WO2000043572A1 - Revetement ceramique - Google Patents

Revetement ceramique Download PDF

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Publication number
WO2000043572A1
WO2000043572A1 PCT/NL2000/000019 NL0000019W WO0043572A1 WO 2000043572 A1 WO2000043572 A1 WO 2000043572A1 NL 0000019 W NL0000019 W NL 0000019W WO 0043572 A1 WO0043572 A1 WO 0043572A1
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Prior art keywords
layer
porous
ceramic
particles
permeable
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PCT/NL2000/000019
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English (en)
Inventor
John Wilhelm Geus
Roland Berend-Jan Tabor
Marieke Paulyne Renate Spee
Adrianus Maria Jacobus Van Der Eerden
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U-Cat B.V.
Universiteit Utrecht
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Priority to JP2000594975A priority Critical patent/JP2002535492A/ja
Priority to AU23311/00A priority patent/AU2331100A/en
Priority to EP00902193A priority patent/EP1153158A1/fr
Publication of WO2000043572A1 publication Critical patent/WO2000043572A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
    • C23C28/044—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material coatings specially adapted for cutting tools or wear applications
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
    • C23C28/048—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material with layers graded in composition or physical properties

Definitions

  • the invention relates to thin ceramic layers applied to non-porous or : coarse-porous ceramic or metallic substrates.
  • 'Coarse-porous' in this connection is understood to mean containing pores of a diameter of about 1 mm or more.
  • the invention comprises both non-porous and hence non-permeable ceramic layers and (high-)porous ceramic layers.
  • 'Thin' is understood to mean a thickness of less than 1 mm to a thickness of about 100 mm.
  • Non-porous ceramic layers are applied as glazing to ceramic substrates and as enamel to metallic substrates.
  • the aim of applying the layers is generally protection or embellishment.
  • the invention is directed especially to the use of thin ceramic layers in the protection of metals and alloys. Primarily, this involves screening against the attack of the metal or the alloy by reaction with carbon- containing gas molecules. It has been observed that upon exposure of metal and alloy surfaces to carbon-containing gas molecules, such as methane or higher hydrocarbons or a mixture of carbon monoxide and hydrogen, metal or alloy particles disappear from the surface. As a result, the thickness of the metal or the alloy can decrease rapidly, giving rise to fracture in equipment working under increased pressure. In cases where work is not done under pressure, the loss of metal or the alloy causes leakage.
  • the exposure of metals or alloys to hydrocarbons at increased temperature leads to the deposition of a relatively dense layer of carbon on the metal or alloy surface.
  • the layer of carbon appears to strongly decrease the heat transfer from the metal or alloy wall to a gas stream.
  • a significant reduction of the heat transfer is unallowable, since the capacity of the plant decreases strongly as a result.
  • the plant must then be stopped and the carbon layer must be removed by oxidation. In general, this occurs by reaction with oxygen or with steam.
  • a second object of the present invention is therefore to provide non-permeable, oxidation-resistant ceramic layers on metals of good weldability. In that case, the metals or alloys can first be brought into the desired form by welding, whereafter the protective layer is applied.
  • the invention is directed especially to rendering metal gauzes resistant.
  • catalytic reactions at (strongly) increased temperature because of the intrinsic high reaction rate, no large catalytically active surface area per unit of volume is necessary.
  • the surface area of a metal gauze is then sufficient.
  • the pressure drop upon passage of a gas stream through one or more metal gauzes is very low.
  • use is therefore made of platinum or palladium gauzes, to which often small amounts of other precious metals have been added.
  • a major drawback is that the precious metal disintegrates during the catalytic reaction. Initially, use was made of a gauze of gold, arranged under the platinum gauze to catch the platinum particles.
  • an object can be to provide protection against attack of the metal or the alloy upon exposure to a high-temperature gas stream.
  • gas turbines where the metal or the alloy exhibits too low a mechanical strength at the desired high temperatures.
  • use can be made of a porous layer of a thermostable material which, through an effectively low heat conductivity of the porous layer, leads to a temperature profile over the porous layer such that the temperature of the metal or the alloy does not exceed a particular limit value.
  • Firm anchorage of such a porous layer when used in gas turbines, is obviously an important condition.
  • a second use contemplated with the invention is the use of a porous layer applied to a solid surface as catalyst.
  • such layers are applied to solid surfaces by using so-called dip coating techniques.
  • dip coating techniques there are two different ways of proceeding. These two procedures relate to the fact that most catalytically active materials sinter strongly under conditions of the required thermal pretreatment or of the catalytic reaction.
  • the catalytically active material is applied to a high-porous thermostable material, a so-called support.
  • the most commonly used catalyst support materials are aluminum oxide and silicon oxide. ..
  • a finely divided support material is loaded with the catalytically active material or a precursor thereof. This thus loaded support material is then applied to the solid surface.
