WO1998011974A1 - Porous nickel filter material - Google Patents

Porous nickel filter material Download PDF

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Publication number
WO1998011974A1
WO1998011974A1 PCT/US1997/016768 US9716768W WO9811974A1 WO 1998011974 A1 WO1998011974 A1 WO 1998011974A1 US 9716768 W US9716768 W US 9716768W WO 9811974 A1 WO9811974 A1 WO 9811974A1
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WO
WIPO (PCT)
Prior art keywords
accordance
nickel
filter
range
layer
Prior art date
Application number
PCT/US1997/016768
Other languages
French (fr)
Inventor
Joseph A. Scroppo
Estela T. Ong
Nellie E. Burton-Gorman
Original Assignee
Bladon International, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Bladon International, Inc. filed Critical Bladon International, Inc.
Priority to AU44291/97A priority Critical patent/AU4429197A/en
Publication of WO1998011974A1 publication Critical patent/WO1998011974A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0041—Inorganic membrane manufacture by agglomeration of particles in the dry state
    • B01D67/00411—Inorganic membrane manufacture by agglomeration of particles in the dry state by sintering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0041—Inorganic membrane manufacture by agglomeration of particles in the dry state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2027—Metallic material
    • B01D39/2031—Metallic material the material being particulate
    • B01D39/2034—Metallic material the material being particulate sintered or bonded by inorganic agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/022—Metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/022—Metals
    • B01D71/0223—Group 8, 9 or 10 metals
    • B01D71/02232—Nickel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/11—Making porous workpieces or articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/15—Use of additives
    • B01D2323/20—Plasticizers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/02—Details relating to pores or porosity of the membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/26—Electrical properties

Definitions

  • This invention relates to filter material for performing microfiltration, ultrafiltration, and separation of ionic species and a process for producing such filter material.
  • Membrane and composite nickel metal separation systems offer significant advantages over existing separation processes, particularly in the hazardous waste, chemical, petroleum and food industries. In addition to consuming less energy than conventional processes, membrane systems are compact and modular, enabling easy retrofit to existing industrial processes.
  • the major developed membrane processes include microfiltration, ultrafiltration, reverse osmosis, electrodialysis, and gas separation with polymer membranes and pervaporation.
  • Microfiltration, ultrafiltration and reverse osmosis are related filtration techniques in which a solution containing dissolved or suspended solutes is forced through a membrane filter. The solvent passes through the membrane and the solutes are retained. These processes differ principally in the size of the particles separated by the membrane.
  • Microfiltration typically utilizes membranes having pore diameters from 0.1 to 10 microns. Microfiltration membranes are used to filter suspended particulates, bacteria or large colloids from solutions. Ultrafiltration utilizes membranes having pore diameters in the range of 20 to 1 ,000 angstroms. Ultrafiltration membranes can be used to filter dissolved macro molecules such as proteins from solution. Ultrafiltration membranes can be sintered directly to the microfilters for more efficient filtering.
  • Reverse osmosis involves membrane pores in the range of about 5-20 A in diameter.
  • the membrane pores of reverse osmosis membranes are so small that they are within the range of the thermal motion of the polymer chains.
  • Reverse osmosis membranes are used to separate dissolved microsolutes, such as salt, from water. By combining the micro and ultra filters ahead of a reverse osmosis membrane, greater efficiency in operation and lower cost result compared to stand-alone reverse osmosis membranes.
  • charged membranes are used to separate ions from aqueous solutions under the driving force of an electrical potential difference.
  • the process utilizes an electrodialysis stack, built on the filter-press principal, and containing several hundred individual cells formed by a pair of anion .and cation exchange membranes.
  • a mixed gas feed at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the feed.
  • the membrane separation process produces a permeate enriched in the more permeable species.
  • Pervaporation is a relatively new process that has elements in common with reverse osmosis and gas separation.
  • U.S. Patent 5,110,541 teaches a method of manufacturing a porous electrode for a molten carbonate fuel cell in which nickel powders and aluminum- base powders are mixed together with a binder, methyl cellulose, and a solvent, water, to form a slurry. The slurry is then tape cast to form a green tape which is then sintered in a vacuum or a reducing atmosphere to form the final porous electrode.
  • U.S. Patent 5,110,541 teaches a method of manufacturing a porous electrode for a molten carbonate fuel cell in which nickel powders and aluminum- base powders are mixed together with a binder, methyl cellulose, and a solvent, water, to form a slurry. The slurry is then tape cast to form a green tape which is then sintered in a vacuum or a reducing atmosphere to form the final porous electrode.
  • Patent 5,041,159 teaches a method for producing a nickel plaque in which particles of nickel/aluminum alloy are slurried, the slurry is tape cast to form a porous cohesive body, and the porous cohesive body is then sintered in an oxidizing path.
  • U.S. Patent 4,734,237 teaches a process for shaping parts from metallic and/or ceramic powders in which the metal and/or ceramic powders are mixed with a gel- forming material (agar), water, ethylene glycol, and dispersants. The resulting mixture is injected at a temperature above the gel point of the gel-forming material into a mold, cooled to a temperature below the gel point of the gel-forming material to produce a self-supporting structure, and removed from the mold. The resulting structure is then air dried or heated as desired.
  • a gel- forming material agar
  • water ethylene glycol
  • dispersants dispersants
  • Patent 4,225,346 teaches a process for producing porous nickel bodies in which powdered nickel is mixed into an aqueous solution of a cellulose derivative preferably methyl cellulose, which, upon heating, gels into a semi-solid body. The body is then sintered at a temperature between about 600 °C and 1200°C in a reducing atmosphere.
  • a cellulose derivative preferably methyl cellulose
  • a process for producing a high-efficiency metal membrane element suitable for use as a filter which includes depositing by air-layering techniques a substantially uniform low-density bed of a sinterable dendritic material into a mold suitable for applying a compressive force thereto, comprising the low-density bed of sinterable dendritic material to form a green form and sintering the green form to produce the end product is taught by U.S. Patent 5,487,771. See also U.S. Patent 5,312,580 which teaches a method of manufacturing porous metal alloy fuel cell components in which particles of a base metal and a master alloy are dispersed and suspended in a liquid medium comprising water, a binding agent, halide activator, and dispersants.
  • the suspension is then formed into the desired shape and heated to form a porous green structure.
  • the green structure is then heat treated to burn out the binder, form an alloy of the alloying metal in the master alloy and the base metal, and sinter together into a coherent, porous metallic structure the particles of the alloy formed by heat treating the green component structure.
