EP1322554A1 - Zirconia in fine powder form, zirconia hydroxycarbonate and methods for preparing same - Google Patents

Zirconia in fine powder form, zirconia hydroxycarbonate and methods for preparing same

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Publication number
EP1322554A1
EP1322554A1 EP01951779A EP01951779A EP1322554A1 EP 1322554 A1 EP1322554 A1 EP 1322554A1 EP 01951779 A EP01951779 A EP 01951779A EP 01951779 A EP01951779 A EP 01951779A EP 1322554 A1 EP1322554 A1 EP 1322554A1
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Prior art keywords
zirconia
ppm
zirconia according
hydroxycarbonate
reaction medium
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German (de)
French (fr)
Inventor
Jean-Valéry MARTIN
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Rhodia Electronics and Catalysis
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Rhodia Terres Rares SA
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C01G25/02—Oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/60—Compounds characterised by their crystallite size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/50—Agglomerated particles
    • 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
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • 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
    • 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
    • C01P2006/14—Pore volume
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • 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
    • C01P2006/80—Compositional purity

Definitions

  • the present invention relates to a zirconia in the form of a fine powder, to a zirconium hydroxycarbonate and to their methods of preparation.
  • Zirconia is a material widely used for the preparation of ceramic compositions with high mechanical, electrical or electronic properties. For these applications, it is necessary to have a zirconia which is particularly pure. Now, the known preparation methods make it possible to obtain products of high purity for a particular chemical element but generally not for several elements at the same time. In addition, fine or easily disaggregable products are also sought in order to facilitate their use and to increase their reactivity.
  • the object of the present invention is the development of a zirconia meeting these characteristics.
  • the zirconia of the invention is characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and it is in the form of a powder consisting either of agglomerates with an average size of at most 1.5 ⁇ m which can be agglomerated into aggregates of average size between 0.1 ⁇ m and 0.6 ⁇ m, that is to say aggregates of average size between 0.1 ⁇ m and 0.6 ⁇ m.
  • the invention also relates to a zirconium hydroxycarbonate, characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and in that it is capable of leading, after calcination, to a zirconia having the characteristics given above.
  • the zirconia of the invention is first of all characterized by its purity in chlorine and in sulfur.
  • the impurity contents are mass contents given by mass of the element concerned with respect to the mass of zirconia. It is specified here that the zirconia can naturally contain up to approximately 2% by mass of Hf0 2 . The contents given are therefore relative to the ZrO 2 + HfO 2 set . Furthermore, these contents 1 are determined by analysis of the GDMS type. More specifically, the zirconia has a chlorine content of at most 300 ppm. The chlorine content can more particularly be at most 100 ppm and even more particularly at most 80 ppm.
  • the sulfur content is at most 30 ppm, but it can be less than 10 ppm and even more particularly less than 5 ppm.
  • the zirconia can also have a high purity compared to other chemical elements.
  • the titanium content can be at most 5 ppm, more particularly at most 3 ppm.
  • the sodium content may be at most 10 ppm, in particular at most 5 ppm.
  • the silicon content can be at most 300 ppm, or even at most 200 ppm.
  • the second characteristic of the zirconia of the invention is its finesse. It is in fact in the form of a powder which can consist of agglomerates of average size of at most 1.5 ⁇ m. Generally this size is between 0.8 ⁇ m and 1.5 ⁇ m. This size is determined by a laser granulometry technique (Coulter type). According to a characteristic of the invention ', these agglomerates are disaggregable into aggregates of average size between 0.1 ⁇ m and 0.6 ⁇ m, the limit values being included here and for the whole of the description as regards the sizes . This size can be more particularly between 0.2 ⁇ m and 0.5 ⁇ m.
  • the size of the aggregates is determined here by analysis by scanning microscopy (SEM) or also by a laser granulometry technique (of the Coulter type).
  • disaggregatable it is meant that one can pass from agglomerates to aggregates by only breaking the bonds between the agglomerates thus leaving whole the particles and the crystallites: As example of grinding allowing such a disaggregation one can cite the grinding to air jet yes; deagglomeration by ultrasound.
  • the aggregates may also have a tight particle size.
  • the dispersion index ⁇ / m of the aggregates can be at most 1. It can more particularly be at most 0.8.
  • - dgo is. the diameter of the aggregates for which 90% by volume of the aggregates have a diameter less than dgo;
  • - dio is the diameter of the aggregates for which 10% by volume of the aggregates have a diameter less than d ' o; - CI50 is the average diameter of the aggregates.
  • the aggregates themselves are made up of elementary particles of average size generally between 50nm and 150nm. The size of the elementary particles is determined here by analysis by transmission microscopy (TEM) or by laser granulometry (Coulter type).
  • the elementary particles consist of crystallites whose average size can vary between 30nm and 65nm.
  • the size of the crystallites is determined here by analysis by transmission microscopy (TEM) or by X-ray diffraction.
  • the zirconia can be in the form of a powder which consists directly of the aggregates as defined above. What has been said above on these aggregates, the " elementary and crystalline les particles applies of course to this embodiment.
  • ""- - " " The zirconia of the invention has a specific surface generally of at most 35m 2 / g, more particularly at most 25ffi 2 / g and which may in particular be between 1 m 2 / g and 25m 2 / g.
  • specific surface means the specific surface B: E; T. Determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)".
  • the total pore volume of the zirconia is generally at most 1.5 ml / g and in particular between 0.05 ml / g and 1 ml / g.
  • This porosity is such that at least 40% of the porosity is provided by pores with a diameter between 100 and 200 n, this pore volume and this distribution of pores being measured with a mercury porosimeter.
  • the zirconia of the invention can be present on a pure crystalline phase of monoclinic type.
