1. 1 Department of Materials Cadmium Replacement Using Zinc Alloys Electrodeposited from Ionic Liquid Electrolytes P.A.Cantwell, P.P.Chung, Han Jiang, G.D.Wilcox and G.W.Critchlow Department of Materials, Loughborough University, Loughborough, Leicestershire, LE11 3TU. UK.

2. 2 Department of Materials Advantageous Properties of Cadmium Coatings  Sacrificial protection for ferrous substrates  Low coefficient of friction  Coating easily repaired  Good paint base  Good ductility  Low electrical resistance  Easily soldered  Good galvanic compatibility with aerospace aluminium alloys

3. 3 Department of Materials Disadvantages of Cadmium  TOXICITY !! - coating - corrosion products - electroplating solution  Hydrogen embrittlement

4. 4 Department of Materials Corrosion Resistance – Neutral Salt Fog Exposure

5. 5 Department of Materials Corrosion Resistance – Marine Exposure

6. 6 Department of Materials Solution Potentials of Some Non-Aluminium Base Metals and also some Aluminium Alloys Aluminium Alloys / V vs SCE 1xxx (min 99% Al) -0.83 V 2xxx (Copper)-0.69 V 3xxx (Manganese)-0.84 V 5xxx (Magnesium)-0.87 V 7xxx (Zinc) -0.96 V

7. 7 Department of Materials Some Alternative Coatings to Cadmium  Zinc - electrodeposited  Zinc alloys – electrodeposited e.g Zn-Ni, Zn- Co, Zn-Sn, Zn-Mn  Zinc-based electrodeposited coatings  Zinc-based multilayer coatings  Aluminium - PVD, UMS, electrodeposited, sprayed  Zinc-aluminium flake dispersion coatings

8. 8 Department of Materials Electrodeposition of Composite Coatings  Particulate phase suspended in electroplating bath  Careful control of agitation required to ensure good particle buoyancy and eventual entrapment

9. 9 Department of Materials Electrodeposition of Multilayer Coatings  Multilayer repetitive structures produced by controlled electrodeposition  Two definable alloy compositions  Electrodeposited from either single or dual electrolytes  Significant gains in mechanical and chemical coating properties possible

10. 10 Department of Materials Ionic liquids Definition : Solvents that are solely composed of ions. By definition their melting points are below 100 o C.  Non-aqueous ionic solvents  Low melting points  Negligible vapour pressures  Good chemical and thermal stabilities  High intrinsic conductivities  Large electrochemical potential windows

11. 11 Department of Materials Ionic Liquids - Background  Melting point of an ionic compound related to the size and charge of the ions  Larger ions and smaller charges result in lower melting points  Tetrabutylammonium bromide melts at 104˚C, sodium bromide melts at 747˚C  Non-symmetrical ions are more difficult to fit into a lattice, the lattice energy and hence melting point will be lower

12. 12 Department of Materials Electrodeposition of Zinc Alloys From Ionic Liquids  Electrodeposition from choline chloride-based ionic liquids: A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and V. Tambyrajah, Chem. Commun. 70 (2003).  Electrodeposition of zinc alloys: A. P. Abbott, G. Capper, K. J. McKenzie and K. S. Ryder, J. Electroanal. Chem. 599 288 (2007).  Electrodeposition of Zn-Mn: P. Y Chen and C. L Hussey, Electrochim. Acta 52 1857 (2007).

13. 13 Department of Materials Zinc-Manganese Electrolyte System  Three simple organic halide salts  Ethylene glycol  Malonic acid  Urea  One chemical to complex ionic liquid to form hydrogen bonds  Choline chloride P.P.Chung, P.A.Cantwell, G.D.Wilcox and G.W.Critchlow. Trans. IMF., 86, 211-219 (2008)

14. 14 Department of Materials Zinc-Manganese Electrolyte System  Mixing ratio 1 M choline chloride to 2 M organic halide salt  Zinc chloride additions 0.1-0.462 M  Manganese chloride additions 0.1-0.747 M

