1 department of materials cadmium replacement using zinc alloys electrodeposited from ionic liquid...
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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.
2Department of MaterialsDepartment of Materials
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
3Department of MaterialsDepartment of Materials
Disadvantages of CadmiumDisadvantages of Cadmium
TOXICITY !! - coating - corrosion products - electroplating solution
Hydrogen embrittlement
4Department of MaterialsDepartment of Materials
Corrosion Resistance – Neutral Salt Fog ExposureCorrosion Resistance – Neutral Salt Fog Exposure
5Department of MaterialsDepartment of Materials
Corrosion Resistance – Marine ExposureCorrosion Resistance – Marine Exposure
6Department of MaterialsDepartment of Materials
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
7Department of MaterialsDepartment of Materials
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
8Department of MaterialsDepartment of Materials
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
9Department of MaterialsDepartment of Materials
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
10Department of MaterialsDepartment of Materials
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
11Department of MaterialsDepartment of Materials
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
12Department of MaterialsDepartment of Materials
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).
13Department of MaterialsDepartment of Materials
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)
14Department of MaterialsDepartment of Materials
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
15Department of MaterialsDepartment of Materials
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)
16Department of MaterialsDepartment of Materials
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)
17Department of MaterialsDepartment of Materials
Electrodeposition of Zinc From an Ionic LiquidElectrodeposition of Zinc From an Ionic Liquid
195 mA cm-267 mA cm-2
18Department of MaterialsDepartment of Materials
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
20Department of MaterialsDepartment of Materials
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.
21Department of MaterialsDepartment 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 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
22Department of MaterialsDepartment of Materials22
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)
23Department of MaterialsDepartment of Materials23
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
24Department of MaterialsDepartment of Materials
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.