U.S. patent application number 13/768040 was filed with the patent office on 2013-08-29 for plasma spray method.
This patent application is currently assigned to Sulzer Metco AG. The applicant listed for this patent is Forschungszentrum Julich GmbH, Sulzer Metco AG. Invention is credited to Malko Gindrat, Andreas Hospach, Georg Mauer, Karl-Heinz Rauwald, Detlev Stover, Robert Vassen, Konstantin von Niessen.
Application Number | 20130224393 13/768040 |
Document ID | / |
Family ID | 45656508 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130224393 |
Kind Code |
A1 |
Hospach; Andreas ; et
al. |
August 29, 2013 |
Plasma Spray Method
Abstract
The invention relates to a plasma spray method which can serve
as a starting point for a manufacture of metal nanopowder, nitride
nanopowder or carbide nanopowder or metal films, nitride films or
carbide films. To achieve an inexpensive manufacture of the
nanopowder or of the film, in the plasma spray in accordance with
the invention a starting material (P) which contains a metal or
silicon oxide is introduced into a plasma jet (113) at a process
pressure of at most 1000 Pa, in particular at most 400 Pa. The
starting material (P) contains a metal or silicon oxide which
vaporizes in the plasma jet (113) and is reduced in so doing. After
the reduction, the metal or silicon which formed the metal or
silicon oxide in the starting material is thus present in pure form
or in almost pure form. The metal or silicon can be deposited in
the form of nanopowder or of a film (124). Nitride nanoparticles or
films or carbide nanoparticles or films can be generated
inexpensively by addition of a reactant (R) containing nitrogen or
carbon.
Inventors: |
Hospach; Andreas; (Julich,
DE) ; Vassen; Robert; (Herzogenrath, DE) ;
Mauer; Georg; (Tonisvorst, DE) ; Rauwald;
Karl-Heinz; (Julich, DE) ; Stover; Detlev;
(Niederzier, DE) ; von Niessen; Konstantin;
(Buttwil, CH) ; Gindrat; Malko; (Wohlen,
CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Forschungszentrum Julich GmbH;
Sulzer Metco AG; |
|
|
US
US |
|
|
Assignee: |
Sulzer Metco AG
Wohlen
CH
Forschungszentrum Julich GmbH
Julich
DE
|
Family ID: |
45656508 |
Appl. No.: |
13/768040 |
Filed: |
February 15, 2013 |
Current U.S.
Class: |
427/452 ;
427/453 |
Current CPC
Class: |
C01B 21/076 20130101;
C22C 29/06 20130101; C23C 14/228 20130101; C01B 21/0821 20130101;
C22C 29/16 20130101; C22C 14/00 20130101; C23C 16/513 20130101;
C23C 4/08 20130101; C22C 27/00 20130101; C23C 16/06 20130101; C22C
16/00 20130101; C23C 14/0021 20130101; B22F 9/14 20130101; B22F
2202/13 20130101; B82Y 30/00 20130101; B22F 1/0018 20130101; C01B
21/0828 20130101; C23C 4/134 20160101; C23C 4/137 20160101; C23C
14/14 20130101 |
Class at
Publication: |
427/452 ;
427/453 |
International
Class: |
C23C 4/12 20060101
C23C004/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2012 |
EP |
12156660.8 |
Claims
1. A plasma spray method, in which a starting material is
introduced into a plasma jet generated by a plasma generator at a
process pressure in a process chamber of at most 1000 Pa, wherein
the starting material contains a metal or silicon oxide which is
vaporized in the plasma jet and is therefore reduced in so
doing.
2. A plasma spray method in accordance with claim 1, characterized
in that the starting material is composed only of metal oxide of a
single metal.
3. A plasma spray method in accordance with claim 2, characterized
in that the starting material is introduced into the plasma jet as
a powder.
4. A plasma spray method in accordance with claim 1, characterized
in that the metal oxide is zirconia, hafnium oxide or titanium
oxide.
5. A plasma spray method in accordance with claim 1, characterized
in that the process pressure amounts to at most 400 Pa.
6. A plasma spray method in accordance with claim 1, characterized
in that a supply rate of the starting material lies in a range
between 0.5 and up to 5 g/min.
7. A plasma spray method in accordance with claim 1, characterized
in that metal or silicon arising in the reduction of the metal or
silicon oxide is deposited from the plasma jet.
8. A plasma spray method in accordance with claim 7, characterized
in that the metal or silicon is deposited in form of particles at a
spacing between 100 and 400 mm remote from an exit nozzle for the
plasma jet.
