U.S. patent application number 10/186601 was filed with the patent office on 2002-12-26 for thin porous layer with open porosity and a method for production thereof.
Invention is credited to Kuhstoss, Andreas, Neumann, Peter, Rothig, Thomas.
Application Number | 20020195188 10/186601 |
Document ID | / |
Family ID | 7934940 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020195188 |
Kind Code |
A1 |
Kuhstoss, Andreas ; et
al. |
December 26, 2002 |
Thin porous layer with open porosity and a method for production
thereof
Abstract
The aim of the invention is to produce a thin porous layer, with
a defined porosity and also, a high strength. Said aim is achieved,
whereby such a layer with open porosity is produced from a mixture,
comprising a sinterable powder with a predetermined powder particle
size distribution. The sintered layer is of a thickness, which
corresponds to about triple the average diameter of the powder
particles employed, has a pore diameter in the range from 0.01 to
50 .mu.m and a tensile strength of in a range from about 5 to 500
N/mm.sup.2. The invention further relates to a method for the
production of said thin porous layer with open porosity.
Inventors: |
Kuhstoss, Andreas;
(Remscheid, DE) ; Rothig, Thomas; (Schwelm,
DE) ; Neumann, Peter; (Remscheid, DE) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
7934940 |
Appl. No.: |
10/186601 |
Filed: |
July 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10186601 |
Jul 1, 2002 |
|
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PCT/EP00/09422 |
Sep 27, 2000 |
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Current U.S.
Class: |
156/89.16 ;
156/89.11 |
Current CPC
Class: |
B01D 2325/12 20130101;
B01D 67/0041 20130101; B22F 3/1121 20130101; B22F 2999/00 20130101;
B01D 39/2075 20130101; B01J 35/065 20130101; B01D 2325/04 20130101;
B01D 69/02 20130101; B01D 71/022 20130101; B22F 3/22 20130101; B22F
3/1121 20130101; B22F 2207/11 20130101; B22F 2207/11 20130101; B22F
3/1103 20130101; B22F 5/10 20130101; B01J 35/1076 20130101; B22F
5/006 20130101; B22F 2998/00 20130101; B22F 2999/00 20130101; B01D
39/2086 20130101; B22F 2998/00 20130101; B01J 35/10 20130101; B01D
69/04 20130101; B22F 3/1103 20130101; B22F 2999/00 20130101 |
Class at
Publication: |
156/89.16 ;
156/89.11 |
International
Class: |
C03B 029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 1999 |
DE |
199 63 698.2 |
Claims
What is claimed is:
1. Thin porous layer with open porosity, manufactured from a
mixture containing sinterable powder with a predetermined powder
particle size distribution, whereby the sintered layer has a
thickness which is at least triple the average diameter of the used
powder particles, a defined pore diameter in a range of about 0.01
to 50 .mu.m and a tensile strength in a range of about 5 to 500
N/mm.sup.2.
2. Thin porous layer in accordance with claim 1, marked by a
maximum thickness of about 500 .mu.m.
3. Thin porous layer in accordance with one of the above claims
marked by self-supporting properties.
4. Thin porous layer in accordance with one of the above claims
marked by a bubble-point pressure in a range of about
8.times.10.sup.6 to 2.times.10.sup.3 Pa.
5. Thin porous layer in accordance with one of the above claims
marked by the content of inorganic and/or organic pore forming
material in the mixture.
6. Thin porous layer in accordance with one of the above claims
marked by a graded design.
7. Procedure for manufacturing thin porous layer with open porosity
in accordance with one of the claims 1 to 6, whereby the layer is
made up of a mixture containing sinterable powder and the
sinterable powder with a predetermined size distribution of powder
particles is suspended along with particles of the defined size as
pore forming material is suspended in a carrier fluid. It is
applied in at least one layer on a carrier body, dried and the
green layer thus formed is sintered.
8. Procedure in accordance with claim 7 marked by the
correspondence of the portion of pore forming materials in the
suspension to the metallic layer to be produced in about the
defined pore volume.
9. Procedure in accordance with claim 7 or 8 marked by the forming
of the carrier fluid by the binding agent liquefied with a
solvent.
10. Procedure in accordance with one of the claims 7 to 9 marked by
the suspension of pore forming materials of different densities
and/or sizes in the solvent for obtaining a graded layer
design.
