WO2012001636A1 - Process for preparing doped or undoped alpha-vanadium oxide - Google Patents

Abstract

Process for preparing vanadium oxide of the empirical formula V_1-xM_xO_2-yA_y, where M is at least one metal other than vanadium, x is from 0 to 0.05, A is an anion other than oxygen and y is from 0 to 0.05 and the vanadium oxide is present in the distorted or undistorted rutile structure, which comprises reduction of vanadium(V)-comprising starting material and heat treatment of the reduction product under an inert gas atmosphere at temperatures of from 500°C to 1000°C.

Description

 Process for the preparation of doped or undoped alpha-vanadium oxide

The present invention relates to a process for the preparation of vanadium oxides of the empirical formula V _1-x M _x O ₂ -yA _y , where M is at least one metal different from vanadium, x is a value from 0 to 0.05, A is a non-oxygen Anion and y is a value from 0 to 0.05.

Furthermore, solids containing vanadium oxide of the empirical formula V _1-x M _x 0 ₂ - _y A _y , where M is at least one other than vanadium metal, x is a value of 0 to 0.05, A is an anion other than oxygen and y is a value of 0 to 0.05, and vanadium is 95 to 99.99 mole percent, based on the total amount of vanadium, in the + IV oxidation state, and 0.01 to 5 mole percent, based on the total amount of vanadium, in the + V oxidation state and / or + III as determined by redox titration.

Likewise, the use of the vanadium oxides or the solids according to the invention produced by the process according to the invention is the subject of the present invention. Preferred embodiments are given in the dependent claims and the description.

Oxides of vanadium are known for their great diversity, both in terms of the oxidation states and the variety of structural modifications.

Of particular technical relevance are, inter alia, oxides of vanadium in the oxidation state + IV.

Vanadium dioxide exists in various modifications: As alpha-vanadium dioxide, such is referred to as a monoclinically distorted rutile structure. The powder diffractogram of this modification is deposited with the International Center for Diffraction Data under the number PDF 01-076-0456. Alpha-VO ₂ is the thermodynamically stable modification at room temperature.

Beta vanadium dioxide crystallizes tetragonally in an undistorted rutile structure.

Gamma-vanadium dioxide crystallizes monoclinically in a structure related to that of V ₆ 0i ₃ . It has long been known that alpha-vanadium dioxide reversibly converts to the beta-modification at a phase transition temperature T. Below the phase transition temperature is alpha vanadium dioxide, above the beta modification. A basic description of this phenomenon is found, for example, in John Goodenough, Journal of Solid State Chemistry 3, 490-500 (1971). For pure, undoped vanadium dioxide, the phase transition temperature is 68 ° C. By suitable doping of the vanadium dioxide, however, it is possible to shift the phase transition temperature up or down. By suitable doping, for example, phase transition temperatures can be lowered to 0 ° C.

While alpha-vanadium dioxide has high transmission for near-infrared radiation (800 to 2000 nm), beta-vanadium dioxide reflects or absorbs infrared rays to a high level. Vanadium dioxide can be prepared by reduction of vanadium compounds in the oxidation state + V.

No. 6,358,307 describes a process for preparing doped or undoped vanadium dioxide by pyrolysis of ammonium hexavanadates (NH ₄ ) ₂ V ₆ O ₆ at temperatures between 400 and 650 ° C.

AT 41 1526 discloses a process for producing doped or undoped vanadium dioxide by pyrolysis of ammonium metavanadate NH ₄ V0 ₃ and tungsten or molybdenum oxide at temperatures between 600 and 700 ° C. In this case, a pyro- lysiertes product is obtained, which is then heat treated under inert gas atmosphere.

The object of the present invention was to provide a simple process by means of which the initially defined vanadium oxides can be prepared in high purity in the alpha or beta modification. The vanadium oxides thus produced are said to contain only a few impurities of vanadium (V) compounds due to incomplete reduction or of vanadium (III) compounds due to overreduction. The object has been achieved by the above-mentioned process for the preparation of vanadium oxide of the empirical formula V _1-x M _x O ₂ - _y A _y , where M is at least one metal different from vanadium, x is a value from 0 to 0.05, A is from Oxygen differs nes anion and y is a value of 0 to 0.05 and wherein the vanadium oxide is present in the distorted or undistorted rutile structure, comprising the reduction of vanadium ^) containing starting material and the annealing of the reductate under inert gas atmosphere at temperatures of 500 ° C to 1000 ° C.

