Outline curriculum 5 lectures each lecture 45 minutes
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Outline Curriculum (5 lectures) Each lecture  45 minutes. Lecture 1: An introduction in electrochemical coating Lecture 2: Electrodeposition of coating Lecture 3: Anodizing of valve metal Lecture 4: Electroless deposition of coating Lecture 5: Revision in electrochemical coating.

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Outline Curriculum (5 lectures) Each lecture  45 minutes

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Outline curriculum 5 lectures each lecture 45 minutes

Outline Curriculum (5 lectures)Each lecture  45 minutes

Lecture 1: An introduction in electrochemical coating

Lecture 2: Electrodeposition of coating

Lecture 3: Anodizing of valve metal

Lecture 4: Electroless deposition of coating

Lecture 5: Revision in electrochemical coating


Lecture 2 of 5 electrodeposition of coating

Lecture 2 of 5Electrodeposition of Coating


Electrochemical surface engineering

Electrochemical Surface Engineering

  • An electro-chemical reaction

  • Cathode: Metals/alloys coatings

  • Anode: Soluble or insoluble

  • Conductive solution: ionic species

  • Transfer of electrons


An example of electroplating of copper

An example of electroplating of copper

Power

Supply

e-

Copper

Anode

Steel

Cathode

Main reaction

Cu2+ + 2e- Cu


Other possible electrochemical reactions

Other possible electrochemical reactions

Electrodeposition of copper Cu2+ + 2e- Cu

Hydrogen evolution2H+ + 2e-  H2

At the cathode

At the anode

Soluble anode

Dissolution of copper Cu 2e- Cu2+

Insoluble anode

Oxygen evolutionH2O  2e-  2H+ + 0.5 O2

Overall reaction

Cu2+ + H2O Cu + 2H+ + 0.5 O2


Definition electron transfer reactions

Definition: Electron transfer reactions

  • Oxidizing agent + n e- = Reducing agent

  • Oxidizing agents get reduced

  • Reducing agents get oxidized

  • Oxidation is a loss of electrons (OIL)

  • Reduction is a gain of electrons (RIG)

OILRIG


Typical steps in the electroplating of metals

Typical steps in the electroplating of metals

  • Cleaning with organic solvent or aqueous alkaline; to remove dirt or grease.

  • Is the surface is covered by oxides as a result of corrosion, clean with acid.

  • Rinse with water to neutralise the surface.

  • Electroplate metals under controlled condition.

  • Rinse with water and dry.

  • Additional step: heat treatment in air or vacuum environment


What is the job of the bath

What is the Job of the Bath?

  • Provides an electrolyte

    • to conduct electricity, ionically

  • Provides a source of the metal to be plated

    • as dissolved metal salts leading to metal ions

  • Allows the anode reaction to take place

    • usually metal dissolution or oxygen evolution

  • Wets the cathode work-piece

    • allowing good adhesion to take place

  • Helps to stabilise temperature

    • acts as a heating/cooling bath


Typically what is in a bath e g watts nickel

Typically, What is in a Bath?e.g., Watts Nickel

  • Ions of the metal to be plated, e.g.

    • Ni2+ (nickel ions) added mostly as the sulphate

  • Conductive electrolyte

    • NiSO4, boric acid, NiCl2

  • Nickel anode dissolution promoter

    • NiCl2 provides chloride ions

  • pH buffer stops cathode getting too alkaline

    • Boric acid (H3BO3)

  • Additives

    • Wetters, levellers, brighteners, stress modifiers..


Current efficiency

Current efficiency

  • pH changes accompany electrode reactions wherever H+ or OH- ions are involved.

  • In acid, hydrogen evolution occurs on the surface of cathode. This will result in a localised increase in pH near the surface of the electrode.

  • In acid, oxygen evolution occurs on the surface of anode. This will result in a drop of pH near the surface of the electrode.

  • pH buffer stops the cathode getting too alkaline.

    • Boric acid (H3BO3)

2H+ + 2e-  H2

H2O  2e-  2H+ + 0.5 O2

H+

Cathode

H2

OH

H2O  H+ + OH


Current efficiency1

Current efficiency

  • Is the ratio between the actual amount of metal deposit, Ma to that calculated theoretically from Faradays Law, Mt.


Parameters that may influence the quality of electrodeposits

Parameters that may influence the quality of electrodeposits

  • Current density (low to high current)

  • The nature of anions/cations in the solution

  • Bath composition, temperature, fluid flow

  • Type of current waveform

  • the presence of impurities

  • physical and chemical nature of the substrate surface


An example of current vs potential curve for electroplating of metal

An example of Current vs. Potential Curve for electroplating of metal


Typical recipe and conditions watts nickel

Typical Recipe and ConditionsWatts Nickel

Component Concentration/g L-1

Nickel sulphate330

Nickel chloride 45

Boric acid 40

Additivesvarious

Temperature60 oC

pH4

Current density2-10 A dm-2


Faraday s laws of electrolysis

Faraday’s Laws of Electrolysis

Amount of material = amount of electrical energy

n = amount of material

q = electrical charge

z = number of electrons

F = Faraday constant


Faraday s laws of electrolysis expanded relationship

Faraday’s Laws of Electrolysis: Expanded Relationship

n = amount of material

w = mass of material

M = molar mass of material

I = current

t = time

z = number of electrons

F = Faraday constant


Current current density surface area

Current, Current density, Surface area

j = current density [mA cm-2]

I = current [A]

A = surface area of the electrode [cm2]

jelectroplate = electroplating current density (metal electroplate)

jcorrosion = corrosion current density (metal corrosion/dissolution)


Faraday s laws of electrolysis average thickness

Faraday’s Laws of Electrolysis: Average thickness

w = weight (mass) of metal

M = molar mass of metal

I = current

t = time

z = number of electrons

F = Faraday constant

x = thickness of plating


Faraday s laws of electrolysis average deposit thickness

Faraday’s Laws of Electrolysis: Average deposit thickness

The thickness of plate depends on:

- the current (I)

- the time for which it passes (t)

- the exposed area of the work-piece (A)

- a constant (M/rAzF)

which depends on the metal and the bath


Faraday s laws of electrolysis question nickel plating

Faraday’s Laws of Electrolysis: Question - Nickel Plating

Nickel is plated from a Watts bath at

a current density of 3 A dm-2.

The current efficiency is 96%.

The molar mass of nickel is 58.71 g mol-1.

The density of nickel is 8.90 g cm-3.

The Faraday constant is 96 485 C mol-1.

What will be the averaged plating thickness

in 1 hour?


Faraday s laws of electrolysis answer nickel plating

Faraday’s Laws of Electrolysis: Answer - Nickel Plating

Assume that the reaction is:

Ni2+ + 2e- = Ni

So, two electrons are involved for every Ni atom,

and z = 2

The current density used in plating nickel is

96% of the total current, i.e., 0.96 x 3 A dm-2.


Faraday s laws of electrolysis answer nickel plating1

Faraday’s Laws of Electrolysis: Answer - Nickel Plating

The average deposit thickness is given by:


Outline curriculum 5 lectures each lecture 45 minutes

Summary

  • Electrodeposition is a versatile coating technique.

  • There is a high degree of control over deposit thickness.

  • Many metals can be electroplated from aqueous baths.

  • So can some alloys, conductive polymers and composites.

  • Rates of electroplating can be expressed via Faraday’s Laws of electrolysis.

    Thank you for your attention!


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