FIELD OF THE INVENTION
The present invention relates to a method for regeneration of silver surface of
silver-electroplated electrodes, used in busbars. More particularly, the present
invention relates to a wet chemical method for rapidly removing both organic
and inorganic impurities from silver surfaces of silver-electroplated electrodes
used in busbars, and or similar articles or products or sub-products thereof.
BACKGROUND OF THE INVENTION
Silver-electroplated electrodes are used for maintaining ohmic contact in busbars
in various electrical transmission and distribution lines. In such electrodes, a thin
layer of silver (thickness usually in the range of 3 - 5 micron) is electroplated on
copper metal in order to take advantage of higher electrical conductivity of silver
with better ohmic contact in the transmission lines.
Since silver is very vulnerable to atmospheric conditions, the surface of the silver
layer gets damaged by the chemical reaction with atmospheric hydrogen
sulphide gas under ambient conditions, resulting in formation of silver sulphide
layer that lead to contamination of materials having inorganic origin. In an
industrial set up or factory premises, such electrodes often come in contact with
various organic chemicals like greasy matters, oily substances, organic dirt etc,

while storing, packing or handling, causing another type of contamination,
which is organic in nature. Such contaminations in excessive quantities in the
surface of the silver electrodes also cause ohmic problem besides a dull look and
hence damaging the aesthetic appearance of the electrodes.
In order to avoid such contaminations from atmospheric conditions, the surface
of the silver in the electrode need to be regenerated by effectively removing all
the contaminants. One limitation is that absolutely no aggressive chemical or
physical process could be applied to remove only the contamination, since the
thickness of the silver layer is merely in the range of 3 - 5 micron that would
result wearing off or leaching out the silver layer in the electrode.
In this context, a cost-effective and convenient solution is to be provided to
regenerate the silver surface by effectively removing such contaminants of both
inorganic and organic origins in quickest time possible. In this context, the
invention was made.
Prior art publication teaches the process for removing silver-sulphide scales from
silver are available articles. US Patent number 5669978 dated July 03, 1995
reported a method for removing scales from silver articles using an aqueous
oxalic acid solution by maintaining oxalic acid dehydrate and water in the weight
ratio of 1:100 to about a limit of solubility of oxalic acid dehydrate and water.

As per the cited invention, it is important to maintain the contact of the surface
scale with the oxalic acid solution for a period of time sufficient to loosen the
scale and thereby removing the surface scale from the silver-containing metal
articles.
German Patent Number 569473 reported a method for cleaning silver sulphide
contamination in alkaline solution with the aid of soap, aldehyde sugar (grape
sugar) and sodium bicarbonate. As per this invention, 10 g of a mixture
containing 92.5% of sodium bicarbonate, 5% of powdered medicinal soap and
2.5% of grape sugar dissolved in 1 litre in an aluminium vessel. This also
reported to damage of aluminium vessel as well.
US Patent 4270932 dated June 02, 1981 describes a physical polishing method
using various silver salts in the form of either 'dry powder' or in the form of a
'paste' in combination with an harsh abrasives or a mild agent like a conventional
filler (e.g. Bentonite or Fullers Earth) so as to clean silver surfaces or restoration
purposes in silver articles. As described in the invention, the constituent for the
said polishing composition should have at least one silver generating salt, i.e.
silver oxide. Different qualities of surface of polished silver object could be

obtained depending on the kind of powder or the abrasive is used in each case
of the derived composition for polishing or restoration of the damaged silver
articles.
Canadian Patent number 930902 dated July 31,1978 also describes a polishing
agent for cleaning or restoration of silver articles which involves deposition of a
molecular layer of silver using a so-called silver complexing agent, followed by a
chemical bonding of the layer to the article being cleaned.
As early as January 26, 1966, US Patent number 3230571 also describes the
design of silver cleaning pads using felt materials primarily for polishing various
domestic silver articles or utensils.
US Patent number 4925491 dated May 15, 1990 describes various non-toxic
solutions and creams for plating and polishing silver articles and electroplated
objects. The silver plating and polishing aqueous solutions in the invention
contain a water soluble silver salt (i.e. silver nitrate),a polyoxyalkylene ester
surfactant, a humectant, a polishing agent, a suspending agent and water
respectively. A typical composition as furnished in the embodiment of this cited
invention, is produced below as an example in this category.


