Oct 2, 2013 - Robert Hark. Rio Tinto Alcan. Arvida Research and Development Centre. Jonquière, Québec, Canada. Rio Tinto Alcan,. Primary Metal Group,.
SELECTION OF SPECTROSCOPIC CERTIFIED REFERENCE MATERIALS FOR THE ANALYSIS OF ALUMINIUM ALLOYS Jean-François Archambault Pierre Bégin
Rio Tinto Alcan Arvida Research and Development Centre Jonquière, Québec, Canada
Robert Hark
Rio Tinto Alcan, Primary Metal Group, Montréal, Québec, Canada
October 2013
12th International Aluminium Conference - Montreal
Plan • Context • Objectives of this presentation • Fundamentals of spark atomic emission spectroscopy (S-AES) • RTA’s methodology for the selection of spectroscopic analytical standard to analyse aluminium alloy compositions
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October 2013
12th International Aluminium Conference - Montreal
Context – Use of Aluminium Alloys TRANSPORT •
Cars (engine blocks, cylinder heads, transmission housings and body panels)
•
Trucks and buses (sheet and plate for bodies)
•
Railway stock
•
Aerospace
CONSTRUCTION •
Sheet products (roofing, wall cladding)
•
Extrusions (windows, doors)
•
Castings (builders' hardware)
PACKAGING •
Sheet (beverage can bodies and tops)
•
Foil (household and commercial wrap, pharmaceutical packaging)
ELECTRICAL •
used in the form of wire, normally reinforced with steel to form cables
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12th International Aluminium Conference - Montreal
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Context – General Classification of Al Alloys AA Family
General Uses
0XXX Experimental 1XXX (Fe, Si, >99% Al)
Foil stock, electrical conductors, lithographic sheets, anodized quality, heat exchanger tubings
2XXX Cu or (Cu+Mg)
Aerospace, truck bodies, screw machine stock
3XXX Mn or (Mn+Mg)
Cooking utensils, roofing, sidings, gutters, heat exchanger tubings, can body stock
4XXX Si
Foundry alloys, brazing sheets, forgings, weld fillers
5XXX Mg
Can ends, transportation alloys, structures
6XXX Mg + Si 7XXX Zn+Mg or Zn+Mg+Cu 8XXX Other combinations 9XXX Remelt
Architectural, structural, building sheet, transportation alloys, high-strength electrical conductors Aerospace (Mg, Cu, Zr), fin stock
Aerospace (Li), high-strength foil stock
October 2013
12th International Aluminium Conference - Montreal
Context - Evolution of Chemical Specifications
•
•
Economics drives the development → How to do more with less ? Customer wants quality products, performance and consistency
• •
Good control of the chemical composition Need for accurate and precise elemental analysis Wet Chemistry (tedious, slow, ~primary)
Spark-AES (OES) (simple, fast, secondary: need comparison)
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October 2013
12th International Aluminium Conference - Montreal
Objectives of this Presentation •
•
Describe the Spark Atomic Emission Spectroscopy (Spark-AES) industrial technique used for the analysis of aluminium alloy composition •
Aluminium alloy sampling & preparation
•
Principles of Spark-AES
Present the systematic approach for the selection of Certified Reference Materials (CRM) needed to produce an alloy and meet customer specification •
Selection of CRM combination.
CRM: A reference material for which the composition or properties are certified by a recognized standardizing agency or group (ASTM E135-01a)
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12th International Aluminium Conference - Montreal
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Aluminium Alloy Sampling & Preparation Aluminium alloy process steps Alloy Sampling
Alloying ingredients Grain Refiner
Molten Electrolytic Aluminium Cells Transport
Sampling
Alloy Preparation
Degassing
Filtration
(50-130 tons)
Preparation
Analysis
Sample
1 spark
(70 g)
(~10 mg)
Ingot Casting
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12th International Aluminium Conference - Montreal
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Fundamental - Instrumentation Al sample
Photomultiplier Tubes
-
Spectrometer Housing Vacuum Region
Slit Frame
Stand
Light
Ar
Ar Flushed Entrance Optics
+
Counter-electrode
Source
Energy
Primary Slit
Each atom has its own excited state energies
Emission
Absorption
}
Ground State
Excited states
∆𝐸 = ℎ𝜈 = ℎ𝑐�𝜆
Grating
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12th International Aluminium Conference - Montreal
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Methodology for Selecting CRMs (Al analysis) • Selection step • Verification step • Approval step
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12th International Aluminium Conference - Montreal
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Methodology: Selection Step 1. Aluminium Alloy Specification General AA specification Element Max Min
Si 0.6
Fe 0.8
Cu 0.25 0.05
Mn 1.4 0.8
3104
Mg 1.3 0.8
Zn 0.25
Ti 0.10
October 2013
12th International Aluminium Conference - Montreal
Methodology: Selection step 2. Evaluation of the impact of spectral interferences and matrix effects
A. Spectral interferences B. Elements impacting the excitation process C. Presence of elements as structure modifiers
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12th International Aluminium Conference - Montreal