  • the unloaded support is deposited on the surface, whereupon the catalytically active component or a precursor thereof is provided in the porous support layer.
  • the surface to be covered is immersed in a suspension of the catalytically active material or of the support, and the surface is removed from the suspension at an empirically determined rate. This method is known by the name of dip-coating or wash-coating.
  • a layer of the catalytically active material of a particular thickness then deposits on the substrate.
  • a thin layer of such an elastomer By dipping or by spin-coating, a thin layer of such an elastomer can be applied to the surface to be covered. Pyrolysis of the thin layer of the elastomer resulting after drying then leads to a high-porous layer of a ceramic material. A so prepared layer of silicon dioxide maintains the porosity up to temperatures of about 700°C.
  • the thermal stability of the ceramic layer, as well as the pore distribution of the layer can be set by adding, for instance, aluminum compounds to the solution of silicone rubber.
  • a compound suitable for this purpose is, for instance, aluminum sec-butoxide.
  • the thus obtained ceramic layers contain no catalytically active components. According to the present state of the art, those are provided by impregnation of the porous ceramic layer with a solution of a precursor of the catalytically active material. Through a thermal treatment, the precursor can be converted to the desired catalytically active component.
  • the present state of the art also encompasses wholly or partly converting a porous silicon dioxide layer applied to a solid substrate to a synthetic clay mineral. See also WO-A-9607613.
  • Clay minerals are catalytically of interest as solid acid catalysts.
  • the application of catalytically active materials to solid, non-porous or little porous surfaces has been found to be of great value when used in gas streams where a low pressure drop is essential.
  • monoliths are used.
  • other materials with a low pressure drop have been developed, whereby an intensive contact between a gas stream and a catalyst surface is effected.
  • Examples are sintered metals, ceramic and metallic foams and in particular special reactor packings of specially shaped metal foils. The action of special reactor packings has been described by G. Gaiser and V. Kottke in Chem.-Ing.-Technik 61 (1989) no. 9, pp. 729-731.
  • the catalytically active material can be applied to the surface of the structure of the reactor packing so as to be firmly anchored thereon.
  • Another motive to apply the catalytically active material to a solid surface is the supply and removal of reaction heat in endothermic and exothermic reactions, respectively.
  • the temperature is to be properly controlled, as in the oxidation of ethylene to ethylene oxide, and it has still been decided to use a fixed catalyst bed, the catalyst is to be applied in a great many (e.g. 20,000) relatively thin tubes. This renders the reactor costly, while the filling of such a large number of tubes with catalyst to the same pressure drop is very time-consuming and labor-intensive.
  • reactors in which metal bodies, such as for instance spheres of a diameter of 1 mm to 1 cm or more, are sintered together and sintered to the reactor wall. This yields a high thermal conductivity.
  • the catalyst it is necessary to apply the catalyst as a porous layer of a thickness up to, for instance, 1 mm on the surface of the sintered metal bodies.
  • a last area where catalytically active materials applied to solid surfaces can be of great significance is that of catalytic liquid-phase reactions or that of catalytic reactions where a gaseous with a liquid reactant occur, as in catalytic hydrogenation or oxidation reactions.
  • work is done with suspended catalysts or with a fixed catalyst bed through which the reactants are passed.
  • a fixed catalyst bed through which a liquid reactant together with a gas stream is allowed to flow down, a so-called trickle flow process.
  • catalyst bodies with dimensions of at least a few millimeters must be used, because otherwise the pressure drop becomes too high.
  • the advantages of the fixed catalyst bed, no separate separation of the catalyst, are combined with those of a suspended catalyst, efficient utilization of the catalyst and good selectivity. Also, a suitable flow pattern of the liquid, and possibly the gas, around the catalyst can be realized. Thus it is possible first to mix the reactants very intimately before they come into contact with the catalyst.
  • a properly protective coverage of a metal, an alloy or a ceramic material can be obtained with a non-porous, non-permeable ceramic layer of a thickness of less than 100 mm, preferably of a thickness of less than 5 mm, and still more preferably of a thickness of less than 1 mm, which has been bonded onto the surface through an intermediary layer which contains ions of the surface to be covered, while in the case of substrates consisting of metals or alloys the oxide of the covered material is not demonstrable with X-ray diffraction.
  • Figure 1 gives a schematic representation of such a layer and the substrate.
  • a thin porous ceramic layer applied to a ceramic or metallic substrate upon treatment at a sufficiently high temperature, can be converted to a dense, non-permeable layer.
  • a thin porous layer is applied by pyrolysis of a thin layer of a suitable elastomer, such as silicone rubber, applied to the surface to be protected.
  • a suitable elastomer such as silicone rubber
  • For applying thicker layers use will be made of dip-coating or spin-coating a suspension of the material to be applied.
