Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
  • C03C8/18—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions containing free metals
• • 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
  • C23D13/00—After-treatment of the enamelled articles
• • 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
  • C23D5/04—Coating with enamels or vitreous layers by dry methods
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2207/00—Compositions specially applicable for the manufacture of vitreous enamels
  • C03C2207/04—Compositions specially applicable for the manufacture of vitreous enamels for steel
• • 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
  • C23D5/005—Coating with enamels or vitreous layers by a method specially adapted for coating special objects
• • 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

Definitions

• the present invention relates to a composition for producing an enamel functional layer, in particular an antistatic layer or an electronically conductive anti-corrosion layer, the use of this composition, methods for producing an enamel coating on a base body and objects comprising a base body and an enamel -functional layer.
• Enamel coatings are used in particular to protect surfaces against atmospheric and chemical influences (e.g. strong acids, alkalis, etc.), especially at high temperatures. Enamel coatings are suitable for protecting surfaces made of metallic materials such as cast iron, steel or aluminium. Typical areas of application are linings and coatings for boilers, apparatus and reactors, pipelines and built-in parts, tubs and containers, tanks and silos, especially for storing, treating and transporting corrosive and abrasive media.
• atmospheric and chemical influences e.g. strong acids, alkalis, etc.
• Enamel coatings are suitable for protecting surfaces made of metallic materials such as cast iron, steel or aluminium.
• Typical areas of application are linings and coatings for boilers, apparatus and reactors, pipelines and built-in parts, tubs and containers, tanks and silos, especially for storing, treating and transporting corrosive and abrasive media.
• Enamel is a typically vitreous solidified mass with an inorganic, essentially oxidic composition that is produced by melting suitable raw materials (see below) and frits (quenching the melt), which is melted in one or more layers onto a base body, for example made of metal .
• the production of enamel comprises two separate thermal process stages, namely the production of a glass melt and the melting (firing) of a mass (frit) formed by quenching the glass melt (frit) onto the base body to be coated. This second stage of the process is also referred to as enamelling.
• the two-stage thermal process lowers the temperature required for remelting by several hundred degrees, thereby reducing the thermal load on the base body to be coated.
• a mixture comprising raw materials for glass production such as quartz, feldspar, soda, potash, borax, cryolite and/or fluorspar and optional additives (adhesive oxides, opacifiers, color oxides) is melted at approx. 1200 °C and then fritted (drained or quenched in water, e.g. between chilled rolls).
• the frit obtained in this way is finely ground, optionally mixed with additives such as pigments, extenders and dispersing agents and applied as an aqueous suspension (slip) or as a fine powder to the pretreated (cleaned and optionally roughened) surface of the base body and melted there again.
• the remelting temperature (firing temperature) of enamel is in the range of 500 °C to 980 °C and depends on the material of the base body, the composition of the material to be burned on and the firing time.
• Enamel contains silicon dioxide and/or boron trioxide as glass-forming oxides (network formers).
• silicon dioxide and/or boron trioxide are added as network modifiers; also suitable additives for adjusting chemical resistance and devitrification behavior, eg aluminum oxide.
• the frit can be applied to the base body in one or more layers. In the case of a multi-layer application, a distinction is made between base enamel and top enamel. The main purpose of the basic enamel is to promote adhesion. In addition, it must compensate for the differences in thermal expansion coefficients between the base body and the cover enamel.
• the base enamel contains the adhesive oxides of cobalt and/or nickel, which are added to the glass melt during the manufacture of the frit. Since the base enamel often shows an irregularly colored, sometimes blistered and usually not smooth surface, a top enamel coating is often carried out afterwards. Depending on the desired visual effect, the top coat contains coloring additives and/or opacifiers.
• pigments e.g. B. from the group consisting of cobalt, iron, manganese or chromium oxide, copper-containing spinel, rutile or zirconium mixed crystals are added.
• the vitreous material formed by melting (firing) the frit on the surface of the base body to be coated is referred to below as the enamel matrix.
• the enamel matrix is an electrical insulator that does not transport any charge carriers up to a certain electrical potential difference (depending on the layer thickness) or a certain electrical field strength. If non-conductive fluids or solids are processed in an apparatus or container with an enamel coating made of a metallic, i.e. electronically conductive material, an electrostatic charge can form due to friction (triboelectric effect). If the critical electric field strength is reached as a result of this electrostatic charging, an undesired breakdown of the enamel layer occurs, during which the charge carriers are abruptly transported away through the damaged area that has formed. In the event of such an unwanted breakdown, the enamel layer suffers punctiform, irreversible damage.
• the electrical insulating effect of the enamel layer fails, because the discharge now continues selectively through the damaged area, and on the other hand the anti-corrosion effect of the enamel layer fails, because in the area of the damaged area the material to be protected is exposed to the corrosive medium at certain points. so that pitting corrosion begins.