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A. Spectral Interference Spectral interferences occur when the dispersion of light is insufficient to completely isolate the radiation emitted by the analyte from other radiations
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
0.35
Sb (I)
Sb (I)
0.30
[λ=259.81 nm]
[λ=231.15 nm]
0.25
Fe (II)
Intensity
Intensity
Fe: 0.12% w/w Ni: 0.009 % w/w Sb: 0.28% w/w
0.20
Ni (I)
0.15 0.10 0.05 0.00
80 84 88 92 96 100 104 108 112 116 120
80 84 88 92 96 100 104 108 112 116 120
Grating Position
Grating Position
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12th International Aluminium Conference - Montreal
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A. Spectral Interference (cont’d) Different methodologies exist for spectral interference correction: − Family curve (use of algorithm to correct the apparent intensity) − Master curve in conjunction with a 2-point standardization curve Iron spectral interference on Sb (λ = 259.81nm)
Nickel spectral interference on Sb (λ = 231.15nm) 6
5 y=
+ 9.8378x - 0.1556 R² = 0.9997
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[Ni] (% w/w)
[Fe] (% w/w)
4
15.608x2
3 2 1
y = 356.75x - 4.3148 R² = 0.9999
4 3 2 1
0
0
0
0.1
0.2
0.3
0.4
Sb161 channel intensity
0
0.005
0.01
0.015
0.02
0.025
Sb391 channel intensity
•
Use a different spectral line when possible
•
Evaluate the impact on the reporting precision required for the specification
0.03
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12th International Aluminium Conference - Montreal
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B. Excitation and Emission 𝑀𝑋 𝑠
1. Fusion 2. Evaporation / Volatilization 3. Dissociation / Atomization
𝑀𝑜 𝑔 +𝑋 𝑜 (𝑔) 𝑀𝑜 ∗ 𝑔
Excitation (∆Ee)
Emission (hν)
𝑀𝑜 𝑔
Ionization (∆Ei)
Electronic recombination
𝐾𝑀 0
𝑀 + 𝑔 + e-
𝑛𝑒 𝑛𝑀 + = 𝑛𝑀 0
Excitation (∆Ee)
Emission (hν)
𝑀+ ∗ 𝑔
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12th International Aluminium Conference - Montreal
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B. Excitation and Emission (cont’d) +
Impact of Electronic Density in the Plasma First IP
First IP
Impact of Electronic Density in the Plasma
+
+
+ (http://physics.nist.gov/PhysRefData/ASD/ionEnergy.html)
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12th International Aluminium Conference - Montreal
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B. Excitation and Emission (cont’d)
𝜆𝑜𝑜𝑜 = 𝑀𝑀382.93𝑛𝑛 (𝐼)
1st IPZr = 6.837 eV 1st IPMg = 7.6462 eV
Zr increases the electron density → [Mg+] ↓ ∴ Mgo* ↑
Higher Zr content (0.014 to 0.047%)
Low Zr content (0.0018% to 0.0027%).
Effect of Zr on the Mg signal on different CRM 6061 series
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12th International Aluminium Conference - Montreal
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C. Structure Modifiers Composition (% w/w) of certified reference materials 3004-AB and 3104-AD
(λMg(I)=382.93nm)
CRM 3004-AB
3104-AD
Si
0.21
0.21
Fe
0.47
0.40
Cu
0.14
0.17
Mn
1.17
0.95
Mg
1.10
1.21
Zn
0.034
0.12
0.05% w/w
1st IPZn = 9.3941 eV 1st IPMg = 7.6462 eV
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Sampling procedures • Tools and their material • Solidification process Internal sample segregation grain size and microstructure
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12th International Aluminium Conference - Montreal
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Methodology for Selecting CRMs (Al analysis) Selection step • Verification step • Approval step
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12th International Aluminium Conference - Montreal
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Methodology: Verification Step 1. Comparison with wet chemistry
The main objective of this step is : Wet Chemistry
Spark-AES (OES)
Proceed with the approval step
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12th International Aluminium Conference - Montreal
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Methodology: Verification Step 2. Finding/Casting new CRMs
The main objective of this step is : Wet Chemistry
• •
Spark-AES (OES)
Might have to use multiple CRMs to be able to analyze the new alloy Possible delay increase before reception of production Certification through wet chemistry
Note: Casting new CRMs is a last resort
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12th International Aluminium Conference - Montreal
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Methodology for Selecting CRMs (Al analysis) Selection step Verification step • Approval step
October 2013
12th International Aluminium Conference - Montreal
Methodology: Approval Step
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October 2013
12th International Aluminium Conference - Montreal
Conclusion Spark-AES is a comparative technique that needs the use of CRMs
The accuracy of the Spark-AES results depends on the selection of CRMs used in the standardization
The quality of the CRM selection depends on : • The spectral resolution power of the instrument • The excitation process within the spark: atom-ion equilibrium • The knowledge of elements inducing “structural modification”
Good correlation between Spark-AES analysis and wet chemistry
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October 2013
Questions
12th International Aluminium Conference - Montreal
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