U.S. patent number 3,617,363 [Application Number 04/698,129] was granted by the patent office on 1971-11-02 for process for electroless metallizing incorporating wear-resisting particles.
This patent grant is currently assigned to General American Transportation Corporation. Invention is credited to Willy Metzger, Rudi Ott, Gunter Pappe, Helmut Schmidt.
United States Patent |
3,617,363 |
Metzger , et al. |
November 2, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
PROCESS FOR ELECTROLESS METALLIZING INCORPORATING WEAR-RESISTING
PARTICLES
Abstract
There are disclosed processes for electroless metallizing
workpieces to provide thereon a metal coating incorporating therein
nonmetallic wear-resisting particles and the coated workpieces
produced by such processes, the processes comprising contacting the
workpieces with an electroless metallizing bath consisting of an
aqueous solution of a metal salt and an electroless reducing agent
therefor and a quantity of nonmetallic wear-resisting particles,
wherein the particles are essentially insoluble in the plating bath
and are noncatalytic and inert with respect thereto, the particles
being present in the bath in an amount by weight no greater than
about four times the weight of the metal in the bath expressed as
free metal, and maintaining the particles in suspension throughout
the bath during the metallizing of the workpiece; the electroless
coating with the wear-resisting particles therein may be heat
treated by heating to an elevated temperature in the range
100.degree. C. to 600.degree. C. for one hour or more further to
harden the coating.
Inventors: |
Metzger; Willy
(Solingen-Merscheid, DT), Ott; Rudi
(Solingen-Merscheid, DT), Pappe; Gunter
(Solingen-Merscheid, DT), Schmidt; Helmut
(Solingen-Merscheid, DT) |
Assignee: |
General American Transportation
Corporation (Chicago, IL)
|
Family
ID: |
6985469 |
Appl.
No.: |
04/698,129 |
Filed: |
January 16, 1968 |
Foreign Application Priority Data
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Jan 18, 1967 [DT] |
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B 90776 |
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Current U.S.
Class: |
427/383.7;
106/1.23; 428/639 |
Current CPC
Class: |
C23C
18/34 (20130101); C23C 18/52 (20130101); C23C
18/405 (20130101); C23C 18/1662 (20130101); Y10T
428/1266 (20150115) |
Current International
Class: |
C23C
18/16 (20060101); C23C 18/40 (20060101); C23C
18/52 (20060101); C23C 18/31 (20060101); C23C
18/34 (20060101); C23c 003/02 () |
Field of
Search: |
;117/130,160,47
;204/3,41 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,041,753 |
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Sep 1966 |
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GB |
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290,590 |
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Jun 1965 |
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NL |
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Other References
Domnikov, Metal Finishing Feb. 1961 pp. 52-54 117-130.
|
Primary Examiner: Kendall; Ralph S.
Claims
What is claimed is:
1. A process of electroless metallizing a body to provide on the
surface thereof a metal coating incorporating therein
wear-resisting particles, which process comprises contacting the
surface of said body with a stable electroless metallizing bath
consisting essentially of an aqueous solution of a metal salt and
an electroless reducing agent therefor and a stabilizer for said
bath and a quantity of wear-resisting particles, wherein said
particles are nonmetallic and essentially insoluble in the plating
bath and are noncatalytic and inert with respect thereto; said
particles being present in said bath in an amount by weight in the
range from about 0.1 percent to about 2 percent of the solids in
said bath and no greater than about 4 times the weight of the metal
in said bath expressed as free metal, and maintaining said
particles in suspension throughout said bath during the metallizing
of said body for a time sufficient to produce a coating having a
thickness of at least about 5 microns, thereby to produce on the
surface of said body a coating of the metal having said particles
uniformly dispersed therethrough.
2. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles are silicon carbide
particles.
3. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles are tungsten carbide
particles.
4. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles are molybdenum sulfide
particles.
5. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles are silica particles.
6. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles are aluminum oxide
particles.
7. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles have dimensions in the range
from about 0.01 micron to about 100 microns.
8. The process of electroless metallizing set forth in claim 1,
wherein said wear-resisting particles have dimensions in the range
from about 0.5 micron to about 25 microns.
9. The process of electroless metallizing set forth in claim 1,
wherein said particles are maintained in suspension throughout said
bath by mechanically agitating said bath and said particles.
10. The process of electroless metallizing set forth in claim 1,
wherein said particles are maintained in suspension throughout said
bath by passing said bath with said particles therein past said
body.
11. The process of electroless metallizing set forth in claim 1,
wherein said particles are maintained in suspension by streams of
minute bubbles of gases passing through said bath.
12. The process of electroless metallizing set forth in claim 1,
wherein said particles are maintained in suspension throughout said
bath by agitation of said body within said bath.
13. The process of electroless metallizing set forth in claim 1,
and further comprising the step of heating said coating to an
elevated temperature for a sufficient period of time to heat-harden
said coating.
14. A process for coating the surface of a body with a nickel
coating incorporating therein wear-resisting particles, which
process comprises contacting the surface of said body with a stable
bath consisting essentially of an aqueous solution of nickel salt
and a reducing agent therefor and a stabilizer for said bath and a
quantity of wear-resisting particles, wherein said particles are
nonmetallic and essentially insoluble in the plating bath and are
noncatalytic and inert with respect thereto, said particles being
present in said bath in an amount by weight in the range from about
0.1 percent to about 2 percent of the solids in said bath and no
greater than about 4 times the weight of nickel in said bath
expressed as nickel metal, and maintaining said particles in
suspension throughout said bath during the coating of said body for
a time sufficient to produce a coating having a thickness of at
least about 5 microns, thereby to produce on the surface of said
body a coating of nickel having said particles uniformly dispersed
therethrough.
15. The process of coating set forth in claim 14, wherein said
reducing agent is a hypophosphite.
16. The process of coating set forth in claim 15, wherein the
absolute concentration of hypophosphite in said bath expressed in
mole/liter is within the range 0.15 to 1.20, and the ratio between
nickel and hypophosphite in said bath expressed in molar
concentrations is within the range 0.25 to 1.60.
17. The process of coating set forth in claim 15, wherein said bath
also includes a complexing agent selected from the group consisting
of lactic acid and slats thereof.
18. The process of coating set forth in claim 17, wherein the
absolute concentration of lactic ions in said bath expressed
mole/liter is within the range 0.25 to 0.60.
