WO2005051846A2

WO2005051846A2 - Method for producing a nanostructured submicronic powder of sesquioxide, oxohydroxide, hydroxide or rare-earth mixed oxide

Info

Publication number: WO2005051846A2
Application number: PCT/FR2004/002996
Authority: WO
Inventors: Marco Flores-Gonzalez; Cédric LOUIS; Stéphane Roux; Kheirreddine Lebbou; Olivier Tillement; Pascal Perriat
Original assignee: Universite Claude Bernard Lyon I; Centre National De La Recherche Scientifique (C.N.R.S.); Institut National Des Sciences Appliquees De Lyon
Priority date: 2003-11-24
Filing date: 2004-11-24
Publication date: 2005-06-09
Also published as: WO2005051846A3; FR2862631B1; EP1689679A2; FR2862631A1

Abstract

The invention relates to a method for producing a single-phase or multiphase powder, optionally in the form of a colloidal suspension of sesquioxide, oxohydroxide, hydroxide or pure rare-earth mixed oxide, while in a mixture or doped, the rare-earth portion representing more than 50 % of the mass of the obtained powder. The invention also relates to essentially spherical powder particles having a mean diameter ranging between 20 and 800 nm and being nanostructured of Ln2O3 and a colloidal suspension.

Description

The present invention relates to the technical field of nanostructured submicron materials. More specifically, the subject of the invention is a process for the preparation of a powder, optionally in the form of a colloidal suspension, of sesquioxide, oxohydroxide, hydroxide or mixed oxide of rare earth and also of submicron particles of Ln ₂ θ ₃ where Ln represents a rare earth, essentially spherical and nanostructured, capable of being obtained by the process according to the invention. Nanostructured submicron powders constitute a new class of materials which have two advantages compared to conventional powders currently developed:

- Their physical properties, in particular optical and magnetic, differ from those of the same materials in the massive state. This is largely explained by surface effects (for spherical particles of one nanometer, 50% of the total number of atoms can be on the surface) and by confinement effects,