9. A plasma spray method in accordance with claim 1, characterized
in that an additional reactant is introduced into the plasma jet
and a reaction can thus take place between the reduced metal oxide
and the reactant to form a reaction product.
10. A plasma spray method in accordance with claim 9, characterized
in that the reactant contains nitrogen and/or carbon.
11. A plasma spray method in accordance with claim 9, characterized
in that particles of the reaction product are deposited from the
plasma jet.
12. A plasma spray method in accordance with claim 11,
characterized in that the particles of the reaction product are
deposited at a spacing between 500 and 2000 mm remote from an exit
nozzle for the plasma jet.
13. A plasma spray method in accordance with claim 7, characterized
in that the metal particles or the particles of the reaction
product are deposited in the form of a powder.
14. A plasma spray method in accordance with claim 7, characterized
in that the metal particles or the particles of the reaction
product are deposited in the form of a film on a substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 of European Patent Application No. 12156660.8 filed on
Feb. 23, 2012, the disclosure of which is expressly incorporated by
reference herein in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A COMPACT DISK APPENDIX
[0003] Not applicable.
BACKGROUND OF THE INVENTION
[0004] It is known that nitride nanopowder or carbide nanopowder
can be manufactured using suitable liquid or gaseous starting
materials, so-called precursors. In this connection, a nanopowder
should be understood as a powder having a grain size of
approximately 1 nm to 1 .mu.m. Suitable precursors, for example
titanium tetrachloride or tetrakis (dimethylamino) titanium, are
very expensive and usually very toxic or dangerous. The precursors
are vaporized for manufacturing the nanopowder and form nanopowder
in a reactive chemical gas phase deposition process (a so-called
CVD process). It is also possible to manufacture a nitride coating
or a carbide coating on a substrate using a comparable process.
[0005] In addition, so-called plasma spray gas phase deposition
processes (so-called PS-PVD processes) are known by means of which
films can be generated on a substrate from a starting material in
powder form. For this purpose, the starting material is introduced
into a plasma and thus converted into the gas phase and is
deposited from the gas phase onto the substrate as a thin film.
Thermal barrier coatings are produced in this manner, for example.
In this respect, yttria stabilized zirconia (abbreviated YSZ) is,
for example used as a non-metallic, inorganic starting
material.
SUMMARY
[0006] Against this background, it is the object of the invention
to propose a plasma spray method which can serve as a starting
point for an inexpensive manufacture of metal nanopowder, nitride
nanopowder or carbide nanopowder or of metal films, nitride films
or carbide films. This object is satisfied in accordance with the
invention by a plasma spray method having the features of claim
1.
[0007] In the plasma spray method in accordance with the invention,
a starting material is introduced into a plasma jet generated by a
plasma generator at a process pressure of at most 1000 Pa, in
particular at most 400 Pa. The starting material contains a metal
or silicon oxide which vaporizes in the plasma jet and is reduced
in so doing. After the reduction, the metal or silicon which had
formed the metal or silicon oxide in the starting material is thus
present in pure form or in almost pure form.
[0008] The term "process pressure" should be understood as that
pressure at which the process runs, that is at which the plasma jet
is formed. Since the required process pressure is much smaller than
the atmospheric pressure, the whole process takes place in a closed
process chamber in which the process pressure can be set.
[0009] The starting material in this respect is composed of in
particular 95% to 100% metal oxide, particularly preferably 100% of
metal oxide, of a single metal or of different metals, in
particular of zirconium oxide (zirconia), hafnium oxide or titanium
oxide. In addition to the metal oxide, the starting material can,
for example, be composed of other oxides, for example silicon
oxide.
[0010] In the method in accordance with the invention, the starting
material containing metal or silicon oxide is injected and thus
introduced into a plasma jet, for example an argon-helium plasma,
generated by a plasma torch known per se. The starting material is
in this respect in particular introduced into the plasma jet as a
powder. It can, for example, be introduced as a loose powder by
means of a carrier gas. The carrier gas is, for example, a noble
gas, a noble gas mixture or an inert gas. Examples for carrier
gases are argon or a helium-argon mixture. It is, however, also
possible that the starting material is introduced into the plasma
jet in a suspension, that is as a dispersed powder in a liquid, for
example in ethanol,
[0011] The plasma gas thereby arising expands in a nozzle of the
plasma torch due to the high temperature of the plasma from 10,000
to 20,000 Kelvin and accelerates to supersonic speed. Due to the
named low process pressure, an expansion of the plasma gas takes
place into a process chamber at low pressure, with a long,
large-area plasma jet with expansion zones and compression zones
arising. The plasma jet in particular has a length between 1 and
2.5 m. The metal or silicon oxide contained in the starting
material vaporizes in the plasma jet due to the high temperature
and to the low pressure. In this respect, an oxygen loss, that is a
reduction of the metal or silicon oxide, takes place due to the low
partial pressure of the oxygen so that the metal or silicon is
present in pure form or in almost pure form in the plasma flow
after the reduction.
