[go: up one dir, main page]

WO1993014023A1 - Process for the production of a powder of fine particles and a plant for performing said process - Google Patents

Process for the production of a powder of fine particles and a plant for performing said process Download PDF

Info

Publication number
WO1993014023A1
WO1993014023A1 PCT/DK1993/000001 DK9300001W WO9314023A1 WO 1993014023 A1 WO1993014023 A1 WO 1993014023A1 DK 9300001 W DK9300001 W DK 9300001W WO 9314023 A1 WO9314023 A1 WO 9314023A1
Authority
WO
WIPO (PCT)
Prior art keywords
aerosol
chamber
powder
droplets
gas
Prior art date
Application number
PCT/DK1993/000001
Other languages
French (fr)
Inventor
Ebbe Skyum JØNS
Svend Danielsen
Original Assignee
Niro Holding A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Niro Holding A/S filed Critical Niro Holding A/S
Publication of WO1993014023A1 publication Critical patent/WO1993014023A1/en

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14—Methods for preparing oxides or hydroxides in general
    • C01B13/34—Methods for preparing oxides or hydroxides in general by oxidation or hydrolysis of sprayed or atomised solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D1/00—Evaporating
    • B01D1/16—Evaporating by spraying
    • B01D1/18—Evaporating by spraying to obtain dry solids
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14—Methods for preparing oxides or hydroxides in general
    • C01B13/18—Methods for preparing oxides or hydroxides in general by thermal decomposition of compounds, e.g. of salts or hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C01G23/006—Alkaline earth titanates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G3/00—Compounds of copper
    • C01G3/006—Compounds containing copper, with or without oxygen or hydrogen, and containing two or more other elements
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G37/00—Compounds of chromium
    • C01G37/006—Compounds containing chromium, with or without oxygen or hydrogen, and containing two or more other elements
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C01P2004/52—Particles with a specific particle size distribution highly monodisperse size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • 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
    • C01P2006/12—Surface area

