Jyrki Tuominen
OES Product Manager
Oxford instruments Analytical
Light Element Detection (Al, Si, Mg) by Portable Metal Analyzers
In recent years, development of portable X-ray Fluoresence (XRF) analyzer
technology has grown rapidly. Analyzers are getting smaller and lighter, as well
as more accurate and faster. User friendliness and data transfer capabilities
have improved significantly. One of the most recent developments is the
capability to measure lighter elements (Al, Mg, Si), which could not be measured
with portable units 5 years ago. They form the basis for all aluminum alloys and
as most titanium alloys contain significant concentrations of aluminum it is
equally important in these alloys too. . Portable optical emission spectroscopy
(OES) analyzers also have a role in titanium production due to limitations of XRF
analyzers when measuring lighter elements.
In order to achieve relatively good detection limits and precise measurements, all
XRF analyzers on the market use either Helium gas or vacuum technology to
make light element detection possible. OES analyzers are much larger but
detection limits and speed of analysis are better than of XRF. Therefore each of
these technologies has certain drawbacks, as well as, unquestionable benefits.
Additionally certain key components, such as the X-ray source or the detector,
limit achievable accuracy. The sample surface and matrix composition also
affects the measurement of light elements.
The aim of this presentation is to highlight certain technical limitations and latest
technical developments to analyze light elements in Ti alloys.
Light Element Detection (Al, Si, Mg) by
Portable Metal Analyzers
Jyrki Tuominen
Oxford Instruments Industrial Analysis
Elk Grove Village, Il
Content
• What are light elements? What applications ?
• Light element analysis
– Technical limitations
• Latest developments
p
• Conclusions
What are light elements ? What
pp
?
applications
• Elements: Aluminum (Al), Magnesium (Mg), Silicon
(Si)
• Typically analyzed in
– Ti alloys (Al), Al alloys (Mg, Si), some Ni alloys (Al), some
Cu alloys (Al, Si)
• Applications: aerospace, metal recycling, Al and Ti
production, positive material identification (PMI)
Light element analysis
• Analysis can be done by using X-ray fluorecence
(XRF) or optical emission spectroscopy (OES)
(OES), both
portable and bench top analyzers used
– Traditionally bench top or laboratory analyzers for chemistry
and/or certification and portable analyzers for sorting and
alloy identification
• Portable XRF and OES offers certain
pros and cons
Optical Emission vs. X-ray Fluorescence
on Mobile
M bil A
Analyzers
l
OES
XRF
Range
Ti and up
(Al, Mg, Si possible w/limitations)
Majors, Minors and Traces
Sensitivity
Majors and Minors and Traces
Low (~ 100 ppm)
Detection Limit
High (~1000 ppm), going down
Speed
Fast
Sample Preparation
Minimal
S
Sample
l Surface
S f
Marking
M ki
T t ll non-destructive
Totally
d t
ti
Ease of Use
Unskilled Operator
Portability
Yes
Calibration
Both empirical and fundamental parameters
(FP)
Good for light elements
(C, S, P, Al, Mg, Si)
Moderate
(Few measurements required)
Substantial
(Clean/grinded surface required)
Yes
(Arc causes burn mark)
Skilled Operator
Yes, limited
Typical weight of unit 20 – 25 kg
Empirical only
Light element analysis
Technical limitations of portable XRF
–
Detector technology; Si-Pin vs. Penta-Pin vs. SDD
•
–
Protecti e windows
Protective
indo s in front of measurement
meas rement head
•
–
Shape and surface has a big influence
X-ray tube technology
•
–
Each offers certain pros and cons
Measured sample
•
–
Thin window is fragile (~10 x thinner than standard windows)
He-purge vs. vacuum technology
•
–
SDD has the best resolution and count-rate tolerance
Thin windows on tubes could be fragile
g
Excitation design
•
Filters needed. Measurement requires often use of 2 filters and X-ray
parameters, one for light elements and other for heavy elements.
Means complex design and calibration.
He purge vs vacuum
Helium purge
Pros
Cons
Vacuum pump
Good transmission
No gap between sample
and analyzer
Reasonable transmission
Not so fragile protective
window
Does not have influence on
detector life time
Protective window fragile
Requires
q
He cylinder
y
May shorten detector life
time
Higher running costs
Gap between sample and
analyzer
Requires vacuum pump
Higher initial costs
Sample surface
•
surface
s
roughnes
s: groove
e
size um
•
Sample must have clean and
even surface
Signal attenuation due to
“dirt” is significant
1
50
100
200
500
Matrix element fluoresence
intensity as a function of
Al matrix Fe matrix Cu matrix
1000
800
600
300
100
1000
990
950
850
500
1000
1000
980
900
700
Latest Developments
•
SDD detectors offers the best choice
– Count rate is 4-6 times higher compared to Si-PIN
– Peak to background ratio 10x better
⇒ Analyzer is significantly faster
– Detection limits are up to 5 times better for Si and Mg compared to
Si-PIN
⇒ Analyzer is significantly more accurate
•
No He p
purge
g nor vacuum needed
–
–
–
–
Lower running and initial costs
Smaller/lighter analyzer package
No travel restrictions
LODs at least as good or better as with Helium/vacuum
What light element analysis offers in
practice ?
p
Alloy
y
Light elements not
analyzed
With light
g elements
Ti 6-4
64
Ti 89%
Ti 93%
Inco 713
Ni 73%
Ni 77%
CDA 645
Cu 98%
Cu 90%
What light element analysis offers in
practice ?
p
Alloy
y
SDD detector
5 sec.
meas.time
SDD detector
10 sec.
meas.time
Ref.
C
Conc.
Ti CP gr
gr.4
4
Al 0.56%
Fe 0.12%
Al 0.22%
Fe 0.15%
Al 0.013%
Fe 0.15%
Ti 6
6-4
4
Al 6.74%
V 4.64%
4 64%
Fe 0.17%
Al 6.44%
V 4.32%
4 32%
Fe 0.16%
Al 6.16%
V 4.00%
4 00%
Fe 0.15%
Ti 6
6-6-2
62
Al 5.31%
V 5.67%
5 67%
Fe 0.65%
Al 6.32%
V 5.29%
5 29%
Fe 0.67%
Al 5.58%
V 5.56%
5 56%
Fe 0.56%
Conclusions
• New SDD detectors offers reasonable analysis for light
elements
– Thin windows (=fragile) and sample surface influence will remain
• Accuracy/analysis speed on “acceptable level”
• Handheld analyzer will not replace lab analysis but it is
getting better and better
• Hand held XRF may replace OES (arc) analyzers used
in metal sorting, especially when analyzer size or nondestructiveness matters
Thank You !
• Questions ?
• Comments ?