Improvements in the Electro-deposition of Metals.
Year: 1896

page_text: Date of Application, 14th Jan., 1896
Complete Specification Left, 14th Oct., 1896-Accepted, 21st Nov., 1895
Improvements in the Electro-deposition of Metals.
I, JOHN CAMERON GRAHAM, of 2 Garden Court, Temple, in the City of
London, Barrister-at-Law, do hereby declare the nature of this invention to be as
follows:-
In depositing metals from their solutions by electricity it is found that when the
density of the current much exceeds a limit which is that in ordinary use the metal
is not properly deposited but is thrown down with a rough surface, and if the
current density be further increased the cathode becomes discoloured and the deposit
is more or less noncoherent.
Various attempts have been made to get over these drawbacks to the use of
higher current densities but they have practically failed. My invention consists
in a method of enabling such current densities to be used and by it I have
obtained good copper deposits with a current of 300 amperes to the square foot.
In carrying out my invention I cause a jet of the electrolyte to be projected on
the face of the cathode. This jet may best be obtained by allowing the electrolyte
to flow from a tank placed above the plating bath so as to give a fall of a foot or
two the electrolyte being returned from the bath by means of a pump. The jet
acts most advantageously when directed perpendicularly to the face of the cathode.
The portion of the surface of the cathode directly controlled by this jet is found to
be covered by an even and regular film of the deposited metal almost in a polished
state. The size of the portion so controlled depends upon a variety of conditions,
such, for example, as the size of the jet, the amount of fall, the electromotive force,
the conductivity of the electrolyte, and the flatness or otherwise of the cathode
surface.
In order to illustrate approximately the effect of the jet when depositing copper
I have ascertained that if the fall be from 12 to 18 inches and if the jet issue from
a pipe about of an inch in diameter and the mouth of the jet be placed about
1 inches from the cathode and the number of cells in series be 6 and the electro-
lyte be nearly saturated sulphate of copper containing five ounces of commercial
sulphuric acid to one cubic feet of water the copper will be deposited in an almost
polished state over a circle of about 5 inches diameter on the cathode which
surface is that which I have above termed the surface "controlled" by the jet.
Immediately outside the controlled area the deposit is noncoherent and the cathode
discoloured.
If it is proposed to deposit on a cathode surface larger than one jet can control,
two or more jets must be employed. In every case it is essential that every part
of the cathode on which it is desired to deposit metal must come within the area of
control during the whole time that the deposition continues. The free circulation
of the electrolyte over the face of the cathode must not be interfered with in any.
way as anything which impedes the circulation or even produces an eddy or swirl
will tend to spoil the deposit at that point.
In order economically to obtain such deposits I use an anode much larger than
the cathode. If they are of the same size or approximately so, and the electro-
motive force remains constant, the current falls in an exceedingly short space of
time to a comparatively very small density. If the anode however be made 8 or
10 times as large as the cathode the initial density of the current will be twice as

page_text: large and will fall very slightly, other circumstances remaining the same. The
most convenient way to obtain this large anode area is to cast the anodes in the
form of grids preferably somewhat deep, something like the leaves of a Venetian
blind when opened so as to admit the light, the bars of which may be brought
within a short distance from one another; some of the spaces between the grids
may be utilized to make room for the jets and also to enable the jets to produce
induced currents of the electrolyte which flow between and wash the grids of the
anode thereby increasing the current density produced by given electromotive
force. These spaces are also useful for enabling the electrolyte after passing over
the cathode to escape. Corrugated anodes may also be used. The relative sizes
of the anode and cathode which will give the greatest current density will depend
on the electromotive force, the conductivity of the electrolyte etc., and can readily
be ascertained by trial.
Another difficulty met with in depositing metals is that tree-like non-coherent
growths of the metal which is being deposited, have a tendency to form on or about
the edges of the cathode.. This is particularly noticeable when working with dense
currents. It may be almost entirely overcome by placing a shield consisting of a
strip about 1 inches wide of some insulator along of the edges of the cathode at a
small distance from the face of the cathode so as to allow the flow produced by the
jet to pass between the shield and the cathode. The shield should overlap the
cathode about half an inch. The edges of the cathode may also in some cases be
coated with some insulating substances such as paraffin or varnish.
In the case of depositing copper from sulphate of copper if the solution be some-
what acidified as in the example above given the character of the deposit is very
much improved.
Although I have hitherto spoken of jets issuing from circular orifices, slit. shaped
orifices can be used if desired, provided that care be taken that the free flow of the
electrolyte be not interfered with but they are much more likely to become choke
with particles of solid matter than circular ones. In coating cylinders however slit
shaped orifices should be used the slits being in planes at right angles to the axis of
the cylinder because owing to the curvature of the cylinders a jet will control only
a very small surface as compared with the surface controlled by a jet playing on a
flat cathode.
It is necessary that the jet should play substantially continuously over the surface
while the current is passing, as an intermittence of even a few seconds will injure
the character of the deposit.
Dated this 14th day of January 1906
MARKS & CLERK,
18, Southampton Buildings, London, W.C., and
13, Temple Street, Birmingham, Agents.
I, JOHN CAMERON GRAHAM, of 2 Garden Court, Temple, London, E.C.
Barrister-at-Law, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
In depositing metals from their solutions by electricity it is found that when the
density of the current much exceeds a limit which is that in ordinary use the metal
is not properly deposited but is thrown down with a rough surface and that if the
current density be further increased the cathode will become discoloured and the
deposit more or less non-coherent.
Various attempts have been made to get over these drawbacks to the use of

