Note: Descriptions are shown in the official language in which they were submitted.
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ELECTkODE AND METHOD FOR MF~SURING LEVELLING POWER
FIELD OF INVENI`ION
This invention is related to the field of measuring the ability of addition
agents to prevent formation of rough and poraus surfaces and nodules during
S electrodeposition.
BACKGROUND OF THE ART AND PRO~3LEM
,
The process of electrodeposition is widely used commercially in
processes such as electrorefining, electrowinning and electroplating. In commercia}
electrodeposition operations organic and/or inorganic addition agents are addcd
10 directly to electrolytic solutions. The addition agents control uniformity of metal
deposition on a cathode. When the addition agents are out of balance for proper
electrodeposition, the metal deposit forms rough porous surfaces and nodules which
encapsulate impurities contained in the electrolyte. Improper deposition typically
greatly reduces the value of the product due to isnpurities mechanically imbedcle(i in
15 the rough cathode surface.
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Copper electrorefineries around the world typically use a combination oE
several addition agents to control electrorefining. Addition agents used Çor
electroreEining include animal glue, thiourea, lignin sulfonate, alkyl sulEonate and
chloride ion. Positively charged addition agents such as animal glue are drawn by
5 electrochernical Eorces to the negatively charged cathode. Positively charged addition
agents are more strongly attracted to increased current density regions of peaks or
nodules forrned on a cathode. The increased concentration of addition agents on
peaks or nodules slows down the metal electrodeposition and levelling takes place.
Advantageously, an addition agent such as glue is preferentially a(lsorbed
10 on the peak or nodule to form a resistance layer which locally increases over-potential
and levelling on the cathode surface takes place. IE excess addition agent is present,
the addition agent adsorbs over an entire cathode surface which causes a loss oflevelling eEfect. If insufEicient addition agent is present, growth on peaks and nodules
is not prevented and the peaks and nodules grow in an uncontrolled accelerated
15 manner. Typical optimum concentration of addition agents is in the parts per million
range. Unfortunately, concentrations of addition agents are very difficult to measure
in a simple and accurate manner. ~urthermore, several addition agents break downinto multiple components and eventually lose levelling effect.
Typical copper electrorefinery addition agent systerns are complicated
20 and include a combination of three or more addition agents. As a result oE high
interactions between addition agents, levelling effects of new combinations of levelling
agents are unpredictable. To evaluate an addition agent system time consuming
laboratory or pilot plating experiments have been required. A typical experimentrequires 7 to 14 days to complete. It would require about 5 to 10 years (without25 simultaneous experiments) to investigate every combination of a system of four
addition agents each at Eour different concentrations.
Several techniques have been developed to monitor addition agent
concentrations in electrolyte. Langner et al, in U.S. Patent No. 4,834,842 describe a
techniquc oE measuring efEectiveness of addition agents by measuring kinetics oE30 cathode polarization under predetermined conditions. Other techniques described in
the literature have measured cathode polarization in an attempt to optimize platin~
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conditions. These cathode polarization techniques are not capable of measuring the
ability of an addition agent or a combination of addition agents to alter cathode
levelling.
It is an object of this invention to provide an apparatus ancl method Eor
5 evaluating the ability oE an addition agent to improve cathode sur~ace during
electrodeposition.
It is a further object of this invention to provide a quick and ef~ctive
method for evaluating addition agents and their combination for cathode levelling.
It is a further object of this invention to provide a method for
10 controlling levelling power of electrolytes to prevent the formation of a rough
nodulated and contaminated surface by adjusting the addition agents concentration.
SUMMARY OF T~E INVENTIO~
The invention provides an apparatus and method for determining
Ievelling power of an electrolyte. An anode and cathode are immersed in the
15 electrolyte. The cathode has a plating surface for electrodeposition oE a metal Erom
the electrolyte. The plating surface has a peak region and a base region separated and
electrically isolated by an insulator. I~le peak region has 2 greater tendency to
electrodeposit the metal per unit surface area than the base region. The anode and
cathode are placed in a test cell or suspended in a commercial electrodeposition cell.
20 A means for applying current between said anode and said cathode is used Eor causing
the metal from the electrolyte to electrodeposit on the plating surface oE the cathocle.
~lle current used in plating metal on the peak region and the base region are
measured separately to determine levelling power of the electrolyte.
DESCRIPTION OF THE D~AWING
Figure I is a schematic diagram of an apparatus Eor measuring levelling
power.
Figure 2 is a schematic side view of an optional peak electroclc having a
projecting pealc rc gion.
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Figure 3 is a graph of cathode peak current versus time with various
concentrations of lignosulfonate in a copper electrorefining solution.
Figure 4 is a graph of levelling power versus concentration for
lignosulfonate in a copper electrorefining solution.
Figure 5 is a graph of cathode peak current versus time with various
concentrations of thlourea in a copper electrore~ming solution.