In case of jewellery industries involving silver articles, silver scaling is removed
by sodium bi-sulphate granules. Often hot sulphuric or nitric acids are also used
to aid the process to remove hard scaling from silver articles. These processes
however often involved loss of silver metal to substantial extent from the
surface.
There are continuing interests in developing techniques for regeneration of
damaged silver layer in any silver containing articles, particularly, electroplated
electrodes those used for various industrial purposes, in which silver has a thin
layer in the top of the article and wherein no silver loss from such layer could not
be compromised by any regeneration technique.

Therefore, the present invention provides an improved wet chemical method for
regenerating silver surface of silver-electroplated electrodes thereby removing all
contaminants both organic and inorganic origin and strictly without loosing any
silver from the silver layer in the electrode. The invention is also applicable to
similar articles of silver or products and sub-products thereof, containing thin or
thick silver layer in the object.
OBJECTS OF THE INVENTION
It is therefore an object of the invention is to propose a wet chemical method for
rapidly removing (regeneration) both organic and inorganic impurities from of
silver surfaces of silver-electroplated electrodes used in busbars.
Another object of this invention is to propose a wet chemical method for rapidly
removing both organic and inorganic impurities from silver surfaces of silver-
electroplated electrodes used in busbars in which silver surfaces having a thin
layer in a range of 3 - 5 micron.
A still another object of this invention is to propose a wet chemical method for
rapidly removing both organic and inorganic impurities from silver surfaces of
silver-electroplated electrodes used in busbars in which formulations, variables
and process parameters of the method is selected such that there is no loss of
silver metal from the contaminated thin layer of silver in the electrode.

A further object of this invention is to propose a wet chemical method for rapidly
removing both organic and inorganic impurities from silver surfaces of silver-
electroplated electrodes used in busbars which is applicable to similar articles of
silver or products and sub-products thereof, containing thin or thick silver layer
in the object.
SUMMARY OF THE INVENTION
Accordingly, there is provided a wet chemical method for rapidly removing both
organic and inorganic impurities from silver surfaces of silver-electroplated
electrodes used in busbars comprising the steps of immersing the electrodes into
an organic solvent and treating the immersed electrodes ultra-sonically for a
period of 5 - 15 minutes; wiping out the excess solvent from the silver surface of
the electrodes by cloth and thereby removing the organic contaminations or
matter/s or compounds, producing thereby organic-contaminations free
electrodes; forming first a solution of either sodium carbonate or sodium bi-
carbonate in water with predetermined concentration (Solution A); forming a
second solution of sodium chloride in water with predetermined concentration
(Solution B); forming a third solution of sodium sulphite in water with
predetermined concentration (Solution C); mixing all the solutions i.e.
(Solution A + Solution B + Solution C) in pre-determined proportions in a
container made out of glass, stainless steel or aluminium metal and thereby
preparing a mixed solution; wrapping/covering the organic-contamination free
electrodes in perforated aluminium foil of about 1 mm diameter with regular'
pattern of holes to ensure that the electrodes are in contact with the foil; dipping
the aluminium-wrapped silver electrodes or articles into the mixed solution;

heating the mixed solution at a specified temperature for a period of 10 - 30
minutes; and taking out the electrode from the aluminium foil and washing the
electrode with tap water and soaking the surface water by a cloth or tissue
wrapper followed by drying at room temperature resulting a silver surface free
from all inorganic contaminants of the electrode.
DETAIL DESCRIPTION OF THE INVENTION
Therefore, the present invention provides an improved wet chemical method for
regenerating silver surface of silver-electroplated electrodes thereby removing all
contaminants both organic and inorganic origin and strictly without loosing any
silver from the silver layer in the electrode used in busbars. The invention is also
applicable to similar articles of silver or products and sub-products thereof,
containing thin or thick silver layer in the object.
The present invention further provides the process parameters and other
experimental variables of the said wet chemical method for regenerating
contaminated silver surfaces using defined chemicals and its solutions in definite
proportions and also by altering the conditions and process parameters, as
defined therein.
Other objects, novel features, advantages and applications of the present
invention is set forth in the description that follows further.

