Coated cerium suboxide particles and their preparation by flame spray pyrolysis

Abstract

The present invention relates to coated cerium oxide particles, a process for preparing coated cerium oxide particles or cerium suboxide particles by flame spray pyrolysis techniques, cerium oxide particles obtained from such processes, compositions comprising such particles, and uses thereof.

Description

[Technical Field]

[0001] The present invention relates to coated cerium suboxide particles, a process for preparing coated cerium oxide particles or cerium suboxide particles by flame spray pyrolysis techniques, cerium oxide particles obtained from such processes, compositions comprising such particles, and uses thereof. [Background technology]

[0002] Metal oxides are used in many applications (cosmetics, paints, varnishes, electronics, rubber, etc.) in particular for their optical properties, and in particular for their light-absorbing and / or scattering properties to protect surfaces from UV radiation and / or to convert ambient light into electricity.

[0003] However, metal oxides have the drawback of being particularly unstable over time. For example, zinc oxide can convert to zinc hydroxide or even ZnO in the presence of water, either from the composition containing it or from atmospheric moisture. 2+ Such decomposition can result in partial or even complete dissolution of zinc oxide in water and can serve to significantly reduce or even eliminate the desirable properties of zinc oxide.

[0004] This instability is particularly problematic when metal oxides are used in photoprotective cosmetic compositions: as the metal oxide decomposes, UV protection actually decreases.

[0005] Coating metal oxides with silica, particularly using a sol-gel process, or grafting fluoro compounds onto metal oxides has been considered. However, these solutions are not entirely satisfactory. Metal oxides coated with silica by the sol-gel process generally have inferior optical properties compared to uncoated particles. With regard to grafting techniques, the use of fluoro compounds can be harmful to the environment and to users.

[0006] It is also known to use a flame spray pyrolysis (FSP) method to prepare metal oxide particles.

[0007] Flame spray pyrolysis or FSP is a well-known method developed today for the synthesis of ultrafine powders of single or mixed oxides of various metals (e.g., SiO, AlO, BO, ZrO, GeO, WO, NbO, SnO, MgO, ZnO) with controlled morphology and / or their deposition on various substrates, generally starting from a wide variety of metal precursors in the form of organic or inorganic, preferably combustible, sprayable liquids. The liquids sprayed into the flame, when consumed, release, among other things, metal oxide nanoparticles that are projected by the flame itself onto the various substrates in question. The principles of this method were recalled, for example, in a recent (2011) publication by Johnson Matthey entitled "Flames of Metal Oxide Particles: A Novel Approach to the Synthesis of Metal Oxides and Mixed Oxides of Metals," vol. 1, No. 1, pp. 111-114, 2011. Numerous variations of FSP processes and reactors are also described, for example, in the following patents or patent applications: U.S. Pat. No. 6,229,499; ... [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 5,958,361 [Patent Document 2] U.S. Patent No. 2,268,337 [Patent Document 3] International Publication No. 01 / 36332 or U.S. Patent No. 6,887,566 [Patent Document 4] International Publication No. 2004 / 005184 or U.S. Patent No. 7,211,236 [Patent Document 5] International Publication No. 2004 / 056927 Pamphlet [Patent Document 6] International Publication No. 2005 / 103900 Brochure [Patent Document 7] International Publication No. 2007 / 028267 or U.S. Patent No. 8,182,573 [Patent Document 8] International Publication No. 2008 / 049954 or U.S. Patent No. 8,231,369 [Patent Document 9] International Publication No. 2008 / 019905 Brochure [Patent Document 10] US Patent Application Publication No. 2009 / 0123357 [Patent Document 11] US Patent Application Publication No. 2009 / 0126604 [Patent Document 12] US Patent Application Publication No. 2010 / 0055340 [Patent Document 13] International Publication No. 2011 / 020204 Brochure [Non-patent literature]

[0009] [Non-Patent Document 1] Johnson Matthey, “Flame Spray Pyrolysis: a Unique Facility for the Production of Nanopowders”, Platinum Metals Rev., 2011, 55, (2), 149-151

[0010] However, the methods used to prepare metal oxides leave room for improvement, particularly to improve the stability of the metal oxide particles over time, more particularly their water resistance. More specifically, these preparation processes do not allow for the easy and large production of intermediate oxidation state metal oxides or metal suboxides. Furthermore, intermediate oxidation state metal oxides and metal suboxides prepared according to these known processes are not stable over time and oxidize to their maximum oxidation state very quickly upon contact with ambient air. Summary of the Invention [Problem to be solved by the invention]

[0011] There is therefore a real need to develop metal oxide particles that have good stability over time, in particular good water resistance, while at the same time maintaining good optical properties in terms of absorption and / or scattering of light, more particularly ultraviolet light; and to develop a process that allows the preparation of such particles.

[0012] In addition, it is of interest to develop processes for preparing such particles, in particular particles of intermediate oxidation states of metal oxides and metal suboxides, which have good stability over time and good optical properties with respect to absorption and / or scattering of light, more particularly ultraviolet light. [Means for solving the problem]

[0013] These objects are achieved by the present invention, one subject of which are in particular cerium suboxide particles, in particular of the Ce-M' suboxide type, having a core / shell structure: (i) Formula (I'): Chief Operating Officer 2-x (I') (In the formula: - x is a non-integer number strictly between 0 and 2) a core 1 comprising at least one cerium suboxide; (ii) an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 having the formula (II): M'p O q (II) (In the formula: M' is an element selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements; - p represents an integer greater than or equal to 1; - q represents an integer of 0 or more), and an upper coating layer 2 composed of at least one compound of Includes.

[0014] It has been found that the coated cerium oxide particles according to the present invention do not decompose significantly over time in the presence of water, even when formulated into compositions, particularly aqueous compositions.

[0015] More particularly, it has been observed that the cerium suboxide particles according to the invention are particularly stable over time (ie the particles remain in their suboxide state).

[0016] It has also been found that the cerium oxide particles according to the invention have good optical properties with respect to light absorption and / or scattering, more particularly, they have high UV absorption and low or high visible scattering, which allows the use of sunscreens etc. and / or modification of the visual appearance, while benefiting from their resistance in the presence of water.

[0017] In addition, the composition containing the coated cerium oxide particles according to the present invention exhibited good shielding power, particularly against long UV-A rays and short UV-A rays.

[0018] Furthermore, compositions comprising the coated cerium oxide particles of the present invention have particularly high transparency, which may prove advantageous when the composition is applied onto a coating, particularly onto the skin, and then dried.

[0019] Additionally, the coated cerium oxide particles according to the present invention do not require a hydrophobic coating and can therefore be used in a wide range of formulations (e.g., in fully aqueous and / or surfactant-free formulations), further reducing the risk of undesirable deposition (on sink edges, pipe walls, or rocks) if the resulting formulation ends up in water (sink drain, lake water, or seawater).

[0020] The present invention also provides (i) Formula (I): Chief Operating Officer 2-x (I) (In the formula: - a core 1 consisting of at least one cerium oxide, where x is equal to 0 or represents a non-integer strictly between 0 and 2; (ii) an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 having the formula (II): M' p O q (II) (In the formula: M' is an element selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements; - p represents an integer greater than or equal to 1; - q represents an integer of 0 or more), and an upper coating layer 2 composed of at least one compound of 1. A process for preparing cerium oxide or cerium suboxide particles coated with an oxide of element M′, in particular of the Ce-M′ (sub)oxide type having a core / shell structure, comprising: At least the following steps: a. preparing composition (A) by adding one or more cerium precursors to a flammable solvent or mixture of flammable solvents; and b. forming a flame in the flame spray pyrolysis device 10 by injecting the composition (A) and the oxygen-containing gas (G) until aggregates of cerium oxide of formula (I) are obtained; and then c. injecting a composition (B) containing one or more precursors of element M' until a top coating layer 2 composed of element M' or an oxide of element M' of formula (II) is obtained on the surface of the cerium oxide aggregates; Includes; The flame spray pyrolysis apparatus 10 is for a process that is isolated from the outside air so that the amount of oxygen present within the apparatus is controlled.