[0012] The starting material is in particular supplied and is thus
introduced into the plasma at a comparatively low feed rate. The
supply rate in particular lies in a range between 0.1 and 5 g/min.
It can thus be achieved that the total metal or silicon oxide or
almost the total metal oxide introduced is completely reduced.
[0013] The total flow rate of the process gate in particular
amounts to between 50 and 200 SLPM (standard liters per minute) and
particularly preferably to 90 to 120 SLPM.
[0014] In an embodiment of the invention, an additional reactant is
introduced into the plasma so that a reaction can take place
between the reduced metal or silicion oxide and the reactant to
form a reaction product. The reactant in particular contains
nitrogen and/or carbon so that the pure metal or silicon arising on
the reduction can react to form a metal or silicon nitride and/or a
metal or silicon carbide. It is thus advantageously possible to
manufacture metal or silicon nitride and/or metal or silicon
carbide from a very inexpensive and non-dangerous starting material
in the form of metal or silicon oxide powder.
[0015] Depending on the partial pressure of the elements in the
reaction to the reaction product, MO.sub.xN.sub.y or
MO.sub.xC.sub.y or MN.sub.y or MC.sub.y, arise, where M stands for
the metal forming the metal oxide, for example zirconium or
titanium. The named partial pressures can be influenced by means of
process parameters such as the process pressure, type of process
gas and the current for generating the plasma, the flow rate of the
process gas or the supply rate of the starting material. A large
reduction is in particular achieved by a high current as well as by
a low powder conveying rate.
[0016] The reactant containing nitrogen can, for example, be pure
gaseous nitrogen or air. The reactant containing carbon can, for
example, be gaseous as carbon dioxide or methane or can be in solid
form as starch or as a polymer.
[0017] The pure metal, the silicon or the reaction product arising
on the reduction can be deposited from the plasma jet. It can be
deposited, for example, in the form of metal or silicon nanopowder.
The deposition in particular takes place at a comparatively small
spacing from a discharge nozzle for the plasma jet. The spacing in
particular amounts to between 100 and 400 mm. The named range is
characterized in that, on the one hand, the reduction of the metal
or silicon oxide is fully or at least almost fully completed and,
on the other hand, the metal or silicon particles have not yet
entered into any other bonds. The named spacing is in particular
advantageous when metal or silicon nanopowder is to be
manufactured.
[0018] The plasma spray method in accordance with the invention
allows an inexpensive manufacture of metal or silicon nanopowder,
nitride nanopowder or carbide nanopowder. In addition, with
corresponding process conditions, nanopowders can thus be
manufactured from non-meltable nitride compounds or carbide
compounds such as silicon nitride (Si.sub.3N.sub.4).
[0019] A method is thus proposed for manufacturing a metal or
silicon powder, a metal or silicon nitride powder or a metal or
silicon carbide powder in which a starting material in the form of
a metal or silicon oxide is used which is introduced at a process
pressure of at most 1000 Pa into a plasma flow which is generated
by a plasma generator and in which the starting material is
vaporized and in so doing reduced and arising metal particles,
metal nitride particles or metal carbide particles are deposited
from the process jet as powder.
[0020] The deposition as a nanopowder in particular takes place
when the plasma jet can form without impacting a barrier, for
example in the form of a substrate. To promote the deposition as a
nanopowder, the plasma jet can also be directly cooled in a defined
region, for example by means of a gas flow; the metal or silicon
can therefore be quenched so-to-say and the formation of metal or
silicon nanopowder can thus be promoted. The gas flow is, for
example, a gas flow from a noble gas (e.g. argon), from a noble gas
mixture (e.g. argon-helium mixture) or from an inert gas and is
oriented transversely to the plasma jet, for example. An
electrostatic filter can also be used for promoting the
deposition.
[0021] The grain size of the arising nanopowder can in particular
be influenced by the type of the plasma gas which has an influence
on the plasma temperature and the plasma speed and by the process
pressure which has an influence on the condensation of the
nanopowder. The grain size in particular becomes smaller as the
current increases and the powder conveying rate decreases.