• electrostatic precipitators e.g. electrostatic precipitators for waste gas streams in incineration plants
• An electrostatic precipitator contains an active voltage source (spray electrode and collecting electrode, the latter e.g. in the form of an enamel layer provided earthed wall of the separator), which generates charge carriers in the medium in contact with the enamel layer.
• the generated charge carriers must be discharged to avoid high field strengths on the collecting electrode. The strength of the electric field is equal to the number of field lines per area.
• WO 2013/083680 A2 discloses an electronically conductive enamel composition, in particular for anti-corrosion coatings.
• the composition comprises an enamel matrix melting at a temperature in the range from 600°C to 900°C and particles of one or more electronically conductive materials embedded in the enamel matrix, the particles having a particle size of 700 ⁇ m or smaller, and selected are from the group consisting of (a) particles of carbon-based electronically conductive materials, (b) particles of other electronically conductive materials that are not noble metals, (c) particles of a combination of carbon-based electronically conductive materials and other electronically conductive materials, that are not precious metals.
• the total concentration of the particles (ii) in the range from 0.09% by volume to 82.6% by volume, based on the sum of the volumes of the enamel matrix and the particles. Particles of stainless steel and graphite are preferred.
• US 2004/0077477 A1 discloses a composition for producing a porcelain glaze (“porcelain enamel”) with a metallic appearance.
• the composition contains a glass component comprising a glass frit that melts at a temperature of less than 600°C and metal particles, e.g., of aluminum, nickel, copper, or stainless steel.
• the proportion of the metal particles is 0.01% by weight to 7% by weight, based on the total mass of the composition.
• the teaching of US 2004/0077477 A1 essentially aims at aesthetic effects, an electronic conductivity of the coating plays no role.
• the object of the present invention is to provide a composition for producing a functional enamel layer, in particular an electronically conductive enamel layer, which is preferably suitable for use as an antistatic layer or as an electronically conductive anti-corrosion layer.
• composition comprising (i) a frit (ii) particles containing at least one metal (a) (iii) an oxide of metal (b) or a precursor to form an oxide of metal (b), wherein the standard potential of metal (b) is more positive than the standard potential of metal (a).
• composition according to the invention can be in the form of a powder or a slip.
• Component (i) of the composition according to the invention comprises a frit as described above.
• additives can be added, e.g. from the group consisting of opacifying agents, pigments, thickening agents and dispersing agents (e.g. clays). These do not count as components of the frit. Additives that are melted down during the manufacture of the frit, such as opacifiers, color oxides and adhesive oxides, on the other hand, count as part of the frit.
• the present invention does not require any restrictions; the frits and additives customarily used for the respective application, or the raw materials customarily used for their production, can be used.
• the melting temperature of the frit is in the range from >600°C to 980°C, preferably 620°C to 950°C, particularly preferably 650°C to 950°C.
• the metals (a) and (b) of components (ii) and (iii) are chosen so that the standard potential of the metal (b) is more positive than the standard potential of the metal (a), i.e. the metal (a) can form oxides of Reduce metal (b) to metal (b). If the composition according to the invention is fired on to produce an enamel functional layer (see below for details of the process), the oxide of the metal (b) is reduced by the metal (a) to form the metal (b), with finely branched crystalline structures of the metal (b ) develop. However, the metal (a) of the particles (ii) is not completely oxidized.
• Smaller particles (ii) of the metal (a) remain in the enamel functional layer due to the consumption of metal (a) due to the redox reaction with the oxide of the metal (b).
• the result is an electronically conductive network running through the enamel matrix, in which particles (ii) of the metal (a) embedded in the enamel matrix of the enamel functional layer are connected by crystalline structures of the metal (b) formed by reduction of its oxide.
• the crystalline structures of metal (b) formed by reduction of its oxide connecting particles (ii) of metal (a) are typically dendritic and/or reticular.
• the oxide of metal (a) formed during the reduction of the oxide of metal (b) is dissolved in the enamel matrix.
• the metal (a) can be present in pure form or can form the main component of an alloy, such as iron in steel.
• Component (iii), i.e. the oxide of the metal (b) or its precursor, is in the form of particles and/or is a component of the frit (i). If component (iii) is a precursor for forming an oxide of a metal (b), then this precursor is preferably the metal (b) in metallic form. If the composition according to the invention is fired on in an oxidizing atmosphere to produce an enamel functional layer, the metal (b) is oxidized, so that an oxide of the metal (b) is formed. However, it is preferred according to the invention that component (iii) of the composition according to the invention is formed by an oxide of the metal (b).
• the oxide of the metal (b) is not or not exclusively present as a component of the frit (i), but in the form of particles of the oxide of the metal (b).
• a "particle of an oxide of the metal (b)” is understood to mean a particle which contains at least 90% by weight of this oxide of the metal (b), preferably at least 95% by weight of this oxide of the metal (b), particularly preferably at least 99 % by weight of this oxide of metal (b). In the particles of a frit containing an oxide of the metal (b), on the other hand, the proportion of this oxide is significantly lower.