  • U.S. Patent 5,096,661 teaches a porous intermediate compact prepared from metal particles, carbon and temporary binder, the compact being heated to remove the binder and then infiltrated with a vapor of a metal having a melting point lower than the compact.
  • U.S. Patent 4,828,930 teaches a method for making seamless, porous metal articles in which a stabilized suspension of a metal particulate is contained within a mold which is rotated at a rate and for a time such that the particulate is separated from the suspension and distributed on the interior wall of the mold, thereby forming a structure conforming to the interior wall of the mold. The formed structure is then dried and sintered to remove volatile material and fuse the individual particles of the particulate to each other.
  • a porous nickel filter produced by mixing a nickel powder having a particle size in the range of about 0.5 to 5.0 microns with organic additives suitable for forming an extrudable or castable composition.
  • the resulting composition is then extruded or cast into a desired shape.
  • the resulting extrusion or casting is then compacted by isostatic pressing at a pressure sufficient to form a coherent green body having an open porosity in a range of about 40% to 70%.
  • the green body is subsequently heated in a reducing atmosphere at a temperature and for a time period sufficient to volatilize the organic additives.
  • the organic additives have a volatilization rate such that the open porosity of the green body is maintained throughout the heating process. Thereafter, the heated green body, with organic additives having been volatilized, is sintered, forming a coherent, structurally strong, filter body with open porosities in the range of about 40 to 70%.
  • the filters produced in accordance with one embodiment of the process of this invention are multilayer, porous nickel-containing filters comprising a nanopore layer of one of nickel and ceramic deposited on a nickel substrate, the nickel substrate having a majority of pore sizes larger than the pore sizes of the nanopore layer. Pore sizes of the nanopore layer are substantially all in the range of about 5A to about 20A and pore sizes of the substrate layer are substantially all in the range of about 20A to about 100 microns.
  • Fig. 1 is a schematic diagram of a microstructure of a membrane cross section of a porous nickel filter in accordance with one embodiment of this invention.
  • Fig. 2 is a graphic representation showing typical pore size distributions of lysimeter tube filters prepared from nickel powders in accordance with one embodiment of this invention.
  • This invention involves the preparation, extrusion and casting of porous nickel elements including alloy and physiochemical modifications for application, for example, in vadose zone and groundwater monitoring devices such as hydraulically installed and other lysimeters, soil pore moisture equipment .and a Quantitative Volative Analyzer with a cone penetrometer (QVAC).
  • QVAC Quantitative Volative Analyzer with a cone penetrometer
  • This invention includes the manufacture of versatile and low cost liquid, ionic and gas separation membranes, sheets, tubes and other cast or extruded shapes capable of performing .any of microfiltration, ultrafiltration, and separation of ionic species commonly achieved by filtration, reverse osmosis, and electrodialysis.
  • One embodiment of this invention utilizes filters having pores fine enough for gas separation; in accordance with another embodiment of this invention, the filters can also be used for separation of dissolved ions used for desalination.
  • the filter material utilized in the process of this invention can be formed into almost any desired shape and, thus, is suitable for use in a wide variety of applications.
  • the filter material in the form of, for example, a membrane, tube or other configuration can be electrically charged to attract oppositely charged ions and repel similarly charged ions. This mechanism can be used to control the passage or retention of the ionic species.
  • nickel as used throughout the specification and claims, we mean nickel metal, nickel alloy, composite metal and/or composite nickel/ceramic materials.
  • nickel, nickel alloy, composite metal or composite nickel/cer.amic filters produced by the process of this invention can be customized to be used for molecular separations, concentration of hazardous wastes, gas separation, wastewater purification and food processing.
  • the process of this invention provides the ability to produce high flux, essentially defect-free, nickel membranes and tubes suitable for use as filters on a large scale as well as the ability to form these filters into compact, high strength, high-surface area, economic modules.
  • the filters have porosities in the range of about 40-70% by volume compared to conventional filters, which typically have porosities in the range of only 25 to 30%. Conventional filters with porosities above 30% are very fragile.
  • Symmetrical membranes are generally uniformly isotropic throughout.
  • the membranes can be porous or dense, but the permeability of the membrane material does not substantially change from point to point within the membrane.
  • Asymmetric membranes typically have higher fluxes than symmetrical membranes and comprise a relatively dense, thin surface layer supported on an open, often microporous substrate. The surface layer generally performs the separation and is the principal barrier to flow through the membrane.
  • the open support layer provides mechanical strength.
  • This invention includes asymmetric nickel metal filters with multiple layers of porous materials, with porosities greater than about 50%, each bonded together and having specially tailored porosities as discrete layers, as well as symmetrical membranes.
  • the filter material in accordance with one embodiment of this invention comprises a porous nickel metal supported ceramic membrane in which a thin nanopore-size nickel or ceramic layer is deposited on a larger pore-size nickel substrate.
  • nanopore as used throughout the specification and claims, we mean pore sizes less than about 20A in diameter. Both porous nickel and ceramic can be graded with respect to porosity .and pore size to retain species of different sizes at different layers.
  • the composition of the membrane materials of this invention may be tailored to suit the chemistry of the liquid. The composition of the metal layer may even be designed to catalyze certain reactions. The reaction product is then separated from the reactants as it is being produced to increase the product yield.
  • the filter material produced by the process of this invention can be formed into sheets or rubes to fit various filter designs as well as pulses of reverse flow.
  • the metal layer is electrically charged to control the passage or retention of certain ionic species through the membrane.
  • Membrane cleaning is achieved by chemical or thermal treatment.
  • the varying porosities of certain embodiments of this invention are used to help prevent clogging. They can withstand high temperatures and pressure.
  • a schematic diagram of the microstructure cross-section of a membrane in accordance with one embodiment of this invention is shown in Fig. 1.
  • the discrete materials comprising the membrane of this invention can be bonded by using the sintering technique of this invention. These porous materials can withstand both high temperatures and pressures.
  • the filter system can be designed to take the shape defined by a specific mold.
  • the process for producing porous nickel filters in accordance with this invention involves the selection of the starting nickel powder and formulation of the powder with organic additives to form an extrudable compound or casting compound for making porous nickel sheets.
  • the nickel powder may be mixed with an alloying material prior to formation of the extrudable or casting compound.
  • the compound is extruded into the desired tubular shape.
  • the extruded tube is placed in an isostatic press and pressurized to form a "green" body having the desired dimensions and open porosity.