[0022] The pure metal or silicon or the reaction product created in
the reduction can also be deposited from the plasma jet as a film
on a substrate. A substrate should be understood in this connection
as a workpiece to be coated, for example a turbine blade. For this
purpose, the plasma jet is directed to the substrate so that a film
of the pure metal or silicon or of the reaction product is formed
on the substrate. The plasma spray method in accordance with the
invention thus makes possible an inexpensive metal or silicon
coating, nitride coating or carbide coating of a substrate. In
addition, on the setting of corresponding process parameters using
the method in accordance with the invention coatings of
non-meltable nitride compounds or carbide compounds such as silicon
nitride (Si.sub.3N.sub.4) can be manufactured. This is not possible
or is only possible with limitations with known spray methods for
coating.
[0023] A method is thus proposed for manufacturing a film on a
substrate using a plasma spray method in which a starting material
in the form of a metal oxide is used which is introduced at a
process pressure of at most 1000 Pa into a plasma flow which is
generated by a plasma generator and in which the starting material
is vaporized and in so doing reduced and arising metal particles,
metal nitride particles or metal carbide particles are deposited as
a film on s substrate.
[0024] The films produced in particular have a thickness between 50
nm and 500 .mu.m and can be deposited over a large area in both a
dense and a porous form. The porous films in particular have a
columnar design. The design and the property of the film as well as
the film growth can be influenced via the named process parameters,
with in particular a higher powder conveying rate resulting in
rather porous films.
[0025] Further advantages, features and details of the invention
result with reference to the following description from embodiments
and with reference to drawings in which elements which are the same
or have the same function are provided with identical reference
numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] There are shown:
[0027] FIG. 1 a schematic representation of a plasma spray
apparatus for manufacturing nanopowder; and
[0028] FIG. 2 a schematic representation of a plasma spray
apparatus for producing a film on a substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0029] In accordance with FIG. 1, a plasma spray apparatus 11
suitable for carrying out a method in accordance with the invention
has a plasma generator 12 known per se and having a plasma torch,
not shown in more detail, for producing a plasma. A process jet 13
is generated in a manner known per se from a starting material P, a
process gas mixture G and electrical energy E using the plasma
generator 12. The feeding of these components E, G and P is
symbolized by the arrows 14, 15, 16 in FIG. 1. The generated plasma
jet 13 exits the plasma generator through an outlet nozzle 17 and
transports the starting material P in the form of the plasma jet 13
in which material particles 18 are dispersed in a plasma. This
transport is symbolized by an arrow 19.
[0030] The process gas G for the production of the plasma is
preferably a mixture of inert gases, in particular a mixture of
argon, hydrogen and helium.
[0031] The plasma spray apparatus 11 is arranged in a process
chamber 20 in which a defined process pressure can be set by means
of pumps, not shown. On the carrying out of the method in
accordance with the invention, a process pressure of less than 1000
Pa, in particular between 100 and 400 Pa, is set. Due to the named
process pressure, a comparatively long plasma jet having a length
between 1 and 2.5 m is produced.
[0032] Specifically, a plasma spray gas deposition method (PS-PVD)
is carried out using the plasma spray apparatus 11 shown in FIG. 1.
In this method, the starting material P which is composed of
titanium oxide (TiO.sub.2, zirconia (ZrO.sub.2), hafnium oxide
(Hf.sub.2O.sub.3) or silica (SiO.sub.2) in powder form is
introduced into the argon-helium plasma generated by the plasma
generator 12, and thus introduced into the plasma jet 13, by means
of a carrier gas, for example in the form of argon.
[0033] The plasma gas thereby arising expands in and after the exit
from the outlet nozzle 17 of the plasma generator 12 due to the
high temperature of the plasma of 10,000 to 20,000 Kelvin and
accelerates to supersonic speed. The metal oxide contained in the
starting material P vaporizes in the plasma jet 13 due to the high
temperature and to the low pressure. In this respect, an oxygen
loss, that is a reduction of the metal oxide, takes place due to
the low partial pressure of the oxygen so that the metal is present
in pure form or in almost pure form in the plasma flow after the
reduction.
[0034] The starting material P is supplied at a comparatively low
supply rate. The supply rate in particular lies in a range between
0.1 and 5 g/min.
[0035] The current set for the generation of the plasma in this
respect has a current between approx. 1000 and 3000 A, in
particular between 2200 and 3000 A.