Definitions

  • the present invention relates to the ' manufacture of a powder of substantially spherical mono-particles of desired components consisting of inorganic salts or oxides or of organic compounds, metals or mixtures thereof. Such powders of submicron particle size or of a median particle size of a few microns are useful in various technological fields.
  • Metal powders of such small size are useful as sintering aids facilitating the sintering of more coarse sinter powders.
  • a commercial interest also exists for wax powders having a median particle diameter of 3-5 microns.
  • the main interest in fine powders of the type dealt with in the present applica- tion is within the high technological ceramic industry, and in the following the invention is primarily de ⁇ scribed in connection with ceramic powders of submicron particle size consisting of inorganic salts or oxides.
  • ceramic powders are sintered to produce components of fuel cells, wear and heat resistant elements for various devices, or to produce supercon ⁇ ducting ceramics or other electronic components.
  • the powders must have spherical shape, high density and a combination of submicron size and low specific surface.
  • the powder is of high purity, is of submicron particle size and has a suf- ficiently narrow size distribution. DESCRIPTION OF PRIOR ART.
  • aqueous homogeneous metal salt solution e.g. an aqueous homogeneous metal salt solution, or a melt is atomized into fine droplets to form an aerosol, and the droplets are treated to form powder particles which possibly are converted, e.g. by heating, possibly in the presence of reactive gases, such as oxygen or hy ⁇ drogen, to obtain the desired chemical and physical transformations before the powder is collected in a dust collector.
  • reactive gases such as oxygen or hy ⁇ drogen
  • the process of the present invention is of this last mentioned type.
  • a special embodiment of this type of process is termed spray pyrolysis, because the drop ⁇ lets are subjected to a high temperature treatment.
  • the invention deals with a process for the production of a powder of fine particles of de- sired components by producing an aerosol of droplets from a solution or melt which by drying, congealing, thermal decomposition and/or interaction and/or react ⁇ ion with gaseous compounds, especially oxygen or hydro- gen, are capable of forming said desired components, and converting the aerosol forming droplets into a powder of said desired components, and recovering said powder, comprising the steps of
  • a preferred embodiment of the present process is for the production of a ceramic powder by producing an aerosol of droplets from a solution of salts which by interaction, reaction wich gaseous compounds, and/or by thermal decomposition are capable of forming a mixture of components desired in the ceramic powder, and sub ⁇ jecting the aerosol to a heat treatment to dry the droplets and convert the solids thereof into a powder of said components, and recovering said powder, com ⁇ prising
  • an aerosol having droplets of a median volume diameter between 1.5 and 2.5 microns which droplets are present in the aerosol in a concen ⁇ tration corresponding to more than 50 g liquid per kg gas.
  • nozzles are used de ⁇ livering a very broad spray, which means that the nozzles should have a very wide spray angle.
  • the nozzle or nozzles are preferably arranged in an upward or downward position and thus delivers a spray having small angles to the horizontal plane.
  • the nozzle operates in an atomizing chamber from where the aerosol produced is carried out solely by the gas provided through the two-fluid nozzle in the atomization process.
  • This is in contrast to several prior art processes where the aerosol is carried away from the nozzle area immediate- ly after formation, by means of a high velocity gas stream.
  • the aerosol resides in the atomizing chamber changes take place as to the median volume diameter and the volume of suspended droplets as well as in the size distribution thereof. This is due to the fact that the microdroplets to a certain extent collide with the chamber walls and with each other and the largest fraction of the particles falls to the chamber bottom by gravity.
  • the above mentioned conversion zone through which the aerosol leaving the atomizing chamber is passed may typically be a high temperature area where ⁇ in the aerosol droplets are dried and converted by interactions between the components of the droplets or by reaction with gaseous components in the carrier gas, such a oxygen or hydrogen.
  • the aerosol droplets may be congealed by being passed through a cooling zone.
  • the particles thus converted may be separated from the carrier gas by means of an electrostatic precipitator or a bag filter. Due to the very fine particle size the resulting powder will usually not be free flowing and it may be most conveniently handled as a suspension or paste.
  • the invention also deals with a plant for pro ⁇ ducing a powder by the above defined processes, which plant is characterized in having an atomizing chamber which is closed except for an outlet for aerosol in the top portion thereof and an outlet for liquid in the bottom, at least one two-fluid nozzle in said chamber which when operating delivers a spray shaped as
  • a cone shell having a cone angle above 90 means for supplying pressurized gas to said at least one two-fluid nozzle, means for supplying said at least one nozzle with a solution or melt acting as precursor for the components desired in the powder, a conversion device into which said outlet for aerosol from the atomizing chamber debouches, and means for recovering the desired powder from a gas stream, said means being connected to the other end of said device.
  • a preferred embodiment of this plant has a plu ⁇ rality of two-fluid nozzles arranged in the .atomizing chamber in a horizontal arrangement, each nozzle having an exit opening pointing either upwards or downwards.
  • the top portion of the atomizing chamber is upward tapering to impart an accelerating upward movement of the aerosol leaving the chamber to enter the conversion device, e.g. a heating device.
  • the conversion device e.g. a heating device.
  • gas is used in a broad sence comprising atmospheric air, oxygen and other oxidizing gases, hydrogen and other reducing gases as well as inert gases such as nitrogen etc.
  • Fig. 1 very schematically depicts a layout for a plant suitable for performing the process of the in ⁇ vention
  • Fig. 2 shows plots referred to in an Example be ⁇ low and showing the aerosol concentration as a function of airflow for different nozzles
  • Fig. 3 is an electron micrograph of particles of maltodextrin produced by the process according to the invention.
  • Fig. 4 is an electron micrograph of particles of nickel ferrite produced by the process according to the inventio .
  • Fig. 5 referred to in an Example below shows a comparison of results using different nozzles, and
  • Fig. 6 illustrates the importance of residence time for aerosol in the atomizing chamber.
  • a spray chamber is generally de ⁇ signated l.
  • the walls thereof are cylindrical and the top portion are taper- ing towards an outlet opening 2.
  • the bottom part slants towards an exit for liquid 3.
