Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~478q,~
The present invention relates to a process ~or coating
inorganic substrates with carbides, nitrides or carbonitrides
or mixtures thereof.
It has been found that inorganic substrates can be
coated in a simple manner ~1ith carbides, nitrides or carb-
nitrides or mixtures thereof, of iron, boron or silicon or
of the transition metals of sub-groups 4-6 of the periodic
table by direct thermal reaction of iron, boron, silicon or
transition metals of s~lb-groups 4-6 of the periodic table or
derivatives thereof with substances which act as sources of
carbon and nitrogen? if desired in the presence of further
additives, by using, as sources of carbon and nitrogen, at
least one compound of the formula I or II
X - C - N or N ~ C - Xl - C - N
(I) (II)
wherein X represents chlorine, -CN, -CH2-NH-CH2CN,
CH2CN
-CH N(CH2CN)2, -CH2-N-CH2CH2-N(CH2CN)2, Y
1-6 carbon atoms, which can be substituted by halogen atoms,
Rl
-N\ or -N ~ CH2)m groups, an alkenyl group with 2-4
R2
carbon atoms which can be substituted by halogen atoms or
~Rl
-N groups, a cycloalkyl group with 3-6 carbon atoms or an
R2
- 2 -
` , ' ., .
109L7~399
~ryl group wi t~l G-10 caIbon a~oms, which can each be sub-
~lt~ted by llalogen atoms, methyl groups or
/~l
-~ g~oups, an~ Xl represents an alkylene group with 1-10
R~
~arban at~m~, an alken~lene group with 2-4 carbon atoms, a
phenylene or cyclohexylene group which can each be sub--
jRl~tlt~ted by halogen atoms or -N\ groups, or a group of the
for~:la R2
--~H,~CH2-- /CN or ~C-~>=c~N
CN CN
~nd ~ ~nd R2 ~ndependently of one another denote hydrogen
or an alkyl group with 1-4 carbon atoms and m deno-tes an
lnteger ~rom 4 to 7.
Compared to known methods, the process according to
tha ln~entioll is di8tinguish~d, above all, by its simplicity
~nd 0con~my~ in that the elements carbon and nitrogen req~lred
to fo~m ~he carbide8, nitride~ or carbonitrides or mixtures
thereof,and,if desired other elements which influence the
course of the reaction, such as hydrogen or halogen or both,
can be ~ed to the reaction zone in a simple manner and in the
desired ratios. Furthermore high deposition rates and smooth
coatings of good to very good adhesion can be achieved in
accordance with the process of the invention,regardless of the
type of substrate and even at reaction temperatures below approx.
.
'-
~04789~9
900C. A further advantage is that the process can in
general be carried out at normal pressure or slightly
reduced or slightly ele~ated pressure (approx. 700-800 mm Hg)
which in many cases permits simplification of the apparatuses
required to carry out the reaction.
The compounds of the formula I and II provide carbon
and nitrogen, and where relevant hydrogen and/or halogen, in
a reactive state, under the reaction conditions.
Alkyl, alkenyl, alkylene and alkenylene groups
' represented by X or Xl, or Rl and R2, can be straight-chain
or branched. Halogen denotes fluorine, bromine or iodine,
but especially chlorine.
Examples of unsubstituted alkyl groups X according to
the definition are the methyl, ethyl, n-propyl, isopropyl, n-
butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl and n-hexyl
group.
If groups according to the definltion and represented
~r by X or Xl are substituted by
-N \ groups, Rl and R2 preferably denote, independently of
.. R2
one another, hydrogen or the meth ~ r ethyl group.
