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Abstract No. 64
Investigations on the mechanism of activation, nucleation and zinc phosphate crystal growth on industrially produced steel sheet
Nicole Weiher, Fabian Junge, Gregor Müller, ThyssenKrupp Steel Europe AG
Zinc phosphate conversion coatings are used for surface finishing of galvanized steel sheet to markedly improve relevant characteristics regarding to processing and product features. This includes particularly the increase of corrosion resistance as well as the improvement of formability and paint adhesion. Zinc phosphate coatings are anorganic crystalline conversion coatings which are precipitated from a liquid process bath. Characteristics of zinc phosphate coatings can be specifically influenced by a prior application of so-called activator particles. The applied activator particles lead to an increasing number of zinc phosphate crystals per unit area as well as to enhanced rate of crystal formations and surface coverage. That in turn leads to a positive effect on surface characteristics like coating weight, corrosion resistance and paint adhesion of the zinc phosphate coating.
In this work the whole process of activation, nucleation and zinc phosphate crystal growth was analyzed with Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM) and Dynamic Light Scattering (DLS) technique. Zinc phosphate crystals belong to the group of so called Mesocrystals which were understood as self-assembling super structures consisting of crystalline nano particles which are able to grow towards a single crystal. In this work it was possible to observe the relevant nucleation and zinc phosphate crystal growth process in characteristic stages and able to first assign these mechanisms to the non-classical crystallization. As a result of increasing activator bath-life, an activator particle agglomeration was observed. So the number of activator particles per unit area is highly increased if these agglomerated particles are applied to the metal surface. The activator particle agglomerate cannot be dissolved fast enough during the following phosphating step. Activation seeds located inside of the activator particles connecting to zinc phosphate crystals which are growing right where the seed particles are released, because of the phosphoric acid attacks on the activator particles. This turns to the formation of stacked zinc phosphate crystals or zinc phosphate crystal agglomerates.
These zinc phosphate crystal agglomerates are hollow, mechanically instable and there is only a very little contact between the zinc phosphate crystals and the metal surface which can have an adverse effect on the paint adhesion. The relation between aging of the activator bath, agglomeration of these particles and paint adhesion on the resulting zinc phosphate crystal conservation coating could be made. CE
TAS
2015
ThyssenKrupp Steel Europe
Investigations on the mechanism of activation, nucleation and zinc phosphate crystal growth on industrially produced steel sheetJunge, F.; Müller, G.; Weiher, N.
CETAS 9, Düsseldorf, 20.05.2015
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Phosphating process
Agenda
1
Motivation2
Activation-, nucleation- and zinc phosphate crystal growth3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5 CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Phosphating process
Agenda
1
Motivation2
Activation-, nucleation- and zinc phosphate crystal growth3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary6
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
belt dryer phosphating
hot air
activation
electrogalvanisingrinse
(multistage)
Phosphating process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle
Zinc surface
Phosphating processPrevious assumption of the phosphating process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle
Zinc surface
Phosphating solution
Phosphating processPrevious assumption of the phosphating process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle
Zinc surface
Phosphating solution
Phosphating processPrevious assumption of the phosphating process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle
Zinc surface
Phosphating solution
Phosphating processPrevious assumption of the phosphating process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle
Zinc surface
Phosphating solution
Phosphating processPrevious assumption of the phosphating process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
electrolytically deposited
zinc layer
Phosphate coating
cold-rolled steel
Phosphating processSchematic cross section of a phosphated steel sheet
CETA
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CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
• Punching plates• Pressing the sheet into components• Cleaning (degreasing)• Activation• Phosphating • Thermal treatment• Cathodic dip painting • Primer• Top Coat
Phosphating process
SEM, zinc phosphate crystalls
Further processing steps at the customers facility
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Motivation
Phosphating process
Agenda
1
2
Activation-, nucleation- and zinc phosphate crystal growth3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5 CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
• Issues with paint adhesion on electrogalvanized and phosphated steel sheet in the past
• No approach to differentiate analytically between good and rejected material
Motivation
Mechanism of activation, nucleation and zinc phosphate crystal growth needs to be investigated fundamentally
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
> 4
0 1 2 3 4 5
evaluation of paint adhesion with cross hatch testing in accordance with DIN EN ISO 2409
Issues of paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activation-, nucleation- and zinc phosphate crystal growth
Motivation
Phosphating process
Agenda
1
2
3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process Comparison of electrolytically galvanized surface before and after activation
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process Comparison of electrolytically galvanized surface before and after activation
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Clarification of the activation, nucleation and zinc phosphate crystal growth process Comparison of electrolytically galvanized surface before and after activation
SEM CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
STEM, activator particle, laterally radiate
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Matrix Activator seedsActivator particle
STEM, activator particle, laterally radiate
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Dissolution of the activator particle matrix and self organisation of theactivator seeds after release
STEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activator particle after short phosphating, self organisation to sphericalshape
SEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
3
1
2
SEM
Zinc phosphate crystal after short phosphating, lateral growth und time-resolved growth stages
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Zinc phosphate crystal after short phosphating, crystallisation of the crystalshell
SEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Zinc phosphate crystal after short phosphating, crystallisation of the crystal shell, Nano Building Units inside the zinc phosphate crystal
pores / cavities
Nano Building Units
STEM
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