  • a nozzle 4 is shown in the chamber 1 .
  • a battery of nozzles arranged horizontally in the chamber.
  • the nozzle 4 is shown as the preferred embodi ⁇ ment which has a resonance body 5 fixed in front of the nozzle opening.
  • This resonance body 5 may typi- cally be in the shape of a cup creating resonance waves which provides the desired cone shell shape of the cloud of droplets produced by the nozzle.
  • the nozzle 4 is supplied with atomizing gas, such as cleaned air or a reactive or inert pressurized gas, as explained above, through conduit 6.
  • atomizing gas such as cleaned air or a reactive or inert pressurized gas, as explained above
  • the liquid is supplied to the nozzle for producing the desired microdroplets.
  • the liquid may be a solution of precursor compounds for the desired powder, e.g. a ceramic powder, or it may be a melt which by ato ization and following congealing pro ⁇ cutes a desired powder.
  • the nozzle 4 produces a mist of the liquid from the source 7, which mist fills up the chamber 1.
  • the liquid which collects in the bottom of the chamber 1 is recovered through exit 3 and preferably recycl ⁇ ed to the source 7 as shown.
  • a ceramic powder In case a ceramic powder is to be produced an aerosol of a solution of precursors for the ceramic powder will be carried up into a heating device 8.
  • This device 8 may typically be a tubular fur ⁇ nace having a height ten or more times the diameter.
  • the aerosol, including the carrier gas is heated and thereby expanded which secures an accelerated movement of the droplets/ particles through the device.
  • the device 8 may have means (not shown) for introducing heating or cooling gas or reactive gases into the aerosol.
  • the atomizing gas introduced through 6, which gas subsequently acts as carrier gas in device 8 may be of a reducing character, or such a gas may be intro ⁇ pokerd separately in the device 8 to convert metal compounds into the free metals during passage through the device 8.
  • the fine particles leave the device 8 through the top portion thereof and are by means of a carrier gas introduced through conduit 9 transported into a particle collector 10, which may be an electrostatic precipitator.
  • the desired powder is recovered through 11, e.g. by washing, whereas the gas leaves through a conduit 12 and may be released to the atmosphere possibly after suitable purification or the gas may be partially recycled to 9.
  • a In the system for drying only the feed solution consisted of maltodextrin (5-40 percent by weight) in water, and B In the system for sintering an aqueous solution of ferric nitrate and nickel nitrate in a mole ratio of Fe/Ni 2:1 was used.
  • Example 1 The aerosol concentration was measured with a Leon Siegler Opacimeter calibrated by weighing the electrostatic precipitator before and after the test.
  • Example 1 The aerosol concentration was measured with a Leon Siegler Opacimeter calibrated by weighing the electrostatic precipitator before and after the test.
  • the Sonicore nozzle was equipped with a resonance cup and the MM nozzle was an externally mixing swirl two-fluid nozzle having an opening of 0.45 mm.
  • the nozzles were mounted in a NIRO spray dryer type Mobile Minor.
  • the powder was collected in a cyclone followed by a two- stage electrostatic precipitator.
  • the products from the two collectors were mixed and analysed.
  • the test results are presented in Table 1 below as test la and lb.
  • the same nozzles were mounted in a chamber having a volume of 15 liters. The outlet was 10 cm in dia ⁇ meter and connected to a 30 cm in diameter duct where hot air was introduced.
  • the product was collected in a two-stage electrostatic precipitator.
  • the test results are presented below as test 2a and 2b.
  • Span is a measure of the size distribution and is defined as (D9o _D ⁇ o) /D 50
  • the two nozzles produce comparable product charact- eristics when used without atomizing chamber.
  • the nozzle with resonance cup produces a much more con ⁇ centrated aerosol than the nozzle without resonance cup.
  • Nozzle 1 Sonicore nozzle no. 52. (With resonance cup)
  • Nozzle 2 Sonicore nozzle no. 47. (With resonance cup)
  • Nozzle 3 MM. (Without resonance cup).
  • the nozzles were operated with different gas flows. All nozzles produce a spray with a significant fraction of droplets below 4 microns under these con- ditions when selecting a proper liquid flow rate to the nozzles.
  • the velocity of the air leaving the nozzles were measured in a sphere at a distance of 50 mm from the nozzle exit.
  • the nozzles were operated without feed under these tests which was necessary to make the measurements.
  • the results are given in fig. 5 as maxi ⁇ mum gas velocity measured 50 mm from nozzle in a circle in 1st quadrant. The unit is m/s.
  • curve 1 refers to nozzle 1 at air flow 6.4 kg/h
  • curve 2 refers also to nozzle l but at air flow 7.5 kg/h
  • Curve 3 refers to nozzle 2 at an air flow of 7.5
  • curve 4 also refers to nozzle 2 but at an air flow of 11.5 kg/h
  • Curve 5 refers to nozzle 3 at an air flow of 7.5 kg/h. It can be seen from the figure 5 that the posi ⁇ tion and size of the maximum values differ from nozzle to nozzle and from operation to operation.
  • the second experiment was to measure concentra ⁇ tion and size of the aerosol leaving the spray chamber with different nozzles in operation under different but comparable conditions. The liquid feed rate was in each case adjusted to give the maximum reading of the gasphase concentration of calcined and sintered aero ⁇ sol. The results are reported below in Table 2.
  • Aerosol concentration and properties as a function of as load to s ecific nozzles Aerosol concentration and properties as a function of as load to s ecific nozzles.
  • the effect of volume of the spray chamber on aerosol MVD, SD (size distribution) and concentration at the chamber exit is illustrated in this Example, covering short retention times.
  • the test material was maltodextrine solutions. The tests were carried out with three chambers of a shape as shown in fig. 1, but with different volumes, leading to 0.3 sec, 1.2 sec. and 4.2 sec. residence time of the gas in the chamber. The gas flow was 6.4 kg/h.
  • Curves A, B and C respectively represent results for retention times of 4.2 sec, 1.2 sec and 0.3 sec. , resp.
  • the curves D and E show the difference between A and B, and A and C respectively; they represent the lost aerosol as function of retention time. It is seen in this experiment that large as well as small droplets disapear, leaving aerosols of suit ⁇ able median volume diameter, size distribution and con ⁇ centration.
  • a pilot plant as the one shown in Fig. 1 was used for preparing a ceramic powder of nickel ferrite (NiFe 2 0 3 ).
  • the volume of the atomizing chamber 1 was 15 liter and the height of the heating device 9 was 2 m and the inner diameter 20 cm.
  • the nozzle 4 was of the type termed Sonicore 52. It had a cup-shaped member 5 fixed 4 mm from the body of the nozzle, providing a wide spray angle (above 90°) .
  • This solution was at ambient temperature atomized in an amount of 1755 ml/h.
  • the heating device was adjusted to obtain a wall temperature of 900 C.
  • the density after being mixed with 4% by weight wax and subjected to a pressure of 150 bar was 3.40g/cm 3 .