Figure 6 is a graph of levelling power versus concentration of thiourea in
a copper electrorefining solution.
~igure 7 is a graph of peak current versus time for two electrolytes
having similar ingredients.
DESCRIPTION OF PREFE~RED ~:MBODIMENT
It has been discovered that a newly developed electrode system has the
ability to measure the levelling effect o~ addition agents in electrolyte. The electrode
system includes a cathode which contains a peak region (or several peak regions) and a
i lat base or valley region. Current flow is measured separately for peak and base
regions to quickly determine the levelling effect of various combinations of addition
agents.
Referring to Figure 1, the apparatus includes galvanostat lU which
generates a constant current through electrolyte 12 between anode 14 and cathode 16.
Electrolyte 12, anode 14 and cathode 16 are all contained in test cell 18. As analternative to test cell 18, any means to hold anode 14 and cathode 16 in electrolyte 12
may be used. For example, anode 14 and cathode 16 may be simply suspended by
clamps, bolts or wires in a commercial electrolytic solution. Cathode 16 is of a"sandwich" structure having three peak regions 20 and three base regions 22 placed
upon an insulating structure. The peak regions are placed closer to anode 14 to create
a current densit~ adjacent the peak regions 20 that is stronger than the current density
adjacent the base regions 22. ~Iternatively, geometry such as a projecting cathode may
be used to create a greater tendency for metal to electrodeposit per unit surEace area
on peak regions 20 than base regions 22. For purposes of the invention, unit surface
area is defined as total plating surface. Galvanostat 10 provides sufficient current to
electrodeposit metal on the peak regions 20 and base regions 22. Alternatively, other
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means for electrodepositing metal on cathode base region 22 and peak region 20 may
be studied. For example, systems that periodical}y reverse current to stir electrolyte
may be studied. When using tçst cell 18, electrolyte 12 is most preferably heated to
within about 5C of the electrolyte to be tested. Test cel} 18 may be heated by any
S means for heating a tesl cell such as a hot plate.
During electrodeposition, current flowing to the peak regions 20 and
base region 22 is determined separately with voltmeters 26 and 2~ and resistors 30 and
32. Advantageously, resistors 30 and 32 have a similar resistance of about 1-5 ohms.
Wiring is used to connect the base and peak regions to current measuring devices.
10 From the rneasured voltage and resistance, current may be calculated. Alternatively,
current may be directly measured with ammeters. Most advantageously, current
flowing to the peak regions and total current flowing to the base and peak regions is
measured. It is recognized that material electrodeposited on the peak regions and
material el~ctrodeposited on the base regions may be weighed separately and
15 compared or simply visually compared to determine levelling effect. However, it is
highly advantageous to simply electrically measure current flows to determine levelling
effect.
The beneficial levelling effect with and without addition agents in an
electrolyte is advantageously determined with the following formula:
LP = l~ - lp x 100
lP
where:
LP = Levelling Power
Ip = Current flowing to the peak electrode(s)
It = Total current flowing to the cathode
The above described system models the rough surface of a cathode and
provides for direct measurement of the blocking effect of addition agents on the peaks
of a rough cathocle. The blocking effect is expressed as a levelling power. Levelling
power is measured by determining ratio of current flowing to base regions and peak
regions. Levelling power may be measured in 15 to 30 minutes. After lS to 30
minutes o~ plating, the electrolyte begins to change anA peak current begins to
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stabilize. Most advantageously, total current over a time range is used to obtain more
accurate results. For éxample, to study levelling power during nucleation, peak current
and total current may be measured for the initial 5 minutes. A measurement of 5
minutes until stabilization of peak current may be used to study electrodeposition
S following nucleation. Wllen peak current stabilizes, the test is completed. Aftcr
measuring levelling power of a commercial electrolyte, addition agents may be
manually adjusted or automatically adjusted to optimize levelling power.
The sandwich electrode of Figure 1 was constructed out of copper and
chlorinated polyvinyl chloride (CPVC3 material using an adhesive. For long term use
an adhesive that can withstand harsh environments at increased tempera~ures or adesign that does not utilize adhesive is preferred. Cathodes 16 are preferably
constructed with base regions and peak regions constructed of a stable metal such as
platinum. Using a platinum cathode allows for cleaning oE the anode by simply
reversing polarity of galvanostat 10 to redissolve plated material into the electrolyte.
Similarly, anode 14 is preferably constructed of metal deposited on the cathode or a
stable metal such as platinum or lead-antimony ailoy to prevent dissolution of the
anode into electrolyte 12, depending upon the process studied. For example, a lead-
antimony alloy is preferred for electrowinning of copper studies. Anode 14 preferably
has a surface area of at least 10 times the surface area of the conductive surface area
of the cathode to provide uniform current flow to the cathode.