Pure vanadium dioxide has the empirical formula V0 ₂ . However, it is possible to dope the crystal lattice of the vanadium dioxide with other metal ions or other anions. This is expressed by the empirical formula V _1-x M _x 02- _y A _y .

It should be noted that this notation customary in solid-state chemistry does not necessarily accurately reflect the actual stoichiometry. Rather, the exact composition of the compound is dictated by the crystal lattice.

If, for example, the lattice is doped with other metal ions M, this has no effect on the stoichiometry if M is in the + IV oxidation state. In all other cases, the total composition is dictated by the crystal lattice. To compensate for the charge balance and, where appropriate, spatial gaps, either further doping with metal ions or anions can be incorporated into the lattice, the charge balance can take place by incorrect occupancy of some cation lattice sites, or it can, for example, vanadium ions in other oxidation tion levels are incorporated into the lattice ,

The same applies to dopants with anions A.

Vanadium oxides which can be prepared by the process according to the invention can either be undoped or can typically contain up to 10 mole percent of metal ions M, based on the total vanadium content (corresponding to x = 0.1). Preferably, x is a value of 0.001 to 0.05 or 0.002 to 0.02. In some embodiments, x is from 0.01 to 0.02, in other embodiments from 0.002 to 0.015, again in others from 0.25 to 0.45.

 In particular, the doping with metal ions M can influence the phase transition temperature T from the alpha to the beta modification of vanadium dioxide. The phase transition temperature can be both increased and decreased.

Suitable metal ions to lower the phase transition temperature are, for example, molybdenum, tungsten, tantalum, niobium, ruthenium, rhenium and titanium.

Preference is given to molybdenum or tungsten.

Suitable metal ions M for increasing the phase transition temperature include, for example, iron, tin, chromium, gallium, aluminum, germanium. Preference is given to iron or tin.

It is possible to dope vanadium dioxide with several different metal ions. As a rule, only metal ions are combined, which either all lower the phase transition temperature or all increase the phase transition temperature. The combination of the phase transition temperature lowering and increasing metal ions is possible but less preferred.

The phase transition temperature T can also be influenced by doping with anions A different from oxygen. A suitable anion A, which lowers the phase transition temperature, is in particular fluoride.

 The doping of the anion lattice, for example, with nitride, however, leads to an increase in the transition temperature. In a preferred embodiment, vanadium oxides which can be prepared by the process according to the invention are not doped with anions A. In further embodiments, they may typically contain up to 10 mole percent of Anions A based on the total oxygen content (corresponding to y = 0.1). Y preferably assumes values of 0.001 to 0.05 or of 0.002 to 0.02. In some embodiments, y takes values from 0.01 to 0.02, in other embodiments from 0.002 to 0.015, again in others from 0.25 to 0.45.

Suitable starting materials for the production of vanadium dioxides by the process according to the invention are all compounds which contain vanadium in the oxidation state + V.

Preferred starting materials are, for example, vanadium pentoxide V ₂ 0 ₅ , metavananadata such as ammonium metavanadate NH ₄ V0 ₃ , monovanadates such as ammonium monovanadate (NH ₄ ) ₃ V0 ₄ , divanadates such as ammonium dodanadate (NH ₄ ) ₄ V ₂ 0 _7, hexavanadates such as ammonium hexavanadate (NH ₄ ) ₂ V ₆ 0i ₆ , decavanadates such as ammonium decavanadate (NH ₄ ) 6V ₁₀ O 28, vanadium (V) halides such as vanadium pentafluoride VF ₅ , vanadium (V) - oxyhalides such as VOF ₃ , VOCl ₃ , VOBr ₃ , and their mixed halides, V0 ₂ F, V0 ₂ Cl, V0 ₂ Br. Particular preference is given to vanadium compounds which are not volatile. In particular, those are preferred which are not completely or partially gaseous under reaction conditions. Particularly preferred starting materials are vanadium pentoxide V ₂ 0 ₅ or ammonium salts of the above-mentioned vanadates.

Alkali or alkaline earth metal salts of the vanadates are generally less preferred. Less preferred is the use of vanadium peroxo compounds.

The use of vanadium oxyhalides is possible but also less preferred since they are volatile and may be partially gaseous under the reaction conditions.