19. The process of coating set forth in claim 15, wherein said bath
also includes an exalting additive selected from the group
consisting of simple short chain saturated aliphatic monocarboxylic
acids including three to five carbon atoms and salts thereof.
20. The process of coating set forth in claim 19, wherein the
absolute concentration of said exalting additive in said bath
expressed in mole/liter is within the range 0.025 to 0.060.
21. The process of coating set forth in claim 15, wherein said bath
also includes a complexing agent selected from the group consisting
of lactic acid and slats thereof, and an exalting additive selected
from the group consisting of simple short chain saturated aliphatic
monocarboxylic acids including three to five carbon atoms and salts
thereof.
22. The process of coating set forth in claim 21, wherein the
absolute concentration of lactic ions in said bath expressed in
mole/liter is within the range 0.25 to 0.06, and the absolute
concentration of said exalting additive in said bath expressed in
mole/liter is within the range 0.025 to 0.060.
23. The process of coating set forth in claim 15, and further
comprising the step of heating said coating to an elevated
temperature for a sufficient period of time to heat-harden said
coating.
24. The process of coating set forth in claim 23, wherein the
coating is heated to a temperature in the approximate range
100.degree. C. to 600.degree. C. throughout a time interval of at
least about 1 hour.
25. The process of coating set forth in claim 14, wherein said
reducing agent is an alkyl-borazane.
26. A process of applying a nickel coating incorporating therein
wear-resisting particles to the surface of a body essentially
formed of a material selected from the group consisting of aluminum
and its alloys, which process comprises contacting the surface of
said body with a stable bath consisting essentially of an aqueous
solution of a nickel salt and a hypophosphite and a stabilizer for
said bath and a quantity of wear-resisting particles and wherein
said particles are nonmetallic and essentially insoluble in the
plating bath and are noncatalytic and inert with respect to the
reduction of the nickel salt by the hypophosphite, said particles
being present in said bath in an amount by weight in the range from
about 0.1 percent to about 2 percent of the solids in said bath and
no greater than about four times the weight of nickel in said bath
expressed as nickel metal, and maintaining said particles in
suspension throughout said bath during the metallizing of said body
for a time sufficient to produce a coating having a thickness of at
least about 5 microns thereby to produce on the surface of said
body a coating of nickel having said particles uniformly dispersed
therethrough.
27. The process of coating as set forth in claim 26, wherein said
bath additionally consists essentially of a fluoride, wherein the
absolute concentration of fluoride anions in said bath expressed in
mole/liter is in the range from about 0.001 to about 0.04.
28. A process of applying a nickel coating incorporating therein
wear-resisting particles to the surface of a body essentially
formed of a material selected from the group consisting of
magnesium and its alloys, which process comprises contacting the
surface of said body with a stable bath consisting essentially of
an aqueous solution of a nickel salt and a hypophosphite and a
stabilizer for said bath and a quantity of wear-resisting
particles, and wherein said particles are nonmetallic and
essentially insoluble in the plating bath and are noncatalytic and
inert with respect to the reduction of the nickel salt by the
hypophosphite, said particles being present in said bath in an
amount by weight in the range from about 0.1 percent to about 2
percent of the solids in said bath and no greater than about four
times the weight of nickel in said bath expressed as nickel metal,
and maintaining said particles in suspension throughout said bath
during the metallizing of said body, for a time sufficient to
produce a coating having a thickness of at least about 5 microns,
thereby to produce on the surface of said body a coating of nickel
having said particles uniformly dispersed therethrough.
29. A process of applying a nickel coating incorporating therein
wear-resisting particles to the surface of a body essentially
formed of a material selected from the group consisting of
beryllium and its alloys, which process comprises contacting the
surface of said body with a stable bath consisting essentially of
an aqueous solution of a nickel salt and a hypophosphite and a
stabilizer for said bath and a quantity of wear-resisting
particles, and wherein said particles are nonmetallic and being
present in said bath in an amount by weight in the range from about
0.1 percent to about 2 percent of the solids in said bath and no
greater than about 4 times the combined weight of the nickel and
the cobalt in said bath expressed as nickel metal and cobalt metal,
and maintaining said particles in suspension throughout said bath
during he coating of said body for a time sufficient to produce a
coating having a thickness of at least about 5 microns, whereby to
produce on the surface of said body a coating of a nickel-cobalt
alloy having said particles uniformly dispersed therethrough.
30. A process of applying a nickel coating incorporating therein
wear-resisting particles to the surface of a body essentially
formed of a material selected from the group consisting of copper
and its alloys, which process comprises contacting the surface of
said body with a stable bath consisting essentially of an aqueous
solution of a nickel salt and a hypophosphite and a stabilizer for
said bath and a quantity of wear-resisting particles, and wherein
said particles are nonmetallic and essentially insoluble in the
plating bath and are noncatalytic and inert with respect to the
reduction of the nickel salt by the hypophosphite, said particles
being present in said bath in an amount by weight in the range from
about 0.1 percent to about 2 percent of the solids in said bath and
no greater than about four times the weight of nickel in said bath
expressed as nickel metal, and maintaining said particles in
suspension throughout said bath during the metallizing of said body
for a time sufficient to produce a coating having a thickness of at
least about 5 microns, thereby to produce an the surface of said
body a coating of nickel having said particles uniformly dispersed
therethrough.
31. A process of coating the surface of a body with a cobalt
coating incorporating therein wear-resisting particles, which
process comprises contacting the surface of said body with a stable
bath consisting essentially of an aqueous solution of a cobalt salt
and a reducing agent therefor and a stabilizer for said bath and a
quantity of wear-resisting particles, wherein said particles are
nonmetallic and essentially insoluble in the plating bath and are
noncatalytic and inert with respect thereto, said particles being
present in said bath in an amount by weight in the range from about
0.1 percent to about 2 percent of the solids in said bath and no
greater than about four times the weight of the cobalt in said bath
expressed as cobalt metal, and maintaining said articles in
suspension throughout said bath during the coating of said body for
a time sufficient to produce a coating having a thickness of at
least from 5 microns, thereby to produce on the surface of said
body a coating of cobalt having said particles uniformly dispersed
therethrough.
32. The process of coating set forth in claim 30, and further
comprising the step of heating said coating to an elevated
temperature for a sufficient period of time to heat-harden said
coating.
