FR2999560A1 - CRISTALLITE POWDER - Google Patents

Abstract

A powder comprising more than 50% by volume of a crystalline phase containing cerium oxide, as a percentage of the total volume of the phases of the powder, and a chemical composition, as a percentage by mass on the basis of the oxides and for a total of of 100%, such as: - CeO 2 ≥ 50%, - SiO 2 ≤ 10%, - 1% 5 ZrO 2 + TiO 2 530%, provided that 0.5% ≤ TiO 2 ≤ 20%, Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (s) ) except CeO2 ≤ 40%, - Al2O3 ≤ 10%, - Na2O + K2O ≤ 5%, - B2O3 ≤ 0,1%, - P2O5 ≤ 0,1%, - other oxides ≤ 5%, and more than 90% in bulk of crystallites, isolated or in agglomerated form, all of said crystallites having a median square circularity C250> 0.95, and - an average dimension dm of between 10 nm and 1000 nm.

Description

TECHNICAL FIELD The invention relates to a powder especially intended for surface polishing applications. The invention also relates to a method of manufacturing such a powder. State of the art Abrasive materials are conventionally used to remove material from a workpiece or to modify its surface characteristics ("surfacing"), such as roughness, gloss, appearance, texture, or flatness. For surfacing a part, in particular a semiconductor substrate, it is known to use a suspension of fine particles. In particular, US2007 / 0204519 discloses fine particles of CeO2 and US2010 / 0022387 discloses fine solution solids ZrO 2 -ECO 2 -oxides of lanthanide (except Ce). In the semiconductor industry, any contamination of the substrate by the particles of the slurry can dramatically decrease the final semiconductor properties. The surface state of the substrate after the surfacing operation must also have a low roughness so as not to generate defects in the layers subsequently deposited on said surface, for example by chemical vapor deposition or "CVD". The manufacturing method described in US 2007/0204519 uses, in particular, a glass based on B203 which can disturb the properties of silicon and reduce semiconductor performance.

There is a need for a powder which can, optionally after suspension, obtain a surface state having a low roughness, with a high rate of removal of material (or "removal rate" in English) and with a reduced rate. contamination, in particular by boron and phosphorus compounds. An object of the invention is to satisfy, at least partially, this need.

SUMMARY OF THE INVENTION According to the invention, this object is achieved by means of a powder having more than 50% by volume of a crystalline phase containing cerium oxide, as a percentage of the total volume of the phases of the powder. and a chemical composition, in percent by weight based on the oxides and for a total of 100%, such as: CeO 2 50%, 10%, - 1% 5. ZrO 2 + TiO 2 5 30%, provided that 0.5% Ti02.5 20%, Sc203 + Y2O3 + lanthanide oxides except CeO2 5, 40%, Al2O3.5. 10%, Na 2 O + K 2 O 5%, 0.1% B 2 O 3, 0.1% P 2 O 5, other 5% 5% oxides and having more than 90% by mass of crystallites, isolated or in agglomerated form, set of said crystallites having a median squared circularity C250> 0.95, and - an average dimension d, r, between 10 nm and 1000 nm. A powder according to the invention can therefore contain up to 10% of other particles than crystallites. Preferably, however, the powder contains more than 95% by weight, more than 98%, more than 99%, or even substantially 100% by mass of crystallites.

As will be seen in more detail in the remainder of the description, the inventors have discovered that such crystallites make it possible to obtain a low roughness and an excellent surface appearance. Preferably, a powder according to the invention also comprises one, and preferably several, of the following optional characteristics, according to all the possible combinations: Said crystalline phase containing cerium oxide represents more than 60%, more than 70% , more than 80%, more than 90%, more than 95%, more than 99%, even substantially 100% of the total volume of the powder phases. The amorphous phase (complement to 100% of the total volume of the crystallized phases) represents less than 20%, less than 10%, less than 5%, or even substantially 0% of the total volume of the phases of the powder.