All vanadium compounds can be used both anhydrous and as hydrates. However, they preferably contain as little or no water of crystallization as possible, that is to say they are preferably essentially anhydrous. Preferably, they are used dry.

It is also possible to use mixtures of starting materials for the process according to the invention.

When undoped vanadium dioxide is prepared, the vanadium (V) containing compounds or the mixture of vanadium (V) containing compounds are generally employed directly for the reduction described below.

If vanadium dioxide is to be produced which is doped with other metal ions M or with anions A, the doping can be achieved in various ways. For the method according to the invention, it is irrelevant on which path the doping is set.

 Depending on the structure of the starting material, the metal ions M or anions A can already be incorporated in the starting material in the crystal lattice. It is also possible that vanadium (V) -containing starting materials are present in the finely divided mixture with the doping material.

The methods for doping are known per se to the person skilled in the art.

It is possible, for example, to stir fine-grained vanadium (V) -containing material with a solution of the doping material to form a paste, which is then dried. Preferably, the solution is aqueous. Less preferred are organic solvents, as formed during drying or at later process steps carbon black can interfere with later applications. If non-aqueous solvents are used, these are preferably readily volatile and generally have a boiling point below 200 ° C. under atmospheric pressure. Suitable compounds for doping the vanadium (V) -containing material by the method described above are any compounds which dissolve in a solvent in which the vanadium (V) -containing material is not soluble. Preferably, the solvent used is water. It is also possible to homogeneously mix fine-grained vanadium (V) -containing material with doping material in the solid state without the addition of solvents. Homogeneity can be achieved, for example, by homogenization using suitable apparatus. For example, vanadium (V) -containing material and doping material can be homogenized by means of mixers known to those skilled in the art for highly viscous systems, for example extruders or kneaders. Another possibility is the homogenization in shakers, possibly supported by ceramic balls such as steatite balls, which are shaken with the powder to be mixed.

Suitable compounds for doping with tungsten as tungsten oxide, tungstates such as ammonium metatungstate (N ^^^ W- ^ O ^ o, ammonium para-tungstate such as (NH4) ₁₀ H2W ₁₂ O42 or hydrates thereof. Suitable tungsten oxides are in particular tungsten (VI) oxide W0 ₃ or oxides of the empirical formula W0 _3-z z with 0 <<1. Less preferred are tungsten oxyhalides such as WO2X2, WOX _4, WX ₆ with X = F, Cl.

Suitable compounds for doping with molybdenum are, for example, molybdenum oxides, molybdate such as ammonium metamolybdates such as (ΝΗ ₄ ) ₆ Η2Μθ _ΐ 2θ ₄ ο, ammonium paramolybdate such as (ΝΗ ₄ ) ₆ Μθ ₇ θ24 or their hydrates. Suitable molybdenum oxides are in particular molybdenum (VI) oxide MoO ₃ or oxides of the empirical formula MoO _3-z with 0 <z <1. Less preferably Molybdänoxyhalogenide as M0O2X2 MoOx _4, MoX ₆ with X = F, Cl.

Suitable compounds for doping with iron are preferably soluble iron salts. For example, FeS0 ₄ , Fe ₂ (S0 ₄ ) ₃ , FeCl ₂ , FeCl ₃ , Fe (OAc) ₂ , Fe (OAc) ₃ or other readily soluble iron salts are suitable. Suitable compounds for doping with tin are, for example, tin halides SnX ₄ , tinoxohalides SnOX ₂ , ammonium hexahalogenostannates (NH ₄ ) ₂ SnX ₆ , where X = F, Cl. Suitable compounds for doping with fluoride are inorganic or organic fluorine compounds. For example, ammonium fluoride NH ₄ F, ammonium bifluoride NH ₄ HF _2, hydrogen fluoride or organic fluorine compounds are preferred.

If salts are used for doping, ammonium salts are generally preferred, while alkali or alkaline earth metal salts are in principle possible but not preferred.

Another suitable method for doping with fluoride is the addition of gaseous vanadium fluorides such as V0 ₂ F or VOF ₃ to gaseous reducing agent. In this case, the doping does not take place at the stage of the starting materials but during the reduction.

Another method of doping the starting material is, for example, the co-grinding of vanadium (V) -containing material with doping material.

