

standards

• uses complex mathematical algorithms for analysis of up

to 79 elements.

• correction for matrix effects and inter-element effects to

provide accurate quantitative results.

• allows for concentration determination of unknown

samples in any matrix

• Counting time can be chosen independently for every

element, e.g. longer for traces and shorter for major and

minor elements

Standard-less UniQuant XRF analysis

“Peak-by-peak” measurement strategy of UniQuant


Standard-less analysis on Cu-Ag alloys

Sample 2

Ref % UQ

Z El/Ox m/m% StdErr

14 0.14 Si 0.0794 0.004

15 P 0.0028 0.001

20 Ca 0.0071 0.0008

29 39.5 Cu 39.67 0.24

30 10 Zn 9.75 0.15

31 0.2 Ga 0.196 0.01

47 50 Ag 50.09 0.25

50 0.2 Sn 0.204 0.01

Ref %

Sample 1

UniQuant

Z El/Ox m/m% StdErr

15 P 0.0057 0.0019

20 Ca 0.01 0.0007

29 59.5 Cu 59.24 0.25

30 16 Zn 15.48 0.18

47 24.5 Ag 25.16 0.22

77 0.03 Ir 0.028 0.0041

Sample 6

Ref % UQ

Z El/Ox m/m% StdErr

20 Ca 0.008 0.001

29 39.4 Cu 40.5 0.25

30 15 Zn 14.62 0.18

31 4 Ga 3.81 0.1

47 38 Ag 37.55 0.24

49 3.5 In 3.41 0.09

50 0.1 Sn 0.097 0.005

Sample 5

Ref % UQ

Z El/Ox m/m% StdErr

20 Ca 0.009 0.0006

29 86.6 Cu 86.17 0.17

30 3 Zn 2.88 0.08

47 10 Ag 10.55 0.15

77 0.4 Ir 0.385 0.019


Small Spot Analysis by XRF

• Recent advances in hardware and software permit narrow spot analysis of specimens

• Requires pinpoint focus through camera with selectable X-ray diameter down to 0.5 mm

• Allows full quantification of the chosen spot when combined with UniQuant standard-less analysis

Focused analysis on any visible grain

of this Granite allows a specific

elemental determination


ARL PERFORM’X: Small Spot Analysis

• Spot location selected with on-

board camera

• Sample positioned by movements

of slide and rotation

• Analysis always focused at the

center of the X-ray beam

• Opens up the capability to analyze

non-homogeneous samples


Small Spot Results

with ARL PERFORM’X


Au calibration: 20 mm vs 0.5 mm

• Au - 0.5 mm aperture

• 0.21 kcps at 100%

•Counting rate difference of 1250x

•Nevertheless the accuracy is sill ok

•Au - 20 mm aperture

•270 kcps at 100%


Ag calibration: 20 mm vs 0.5 mm

Ag - 20 mm aperture Ag - 0.5 mm aperture


Cu calibration: 20 mm vs 0.5 mm

Cu - 20 mm aperture Cu - 0.5 mm aperture


Zn calibration: 20 mm vs 0.5 mm

Zn - 20 mm aperture Zn - 0.5 mm aperture


Mapping Results

with ARL PERFORM’X


• Many adjacent spots of 0.5 mm are measured over a defined area

• Steps of 0.1 mm to 0.5 mm at choice

• Camera viewing for selecting the area on the sample

• Maximum diameter of 30 mm

• Choice of area: Square, rectangle, disk, ring or segment and straight line

• Analysis of major and minor elements for 2 s to 30 s each depending on demanded precision

Mapping with WDXRF: principle


• Printed circuit board

• Camera viewing for selecting the area

• Round area chosen (Maximum diameter is 30 mm)

Mapping for Metals Recyclers


• A client complains about

repeatability of his portable

XRF instrument

• Nothing wrong was found

on the Niton XRF analyzer

• We were asked to check

the samples homogeneity

Mapping on a non-homogenous gold coin

Image of the sample

Cu and Zn band


Application of Spark-DAT on ARL iSpark Optical Emission Spectrometer

Silver purity levels

ARL iSpark 8860 OES


Optical Emission Spectrometry: Principle

Sp

ark

i

Sample

• We spark the sample surface by applying a high voltage through an electrode at 400 Hz