[0021] It has been found that the process according to the invention makes it possible to obtain cerium oxide and cerium suboxide particles coated with a layer of an inorganic material based on element M′ that is particularly stable over time and has good water resistance.

[0022] Furthermore, unlike conventional coating processes, the process according to the invention has the advantage of maintaining the good intrinsic performance qualities of the core despite the presence of the top coating layer: indeed, due to the specific properties of the top coating layer, for a given particle mass it is possible to reduce the properties of cerium oxide or cerium suboxide and / or to lower the proportion of said cerium oxide or cerium suboxide without adversely affecting said properties.

[0023] Thus, the process of the present invention makes it possible to prepare stable cerium oxide and cerium suboxide particles while avoiding the drawbacks resulting from the increased amounts of particles previously required to maintain the good optical properties of cerium oxide or cerium suboxide.

[0024] The present invention also relates to a composition, preferably a cosmetic composition, comprising one or more cerium oxide particles according to the invention.

[0025] The invention will be more clearly understood by studying the detailed description of embodiments given by way of in no way limiting example as illustrated by the accompanying drawings, which are not necessarily to scale. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a cross-sectional view of a cerium suboxide particle of formula (I′) coated with a compound of formula (II) according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a flame spray pyrolysis apparatus for preparing particles according to the present invention. [Figure 3] FIG. 2 is a schematic diagram of a flame spray pyrolysis apparatus for preparing particles according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Other characteristics, aspects and advantages of the present invention will become more clearly apparent from a reading of the following description and examples.

[0028] In this specification, unless otherwise indicated, - the expression "at least one" is equivalent to and can be substituted for the expression "one or more"; - the expression "~" means that it is equivalent to and can be substituted for the expression "extending to" and that the limit is included; - the expression "strictly between" is equivalent to and can be substituted for the expression "strictly in the range of" and means that no limit points are included; - the expression "keratinous substances" denotes in particular skin and human keratinous fibers, such as hair; - Core 1, also known as the "heart" or "core"; the upper coating layer 2, also called the "outer layer", "casing", "coating" or "shell"; - for the purposes of the present invention, the term "elements of the third column of the periodic table of the elements" means scandium and yttrium. In other words, elements of the lanthanide and actinide families do not belong to the elements of the third column of the periodic table of the elements within the meaning of the present invention; The term "alkyl" means an "alkyl radical", i.e., a linear or branched C1-C 10, in particular C1-C8, more particularly C1-C6 and preferentially C1-C4 hydrocarbon-based radicals, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl or tert-butyl; the term "aryl" group denotes a monocyclic or fused or non-fused polycyclic carbocyclic group containing 6 to 22 carbon atoms, at least one ring of which is aromatic, preferentially an aryl group being phenyl, biphenyl, naphthyl, indenyl, anthracenyl or tetrahydronaphthyl, preferably phenyl; - The term "arylate" group refers to one or more carboxylates -C(O)O - means an aryl group containing a group, for example, naphthalate or naphthenate; - the term "complexed metal" means that a metal atom forms a "metal complex" or "coordination compound" in which the metal ion corresponding to the central atom, i.e., M, is chemically bound to one or more electron donors (ligands); The term "ligand" means a coordinating organic chemical group or compound, i.e., which contains at least one carbon atom and is capable of coordinating with a metal M, resulting, once coordinated or complexed, in a metal compound (internal complex or chelate) that corresponds to the principle of a coordination sphere with a given number of electrons - see Ullmann's Encyclopedia of Industrial Chemistry, "Metal-Complex Dyes", 2005, pages 1-42. More particularly, the ligand is an organic group that contains at least one group that is electron-donating via the inductive and / or mesomeric effect, more particularly an organic group that carries at least one amino, phosphino, hydroxy, or thiol electron-donating group, or the ligand is a persistent carbene, in particular of the "argengo" type (imidazol-2-ylidene), or contains at least one carbonyl group. More particularly, mention may be made of the following ligands: i) those containing at least one phosphorus-P< atom, i.e. phosphines such as triphenylphosphine; ii) bidentate ligands of formula RC(X)-CR'R''-C(X)-R''', such as acetylacetone or β-diketones, where R and R''', which may be identical or different, represent a linear or branched (C1-C6) alkyl group, and R' and R'', which may be identical or different, are a hydrogen atom or a linear or branched (C1-C6) alkyl group, preferentially R' and R'' represent a hydrogen atom and X represents an oxygen atom, a sulfur atom or a group N(R), where R represents a hydrogen atom or a linear or branched (C1-C6) alkyl group; iii) lactic acid, glycolic acid, tartaric acid, citric acid and maleic acid, and arylates, such as naphthalates, of formula [HO-C(O)] n-AC(O)-OH (poly)hydroxycarboxylic acid ligands and their deprotonated forms, in which A represents a monovalent group when the value of n is zero, or a polyvalent group when n is 1 or more, which is saturated or unsaturated, cyclic or acyclic, aromatic or non-aromatic, based on a hydrocarbon containing 1 to 20 carbon atoms, optionally interrupted by one or more heteroatoms and / or optionally substituted, in particular by one or more hydroxyl groups; preferably A represents a monovalent (C1-C6) alkyl group or a polyvalent (C1-C6) alkylene group, optionally substituted by one or more hydroxyl groups, and n represents an integer between 0 and 10 (inclusive), preferably n is 0 to 5, for example 0, 1 or 2; and iv) C2-C alkyl groups containing 2 to 5 hydroxyl groups. 10 Polyol ligands, especially ethylene glycol or glycerol; more particularly ligands having carboxy, carboxylate, or amino groups; in particular ligands selected from acetate, (C1-C6)alkoxylate, (di)(C1-C6)alkylamino, and arylate, e.g., naphthalate or naphthenate groups; The term "flammable" means a liquid compound or gas that, together with dioxygen and energy, is consumed in an exothermic chemical reaction: combustion. In particular, liquid combustibles are selected from protic solvents, in particular alcohols (such as methanol, ethanol, isopropanol or n-butanol); esters (such as methyl esters) and those derived from acetates (such as 2-ethylhexyl acetate), acids (such as 2-ethylhexanoic acid (EHA)), acyclic ethers (such as ethyl ether, methyl tert-butyl ether (MTBE), methyl tert-amyl ether (MTAE), methyl tert-hexyl ether (MTHE), ethyl tert-butyl ether (ETBE), ether tert-amyl ether (ETAE) or diisopropyl ether (DIPE)), cyclic ethers (such as tetrahydrofuran (THF)), aromatic hydrocarbons or arenes (such as xylene), aprotic solvents chosen in particular from non-aromatic hydrocarbons, and mixtures thereof. The combustible may optionally be selected from liquefied hydrocarbons such as acetylene, methane, propane, or butane; and mixtures thereof.

[0029] Coated cerium suboxide particles Cerium suboxide particles, especially of the Ce-M' suboxide type with a core / shell structure, are: (i) Formula (I'): Chief Operating Officer 2-x (I') (In the formula: - x is a non-integer number strictly between 0 and 2) a core 1 comprising at least one cerium suboxide; (ii) an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 having the formula (II): M' p O q (II) (In the formula: M' is an element selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements; - p represents an integer greater than or equal to 1; - q represents an integer of 0 or more), and an upper coating layer 2 composed of at least one compound of Includes.

[0030] In accordance with the present invention, the non-integer x in formula (I') is strictly between 0 and 2. Therefore, x in formula (I') cannot be 0 (zero) or 2. In other words, cerium oxide CeO2 (x=0) and pure elemental cerium (x=2) are not included within the scope of cerium suboxide in formula (I').

[0031] Preferably, the core 1 is in a crystalline state.