When precipitation of vanadium (V) -containing material and doping material under the same conditions is possible, doped starting material may also be obtained by coprecipitation of vanadium (V) -containing material and doping material from a solution. Suitable vanadium (V) -containing material has, for example, particle sizes of 5 to 10 μm. The drying of the material is usually done at temperatures that allow a rapid drying of the paste, but do not induce changes in the composition of the material. Typical drying temperatures are for example at 80 to 120 ° C. If lower drying temperatures are used, drying is usually assisted by applying a vacuum. The exact drying process is not critical to the practice of the process of this invention.

The starting material for the reduction typically has average particle sizes of 1 to 100 μm (weight average determined by sieving method), preferably 5 to 20 μm, and a BET surface area (determined according to DIN ISO 9277) of 0.1 to 10 n of Yg. Before carrying out the reduction, it may be appropriate to deagglomerate the starting material. This can be done for example by mixers such as vibromixers, vibrators, vibrating sieves, mills such as knife mills or jet mills. On a laboratory scale, this can be achieved, for example, by means of a laboratory mill.

According to the invention, the reduction of the starting material is carried out so that vanadium (V) is completely reduced to vanadium (IV), but further reduction to vanadium (III) or lower oxidation states occurs only to a minor extent. Vanadium dioxide obtained by the process of this invention is typically greater than 95 mole percent, based on the total amount of vanadium, in the + IV oxidation state, more than 97 mole percent in particular embodiments. It is also possible to produce vanadium oxides present in excess of 99 or 99.9 mole percent in the + IV oxidation state. The homogeneity of the vanadium with respect to the oxidation state can be determined up to a value of about 95 mol% by means of powder diffractometry. For higher purities and more accurate values, the determination is usually done by redox titration.

In a preferred embodiment, the reduction is carried out under a reducing atmosphere containing one or more inert gases and one or more gaseous reducing agents under the reaction conditions.

Suitable reducing agents are in principle all substances which can bring about the reduction of vanadium ^) to vanadium (IV). As a rule, reducing agents are chosen in which both the reducing agent and its oxidation product are gaseous.

Suitable reducing agents are, for example, ammonia, hydrogen, carbon monoxide, aldehydes, alcohols, formic acid, amines, hydrazine, hydrocarbons such as alkanes, alkenes, alkynes, hydrogen sulfide, sulfur dioxide, thiols.

Suitable hydrocarbons are, for example, methane, ethane, propane, butane, ethene, propene, butenes, acetylene (ethyne), propyne. Suitable aldehydes are preferably readily volatile and gaseous under the reaction conditions, for example formaldehyde, acetaldehyde, propanal, butanal. Suitable alcohols are preferably readily volatile and gaseous under the reaction conditions, such as, for example, methanol, ethanol, n / iso-propanol

Particularly preferred reducing agents are ammonia, hydrogen, carbon monoxide, methane, ethane, aliphatic amines, sulfur dioxide or mixtures thereof

Particularly preferred are ammonia, carbon monoxide or hydrogen. Sulfur-containing compounds are less preferred because they can react with the vanadium oxide to form unwanted by-products such as vanadium oxysulfides or sulfonovanadates.

It is possible to form reducing agents in situ from the starting material, for example by pyrolysis of the starting material. In this case, for example, ammonia can be released from ammonium salts or carbon monoxide from formates, oxalates or oxalic acid.

According to the invention, however, a reducing atmosphere is preferably produced by adding external reducing agent.

In a preferred embodiment of the method according to the invention, the reduction is carried out under a gas atmosphere. Particularly preferably, the gas atmosphere is fluid. This means that constantly fresh reducing agent is passed over the starting material. This has the consequence that the atmosphere is constantly renewed, so that you can keep the reaction conditions, if desired, constant. It also makes it possible to run a reaction program with changing conditions. The targeted addition of reducing agent also makes the reduction well reproducible. Furthermore, this makes it easier to carry out the method according to the invention continuously.

In contrast to methods in which reducing agent is generated only in situ, when performing the reduction under a flowing atmosphere of the partial pressure of reducing agent, the temperature, the flow rate of the gas, the time and thus the amount of reducing agent, with the Starting material has contact, be targeted. The flow rate of the gas atmosphere is usually adjusted by controlling a gas volume flow per unit time.

However, it is also possible to adjust the gas volume flow so that the gas volume of the reactor is statistically exchanged one to 100 times per hour. Preferably, the gas volume of the reactor is exchanged 2 to 50 times, more preferably 5 to 25 times per hour.