  • the present invention applies to the case of a pur ⁇ zirc ⁇ ne; that is to say of a " zirconia born having no elements other * ' than the usual impurities and those mentioned above; but it also applies, according to another variant, to a zirconia which comprises at least one element stabilizer selected from calcium, magnesium, CERIU 'm, lanthanum, scandium and yttrium, the proportion of the stabilizing element may vary in particular in a molar ratio stabilizing element / Zr0 2 -. between 1/100 and 20 / 100.
  • the invention also relates to a zirconium hydroxycarbonate which is a precursor of the zirconia which has just been described above.
  • This zirconium hydroxycarbonate is therefore characterized by its purity, that is to say by a chlorine and sulfur content as given above.
  • this hydroxycarbonate when calcined, leads to a zirconia having the characteristics which have been given above.
  • the hydroxycarbonate of the invention is also in the form of a powder consisting of agglomerates of average size of at most 2 ⁇ m, generally between 0.3 ⁇ m and 2 ⁇ m. This size is determined here by a sedimentation technique of the Sedigraph type. It can be estimated that the agglomerates are made up of aggregates of size less than 1 ⁇ m.
  • This process comprises a first step of reacting a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH of the reaction medium constant; a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH of the reaction medium constant; a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH of the reaction medium constant; a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH of the reaction medium constant; a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH
  • controlled pH is meant maintaining the pH of the precipitation medium at a certain value, constant or substantially constant, by adding basic compounds or buffer solutions, to the medium.
  • the pH of the medium will thus vary by at most 0.5 pH unit around the set target value, and more preferably by at most 0.1 pH unit around this value.
  • suitable basic compound there may be mentioned, by way of example, metal hydroxides (NaOH, KOH ,. Ca (OH) 2 , ...-.) Or ammonium hydroxide, or any other basic compound of which species "component will not form any precipitated upon addition into the medium 0 reaction, by combination with a 'i: species also contained in this medium, and allowing uh control-d pH 1 precipitation medium a.
  • preferred basic compound of the invention is ammonia; in- put work advantageously in the form of aqueous solution.
  • the starting reaction medium contains a salt of this stabilizing element.
  • This salt can in particular be a salt of an inorganic acid such as a nitrate. It is also possible to use as starting material a zirconium oxychloride already containing a salt or an oxide of the stabilizing element.
  • the reaction pH value is preferably between 4 and 6. It may be advantageous to conduct the reaction semi-continuously, that is to say by simultaneously introducing the reagents into a reactor containing at the start of the reaction one foot of water tank.
  • the precipitation temperature is not critical but, advantageously, one works at a temperature which can be understood, between 15 ° C. and 50 ° C.
  • the precipitation generally takes place with stirring of the reaction medium.
  • the precipitate obtained can be separated from the medium and reacted by any suitable means, in particular by filtration.
  • the precipitate can be washed, for example, with water. .
  • the zirconium hydroxycarbonate of the invention is thus obtained.
  • the hydroxycarbonate or the dried product are calcined in the air at a temperature which may be between 650 ° C. and 1200 ° C.
  • the calcination temperature is fixed in particular as a function of the specific surface area of the product that one seeks to obtain and of its loss on ignition,
  • the product obtained usually present in the form of a powder consisting of particles which are agglomerates of average size of at most 1.5 ⁇ m. However, if it is desired to obtain a finer particle size, the product can be deagglomerated. A disaggregation in mild conditions by. example a grinding of the micronization type (air jet grinding) is sufficient to deagglomerate the aforementioned particles and to obtain the product in the form of a powder which then consists of aggregates of average size between 0.1 ⁇ m and 0 , 6 .mu.m.
  • the zirconia obtained can be used in particular in the manufacture of materials with dielectric properties such as capacitors. or microwaves, or with piezoelectric properties, -. or in the manufacture of ferrites, oxygen sensors, fuel cells or in the preparation of catalysts or catalyst supports
  • the measurement of the size of the agglomerates or of the aggregates is carried out on a dispersion of the product in an aqueous solution at 0.05% by weight of sodium hexametaphosphate and which has previously undergone passage through the ultra- sounds (probe with 13mm diameter tip, 20KHz, 120W) for 3 minutes
  • the pH is controlled and maintained at a value of 4.8, using 12 mol ammonia. L '1 .
  • the pulp is filtered on a b ⁇ chner type filter in order to recover the solid formed.
  • the hydroxycarbonate thus synthesized is washed thoroughly with demineralized water.
  • the cake is then dried in an oven for 12 hours at 100 ° C, then calcined in an oven at temperature-from 700 ° C by applying a 4 hours step and then cooled in air. Finally, the product is subjected to an air jet grinding. A zirconium oxide is obtained, the characteristics of which are given in Table 1. ' -
  • Agglomerates of 1 ⁇ m can be disaggregated by wet grinding into aggregates whose size is evaluated by SEM at 0.5 ⁇ m.
  • Example 3 repeats the same sequence as Example 1 except that the calcination temperature is 1100 ° C. and with a single grinding with an air jet. The characteristics of the zirconium oxide formed under these conditions are given in Table 1.
  • Example 3 The characteristics of the zirconium oxide formed under these conditions are given in Table 1.
  • Example 2 uses the same sequence as Example 1 except that the calcination temperature is 1050 ° C. and with a single grinding with an air jet.
  • the characteristics of the zirconium oxide formed under these conditions are given in Table 1.