[0032] The crystalline state of Core 1 and its composition can be determined, for example, by conventional X-ray diffraction methods.

[0033] Advantageously, the core 1 of the particle according to the invention consists of one or more agglomerates of crystalline primary cerium suboxide particles, in other words, it consists of several cerium suboxide microcrystals.

[0034] The coated cerium suboxide particles according to FIG. 1 have an average diameter D m Includes Core 1.

[0035] Also, the coated cerium suboxide particles according to FIG. 1 are composed of a compound of formula (II), completely coating the surface of the core 1 and having an average thickness d m The upper coating layer 2 includes:

[0036] Number average diameter D of core 1 m can be determined, for example, by transmission electron microscopy (abbreviated as TEM). Preferably, the number-average diameter D of the core 1 of the particles according to the invention m is in the range of 3 to 5000 nm, more preferentially 10 to 3000 nm, and even more preferentially 30 to 1000 nm.

[0037] The coated cerium suboxide particles according to the present invention comprise an upper coating layer 2 covering the surface of a core 1 and comprising a compound of formula (II).

[0038] Advantageously, the top coating layer 2 covers at least 90% of the surface of the core 1. More preferentially, the top coating layer 2 covers the entire surface of the core 1.

[0039] The coverage of the core by the upper coating layer can be determined, for example, by visual analysis of the TEM-BF or STEM-HAADF type combined with STEM-EDX analysis.

[0040] Each analysis is carried out on a statistical particle count, in particular at least 20 particles. The particles are deposited on a metal grid made of metal other than any metal that forms part of the particle (whether in the core or in the top coating layer). For example, the grid is made of copper.

[0041] Visual analysis of the TEM-BF and STEM-HAADF images allows one to infer, based on contrast, whether the coating completely surrounds the particle's core. By analyzing each of the 20 (or more) images, it is possible to infer the coverage of the core therefrom and then average them to determine the average coverage.

[0042] STEM-EDX analysis makes it possible to verify that the coating indeed contains mainly or exclusively the element M'. For this purpose, pointing must be carried out at the edge of the particles (for at least 20 particles), which reveals the element M'.

[0043] STEM-EDX analysis can also demonstrate that the core contains cerium. For this, pointing must be performed in the center of the particles (for at least 20 particles), which reveals cerium and the element M'.

[0044] According to the invention, the element M' is selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements.

[0045] Therefore, according to the invention, the element M' is different from cerium.

[0046] Preferably, element M' is selected from selenium, titanium, aluminum and elements of column 14 of the periodic table of the elements.

[0047] More preferentially, the element M' is chosen from selenium, titanium, aluminum, carbon and silicon.

[0048] Most particularly preferably, the element M' is selected from carbon and silicon.

[0049] According to a preferred embodiment, the element M' is silicon.

[0050] According to another embodiment of the invention, the element M' is carbon.

[0051] Preferably, the integer p ranges from 1 to 4. More preferentially, the integer p is equal to 1 or 2, and even better still, p is equal to 1.

[0052] Preferably, the integer q ranges from 0 to 4. More preferentially, the integer q is strictly greater than 0. Even more preferentially, the integer q ranges from 1 to 4.

[0053] Preferably, the compound of formula (II) is selected from carbon, SiO2, SnO2, and Al2O3.

[0054] More preferentially, the compound of formula (II) is chosen from carbon and SiO2.

[0055] of formula CeO in core 1 of the particle according to the invention 2-x Cerium oxide has a non-stoichiometric intermediate oxidation state.

[0056] For purposes of the present invention, the term "intermediate oxidation number" means an oxidation number between 0 (not included) and the maximum oxidation number of the metallic element (not included).

[0057] More generally, an oxidation number is referred to as a stoichiometric intermediate oxidation number if it is an integer. For example, if the metal element having an intermediate stoichiometric oxidation number is iron, the iron oxide may be FeO and Fe3O4. As another example, if the metal element having an intermediate stoichiometric oxidation number is copper, the copper oxide may be Cu2O.

[0058] If the oxidation number is not an integer, the expression "non-stoichiometric intermediate oxidation number" is used. When a metal element has a non-stoichiometric intermediate oxidation number, it is called a metal element suboxide. For example, if the metal element having a non-stoichiometric intermediate oxidation number is iron, the iron suboxide has the formula FeO 1-x A compound of formula FeO 4-x and compounds of the formula FeO 3-x As another example, if the metallic element having a non-stoichiometric intermediate oxidation state is copper, then cuprous oxide can be a compound of the formula CuO 1-x and the compound of formula CuO 1-x The compound may be:

[0059] According to a preferred embodiment of the present invention, the particles are: - cerium suboxide CeO of formula (I') 2-x Core 1, consisting of: (where x is a non-integer number strictly between 0 and 2); an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 being composed of a compound of formula (II) selected from carbon, SiO2, SnO2 and Al2O3, preferentially SiO2; Includes.

[0060] According to another particularly preferred embodiment of the invention, the particles comprise: - cerium suboxide CeO of formula (I') 2-x Core 1, consisting of: (where x is a non-integer number strictly between 0 and 2); an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 being composed of a compound of formula (II) selected from carbon and SiO2, preferentially SiO2; Includes.

[0061] The number average thickness of the upper coating layer, d m can be determined by transmission electron microscopy.

[0062] Preferably, the number average thickness d of the upper coating layer m is in the range of 1 to 20 nm, more preferentially 1 to 10 nm, and even more preferentially 2 to 6 nm.

[0063] Advantageously, the top coating layer 2 is amorphous.

[0064] Advantageously, the top coating layer 2 is transparent.

[0065] Advantageously, the particles according to the invention comprise cerium and the element M' in a specific molar atomic ratio (Ce / M').

[0066] Said ratio corresponds on the one hand to the molar amount of cerium present in the particles according to the invention and on the other hand to the molar amount of element M' present in the particles according to the invention.

[0067] This ratio can be determined by spectroscopic measurements according to one of the following two methods: According to the first method, the powder is spread and an X-ray fluorescence measurement study is carried out by an X-ray spectrometer, from which the metal ratio is inferred; According to the other method, the particles of the present invention are dissolved in acid beforehand. Then, an elemental analysis is carried out on the obtained material by ICP-MS (Inductively Coupled Plasma Mass Spectrometry), from which the metal ratio is inferred.

[0068] Preferably, the molar atomic ratio (Ce / M') of the particles according to the invention is strictly greater than 0.2; more preferentially greater than or equal to 1; even more preferentially in the range from 1 to 100; better still in the range from 1 to 10, and even better still in the range from 1.5 to 10.

[0069] The number average diameter of the particles according to the present invention can be determined by transmission electron microscopy. Preferably, the number average diameter of the particles according to the present invention is in the range of 4 to 5000 nm, more preferably 10 to 3000 nm, and even more preferably 30 to 1000 nm.

[0070] Preferably, the particles according to the invention have a BET specific surface area of ​​1 m 2 / g~200m 2 / g, more preferentially between 30 and 100 m 2 / g.

[0071] Also, according to certain embodiments of the present invention, the coated particles according to the present invention may optionally comprise an additional coating layer covering the top coating layer 2 and comprising at least one hydrophobic organic compound.

[0072] The hydrophobic organic compounds contained in the additional coating layer are more preferentially selected from silicones, in particular silicones containing at least one fatty chain, carbon-based derivatives containing at least 6 carbon atoms, in particular fatty acid esters; and mixtures thereof.

[0073] The additional coating layer can be produced via a liquid route or a solid route. Via the liquid route, hydroxyl functional groups react with reactive functional groups of the compound that will form the coating (typically silanol functional groups of silicones or acid functional groups of carbon-based fatty substances). Via the solid route, the particles are placed in contact with a liquid or pasty compound that contains a hydrophobic substance.

[0074] Preferably, the coated particles according to the invention are obtained by the inventive preparation process described below.