The powder according to the invention has a composition such that CeO2> 60%, or even CeO2> 70%, or even CeO2> 75%, or even CeO2> 80%, or even CeO2> 90%, or even CeO2> 95%, and / or SiO2 <8%, preferably <5%, even <2%, or even <1%, or even <0.5%, or even <0.3%, or even <0.1%, or even <0.05% and / or > 0.01%, and / or - ZrO 2> 1%, preferably> 5% and / or ZrO 2 <29.5%, preferably <25%, preferably <20%, or even <15%, and / or TiO2> 1%, preferably 5% and / or TiO2 <15%, preferably <10%, and / or - Sc203 + Y203 + lanthanide oxides (s) except CeO2 <30%, preferably <20%, or <15%, and / or A1203 <5%, preferably <1%, or even <0.5%, and / or Na20 + K20 <3%, preferably <1%, or even <0.5%, and / or or B203 <0.05%, or even <0.01%, and / or P205 <0.05%, or even <0.01%, and / or - other oxides <3%, preferably <2%, preferably <1%, or even <0.5%, or even <0.3%, or even <0.1%. The powder according to the invention comprises more than 98% by mass of crystallites. The powder according to the invention has a composition such that at least one sum of oxides S chosen from - CeO 2 + Sc 2 O 3 + Y 2 O 3 + oxides of lanthanide (s) except CeO 2, preferably CeO 2 + La 2 O 3, and - CeO 2 + ZrO 2 + TiO 2 + Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (s) except CeO 2, preferably CeO 2 + ZrO 2 + TiO 2 + La 2 O 3, or even CeO 2 + ZrO 2 + TiO 2, is such that S> 60%, or even> 70%, or even> 80% or even> 90%, even> 95%. The powder according to the invention has a composition such - 5% <Y03 <10%, and / or - 10% <La203 <30%. Preferably, said lanthanide oxides, excluding CeO 2, are chosen from the group folated by La, Nd, Pr and Gd oxides and mixtures thereof. Preferably, the lanthanide oxide is La203. In one embodiment, the other oxides are impurities. The oxides represent more than 90%, more than 95%, more than 99%, or even substantially 100% of the mass of the powder. The median square circularity, C250, is> 0.98, preferably substantially equal to 1. In one embodiment, the average crystallite size is between 50 and 100 nm. This dimension of crystallites is particularly well suited to three-way catalysis, or "TVVC" for "Three Way Catalysis" in English. In one embodiment, the average crystallite size is between 100 and 200 nm. This dimension of crystallites is particularly well suited to chemical mechanical polishing ("CMP"), especially for the finishing of parts. In one embodiment, the average crystallite size is between 200 and 500 nm. This dimension of crystallites is particularly well suited to polishing type "CMP", especially for roughing parts. In one embodiment, the average crystal size is between 500 and 1000 nm. In one embodiment, the particle size dispersion index (especially comprising crystallites and agglomerates of such crystallites), (D90-D10) / D50, is less than 10, or even less than 5, or even less than 3, or even less than 2, or even less than 1. The roughness after polishing is advantageously improved. In one embodiment, the powder comprises more than 50%, more than 60%, more than 70%, more than 90%, more than 95%, more than 99%, or even substantially 100% by volume of a phase. crystalline selected from the group formed by the cubic CeO 2 phase, the solid solutions CeO 2 - (ZrO 2 and / or TiO 2), the solid solutions CeO 2 - (Sc 2 O 3 and / or Y 2 O 3 and / or oxide (s) of lanthanide (s) except CeO 2 ), Ce2 (Zr, Ti) 207 and mixtures thereof, preferably selected from the group consisting of the cubic CeO2 phase, the solid solutions CeO2- (ZrO2 and / or TiO2), and the solid solutions CeO2- (Sc2O3 and / or Y 2 O 3 and / or lanthanide oxide (s) except CeO 2), in percentage by volume based on the total volume of the phases of the powder. The specific surface area of the powder according to the invention is greater than 5 m 2 / g, preferably greater than 10 m 2 / g and / or less than 100 m 2 / g, preferably less than 50 m 2 / g, preferably less than 30 m2 / g. The powder according to the invention has a specific surface area greater than 10 m 2 / g and a pore volume greater than 0.05 cm 3 / g, preferably greater than 0.1 cm 3 / g, when the powder comprises agglomerates of crystallites. The powder according to the invention has a specific surface area greater than 10 m 2 / g and a median pore size of between 1 nm and 100 nm, when the powder comprises agglomerates of crystallites. - In one embodiment, the pore size dispersion index (P90-P10) / P50 of said powder is less than 20, or even less than 10, or even less than 5, or even less than 2, when the powder comprises agglomerates of crystallites.