` Preferred substituents -N (CH2)m are those wherein m
represents an integer from 4 to 6.
r, Preferred compounds of the formula I are those wherein
X denotes -CH2-NH-CH2CN, -CH2-N~ CH2CN)2,
-CH2-~N-CH2CH2-N---~CH2CN)2, an alkyl group with 1-6 carbon
CH2CN ~ / 1
atoms which can be substituted by halogen atoms, -N
- -- 4 --
.;
:
1047~399
or - ~ CHz)m groups, an alken-yl group with 2-4 carbon atoms
which can be substituted by halogen atoms or
~Rl
-N~ groups, a cycloalkyl group with 3-6 carbon atoms or an
aryl group with 6-10 carbon atoms which can each be substituted
~Rl
by halogen atoms, methyl groups or -N\ groups, and Rl and
. R2
R2 independently of one another represent hydrogenor an alkyl
group with 1-4 carbon atoms and m represents an integer from
4 to 7.
According to a further preference, X represents an
alkyl group with 1-4 carbon atoms which can be substituted by
chlorine atoms or _N\ 1 groups, an alkenyl or chloroalkenyl
group with 2-4 carbon atoms or a phenyl group which can ~e
substituted by halogen atoms, methyl groups or _N\ 1 groups,
R2
and Rl and R2 independently of one another denote hydrogen
or an alkyl group with 1 or 2 carbon atoms.
The compounds of the formula II which are used are
advantageously those wherein Xl represents an unsubstituted
alkylene group with 1-4 carbon atoms, an unsubstituted
phenylene or cyclohexylene group or a group of the formula
\C-C/
CN - ~
The use of acetonitrile, propionitrile, acrylonitrile,
succinodinitrile, adipodinitrile or tetracyanoethylene as
-- 5 --
,, ' : '
', : - ~ . ,~' .
.
104789'~
compounds of the formula I or II is very particularly pre-
ferred.
The compounds o~ the formula I and II are known or
can be manufactured in a known manner. The following may be
mentioned specifically as compounds of the formula I or II~
cyanogen chloride, cyanogen, bis-cyanomethylamine (iminodi-
acetonitrile), tris-cyanomethyl-amine (nitrilotriacetonitrile),
N,N,N',N'-tetrakis-(cyanomethyl)-ethylenediamine (ethylene-
diamine-tetraacetonitrile), acetonitrile, monochloroaceto-
nitrile, dichloroacetonitrile and trichloroacetonitrile,
aminoacetonitrile, methylaminoacetonitrile, dimethylamino-
acetonitrile, propionitrile, 3-chloropropionitrile, 3-bromo-
propionitrile, 3-aminopropionitrile, 3-methylaminopropionitrile,
3-dimethylaminopropionitrile and 3-diethylaminopropionitrile,
butyronitrile, 4-chlorobutyronitrile, 4-diethylaminobutyro-
nitrile, capronitrile, isocapronitrile, oenanthonitrile, N-
pyrrolidino-, N-piperidino- and hexamethyleneimino-aceto-
nitrile, 4-(N-pyrrolidino)-, 4-(N-piperidino)- and 4-(N-
hexamethyleneimino)-butyronitrile, acrylonitrile, a-meth-
acrylonitrile, 2-chloroacrylonitrile, 3-vinylacrylonitrile,
cyclopropanecarboxylic acid nitrile, cyclopentanecarboxylic
acid nitrile, cyclohexanecarboxylic acid nitrile, chloro-
cyclohexanecarboxylic acid nitrile, bromocyclohexanecar-
boxylic acid nitrile or methylcyclohexanecarboxylic acid
nitrile, 4-(N,N-dimethylamino)-cyclohexanecarboxylic acid
nitrile, benzonitrile, 1- or 2-naphthonitrile, 2-, 3- or 4-
chlorobenzonitrile, 4-bromobenzonitrile, o-, m- or p-tolu-
nitrile, aminobenzonitrile, 4-dimethylaminobenzonitrile and
.
.-
' . ' '''
.
.
