Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0215—Coating
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
  • G21C3/02—Fuel elements
  • G21C3/04—Constructional details
  • G21C3/16—Details of the construction within the casing
  • G21C3/20—Details of the construction within the casing with coating on fuel or on inside of casing; with non-active interlayer between casing and active material with multiple casings or multiple active layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/0004—Preparation of sols
  • B01J13/0047—Preparation of sols containing a metal oxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/024—Multiple impregnation or coating
• • 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
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1254—Sol or sol-gel processing
• • 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
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D5/00—Coating with enamels or vitreous layers
  • C23D5/02—Coating with enamels or vitreous layers by wet methods
• • 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
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D5/00—Coating with enamels or vitreous layers
  • C23D5/10—Coating with enamels or vitreous layers with refractory materials
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/10—Solid density
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S376/00—Induced nuclear reactions: processes, systems, and elements
  • Y10S376/90—Particular material or material shapes for fission reactors

Definitions

• This invention relates to the provision of coatings on substrates, which coatings may be useful, for example, as protective coatings for the substrate or for carrying catalytically active material.
• gel coatings may be produced from sols, which coatings have a lower porosity and higher density than the aforementioned coatings, and that such gel coatings are convertible to ceramic coatings of low porosity and high density even after relatively mild heat treatment. This may be done by using sols comprising unaggregated colloidal primary particles, or aggregated colloidal primary particles with additional components to occupy the gaps in the aggregated particles.
• the present invention provides, in one aspect, a method of providing a substrate with a gel coating, characterised in that the substrate is contacted with a sol of a refractory material and capable of being converted to gel of the refractory material, the bulk density of the gel being at least 40% , preferably at least 45%, of the theoretical density of the refractory material, and the sol is converted to a gel to provide the substrate with the gel coating.
• the invention also provides a substrate carrying an adherent coating of a gel of a refractory material, wherein the density of the gel is at least 40% of the theoretical density of the refractory material.
• the refractory material in the sol and the gel of our invention is present in the form of a precursor of the refractory material itself, such as a hydrated form of the material in the case of an aquasol or gel produced therefrom. Such a precursor always gives the material itself on firing.
• the gel-coated substrate of our invention is fired to give a substrate with a ceramic coating of the refractory material itself, which ceramic may have a bulk density which is at least 60% of the theoretical density of the refractory material. It should be noted that, whilst it may be possible to produce such dense ceramic coatings by prolonged heat treatment of known gel coatings, our dense ceramic coatings may be produced by heat treatment under much milder conditions.
• 'bulk density' in this specification is meant the average density of the material inclusive of the matrix and open and closed pores.
• 'theoretical density' is meant the density of the refractory material as such, i.e., the density of the material in the absence of any cavities, pores or the like.
• the density of a gel which has been dried at an elevated temperature may, in some cases, be somewhat less than that of a gel which has been dried at ambient temperature due to loss of water on drying.
• the bulk density values in our invention are to be taken to relate to a gel when dried at ambient temperature, whether actually or notionally.
• thin coatings i.e. of the order of microns
• the coated substrates off our invention have a number of valuable applications dependent upon the substrate and refractory material chosen.
• the coatings may be used, for example, to confer oxidation resistance to the substrate, as a pre-coat on the substrate for carrying subsequently applied catalytically active material, and to inhibit carbon deposition in certain environments.
• the general role of the coating is to confer a high degree of protection to the substrate by virtue of its high density and low porosity.
• the coating therefore isolates the substrate from its environment thereby protecting it from attack by gaseous species in the environment.
• the coating carries an additional layer such as of catalytically active material, the latter is protected from attack by the substrate such as when the substrate contains mobile metal ions.
• the coating may be catalytically active in its own right.
• sols used in the present invention need not necessarily comprise colloidal particles of one refractory material only. Thus, they may be 'mixed' sols comprising colloidal particles of more than one refractory material. Also, the sols may contain additional components dispersed in the liquid medium of the sol, for example, in solution in the liquid medium.
• a preferred way of carrying out the method of the invention is to use, as the sol, a dispersion of substantially unaggregated colloidal primary particles of the refractory material in a liquid medium. Because of the lack of aggregation, such sols are readily convertible, on drying, to dense, low porosity gels as required in the present invention, i.e., the primary particles can readily 'pack down' to a dense, low porosity structure upon drying and firing.
