Note: Descriptions are shown in the official language in which they were submitted.
1~)4'~73'~
This invention relates to copper coated composite
powders and to a method of production of such powder. The
powder with which the invention is particularly concerned is
useful as an abradable or hard surface coating material on
metallic and non-metallic surfaces. The method to which the
invention is particularly related involves precipitation and
deposition of a layer of metallic nickel on a core material
by gas reduction from solution followed by displacement of
the nickel layer with copper by cementation.
Wide use is made in industry of powders composed of
core particles surrounded by and encased in an outer metallic
layer. These powders, referred to herein as "composite
powders", are used, for example, in the flame spraying and
plasma spraying fields, in the manufacture of strip by roll
compaction and in the manufacture of special metal parts by
compaction in a die.
i The method of production of composite powders depends
upon the composition of their coating material and their cores.
; Coating material can, for example, be applied to metallic core
' 20 materials by cementation provided the coating material is
metallic and is higher in the electromotive series than the core
material. Another method for the production of certain com-
posite powders involves dispersing solid particles of material'
which is to form the core of the powders in an ammoniacal solu-
tion containing a soluble salt of the metal which is to form the
coating of the powder. The solution is contacted at elevated
temperature and pressure with a reducing gas to cause the
coating metal to precipitate and deposit onto the core parti-
cles. Metals which can be deposited on core particles by this
method include cobalt, nickel, gold, silver, cadmium and others.
The latter method is described in numerous patents including
Canadian patents Nos. 561,~2~, 562,160 and 632,7~5.
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The production of copper-coated composite particles
poses serious technical problems. When copper is precipitated
from an ammoniacal solution containing suspended core particles,
most of the copper will precipitate in the form of discrete
particles separate from the core particles. The little copper
which does bond to the core particles will form a discontinuous
spotty deposit. Most of the outer surfaces of the core parti-
cles will however be completely free of copper.
A much higher quality copper-coated composite powder
can be produced by cementation but metals commercially important
as core material and higher than copper in the electromotive
series are limited.
It is an object of the present invention to provide a
method by which a uniform coating of copper can be applied to
particles of a variety of materials which cannot be coated
uniformly with copper by the known methods described above.
Specifically, the materials may be metal alloys and elementary
metals below copper in the electromotive series. In addition,
a wide range of non-metallic materials may be coated with copper
by the method of the present invention.
It is a further object of the invention to provide
copper coated metallic and non-metallic particles suitable for
use as abradable or hard surface coating material on metallic
and non-metallic surfaces.
The method of the present invention broadly involves
the steps of providing solid particles of a core material
selected from the group comprising: non-metals, metal alloys
and elementary metals lower than copper in the electromotive
series; forming a slurry of said particles dispersed in an
~0 aqueous ammoniacal ammonium salt solution in which said parti-
cles are insoluble and which contains dissolved nickel values;
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4;~7~15
reacting said slurry with a reducing gas at elevated temperature
and pressure to cause nickel to precipitate from solution and to
coat said dispersed particles; terminating the reaction when the
weight of nickel coating the dispersed particles i9 substantially
the molecular equivalent of the weight of copper desired in the
coating of the finished composite powder; dispersing said nickel
coated particles in a solution having a pH no higher than about 7
and containing dissolved copper values, and contacting the last-
mentioned solution with hydrogen gas under a pressure of from
about 50 to about 500 psig to cause cementation of copper onto
the core particles with concurrent dissolution of substantially
~ the entire nickel coating.
.~ :
The product of the invention may be characterized as
a powder composition consisting of metallic or non-metallic core
particles coated with copper. Especially useful and novel powder
- compositions within the class are composite particles consisting
of particles of calcium fluoride, molybdenum disulphide, cobalt
oxide or diatomaceous earth coated with copper.
The invention is described in detail below with refer-
ence to the accompanying drawing which shows graphically changesin concentration of nickel and copper in solution during the
- cementation reaction.
Since the suhject invention is directed to a method
of applying a coating of copper to material which cannot be
coated with copper by cementation, the material of which the
starting particles of the invention is composed will normally
be restricted to such material. The material of the starting
particles will also be restricted to ones which are insoluhle
in a nickel-containing ammoniacal ammonium salt solution sub-
jected to gas reduction at elevated temperature and pressure.