In one embodiment, more than 80%, more than 90%, even substantially 100% by number of the crystallites are agglomerated in the form of agglomerates. Preferably, the median size of all these agglomerates is greater than 0.1 mm and / or preferably less than 1 mm, preferably less than 0.5 mm, or even less than 0.25 mm. The invention also relates to a process for manufacturing a powder of crystallites, optionally agglomerated, comprising the following successive steps: a) b) 20 e) 25 preparation of a suitable starting charge for obtaining, at the end of the step e), product comprising, in weight percent based on the oxides: - 10% SiO 2, and - CeO 2 + Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (s) except CeO 2 5. 40%, and - 1% ZrO 2 + TiO 2 30%, other oxides: <5% the ratio R of the number of moles of (CeO 2 + Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (except CeO 2)) on the number of moles of SiO 2 being greater than or equal to 0.2, and the ratio R 'of the mass of CeO 2 on the mass of (ZrO 2 + TiO 2 + Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (except CeO 2) being greater than or equal to 1, melting of the starting charge so as to obtain a liquid mass quenching of the liquid mass in order to obtain a melted product comprising less than 50% by volume of crystallized phase (s), more than 95% of the crystallites having a dimension less than 1000 nm, or even an amorphous molten product, eristallites in a glassy phase, solubilization of the glassy phase and separation of said crystallites, rinsing and filtration of said crystallites, optionally, wet-milling of said crystallites, optionally, drying said crystallites optionally, lopping and / or grinding said crystallites. a crystallization heat treatment so as to obtain a structure constituted by d) of this process makes it possible to manufacture a powder according to the invention. Preferably, a method according to the invention also comprises one, and preferably several, of the following optional characteristics, according to all the possible combinations: in step a), the initial charge is adapted to obtain, at the end of step c), a product having a ratio R less than 3, or even less than 1.5 and / or greater than 0.7. - In step a), the starting charge is adapted to obtain, at the end of step c), a product having a ratio R 'greater than 2.3. In step c), the cooling rate is greater than 500 ° C./s. The invention also relates to a suspension comprising a liquid and a crystallite powder according to the invention, optionally agglomerated, suspended in said liquid. Preferably, a suspension according to the invention also comprises one, and preferably several, of the following optional characteristics: the powder according to the invention represents more than 90%, more than 95%, or even substantially 100% of the solid substance of suspension. The suspension comprises more than 0.1%, preferably more than 0.5% and / or less than 20%, preferably less than 10%, preferably less than 5% of crystallite powder according to the invention, mass percentage based on the mass of said suspension. - Water represents more than 80%, more than 90%, of the volume of said liquid. - The liquid comprises more than 5%, in volume percentage, of an alcohol, preferably selected from the group formed by ethanol, methanol, propanol and mixtures thereof. The liquid comprises more than 1%, in percentage by volume, of a surfactant for dispersing the crystallites, for example an ammonium polyacrylate or an ammonium polycarboxylate. The invention also relates to the use of a suspension according to the invention for a polishing operation, in particular CMP (or "Cheinieal Mechanical Polishing" in English). The invention also relates to the use of a powder according to the invention - in a catalytic coating (or "washcoat" in English), in particular for automotive catalysis, for example in a three-way catalytic device, or "TWC For "Three Way Catalysis" in English, or for reducing catalysis of nitrogen oxides NO ', as a raw material for the manufacture of an electrode or an ionic conductor based on Y oxides, Ce, Gd, and mixtures thereof, as raw material for the manufacture of a technical ceramic made up of more than 90% by weight of CeO 2 and ZrO 2, or as a powder for polishing, in particular for the polishing of an LCD glass, a photomask, a mirror, an integrated circuit, and a semiconductor element. The invention finally relates to such washcoats, electrodes, ionic conductors, and technical ceramics made up of more than 90% by weight of CeO 2 and ZrO 2, incorporating crystallites of a powder according to the invention and LCD glasses, photo-masks , mirrors, integrated circuits, and semiconductor elements polished by means of a powder or a suspension according to the invention also relates to a film constituted by an agglomeration of crystallites of a powder according to the invention, said film exhibiting a thickness less than 250 pm, or even less than 200 .1111, or even less than 100 .mu.m, said film being able to be secured to a substrate or not. Definitions A "particle" is an individual solid element of a powder or suspension. A crystallite and an agglomerate of crystallites are examples of particles. Unless otherwise indicated, when reference is made to crystallites, reference is made generally to isolated, i.e., non-agglomerated, crystallites and agglomerated crystallites. In an "agglomerate", the association of crystallites results from a low intensity bond, for example by charge effects or by polarity, unlike a bond resulting from a partial melting, for example resulting from sintering. - "Lanthanide" is a member of the periodic table of elements having an atomic number between 57 and 71. "Particle size" means the size of a particle conventionally given by a particle size distribution characterization performed. with a laser granulometer. The laser granulometer used here is a Partica LA-950 from the company HORIBA. The "size" of the crystallites (which can be agglomerated, and thus impossible to measure individually by laser granulometry) is measured from clichés, the dimension of a crystallite being the diameter of the smallest circle including crystallite.

Percentiles or "percentiles" 10 (A10), 50 (A50), 90 (A90) and 99.5 (A99.5), and more generally "n" A 'of a property A of a population, for example of a population of particles or pores are the values of this property corresponding to the percentages, by number, of 10%, 50%, 90%, 99.5% and n%, respectively, on the cumulative distribution curve relative to this property, the values relative to this property being ranked in ascending order. In particular, the percentiles D, P1, and C211 relate to particle sizes, pore sizes, and crystallite squares, respectively. Depending on the property considered, the percentages may be in bulk, for example for the percentiles D 'or C2', or in volume, for example for the 13 'percentiles. The percentile 50 is classically called the "median" percentile. For example, C250 is conventionally called "median squared circularity". Similarly, the percentile D50 is conventionally called the "median size" of the particles.

For example, 10% by weight of the particles of the powder have a size less than D10 and 90% of the particles by mass have a size greater than or equal to D10. Percentiles for particle size can be determined using a particle size distribution using a laser granulometer. Likewise, for example, 10% by volume of the pores of the particles of the powder have a size less than 10 μm and 90% of the pores by volume have a size greater than or equal to 10 μm. These percentiles can be determined using a physical N2 adsorption / desorption distribution at -196 ° C on a Nova 2000 model marketed by Quantachrome. The "roundness squared" of the crystallites of the powder is conventionally determined in the following way: The powder is suspended in n-propanol, with the application of ultrasound so as to break the agglomerates of crystallites and favor the observation of individual crystallites. This suspension is then spread on a conductive support, such as carbon scotch used in electronic imaging. Images are then made using a Scanning Electron Microscope (SEM) so that at least 500 crystallites can be observed. These images are then analyzed using image processing software.