  • the thickness of the layer can be varied within wide limits, for instance from less than 1 to more than 100 mm. If necessary, if relatively thick layers are desired, several layers are applied one after another.
  • thin protective ceramic layers can be obtained by applying a thin layer of silicone rubber and pyrolyzing this material first at a temperature of about 450°C and thereupon sintering the layer in an inert gas atmosphere at a greatly increased temperature to a non-porous, non-permeable layer.
  • the thin protective non-permeable layer therefore consists substantially of silicon dioxide.
  • the metal surface needs to be covered with a thin oxide layer. When this layer is too thick, no good bonding is obtained. In traditional enameling this is a problem-.
  • a ceramic layer having a high softening or melting temperature must be applied.
  • composition of the solution of the elastomer by adding, in accordance with the state of the art, to, for instance, silicon dioxide, certain components, such as aluminum oxide or titanium dioxide. It is of importance to be able to manage the chemical composition of the layer substantially consisting of silicon dioxide so as to control the melting point of the layer and hence the temperature needed to come to a non-permeable, non-porous layer. When it is desired to use the protective ceramic layer at highly elevated temperatures, it is of importance to set the softening point of the ceramic layer as high as possible. This can be done by incorporating aluminum oxide or titanium dioxide into the silicon dioxide.
  • an alcoholate of aluminum can be added, such as the isopropoxide.
  • Titanium and zirconium compounds can be added as the ammonium salt of a chelate with lactic acid of a titanate or a chelate of diethyl citrate of a zirconate.
  • silicon dioxide such as it is obtained by pyrolysis of silicone rubber, a temperature above about 800°C is needed to obtain a non-porous layer. When it is intended to work with the protective layer at a lower temperature, it is attractive to obtain a dense, non-permeable layer by sintering at a lower temperature.
  • the method therefore starts from a water glass solution when the covered metal or alloy surface is not subsequently exposed to very high temperatures.
  • a water glass solution a thin, non-porous, strongly bonding layer can be readily applied to metal and alloy surfaces.
  • the addition of titanium compounds readily leads to acid-resistant enamel layers, which are part of the invention. According to the method of the invention, such layers can be readily applied to the wall of reactors.
  • Alkali- resistant layers are obtained according to the invention by adding zirconium to silicon dioxide, alone or in combination with tin oxide.
  • boron oxide is added preferably by addition of suitable boron compounds, such as for instance aluminum borohydride, to the solution of the elastomer.
  • a second procedure for incorporating certain components into the initial porous layer is impregnation of the porous layer with solutions of suitable compounds or deposition-precipitation of certain compounds in the porous layer.
  • suitable compounds such as nickel oxide and cobalt oxide.
  • Reaction with the silicon dioxide can be readily obtained by deposition-precipitation of these elements, but impregnation is also attractive in many cases.
  • nickel oxide and cobalt oxide greatly improve the bonding of silicon dioxide-containing layers to metal and alloy surfaces.
  • the impregnation of a suitable solution of components to be included in the ceramic layer is preferably done in the evacuated layer, whereby a volume of solution is impregnated which corresponds to the pore volume of the porous layer.
  • the magnitude of the exposed catalytically active surface is generally of less importance than the (thermal) stability of the catalyst system. Therefore, according to the invention, a metal or ceramic covered with a non-porous, non-permeable ceramic layer is used as catalyst support.
  • the catalytically active material is applied to this surface in, if necessary, finely divided form.
  • the invention is preferably practiced with gauze-shaped metal substrates.
  • Figure 2 schematically represents such a surface.
  • the reaction on the catalytically active surface typically proceeds at such a rate that the transport of the reacting molecules in the pores of the catalyst occurs sufficiently fast. In that case, a large catalytically active surface area per unit of volume of the reactor is of great significance.
  • a protective non-porous, non-permeable layer is applied, whereafter a porous ceramic layer is deposited on the non-porous layer.
  • active components can be provided in finely divided form. The distribution over the surface of the porous material leads to a thermostable catalyst.
  • the non-porous, non-permeable layer causes the metal to be oxidized upon the thermal pretreatment necessary to provide a next porous layer or to activate a precursor of a catalytically active component. Oxidation of the metal surface leads to a greatly reduced bonding of the porous layer to the metal.
  • Figure 3 schematically represents the two layers which have been applied to a surface in accordance with the invention.
  • the non-porous, non-permeable layer prevents the occurrence of carbon deposition on the metal surface under the porous layer upon heating in a gas atmosphere with carbon-containing molecules. Growth of carbon under the porous layer also greatly reduces bonding of this layer.
  • the non-porous layer therefore protects the underlying material against undesired reactions with gases at increased temperature or against corrosive action of liquids. This last can lead to a highly undesirable contamination of the reaction product.
  • the underlying material can also exhibit undesired catalytic reactions by which selectivity is impaired.
