Patent Application
20070251389
As has been stated above, in the membrane according to the invention, the substrate generally defines obverse and reverse sides. This means that in general, the substrate, considered as a three-dimensional object, will have a configuration in which two dimensions are much greater than the third dimension, as in e.g. a foil or plate, or a self-supporting film. However, this laminar nature of the substrate does not preclude such configurations as hollow geometrical shapes such as tubes, cylinders and helices, as well as spiral-wound substrates.
Where the ceramic layer consists essentially of a mixture of metal(s) and oxide(s) thereof, such mixture imparts additional mechanical strength to the ceramic layer. In the embodiments where the composite membrane includes a layer of metal on the surface of the ceramic layer, the metal can be e.g. palladium, or an alloy of palladium with other metals such as those mentioned previously herein. Where the substrate is stainless steel mesh or aluminum foil, these are examples of substrates which can impart to the composite membrane sufficient flexibility enabling it to be rolled up and unrolled.
Typically, the ceramic layer of the membrane of the present invention has a structure which is characterized by a relatively wide range of pore width, i.e. possessing diverse pore widths. An example of such a layer is a fractal structured layer, which can be e.g. of dendrite, cauliflower-like or coral-like types.
In the aspect of the composite membrane of the invention which includes a multi-layer system, this system comprises more than one ceramic layer and at least one metallic layer; the metallic layer(s) and the ceramic layers are arranged in such a manner that each ceramic layer and each metallic layer are alternated. The metallic layer, if applied, can be either porous or non-porous (dense). Both the ceramic layer and the metallic layer, if present, are applied by a vacuum deposition technique.
The structure of the composite membrane according to the first aspect of the invention is illustrated schematically by
In an embodiment of the membrane with metallic layer(s) at least one of the ceramic or metallic layers is a permselective layer, that is a layer responsible for selective permeability therethrough of at least one component of the mixture and retention of the rest of the components (or single component). In a modification of the membrane with sorbent layer(s) the separation mechanism differs in that the sorbent layer(s) selectively sorb(s) the targeted component(s) or biological specie(s) thus separating them from other components or immobilizing them on the binding surface.
As mentioned above, the ceramic layer comprises at least one metal oxide selected from the group consisting of oxides of aluminum, titanium, tantalum, niobium, zirconium, silicon, thorium, cadmium and tungsten and is produced by a vapor deposition technique. In the present invention, metal oxide(s) of the ceramic layer is (are) produced as a result of a chemical reaction occurring in the vacuum environment between a metal which is converted from the solid phase to the vapor phase, e.g. by thermal evaporation, and an oxidizing agent, e.g. gaseous mixture comprising oxygen. Thus the process that we call “deposition” comprises the following stages: changing the state of the metal from the solid phase to the gaseous phase, chemical reaction, and the deposition stage proper. The process conditions can be chosen so as to produce a coating composed of metal oxide(s) only, or a coating composed of a mixture of metal oxide(s) with metal(s). Thus, in addition to metal oxides the ceramic layer can contain metals, such as aluminum, titanium, tantalum, niobium, zirconium, silicon, thorium, cadmium and tungsten. Metal component(s) of the ceramic coating may improve its mechanical strength, and as a result the mechanical strength of the entire membrane. The preferable material of the ceramic layer is aluminum oxide (alumina) or a mixture of alumina with aluminum.
The substrate of the composite membrane can be a metal substrate, either rigid or flexible. In the latter case, the composite membrane desirably exhibits sufficient flexibility enabling it to be rolled up and unrolled. The flexibility of the membrane enables its usage in compact membrane elements, e.g. of spiral-wounded type and in long (1 to 3 meters length) tubular membrane elements.
In the membrane according to the first aspect of the invention as defined above, various embodiments are possible. Thus, for example, in absence of any metallic layer, it is the ceramic layer that performs a permselective function. On the other hand, when the membrane includes a metallic layer, this layer may be permselective, while the ceramic layer can be also permselective, or serve merely as a support for the metallic layer. It may be noted that in certain embodiments, the ceramic layer may effectively operate as a barrier for preventing intermetallic diffusion. Typical materials for the metallic layer are e.g. palladium, palladium-silver alloy, and palladium-cooper alloy.