[0036] The starting material P is injected into the plasma as a
powder jet with a conveying gas, preferably argon or a helium-argon
mixture. The flow rate of the conveying gas preferably amounts to 5
to 40 SLPM (standard liters per minute), in particular to 10 to 25
SLPM.
[0037] The process gas for the generation of the plasma is
preferably a mixture of inert gases, in particular a mixture of
argon Ar, helium He and hydrogen H. In practice, a total gas flow
between 50 and 200 SLPM, in particular 90 to 120 SLPM has proven
itself. Of this in particular approximately 1/3 is argon and 2/3
helium. In addition, a portion of up to 10 SLPM hydrogen is
conceivable.
[0038] To promote a deposition of the created metal particles in
the form of a nanopowder, the plasma jet 13, and thus also the
metal particles 18 contained in the plasma jet 13, are directly
cooled by a gas flow 21 oriented transversely to the plasma flow 13
and the metal is thus quenched so-to-say. A condensation of the
gaseous metal particles 18 is triggered and nanopowder 22 is formed
which collects in a collection apparatus 23.
[0039] The gas flow 21 in this respect has a spacing D1 from the
exit nozzle 17 between 100 and 400 mm, in particular 150 mm.
[0040] A plasma spray apparatus 111 for generating a film 124 on a
substrate 125 is shown in FIG. 2. The design of the plasma spray
apparatus 111 corresponds in large parts to the plasma spray
apparatus 11 of FIG. 1 so that mainly the differences of the two
plasma spray apparatus will be looked at.
[0041] A reactant R, whose infeed is symbolized by an arrow 126, is
supplied to a plasma generator 112 of the plasma spray apparatus
111 in addition to the starting material P which is in turn
titanium oxide (TiO.sub.2) or zirconia (ZrO.sub.2) in powder form.
The reactant in particular contains nitrogen or carbon so that the
pure metal arising on the reduction of the metal oxide can react to
form a metal nitride and/or a metal carbide. The reactant
containing nitrogen can, for example, be pure gaseous nitrogen. The
reactant containing carbon can, for example, be gaseous as carbon
dioxide or methane or can be in solid form as starch or as a
polymer. When the reactant is supplied in solid form, this is also
done using a transport gas. In this respect, it can be the same
transport gas as for the starting material P or a transport gas
differing therefrom.
[0042] After the above-described reduction of the metal oxide of
the starting material P, a reaction of the pure metal with the
reactant R to form a reaction product takes place in the plasma
flow 113. If one looks at the total method, the oxygen bound in the
metal oxide is replaced with nitrogen or carbon of the reactant R
to gain the reaction product.
[0043] Depending on the partial pressure of the elements on the
reaction to the reaction product, MO.sub.xN.sub.y or
MO.sub.xC.sub.y or MN.sub.y or MC.sub.I, arise, where M stands for
the metal forming the metal oxide, that is zirconium or titanium.
The named partial pressures can be influenced by means of process
parameters such as the process pressure, type of process gas and
the current for generating the plasma, the flow rate of the process
gas or the supply rate of the starting material.
[0044] The substrate 125 is arranged at a spacing D2 from an exit
nozzle 117 of the plasma generator 112. The spacing D2 can be
selected as larger than the spacing D1 in FIG. 1; it in particular
amounts to between 500 and 2000 mm. The named reaction product is
deposited at the substrate 125 as a film 124. The film 124 can have
a thickness between 50 nm and 500 .mu.m and can be made both dense
and porous. The design and the property of the film as well as the
film growth can be influenced via the named process parameters.
[0045] It is naturally also possible that, in the generation of
nanopowder in accordance with FIG. 1, a reactant is supplied and
thus a nitride nanopowder or carbide nanopowder is generated. It is
equally possible to dispense with the supply of a reactant in the
generation of a film on a substrate in accordance with FIG. 2 and
thus to generate a film of pure metal. To achieve satisfactory
results, specific adaptations of the process parameters will be
necessary under certain circumstances.
[0046] It is noted that the foregoing examples have been provided
merely for the purpose of explanation and are in no way to be
construed as limiting of the present invention. While the present
invention has been described with reference to an exemplary
embodiment, it is understood that the words which have been used
herein are words of description and illustration, rather than words
of limitation. Changes may be made, within the purview of the
appended claims, as presently stated and as amended, without
departing from the scope and sprit of the present invention in its
aspects. Although the present invention has been described herein
with reference to particular means, materials and embodiments, the
present invention is not intended to be limited to the particulars
disclosed herein; rather, the present invention extends to all
functionally equivalent structures, methods and uses, such as are
within the scope of the appended claims.
* * * * *