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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
  • B22F2009/088—Fluid nozzles, e.g. angle, distance
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2201/00—Treatment under specific atmosphere
  • B22F2201/01—Reducing atmosphere
  • B22F2201/013—Hydrogen
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2201/00—Treatment under specific atmosphere
  • B22F2201/03—Oxygen
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2302/00—Metal Compound, non-Metallic compound or non-metal composition of the powder or its coating
  • B22F2302/25—Oxide

Definitions

• the invention relates to a process for producing tungsten oxide powders by means of flame spray pyrolysis.
• Tungsten oxides are known infrared-absorbing substances which can also show good electrical conductivity.
• Such a mixed oxide is generally obtained by providing a solution comprising a tungsten compound and optionally a compound of a mixed oxide component, subsequently removing the solvent and treating the remaining solid at temperatures of about 500° C. in a reducing atmosphere.
• tungsten mixed oxides are produced by means of flame spray pyrolysis.
• a solution comprising a tungsten compound and a compound of the mixed oxide component is introduced into a flame and oxidized there.
• materials having a BET surface area of about 60-80 m 2 /g are disclosed.
• the material from the flame spray pyrolysis is subsequently subjected to thermal treatment which reduces the BET surface area to values of about 20 m 2 /g. This has a deleterious effect on dispersibility.
• a process allowing production of tungsten oxides having high crystallinity and good dispersibility would be desirable.
• the invention provides a single-stage process and a two-stage process for producing tungsten oxide or a tungsten mixed oxide. Both processes comprise a flame spray pyrolysis.
• the BET surface area of the tungsten oxide powder produced by the process according to the invention is 1-10 m 2 /g.
• the first reaction zone begins at the point of introduction of the aerosol into the reaction space.
• the second reaction zone is immediately downstream of the first.
• v 1 is the average velocity in the first reaction zone
• v 2 the average velocity in the second reaction zone.
• v 1 is greater than v 2 . This can be achieved for example by a smaller cross section in the first reaction zone.
• v 1 and v 2 are calculated based on the gas volumes of the unconverted starting materials, for example nitrogen or excess oxygen, and of the products, substantially water vapour.
• the velocity figures are normalized velocities. They are found by dividing the volume flow rate having the unit Nm 3 /h by the cross-sectional area.
• the index “O 2 , primary” refers to the oxygen in the air or optionally in the oxygen-enriched air which forms the flame. In addition it may be useful to additionally introduce, separately from this air, air referred to here as secondary air directly into the reaction space.
• the index “O 2 , secondary” then refers to the oxygen in the secondary air.
• the secondary air is preferably directed such that it enters the reaction space only in reaction zone 2.
• the atomization of the solution may also be effected by means of air.
• the index “O 2 , atomization” then refers to the oxygen in the atomization air.
• the index “O 2 , ttl” refers to the total oxygen. The total oxygen is preferably chosen such that
• the ratio O 2,ttl /0.5H 2 or O 2,primary /0.5H 2 stems from the reaction of 2 mol of hydrogen with 1 mol of oxygen as per 2H 2 +O 2 ⁇ 2H 2 O.
• the BET surface area of the reduced material is smaller than that of the material from the flame spray pyrolysis.
• the ratio BET reduced /BET FSP is normally 0.60-0.95.
• the hydrogen/oxygen flame which burns into the reaction space is formed by igniting an oxygen-comprising gas and a combustion gas which upon reaction with oxygen forms water.
• the average residence times of the reaction mixture in reaction zone 1 and reaction zone 2 are chosen such that t 2 >0.5 t 1 , preferably 0.7 t 1 ⁇ t 2 ⁇ 0.9 t 1 , wherein t 1 is the average residence time of the reaction mixture in reaction zone 1 and t 2 is the average residence time of the reaction mixture in reaction zone 2.
• the average residence time t 1 is preferably 0.2-1 s, particularly preferably 0.3-0.7 s.
• the average residence time t 2 is preferably 0.1-0.8 s, particularly preferably 0.2-0.5 s.
• Contemplated reducing gas streams are hydrogen, hydrogen/nitrogen mixtures or hydrogen/noble gas mixtures.
• a single-stage process where the reduction step may be eschewed also forms part of the subject matter of the invention.
• lambda means that hydrogen and oxygen are to be chosen such that there is a stoichiometric excess of hydrogen in terms of the equation H 2 +0.5 O 2 ⁇ H 2 O. It is preferable when 0.6 ⁇ lambda ⁇ 1, particularly preferable when 0.7 ⁇ lambda ⁇ 0.95 and very particularly preferable when 0.8 ⁇ lambda ⁇ 0.9.