As to the sorbent layer, the mechanism of its functioning, the methods of its deposition and possible materials will be discussed further below.
As pointed out above, the ceramic and the metallic layers are fabricated by a vacuum deposition technique, e.g. physical vapor deposition (PVD) including thermal evaporation, electron-beam evaporation, sputtering, or by e.g. chemical vapor deposition. Both layer types (ceramic and metallic) can be produced by the same deposition technique, or by different deposition techniques.
In a particular embodiment, the ceramic layer is disposed on both sides of the substrate thus defining two ceramic layer surfaces, both ceramic layers being also bonded to each other through the pores of the substrate, thereby imparting improved mechanical strength to the composite membrane. Optionally, a metallic layer can be disposed on only one ceramic surface, or on both of them. The metallic layer(s) have a lesser porosity and (or) average pore width than that of the ceramic layer, and this characteristic includes also dense (micro-porous) metallic layers.
The deposition of the ceramic layer on the second side and the optional deposition thereon of the metallic layer or the sorbent layer is performed similarly to the deposition on the first side of the substrate. The properties (composition, structure, porosity, average pore width, thickness, etc.) of the ceramic and metallic (or sorbent) layer deposited on the second side of the substrate can be either same, or different from those of the layers deposited on the first side.
The metallic layer, when present, generally bears the burden of the permselectivity function, and therefore should be as thin as possible to ensure maximum flux of the permeate component or components of the mixture (e.g. hydrogen in the steam reforming process), since the flux is inversely proportional to the membrane thickness. Preferably, the metallic layer of the membrane of the present invention is dense (non-porous), but a micro-porous metallic layer having a pore volume less than the ceramic layer is also applicable.
When the ceramic layer (or layers) functions as support for one or more metallic layers, the ceramic layer should be mechanically as strong as possible. Additionally, the ceramic layer should meet the following requirements. Its surface must be as smooth as possible in order to support well a very thin metallic layer. If the support has a rough surface (with relatively big size of the surface irregularities, “peaks” and “valleys”), a thin metallic layer will tend to collapse into the “valleys” of the surface. On the other hand, the ceramic support must be sufficiently porous in order not to reduce significantly the flux of the permeate component or components. Typically, the techniques used so far for increasing porosity of materials, are directed to the increase of the surface area by producing irregularities on the surface. Examples of applications which employ these techniques are lithographic printing plates, electrodes for electrolytic capacitors, and many others. However, such techniques, being applied to the ceramic layer, would result in a surface with irregularities of relatively big size, thereby contradicting the requirement of a substantially smooth surface. In the present invention the two foregoing contradictory requirements are reconciled in the following way.
In the present invention, a ceramic support for the metallic layer is implemented in the form of a coating fabricated by a vacuum deposition technique. It is known in the art that vacuum deposition techniques can fabricate coatings with the desired surface structure (morphology). More specifically, it is possible to control the structure of the coating by the appropriate selection of raw materials (e.g., metals, oxidizing agents) and process conditions (flow and composition of the oxidizing agent, pressure, etc.). In the present invention, the raw materials and the process conditions are selected so as to preferably impart a fractal surface structure to the ceramic layer, that is, a surface composed of fractals. Fractals are unusual, difficultly defined, mathematical objects which observe self-similarity, so that the parts are somehow self-similar to the whole. This self-similarity feature implies that fractals are essentially scale-invariant—you cannot in principle distinguish a small part from the larger structure, e.g. a tree branching process.
Coatings having fractal structures are described in the prior art, e.g. U.S. Pat. No. 6,933,041 and U.S. Pat. No. 6,764,712 (both Katsir et. al), U.S. Pat. No. 5,571,158 (Bolz et al), U.S. Pat. No. 6,974,533 (Zhou), U.S. Pat. No. 6,994,045 (Pazkowski). For example, U.S. Pat. No. 6,933,041 teaches a porous coating, produced by a vacuum deposition technique, composed of a mixture of valve metal and its oxide. The described coating has a fractal structure, particularly, a cauliflower-like structure and is used in applications where high surface area of the substrate is required, e.g. electrodes of electrolytic capacitors.