As shown in FIG. 1, in order to evaluate the "circularity" C of a Cr crystallite, the perimeter PQ of the disk Q having an area equal to the area A of the Cr crystallite is determined on an image of this crystallite. The perimeter I '' of this crystallite is also determined. The circularity is equal to the ratio of PQ / Pc. The circularity squared is therefore equal to (PQ / 13) 2, ie C2 = 4 * e * A,. The longer the crystallite is of elongated form, the smaller the circularity squared. Unless otherwise indicated, an average is an arithmetic mean. Unless otherwise indicated, the "other oxides" are oxides other than CeO 2, SiO 2, ZrO 2 TiO 2, Sc 2 O 3, Y 2 O 3, lanthanide oxides (s) except CeO 2, Al 2 O 3, Na 2 O, 1 (20, B 2 O 3, and P 2 O 5. conventionally the chemical composition, the content of an element in the oxide form being conventionally evaluated by the measurement of its most stable oxide form, and the nature of the phases For example, the total content of cerium oxide is evaluated by measuring the content of CeO 2, whatever the phase in which cerium is incorporated, for example cerium may be in the form of a CeO 2 phase, but also (in a non-exhaustive manner) of Ce 2 (Zr, Ti) 207 phase. Unless otherwise indicated, all the percentages relative to the composition of a powder according to the invention are percentages by mass on the basis of the oxides, unless otherwise indicated, all the percentages relative to the volumes of a crystallized phase, in particular of phase crystallized containing cerium oxide, are percentages by volume based on the total volume of the phases of the powder. BRIEF DESCRIPTION OF THE FIGURES Other objects, aspects, properties and advantages of the present invention will become apparent from the following description and examples and from the accompanying drawing in which Figure 1 illustrates the method which is used to evaluate the circularity of a crystallite. DETAILED DESCRIPTION PROCESS OF THE INVENTION In step a), a feedstock is prepared: The source of cerium oxide is preferably selected from the group consisting of CeO 2, Ce 2 O 3, cerium oxide precursors such as a cerium carbonate, a cerium nitrate, a cerium chloride, or a cerium sulfate, and mixtures thereof. Preferably, the source of cerium oxide is selected from the group consisting of CeO 2, Ce 2 O 3, a cerium carbonate and mixtures thereof. The sources of Sc203, Y203 and lanthanide oxides, except CeO2, are preferably chosen from the group formed by these oxides and the precursors of these oxides, preferably from the group formed by these oxides. The source of SiO 2 is preferably selected from the group consisting of zircon and powders containing more than 80% by weight of silica, preferably silica sand. The source of ZrO 2 is preferably selected from the group consisting of zircon and powders containing more than 90%, preferably more than 95%, preferably more than 98% by weight of zirconia. The TiO 2 source is preferably selected from the group consisting of rutile and / or anatase powder. Preferably, the compounds providing the cerium, scandium, yttrium, other lanthanide, silicon, zirconium and titanium oxides together represent more than 90%, preferably more than 99%, in percentages by weight, of the solid constituents of the feedstock. Preferably, no compounds other than those providing the cerium, other lanthanide, scandium, yttrium, silicon, zirconium and titanium oxides are intentionally introduced into the feedstock. The amounts of cerium oxides, other lanthanides, scandium, yttrium, silicon, zirconium and titanium of the feedstock are found substantially completely in the manufactured melt. A part of the constituents, for example silica, which varies according to the melting conditions, volatilises during the melting step. By his general knowledge, or by simple routine tests, a person skilled in the art knows how to adapt the amount of these constituents in the starting charge according to the content he wishes to find in the melted products and the conditions of fusion implemented. The initial charge is adapted to obtain at the end of step c), a product having a ratio R preferably greater than 0.25, or even greater than 0.3, or even greater than 0.5, or even greater than at 0.7 and / or less than 3, or even less than 2.5, or even less than 2, or even less than 1.5, or even less than 1.2.

The initial charge is adapted to obtain at the end of step c), a product having a ratio R 'preferably greater than 1.5, or even greater than 2.3, or even greater than 3, or even greater than 4 or even greater than 9, or even greater than 19. The particle sizes of the powders used may be those commonly encountered in conventional melting processes. Intimate mixing of the raw materials can be done in a mixer. This mixture is then poured into a melting furnace. In step b), the feedstock is melted. All known furnaces are conceivable, such as an induction furnace, a laser furnace, a plasma furnace, an arc furnace, provided that they allow to melt the starting charge. A crucible melting in a heat treatment furnace, preferably in an electric furnace, preferably in an oxygenated environment, for example in air, is also conceivable. Preferably, a Héroult type arc furnace is used.