  • the underlying metal can react with a catalytically active component to form a non-active or less active compound.
  • zeolites can take up metal ions of an underlying metal layer and thereby lose the catalytic activity. The use of such a non-porous intermediary layer thus constitutes an essential improvement of the prior art.
  • a non-porous, non-permeable layer applied to a solid surface, with a porous layer thereon is moreover of significance in the use of porous layers as catalytically active material or as support for one or more catalytically active components.
  • catalysts generally lose activity during use, for instance by poisoning.
  • replacing the catalyst is extremely simple.
  • the catalyst can be removed from the reactor and be replaced with a new catalyst charge, although this can be relatively labor-intensive. If the catalyst is applied as a thin porous layer on a special reactor packing, the consequence of deactivation of the catalyst might be that the entire, often costly reactor packing must be replaced.
  • the deactivated catalyst can be relatively readily removed from the surface of the reactor packing. According to the invention, this occurs by treating the reactor packing with an alkaline or acid liquid.
  • an alkaline liquid can be used because metals such as iron and nickel are resistant to alkaline liquids, while silicon dioxide-containing porous layers often dissolve readily in alkaline liquids.
  • a metal such as aluminum however, this presents problems, since aluminum also dissolves in alkaline liquids, forming hydrogen. Because aluminum, in view of the low density, is especially attractive as reactor packing in larger reactors, protection of the aluminum is highly desirable.
  • the substrate on which the catalytically active layer is applied is provided with a non-permeable ceramic layer which is resistant to either acid, or basic, or acid or basic solutions.
  • a non-permeable ceramic layer which is resistant to either acid, or basic, or acid or basic solutions.
  • enamel layers that are resistant to acid, to alkali, or to both.
  • acid-resistant enamel is obtained by incorporating inter alia titanium dioxide into the enamel. Resistance to strongly acid liquids is achieved by also incorporating fluorine, which, according to the invention, is readily possible by impregnation.
  • Lye-resistant enamel types contain zirconium dioxide often together with fluorine, which, according to the invention, can also be readily included in non-porous, non-permeable layers according to the invention.
  • enamel types that are resistant to both acid and lye.
  • such materials are also readily applicable as thin layers on metal substrates.
  • the starting point is a thin layer of silicone rubber, which is subsequently pyrolyzed in air, whereby a porous layer of silicone dioxide is formed.
  • This layer is impregnated with the components of the desired enamel, whereafter the thus covered surface is heated, preferably in a non-oxidizing gas atmosphere, at such a high temperature that a chemically homogeneous, non-porous; non-permeable layer is obtained.
  • the porous layer of catalyst support material can be applied according to the known prior art.
  • porous layer by dip -coating or spin-coating.
  • excellent results have also been achieved by applying onto the surface of the non-permeable layer a layer of a suitable compound, such as silicone rubber, titanium and zirconium compounds as the ammonium salt of a chelate with lactic acid of a titanate or a chelate of diethyl citrate of a zirconate, and subsequently pyrolyzing the layer.
  • a suitable compound such as silicone rubber, titanium and zirconium compounds as the ammonium salt of a chelate with lactic acid of a titanate or a chelate of diethyl citrate of a zirconate
  • thermostable fine division can be obtained by dissolving a suitable compound of the catalytically active metal, generally a precious metal, in the solution of the elastomer.
  • acetic acid salts of palladium and platinum are found to be highly satisfactory.
  • organometallic complexes such as acetyl acetonate complexes, are found to be highly satisfactory.
  • the thickness of the porous layer at which no transport impediments in the porous layer occur yet depends, as noted above, on the rate of the catalytic reaction, on the diffusion coefficients of the reactants and the reaction products, and on the diameter of the pores. Since in the gas phase the diffusion coefficients are a factor of 100 higher than in the liquid phase, in gas phase reactions preferably somewhat thicker porous layers in which the catalytically active component(s) is/are provided will be employed. In relatively slow reactions in the liquid phase, a thickness of 50 mm can be utilized without this giving rise to transport impediments. It will be clear that the application of 50 layers, with requisite intermediate calcination to remove the organic constituents, is extremely laborious.
  • thermostable oxide which is strongly bonded onto a solid surface, is capable of eminently anchoring ceramic particles, such as used as catalyst support.
  • 'Thin' in this connection is understood to mean a layer thickness of about 1 mm.
  • thermostable oxides are silicon dioxide, titanium dioxide and zirconium dioxide. According to a special embodiment of the invention, therefore, a porous layer of a thermostable oxide is applied to the non-permeable layer according to the invention, on which a relatively thick catalytically active layer according to the known prior art has been applied.
  • a support which may or may not be loaded with the active material, is applied to the porous intermediary layer by dip-coating in a suspension of the finely divided material.
  • dip-coating layers of a thickness of 50 mm or more can be applied.
  • Figure 4 schematically represents such a composite layer.
