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March 20, 1956
2,739,276
W. IRBY
COPPER OXIDE RECTIFIER AND METHOD OF‘ MAKING THE SAME
Filed Feb. 23. 1951
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Inventor:
William Irby,
by
w X/M
I-Iis Attorney.
.
Unite States Patent 0
i
1
C6
2,739,276
Patented Mar. 20, 1956
2
It is evident of course that, in general, it is always desir
2,739,276
COPPER OXIDE RECTIFIER AND METHOD OF
MAKING THE SAME
William Irby, Saugus, Mass, assignor to General Electric
Company, a corporation of New York
Application February 23, 1951, Serial No. 212,385
9 Claims. (Cl. 317-238)
able to provide a cell whose reverse leakage current is
low (i. e. reverse resistance is high) and whose forward
resistance is relatively low. It is further desirable that
the normal rise in forward resistance and decrease in
reverse resistance which is experienced upon ?rst plac~
ing a new cell in service shall be relatively temporary and
shall not exceed predetermined limits, so that the cell
does not destroy itself by overheating. The normal volt
10 age rating of any cell, that is the maximum voltage which
may normally be applied to the cell in a reverse direction
in operation, is usually determined not by any initial
tendency of the cell to break down as a dielectric, but
by the fact that beyond a predetermined voltage any par
My invention relates to dry plate recti?ers, and more 15 ticular cell demonstrates such an unfavorable aging char
particularly to copper oxide recti?ers and to methods of
acteristic in the reverse direction that it will destroy it
making such recti?ers.
self as a recti?er or break down dielectrically due to over
heating.
A copper oxide recti?er cell, or element, consists es
sentially of a plate of copper coated on at least one side
It is supposed that current recti?cation in a copper oxide
with a layer of cuprous oxide and provided with a contact 20 cell results from a crystalline and chemical situation
layer, such as nickel plating or the like, over the cuprous
wherein the electron flow in one direction is limited
oxide. It is well known that such a cell possesses a barrier
‘by an energy barrier between the copper base and
plane or blocking layer at the junction between the copper
the cuprous oxide layer. The energy barrier results
base and the cuprous oxide layer, which barrier plane evi
from a di?erence in effectiveness of the materials on
dences itself in the characteristic whereby the cell conducts 25 opposite sides of the barrier in acting as electron
electric current much more readily across the plane in
donors and electron acceptors. The effectiveness of the
one direction than in the other direction. This means of
‘barrier depends upon the chemical constitution of the
course, that the electric resistance of the cell in one direc
cell as well as upon its physical treatment during the
tion, known as the forward direction, is very appreciably
process of manufacture.
less than its electric resistance in the other direction, 30
Accordingly, therefore, it is a general object of my in
known as the reverse direction. Because of this great
vention to increase the normal operating voltage of a cop
di?erence between forward and reverse resistance of the
‘per oxide recti?er cell appreciably beyond that which has
cell across the barrier plane, the cell exhibits a rectifying
heretofore been attainable, whereby for a given voltage
action when an alternating potential is applied across the
the number of recti?er cells, or elements in a recti?er
cell. In such a cell “forward” current is that passing into 35 stack, or assembly, may be signi?cantly reduced.
the copper base from the oxide.
It is another obiect of my invention to thus increase
In the manufacture of copper oxide recti?er cells by
the normal operating voltage of a recti?er cell, or ele
processes heretofore known, copper plates of commercial
ment, without adversely affecting the reverse or leakage
purity are ?rst thoroughly cleaned and preferably etched
current through the element.
by dipping in nitric acid. The plates are then “?red” by 40
It is a more particular object of my invention to provide
exposure to an oxidizing atmosphere in a furnace at about
1800“ F. to 1900° F. for a period of about 14 minutes.
a copper oxide element capable of withstanding a normal
operating voltage at least two to three times as high as that
Thereafter the plates are cooled for about 21/2 minutes
heretofore commonly used, without adversely affecting its
in a cooling zone of the furnace which is maintained at
reverse current or leakage aging characteristic, and with
about 870° to about 930° F. The plates are then an 45 out unduly affecting its forward voltage aging character
nealed for about 9 minutes at a temperature of about
istic at constant current.