• the total concentration of oxide of the metal (b) in the composition according to the invention corresponds at most to the saturation concentration of this oxide in the melt that occurs when the composition according to the invention is fired on to produce a functional enamel layer (for details of the method see below).
• the particles (ii) are steel particles, i.e. the metal (a) is iron. Particularly preferred is stainless steel, especially grade 3161.
• the metal (b) of component (iii) is preferably copper.
• Component (iii) is preferably formed by one or more oxides of copper, in particular copper(II) oxide CuO and/or copper(I) oxide CU2O.
• copper(II) oxide CuO and copper(I) oxide CU2O are combined under the term "copper oxide", meaning both the individual oxides and mixtures of both oxides.
• the copper oxide is in the form of particles and/or is part of the frit (i). Frits containing copper oxide, e.g. as color oxide, are known in principle. If the frit contains copper oxide, the composition according to the invention can contain additional copper oxide in the form of particles.
• the total concentration of copper oxide in the composition according to the invention corresponds at most to the saturation concentration of copper oxide in the melt that occurs when the composition according to the invention is fired on to produce an enamel functional layer (for details of the method see below).
• the component (iii) can be formed by metallic copper. If the composition according to the invention is fired on in an oxidizing atmosphere to produce an enamel functional layer, the metallic copper is oxidized, so that an oxide of the metal (b) is formed.
• component (iii) of the composition according to the invention is formed by copper oxide. It is preferred that the copper oxide is not or not exclusively present as a component of the frit, but in the form of copper oxide particles.
• a “copper oxide particle” is understood to mean a particle which contains at least 90% by weight of copper oxide, preferably at least 95% by weight of copper oxide, particularly preferably at least 99% by weight of copper oxide. In the particles of a frit containing copper oxide, on the other hand, the proportion of copper oxide is significantly lower.
• Constituent (iii) is particularly preferably copper(II) oxide CuO, preferably in the form of CuO particles.
• a “CuO particle” is understood to mean a particle that contains at least 90% by weight of copper(II) oxide, preferably at least 95% by weight of copper(II) oxide, particularly preferably at least 99% by weight of copper(II) oxide .
• the proportion of copper(II) oxide is significantly lower.
• the proportion of particles (iii) of copper oxide is 5% to 20%, based in each case on the mass of component (i).
• the composition according to the invention is fired on to produce an enamel functional layer (see below for details of the method)
• copper oxide is reduced by iron (metal (a)) from the steel particles (ii) to copper (metal (b)), with finely branched crystalline structures made of copper.
• iron in the steel particles (ii) is not completely oxidized.
• Reduced steel particles (ii) remain in the enamel functional layer due to the consumption of iron due to the redox reaction with copper oxide.
• the result is an electronically conductive network running through the enamel matrix, in which steel particles (ii) embedded in the enamel matrix of the enamel functional layer are connected by crystalline structures made of the copper formed by reduction of the copper oxide.
• the crystalline structures of the copper formed by reduction of copper oxide which connect the steel particles (ii) are typically dendritic and/or reticulated. Iron oxide formed during the reduction of the copper oxide is dissolved in the enamel matrix.
• the term "iron oxide” includes both the individual oxides of iron and their mixtures.
• the proportion of particles (ii) is preferably 10% to 100%, more preferably 15% to 90%, more preferably 20% to 80%, particularly preferably 30% to 70%, based in each case on the mass of the component (i).
• the proportion of particles (ii) is preferably greater than 7%, based on the total mass of the composition according to the invention, and the proportion of particles (ii) is particularly preferably 10% or more, based on the total mass of the composition according to the invention.
• the proportion of particles (ii) made of stainless steel is 10% to 100%, more preferably 15% to 90%, more preferably 20% to 80%, particularly preferably 30% to 70%, based in each case on the Mass of component (i).
• the particles (ii) preferably have a dso value of from 5 ⁇ m to 200 ⁇ m, more preferably from 50 ⁇ m to 200 ⁇ m, particularly preferably from 80 ⁇ m to 200 ⁇ m, determined in each case by means of laser granulometry.
• Constituent (iii) is preferably present in the form of particles which have a dso value of 1 pm to 5 pm, determined in each case by means of laser granulometry.
• the particles (ii) are particularly preferably particles of stainless steel with a dso value of from 5 gm to 200 gm, more preferably from 50 gm to 200 gm, particularly preferably from 80 gm to 200 gm, determined in each case by means of laser granulometry.
• Constituent (iii) is particularly preferably in the form of particles of copper oxide, in particular CuO, which have a dso value of 1 ⁇ m to 5 ⁇ m, determined in each case by means of laser granulometry.
• the redox reaction between metal (a), e.g. iron, and the oxide of the metal (b), e.g. copper oxide, which takes place when the composition according to the invention is fired, begins on the surfaces of the particles (ii), where the metal (a), e.g. iron, in is in contact with the melted frit in which the oxide of the metal (b), e.g. copper oxide, is dissolved (for further details reference is made to the description of the process according to the invention further below).
