U.S. patent application number 09/848026 was filed with the patent office on 2001-10-18 for high porosity three-dimensional structures in chromium based alloys.
Invention is credited to Bugnet, Bernard, Doniat, Denis, Rouget, Robert.
Application Number | 20010031375 09/848026 |
Document ID | / |
Family ID | 27443852 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010031375 |
Kind Code |
A1 |
Bugnet, Bernard ; et
al. |
October 18, 2001 |
High porosity three-dimensional structures in chromium based
alloys
Abstract
The invention relates to metallic products and a process for
producing these which allows, despite the complexity of their
structure, for them to be produced in refractory alloys based on
chromium. The chromium is deposited by electrolysis, this being
carried out by means of a bath with high throwing power. The
formation of the alloy with layers of other metallic constituents
is obtained by thermal diffusion. The provision of aluminium is
controlled in the form of particles by immersing, by spraying or
"painting". The structures according to the invention are
particularly intended to be used as catalyst supports or filtering
agents.
Inventors: |
Bugnet, Bernard; (Le
Plessis-Trevise, FR) ; Doniat, Denis; (Paris, FR)
; Rouget, Robert; (Paris, FR) |
Correspondence
Address: |
HENDERSON & STURM LLP
1213 MIDLAND BUILDING
206 SIXTH AVENUE
DES MOINES
IA
50309-4076
US
|
Family ID: |
27443852 |
Appl. No.: |
09/848026 |
Filed: |
May 3, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09848026 |
May 3, 2001 |
|
|
|
09333598 |
Jun 15, 1999 |
|
|
|
Current U.S.
Class: |
428/613 ;
428/666 |
Current CPC
Class: |
B22F 2998/00 20130101;
Y10T 428/12479 20150115; B01D 39/2051 20130101; Y10T 428/12424
20150115; C25D 1/08 20130101; B22F 2998/00 20130101; B22F 2998/10
20130101; Y10T 428/12847 20150115; B22F 3/114 20130101; B22F 3/1125
20130101; B22F 3/24 20130101; B22F 3/114 20130101; B22F 3/1137
20130101; B22F 2998/10 20130101 |
Class at
Publication: |
428/613 ;
428/666 |
International
Class: |
B32B 015/02 |
Claims
1. Production process for "three-dimensional" metallic structures
with high porosity, of reticular honeycomb types, in refractory
alloys, characterized in that this alloy contains chromium and that
the provision of chromium is carried out by electrolytic
deposition, the three-dimensional structure being a non-sintered
sponge, a felt or a woven item.
2. Production process for metallic structures according to claim 1,
characterized in that this alloy contains chromium and that the
provision of chromium is carried out by electrolytic deposition in
a bath containing potassium and/or sodium dichromate.
3. Production process for metallic structures according to claim 1,
characterized in that said refractory alloys are ternary or
quaternary, of nickel-chromium-aluminium, iron- chromium-aluminium
or nickel- iron- chromium types.
4. Production process for metallic structures according to claims 1
and 3, characterized in that the provision of aluminium is carried
out by immersing in a slip containing aluminium particles in
suspension.
5. Production process for metallic structures according to claims 1
and 3, characterized in that the provision of aluminium is carried
out by spraying a suspension of aluminium particles.
6. Production process for metallic structures according to claims 1
and 3, characterized in that the provision of aluminium is carried
out by painting the structure using a lacquer or paint containing
aluminium particles.
7. Production process for metallic structures according to claims 1
and 3, characterized in that the iron and/or nickel are provided by
electrolytic deposition(s).
8. Production process for metallic structures according to claim 1,
characterized in that the alloy is produced by thermal diffusion
treatment of its various constituents.
9. Production process for metallic structures according to claim 1,
characterized in that the chromium electrolysis bath contains 25%
and 150% of potassium or sodium dichromate by weight relative to
the chromic acid.