• sols are known in the art and examples include certain sols of refractory oxides such as a CeO 2 sol described at page 3 line 4.9 of our U.K. Patent Specification No. 1 342 893 and at column 3 line 63 of our corresponding U.S. Patent Specification No. 3 761 57 1.
• the conditioned slurry specifically mentioned in Example 3 of each of these specifications may be diluted with water to give such a sol, and the gel specifically described in the same example may be redispersed in water to give such a sol. Also, the gel specifically described in Example 5 of each of the above specifications may be redispersed in water to give such a sol.
• sols which may be used in the present invention are a ZrO 2 sol as described in our U.K. Patent Specification No. 1 181 794 (corresponding to our U.S. Patent Specification No. 3 518 050), a TiO 2 sol as described in our U.K. Patent Specification No.
• SiO 2 sol believed to be made by hydrolysing sodium silicate and sold commercially by Monsanto under the trade name of 'Syton', and ThO 2 sol made for example by thermally denitrating hydrated thorium nitrate at not more than 490oC and dispersing the product in water.
• the particle sizes of the colloidal particles in the sols are typically in the range of 20 ⁇ to 500 ⁇ , for example 50 ⁇ to 200 ⁇ . It should be noted however, that the above exemplified sols are not necessarily of equal utility in the applications of the present invention, i.e., some sols may be better than others for specific applications.
• the preferred sols above may, if desired, contain components additional to the unaggregated primary colloidal particles. For example, they may contain colloidal particles comprising loose aggregate structures of primaryparticles, wherein the colloidal particles have been made by dispersing primary-particles, made by a vapour phase condensation method such as flame hydrolysis, in water and as described in the specification of aforementioned West German OLS No. 2 647 702. Such additional components, for example Al 2 O 3 , may be used to provide the coatings in our invention with other desired properties such as improving their ability to cause further layers to adhere thereto.
• the sols used ⁇ n the method of our invention may comprise colloidal particles which arc aggregated, but where the sols contain additional components dispersed therein which substantially fill the gaps in the aggregated particles so that the sols give rise to a dense gel coating according to the invention when converted to a gel.
• additional components may, for example, comprise salts in solution in the liquid medium of the sol and of sufficient concentration for the ions of the salt to substantially fill the gaps in the aggregated colloidal particles.
• a preferred example of such a sol is a sol comprising components which when dried to give a gel and subsequently fired are convertible to a glass-based coating.
• Such a sol may comprise, for example, a SiO 2 sol containing aggregated colloidal particles and w-hich contain additional components, in solution, which are capable of reacting together and with the SiO 2 on firing to give a glass-based material.
• Such components may include, for example, soluble borates, and soluble Li and Na salts in solution in the sol.
• the SiO 2 sol may, for example, be a sol made by dispersing in water SiO 2 which has been made by a vapour phase condensation method such as flame hydrolysis and to which reference has already been made herein.
• coatings comprising glass-based materials may be provided according to our invention using sols comprising substantially unaggregated colloidal primary particles, such as the abovementioned 'Syton' SiO 2 sol.
• Glass-based materials include, for example, conventional glasses and also glass-ceramics.
• the method of our invention may be carried out very simply, for example by immersing the substrate in the sol, removing and drying to convert the sol to the corresponding gel, optionally followed by firing if a non-gel ceramic coating. is desired.
• a substrate of complex shape may readily be treated to provide a coating.
• a coating of controlled thickness may be produced, typically, 1 ⁇ m or less, so that significant dimensional changes are avoided, even if more than one coating is provided.
• the substrate in the invention may be either metallic or non-metallic, though we prefer the former since protective coatings are more often required for metallic substrates.
• metallic substrates such as steels
• An example of a metallic substrate which may be used is an aluminium bearing ferritic alloy such as an alloy of Fe, Cr, Al and Y, a specific example of which is an alloy having proportions by weight of up to 20% Cr, 0.5% to 12% Al, 0.1% to 3% Y, and the balance Fe.
• Such alloys are known to be very useful substrates in catalysts for the treatment of the noxious constituents of motor vehicle exhause gases (see, for example, the specification of our U.K. Patent No.