• the kinetics of the redox reaction between metal (a), e.g. iron, and the oxide of the metal (b), e.g. copper oxide, which takes place when the composition according to the invention is burnt on, is very strongly dependent on the grain size of the particles (ii).
• metal (a) e.g. iron
• the particles (ii), in particular particles of stainless steel have a dso value of at least 5 ⁇ m, preferably a dso value of at least 50 ⁇ m, particularly preferably a dso value of at least 80 ⁇ m. each determined by means of laser granulometry.
• the entry of oxide(s) of metal (a), eg oxide(s) of iron, into the enamel melt is all the greater, and the saturation concentration of the oxide of the metal (a) in the enamel melt is reached more rapidly the smaller the particles (ii) containing the metal (a), eg iron, are.
• the concentration of the particles (ii) relative to the frit (i) can be selected to be smaller, the smaller the particles (ii) are.
• particles (ii), in particular particles made of stainless steel are not too are small. Therefore, particles (ii), in particular particles of stainless steel, have a dso value of at least 5 gm, preferably a dso value of at least 50 gm, particularly preferably a d50 value of at least 80 gm, each determined by laser granulometry .
• particles (ii) made of stainless steel with a dso value of 5 gm are used, their concentration in the composition according to the invention should be less than 35%, preferably less than 30%, based in each case on the mass of component (i) . If particles (ii) made of stainless steel with a dso value of 80 ⁇ m are used, their concentration in the composition according to the invention can be up to 100%, based on the mass of component (i).
• the upper limit of the size of the particles (ii), for example particles of stainless steel, is determined by the layer thickness of the enamel functional layer to be produced from the composition according to the invention.
• the upper limit of the particle size is described by the dioo value of the particle size distribution: 100% of all particles have a size smaller than or equal to the dioo value.
• the ratio between the dioo value of the particles (ii) and the layer thickness of the functional enamel layer to be produced from the composition according to the invention is usually less than 1, preferably 0.8 or less, and is at least 0.05.
• the ratio between the dioo value of the particles (ii) and the layer thickness of the functional enamel layer to be produced from the composition according to the invention is preferably in the range from 0.5 to 0.8.
• Particles (ii) with an approximately spherical shape are preferred, since they have a low tendency to oxidize because of their small surface area relative to the volume.
• particle shapes such as chips or flakes are not excluded. Particles produced by water jet atomization, which typically have an irregular shape, can also be used.
• oxide of metal (b) eg copper oxide
• the composition according to the invention preferably contains less than 1% by weight of noble metals, based on the sum of the masses of component (i) and the noble metals contained, more preferably less than 0.5% by weight of noble metals, based on the sum of Mass of component (i) and the noble metals present and particularly preferably less than 0.1% by weight of noble metals, based on the sum of the masses of component (i) and the noble metals present.
• the composition according to the invention particularly preferably contains no noble metals.
• Noble metals are understood as meaning the metals selected from the group consisting of gold, silver, mercury, rhenium, ruthenium, rhodium, palladium, osmium, iridium and platinum.
• a composition according to the invention in particular in its preferred embodiments defined above, is suitable for the production of an electronically conductive enamel layer. Accordingly, the use of a composition according to the invention for producing an electronically conductive enamel layer forms an essential aspect of the present invention.
• electroconductive means that the charge is transported by electrons.
• the electronic conductivity of an electronically conductive enamel layer produced using a composition according to the invention is preferably 10 ⁇ 1 ° S/cm or more, preferably 10 -9 S/cm or more, particularly preferably 10 -8 S/cm or more
• a measuring method is described in the examples
• the composition according to the invention is particularly suitable for the production of an electronically conductive anti-corrosion layer on the discharge electrode and the collecting electrode of an electrostatic precipitator (electrostatic filter).
• the requirements for the breakdown resistance of the enamel layer are particularly high here, since high concentrations of charge carriers are generated in the medium that comes into contact with the enamel layer due to the active voltage source, i.e. a constant, very high external electrical voltage potential from the outside onto the surface of the enamel layer.
• the compositions which are particularly preferred according to the invention are suitable for coating the collecting electrode of an electrostatic precipitator, because their high electronic conductivity prevents the formation of secondary charge carriers and their spraying back to the discharge electrode.
• a functional enamel layer formed from a composition according to the invention is usually covered with an enamel top layer, the concentration of particles (ii) containing at least one metal (a) being lower in the enamel top layer than in the email functional layer.
• the concentration of particles (ii) containing at least one metal (a) in the enamel top layer is preferably less than 2% by volume.
• the enamel top layer does not contain any metallic components whose standard potential is more negative than the standard potential of the metal (b).
• the enamel cover layer largely prevents particles (ii) containing a metal (a) from being exposed on the surface of the enamel coating and thus being exposed to corrosive influences.