Although cathodes preferably have flat base and peak regions, peak
regions may have a projecting con~lguration. Referring to Figure 2~ peak region 34 oli
cathode 36 has a solid conical shape. Peak tegion 34 preferably projects toward an
anode to create a greater tendency to electrodeposit metal per unit surface area. Base
regions 38 are isolated from peak region 34 with insulator 40. Preferably, surface area
of peak region 34 is equal to surface area of base regions 38. The advantage of the
structure of Figure 2 is that CPVC adhesive may be used to hold the entire cathode
structure together.
An experimental set-lp was produced having a copper anode. The
3~) copper anode had a surface area of 4 cm2. The cathode used had a structure similar
to the cathode of Figure 2. The cathode had 3 flat platinum base regions ancl 1
conically shaped peak region. The surface area of the base region and peak region
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were each about 0.053 cm2. The base regions were spaced 3.5 rnm from the peak
region. The above experimental setup was used for the following Examples.
EXAMPLE I
A synthetic electrolyte of the following composition was used:
S Cu - 40 g/Q
Ni - 20 g/Q
H2SO4 - lS() g/Q
Cl- - 20 mg/Q
The electrolyte temperature during measuring was 65C and the average
cathode current density was 182 Alm~ which simulated a commercial copper
electrorefining operation. Measurements are preferably made at temperatures and
current densities that simulate commercial conditions. DiEferent amounts of TembindrM
(a lignosulonate produced by Temfibre Inc. of Temiscaming, Quebec) were added to
the electrolyte and the cathode peak current time profile was recorded. Cathode peak
current was calculated from the measured voltage and a predetermined constant
resistance. The recorded current time profile is shown in Figure 3. The results of the
experiment are summarized in Table 1 and the ef~ect of Tembind concentration on the
levelling power is shown in Figure 4. The lowest levelling power (LP) of the
electrolyte in the presence of 20 mg/Q Cl- is around 10 mg/Q Tembind. Above 10
mg/Q Tembind, the levelling power sharply rises with increased Tembind concentration
and reaches its maximum at concentrations over 100 mg/Q.
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TABLE1
Effect of Tembind Concentration on
Cathode Peak Cllrrent ~nd Levellin~ Power
Current DeDsity = 182A/m2;
Cathode Total CulTent = 1.93 mA;
Plating t;me = 15 min.
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Tembind ¦ Cathode Peak Current Levelling Power
(m~/Q) (mg/Q) _ .
O 1 043 ~5.0
~ _
j 10 , 1.196_ _6l.4
1 20 _61 81.9
i- 50 0g76 _ 97.9
100 0.~53 102.5
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EXAMPLE 2
A synthetic electrolyte oE the same composition and temperature as in
~xample 1 was used. Animal glue was added to the electrolyte in such a quantity that
the final concentration was 1 mg/Q. Animal glue is a protein derivative ~ormed
primarily from animal skins, hides, bones and tendons. DifEerent amounts of thiourea
were then added to the electrolyte and the cathode peak current time pro~lle was20 recorded. The results and parameters of the experiment are summarized in Table 2.
The recorded time profles are shown in Figure 5. The effect of thiourea on levelling
power is shown in Figure 6. As can be seen the levelling power in the electrolyte
increases with thiourea concentration.
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TABLE 2
E~ect of Thiourea CDncentratioll on
Cathode Penk CurTel~t ~nd Levelli~ Power
Current I)ensity--209 A/m~;
S ~thode Total Current a 2.22 mA;
Plating Time = 30 nnîn.;
Cl- - 20 mg/~,
Glu~ ~ 1 mg/l
, _ _ ~
Thiourea Cathode Peak Current Levelling Power
(mglQ) _(mA) t%)
0 1.223 81.5
_ _ _ 11
1 _ 1.187 __ 87.0
2_ 1.169 _ 89.9 _
S _ 1.133__ ~S.g
S0 1.062 109.0
__ _ . . .
EX~MPLE 3
In this example the levelling power of electrolytes from two independent
plant plating circuits for copper electrorefining were tested. The electrolytes contained
20 mg/Q Cl~, animal glue and Tembind. Figure 7 illustrates that the electrolytes20 produced two similar cathode peak current time profiles. ThereEore, since the two
profiles were similar, the levelling power o~ both plant electrolytes were experimentally
verified to be substantially identical.
In summary, the apparatus and method of the invention provide several
aclvantages. The method of the invention provides the ability to measure the levelling
25 power ot an electrolyte. The method Oe the invention also reduces the time oEevaluating an electrolyte system from 7 to 14 days to only IS to 30 minutes. Finally,
commercial electrolytcs may be evaluated Eor levelling power to provide a basis Eor
optimizing electrodeposition by adjusting electrolyte addition agents.
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While in accordance with the provisions of the statute, there is
illustrated and described herein specific embodiments of the invention, those skilled in
the art will understand that changes may be made in the form of the invention covered
by the claims and that certain features of the invention may sometimes be used to
S advantage without a corresponding use of the other features.
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