Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly nonmetal substrate
Reexamination Certificate
1996-08-02
2001-09-18
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly nonmetal substrate
C205S160000, C205S205000, C205S210000
Reexamination Certificate
active
06290832
ABSTRACT:
The invention concerns, in general, the manufacture of complex porous metallic or metallized structures.
This invention relates more particularly to the manufacture of complex porous metallic or metallized structures for application as electrodes for the electrolysis of liquid effluents, as electrode supports for electrochemical generators, as catalyst supports, filtration media, phonic insulation, electromagnetic and nuclear protection structures, or for other applications.
The metallic or metallized structures according to the invention are of the foam, felt or fabric type having a high level of open porosity, and having the aspect of a dense network of fibers or mesh with a three dimensional skeletal structure defining a plurality of open spaces intercommunicating with one another and with the exterior of the structures.
Foams are reticulated cellular structures of high porosity (greater than 80%, and possibly reaching 98%) and having an open porosity by inhibiting cell wall formation, wherein the totality of the network's openings, or at least a high proportion thereof, are in communication with one another.
Felts are randomly interlaced matted fibers defining therebetween inter-fiber spaces of variable shapes and dimensions, communicating with one another.
Fabrics are structures constituted by an assembly of textile threads or fibers that are interlaced, either woven or netted. They may be in the form of thick and complex structures, in particular when they are made of two external woven faces connected by knitted threads that hold them simultaneously spaced apart and interconnected, as for example can be produced using Raschel type knitting machines.
These various complex porous structures, that according to the invention will be metallized throughout their entire thickness, over all their developed surface, without clogging of their porosity, may be provided starting from various base materials.
For foams, organic, mineral or synthetic materials are used, and in particular polymers such as polyester, polyamide, polyurethane or polyether.
For felts and fabrics, organic mineral or synthetic materials are also used such as the previously-cited polymers, or glass, rock or carbon fibers, or natural fibers such as cotton, wool or the like.
Various processes for metallizing such structures have already been proposed, including:
chemical deposition, followed by one or several electrochemical depositions,
deposition of carbon or graphite particles, followed by one or several electrochemical depositions,
vacuum deposition of metals, in particular by cathodic vaporization, gas diffusion or ionic deposition. followed by one or several electrochemical depositions,
chemical vapor deposition.
Whenever electrochemical deposition will be carried out, one should previously prime the surface to be electroplated, to render it electrically conductive. This is the purpose of the “pre-metallizing” stage incorporated in most of the cited processes (chemical deposition, deposition of carbon particles, vacuum deposition).
The present invention is concerned particularly with carrying out a pre-metallization process in the manufacture of complex porous metallic structures, which process provides various advantages relative to the previous techniques for the production of said products.
Chemical deposition on an industrial scale is an expensive process and is somewhat difficult to control. It involves the consumption of expensive chemical products (tin, palladium, . . . ) and necessitates, between each of its steps, careful rinsing operations on complex porous structures which have a high retentive power, in order to avoid undesirable contamination by transfer of the reactive components from one treatment bath to the next. This process generally provides a very efficient pre-metallization, in particular with a high penetrating power in the structures to be treated, but generates additional costs due to the necessity of retreating its liquid effluents.
The deposition of carbon or graphite particles, which is widely used up to date on an industrial scale for the production of metallic foams, is relatively inexpensive, both in terms of the products consumed and as regards the investments necessary for carrying it out. It however has three types of drawback:
the carbon particles do not form a continuous conductive deposit on the surface of the structure's openings. Electrochemical metallization therefore has to provide a bridging of these particles between one another. In some cases, the initial phase of propagation of the electroplated deposit through the entire volume of the structure is slow, and should preferably be carried out with enhancement of the structure's conductivity using metallic anodic contacts, in order to achieve economically acceptable recovery rates;
because of the size of the carbon particles, It is not possible with this method, without clogging the internal porosity, to treat denser structures: foams having a porosity greater than 100 ppl (100 pores per linear inch), dense felts, or thick and dense fabrics made of fine fibers whose external woven faces are connected by knitted threads that maintain the external faces simultaneously spaced apart and interconnected;
the deposition of carbon particles complicates the step of pyrolysis of the organic materials after metallization, due to a substantial increase of their mass.
Among vacuum deposition methods, only cathodic vapor deposition is industrially used for the pre-metallization of complex porous structures like those used in the invention. This method, described in French Patent 2,558,485 of Jan. 25, 1984, is generally regarded as the most efficient one for the application under consideration.
It however requires the use of sophisticated industrial devices, precise and delicate operating procedures must be followed, and the investment in production equipment is relatively high. At the present time, there are two limitations with this process:
although it enables a homogeneous continuous deposition within complex porous structures with a high penetrating power, the process nevertheless has limitations in terms of the thickness of the substrate to be treated and the density of fibers or openings (these two criteria being combinable), in particular when the substrate is constituted of an organic material that must not be subject to great increases of temperature;
at the present time, this method enables a batch operation (for the treatment of plates) or a semi-continuous operation (treatment using rollers) but not a truly continuous operation at an economically acceptable cost.
The pre-metallization processes summarized above are satisfactory from the point of view of industrial production on a large scale, but nevertheless have the described drawbacks.
It is furthermore generally speaking always desirable to reduce the cost of known processes and to simplify the carrying out of these processes, in order to reduce the cost of the resulting products. These are two of the advantages obtained by the present invention.
The present invention, through a specific adaptation of a process which is known for applications that are simpler to carry out, aims to permit the electroplating (galvanic metallization) of the above-defined porous complex structures by providing a pre-metallization by the preliminary deposition of a conductive polymer, so the later metallization can then itself be carried out in specific conditions related to the nature of the pre-metallization layer.
The use of conductive polymers has already been described to permit electroplating to be carried out. This use, as with other prior pre-metallization techniques, has been designed, defined and made operational for application to simple or relatively simple surfaces: smooth surfaces, or smooth surfaces connected by holes of diameter greater than 0.5 mm, the depth of the holes being of the order of 1 mm. The prior use notably concerned the pre-metallization of printed circuit boards.
The pre-metallization treatment of the complex porous structures as descri
Bugnet Bernard
Costa Max
Doniat Denis
Henderson & Sturm LLP
S.C.P.S. Societe de Conseil et de Prospective Scientifique S.A.
Wong Edna
LandOfFree
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