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Oxygen, Ozone, And Oxides In General (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)

Abstract

A fine powder of narrow particle size distribution is produced by forming an aerosol by two-fluid nozzle (4) atomization in a chamber (2), maintaining the aerosol in said chamber to remove between 50 and 95 percent by volume of the droplets from the aerosol and passing the residual aerosol from the atomizing chamber through a conversion zone (8). A plant for producing the powder has a closed atomizing chamber with at least one two-fluid nozzle delivering a spray shaped as a cone shell having cone angle above 90°. The plant further having a conversion device into which an outlet for aerosol from the atomizing chamber debouches.

Description

Process for the production of a powder of fine particles and a plant for performing said process.
FIELD OF THE INVENTION. The present invention relates to the'manufacture of a powder of substantially spherical mono-particles of desired components consisting of inorganic salts or oxides or of organic compounds, metals or mixtures thereof. Such powders of submicron particle size or of a median particle size of a few microns are useful in various technological fields.
Metal powders of such small size are useful as sintering aids facilitating the sintering of more coarse sinter powders. A commercial interest also exists for wax powders having a median particle diameter of 3-5 microns.
However, currently the main interest in fine powders of the type dealt with in the present applica- tion is within the high technological ceramic industry, and in the following the invention is primarily de¬ scribed in connection with ceramic powders of submicron particle size consisting of inorganic salts or oxides. Such ceramic powders are sintered to produce components of fuel cells, wear and heat resistant elements for various devices, or to produce supercon¬ ducting ceramics or other electronic components. To be suitable for tapecasting and printing the powders must have spherical shape, high density and a combination of submicron size and low specific surface.
To obtain reproducibly the desired properties of the ceramic products resulting from the sintering of the powder, it is essential that the powder is of high purity, is of submicron particle size and has a suf- ficiently narrow size distribution. DESCRIPTION OF PRIOR ART.
Several processes have been used or suggested for producing fine powders, including ceramic powders, of the type in question. Thus, mechanical procedures involving grinding and sieving operations have been used. However, this type of processes involves a substantial risk of con¬ tamination of the product. Besides, the waste of expensive starting materials can be substantial and the shape of the resulting powder particles is not optimal for producing dense sintered products.
It has also been suggested to synthezise oxide powders using metal alkoxides which are precipitated and polymerised from an alkoholic solution, forming particles which are dried and oxidized. However, this process is described as being too expensive due to high starting material costs (confer J.C.Schuster: Physika- lish-chemische Basis der Synthese von Oxidpulvern mit kontrollierten Eigenschaften. Proceedings Internatio- naler Kongress fiir Technische Keramik, 1-3 Marz 1989, Wiesbaden, Germany).
In a further type of process solution, e.g. an aqueous homogeneous metal salt solution, or a melt is atomized into fine droplets to form an aerosol, and the droplets are treated to form powder particles which possibly are converted, e.g. by heating, possibly in the presence of reactive gases, such as oxygen or hy¬ drogen, to obtain the desired chemical and physical transformations before the powder is collected in a dust collector.
The process of the present invention is of this last mentioned type. A special embodiment of this type of process is termed spray pyrolysis, because the drop¬ lets are subjected to a high temperature treatment. For further description of methods for producing ceramic powders by means of spray pyrolysis reference is made to the following:
1. Processing of ceramic powders by the spray pyrolysis method, influence of the precursors. Examples of Zirconia and YBa2,Cu307.
P. Odier, B. Dubois, C. Clinard, H. Stroumbos and
Ph. Monod.
Ceram. Trans. 12, page 75-89 (1990).
2. Generation of Complex Metal Oxides by Aerosol Processes: Superconducting Ceramic Particles and
Films, Toivo T. Kodas. Advanced Materials, 1989, no. 6, pp 180-192. (1989)
3. German Patent Specification No. 37 29 391 (Published 16 March 1989) . 4. Preparing and sintering characteristics of MgO, MgO.Cr203 and MgO.Al203, M.J. Ruthner. Science of Sintering, Vol 6, no. 1/2, pp 81-94,1974.
5. Generation of Complex Metal Oxides by Aerosol Processes: Superconducting Ceramic Particles and Films. Toivo T. Kodas. Advanced Materials, 1989, no. 6, pp 180-192.
6. Synthesis of YBa2Cu30,7_v x and YBa2Cu408 by Aerosol Decomposition. Saket Chadda, Ward, Carim, Kodas, Ott and Kroeger. Journal of Aerosol Science, vol. 22, no. 5, pp 601-616, 1991.
7. Preparation of fine hollow spherical NiFe203 powders. Ahmen M. Gadella and Hsuan-Fu Yu. Journal of Materials Research, vol. 5, no. 12, pp 2923-27, 1990.
Although substantial reseach has concentrated on developing suitable processes for the manufacture of the above defined powders, including spray pyrolysis processes, no process exists which is really suitable for commercial production of the powders in industrial scale. For production in relatively large scale by an aerosol based process the aerosol has to be formed by means of a two-fluid nozzle since the capacity of other systems for producing aerosols is insufficient for in- dustrial application.
However, it has turned out (see for instance the reference numbered 7 above) that when using the prior art two-fluid nozzle processes fine particle size and narrow size distribution can only be obtained when the concentration of aerosol droplets is small in the gas wherein the droplets are suspended. However, a small droplet concentration in the aerosol means a small yield of product.
In spray pyrolysis processes where the aerosol consisting of carrier gas and suspended droplets is heated at high temperatures, much energy is required for heating a relative large proportion of carrier gas meaning a high energy consumption for each gram of powder produced. Efforts to increase the concentration of drop¬ lets in the aerosol has hitherto resulted in deteriora¬ tion of product quality, especially when an aqueous solution is atomized.
SUMMARY OF THE INVENTION.
It has turned out that by proper selection of the type of two-fluid nozzles to be used for creating the aerosol and by taking special measures and adapting process characteristics as defined below it is possible to operate a process of the above defined type main¬ taining a higher aerosol concentration and thus a higher production capacity and still obtain a powder consisting of spheres with fine size and narrow size dis ribution. Accordingly, the invention deals with a process for the production of a powder of fine particles of de- sired components by producing an aerosol of droplets from a solution or melt which by drying, congealing, thermal decomposition and/or interaction and/or react¬ ion with gaseous compounds, especially oxygen or hydro- gen, are capable of forming said desired components, and converting the aerosol forming droplets into a powder of said desired components, and recovering said powder, comprising the steps of
(i) producing said aerosol by atomizing said solu- tion or melt by means of pressurized gas using at least one two-fluid nozzle delivering a spray shaped as a cone shell having a cone angle above 90 , into an atomizing chamber and ensuring that the temperature and humidity and chemical reactivity of the atmosphere in the chamber are kept at such levels that any substantial con¬ version of the atomized droplets is avoided while they reside in said chamber, (ii) maintaining the aerosol in said chamber for the time needed to have between 50 and 95% by volume of the atomized droplets collecting as solution or melt at the bottom portion of the atomizing chamber, (iii) removing the solution or melt thus collected, (iv) carrying the residual gassuspended aerosol drop¬ lets out from the atomizing chamber, using the gas from the at least one two-fluid nozzle as sole carrier gas, (v) passing the gassuspended aerosol droplets leav- ing said chamber through a conversion zone to effect the desired conversion of the droplets, (vi) passing gas with entrained particles leaving the conversion zone through a particle collector to collect the desired powder as substantially spherical mono-particles, and
(vii) recovering the desired powder from said particle collector.
A preferred embodiment of the present process is for the production of a ceramic powder by producing an aerosol of droplets from a solution of salts which by interaction, reaction wich gaseous compounds, and/or by thermal decomposition are capable of forming a mixture of components desired in the ceramic powder, and sub¬ jecting the aerosol to a heat treatment to dry the droplets and convert the solids thereof into a powder of said components, and recovering said powder, com¬ prising
(i) producing said aerosol by atomizing said so¬ lution by means of pressurized gas using at least one two-fluid nozzle delivering a spray shaped as a cone shell having a cone angle above
0
90 , into an atomizing chamber, wherein the temperature and humidity are kept at such levels that any substantial evaporation of the atomized droplets is avoided while they are in said chamber,