As per the invention, there are two steps for regeneration of damaged silver
layer. The first step comprises removal of contaminants of organic origin and the
second step is to remove the contaminants of inorganic origin. Organic
contaminants could be greasy, oily or substances having organic dirt that might
have been accumulate during handling, packing or storing and also might be,
certain atmospheric conditions etc. And inorganic contaminants primarily consists
silver sulphide that is normally accumulated during aerial or atmospheric
exposure of the electrodes by a well known chemical reaction with silver and
atmospheric hydrogen sulphide.
In order to remove the organic contaminants, the contaminated electrodes first
are to be immersed in an organic solvent and to be treated ultrasonically for a
period of 5-15 minutes at ambient temperature. After this solvent treatment,
the electrodes are to be wiped out using a cloth and would be free from organic
contaminants. However, these electrodes would contain, particularly, layers of
silver sulphide on silver metal surface in the electrodes, which are to be removed
from the surface by the next level of treatment. This step of removal is very
important, since the thickness of the silver layer is merely in the range of 3 - 5
micron and any aggressive chemical or mechanical process would destroy the
silver layer and damage the entire electrode. Hence the task of the next level of
removal is also to ensure no silver loss from the electroplated layer has been
taken place.

In order to remove the inorganic contaminants, a mixed solution is to be
prepared by mixing another three solutions using different chemicals with
variable levels of concentration in each solution. These three solutions, as
termed in this description are 'Solution A', 'Solution B' and 'Solution C
respectively. Solution A refers to an aqueous solution of 'sodium carbonate' or
'sodium bi-carbonate' with the concentration range of 25 - 100 g/litre, which is
to be prepared by dissolving the chemical/s, i.e. sodium carbonate or sodium bi-
carbonate in water (tap water or deionised water) in appropriate quantity for
maintaining the desired concentration level. Similarly, 'Solution B' refers to an
aqueous solution of 'sodium chloride' with the concentration range of 15 - 75
g/litre, whereas, 'Solution C refers to an aqueous solution of 'sodium sulphite'
with the concentration range of 10 - 50 g/litre respectively. And both of the
solutions are to be prepared similarly to that of the 'Solution A'. These three
solutions are then to be mixed by maintaining a volume ratio in the range of
60:20:20 - 70:30:30. In order to get the aforesaid mixed solution.
Organically removed electrodes are now to be wrapped in a perforated
aluminium foil and then to be immersed in the mixed solution in a container
(either glass, stainless steel or aluminium) and to be heated in the temperature
range of 60° - 100°C for a period 10 - 30 minutes. After this heating process is
completed, the electrodes are to be removed from the aluminium foil and to be
washed with tap water and then excess water from the surface of the electrodes
are to be wiped out using a cloth or a tissue paper,. Now, the electrodes are free
from the inorganic contaminants are the damaged surface of the silver metal in
the electrode is regenerated. The process step 1 represents the regeneration
process:

The following Table 1 exhibits the possible chemicals those are to be used for
said regeneration process:

The invention could be better understood through perusals of the following
examples:
EXAMPLE 1:
This example illustrates regeneration of contaminated silver surface of a silver
electroplated electrode having thickness about 5 micron that is used in busbars.

The electrode was immersed in a ultrasound bath using commercial grade of
acetone and treated ultrasonically for a period of 10 minutes. The electrode was
then taken out from the bath and wiped out with a cloth and thus organic
contaminants from the electrode were removed.
A 'Mixed Solution' in this example was prepared by mixing 'Solution A' (50 g/litre
of sodium bi-carbonate in water). 'Solution B' (20 g/litre of sodium chloride in
water) and 'Solution C' (20 g/litre of sodium sulphite in water) in the volume
ratio of 60:20:20 respectively and the solution had a pH of 8.5.
The electrode after removal of organic contaminations was wrapped in ah
aluminium foil (foils with a regular pattern of holes with a diameter of about 1
mm) and immersed in the above mixed solution. The mixed solution was then
heated at a temperature to boiling (about 100°C) and continued heating for a
period of 10 minutes at this boiling temperature.
After the heating process was completed, the electrode was removed from the
aluminium foil and washed thoroughly with tap water and excess water is wiped
out from the surface of the electrode.
The silver surface of the electrode is shiny again and now regenerated and hence
all the contaminants both of organic and inorganic origin are removed by the
aforesaid procedure.

