Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Of inorganic materials
Reexamination Certificate
1998-08-07
2001-05-15
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Of inorganic materials
C264S044000, C264S628000, C264S640000, C419S002000
Reexamination Certificate
active
06231792
ABSTRACT:
This invention relates to the production of composite structures, and more particularly, to the production of porous products comprised of a fibrous network of material.
U.S. Pat. Nos. 5,304,330; 5,080,963, 5,102,745; and 5,096,663 are directed to the production of porous composites comprised of a fibrous network of material. In accordance with such production, there is a provided a mixture comprised of fibers for forming the porous composite and a structure forming agent which functions as a binder (in particular, a cellulosic material), which are dispersed in an appropriate liquid. After preforming into a desired form, liquid is removed and the composite is heated to a temperature to effect sintering of the fibers at junction points to produce a porous composite comprised of a three-dimensional network of fibers. The structure forming agent, in particular, a cellulosic material, is removed during the sintering process or may be removed after the sintering process.
The present invention is directed to a process for producing a porous composite comprised of a fibrous network of materials wherein the structure forming agent or binder is gasified prior to sintering of the fibers at junction points.
The gasification, prior to sintering, is effected to gasify at least 50% of the structure forming agent or binder, preferably at least 70% and more preferably at least 90%. In many cases, at least 95% up to 99% or better of the binder is gasified prior to sintering.
The gasification of binder or structure forming agent, which may include polymer fiber or cellulose fibers, may be accomplished, for example, by heating the fibrous network to a gasification temperature which is below the sintering temperature for the fibrous network. The temperature which is used is dependent in part on the binder, the sintering temperature of the fibrous network and the amount of binder which is to be removed.
The gasification of binder may be accomplished in a wide variety of atmospheres and with or without a catalyst, and with a series of different pretreatment steps, if desired. Thus, the gasification may be effected in an inert atmosphere in the presence or absence of steam with or without catalyst; or in the presence of oxygen or oxygen in an essentially inert gas with or without the presence of a catalyst, or in the presence of hydrogen with or without a catalyst or in the presence of a combination of hydrogen and steam with or without catalyst or in the presence of oxygen and steam with and without catalyst in any number or sequence of pretreatment steps.
In the case where gasification below sintering temperatures does not remove essentially all of the binder, the remainder of the binder may be gasified at the sintering temperature. The choice of sintering temperature or temperatures depends on the metal or alloy used, metal fiber diameter, sintering time, and the desired physical properties in the final metal fiber mat structure, or that of the composite structure, or that of the composite structure consisting of other fibers or inorganic particles.
If a catalyst is used, the catalyst is one which permits the binder or structure forming agent to be gasified at temperatures lower than the temperatures at which the fibers forming the composite will be sintered. As hereinabove indicated, in accordance with a preferred embodiment, the binder or structure forming agent is a polymer fiber or a cellulosic material. In accordance with such preferred embodiment, the catalyst which is employed for permitting gasification of the cellulosic material at temperatures below the sintering temperatures may be one or more of the following oxide or metal catalysts or, combinations thereof. As an example, oxide catalysts may be potassium hydroxide, vanadium oxide, calcium hydroxide, rhenium oxide, ruthenium oxide. Metal catalyst can be one or more of the following catalysts: platinum, palladium, ruthenium, rhodium, nickel, etc. These and other catalysts should be apparent to those skilled in the art from the teachings herein. The catalyst, if used, may be part of the binder or may be added to the preform.
In the case where steam is used, steam may be added or the steam can be generated in situ from, for example, residual water present in the composite or by “wetting” the composite. In general, the steam is added in an amount of from 0.05 to 97 volume percent
The gasification may be effected at a temperature of less than 400° C. and more generally at a temperature less than 350° C.
In another embodiment, the binder can be gasified by the generation of free radicals such as the use of plasma to generate such radicals.
In the case where the preform includes a metal which can be oxidized and the oxidation is not easily reversed, the gasification is preferably accomplished in a reducing atmosphere.
As hereinabove indicated, the preferred binder or structure forming agent is a cellulosic material, which may be cellulose or a cellulose derivative.
As hereinabove noted, the procedure and materials for producing a porous composite comprised of a network of fibers is described in the aforementioned U.S. patents. As described therein, the fibers employed in producing the composite may be metal and/or carbon and/or a ceramic. In producing such a composite, the fibers may be formed from one or more metals and may be formed from one or more metals and may further include carbon and/or ceramic fibers.
Illustrative but not exhaustive examples of metal fibers which may be used in the practice of this invention include aluminum, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, hafnium, tantalum, tungsten, rhenium, osmium, platinum, gold, antimony, beryllium, iridium, silicon, magnesium, manganese, gallium, and combinations of the above. Metal alloys also may be used in the practice of this invention, as exemplified by constantin, hastelloy, nichrome, inconel, monel, carpenter's metal, and various steels, especially stainless steels, and other alloys. As can be appreciated, there is enormous flexibility in the choice of metal fibers which adds to the attractiveness of our invention.
The diameter of the fibers may vary over a wide range. Thus, for example, the fiber diameter may be as low as about 0.5 micron or may be up to 25 microns or more. The selection of a specific diameter is within the scope of those skilled in the art from the teachings herein.
In producing the composite, the dispersion which includes the fibers and the structure forming agent may further include particles which are to be entrapped in the interstices of the mesh-like structure of the composite. In a preferred embodiment, such particles may be a catalyst, a catalyst support, a catalyst precursor or a supported catalyst or a supported catalyst precursor. When such particles are included in the dispersion, such particles become entrapped in the interstices of the mesh.
The fibers and other components, if any, are dispersed in a liquid by any suitable means. It is not essential to have a uniform dispersion, although often such uniformity is desirable. Dispersion may be effected by such means as sonication, agitation, ball milling, and so forth. The purpose of the liquid is merely to facilitate effective dispersion of the solids, especially where one wants as uniform a dispersion as is feasible in the final preform. Normally the liquid used will be unreactive with the other components of the dispersion, but one can envisage special cases where a functionally desirable reactive property of the medium may be advantageously combined with its fluidity. Since the liquid is later removed, it is clear that it should be readily removable, as by volatilization. Water is normally a quite suitable liquid, although water-alcohol mixtures, and especially water-glycol mixtures, may be used. Illustrative examples of other liquids include methanol, ethanol, propanol, ethylene glycol, propylene glycol, butylene glycol, poly(ethylene glycol)(s), poly(propylene glycol)(
Chang Yung-Feng
Khonsari Ali M.
Meffert Michael W.
Murrell Lawrence L.
Overbeek Rudolf A.
ABB Lummus Global Inc.
Fiorilla Christopher A.
Lillie Raymond J.
Olstein Elliot M.
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