15. 15 Department of Materials Cathodic Polarisation of Zinc and Manganese Chloride Ionic Liquid Electrolytes Figure 3 Cathodic polarisation curve of 2:1 urea/ChCl containing ZnCl 2 and MnCl 2.4H 2 O as a function of potential and composition. P.P.Chung, P.A.Cantwell, G.D.Wilcox and G.W.Critchlow. Trans. IMF., 86, 211-219 (2008)

16. 16 Department of Materials Potentiostatic Electrodeposition of Zn-Mn Alloy Figure 8 Current-time curves for the deposition of Zn-Mn alloys from 0.4M ZnCl 2 /0.7M MnCl 2.H 2 O in 2:1 urea/ChCl at a potential of -1.6 V and temperatures of 20ºC, 40ºC and 60ºC. P.P.Chung, P.A.Cantwell, G.D.Wilcox and G.W.Critchlow. Trans. IMF., 86, 211-219 (2008)

17. 17 Department of Materials Electrodeposition of Zinc From an Ionic Liquid 195 mA cm -2 67 mA cm -2

18. 18 Department of Materials Effects of Electrolyte Agitation on Zinc Electrodeposition 0.2 A/dm 2 0.4 A/dm 2 0.2 A/dm 2 0.4 A/dm 2 No agitationUltrasonic agitation

19. 19 Department of Materials 19 Electroeposition of Zinc-Manganese from Ionic Liquids Figure shows a micrograph of 40 wt.% Mn deposit at 40 °C, current density of 0.4 Adm- 2. Scale bar 600 μm Figure shows a micrograph of 40 wt.% Mn deposit at 40 °C, current density of 0.4 Adm- 2. Scale bar 20 μm

20. 20 Department of Materials Manganese Content and Morphology of Zn-Mn Electrodeposits Electrolyte : 0.4M ZnCl 2 /0.7M MnCl 2.H 2 O/0.8M H 3 BO 3 in 2:1 urea/ChCl at 40ºC.

21. 21 Department of Materials Micrograph of Zn-Mn electrodeposition onto aluminium 2024 at 0.2 A dm -2. Composition of 52 wt.% Mn, 45 wt.% Zn, 2 wt.% Al identified through EDS Zinc-Manganese Electrodeposits on Al 2024 Substrates Micrograph of Zn-Mn electrodeposition onto aluminium 2024 at 0.1 A dm -2. Composition of 51 wt.% Mn, 48 wt.% Zn, identified through EDS

22. 22 Department of Materials 22 Electroeposition of Zinc-Manganese from Ionic Liquids – Corrosion Data 97 94 90 Not known Cathode current efficiency (%) 130 200.07 0.4M ZnCl 2 0.7 M MnCl 2.H 2 O 200300.2 0.4M ZnCl 2 0.7 M MnCl 2.H 2 O 240400.4 0.4M ZnCl 2 0.7 M MnCl 2.H 2 O 271.48Not knownCadmium to Def. Stan. 03- 19/1 [1] Average polarisation resistance (  ) % Alloy element (wt.%) Current density (Adm -2 ) Coating system Table identifies rest potential and polarisation resistance data for Zn-Mn coatings and cathode current efficiency [1] M. Simmons, ‘Zinc based composite coatings as an Alternative to Electrodeposited Cadmium’ Thesis, IPTME, August (2001)

23. 23 Department of Materials 23 Zn-Mn Electrodeposits from Ionic Liquids – Main Findings  Uniform Zn-Mn deposits have been achieved with ionic liquids  Hydrogen evolution issue has been significantly reduced  Mn content (wt.%) dependant on composition of electrolyte (Zn+Mn levels and additives), pH, temperature and agitation  High levels of Mn content (40 wt.%) have been achieved

24. 24 Department of Materials Zn-Mn Electrodeposits from Ionic Liquids – Main Findings  Linear polarisation resistance values close to cadmium electrodeposited coatings 230 .cm 2  Ionic liquids appear to be stable over significant periods of time (~1 year)  Other zinc alloys electrodeposited from ionic liquids – Zn-Mg being investigated presently.

25. 25 Department of Materials Cadmium - the last word?? “In many critical applications, no substitute has been found, and a universal substitute probably never will be.” (J.S. Hadley, Transactions of the Institute of Metal Finishing, May 10-12, 1991)