EXAMPLE 2:
The procedure in this Example was
followed substantially as per Example 1, except that the sodium bi-carbonate
was replaced by sodium carbonate.
A 'Mixed Solution' was prepared by mixing 'Solution A' (50 g/litre of sodium
carbonate in water) 'Solution B' (20 g/litre of sodium chloride in water) and
'Solution C' (20 g/litre of sodium sulphite in water) in the volume ratio of
60-20:20 respectively and the solution had a pH 8.4.
The electrode after removal organic contaminations following the procedure in
Example 1 was wrapped in an aluminium foil and immersed in the above mixed
solution. The mixed solution was heated at a temperature to boiling (about
100°C) and heating continued for a period of about 10 minutes at this boiling
temperature.
The electrode was removed from the aluminium foil and washed thoroughly with
tap water and excess water was wiped out from the surface of the electrode.
The silver surface of the electrode was now regenerated and hence all the
contaminants both organic and inorganic origin were removed by the aforesaid
procedure.

EXAMPLE 3:
The procedure in this Example was followed substantially as per Example 1,
except that the organic solvent for cleaning the organic contaminants was
replaced by alcohol i.e. isopropyl alcohol.
The electrode was immersed in a bath using a known commercial grade of
isopropyl alcohol and treated ultrasonically for a period of about 10 minutes. The
electrode was taken out from the solvent bath and wiped out with a cloth and
thus organic contaminants were removed.
A 'Mixed Solution' was prepared by mixing 'Solution A' (50 g/litre of sodium bi-
carbonate in water), 'Solution B' (20 g/litre of sodium chloride in water) and
'Solution C (20 g/litre of sodium sulphite in water ) in the volume ratio of
60:20:20 respectively and the solution had a pH of 8.5.
The electrode after removal organic contaminants was wrapped in an aluminium
foil and immersed in the above mixed solution. The mixed solution was heated at
a temperature to boiling (about 100°C) with heating continued for a period of
about 10 minutes at this boiling temperature.
The electrode was removed from the aluminium foil and washed thoroughly with
tap water and excess water was wiped out from the surface of the electrode.
The silver surface of the electrode was now regenerated and hence all the
contaminants both of organic and inorganic origin were removed by the
aforesaid procedure

EXAMPLE 4
In this Example, the organic solvent for cleaning the organic contaminants was
replaced by a mixture of alcohol (ethyl alcohol) and acetone in volume ratio of
50:50.
The electrode was immersed in a bath using known commercial grades of
acetone and ethyl alcohol and treated ultrasonically for a period of about 15
minutes. The electrode was taken out from the solvent bath and wiped out with
a cloth and thus organic contaminants were removed.
A 'Mixed Solution' was prepared by mixing 'Solution A' (80 g/litre of sodium bi-
carbonate in water), 'Solution B' (50 g/litre of sodium chloride in water) and
'Solution C (30 g/litre of sodium sulphite in water) in the volume ratio of
60:20:20 respectively and the solution had a pH of 8.8.
The electrode after removal organic contamination was wrapped in an aluminium
foil and immersed in the above mixed solution. The mixed solution was heated at
a temperature of about 80°C and heating was continued for a period of 15
minutes at this temperature.

The electrode was removed from the aluminium foil and washed thoroughly with
tap water and excess water was wiped out from the surface of the electrode.
The silver surface of the electrode was now regenerated and hence all the
contaminants both of organic and inorganic origin are removed by the aforesaid
procedure.
EXAMPLE 5:
In this Example, the article was changed from electrode to a silver plate.
Organic solvent for cleaning the organic contaminants was replaced by a mixture
of alcohol (methyl alcohol) and acetone in volume ratio of 30:70.
The electrode was immersed in a bath using known commercial grades of
acetone and methyl alcohol and treated ultrasonically for a period of about 15
minutes. The electrode was taken out from the solvent bath and wiped out with
a cloth and thus organic contaminants were removed.