  • zeolite crystals on a solid substrate is of great practical significance.
  • the transport in the relatively narrow pores of zeolites proceeds slowly, so that small crystallites are eminently suitable for catalytic reactions. This applies to gas-phase reactions, but especially also to liquid-phase reactions.
  • the synthesis of zeolites leads indeed to small crystallites. In some zeolites, crystallites or strongly agglomerated crystallites of about 1 to 10 mm are obtained, whereas in other zeolites, such as zeolite-b, much smaller crystallites, viz. smaller than 0.1 mm are formed upon synthesis. In gas-phase reactions, however, a gas stream is to be passed through a catalyst bed.
  • a fixed catalyst bed can be used, but in connection with the allowable pressure drop and the prevention of channeling, no bodies smaller than about 1 mm can be used.
  • the catalyst In gas-phase reactions the catalyst can also be provided in a fluidized bed, but this requires the use of bodies of a diameter of 60 to 150 mm or greater.
  • no small catalyst bodies In liquid-phase reactions no small catalyst bodies can be used either, since crystallites smaller than 1 mm cannot be properly separated from the reaction product by filtration or centrifugation. It is therefore either endeavored to synthesize larger zeolite crystallites, which is often a great problem, or extremely small zeolite crystallites are included in a so-called binder, silicon dioxide or silicon dioxide/aluminum oxide, after which the combination is formed into larger bodies.
  • zeolite/binder combination Processing the zeolite/binder combination to form wear-resistant bodies of dimensions of 3 to 10 mm, however, is technically cumbersome, while the binder often impedes transport and can lead to poor selectivity. Also, the binder may react with the zeolite to form a non-active or less active compound. Zeolite crystallites applied to a solid substrate are therefore of great technical significance.
  • zeolite crystallites are used which have been applied via a non-permeable, non-porous layer on a surface of suitable moldings.
  • a zeolite layer is applied to the surface of a metal or an alloy.
  • the starting point will generally be a layer of porous silicon dioxide applied to a ceramic or metallic molding.
  • a continuous non-permeable intermediary layer according to the invention is needed, it will suffice, in special cases where moldings of relatively inert materials are used, to use a porous silicon dioxide layer and to grow the zeolite crystallites therefrom.
  • a silicate layer be present which does not react to form zeolite. In that case, however, the intermediary layer does not need to be continuous.
  • the necessary ingredients for the zeohte synthesis that are not already present in the porous layer are impregnated in the pores of the zeoUte.
  • a 'template' molecule is necessary for the- synthesis of the zeohte
  • a solution of this template is impregnated in the porous ceramic layer obtained by pyrolysis of the dried silicone elastomer layer.
  • the aluminum necessary for the synthesis of the zeohte will generally be provided in the porous layer by dissolving in the solution of the elastomer.
  • the volume of the solution of the ingredients of the zeohte synthesis is chosen to be equal to the pore volume of the porous layer, which is preferably impregnated after evacuation. After the impregnation, the layer is brought under the conditions required for the nucleation and growth of the zeohte crystallites. In general, hydrothermal conditions are required for this purpose. Especially in the case of metallic substrates, it is extremely simple to accurately set and maintain the temperature during the synthesis.
  • the surface covered with porous silicon dioxide will mostly be introduced into a liquid which contains the ingredients for forming zeolite crystals.
  • the zeohte crystallites formed in the liquid preferentially deposit, firmly anchored, on the surface on which the porous silicon dioxide layer has been applied. According to the invention, therefore, the surface covered with porous sihcon dioxide is introduced into a synthesis solution of the desired zeohte, whereafter the zeohte synthesis is allowed to proceed.
  • zeohte crystallites very strongly bonded to solid surfaces are obtained. It is possible, according to the invention, to allow the initial porous layer to react wholly or partly to form zeohte crystaUites.
  • the thickness of the layer initiaUy appUed, consisting substantiaUy of siUcon dioxide, determines the density of the zeohte crystaUites on the surface. It is of great significance that the surface to be covered with zeohte crystaUites does not need to be horizontaUy oriented during the zeohte synthesis. This makes it possible without any problem to cover complex reactor packings.
  • Characteristic of zeohte crystaUites applied, according to the method of the invention, to sohd ceramic or metallic substrates, is that a non-porous, non-permeable layer is present at the interface between the substrate and the zeohte crystaUites. It is possible for this layer to comprise not much more than a few layers of atoms, but the layer is always present. As noted above, it is of great importance, for the purpose of replacing deactivated catalysts, that the catalyticaUy active layers or the catalyticaUy active particles can be readily removed, without the ceramic or metallic substrate being affected. Therefore, according to a preferred embodiment of the invention, the zeohte crystaUites are applied to an alkali-resistant non-permeable intermediary layer.
  • zeohtes can also be practiced with zeohtes.
  • This provides the advantage that the zeohte can be prepared separately. Since zeohtes typicaUy crystallize to (extremely) smaU particles, it is relatively easy to make a suspension of them which is suitable for applying the zeohtes to a surface covered with a sihcon dioxide layer which may or may not be porous.