33. A process of coating the surface of a body with a nickel-cobalt
alloy incorporating therein wear-resisting particles, which process
comprises contacting the surface of said body with a stable bath
consisting essentially of an aqueous solution of nickel salt and
cobalt salt and a reducing agent therefor and a stabilizer for said
bath and a quantity of wear-resisting particles, wherein said
particles are nonmetallic and essentially insoluble in the plating
bath and are noncatalytic and inert with respect thereto, said
particles,
34. The process of coating set forth in claim 33, and further
comprising the step of heating said coating to an elevated
temperature for a sufficient period of time to heat-harden said
coating.
35. The process of coating said coating set forth in claim 34,
wherein said coating is heated is the approximate range 100.degree.
C. to 600.degree. C. throughout a time interval of at least about 1
hour.
36. A process of coating the surface of a body with a copper
incorporating therein wear-resisting particles, which process
comprises contacting the surface of said body with a stable bath
consisting essentially of an aqueous solution of a copper salt and
a reducing agent therefor and a stabilizer for said bath and a
quantity of wear-resisting particles, wherein said particles are
nonmetallic and essentially insoluble in the plating bath and are
noncatalytic and inert with respect thereto, said particles being
present in said bath in an amount by weight in the range from about
0.1 percent to about 2 percent of the solids in said bath and no
greater than about four times the weight of the copper in said bath
expressed as copper metal, and maintaining said particles in
suspension throughout said bath during the coating of said body for
a time sufficient to produce a coating having a thickness of at
least about 5 microns, thereby to produce on the surface of said
body a coating of copper having said particles uniformly dispersed
therethrough.
37. The process of coating set forth in claim 36, wherein said
reducing agent is formaldehyde.
Description
The present invention is directed to processes for electroless
metallizing workpieces wherein the resultant metal coating has
incorporated therein wear-resisting particles.
It is an important object of the present invention to provide a
process for electroless metallizing a body to provide thereon a
metal coating incorporating therein wear-resisting particles so as
to provide a highly wear-resistant coating on the body to protect
such bodies that are subject to wear by reason of sliding contact,
rubbing contact, and the like in use; the process comprising
contacting the body with the electroless metallizing bath
consisting essentially of an aqueous solution of the metal salt and
an electroless reducing agent therefor and a quantity of
wear-resisting particles, wherein the particles are essentially
insoluble in the plating bath and are noncatalytic and inert with
respect thereto, the particles being present in the bath in an
amount by weight no greater than about 4 times the weight of the
metal in the bath expressed as free metal, and maintaining the
particles in suspension throughout the bath during the metallizing
of the body, thereby to produce on the surface of the body a
coating of metal having the particles uniformly dispersed
therethrough.
Another object of the invention is to provide a process of
electroless metallizing of the type set forth wherein the
wear-resisting particles have dimensions in the range 0.01 micron
to 100 microns, a further preferred range being from about 0.5
micron to about 25 microns, the particles being maintained in
suspension in the bath by mechanical agitation in the bath or by
passing the bath with the particles therein across the body, or by
streams of minute bubbles of gases passing through the bath or by
agitation of the body within the bath.
Still another object of the invention is to provide a process of
the type set forth and further comprising the step of heating the
coating to an elevated temperature for a sufficient period of time
to heat-harden the coating, a typical coating being heat-hardened
by heating to a temperature in the range from about 100.degree. C.
to about 600.degree. C. for about 1 hour.
Still another object of the invention is to provide a process of
the type set forth which is particularly suited for applying
wear-resistant coatings to bodies formed of a material selected
from the group consisting of aluminum, magnesium, copper, beryllium
and their alloys, whereby additional heat-hardening of the coating
is not required to provide adequate wear-resistance in the
coating.
Further features of the invention pertain to the particular
arrangement of the steps of the processes and the compositions of
the bath used therein and of the wear-resistant coatings produced
thereby, whereby the above-outlined and additional operating
features thereof are attained.
The invention, both as to its organization and method of operation,
together with further objects and advantages thereof, will best be
understood by reference to the following specification and to the
several illustrative examples set forth therein.
In accordance with the present invention, there is provided a
workpiece or article of manufacture having an outer surface that is
to carry the desired wear-resistant coating, the outer surface
typically being one that will be subject to sliding contact or
rubbing contact with another surface, whereby to subject it to
substantial wearing and bearing pressures. First, the workpiece is
cleaned using one of several well-known cleaning methods, after
which the workpiece is contacted with an electroless metallizing
bath containing a quantity of wear-resisting particles, the bath
being for example a conventional chemical nickel plating bath of
the nickel cation-hypophosphite anion type, and the particles being
essentially insoluble in the plating bath and noncatalytic and
inert with respect thereto and being present in the bath in an
amount by weight no greater than about four times the weight of the
metal in the bath expressed as free metal. During the plating
process, the wear-resisting particles are maintained in suspension
throughout the bath, whereby after a suitable time interval there
is produced on the surface of the workpiece a coating of the metal,
such as nickel, having uniformly dispersed therethrough a quantity
of the wear-resisting particles. Thereafter the workpiece may be
subjected to a heat-hardening step in order to render the composite
coating thus produced intimately bonded thereto and of harder and
more wear-resistant character.
The term "wear-resistant coating" as used herein refers to a
coating, the properties of which changed in any manner whatsoever
to increase the wear-resistant properties thereof; for example, the
term includes increasing the hardness of the coating by the
incorporating therein materials that are intrinsically harder than
the coating itself; on the other hand, the term as used herein may
include coatings wherein a lubricating material, such as molybdenum
disulfide, has been added to the coating so that the lubricated
surface of the coating wears longer due to the lubricating
properties thereof. Finally, it will be understood that the
term"wear-resistant coating" may also refer to a coating which
embodies both particles which are intrinsically harder than the
coating and particles which add a lubricating property to the
coating.
While the processes of the present invention are fundamentally
independent of the composition of the workpiece, ordinarily the
workpiece is formed of an industrial metal, such for example, as
steel, although the workpiece may be formed of a nonmetallic
material. In the last mentioned instance, the workpiece is first
subjected to pretreatment in order to activate the surface thereof
so that it may subsequently receive the electroless metallized
coating that is inherently produced in the metallizing process.