• a small proportion of particles (ii) containing at least one metal (a) in the enamel top layer ensures that the properties of the surface of the enamel coating, which contains an enamel functional layer formed from a composition according to the invention, largely match the properties equivalent to a conventional enamel coating, particularly in terms of hydrolytic and chemical resistance and impact resistance. This is an advantage over the enamel coatings known from WO 2013/083680 A2.
• a composition according to the invention is therefore preferably used in combination with a composition for producing an enamel top layer.
• the composition for preparing the enamel top layer contains a frit suitable for forming a top enamel.
• Component (ii) of the composition according to the invention is not contained in the composition for producing the enamel top layer.
• the composition for producing the enamel top layer contains the same oxide of a metal (b) or a precursor for forming an oxide of the same metal (b) as the composition according to the invention. The result of this is that the finely branched crystalline structures of the metal (b) produced by reduction of the oxide of the metal (b) grow up to the surface of the enamel cover layer.
• kits comprising (1) a composition according to the invention as described above
• composition (2) comprising a frit for forming an enamel matrix, an oxide of a metal (b) or a precursor for forming an oxide of a metal (b), wherein the Oxide of the metal (b) or the precursor for forming an oxide of a metal (b) in the compositions (1) and (2) is identical wherein composition (2) does not contain component (ii) as defined above.
• Composition (2) for producing an enamel top layer does not contain component (ii) of a composition according to the invention, i.e. composition (2) does not contain particles of a metal (a).
• the composition (2) preferably contains no metallic components whose standard potential is more negative than the standard potential of the metal (b).
• the total concentration of oxide of metal (b) in composition (2) corresponds at most to the saturation concentration of this oxide in the melt that is formed when composition (2) is fired to produce an enamel top layer (for details of the process, see below).
• preferred oxides of metals (b) or their precursors the same applies as stated above for the composition according to the invention.
• Frits suitable for producing a covering enamel are known to the person skilled in the art, cf. the above statements.
• a kit is particularly preferred
• Component (iii) is an oxide of copper, preferably CuO, and is in the form of particles and
• composition (2) a composition for producing an enamel cover layer, wherein the composition (2) comprises a frit suitable for forming a cover enamel, a particulate copper oxide identical to component (iii) of the composition (1), preferably CuO, wherein the composition (2 ) does not contain any metallic components.
• a kit according to the invention in particular in the preferred embodiments defined above, is suitable for producing an object comprising an enamel functional layer and on the surface of the enamel Functional layer arranged enamel top layer.
• the composition (2) for producing an enamel top layer contains the same particulate copper oxide as the composition according to the invention for producing the functional layer. The result of this is that the finely branched crystalline structures of copper produced by reduction of the oxide of the metal (b) grow up to the surface of the enamel cover layer.
• Another aspect of the present invention is a method for producing an enamel coating on a base body.
• the method according to the invention comprises the following steps: (S1) Providing a base body
• each layer being formed by applying a composition comprising a frit to form an enamel matrix, at least one of the applied compositions being a composition according to the invention as defined above and the last applied composition a composition (2) for the preparation of an enamel coating is as defined above
• the method according to the invention serves to produce an object comprising a base body, an enamel functional layer which is electronically conductive, and an enamel top layer.
• the type and nature of the base body to be provided in step (S1) of the method according to the invention depends on the object to be produced.
• the base body as a whole or at least the surface of the base body on which an enamel functional layer is to be produced typically consists of metallic materials such as cast iron, steel or aluminum.
• step (S2) of the method according to the invention two or more layers are formed on the surface of the base body, each layer being formed by applying a composition comprising a frit to form an enamel matrix.
• At least one of the compositions applied is a composition according to the invention as defined above, preferably one of the preferred compositions according to the invention described above, and the composition applied last is a composition (2) for producing an enamel top layer as defined above, preferably one of the preferred ones described above compositions (2).
• the layer formed from the composition according to the invention represents the preliminary stage of the enamel functional layer to be produced.
• the last layer formed represents the preliminary stage of an enamel top layer.
• Step (S2) comprises a number of sub-steps corresponding to the number of layers to be formed. At least one of the compositions applied is a composition according to the invention as described above. Multiple layers can also be formed by applying a composition of the invention.
• only one layer is formed by applying a composition of the present invention, and an enamel top layer by applying a composition (2) as defined above for preparing an enamel top layer.
• composition for the layer to be formed directly on the surface of the base body expediently contains a frit comprising one or more adhesive oxides.
• This layer represents the preliminary stage of an enamel base layer. If the composition according to the invention is applied directly to the surface of the base body, this composition according to the invention expediently contains a frit comprising one or more adhesive oxides.
• the composition for producing the enamel top layer contains the same oxide of a metal (b) or a precursor for forming an oxide of the same metal (b) as the composition according to the invention.
• the result of this is that the finely branched crystalline structures of metal (b) produced by reduction of the oxide of metal (b) grow up to the surface of the enamel cover layer.