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Abstract

The invention concerns a zirconia in fine powder form, a zirconia hydroxycarbonate and their methods of preparation. The zirconia has a chlorine content of more than 300 ppm and a sulphur content of more than 30 ppm and is in the form of a powder consisting of medium-size agglomerates of at least 1.5 mu m capable of being broken down into medium-size aggregates ranging between 0.1 mu m and 0.6 mu m. The zirconia hydroxycarbonate has the same chlorine and sulphur contents and is capable of resulting, after calcination, in a zirconia having the above-mentioned characteristics. The inventive zirconia can be used in particular in the manufacture of condensers of oxygen probes or for preparing catalysts.

Description

Zircone sous forme de poudre fine, hydroxycarbonate de zirconium et leurs procédés de préparation Zirconia in the form of a fine powder, zirconium hydroxycarbonate and processes for their preparation
La présente invention concerne une zircone sous forme de poudre fine, un hydroxycarbonate de zirconium et leurs procédés de préparation.The present invention relates to a zirconia in the form of a fine powder, to a zirconium hydroxycarbonate and to their methods of preparation.
La zircone est un matériau très utilisé pour la préparation de compositions céramiques à hautes propriétés mécaniques, électriques ou électroniques. Pour ces applications, il est nécessaire de disposer d'une zircone qui soit particulièrement pure. Or, les procédés de préparation connus permettent d'obtenir des produits de pureté élevée pour un élément chimique particulier mais généralement pas pour plusieurs éléments à la fois. En outre, on recherche aussi des produits fins ou facilement désagglomérables de manière à faciliter leur utilisation et à augmenter leur réactivité. L'objet de la présente invention est la mise au point d'une zircone répondant à ces caractéristiques.Zirconia is a material widely used for the preparation of ceramic compositions with high mechanical, electrical or electronic properties. For these applications, it is necessary to have a zirconia which is particularly pure. Now, the known preparation methods make it possible to obtain products of high purity for a particular chemical element but generally not for several elements at the same time. In addition, fine or easily disaggregable products are also sought in order to facilitate their use and to increase their reactivity. The object of the present invention is the development of a zirconia meeting these characteristics.
Dans ce but la zircone de l'invention est caractérisée en ce qu'elle présente une teneur en chlore d'au plus 300ppm et en soufre d'au plus 30ppm et elle se présente sous la forme d'une poudre constituée soit d'agglomérats de taille moyenne d'au plus 1 ,5μm désagglomérables en agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm, soit d'agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm.For this purpose the zirconia of the invention is characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and it is in the form of a powder consisting either of agglomerates with an average size of at most 1.5 μm which can be agglomerated into aggregates of average size between 0.1 μm and 0.6 μm, that is to say aggregates of average size between 0.1 μm and 0.6 μm.
L'invention concerne aussi un hydroxycarbonate de zirconium, caractérisé en ce qu'il présente une teneur en chlore d'au plus 300ppm et en soufre d'au plus 30ppm et en ce qu'il est susceptible de conduire, après calcination, à une zircone présentant les caractéristiques données ci-dessus.The invention also relates to a zirconium hydroxycarbonate, characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and in that it is capable of leading, after calcination, to a zirconia having the characteristics given above.
D'autres caractéristiques, détails et avantages de l'invention apparaîtront encore plus complètement à la lecture de la description qui va -suivre, ainsi que des divers exemples concrets mais non limitatifs destinés à l'illustrer. La zircone de l'invention est tout d'abord caractérisée par sa pureté en chlore et en soufre.Other characteristics, details and advantages of the invention will appear even more completely on reading the description which will follow, as well as the various concrete but nonlimiting examples intended to illustrate it. The zirconia of the invention is first of all characterized by its purity in chlorine and in sulfur.
Pour l'ensemble de la description, les teneurs en impuretés sont des teneurs massiques données en masse de l'élément concerné par rapport à la masse de zircone. On précise ici que la zircone peut contenir naturellement jusqu'à environ 2% en masse d'Hf02. Les teneurs données le sont donc par rapport à l'ensemble ZrO2+HfO2. Par ailleurs, ces teneurs1 sont déterminées par analyse du type GDMS. Plus précisément, la zircone présente une teneur en chlore d'au plus 300ppm. La teneur en chlore peut être plus particulièrement d'au plus 100ppm et encore plus particulièrement d'au plus 80ppm.For the whole of the description, the impurity contents are mass contents given by mass of the element concerned with respect to the mass of zirconia. It is specified here that the zirconia can naturally contain up to approximately 2% by mass of Hf0 2 . The contents given are therefore relative to the ZrO 2 + HfO 2 set . Furthermore, these contents 1 are determined by analysis of the GDMS type. More specifically, the zirconia has a chlorine content of at most 300 ppm. The chlorine content can more particularly be at most 100 ppm and even more particularly at most 80 ppm.
La teneur en soufre est d'au plus 30ppm mais elle peut être inférieure à 10ppm et encore plus particulièrement inférieure à 5ppm.The sulfur content is at most 30 ppm, but it can be less than 10 ppm and even more particularly less than 5 ppm.
Selon des modes de réalisation particuliers de l'invention, la zircone peut aussi présenter une pureté élevée par rapport à d'autres éléments chimiques. Ainsi, la teneur en titane peut être d'au plus 5ppm, plus particulièrement d'au plus 3ppm. Par ailleurs, la teneur en sodium peut être d'au plus 10ppm, notamment d'au plus 5ppm. En outre, la teneur en silicium peut être d'au plus 300ppm, voire d'au plus 200ppm.According to particular embodiments of the invention, the zirconia can also have a high purity compared to other chemical elements. Thus, the titanium content can be at most 5 ppm, more particularly at most 3 ppm. Furthermore, the sodium content may be at most 10 ppm, in particular at most 5 ppm. In addition, the silicon content can be at most 300 ppm, or even at most 200 ppm.