When the metallizing metal is nickel, pretreatment may be that as
disclosed in U.S. Pat. No. 2,690,401, granted on Sept. 28, 1954 to
Gregoire Gutzeit, William J. Crehan and Abraham Krieg, and in U. S.
Pat. No. 2,690,402 granted on Sept. 28, 1954 to William J.
Crehan.
The processes of the present application are particularly
beneficial in providing wear-resistant coatings on workpieces
formed of materials, such as aluminum, magnesium, copper, or
beryllium which are not readily heat hardenable and which
ordinarily are not heated after fabrication thereof, the inventive
coating having wear-resistant properties such that additional
treatment thereof is not necessary to provide a satisfactory
wear-resistant surface.
It will be understood that a large number of metallizing processes
of the electroless type may be utilized including electroless
nickel processes, electroless cobalt processes and electroless
copper processes. The invention is of particular applicability in
the case of electroless nickel processes, specifically those using
hypophosphite anions as the electroless reducing agent.
Furthermore, the electroless metallizing process in the case of
electroless nickel is independent of the particular composition of
the nickel plating bath of the nickel cation-hypophosphite anion
type that is employed in the chemical nickel plating step, whereby
a wide variety of these conventional chemical nickel plating baths
may be employed; which plating baths inherently produce coatings
essentially comprising by weight about 85 percent to 97 percent
nickel and about 3 percent to 15 percent phosphorus.
The plating bath disclosed in U.S. Pat. No. 2,822,294, granted on
Feb. 4, 1958 to Gregoire Gutzeit, Paul Talmey and Warren G. Lee is
particularly recommended due to its simplicity and economy. More
particularly, this plating bath is of the nickel
cation-hypophosphite anion type, also containing lactic anion and
having a pH in the acid range 3.0 to A typical example of this
chemical nickel plating bath useful in the present invention has
the following composition:
---------------------------------------------------------------------------
EXAMPLE 1
NiSO.sub.4 .6H.sub.2 0 0.08 mole/1. NaH.sub.2 PO.sub.2.H.sub.2 O
0.23 mole/1. Lactic anion 0.30 mole/1. Propionic anion 0.03 mole/1.
Lead ion 1 part per million pH 4.6
__________________________________________________________________________
a quantity of the above plating bath was placed in a plating vessel
having a magnetic stirrer therein, after which there was added
thereto 1 percent by weight of the solids in the plating bath of
600 grit silicon carbide particles, it being noted that the nickel
content of the bath on the solid basis expressed as nickel metal is
about 0.5 percent. A steel workpiece having a bearing surface
thereon was then placed in the plating bath while the silicon
carbide particles were maintained in agitated suspension throughout
the plating bath, and while the temperature of the plating bath was
maintained in the general range 93.degree. C. to 98.degree. C.
After about an hour, there was present on the exposed surfaces of
the workpiece about one mil of a wear-resistant coating comprising
electroless nickel and a quantity of the silicon carbide particles
embedded in and distributed therethrough. The coating that is
inherently produced by the particular plating bath essentially
comprises by weight about 86 percent nickel and about 9 percent
phosphorus, and about 5 percent silicon carbide.
The surface of the coated workpiece was rough and dull in
appearance and had a hardness in the nickel-phosphorus alloy area
of 525 V.P.N. (Vickers Pyramid Number). The Taber Wear Index (TWI)
was determined and was found to be 4.7. The Taber Wear Index is
defined as the loss of weight in mg. per 1000 revolutions of two
CS-10 rubber wheels under a 1000 grams load, a TWI of 5
representing a loss in thickness of about 0.01 mil of coating. By
contrast an electroless nickel coating made using the bath of
example 1 without the addition of wear-resisting particles thereto
has a TWI of 15.2 whereby the coating of the present invention
incorporating therein the silicon carbide wear-resisting particles
materially imposes the wear-resistance of the coating, the
improvement being essentially by a factor of 3.
In the chemical nickel plating bath of example 1, the absolute
concentration of hypophosphite in the bath expressed in mole/liter
may vary within the range from about 0.15 to about 1.20, and ratio
between the nickel cations and hypophosphite anions in the bath
expressed in molar concentrations may vary within the range from
about 0.25 to about 1.60. The lactic anion serves as a complexing
agent and may be derived from lactic acid or salts thereof, the
absolute concentration of lactic ions in the bath expressed in
mole/liter being within the range from about 0.25 to about 0.60.
The bath also includes an exalting additive, namely, the propionic
anion, which has a concentration in the bath expressed in
mole/liter in the range from about 0.025 to about 0.060. Other
exalting additives may be used in place of the propionic anion, the
exalting additive being selected from the group consisting of
simple short chain saturated aliphatic monocarboxylic acids,
including three to five carbon atoms and salts thereof. Further
details of the composition of the bath and the method of using the
same are set forth in the aforementioned U.S. Pat. No. 2,822,294
and the disclosure thereof is incorporated herein by reference.
The silicon carbide particles useful in the process of example 1
may have a particle size in the range from about 0.5 micron to
about 25 microns, in order to obtain good suspension of the
particles in the plating bath and in order to to obtain uniform
distribution of the particles in coating. Smaller particles inhibit
the plating action, due to close packing, while larger particles
are kept dispersed in the plating bath only with extreme
difficulty. The concentration of the silicon carbon carbide
particles in the plating bath should not exceed about 4 times the
weight of the nickel metal present in the bath expressed as free
metal, although smaller concentration of the silicon carbide
particles may be utilized, it being understood that the volume of
silicon carbide in the coating will be a function of the
concentration of the silicon carbide particles in the plating bath
as well as the effectiveness of the dispersion thereof. In example
1, the silicon carbide comprises about 15 percent by volume of the
wear-resistant coating, although it will be understood that the
volume of the silicon carbide particles may vary from as little as
1 percent up to as much as 40 percent of the volume of the
coating.
Other thicknesses of the coating may be provided, and the coating
may have a thickness in the range from about 5 microns to about 200
microns or more if desired.
Summarizing, with respect to example 1 above, there is provided a
process of "electroless" plating of a nickel-phosphorus alloy
coating on a workpiece, the coating containing silicon carbide
particles distributed therethrough and being a relatively thick
"dispersion hardened" metal deposit. The expression "electroless
plating" as used herein refers to the plating of metal coatings
without the application of an external electrical current, and
preferably by a chemical reduction of the electroless metal
utilizing an electroless reducing agent for the metal, thereby to
accomplish a process of electroless metallizing. The term
"dispersion hardened" as used herein refers to the described metal
coatings in which are embedded inert solid particles during the
laying down of the metal coating, the particles being partially or
completely embedded in and held in position by the coating.