page_text: higher current densities but they have practically failed. My invention consists in
a method of enabling such current densities to be used and by it I have obtained.
good copper deposits with a current of 300 amperes to the square foot.
In carrying out my invention I cause a jet of the electrolyte to be projected on,
the face of the cathode. This jet may best be obtained by allowing the electrolyte.
to flow from a tank placed above the depositing bath so as to give a fall of a foot or
two, the electrolyte being returned from the bath by means of a pump. The jet
acts most advantageously when directed perpendicularly to the face of the cathode.
The portion of the surface of the cathode directly controlled by this jet is found to
be covered by an even and regular film of the deposited metal almost in a polished.
state. The size of the portion of the cathode surface so controlled depends upon a
variety of conditions such for example as the size of the jet, the amount of fall, the
electromotive force and the density and conductivity of the electrolyte, and the
flatness or otherwise of the cathode surface.
In order to illustrate approximately the effect of the jet when depositing copper:
I have ascertained that if the fall be from 12 to 18 inches and if the jet issue from
a pipe about of an inch in diameter and the month of the jet be placed about
1 inches from the cathode and the number of cells in series be 6 and the electro-
lyte be nearly saturated, sulphate of copper containing five ounces of commercial
sulphuric acid to one cubic foot of water the copper will be deposited in an almost
polished state over a circle of about 5 inches in diameter on the cathode which
surface is that which I have above termed the surface "controlled" by the jet.
Immediately outside the controlled area the deposit is non-coherent and the cathode
discoloured.
If it is proposed to deposit on a cathode surface larger than one jet can control,
two or more jets must be employed; for example a good result can be obtained by
using a number of jets distributed uniformly over the surface at a distance from each
other depending upon the above named conditions viz.; the size of the jets, the
current density etc.
In every case it is necessary that every part of the cathode on which it is desired;
to deposit metal should come within the area of control during the whole time that.
the deposition continues. The free circulation of the electrolyte over the face of"
the cathode must not be interfered with in any way as anything which impedes the
circulation or even produces any eddy or swirl will tend to spoil the deposit at
that point.
Jets so disposed will make it possible to use a very high current density. It
will be found however, that wherever the currents from two adjacent jets meet
a peculiar mark is formed on the cathode. If this is of importance the defect can
be cured by giving a slow reciprocating movement to the cathode.
In order to obtain such deposits economically when using copper as the anode I
use an anode much larger than the cathode. If they are of the same size or
approximately so, and the electromotive force remains constant with voltages
considerably higher than those now used the current density falls in an exceedingly
short space of time to a comparatively small density and cannot be kept at the
initial density by raising the electromotive force without a great waste of energy.
The most convenient way to obtain this large area with a copper anode is to cast
the anodes in the form of grids preferably somewhat deep something like the leaves
of a Venetian blind when opened so as to admit the light, the bars of which
may be brought within a short distance from one another, some of the spaces
between the grids may be utilized to make room for the jets and also to enable the
jets to produce induced currents of the electrolyte which flow between and wash
the grids of the anode thereby increasing the current density produced by given
electromotive force. These spaces are also useful for enabling the electrolyte
after passing over the cathode to escape. Corrugated anodes may also be used.
The relative sizes of the anode and cathode which will give the greatest current
density will depend on the electromotive force the conductivity of the electrolyte
etc. and can readily be ascertained by trial.

page_text: Another difficulty met with in depositing metals is that tree-like non-coherent.
growths of the metal which is being deposited have a tendency to form on or about
the edges of the cathode. This is particularly noticeable when working with dense
currents. It may be almost entirely overcome by placing a shield consisting of a
thin strip about 1 inches wide of some substance like vulcanite along the edges of
the cathode at a small distance from the face of the cathode so as to allow the flow
produced by the jets to pass between the shield and the cathode. The shield should
overlap the edges of the cathode about three quarters of an inch. The extreme
edges of the cathode may also in some cases be coated with some insulating
substance such as paraffin or varnish. The shield cuts off most of the lines of
force extending from the anode to the cathode at the place where it overlaps
the cathode.
In the case of depositing copper from sulphate of copper if the solution be
acidified as in the example above given the character of the deposit is very much
improved.
Although I have hitherto spoken of jets issuing from circular orifices, slit shaped
orifices can be used if desired, provided that care be taken that the free flow of the
electrolyte be not interfered with, but they are much more liable to become choked
with particles of solid matter than circular ones, and require a larger quantity of
electrolyte.
It is necessary that the jets should play substantially continuously over the surface
while the current is passing and over the whole of the surface over which the
deposition is taking place so as to bring it under control, otherwise the deposit will
be spoiled if the current is dense.
Referring to the accompanying sheet of drawings-
Figure 1 shows diagrammatically in cross section an apparatus for carrying my
invention into effect and
Figure 2 is an elevation showing the cathode in dotted lines behind the shield.
A is the cathode, B the anode, C is a powerful jet, D is the shield, E is the pipe
connected to a tank, down which the electrolyte flows, and F is the return pipe to
the tank; G is the pump and H the tank.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is-
(1.) The method of depositing metals upon flat surfaces by means of jets of the
electrolyte so arranged as to control the whole of the flat cathode surface upon
which such deposit is desired, substantially as herein before described.
(2.) In combination with the method claimed in the first claim the use of copper
anodes with surfaces much greater than the surface upon which the deposit is to
take place such surfaces being by preference of a spiral corrugated or grid-like
form.
(3.) In the deposition of metals as claimed in the first claim the use of shields
for the purpose of preventing the irregular deposits on the edges of the cathode
substantially as herein above described.
Dated this 14th day of October 1896.
MARKS & CLERK,
18, Southampton Buildings, London, W.C., and
13, Temple Street, Birmingham, Agents.