La seconde caractéristique de la zircone de l'invention est sa finesse. Elle se présente en effet sous forme d'une poudre qui peut être constituée d'agglomérats de taille moyenne d'au plus 1 ,5μm. Généralement cette taille est située entre 0,8μm et 1 ,5μm. Cette taille est déterminée par une technique de granulométrie laser (type Coulter). Selon une caractéristique de l'invention', ces agglomérats, sont désagglomérables en agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm, les valeurs limites étant incluses ici et pour l'ensemble de la description en ce qui concerne les tailles. Cette taille peut être comprise plus particulièrement entre 0,2μm et 0,5μm. La taille des agrégats est déterminée ici par analyse par microscopie à balayage (MEB) ou aussi par une technique de granulométrie laser (de type Coulter). Par "désagglomérables", on entend que l'on peut passer des agglomérats aux agrégats en ne cassant que les liaisons entre les agglomérats en laissant ainsi entiers les particules et les cristallites: Comme exemple de broyage permettant une telle désagglomération on peut citer le broyage à jet d'air oui; la désagglomération par ultra-sons.The second characteristic of the zirconia of the invention is its finesse. It is in fact in the form of a powder which can consist of agglomerates of average size of at most 1.5 μm. Generally this size is between 0.8μm and 1.5μm. This size is determined by a laser granulometry technique (Coulter type). According to a characteristic of the invention ', these agglomerates are disaggregable into aggregates of average size between 0.1 μm and 0.6 μm, the limit values being included here and for the whole of the description as regards the sizes . This size can be more particularly between 0.2 μm and 0.5 μm. The size of the aggregates is determined here by analysis by scanning microscopy (SEM) or also by a laser granulometry technique (of the Coulter type). By "disaggregatable", it is meant that one can pass from agglomerates to aggregates by only breaking the bonds between the agglomerates thus leaving whole the particles and the crystallites: As example of grinding allowing such a disaggregation one can cite the grinding to air jet yes; deagglomeration by ultrasound.
Les agrégats peuvent présenter en outre une granulométrie resserrée. Ainsi, l'indice de dispersion σ/m des agrégats peut être d'au plus 1. Il peut être plus particulièrement d'au plus 0,8.The aggregates may also have a tight particle size. Thus, the dispersion index σ / m of the aggregates can be at most 1. It can more particularly be at most 0.8.
On entend par indice de-dispersion le rapport : σ/m = (d9o-d 0)/2d5o dans lequel :By dispersion index is meant the ratio: σ / m = (d 9 od 0 ) / 2d5o in which:
- dgo est. le diamètre des agrégats pour lequel 90% en volume des agrégats ont un diamètre inférieur à dgo;- dgo is. the diameter of the aggregates for which 90% by volume of the aggregates have a diameter less than dgo;
- dio est le diamètre des agrégats pour lequel 10% en volume des agrégats ont un diamètre inférieur à d'^o; - CI50 est le diamètre moyen des agrégats. Les agrégats sont eux-mêmes constitués de particules élémentaires de taille moyenne comprise généralement entre 50nm et 150nm. La taille des particules élémentaires est déterminée ici par analyse par microscopie à transmission (MET) ou par granulométrie laser (type Coulter).- dio is the diameter of the aggregates for which 10% by volume of the aggregates have a diameter less than d ' o; - CI50 is the average diameter of the aggregates. The aggregates themselves are made up of elementary particles of average size generally between 50nm and 150nm. The size of the elementary particles is determined here by analysis by transmission microscopy (TEM) or by laser granulometry (Coulter type).
Les particules élémentaires sont constituées de cristallites dont la taille moyenne peut varier entre 30nm et 65nm. La taille des cristallites est déterminée ici par analyse par microscopie à transmission (MET) ou par diffraction RX. Selon un autre mode de réalisation de l'invention, la zircone peut se présenter sous forme d'une poudré qui est constituée directement des agrégats tels que définis plus haut. Ce qui a été dit précédemment sur ces agrégats, les particules "élémentaires et lés cristallites s'applique bien entendu à ce mode de réalisation. ' " ' - '" La zircone de l'invention possède une surface spécifique généralement d'au plus 35m2/g, plus particulièrement d'au plus 25ffi2/g et 'qui peut être notamment comprise entre 1 m2/g et 25m2/g. On entend par surface spécifique, la surface spécifique B:E;T. déterminée par adsorption d'azote conformément à la norme ASTM D 3663-78 établie à partir de la méthode BRUNAUER - EMMETT- TELLER décrite dans le périodique "The Journal of the American Chemical Society, 60, 309 (1938)".The elementary particles consist of crystallites whose average size can vary between 30nm and 65nm. The size of the crystallites is determined here by analysis by transmission microscopy (TEM) or by X-ray diffraction. According to another embodiment of the invention, the zirconia can be in the form of a powder which consists directly of the aggregates as defined above. What has been said above on these aggregates, the " elementary and crystalline les particles applies of course to this embodiment. ""- - " "The zirconia of the invention has a specific surface generally of at most 35m 2 / g, more particularly at most 25ffi 2 / g and which may in particular be between 1 m 2 / g and 25m 2 / g. The term "specific surface" means the specific surface B: E; T. Determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)".
Pour les valeurs de surface spécifique données ci-dessus, le volume poreux total de la zircone est généralement d'au plus .1 ,5ml/g et notamment compris entre 0,05ml/g et 1 ml/g. Cette porosité est telle qu'au moins 40% de la porosité sont apportés par des pores de diamètre compris entre 100 et 200 n , ce volume poreux et cette distribution des pores étant mesurés au porosimètre à mercure.For the specific surface area values given above, the total pore volume of the zirconia is generally at most 1.5 ml / g and in particular between 0.05 ml / g and 1 ml / g. This porosity is such that at least 40% of the porosity is provided by pores with a diameter between 100 and 200 n, this pore volume and this distribution of pores being measured with a mercury porosimeter.
