Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G41/00—Compounds of tungsten
  • C01G41/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G41/00—Compounds of tungsten
• • 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
  • C23C18/1204—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 inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/1208—Oxides, e.g. ceramics
  • C23C18/1216—Metal oxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/02—Amorphous compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
  • C01P2002/84—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by UV- or VIS- data
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
  • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
  • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
  • C01P2004/86—Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
• • 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
• • 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
  • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

• Tungsten oxide (WO 3 ) is an electrochromic material which has been widely used as the basis for electrochromic-based devices such as displays and light modulating windows. Numerous methods are known for depositing tungsten oxide coatings onto a substrate. Vacuum deposition methods such as sputtering and evaporation are the most commonly used processes, although solution deposition methods are known as well. These solution-based methods generally involve one of three general types of tungsten oxide precursors: colloidal sols, alkoxide derivatives, and peroxy tungstic acid.
• the invention features a process for producing a tungsten oxide precursor solution in which a peroxypolytungstate solution is converted to a stable oxide polytungstate solution.
• the process includes the step of treating a polytungstate solution (for example, an acidified ammonium metatungstate solution) with a peroxide (for example, hydrogen peroxide) to form the peroxypolytungstate solution.
• a polytungstate solution for example, an acidified ammonium metatungstate solution
• a peroxide for example, hydrogen peroxide
• the amount of peroxide preferably ranges from about 0.2 to about 2.0 moles of hydrogen peroxide per mole of tungsten, more preferably from about 0.7 to about 1.3 moles of hydrogen peroxide per mole of tungsten.
• the process preferably includes the steps of (i) drying the peroxypolytungstate solution to form a powder; (ii) dissolving or dispersing the powder in a solvent that includes an alcohol (for example, ethanol) to form an alcoholic solution; and (iii) heating the alcoholic solution (for example, at its boiling point) to convert the peroxypolytungstate solution to the stable oxide polytungstate solution.
• a solvent that includes an alcohol (for example, ethanol) to form an alcoholic solution
• heating the alcoholic solution for example, at its boiling point
• the stable oxide polytungstate solution preferably is substantially free of peroxide species (for example, tungstate ions, clusters, polymers, and/or colloids containing peroxide chemical bonds) and peroxytungstic acid. Moreover, the stable oxide polytungstate solution preferably includes no greater than 50% by weight water, more preferably no greater than 20% by weight water, and even more preferably no greater than 8% by weight water. Even more preferred are stable oxide polytungstate solutions that are substantially free of water.
• the invention also features a process for producing tungsten oxide by transforming the above-described stable oxide polytungstate solution to tungsten oxide.
• the transformation is preferably effected by drying the stable oxide polytungstate solution to form a residue, and then heating the residue at a temperature ranging from about 100°C to about 350°C, and more preferably from about 150X to about 250°C.
• the invention features a process for producing a tungsten oxide precursor solution that includes converting an acidified ammonium metatungstate solution to a stable oxide polytungstate solution, for example, by exposing the acidified ammonium metatungstate solution to a peroxide to form a peroxypolytungstate solution, and then converting the peroxypolytungstate solution to the stable oxide polytungstate solution.
• the stable oxide polytungstate solution can then be transformed to tungsten oxide.
• 'Tungsten oxide precursor solution refers to a sol or solution that can be transformed to tungsten oxide.
• Polytungstate solution refers to an essentially clear or slightly translucent sol or solution that includes tungstate ions, polymers, and/or 5 colloidal particles.
• Peroxypolytungstate solution refers to an essentially clear or slightly translucent sol or solution that includes tungstate ions, polymers, and/or colloidal particles, and is further characterized by the presence of peroxy chemical bonds as manifested, for example, in a tungsten-peroxy 0 peak appearing at about 550-570 cm "1 in a Raman spectrum of the corresponding dried solid.
• Acidified ammonium metatungstate solution refers to a polytungstate solution prepared by acidifying an ammonium metatungstate solution that includes species having the nominal formula (NH 4 )6H 2 W 12 O4o 5 + XH 2 O.
• “Stable oxide polytungstate solution” refers to a solution or sol formed from a peroxypolytungstate species in which at least a substantial number of the peroxide bonds have been converted to oxide bonds.
• the conversion is manifested, for example, as a decrease in the tungsten- o peroxy peak appearing at about 550-570 cm “1 in a Raman spectrum of the dried solid corresponding to the initial peroxypolytungstate and the appearance of a broad peak at 700-800 cm *1 (corresponding to the dried solid form of the oxide polytungstate).
• a reduction of at least about 50% in the area of the tungsten-peroxy peak is desirable. 5
• the conversion is generally accompanied by changes in the polytungstate species, for example, growth of the species.
• tungsten oxide compositions prepared according to the invention generally are reversible with respect to lithium intercalation when fired at 150°C-250°C.