The melting temperature is preferably greater than 1400 ° C, preferably greater than 1600 ° C. After melting, the feedstock is in the form of a liquid mass, which may optionally contain some solid particles, but in an amount insufficient for them to structure said mass. By definition, to maintain its shape, a liquid mass must be contained in a container. The liquid mass obtained can be stirred so as to increase its homogeneity, for example by blowing a gas, preferably air, into the liquid mass using a device such as that described in FR 1 208 577. In step c), the liquid mass undergoes a sudden cooling, or "quenching", so as to be solidified. The cooling rate is preferably greater than 100 ° C / s, preferably greater than 500 ° C / s, or even greater than 1000 ° C / s. The sudden cooling can for example result: the casting of the liquid mass in a cooler liquid bath, for example water, the casting of the liquid mass between rolls rotating at high speed, the dispersion of the liquid mass under liquid droplet form with a fluid jet, preferably oxygenated, followed by solidification of these liquid droplets by contact with a fluid, preferably oxygenated, preferably air, so as to obtain particles fondues. In a preferred embodiment, the melted particles obtained have less than 40%, preferably less than 20%, preferably less than 10%, preferably less than 5%, in percentage by volume, preferably substantially no crystalline phase. In other words, the most preferred mode is to obtain amorphous fused particles. The quenching may, however, lead to crystallization in the form of crystallites, these crystallites being bound by a vitreous binder phase mainly consisting of silica. Most crystallites are substantially spherical. More than 97%, more than 99%, or substantially 100% by number of the crystallites formed in step c) have a dimension less than 1000 nm. Preferably, more than 95% by number of said crystallites have a dimension of less than 500 nm, preferably less than 300 nm, or even less than 200 nm. The amount of crystalline phase and the size of the crystallites depend on the cooling conditions, as is well known. The solidified mass may be in the form of a block or a powder. Preferably, the solidified mass is converted, if necessary, in the form of a particle powder having a size, before thermal crystallization treatment, of less than 300 μm, or even less than 200 μm. For example, grinding can be performed. All types of grinders are usable, in particular an air jet mill or ball mill. Step d) consists of a crystallization treatment to increase the amount of crystallites. The crystallization heat treatment is preferably carried out in an oxygenated fluid, preferably in air. The rates of rise and fall in temperature during this crystallization heat treatment may be, for example, between 10 ° C./h and 1200 ° C./h, preferably between 15 ° C./h and 500 ° C. / h, preferably between 20 ° C / h and 200 ° C / h. A speed of 100 ° C / h is well suited. The heat treatment may comprise a single temperature step. In one embodiment, the heat treatment comprises a single bearing at a temperature between 800 ° C and 950 ° C, preferably at a temperature of between 820 ° C and 880 ° C, and more preferably at about 850 ° C. C, preferably for a period greater than 1 hour, preferably greater than 2 hours, preferably greater than 3 hours, more preferably greater than 5 hours. The duration of level maintenance can be less than 100 hours, or even less than 50 hours. In one embodiment, the heat treatment comprises a single step at a temperature of between 950 ° C and 1100 ° C, preferably at a temperature of between 970 ° C and 1070 ° C, and more preferably at about 1000 ° C preferably for a period greater than 1 hour, preferably greater than 2 hours, preferably greater than 3 hours, more preferably greater than 5 hours. The duration of level maintenance can be less than 100 hours, or even less than 50 hours.

Preferably, the heat treatment cycle comprises first and second stages. Advantageously, the particle size dispersion index (especially comprising crystallites and agglomerates of such crystallites), (D90-D10) / D50, is decreased. Preferably, the first step is determined to generate seed crystals in the vitreous phase and the second step is determined to grow these seeds. The temperature of the second bearing is greater than that of the first bearing, preferably greater than at least 50 ° C, at least 80 ° C, at least 100 ° C, or even at least 150 ° C at the temperature. In one embodiment, the first step is at a temperature between 800 ° C and 950 ° C, preferably at a temperature of between 820 ° C and 880 ° C, and more preferably at about 850 ° C, and the second step is at a temperature of 950 ° C to 1250 ° C, preferably at a temperature of 970 ° C to 1100 ° C, and more preferably at about 1000 ° C. Preferably, the temperature keeping time of at least one of the first and second bearings, preferably of each of these two stages, is greater than 1 hour, preferably greater than 2 hours, preferably greater than 3 hours, preferably even greater than 5 hours. For each of the two levels, a level maintenance time may be less than 100 hours, or even less than 50 hours. The implementation of a post-solidification heat treatment makes it possible to control the generation of the crystallites, and in particular to determine the degree of crystallization and / or to adjust the size of the crystallites: Thus, the inventors have found that the majority crystallites are created during the first stage or, when the heat treatment comprises a single stage, during the rise in temperature. The duration of treatment determines the number of crystallites, a longer duration corresponding to a greater amount of crystallites. This observation has also led the inventors to recommend the implementation of two stages, the control of the creation of crystallites being further improved. The inventors have also found that the size of the crystallites increases with the temperature of the second stage. After crystallization heat treatment, a melted product composed of crystallites embedded in a vitreous phase rich in silica is obtained. An optional grinding step is performed after the heat treatment step d) and before step e). All types of grinders are usable, in particular an air jet mill or ball mill. In step e) of solubilization, the crystallites, optionally agglomerated, according to the invention are separated from the vitreous phase rich in silica. A base can be used for this purpose, for example soda or potash. The base may be heated and / or ultrasound may be applied to accelerate the solubilization of the silica-rich vitreous phase. This step can be carried out several times in order to solubilize substantially the entire vitreous phase based on silica. In step 0 rinsing / filtration, any known rinsing and filtration technique may be implemented, for example rinsing with deionized water followed by filtration. In step g), optionally, the powder of crystallites, generally agglomerated, obtained is milled, according to any known technique, preferably wet, so as to adjust the size of the agglomerates of crystallites. In step h) of drying, optional, any method known to those skilled in the art, for example atomization or baking, can be used. The drying temperature is generally less than 500 ° C, preferably less than 200 ° C, preferably about 110 ° C. The drying time is adjusted so that the crystallite powder according to the invention, optionally agglomerated, has at the end of this stage a residual moisture preferably less than 1% by weight. In step 0 of grinding / grinding, optional, the powder obtained in the previous step is swept. The process described above makes it possible to manufacture a powder according to the invention. Examples The following examples are provided for illustrative purposes and do not limit the invention.

The determination of the crystallite size is carried out as follows: After ultrasonic dispersion of a sample to be characterized, more than five snapshots in Scanning Electron Microscopy (SEM) are made. From these cliches, the size of the crystallites is determined by statistical counting.