In another embodiment, the gas volume flow is adjusted so that, based on the starting material to be reduced, 1 to 50 redox equivalents of the gaseous reducing agent are fed per hour. Preferably, 2 to 30, more preferably 4 to 10 redox equivalents are fed per hour.

Preferably, the reaction is carried out at atmospheric pressure. The reducing agents generally have a partial pressure of 10 to 500 mbar, preferably 50 to 300 mbar. In one embodiment, the partial pressure is 70 to 150 mbar, in another embodiment 150 to 250 mbar.

The design under increased pressure is possible, but makes higher demands on the appropriate apparatus and is therefore less preferred.

In addition to the one or more reducing agents, the remaining atmosphere typically consists of one or more inert gases. Inert gases in the sense of the invention are all those which undergo no chemical reaction with the remaining atmosphere, the starting material or the reductate under the reaction conditions. Typical inert gases are nitrogen or argon. Less preferred inert gases are carbon dioxide, helium, neon, krypton, xenon, sulfur hexafluoride, or perhalogenated hydrocarbons. However, these may be used if desired. It is also possible to use mixtures of different inert gases.

The temperature at which the reduction is carried out is typically in the range of from 200 to 600 ° C, preferably from 250 to 450 ° C, more preferably from 350 to 450 ° C. The amount of time the starting material is exposed to the reducing atmosphere depends on the boundary conditions. If the reaction time is too short, vanadium ^) is not completely reduced. If the time is too long, it may be possible to terreduction to vanadium (III) or (II) occur. Typically, the starting material and the reducing atmosphere are heated at a heating rate of 10 to 500 Kelvin per hour, preferably at a heating rate of 50 to 300 K / h. Subsequently, the temperature is kept at the reaction temperature for a certain period of time. This period can be, for example, 15 to 300 minutes. In a preferred embodiment, it is preferably 30 to 120 minutes. It is also possible to run temperature programs with different temperature ramps and levels. If the process according to the invention is carried out continuously, the starting material can be introduced, for example, into the preheated reactor. In this case, the heating rates for the starting material may be significantly higher and, for example, from 300 to 3000 K / h. The reduction of the starting material can be carried out in a variety of apparatus, the nature of which is not crucial for the implementation. Quartz flasks are particularly suitable on a laboratory scale. On an industrial scale, the process according to the invention is usually carried out in continuous operation in a rotary kiln, oscillating kiln, or discontinuously in heatable crucibles.

In a preferred variant, the process is carried out continuously.

In a preferred embodiment, the reduction is carried out such that the starting material continuously passes through an oven through which a reducing gas stream is passed in countercurrent. Suitable furnaces for this purpose are known to the person skilled in the art.

After the reduction has been completed, the reductate usually contains most, typically at least 90% by weight, of vanadium oxide, which for the most part, as a rule at least 70% by weight, is present in the gamma modification.

After the reduction, the reductate according to the invention is subjected to a heat treatment under an inert gas atmosphere. Suitable inert gases are all gases which can also be used during the reduction as inert gases and mixtures thereof. The heat treatment is usually carried out at a temperature of 500 to 1000 ° C. A temperature of 600 to 900 is preferred. In a particularly preferred embodiment, the temperature is from 650 to 800 ° C. The heating rate to reach the annealing temperature has no significant effect on the product. Typically, the temperature of the reduction after heating the inert gas atmosphere is heated at a rate of 1 to 50 K / h, preferably 10 to 30 K / h. If the reductate is introduced into a preheated reactor, the heating rates can be significantly higher and, for example, from 300 to 3000 K / h.

The duration of annealing may vary over a wide period of time. For example, it can be from 15 minutes to 300 minutes. In a preferred embodiment, it is from 30 to 150 minutes, more preferably from 45 to 90 minutes.

During annealing, the proportion of vanadium dioxide present in the gamma modification is converted to the beta modification (rutile structure), which prevails at the temperature of the annealing. After annealing, the product is generally cooled to room temperature under inert gas atmosphere. The cooling is usually also under inert gas.

Thereafter, the product may optionally be subjected to further treatments to adjust properties necessary for later use.

Usually, the product is comminuted by suitable grinding methods to desired particle sizes. This can be done for example by jet milling or wet grinding by means of a suitable mill, for example a mill with ceramic grinding media. Common particle sizes for solid powder are, for example, average particle sizes of 30 to 300 nm (d ₅₀ value, determined by laser diffraction).