The lead content of the nickel plating bath of example 1 performs
the important function of stabilizing the bath during the plating
operation. It will be understood that other types of stabilizers
and other amounts of stabilizers may be advantageously utilized in
connection with the present invention, suitable such stabilizers
being disclosed in U.S. Pat. No. 2,762,723 granted Sept. 11, 1958
to Paul Talmey and Gregoire Gutzeit, the disclosure of that patent
being incorporated herein by reference.
Alkaline nickel plating baths may be utilized advantageously in the
present invention, and particularly when coating certain plastics
and certain metals such as magnesium, examples of suitable alkaline
baths being set forth in U.S. Pat. No. 3,211,578 granted Oct. 12,
1965 to Gregoire Gutzeit, the disclosure thereof being incorporated
herein by reference.
In general any nonmetallic particle may be utilized as a
wear-resisting particle in the process of example 1, it simply
being necessary that the particles be essentially insoluble in the
plating bath and that the particles be noncatalytic and inert with
respect to the reducing of the metal salt by the electroless
reducing agent therefor. In this connection it is pointed out that
a wide variety of such nonmetallic wear-resisting particles may be
used, and more specifically, there may be used the following:
kaolin; glass flour, talc, synthetic organic plastic resin powders;
and oxides, carbides, nitrides, borides, silicides, sulfides,
silicates, sulfates, carbonates, phosphates, oxalates or fluorides
of aluminum, boron, chromium, hafnium, molybdenum, silicon,
titanium, tantalum, vanadium, tungsten, zirconium, nickel,
magnesium calcium, barium, strontium, cerium, iron or manganese.
The particle size of the wear-resisting particles may be of the
order of 0.01 micron to 100 microns, a preferred size being in the
range from about 0.5 micron to about 25 microns.
Furthermore, the particles must be essentially insoluble in the
plating bath, i.e., must have a very low solubility therein on the
order of no more than about 0.01 mole per liter. In addition, the
wear-resisting particles must be noncatalytic and inert with
respect to the reducing agent and the reaction of the reducing
agent with the coating metal in the bath, and also the particles
must not interfere with or stop the plating reaction. The
concentration of the wear-resisting particles in the plating bath
is preferably in the range from about 0.1 percent by weight of the
solids to about 2 percent by weight of the solids, but in any event
not more than 4 times the weight of the electroless plating metal
in the bath when the weight of the metal is expressed as the free
or reduced metal. In certain instances it may be desirable to
provide an acid or solvent wash to the particles before the
addition thereof to the plating bath, thereby to avoid
contamination and to increase the stability of the plating
bath.
Other suitable methods of maintaining the wear-resisting particles
in suspension may be used in addition to that described above with
respect to example 1. For example, a mixture of the plating
solution and the wear-resisting particles may be advantageously
pumped through the bottom of the plating vessel, the bottom of the
plating vessel being dish-shaped and symmetrical, whereby a uniform
stream of the plating bath with the wear-resisting particle
suspended and entrained therein is passed or flooded across the
surfaces of the workpiece being coated.
Another advantageous system for maintaining the wear-resisting
particles in suspension is to provide a symmetrical plating bath
having dispersed in the bottom thereof a spider including a number
of very small gas outlets therein. In this manner very fine air
bubbles can be introduced into the plating bath via the spider, the
air bubbles serving to hold the wear-resisting particles in
suspension throughout the plating solution. Other gases such as
nitrogen, or one of the noble gases, may be used in place of
air.
Yet another method of maintaining the wear-resisting particles in
suspension is to agitate and move the workpiece within the plating
solution, such movement of the workpiece causing currents in the
plating solution which tend to hold the wear-resisting particles in
suspension. Each of the above-mentioned alternative methods of
maintaining the wear-resisting particles in suspension has been
successfully utilized in conjunction with the process of example 1
above.
It will be appreciated that the process of example 1 is
particularly useful when applied to workpieces having surfaces that
are to be employed in sliding applications, such as slide bearings,
motor housings, shafts, and the like. It will be understood,
however, that the incorporation of the wear-resisting particles in
the electroless deposited metal coating affects other properties of
the coating in addition to the hardness and wear-resistance
thereof. In general the physical, chemical and electrochemical
properties of the coating are affected including the coefficient of
friction, the temperature stability of the coating, the oxidation
stability of the coating, the corrosion stability of the coating,
the reflectivity and/or gloss thereof, etc.
Turning now to a consideration of the electroless chemical nickel
plating baths useful in the present invention, there are a number
of suitable available compositions, such for example, as disclosed
in U.S. Pat. No. 2,532,283, granted on Dec. 5, 1950 to Abner
Brenner and Grace E. Riddell, U.S. Pat. No. 2,658,841, granted on
Nov. 10, 1953 to Gregoire Gutzeit and Abraham Krieg, or U.S. Pat.
No. 2,658,842 granted on Nov. 10, 1953 to Gregoire Gutzeit and
Ernest J. Ramirez.
The following are additional examples of such baths useful in the
present invention.
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EXAMPLE 2
Nickel chloride 30 g./1. Sodium acetate 13 g./1. Sodium
hypophosphite 10 g./1. pH 4 Temperature 95.degree. C.
__________________________________________________________________________
a plating bath as set forth above was placed in a symmetrical
plating vessel and there was added 240 grit silicon carbide
particles in an amount equal to 2 percent of the solids in the
plating bath. After an hour of plating, a rough dull coating having
a thickness of 0.65 mil was provided on a workpiece disposed
therein, the plating solution being continuously agitated by
stirring to hold the silicon carbide particles in suspension
therein. The resultant coating has the valuable properties as set
forth both with respect to the coating of example 1.
---------------------------------------------------------------------------
EXAMPLE 3
Nickel sulfate 30 g./1. Sodium citrate 100 g./1. Ammonium chloride
50 g./1. Sodium hypophosphite 10 g./1. pH 8-10 Temperature
95.degree. C.
__________________________________________________________________________
The plating process of example 1 was repeated utilizing the bath of
the above composition, there being produced on the workpiece an
electroless nickel coating having the silicon carbide particles
uniformly dispersed therethrough, the coating possessing the
valuable properties described with respect to example 1.