[0075] Process for preparing coated particles Another subject of the present invention relates to a process for preparing cerium oxide or cerium suboxide particles of the following formula (I) coated with an oxide of element M', in particular an oxide of the Ce-M' (sub)oxide type with a core / shell structure, comprising at least a step a. of preparing composition (A), then a step b. of forming a flame, and a step c. of injecting composition (B).

[0076] The cerium (sub)oxide particles coated with an oxide of element M′ that can be prepared by the preparation process according to the invention are: (i) Formula (I): Chief Operating Officer 2-x (I) (In the formula: - a core 1 consisting of at least one cerium oxide, where x is equal to 0 or represents a non-integer strictly between 0 and 2; (ii) an upper coating layer 2 covering the surface of the core 1, the upper coating layer 2 having the formula (II): M' p O q (II) (In the formula: M' is an element selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements; - p represents an integer greater than or equal to 1; - q represents an integer of 0 or more), and an upper coating layer 2 composed of at least one compound of Includes.

[0077] The cerium (sub)oxide particles of formula (I) above are: cerium suboxide CeO of the above formula (I') 2-x and a cerium suboxide particle according to the present invention, comprising a core 1 consisting of: Cerium oxide particles containing a core 1 composed of cerium oxide CeO2 (x equals 0) Includes.

[0078] Step a. of the process according to the invention consists in preparing a composition (A) by adding one or more cerium precursors to a flammable solvent or mixture of flammable solvents.

[0079] The cerium precursors and flammable solvents that can be used in accordance with the present invention can be selected from cerium precursors and flammable solvents conventionally used in flame spray pyrolysis.

[0080] Preferably, the cerium precursor contained in composition (A) is selected from cerium (III) salts, cerium (IV) salts, and mixtures thereof.

[0081] The cerium(III) and cerium(IV) salts used may be in anhydrous or hydrated form.

[0082] More preferentially, the cerium precursor contained in composition (A) is chosen from cerium(III) ethylhexanoate, cerium(III) acetate, cerium(III) chloride, cerium(III) nitrate, cerium(IV) sulfate, cerium(IV) naphthenate, and mixtures thereof.

[0083] More preferentially, the cerium precursor contained in composition (A) is chosen from cerium(III) ethylhexanoate, cerium(III) chloride, cerium(III) nitrate, and mixtures thereof.

[0084] Preferably, the flammable solvent is selected from protic flammable solvents, aprotic flammable solvents, and mixtures thereof; more preferentially alcohols, esters, acids, acyclic ethers, cyclic ethers, aromatic hydrocarbons or arenes, non-aromatic hydrocarbons, such as liquefied hydrocarbons, for example acetylene, methane, propane, or butane, and mixtures thereof; and even more preferably, 2-ethylhexyl acetate, 2-ethylhexanoic acid (EHA), ethyl ether, methyl tert-butyl ether (MTBE), methyl tert-amyl ether (MTAE), methyl tert-hexyl ether (MTHE), ethyl tert-butyl ether (ETBE), ether tert-amyl ether (ETAE), diisopropyl ether (DIPE), tetrahydrofuran (THF), xylene, and mixtures thereof.

[0085] In particular, the flammable solvent may be selected from aprotic flammable solvents containing at least three carbon atoms and mixtures thereof; and even better, from xylene, toluene, tetrahydrofuran, 2-ethylhexyl acetate, 2-ethylhexanoic acid (EHA), and mixtures thereof.

[0086] According to a particular embodiment of the present invention, composition (A) comprises a mixture of flammable solvents, preferably comprising at least two of the following flammable solvents: 2-ethylhexanoic acid (EHA), toluene, absolute ethanol, and diethylene glycol monobutyl ether.

[0087] Even better, composition (A) comprises a flammable solvent mixture consisting of 2-ethylhexanoic acid (EHA), toluene, absolute ethanol, and diethylene glycol monobutyl ether.

[0088] Even better, composition (A) comprises a flammable solvent mixture consisting of at least 5% by volume of 2-ethylhexanoic acid (EHA), at least 5% by volume of toluene, at least 5% by volume of absolute ethanol, and at least 5% by volume of diethylene glycol monobutyl ether, based on the total volume of the flammable solvent mixture.

[0089] Advantageously, the content of cerium precursor in composition (A) is between 1% and 60% by weight, preferably between 15% and 30% by weight, relative to the total weight of composition (A).

[0090] The preparation process according to the present invention also includes step b. of injecting the composition (A) and an oxygen-containing gas (G) into a flame spray pyrolysis (FSP) apparatus 10 to form a flame.

[0091] The flame spray pyrolysis apparatus 10 is described in more detail below with reference to FIGS.

[0092] During this step b., the composition (A) and the oxygen-containing gas (G) are advantageously injected into the flame spray pyrolysis device 10 .

[0093] Preferably, the flame formed during step b. has a temperature of 2000° C. or greater at at least one point within the flame.

[0094] Step b. may also optionally include the additional injection of a "premix" gas mixture (P) containing oxygen and one or more combustible gases, such as methane. This "premix" gas mixture (also referred to as "supporting flame oxygen") allows the generation of a supporting flame intended to ignite and sustain the flame resulting from composition (A) and oxygen-containing gas (G) (i.e., "dispersed oxygen"). The mixture of composition (A) with gas (G) on the one hand, and premix (P) on the other hand, are injected separately. That is, the mixture of composition (A) with oxygen-containing gas (G) is injected through one tube, and premix (P) is injected through another tube.

[0095] Preferably, during step b., composition (A), oxygen-containing gas (G) and optional "premix" gas mixture (P), if present, are injected into a reaction tube (also called a "filled tube"). Preferably, this reaction tube is made of metal or quartz. Advantageously, the reaction tube has a height of at least 30 cm, preferably at least 40 cm and more preferentially at least 50 cm. Preferentially, the length of said reaction tube is between 30 cm and 300 cm, in particular between 40 cm and 200 cm, more particularly between 45 cm and 100 cm, for example 50 cm.

[0096] The mass ratio of the mass of solvent present in the composition (A) on the one hand to the mass of the oxygen-containing gas (G) on the other hand is defined as follows:

[0097] First, the amount of oxygen-containing gas (also called "oxidizing compound") is calculated so that composition (A), i.e., the combination of combustible solvent and cerium precursor, on the one hand, and oxygen-containing gas, on the other hand, can react together in a combustion reaction in stoichiometric ratios (i.e., without any excess or deficiency of oxidizing compound).

[0098] Starting from this calculated amount of oxygen-containing gas (also referred to as "calculated oxidant"), a new calculation is performed to derive therefrom the amount of oxygen-containing gas to be injected (also referred to as "injected oxidant") according to the following formula: Injected oxidant = calculated oxidant / φ In the formula, φ is a correction factor preferably between 1 and 2.2, more preferentially between 1.05 and 2, even more preferentially between 1.1 and 1.8, and even better still between 1.2 and 1.4.

[0099] This method is defined, inter alia, by Turns, S.R. in An Introduction to Combustion: Concepts and Applications, 3rd ed.; McGraw-Hill: New York, 2012.

[0100] Preferably, the molar amount of oxygen-containing gas (G) injected during step b. is strictly less than the molar amount of oxygen-containing gas required to react composition (A) with oxygen in a stoichiometric ratio.

[0101] The flame spray pyrolysis apparatus 10 that can be used in the preparation process according to the invention may comprise one or more chambers. Preferably, the flame spray pyrolysis apparatus 10 that can be used in the preparation process according to the invention comprises several chambers, more preferentially two chambers.

[0102] Preferably, the flame spray pyrolysis apparatus 10 is pressurized with an inert gas (G2) selected, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia; more preferentially from nitrogen, methane, hydrogen, and argon; even more preferentially from nitrogen and argon, and even better from nitrogen.