  • the open porosity of the filter materials produced in accordance with the process of this invention, independent of the material shape, is in the range of about 40% to 70%.
  • Nickel powders that can be used in this invention comprise the carbonyl nickel powders manufactured by International Nickel Company (INCO).
  • nickel powders which are suitable for use in this invention are selected from the group consisting of Type 123 nickel powders (4.7 micron particle size, individual spikey particles), Type 255 nickel powders (2.6 micron particle size, long fiber chains), Type 287 nickel powders (3.0 micron particle size, a more compact version of Type 255 nickel powders), MSP (2.6 micron particle size, coarse fraction of Type 255 nickel powders), and Type 210 nickel powders (0.6-1 micron particle size, very fine fibers).
  • the MSP type powder is particularly preferred. Applications requiring finer pore sizes may utilize the Type 210 powder, while applications requiring larger pore sizes may use the Type 123 powders. Powders may also be blended to tailor the resulting filter to the desired porosity and pore size.
  • solvent, binder, plasticizer and dispersant are mixed together to make a plastic compound.
  • methyl cellulose is used as a binder
  • ethylene glycol is used as the plasticizer
  • tri-butylphosphate is used as the dispersant.
  • Water is a suitable solvent.
  • saffil alumina fibers are added to the formulation.
  • the plastic compound referred to hereinabove is fed into a screw driven extruder and extruded through a die designed to yield the size and dimensions of the desired tube product.
  • the tube porosity is reduced to near target dimension by isostatic pressing. This is done by inserting the extruded tube into a mandrel and placing the tube and mandrel in a rubber bag for isostatic pressing. A pressure of 5,000-10,000 psi is typically applied, depending on the tube material and the extent of compaction needed to meet the target.
  • the tube After pressing, the tube is laid along its length and fired in an air environment at a temperature of 400-700°C depending on the lysimeter material and size to burn off the organics.
  • the nickel becomes partially oxidized by this heat treatment, but the tube is not deformed by the oxidation.
  • the tube is then heated in a reducing atmosphere to reduce the nickel to metal and to sinter the particles to produce a coherent body.
  • the heat treatment is done at a temperature of 500-600°C with a soak time of 2-4 hours and an atmosphere provided by a feed gas whose composition is 60% H 2 , 20% CO 2 , 20% H 2 O. A strong and impact resistant porous nickel tube is thus obtained.
  • the material composition produced in this manner was extruded to form a tube with a Killion 3 Hp screw type extruder.
  • the extrusion die used WEIS designed to provide .an internal diameter of 1.680 inches and an external diameter of 2.700 inches for the tube.
  • the tube was dried in an oven at about 100°C.
  • the dimensions of the dried tube are given in Table I.
  • the open porosity of the dried tube was about 81%.
  • the tube was trimmed down because the ends were not straight.
  • the new tube dimensions are given in Table I.
  • the tube was inserted into a mandrel and isostatically pressed at 7,640 psi after which the open porosity was about 60%.
  • the pressed tube dimensions are given in Table I.
  • the tube was trimmed to near target size and its dimensions are given in Table I.
  • the tube was heated to 450°C with 30 minutes hold to burn off the binder. After cool down, it was turned around and reheated to 450°C, again with a 30 minute hold.
  • the tube dimensions after this step are given in Table I.
  • the tube was heated in a muffle furnace which was fed with a gas of 60% H 2 , 20% CC ⁇ , 20% H 2 O composition, by ramping to 560°C over a 4 hour period and holding at 560°C for 3 hours.
  • the final dimensions of the tube are given in Table I. It had an open porosity of 61%.
  • a typical pore size distribution of the described tube is given in Fig. 2.
  • the bubble pressure which is the pressure at which air appears when the tube is pressurized in water, was determined to be at least 15 psi.
  • This tube was then assembled into a lysimeter, the tube having been trimmed to exactly fit the lysimeter, and then sealed against the lysimeter body with O-rings or indium metallic gaskets.
  • the porous nickel tubes can be cut or machined to fit the dimensions of other groundwater monitoring equipment without closing the filter pores.
  • Example 2 Lysimeter Tubes from Ni-210 The materials listed below were weighed out into a plastic bag.
  • the material composition was extruded to form a tube with a Killion 3 Hp screw type extruder.
  • the dimensions of the extrusion die provided a 1.500 inch internal diameter and a 2.400 inch outside diameter to the tube.
  • the tube was dried in an oven at about 100°C.
  • the dimensions of the dried tube are given in Table 2.
  • the open porosity of the dried tube was about 76%.
  • the tube was trimmed down because the ends were not straight.
  • the new tube dimensions are given in Table 2.
  • the tube was inserted into a mandrel and isostatic pressed at 5,000 psi.
  • the pressed tube dimensions are given in Table 2.
  • the resulting open porosity was about 67%.
  • the tube was trimmed to near target size and its dimensions are given in Table 2.
  • the tube was heated to 600°C in air with 30 minutes hold to burn off the binder.
  • the tube dimensions after this step are given in Table 2.
  • the tube was heated in a muffle furnace which was fed with a gas of 60% H 2 , 20% CO 2 , 20% H 2 O composition, by ramping to 535 °C over a 4 hour period and holding at 535 °C for 3 hours.
  • the final dimensions of the tube are given in Table 3. It had an open porosity of 60%.
  • a typical pore size distribution of this tube is also shown in Fig. 2.
  • Example 3 Porous Nickel Sheet Sintered to a Perforated Nickel Sheet
  • a sheet of unsintered nickel formed from the following materials was sintered to a perforated nickel Type 200 sheet and then rolled without cracking.
  • the nickel Type 200 sheet was 0.036" thick and perforated with 0.093" diameter holes on 0.156" staggered centers. This demonstrated the ability to achieve strong adhesion between the nickel sheet and resulting porous nickel filter, with 65% porosity, which resulted after sintering.
  • the perforated nickel sheet was degreased with methanol. The sheet was 5 inches in length and 5 inches wide. It was then etched with a solution consisting of 50% concentrated nitric acid and 50% concentrated acetic acid. The etched perforated nickel sheet was dried.
  • An unsintered sheet of anode material was placed on the etched perforated sheet and placed in a sintering furnace.
  • the sintering furnace was ramped to 1000°C in 4 hours and let to soak for 1 hour.
  • the furnace atmosphere was changed from 100% nitrogen to 4% hydrogen at 470 °C.
  • the atmosphere of 4% hydrogen was continued until the furnace cooled to 230°C and then the furnace was shut off.