-
900° to 1100" F. After annealing such plates have here
In carrying out my invention in one form I attain the ,
tofore been quenched immediately in cold water, and
foregoing and other objects by forming copper oxide recti
thereafter dried and prepared for the application of a
?er elements from copper base plates which have had
metal contact layer over the cuprous oxide layer formed 50 formed upon their surfaces prior to ?ring or oxidation an
upon the copper during the ?ring operation. In apply
alloy of copper and another metal, such as antimony.
ing such a contact layer the thin outer layer of cupric, or
Such an alloy may suitably be formed by coating the cop
black, oxide which appears upon the outer surface of
per surface with a thin ?lm of antimony, the antimony
the cuprous, or red, oxide is ?rst removed, preferably by _
alloying with the copper at the surface when the coated
electrolytic reduction. Thereafter, a layer of metal, 65 plate is exposed to an oxidizing atmosphere at elevated
such as nickel, is applied to the outer surface of the
temperature. Before ?ring, however, the antimony
cuprous oxide, as by electrolytic deposition.
coated plate is dipped in a dilute solution of certain
The electric characteristics of any particular copper
salts. Such a solution preferably includes a soluble salt of
oxide rectifying cell are not ?xed, but change gradually
antimony, a tetraborate, a nitrate of heavy metal, and an
over the useful life of the cell. This is particularly true 60 organic acid. After the plate is ?red, cooled and annealed
during the ?rst few days of the cell’s use. Thereafter
in the usual way the oxidized plate is exposed to cold air
the electrical characteristics of an acceptable cell tend to
for a predetermined delay interval and then quenched in
become relatively ?xed or stabilized. The graphical
cold water. The oxidized plate is then prepared for use
representations of such electrical characteristics over a
in the usual manner by nickel plating, or the like, over
period of time are known as the aging characteristics of 65 the oxide surface.
the cells. The aging characteristics which are commonly.
My invention itself will be more fully understood
utilized to determine the quality of the cell are its reverse
and its various objects and advantages further appreciated
leakage current characteristic at constant voltage, and
by referring now to the following detailed speci?cation
its forward voltage drop characteristic at constant cur
taken in conjunction with the accompanying drawing,
rent. These aging characteristics are representative, re 70 in which Fig. 1 is a schematic sequence diagram indicating
spectively, of the manner in which the reverse and for
the principal steps in a preferred process of forminga
ward electrical resistance of a cell vary with use.
_ recti?er element embodying my invention; Fig. 2 is a,
area-are.
4
3
graphical representation of the reverse current or leakage
aging characteristics of a recti?er element embodying
noted that a standard copper oxide cell of the type here
tofore commonly known and having a normal alternat
my invention, shown in comparison with similar char
ing current operating potential of about 6 volts,
acteristics of a. recti?er element of a type heretofore com
Referring now to the'drawing, a preferred process for‘
manufacturing copper oxide recti?er cells in accordance
with my invention is illustrated schematically in the‘
demonstrates the reverse aging characteristics illustrated
at curve A, Fig. 2, and the forward aging characteristic
of curve A1, Fig. 3. Fig. 2 shows at curve A the manner
in which reverse current, or leakage of such a recti?er,
becomes stabilized after a number of days of operation,
while Fig. 3 shows at curve A1 the manner in which
10 the forward voltage drop increases only slightly over a
sequential block diagram of Fig. 1. As there indicated,
number of‘ days of operation at constant current in the
monly- used; and Fig. 3‘ is a similar graphical represent‘a'a
tion of the forward voltage drop at constant current, or
forward aging, characteristics, of such recti?er cells.
copper base plates of. commercial purity are ?rst‘
forward direction. The effect of operating such a 6 volt
recti?er cell at approximately twice‘ its normal operating
thoroughly cleaned, and preferably etched by dipping
in nitric acid. The clean copper‘ plates are then coated
voltage, for example 12 volts, is illustrated at curve B at
with a very thin ?lm'of antimony having a thickness of 15 Fig. 2. Curve B shows that the leakage current of such a
cell, when operated at twice normal operating voltage,
the order. ofl.000003- to .000005 of an inch. Suclran
increases very rapidly, so that the element soon heats
antimony film is preferably formed by aflash electroe
up‘3 andb'e'comes-useless as a recti?er.
plating, such as for ltlisecon'dsiat 6 amperes, or the equiva-‘
lent. While I- prefer an antimony coating, I ?nd that
I have‘? discovered that av thin coating of certain metals}
other metals selected from'the group" consisting of anti-' 20 and particularly antimony, applied to the copper base
plate before ?ring has the eifect of signi?cantly increas
mony, bismuth, lead, cadmium, iron and maganese may
ing- both‘ forward‘ and reverse resistance of a cell. Curve"
be utilized to. coat the copper base.