: La zircone de l'invention peut se présenter sόus une phase cristalline pure de- type monoclinique. La présente invention s'applique au cas d'une zircύne purβ; c'est à dire d'une" zircone né comportant pas d'éléments autres* ' que les impuretés habituelles et celles mentionnées plus haut; mais elle s'applique aussi, selon uhe autre variante, à une zircone qui comprend au moins un élément stabilisant choisi parmi le calcium, le magnésium, le cériu'm, le lanthane, le scandium et l'yttrium. La proportion de cet élément stabilisant peut varier notamment dans un rapport molaire élément stabilisant/Zr02- compris entre 1/100 et 20/100. L'invention concerne aussi un hydroxycarbonate de zirconium qui est un précurseur de la zircone qui vient d'être décrite ci-dessus. Cet hydroxycarbonate de zirconium est donc caractérisé par sa pureté, c'est à dire par une teneur en chlore et en soufre telle que donnée précédemment. En 5 outre, cet hydroxycarbonate, lorsqu'il est calciné, conduit à une zircone présentant les caractéristiques qui ont été données ci-dessus.: The zirconia of the invention can be present on a pure crystalline phase of monoclinic type. The present invention applies to the case of a purβ zircύne; that is to say of a " zirconia born having no elements other * ' than the usual impurities and those mentioned above; but it also applies, according to another variant, to a zirconia which comprises at least one element stabilizer selected from calcium, magnesium, CERIU 'm, lanthanum, scandium and yttrium, the proportion of the stabilizing element may vary in particular in a molar ratio stabilizing element / Zr0 2 -. between 1/100 and 20 / 100. The invention also relates to a zirconium hydroxycarbonate which is a precursor of the zirconia which has just been described above. This zirconium hydroxycarbonate is therefore characterized by its purity, that is to say by a chlorine and sulfur content as given above. In addition, this hydroxycarbonate, when calcined, leads to a zirconia having the characteristics which have been given above.
L'hydroxycarbonate de l'invention se présente aussi sous forme d'une poudre constituée d'agglomérats de taille moyenne d'au plus 2μm, généralement entre 0,3μm et 2μm. Cette taille est déterminée ici par une 0 technique de sédimentation du type Sédigraph. On peut estimer que les agglomérats sont constitués d'agrégats de taille inférieure à 1 μm.The hydroxycarbonate of the invention is also in the form of a powder consisting of agglomerates of average size of at most 2 μm, generally between 0.3 μm and 2 μm. This size is determined here by a sedimentation technique of the Sedigraph type. It can be estimated that the agglomerates are made up of aggregates of size less than 1 μm.
Le procédé de préparation de l'hydroxycarbonate de zirconium et de la zircone de l'invention va maintenant être décritThe process for preparing the zirconium hydroxycarbonate and the zirconia of the invention will now be described
Ce procédé comprend une première étape de réaction d'un oxychlorure 5 de zirconium (ZrOGI2) et de carbonate ou bicarbonate d'ammonium, d'alcalin ou d'alcalino^-terreux, en maintenant constant le pH du milieu réactionnel; uneThis process comprises a first step of reacting a zirconium oxychloride (ZrOGI 2 ) and ammonium, alkali or alkaline-earth carbonate or bicarbonate, keeping the pH of the reaction medium constant; a
:- '- étape de séparation du précipité résultant et une étape de calcination de ce précipité dans le cas de la préparation de la zircone. : - ' - step of separation of the resulting precipitate and a step of calcination of this precipitate in the case of the preparation of zirconia.
Une des caractéristiques du procédé de l'invention réside dans le fait que 0 la réaction entre l'oxychlorure et; le carbonate ou le bicarbonate a lieu à pH constant ou contrôlé. Par "pH contrôlé", on entend un maintien du pH du milieu de précipitation à une certaine valeur, constante ou sensiblement constante, par addition de composés basiques ou de solutions tampons, dans le milieu.One of the characteristics of the process of the invention resides in the fact that the reaction between the oxychloride and ; carbonate or bicarbonate takes place at constant or controlled pH. By "controlled pH" is meant maintaining the pH of the precipitation medium at a certain value, constant or substantially constant, by adding basic compounds or buffer solutions, to the medium.
Le pH du milieu variera ainsi d'au plus 0,5 unité de pH autour de la valeur de 5 consigne fixée, et de préférence encore d'au plus 0,1 unité de pH autour de cette valeur. Comme composé basique convenable, on peut citer, à titre d'exemples, les hydroxydes métalliques (NaOH, KOH,. Ca(OH)2,...-.) ou l'hydroxyde d'ammonium, ou tout autre composé basique dont les espèces" le constituant ne formeront aucun' précipité lors de leur addition dans le milieu 0 réactionnel, par combinaison avec une' desi:espèces par ailleurs contenues dans ce milieu, et permettant uh contrôle-d pH du1 milieu de précipitation. Un composé basique préféré de l'invention est l'ammoniac,; mis en- œuvre avantageusement sous forme de solution aqueuse.The pH of the medium will thus vary by at most 0.5 pH unit around the set target value, and more preferably by at most 0.1 pH unit around this value. As suitable basic compound, there may be mentioned, by way of example, metal hydroxides (NaOH, KOH ,. Ca (OH) 2 , ...-.) Or ammonium hydroxide, or any other basic compound of which species "component will not form any precipitated upon addition into the medium 0 reaction, by combination with a 'i: species also contained in this medium, and allowing uh control-d pH 1 precipitation medium a. preferred basic compound of the invention is ammonia; in- put work advantageously in the form of aqueous solution.