[0103] According to a preferred embodiment of the present invention, when the flame spray pyrolysis apparatus 10 comprises only one chamber, the chamber of the flame spray pyrolysis apparatus 10 is pressurized with an inert gas (G2) selected, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia; preferably from nitrogen, methane, hydrogen, and argon; more preferentially from nitrogen and argon, and even better from nitrogen.

[0104] According to another preferred embodiment of the invention, when the flame spray pyrolysis apparatus 10 comprises several chambers, the first chamber 20 of said flame spray pyrolysis apparatus 10 is pressurized with an inert gas (G2) selected, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia; preferably from nitrogen, methane, hydrogen, and argon; more preferentially from nitrogen and argon, and even better from nitrogen.

[0105] Preferably, the flow rate of the inert gas (G2) injected into the flame spray pyrolysis apparatus 10 ranges from 5 L / min to 70 L / min; more preferentially from 10 L / min to 50 L / min.

[0106] More preferentially, the flow rate of nitrogen (G2) injected into the flame spray pyrolysis device 10 ranges from 5 L / min to 70 L / min; more preferentially from 10 L / min to 50 L / min.

[0107] According to a particularly preferred embodiment of the invention, the correction factor φ is between 1 and 2.2, more preferentially between 1.05 and 2, even more preferentially between 1.1 and 1.8, and even better between 1.2 and 1.4. The flow rate of the inert gas (G2), more particularly nitrogen, injected into the flame spray pyrolysis device 10 ranges between 5 L / min and 70 L / min; more preferentially between 10 L / min and 50 L / min.

[0108] The preparation process according to the invention also comprises a step c., which comprises injecting a composition (B) comprising one or more precursors of element M' until a top coating layer 2 composed of element M' or an oxide of element M' is obtained on the surface of the cerium oxide aggregates.

[0109] As stated above, according to the present invention, the element M' is selected from selenium and the elements of columns 4, 13 and 14 of the periodic table of the elements.

[0110] Therefore, according to the invention, the element M' is different from cerium.

[0111] Preferably, element M' is selected from selenium, titanium, aluminum and elements of column 14 of the periodic table of the elements.

[0112] More preferentially, the element M' is chosen from selenium, titanium, aluminum, carbon and silicon.

[0113] Most particularly preferably, the element M' is selected from carbon and silicon.

[0114] According to a preferred embodiment, the element M' is silicon.

[0115] According to another embodiment of the invention, the element M' is carbon.

[0116] Preferably, the precursor of element M' comprises at least two M' atoms and several M'-carbon covalent bonds. More preferentially, the precursor of element M' comprises at least three M' atoms and several M'-carbon covalent bonds.

[0117] More preferentially, the precursor of element M′ is a hexa(di)(C1-C4)alkyldisiloxane, such as hexadimethyldisiloxane, a (di)(tri)(tetra)(C1-C4)alkoxysilane, such as tetraethoxysilane, a bis[(di)(tri)alkoxysilyl](C1-C4)alkane, such as 1,2-bis(triethoxysilyl)ethane or 1,2-bis(trimethoxysilyl)ethane, a (C1-C4)alkoxy(di)(tri)(C1-C 4) Alkylsilanes such as methoxytrimethylsilane, hydrocarbon gases such as acetylene, aluminum (di)(C1-C6) alkoxylates, aluminum (di)(C1-C6) alkylcarboxylates such as aluminum hydroxide diacetate, (poly)(C1-C6) alkoxylate stannates, (poly)(C1-C6) alkylcarboxylate stannates such as tetraacetate stannate, and mixtures thereof.

[0118] Even more preferentially, the precursor of element M' is chosen from hexadimethyldisiloxane, tetraethoxysilane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)ethane, methoxytrimethylsilane, and mixtures thereof.

[0119] According to a particular embodiment of the invention, composition (B) can be injected with an inert gas (G3) chosen, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia; preferably from nitrogen, methane, hydrogen and argon; and more preferentially from nitrogen and argon.

[0120] For example, nitrogen can be bubbled into composition (B) before its injection during step c. The injection flow rate of composition (B) can then be controlled by pressure determinations known to those skilled in the art, such as the method defined by Scott, DW; Messerly, JF; Todd, SS; Guthrie, GB; Hossenlopp, IA; Moore, RT; Osborn, AG; Berg, WT; McCullough, JP, Hexamethyldisiloxane: chemical thermodynamic properties and internal rotation about the siloxane linkage, J. Phys. Chem., 1961, 65, 1320-6.

[0121] Preferably, the content of precursor of element M' in composition (B) injected during step c. of the process according to the invention is between 1% and 60% by volume, more preferentially between 5% and 30% by volume, relative to the total volume of composition (B).

[0122] Advantageously, composition (B) may also contain one or more solvents. Preferably, the solvents present in composition (B) are chosen from polar protic solvents other than water, more preferentially from (C1-C8) alkanols. Even more preferentially, composition (B) contains ethanol.

[0123] Preferably, the solvent present in composition (B) is selected from solvents that are flammable at the flame temperature of step c., preferably flammable at temperatures between 200° C. and 600° C., more preferentially between 300° C. and 400° C. Better still, the solvent present in composition (B) has a boiling point above ambient temperature (25° C.), more preferentially between 50° C. and 120° C.

[0124] During the process according to the invention, the molar atomic ratio (Ce / M') injectedThis ratio corresponds, on the one hand, to the molar amount of cerium atoms implanted during step b., and, on the other hand, to the molar amount of element M′ implanted during step c.

[0125] Preferably, the molar atomic ratio (Ce / M') injected is greater than or equal to 0.25, more preferentially in the range 0.25 to 120, even more preferentially in the range 0.25 to 99, even better in the range 1 to 80; even better in the range 2 to 20.

[0126] According to the present invention, the flame spray pyrolysis apparatus 10 is isolated from the outside air so that the amount of oxygen present in said apparatus 10 is controlled, and more preferentially so that the oxygen present in said apparatus 10 comes only from said gas (G), and optionally from the mixture (P). In other words, atmospheric dioxygen cannot enter the combustion chamber and react with the composition (A) and the solvent.

[0127] Preferably, step b is carried out in a first chamber 20 of the flame spray pyrolysis apparatus 10 and step c is carried out in a second chamber 30 of said apparatus 10 that is in fluid communication with the first chamber 20 .

[0128] 2 and 3, the second chamber 30 is continuous with and extends the first chamber 20. Alternatively, the two chambers may be connected by a pipe.

[0129] The present invention also relates to coated cerium (sub)oxide particles of formula (I) or (I') obtained according to the preparation process according to the invention described above.

[0130] Flame spray pyrolysis equipment A flame spray pyrolysis apparatus that can be used to carry out the preparation process of the present invention preferably comprises a first chamber, a second chamber in fluid communication or connection with the first chamber, an injection system comprising a first supply, e.g., a first tube, opening into the first chamber and capable of delivering a first composition (A) and a first oxygen-containing gas (G), and a second supply, e.g., a second tube, opening into the first chamber and capable of delivering a mixture (P) comprising oxygen and one or more combustible gases, wherein the first supply and the second supply are different from each other.

[0131] The apparatus also includes a third supply capable of delivering a second composition (B) comprising one or more precursors of element M' into the second chamber.

[0132] The first and second chambers of the device are isolated from the outside air so that the amount of oxygen present in the device is controlled, more preferentially so that the oxygen present in the first and second chambers comes only from the first gas (G), and optionally from the mixture (P).

[0133] For example, and without limitation, the second chamber may be coaxial with the first chamber and may be, for example, disposed in an extension of said first chamber.

[0134] Advantageously, the first and second supply parts are coaxial, the second supply part at least partially surrounding the first supply part.

[0135] According to one embodiment, the first chamber comprises two separate compartments, the first compartment having a first opening through which the injection system emerges and a second opening opposite the first opening, the second compartment at least partially surrounding the first compartment and being isolated from the outside air, said second compartment being separated from the first compartment by a first partition.