- their morphology which is spherical, their controlled submicron size and their dispersability make it possible to envisage new applications and the use of new deposition and shaping processes. Much research has already been done to synthesize nanostructured submicron mineral powders. Among them, conventional ceramic approaches, using solid-state chemistry at high temperature and controlled decompositions in particular, have often proved unsuitable for obtaining monodisperse submicronic nanoparticles, also making it difficult to obtain controlled nanometric structuring. Physical or combined approaches, of the mechanosynthesis type, or vacuum evaporation / condensation, or laser ablation or spray-pyrolysis are, for their part, often too expensive to be industrialized. Finally, the so-called “soft chemistry” approaches of the sol-gel or precipitation in organic medium type have been widely explored over the past twenty years and many original results have been obtained for the controlled synthesis of submicronic compounds. In the field of sesquioxides, oxohydroxides, hydroxides or mixed oxides of rare earth or containing a high proportion of rare earths, the techniques of synthesis by soft chemistry of submicronic powders are still quite limited, in particular for oxides. Initially proposed almost 25 years ago for the development of micrometric metallic powders, the so-called “polyol” method has been used in recent years to develop submicron and nanometric metallic particles and more recently different types of oxides. This “polyol” method consists in direct precipitation of a solid within a polyalcohol brought to a temperature generally between 150 ° C. and 250 ° C. A metal precursor is dissolved beforehand in the polyol (for example diethylene glycol), then after optional addition of a reagent, the solution is brought to a temperature above 150 ° C. The polyol acts as a stabilizer, limits the growth of particles and minimizes the agglomeration of powders. With this method, various submicron oxide powders have already been synthesized, such as CeO ₂ , LaPO ₄ doped Ce ³⁺ (C. Feldmann, Advanced Materials, 13, (2003), 101), and Y ₂ O ₃ doped Eu ³⁺ (C. Feldmann, J. Merikhi, Journal of Materials Science 38 (2003) 1731-1735). No powder of lanthanide-based sesquioxide particles of an average size between 20 and 800 nm has so far been obtained directly by this method, that is to say without the need for subsequent heat treatment, often above 500 ° C, to form the oxide. Only precipitates of the yttrium hydroxide or oxycarbonate types (C. Feldmann, J. Merikhi, Journal of Materials Science 38 (2003) 1731-1735) or of the acetate or organometallic yttrium type (C Feldmann, Advanced Materials, 13, (2003), 101). Obtaining submicron oxide powders is then only possible after a high heat treatment of the powder collected, above 600 ° C. than oxide colloids less than 5 nm in size. In this case, the colloidal solution is stable and the recovery of calibrated submicron powders is not possible. Such powders have been obtained by using chlorides precursors in the polyol route. Nanoparticles ultrafine spheres (of the order of 5 nm) of rare earth oxides (YO ₃ , Eu ₂ O ₃ , Gd O ₃ ) were thus obtained (R. Bazzi, MA Flores-Gonzalez, C. Louis, K. Lebbou, C. Dujardin, A. Brenier, W. Zhang, O. So, E. Bernstein and P. Perriat, Journal of Luminescence, 102-103, (2003), 445-450). In this context, the present invention aims to provide a new preparation process making it possible to obtain single-phase or polyphase, submicronic, nanostructured powders of sesquioxide, oxohydroxide, hydroxide or mixed oxide of selected rare earth and this with a control of their particle size with an average diameter between 20 and 800 nm. This process must be easily industrializable and must therefore use soft chemistry, with synthesis temperatures below 300 ° C. The process of the invention is a process for preparing a single-phase or multi-phase powder, optionally in the form of a colloidal suspension, sesquioxide, oxohydroxide or rare earth hydroxide chosen from the list Y, La, Pr, Nd, Sm, Eu , Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, or a mixed oxide of formula Ln _x A _2-x ( O) _y or Ln _x A _2-x O _v (OH) _z , with x in the range from 0 to 2, including in the range from 3 to 4, v in the range from 0 to 4 and z included in the range from 0 to 8-2v, Ln a rare earth as defined above and A a transition metal cation or B ³⁺ , Al ³⁺ , Si ⁴⁺ , P ⁵⁺ or Bi ³⁺ , the rare earth part representing more than 50% of the mass of the powder obtained, which comprises the following successive stages: a) dissolving precursors of the rare earth and possibly of A defined above, at least 50% in mass of this s precursors being rare earth nitrates defined above, in a solvent or mixture of polar organic solvents whose boiling point at atmospheric pressure is greater than 200 ° C., at a rate of 10 to 500 g of precursors per liter of solvent, in the presence of the amount of water at least necessary for the formation of the desired sesquioxide, oxohydroxide, hydroxide or mixed oxide, b) heating the solution obtained in step a) at a temperature above 170 ° C and below the boiling point of the solvent or mixture of organic solvents polar in the pressure conditions used for heating, preferably at a temperature between 170 and 250 ° C and preferably between 175 and 185 ° C, for a time sufficient to obtain the precipitation of a powder of sesquioxide, oxohydroxide, desired hydroxide or mixed oxide, in the form of nanostructured, submicron particles with an average diameter of between 20 and 800 nm, c) optionally separation of the powder obtained from the organic polar solvent, which can be followed by drying, d) optionally redispersion of the powder obtained in step c) in an appropriate solvent. The originality of the process according to the invention is based in particular on the use of a rare earth nitrate as a precursor. Until now, only metal precursors of the organometallic salt type (acetates, alcoholates), of the chlorides type or even a mixture of these two types of precursors have been used as organic solvent. In the case of lanthanides, the high reactivity of the cations towards basic organic compounds and the sensitivity to the precipitation of hydroxides or carbonates prevented any synthesis of pure rare earth oxides from organometallic salts. As for the chloride pathway, even if the Cl ^" anions constitute an advantage for a controlled synthesis of rare earth nanoparticles, it requires the addition of an external base, often limiting the yield and the efficiency of the reaction. In addition it leads to stable colloids without the possibility of recovering the powder. The use of metallic nitrate as a precursor has a double advantage, it allows a very strong solubilization of the rare earth cations within the initial polar organic solvent and the very weakly basic nitrate (pKa of the order of -1.5), makes it possible to control and adapt much more finely the precipitation of the desired rare earth derivative, without systematically requiring the addition of external base or other reagents Coupled with the controlled addition of a water-base type reagent (inorganic or organic), the use of nitrate makes it possible to directly obtain submicronic powders d sesquioxides, oxohydroxides of hydroxides or mixed oxides of rare earth. The subject of the invention is also a powder of Ln ₂ O particles and their colloidal suspensions, capable of being obtained according to the method of the invention, where Ln is a rare earth chosen from the list Y, La, Pr, Nd , Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, characterized in that these particles are essentially spherical with a average diameter between 20 and 800 nm, nanostructured and are composed of an agglomerate of crystallites of average size between 2 and 10 nm. As a preamble to the more precise description of the invention, the definitions of the terms used in the rest of the description are given below. The lanthanides are Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. The mean diameter or median diameter, named d ₅ o, is defined by the diameter below from which we find 50% of the mass of the particles and determined by the laser scattering technique (photon correlation spectroscopy). A powder is said to be isodisperse or monodisperse in particle diameter if the particle size dispersion within the powder is tightened. More precisely, a colloidal dispersion is said to be isodisperse, if the size distribution measured by laser scattering is very tight, that is to say, for example, that more than 90% of the particles have a diameter comprised between the mean diameter of the dispersion plus or minus 20% of the d ₅₀ . The tighter the distribution in diameter, the more the system is called isodisperse or monodisperse. A sesquioxide Ln O ₃ is said to be doped with a rare earth Ln ′ if Ln ′ represents less than 25% of the metal cations. A particle is said to be nanostractured when it is composed of an aggregate of crystallites of nanometric size. By crystallites is meant elementary structures whose periodicity is sufficient to allow their detection by X-rays. The size of the crystallites is that determined, either from the widening of the X-ray diffraction lines, or from a sum of observations by transmission electron microscope. Certain precautions were taken during the different characterizations of the powders after synthesis: laser granulometry and transmission or scanning electron microscopy. - For the laser granulometry, the powders were dispersed directly in diethylene glycol, ethanol, methanol, propanol, water or any other solvent, with or without the addition of dispersant and / or acid, in an amount of 0.01 gl ^"1 to lg.l ^{" 1} of oxide obtained after synthesis, the whole treated by ultrasound or by mechanical or magnetic stirring for at least 5 minutes. For transmission or scanning electron microscopy, the powders were either observed directly by application to the observation grid of the solution after synthesis, or by dispersion of the latter in alcohol, acetone, water or any other volatile solvent, all after treatment for a few minutes by ultrasound or mechanical or magnetic stirring. The following ligatures provide a better understanding of the invention. Fig. 1 represents an image produced by transmission electron microscopy of the spherical particles of YO ₃ doped with Eu ³⁺ (5%) of the powder of Example 8, obtained directly after synthesis. The fig. 2 represents an image produced by scanning electron microscopy of particles of YO ₃ doped with Eu ³⁺ (5%) of the powder of Example 8, having an d ₅₀ of 400 nm.

Fig. 3 represents the laser particle size of Y ₂ O ₃ doped Eu ³⁺ (5%), 30 gT ¹ with 2 ml 3N NaOH, with d ₅₀ = 400 nm, of the powder of Example 8 dispersed in diethylene glycol.