11. Procedure in accordance with one of the claims 7 to 10 marked
by the application of the suspension in many partial layers one
after another on the carrier body.
12. Procedure in accordance with one of the claims 7 to 11 marked
by drying of the earlier partial layer before the application of
the next partial layer.
13. Procedure in accordance with one of the claims 7 to 12 marked
by the sintering of the earlier partial layer before application of
the next partial layer.
14. Procedure in accordance with one of the claims 7 to 13 marked
by the application of the suspension on the carrier body by the
process of thin layer pouring, spraying or immersing.
15. Procedure according to one of the claims 7 to 14 marked by the
application of the suspension on at least on one of the walls of a
porous, preferably pipe-shaped carrier body made from sinterable
material, dried and the green layer thus formed subsequently firmly
sintered on the carrier body.
16. Procedure in accordance with one of the claims 7 to 15 marked
by the rotation of the pipe-shaped carrier body around the axis of
the pipe during application of suspension and at least during some
part of the drying period.
17. Using a thin porous layer with open porosity in accordance with
one of the claims 1 to 6 as filter material, catalyst, membrane
reactor, friction substance, filter cartridge and/or filter pipe.
Description
RELATED APPLICATIONS
[0001] This is a continuation of International Application No.
PCT/EP00/09422 filed Sep. 27, 2000, which claims priority to German
Application No. 199 63 698.2 filed Dec. 29, 1999.
BRIEF DESCRIPTION OF THE INVENTION
[0002] The invention concerns a thin porous layer with open
porosity, manufactured from a mixture containing sinterable powder,
and also a procedure for its production.
[0003] Porous bodies are required for the most varied applications
in technology. These bodies flow through a flowing medium whereby
either reactive processes take place or the solid particles
contained in the flowing medium are retained or filtered. Filter
pads made from ceramic material must generally be relatively thick
to prevent breakage. The low strength and low resistance to
temperature limit the use of plastics as filter material. Metallic
material is used as a porous layer in the form of tissues or
fabrics manufactured from metallic fibers. Filter pads made from
pressed and sintered metallic powders are also relatively thick due
to technical reasons. These filter pads must be manufactured
relatively thick mainly because they do not exhibit the required
strength, particularly the tensile and shearing strength. Since the
thickness does not reduce (particularly in case of extremely fine
porous material), the flow resistances increase.
[0004] Irrespective of the material used, the unwanted flow
resistances in case of a porous layer flowing through from a medium
must be reduced by making the layer as thin as possible and the
layers given adequate strength. Thin layers, for example with
thickness of about 100 .mu.m can be produced from metallic tissues
or fabrics.
[0005] However, these are less strong, have relatively larger pores
and high porosity tolerances. The manufacture of such type of
tissues and fabrics requires correspondingly thin and also
expensive threads. Hence, the tissues and fabrics manufactured from
these are also expensive.
[0006] EP 0 525 325 B1 puts forth a procedure for manufacturing
porous, metallic sintered workpieces, whereby a metallic powder is
suspended in a carrier fluid containing a binding agent dissolved
in a solvent and the fluid adjusted such that the suspension can be
poured. This suspension is poured into a mould. The solvent is then
evaporated so that the remaining binding agent strengthens the
metallic powder in the shape given by the mould and forms a
commercially viable green body. After removing from the mould, the
green body is sintered in the usual way. This known procedure is
preferred for manufacturing relatively thick-walled sintered parts,
which, owing to their geometry, can be better manufactured with the
pouring process than the traditional method, in which metallic
powder is pressed in a mould. Thin-layered, open porous parts
cannot be manufactured with this procedure. The thin layers
manufactured by this procedure are brittle; they do not exhibit
adequate strengths.
[0007] The invention has the task of producing a thin porous layer
with a defined porosity and sufficient strength and devising a
procedure for its manufacture.
[0008] The solution is a thin porous layer with open porosity
manufactured from a mixture of sinterable powder with a
predetermined powder particle size distribution. The sintered layer
exhibits a thickness, which corresponds to about triple the average
diameter of the powder particles used.
[0009] Moreover, the thickness mainly lies within a range of about
3 times to 25 times, preferably 3 times to 10 times the diameter of
the powder particles, has a defined pore diameter in the range of
about 0.01 to 50 .mu.m and a tensile strength in the range of about
5 to 500 N/mm.sup.2, preferably 20 to 400 N/mm.sup.2, and more
preferably 50 to 300 N/mm.sup.2, measured in accordance with DIN EN
10002.