~ L047899
4-diethylaminobenzo-nitrile, malodinitrile, chloromaleodinitrile,
fumarodinitrile, succinodinitrile, glutarodinitrile, 3-methyl-
glutarodinitrile, adipodinitrile, pimelodinitrile, decanoic
acid dinitrile, dodecanoic acid dinitrile, undecanoic acid
dinitrile, 2-methylene-glutarodinitrile (2,4-dicyano-1-
butene), 3-hexenedicarboxylic acid dinitrile (1,4-dicyano-2-
butene), phthalodinitrile, 4-chlorophthalodinitrile, 4-amino-
phthalodinitrile, isophthalodinitrile, terephthalodinitrile,
hexahydroterephthalodinitrile, tetracyanoethylene, 1,2-bis-
(cyanomethyl)-benzene and 7,7,8,8-tetracyano-quinodimethane
[2,5-cyclohexadiene-~1'a 4'a -dimalononitrile].
Examples of transition metals of sub~groups 4-6 of the
periodic table which can be used in the process according to
the invention are titanium, zirconium, hafnium, vanadium,
niobium, tantalum, chromium, molybdenum, tungsten and uranium.
Preferred elements are iron, uranium, tantalum, vanadium and
tungsten, but especially boron, silicon and titanium.
The iron, boron and silicon and the transition metals
of sub-groups 4-6 of the periodic table can be employed in
any desired form, for example in the form of the elements.
However, they are-conveniently used in the form of derivatives,
especially in the case of the transition metals according to
the definition. Examples of suitable derivatives are
hydrides, carbonyls, carbonyl-hydrides, organometallic com-
' pounds and halides, such as silicon hydride (SiH4), titanium
hydride (TiH2), zirconium hydride (ZrH2), boranes, chromium
hexacarbonyl, molybdemlm hexacarbonyl and tungsten hexa-
carbonyl, iron pentacarbonyl [Fe(CO)5], FeH2(CO)4, tetra-
-- 7 --
,.
,',: ~ :
.
,: :
' ' : ' ' ~.'' : ' .' ~ ' ' ~
1~ 47 8 9~
ethyltitanium, te~netllylsllane and tetraethyl~ e, Inethyl-
dlchloro~llane~ ~richlorosil~le, methyl-tricllloro~llane, et~lyl-
~rlchloro3ilane, trlmet~lylchloro~ilane, boron tric~oride,
sllloon tetrac~oride, ti~anium dlbromlde, tit~nium trichlorlde,
tltanlu~ tetrac~orlde and titanium tetrabromlde, zirconium
tetr~chloride, vanadium trichlorlde and vanadium tetrachlorlde,
nioblum pentachloride, t~ntalum pentachloride, chromlum trl-
chlor~de, tungsten hexachloride and tungsten hexafluoride,
Iron-~I chloride and lron Il~ chloride, uranium te trachlorlde
an~ ~ra~ium hexafluorlde.
~ he hallde~, e~peclally the chlo~ldes, abo~e all tho~e
Of boron~ sllicon and the tr~nsltion met~ls, are p~eferr~d.
Boron trlohlor~de, ~lllcon tetrachlorld~ and titan~um te~ra-
~hlor~de are very par~ic~larly preferred.
~ ep~nding on the end use and/or the type of compound
Of th~ formula ~ or II, it can be desira~le to carry out the
re~c~on ln the presence of further Addltives~ such as hydro-
~sn~ bydrogen chloride, ~tomic or molecular nltrogen or other
~o~pound~ which ae~ as sources of nltrogen or carbon or
mixtures thereof under the reaction conditions. These sub-
stances or compounds can contribute to the formation of the
carbides, nitrides or carbonitrides or shift the equilibrium
of the formation reaction more towards the nitrides or the
carbides. Examples of such additional compounds which act as
sources of nitrogen or carbon or mixtures thereof under the
reaction conditions are methane, ethane, n-butane, N-methyl-
- amine, N,N-diethylamine, ethylenediamine, benzene and ammonia.
The coating, according to the invention, of inorganic
- 8 -
,, , ~, . . . ~ . . . _ .
1047~9C~
substrates with carbides, nitrides or carbonitrides or mix-
tures thereof can be carried out, within the scope of the
definition, in accordance with any desired methods which are
in themselves known.