Coatings with a fractal surface structure are characterized by pores of diverse width in the sense that the width of the pore canal covers a relatively wide range of values. Based on this feature the inventors consider fractal-structured coatings (ceramic layers) as ideal candidates to serve as a support for the metallic layer(s) or sorbent layer(s) of the composite membrane of the present invention. In embodiments with metallic layer(s) pores of relatively small width, on the one hand, facilitate the disposal of the particles of the metallic layer(s) on the supporting ceramic layer(s). This means that the fine structure of the surface of the ceramic layer(s) permits a deposition thereon of extremely thin films of the metallic layer(s) and ensures good adhesion of the metallic layer(s) to the ceramic layer(s). On the other hand, the layer with a fractal-like structure also contains pores of relatively large width, therefore, such a layer does not reduce significantly the flux of permeate, e.g. hydrogen. As to the embodiment with sorbent layer(s) relatively small (in view of the width) pores of the ceramic layer(s) facilitate an adhesion of the affinity ligands, while relatively big (in view of the width) pores facilitate binding of the species of the bound material.
Unlike fractal-structured coatings of the cited prior art, the fractal structure of the layers (coatings) of the present invention is used not primarily for increasing the surface area of a coating, but rather for producing a surface structure having diverse pore canal widths.
The fractal-structured coatings can be better understood from the following explanation, in which a certain type of fractal structure, namely the cauliflower-like structure, is taken as an example. The membranes with cauliflower-like structure of the ceramic layer are schematically illustrated by
In
It is clear from the foregoing description that the cauliflower-like structure is characterized by the florets of diverse width and by pores of diverse width. Such ceramic coatings can serve as an excellent support for a metallic layer deposited thereon. Small florets, being located in the upper sub-layer, form a relatively smooth surface, which ensures good adhesion of the metallic layer. As a result, the prior art problem of delamination of the permselective layer from its supporting surface, is avoided. On the other hand, big heads, being located in a lower sub-layer, ensure mechanical strength of the support. Thus, an asymmetric structure of the support, which includes pores of diverse width, is preferred. Narrow pores form a relatively fine smooth surface on the coating, while wide pores being located between the cauliflower heads, form relatively straight canals, oriented substantially in the transverse direction. Relatively straight, wide pores oriented in the transverse direction do not substantially reduce the flux of hydrogen.
The foregoing structure permits deposition, onto the surface of the ceramic layer, an extremely thin layer of metallic material (metal or metal alloy) and ensures good adhesion of the metallic layer to the ceramic layer. Thus, the coating with a cauliflower-like surface structure can serve as an ideal support for a thin metallic layer, because narrow pores contribute to the smoothness of the surface, while wide, and substantially straight pores, having low hydrodynamic resistance, contribute to the flux of hydrogen.
Other fractal structures of the ceramic vacuum deposited coatings of the present invention may be of dendrite (
The preferred material for the ceramic layer is aluminum, or an aluminum/alumina mixture, in which alumina can be either in γ-modification or in α-modification. However, other materials capable of forming a layer with similar properties (mechanical strength, surface structure, etc.) can be used alternatively.
The metallic layer, when present in the composite membrane of the present invention, may be composed of e.g., Pd, Group V metals, or their alloys with other metals. In a particular embodiment, the metal is palladium-silver alloy, preferably containing e.g. 23% by weight of palladium. In another embodiment, the metal is a palladium-copper alloy, preferably containing 40% by weight of copper. Alloys containing three or more components can be also used, e.g. Pd—Ru—In.
The metallic and ceramic layers may be deposited, e.g. by one of the following vacuum deposition techniques: thermal evaporation, e-beam evaporation, sputtering, or chemical vapor deposition. Different deposition techniques can be employed for depositing different layers, for example vacuum evaporation and sputtering. If a sputtering technique is used for the deposition of an alloy (in the case of a metallic layer), it can be deposited as a single component (that is from one target), or alternatively distinct targets can be used for distinct deposition of each component of the alloy. The deposition from distinct targets is especially advantageous, when an alloy of special composition, which is not manufactured by the industry, is required. The process of distinct deposition of alloy components enables the use of alloys with a predetermined composition, in which the alloy is fabricated not prior to, but simultaneously with the deposition process.