• a catalyst may then be prepared by applying a catalytically active material, such as a platinum group metal, to the coating, for example, in combination with a high surface area refractory oxide such as Al 2 O 3 as described in the specification of our aforementioned West German OLS No. 2 647 702.
• the CeO 2 coating in such a case acts as a temporary protective barrier until such time as alumina is generated from the alloy during use of the catalyst.
• the present invention also has application in situations where it is desirable to alter the surface chemistry of a metal and thereby eliminate certain undesirable chemical effects.
• One such effect is the deposition of carbonaceous layers on steel surfaces which are exposed to hydrocarbon-containing environments. This can occur, for example, in chemical plant such as plant for the thermal cracking of hydrocarbons where the formation of carbonaceous deposits on heated steel cracker tubes gives rise to an undesirable insulation effect.
• carbonaceous deposits can occur in nuclear reactors, such as the Advanced Gas Cooled Reactor (known in the art and referred to hereinafter as the 'AGR') where stainless steel fuel cans are exposed to a hydrocarbon-containing coolant gas.
• the 'AGR' Advanced Gas Cooled Reactor
• Examples of steels which may be used in the 'AGR' as the fuel can material and which are suitable for coating according to our invention are Cr bearing austenitic steels, for example, stabilised by Nb, a particular example of which is the so-called "20/25" steel which contains 20% Cr, 25% Ni , about 0.1% Nb and the balance iron, wherein the proportions are by weight.
• the role of the coating in the inhibition of carbonaceous deposition may be twofold. Firstly, it may act to isolate the substrate from the environment, thereby preventing certain constituents in the substrate from catalysing chemical reactions giving rise to carbonaceous deposition. Secondly, the coatings may themselves act catalytically in processes which prevent carbonaceous deposition.
• the aforementioned CeO 2 sol is particularly advantageous in this respect.
• the coatings of our invention may be provided with additional constituents in order to achieve particular aims or properties.
• the aforementioned provision of glasses on substrates is an example of this.
• coatings with controlled electrical properties may be provided on electrically conductive or non-electrically conductive substrates. A number of ways of carrying out the invention are described in detail in the examples below.
• 0.2 ml of a 20% polyvinyl alcohol solution were added per 100 ml of a CiO 2 aquasol prepared as above and adjuste to a concentration of 100 g of CeO 2 per 1, and also a few drops of a 1% solution of BDH Nonidet (Registered Trade Mark) P40 wetting agent.
• a specimen of an austentitic stainless steel containing 18% Cr by weight, 8% Ni by weight, and a small amount of Ti (the 'so called' 18/8/Ti steel) was immersed in the CeO 2 aquasol prepared as above. The specimen was removed and dried to convert the CeO 2 sol coating to a CeO 2 gel coating. The specimen was next fired at 850oC for 5 minutes to give a CeO 2 coated steel product.
• Specimens of 20/25/Nb stainless steel were provided with CeO 2 coatings as described in Example 1.
• the coated specimens were stacked on a steel rod and placed in a test rig in a materials testing reactor (known as 'DIDO') and exposed at a temperature of 650oC for 1200 hours at a dose rate of 1 W.g -1 to recirculate CO 2 gas containing 2% CO,
• Fecralloy (Registered Trade Mark) aluminium bearing ferritic alloy of composition by weight of up to 20% Cr, 0.5% to 12% Al, from 0.1% to 3% Y and the balance Fe, was immersed in a CeO 2 sol as used in Example 1, removed and dried to convert the sol to a gel, and fired for a few minutes at 500° to 600oC to give a CeO 2 coated product, wherein the alloy was observed to have retained its silvery appearance after the firing.
• an untreated sample of the alloy acquired a golden colour, due to oxidation, after similar firing).
• Finely powdered Al 2 O 3 having a small particle size
• the CeO 2 coated alloy was immersed in the above final sol, removed, dried and fired in air at 850oC for 15 minutes to produce a catalyst where the CeO 2 coated alloy had a catalytically active coating of Pt carried by Al 2 O 3 .
• Standard tests were carried out on the catalys for treatment of motor vehicle exhaust gases and gave almost identical results to those obtained with a catalyst prepared as above but wherein the alloy had been oxidised at 1000°C ffor 12 hours instead of being provided with a CeO 2 coating.