One of the mos-t important processes is the chemical
deposition from the gas phase, also referred to as the CVD
process (chemical vapour deposition). The reaction in the
gas phase can be carried out wi-th application of heat or
radiant energy. In this process, the iron, boron and sili-
con or the transition metals, and the compounds of the formula
I or II, are usually employed in the form of gaseous com-
pounds. The reaction temperatures are in general between
about 500 and 1,800C, preferably between 800 and 1,500C.
Hydrogen is preferably used as the reducing a~ent.
~n certain cases it can also be advantageous to use a carrier
gas, such as argon, to transport the starting materials into
the reaction zone.
According to another method, the substrates to be
coated can also be covered with mixtures of materials, for
example powder mixtures, or be mixed, and optionally compacted
with other materials which contain all or - preferably - some
of the starting materials required to form the carbides,
nitrides or carbonitrides.
Thereafter, the whole is heated, preferably to temperatures
of between 500 and 2,000C, the heating being carried out,
in accordance with the composition of the mixture of materials,
in the presence of the starting materials which are as yet
lacking in the mixture, that is to say in the presence of a
gaseous compound of the formula I or II or in the presence of
_ 9 _
s
~: - - - .. . .
1047899
suitable derivatives, in the gaseous state, of iron, boron or
silicon or of a transition metal.
The coating of the substrates with carbides, nitrides
or carbonitrides or mixtures thereof can also be carried out
by r~action of the starting materials in a plasma, for example
by so-called plasma spraying. The plasma can be produced in
any desired manner, for example by means of an electric arc,
glow discharge or corona discharge. The plasma gases used
are pre~erably argon or hydrogen.
Coatings according to the definition can furthermore
be produced in accordance with the flame spraying process,
-wherein hydrogen/oxygen or acetylene/oxygen flames are
generally used.
A further method is to impregnate the substrate which
. ls to be coated with a solution or suspension of a suitable
j. derivative of iron, boron or silicon or of a transition metal
and subsequently to react the impregnated material, at
elevated temperatures, with a compound of the formula I or II.
. The process according to the invention is preferably
carried out in accordance with the CVD technique.
Inbrganic substrates which can be coated with the aid
of the process according to the invention are above all
metallic and metalloid substrates, sintered metal carbides
. and carbon materials of any desired typè, which can also con-
tain incompletely pyrolysed constituents, such as glassy
, (amorphous) carbon, partially graphitised carbon and graphite.
The process according to the invention is also suitable for
coating ceramic substrates, glasses, oxides, nitrides and
s -- 10 --
~9 .
- ~ - ,,,
,, ,
,... -
~0478991
carbides.
Exarnples of metallic substrates are ferrous metals,
such as steel and cast iron, t:itanium, and high-melting
metals, such as tungsten, molybdenum, niobium, vanadium and
tantalum. Examples of suitable me-talloids are boron and
silicon, whilst suitable sintered metal carbides, that is to
say sintered materials consisting of carbides of the transi-
tion metals of sub-groups 4-6 of the periodic table and
cobalt as the binder,are above all alloys of tungsten car-
bide/cobalt, tungsten carbide/tantalum carbide/cobalt,
tungsten carbide/titanium carbide/cobalt, tungsten carbide/
vanadium carbide/cobalt, tungsten carbide/titanium carbide/
tantalum carbide/cobalt, tungsten carbide/tantalum carbide/
niobium carbide/cobalt and tungsten carbide/titanium carbide/
tantalum carbide/niobium carbide/cobalt. Examples of suit-
able ceramic substrates and oxides are porcelain, chamotte
and clay materials, or aluminium oxide, SiO2 and zirconium
dioxide. Examples of nitrides and carbides are Si3N4, SiC
and chromium carbides.
If carbon materials are used as substrates, a con-
siderable improvement in the oxidation resistance and
corrosion resistance of the carbon materials can in some cases
be ~chieved by coating the materials in accordance with the
invention.