Particle size distribution of a powder is measured with a laser granulometer by Horiba. The analysis of the chemical composition is carried out by X-ray fluorescence spectroscopy if the content of the element to be measured is greater than 0.1% by mass or else by ICP (Induction Coupled Plasma), on a Vista AX model (marketed by the Varian company).

The pore volume, the pore size distribution and the specific surface are determined by physical adsorption / desorption of N2 at -196 oc in a Nova 2000 model marketed by Quantachrorne. The samples are desorbed beforehand under vacuum at 250 ° C. for 2 hours. The specific surface ("SS" in Table 2) is calculated by the BET method (Brunauer Emmet Teller) as described in Journal of the American Chernical Society 60 (1938), pages 309 to 316. Determination of crystallized phases is carried out from powder X-ray diffraction patterns obtained with a BRUKER D5005 diffractometer, using copper Ka radiation (1.54060 Å). The intensity data are recorded over a range of 3-80 ° with a pitch of 0.02 ° and a counting time of 1s per step. The crystallized phases are identified by comparison with the standard JCPDS files. Table 2 provides the main crystallized phase detected ("Ph: Crist 1"). The product according to Example 4 has zircon as a secondary crystallized phase ("Ph. Cryst 2") in an amount of about 15%. The circularity squared of the crystallites is measured by a software of image processing from photographs made using a Scanning Electron Microscope (SEM). The powders of the examples were prepared from the following raw materials: TiO 2 powder comprising more than 98% of TiO 2, sold by the company Altichem, SiO 2 powder with a purity higher than 99.5% and a median size equal to 208 μm sold by the company Sifraco, a CeO2 powder with a purity greater than 99.9% and a median size equal to 3 gm, marketed by the company Affichent, a La203 powder with a purity greater than 99% and a median size equal to 5 gm sold by the company Treibacher, Y203 powder of greater than 99% purity and a median size equal to 5 gm, marketed by Altichem, Zr02 powder CC10 marketed by Saint-Gobain ZirPro. In step a), different starting charges were made according to the following Table 1. This table does not indicate the chemical composition of the feedstocks, but only the mass quantities of the abovementioned raw materials used for the various examples. Example powder CeO 2 ZrO 2 TiO 2 La 2 O 3 Y 2 O 3 SiO 2 molar ratio (CeO 2 + La 2 O 3 + Y 2 O 3) / SiO 2 60 9 5 - 26 0.8 2 60 9 5 - 26 0.8 3 60 9 5 - 26 0.8 4 60 9 5 In step b), the different starting charges were melted in an arc furnace of the same type. Héroult, under air, so as to obtain a liquid mass. In step c), the various liquid masses were cast in the form of a net of liquid, and then dispersed in the form of balls by blowing compressed air. The beads obtained were substantially entirely amorphous. The beads obtained were then dry-milled in a jar mill using zirconia balls stabilized at 3% by mass of magnesia. The powder thus obtained is then sieved so as to select the loop at 250 gm. Each powder obtained was then heat-treated, during step d), under air in an electric oven in the following thermal cycle: from 20 ° C. to 850 ° C.: rise to 100 ° C./h up to 850 ° C. ° C, - 10 hours at 850 ° C, 850 ° C to T: rise at 100 ° C / h, 10 hours at temperature T, - natural cooling at about 300 ° C / h, the temperature T being 900 ° C, 1000 ° C, 1100 ° C, 250 ° C, 1100 ° C and 1100 ° C, for the powders of Examples 1 to 6, respectively. In step e), the heat-treated powders were suspended in a 5 mol / l NaOH sodium hydroxide solution at 150 ° C. for 5 hours in order to solubilize the silicate glass phase.

In step 1), each suspension was filtered on a paper filter having pores with a diameter of 5 mm. The solid residue obtained was washed 5 times with deionized water. In step h), the wet cake obtained was dried at 110 ° C. for 12 hours and then spun in step i). The powders according to Examples 1 to 6 are powders according to the invention. The powder according to Example 7, apart from the invention, is a powder obtained by heat treatment at 1000 ° C. of cerium carbonate marketed by the company Sigma, and micro-milled in suspension with balls of diameter equal to 0.8 mm, and then dried. at 110 ° C for 12h. The powder according to Example 8, apart from the invention, is a powder marketed by Ferro under the name SRS-650. The characteristics of the powders obtained are given in Table 2 below: Ex. 1 2 3 4 5 6 7 * 8 * Chemical composition (in percentage on the basis of the oxides) Ce02 77.7 80.3 80.7 78.3 66, 6 79.3 99 57 SiO2 2 0.7 0.23 3.4 3.4 1.3 0.1 0.3 Zr02 + TiO2 16.7 18.1 18.6 18 15 11.5 - - Y203 + La203 - - - 14.8 6.9 - 42 Na2O 1.5 0.3 0.1 0.05 0.1 0.2 - A1203 0.04 0.03 0.03 0.03 0.02 0.02 0.03 0.01 1 (20 0.01 0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 B203 <0.01 <0.01 <0 , 01 <0.01 <0.01 <0.01 <0.01 <0.01 P205 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0, 01 0.01 Other 2.04 0.55 0.32 0.2 0.06 0.76 0.83 0.67 Including Zr02 10.5 11.8 12.1 12 9.5 8.5 - Ti 02 6.2 6,3 6,5 6,5,5 3 - La203 - .. - - 14,8 38 Y203 - - - - 6,9 - 4 Particle size distribution of the particles D10 0,12 μm 0,14 gni 2 0 , 1.2 μm 0.2 μm 0.2 μm 0.1 μm 1.1 μm 1 μm D50 0.2 μm 0.3 μm 3 μm 0.3 μm 0.3 μm 0.3 2.4), im 0.2.5 1-1M D90 1.0 1.11 gin 1 1, 6.7 i.tin 1.2! lm 1.1 pm 1.2 Ftm 6.3 1.1m! Im Crystalline characteristics C250 0.99 0.99 0.99 0.98 0.99 0.99 0.90 0.85 dm 12 nm 24 nm 66 nm 70 nrn 25 nm 25 nm 25 nm 150 nm Other features Ph. Crist. 1 Ce02 cubic% of Ph. Crist. 1, in> 95> 95> 95 85> 95> 95> 95. % of the total volume> 95 of the phases of the powder Ph. Crist. 2 zircon SS (m 2 / g) 60 21 7.5 0.7 24 23 20 2.5 *: Examples outside the invention Table 2 To evaluate the polishing performance of the powders of Examples 2 and 5 according to the invention, and 7 and 8 out of the invention, a suspension of each powder was prepared by mixing 10% by weight of powder, 1% of ammonium polyaerylate, the balance being deionized water. One kilogram of the suspension obtained was milled for 60 minutes in a LME-1 micro-grinder, in recirculation configuration, before starting the test, in order to agglomerate the agglomerates of crystallites.