• Various wavelengths of the emitted light are counted by photomultipliers

• Typical OES analysis is done over 5 seconds

• The 2000 sparks are integrated to provide the average counts per element

• Quantitative determination for each element is obtained through the calibration curves


Intensity peak vs. Inclusion: principle

• With new electronics we are able to separately acquire the intensity signals of individual sparks

• An inclusion gives rise to intensity peaks because the concentration of some elements is higher

in the inclusion than in the matrix

• Elements presented in the same inclusion have high probability of appearing as coincident

intensity peaks

Ca

Al

single spark number

+ other elements

Sample


Ca

Al

Single spark number

Spark-DAT Software Suite

Principles of Spark-DAT inclusion analysis

Baseline

=

Signal due to low concentration

of Ca atoms in solution in the matrix

Ca intensity peak=

Signal due to the large numberof Ca atoms in an inclusion

Al peak coincident

with Ca peak

The inclusion contains Ca and Al

(e.g. Ca aluminate)

No Al peak coincident

with the Ca peak

The inclusion contains Ca but

not Al

(e.g. Ca oxide)


SUS low n42 - Ag 99.998% LBMA Ag RM1 - Ag 99.9576% LBMA Ag RM2 - Ag 99.9461%

O

Al

Mg

Si

0.51 ppm 8.6 ppm 61 ppm

0.45 ppm 14 ppm 47 ppm

< DL 8.7 ppm 49 ppm

• Higher presence of O, Al, Mg, Si induce more occurrences and higher counts as well

• Higher soluble concentration in the matrix is seen by higher background for example in Si and

Mg third column (and less so on Al)

• Elements of which number of peaks and peaks intensities were found to be significant:

• Al, Ca, Mg, Si, Na, Fe, Ni, O, Cr, W, C in all the samples

• There were also few significant peaks on K, B, Cu, Zn, Bi and Sn

Application of Spark-DAT on ARL iSpark OES

Inclusions in Ag


• Peak events per element or as a sum give useful information about the inclusion content without detail about

inclusion type

• Depending on intensity levels we can classify the inclusions into relative size groups:

• Large/Medium/Small inclusions (L/M/S)


Inclusions in Ag

Count of element peaks


• With adequately designed algorithms one can quantify the oxide inclusion types and

relative contents

• Depending on intensity levels we can classify the inclusions into relative size groups:

• Large/Medium/Small inclusions (L/M/S)


Inclusions in Ag

Count of the most common oxide inclusions in the samples


SUS low n42 - Ag 99.998% LBMA Ag RM1 - Ag 99.9576% LBMA Ag RM2 - Ag 99.9461%

OIntegrated intensity of peaks: 4066 Integrated intensity of peaks: 3772 Integrated intensity of peaks: 42270

Usual OES integration

Spark-DAT data


Possibility of quantifying Oxygen (oxides)

• Spark-DAT gives more details on the presence of oxygen in silver samples than usual

OES analysis

• Information is different between the Spark-DAT data and the usual OES analysis

• Apparently, integrated intensity of peaks is proportional to the content level of oxygen in inclusions

• It would be interesting to compare with oxygen reference concentrations


•WDXRF is a very useful tool in the precious metal industry

•Standard-less analysis program have improved and provide good quantitative

data for difficult alloys

•Small spot analysis and elemental mapping open up WDXRF to the analysis of

non-homogeneous samples

•Latest single spark analysis in OES spectrometry can help determine micro-

inclusions presence in alloys and derive the oxygen content

•More work with known samples will help provide more quantitative data

Conclusion


Thank you for your attention !

Any questions?

Documents

Small Spot and Mapping Analysis of Gold and Silver Alloys 2019/S2 Bonvin.pdf · •Standard-less analysis program have improved and provide good quantitative data for difficult alloys