crystal structure from transition clusters
Clarification of the activation, nucleation and zinc phosphate crystal growth process
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Non-ClassicalCrystallization
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Clarification of the activation, nucleation and zinc phosphate crystal growth process - Summary
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Clarification of the activation, nucleation and zinc phosphate crystal growth process - Summary
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Clarification of the activation, nucleation and zinc phosphate crystal growth process - Summary
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Aufklärung des Aktivierungs-, Keimbildungs- und Zinkphosphatwachstumsprozess - Zusammenfassung
Ideal growth path
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activation-, nucleation- and zinc phosphate crystal growth
Motivation
Phosphating process
Agenda
1
2
3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5 CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
belt dryer phosphating
hot air
activation
electrogalvanizingrinse
(multistage)
Influence of activator bath stability on the paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
belt dryer phosphating
hot air
activation
electrogalvanisingrinse
(multistage)
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
1
10
100
1000
10000
0 25 45 51 140
Particlesize
[nm]
Time of measurement [h after start]
D10 D50 D90
Influence of activator bath stability on paint adhesionAgglomeration of activator particles, measured with Dynamic Light Scattering
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
1
10
100
1000
10000
0 25 45 51 140
Part
icle
size
[nm
]
Time of measurement [h after start]
D10 D50 D90
1-21-21-2
1-21-21-2
231
555
555
cross cut ratings
Influence of activator bath stability on paint adhesionAgglomeration of activator particles, measured with Dynamic Light Scattering
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM, agglomerated activator particle
Agglomeration of activator particles inside the activator bath leads to agglomerated particles on the metal surface
Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Agglomerated activator particle after short time of phosphating, dissolving of the agglomerate, zinc phosphate crystal growth preferred at the flank area
SEM
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Agglomerated activator particle after short time of phosphating, dissolving ofthe agglomerate, zinc phosphate crystal growth preferred at the flank area
SEM
Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Agglomerated activator particle after short time of phosphating, dissolving ofthe agglomerate, zinc phosphate crystal growth preferred at the flank area
SEM
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Agglomerated activator particle after short time of phosphating, dissolving ofthe agglomerate, zinc phosphate crystal growth preferred at the flank area
Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Agglomerated activator particle after short time of phosphating, dissolving ofthe agglomerate, zinc phosphate crystal growth preferred at the flank area
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Agglomerated activator particle after short time of phosphating, dissolving ofthe agglomerate, zinc phosphate crystal growth preferred at the flank area
Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Agglomerated activator particle after longer time of phosphating, zincphosphate crystal agglomerat
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Cavities inside a zinc phosphate crystal agglomerate (FIB-cut)Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
Cavities inside a zinc phosphate crystal agglomerate (FIB-cut)Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
1
10
100
1000
10000
0 25 45 51 140
Particlesize
[nm]
Time of measurement [h after start
D10 D50 D90
1-21-21-2
1-21-21-2
231
555
555
cross cut ratings
Influence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
1-21-21-2
555
D90: 2533 ± 754 nm
D90: 164 ± 27 nm
cross cut ratingsgood
cross cut ratingspoor
FIB-cuts at good and rejected material (SEM)
Cavities
Zinc phosphate crystals
Zinc layer
Platinumlayer
Influence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Zinc layer
Zinc phosphate crystals
SEM
brittle fracture on sample with poor cross cut ratingsInfluence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Cavities
SEM
Zinc layer
Zinc phosphate crystals
brittle fracture on sample with poor cross cut ratingsInfluence of activator bath stability on paint adhesion
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
SEM
FIB-cut on a painted sample with poor cross cut ratingsInfluence of activator bath stability on paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Ideal Zinc Phosphate Building ProcessSummary
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Zinc Phosphate Building Process WithAgglomerated Activator Particles
Ideal Zinc Phosphate Building ProcessSummary
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activation-, nucleation- and zinc phosphate crystal growth
Motivation
Phosphating process
Agenda
1
2
3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5 CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
10
510
1010
1510
2010
2510
3010
3510
4010
4510
Particlesize
[nm]
Time of measurement [h after start]
D90‐ohne Gegenmaßnahmen
1-21-21-2
1-21-21-2
231
555
555
Measures for increasing the activator bath stability
D90 - Without countermeasure
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
10
510
1010
1510
2010
2510
3010
3510
4010
4510
0
0,5 1
1,5 2
2,5 3
20
21
22
23
24
25
26
27
27,5 44
45
46
47
48
49
50
50,5 51
68
69
70
71
72
73
74
140
141
142
Particlesize
[nm]
Time of measurement [h after start]
D90‐ohne Gegenmaßnahmen
D90‐mit Gegenmaßnahmen
1-21-21-2
1-21-21-2
231
555
555
Measures for increasing the activator bath stability
D90 - Without countermeasureD90 - With countermeasure
CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
10
510
1010
1510
2010
2510
3010
3510
4010
4510
0
0,5 1
1,5 2
2,5 3
20
21
22
23
24
25
26
27
27,5 44
45
46
47
48
49
50
50,5 51
68
69
70
71
72
73
74
140
141
142
Particlesize
[nm]
Time of measurement [h after start]
D90‐ohne Gegenmaßnahmen
D90‐mit Gegenmaßnahmen
1-21-21-2
1-21-21-2
231
555
555
111
111
111
111
111
Measures for increasing the activator bath stability
D90 - Without countermeasureD90 - With countermeasure
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Activation-, nucleation- and zinc phosphate crystal growth
Motivation
Phosphating process
Agenda
1
2
3
Influence of agglomerated activator particles on the zinc phosphate crystal growth4
Measures for increasing the activator bath stability5
Summary5 CETA
S 20
15
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Summary
• Technology to monitor the activator bath condition (Particle Size Distribution) was found in form of Dynamic Light Scattering (DLS)
• Correlation between agglomeration of the activator particles and decreased paint adhesion was shown
• Process of activation, nucleation and zinc phosphate crystal growth process was clarified
• Countermeasures against agglomeration of activator particles can be taken in order to improve paint adhesion
CETAS 920.05.2015, DüsseldorfDr. Fabian Junge ThyssenKrupp Steel Europe
Thank you for your attention
CETA
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