(ii) maintaining the aerosol in said chamber for the time needed to have between 50 and 95% volume of the atomized droplets collecting as solution at the bottom portion of the atomizing chamber, (iii) removing the solution thus collected and re¬ cycling it to the solution to be atomized, (iv) carrying the residual gassuspended aerosol drop¬ lets out from the atomizing chamber, using the gas from the at least one two-fluid nozzle as sole carrier gas,
(v) passing the gassuspended aerosol droplets leav¬ ing said chamber through a heating device con¬ nected to said chamber, to effect the desired drying and conversion of the solids of the drop- lets,
(vi) passing gas with entrained particles leaving the heating device through a particle collector to collect the desired ceramic powder as substant¬ ially spherical mono-particles, and (vii) recovering the desired powder from said particle collector.
In the process of the invention it is possible to produce a stable aerosol having droplets of a median volume diameter of less than 4 microns and containing more than 40 gram liquid per kg gas, and having less than 10 volume percent droplets larger than 7 microns and less than 10 vol percent smaller than 0.5 microns.
Especially when producing ceramic powders it is preferred to produce an aerosol having droplets of a median volume diameter between 1.5 and 2.5 microns which droplets are present in the aerosol in a concen¬ tration corresponding to more than 50 g liquid per kg gas.
To obtain a stable aerosol of such high volume concentration of fine droplets of narrow particle size distribution it is essential that nozzles are used de¬ livering a very broad spray, which means that the nozzles should have a very wide spray angle. The nozzle or nozzles are preferably arranged in an upward or downward position and thus delivers a spray having small angles to the horizontal plane.
The best results have been obtained using two- fluid nozzles having a plate, a resonance cup or an im- pactor body fixed in front of the nozzle opening.
It is also essential that the nozzle operates in an atomizing chamber from where the aerosol produced is carried out solely by the gas provided through the two-fluid nozzle in the atomization process. This is in contrast to several prior art processes where the aerosol is carried away from the nozzle area immediate- ly after formation, by means of a high velocity gas stream. When the aerosol resides in the atomizing chamber changes take place as to the median volume diameter and the volume of suspended droplets as well as in the size distribution thereof. This is due to the fact that the microdroplets to a certain extent collide with the chamber walls and with each other and the largest fraction of the particles falls to the chamber bottom by gravity.
By maintaining the aerosol in the chamber for such time that between 50 and 95 percent by volume of the droplets disappear a suitable droplet size and size distribution will usually be obtained. This corre¬ sponds to a residence time in the chamber of between 0.1 and 4 seconds. The liquid which collects at the bottom of the atomizing chamber is, as mentioned above, preferably recycled to be atomized once more, and thereby the reduction of the droplet concentration in the aerosol in the atomizing chamber does not necessarily mean any loss of starting material for the process.
However, to enable reuse of the liquid collected in the chamber and to avoid scaling or deposits in the chamber it is essential that evaporation of the drop¬ lets or chemical conversions of the components therein are substantially avoided, which means that the com¬ position of the liquid recovered in the bottom of the chamber is nearly the same as that of the freshly prepared liquid to be atomized.
The above mentioned conversion zone through which the aerosol leaving the atomizing chamber is passed, may typically be a high temperature area where¬ in the aerosol droplets are dried and converted by interactions between the components of the droplets or by reaction with gaseous components in the carrier gas, such a oxygen or hydrogen. Alternatively, the aerosol droplets may be congealed by being passed through a cooling zone. The particles thus converted may be separated from the carrier gas by means of an electrostatic precipitator or a bag filter. Due to the very fine particle size the resulting powder will usually not be free flowing and it may be most conveniently handled as a suspension or paste.
The invention also deals with a plant for pro¬ ducing a powder by the above defined processes, which plant is characterized in having an atomizing chamber which is closed except for an outlet for aerosol in the top portion thereof and an outlet for liquid in the bottom, at least one two-fluid nozzle in said chamber which when operating delivers a spray shaped as
0 a cone shell having a cone angle above 90 , means for supplying pressurized gas to said at least one two-fluid nozzle, means for supplying said at least one nozzle with a solution or melt acting as precursor for the components desired in the powder, a conversion device into which said outlet for aerosol from the atomizing chamber debouches, and means for recovering the desired powder from a gas stream, said means being connected to the other end of said device.
A preferred embodiment of this plant has a plu¬ rality of two-fluid nozzles arranged in the .atomizing chamber in a horizontal arrangement, each nozzle having an exit opening pointing either upwards or downwards. By having the nozzles arranged in this way the droplets leave the nozzles in paths having a substantial horizontal component which apparently is essential for obtain eπt of the aerosol having the desired character- istics as explained above.
The importance of the volume of the atomizing chamber compared to the capacity of the nozzles there- in has not been fully investigated, but preliminary experiments suggest that it is advantageous to adapt the operational gas consumption of the nozzles and the effective volume of the atomizing chamber to obtain a residence time for the aerosol in the chamber between 0.1 and 4 seconds.
To minimize collision between the droplets when passing from the central part of the atomizing chamber to the treatment zone it is preferred that the top portion of the atomizing chamber is upward tapering to impart an accelerating upward movement of the aerosol leaving the chamber to enter the conversion device, e.g. a heating device. Thus, it is possible to mini¬ mize droplets collision immediately before drying, which would lead to the formation of undesired large particles.
In the present specification and claims the term gas is used in a broad sence comprising atmospheric air, oxygen and other oxidizing gases, hydrogen and other reducing gases as well as inert gases such as nitrogen etc.
In the following the invention is further de¬ scribed by reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS. On the drawings:
Fig. 1 very schematically depicts a layout for a plant suitable for performing the process of the in¬ vention, Fig. 2 shows plots referred to in an Example be¬ low and showing the aerosol concentration as a function of airflow for different nozzles, and
Fig. 3 is an electron micrograph of particles of maltodextrin produced by the process according to the invention.
Fig. 4 is an electron micrograph of particles of nickel ferrite produced by the process according to the inventio . Fig. 5 referred to in an Example below shows a comparison of results using different nozzles, and
Fig. 6 illustrates the importance of residence time for aerosol in the atomizing chamber.
DESCRIPTION OF PREFERRED EMBODIMENTS
In fig. 1 a spray chamber is generally de¬ signated l. In the depicted embodiment the walls thereof are cylindrical and the top portion are taper- ing towards an outlet opening 2.
The bottom part slants towards an exit for liquid 3.
In the chamber 1 a nozzle 4 is shown. For simplicity only one nozzle is depicted, however, it is preferred to use a battery of nozzles arranged horizontally in the chamber.
The nozzle 4 is shown as the preferred embodi¬ ment which has a resonance body 5 fixed in front of the nozzle opening. This resonance body 5 may typi- cally be in the shape of a cup creating resonance waves which provides the desired cone shell shape of the cloud of droplets produced by the nozzle.
The nozzle 4 is supplied with atomizing gas, such as cleaned air or a reactive or inert pressurized gas, as explained above, through conduit 6.
From a source 7 a liquid is supplied to the nozzle for producing the desired microdroplets. The liquid may be a solution of precursor compounds for the desired powder, e.g. a ceramic powder, or it may be a melt which by ato ization and following congealing pro¬ duces a desired powder.
The nozzle 4 produces a mist of the liquid from the source 7, which mist fills up the chamber 1.
During the residence time of this aerosol mist in the chamber a substantial amount of the liquid actually disappears from the aerosol and collects at the bottom of the chamber. This involves certain advantages as to the median particle size of the remaining suspended droplets as well as to the size distribution thereof. The liquid which collects in the bottom of the chamber 1 is recovered through exit 3 and preferably recycl¬ ed to the source 7 as shown.
Due to the continuous introduction of atomizing gas through 6 into the chamber 1 the aerosol in this chamber will be driven upwards through the exit 2 at accelerating velocity due to the tapering shape of the upper part of the chamber 1.
In case a ceramic powder is to be produced an aerosol of a solution of precursors for the ceramic powder will be carried up into a heating device 8. This device 8 may typically be a tubular fur¬ nace having a height ten or more times the diameter.
