selection of spectrographic certified reference ...

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


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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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


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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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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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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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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Methodology for Selecting CRMs (Al analysis) • Selection step • Verification step • Approval step

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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

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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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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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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

5

[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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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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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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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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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

•

Sampling procedures • Tools and their material • Solidification process  Internal sample segregation  grain size and microstructure

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Methodology for Selecting CRMs (Al analysis)  Selection step • Verification step • Approval step

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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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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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Methodology for Selecting CRMs (Al analysis)  Selection step  Verification step • Approval step

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Methodology: Approval Step

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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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Questions


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