  • the pore size of the sintered nickel filter on the perforated sheet was approximately 4 to 6 microns.
  • the sintered material was approximately 2 mm thick.
  • the sintering furnace was ramped to 1000°C in 4 hours and soaked for 1 hour. At the start of sintering, the furnace atmosphere was 100% nitrogen. Two hours after furnace heat up, the temperature reached 538 °C and the atmosphere was changed to 4% hydrogen. This atmosphere was kept until furnace cool down. The furnace was purged with nitrogen before opening the door.
  • the sintered components had excellent adhesion and were 63.1 % porous.
  • the pore sizes were approximately 4 to 6 microns.
  • the sintered materials were flat and square.
  • the anode material was magnetic. Sintering reduced the thickness by 23.4%. Other dimensions were:
  • a pressure of 72 psi was applied for 30 minutes and the resulting laminate removed from the device and inspected.
  • the laminated material was moist to the touch.
  • Pressure of 72 psi was reapplied for 1 hour and the laminate removed and reinspected.
  • the laminate had good adhesion and was trimmed.
  • the laminated material was dried and then sintered as in Example 4 with the exception that it was sintered between graphite blocks to maintain flatness during sintering.
  • the filter of this invention has pore sizes ranging from macro particle sizes of greater than 100 microns to molecular range of less than 0.01 microns and provides porosities in the range of about 40 to 70% by volume.
  • the use includes particle filtration and ultrafiltration. Nano-sized pores can be combined with larger sized pores and can be mated with ionic range filters having pore sizes of approximately 0.001 microns without significant reductions of porosities.
  • Applications in which the nickel-based filter material of this invention may be utilized include yeast cells, bacteria, paint pigment, tobacco smoke, carbon black, sugars, coal dust, pollens, milled flour, red blood cells, colloidal silica, albumin protein, viruses, pyrogen, aqueous salts, metal ions, and gas separation.
  • porous nickel sheets are sintered to perforated or wire nickel screen for support or to match a desired configuration.

Abstract

A process for producing porous nickel filters having a narrow pore size distribution in which a nickel powder having a particle size in a range of about 0.5 to 5.0 νm is mixed with organic additives suitable for forming one of an extrudable composition and a castable composition, which composition is formed into a desired shape. The desired shape is compacted by isostatic pressing at a pressure sufficient to form a green body having an open porosity in a range of about 40 % to 65 %. The green body is heated in a reducing atmosphere at a temperature and for a time period sufficient to volatilize the organic additives, the organic additives having a volatilization rate such that the open porosity of the green body is maintained. The green body is then sintered, forming a coherent filter body having an open porosity in the range of about 40 % to 70 % by volume.

Description

POROUS NICKEL FILTER MATERIAL
BACKGROUND OF THE INVENTION FIELD OF THE INVENTION
This invention relates to filter material for performing microfiltration, ultrafiltration, and separation of ionic species and a process for producing such filter material.
DESCRIPTION OF PRIOR ART
Industrial separation processes such as distillation, drying and evaporation consume a significant portion of the energy used in the United States. Membrane and composite nickel metal separation systems offer significant advantages over existing separation processes, particularly in the hazardous waste, chemical, petroleum and food industries. In addition to consuming less energy than conventional processes, membrane systems are compact and modular, enabling easy retrofit to existing industrial processes.
The major developed membrane processes include microfiltration, ultrafiltration, reverse osmosis, electrodialysis, and gas separation with polymer membranes and pervaporation. Microfiltration, ultrafiltration and reverse osmosis are related filtration techniques in which a solution containing dissolved or suspended solutes is forced through a membrane filter. The solvent passes through the membrane and the solutes are retained. These processes differ principally in the size of the particles separated by the membrane.
Microfiltration typically utilizes membranes having pore diameters from 0.1 to 10 microns. Microfiltration membranes are used to filter suspended particulates, bacteria or large colloids from solutions. Ultrafiltration utilizes membranes having pore diameters in the range of 20 to 1 ,000 angstroms. Ultrafiltration membranes can be used to filter dissolved macro molecules such as proteins from solution. Ultrafiltration membranes can be sintered directly to the microfilters for more efficient filtering.
Reverse osmosis involves membrane pores in the range of about 5-20 A in diameter. The membrane pores of reverse osmosis membranes are so small that they are within the range of the thermal motion of the polymer chains. Reverse osmosis membranes are used to separate dissolved microsolutes, such as salt, from water. By combining the micro and ultra filters ahead of a reverse osmosis membrane, greater efficiency in operation and lower cost result compared to stand-alone reverse osmosis membranes.
In an electrodialysis process, charged membranes are used to separate ions from aqueous solutions under the driving force of an electrical potential difference. The process utilizes an electrodialysis stack, built on the filter-press principal, and containing several hundred individual cells formed by a pair of anion .and cation exchange membranes.
In a gas separation process, a mixed gas feed at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the feed. The membrane separation process produces a permeate enriched in the more permeable species.
Pervaporation is a relatively new process that has elements in common with reverse osmosis and gas separation.
Membranes suitable for utilization in these applications can be produced by any number of known processes. U.S. Patent 5,110,541 teaches a method of manufacturing a porous electrode for a molten carbonate fuel cell in which nickel powders and aluminum- base powders are mixed together with a binder, methyl cellulose, and a solvent, water, to form a slurry. The slurry is then tape cast to form a green tape which is then sintered in a vacuum or a reducing atmosphere to form the final porous electrode. U.S. Patent 5,041,159 teaches a method for producing a nickel plaque in which particles of nickel/aluminum alloy are slurried, the slurry is tape cast to form a porous cohesive body, and the porous cohesive body is then sintered in an oxidizing path.
U.S. Patent 4,734,237 teaches a process for shaping parts from metallic and/or ceramic powders in which the metal and/or ceramic powders are mixed with a gel- forming material (agar), water, ethylene glycol, and dispersants. The resulting mixture is injected at a temperature above the gel point of the gel-forming material into a mold, cooled to a temperature below the gel point of the gel-forming material to produce a self-supporting structure, and removed from the mold. The resulting structure is then air dried or heated as desired. U.S. Patent 4,225,346 teaches a process for producing porous nickel bodies in which powdered nickel is mixed into an aqueous solution of a cellulose derivative preferably methyl cellulose, which, upon heating, gels into a semi-solid body. The body is then sintered at a temperature between about 600 °C and 1200°C in a reducing atmosphere.