  • a non-permeable, non-porous layer is present between the catalyticaUy active layer and the substrate . It has been found that a porous sihcon dioxide layer apphed to the non-porous layer strongly increases the bonding of the zeohte layer.
  • electrophoresis is eminently suitable to apply support particles which may or may not be loaded with catalyst, or small catalyst particles.
  • a layer is apphed through electrophoresis.
  • the metal or aUoy surface has priorly been covered with a non-porous, non-permeable layer, on which preferably a porous layer has been provided to improve bonding.
  • a preferred embodiment of the catalyticaUy active materials according to the invention therefore concern catalyticaUy active porous layers apphed to electricaUy conductive surfaces having a thickness up to about 50 mm, whUe between the metal or the ahoy a thin (less than about 1 mm) non-porous layer and preferably a thin (less than about 1 mm) porous layer for improving the bonding is present.
  • Figure 4 schematicaUy represents the structure of the system. In general, in the electrophoresis, the starting point will be a suspension of particles having dimensions of less than 1 mm to about 10 mm.
  • the support particles can be priorly loaded with (a precursor of) the catalyticaUy active component(s) and bonding these particles to the surface by electrophoresis.
  • the layers are provided on structured metal surfaces, such as static mixers. In this case, a very good contact is obtained between a gas phase and a hquid phase or between two hquid phases.
  • layers of zeohtes or synthetic clay minerals which can be used as sohd acid catalysts are apphed to metal or aUoy surfaces by electrophoresis.
  • Zeohtes are generaUy negatively charged, so that the metal surface to be covered needs to be brought to a positive voltage to enable deposition of the zeohte on the surface.
  • Clay minerals too can be eminently deposited on metal or aUoy surface by electrophoretic route.
  • a catalyticaUy active layer of a thickness of about 50 mm at a maximum is applied to non-porous particles of dimensions of about 0J mm to about 10 mm.
  • smaU metal particles having dimensions of about 0.1 mm to about 1 cm are eminently suitable for this purpose.
  • metal particles in accordance with the above methods, are a bonding layer and a porous layer containing the catalytically active component.
  • a bonding layer When it is desired to pass a hquid . stream at a relatively high rate in upward direction through a bed of metal particles loaded in such a manner, it is attractive to use relatively heavy metal particles. It may also be advantageous to use ferromagnetic metal particles and to fix these particles with an inhomogeneous magnetic field in the reactor.
  • metal particles having dimensions of about OJ to about 10 mm, covered with a layer, which may or may not be porous, in which or on which the catalyticaUy active component is present.
  • a more special embodiment of the invention concerns ferromagnetic metal particles. Such ferromagnetic bodies which are fixed in a reactor by an inhomogeneous magnetic field or which can be separated from the hquid by an inhomogeneous magnetic field.
  • ElectrophoreticaUy covering smaU metal particles with a catalyst support layer can be done by using a fluidized bed of the metal particles. In that case, the particles are held in floating condition by a hquid stream, wrhle one or more electrodes make contact with the bed of the particles.
  • ferromagnetic particles are used which by means of an inhomogeneous magnetic field are held in floating condition in the liquid in which the electrophoresis is being carried out.
  • a layer of a suitable support is provided on a surface on which priorly a firmly anchored porous layer has been deposited, which apphed support has priorly been loaded with particles or a precursor of particles from which carbon fibrils can grow, or which apphed support has been loaded with a precursor of particles from which carbon fibrils can grow only after it has been apphed to the surface, whereafter carbon fibrils are grown from the particles and finaUy a catalyticaUy active material is apphed to the carbon fibrils.
  • the conditions wiU generaUy be chosen such that upon termination of the growth process the metal particles from which the fibrils grow have been encapsulated by carbon. In this case, the smaU metal particles will be incapable of exhibiting any unwanted reactions with the hquid to be treated.
  • wiU be made of a bonding layer and a support layer of titanium dioxide or zirconium dioxide.
  • a non-porous bonding layer of sihcon dioxide wiU be apphed to the metal surface and then a catalyst support layer, likewise of sihcon dioxide.
  • Such a surface loaded with carbon fibrils is also eminently suitable for applying an ion exchanger thereto.
  • the ion exchanger can be used as catalyst, but it is also attractive as an ion exchanger, because a relatively large fraction of the ion exchanger can be utilized due to good accessibihty.
  • Ion exchangers applied to carbon fibrils grown on the surface of materials are therefore part of the invention.
  • such carbon fibrils loaded with ion exchangers are apphed to surfaces of static mixers.
  • Figure 1 Schematic picture of a protective layer apphed to a solid surface, (a) substrate, preferably a metal or an alloy; (b) protective layer.
  • Figure 2 Schematic picture of a surface covered with an non-porous, non-permeable protective layer on which a catalyticaUy active component is provided, (a) substrate, preferably a metal or an aUoy; (b) protective layer; (c) catalytically active material.