A chemical mechanical polishing ("CMP") was carried out with the suspensions obtained on a Buehler POWERPRO 4000 Grinderpolisher machine on a soda-lime glass of 3 cm in diameter. The glass support rotated at 60 rpm and the table turned at 400 rpm. The duration of the test was 30 minutes. The rate of removal of material or "removal rate" is defined as the thickness removed during polishing divided by the polishing time, in Angstrom / min. The removed thickness is calculated to be equal to [4. (weight before polishing - mass after polishing)] / [(density of machined glass) .n.d21, d being equal to the diameter of the machined glass piece, c that is 3 cm. After polishing, the roughness Ra is measured and a qualitative criterion of the surface appearance is assigned to said surface. The results obtained are shown in Table 3 below: Powder according to rate of removal Roughness Ra Qualitative criterion of the example of material (AJmin) (Inn) surface appearance 2 4000 7 Excellent 5 4000 8 Excellent 7 * 3000 15 Medium As it is now clear, a powder according to the invention makes it possible to achieve a high rate of removal of material, to obtain an excellent surface state, while reducing the risk of contamination of the surface. said surface, in particular thanks to the low content of B203 and P205. Of course, the present invention is not limited to the described embodiments provided as illustrative and non-limiting examples.

Claims (25)

REVENDICATIONS1. A powder comprising more than 50% by volume of a crystalline phase containing cerium oxide, as a percentage of the total volume of the phases of the powder, and a chemical composition, as a percentage by mass on the basis of the oxides and for a total of of 100%, such as: CeO 2 50%, SiO 2, 10%, 1% ZrO 2 + TiO 2 5. 30%, provided that 0.5% TiO 2, 20%, Sc 2 O 3 + Y 2 O 3 + lanthanide oxides ( s) except CeO 2 5 40%, Al 2 O 3 5 10%, - Na 2 O + K 2 O 5 5%, - other 5 5% oxides, and comprising more than 90% by mass of crystallites, isolated or in agglomerated form, all of said crystallites having a median squared circularity C250> 0.95, and - an average dimension dm of between 10 nm and 1000 nm. 2. Powder according to the immediately preceding claim, having a composition such that: CeO 2> 60%, and / or SiO 2 <8%, and / or ZrO 2> 1% and ZrO 2 <25%, and / or TiO 2> 1% and TiO 2 <15%, and / or - Sc203 + Y203 + lanthanide oxides (s) except Ce02 <30%, and / or A1203 <5%, and / or Na20 + K20 <3%, and / or - B203 <0, 05%, and / or P205 <0.05%, and / or other oxides <3%. B203 0.1%, P205 0.1%, 3. Powder according to the immediately preceding claim, having a composition such that: CeO 2> 75%, and / or SiO 2 <2%, and / or ZrO 2> 5% and ZrO 2 <20%, and / or TiO 2> 5% and TiO 2 <10%, and / or Sc203 + Y203 + lanthanide oxides except Ce02 <20%, and / or A1203 <1%, and / or Na20 + K20 <1%, and / or B203 <0.01% , and / or P205 <0.01%, and / or other oxides <1%. 4. Powder according to the immediately preceding claim, having a composition such that: CeO 2> 90%, and / or SiO 2 <0.5%, and / or ZrO 2 <15%, and / or - Sc 2 O 3 + Y 2 O 3 + lanthanide oxides ( s) except Ce02 <15%, and / or - A1203 <0.5%, and / or Na20 + K20 <0.5%, and / or - other oxides <0.1%. 5. Powder according to any one of the preceding claims, comprising more than 98% by mass of crystallites. 6. Powder according to any one of the preceding claims, having a composition such that at least one sum of S oxides selected from - Ce02 + Sc203 + Y203 + lanthanide oxides (s) except Ce02, preferably Ce02 La203, and - CeO 2 + ZrO 2 + TiO 2 + Sc 2 O 3 + Y 2 O 3 + oxides of lanthanide (s) except CeO 2, preferably CeO 2 + ZrO 2 + TiO 2 + La 2 O 3, or even CeO 2 + ZrO 2 + T / O 2, is greater than 60%. Powder according to the immediately preceding claim, wherein S> 90%. 8. Powder according to any one of the preceding claims, having a composition such as 5% <Y203 <10% and / or 10% <La203 <30%. 9. The powder according to any one of the preceding claims, wherein C250> 0.98. 10. Powder according to any one of the preceding claims, consisting of more than 50% of a crystalline phase selected from the group formed by the cubic CeO 2 phase, the solid solutions CeO 2 - (ZrO 2 and / or TiO 2), the solid solutions CeO 2 - (Se 2 O 3 and / or Y 2 O 3 and / or lanthanide oxides (except CeO 2), Ceer, Ti) 207 and mixtures thereof. 