In this device 8 the aerosol, including the carrier gas is heated and thereby expanded which secures an accelerated movement of the droplets/ particles through the device.
The device 8 may have means (not shown) for introducing heating or cooling gas or reactive gases into the aerosol.
During the passage through the heating device 8 an initial drying followed possibly by a calcinating and sintering process takes place.
In case it is desired to produce a fine metal powder the atomizing gas introduced through 6, which gas subsequently acts as carrier gas in device 8, may be of a reducing character, or such a gas may be intro¬ duced separately in the device 8 to convert metal compounds into the free metals during passage through the device 8.
After the desired conversion the fine particles leave the device 8 through the top portion thereof and are by means of a carrier gas introduced through conduit 9 transported into a particle collector 10, which may be an electrostatic precipitator.
From the collector 10 the desired powder is recovered through 11, e.g. by washing, whereas the gas leaves through a conduit 12 and may be released to the atmosphere possibly after suitable purification or the gas may be partially recycled to 9.
The invention is further illustrated below by means of examples.
Examples
General basis for the below tests results Measuring aerosol size distribution.
All data relating to liquid aerosol properties were calculated, based on measurements on the solid particles formed from the liquid aerosol either by dry¬ ing alone or by drying, calcining and sintering the aerosol. Two types of products have been tested.
A In the system for drying only the feed solution consisted of maltodextrin (5-40 percent by weight) in water, and B In the system for sintering an aqueous solution of ferric nitrate and nickel nitrate in a mole ratio of Fe/Ni = 2:1 was used.
Both systems provide apparently dense particles as it appears from the SEM pictures in fig. 3 (malto¬ dextrin) and fig. 4 (nickel ferrite) . The powder size distribution has been measured on either Sedigraph 5000, Malvern Master Sizer or Malvern 2600, in all cases based on powders collected in a Honywell 2-stage electrostatic precipitator and redispersed.
The aerosol concentration was measured with a Leon Siegler Opacimeter calibrated by weighing the electrostatic precipitator before and after the test. Example 1
Direct atomization in drying chamber compared with atomization in atomizing chamber and subsequent trans- fer of aerosol to drying chamber and comparison of two different types of nozzles.
Two commercially available two-fluid nozzles (Sonicore 52 (Son 52) and a Schlick nozzle (in the following termed MM)) were used in these tests. The Sonicore nozzle was equipped with a resonance cup and the MM nozzle was an externally mixing swirl two-fluid nozzle having an opening of 0.45 mm. The nozzles were mounted in a NIRO spray dryer type Mobile Minor. The powder was collected in a cyclone followed by a two- stage electrostatic precipitator. The products from the two collectors were mixed and analysed. The test results are presented in Table 1 below as test la and lb. The same nozzles were mounted in a chamber having a volume of 15 liters. The outlet was 10 cm in dia¬ meter and connected to a 30 cm in diameter duct where hot air was introduced. The product was collected in a two-stage electrostatic precipitator. The test results are presented below as test 2a and 2b.
T A B L E 1
Comparison of powders obtained by direct drying and by use of atomizin chamber for two different nozzles.
Figure imgf000017_0001
*) Span is a measure of the size distribution and is defined as (D9o_Dιo)/D50
The following conclusions can be drawn from the results in the Table:
The two nozzles produce comparable product charact- eristics when used without atomizing chamber.
The difference, however, is significant when the two nozzles are placed in an atomizing chamber: The nozzle with resonance cup produces a much more con¬ centrated aerosol than the nozzle without resonance cup.
The above test results are further substantiated by a larger data collection shown in fig. 2. The plots termed 52 and 47 refer to nozzles having resonance cups while the plots 52-u and MM refer to nozzles without such resonance cups. It appears that the difference in concentration of the aerosols produced by the two types of nozzles are significant, measured as the optical density of the gas leaving the heating device 8 af¬ ter calcination/sintering of the aerosol particles. Example 2
Comparison of different two-fluid nozzles (Aerosol concentration and spray angles.)
The following experiments illustrate the import¬ ance of selection of nozzle type and selection of ope¬ rating parameters of the chosen nozzle. Two sets of experiments were carried out with three different nozzles.
Nozzle 1: Sonicore nozzle no. 52. (With resonance cup) Nozzle 2: Sonicore nozzle no. 47. (With resonance cup) Nozzle 3: MM. (Without resonance cup).
The nozzles were operated with different gas flows. All nozzles produce a spray with a significant fraction of droplets below 4 microns under these con- ditions when selecting a proper liquid flow rate to the nozzles.
The velocity of the air leaving the nozzles were measured in a sphere at a distance of 50 mm from the nozzle exit. The nozzles were operated without feed under these tests which was necessary to make the measurements. The results are given in fig. 5 as maxi¬ mum gas velocity measured 50 mm from nozzle in a circle in 1st quadrant. The unit is m/s.
In fig. 5 curve 1 refers to nozzle 1 at air flow 6.4 kg/h, curve 2 refers also to nozzle l but at air flow 7.5 kg/h. Curve 3 refers to nozzle 2 at an air flow of 7.5 and curve 4 also refers to nozzle 2 but at an air flow of 11.5 kg/h. Curve 5 refers to nozzle 3 at an air flow of 7.5 kg/h. It can be seen from the figure 5 that the posi¬ tion and size of the maximum values differ from nozzle to nozzle and from operation to operation. The second experiment was to measure concentra¬ tion and size of the aerosol leaving the spray chamber with different nozzles in operation under different but comparable conditions. The liquid feed rate was in each case adjusted to give the maximum reading of the gasphase concentration of calcined and sintered aero¬ sol. The results are reported below in Table 2.
Tabel 2
Aerosol concentration and properties as a function of as load to s ecific nozzles.
Figure imgf000019_0001
* MVD = Median Volume Diameter
When comparing the results from figure 5 and Table 2 it is seen that tests which show high sprayangles in figure 5 show high aerosol concentration and narrow size distribution (Dgo~Dio)^D50' ^ -*-s seen that opti¬ mum operation with the spray chamber is obtained with the highest spray angle. Example 3
Retention time comparison.
The effect of volume of the spray chamber on aerosol MVD, SD (size distribution) and concentration at the chamber exit is illustrated in this Example, covering short retention times. The test material was maltodextrine solutions. The tests were carried out with three chambers of a shape as shown in fig. 1, but with different volumes, leading to 0.3 sec, 1.2 sec. and 4.2 sec. residence time of the gas in the chamber. The gas flow was 6.4 kg/h.
The results are shown in fig. 6 as particle size distributions of the dried, collected and redispersed aerosols. Explanation to the figure:
The area under each curve is proportional to the aerosol concentration out of the chamber, Curves A, B and C respectively represent results for retention times of 4.2 sec, 1.2 sec and 0.3 sec. , resp.
The curves D and E show the difference between A and B, and A and C respectively; they represent the lost aerosol as function of retention time. It is seen in this experiment that large as well as small droplets disapear, leaving aerosols of suit¬ able median volume diameter, size distribution and con¬ centration.
Example 4
In this Example a pilot plant as the one shown in Fig. 1 was used for preparing a ceramic powder of nickel ferrite (NiFe203). The volume of the atomizing chamber 1 was 15 liter and the height of the heating device 9 was 2 m and the inner diameter 20 cm. The nozzle 4 was of the type termed Sonicore 52. It had a cup-shaped member 5 fixed 4 mm from the body of the nozzle, providing a wide spray angle (above 90°) . As feed for the nozzle an aqueous nitrate solu¬ tion prepared from analytical grade chemicals was used. Concentration: 0.15 m, pH = 1.5. Mole ratio Fe:Ni = 2:1. This solution was at ambient temperature atomized in an amount of 1755 ml/h. As atomizing gas ambient air was used in an amount of 6.5 kg/h. Before being let to the nozzle the air was purified by means of an electrostatic precipi¬ tator (not shown) .
At the bottom of the chamber 1 solution collect- ed in an amount of 1470 ml/h. Since the relative humidity in the chamber was near 100%, the composition of this solution was substantially the same as when it was let to the nozzle, and it was therefore recycled to the feed source 7. To avoid increase of temperature and drying in the chamber the portion connecting the upper part of the chamber with the heating device 8 was provided with ducts for cooling water (not shown) .
The heating device was adjusted to obtain a wall temperature of 900 C.
From the separator 10 a powder of nickel ferrite was recovered in an amount corresponding to 8.2 g/h.
The median particle diameter of this powder was 0.4-0.8 microns and the specific surface (BET) = 4.5 - 6.0 m2/g. The density after being mixed with 4% by weight wax and subjected to a pressure of 150 bar was 3.40g/cm3.
Satisfactory results have also been obtained when preparing powders of lanthanum-calcium chromite, bariumtitanate and superconducting materials comprising yttrium, barium and copper oxides.

