smart coating-roadshow-feb-2015-wet-surface-treatment-vitry
TRANSCRIPT
Faculté Polytechnique
Electro and electroless plating
Wet surface treatment
[email protected]. Véronique Vitry
Université de Mons
Poss
ible
in li
qu
idp
has
e
Coatings Conversion
Diffusion treatment
Structural modification
Wet surface treatment?
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
They represent an important part of the surface treatment industry : 25% of the surface treatment business (paint excluded)
4 main types: - Electroplating
- Electroless plating
- Conversion
- Sol-gel coatings
Liquid phase surface treatment in the industry
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Wet metallic coatings: general principles
Reduction
Concept : oxido-reduction process
Metal deposition
Me1 n++ ne-Me1
External currentsource
ne-
Electroplating
Metal oxidation
Me2Me2n+ + ne-
Displacement
Chemical agent oxidation
Red Ox + ne-
Electroless plating
Origin of the electrons
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Metallic coatings appear during the ‘Ancient History’ by mercury amalgamation
First electrochemical plating processes : pre-Columbian civilizations
Displacement of copper on iron used during the Middle Ages
Historical point of view of wet metalliccoatings
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
First electrochemical plating process with external current source: 1805 by Luigi Brugnatelli, friend of Volta who plated gold on silver
Numerous developments during the 19th century:
Silver and gold: Elkington 1836, by displacement
Gold electroplating: 1840 – adhesive and cohesive coating
Nickel : first efficient process : 1843- Bottger(used after that for 70 years)
Electroforming patented in 1837 by Jacobi
Historical point of view of wet metalliccoatings
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Use of external batteries from1839 (Jacobi)
Alloy electroplating since 1842
Electroplating on non-metallic substrates in 1840 (Jacobi) after graphite coating
Electroless nickel deposition in 1844 (Wurtz), but not efficiently
Additives in electroplating baths from 1847, mainly by serendipitous discovery (partial dissolution of molds, fall of various substances in the bath,..…)
Mechanical agitation
Historical point of view of wet metallic coatings
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Large scale use from 1850: street furniture, tableware (Christofle)
Historical point of view of wet metallic coatings
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
20th century:
‘Watts’ bath in 1916 allows quicker nickel electroplatingmix of nickel sulphate and chloride + boric acid
Development of chromium electroplating in the 20’s
Development of zinc electroplating in the 20’s (increase of automobile production)
Bright nickel is developed in 1934 : watts nickel modified with levelling and shining agents
1950’s : loss of interest of scientific sphere for the technology, deemed ‘mature’
1946: Brenner et Riddell rediscover electroless nickel plating
1949: Schlesinger discovers the borohydride ion
1954: first electroless nickel-boron plating
1978 - 1982: development of high P electroless nickel
1970’s: development of electroplating in the electronic industry
Historical point of view of wet metallic coatings
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Principle
The coating is formed on the cathode by the reduction of metallic ions by an external current source.
The metallic ions are generated by the progressive dissolution of the anode.
Amount of deposited metal:
𝑀 =𝜌𝐹 × 𝐼 × 𝑡 × 𝑀𝑀
𝑛 × 𝐹
Electroplating
e-e-
- +
Me2n+
Xn-
Me2
Me2Me1
cathode anode
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
How to determine plating conditions?
Low potential
Hull cell with current density gradient
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
How to determine plating conditions?
Use of polarisation curves
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Good zone
Bad zone (unsufficient coverage)
Dendritic coating
Université de Mons
What do you put in a plating bath?
- Metallic salts Nickel: sulphate and chloride ; sulfamate: Ni (SO3NH2)2
Chrome (VI): Cr2O3
Chrome (III): sulphate or chloride (! Avoid formation of CrVI at the anode)
Gold: cyanide (Au(CN)2); sulphite (Au(SO3)2-3 ), thiosulphate (Au(S2O3)2
-3 )
Copper: sulphate
- Buffers:Boric, sulfuric acids, sodium hydroxide, potassium citrate and nitrate, sodium carbonate, …
- Additives Complexing agents
Brightening agents : heavy metals salts; organic compounds
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Problems due to complex shapes: Throwing power
Current density is influenced by local instabilities (diffusion) and edge effects
This helps!
Pulsed current
Additives
Electroless plating
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Pulsed current:Periodical modification of plating current to
increase coating quality
Effects of pulse plating:
Decrease of thickness variations
Decrease of edge effects
Plating in holes
Better crystallinity
Higher germination (possibility of nanostructured coatings)
Increase of selectivity
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Alloy electroplating
Possible if two metals are reduced simultaneously at a single potential
How to do this?
Similar redox potentials
Electroplating
ic
E(-)
i2
i1
Me1 Me1
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Alloy electroplating
Possible if two metals are reduced simultaneously at a single potential
How to do this?
Dissimilar potentials but helpful overpotential
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Alloy electroplating
Possible if two metals are reduced simultaneously at a single potential
How to do this?