The substrates can consist wholly or partially of one
or more of the materials mentioned and can be in any desired
form, for example in the form of powders, fibres, foils,
filaments, machined articles or components of very diverse
-- 11 --
~. .
. ,
104~899~
types.
Depending on the choice of the starting materials and
additives, the reaction temperatures or tne substrates, or
both, carbides, nitridesJ carbonitrides or mixtures thereof
-are formed in accordance with the process of the invention.
. The principal fields in which the process according
to the invention is applied are: the surface improvement or
surface hardening of metals and sintered metal carbides to
increase the wear resistance and corrosion resistance, for
example in the case of tool steel, cast iron, titanium,
metal substrates containing -titanium, sheet tantalum, sheet
vanadium and sheet iron and sintered metal carbides of the
abovementioned type, such as WC-Co alloys, for example for
use in lathe tools, press tools, punches, cutting tools and
drawing dies, engine components, precision components for
watches and textile machinery, rocket jets, corrosion-
resistant apparatuses for the chemical industry, and the like; -
the coating of carbon electrodes and graphite electrodes, of
carbon fibres, including so-called "chopped fibres", to pro-
~ect the fibres, to improve the adhesion and wettability by
the metal matrix and to prevent undesired reactions between
the carbon fibres and the metal matrix, of carbon-carbon
composites, above all for turbine construction, of graphite
seals and the like; the coating of ceramic materials or
glasses, for example ceramic supports for catalysts and-
filter glasses, and, finally, the coating of boron, silicon
and tungsten fibres or filaments to achieve better wettability
by the metal matrix, and to protect the fibres.
'','~
,, ,
,
'
.
)4789~
Depen~ing on the choice of -the starting materials,
additives ~ld reaction temperatures, carbides, nitrides,
carbonitrides or mixtures -thereof are formed in accordance
with the process of the invention.
Example 1
The experiments are carried out in a vertical CVD
reactor of Pyrex glass ("Pyrex" is a trade mark) which is
closed at the top and bottom by means of a flange lid. The
reaction gases are passed into the reactor through a spray-
head, to achieve a uniform stream of gas. The ~emperature
on the substrate is measured by means of a pyrometer. The
compounds'of the formula I or II are - where necessary -
vaporised in a vaporiser device inside or outside the reactor.
The substrate can be heated by resistance heating,
high frequency heating or inductive heating or in a reactor
externally heated by means of a furnace.
A steel wire of diameter 0.78 mm (1%
by weight of C, 0.1% by weight of Si, 0.25% by weight of Mn,
0.1~ by weight of V) is heated to 950C by resistance heating
in an argon atmosphere in an apparatus of the type described
~bove. At this temperature, a gas mixture consisting of
95~ by volume of hydrogen, 2.4% by volume of argon, 1% by
volume of titanium tetrachloride and 1.6% by volume of cyano-
gen chloride is passed over the substrate in the course of 30 '
minutes, the total gas flow being 0.21 litre/minute [l/min.]
and the internal pressure in the reactor being 720 mm Hg.
After this period, a dark yellow layer has formed on the sub-
strate. Layer thickness approx. 12 ~m; Vickers micro-hardness
,
~ 13 ~
. .
~. . ' ... .. , .'.. ~.', .j .
1047899
HVo 015 = 2,270 kg/cm .
Example 2
A steel wire of 0.78 mm d~iameter is provided, by the
CVD process, with a 6 ~m thick layer of chromium carbide.
This coated steel wire is then treated~by the method described
in Example 1, for 2 hours at 950C/720 mm Hg, with a gas mix-
ture consisting of 97% by volume of hydrogen, 1% by volume of
titanium tetrachloride and 2% by volume of propionitrile
(total gas flow 1.03 l/min~). A dark grey layer, approx.
30 ~m thick, having a micro-hardness HVo-025 = 2,280 kg/mm2,
forms.
Examples 3 - 31
The Table I which follows lists further substrates
which were coated in the manner described above.