There exists a very large number of materials havingthe properties described in the preceding paragraph. The core
.~ . .
~ rial may be composed of elementary metals lower than copper
in the electromotive series. Examples of such metals are silver,
platinum, gold and lead. The core material may also be composed
of metal alloys or it may be composed of non-metals such as re-
fractory oxides, nitrides, borides, graphite, diamonds and all
other crystalline forms of carbon. Also, the core material may
be composed of calcium fluoride, diatomaceous earth, molybdenum
disulphide, cobalt oxide, silica, boron nitride and carbides such
as chromium carbide and tungsten carbide.
The starting particles should be sufficiently small that
they will remain in suspension in an agitated solution7 In general,
particles of about 32 mesh standard Tyler screen or smaller meet
~his requirement where the specific gravity of the particles is
less than about 10. Where the particles have a higher specific
gravity their size should generally not exceed about 100 mesh. How-
ever, the shape of the particles will have a bearing on whether
they can be kept in suspension, thus there is no hard and fast
relationship between particle size and specific gravity.
The first step in the process of the subject invention
is to apply a coating of nickel onto the core material. The
method of doing so is known and is described in the Canadian
patents mentioned before. Since the method is known, it will be
only briefly summarized herein. According to the method the
core particles are dispersed in an ammoniacal ammonium salt
solution containing dissolved nickel values. The resulting slurry
is reacted at elevated temperature, usually 250F or over with
a reducing gas, usually hydrogen, under a partial pressure of
100 psi or over. The reaction results in precipitation of nickel
from solution and deposition thereof as a continuous coating onto
the particles of the core material.
The quantity of nickel which is deposited onto the core
particles should be substantially the molecular equivalent of the
:.
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~uantity of copper desired on the finished composite particles.
For example, assume -that it is required to produce lO0 grams
of finished composite particles of which the copper coating
is to account for approximately ~0~ of the total weight and the
core is to account for the balance. The finished particles
must therefore contain ~0 grams or l.26 moles of copper. The
nickel-coated particles from which the finished composite
particles are produced must also contain approximately 1.26
moles of nickel or 7~ grams of nickel. Thus, approximately
7~ grams of nickel should be deposited onto the core particles.
It is generally found desirable to adjust the con-
centration of the nickel in ammoniacal solution according to
the quantity of nickel which is desired to be deposited on the
core particles. Under normal conditions, dissolved nickel
values in the solution can be decreased to below l gram per
litre very easily. Thus, it is only necessary to adjust the
concentration of nickel in the ammoniacal solution such that
there is a slight excess of nickel values over the amount of
nickel desired to be precipitated, generally about l gram per
litre. For example, to prepare the composite particles des-
- cribed in the preceding paragraph, a given amount of core
material e.g. 20 grams is suspended in a nickel-containing
solution. The solution should contain 7~ grams of dissolved
nickel plus an additional l gram of nickel per litre of
solution.
The concentration of nickel in the ammoniacal
solution must be below that at which crystallization of the
nickel values occurs. Where the nickel values are in the form
of nickel sulphate, the concentration of the nickel sulphate
should be between 25 and 75 grams per litre. Preferably, the
concentration should be maintained at about 50 grams per litre.
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The r~action is terminated when the desired amount of
nickel has deposited onto the core particles. Where the solution
is initially only provided with a slight excess of dissolved
nickel over the amount desired to be precipitated, the reaction
is of course terminated when the solution is substantially depleted
of nickel values. When the solution is depleted, the consumption
of hydrogen ceases. Usually hydrogen is no longer consumed after
15 to 30 minutes from commencement of reduction at the preferred
operating conditions.
Following deposition of nickel on the core material,
the resulting composite particles are separated from solution by,
for example, filtration and are then dispersed in an aqueous solu-
tion having a pH of no higher than about 7 and containing dissolved
copper values. The copper values in solution may be in the form
of copper sulphate or copper chloride and will desirably be in
slight excess over the amount which is to be cemented onto the
particles, the solution may contain 80 grams of copper plus an
; additional 1 to 5 grams of copper per liter of solution.