In a preferred variant of the process according to the invention, ammonium metatungstate is dissolved in water and stirred with suitable vanadium (V) compounds to give a paste. This is dried. The resulting powder is deagglomerated and exposed at a temperature of 350 to 450 ° C a flowing atmosphere of inert gas and ammonia. It is then annealed at 600 ° C.

In another preferred embodiment, molybdenum oxide MoO _{3 is} homogeneously mixed with vanadium pentoxide in the solid state and then deagglomerated. Subsequently, the powder is exposed at about 400 ° C, for example at a temperature of 390 to 410 ° C, a flowing atmosphere of inert gas and ammonia. Finally, the mixture is tempered at a temperature of 600 to 800 ° C. In a further preferred embodiment, ammonium molybdate is dissolved in water and kneaded with vanadium pentoxide. The paste is dried and then deagglomerated. Subsequently, the resulting powder is exposed at about 400 ° C, for example at a temperature of 390 to 410 ° C, a flowing atmosphere of inert gas and ammonia. Finally, the mixture is tempered at a temperature of 600 to 800 ° C.

A further subject of the present invention are solids which contain vanadium oxide of the empirical formula V _1-x M _x O 2- _y A _y , where M is at least one metal other than vanadium and x is a value from 0 to 0.05, and A a is an anion other than oxygen, and y is a value of 0 to 0.05, and wherein vanadium is 95 to 99.99 mole percent, based on the total amount of vanadium, in the + IV oxidation state, and 0.01 to 5 mole percent to the total amount of vanadium, in the oxidation state + V and / or + III, determined by redox titration. In one embodiment, solids of the invention contain vanadium oxide containing vanadium in the + V oxidation state but no vanadium in the + III oxidation state.

In another embodiment, solids according to the invention contain vanadium oxide which contains vanadium in the oxidation state + III but no vanadium in the oxidation state + V.

In the preferred embodiment, solids of the invention contain vanadium dioxide in the alpha (below the phase transition temperature T) or beta modification (above the phase transition temperature T). Particularly preferably, the vanadium dioxide is at least 95 mole percent in the alpha or beta modification. Preference is given to preparing solids according to the invention by a process according to the invention.

Solids of the invention either can not be doped with vanadium-different metal ions M or can typically contain up to 10 mole percent metal ions M based on the total vanadium content (corresponding to x = 0.1). Preferably, x is from 0.001 to 0.05 or from 0.002 to 0.02. In some embodiments, x is from 0.01 to 0.02, in other embodiments from 0.002 to 0.015, again in others from 0.25 to 0.45.

Suitable metal ions to lower the phase transition temperature are, for example, molybdenum, tungsten, tantalum, niobium, ruthenium, rhenium or titanium.

Preference is given to molybdenum or tungsten. Suitable metal ions M for increasing the phase transition temperature are, for example, iron, tin, chromium, gallium, aluminum or germanium.

Preference is given to iron or tin.

In a preferred embodiment, solids according to the invention are not doped with anions A other than oxygen. In further embodiments, they may typically contain up to 10 mole percent of Anions A based on the total oxygen content (corresponding to y = 0.1). Y preferably assumes values of 0.001 to 0.05 or 0.002 to 0.02. In some embodiments, y assumes values of 0.01 to 0.02, in other embodiments, 0.002 to 0.015, again in others of 0.25 to 0.45.

Suitable anions A are in particular fluoride or nitride.

Inventive solids are characterized by a high proportion of vanadium in the oxidation state + IV. Preferably 95 to 99.99 mole percent of the vanadium contained in the solid according to the invention in the oxidation state + IV are present. Preferably, these are 97 to 99.9 mole percent, and more preferably 90 to 99.5 mole percent. The remaining vanadium atoms are in the oxidation state + V and / or + III. The ratio of vanadium (IV) to vanadium (III) or vanadium (V) is determined by redox titration. This process is known per se to the person skilled in the art. In a particular embodiment, the solid according to the invention has an average particle size of 30 to 300 nm (d ₅₀ value, determined by laser diffraction).