It will be appreciated by those skilled in the art, that the materials for the metallic and the ceramic layers are not limited to the above-mentioned metals, metal oxides and metal alloys. For example, any material which is capable of being applied by a vacuum deposition technique and has similar characteristics in view of selectivity and flux with respect to particular permeates (e.g. hydrogen) can also be used for a metallic layer. As to the ceramic layer, any material, within the definition herein, which is capable of forming a fractal structure with similar characteristics (width of heads and florets, pore width distribution, etc.) also can be used.
The substrate, which is an essential element of the composite membrane of the invention, should be desirably mechanically strong and flexible.
Additionally, the pores must be relatively wide to allow permeate to pass readily through the substrate, but not too wide to detract from adequate support of the ceramic layer. In view of these desired properties, a stainless steel mesh and a through-hole type etched aluminum foil are preferably used. In the case of stainless steel mesh, the preferred characteristics of the substrate are as follows: (a) thickness between 36 μm and 42 μm, more preferably 38±2 μm; (b) aperture size between 33 μm and 41 μm, more preferably 46 μm; (c) strand width less than 30 μm, more preferably 18 μm; and (d) open area is between 42% and 52%, more preferably 51%.
The material of the substrate is not essentially limited to the foregoing materials. Any porous material which has similar properties (flexibility, mechanical strength, thickness, aperture size, etc.) also can be used.
The preferred thickness of the metallic layer(s) is between 0.05 and 2 μm, more preferably between 0.1 and 0.5 μm; the preferred thickness of the ceramic layer(s) is between 5 and 40 μm, more preferably between 10 and 20 μm.
In a modification of the membrane of this aspect, optional metallic layer(s) is (are) replaced with sorbent layer(s). Said sorbent layer(s) selectively sorb(s) at least one component of the separated mixture (e.g. in the case when the sorbent layer is made of zeolite), or alternatively, selectively bind(s) to the species of at least one component of the separated mixture (e.g. in the case when the sorbent layer is an amino acid resin). The selective binding can be either releasable, that is the selectively bound substance or biological specie can be further released, e.g. by elution, or non-releasable. As mentioned above, typical application of a biological separation based on the principle of selective binding is affinity chromatography, which is widely used in biological separations, including immobilization (isolation) of the targeted species. Typically, the substances which can be separated or immobilized with the membrane of this modification are proteins, nucleic acids, polysaccharides, lipids, terpenoids, etc, or biological species. Other possible applications of this membrane are ion-exchange chromatography and bioreactors. When used as a bioreactor, for example, an enzyme may be affixed to the activated sites on the membrane, either directly or through a ligand. A carrier liquid containing the substance to be lysed is then passed through the membrane so that the bound enzyme acts upon such substance.
Unlike the membranes of the previously disclosed embodiments, the substrate of the membrane of this embodiment is not restricted in view of its porosity and pore width. In other words, the substrate can be either porous with unrestricted porosity and pore width or non-porous (dense). An example of a dense substrate is a conventional metallic foil, e.g. aluminum foil.
Similar to the metallic layer of the membrane of previously described embodiments, in this embodiment the selective sorbent layer can be disposed on one or both ceramic surfaces. A membrane having selective sorbent layers on both the obverse and reverse sides enhances its sorbent capability by a factor of 2.
The technique used for depositing the sorbent material on the surface of the ceramic layer(s) depends upon the properties of the material to be deposited. For example, zeolite particles can be applied by electrophoretic deposition, affinity ligands can be applied by surface modification, as, for example, disclosed in U.S. Pat. No. 5,904,848. The preferable thickness of the ceramic layer(s) of the membrane according to this modification is 5 to 10 μm, while preferable thickness of the selective sorbent layer(s) is 5 to 100 μm. More preferable thickness of the selective sorbent layer(s) depends upon the application of the membrane.
