Purpose of Electrodeposition
To modify surface properties
-For decoration purpose
--for corrosion resistance
--to impart mechanical properties to surface
Like heat and wear resistance
Deposition of
-Polymer
-another metal (Sn,Cu,Ni,Zn etc) or
alloy (Cu/Zn, Ni/Cr, Ni/Co) on a metal
surface
--Composite (metal containing solids like PTFE,
WC2)
Electrical requirement
For deposit of even thickness over the whole
of the surface of substrate -the potential
should be the same at each point over the
surface of cathode
In general
Electroplating is carried out with very high
current efficiency
Electroplating Bath
•Chemical requirement
Plating bath is normally a complex mixture of
• metal being plated
•Electrolytes
•Additives
Complex Forming agents: main purposes-
1.To stabilise the cation ; Some metal cations (e.g.
gold) are not stable in the simple aquated form.
They are much more stable when complexed
with some ligands
2.To hold the aquated form at suitably low
concentration allowing control of the evenness
of plating
3.Improve the throwing power of the bath
Complex Forming agents: main purposes-
1.Prevent passivation of anode and therefore loss
of current efficiency in the corrosion reaction
2. CN- is a common ligand forming complex ion
such as Zn(CN)42- , Cu(CN)42, Ag(CN)2- , Au(CN)2-
3. Other examples are hydroxide, more recently
sulphamates
(Sulphmic acid)
Bath lining
•The plating solution is contained in a tank
•It must be of a material appropriate to the
solution it contains:
for alkaline solutions Plain mild steel
For acid solution steel lined with rubber/
various plastics / glass/ lead
Agitation
• Often under-appreciated step in
electroplating is agitation.
•The better the agitation, the better the
finish is going to be.
•Agitation is important to dislodge bubbles
of hydrogen or air from the cathode surface,
which might otherwise cause pitting
Agitation
•Agitation also overcomes stratification
and
• Assists in maintaining a uniform
temperature through out the solution
There are several methods for agitation.
•Air is the cheapest. A simple air pump like
those found in fish tank is often sufficient
agitation.
• mechanical agitation, which can be as simple
as stirring the electrolyte while plating. This is a
particularly useful method for fine delicate work,
• for stirring the electrolyte for a long period of
time a small electric motor.
•Ultrasonic waves
•Centrifugation
•Filtration (also used during plating)
•Reverse osmosis or ultrafiltration
•Activated carbon
Filtration ( of electrolyte during plating)
It is very important for an electrolyte to be
free from dust and other fine almost invisible
particles.
These particles interfere in the performance
of the bath solution and should be removed
through proper filtration
Continuous filtration is needed and must be
properly maintained and controlled.
Filtration with or without centrifugation is one
of the widely used and effective methods for
prolonging and improving the life of the bath
The required rate of filtration partly depends on
the input of contamination and also on the
thickness of the metal being plated
The flow rate and/ or pressure reading can
provide guidance on the performance of the
filters and the need for cleaning or replacement
Air agitated baths generally require more
filtration than non agitated solutions.
As a guide , most air agitated baths should be
filtered at a rate that will turn the solution
volume over at least once per hour and
preferably 2-3 times per hour
Filtration equipments
• Activated carbon filters are widely used to
remove dissolved organic impurities in
addition to its action in removing solids .
• Such filters are used continuously or
intermittently during plating.
•Some filters use replaceable cartridges or
filter pads which can be obtained in a rannge
of micron ratings.
for most purposes , filter media designed to
remove 5 to 15 micron particles are
satisfactory
•In cloth type unit - filter aids, based on
fibrous materials such as cellulose is used to
achieve satisfactoryfiltration
PCI Elefil Process Filters are manufactured in both disc type
and cartridge type as per the specific requirements and the
range of capacities available will meet the majority of
automatic and manual plating installation requirements. PCI
Elefil filter units provide a large filtration area, are easy to
clean and maintain, and provide effective retention of
activated carbon or filter aids.The unit is available in
different number and sizes of pure polypropylene plates.
The dome type Elefil filter is available in MS (with
PVC/Rubber lining) or electropolished SS 316 (with or
without lining) installed on a trolley complete with
polypropylene plates, filter cloth, motor, pumps and with
two 3 meter (10ft.) lengths of reinforced acid resistant hose
including appropriate spigots.
Filtration ( for waste minimization and metal
recovery)
•Technologies for recovering and regenerating
chemicals, should be aggressively employed.
•Both filtration and centrifugation produce
concentrated impurities that offer the
possibility of recovery
Filtration ( for waste minimization and metal
recovery)
•The general objective should be to treat
wastes as close as possible to the source
(individual manufacturing process) and to
reuse as much material as possible.
•Reverse osmosis is also an effective method
for recovery of substances