 By producing particle sizes of the order of magnitude of or below the wavelength of the visible light, it is possible to apply solids according to the invention such that the objects which comprise the solid according to the invention are, if desired, not rendered opaque and remain transparent in color , Vanadium oxides which have been prepared by the process according to the invention and solids according to the invention are distinguished by a high purity with respect to the homogeneity of the oxidation state of the vanadium. As a result, articles or coatings can be produced which have very uniform properties with regard to the switchability of the thermochromism. In particular, vanadium dioxides which have been prepared by the process according to the invention and solids according to the invention have a very sharp transition between the phases.

They are suitable, inter alia, for use as pigments, in particular as thermochromic pigments. With these, in particular, polymeric substances such as paints or plastics such as thermoplastics or thermosetting plastics can be dyed.

As such, they can support thermal management of, for example, buildings or vehicles such as cars, ships, rail vehicles or aircraft or technical devices.

For use, vanadium oxides which have been prepared by the process according to the invention or solids according to the invention can be incorporated into solid, liquid or pasty pigment preparations. Vanadium oxides which have been produced by the process according to the invention or solids according to the invention are furthermore of interest for use in IR detectors, as optical filters, in particular switchable optical filters or in laser welding. Examples

The following examples are intended to illustrate the properties of this invention without, however, limiting it.

 Parts, percent or ppm in this document, unless otherwise stated, parts by weight understood.

Example 1: Comparative Example 15 g of ammonium metavanadate NH ₄ VO ₃ (Sigma Aldrich, purity 99%) were heated at 500 ° C. for 20 minutes in a slow stream of nitrogen (10 ml / min). The pyrolysis product was analyzed by powder diffractometry and consisted of V ₂ 0 ₅ and V ₆ 0i ₃ .

Example 2: Comparative Example

59.3 g ammonium metavanadate NH ₄ V0 ₃ (Sigma Aldrich, purity 99%) and 135.05 g anhydrous oxalic acid were homogenized with the aid of 100 g steatite balls (diameter 10 mm) for five minutes using a shaking mixer. The mixture was then deagglomerated with a knife mill.

 60 g of this mixture were treated in a rotating, heated 250 mL quartz flask with gas inlet as follows:

The product obtained was analyzed by powder diffractometry and compared with the powder diffractograms of known compounds. The product obtained was a mixture of V ₂ 0 ₃ and V ₄ 0 ₇ .

Example 3 Inventive Example 1 3 g of ammonium metatungstate (ΝΗ ₄ ) ₁₀ Η ₂ νν ₁₂ θ ₄₂ were dissolved in 10 ml of water and stirred with 30.0 g of ammonium metavanadate NH ₄ V0 ₃ . The paste was applied at room temperature. dried in a vacuum drying oven to constant weight and then deagglomerated with a laboratory mill.

 15.0 g of the resulting mixture was treated in the rotating, heated quartz flask of 100 ml volume with gas inlet as follows:

The reductate thus obtained was analyzed by powder diffractometry and consisted of alpha-V0 ₂ with an admixture of W0 ₃ . Less than 2 mol% tungsten was incorporated into the V0 ₂ lattice relative to vanadium.

The phase transition temperature for the transition to beta-V0 ₂ was 65.2 ° C on heating and 61, 2 ° C on cooling (differential thermal analysis (DSC), heating rate 1 K / min).

The determined phase transition temperature suggests that only a small part of the tungsten used is present as doping in the V0 ₂ lattice.

Example 4 Example According to the Invention

1.44 g of molybdenum oxide MoO ₃ and 44.6 g of V ₂ O ₅ were homogenized with the aid of a shaking mixer and 100 g of steatite balls (diameter 10 mm) for 5 minutes. The resulting mixture was then deagglomerated with a laboratory mill.

12.3 g of the resulting mixture were treated in the rotating, heated 100 mL quartz flask with gas inlet as follows: Time inside temperature gas flow N ₂ gas flow NH ₃

 quartz bulb

 Rinse 15 min 25 ° C 12 l / h 10 l / h

 Heating 1 h 25 - »400 ° C 12 l / h 10 l / h

 Waiting time 50 min 400 ° C 12 l / h 10 l / h

 Waiting time 10 min 400 ° C 15 l / h -

 Heating up 30 min 400 - »600 ° C 15 l / h -

 Waiting time 30 min 600 ° C 15 l / h -

 Cooling 5 h 600 ° C ^ RT 15 l / h -

The product obtained was examined by powder diffractometry. It consisted of powdery diffractometrically pure alpha-V0 ₂ . The product therefore has the empirical formula ν ₀ , 98Μθο, ο 2θ 2 - It had a phase transition temperature of 52.9 ° C when heated and 30.6 ° C on cooling (DSC, heating rate 1 K / min).