After coating the copper plate‘ with antimony, the
E, Fig. 2, is the2 reverse aging characteristic at 12 volts“
antimony coated‘ copper‘ plate is‘ dipped-in a dilute solu‘
for a5v cell formed. in: the same manner as the cell of’
tion (for example less than. 1% concentration) of a 25 curves A, A1‘ and B‘with the single addition‘ of antimony’
plating? before ?ring. The‘ difference in curves’ B and’
soluble- salt of,v antimony. Preferably such a solution
includes also a small. amount of a tetrab'orate, a quantity‘
of a nitratetof. a heavy metal, and an. organic acid to
E‘ illustrates‘ the‘ increase‘ in‘ reverse resistance‘ due't'o'
antimonyv plating‘.
Similarly, the curve E1, Fig‘; Skis":
the forward aging'characteristics' of such any antimony;
particular‘ solution whichsl. have found to be‘ satisfactory 30 plated cell, and the difference between curves A1 and‘ Er;
stabilize the antimony salt andholdit insolution'. One?
consists of, by weight, 5%“ antimonychloride, 05%
taken atlthe same‘ constant forward current, illustrates‘?
sodium tetraborate, .l% ferric nitrate, ab'out43% tartaric
acid an'dithe- remainder water.v I ?nd‘ that certain other
the?‘ increase‘in" forward resistance due to antimony‘ plat?
mg.‘
This increasef'in' resistance in both directions maybe‘
the nitrates and perchloratesas‘well as‘theichlo‘rid'es" and 35 explained‘ by’ the? fact that antimony, being present in‘
both-‘thecopper'ahd'rthe cuprous oxide on- oppositei'sideis"
other halides (i. e.,_ ?uorides, bromides. or. iodides) of
of thei‘b‘arrier plane; produces an unfavorable‘ condition’
antimony, bismuth: or iron have signi?cantly'bene?cial
for: electron‘?ow’inleither direction. In the ?ring/process
results. l-prefer, however, to utilize the‘ foregoing solu
it is likely that the antimony coating ?rst alloys with"
tion of antimony‘ chlonide‘an'd» iron nitrate. The tartaric
acid in my preferred solution serves-principally to'increase' 40 tliefcopper-atithe' surface of the plate. After oxidation
the amount of antimony chloride held in solution. The‘
antirr'i'o yrs‘ present, on both sides of the barrier plane?
Antimony’ is a' good electron donor, but not an e?icier‘it“
sodium tetraborate serves principally‘ as a-cleaningl'?uxl
electron-acceptor} The same result in different degree"
After dipping the antimony coatedcop'per p'l'ate in'the
solution described above, the: plate‘ is v?red in the usual
arises? frorr'li- coating with bismuth, lead, cadmium} iron‘
manner by exposure to‘ an‘ oxidizing atmosphere at a 45 or-' manganese before ?ring;
there: also discovered if an antimony coated‘ copper
temperature of about l8(l0°' to‘ 1900’ F., preferably
plate-is'i?'r'ediin the usual manner and then’ delayed'laridi
1860°' F., for a period of? about 14 minutes, cooled'for»
air? cooled before quenching in cold water‘, both forward5
about 21/2 minutes‘in a cooling z'on'c maintained at about‘
870° to about 930° F., and then annealed for about-9
andlrevei'isefresistance’ are further increased. Th‘ese?eff
minutes'at a temperatureio'f‘ about 900° F. to‘ 11100“ R, 50 feots’iare-illustiatedat'curves'C and Cr, respectively,-Fig .'
2a‘n‘d 3>,'-ciifveFC~-béing1 taken for 12 volt operation, arid-1
preferably at 1050° F;
After annealing the oxidized plate is air cooled? to“
curve/‘Crbeing'take'ni
renti'u's‘ed 'ror- allithe curves'of
at the samev
Fig‘. constant
3. These
forwardj
curvesla‘iei
c'ti
about 590° to 600° 'F., as by‘exposure to‘cold air- (for,
taken'foria cellforfried b‘y'the preferred process described?
example at about room‘ temperature) fo'r'a' delaylinterval'l
of'about 1/2 to 2 minutes, and: is"then'quenched in'c'old" 55 he'r'eihbefo'reeiteept that the salt- predip" before ?ring is?
oinitt'etll-i The’- forward aging characteristic of curve?‘ 611‘
water.
is' not‘ a“ satisfactory one, for it does not show a teii‘deiicyi'“
When the plates,‘ or‘cells," are'removed frorrr the‘coldi
water quench they are dn'ed'and‘prepared for the applica-~
tofsvta'biliz'e'“ iri'va" reasonable time, but theleakage'lcharaiii
salts‘ are also effective‘ as a prfe?ringfdip‘r In general‘,
tion of a metal contact‘layer,‘ or counter electrode, over
teri‘s'tic‘ of ~ cu'r'v C» is highly satisfactory.
the cuprous oxide layer'formed' during the ?ring opera‘ 60
To improve-‘theifo‘r'ward resistance characteristic of-‘tlie‘
cell=withoi1t signi?cantly affecting the reverse resistaniciel
tion. The cells as they come out‘of the quench’ bath‘
usually have formed over-the'cuprou's oxide a thiula'yen
of cupric, or black, oxide'asla' result of- exposure to air.