The hardness of the electroless nickel coatings incorporating
therein the silicon carbide particles as described in conjunction
with examples 1 to 3 above can be further hardened and rendered
even more wear-resistant by a heat treatment of the coating after
deposition thereof. There is disclosed in U.S. Pat. No. 2,908,419,
granted on Oct. 13, 1959 to Paul Talmey and William J. Crehan a
suitable heat treatment process to increase the hardness of such
electroless nickel coatings, and the disclosure of that patent is
incorporated herein by reference. The electroless nickel portion of
the coatings of examples 1 to 3 may contain from about 85 percent
to about 97 percent nickel and from about 3 percent to about 15
percent phosphorus by weight, certain of the baths such as that of
example 1 actually providing compositions in the range from 88
percent to 94 percent nickel and from about 6 percent to about 12
percent phosphorus by weight. The electroless nickel coating more
specifically after heat treatment constitutes a stable solid
characterized by the presence of substantial microcrystals of
nickel phosphide dispersed in a matrix of nickel metal and having a
resultant hardness as high as 1200 V.P.N. the hardness varying down
to about 575 V.P.N. depending upon the heating temperature and
time.
The following is an example of the heat treatment of the novel
coating of example 1.
EXAMPLE 4
A workpiece having a coating thereon produced as in example 1 was
gradually heated in an oven from 100.degree. C. to 400.degree. C.
for a period of 1 hour. At the end of the hour it was found that
the hardness of the electroless nickel portion of the coating was
1,081 V.P.N. and the wear-resistance was 1.9 TWI. This compared
with a TWI of 4.2 for the electroless nickel coating alone without
the addition of the wear-resisting particles thereto.
It will be appreciated that the coatings of examples 2 and 3 above
can be likewise heat-hardened by processing in accordance with
example 4 herein, and further as explained in the U.S. Pat. No.
2,908,419 referred to above.
It has been found that sulfides are also useful as wear-resisting
particles in the present invention, the following being examples of
the use of molybdenum sulfide particles as the wear-resisting
particles.
EXAMPLE 5
The plating bath and the coating process of example 1 were
duplicated but the plating bath had disposed therein 1 percent
weight of the dry solids of granulated molybdenum disulfide having
an average particle size of about 50 microns. There resulted from
one hour of plating a coating having a thickness of 0.78 mil and
possessing a rough texture. The hardness of the electroless nickel
coating was 508 V.P.N. and the wear-resistance thereof was 4.9 TWI.
The coated workpiece made in accordance with example 5 had good
lubricating properties imparted thereto by the molybdenum disulfide
and possessed the other advantages and properties as described
above with respect to example 4.
The coating of example 5 may also be heat-hardened, an example of
such a process being as follows:
EXAMPLE 6
workpiece with the coating of example 5 thereon was further
processed and heat treated as in example 4 above to provide a
heat-hardened coating having a hardness of 1018 V.P.N. and a wear
resistance of 1.1 TWI.
Metal oxides are examples of other wear-resisting particles which
are useful in carrying out the processes of the present invention.
The following is an example utilizing aluminum oxide particles:
EXAMPLE 7
The plating bath and process of example 1 was utilized but there
was substituted for the silicon carbide particles aluminum oxide
particles having a size of about 0.5 micron, and having a
concentration by weight of about 1 percent of the dry solids in the
plating bath. There was produced a bright coating of electroless
nickel having dispersed therethrough the aluminum oxide particles,
0.6 mil of the coating being produced in one hour's time. The
hardness of the coating in the nickel area was 572 V.P.M. and the
wear-resistance thereof was 9.8 TWI. The wear-resistant coating
made in accordance with example 7 had the other desirable
properties of the coating produced by the process of example 1 as
set forth above.
The process of example 7 was repeated utilizing a concentration of
the aluminum oxide particles of 0.1 percent by weight on a dry
basis of the solids in the plating bath. There resulted after one
hour of plating a coating having a thickness of 0.6 mil and a
hardness of 627 V.P.N. In another process in accordance with
example 7, the aluminum oxide particles were present in the plating
bath in a concentration of 2 percent by weight on a dry basis of
the solids, there resulting a rough coating having a thickness of
0.43 mil and a hardness of 642 V.P.N. In yet another variation of
the process of example 7, the aluminum oxide particles utilized had
a size of 0.05 micron and a concentration of 1 percent in the bath,
thereby to produce after one hour a bright coating having a
thickness of 0.67 mil and a hardness of 612 V.P.N.
Finally, there was carried out a variation of the process of
example 7, wherein the aluminum oxide particles had a size of 1
micron and were present in a concentration of 1 percent in the
bath, there resulting after 1 hour of plating a rough coating
having a thickness of 0.52 mil and a hardness of 572 V.P.N.
The coatings made in accordance with example 7 may also be
heat-treated to improve the wear-resistant properties thereof, the
following being an example of such a process.
EXAMPLE 8
A workpiece coated in accordance with the process of example 7 was
heat-treated in accordance with the process of example 4, the
resultant coating having a hardness of 1049 V.P.N. and a
wear-resistance of 4.6 TWI.
A wide variety of metal oxides may be utilized in the place of
aluminum oxide in examples 7 and 8, and more specifically, titanium
oxides may be utilized to provide a dull rough coating having a
thickness of 0.54 mil after 1 hour of plating and a hardness of 572
V.P.N. Tin oxide powder substituted for the aluminum oxide in
example 7 provided after 1 hour a bright coating having a thickness
of 0.59 mil and a hardness of 536 V.P.N. While chromium oxide when
substituted in example 7 in the form of a liquid containing
particles of 0.5 micron size after 1 hour produced a dull smooth
coating having a thickness of 0.69 mil and a hardness of 525
V.P.N.
Silicas having a small particle size comprise another class of
materials that are particularly useful as wear-resisting particles
in the processes of the present invention, examples of which are as
follows:
EXAMPLE 9
The process of example 1 was repeated using the bath thereof but
substituting silica as the wear-resisting particles therein, the
silica utilized being that sold under the trade designation "Syloid
244" and having a particle size in range 1-5 microns. After 1 hour
of plating with a 1 percent concentration of the silica in the bath
on a dry weight basis, there was produced a bright coating having a
thickness of 0.76 mil, a hardness of 525 V.P.N. and a
wear-resistance of 14.6 TWI. Comparable results were obtained
utilizing other synthetic silicas including that sold under the
trade designation "Syloid 266" and that sold under the trade
designation "QUSO G-30 ".