[0010] Sinterable powders, according to the invention, refer to
powders manufactured from metals, metallic oxides, ceramics and/or
plastics. Usable metallic powders according to this invention are
not only powders made from pure metals, but also those made from
metallic alloys and/or powder mixtures of different metals and
metallic alloys. These metals are particularly steels, preferably
chromium-nickel-steels, bronzes, nickel-based alloys such as
Hastalloy, Inconel or the like. Powder mixtures can also contain
high melting components like platinum or the likes. The used
metallic powder and its particle size depend on the purpose of use.
Preferred powders are the alloys 316 L, 304 L, Inconel 600, Inconel
625, Monel and Hastalloy B, X and C.
[0011] The abovementioned ratio of layer thickness to particle
diameter ensures that many layers of particles are arranged one on
top of the other and holes larger than the desired pore diameter
are avoided, thereby also avoiding through holes. The grain size
and therefore the diameter of the used powder particles lie in a
range of 0.05 .mu.m to 150 .mu.m, preferably, in a range of about
0.5 .mu.m to 100 .mu.m, more preferably in a range of 0.5 .mu.m to
6 .mu.m.
[0012] Non-homogeneity and hollow spaces in the thin porous layer
are thus positively avoided. It is also possible to influence the
porosity range up to a certain degree through the particle size of
the used sinterable powder.
[0013] The maximum thickness of the invented layer is about 500
.mu.m; it preferably lies in a range of about 5 to 300 .mu.m, more
preferably 5 to 18 .mu.m. Such types of thin layers with sufficient
strength were not manufactured so far. The invented layer shows
remarkably low flow resistance while passing through with fluid or
gaseous media and also a sufficiently high strength and stiffness.
Thus, the invented layer can be used without a carrier body as
films or membrane or can be bound firmly with a carrier body. The
invented layer also adjusts excellently to an uneven, for example
bent surface on account of its retained flexibility.
[0014] Another preferred type is the thin porous self-supporting
layer. Self-supporting in the sense of this invention means that
the invented layer can be used without any carrier body and yet
does not become fragile or brittle. Thus, it is possible to
manufacture film sheets and place them one on top of the other in
many layers and if necessary, cut them as per the requirements.
Because of their self-supporting properties, the invented layers
can be used as filters and catalyst materials wherever, for
example, materials similar to paper were used so far. The invented
thin porous layers made from sinterable powders are superior to the
familiar paper films or films made from paper-like material because
of their distinctly higher service lives, better backwashing
properties and a broader area of application, particularly in view
of the possible temperatures and pH-values.
[0015] The bubble-point pressure of the invented layer lies
preferably in a range of about 8.times.10.sup.6 to 2.times.10.sup.3
Pa, especially preferred in a range of about 8.6.times.10.sup.6 to
1.72.times.10.sup.2 Pa, determined according to DIN 30911.
[0016] In another invented design, the mixture (from which the thin
porous layer is manufactured) is made up of inorganic and/or
organic pore forming materials. Urea is especially suitable for
this purpose. It exists in the crystalline form and therefore in
defined particle sizes. Anyway, it is also possible to use ammonium
carbonate and other inorganic salts. Styropor, sucrose, gelatins
and tapestry glues are the organic pore forming materials used.
However, the usual binding agents or paraffin, which are used as
auxiliary materials for reducing the friction in the tools used in
powder metallurgy, can also be used. These binding agents and
paraffin are not used in the usual low concentrations but are used
in a portion of at least about 5 vol.-%, preferably more than 12
vol.-% in the mixture for manufacturing the thin porous layer. The
pore forming materials can exist in the defined particle form and
particle size and also as a solution and soluble dissolved in a
solvent to be used. The pore forming materials generally exist in
defined particle form and size.
[0017] The pore forming materials can be divided into two different
groups, firstly a group of pore forming materials that serve as
retainers for the mixture to be sintered for the fine pores formed
later. The other group consists of pore-forming materials that are
used as fillers usually to achieve high porosity. In the first
mentioned group, in which the pore forming materials function as
retainers, the same are used in a particle size (grain size) that
lies in the size range that must exhibit the fine pores contained
in the thin porous layer.