[0136] For example, the first partition is porous to allow the passage of gas into the first compartment, and the second compartment is pressurized with a gas selected from, for example, nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia, or by heating.

[0137] For example, the apparatus may comprise an injector configured to inject a second gas into a second compartment of the first chamber, thereby pressurizing said second compartment.

[0138] According to one embodiment, the second chamber comprises two separate compartments, the first compartment comprising a first opening in fluid communication or connection with the second opening of the first chamber and a second opening opposite the first opening, the second compartment at least partially surrounding the first compartment and isolated from the outside air, said second compartment being separated from the first compartment by a second partition wall, and comprising a supply for supplying the second composition (B) into the second chamber.

[0139] For example, the apparatus may comprise an additional supply configured to inject a third gas into the second compartment of the second chamber, thereby pressurizing said second compartment.

[0140] For example, the second partition is porous or perforated to allow the second composition (B) to pass through the first compartment of the second chamber, which is pressurized with a third gas (G3) selected from, for example, nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia, or by heating.

[0141] For example, the apparatus also includes a collection system, e.g., coaxial with the two chambers, disposed above the second chamber and configured to stop particles while allowing gas to pass through. In other words, the collection system is gas-permeable. For example, the collection system includes a filtration system attached inside the collection system and a vacuum system configured to generate a negative pressure inside the collection system.

[0142] The injection system, the first chamber, the second chamber and the collection system are assembled, for example by screwing or welding, in a manner that makes it possible to ensure complete leak-proofness of the device and to prevent access of outside air into said device.

[0143] Completely without limitation, the injection system, the first chamber, the second chamber and the collection system are arranged within a housing in a manner that makes it possible to ensure complete leak-proofness of the device and to prevent access of outside air into said housing, the interior of which is placed under negative pressure by a vacuum system.

[0144] An example of a flame spray pyrolysis apparatus 10 is shown in FIG.

[0145] The flame spray pyrolysis apparatus 10 comprises a first chamber 20 using a composition (A) and an oxygen-containing gas (G), and a second chamber 30 using a composition (B) comprising one or more precursors of element M'.

[0146] Flame spray pyrolysis apparatus 10 also includes an injection system 40 comprising a first tube 42 emerging into first chamber 20 and delivering composition (A) and an oxygen-containing gas (G), and a second tube 44 emerging into first chamber 20 and delivering a "premix" mixture (P) comprising oxygen and one or more combustible gases, such as methane. Second tube 44 provides the flame necessary to ignite the compounds coming from first tube 42.

[0147] The first and second tubes 42, 44 are separate from each other.

[0148] As shown, the first and second tubes 42 , 44 are coaxial, with the second tube 44 at least partially surrounding the first tube 42 .

[0149] Without being limiting, the injection system 40 of the apparatus 10 also comprises an additional supply 46 of an inert gas, for example nitrogen, into the first chamber 20. The additional supply 46 may be in the form of a porous part, from which the inert gas is introduced at a pressure between 2 and 20 bar (i.e., 2×105 ~20×10 5 It can appear at pressures between 100 and 200 Pa.

[0150] The composition (A), oxygen-containing gas (G) and combustibles (P) coming from the injection system 40 are incinerated in the first chamber 20 .

[0151] As shown, the first chamber 20 includes two separate compartments 22, 24. The first compartment 22 includes a first lower opening 22a through which the injection system 40 emerges and a second upper opening 22b opposite the first opening 22a.

[0152] The second compartment 24 surrounds the first compartment 22 and is isolated from the outside air. The second compartment 24 is separated from the first compartment 22 by a gas-permeable partition 26.

[0153] The second compartment 24 comprises a top wall, a bottom wall and side walls (not referenced) that form an enclosed housing isolated from the outside air.

[0154] The second compartment 24 is pressurized with a gas (G2) selected from, for example, nitrogen, methane, argon, hydrogen, hydrogen sulfide, and ammonia. The gas (G2) is injected into the second compartment 24 via an injector 28. For example, the injector 28 comprises a single tube emerging into the second compartment 24. Alternatively, the injector 28 may comprise two or more tubes emerging into the second compartment 24. The tubes may or may not be evenly spaced around the circumference of the second compartment 24.

[0155] The partition 26 separating the two compartments 22, 24 is configured to allow the gas (G2) to pass through into the first compartment 22. For example, the partition 26 is made of a porous material. The pores of the partition 26 are, for example, 10 μm to 100 μm.

[0156] The first chamber 20 has a height H1 of, for example, 10 cm to 1 m.

[0157] The second chamber 30 is configured to use a composition (B) that includes one or more precursors of element M'.

[0158] As shown, the second chamber 30 includes two separate compartments 32, 34. The first compartment 32 includes a first lower opening 32a that aligns with the second opening 22b of the first chamber 20, and a second upper opening 32b opposite the first opening 32a.

[0159] Alternatively, the first lower opening 32a may be laterally offset from the second opening 22b of the first chamber 20. The first chamber 20 may be adapted to be connected to the second chamber 30 by a tube.

[0160] The second compartment 34 surrounds the first compartment 32 and is isolated from the outside air. The second compartment 34 is separated from the first compartment 32 by a gas-permeable partition wall 36.

[0161] The second compartment 34 comprises a top wall, a bottom wall and side walls (not referenced) that form an enclosed housing isolated from the outside air.

[0162] The second compartment 34 is provided with a supply 38 for supplying composition (B) into the second chamber 30 .

[0163] The supply 38 is pressurized, for example, with a gas (G3) selected from nitrogen, methane, argon, or hydrogen, or by heating the composition (B). For example, the supply 38 comprises a single tube emerging into the second compartment 34. Alternatively, the supply 38 comprises two or more tubes emerging into the second compartment 34. The tubes may or may not be evenly spaced around the circumference of the second compartment 34.

[0164] The partition 36 separating the two compartments 32, 34 is configured to allow the passage of the composition (B) from the second compartment 34 to the first compartment 32. For example, the partition 36 may be configured to separate the two compartments 32, 34 from each other within 1 cm of the separating partition 36. 2It has a plurality of perforations (not shown) of about 0.1 mm to 0.5 mm, with 1 to 10 perforations per hole.

[0165] The second chamber 30 has a height H2 of, for example, 10 cm to 1 m.

[0166] Preferably, the height H1 of the first chamber 20 is equal to the height H2 of the second chamber 30 plus or minus 10%. Preferably, the dimensions of the first chamber 20 are equal to the dimensions of the second chamber 30.

[0167] The flame spray pyrolysis apparatus 10 also includes a collection system 50 configured to stop the particles while allowing the gases to pass through.

[0168] In this case, the collection system 50 is coaxial with the two chambers 20, 30 and is positioned above the second chamber 30. Alternatively, the collection system 50 may be laterally offset from the chambers 20, 30.

[0169] The collection system 50 is bounded radially by one or more side partitions 52 and axially by a lower wall 54 with an opening 54a emerging into the second chamber 30 and an upper wall 55 opposite the lower wall 54.

[0170] The collection system 50 also includes a filtration system 56 mounted inside the collection system between the side walls 52 and a vacuum system 58 , such as a pump, mounted on the top wall 55 of the system 50 .

[0171] The pump 58 is configured to generate a negative pressure inside the collection system 50 so as to isolate the chambers 20, 30 from the outside air. Advantageously, the negative pressure inside the collection system 50 is between 0.5 and 0.8 bar (i.e., 5×10 4 Pa~8×10 4 Pa).

[0172] Without being limiting, the collection system 50 is axially spaced from the second chamber 30 by a spacer 60 .

[0173] As shown in FIG. 2, the injection system 40, the first chamber 20, the second chamber 30 and the collection system 50, or even the spacer 60 if present, are assembled, for example by screwing or welding, to ensure complete leak-proofness of the device 10, in particular of the chambers 20, 30, making it possible to prevent access of outside air into said device 10.