Claims

C A I M S
1. A process or the production of a powder of fine particles of desired components by producing an aerosol of droplets from a solution or melt which by drying, congealing, thermal decomposition and/or inter- action and/or reaction with gaseous compounds especial¬ ly oxygen or hydrogen, are capable of forming said de¬ sired components, and converting the aerosol forming droplets into a powder of said desired components, and recovering said powder, comprising the steps of (i) producing said aerosol by atomizing said solu¬ tion or melt by means of pressurized gas using at least one two-fluid nozzle delivering a spray shaped as a cone shell having cone angle above
0
90 , into an atomizing chamber and ensuring that the temperature and humidity and chemical reactivity of the atmosphere in the chamber are kept at such levels that any substantial con¬ version of the atomized droplets is avoided while they reside in said chamber, (ii) maintaining the aerosol in said chamber for the time needed to have between 50 and 95% by volume of the atomized droplets collecting as solution or melt at the bottom portion of the atomizing chamber, (iii) removing the solution or melt thus collected,
(iv carrying the residual gassuspended aerosol drop¬ lets out from the atomizing chamber, using the gas from the at least one two-fluid nozzle as sole carrier gas, (v) passing the gassuspended aerosol droplets leav¬ ing said chamber through a conversion zone, to effect the desired conversion of the droplets, (vi) passing gas with entrained particles leaving the conversion zone through a particle collector to collect the desired powder as substantially spherical monoparticles, and (vii) recovering the desired powder from said particle collector.
2. The process of claim 1, wherein the removed solution or melt is recycled to the solution or melt being atomized.
3. A process for the production of a ceramic powder of fine particles of desired components by pro¬ ducing an aerosol of droplets from a solution of salts which by interaction, reaction wich gaseous compounds, and/or by thermal decomposition are capable of forming a mixture of components desired in the ceramic powder, and subjecting the aerosol to a heat treatment to dry the droplets and convert the solids thereof into a powder of said components, and recovering said powder, comprising
(i) producing said aerosol by atomizing said so¬ lution by means of pressurized gas using at least one two-fluid nozzle delivering a spray shaped as a cone shell having cone angle above
0 90 , into an atomizing chamber, wherein the temperature and humidity are kept at such levels that any substantial evaporation of the atomized droplets is avoided while they are in said chamber, (ii) maintaining the aerosol in said chamber for the time needed to have between 50 and 95%, prefer¬ ably 80-90, volume of the atomized droplets collecting as solution at the bottom portion of the atomizing chamber, (iϋ) removing the solution thus collected and re¬ cycling it to the solution to be atomized, (iv) carrying the residual gassuspended aerosol drop¬ lets out from the atomizing chamber, using the gas from the at least one two-fluid nozzle as sole carrier gas,
(v) passing the gassuspended aerosol droplets leav- ing said chamber through a heating device con¬ nected to said chamber, to effect the desired drying and conversion of the solids of the drop¬ lets, (vi) passing gas with entrained particles leaving the heating device through a particle collector to collect the desired ceramic powder as substanti¬ ally spherical mono-particles, and (vii) recovering the desired powder from said particle collector.
4. The process of claims 1 or 3, wherein an aerosol is produced in step (ii) having droplets of a median volume diameter of less than 4 microns and con¬ taining more than 40 g liquid per kg gas, and having less than 10 %vol of the droplets larger than 7 microns and less than 10 %vol smaller than 0.5 microns.
5. The process of claims 1 or 3, wherein an ae¬ rosol is produced in step (ii) having droplets of a median volume diameter between 1.5 and 2.5 microns and are present in the aerosol in a concentration corre¬ sponding to more than 50 g liquid per kg gas.
6. The process of claim 1 or 3, wherein the atomization in step (i) is performed by means of a two fluid nozzle having a plate, a resonance cup or an im- pactor body fixed in front of the nozzle opening.
7. A plant for producing a powder by the pro¬ cess of claim 1 or 3, characterized in having a closed atomizing chamber except for an outlet for aerosol in the top portion thereof and an outlet for liquid in the bottom, at least one two-fluid nozzle in said chamber which, when operating, delivers a spray shaped as a cone shell having a cone angle above 90 deg., means for supplying pressurized gas to said at least one two-fluid nozzle, means for supplying said at least one nozzle with a solution or melt acting as precursor for the com¬ pounds desired in the powder, a conversion device into the end of which said out¬ let for aerosol from the atomizing chamber debou- ches, and means for recovering the desired powder from a gas stream, said means being connected to said conver¬ sion device.
8. A plant according to claim 7, characterized in having a plurality of two-fluid nozzles arranged in the atomizing chamber in a horizontal arrangement.
9. A plant according to claim 7, characterized in that the at least one nozzle has an impactor plate, resonance cup or other object fixed at a distance less than 1 cm from the nozzle exit, providing for a spray angle above 100 deg.
10. A plant according to claim 7, characterized in that the operational gas consumption of the at least one nozzle and the effective volume of the atomizing chamber are adapted to obtain a residence time for the aerosol in the chamber between 0.1 and 4 seconds.
11. A plant according to claim 7, characterized in that the top portion of the atomizing chamber is up¬ ward tapering to impart an accelerating upward move- ment of the aerosol leaving the chamber and entering the heating device.
12. A plant according to claim 7, characterized in having means for connecting the outlet for liquid in the bottom of the atomizing chamber with a source of the solution being atomized.
PCT/DK1993/000001 1992-01-15 1993-01-05 Process for the production of a powder of fine particles and a plant for performing said process WO1993014023A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DK4892A DK4892A (en) 1992-01-15 1992-01-15 PROCEDURE FOR MANUFACTURING A POWDER OF FINE PARTICULARS AND A PLANT FOR EXERCISING THE PROCEDURE
DK48/92 1992-01-15