This cupric' oxide is?rst removed, preferablyiby’elec'troe
provide ‘Y the‘salt'idipi before ?ring previously describediiri“
conjunction‘with“a“delayed quench.v When‘such a- dip‘1 1s”
utilized-‘in 'proces'sing’ah antimony coated plate-anditlie’i
lytic‘reduction to metallic ‘copper. Thereafter, a'contact 65 cold?water"q1ier'ich1 delayed, as fully described hereinbéi‘
fore,l~th‘e‘~aging characteristics of the resultant" cell? are“
layer of; metal, suchv asi-nicke‘l, is" applied to the‘=outer"'
surface of‘the vcuprous- oxide, as by electrolytic‘depo's'ie
shawnar-curves'niand D1, respectively, Figs; 2 and???
tion. Finally a peripheral area of the cell-is‘str‘ip'ped‘ofi
By'c'onip'a'ris'on with' curves C and C1 the effect 'of'ithe“
nickel‘ to expose thered- oxide, as by treatment in sul
salt‘predip’ is‘ evident. Curve D, Fig.‘ 2," shows'ithaftj'
phuric‘acid-solution~ or the'like, and the resulting rectifierv 70 reverse‘ resistahc'ei'is"decreased (i. e., leakageincreased)~
cells“ are subjected to suitable ‘ testing "operations.
only'sligh'tly. curve-D1, however, shows that the forward‘
re'si‘stance' is“-v‘ery'- materially decreased. While theifori"
The effect, of ’my new and novel process of manu~
facturingcopperi oxide recti?er‘ cells may‘ now bestL bev
War'd resistance represented by the curve D1 higher than?
appreciated ~by~referring to the characteristic curves shown‘
that ofi'a" standard cell (‘curve A1) it is within acceptable?
at Figs. 2 and 3’. As- a basis-ofcomparison it‘rnay‘ be" 76 limits botlr‘in absolute value and in rate‘ of increase.‘ The“
2,789,276
6
absolute value of forward resistance is not so signi?cant
as is its rate of increase, which must be kept low.
The e?ect of my salt predip in decreasing forward re
sistance more than it decreases reverse resistance may be
which includes coating at least one surface of a copper
plate with a thin ?lm of antimony, dipping said coated
plate in a water solution containing by weight .5% anti
mony chloride and .l% ferric nitrate, heating said plate
explained from the action of the acid radical (preferably
in an oxidizing atmosphere to form a layer of cuprous
a chloride) in the dip. In the ?ring process the chloride
oxide on the coated surface thereof, exposing said oxidized
radical Will react with copper in the base layer of the cell
plate to cold air for a delay interval of the order of 1/2 to 2
to form cupric chloride and cuprous chloride. Any cupric
minutes and then quenching said plate in cold water.
chloride present will undergo reduction to form cuprous
5. The method of producing a copper. oxide recti?er
chloride and free chlorine, and the free chlorine will re 10 cell which includes coating at least one surface of a copper
act to form more cuprous chloride. In the oxide layer,
plate with a thin ?lm of antimony, dipping said coated
on the other hand, any free chlorine will not react but will
plate in a water solution containing .5 % antimony chlo
remain entrapped in the layer. Free chlorine is a very
ride, .05% sodium tetraborate, .l% ferric nitrate and
good electron acceptor, and the presence of a good elec
about 3% tartaric acid, heating said plate in an oxidizing
tron acceptor in the oxide layer improves forward conduc 15 atmosphere at about 1800° to 1900° F. for a period of
tion (i. e., reduces forward resistance). The ferric nitrate
about 14 minutes to form upon the antimony coated sur
probably has a similar effect in providing free oxygen in
face thereof a layer of cuprous oxide, cooling said plate
the oxide layer, and oxygen is also known as an effective
for about 21/2 minutes in a cooling zone maintained at
electron acceptor.