.. . .
- 14 -
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- 19- 10~7899
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10478919
Example 32
.
A graphite rod of 2 mm diameter is heated by resistance
heating to 950C in an argon atmosphere in an apparatus of the
type described in Example 1. At this temperature, a gas mix-
ture consisting of 97% by volume of hydrogen, 2% by volume of
acetonitrile and 1% by volume of titanium te-trachloride is
passed over the substrate for 2 hours, the total gas flow being
1.03 litre/minute [l/min.] and the internal pressure in the
reactor being 720 mm Hg. After this time, a grey-violet,
hard layer has formed on the graphite rod. The layer, which
adheres very firmly, is 70 ~m thick and has a Vickers micro-
hardness of HVo 01 > 4,000 kg/mm .
~ Example 33 -
i~ A graphite rod of 2 mm diameter is heated to 950C in
~;
an argon atmosphere in an apparatus of the type described above.
At this temperature, a gas mixture consisting of 94.4% by
volume of hydrogen, 2.3% by volume of argon, 1.4% by volume of
titanium tetrachloride and 1.9% by volume of cyanogen chloride
is passed over the substrate for 1 hour, the total gas flow
being 0.21 l/min. and the internal pressure in the reactor
~; .
being 720 mm Hg. After this time, a grey, hard layer has
formed on the graphite rod. The layer, which adheres very
firmly, is 30 ~m thick and has a Vickers micro-hardness of
s HVo-05 = 3,700 kg/mm .
Examples 34 - 46
Table II which follows lists further carbon materials
which were coated in the manner described above:
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1~47899
Example 47
The experiment is carried out in a plasma reactor using
a plasma torch of conventional construction [Model PJ 139 H of
Messrs. Arcos, Brussels; torch rating: 7.8 kw (30 V, 260 A)].
The reactor is located in a water-cooled reaction chamber of
stainless steel, sealed from the outside atmosphere. The
plasma is produced by a DC light arc formed between the tung-
sten cathode and the copper anode of the plasma torch. The
cathode and anode are also water-cooled. Argon or hydrogen
can be used as plasma gases. The reaction gases are introduced
into the plasma beam with the aid of a carrier gas, through
lateral bores in the outlet jet of the copper anode. The con-
centration of the reaction gases in the stream of carrier gas
is adjusted by means of thermostatically controllable vaporiser
devices a~d flow regulators. The substrate, which under
certain circumstances can be water-cooled, is at a distance of
1-5 cm in front of the outlet orifice of the plasma beam in
the copper anode.
At the beginning of the experiment, the reaction chamber
is evacuated, flushed and filled with argon. The plasma gas
(argon, 90 mols/hour) is then introduced and the plasma flame
is lit. A graphite substrate is located at a distance of 2 cm
from the outlet orifice of the plasma beam and the reaction
gases and the carrier gas are introduced into the plasma beam
as follows: titanium tetrachloride: 0.02 mol/hour; carrier
gas (hydrogen) for TiCI4: 1 mol/hour; acetonitrile: 0.05 mol/
hour; carrier gas (argon) for acetonitrile: 0.25 mol/hour.
The temperature of the plasma flame is above 3,000C; the
- 24 -
.
, - - : - , : .
,
1~4789~
temperature of the substrate surface is approx. 2,500C.
After a reaction time of 15 minutes the plasma torch is
s~itched off and the coated substrate is cooled in the gas-
filled reaction chamber. A homogeneous, grey, well-adhering
layer having a metallic gloss is obtained; thickness 4 ~m;
composition as determined by X-ray diffraction: TiC (lattice
constant a = 4.33 ~).
Example 48
An aluminium oxide substrate is treated analogously
to the method described in Example 47. The temperature of the
substrate surface during coating is approx. 1,900C. A hard,
relatively porous layer is obtained, which is built up of
several zones of different colour. The outermost 7 grey layer
has a lattice constant a = 4.31 ~.
.
- 25 -
.