A process for producing a high-efficiency metal membrane element suitable for use as a filter which includes depositing by air-layering techniques a substantially uniform low-density bed of a sinterable dendritic material into a mold suitable for applying a compressive force thereto, comprising the low-density bed of sinterable dendritic material to form a green form and sintering the green form to produce the end product is taught by U.S. Patent 5,487,771. See also U.S. Patent 5,312,580 which teaches a method of manufacturing porous metal alloy fuel cell components in which particles of a base metal and a master alloy are dispersed and suspended in a liquid medium comprising water, a binding agent, halide activator, and dispersants. The suspension is then formed into the desired shape and heated to form a porous green structure. The green structure is then heat treated to burn out the binder, form an alloy of the alloying metal in the master alloy and the base metal, and sinter together into a coherent, porous metallic structure the particles of the alloy formed by heat treating the green component structure.
U.S. Patent 5,096,661 teaches a porous intermediate compact prepared from metal particles, carbon and temporary binder, the compact being heated to remove the binder and then infiltrated with a vapor of a metal having a melting point lower than the compact. U.S. Patent 4,828,930 teaches a method for making seamless, porous metal articles in which a stabilized suspension of a metal particulate is contained within a mold which is rotated at a rate and for a time such that the particulate is separated from the suspension and distributed on the interior wall of the mold, thereby forming a structure conforming to the interior wall of the mold. The formed structure is then dried and sintered to remove volatile material and fuse the individual particles of the particulate to each other. SUMMARY OF THE INVENTION
It is an object of this invention to provide a versatile and low cost porous filter material suitable for performing microfiltration, ultrafiltration, and separation of ionic species commonly achieved by reverse osmosis.
It is another object of this invention to provide a versatile and low cost porous filter material suitable for gas separation.
It is yet another object of this invention to provide a versatile and low cost liquid separation system capable of simultaneously performing microfiltration, ultrafiltration, and separation of ionic species commonly achieved by reverse osmosis. It is yet another object of this invention to provide a versatile and low cost gas separation system.
It is yet another object of this invention to provide a method for producing thin composite sheets, tubes or other suitable shapes of nickel and other suitable filter materials such as metal, ceramics and plastics having porosities in the range of 50 to 70% by volume while still maintaining structural strength and integrity.
These and other objects of this invention are achieved by a porous nickel filter produced by mixing a nickel powder having a particle size in the range of about 0.5 to 5.0 microns with organic additives suitable for forming an extrudable or castable composition. The resulting composition is then extruded or cast into a desired shape. The resulting extrusion or casting is then compacted by isostatic pressing at a pressure sufficient to form a coherent green body having an open porosity in a range of about 40% to 70%. The green body is subsequently heated in a reducing atmosphere at a temperature and for a time period sufficient to volatilize the organic additives. The organic additives have a volatilization rate such that the open porosity of the green body is maintained throughout the heating process. Thereafter, the heated green body, with organic additives having been volatilized, is sintered, forming a coherent, structurally strong, filter body with open porosities in the range of about 40 to 70%.
The filters produced in accordance with one embodiment of the process of this invention .are multilayer, porous nickel-containing filters comprising a nanopore layer of one of nickel and ceramic deposited on a nickel substrate, the nickel substrate having a majority of pore sizes larger than the pore sizes of the nanopore layer. Pore sizes of the nanopore layer are substantially all in the range of about 5A to about 20A and pore sizes of the substrate layer are substantially all in the range of about 20A to about 100 microns. BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:
Fig. 1 is a schematic diagram of a microstructure of a membrane cross section of a porous nickel filter in accordance with one embodiment of this invention; and
Fig. 2 is a graphic representation showing typical pore size distributions of lysimeter tube filters prepared from nickel powders in accordance with one embodiment of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
This invention involves the preparation, extrusion and casting of porous nickel elements including alloy and physiochemical modifications for application, for example, in vadose zone and groundwater monitoring devices such as hydraulically installed and other lysimeters, soil pore moisture equipment .and a Quantitative Volative Analyzer with a cone penetrometer (QVAC). This invention includes the manufacture of versatile and low cost liquid, ionic and gas separation membranes, sheets, tubes and other cast or extruded shapes capable of performing .any of microfiltration, ultrafiltration, and separation of ionic species commonly achieved by filtration, reverse osmosis, and electrodialysis. One embodiment of this invention utilizes filters having pores fine enough for gas separation; in accordance with another embodiment of this invention, the filters can also be used for separation of dissolved ions used for desalination.
The filter material utilized in the process of this invention can be formed into almost any desired shape and, thus, is suitable for use in a wide variety of applications. The filter material in the form of, for example, a membrane, tube or other configuration can be electrically charged to attract oppositely charged ions and repel similarly charged ions. This mechanism can be used to control the passage or retention of the ionic species.
The mechanical, chemical, thermal, electrical and barometric properties of the materials covered by the material and process of this invention provide many advantages over presently used polymeric membr.anes and ceramic filters. By the term "nickel" as used throughout the specification and claims, we mean nickel metal, nickel alloy, composite metal and/or composite nickel/ceramic materials. The nickel, nickel alloy, composite metal or composite nickel/cer.amic filters produced by the process of this invention can be customized to be used for molecular separations, concentration of hazardous wastes, gas separation, wastewater purification and food processing.
The process of this invention provides the ability to produce high flux, essentially defect-free, nickel membranes and tubes suitable for use as filters on a large scale as well as the ability to form these filters into compact, high strength, high-surface area, economic modules. The filters have porosities in the range of about 40-70% by volume compared to conventional filters, which typically have porosities in the range of only 25 to 30%. Conventional filters with porosities above 30% are very fragile.
Symmetrical membranes are generally uniformly isotropic throughout. The membranes can be porous or dense, but the permeability of the membrane material does not substantially change from point to point within the membrane. Asymmetric membranes, on the other hand, typically have higher fluxes than symmetrical membranes and comprise a relatively dense, thin surface layer supported on an open, often microporous substrate. The surface layer generally performs the separation and is the principal barrier to flow through the membrane. The open support layer provides mechanical strength. This invention includes asymmetric nickel metal filters with multiple layers of porous materials, with porosities greater than about 50%, each bonded together and having specially tailored porosities as discrete layers, as well as symmetrical membranes.