The fig. 4 represents the laser particle size of Gd ₂ O ₃ doped with Eu ³⁺ (5%), 20 gl ^"1 with 3 ml NaOH 3N, with d ₅₀ = 165 nm, of the powder of Example 5 dispersed in diethylene glycol .

Fig. 5 represents the laser granulometry of Gd ₂ O ₃ doped Eu ³⁺ (5%), 20 gl ^"1 with 1 ml NaOH 3N, with d ₅₀ = 320 nm, of the powder of Example 6 dispersed in diethylene glycol .

The fig. 6 represents the laser granulometry of Gd ₂ O doped Eu ³⁺ (5%), 20 gl ^"1 with 3 ml NaOH 5N, with d ₅₀ = 160 nm, of the powder of Example 7 dispersed in diethylene glycol. Fig. 7 represents the laser particle size of Y ₃ O ₃ doped Eu ³⁺ (5%), 20 gl ^"1 with

5 ml NaOH IN, with a d ₅₀ = 170 nm, of the powder of Example 2 dispersed in diethylene glycol. Fig. 8 represents the laser granulometry of YO ₃ doped with Eu ³⁺ (5%), 20 gl ^"1 with

5 ml NaOH IN, with d ₅₀ = 303 nm, of the powder of Example 2 heated to 800 ° C in successive stages of 2 hours every 200 ° C, dispersed in an aqueous solution of HCl, 0.1 M Fig. 9 represents the laser particle size of YO ₃ doped with Eu ³⁺ (5%), 20 gl ^"1 with

7 ml 3N NaOH, with a d ₅₀ = 203 nm, of the powder of Example 4 dispersed in diethylene glycol.

Fig. 10 represents the laser granulometry of Gd O ₃ doped Eu ³⁺ (5%), 10 gl ^"1 with the addition of 2 ml of 3.6nm germs in the initial solution, with d ₅₀ = 395 nm, of the powder of l Example 14 dispersed in ethanol.

Fig. 11 represents the laser particle size of Y ₂ O ₃ doped with Eu ³⁺ (5%), 10 gl ^"1 with addition of the stoichiometric amount of water, with d ₅₀ = 500 nm, of the powder of Example 15 dispersed in diethylene glycol.

Fig. 12 represents the laser granulometry of Y ₂ O doped with Eu ³⁺ (5%), 10 gl ^"1 with 75% Y (NO ₃ ) ₃ , 6H ₂ O and 25% YCl, 6H ₂ O by mass as precursors, with ad ₅₀ = 155 nm, of the powder of Example 24 dispersed in diethylene glycol.

Fig. 13 represents the evolution of the DRX of Y ₂ O ₃ doped Eu ³⁺ (5%) as a function of the temperature (100 to 900 ° C.) of the powder of Example 1.

Fig. 14 shows the luminescence spectra of Y ₂ O ₃ doped Eu ³⁺ (5%) as a function of the temperature, at λ _exc = 254 nm, of the powder of Example 1.

Fig. 15 represents the evolution of the DRX of Y ₂ O ₃ doped with Eu ³⁺ heated to T = 700 ° C. as a function of the percentage of Eu ³⁺ (1 to 25%) of the powders of Examples 9 to 13.

Fig. 16 shows the luminescence spectra of Eu ³⁺ doped YO heated to

700 ° C as a function of the percentage of Eu ³⁺ (1 to 25%), at λ _exc - 254 nm, of the powders of Examples 9 to 13.

Fig. 17 shows the evolution of the laser particle size of the oxide particles

Y ₂ O doped with Eu ³⁺ after synthesis, as a function of the percentage of Eu ³⁺ (1 to 25%) in ethanol, of the powders of Examples 9, 10, 12, 13.

Fig. 18 represents the evolution of the DRX of Y ₂ O ₃ doped Tb ³⁺ , as a function of the percentage of Tb ³⁺ (5 to 25%) of the powders of Examples 21 to 23 heated to

T = 700 ° C under Ar / H ₂ flow. Fig. 19 represents the excitation spectrum of Y ₂ O doped Tb (5%), of the powder of Example 21 heated to T = 700 ° C under Ar / H ₂ flow.

Fig. 20 represents the luminescence spectra of YO ₃ doped Tb ³⁺ as a function of the percentage of Tb ³⁺ (5 to 25%), at λ _exc = 280 nm, of the powders of Examples 21 to 23 heated to 700 ° C.

Fig. 21 represents the evolution of the particle size distribution of the doped Gd ₂ O ₃ particles

Eu ³⁺ (5%) depending on the final oxide concentration expected from the powders of Examples 18 to 20.

Fig. 22 represents the evolution of the particle size of the particles of Gd ₂ O ₃ doped Eu ³⁺ (5%) as a function of the concentration of NaOH added during the synthesis, of the powders of Examples 3, 5 and 7.

Fig. 23 represents the evolution of the particle size of the doped Y ₂ O ₃ particles

Eu ³⁺ (5%) depending on the amount of water added during the synthesis, of the powders of Examples 15 to 17. FIG. 24 represents the evolution of the particle size of the doped Gd O particles

Eu ³⁺ (5%) depending on the pH of the solution added during the synthesis, of the powders of Examples 6, 19 and 25.