[0018] If for example, the aim is to achieve fine pores in a range
of 1 .mu.m, the pore forming materials should not be considerably
above or below 1 .mu.m. Thereby, it is ensured that the desired
pore sizes are achieved in spite of the shrinkage process during
sintering of the mixture into the thin porous layer. It must be
presumed that shrinkage will take place. The use of pore forming
materials as fillers is especially recommended when the invented
thin porous layers must have low thickness and an extremely high
flow. According to the invention, it is also possible to use
mixtures, particularly the above-mentioned substances, also with
varying thickness and/or sizes as pore forming materials. The
invention also provides for combinations of pore forming materials
in the mixture, in which these serve as retainers as well as
fillers.
[0019] The sinterable powder contained in the mixture is made of
ball-shaped and/or spattered particles. The ball-shaped particles
ensure a uniform distribution of the sinterable powder and if
necessary of substances, particularly pore forming materials in the
mixture. Thus, the sinterable powder particles do not stick
together. Spattered sinterable powders on the other hand, make
feasible layers with lower thickness and relatively larger pores
for the same high strength since they form more and therefore
better bonds with the neighboring spattered particles than
ball-shaped particles. The sinterable powder is at least partially
made up of short fibers. Here, metallic fibers can be taken into
account having diameters between 0.1 and 250 .mu.m, preferably 1
.mu.m to 50 .mu.m, and a length of lesser .mu.m up to millimeter
size, preferably in a range of 0.1 to 500 .mu.m.
[0020] Thus, very thin sintered open-porous layers with defined
porosity can be manufactured by mixing sinterable particles in the
fiber structure with sinterable particles in the ball structure in
combination with the suspended pore forming materials depending on
the purpose of application. Thus the permeability of the layer is
increased.
[0021] In another type, the invented layer shows a graded design.
This means that smaller pores exist in a separate thin porous layer
on one side than the opposite side of the porous layer. With the
graded design, the flow resistance of the thin-pored layer can be
adapted exactly to the requirements. In order to retain the
penetrating particles on the side of the invented layer with
smaller pore diameter and to enable the flowing gas or fluid to
pass easily on the opposite side of the layer in the area of the
larger pore diameter, such type of graded layers have a lesser flow
resistance as compared to non-graded layers. A graded design is
preferred in case of a single layer. This reduces the production
times and costs. Moreover, separation and binding problems such as
leakage are eliminated, for example with aging.
[0022] Further, the invention also concerns a procedure for the
manufacture of a thin porous layer with open porosity, whereby the
sinterable powder with the predetermined size distribution of
powder particles is suspended along with particles of predetermined
size as pore forming material in a carrier fluid. At least one such
layer is applied on the carrier body, dried and the green layer
thus formed sintered.
[0023] While sintering a green layer formed out of sinterable
powder, preferably a metallic powder, the individual powder
particles bind firmly with one another whereby free spaces remain
between the powder particles. These free spaces give an open
porosity with respect to the thickness of the sintered layer such
that the layer becomes permeable for flowing media.
[0024] After the sintering process, the layer can either be removed
from the carrier or further processed along with it. Filter
cartridges can be manufactured in a simple way in a single
procedural step, i.e. manufacturing the sintered layer without
carrier body without prior separation and then applying it on a
filter cartridge. This is possible because the firm bonding
achieved between the carrier body and the layer after the sintering
step as long as the carrier body is able to bind with the
sinterable powder, whereby the bond can be further improved by
about 3 to 8 times by using highly sinter-active metallic
components.
[0025] There exists a dependency between the particle size and the
target pore size of the finished sintered layer. The mechanical
strength of a porous sintered layer also depends on the particle
size. Finer the powder particle, higher is the mechanical strength.
Since the resistance to flow also depends on the thickness of the
finished sintered layer depending on the medium (fluid or gaseous),
porous layers with larger pore sizes have a lower mechanical
strength than a porous layer with same thickness with smaller pore
size. Thus, the mechanical strength of layers with larger pore size
can be increased merely by increasing the layer thickness and
thereby the resistance to flow.
[0026] This problem can be solved only with the help of the
invented procedure by suspending the sinterable powder along with
particles with predetermined size or size distribution as pore
forming material in the carrier fluid.
