Transcript Outline Curriculum (5 lectures) Each lecture  45

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 1 of 5
An Introduction In
Electrochemical Coating
Electrochemical Surface Engineering
(Electrochemical Coating)
• Is it about the deposition a coating onto
surface, via electrochemical reactions.
• The coating can be (a) metallic, (b) metal
oxide or (c) conductive polymer.
• Metallic coating: Electroplating
• Metal oxide, conductive polymer: Anodizing
• Electroless deposition
Electrochemical Surface Engineering
•
•
•
•
•
An electro-chemical reaction
Cathode: Metals/alloys coating
Anode: Metal oxides
Conductive solution: ionic species
Transfer of electrons
Electroplating of copper
Anodizing
• An electrolytic passivation process.
• To form a thick oxide layer on a metal.
• Metal oxide forms on the anode.
Electroless deposition
• Electroplating: consisting of two electrodes, electrolyte,
and external source of current.
• Electroless deposition: this process uses only one
electrode and no external source of electric current.
• Electroless deposition: the solution needs to contain a
reducing agent so that the reaction can proceed:
• Metal ion + Reduction solution
 Metal solid + oxidation solution
Catalytic
surface
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)
OILRIG
• Reduction is a gain of electrons (RIG)
Industrial scale anodizing of Aluminium
Example of anodizing
Brush electroplating of gold onto
stainless steel substrate
Tin-Zinc coating onto steel substrate
Benefits of electroplated
metallic surfaces:
1.
2.
3.
4.
Improved corrosion resistance.
Improved wear resistance.
Longer lifetime.
Aesthetic surface finish.
Optical micrograph of 21 mm PEO
coating on Mg alloy:
Optical micrograph of 12 mm PEO
coating on Mg alloy:
Porosity in electroless
Ni-P deposits (<5 mm) on mild steel
Log-log Porosity vs. thickness for
electroless Ni-P deposits on steel
% Porosity
100
10
1
1
Deposit thickness/mm
10
Electrochemical anodizing
Transformation of Ti foil to TiO2 nanotubes
Anodizing e.g. 10-100 V
Competing reactions for the
formation of TiO2 nanotubes
Electrochemical formation of oxide
Ti + 2H2O → TiO2 + 4H+ + 4eChemical dissolution of oxide
TiO2 + 6F- + 4H+ → TiF62- + 2H2O
Green electrolyte, CH3SO3H
Anodizing of TiO2 nanotubes from Ti foil
100 nm
200 nm
100 nm
200 nm
Surface microstructure
Nanotubes Au-TiO2 vertically aligned array
1 mm
100 nm
100 nm
Reflective nanocrystalline PbO2
Application: Solar heat absorber
20
Rotating Cylinder Reactor
High throughput electrodeposition Cu-Sn alloys
Rotating Cylinder Reactor
High throughput electrodeposition Cu-Sn alloys
Nanoparticles SiC in a nickel matrix
Wear resistance coating
Darker contrast:
nanoparticle SiC
100 nm
Ni-SiC coating
Copper substrate
200 mm
TEM image
Nanotubes TiO2 in a nickel matrix
Nanotubes TiO2
20 nm
Nickel
matrix
100 nm
Electrodeposition of polypyrrole
Stainless steel substrate
Polypyrrole
1.0 cm
1.0 cm 25
Electrocatalysts for H2O electrolysis
Nanocrystalline and amorphous Ni-Co alloys
0g Co 2 g
10 g
20 g
40 g
60 g
80 g 100 g 150 g 200 g
100g Ni
1.0 cm
Co content in alloyed electrocatalyst increases
More effective electrocatalyst to evolution oxygen
26
Large scale electrodeposition
Thick film, multilayered Ni-Co on Fe substrate
200 μm
Ni
Ni
Fe
20 cm
Each tank = 5 Litres
Co
Multilayered - and -PbO2
α- and β-PbO2
β-PbO2
28
Thin film lead-acid battery
Nanosized materials
Nanosized material
PbO2 + PbSO4
100 nm
29
Summary
• Electrochemical coatings range from nanoparticles of
metal on nanostructured, inorganic supports through
to hard <100 mm Cr coatings on steel.
• Applications include catalysts, fuel cell-, solar cell- and
battery electrodes together with tribological/corrosion
resistant coatings for electronic materials, transport
and heavy engineering.
• Plasma electrolytic oxidation uses the application of a
high a.c. voltage to produce a hard, wear resistant
oxide coating on light metals (such as Mg alloys) for
automotive, aerospace and leisure.
• Electroless Ni deposits (typically <20 mm in thickness)
on steel or Al alloys are widely used in engineering
applications for their corrosion and wear resistance.
Thin coatings tend to have high porosity.