11. The powder according to the immediately preceding claim, consisting of more than 90% of a crystalline phase chosen from the group formed by the cubic CeO 2 phase, the solid solutions CeO 2 - (ZrO 2 and / or TiO 2), the solid solutions CeO 2 - ( Sc203 and / or Y203 and / or lanthanide oxides except Ce02), Ce2 (Zr, Ti) 207 and mixtures thereof. The powder according to any one of the preceding claims, wherein the particle size dispersion index of the powder, (D90-DeD50, is less than 10. 13. Powder according to the immediately preceding claim, wherein (D90-D10) / D50 is less than 5. 14. Powder according to any one of the preceding claims, having a specific surface area greater than 5 m 2 / g. 15. Powder according to the immediately preceding claim, having a specific surface area greater than 10 m 2 / g. 16. Powder according to any one of the preceding claims, having a pore volume greater than 0.05 em3 / g and / or a median pore size of between 1 min and 100 min. 17. Powder according to the immediately preceding claim, having a pore volume greater than 0.1 cm3 / g. 18. The powder according to any one of the preceding claims, wherein the pore size dispersion index (P90-P10) / P50 of the agglomerates of said crystallites is less than 20. Powder according to any one of the preceding claims, wherein more than 80% by number of said crystallites are agglomerated in the form of agglomerates, the median size of all these agglomerates being greater than 0.1 mm and less at 1 mm. 20. Use of a powder according to any one of the preceding claims, for a TWC-type polishing, the mean dimension of said crystallites being between 50 and 100 ntri or for a CMP-type polishing, the average dimension of said crystallites being between 100 and 200 minutes or for a polishing of CMP type, the mean dimension of said crystallites being between 200 and 500 nm, or - to make a film having a thickness of less than 250 μm, or - to manufacture a suspension comprising more than 0.1% and less than 20% of said crystallites, in weight percentage on the basis of the mass of said suspension, or in a catalytic coating, in particular for automotive catalysis, for example in a three-way catalysis device or N0x nitrogen oxides reduction catalyst, or - as raw material for the manufacture of an electrode or an ionic conductor based on oxides of Y, Ce, Gd, and their mixtures, or - as a raw material for the manufacture of a technical ceramic made up of more than 90% by weight of CeO 2 and ZrO 2, or - as a powder for polishing, in particular for polishing an LCD glass, a photo-mask, a mirror, an integrated circuit, and a semiconductor element. 21. A method of manufacturing a powder according to any one of claims 1 to 19, comprising the following successive steps: a) preparation of a feedstock adapted to obtain, after step c), a product comprising, in weight percent on the oxide basis: - 10% SiO2, and CeO2 + Se203 + Y203 + lanthanide oxides (s) except CeO2, 40%, and - 1% ZrO2 + TiO2 5_ 30%, - Other oxides: <5% the ratio R of the number of moles of (CeO 2 + Sc 2 O 3 + Y 2 O 3 + lanthanide oxides (except CeO 2)) on the number of moles of SiO 2 being greater than or equal to 0.2, and the ratio R ' of the mass of CeO 2 on the mass of (ZrO 2 + TiO 2 + Se 2 O 3 + Y 2 O 2 + lanthanide oxides (except CeO 2) being greater than or equal to 1, b) melting of the starting charge so as to obtain a liquid mass, c ) quenching of the liquid mass, in order to obtain a molten product having less than 50% by volume of crystallized phase (s), more than 95% of the crystallites having a smaller dimension less than 1000 nm, or even an amorphous melt, d) crystallization heat treatment so as to obtain a crystallite structure in a vitreous phase, e) solubilization of the glass phase and separation of said crystallites, f) rinsing and / or filtration said crystallites, g) optionally, wet microgrinding, h) optionally, drying, i) optiormally, crumbling and / or grinding. 22. Method according to the immediately preceding claim, wherein in step a), the initial charge is adapted to obtain, after step c), a product having a ratio R less than 3. 23. Method according to the preceding claim, wherein the ratio R is greater than 0.7 and / or less than 1.5. 24. A method according to any one of the three immediately preceding claims, wherein in step a), the feedstock is adapted to obtain, at the end of step c), a product having a ratio R '. greater than 2.3. 25. A process according to any one of the four immediately preceding claims wherein in step c) the cooling rate is greater than 500 ° C / sec.