  • Figure 3 Schematic representation of a solid surface covered with a non-porous, non-permeable layer on which a porous layer with a catalyticaUy active component is provided, (a) substrate, preferably a metal or an aUoy;
  • FIG. 4 Schematic representation of a solid surface covered with a non-porous, non-permeable layer (a), a porous bonding layer (b) and a porous layer
  • Figure 6 Higher magnification of a stainless steel plate covered with clay mineral by electrophoretic route. Recording with a Philips XL 30 FEG scanning electron microscope.
  • Figure 7 Carbon fibrils grown on a stainless steel plate after being covered with sihcon dioxide and aluminum oxide.
  • the nickel particles were present from which the carbon fibrUs were grown through decomposition of methane.
  • the invention is elucidated with the foUowing examples.
  • the starting material was silicone rubber in the form of a commercial product, viz. Bison, "transparent", based on polydimethyl siloxane. This material was dissolved in diethyl ether. To the obtained solution was added aluminum sec-butoxide (ACROS), titanium isopropoxide (Jansen Chimica), or zirconium isopropoxide (Fluka). The concentration of silicone rubber in the solution was 6 to 10% by weight. With aluminum, a series having different Si/Al ratios was prepared, viz. SiggAli, Si 7 oAl3o, Si ⁇ oA o, Si ⁇ sA s, SisoAl ⁇ o, and Sis ⁇ Al ⁇ s.
  • the titanium dioxide- and zirconium dioxide-containing sihcon dioxide preparations contained Si/Ti and Si/Zr ratios of 80/20. After pyrolysis at 873K, the pore volume of the material was determined as a function of the Si/Al ratio. WhUe the pure sihcon dioxide exhibited a pore volume of about 0.2 ml g, the pore volume increased to 1.4 ml/g at an Al fraction of 0.2, to decrease at higher Al fraction to about 0.4 ml/g.
  • the accessible surface area determined by nitrogen adsorption according to the BET theory, increased from 100 m 2 /g for pure sihcon dioxide to 580 m 2 /g for an Al fraction of 0.75, then to decrease again to about 300 m 2 /g for pure aluminum oxide.
  • the accessible surface area was determined as a function of the temperature. The samples were held at the different temperatures for 3 hours. For aU three preparations the surface area of 200 to 260 m 2 /g after calcining at 873K graduaUy decreased to 70 to 180 m 2 /g after calcining at 1173K. The material with zirconium dioxide was found, after calcining at 1173K, to exhibit the highest surface area. While pure sUicon dioxide can be readily sintered at about 1073K to form a non- permeable layer, it is necessary, with increasing contents of aluminum, zirconium or titanium, to heat at considerably higher temperatures. The content of aluminum, titanium or zirconium is selected depending on the temperature at which the material covered with a protective layer is to be used.
  • the material with SiggAli was used to examine the density. To that end, the material was apphed to stainless steel. A sample of the stainless steel, without having been covered with a layer, was heated at 900°C in a thermobalance. A rapid weight increase showed that the material oxidized relatively fast. Analysis showed that the surface was covered with a high-porous mass of chromium oxide upon completion of the experiment. When on a simUar plate of stainless steel a layer with the specified ratio of Si/Al had been apphed, which was subsequently sintered in an inert atmosphere at 1200°C, not any change in weight was observed after correction for change of the upward pressure upon increase of the temperature. Application of ZSM-5 (MFI) zeolite crystallites on a stainless steel substrate.
  • MFI ZSM-5
  • the starting point was a layer of porous sihcon dioxide prepared by applying sihcone rubber to stainless steel and decomposition of the silicone rubber layer at 773K.
  • the tetramethylammonium from CFZ (Chemische Fabriek Zaltbommel) was used. Together with NaOH the tetrapropylammonium was impregnated in the pore volume of the porous layer.
  • the zeohte was synthesized under hydrothermal conditions at 140°C.
  • Figures 1 and 2 give at two different magnifications a picture with secondary electrons of the resulting surface. It is clear that the surface is homogeneously covered with zeohte crystaUites.
  • the stainless steel powder was introduced into a cylindrical wire net of stainless steel of a diameter of 2 cm. Contact with the stainless steel particles was made with two electrodes.
  • the cyhnder was placed in a 200 ml beaker in which a platinum electrode was present.
  • the clay suspension was recirculated by means of a peristaltic pump. To that end, the suspension was withdrawn under the cyHnder and recycled to the top of the cyHnder. Using a magnetic stirrer, the clay particles were held in suspension.
  • Fig. 6 schematicaUy represents the setup used.
  • the electrophoresis was carried out in this way.
  • the current strength was 0.1 to 0.2 A.
  • 78 mg of clay was deposited on 1.3 grams of metal powder.
  • the surface of the uncovered metal powder was immeasurably smaU, whUe after coverage the surface was 68 m 2 per gram. This surface was measured in equipment of Micromeretics with adsorption of nitrogen at 77 K.
  • the pore volume of the clay layer was 0.06 ml per gram.
  • a layer of sihcon dioxide was apphed, of a thickness of about 0.7 ⁇ m. This was done by dipping the plate in a solution of silicone rubber in ethyl acetate. After pyrolysis of the sUicone rubber at 400° C the coated plate was held in an inert atmosphere (argon with 1% hydrogen) at 900° C for 16 hours. Then, by electrophoretic route, aluminum oxide was applied to the plate, having a specific surface area of 270 m 2 per gram. The procedure in the electrophoresis was analogous to that of the above example in which a stainless steel plate was covered with clay mineral. After calcination of the thus covered plates for 4 hours at 450° C and cooling to room temperature,