• the compositions return substantially to their original uncolored state.
• the oxide polytungstate solution is "stable" in the sense that it exhibits negligible changes in viscosity, appearance, and properties over time scales typically encountered for storing solutions for subsequent coating (for example, on the order of several days to several months) under typical storage conditions.
• the invention provides a reliable, reproducible method for producing electrochromic tungsten oxide.
• the method uses inexpensive and readily available starting materials, and can be performed in a few hours.
• the method does not produce corrosive by-products and results in stable, ion-intercalating tungsten oxide materials suitable for use in electrochromic devices.
• the invention features a process in which a tungsten oxide precursor solution is transformed to tungsten oxide (for example, in the form of a coating on a substrate such as glass or plastic).
• the precursor solution is preferably prepared by treating an initial polytungstate solution with a peroxide to form a peroxypolytungstate solution, followed by converting the peroxypolytungstate solution to a stable oxide polytungstate solution.
• the initial polytungstate solution is preferably in the form of an aqueous solution, and may be prepared according to a variety of methods, including acidification of soluble tungstate salts (for example, Na 2 WO 4 ) or hydrolysis of tungsten alkoxides.
• a particularly preferred initial polytungstate solution is an aqueous solution of acidified ammonium metatungstate ("AMT").
• AMT solutions are clear, colorless, and resist forming coagulated gels. They may be prepared at ambient temperature by eluting an aqueous ammonium metatungstate solution (containing, for example, about 20 g of ammonium metatungstate per 100 g of distilled, de-ionized water) through an acidified cation exchange column or by mixing the metatungstate solution with the acidified cation exchange resin, followed by removing the resin by filtering, decanting, or a comparable method.
• Other acidification methods for example, dropwise addition of an acid such as HCl, followed by dialysis may be used as well.
• the cation exchange column offers the advantage of removing unwanted cations without the need for further purification.
• suitable acidified cation exchange media are commercially available and include Amberlite IR 120+ acidic ion exchange resin from Aldrich Chemical Co. of Milwaukee, Wl.
• the acidification reaction is preferably conducted such that the product solution has a pH no greater than about 2.0.
• the initial polytungstate solution is preferably stable over the time scale generally encountered in preparing the tungsten oxide precursor solution (for example, on the order of several hours to several days) in the sense that it exhibits negligible changes in viscosity, appearance, and properties over this time period.
• the initial polytungstate solution also preferably has the ability to be dried to a powder and then dissolved in aqueous or polar organic solvents (for example, alcohols) to form an optically clear, substantially gel-free solution.
• the next step is to treat the initial polytungstate solution with a peroxide to form a peroxypolytungstate solution.
• a peroxide solution is added to the polytungstate solution with stirring for a period of about 20 minutes.
• the preferred peroxide is hydrogen peroxide.
• the amount of peroxide is selected to form a peroxypolytungstate which can be dried without substantial gelation, easily re-dispersed or re-dissolved following drying, and readily converted in solution to a stable oxide polytungstate solution.
• the amount of peroxide typically ranges from 0.2 to 2 moles of hydrogen peroxide per mole of tungsten, and more preferably from 0.7 to 1.3 moles.
• the initial polytungstate solution is not AMT, but rather the product of acidification of an alkali tungstate such as Na 2 WO 4 , particular care must be taken prior to and during the peroxide treatment to avoid formation of intractable gels or coagulated solids. This may be accomplished by using a dilute tungstate salt solution and collecting the acidified product directly into the peroxide solution. In addition, the amount of peroxide may have to be adjusted to ensure formation of a peroxy product that will dissolve.
• An alternate (albeit less preferred) method for forming the peroxypolytungstate solution involves digesting tungsten metal or tungsten carbide in aqueous or alcoholic peroxide solutions to form a peroxytungstic acid solution.
• the peroxypolytungstate solution is converted to a stable oxide polytungstate solution.
• One way of accomplishing the conversion is to age the peroxypolytungstate solution for an extended period of time (for example, on the order of months).
• conversion is accomplished by drying the peroxypolytungstate solution to form a powder, dissolving the powder in an alcohol (preferably ethanol), and then refluxing the resulting solution at or near its boiling point. Drying is typically accomplished by evaporating solvent (typically water) at slightly elevated temperatures (for example, about 40 ⁇ C). A rotary evaporator may be used for the drying step, although other drying methods such as spray drying may be used as well.
• Dissolution in alcohol is preferably effected by adding the alcoholic solvent to the dried powder, heating the resulting mixture to about 30-60°C (for example, in the case where the alcohol is ethanol), and stirring the mixture until a clear solution is obtained.
• Concentrations convenient for subsequent coating formation for example, about 10-20% by weight tungsten oxide are generally used.