The filter material in accordance with one embodiment of this invention comprises a porous nickel metal supported ceramic membrane in which a thin nanopore-size nickel or ceramic layer is deposited on a larger pore-size nickel substrate. By the term "nanopore," as used throughout the specification and claims, we mean pore sizes less than about 20A in diameter. Both porous nickel and ceramic can be graded with respect to porosity .and pore size to retain species of different sizes at different layers. The composition of the membrane materials of this invention may be tailored to suit the chemistry of the liquid. The composition of the metal layer may even be designed to catalyze certain reactions. The reaction product is then separated from the reactants as it is being produced to increase the product yield.
The filter material produced by the process of this invention can be formed into sheets or rubes to fit various filter designs as well as pulses of reverse flow. In accordance with one embodiment of this invention, the metal layer is electrically charged to control the passage or retention of certain ionic species through the membrane.
Membrane cleaning is achieved by chemical or thermal treatment. The varying porosities of certain embodiments of this invention are used to help prevent clogging. They can withstand high temperatures and pressure. A schematic diagram of the microstructure cross-section of a membrane in accordance with one embodiment of this invention is shown in Fig. 1. The discrete materials comprising the membrane of this invention can be bonded by using the sintering technique of this invention. These porous materials can withstand both high temperatures and pressures. The filter system can be designed to take the shape defined by a specific mold.
The process for producing porous nickel filters in accordance with this invention involves the selection of the starting nickel powder and formulation of the powder with organic additives to form an extrudable compound or casting compound for making porous nickel sheets. In accordance with one embodiment of this invention, the nickel powder may be mixed with an alloying material prior to formation of the extrudable or casting compound. For making porous tubes, the compound is extruded into the desired tubular shape. The extruded tube is placed in an isostatic press and pressurized to form a "green" body having the desired dimensions and open porosity. The open porosity of the filter materials produced in accordance with the process of this invention, independent of the material shape, is in the range of about 40% to 70%. This is substantially higher than the 25% open porosity of filter materials produced by more conventional methods. The "green" body is then heated to burn off organic additives, sintered to form a coherent body, and then finished to its exact final dimensions. Surprisingly, the resulting filter material is structurally strong. By comparison, conventional filter materials produced by known methods are limited to porosities in the range of 25 to 30%. Above 30%, the conventional filters become too fragile to be usable. Nickel powders that can be used in this invention comprise the carbonyl nickel powders manufactured by International Nickel Company (INCO). Without intending to limit the scope of the nickel powders which are suitable for use in this invention, in accordance with certain embodiments of this invention, nickel powders which are suitable for use in the process of this invention are selected from the group consisting of Type 123 nickel powders (4.7 micron particle size, individual spikey particles), Type 255 nickel powders (2.6 micron particle size, long fiber chains), Type 287 nickel powders (3.0 micron particle size, a more compact version of Type 255 nickel powders), MSP (2.6 micron particle size, coarse fraction of Type 255 nickel powders), and Type 210 nickel powders (0.6-1 micron particle size, very fine fibers). We have found that for lysimeters and other filter applications requiring pore sizes in the range of 1-2 microns, the MSP type powder is particularly preferred. Applications requiring finer pore sizes may utilize the Type 210 powder, while applications requiring larger pore sizes may use the Type 123 powders. Powders may also be blended to tailor the resulting filter to the desired porosity and pore size.
To extrude nickel powder into a tube form or to mold it to a desired shape, solvent, binder, plasticizer and dispersant are mixed together to make a plastic compound. In accordance with one preferred embodiment of this invention, methyl cellulose is used as a binder, ethylene glycol is used as the plasticizer and tri-butylphosphate is used as the dispersant. Water is a suitable solvent. In accordance with one embodiment of this invention, in order to reinforce and strengthen the resulting porous filter, saffil alumina fibers are added to the formulation.
To form a nickel-based filter tube in accordance with the process of this invention, the plastic compound referred to hereinabove is fed into a screw driven extruder and extruded through a die designed to yield the size and dimensions of the desired tube product. After drying in air, the tube porosity is reduced to near target dimension by isostatic pressing. This is done by inserting the extruded tube into a mandrel and placing the tube and mandrel in a rubber bag for isostatic pressing. A pressure of 5,000-10,000 psi is typically applied, depending on the tube material and the extent of compaction needed to meet the target. After pressing, the tube is laid along its length and fired in an air environment at a temperature of 400-700°C depending on the lysimeter material and size to burn off the organics. The nickel becomes partially oxidized by this heat treatment, but the tube is not deformed by the oxidation. The tube is then heated in a reducing atmosphere to reduce the nickel to metal and to sinter the particles to produce a coherent body. The heat treatment is done at a temperature of 500-600°C with a soak time of 2-4 hours and an atmosphere provided by a feed gas whose composition is 60% H2, 20% CO2, 20% H2O. A strong and impact resistant porous nickel tube is thus obtained.
EXAMPLES OF INVENTION
Example 1. Lysimeter Tube from MSP Nickel
The materials listed below were weighed out into a plastic bag.
MSP Type Ni (Novamet) 5453 g
Methocel A4C (Dow Chem.) 292 g
Deionized water 4489 g
Tri-butyl Phosphate 285 g
Ethylene Glycol 231 g
Saffil Alumina Fiber (ICI) 133 g
Total weight 10,883 g
The materials were mixed according to the procedure outlined below.
1. Add the measured ingredients into a plastic bag;
2. Hand knead the material to a moist consistency;
3. Pass the mixture through a single screw auger to homogenize;
4. Store in a sealed plastic bag until ready for use.
The material composition produced in this manner was extruded to form a tube with a Killion 3 Hp screw type extruder. The extrusion die used WEIS designed to provide .an internal diameter of 1.680 inches and an external diameter of 2.700 inches for the tube. The tube was dried in an oven at about 100°C. The dimensions of the dried tube are given in Table I. The open porosity of the dried tube was about 81%. The tube was trimmed down because the ends were not straight. The new tube dimensions are given in Table I. The tube was inserted into a mandrel and isostatically pressed at 7,640 psi after which the open porosity was about 60%. The pressed tube dimensions are given in Table I. The tube was trimmed to near target size and its dimensions are given in Table I. The tube was heated to 450°C with 30 minutes hold to burn off the binder. After cool down, it was turned around and reheated to 450°C, again with a 30 minute hold. The tube dimensions after this step are given in Table I. Next, the tube was heated in a muffle furnace which was fed with a gas of 60% H2, 20% CC^, 20% H2O composition, by ramping to 560°C over a 4 hour period and holding at 560°C for 3 hours. The final dimensions of the tube are given in Table I. It had an open porosity of 61%. A typical pore size distribution of the described tube is given in Fig. 2. When subjected to a bubble pressure test by filling the tube with water and then pressurizing the water, the bubble pressure, which is the pressure at which air appears when the tube is pressurized in water, was determined to be at least 15 psi. This tube was then assembled into a lysimeter, the tube having been trimmed to exactly fit the lysimeter, and then sealed against the lysimeter body with O-rings or indium metallic gaskets.