In the composite membrane of the invention which includes a multi-layer system (i.e. containing more than one metallic layer and more than one ceramic layer), such system may be illustratively disposed on substrate 1 (
The multi-layer structure reduces the risk of selectivity decrease, in the case where micro-cracks or (and) pinholes are formed in the metallic layer(s). Since all the metallic layers are independent from each other, each layer can be considered as a back-up layer for the case of micro-cracks or(and) pinholes. The multi-layer system may also reduce the risk of de-lamination of the layers, because the ceramic layers bind the interleaved metallic layers. Furthermore, both ceramic layers being bonded to each other through the pores of the substrate imparts improved mechanical strength to the composite membrane.
In the composite membrane including the multi-layer system, the following conditions are optionally fulfilled: at least one ceramic layer has a fractal surface structure (e.g. dendrite, cauliflower-like or coral-like); the membrane has sufficient flexibility enabling it to be rolled up and unrolled; there is disposed on the surface of any outermost ceramic layer a vacuum-deposited metallic layer, which is non-porous or has a porosity lower than that of the outermost ceramic layer.
The multi-layer system can be disposed on one side only of the substrate (as shown in
In a particular embodiment, the membrane comprises a multi-layer system disposed on one side of the substrate and a ceramic layer disposed on the other side of the substrate. Optionally, a metallic layer can be disposed on the outmost ceramic layer of one side only, or on both sides.
As regards the materials and the properties of the metallic layers, the ceramic layers and the substrate, the membrane including the multi-layer system is similar to the membrane of the first aspect of the invention. However, the metallic and ceramic layers of the multi-layer membrane are thinner than the corresponding layers of the membrane of the first aspect of the invention. A preferable thickness of the metallic layers is between 0.01 and 1 μm, more preferably between 0.05 and 0.2 μm; the thickness of the ceramic layers is between 0.2 and 5 μm, preferably between 0.5 and 1 μm. The pore volumes of the ceramic and metallic layers are similar in the membranes of both aspects of the invention.
The composite membrane of the present invention can be manufactured in the form of flexible sheets or in the form of continuous long rolled webs. Typically, the membranes in the form of sheets are produced in an apparatus operating in a batch mode, while the membranes in the form of continuous rolled webs are typically produced in an apparatus operating in a continuous mode. In the latter case, different deposition techniques, for example vacuum evaporation and sputtering, can be employed for depositing ceramic and metallic layers, even under different degrees of vacuum. Moreover, in the case of membranes comprising more than one ceramic layer and (or) more than one metallic layer—for example, membranes in which the ceramic and (or) the metallic layers are disposed on both sides of the membrane, or membranes comprising the multi-layer system—different ceramic and (or) different metallic layers can be deposited using different deposition techniques.
The composite membranes with ceramic layer(s) only and with ceramic and metallic layer(s) can be incorporated mainly, but not mandatory, in membrane elements of the tubular type, spirally wound type, or plate-and-frame type.
For example, in the spiral wound element the composite single-sided membrane is spirally wound around a perforated hollow pipe. Such design ensures high values of the membrane surface area to unit of assembly volume ratio.
The spirally wound membrane element comprises a plurality of membrane envelopes 102 separated by feed spacers 103 (
In another design the membrane element is placed in a pressure casing 18 (
If a membrane element of the tubular type is applied, it is placed in the tubular pressure casing, thereby forming a membrane module. The membrane element of tubular type comprises composite membrane 25 in the form of a flexible sheet or roll (
In the case where at least one chemical reaction occurs in the reaction mixture, the membrane elements and modules described in the present invention can operate as membrane reactors. They can be used to increase at least one of the following characteristics of the chemical process: yield, selectivity, conversion.