On utilisera de préférence le carbonate ou le bicarbonate d'ammonium 5 pour la 'préparation des produits à haute pureté en sodium.We preferably use the carbonate or ammonium bicarbonate 5 for the 'preparation of high purity sodium products.
Dans le cas de la^ préparation d'une zircone contenant- un élément stabilisant, le milieu réactionnel de départ contient un sel de cet élément stabilisant. Ce sel peut être notamment un sel d'u acide inorganique comme un nitrate. On peut aussi utiliser comme produit de départ un oxychlorure de zirconium contenant déjà un sel-ou un oxyde de l'élément stabilisant.In the case of the preparation of a zirconia containing a stabilizing element, the starting reaction medium contains a salt of this stabilizing element. This salt can in particular be a salt of an inorganic acid such as a nitrate. It is also possible to use as starting material a zirconium oxychloride already containing a salt or an oxide of the stabilizing element.
La valeur du pH de réaction est de préférence comprise entre 4 et 6. Il peut être avantageux de conduire la réaction en semi-continu, c'est à dire en introduisant simultanément les réactifs dans un réacteur contenant au démarrage de la réaction un pieds de cuve d'eau.The reaction pH value is preferably between 4 and 6. It may be advantageous to conduct the reaction semi-continuously, that is to say by simultaneously introducing the reagents into a reactor containing at the start of the reaction one foot of water tank.
La température de précipitation n'est pas critique mais, avantageusement, on travaille à une température qulpeut être comprise,e.ntre 15°C et 50°C. La précipitation a lieu généralement sous agitation du milieu de réaction.The precipitation temperature is not critical but, advantageously, one works at a temperature which can be understood, between 15 ° C. and 50 ° C. The precipitation generally takes place with stirring of the reaction medium.
Le précipité obtenu peut être séparé du milieu, réactionnel par tout moyen convenable, notamment par.filtration. Le précipité peut être lavé par exemple avec de l'eau. .The precipitate obtained can be separated from the medium and reacted by any suitable means, in particular by filtration. The precipitate can be washed, for example, with water. .
. A l'issue de l'étape de séparation et éventuellement de lavage du précipité on obtient ainsi l'hydroxycarbonate de zirconium de l'invention.. At the end of the separation and optionally washing of the precipitate, the zirconium hydroxycarbonate of the invention is thus obtained.
Pour obtenir la zircone de l'invention il y a lieu de procédera une étape de calcination..de l'hydroxycarbonate.To obtain the zirconia of the invention, a calcination step of the hydroxycarbonate will have to be carried out.
Préalablement à la calcination, il est possible de procéder à un séchage du produit à une température d'environ 100°C pendant 2 à 12 heures. Cette étape de. séchage permet d'obtenir une zircone, à .surface spécifique plus élevée. Il est aussi possible de procéder à un mûrissement de l'hydroxycarbonate par remise en suspension de celui-ci dans un milieu alcalin à une température par exemple d'environ 100°C pendant 2 à 4 heures..Before calcination, it is possible to dry the product at a temperature of around 100 ° C for 2 to 12 hours. This stage of. drying makes it possible to obtain a zirconia, with a higher specific surface. It is also possible to ripen the hydroxycarbonate by resuspending it in an alkaline medium at a temperature for example of around 100 ° C. for 2 to 4 hours.
L'hydroxycarbonate ou le produit séché sont calcinés -sous air à une température qui peut être comprise entre 650°C et 1200°C. La température de calcination est fixée notamment en fonction de la surface spécifique du produit que l'on cherche à obtenir et de sa perte au feu,The hydroxycarbonate or the dried product are calcined in the air at a temperature which may be between 650 ° C. and 1200 ° C. The calcination temperature is fixed in particular as a function of the specific surface area of the product that one seeks to obtain and of its loss on ignition,
A l'issue de. la calcination, le produit obtenu se. présente habituellement sous la forme d'une poudre constituée de particules qui sont des agglomérats de taille moyenne d'au plus 1 ,5μm. Cependant,' si on souhaite obtenir une granulométrie plus fine, le produit peut être -désaggloméré. Une désagglomération dans des conditions douces par. exemple un broyage du type micronisation (broyage jet d'air), est suffisant pour désagglomérer lés particules précitées et pour obtenir le produit sous forme d'une poudre qui est alors constituée d'agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm.After. calcination, the product obtained. usually present in the form of a powder consisting of particles which are agglomerates of average size of at most 1.5 μm. However, if it is desired to obtain a finer particle size, the product can be deagglomerated. A disaggregation in mild conditions by. example a grinding of the micronization type (air jet grinding) is sufficient to deagglomerate the aforementioned particles and to obtain the product in the form of a powder which then consists of aggregates of average size between 0.1 μm and 0 , 6 .mu.m.
La zircone obtenue peut être utilisée notamment dans la fabrication de matériaux à propriétés diélectriques tels que les condensateurs. ou les fitres à micron-ondes, ou à propriétés piézoélectriques,-. ou dans la fabrication de ferrites, de sondes à oxygène, de piles à combustibles ou encore dans la préparation de catalyseurs ou de supports de catalyseursThe zirconia obtained can be used in particular in the manufacture of materials with dielectric properties such as capacitors. or microwaves, or with piezoelectric properties, -. or in the manufacture of ferrites, oxygen sensors, fuel cells or in the preparation of catalysts or catalyst supports
Des exemples vont maintenant être donnés.Examples will now be given.