Example 5 Example According to the Invention

1, 77 g of ammonium molybdate (ΝΗ ₄ ) ₆ Μο ₇ θ24-7Ι-θ2θ were dissolved in 20 ml of water and kneaded with 44.6 g of vanadium pentoxide V ₂ 0 ₅ . The paste was dried at room temperature in a vacuum oven to constant weight and then disagglomerated with a laboratory mill.

 12.3 g of the mixture thus obtained were treated in the rotating, heated quartz flask with gas inlet as follows:

Time inside temperature gas flow N ₂ gas flow NH ₃

 quartz bulb

 Rinse 15 min 25 ° C 12 l / h 10 l / h

 Heating 1 h 25 - »400 ° C 12 l / h 10 l / h

 Waiting time 1 h 400 ° C 12 l / h 10 l / h

 Waiting time 10 min 400 ° C 15 l / h -

 Heating up 30 min 400 - »600 ° C 15 l / h -

 Waiting time 30 min 600 ° C 15 l / h -

Cooling 5 h 600 ° C ^ RT 15 l / h - The product obtained was analyzed by powder diffractometry. It consisted of powdery diffractometrically pure alpha-V0 ₂ doped with molybdenum. The product has the empirical formula Vo _{, 98} Moo _, o ₂ 0 ₂ . It had a phase transition temperature of 52.1 ° C on heating and 29.6 ° C on cooling (DSC, heating rate 1 K / min).

Claims

claims I. Process for the preparation of vanadium oxide of the empirical formula V _1-x M _x O 2-yA _y , where M is at least one metal different from vanadium, x is a value from 0 to 0.05, A is an anion other than oxygen and y is a value from 0 to Is 0.05 and the vanadium oxide is present in the distorted or undistorted rutile structure, comprising the reduction of vanadium (V) -containing starting material and the annealing of the reductate under inert gas atmosphere at temperatures of 500 ° C to 1000 ° C. 2. The method of claim 1, wherein vanadium (V) -containing starting material is used, which is doped with metal ions M. A method according to any one of the preceding claims, wherein M is selected from molybdenum, tungsten, tantalum, niobium, ruthenium, rhenium and titanium. 4. The method of claim 1 or 2, wherein M is selected from iron, tin, chromium, gallium, aluminum and germanium. 5. The method according to at least one of the preceding claims, wherein A is fluoride. 6. The method according to at least one of the preceding claims, wherein the reduction is carried out with a gaseous reducing agent under the reaction conditions. 7. The method according to at least one of the preceding claims, wherein the reduction is carried out with ammonia as the reducing agent. 8. The method according to at least one of the preceding claims, wherein the reduction is carried out under a flowing gas atmosphere. 9. The method according to at least one of the preceding claims, wherein the reduction is carried out with a gaseous reducing agent at a partial pressure of 10 to 500 mbar in admixture with an inert gas. 10. The method according to at least one of the preceding claims, wherein the reduction is carried out at a temperature of 200 to 500 ° C. II. Solids containing vanadium oxide of the empirical formula V _1-x M _x O 2- _y A _y , where M is at least one metal different from vanadium, x is a value from 0 to 0.05, A is an oxygen atom. and y is a value of 0 to 0.05 and vanadium is 95 to 99.99 mole percent, based on the total amount of vanadium, in the + IV oxidation state and 0.01 to 5 mole percent, based on the total amount Vanadium, in the oxidation state + V and / or + III, determined by redox titration. 12. A solid according to claim 1 1, wherein it is present in an average particle size of 20 to 2000 nm, determined by laser diffraction. 13. Use of solids according to claims 1 1 to 12 or vanadium oxides, which have been prepared according to claims 1 to 10, as a pigment. 14. Use of solids according to claims 1 1 to 12 or vanadium oxides, which have been prepared according to claims 1 to 10, as a thermochromic pigment. 15. Use of solids according to claims 1 1 to 12 or vanadium oxides, which have been prepared according to claims 1 to 10, for thermal management of buildings, vehicles or technical devices. 16. Use of solids according to claim 15 in detectors, optical filters, switchable optical filters or laser welding.