Fig. 25 represents the luminescence spectra of Gd ₂ O ₃ doped Eu ³⁺ (5%) as a function of the pH of the solution added during the synthesis, of the powders of Examples 6, 19 and 25. Step a) of the process consists in the complete dissolution in a solvent or mixture of polar organic solvents whose boiling point at atmospheric pressure is higher than 200 ° C, metallic precursors of which at least

50% by moles, and preferably at least 90%, are composed of nitrates of rare earth chosen from lanthanum, yttrium and lanthanides, pure, doped or in mixture with another rare earth defined above. The rest of the metal precursors can be of the halide (Cl ^" , Br ^" , I ^" ), NO ₃ ^" , SO ^{2 "} , acetates or any other organometallic compound type. In the case where it is desired to prepare mixed oxides, will use, in addition to the rare earth precursors, soluble salts such as halides, nitrates or organometallic compounds (acetates) of transition metal or B ³⁺ , Al ³⁺ , Si ⁴⁺ , P ⁵⁺ or Bi ³⁺ . As suitable transition metal, mention may in particular be made of Cu, V, Fe, Ni, Co, Cr, Ti. The polar organic solvent is advantageously chosen from alcohols, glycines, oils or preferably polyols, alone or as a mixture and is preferably a polyol chosen from ethylene glycol, polyethylene glycol, propan-l, 2- diol or preferably diethylene glycol. Dissolve between 10 and 500 g, preferably between 100 and 200 g of metal precursors per liter of polar organic solvent, so as to obtain, after precipitation in step b) of the process, between 5 and 200 g, preferably between 20 and 50 g of sesquioxide, oxohydroxide, hydroxide or mixed rare earth oxide powder desired, per liter of solvent. After homogenization, the dissolution is carried out by heating at a temperature generally between 120 and 150 ° C and preferably around 140 ° C. At the end of this step, the solution is clear. This solution must contain at least an amount of water sufficient for the formation of the sesquioxide, oxohydroxide, hydroxide or mixed oxide desired. This water can come from the solvent or from the precursors used in the hydrated state or can be obtained by adding water or an aqueous solution. Advantageously, an amount of water of between 1 and 200 g, preferably between 10 and 100 g, of water is used per liter of solvent. After homogenization of the solution and depending on the desired composition, water and / or a base of NaOH, KOH, Ca (OH), NH _{3 type} , amines, glymes, acetates or other basic organic compounds can therefore be added to the reaction mixture. The quantities are variable and can exceed stoichiometry, the use of 0.01 to 1 mol of base per liter of solvent is nevertheless preferred. According to step b) of the process, the clear solution thus obtained is heated to a temperature above 170 ° C. and below the boiling point of the solvent or mixture of polar organic solvents under the pressure conditions used for heating, preferably at a temperature between 170 and 250 ° C and preferably between 175 and 185 ° C, for a time sufficient to obtain the precipitation of a powder of the desired sesquioxide, oxohydroxide, hydroxide or mixed oxide, in the form of particles nanostructured, submicron with an average diameter between 20 and 800 nm. The heating is preferably carried out at atmospheric pressure. Advantageously, the heating is maintained for at least 5 minutes and preferably at least 2 hours. The colloid thus formed has, directly after synthesis, a solid mass charge of between 5 and 200 g of powder per liter of solvent and preferably between 20 and 50 g of powder per liter of solvent. The particle sizes carried out directly after synthesis in the polyalcoholic solvent reveal highly monodisperse powders of particle size less than one micron and which can be adapted between 20 and 800 nm. Less than 0.01% of the particles formed have a size greater than one micron. In addition, more than 50%, or even more than 90 mol% of the rare earth ions introduced into the initial solution are found in the powder. The particles obtained are essentially spherical, as shown in FIGS. 1 and 2. These submicron particles, with an average diameter of between 20 and 800 nm, are nanostructured, that is to say that they consist of a combination of nanoparticles or coherent elementary structures of average size between 2 and 60 nm, in particular between 2 and 10 nm, as illustrated in figs 13 and 15. The amount of nitrates used per liter of solvent, the amount of water or base, the pH of the added aqueous solution influence in particular the size of the sesquioxide, oxohydroxide, hydroxide or mixed rare earth oxide particles obtained. Fig.21 in particular shows a case where the increase in the concentration of sesquioxide obtained, due to an increase in the quantity of metal precursors used, is accompanied by a reduction in the average diameter of the particles obtained. Fig. 22, for its part, shows a case where the increase in the concentration of sodium hydroxide added to the reaction mixture is accompanied by a decrease in the average diameter of the particles obtained. Fig. 23 shows a case where the increase in the concentration of water added to the reaction mixture is accompanied by an increase in the average diameter of the particles obtained. Fig. 24 illustrates the importance of the pH of the added aqueous solution on the size of the sesquioxide particles obtained. In the case where it is desired to prepare rare earth sesquioxide, it is also possible to use seeds of the desired sesquioxide to initiate precipitation. In this case, germs with an average diameter of less than 10 nm obtained, for example, according to R. Bazzi, MA Flores-Gonzalez, C. Louis, K. Lebbou, C. Dujardin, A. Brenier, W. Zhang, O. Tillement, E. Bernstein and P. Perriat, Journal of Luminescence, 102 -103, (2003), 445-450, can be used. The colloidal suspension obtained according to the process of the invention can be used directly or undergo different stages of purification, extraction, treatment and redispersion with or without surface modifier in the original solvent or any type of aqueous or organic solvent. Thus, the powder can be separated from the solution by filtration or by centrifugation. Several centrifugation steps may be necessary, each time with redispersion in an appropriate water or organic