The coating of example 10 can be further hardened by heat treatment
thereof and the following is as example:
EXAMPLE 10
A workpiece carrying a coating made in accordance with example 9
was heat treated in accordance with example 4, and there resulted a
coating having a hardness of 1064 V.P.N. and a wear-resistance of 6
TWI.
The present invention is also particularly useful in applying
wear-resistant coatings to aluminum castings and forgings which
cannot be heat-hardened, but which have surfaces that must be
wear-resistant. The following is an example of the application of a
wear-resistant coating to an aluminum workpiece:
EXAMPLE 11
The plating bath of example 1 was modified by adding thereto 0.5
grams per liter of potassium fluoride dihydrate, the preferred
concentration being in the range from about 0.001 to about 0.04
mol./liter. An aluminum workpiece was then coated in accordance
with the process of example 1 to provide thereon a rough dull
coating having a thickness after 1 hour of plating of 0.54 mil, a
hardness of 508 V.P.N. and a wear-resistance of 4.5 TWI. It will be
appreciated that this workpiece has a bearing surface provided by
the coating that is materially more wear-resistant than either the
aluminum metal or the electroless nickel plate without the addition
of the silicon carbide particles thereto.
In certain instances, it is possible to heat treat aluminum base
workpieces, the following being an example of such a heat
treatment:
EXAMPLE 12
The aluminum workpiece of example 11 was heated to 175.degree. C.
for 1 hour to provide a heat-hardening of the coating thereon. More
specifically, the coating now had a hardness of 724 V.P.N. and a
wear-resistance of 3.2 even after this mild heat treatment of the
workpiece.
As noted above, the workpiece of examples 11 and 12 are rough and
dull in appearance. It has been found that if the surface of the
coating of example 11, i.e., without heat-treatment, is honed or
lapped to render the surface smooth, the wear-resistance thereof is
improved and more specifically the TWI is decreased to about
2.2.
Other carbides are useful as wear-resisting particles when applied
to aluminum base workpieces, the following being an example
thereof:
EXAMPLE 13
The process of example 11 was repeated, but there was substituted
for the silicon carbide particles therein tungsten carbide
particles having a size of 400 mesh maximum, the tungsten carbide
being that sold under the trade designation "Haynes Alloy No. 956."
The tungsten carbide particles were utilized in a concentration of
1 percent of the dry solids in the bath, and after 1 hour of
plating, there was provided a rough coating having a thickness of
0.45 mil, a hardness of 593 V.P.N., and a wear-resistance of 6.6
TWI.
The coating of example 13 can also be further hardened by heat
treatment thereof, the following being an example:
EXAMPLE 14
The aluminum workpiece with the coating of example 13 thereon was
heat treated by being heated to a temperature of 270.degree. C. for
16 hours. The heat treated coating was found to have a hardness of
1,145 V.P.N. and a wear-resistance of 2.1 TWI.
Certain metal sulfides may also advantageously be incorporated in
electroless nickel plating applied to aluminum base alloys, the
following being an example thereof:
EXAMPLE 15
The process of example 5 was repeated by substituting an aluminum
base workpiece for the steel workpiece thereof, whereby there was
provided after 1 hour of plating a rough coating having a thickness
of 0.78 mil, a hardness of 606 V.P.N. and a wear-resistance of
2.7.
The workpiece of example 15 if heat treated can have the hardness
of the coating thereon increased, the following being an
example:
EXAMPLE 16
The aluminum base workpiece carrying the coating of example 15 was
heated to 270.degree. C. for a period of 8 hours to provide a
heat-hardened coating having a hardness of 927 V.P.N. and a
wear-resistance of 1.5 TWI.
In the above examples, metallizing baths have been illustrated
wherein nickel cations have been chemically reduced by
hypophosphite anions. It will be understood that other electroless
reducing agents may be utilized, the following being an example
thereof:
EXAMPLE 17
There was provided an electroless nickel plating bath having the
following composition and characteristics:
Nickel chloride 30 g./1. Sodium citrate 10 g./1. Sodium acetate 20
g./1. Sodium succinate 20 g./1. N-diethylborazane 30 ml./1. Lead
chloride 0.01 g./l. Methanol 50 ml./l. pH 6 Temperature 65.degree.
C.
a quantity of silicon carbide particles was added to the above
plating bath with a concentration of 1 percent of the dry
ingredients in the bath, the silicon carbide having a size of grit
600. A steel workpiece was immersed in the plating bath and the
particles were held in suspension by stirring of the bath. After 1
hour, there was provided a coating of electroless coating on the
workpiece, the coating having dispersed therein silicon carbide
particles. The coating had all of the useful characteristics and
advantages described above with respect to the coating produced by
the process of example 1.
Other borazane reducing agents may be used in place of that set
forth in example 17 above. In general, any aklkyl-borazane may be
used, another preferred reducing agent being dimethyl-borazane.
Also useful is sodium borahydride.
The present invention is also applicable to processes wherein other
metals are plated by electroless plating, the following being
examples of the plating of cobalt coatings on steel workpieces and
incorporating in the coatings wear-resisting particles, all in
accordance with the present invention.
EXAMPLE 18
There was formulated an electroless cobalt plating solution having
the following composition and characteristics:
Cobalt chloride 35 g./1. Sodium acetate 20 g./1. Sodium
hypophosphite 10 g./1. pH 4.5 Temperature 95.degree. C.
there was added to this solution 1 percent by weight of the dry
ingredients thereof of silicon carbon particles having the size of
600 grit. After 1 hour of plating during which the solution was
thoroughly agitated uniformly to suspend the silicon carbide
particles, there was produced on the surface of the workpiece an
electroless cobalt coating having uniformly dispersed therethrough
silicon carbide particles. The resultant coating had the desirable
characteristics described above with respect to the coating
produced by the process of example 1.
EXAMPLE 19
A plating solution having the following composition and
characteristics was formulated:
Cobalt sulfate 30 g./l. Sodium citrate 110 g./l. Ammonium chloride
45 g./1. Sodium hypophosphite 12 g./l. pH 9 Temperature 95.degree.