about 870° to 930° F., annealing said oxidized plate for
While I have described a preferred process for making 20 about 9 minutes at a temperature of about 900° to 1100"
copper oxide recti?er cells as including the three signi
F., exposing said plate to cold air for a delay interval of
?cant steps of coating a copper base plate with metal, dip
about 1/2 to 2 minutes and then quenching said plate in
ping the coated plate in a salt solution before ?ring and
cold water.
delaying the cold water quench after annealing, I ?nd
6. The method of producing a copper oxide recti?er
that even without metal coating prior to ?ring, the
cell which includes electroplating upon at least one sur
delayed quench described, will increase forward and re
face of a copper plate a thin ?lm of antimony to a
verse cell resistance. When a salt predip of the type de
thickness less than .000005 of an inch, dipping said
scribed is utlized to restore an acceptable forward resist
plate in a dilute water solution containing less than 1%,
ance without adversely affecting the reverse resistance of
by weight, of antimony chloride, heating said plate in an
such a cell (i. e., quench delayed but metal coating before 30 oxidizing atmosphere to form upon the antimony coated
?ring omitted) an improved high voltage cell results.
surface thereof a layer of cuprous oxide, annealing said
This procedure involving these two signi?cant steps of
oxidized plate at about 900° to 1100° F., exposing said
salt predip and delayed quench has been described and
plate to cold air for a delay interval of the order of 1/z to 2
claimed in my co-pending application Serial No. 433,223,
minutes, and then quenching said plate in cold water.
?led May 28, 1954, which is a continuation in part of this
7. The method of producing a copper oxide recti?er cell
application as to this subject matter. Preferably, however,
which includes coating at least one surface of a copper
1 utilize all three steps to improve my copper oxide recti
plate With a thin ?lm of antimony, dipping said coated
?er cells. I have found that by this method I have
plate in a water solution containing by weight .5 % anti
been able to make cells which are entirely satisfactory at
mony chloride and .l% ferric nitrate, heating said plate
operating voltages up to three times those previously
at about 1800° and 1900° F. in an oxidizing atmosphere
used.
to form upon the metal coated surface thereof a layer of
Thus, while I have described a preferred embodiment of
my invention by way of illustration, many modi?cations
cuprous oxide, annealing said oxidized plate at about 900°
to 1100° F., exposing said plate to cold air for a delay
will occur to those skilled in the art, and I therefore wish
interval on the order of 1/2 t0 2 minutes and then quench
to have it understood that I intend in the appended claims ‘1'
ing said plate in cold water.
to cover all such modi?cations as fall within the true
8. A copper oxide recti?er cell comprising a base plate
of copper containing adjacent one surface thereof a
spirit and scope of my invention.
What I claim as new and desire to secure by Letters
Patent of the United States is:
l. The method of producing a copper oxide recti?er cell
which includes coating at least one surface of a copper
quantity of antimony, and an integral layer of cuprous
oxide overlying said one surface and containing antimony.
9. A copper oxide recti?er cell comprising a base plate
of copper containing antimony and cuprous chloride, and
plate with a thin ?lm of antimony, dipping said coated
an integral layer of cuprous oxide upon at least one sur
plate in a dilute Water solution of antimony chloride,
face of said plate containing antimony and cuprous chlo
heating said plate in an oxidizing atmosphere to form a
ride.
layer of cuprous oxide upon the coated surface thereof, 55
cooling said oxidized plate in air for an appreciable de
References Cited in the ?le of this patent
lay interval, and then quenching said plate in cold Water.
UNITED STATES PATENTS
2. The method of producing a copper oxide recti?er
cell which includes coating at least one surface of a
copper plate with a thin ?lm of antimony, dipping said 60
coated plate in a dilute water solution of antimony chlo
ride, heating said plate in an oxidizing atmosphere to form
a layer of cuprous oxide upon the coated surface thereof,
cooling said oxidized plate in air to about 500° to 600°
F, and then quenching said plate in cold water.
3. The method of producing a copper oxide recti?er
cell which includes coating at least one surface of a copper
plate with a thin ?lm of antimony, dipping said coated
plate in a dilute Water solution containing less than 1%,
by weight, of antimony chloride, heating said plate in an 70
oxidizing atmosphere to form a layer of cuprous oxide
on the coated surface thereof, exposing said oxidized plate
to cold air for a delay interval of the order of 1/2 to 2
minutes, and then quenching said plate in cold water.
4. The method of producing a copper oxide recti?er cell 75
1,769,852
1,834,275
1,926,132
1,936,792
2,060,905
2,081,051
2,172,576
Ogden ______________ __ July 1,
Geiger ______________ __ Dec. 1,
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Smith ______________ __ Nov. 17,
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