Download - 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

1Department of MaterialsDepartment of Materials

Cadmium Replacement Using Zinc Alloys Cadmium Replacement Using Zinc Alloys Electrodeposited from Ionic Liquid Electrodeposited from Ionic Liquid

ElectrolytesElectrolytes

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.


Advantageous Properties of Cadmium CoatingsAdvantageous 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


Disadvantages of CadmiumDisadvantages of Cadmium

TOXICITY !! - coating - corrosion products - electroplating solution

Hydrogen embrittlement


Corrosion Resistance – Neutral Salt Fog ExposureCorrosion Resistance – Neutral Salt Fog Exposure


Corrosion Resistance – Marine ExposureCorrosion Resistance – Marine Exposure


Solution Potentials of Some Non-Aluminium Base Solution Potentials of Some Non-Aluminium Base Metals and also some Aluminium AlloysMetals and also some Aluminium Alloys

Metal Potential,V vs SCE

Magnesium -1.73Zinc -1.10Cadmium -0.82Mild steel -0.58Lead -0.55Tin -0.49Copper -0.20Bismuth -0.18Stainless steeltype 430

-0.09

Silver -0.08Nickel -0.07

Aluminium Alloys / V vs SCE1xxx (min 99% Al) -0.83 V2xxx (Copper) -0.69 V3xxx (Manganese) -0.84 V5xxx (Magnesium) -0.87 V7xxx (Zinc) -0.96 V


Some Alternative Coatings to CadmiumSome 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


Electrodeposition of Composite CoatingsElectrodeposition of Composite Coatings

Particulate phase suspended in electroplating bath

Careful control of agitation required to ensure good particle buoyancy and eventual entrapment


Electrodeposition of Multilayer CoatingsElectrodeposition 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


Ionic liquidsIonic liquids

Definition : Solvents that are solely composed of ions. By definition their melting points are below 100 oC.

Non-aqueous ionic solvents Low melting points Negligible vapour pressures Good chemical and thermal stabilities High intrinsic conductivities Large electrochemical potential windows


Ionic Liquids - BackgroundIonic 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


Electrodeposition of Zinc Alloys From Ionic LiquidsElectrodeposition 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).


Zinc-Manganese Electrolyte SystemZinc-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)


Zinc-Manganese Electrolyte SystemZinc-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


Cathodic Polarisation of Zinc and Manganese Chloride Ionic Cathodic Polarisation of Zinc and Manganese Chloride Ionic Liquid ElectrolytesLiquid Electrolytes

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-2-1.8-1.6-1.4-1.2-1-0.8-0.6-0.4-0.20Potential vs. Silver Chloride Reference Electrode (V)

Cu

rren

t (m

A)

0.2M ZnCl2 + 0.9M MnCl2.4H2O 0.4M ZnCl2 + 0.7M MnCl2.4H2O0.5M ZnCl2 + 0.5M MnCl2.4H2O 0.7M ZnCl2 + 0.4M MnCl2.4H2O

Figure 3 Cathodic polarisation curve of 2:1 urea/ChCl containing ZnCl2 and MnCl2.4H2O 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)


Potentiostatic Electrodeposition of Zn-Mn AlloyPotentiostatic Electrodeposition of Zn-Mn Alloy

Figure 8 Current-time curves for the deposition of Zn-Mn alloys from 0.4M ZnCl2/0.7M MnCl2.H2O 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)


Electrodeposition of Zinc From an Ionic LiquidElectrodeposition of Zinc From an Ionic Liquid

195 mA cm-267 mA cm-2


Effects of Electrolyte Agitation on Zinc Effects of Electrolyte Agitation on Zinc ElectrodepositionElectrodeposition

0.2 A/dm2

0.4 A/dm2

0.2 A/dm2

0.4 A/dm2

No agitation Ultrasonic agitation

19Department of MaterialsDepartment of Materials19

Electroeposition of Zinc-Manganese from Ionic Electroeposition of Zinc-Manganese from Ionic LiquidsLiquids

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


Manganese Content and Morphology of Zn-Mn Manganese Content and Morphology of Zn-Mn ElectrodepositsElectrodeposits

Electrolyte : 0.4M ZnCl2/0.7M MnCl2.H2O/0.8M H3BO3 in 2:1 urea/ChCl at 40ºC.


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 Zinc-Manganese Electrodeposits on Al 2024 SubstratesSubstrates

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


Electroeposition of Zinc-Manganese from Ionic Electroeposition of Zinc-Manganese from Ionic Liquids – Corrosion DataLiquids – Corrosion Data

97

94

90

Not known

Cathode current

efficiency (%)

130200.070.4M ZnCl20.7 M MnCl2.H2O

200300.20.4M ZnCl20.7 M MnCl2.H2O

240400.40.4M ZnCl20.7 M MnCl2.H2O

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)


Zn-Mn Electrodeposits from Ionic Liquids Zn-Mn Electrodeposits from Ionic Liquids – Main Findings– 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


Zn-Mn Electrodeposits from Ionic Liquids Zn-Mn Electrodeposits from Ionic Liquids – Main Findings– Main Findings

Linear polarisation resistance values close to cadmium electrodeposited coatings 230 .cm2

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.


Cadmium - the last word??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)

Download - 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

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