Dans ces exemples, la mesure de la taille des agglomérats ou des aggrégats est effectuée sur une dispersion du produit dans une solution aqueuse à 0,05% en poids d'hexamétaphosphate de sodium et qui a préalablement subi un passage à la sonde à ultra-sons (sonde avec embout de 13mm de diamètre, 20KHz, 120W) pendant 3 minutesIn these examples, the measurement of the size of the agglomerates or of the aggregates is carried out on a dispersion of the product in an aqueous solution at 0.05% by weight of sodium hexametaphosphate and which has previously undergone passage through the ultra- sounds (probe with 13mm diameter tip, 20KHz, 120W) for 3 minutes
Exemple 1Example 1
Réactifs : ZrOCI2 : 100 g. L"1 Ammoniaque 12 mol.L"1 ' " HC03NH4 : 1.3 mol.L-1 Eau déminéraliséeReagents: ZrOCI 2 : 100 g. L "1 Ammonia 12 mol.L " 1 '" HC0 3 NH 4 : 1.3 mol.L- 1 Demineralized water
On mélange de façon semi-continue dans un réacteur d'un volume de 1 litre, contenant 268 ml d'eau déminéralisée, 450 ml d'une solution de ZrOCI2 àIs mixed semi-continuously in a reactor with a volume of 1 liter, containing 268 ml of demineralized water, 450 ml of a solution of ZrOCI 2 to
100 g/L (Zr02) avec 282 ml d'une solution de bicarbonate d'ammonium durant une heure. Dans ces conditions, le ratio molaire CO3'7Zr est égal à l'unité. Une agitation est assurée au moyen d'une hélice 4 pales tournant à 500 min-1.100 g / L (Zr0 2 ) with 282 ml of an ammonium bicarbonate solution for one hour. Under these conditions, the CO3 ' 7Zr molar ratio is equal to unity. Stirring is ensured by means of a 4-blade propeller rotating at 500 min -1 .
Durant l'opération, le pH est contrôlé et maintenue à une valeur de 4.8, à l'aide d'ammoniaque à 12 mol.L'1. La précipitation terminée, la pulpe est filtrée sur un filtre de type bϋchner afin de récupérer le solide formé. L'hydroxycarbonate ainsi synthétisé est lavé abondamment avec de l'eau déminéralisée. Le gâteau est ensuite séché dans une étuve durant 12h à 100°C, puis calciné dans un four à la température- dé 700°C en appliquant un pallier de 4h puis refroidi à l'air. On fait enfin subir au produit un broyage au jet d'air. On obtient un oxyde de zirconium dont les caractéristiques sont reportées dans le tableau 1. ' -During the operation, the pH is controlled and maintained at a value of 4.8, using 12 mol ammonia. L '1 . When the precipitation is complete, the pulp is filtered on a bϋchner type filter in order to recover the solid formed. The hydroxycarbonate thus synthesized is washed thoroughly with demineralized water. The cake is then dried in an oven for 12 hours at 100 ° C, then calcined in an oven at temperature-from 700 ° C by applying a 4 hours step and then cooled in air. Finally, the product is subjected to an air jet grinding. A zirconium oxide is obtained, the characteristics of which are given in Table 1. ' -
Les agglomérats de 1 μm peuvent être désagglomérés par broyage humide en agrégats dont la taille est évaluée par MEB à 0,5μm.Agglomerates of 1 μm can be disaggregated by wet grinding into aggregates whose size is evaluated by SEM at 0.5 μm.
Exemple 2Example 2
L'exemple reprend le même enchaînement que l'exemple 1 à ceci près que la température de calcination est de 1100°C et avec un seul broyage au jet d'air. Les caractéristiques de l'oxyde de zirconium formé dans ces conditions sont reportées dans le tableau 1. Exemple 3The example repeats the same sequence as Example 1 except that the calcination temperature is 1100 ° C. and with a single grinding with an air jet. The characteristics of the zirconium oxide formed under these conditions are given in Table 1. Example 3
L'exemple reprend le même enchaînement que l'exemple 1 à ceci près que la température de calcination est de 1050°C et avec un seul broyage au jet d'air. Les caractéristiques de l'oxyde de zirconium formé dans ces conditions sont reportées dans le tableau 1.The example uses the same sequence as Example 1 except that the calcination temperature is 1050 ° C. and with a single grinding with an air jet. The characteristics of the zirconium oxide formed under these conditions are given in Table 1.
Tableau 1Table 1

Claims

REVENDICATIONS
1- Zircone caractérisée en ce qu'elle présente une teneur en chlore d'au plus 300ppm et en soufre d'au plus 30ppm et en ce qu'elle se présente sous la forme d'une poudre constituée soit d'agglomérats de taille moyenne d'au plus 1 ,5μm désagglomérables en agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm, soit d'agrégats de taille moyenne comprise entre 0,1 μm et 0,6μm.1- Zirconia characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and in that it is in the form of a powder consisting of either medium-sized agglomerates not more than 1.5 μm disaggregable into medium-sized aggregates of between 0.1 μm and 0.6 μm, that is to say of medium-sized aggregates of between 0.1 μm and 0.6 μm.
2- Zircone selon la revendication 1 , caractérisée en ce qu'elle présente une teneur en titane d'au plus 5ppm.2- Zirconia according to claim 1, characterized in that it has a titanium content of at most 5 ppm.
3- Zircone selon la revendication 1 ou 2, caractérisée en ce qu'elle présente une teneur en sodium d'au plus 10ppm.3- Zirconia according to claim 1 or 2, characterized in that it has a sodium content of at most 10 ppm.
4- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle présente une teneur en silicium d'au plus 300ppm.4- Zirconia according to one of the preceding claims, characterized in that it has a silicon content of at most 300 ppm.
5- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle présente une teneur en chlore d'au plus 100ppm, plus particulièrement d'au plus 80ppm.5- Zirconia according to one of the preceding claims, characterized in that it has a chlorine content of at most 100 ppm, more particularly at most 80 ppm.
6- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle présente une teneur en soufre d'au plus 10ppm, plus particulièrement d'au plus 5ppm.6- Zirconia according to one of the preceding claims, characterized in that it has a sulfur content of at most 10 ppm, more particularly at most 5 ppm.
7- Zircone selon l'une des revendications précédentes, caractérisée en ce que les agrégats sont constitués de particules de taille moyenne comprise entre 50nhι et 150nm.7- Zirconia according to one of the preceding claims, characterized in that the aggregates consist of particles of average size between 50nhι and 150nm.
8- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle présente une surface spécifique d'au plus 35m2/g, plus particulièrement d'au plus 25m2/g.8- Zirconia according to one of the preceding claims, characterized in that it has a specific surface of at most 35m 2 / g, more particularly at most 25m 2 / g.
9- Zircone selon la revendication 8, caractérisée en ce qu'elle présente un volume poreux total d'au plus 1 ,5ml/g et en ce qu'au moins 40% de sa porosité est apporté par des pores de diamètre compris entre 100 et 200 nm. 10- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle se présente sous une phase cristalline pure monoclinique.9- Zirconia according to claim 8, characterized in that it has a total pore volume of at most 1.5 ml / g and in that at least 40% of its porosity is provided by pores with a diameter between 100 and 200 nm. 10- Zirconia according to one of the preceding claims, characterized in that it occurs under a pure monoclinic crystalline phase.
11- Zircone selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend au moins un élément stabilisant choisi parmi le calcium, le magnésium, le cérium, le lanthane, le scandium et l'yttrium.11- Zirconia according to one of the preceding claims, characterized in that it comprises at least one stabilizing element chosen from calcium, magnesium, cerium, lanthanum, scandium and yttrium.
12- Hydroxycarbonate de zirconium, caractérisé en ce qu'il présente une teneur en chlore d'au plus 300ppm et en soufre d'au plus 30ppm et en ce qu'il est susceptible de conduire, après calcination, à une zircone selon l'une dès revendications précédentes.12- Zirconium hydroxycarbonate, characterized in that it has a chlorine content of at most 300 ppm and sulfur of at most 30 ppm and in that it is capable of leading, after calcination, to a zirconia according to one from previous claims.
13- Procédé de préparation d'une zircone selon l'une dès revendications 1 à 10, caractérisé en ce qu'il comprend les étapes suivantes : '13- A method of preparing a zirconia according to one from claims 1 to 10, characterized in that it comprises the following steps: '
- on fait réagir un oxychlorure de zirconium et du carbonate ou bicarbonate d'ammonium, d'alcalin ou d'alcalino-terreux en maintenant constant le pH du milieù-réactionnel; - •, - .- . - . - A zirconium oxychloride and ammonium, alkali or alkaline earth carbonate or bicarbonate are reacted while keeping the pH of the reaction medium constant; - • , - . - . - .
- on: sépare le précipité résultant; ' - on calcine ce précipité.- On : separates the resulting precipitate; ' - this precipitate is calcined.
14- Procédé de préparation d'une zircone selon la revendication 11 , caractérisé en ce qu'il comprend les étapes suivantes :14- A method of preparing a zirconia according to claim 11, characterized in that it comprises the following steps:
- on fait réagir un oxychlorure de zirconium contenant un sel ou un oxyde de l'élément stabilisant, et du carbonate ou bicarbonate d'ammonium, d'alcalin ou d'alcalino-tërreux en maintenant constant le pH du miiieu réactionnel;' - a zirconium oxychloride containing a salt or an oxide of the stabilizing element is reacted, and ammonium, alkali or alkaline-earth carbonate or bicarbonate while keeping the pH of the reaction medium constant; '
- on sépare le précipité résultant; • '--'- ' - The resulting precipitate is separated; • ' --'- '
- on calcine ce précipité.- This precipitate is calcined.
15- - Procédé de préparation d'une zircone selon la revendication 11 , caractérisé en ce qu'il comprend les étapes suivantes :15- - Process for preparing a zirconia according to claim 11, characterized in that it comprises the following steps:
- on fait réagir un oxychlorure de zirconium, et du carbonate ou bicarbonate d'ammonium, d'alcalin ou d'alcalino-terreux en maintenant constant le pH du milieu réactionnel, le milieu réactionnel contenant en outre un sel de l'élément stabilisant;- A zirconium oxychloride and ammonium, alkali or alkaline earth carbonate or bicarbonate are reacted while keeping the pH of the reaction medium constant, the reaction medium also containing a salt of the stabilizing element;
- on sépare le précipité résultant;- The resulting precipitate is separated;
- on calcine ce précipité. 16-. Procédé de préparation d'un hydroxycarbonate de zirconium selon la revendication 12, caractérisé eh ce qu'il comprend les étapes suivantes :- This precipitate is calcined. 16-. Process for the preparation of a zirconium hydroxycarbonate according to claim 12, characterized in that it comprises the following steps:
- on fait réagir un oxychlorure de zirconium et du carbonate ou bicarbonate d'ammonium, d'alcalin ou d'alcalino-terreux en maintenant constant le pH du milieu réactionnel;- A zirconium oxychloride and ammonium, alkali or alkaline earth carbonate or bicarbonate are reacted while keeping the pH of the reaction medium constant;
- on sépare le précipité résultant.- The resulting precipitate is separated.
17- Procédé, selon l'une des revendications 13 à 16, caractérisé en ce qu'on maintient le pH du milieu réactionnel à une valeur comprise entre 4 et 6. 17- Method according to one of claims 13 to 16, characterized in that the pH of the reaction medium is maintained at a value between 4 and 6.
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