• this composition preferably contains the same oxide of a metal (b) or a precursor for forming an oxide of the same metal (b), eg copper oxide , like the composition according to the invention.
• a metal (b) or a precursor for forming an oxide of the same metal (b), eg copper oxide like the composition according to the invention.
• Additional metal (b) is formed by reduction of the oxide of metal (b) contained in the composition for the preparation of the enamel base layer by iron or other metals from the base body which have a more negative standard potential than metal (b).
• Suitable techniques for applying the compositions are known to those skilled in the art, for example spraying, spraying, dipping and flooding.
• step (S3) of the method according to the invention the layers formed on the surface of the base body are burnt on, so that a layer comprising an enamel matrix results from each applied composition.
• the firing can take place in each case after the application of an individual composition, or after the application of several or all of the compositions. In any case, after the last composition has been applied, a burn-out takes place.
• the frit (i) is melted and the oxide of the metal (b) is reduced by the metal (a) to form the metal (b), and a comprehensive enamel functional layer is formed
• the oxide of the metal (b), eg copper oxide dissolves in the resulting glass melt.
• the oxide of the metal (b), eg copper oxide is present in the glass melt in dissolved form.
• the particles (ii), eg steel particles, are therefore in contact with a melt which, in addition to the components of the frit (i), contains the oxide of the metal (b), eg copper oxide.
• the oxide of metal (b), e.g. copper oxide is then reduced to crystals of metal (b), e.g.
• the enamel matrix of the enamel functional layer runs through an electronically conductive network generated in situ during firing, in which particles (ii) of the metal (a) embedded in the enamel matrix of the enamel functional layer (a) through crystalline structures (iii) from the through Reduction of its oxide formed metal (b) are connected.
• the crystalline structures of metal (b) formed by reduction of its oxide connecting particles of metal (a) are typically dendritic and/or reticular.
• the composition for producing the enamel top layer contains the same oxide of a metal (b), e.g. copper oxide, or a precursor for forming an oxide of the same type (b) as the composition according to the invention, the finely branched crystalline structures of newly formed metal (b ), e.g. copper, up to the surface of the enamel top layer.
• a metal e.g. copper oxide
• a precursor for forming an oxide of the same type (b) as the composition according to the invention
• the electronically conductive contact to the surface of the base body is made by replacing the oxide of metal (b), e.g. copper oxide, present in the composition for producing an enamel base layer with iron or other metals from the base body, which have a more negative standard potential than the metal (b), is reduced, so that finely branched crystalline structures of the metal (b) are also formed in the enamel base layer.
• the oxide of metal (b) e.g. copper oxide
• the enamel base layer is then supplied with the oxide of the metal (b), e.g.
• step (S3) comprises a number of sub-steps corresponding to the number of layers to be deposited, each sub-step of step (S3) following the corresponding sub-step of step (S2).
• Suitable techniques and devices for burning on the layers are known to those skilled in the art.
• the temperature at which the firing of individual or multiple layers takes place depends on the composition of the layer, in particular the frit contained therein, and the type of base body and the object to be produced.
• the firing temperature of the functional layer is in the range from >600°C to 980°C, preferably 620°C to 950°C, particularly preferably 650°C to 950°C.
• the person skilled in the art is able to select the appropriate baking temperature on the basis of his specialist knowledge. The same applies to the duration of the burning.
• the baking time is typically in the range from 0.5 to 60 minutes.
• the method according to the invention comprises the steps (S1) providing a base body (S2a) forming a first layer by applying a composition according to the invention as defined above, comprising a frit containing one or more adhesive oxides typical of a base enamel
• the method according to the invention comprises the steps
• Base enamel contains typical adhesive oxides
• the method according to the invention comprises the
• the method according to the invention comprises the
• steps (S1) Providing a base body
• step (S3b) firing the layer formed in step (S2b); (S2c) forming a third layer by applying a composition (2) as defined above to produce an enamel top layer
• the method according to the invention comprises the
• Steps (S1) Providing a base body
• the method according to the invention comprises the
• Step (S2a) applying a composition for producing an enamel base layer 2, which contains no metallic components, on the surface of a
• Step (S2b) Application of a composition according to the invention containing particles of stainless steel 5 as component (ii) and particulate CuO as component (iii) for the production of an enamel functional layer 3
• Step (S2c) Application of a composition for the production of an enamel top layer 4, which contains the same component (iii) (particulate CuO) as the composition according to the invention applied in step (S2b), and no metallic components
• FIG. 1a shows a cross section through the layers 2, 3 and 4 formed on the base body 1 by applying the above-mentioned compositions in steps (S2a)-(S2c) before the start of firing.
• steps (S2a)-(S2c) before the start of firing.
• step (S2b) particles (ii) of stainless steel 5 are isolated, and there is no electronic contact between the particles (ii) of stainless steel 5 and the surface of the base body 1 or the surface of the in Step (S2c) applied layer 4.
