Classifications

• • 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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• 2000
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• 2001
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