The porous nickel tubes can be cut or machined to fit the dimensions of other groundwater monitoring equipment without closing the filter pores.
Example 2. Lysimeter Tubes from Ni-210 The materials listed below were weighed out into a plastic bag.
Ni-210 type Powder (Novamet) 3252 g
Methocel A4C (Dow Chem.) 130 g
Deionized water 2470 g
Tri-butyl Phosphate 180 g
Ethylene Glycol 216 g
Saffil Alumina Fiber (ICI) 67 g
Total weight 6315 g
The materials were mixed according to the procedure outlined below.
1. Add the measured ingredients into a plastic bag;
2. Hand knead the material to a moist consistency;
3. Pass the mixture through a single screw auger to homogenize;
4. Store in a sealed plastic bag until ready for use.
The material composition was extruded to form a tube with a Killion 3 Hp screw type extruder. The dimensions of the extrusion die provided a 1.500 inch internal diameter and a 2.400 inch outside diameter to the tube. The tube was dried in an oven at about 100°C. The dimensions of the dried tube are given in Table 2. The open porosity of the dried tube was about 76%. The tube was trimmed down because the ends were not straight. The new tube dimensions are given in Table 2. The tube was inserted into a mandrel and isostatic pressed at 5,000 psi. The pressed tube dimensions are given in Table 2. The resulting open porosity was about 67%. The tube was trimmed to near target size and its dimensions are given in Table 2. The tube was heated to 600°C in air with 30 minutes hold to burn off the binder. The tube dimensions after this step are given in Table 2. Next, the tube was heated in a muffle furnace which was fed with a gas of 60% H2, 20% CO2, 20% H2O composition, by ramping to 535 °C over a 4 hour period and holding at 535 °C for 3 hours. The final dimensions of the tube are given in Table 3. It had an open porosity of 60%. A typical pore size distribution of this tube is also shown in Fig. 2. When subjected to a bubble pressure test by filling the tube with water and then pressurizing the water, the bubble pressure indicated by the pressure at which air appears when the tube is pressurized in water was at least 80 psi.
Example 3. Porous Nickel Sheet Sintered to a Perforated Nickel Sheet
A sheet of unsintered nickel formed from the following materials was sintered to a perforated nickel Type 200 sheet and then rolled without cracking.
Ni-255 Type Ni (Novamet) 5453 g
Powdered chrome 273 g
Methocel A4C (Dow Chem.) 292 g
Deionized water 4489 g
Tri-butyl Phosphate 285 g
Ethylene Glycol 231 g
Saffil Alumina Fiber (ICI) 133 g
Total weight 11,156 g
The nickel Type 200 sheet was 0.036" thick and perforated with 0.093" diameter holes on 0.156" staggered centers. This demonstrated the ability to achieve strong adhesion between the nickel sheet and resulting porous nickel filter, with 65% porosity, which resulted after sintering.
The perforated nickel sheet was degreased with methanol. The sheet was 5 inches in length and 5 inches wide. It was then etched with a solution consisting of 50% concentrated nitric acid and 50% concentrated acetic acid. The etched perforated nickel sheet was dried.
An unsintered sheet of anode material was placed on the etched perforated sheet and placed in a sintering furnace. The sintering furnace was ramped to 1000°C in 4 hours and let to soak for 1 hour. In the cool down process, the furnace atmosphere was changed from 100% nitrogen to 4% hydrogen at 470 °C. The atmosphere of 4% hydrogen was continued until the furnace cooled to 230°C and then the furnace was shut off.
The pore size of the sintered nickel filter on the perforated sheet was approximately 4 to 6 microns. The sintered material was approximately 2 mm thick.
Example 4. Three Sheets of Porous Nickel (Example 3 Formulation) Laminated
Three sheets of unsintered nickel of the formulations of Example 3 were cut. The sheets were cut to approximately 5 inches by 5 inches. The sheets were wetted with deionized water between the layers and set on a sheet of Teflon during pressing. This kept the nickel sheets from sticking to the base of the pressure machine. A pressure of 50 psi was applied to the three sheets for 15 minutes. The pressed sheets were placed on a laboratory table and were kept flat with two metal bars each weighing 3,660 grams. This equates to approximately 16.1 pounds or 0.6 psi. The dimensions of the laminated sheets prior to sintering were:
Length 123.5 mm
Width 65.0 mm
Thickness 2.94 mm
Weight 42.3 grams
Density 1.79 grams per cubic centimeter
The sintering furnace was ramped to 1000°C in 4 hours and soaked for 1 hour. At the start of sintering, the furnace atmosphere was 100% nitrogen. Two hours after furnace heat up, the temperature reached 538 °C and the atmosphere was changed to 4% hydrogen. This atmosphere was kept until furnace cool down. The furnace was purged with nitrogen before opening the door.
The sintered components had excellent adhesion and were 63.1 % porous. The pore sizes were approximately 4 to 6 microns. The sintered materials were flat and square. The anode material was magnetic. Sintering reduced the thickness by 23.4%. Other dimensions were:
Length 97.0 mm
Width 57.0 mm
Thickness 2.25 mm
Weight 40.0 grams
Density 3.2 grams per cubic centimeter
Example 5. Three Sheets of A Porous Nickel fNi-255 Formulation without chrome) Laminated
Three sheets of unsintered nickel formed from the following materials were cut.
Ni-255 Type Ni (Novamet) 5453 g
Methocel A4C (Dow Chem.) 292 g
Deionized water 4489 g
Tri-butyl Phosphate 285 g
Ethylene Glycol 231 g
Saffil Alumina Fiber (ICI) 133 g
Total weight 10,883 g
They were approximately 50 mm by 221 mm in size. Only the top side of the middle sheet was wetted with deionized water. The combined three sheets were sandwiched between Teflon to eliminate sticking in the pressure device.
A pressure of 72 psi was applied for 30 minutes and the resulting laminate removed from the device and inspected. The laminated material was moist to the touch. Pressure of 72 psi was reapplied for 1 hour and the laminate removed and reinspected. The laminate had good adhesion and was trimmed.
The laminated material was dried and then sintered as in Example 4 with the exception that it was sintered between graphite blocks to maintain flatness during sintering.