The cementation reaction will generally, in practice,
be carried out at temperatures~in the range of from about 100 to
300F. The principal reaction which occurs during cementation
(where cementation takes place in an aqueous sulphuric acid solu-
tion) is as follows:
Ni + CuS04 ~ Cu + NiS04 (1)
The cementation reaction is conducted under a hydrogen
` overpressure of from about 50 to about 500 psig, and more prefer-
ably within the range of from about 50 to about 350 psig, to
displace the equilibrium of the reversible side reaction so that
formation of a product which tends to diminish the quality of the
finished composite particles is suppressed. The side reaction
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ch occurs concurrently with reaction (l) is as follows:
Cu ~l2S~4 ~ C~ 04 + l~2 (2)
; Hydrogen is helieved to shift the eguilibrium of reac-
tion (2) to favour the ~ro~uction of ~etallic copper. As a result,
copper which displaces nickel according to reaction (l) and which
cements onto the core particles tends to re~ain intact. The fin-
ished composite particles will have a uniform continuous coating
of copper and are highly desirable for this reason.
In the absence of hydrogen, reaction (2) tends to pro-
l~ ceed to the right so that the deposit of copper on the core par-
ticles reacts with sulphuric acid. ~s a result, the copper
deposited on the core particles at the completion of the cementa-
tion reaction represents only a portion of the total copper con-
tent of the solution at the beginning of the reaction. Since it
is difficult to control the proportion of copper initially in
solution which deposits onto the core particles, the cementation
~` reaction is conducted in the presence of hydrogen so that the
finished composite powder will have the desired copper content.
The cementation reaction is usually complete in ahout
30 to 60 minutes depending on temperature. ~here the concentra-
tion of copper in the solution is adjusted according to the
quantity of copper which is to be cemented onto the particles,
the reaction will, of course, he complete when the solution is
; substantially depleted of copper. IJpon completion of the
cementation reaction, the finished copper coated particles are
separated from solution by means of, for example, filtration.
The finished composite particles can be used in a
number of ways depending upon the composition of the core
material. They can, for example, he used as abradable coating
material such as abradable seals. In such event, the core
material must he ahradable, erosion resistant and corrosion
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1'~4~7;~,5
sistant in the environment in which the particles are used.
Suitahle core materi~ls for this purpose include yraphite,
diatomaceous e~rth, calcium fluoride, mol~bdenum disulphide,
cohalt oxide and horon nitri~e. secause graphite oxidizes at
low temperatures, its use as a core material in engine seals
Composed of copper coated particles is limited to temperatures
up to about 1022F. For higher service temperatures, composite
powders having more refractory abradable cores are required.
Diatomaceous earth and calcium fluoride are suitahle for this
purpose.
The finished composite particles can also he used as
coating material to impart a hard wear resistant characteristic
to a substrate. Particles suitable for this purpose will have
a core composed of a refractory oxide such as alumina, a carbide
of such element as chromium, tungsten, titanium and so on.
The following example illustrates the effect of
;- hydrogen pressure on the properties of the finished copper
coated composite partic]es.
EXAMPLE
The starting material for this example was nickel- -
~ coated graphite composite powder prepared according to the
; procedure described in canadian patent ~o. 632,785. The com-
posite powder was made up of 80% nickel and 20% graphite by
weight and had the following screen analysis (standard Tyler
` scale) +100 mesh:trace, -100 +200 mesh: 10%; -200 +325 mesh:
50.0%, -325 mesh: 40.0%.
Samples of the powder were dispersed in an autoclave
containing from 100 - 210 gpl copper sulphate in solution.
The resulting slurries were heated to 300F, in some cases
under an overpressure of hydrogen of 350 psig and in other
cases in the absence of a hydrogen overpressure. The solution
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1~)4;~7~5,
~as analyzed for nickel and copper at various times during heat-
ing and the results are illustrated in the drawing.
The results show that hydrogen pressure promotes
the cementation reaction. After 60 minutes, the concentration
of nickel in solution at ~ psig H2 overpressure is 0.31 mole
per liter while at 350 psig H2 the concentration is 0.52 mole
per liter. The concentration of copper in solution at 0 and
350 psig H2 overpressure after 60 minutes is 0.2 and 0.05 mole
per liter respectively. Thus a higher proportion of nickel
displaces copper from solution under a hydrogen overpressure
than in the absence of hydrogen.
.
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