Publications (1)

Publication Number Publication Date
WO1993014023A1 true WO1993014023A1 (en) 1993-07-22

Family

ID=8089145

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DK1993/000001 WO1993014023A1 (en) 1992-01-15 1993-01-05 Process for the production of a powder of fine particles and a plant for performing said process

Country Status (3)

Country Link
AU (1) AU3448493A (en)
DK (1) DK4892A (en)
WO (1) WO1993014023A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2831466A1 (en) * 2001-10-30 2003-05-02 Dgtec POWDER MANUFACTURING DEVICE BY AEROSOL PYROLYSIS
US6613300B2 (en) 1996-12-05 2003-09-02 Degussa Ag Doped, pyrogenically prepared oxides
CN106606887A (en) * 2015-10-22 2017-05-03 中国石油化工股份有限公司 Slurry spray-drying method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0277245A1 (en) * 1986-07-26 1988-08-10 Chemirite, Ltd. Process for producing complex oxide to be used for producing ferrite
EP0285339A1 (en) * 1987-04-01 1988-10-05 Corning Glass Works Metal oxide and metal sulfide particles and production thereof
WO1990015020A2 (en) * 1989-06-09 1990-12-13 Worcester Polytechnic Institute High-temperature aerosol decomposition process and products produced

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0277245A1 (en) * 1986-07-26 1988-08-10 Chemirite, Ltd. Process for producing complex oxide to be used for producing ferrite
EP0285339A1 (en) * 1987-04-01 1988-10-05 Corning Glass Works Metal oxide and metal sulfide particles and production thereof
WO1990015020A2 (en) * 1989-06-09 1990-12-13 Worcester Polytechnic Institute High-temperature aerosol decomposition process and products produced

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
AMERICAN CERAMIC SOCIETY BULLETIN vol. 56, no. 11, 1977, COLUMBUS (US) pages 1023 - 1024 D.M.ROY ET AL. 'PREPARATION OF FINE OXIDE POWDERS BY EVAPORATIVE DECOMPOSITION OF SOLUTIONS' *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6613300B2 (en) 1996-12-05 2003-09-02 Degussa Ag Doped, pyrogenically prepared oxides
FR2831466A1 (en) * 2001-10-30 2003-05-02 Dgtec POWDER MANUFACTURING DEVICE BY AEROSOL PYROLYSIS
WO2003037498A3 (en) * 2001-10-30 2003-10-09 Dgtec Device for producing powder by aerosol pyrolysis
CN106606887A (en) * 2015-10-22 2017-05-03 中国石油化工股份有限公司 Slurry spray-drying method

Also Published As

Publication number Publication date
DK4892D0 (en) 1992-01-15
DK4892A (en) 1993-07-16
AU3448493A (en) 1993-08-03

Similar Documents

Publication Publication Date Title
US5928405A (en) Method of making metallic powders by aerosol thermolysis
KR100288095B1 (en) Manufacturing method of silver powder by aerosol decomposition
EP0591881B1 (en) Method for making palladium and palladium oxide powders by aerosol decomposition
Messing et al. Ceramic powder synthesis by spray pyrolysis
AU635378B2 (en) Spray conversion process for the production of nanophase composite powders
Milošević et al. Preparation of fine spherical ZnO powders by an ultrasonic spray pyrolysis method
Gurav et al. Aerosol processing of materials
US5081102A (en) Preparation of precursor superconductor metal oxide powders by spray calcination from atomized nitrate solution
CA1233810A (en) Catalyst composition suitable for synthesis of methanol
EP0761349B1 (en) Method for making gold powders by aerosol decomposition
Panatarani et al. Synthesis of single crystalline ZnO nanoparticles by salt-assisted spray pyrolysis
EP0339914A1 (en) Process for producing finely divided spherical metal powders
CN113479926B (en) Method for preparing metal oxide powder by heating and decomposing nitrate in fluidized bed furnace
Yu et al. Preparation of NiFe2O4 powder by spray pyrolysis of nitrate aerosols in NH3
CN104690295A (en) Method for preparing monodispersed ultrafine particles
Gadalla et al. Preparation of fine, hollow, spherical NiFe2O4 powders
JP4516642B2 (en) Spray pyrolysis equipment
WO1993014023A1 (en) Process for the production of a powder of fine particles and a plant for performing said process
EP0562566A1 (en) Method of manufacturing composite ferrite
Gadalla et al. Thermal behaviour of Ni (II) nitrate hydrate and its aerosols
JPH0244766B2 (en)
Lyons et al. Nanophase oxide formation by intraparticle reaction
CN115888584A (en) Spray pyrolysis device system and method for synthesizing metal oxide
EP0235098B1 (en) A process for preparing a lithium aluminate powder in gamma phase
KR101757414B1 (en) Method for continuous preparation of metal oxide particles

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AT AU BB BG BR CA CH CZ DE DK ES FI GB HU JP KP KR LK LU MG MN MW NL NO NZ PL PT RO RU SD SE SK UA US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IE IT LU MC NL PT SE BF BJ CF CG CI CM GA GN ML MR SN TD TG

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
REG Reference to national code

Ref country code: DE

Ref legal event code: 8642

122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: CA