[0174] 3, in which like elements have the same reference numerals, differs from the embodiment shown in Figure 2 only in that the injection system 40, the first chamber 20, the second chamber 30 and the collection system 50, or even the spacer 60, if present, are arranged in a housing 70 so as to ensure complete leakproofness of the device 10, in particular of the chambers 20, 30, and to prevent access of outside air into said housing 70. The interior of the housing 70 is put under negative pressure by a pump 58.

[0175] According to a preferred embodiment of the device, said device has an axis of symmetry Δ passing through the center / centre of the injection system 40 and the center / centre of the collection system 50. More preferentially, the device is symmetrical, and in particular cylindrical, passing through said axis of symmetry Δ.

[0176] composition Another subject of the present invention relates to a composition, preferably a cosmetic composition, comprising one or more coated cerium suboxide particles of formula (I') above and / or preferably obtained via a preparation process according to the invention.

[0177] The compositions according to the invention are intended to be applied to keratinous materials, preferably the skin (in particular the face) and / or the hair, to dye and / or make up the keratinous materials, with an optional step of drying the keratinous materials.

[0178] The compositions according to the invention may be in various presentation forms: they may thus be in the form of a powder (pulverulent) composition or a liquid composition, or in the form of a milk, cream, paste or aerosol composition.

[0179] The compositions according to the invention are in particular cosmetic compositions, i.e. the materials of the invention are in a cosmetically acceptable carrier. The term "cosmetically acceptable carrier" means a medium suitable for application to keratinous materials, in particular human keratinous materials such as the skin, said cosmetic carrier generally consisting of water or a mixture of water and one or more organic solvents, or a mixture of organic solvents.

[0180] The composition according to the invention is advantageously an aqueous composition.

[0181] Preferably, the composition comprises water in a content ranging from 5% to 95%, inclusive, in particular relative to the total weight of the composition.

[0182] For purposes of the present invention, the term "organic solvent" means an organic substance that is capable of dissolving another substance without chemical modification.

[0183] Examples of organic solvents that may be mentioned include lower C2-C6 alkanols, such as ethanol and isopropanol; polyols and polyol ethers, such as 2-butoxyethanol, propylene glycol, propylene glycol monomethyl ether, and diethylene glycol monoethyl ether and monomethyl ether, as well as aromatic alcohols, such as benzyl alcohol or phenoxyethanol, and mixtures thereof.

[0184] Preferably, the organic solvent is present in the composition according to the invention in a content of from about 0.1% to 40% by weight, inclusive, more preferentially from about 1% to 30% by weight and even more particularly from 5% to 25% by weight, inclusive, relative to the total weight of the composition.

[0185] The compositions of the invention may contain a fatty phase and may be in the form of a direct or inverse emulsion.

[0186] The compositions according to the invention may be prepared in the form of simple emulsions such as creams, milky or creamy gels or complex emulsions (abbreviated as oil-in-water or O / W, water-in-oil or W / O, oil-in-water-in-oil or O / W / O, or water-in-oil-in-water or W / O / W) according to techniques well known to those skilled in the art.

[0187] According to a specific embodiment of the present invention, the composition according to the present invention can also be in the form of anhydrous composition, for example in the form of oil.The term "anhydrous composition" means a composition that contains less than 2% by weight of water, preferably less than 1% by weight of water, and more preferentially less than 0.5% by weight of water, relative to the total weight of the composition, and does not actually contain water.In this type of composition, the water that may be present is not added during the preparation of the composition, but corresponds to the residual water that is brought about by the mixed components.

[0188] The particles according to the invention may be in dry form (powder, flakes, plates), as a dispersion, as a liquid suspension or as an aerosol. The particles according to the invention may be used as such or mixed with other components.

[0189] Preferably, the composition of the invention contains from 0.1% to 40% by weight, more preferentially from 0.5% to 20% by weight, even more preferentially from 1% to 10% by weight, and better still from 1.5% to 5% by weight of particles according to the invention relative to the total weight of the composition.

[0190] The composition of the present invention can be used in a single application or multiple applications. When multiple applications of the composition of the present invention are intended, the content of the particles of the present invention is generally lower than when a single application of the composition is intended.

[0191] For purposes of the present invention, the term "single application" means a single application of the composition, which can be repeated several times a day, if desired, with an interval of at least one hour between each application, or can be a single application per day.

[0192] For purposes of the present invention, the term "multiple applications" refers to several, typically 2 to 5, repeated applications of the composition, with a gap of a few seconds to a few minutes between each application. Each of the multiple applications may be repeated several times a day, with a gap of at least an hour between each application, or may be performed once a day, as desired.

[0193] Another subject of the present invention is a process in which keratinous materials, in particular human keratinous materials such as the skin, are treated by applying, preferably 1 to 5 successive applications of the composition defined above to said materials, the applications being sprayed or the like, with drying between layers.

[0194] According to one embodiment of the present invention, multiple applications are performed on the keratinous material, with a drying step between successive applications of the cosmetic composition comprising the metal oxide particles of the present invention. The drying step between successive applications of the cosmetic composition comprising at least one metal oxide particle of the present invention can be performed outdoors or artificially, for example by a hot air drying system such as a hair dryer.

[0195] Another subject of the present invention is a composition according to the invention, preferably a cosmetic composition used to protect the skin, preferably human skin, from visible radiation (i.e. wavelengths between 400 nm and 800 nm) and / or ultraviolet radiation (i.e. wavelengths between 100 nm and 400 nm), UV-A radiation (i.e. wavelengths between 320 nm and 400 nm), and / or UV-B radiation (i.e. wavelengths between 280 nm and 320 nm), preferably UV-A radiation. The composition according to the invention allows for effective screening of broad-spectrum solar radiation, in particular UV-A radiation (including long UV-A), while at the same time being particularly stable over time under UV exposure.

[0196] The composition according to the invention may optionally comprise, in addition to the metal oxide particles according to the invention, one or more additional UV filters selected from hydrophilic, lipophilic or insoluble organic UV filters and / or one or more inorganic pigments. The composition according to the invention is preferentially composed of at least one hydrophilic, lipophilic or insoluble organic UV filter.

[0197] The subject of the present invention is also the use of the cerium oxide particles described above and / or obtained via the preparation process described above, in particular for the formulation of cosmetic or pharmaceutical compositions having antiperspirant action, or for regulating the pH of the skin, or intended to protect the skin from visible and / or ultraviolet radiation or to modify its appearance.

[0198] Another subject of the present invention is the use of one or more cerium oxide particles as defined above as a screening agent for UV-A and / or UV-B, preferably UV-A, for protecting keratinous materials, in particular the skin. The following examples serve to illustrate the invention and are not limiting in nature. [Example]

[0199] Example 1: 1.1 In a first step, composition (A) was prepared from cerium(III) ethylhexanoate (500 mM) in xylene.

[0200] Uncoated cerium oxide particles P1 (higher oxidation number) were then prepared via the conventional FSP Prep 1 preparation process with previously prepared composition (A) (outside the scope of the present invention).

[0201] The parameters for the Prep 1 process are as follows: - ratio (composition (A) / O2) = 5 mL / min of composition (A) and 5 L / min of gas (O2), - Gas mixture to ensure flame of 1L / min methane and 2L / min dioxygen An inert gas (G2) flow of 10 L / min of nitrogen is injected into the FSP device. - φ=0.7 is used to adjust the oxygen flow rate.

[0202] 1.2 Uncoated cerium suboxide particles P2 were then prepared via the FSP Prep 2 preparation process according to the previously prepared composition (A) (outside the scope of the present invention).

[0203] The parameters for the Prep 2 process are as follows: - ratio (composition (A) / O2) = 5 mL / min of composition (A) and 5 L / min of gas (O2), - Gas mixture to ensure flame of 1L / min methane and 2L / min dioxygen - An inert gas (G2) flow of 20 L / min of nitrogen is injected into the FSP device. - φ=1.2 is used to adjust the oxygen flow rate.