'Mixed Solution' was prepared by mixing 'Solution A' (80 g/litre of sodium bi-
carbonate in water), 'Solution B' (50 g/litre of sodium chloride in water) and
'Solution C' (30 g/litre of sodium sulphide in water) in the volume ratio of
60:20:20 respectively and the solution had a pH of 8.8.
The electrode after removal organic contamination was wrapped in an aluminium
foil and immersed in the above mixed solution. / The mixed solution was heated
at a temperature about 70°C and continued heating for a period of 15 minutes at
this temperature.
The electrode was removed from the aluminium foil and washed thoroughly with
tap water and excess water is wiped out from the surface of the electrode.
The silver surface of the electrode is now regenerated and hence all the
contaminants both of organic and inorganic origin are removed by the aforesaid
procedure.

WE CLAIM:
1. A method for rapid regeneration of silver surface from a contaminated silver
surface (all forms of contaminants both organic and inorganic origin) of silver
electroplated copper electrodes used in busbars and also for all similar silver
containing articles and products or sub-products thereof, comprising the
following steps:
i) immersing the electrodes into an organic solvent and treating the immersed
electrodes ultra-sonically for a period of 5 - 15 minutes;
ii) wiping out the excess solvent from the silver surface of the electrodes by
cloth and thereby removing the organic contaminations or matter/s or
compounds, producing thereby organic-contamination free electrodes;
iii) forming a first a solution of either sodium carbonate or sodium bi-carbonate
in water with predetermined concentration (Solution A);
iv) forming a second solution of sodium chloride in water with predetermined
concentration (Solution B);
v) forming a third solution of sodium sulphite in water with predetermined
concentration (Solution C);

vi) mixing all the solutions i.e. (Solution A + Solution B + Solution C) in
pre-determined proportions in a container made out of glass, stainless steel or
aluminium metal and thereby preparing a mixed solution;
vii) wrapping/covering the organic-contamination free electrodes in perforated
aluminium foil of about 1 mm diameter with regular pattern of holes to ensure
that the electrodes are in contact with the foil;
viii) dipping the aluminium-wrapped silver electrodes or articles into the mixed
solution;
ix) heating the mixed solution at a specified temperature for a period of 10 - 30
minutes; and
x) taking out the electrode from the aluminium foil and washing the electrode
with tap water and soaking the surface water by a cloth or tissue wrapper
followed by drying at room temperature resulting a silver surface free from all
inorganic contaminants of the electrode.
2. The method as claimed in claim 1, wherein the solvents is selected from
several groups of organic solvents for example, groups of ketones, alcohols
representing acetone, iso-propyl alcohol, ethyl alcohol, methyl alcohol, or
other alcohols or their mixture/s in any volume proportion.

3. The method as claimed in claim 1, wherein the aqueous solution of
sodium carbonate or sodium bi-carbonate varies in a range of 2.5 to
10.0% by weight sodium carbonate or sodium bi-carbonate in a solution
having a pH in the range of 8 - 9.
4. The method as claimed in claim 1, wherein the aqueous solution of
sodium chloride varies in the range of 1.5 to 7.5% by weight 'sodium
chloride' in the solution.
5. The method as claimed in any of claims 3 and 4, wherein the aqueous
solution of sodium sulphite varies in the range of 1.0 to 5.0% by weight
'sodium sulphite' in the solution.
6. The method as claimed in claim 1 wherein i) the aqueous solution of
sodium carbonate or sodium bi-carbonate (Solution A), ii) aqueous
solution of sodium chloride (Solution B) and iii) aqueous solution of
sodium sulphite (Solution C) are to be mixed in a volume ratio of 60:20:20
to 40:30:30 for producing a Mixed Solution and the resultant mixed
solution has a pH in the range of 8-9.
7. The method as claimed in claim 1, wherein the contaminated silver
electroplated electrodes for busbars are covered with the aluminium foil
and dipped into the resultant mixed solution, and wherein the solution is
heated in the temperature range of 60-100°C for a period of 10 - 30
minutes.

8. The method as claimed in claim 1, wherein the electrodes are taken out
from the mixed solution after the heating process is completed and
removed from the foil and cleaned with tap water and excess water from
surface wiped out using cloth.
9. The method as claimed in any of claims 1 to 8 wherein the silver surfaces
in the contaminated electrodes are regenerated which is free from both
organic and inorganic contaminants.
10. The method as claimed in claim 1 wherein removing of both organic and
inorganic contaminants from silver articles or products or sub-products
without loosing any silver from the surface in the article/s or products can
be achieved.