solvent (preferably an alcohol, ether or acetone). The powder thus obtained can then be dried by gentle heating, in air or under vacuum. A heat treatment at high temperature, under an inert atmosphere or under oxidizing or reducing conditions, can also be provided, in particular to decompose the organic compounds remaining on the surface of the particles or the hydroxides, modify the crystal structure, the size of the crystallites, the valences elements or even the size of the powders. Due to their manufacturing process, the powders can undergo a significant heat treatment without significant irreversible agglomeration. The powder can be gradually heated to a final temperature between 500 and 1500 ° C, preferably greater than 800 ° C. Advantageously, this heat treatment will be carried out, between 100 ° C. and 700 ° C., in stages every 200 ° C. and, between 700 to 1000 ° C., in stages every 100 ° C. This heat treatment causes sintering inside the particles or aggregates; the agglomeration phenomena between the aggregates being extremely limited. This allows them to be easily redispersed in aqueous or organic solvents to form submicrometric soils. During the heat treatment, the aggregates, while remaining essentially spherical, become dense and polycrystalline: they are then formed from a combination of crystallites of average diameter between 20 and 100 nm. The redispersion of dried or obtained powders after heat treatment can be facilitated by the addition of chemical dispersing compounds representing 0.01 at 5% of the volume of the solvent, or by modification of the ionic strength and / or of the pH or finally by mechanical or ultrasonic stirring. As suitable dispersing compounds, there may be mentioned dispex® A40 (Alliet Colloids, UK), Doremax® D3007 (Rohm and Haas), anionic polymers, poly (vinylpyrrolidinone) (PVP) or poly (vinyl alcohol) (PVA). Under appropriate conditions, the powders can be dispersed in solvents with a particle size between 20 and 800 nm, a mass load of the colloid between 30 and 300 g per liter of solvent and preferably between 50 and 100 g per liter. The final redispersion can be carried out in an organic solvent, for example of polyol type, primary alcohol (ethanol, methanol, propanol), ether, acetone or in water. The powders can also be heat treated above 1000 ° C: in this case, the redispersion will be more delicate. For more details, the method according to the invention makes it possible to obtain: - rare earth sesquioxides of the Ln ₂ O _{3 type} with Ln a rare earth chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd , Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, oxohydroxides of the preceding compounds, in the form of a mixture (Ln (OH) ₃ and Ln O ₃ ) or of crystallized oxohydroxides or more generally Ln (OH) _w O _{(3-w 2} with w included in the range going from 0 to 3, - pure hydroxides of the preceding compounds, - compounds of type a mixed oxide of formula Ln _x A _-x (O) _y with x included in the range going from 0 to 2, including in the range going from 3 to 4 and A other cations of type transition metals or B ³⁺ , Al ³⁺ , Si ⁴⁺ , P ⁵⁺ or Bi ³⁺ . The rare earth part in the final compound representing more than 50% by mass of the product (for example YAlO ₃ , Y Al ₅ O ₁₂ , LuSiO ₄ , LuAl O ₃ , Luι _-t Y _t A10 ₃ ...) pure or doped with d es lanthanides, compounds of mixed oxide type or Ln _x A _2-x O _v (OH) _z , x as defined above, v included in the range going from 0 to 4, z included in the range going from 0 at 8-2v, and A other transition metal cations or B ³⁺ , Al, Si, P or Bi ^J. The rare earth part in the final compound representing more than 50% by mass of the product (YAlO ₃ , Y ₃ Al ₅ O ₃ , LuSiO ₄ , LuAl ₂ O ₃ , Luι, _u Y _u A10 ₃ ...) pure or doped by lanthanides. These compounds can be obtained in relatively pure form, we will then speak of single-phase powder, or in the form of mixtures, we will then speak of polyphase powder. To obtain a sesquioxide, oxohydroxide or hydroxide, a person skilled in the art will play, in particular, on the temperature and the heating time of step b) and on the nature and the concentration of the base added. In particular, to obtain mainly a hydroxide or an oxohydroxide, it will be advisable to heat in step b) at a temperature below 200 ° C, and preferably below 180 ° C. Similarly, the use of initial solutions containing more than 50 ml of water per liter of solvent and more than 0.1 mole of base per liter of solvent will be advised. To obtain a predominantly sesquioxide or mixed oxide, it will be advisable to heat in step b) to a temperature above 180 ° C. and to use an amount of sodium hydroxide less than the number of moles of metal ions. Advantageously, the method according to the invention makes it possible to obtain powders containing more than 50% by weight, preferably more than 80% by weight of rare earth sesquioxide or mixed oxide as defined above. Advantageously, the method according to the invention makes it possible to obtain rare earth sesquioxide chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure , mixed or doped with a rare earth defined above or with Ce and preferably rare earth sesquioxide chosen from the list La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb , Read, pure, mixed or doped with a rare earth defined above. The method according to the invention is particularly suitable for the preparation of rare earth sesquioxide as defined above and, in particular, of Gd, Eu, Tb, Nd, Lu, Yb, Er, pure or doped with Eu, Tb, Nd , Yb, Er. Advantageously, the method according to the invention is used for the preparation of Gd or Y sesquioxide, optionally doped with another rare earth and in particular with 0.01 to 25% of Eu or Tb. According to another of its aspects, the invention relates to powders of particles of Ln ₂ O ₃ and their colloidal suspensions where Ln represents a rare earth chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, characterized in that these particles are essentially spherical with an average diameter between 20 and 800 nm, nanostructured and composed of an agglomerate of crystallites of average size between 2 and 10 nm. Preferably, Ln represents a rare earth chosen from the list La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth above defined. In particular,