In another aspect of the invention relating to TLC and column chromatography, the method of coating the substrate is reactive PVD, preferably in a continuous roll to roll process. TLC plates are constructed from a support layer and an alumina adsorbent layer. The support layer (substrate) is generally aluminum foil 30-150 microns thick or alternatively may be any suitable plastic film. The adsorbent layer is typically 100-350 microns thick and it is thermally evaporated by reactive PVD to obtain a highly porous, powder-like alumina coating with porosity ranging from 60% up to 95%. (For some applications, however, the layer may have a thickness of about 5-50 microns.) This highly porous alumina layer requires no adhesives or bonding compounds to maintain mechanical stability and therefore, in principle is completely free from possible contaminants. Additional sub-layers and top layers can be applied in order to better highlight fluid flow or to protect the adsorbent coating. The alumina coating is produced inside a vacuum roll coater, where aluminum web is transported over an aluminum thermal evaporator. The evaporated aluminum interacts and oxidizes in a controlled environment containing an oxygen/argon gas mixture prepared inside the vacuum chamber. The substrate is pre-treated by a plasma process to remove all contaminants and to provide reliable coating adhesion to the substrate surface.
Further, an oxide tie-layer is desirably sputtered on the substrate prior to the adsorbent layer to promote interlayer bonding. The temperature of the substrate reaches 400° C. during the coating process, and the pressure in the deposition cloud is maintained at 7×10−3 mbar.
As regards the aspect of the invention in which a membrane is adapted as a plate for thin layer chromatographic (TLC) identification and (or) separation of components of fluid mixtures, the TLC plates are constructed from a non-porous substrate or support layer and an alumina adsorbent layer. The support layer (substrate) is preferably aluminum foil 30-150 microns thick or alternatively can be any suitable polymeric film or sheet.
By way of example of polymeric substrates, polyester sheets (about 0.2 mm thick) can be economically coated, since they can be manufactured in roll form. Other advantages are that polyester sheets are practically unbreakable, and they need less packing and less shelf space for storage. Furthermore, they can be cut and eluted, etc. Small sheets, such as 8×4 cm, can be economically manufactured and packed. The charring technique can be applied for silica coated sheets, however, at somewhat lower temperatures than on glass. The typical maximum temperature for such sheets is 160° C. Similar sheets are also available with aluminum oxide, cellulose, and polyamide layers.
The adsorbent layer is 100-350 microns thick and is thermally evaporated by reactive PVD to obtain a highly porous, powder-like alumina coating with porosity ranging from 60% to 95%! This highly porous alumina layer requires no adhesives or bonding compounds to maintain mechanical stability and therefore is completely free from such contaminants. Additional sub layers and top layers can be applied in order to better highlight fluid flow or protect the adsorbent coating.
As regards the aspect of the invention in which a membrane is adapted for column chromatography, the column is constructed from an outer tube casing into which a rolled coated foil is inserted. The rolled coated foil resembles that of the TLC application; however, the substrate would preferably be as thin and soft as possible. The coating is of the same nature—highly porous reactively deposited alumina, and can be of greater thicknesses then in the case of the TLC application. The column can be used as a separator device with outlets at different heights in the column casing.
Advantages of the Present PVD-Deposited Coatings for TLC and Column Chromatography
11. These chromatographic tools may be applied e.g., for analysis and separation of a wide variety of materials, such as organic and inorganic chemical compositions, biochemical compositions, drugs, drug metabolites, cells, cell material, micro-organisms, peptides, polypeptides, proteins, lipids, carbohydrates, nucleic acids, and combinations thereof.
The invention is illustrated by the following non-limiting examples.
The substrate is a stainless steel mesh from KOIWA KANAAMI CO. having the following parameters: thickness of 38±2 μm, aperture size 46 μm, strand width 18 μm; and open area 51% was annealed for one hour at a temperature of 450-500° C. to remove residual oil and was placed in a deposition chamber from which air was then evacuated until a vacuum of 2·10−4 Torr was attained. An aluminum wire intended for evaporation was wound onto a drum and fed to the evaporation boat at a rate of 0.64-0.68 g/min, where it was evaporated by thermal resistive evaporation onto one side of the stainless steel mesh at a temperature of about 250-270° C., while oxygen in an amount varied between 320 cc/min and 340 cc/min, and argon in an amount varied between 45 cc/min and 50 cc/min (volume flow rates of both gases are referred to standard conditions) were introduced into the chamber. Partial pressures of oxygen varied within 6.0·10−4-8.0·10−4 Torr and argon within 4.0·10−3-4.5·10−3 Torr. Other gases (such as hydrogen, nitrogen, carbon dioxide and water vapor) in an amount significantly less than the amounts of oxygen and argon were also present in the chamber. The deposit which is a porous alumina layer having a thickness of 15 μm was applied onto the substrate at a rate of 600 to 750 Å/sec. The product is a composite membrane having a ceramic selective layer.