10. "Three-dimensional" metallic structures with high porosity, in
refractory alloys, of reticular honeycomb types, characterized in
that these alloys contain chromium and that the chromium is
deposited by electrolytic route, the alloy being obtained by
thermal diffusion treatment of its various constituents and the
three-dimensional structure being a non-sintered sponge, a felt or
a woven item.
11. Metallic structures according to claim 10, characterized in
that the refractory alloys are ternary or quaternary, of
nickel-chromium-aluminium- , iron-chromium-aluminium or
nickel-iron-chromium-aluminium types, the aluminium being provided
in the form of particles in a slip, in a lacquer or paint, or in a
sprayable suspension.
Description
[0001] The present invention relates to the field of catalyst
supports and that of filtering agents.
[0002] More particularly it relates to the use of metallic
structures of high porosity produced in refractory alloys for uses
in catalysis and in filtration.
[0003] The widespread use of nickel (Ni) sponges as supports and
collectors for positive electrodes of metallic nickel-cadmium and
nickel hydride alkaline batteries is known. These products have
reticular honeycomb structures with total or very widely open
porosity.
[0004] The nickel sponges constitute one of the families of
"three-dimensional" metallic structures (or "3D") with high
porosity, which also include felt type products (interlocking of
nonwoven fibres), as well as woven types. The latter are most often
constituted by two woven surfaces connected by coupling, by threads
which are approximately transverse to the surfaces.
[0005] The "3D" metallic structures are most often produced
according to a process which respects the sequence of the following
operating stages:
[0006] conductive activation of a base substrate of organic
material; metallization by electrolysis; burning off the organic
materials (original substrate and optionally the conductive
activation products); deoxidation and annealing of the metallic
structure obtained.
[0007] The use of these structures for applications such as
filtration or catalysis often proves to be particularly useful due
to their high porosity and levels of loss of potential which can be
chosen as a function of requirements.
[0008] One of the limitations to these applications relates to
particular thermal or chemical constraints which can be
encountered, and which means that structures produced in nickel can
oxidize or corrode, in an oxidizing environment, at high
temperature.
[0009] In order to overcome these drawbacks and to obtain
satisfactory results, it is necessary to resort to so-called
refractory alloys, one of the components of which is chromium
(Cr).
[0010] The production processes for "3D" metallic structures, as
has been mentioned, generally require a galvanic deposition stage
which makes the production of complex alloys difficult.
[0011] To respond in part to this problem, various routes have been
proposed, applied to the family of sponges:
[0012] the production of sponges of alloys, by particle
sintering,
[0013] case hardening of chromium, on the nickel sponges.
[0014] The first technique is delicate to implement and is
difficult to exploit industrially due to constraints related to
handling the powders and the difficulty in sintering particles of
refractory alloys.
[0015] The second technique requires commercially available
supports (nickel sponges) and a known technique (case hardening).
Thus, DUNLOP patents mention the production of a nickel-chromium
alloy sponge (Ni-Cr) based on this principle.
[0016] The case hardening of chromium (chromizing) is traditionally
applied to items with a simple shape, of small to medium size. When
it is implemented with supports with very complex shapes, such as
metallic sponges, several difficulties are apparent:
[0017] the case hardening composition, constituted by chromium
powder and a gel, must penetrate uniformly inside the porous
structure. The operation is difficult to carry out in a homogeneous
manner with sponges with an average pore size (between 45 and 80
PPI), impossible with structures which have a very fine pore size
(sponges between 80 and 100 PPI), are highly tortuous (felts), or
thick and dense (woven);
[0018] at the end of the treatment cycle, the case hardening
composition must be eliminated; the chromium grains have a tendency
to agglomerate, and mechanical operations are then necessary to rid
the sponges of the case hardening composition.
[0019] Moreover, the penetration of the chromium thus deposited
within the nickel layer is superficial, as a result of the
production principle. The alloys formed by diffusion of the
components provided in the forms indicated is therefore
heterogeneous and this limits the thermal resistance of the
structure due to the risk of oxidation of the sub-layer of metal
which is an alloy with a low chromium content.