[0027] This carrier fluid is then applied in at least one layer on
the carrier body, dried and sintered. In another procedural step,
the sintered layer can be removed from the carrier body or the
carrier body bound firmly with the sintered layer, for example by
the sintering process itself. By adding the pore forming material,
it is possible to achieve a defined pore size. The sinterable
powder particles distributed in the suspension and thereby in the
applied thin layer and the pore forming material combine to form a
lattice structure. Thus, a definite pore structure can be defined
on the basis of the size or size distribution of the pore forming
material, practically independent of the size and size distribution
of the sinterable powder. This also means that the size and size
distribution of the sinterable powder can be chosen exclusively
keeping in view the mechanical strength, i.e. very fine sinter
powder can be used. On the other hand, the pore forming material
can be chosen keeping in the view the required porosity.
[0028] Since the sinterable powder, preferably metallic powder and
the pore forming materials are suspended in a carrier fluid,
particles of materials with thickness lower than that of the
sinterable powder can be uniformly distributed and suspended for
the pore forming material, irrespective of the varying thickness of
materials and in keeping with the consistency of the suspension.
Thus, it is possible to form a layer on a carrier body, in which
the particles that exist as pore forming materials are uniformly
distributed.
[0029] If the pore forming materials serve as retainers, these must
evaporate under the effect of heat, i.e. during the sintering
process preferably without any residue and remain inert as against
the material of the sinterable powder even at sintering
temperatures. As a result, no chemical reactions take place between
the pore forming material and the sinterable material, which is, as
a rule, a metal.
[0030] Evaporable solvents like ethanol, methanol, Toulon,
trichlorethylene, diethyl ether and also lower molecular aldehydes
and ketones can be used as carrier fluid especially at temperatures
below 100.degree. C. Paraffin, shellac as well as polymer compounds
can be used as binding agents, whereby preferably polyalkylene
oxide or polyglycols, especially polyethylene glycols can be used.
Polyalkylene oxide and polyglycols are used preferably as polymers
and/or copolymers with average molecular weights in a range of 100
to 500,000 g/moles, preferably 1,000 to 350,000 g/moles, and more
preferably 5,000 to 6,500 g/moles.
[0031] In another design of the invented procedure, the portion of
the pore forming materials in the suspension more or less matches
with the defined pore volume of the porous layer to be produced.
Thus it is possible, for example, to specify a defined porosity of
the porous layer to be produced for a very fine and thereby highly
sinter-active sinterable powder by specifying the volumetric
details when the size of the particles of the pore forming material
is given.
[0032] The consistency of the suspension adjusted on the basis of
the carrier fluid mainly depends on the application of the
suspension on the carrier body. The suspension can be adjusted to a
thick-fluid consistency while pouring, if necessary with subsequent
coating of the excess of the poured suspension layer. A thin fluid
consistency must be provided for the so-called film pouring or
spraying. The carrier fluid can be formed with a binding agent
liquefied with an evaporable solvent. Hereby, it is ensured that
the green layer has sufficient strength resulting from the bonding
of individual powder particles one below the other with the binding
agent.
[0033] In another form of the invention, a suspension is used for
achieving a graded layer design. This suspension comprises of pore
forming materials of different densities and/or size suspended in
solvent. Here, there arises a balance within the layer while adding
the suspension to the carrier body. As a result, the lighter
particles of the pore forming materials collect in the upper area
of the layer, whereas the heavier particles of the pore forming
material collect closer to the side facing the carrier body of the
layer. Obviously, this balance is influenced by the grain size of
the used sinterable powder. If particles from a material with
different sizes are used in the suspension as pore forming material
then, for example, the finished sintered layer shows a gradient
with respect to the pore diameter of the same. This is particularly
advantageous since the flow resistance can thus be further
reduced.
[0034] In a specific form of the invention, the suspension is
applied in many thin partial layers one after the other on the
carrier body. Hereby, the individual partial layers can be made up
of an identical suspension. It is possible to use suspensions with
different size distributions for the individual partial layers for
the powder used and/or different particle geometries and/or
different powders. This allows for example, the use of powders that
give an especially good porosity to the fully sintered layer on one
hand and to manufacture at least one layer that shows especially
favorable, for e.g. catalytic properties in its composition for the
purpose of application.
[0035] It is necessary to dry the coated partial layer before
coating the next partial layer. Hereby, it is ensured that the
first coated partial layer is properly fixed so that it is not
deformed by the coating procedure, e.g. spraying of the next
partial layer.
[0036] On the other hand, the remaining portion of the solvent in
the previously coated, dried partial layer ensures that even the
next partial layer is properly bound with same packing density and
the finished green layer has the desired strength.