• the average residence time in the reaction space for the single-stage process is preferably 1-5 s.
• fine droplets of the solution are a constituent of the aerosol.
• the fine droplets preferably have an average droplet size of less than 120 ⁇ m, particularly preferably of 30-100 ⁇ m.
• the droplets are typically produced using single- or multi-component nozzles.
• the solution employed shall have as high a concentration as possible.
• the intention is to achieve an optimum balance between production output and the properties of the powder.
• these requirements are best fulfilled in a range of 5-60 wt %, particularly preferably 25-55 wt %, very particularly preferably 30-50 wt %, in each case based on the sum of W and M and based on the metal.
• the best results in terms of homogeneity of the powder are obtained when the tungsten and alkali metal compounds are present in a solution.
• the solution may be heated to achieve solubility and to attain a suitable viscosity for atomization of the solution.
• All soluble metal compounds convertible into the oxides under the reaction conditions may in principle be employed. These may be inorganic metal compounds, such as nitrates, chlorides, bromides, or organic metal compounds, such as alkoxides or carboxylates. Nitrates may be particularly advantageously employed.
• Examples 1-5 show the production of alkali metal-tungsten mixed oxide powders by the two-stage process according to the invention.
• Example 6 shows a comparative example of a two-stage process.
• Examples 7-11 show the production of potassium-tungsten mixed oxide powders by the single-stage process according to the invention.
• a solution of 2165 g of ammonium metatungstate, 335 g of caesium nitrate and 12 020 g of water is produced.
• the total concentration of W and Cs, as metal in each case, is 12.7 wt %.
• Reaction zone 1 Jetting 2500 g/h of this solution with 5 Nm 3 /h of air as jetting gas by means of a two-material nozzle at room temperature (23° C.) affords an aerosol. This is brought to reaction with 8 Nm 3 /h (0.357 kmol/h) of hydrogen and 30 Nm 3 /h of air (0.281 kmol 02/h). The temperature 50 cm below the burner mouth is 527° C.
• reaction zone 1 The residence time in reaction zone 1 is 0.48 seconds at a gas velocity of 2.89 Nm/s.
• Reaction zone 2 15 Nm 3 /h of secondary air (0.141 kmol 02/h) are additionally introduced into the reactor outside reaction zone 1.
• reaction zone 2 The residence time in reaction zone 2 is 0.36 seconds at a gas velocity of 1.65 Nm/s. Subsequently, the reaction mixture is cooled and the obtained solid separated from the gaseous materials on a filter.
• the solid has a BET surface area of 7.2 m 2 /g.
• the solid from the FSP is heated under a nitrogen atmosphere at a heating rate of 8.0° C./min to an end temperature of 500° C. and there treated in a forming gas atmosphere (70/30 vol % N 2 /H 2 ,volume flow 100 NI/h) over a period of 2 hours at a temperature of 500° C.
• the obtained reduced solid has a BET surface area of 5.4 m 2 /g.
• a dispersion of the solid, 18 wt % in 1-methoxy-2-propanol, is deep blue in colour.
• Example 6 is a comparative example where the average velocities in both reaction zones are identical. Starting materials and reaction conditions may be found in table 1. Table 2 shows calculated values.
• the two-stage process according to the invention is directed at obtaining in a flame pyrolytic process a material having a low BET surface area coupled with a rather high crystallinity.
• the BET surface area is reduced only to a small extent while the reduction proceeds rapidly under moderate conditions without appreciable sintering. This material is correspondingly readily dispersible.
• a material having an increased BET surface area is obtained from the FSP. This material is more difficult to reduce. The reduced material itself is more difficult to disperse.
• a solution of 4316 g of ammonium metatungstate, 502 g of potassium acetate, 64 g of glacial acetic acid and 4831 g of water is produced.
• the total concentration of W and K, in each case as metal, is 34.2 wt %.
• the solid has a BET surface area of 2.4 m 2 /g.
• X-ray structural analysis shows a hexagonal potassium-tungsten mixed oxide.
• Examples 7 to 11 show that reduced powders are producible by means of a single-stage process, namely a flame-spray pyrolysis.

Applications Claiming Priority (3)

Publications (1)

Family

ID=55272254

Family Applications (1)

Country Status (5)

Cited By (3)

Families Citing this family (9)

Family Cites Families (10)

• 2017
  • 2017-01-23 WO PCT/EP2017/051309 patent/WO2017129516A1/de active Application Filing
  • 2017-01-23 CN CN201780008356.1A patent/CN109071261A/zh active Pending
  • 2017-01-23 EP EP17700861.2A patent/EP3408227B1/de active Active
  • 2017-01-23 US US16/072,467 patent/US20200230703A1/en not_active Abandoned
  • 2017-01-23 JP JP2018539062A patent/JP7021091B2/ja active Active

Also Published As

Similar Documents

Legal Events