• the present invention also relates to an object comprising a base body and an enamel functional layer and an enamel cover layer arranged on the surface of the enamel functional layer facing away from the base body.
• the object according to the invention consists of a base body, an enamel functional layer and an enamel cover layer arranged on the surface of the enamel functional layer facing away from the base body.
• the enamel functional layer of the object according to the invention contains (i) an enamel matrix and is embedded in the enamel matrix
• the particles (ii) are present as discrete particles that are optically distinguishable from the enamel matrix (i).
• the proportion of particles (ii) in the enamel functional layer is preferably 2% by volume to 40% by volume, based on the volume of the enamel functional layer.
• the concentration of particles (ii) containing at least one metal (a) in the enamel top layer is lower than in the enamel functional layer.
• the concentration on is preferred Particles (ii) containing at least one metal (a) in the enamel top layer less than 2% by volume.
• the enamel covering layer preferably contains no particles (ii) containing at least one metal (a).
• the enamel top layer does not contain any metallic components whose standard potential is more negative than the standard potential of the metal (b).
• the enamel functional layer and the enamel top layer of the article according to the invention contain crystals of the metal (b) formed by reduction of an oxide, the standard potential of which is more positive than the standard potential of the metal (a). (It follows from the above statements that the metal (b) in the enamel functional layer and in the enamel top layer is identical, i.e. the enamel functional layer and enamel top layer contain the same metal (b)).
• the metal formed by reduction of an oxide (b) forms finely branched crystalline structures (iii), which in the enamel matrix (i) of the enamel functional layer embedded particles (ii) to an electro - connect nically conductive network.
• the crystalline structures (iii) of the metal (b) formed by reduction of an oxide, which connect the particles (ii), are typically dendritic and/or reticular and extend from the surface of the base body to the surface of the enamel top layer.
• the oxide of the metal (a) formed during the reduction of the oxide of the metal (b) is dissolved in the enamel matrix (i).
• the finely branched crystalline structures (iii) of the metal (b) formed by reduction of its oxide have less influence on the continuity and properties of the enamel matrix (i) because they interlock with the enamel matrix and do not interrupt it, as this is done by massive discrete particles.
• the thickness of the enamel top layer is at most 50% of the thickness of the enamel functional layer, preferably 25% of the thickness of the enamel functional layer or less, particularly preferably 5% of the thickness of the enamel functional layer or less.
• the enamel functional layer contains the object according to the invention
• the concentration of particles (ii) containing stainless steel in the enamel top layer is preferably less than 2% by volume.
• the enamel top layer particularly preferably contains no particles (ii) containing at least one metal (a) whose standard potential is more negative than the standard potential of copper.
• the enamel top layer does not contain any metallic components whose standard potential is more negative than the standard potential of copper.
• the enamel functional layer preferably has a thickness of 100 ⁇ m to 500 ⁇ m, particularly preferably 200 ⁇ m to 30 ⁇ m, and the enamel top layer has a thickness in the range from 1 ⁇ m to 50 ⁇ m, particularly preferably 10 ⁇ m to 50 ⁇ m. each determined by means of magnetoinductive measurement.
• Copper forms crystalline structures (iii) in the enamel functional layer and the enamel cover layer of the object according to the invention, which connect the particles (ii) embedded in the enamel matrix (i) of the enamel functional layer to form an electronically conductive network.
• the crystalline structures (iii) of the copper formed by reduction of copper oxide, which connect the particles (ii), are typically dendritic and/or reticulated. Iron oxides formed during the reduction of the copper oxide are dissolved in the enamel matrix (i).
• the steel particles (ii) are present as discrete particles which can be distinguished optically from the enamel matrix (i).
• the proportion of the steel particles (ii) in the enamel functional layer is preferably 2% by volume to 40% by volume, based on the volume of the enamel functional layer.
• the proportion of metallic copper (iii) in the enamel functional layer is preferably 3% to 20%, based on the mass of the enamel functional layer.
• a preferred object according to the invention additionally comprises an enamel base layer arranged between the surface of the base body and the enamel functional layer, preferably with a thickness in the range from 1 ⁇ m to 50 ⁇ m, particularly preferably 10 ⁇ m to 50 ⁇ m, with the enamel Base layer, the concentration of particles (ii) containing at least one metal (a) is smaller than in the enamel functional layer.
• the enamel base layer preferably contains no particles (ii) containing at least one metal (a).
• the enamel top layer particularly preferably contains no metallic components whose standard potential is more negative than the standard potential of the metal (b).
• the thickness of the enamel base layer is at most 50% of the thickness of the enamel functional layer, preferably 25% of the thickness of the enamel functional layer or less, particularly preferably 5% of the thickness of the enamel functional layer or less.
• the enamel base layer, the enamel functional layer and the enamel top layer of the article according to the invention contain crystals of the metal (b) formed by reduction of an oxide whose standard potential is more positive than the standard potential of the metal (a).