[0020] The authors of the present invention have shown that in
order to overcome these various problems, it is appropriate to
implement specific electrolytic deposition techniques, to deposit
the chromium within the porous structure, over the totality of its
developed surface, and to produce the alloy by thermal diffusion
between the layers created with its various constituents.
[0021] In order, in particular, to produce refractory alloys,
capable of resisting high temperatures, it is necessary to form
ternary alloys such as Ni-Cr-Al, Fe-Cr-Al, or quaternary alloys,
Ni-Fe-Cr-Al.
[0022] These alloys could only be produced with difficulty by
codepositions. It is therefore necessary to resort to successive
provisions of each of the constituents of the intended alloys.
[0023] It is known that the deposition of nickel is carried out by
electrolytic route, on structures of sponge type or of felt type
which have been rendered conductive (activated).
[0024] Furthermore, an activation technique for porous polymeric
supports (sponges, felts or woven items) has been developed and
patented which allows, under excellent conditions, for a good level
of conductivity to be conferred and for various metals such as
nickel, iron, copper or binary or ternary alloys of these metals to
be applied by electrolytic deposition.
[0025] This technique is the activation of polymer conductors by
chemical deposition (French Patent No. 95 09547, publication No. 2
737 507).
[0026] The provision of chromium can also be carried out
industrially by electrolytic deposition, However, this operation is
usually carried out on metal items with a relatively simple shape
and with smooth surfaces. In fact, a person skilled in the art
knows that chromium baths used for hard chromium plating or for
decorative chromium plating have a reduced throwing power, which
leads to the lack of chromium deposit or a poor quality deposit in
certain areas of the item to be treated, as a function of the
characteristics of the lines of electric flux.
[0027] The artifices which consist, for example, of using anodes
with a special shape which will concentrate the lines of electric
flux in the areas where they are little present, cannot be
considered for structures with such complex shapes as "3D" products
(sponges, felts or woven items).
[0028] As well as the low throwing power, which leads to a lack of
chromium deposit in the areas masked vis-a-vis the anode or at the
core of the porous structure, the electrolysis operating conditions
lead to deposition characteristics which are not satisfactory:
growths on the edges or streaks on the surface of the "3D", burnt
and friable deposits, etc.
[0029] The authors of the invention which is the subject of the
present description have therefore developed chromium baths which
allow all of these defects to be suppressed and allow chromium
deposits to be obtained which are thick and uniform on complex
surfaces, such as "3D" sponges, felts or woven items, i.e. through
all the thickness of these structures, over the totality of their
developed surface (by a complete covering of meshes of sponges,
threads or fibres of felts and woven items), without closing their
porosity.
[0030] The most commonly used baths in industry are based on
chromic acid and sulphuric acid. In order to increase the covering
power of the bath, which requires the reduction of the current
density at which the deposit starts to form, it is recommended by
persons skilled in the art to respect a given ratio between the
bath concentration of chromic acid and that of sulphuric acid.
Therefore, for a chromic acid concentration of 300 g/l, the chromic
acid/sulphuric acid ratio will have to be 140.
[0031] For the treatment of sponge type structures, this precaution
remains insufficient if the intention is to produce a homogeneous
chromium deposit, covering each strand.
[0032] It is also recommended to use baths containing fluorinated
acids, such as fluosilicic acid, hydrofluoric acid, fluoboric acid.
Therefore, in order to increase the covering power, baths are
produced the composition of which is of the following type:
1 chromic acid: 250 g/l sulphuric acid: 0.6 g/l fluosilicic acid
H.sub.2SF.sub.6: 1%
[0033] However, and in particular with a sponge called "45 PPI"
(measurement of approximately 45 pores per linear inch of the
surface), thickness 5 mm, such a composition principle does not
allow the deposition of chromium at the core of the "3D"
structure.