• An alumina sol with a concentration of 289 g Al 2 O 3 /l was prepared as described in Example 3 and yttrium nitrate solution was added to give relative proportions by weight of 99.8% Al 2 O 3 and 0.2% Y 2 O 3 .
• 0.2 ml of a 20% PVA solution per 100 ml of the sol and a few drops of Nonidet P40 wetting agent were also added.
• a 10 ml aliquot of the resulting sol was then mixed with 100 ml of a CeO 2 sol, prepared as in Example 1 and containing 260 g CeO 2 /l, to give a mixed sol wherein the relative proportions by weight were: CeO 2 89.78%; Al 2 O 3 10.03%; Y 2 O 3 0.19%.
• Example 3 A specimen of 'Fecralloy' alloy, as used in Example 3 was immersed in the mixed sol, removed, dried and fired for a few minutes at 500 to 600oC. In the coated product, the alloy had retained its silvery appearance, and the presence of the Al 2 O 3 , which was porous, was found to assist in the 'keying' of subsequently applied coatings.
• a proprietory silica sol (SYTON-X30) (250 ml) contain 34 ⁇ g/l SiO 2 was added to give a total oxide concentration of 159 g/l. 0.2 ml of a 20% PVA solution per 100 ml of the sol and a few drops of
• Nonidet P40 wetting agent were also added. After mixing for 5 minutes the fluid sol was aged to 24oC and found to be thixotropic, e.g., within a few hours the sol assumed a jelly-like condition but when gentl agitated it regained its former fluidity.
• the densities of the gels are considered as percentages of the theoretical densities of the appropriate hydrous oxides rather than of the final anhydrous oxides as used above, the values are considerably higher, e.g., the ZrO 2 gel density is 87-9% of the theoretical density of zirconium hydroxide.
• the density of a gel which has been dried at an elevated temperature may, in some cases, be somewhat less than that of a gel which has been dried at ambient temperature.
• the above ZrO 2 gel, if dried at an elevated temperature was found to have a % bulk density of 48.8% of the theoretical densit of the anhydrous oxide.
• a sample of mild steel was immersed in a CeO 2 sol prepared as in Example 1 and containing additionally a water soluble silicone.
• the concentrations were: CeO 2. 37.5 g/l; silicone 3.5 g/l.
• the sample was then removed and dried to convert the sol to a gel.
• the silicone was provided because CeO 2 sol itself may be sufficiently acidic to attack mild steel.
• the gel coated sample was then fired at 200oC for 10 minutes. This gave a ceramic coating which was found to improve the resistance of the mild steel to atmospheric corrosion and which was capable of acting as a primer for a subsequently applied paint layer.
• Example 7 The procedure of Example 7 was repeated but using, instead of the silicone containing CeO 2 sol, proprietory silica sol (SYTON-X30) of concentration 20 g/l. The results were substantially similar to those of Example 7.

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• 1978
  • 1978-10-23 JP JP54500023A patent/JPH024677B2/ja not_active Expired - Lifetime
  • 1978-10-23 GB GB8116131A patent/GB2087250B/en not_active Expired
  • 1978-10-23 DE DE19782857147 patent/DE2857147C2/de not_active Expired
  • 1978-10-23 GB GB7920425A patent/GB2023453B/en not_active Expired
  • 1978-10-23 GB GB8116130A patent/GB2087632B/en not_active Expired
  • 1978-10-23 WO PCT/GB1978/000029 patent/WO1979000247A1/en unknown
  • 1978-10-25 US US05/954,532 patent/US4297246A/en not_active Expired - Lifetime
  • 1978-10-31 IT IT69505/78A patent/IT1160899B/it active
  • 1978-10-31 FR FR7830886A patent/FR2416743A1/fr active Granted
  • 1978-10-31 CA CA000315563A patent/CA1118301A/en not_active Expired
  • 1978-11-01 NL NL7810883A patent/NL7810883A/xx not_active Application Discontinuation
• 1979
  • 1979-06-28 SE SE7905690A patent/SE431233B/sv not_active IP Right Cessation
• 1981
  • 1981-02-24 US US06/237,639 patent/US4427721A/en not_active Expired - Fee Related
• 1982
  • 1982-03-15 SE SE8201621A patent/SE8201621L/xx unknown

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