TABLE 1
Dimensions of a Lysimeter Porous Tube From MSP Ni Powder
After Various States of Fabrication
Inside Outside Wall
Weight Length Diameter Diameter Thickness
Steps (g) (in.) (m.) (in.) (m.)
As Extruded - - 1.680 2.700 0.510
After Drying 453 5.445 1.581 2.503 0.461
After Trimming 405 4.739 1.426 2.503 4461
After Isostatic Press 405 4.542 1.426 2.002 0.288
After Second Tπm 323 3.713 1.426 2.002 0.288
After Binder Removal 338 3.682 1.423 1.990 0.289
After Sintering 304 3.653 1.430 1.978 0.274
TABLE 2
Dimensions of a Lysimeter Porous Tube From Ni-210 Powder
After Various States of Fabrication
Inside Outside Wall
Weight Length Diameter Diameter Thickness
Steps (g) (in.) (m.) (in.) (in.)
As Extruded - - 1.500 2.400 0.450
After Drying 331 5.414 1.444 2.100 0.328
After Trimming 211 4.110 1.557 2.076 0.260
After Isostatic Press 215 4.020 1.449 1.877 0.214
After Second Tπm 208 3.910 1.447 1.870 0.212
After Binder Removal 185 2.950 1.425 1.870 0.223
After Sinteπng 161 3.031 1.422 1.868 0.223
The filter of this invention has pore sizes ranging from macro particle sizes of greater than 100 microns to molecular range of less than 0.01 microns and provides porosities in the range of about 40 to 70% by volume. The use includes particle filtration and ultrafiltration. Nano-sized pores can be combined with larger sized pores and can be mated with ionic range filters having pore sizes of approximately 0.001 microns without significant reductions of porosities. Applications in which the nickel-based filter material of this invention may be utilized include yeast cells, bacteria, paint pigment, tobacco smoke, carbon black, sugars, coal dust, pollens, milled flour, red blood cells, colloidal silica, albumin protein, viruses, pyrogen, aqueous salts, metal ions, and gas separation.
In accordance with one embodiment of the filter material of this invention, porous nickel sheets are sintered to perforated or wire nickel screen for support or to match a desired configuration.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.

Claims

WE CLAIM:
1. A process for producing porous nickel filters having a narrow pore size distribution comprising the steps of: mixing a nickel powder having a particle size in a range of about 0.5 to 5.0 μm with organic additives suitable for forming one of an extrudable composition and a castable composition; one of extruding and casting said composition into a desired shape; compacting said desired shape by isostatic pressing at a pressure sufficient to form a green body having an open porosity in a range of about 40% to 70%; heating said green body in a reducing atmosphere at a temperature and for a time period sufficient to volatilize said organic additives, said organic additives having a volatilization rate such that said open porosity of said green body is maintained; and sintering said heated green body in a reducing atmosphere, forming a coherent filter body having a porosity in a range of about 40% to 70%.
2. A process in accordance with Claim 1 , wherein said organic additives comprise a binder and a plasticizer.
3. A process in accordance with Claim 2, wherein said binder is methyl cellulose and said plasticizer is ethylene glycol.
4. A process in accordance with Claim 1, wherein saffil alumina fibers are added to said composition.
5. A process in accordance with Claim 1, wherein said coherent filter body is electrically charged.
6. A process in accordance with Claim 1, wherein said coherent filter body is magnetized.
7. A process in accordance with Claim 1, wherein said nickel powder is a nickel alloy.
8. A process in accordance with Claim 1 , wherein said composition further comprises a solvent and a dispersant.
9. A process in accordance with Claim 8, wherein said solvent is water.
10. A process in accordance with Claim 8, wherein said dispersant is tributylphosphate.
11. A process in accordance with Claim 1, wherein a plurality of said green bodies are formed and said green bodies are layered one upon another, resulting in formation of a multilayer green body.
12. A multilayer porous nickel-containing filter comprising: a first layer of nickel deposited on a nickel substrate layer, said first layer having pore sizes suitable for reverse osmosis and said nickel substrate layer having pore sizes suitable for at least one of microfiltration and ultrafiltration, said filter having a porosity in a range of about 40% to about 70%.
13. A filter in accordance with Claim 12 , wherein said first layer has pore sizes substantially all in a range of about 5A to about 2 A.
14. A filter in accordance with Claim 12, wherein said nickel substrate layer has pore sizes substantially all in a range of about 2θA to about lOOμm.
15. A filter in accordance with Claim 12 further comprising an intermediate nickel layer between said first layer and said nickel substrate layer, said intermediate nickel layer having pore sizes suitable for ultrafiltration and said nickel substrate layer having pore sizes suitable for microfiltration.
16. A filter in accordance with Claim 12, wherein said filter is electrically charged.
17. A filter in accordance with Claim 12, wherein said filter is magnetized.
18. A filter in accordance with Claim 12, wherein said filter is catalyzed.
19. A filter in accordance with Claim 15, wherein said first layer has pore sizes substantially all in a range of about 5A to about 2θA, said intermediate layer has pore sizes substantially all in a range of about 2θA to about lOOOA, and said nickel substrate layer has a pore size substantially all in a range of about lOOOA to about lOOμ .
PCT/US1997/016768 1996-09-23 1997-09-22 Porous nickel filter material WO1998011974A1 (en)

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SG90265A1 (en) * 2000-10-12 2002-07-23 Toray Industries A leaf coater and method for producing leaf type coated substrates
WO2002090916A1 (en) * 2001-05-09 2002-11-14 Endress + Hauser Gmbh + Co. Kg Device comprising a wet filter containing a hydrophobic or hydrophobicized nanoporous material
US6675654B2 (en) 2001-05-09 2004-01-13 Endress + Hauser Gmbh + Co. Kg Pressure sensing device with moisture filter
KR100982913B1 (en) * 2008-05-19 2010-09-20 한양대학교 산학협력단 Manufacturing method of porous nickel membrane using hybrid nickel oxide powder
CN113559615A (en) * 2020-04-29 2021-10-29 成都易态科技有限公司 Use of nickel-copper alloy for preparing filter material for blocking and/or inhibiting virus

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SG90265A1 (en) * 2000-10-12 2002-07-23 Toray Industries A leaf coater and method for producing leaf type coated substrates
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CN113559615A (en) * 2020-04-29 2021-10-29 成都易态科技有限公司 Use of nickel-copper alloy for preparing filter material for blocking and/or inhibiting virus

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