Ln represents Gd, Eu, Tb, Nd, Lu, Yb, Er, pure or doped with Eu, Tb, Nd, Yb, Er.

Advantageously, Ln represents Gd or Y, optionally doped with another rare earth and in particular with 0.01 to 25% of Eu or Tb. The process according to the invention makes it possible, without heat treatment, to obtain nanostructured particles composed of oxide aggregates whose average size of the crystallites is between 2 and 10 nm, preferably between 2 and

5 nm. Such nanostructuring with small-sized crystallites makes it possible in particular to improve the reactivity, the dispersibility and the control, as an additive, of the powders obtained. A high temperature heat treatment allows the sintering of these elementary structures whose average size increases and is advantageously between 20 and 60 nm. The particles obtained are then dense and polycrystalline. The nanostructured submicron powders obtained according to the invention can be used in different forms, either directly dispersed in the polar organic solvent used in the preparation process or any other organic or aqueous solvent, or in dry form after filtration and / or centrifugation , with or without heat treatment. The sectors of activity concerned by the application of these powders are varied: luminescence (lighting, display), fine chemistry (reagents, catalysis supports, active charges ...) and electronics where the trend is towards miniaturization. More precisely, the fields of application of the powders obtained according to the process of the invention are, according to their composition, their morphology and their structure,: - phosphor and phosphorescent pigments for display, lighting, panel technology plasma, and large flat screens, - colored pigments with very high gloss (plastics, paints, road markings, safety lines and tapes, paper, graphic arts), and magnetic for magnetizable inks, - materials adapted to active support properties for catalysis: depollution automotive, polymerization catalysis, air and water purification, refining, - powders allowing fiduciary marking, textiles or plastics - fluorescent lighting: rare earth phosphors allowing the reconstitution of daylight, lamps compacts for domestic applications, - medical imaging: phosphor transforming X-rays into visible light, - reinforcements and better resistance to the scratching of polymers by surface deposition or coating, - materials for electronics (additives, functional ceramics, probes), - cosmetic additives. The examples below illustrate the invention without, however, limiting it.

Example 1:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu for a final oxide concentration of 40 g.! ^"1 .

In a 500 ml flask surmounted by a condenser, 250 ml of diethylene glycol are introduced and 129.2 gl ^"1 of Y (NO ₃ ) ₃ , 6H ₂ O (99.99%) and 6.8 gl ^{" 1} of Eu (NO ₃ ) ₃ , 6H ₂ O (99.99%) in order to obtain the desired final concentration. The solution is heated in an oil bath at different temperatures and heating times:

- 60 ° C for 45 minutes, then 30 minutes of progressive heating up to 140 ° C

- 140 ° C for 60 minutes, with the addition of 2ml of water then progressive heating in 30 minutes at 180 ° C - 180 ° C for 120 minutes.

The solution obtained is gradually cooled to room temperature, then it is diluted by adding 100 ml of ethanol with stirring and ultrasound, and filtered with a filter at 200nm. The powder obtained is redispersed in 100ml of ethanol with stirring and ultrasound then filtered at 200nm. This last operation is repeated 2 times and the final powder is dried in the oven for one hour.

The powder is heated to temperatures of the order of 100 ° C for 2 h, 300 ° C for 12 h, 500 ° C for 1 h, 700 ° C for 1 h and 900 ° C for 2 h, which makes it possible to obtain oxides luminescent free from organic products.

Example 2:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.l ^" .

In a 100ml flask surmounted by a condenser, 60ml of diethylene glycol are introduced and 64.6 gl ^"1 of Y (NO ₃ ) ₃ , 6H ₂ O (99.99%) and 3.4 gl ^{" 1} of Eu (NO ₃ ) ₃ , 6H ₂ O (99.99%) in order to obtain the desired final concentration. The solution is heated in an oil bath at different temperatures and heating time: - 60 ° C for 45 minutes, then 30 minutes of progressive heating to 120 ° C

- 120 ° C for 60 minutes, with the addition of 5 ml of NaOH IN then progressive heating in 30 minutes at 180 ° C

- 180 ° C for 120 minutes.

The solution obtained is gradually cooled to room temperature, then it is diluted by adding 100 ml of ethanol with stirring and ultrasound, and filtered with a filter at 200 nm. The powder obtained is redispersed in 100ml of ethanol with stirring and ultrasound then filtered at 200nm. This last operation is repeated 2 times and the final powder is dried in the oven for one hour, and part is heated to

800 ° C in successive steps of 2 hours every 200 ° C.

Example 3:

Preparation of Gd O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.l ^_1 .

The powder was prepared under the same conditions as those of Example 2, with the addition of 3 ml of sodium hydroxide for a concentration of IN. Example 4:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.i ^"1 .

The powder was prepared under the same conditions as those of Example 2, with the addition of 7 ml sodium hydroxide for a concentration of 3N.

Example 5:

Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.ι ^"1. The powder was prepared under the same conditions as those of Example 2, with the addition of 3ml sodium hydroxide for a concentration of 3N.

Example 6:

Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.l ^"1 .

The powder was prepared under the same conditions as those of Example 2, with the addition of 1 ml of sodium hydroxide for a concentration of 3N.

Example 7: Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 g.! ^"1 .

The powder was prepared under the same conditions as those of Example 2, with the addition of 3 ml of sodium hydroxide for a concentration of 5N.

Example 8:

Preparation of oxide particles Y ₂ O doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 30 g.l ^_1 .

The powder was prepared under the same conditions as those of Example 2, with the addition of 2 ml of sodium hydroxide for a concentration of 3N. Example 9:

Preparation of oxide particles Y ₂ O ₃ doped at 1% by mass with Eu ³⁺ for a final oxide concentration of 15 g.l ^" .

The powder was prepared under the same conditions as those of Example 1.

Example 10:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu ³⁺ for a final concentration of lSg.l ^"1 oxide.

The powder was prepared under the same conditions as those of Example 1.

Example 11:

Preparation of oxide particles Y ₂ O ₃ doped at 10% by mass with Eu ³⁺ for a final oxide concentration of 15 g.l ^" .