[0034] On the other hand the authors have shown that the use of
potassium and/or sodium dichromate allows the throwing power and
covering power to be sufficiently improved so that chromium is
deposited at the core of thick sponges or felts, in particular with
dichromate/chromic acid ratios comprised between 0.25 and 1.50 by
weight, and in particular between 0.80 and 1.20.
[0035] This development in chromium plating baths therefore makes
the metallization of "3D" structures possible under the sought
conditions, either through the full thickness of these structures
or over the totality of their developed surface (by the complete
covering of meshes of sponges, threads or fibres of felts or woven
items), without closing their porosity.
[0036] Another of the essential components of refractory alloys is
aluminium. At high temperature, aluminium in fact forms a
protective oxide layer of the alloy.
[0037] The aluminium can be introduced, during the operating
process, in different ways:
[0038] by immersing in a slip containing aluminium particles in
suspension,
[0039] by spraying a suspension of aluminium particles,
[0040] by "painting" using a lacquer or paint containing aluminium
particles.
[0041] A thermal diffusion of the constituents of the intended
alloys can be carried out, in one go after setting up the totality
of the constituents, or in several sequences, including the
possibility of carrying it out after each provision of a layer of
constituent
[0042] It is possible to use very fine particles of aluminium
(<10 microns). The diffusion of the aluminium through the
metallic layers therefore occurs easily.
[0043] The operating process for the preparation of a sponge of
Ni-Cr-Al alloy is given hereafter as an illustrative but non
limitative example of the present invention.
EXAMPLE
[0044] A "45 PPI" sponge, the average pore diameter of which is 0.3
mm, is cut into 5 mm thick sheets. Activation is carried out on a 1
dm.sup.2 sheet according to the technique described in the French
Patent No. 95 09547 in order to render the sponge electrically
conductive. A first deposit of nickel is produced using a nickel
sulphamate bath at the rate of 800 g/m.sup.2 of the apparent
surface of the sponge.
[0045] Then a chromium deposit is carried out using a bath, the
composition of which is as follows:
2 chromic acid: 300 g/l sodium dichromate: 80 g/l sodium sulphate:
3 g/l
[0046] In this example the provision of sulphate ions is controlled
by the introduction of sodium sulphate.
[0047] The operation is carried out with a current density of 40
A/dm.sup.2, at temperatures comprised between approximately 15 and
25.degree. C.
[0048] The anodes are constituted by lead with an active surface
twice as great as the apparent surface of the nickel sponge.
[0049] A quantity of chromium is deposited corresponding to 200
g/m.sup.2, i.e. a thickness of approximately 2.5 microns.
[0050] The sponge obtained is then painted by spraying using a
suspension of aluminium particles.
[0051] The whole is finally treated in an oven with an inert
atmosphere for 4 hours. In the first instance the operation is
carried out with a stage at a temperature of approximately
500.degree. C., which is lower than the melting point of aluminium,
in order to allow the diffusion of the aluminium into the metallic
layers, then the temperature is raised to approximately
1000.degree. C. in order to realise the diffusion of all the other
constituents of the alloy.
[0052] X-ray microanalysis, performed on sections of the metallic
covering thus forming the constitutive strands of the structure,
shows that from the core to the surface of this, the development of
the alloy composition is as follows:
3 nickel: 80 to 75% chromium: 14 to 17% aluminium: 6 to 9%
[0053] It should be noted that the technique for chromium
deposition used and the addition of aluminium produce coverings
which can be referred to as homogeneous and which answer the
problem posed in a satisfactory manner.
[0054] If the operation is carried out according to the operating
method of the example indicated above with a 90 PPI sponge, the
observed distribution of the components of the alloy is
identical.
[0055] Naturally, and moreover as results largely from what
precedes, the invention is not limited to the particular
embodiments described as examples. The invention is not limited to
the examples provided, but can encompass all variants.
* * * * *