Presentation title, change View >> Header & Footer Tata Steel Slide Arnoud de Vooys Trivalent chromium plating, anode and cathode Making packaging steel in the 21st century
Tata Steel Slide 2 ECCS packaging steels ECCS = Electrolytically Chromium Coated Steel ECCS excels in adhesion to organic coatings (lacquers, polymer coatings) ECCS is used in the production of DRD (Drawn & Redrawn) two-piece cans and components that do not have to be welded, such as ends, lids, crown corks, twist-off caps and aerosol bottoms and tops
Tata Steel Slide 3 ECCS electroplating process Tata makes ca. 200-300 ktonnes/year Say 200.000.000 m2 Typical coil dimensions: Length: 10000 m Width: 1.2 m Thickness: 0.2 mm Coating weight: 50 100 mg m -2 Cr 7 35 mg m -2 CrOx Line speed: Up to 10 m s -1 Total rectifier current: 50000 A Deposition time: A few seconds
Tata Steel Slide 4 Cr6+ replacement ECCS requires hexavalent chromium electrolytes, a.k.a Cr6+ Hexavalent chromium is considered a hazardous substance In response to REACH legislation, Tata Steel R&D has developed an electrolyte based on Cr3+ and formic acid Registration, Evaluation, Authorization & Restriction of CHemicals 2017 Cr 6+ + 3e - Cr 3+
ECCS replacement How hard can it be? Tata Steel Slide Pretty hard actually: ECCS works very well Search for alternatives (brittle, electrochem. active, soluble, poisonous, etc.) In the end, we went back to Chrome with different application
Tata Steel Slide Characterising Cr layer, FIB-TEM cross section Smooth part, homogeneous Cr layer Cr layer, Lower density than Fe
Tata Steel Slide Characterising Cr layer, FIB-TEM cross section Rough part Chrome follows surface roughness Steel shows surface crack
Tata Steel Slide Characterising Cr layer, FIB-TEM cross section Rough part Steel had small surface crack Chrome is deposited in the crack Good throwing power
Tata Steel Slide Does it work? the proof of the pudding is in the eating Cr layer was coated with PET laminate and compared to PET laminated ECCS Material was shaped into cans, filled with de-aerated brine, sterilised, stored for two weeks and evaluated visually Laminated ECCS reference Laminated Cr layer
Tata Steel Slide One danger: the anode In theory it is possible to oxidise Cr3+ to Cr6+ at the anode (steel coil is the cathode) Need to check to avoid danger
Tata Steel Slide 11 Results of long-term galvanostatic experiments anode Cr(VI) mg l -1 current efficiency % Pt 150 15 ca. 12.6 MMO IrO 2 + Ta 2 O 5 0 0 -applied current density = 92 ma (ca. 5000 A m -2 ) for 3600 s Cr6+ is not just a theory, but can happen with the wrong anode
Tata Steel Slide 12 Core of electrolyte is Cr3+ and formic acid stable complex 3 6 Cr(H 2 O) formate + destabilised complex 2 2 5(HCOO ) Cr(H O) Source: Zhixiang Zeng, Yaling Sun and Junyan Zhang, Electrochem. Commun., 11 (2009) 331 334.
Tata Steel Slide 13 Formic acid on Pt i / ma cm -2 10 9 8 7 6 5 4 3 2 1 0-1 Reaction 1: formic acid to CO2 Reaction 2: formic acid to CO, which sticks to the electrode CO is a poison to the reaction (not just for humans) Hence the drop in current = drop in reaction rate -0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 E vs. SCE / V
Tata Steel Slide 14 Cr3+ and formic acid on Pt i / ma cm -2 4 3 2 No CO 2 formation: Cr(III) complex blocks formic acid So it adsorbs, sticks Pt does something to Cr3+ question: is sticking the only thing that happens? 1 0-1 -0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 E vs. SCE / V
I / ma ion current CO 2 (m/z = 44) / a.u. I / ma ion current O 2 (m/z ION Meeting 2016 100 Cr3+ and formic acid on Pt 3.0E-09 Tata Steel Slide 15 arb. unit 2500 0.0E+00 1 2.5E-08-0.4Mass -0.2spectrometer 0.0 0.4 0.6 0.8 1.0 1.2 1.4 200 measures no CO2 E nor vs. SCE / V CO 2 2.0E-08 Formic acid has 150 nothing to do with it Must be Cr3+ CO 2 1.5E-08 100 Cr3+ oxidation 1.0E-08 50 uh oh 5.0E-09 O 2 0 0.0E+00-0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 E vs. SCE / V
i / ma cm -2 ION Meeting 2016 Tata Steel Slide 16 MMO: sodium sulphate + sodium formate + chromium(iii) sulphate 30 No sticking of Cr3+ no oxidation of Cr3+ no Cr6+ 25 20 15 10 5 0-5 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 E vs. SCE / V
Tata Steel Slide 17 Conclusions Cr(III)-formate adsorbs strongly on platinum Cr(III)-formate is oxidised at platinum Platinum is therefore catalytically active for Cr(VI) formation Cr(III) adsorption and Cr(VI) formation also occurs in the absence of formate (not shown here) Adsorption of Cr(III)-formate is absent on MMO and consequently no Cr(VI) is formed at MMO
Tata Steel Slide 21st century ECCS 21st century ECCS formally presented at Tinplate Conference in London (international fair for steel packaging producers and users) Launch: soon