A scanning electron microscope (SEM) micrograph of the fabricated layer is shown in
The substrate is a stainless steel mesh from KOIWA KANAAMI CO. having the following parameters: thickness of 38±2 μm, aperture size 46 μm, strand width 18 μm; and open area 51% was annealed for one hour at a temperature of 450-500° C. to remove residual oil and was placed in a deposition chamber from which air was then evacuated until a vacuum of 2·10−4 Torr was attained. An aluminum wire intended for evaporation was wound onto a drum and fed to the evaporation boat at a rate of 0.64-0.68 g/min, where it was evaporated by thermal resistive evaporation onto one side of the stainless steel mesh at a temperature of about 270-300° C., while oxygen in an amount varied between 90 cc/min and 100 cc/min, and argon in an amount varied between 45 cc/min and 50 cc/min (volume flow rates of both gases are referred to standard conditions) were introduced into the chamber. Partial pressures of oxygen varied within 4.5·10−5-5.5·10−5 Torr and argon within (4.5-5.5)·10−3 Torr. Other gases (such as hydrogen, nitrogen, carbon dioxide and water vapor) in an amount significantly less than the amounts of oxygen and argon were also present in the chamber. The deposit, which is a porous layer having a thickness of 20 μm, composed of aluminum and aluminum oxide, was applied onto the substrate at a rate of 500 to 600 Å/sec. The product is a composite membrane having a ceramic selective layer.
Top view images, obtained by an optical microscope, of the composite membrane are shown in
This was carried out similarly to Example 1, with the difference that the substrate was through hole-type etched aluminum foil and the deposited layer had a thickness of 12 μm. The product is a composite membrane having a ceramic selective layer.
A SEM micrograph of the deposited layer is shown in
This was carried out similarly to Example 2, with the difference that the substrate was the through hole-type etched aluminum foil and the deposited layer had a thickness of 18 μm. The resultant product was a composite membrane having a ceramic selective layer. The SEM micrograph of the deposited layer is shown in
In this example, the ceramic layer and the metallic layer were sequentially deposited onto one side of the substrate in the combined evaporation-sputtering apparatus, including an evaporation zone and a sputtering zone and operating in continuous mode (
Thereafter, the web was allowed to travel towards a sputtering zone 156, where a 0.5 μm-thick metallic layer composed of Pd and Ag was deposited onto the surface of the previously deposited ceramic layer in an atmosphere of argon with pressure of 0.5·10−2 Torr. Sputtering was performed with a DC power supply using a power control method allowing equipment to automatically determine the sputtering voltage and current in order to maintain constant power with maximum deposition control. The layer was applied using a planar cathode with a single target which is Pd—Ag alloy.
The web 158 with the deposited ceramic and metallic layers was then passed on several rolls 157 so as to change its travel direction, and was allowed to travel toward the second evaporation zone 10, and then toward the second sputtering zone 112 where a 20 μm-thick ceramic layer (mixed aluminum/alumina) and a 0.5 μm-thick metallic layer (composed of Pd and Ag) were sequentially deposited onto the other side of the web in a manner and with deposition conditions similar to those of the first side. Finally, the substrate with deposited ceramic and metallic layers on both sides (double-sided composite membrane) passed on several rolls 111 and was allowed to travel toward roll-up roll 113 where it was rolled up.
This was carried out similarly to Example 5, with the difference that the deposition in zones 10 and 112 was not conducted. After deposition of the metallic layer in zone 156 web 158, which is a single-sided composite membrane, sequentially passed on rolls 157, 9 and 111 and was allowed to travel toward roll-up roll 113 where it was rolled up.
In this example, a plurality of ceramic layers and metallic layers were sequentially deposited in an alternating manner onto one side of the substrate in the combined evaporation-sputtering apparatus, including one evaporation zone 154 and one sputtering zone 156 and operating in continuous mode. In the process of this example, evaporation zone 10 and sputtering zone 112 did not operate.