C.
There was added to the plating solution silicon carbide particles
in a concentration of 1 percent of the dry ingredients of this
plating solution, the particles having the size of 600 grit. A
steel workpiece was placed in the plating solution and the solution
was vigorously stirred to suspend the silicon carbide particles
uniformly therethrough; after an hour, there was produced on the
surface of the workpiece a coating of electroless cobalt having
silicon carbide particles uniformly dispersed therethrough. The
coating had all of the desirable characteristics and advantages of
the coating of the process of example 1, described above.
Two electroless metals may be codeposited from an electroless
plating solution as is known in the art and such plating solutions
are useful in carrying out the process of the present invention,
the following being examples thereof:
EXAMPLE 20
An electroless plating solution was formulated having the following
composition and characteristics:
Nickel chloride 20 g./1. Cobalt chloride 10 g./1. Sodium citrate 20
g./1. Sodium hypophosphite 10 g./1. pH 4.2 Temperature 95.degree.
C.
to the plating solution there was added silicon carbide particles
in a concentration of 1 percent of the dry ingredients by weight,
the particles having the size of 600 grit. A steel workpiece was
immersed in the plating solution while the plating solution was
vigorously stirred so as uniformly to suspend the silicon carbide
particles throughout the volume thereof. After an hour of plating,
there was provided on the workpiece a nickel-cobalt coating having
uniformly dispersed therethrough silicon carbide particles. The
resultant coating had the several desirable properties and
characteristics discussed above with respect to the coating
produced by the process of example 1.
EXAMPLE 21
An electroless plating solution was formulated having the following
composition and characteristics:
Nickel sulfate 25 g./l. Cobalt chloride 5 g./l. Ammonium chloride
60 g./l. Sodium hypophosphite 15 g./l. pH 9.5 Temperature
95.degree. C.
to this plating solution was added silicon carbide particles in a
concentration of 1 percent by weight of the dry ingredients
therein, the particles having a size of 600 grit. A steel workpiece
was immersed in the plating solution while the solution was
vigorously agitated to maintain the silicon carbide particles in
suspension throughout the solution during the coating of the
workpiece. After an hour, the workpiece had thereon a nickel-cobalt
coating having silicon carbide particles uniformly dispersed
therethrough. The coating was wear-resistant and had the desirable
properties and characteristics discussed above with respect to the
coating produced by the process of example 1.
It will be understood that the hardness and wear-resistance of the
coatings of examples 17 through 21 can be improved by heat
treatment thereof, i.e., by the heating thereof to an elevated
temperature for a sufficient period of time to effect a
heat-hardening thereof.
The following is an example of yet another electroless metal and an
electroless plating solution useful in carrying out the present
invention:
EXAMPLE 22
An electroless plating bath was formulated having the following
composition and characteristics:
Copper sulfate 20 g./l. Triethanolamine 100 g./l. Formaldehyde
solution 20 ml./l. pH 12.5 Temperature 25.degree. C.
there was added to the electroless plating solution silicon carbide
particles in a concentration of 1 percent by weight of the dry
ingredients in the solution, the silicon carbide particles having a
size of 600 grit. A steel workpiece was immersed in the plating
solution and the solution was vigorously agitated to maintain the
silicon carbide particles in suspension throughout the solution
during the coating of the workpiece, After an hour, the workpiece
had an appreciable coating thereon of copper having dispersed
uniformly therethrough silicon carbide particles. The resultant
coating had the hardness and wear-resistance and other desirable
properties and characteristics discussed above with respect to the
coating provided by the process of example 1.
The following are yet other examples of workpieces which may be
successfully coated utilizing the present invention, the chemical
composition being other than the steel and aluminum given in the
above specific examples.
EXAMPLE 23
The process of example 1 was repeated using a workpiece consisting
of copper with essentially the same results in regard to the
wear-resistance of the coating obtained.
EXAMPLE 24
The process of example 1 was repeated using a workpiece consisting
of brass with essentially the same results in regard to the
wear-resistance of the coating obtained.
EXAMPLE 25
Example 25
The process of example 1 was repeated using a workpiece consisting
of beryllium alloy with essentially the same results in regard to
the wear-resistance of the coating obtained.
Example 26
The process of example 1 was repeated using a workpiece consisting
of nickel with essentially the same results in regard to the
wear-resistance of the coating obtained.
EXAMPLE 27
The process of example 17 was repeated using a workpiece of
magnesium. The coating had all of the characteristics described
above with respect to the wear-resistance of the coating of example
17.
Yet other wear-resisting particles may be utilized advantageously
in the present invention as follows:
EXAMPLE 28
The electroless plating bath of example 1 was utilized in the
process of example 1, but 1 percent by weight on the dry basis of
boron nitride was substituted for the silicon carbide therein. The
coating obtained after one hour of plating had much improved
wear-resistance due fundamentally to the lubricating properties of
the boron nitride particles.
EXAMPLE 29
The plating solution and the process of example 1 were repeated but
there was substituted for the silicon carbide therein 1 percent by
weight of "Microthene FN-510," a polyethylene resin powder having a
particle size in the range less than 30 microns. There was obtained
an electroless metal coating which had improved wear-resistance due
to the incorporation of the plastic particles therein.
It will be understood that the wear-resisting properties of the
coatings made in accordance with the present invention may be
derived from both the incorporation of hard particles therein and
the incorporation of lubricating particles therein. The following
is an example of such a process and coating derived therefrom.
EXAMPLE 30
The plating bath and the process of example 1 were utilized but
there was in addition added thereto 1 percent by weight on a dry
basis of molybdenum disulfide having a particle size of about 50
microns. The resultant coating had much improved wear-resistance,
the wear-resistance being imparted thereto both by the hard silicon
carbide particles and the lubricating molybdenum disulfide
particles.
From the above, it will be seen that there have been provided
processes for electroless metallizing of workpieces to provide
thereon metal coatings incorporating therein wear-resisting
particles, which processes fulfill all of the objects and
advantages set forth above. In addition, the processes provide
coated workpieces with the improved coatings thereon, all in
accordance with the objects set forth above.
While there have been described what are at present considered to
be certain preferred embodiments of the invention, it will be
understood that various modifications may be made therein, and it
is intended to cover in the appended claims all such modifications
as fall within the true spirit and scope of the invention.
* * * * *