• the reflux period must be sufficiently long to produce the desired oxide polytungstate solution without concurrent formation of substantial amounts of haze, precipitation, viscosity increase, or gelation, which may occur if the reflux period is too long. On the other hand, if the reflux period is too short, inadequate conversion to the oxide polytungstate may occur, resulting ultimately in tungsten oxide coatings that do not fully bleach upon de-intercalation of lithium ions.
• Typical reflux periods are on the order of about 60 minutes.
• reflux periods ranging from about 40- 60 minutes have been found to produce satisfactory oxide polytungstate solutions.
• incorporation of small amounts of water may increase the reflux "window" to two hours or more. Large amounts of water, however, are preferably avoided because they may result in optical defects and/or inadequate conversion, resulting ultimately in tungsten oxide coatings that do not fully bleach upon de-intercalation of lithium ions.
• the amount of water is no greater than about 20% by weight (which translates to about 15 moles of water per mole of tungsten for a peroxypolytungstate solution having 17% by weight tungsten oxide).
• the amount of water ranges from 2 to 8% by weight.
• the resulting oxide polytungstate solutions are stable, as defined above.
• the above-described solution prepared from AMT is stable for periods up to 50 days at room temperature, and for at least several months when refrigerated at a temperature of from 5-10°C. Stability may be enhanced further through incorporation of additives such as 2,4-pentanedione.
• the solution may further include other additives as well.
• the solution may include inorganic additives such as TiO 2 that affect the structure and properties of the final tungsten oxide coating.
• Other additives which may be included are fugitive organic materials that may affect solution stability or oxide microstructure.
• the solution is preferably applied to the surface of a substrate (for example, a glass or plastic substrate provided with a transparent conductor), dried to solid form, and then heated to remove any remaining solvent and transform the oxide polytungstate to tungsten oxide.
• a substrate for example, a glass or plastic substrate provided with a transparent conductor
• Suitable application methods include dipping the substrate into the solution or spreading the solution onto the substrate surface. Heating is preferably conducted at temperatures ranging from 100°C to 350°C (more preferably from 150°C to 250°C) for a period of time ranging from 1-40 minutes (more preferably from 5-20 minutes).
• This example describes the preparation of tungsten oxide coatings.
• ITO-coated glass plates (Libbey-Owens-Ford, Toledo, OH) were dipped into a beaker containing the stable oxide polytungstate solution and withdrawn at a rate of about 20 cm per minute. The coated samples were then air-dried, after which they were heat-treated at about 225°C for about
• the average coating thickness was calculated to be approximately 3000 angstroms, assuming a density of about 5.0 g/cm 3 for the amorphous tungsten oxide coating.
• the samples were tested using an electrochemical test apparatus consisting of a scanning potentiostat (Model 100B, available from Bioanalytical Systems, West Lafayette, IN or Model 362, available from EG&G PARC, Princeton, NJ), a three electrode cell containing the test electrode, a Ag/AgCI 2 reference electrode, and a Pt auxiliary electrode, and a test solution of 0.1 N CF 3 SO 3 Li (available as FC-122 from 3M, St. Paul, MN) or lithium trifluoromethanesulfonylimide (available as HG-115 from 3M, St. Paul, MN) in acetonitrile. Charging and discharging were done at -1.0 and +1.0 volts, respectively.
• a scanning potentiostat Model 100B, available from Bioanalytical Systems, West Lafayette, IN or Model 362, available from EG&G PARC, Princeton, NJ
• FC-122 available as FC-122 from 3M, St. Paul, MN
• Tungsten oxide-coated samples were prepared according to the procedure of Example 1 , but with the following changes.
• About 24.2 g of sodium tungstate (Na 2 WO 4 + 2H 2 O) was used instead of ammonium metatungstate and combined with 150 g of distilled, de-ionized water.
• a larger ion exchange column provided with 450 cm 3 of ion exchange resin was used for the acidification step.
• the acidified solution was collected directly into a beaker containing about 10 g of 30% hydrogen peroxide solution.
• Example 3 The coated glass samples were heated at 175°C for 15 minutes. The average initial integrated transmission, charged transmission, and discharged transmission values were about 80-81 %, 18-28%, and 79-81%, respectively.
• Example 3 The average initial integrated transmission, charged transmission, and discharged transmission values were about 80-81 %, 18-28%, and 79-81%, respectively.
• a peroxytungstic acid solution was prepared by adding 8 g of tungsten metal powder (Alfa Chemicals, -22 mesh, 99.999%) to a mixture of about 50 g of distilled, de-ionized water and 50 g of 30% aqueous
• Example 2 Tungsten oxide-coated glass samples were prepared and tested according to the procedure described in Example 2. The initial, charged, and discharged integrated transmission values were 81%, 21%, and 79%, respectively.

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• 1996
  • 1996-04-24 US US08/639,020 patent/US5772978A/en not_active Expired - Lifetime
• 1997
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