[0037] In another form of the invention, the partial layer is
sintered before applying the next partial layer. This procedure is
especially advantageous when powder made from different sintered
materials, for example having deviating sintering temperatures, is
used for a multiple-layer design. Thus, it is possible to first
apply the partial layer containing the powder with the maximum
sintering temperature on the carrier body, and after sintering of
the first layer in the corresponding sequence to apply the
subsequent partial layers with lower sintering temperatures and
subject them to the sintering process. This has the advantage that
the desired porosity of the individual partial layers remains
intact because of the individual sintering steps. This porosity
would have been lost if the suspension was coated with such a
heterogeneous powder mixture in one layer and sintered in just one
step. In this process, the remaining low sintered powder parts
would have densely sintered because of the high sintering
temperatures required for only one portion in the powder mixture.
As a result, the porosity would be further lost.
[0038] If the carrier body is also part of the finished part and
if, correspondingly the porous layer is fixed firmly with it,
another form provides for the suspension to be applied on at least
one of the walls of the carrier body made from sinterable material,
dried and the green layer subsequently sintered firmly on to the
carrier body.
[0039] The carrier body can be a sintered molded part or even a
porous sintered molded part with a coarse pore structure. The
suspension can be applied once again through thin layer required,
spraying or immersion on the upper surface of the carrier body. The
layer can be coated on the outer wall and/or on the inner wall
depending on the purpose of application.
[0040] If the carrier body is formed by a pipe-shaped carrier body,
the invented procedure provides for the rotation of the carrier
body around the axis of the pipe during the application of the
suspension and at least during part of the drying period. This
ensures that the thickness of the layer remains intact till the
fixing of the suspension as a green layer on the carrier body.
Therefore, it is necessary that the suspension outlet be moved in a
defined way against the surface in addition to rotation,
particularly during thin layer pouring and spraying.
[0041] Porous layers applied as films or membrane or on a porous
carrier body are particularly suitable as filter material and also
as micro filters, provided that they have the required porosity. In
case of impermeable carrier bodies, such a component can be used as
a catalyst or membrane reactor, provided that it has the required
powder composition and porosity, for example mixed with palladium
or coated. It is further possible to use the layer as friction
material, e.g. on iron base. It can be applied on a friction
surface of a synchronous body for gears.
[0042] The invented porous layer can also be used in filter pipes
and filter cartridges having a length of 10 mm to 1,500 mm. It is
also possible to manufacture filter cartridges that exhibit a
porous coating on the front side. Further, filter cartridges can be
manufactured with a sintered flange that does not have any welded
joints.
[0043] With the help of the invented procedure, it is possible to
improve the permeability of filters while reducing the
filter-active layer depending on the porosity. By reducing the
thickness of the filter-active layer, the pressure loss can be
distinctly reduced for constant permeability.
[0044] According to this invention, thin porous layers enable flow
rates for gaseous medium such as air ranging from 1 to 1500
m.sup.3/hm.sup.2 at a differential pressure of e.g. 100 mbar. For
fluids such as water, the flow rates at a differential pressure of,
e.g. 100 mbar are 0.1-to 30-m.sup.3/hm.sup.2. The permeability
coefficient is about 0.002.times.10.sup.-12 to 3.times.10.sup.-12
m.sup.2 for a layer thickness of 50 to 500 .mu.m, measured
according to DIN ISO 4022.
[0045] A thin porous layer was manufactured having a thickness of
15 .mu.m. The carrier fluid was manufactured from isopropyl
alcohol, in which 1 weight %--with respect to the quantity of
powder used--of polyethylene glycol having an average molecular
weight of 6,000 g/moles was dissolved. Inconel metallic powder was
used as powder, which had an average diameter of about 1 .mu.m.
Urea was used as pore forming material, which had an average
diameter of about 2 .mu.m. The above components were mixed for 3
hours in a mixer and finally sprayed on a plastic film. The ratio
of powder to pore forming material was about 1:1, similar to that
of powder to carrier fluid. The mixture was dried at room
temperature for 24 hours and then sucked from the plastic film and
sintered at a temperature of up to 950.degree. C. in a sintering
oven for 10 hours.
[0046] The thin open-porous film so obtained had a tensile strength
of 284 N/mm.sup.2. The pore structure was uniform, whereby the
pores had an average diameter of about 2 .mu.m and the porosity was
about 50%.
* * * * *