The powder was prepared under the same conditions as those of Example 1.

Example 12:

Preparation of oxide particles Y ₂ O ₃ doped at 15% by mass with Eu ³⁺ for a final oxide concentration of 15 g.! ^"1 .

The powder was prepared under the same conditions as those of Example 1.

Example 13:

Preparation of oxide particles Y ₂ O ₃ doped at 25% by mass with Eu ³⁺ for a final oxide concentration of 15 g.l ^"

The powder was prepared under the same conditions as those of Example 1.

Example 14:

Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of lθg.1 ^" .

In a 250 ml flask surmounted by a condenser, 100 ml of diethylene glycol are introduced into which were dispersed seeds of 3.6 nm of Gd O ₃ doped with 5% by mole of Eu ³⁺ and 23.75 gl ^"1 of Gd (NO ₃ ) ₃ , 6H ₂ O (99.99%) and 1.25 gl ^"1 of Eu (NO ₃ ) ₃ , 6H ₂ O (99.99%). The solution is heated in an oil bath at different temperatures and heating times:

- 60 ° C for 30 minutes, then 30 minutes of gradual heating up to 120 ° C

- 120 ° C for 60 minutes, then progressive heating in 30 minutes at 180 ° C - 180 ° C for 60 minutes.

Example 15:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu ³⁺ for a final concentration of oxide of 10g. ^1. The powder was prepared under the same conditions as those of Example 2, for a synthesis volume of 60 ml of diethylene glycol and with the addition at 120 ° C. of a stoichiometric amount of water necessary for obtaining the oxide.

Example 16: Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu ³⁺ for a final oxide concentration of lθg.1 ^"1 .

The powder was prepared under the same conditions as those of Example 15, with the addition at 120 ° C of twice the amount of stoichiometric water necessary to obtain the oxide.

Example 17:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Eu for a final concentration of lOgl ^"1 oxide.

The powder was prepared under the same conditions as those of Example 15, with the addition at 120 ° C of four times the amount of stoichiometric water necessary to obtain the oxide.

Example 18:

Preparation of Gd O ₃ oxide particles doped at 5% by mass with Eu for a final concentration of lOg.l ^"1 oxide.

The powder was prepared under the same conditions as those of Example 15. Example 19:

Preparation of Gd O ₃ oxide particles doped at 5% by mass with Eu for a final oxide concentration of 20 g.! ^"1 .

The powder was prepared under the same conditions as those of Example 15.

Example 20:

Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu for a final oxide concentration of 40 g.! ^"1 .

The powder was prepared under the same conditions as those of Example 15.

Example 21:

Preparation of oxide particles Y ₂ O ₃ doped at 5% by mass with Tb ³⁺ for a final oxide concentration of 30 g.! ^"1 .

In a 100ml flask surmounted by a condenser, 50ml of diethylene glycol are introduced and 96.9 gl ^"1 of Y (NO ₃ ) ₃ , 6H ₂ O (99.99%) and 5.1 gl ^{" 1} of Tb (NO ₃ ) ₃ , 6H ₂ O (99.99%) in order to obtain the desired final concentration. The solution is heated in an oil bath at different temperatures and heating times:

- 60 ° C for 60 minutes, then 30 minutes of progressive heating up to 140 ° C

- 140 ° C for 60 minutes, with the addition of 2ml of water then progressive heating in 30 minutes at 180 ° C

- 180 ° C for 120 minutes.

The solution obtained is gradually cooled to room temperature, then it is diluted by adding 100 ml of methanol with stirring and ultrasound, and filtered with a filter at 200 nm. The powder obtained is redispersed in 100ml of methanol with stirring and ultrasound then filtered at 200nm. This last operation is repeated 2 times and the final powder is dried in an oven for one hour, then heated from 100 ° C to 700 ° C under a controlled atmosphere (Ar / H ₂ ), in steps of 200 ° C.

Example 22 Preparation of Y ₂ O ₃ oxide particles doped at 15% by mass with Tb for a final oxide concentration of The powder was prepared under the same conditions as those of Example 21. Example 23:

Preparation of oxide particles Y ₂ O ₃ doped at 25% by mass with Tb for a final oxide concentration of 30 g.l ^" .

The powder was prepared under the same conditions as those of Example 21.

Example 24:

Preparation of oxide particles Y ₂ O ₃ doped at 6% by mass with Eu ³⁺ for a final concentration of lOg.F oxide.

In a 100 ml flask surmounted by a condenser, 50 ml of diethylene glycol are introduced and a mixture of 75/25 nitrates / chlorides of Y (NO ₃ ) ₃ , 6H ₂ O (99.99%), Y (C1) ₃ , 6H ₂ O (99.99%) and Eu (NO ₃ ) ₃ , 6H ₂ O (99.99%) corresponding to 25.4 gl ^"1 of nitrates and 6.72 gl ^{" 1} of chlorides, in order to obtain the desired final concentration. The solution is heated in an oil bath at different temperatures and heating times:

- 60 ° C for 60 minutes, then 30 minutes of progressive heating up to 120 ° C

- 120 ° C for 60 minutes, with the addition of 2ml of water then progressive heating in 30 minutes at 180 ° C - 180 ° C for 60 minutes.

Example 25:

Preparation of Gd ₂ O ₃ oxide particles doped at 5% by mass with Eu ³⁺ for a final oxide concentration of 20 gl ^" . The powder was prepared under the same conditions as those of Example 2, for a synthesis volume of 60 ml of diethylene glycol and with the addition at 120 ° C. of a stoichiometric quantity of water necessary for obtaining the oxide, from an aqueous solution of [HC1] = 0.01N.