Modifiying the concentrations (by the use of complexingagents)
Using tensioactive agents to delay the deposition of one metal
Electroplating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Concept:
• Deposition by aqueous reduction of the metallic ions by a chemical agent
• No external current source
• Catalytic process
• Suitable for conducting and isolating materials
• OK for hollow parts and blind holes
• Constant thickness
Electroless plating
• External current source
• Non catalytic process
• Suitable only for conducting materials
• Difficult for hollow parts
• Thickness may vary
Electroplating
Université de Mons
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Metal deposition
Me1n++ ne-
Me1
External current
ne-
Oxidation of a metal
Me2Me2n+ + ne-
Oxidation of a chemical reagent
Red Ox + ne-
Global reaction of electroless deposition
Men+ + Red Me + Ox
• Thermodynamics:
Université de Mons
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Kinetics:
catalytic metal
non catalytic
metalAnodic polarisation
Cathodic polarisation
Mixed potential theory
• Deposition occurs at mixed potential
• │Idep│= │Ired│ =│Iox│
Deposition rate
• Influenced by overpotential
Catalytic activity
• Of the substrate (early stages)
• Of the coating (later stages)
Université de Mons
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Bath chemistry
COMPONENTS ROLE
Metallic ions Source of metal to be deposited
Reducing agentSource of electrons + co-deposited metal
Complexing agent
Complexes the metallic ions to
• increase the metallic ions solubility
• increase the stability by avoiding precipitation
BUT decreases the deposition current
StabilizerRegulate deposition speed by blocking a part of the catalytic sites
pH adjuster Regulates pH
Université de Mons
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Metals that can be plated electrolessly
Oth
er
elec
tro
less
allo
ys
Can
be
co-d
epo
site
dw
ith
Co
or
Ni
Can
be
pla
ted
alo
neNi
Co
Cu
Cd
Pb
Sb
Bi
Ag
Au
Pt
Pd
Rh
Ru
Sn
In
P
B
V
Mo
W
Mn
Re
Fe
Zn
Tl
CuNi
CuCo
CuCd
CuAu
PdNiP
PdCoP
PdZnP
AuAg
AuSn
PbSn
AuIn
Université de Mons
Choosing a reducing agent
Redox potential for the reducing agent (including overpotential) < Redox potential for the metal
In the case of nickel:
Electroless plating
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Choosing a complexing agent
Choosing a stabilizer4 classes
S, Se, Te compounds
Oxides : AsO2-, IO3
-, MoO42-
Heavy metal ions: Sn2+; Pb2+; Tl2+,
Oganic acids (maleic, itaconic, ….)
Bath pH is important
Electroless plating
Metal Complexing agents
Ni, Co Acetate, propionate, succinate, hydroxyacetate, aminoacetate,ethylenediamine, malonate, pyrophosphate, malate, citrate, tartrate
Cu Tartrate, acide glycolique, triethyl amine, EDTA, cyanures
Au Cyanure, sulfite, ethanolamine, citrate, chlorure
Ag Cyanure, ammonium
Pd, Pt, Ru Citrate, succinate, acetate, ammonium, ethylenediamine
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Gold electroplating: conductivity and corrosion resistance - electronics
Silver electroplating : high electrical and thermal conductivity – low contact resistance – antibacterial activity
Copper electroplating: high electrical and thermal conductivity – good adhesion
Tin electroplating: corrosion resistance – solderability – non-toxic (food industry)
Chromium electroplating: wear and corrosion resistance - aesthetics
Zinc electroplating: sacrificial protection of steel
Precious metals electroplating: precision mechanics and electronics
Nickel electroplating: high resistance to atmospheric corrosion – magnetic –wear resistance – diffusion barrier – adhesion promoter
Electroless nickel : wear and corrosion resistance – electronics (hard drives)
Various wet metallic coatings and theirproperties
Multipurpose, efficient and relatively cheap
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Various electroless nickel grades and their properties
• NH2NH2
Pure Nickel
• NiP with NaH2PO2 : low, mid and high P from 2 to 13 wt.% P
• NiB with NaBH4 or DMAB : can containeither Pb or Tl
Binary alloys
• Ni-P-B
• Ni-X-P or Ni-X-B with X = co-depositedmetal
Ternary alloys
• Co-deposited particles
Composite coatings
• NiB > NiP
Hardness
• NiB > NiP
Wear resistance
• NiB < NiP
Corrosion resistance
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Constant thickness
Bright aspect
Columnar growth
Cauliflower-like
surface texture
Smooth coating
Solderability
Properties
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Good adhesion
Properties
Low P
Mid P
High P
NiB Tl
NiB-Pb
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Hard
Good wear resistance
Corrosion resistance
Hardness, wear and corrosion
resistance improved by heat
treatment
Properties
LowP MidP HighP Ni-B-Tl Ni-B-Pb
TWI As-plated
average 16,29 24,3 19,37 35,59 23,2standard deviation
1,4 1,98 0,02 3,8 1,08
TWIHeat treated
average 10,17 15,525 11,265 19,69 8
standard deviation
0,48 1,515 0,565 3,21 0,29
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Hard
Good wear resistance
Corrosion resistance
Hardess, wear and corrosion
resistance improved by heat
treatment
Properties
Université de Mons
Electroless nickel
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015
Applications of electroless nickel
Aeronautics
Automobile
Food industries
Electronics (hard
drives substrates,
printed boards, ..)
Chemical and oil
industries
Polymer injection
Fire arms
Cutting tools
Université de Mons
Wet metallic coatings can solve a lot of technological problems because they are so many of them with very different properties
The bottom line is that Electroplating is a Solution in Search of a Problem. We just need to go out and FIND THE PROBLEMS!
— G. Dan Hutcheon
Closing word
Dr. V. Vitry | UMONS - metallurgie | 12/02/2015