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  • Metallurgy (AREA)
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  • Inorganic Chemistry (AREA)
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  • Chemically Coating (AREA)
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Abstract

L'invention concerne des couches céramiques de protection imperméables non poreuses, qui présentent une épaisseur inférieure à 50 νm, de préférence une épaisseur inférieure à 5 νm ou, mieux encore, une épaisseur inférieure à 1 νm. Ces couches sont fixées à un substrat par une couche intermédiaire contenant des ions de la surface à revêtir. Dans le cas de substrats constitués de métaux ou d'alliages, l'oxyde du matériau revêtu n'est pas déterminable par cristallographie par rayons X.
PCT/NL2000/000019 1999-01-21 2000-01-13 Revetement ceramique WO2000043572A1 (fr)

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JP2000594975A JP2002535492A (ja) 1999-01-21 2000-01-13 セラミックコーティング
AU23311/00A AU2331100A (en) 1999-01-21 2000-01-13 Ceramic coating
EP00902193A EP1153158A1 (fr) 1999-01-21 2000-01-13 Revetement ceramique

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NL1011098A NL1011098C2 (nl) 1999-01-21 1999-01-21 Keramische deklaag.

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1319416A1 (fr) 2001-12-12 2003-06-18 Hehrlein, Christoph, Dr. Stent métallique poreux avec un revêtement céramique
WO2010098664A1 (fr) 2009-02-25 2010-09-02 K.M.W.E. Management B.V. Procédé de production d'hydrogène à partir de méthanol
WO2010098665A1 (fr) 2009-02-25 2010-09-02 K.M.W.E. Management B.V. Procédé et réacteur pour l'extraction de composés organiques hors de flux gazeux
CN115028473A (zh) * 2022-05-06 2022-09-09 深圳市吉迩技术有限公司 覆有金属涂层的多孔陶瓷的制备方法及气溶胶生成装置

Citations (6)

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GB547532A (en) * 1940-04-10 1942-09-01 Westinghouse Electric Int Co Improvements in or relating to vitreous coatings
WO1979000247A1 (fr) * 1977-11-01 1979-05-17 Atomic Energy Authority Uk Revetement de substrats
US4460630A (en) * 1978-03-15 1984-07-17 Matsushita Electric Industrial Co., Ltd. Method of forming porcelain enamels on aluminized steel
US4879142A (en) * 1987-03-06 1989-11-07 Wacker-Chemie Gmbh Process for preparing a silicon carbide protective coating
EP0783179A2 (fr) * 1996-01-05 1997-07-09 Siemens Aktiengesellschaft Méthode de fabrication d'une couche de SiO2 sur une topographie
EP0878520A2 (fr) * 1997-05-12 1998-11-18 Fraunhofer-Gesellschaft Zur Förderung Der Angewandten Forschung E.V. Composition pour revêtements réfractaires, pyrolitiquement céramisables

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB547532A (en) * 1940-04-10 1942-09-01 Westinghouse Electric Int Co Improvements in or relating to vitreous coatings
WO1979000247A1 (fr) * 1977-11-01 1979-05-17 Atomic Energy Authority Uk Revetement de substrats
US4460630A (en) * 1978-03-15 1984-07-17 Matsushita Electric Industrial Co., Ltd. Method of forming porcelain enamels on aluminized steel
US4879142A (en) * 1987-03-06 1989-11-07 Wacker-Chemie Gmbh Process for preparing a silicon carbide protective coating
EP0783179A2 (fr) * 1996-01-05 1997-07-09 Siemens Aktiengesellschaft Méthode de fabrication d'une couche de SiO2 sur une topographie
EP0878520A2 (fr) * 1997-05-12 1998-11-18 Fraunhofer-Gesellschaft Zur Förderung Der Angewandten Forschung E.V. Composition pour revêtements réfractaires, pyrolitiquement céramisables

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1319416A1 (fr) 2001-12-12 2003-06-18 Hehrlein, Christoph, Dr. Stent métallique poreux avec un revêtement céramique
WO2010098664A1 (fr) 2009-02-25 2010-09-02 K.M.W.E. Management B.V. Procédé de production d'hydrogène à partir de méthanol
WO2010098665A1 (fr) 2009-02-25 2010-09-02 K.M.W.E. Management B.V. Procédé et réacteur pour l'extraction de composés organiques hors de flux gazeux
EP2228340A1 (fr) 2009-02-25 2010-09-15 K.M.W.E. Management B.V. Procédé de production d'hydrogène à partir de méthanol
EP2228122A1 (fr) 2009-02-25 2010-09-15 K.M.W.E. Management B.V. Procédé et réacteur pour l'élimination de composés organiques de flux gazeux
CN115028473A (zh) * 2022-05-06 2022-09-09 深圳市吉迩技术有限公司 覆有金属涂层的多孔陶瓷的制备方法及气溶胶生成装置
CN115028473B (zh) * 2022-05-06 2024-02-09 深圳市吉迩技术有限公司 覆有金属涂层的多孔陶瓷的制备方法及气溶胶生成装置

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JP2002535492A (ja) 2002-10-22

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