• the metal (b) formed by reduction of an oxide forms finely branched crystalline structures which form the particles (ii) embedded in the enamel matrix (i) of the enamel functional layer connect to an electronically conductive network.
• the crystalline structures of the metal (b) formed by reduction of an oxide, which connect the particles (ii), are typically dendritic and/or reticular and extend from the surface of the base body to the surface of the enamel covering layer.
• a particularly preferred object according to the invention comprises an enamel base layer arranged between the surface of the base body and the enamel functional layer, preferably with a thickness in the range from 1 ⁇ m to 50 ⁇ m, particularly preferably 10 ⁇ m to 50 ⁇ m, and on the surface facing away from the base body enamel top layer arranged on the enamel functional layer, preferably with a thickness in the range from 1 ⁇ m to 50 ⁇ m, particularly preferably 10 ⁇ m to 50 ⁇ m, the concentration of particles (ii) in the enamel base layer and in the enamel top layer at least one metal (a) is smaller than in the enamel functional layer.
• the concentration of particles (ii) containing at least one metal (a) in the enamel top layer and in the enamel base layer is preferably less than 2% by volume.
• the enamel base layer and the enamel top layer preferably contain no particles (ii) containing at least one metal (a).
• the enamel base layer and the enamel top layer do not contain any metallic components whose standard potential is more negative than the standard potential of the metal (b).
• the object having an enamel functional layer is preferably selected from the group consisting of
• Containers and tubs in particular for storing corrosive media.
• a further aspect of the present invention is the use of an enamel functional layer as defined above as an antistatic coating or as an electronically conductive anti-corrosion coating.
• the enamel functional layer is preferably able to fulfill both functions.
• the use as an antistatic layer relates to areas of application where enamel layers are exposed to high electrical voltages due to triboelectric charging, which can lead to voltage breakdowns, eg silos for bulk goods, tanks for electrically insulating liquids and chemical reactors.
• the use as an electronically conductive anti-corrosion layer relates to areas of application where a high resistance to chemical corrosion is required and at the same time sufficient electronic conductivity is absolutely necessary, for example discharge electrodes and collecting electrodes for dust separation from the exhaust gas stream of a combustion system, e.g. a combustion system operated with biomass.
• Articles were thus obtained comprising an enamel base layer arranged between the surface of the base body and the enamel functional layer, and in some cases an enamel top layer arranged on the surface of the enamel functional layer remote from the base body.
• the thicknesses of the coating obtained were determined magnetoinductively using a paint layer thickness gauge. The values can be found in Table 1.
• the surface of the HV electrode 1 made of copper lies directly on the surface of the semiconductor body 5 (thickness 1 mm), which in turn lies on the surface of the test body 2 to be examined.
• the test body 2 to be examined is electrically connected via the contact 3 to the HV electrode 4 made of copper.
• the HV electrode 4 has insulation 6 on the side and rear.
• a defined surface of the test specimen 2 is exposed through an insulation 7 lying on the surface of the test specimen 2, in which an area with an area of 25 cm 2 is left open.
• This experimental setup is surrounded by a shield 8 .
• the voltage was supplied with a DC generator 9.
• the current is measured with the ammeter A.
• the ambient conditions temperature and humidity
• the resistance of the test body 2 is obtained by subtracting the resistance of the semiconductor body 5 from the total resistance. The specific conductivities calculated from this can be found in Table 1.
• samples 1-3 with samples 4-6 and samples 7-9 with samples 10-12 shows: an additional top layer of enamel made from a composition containing copper oxide and no metal particles causes only a slight decrease in the Conductivity, compared with the samples with identical composition of the enamel base layer and enamel functional layer and without a top layer. This shows that the reduction of the copper oxide by iron extends from the steel particles to the top layer of enamel and extends to the surface of the base body, although the composition for the enamel base layer did not contain CuO.
• the composition for the enamel base layer contained particles of CuO in an amount of 10% based on the mass of the frit (i). - Only particles (ii) made of stainless steel 3161 with a particle diameter of 80 ⁇ m to 90 ⁇ m were used for the enamel functional layer
• reference samples were produced by (S1) providing a base body made of hot-rolled steel, as is commonly used in container construction
• compositions applied in steps (2a) and (2c) did not contain the components (ii) and (iii) of compositions according to the invention defined above.
• the layer thickness of the enamel coating of the reference sample determined magnetoinductively using a paint layer thickness gauge, was 200 ⁇ m.
• Comparing Sample 3 with Sample 2 shows that the enamel topcoat significantly increases hydrolytic resistance to steam and hot water, resembling the properties of a conventional enamel coating (Sample 1) without the enamel made from a composition of the invention. Functional layer approaches. Further improvements can be achieved by adding suitable additives such as quartz powder to the composition for the enamel top layer.

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• 2021
  • 2021-06-21 DE DE102021116028.6A patent/DE102021116028A1/de active Pending
• 2022
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