Substrate 1 which is a stainless steel mesh web from KOIWA KANAAMI CO. with the same characteristics as in Example 2 was unrolled in the inside of a vacuum chamber by means of a let-off roll 151. Then the web passed on roll 155 and was allowed to travel toward evaporation zone 154 of the vacuum chamber, where a mixed aluminum/alumina (ceramic) layer of about 1 μm-thick was deposited onto the substrate in a free-span mode under the same deposition conditions as in Example 2. Sputtering zone 156 of the apparatus did not operate. Afterwards, the web passed on several rolls 157, 9 and 111 and was allowed to travel toward roll-up roll 113 where it was rolled up. Further direction of rotation of all the rolls was reversed, thereby reversing the traveling direction of the web. As a result, the web started unrolling on roll 113 and it was allowed to travel toward sputtering zone 156, where a metallic layer of about 0.1 μm-thickness composed of Pd and Ag was deposited onto the surface of the previously deposited ceramic layer under conditions similar to those of Example 5 (when the web traveled in the reversed direction, evaporation zone 154 of the apparatus did not operate).
After that, the web passed on roll 155 and was allowed to travel toward roll 151 where it was un-rolled. The resulting web was coated with one ceramic layer and one metallic layer. After that, the steps of direction reversing, deposition by evaporation (without sputtering) and deposition by sputtering (without evaporation) were repeated two times. The total thickness of the produced coating was 3.3 μm.
A ceramic layer with a thickness of 5 μm was deposited on one side of the non-porous aluminum foil in the apparatus of Example 1 and with deposition conditions the same as in Example 1. Furthermore, the produced membrane was placed in an electrophoretic deposition bath containing a slurry of ion-exchanged X-type zeolite particles with a size less than 1 μm where a layer of said zeolite having a thickness of 60 μm was deposited thereon.
The product which is a composite membrane comprising non-porous aluminum foil substrate 1, ceramic layer 2 (alumina) and selective sorbent layer 30 (X-type zeolite) is shown schematically in
A ceramic layer with a thickness of 5 μm was deposited on one side of a stainless steel mesh from KOIWA KANAAMI CO with the following characteristics: thickness—38±2 μm, aperture size—46 μm, strand width—18 μm, open area—51% in the apparatus of and under deposition conditions the same as in Example 1. The obtained product was a membrane having a single fractal-structured surface.
A dispersion of latex containing oxirane groups was prepared according to the technique disclosed in Example 2 of U.S. Pat. No. 5,976,527. The particles of the latex produced then were coated onto the surface of the ceramic layer of the single-fractal-structured-surface membrane by dip coating. Another side of the membrane (which does not contain a ceramic layer) was protected from the latex particles by a screen.
Similar to the system taught in U.S. Pat. No. 5,976,527 the manufactured composite membrane can be used for immobilizing enzymes or proteins.
In a PVD roll coating apparatus, a hard-tempered non-porous aluminum web having 120 micron thickness and 300 mm width, having been pretreated by a plasma process to remove all contaminants from its surface, and on which a tie layer of dense 2-4 nm thick Al2O3 has been reactively sputtered to promote interlayer bonding (adhesion), is transported over an aluminum thermal evaporator. The evaporated aluminum reacts in a controlled environment containing an oxygen/argon mixture. During the travel from evaporator to substrate, the reacted aluminum particles cluster to form Al2O3 in a unique highly porous structure having a thickness of approximately 250 microns. The alumina clusters then accumulate on the substrate to form the required adsorbent layer for TLC chromatography. The temperature of the substrate reaches 400° C. during the coating process. The total pressure in the chamber is maintained at 0.007 mllibar (=0.00525 torr or 0.0007 kPa).
The coating procedure is similar to Example 10, except that the non-porous substrate was soft tempered aluminum foil, 60 microns thick and 300 mm in width. The coated substrate, when rolled up, may be adapted for insertion into columns of various sizes, e.g., a glass column, inner diameter 16 mm, length 100 to 300 mm.
Although the invention has been described with respect to a limited number of embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 175270 | Apr 2006 | IL | national |