Claims

CLAIMS 1 - Process for the preparation of a single-phase or multi-phase powder, optionally in the form of a colloidal suspension, of sesquioxide, oxohydroxide or rare earth hydroxide chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, or a mixed oxide of formula Ln _x A _2-x (O) _y or Ln _x A _-x O _v (OH) _z , with x in the range from 0 to 2, including in the range from 3 to 4, v in the range from 0 to 4 and z in the range ranging from 0 to 8-2v, Ln a rare earth as defined above and A a transition metal cation or B ³⁺ , Al ³⁺ , Si ⁴⁺ , P ⁵⁺ or Bi ³⁺ , the earth part rare representing more than 50% of the mass of the powder obtained, which comprises the following successive stages: a) dissolving precursors of the rare earth and optionally of A defined above, at least 50% by mass of these precursors both the rare earth nitrates defined above, in a solvent or mixture of polar organic solvents whose boiling temperature at atmospheric pressure is greater than 200 ° C., at a rate of 10 to 500 g of precursors per liter of solvent, in the presence of the amount of water at least necessary for the formation of the desired sesquioxide, oxohydroxide, hydroxide or mixed oxide, b) heating the solution obtained in step a) to a temperature above 170 ° C and below the temperature of boiling of the solvent or mixture of polar organic solvents under the pressure conditions used for heating, preferably at a temperature between 170 and 250 ° C and preferably between 175 and 185 ° C, for a time sufficient to obtain the precipitation of a desired sesquioxide, oxohydroxide, hydroxide or mixed oxide powder, in the form of nanostructured, submicron particles with an average diameter n is between 20 and 800 nm, c) optionally separation of the powder obtained from the organic polar solvent, which can be followed by drying, d) optionally redispersion of the powder obtained in step c) in an appropriate solvent. 2 - Process according to claim 1 characterized in that at least 90% by moles of the rare earth precursors are nitrates of rare earth. 3 - Process according to claim 1 or 2 characterized in that in step a), between 100 and 200 g of precursors are dissolved per liter of polar organic solvent. 4 - Method according to one of claims 1 to 3 characterized in that the polar organic solvent is chosen from alcohols, polyols, glycines, oils alone or as a mixture and is preferably a polyol chosen from ethylene glycol, polyethylene glycol, propan-1,2-diol or preferably diethylene glycol. 5 - Method according to one of claims 1 to 4 characterized in that the solution obtained in step a) further contains an amount of water between 1 and 200 g, preferably between 10 and 100g, of water per liter of solvent. 6 - Method according to one of claims 1 to 5 characterized in that the solution obtained in step a) further contains a base, preferably chosen from NaOH, KOH, Ca (OH), NH ₃ , amines, glymes , acetates, advantageously in an amount of 0.01 and 1 mol / 1 of solvent. 7 - Process for preparing sesquioxide according to one of claims 1 to 6 characterized in that the heating of step b) is carried out in the presence of seeds of the desired sesquioxide. 8 - Method according to one of claims 1 to 7 characterized in that the heating of step b) is carried out for at least 5 minutes and preferably for at least 2 hours. 9 - Method according to one of claims 1 to 8 characterized in that the powder obtained is dried according to step c) then gradually heated to a final temperature between 500 and 1500 ° C, preferably greater than 800 ° vs. 10 - Process according to claim 9 characterized in that the powder heated between 100 ° C and 700 ° C in steps every 200 ° C and between 700 to 1000 ° C in steps every 100 ° C. 11 - Process according to claim 9 or 10 characterized in that the powder obtained after heating is redispersed in an appropriate solvent of the polyol, primary alcohol, ether, acetone, water type, optionally in the presence of a dispersant representing 0.01 at 5% of the volume of the solvent. 12 - Method according to one of claims 1 to 11 characterized in that the powder obtained is isodisperse. 13 - Method according to one of claims 1 to 12 characterized in that one obtains powders containing more than 50% by weight, preferably more than 80% by weight of rare earth sesquioxide as defined in claim 1 or mixed oxide. 14 - Method according to one of claims 1 to 13 characterized in that one obtains rare earth sesquioxide chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er , Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce. 15 - Method according to claim 14 characterized in that one obtains rare earth sesquioxide chosen from the list La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above. 16 - Process according to claim 14 characterized in that one obtains sesquioxide of Gd, Eu, Tb, Nd, Lu, Yb, Er, pure or doped with Eu, Tb, Nd, Yb, Er. 17 - Process according to claim 14 characterized in that one obtains sesquioxide of Gd or Y, possibly doped with another rare earth and in particular with 0.01 to 25% of Eu or Tb. 18 - Powder of Ln ₂ O ₃ particles and colloidal suspension of such particles where Ln represents a rare earth chosen from the list Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy,

Ho, Er, Tm, Yb, Lu, pure, mixed or doped with a rare earth defined above or with Ce, characterized in that these particles are essentially spherical with an average diameter between 20 and 800 nm, nanostructured and composed of an agglomerate of crystallites of average size between 2 and 10 nm. 19 - Particle powder and colloidal suspension according to claim 18 characterized in that Ln represents a rare earth chosen from the list La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu , pure, mixed or doped with a rare earth defined above. 20 - Particle powder and colloidal suspension according to claim 18 or 19, characterized in that the crystallites are of average size between 2 and 5 nm. 21 - Powder of particles and colloidal suspension according to one of claims 18 to 20 characterized in that Ln represents Gd, Eu, Tb, Nd, Lu, Yb, Er, pure or doped with Eu, Tb, Nd, Yb, Er . 22 - Powder of particles and colloidal suspension according to one of claims 18 to 20, characterized in that Ln is Gd or Y, optionally doped with another rare earth and in particular with 0.01 to 25% of Eu or Tb.