[0204] 1.3 Cerium suboxide particles coated with silicon dioxide P3 were then prepared in a double-chamber FSP apparatus via the Prep 3 preparation process according to the present invention with composition (A) comprising cerium(III) ethylhexanoate (400 mM) in xylene and composition (B) comprising hexadimethyldisiloxane (100 mM in xylene) and ethanol in a 3:1 mass ratio (present invention).

[0205] The parameters for the Prep 3 process are as follows: - injecting composition (A) and oxygen-containing gas (G) into a first chamber of the FSP device according to a (composition (A) / O2) ratio = 5 mL / min of composition (A) and 5 L / min of gas (O2); - a gas mixture to ensure a flame of 1 litre / min methane and 2 litres / min dioxygen; - Injecting a flow of nitrogen inert gas (G2) of 25 L / min into the first chamber of the double-chamber FSP device; - Composition (B) is injected into the second chamber of the FSP device by means of a nitrogen flow of 3 L / min. - φ=1.3 is used to adjust the oxygen flow rate.

[0206] Upon preparation of the P3 particles, it was observed that the resulting cerium suboxide particles P3 were crystalline.

[0207] Furthermore, the P3 particles obtained according to the Prep 3 process according to the present invention are coated with a top layer of silicon dioxide about 5 nm thick, with an atomic ratio (Ce / Si) particle is 2.

[0208] The BET specific surface area of ​​particle P3 is 62 m 2 / g.

[0209] Particles P3 have a number average diameter of 15 nm.

[0210] The oxidation of particles P1-P3 was monitored by X-ray diffraction.

[0211] 1.4 Next, the optical properties of particles P1 to P3 were evaluated.

[0212] It has been observed that the particles P3 according to the invention have an excellent ability to block UV-A rays.

[0213] It was also observed that the particles P3 according to the invention have a UV screening power that is 2.47 times greater (for an equal volume) than that of the uncoated cerium oxide particles P1 (outside the scope of the invention).

[0214] In addition, it was observed that the particles P3 according to the invention have a UV screening power that is 1.62 times greater (for an equal volume) than the screening power of the uncoated cerium suboxide particles P2 (outside the scope of the invention).

[0215] Example 2: 2.1 Carbon-coated cerium suboxide particles P4 were then prepared in a single-chamber FSP apparatus via the Prep 4 preparation process according to the present invention, with composition (A) comprising cerium(III) ethylhexanoate (500 mM) in xylene and composition (B) consisting of acetylene (present invention).

[0216] The parameters for the Prep 4 process are as follows: - Inject the composition (A) and the oxygen-containing gas (G) into the FSP device at a ratio (composition (A) / O2) = 5 mL / min of composition (A) and 5 L / min of gas (O2). - Gas mixture to ensure flame of 1L / min methane and 2L / min dioxygen - Nitrogen inert gas (G2) flow of 50L / min - Acetylene (composition (B)) is injected into the FSP device at 2.5 L / min. - φ=1.9 is used to adjust the oxygen flow rate.

[0217] 2.2 Carbon-coated cerium suboxide particles P5 were prepared in a double-chamber FSP apparatus via the Prep 5 preparation process according to the present invention with composition (A) comprising cerium(III) ethylhexanoate (500 mM) in xylene and composition (B) consisting of acetylene (invention).

[0218] The parameters for the Prep 5 process are as follows: - injecting composition (A) and oxygen-containing gas (G) into a first chamber of the FSP device according to a (composition (A) / O2) ratio = 5 mL / min of composition (A) and 5 L / min of gas (O2); - A gas mixture to ensure a flame of 1 L / min methane and 2 L / min dioxygen was injected into the first chamber of the FSP device. - A flow of 25 L / min of nitrogen inert gas (G2) is injected into the first chamber of the FSP device. Acetylene (composition (B)) was injected into the second chamber of the FSP device at 2.5 L / min. - φ=1.6 is used to adjust the oxygen flow rate.

[0219] Upon preparation of particles P4 and P5, it was observed that the resulting cerium suboxide particles P4 and P5 were crystalline.

[0220] Furthermore, the particles P4 obtained according to the Prep 4 process according to the invention are coated with a top layer of carbon about 1.5 nm thick, with an atomic ratio (Ce / C) particle is 0.3.

[0221] The BET specific surface area of ​​particle P4 is 74 m 2 / g.

[0222] Particles P4 have a number average diameter of 14 nm.

[0223] The particles P5 obtained through the Prep 5 process according to the invention are coated with a top layer of carbon about 1 nm thick, with an atomic ratio (Ce / C) particle is 0.57.

[0224] The BET specific surface area of ​​particle P5 is 70m 2 / g.

[0225] Particles P5 have a number average diameter of 16 nm.

[0226] The oxidation of particles P4 and P5 was monitored by X-ray diffraction.

[0227] 2.3 The optical properties of particles P4 and P5 were then evaluated.

[0228] It was observed that particles P4 and P5 according to the invention have an excellent ability to block UV-A rays.

[0229] It was also observed that the particles P4 according to the invention have a UV screening power that is 2.04 times greater (for equal volume) than the screening power of the uncoated cerium oxide particles P1 (outside the scope of the invention).

[0230] In addition, it was observed that the particles P5 according to the invention have a UV screening power that is 2.35 times greater (for an equal volume) than the screening power of the uncoated cerium suboxide particles P1 (outside the scope of the invention).

Claims

1. (i) Formula (I'): CeO ２－ｘ (I’) a core (1) composed of at least one cerium suboxide of the formula: wherein x represents a non-integer and 0<x<2; (ii) an upper coating layer (2) covering the surface of the core (1), the upper coating layer (2) having the formula (II): M' ｐ O ｑ (II) and at least one compound of the formula: M' is an element selected from selenium and elements of columns 4, 13, and 14 of the periodic table of the elements; p represents an integer of 1 or more; an upper coating layer (2), wherein q represents an integer ranging from 0 to 4, and when q is equal to 0, M' is carbon; A particle having a core / shell structure comprising:

2. 2. The particle according to claim 1, wherein p represents an integer ranging from 1 to 4.

3. 2. Particles according to claim 1, characterized in that the element M' is selected from selenium, titanium, aluminum, carbon and silicon.

4. The compound of formula (II) is a compound of carbon, SiO ２ , SnO ２ , and Al ２ O ３ 2. The particle according to claim 1, characterized in that it is selected from:

5. The particle according to claim 1 , wherein the particle has a molar atomic ratio (Ce / M′) of 1 or more.

6. the number average thickness d of the upper coating layer (2) measured by transmission electron microscopy; ｍ The particles according to claim 1, characterized in that the particle diameter is in the range of 1 to 20 nm.

7. 2. The particles according to claim 1, wherein the number average diameter of the particles determined by transmission electron microscopy is in the range of 4 to 5000 nm.

8. 2. Particle according to claim 1, characterized in that the upper coating layer (2) of the particle covers at least 90% of the surface of the core (1).

9. (i) Formula (I): CeO ２－ｘ (I) a core (1) composed of at least one cerium oxide of the formula: wherein x is a) equal to 0 or b) a non-integer, 0<x<2; (ii) an upper coating layer (2) covering the surface of the core (1), the upper coating layer (2) having the formula (II): M' ｐ O ｑ (II) and at least one compound of the formula: M' is an element selected from selenium and elements of columns 4, 13, and 14 of the periodic table of the elements; p represents an integer of 1 or more; an upper coating layer (2), wherein q represents an integer ranging from 0 to 4, and when q is equal to 0, M' is carbon; 1. A method for preparing coated cerium oxide or cerium suboxide particles having one or more core / shell structures, comprising: At least the following steps: a. preparing composition (A) by adding one or more cerium precursors in one or more flammable solvents; and b. forming a flame in the first chamber (20) of the flame spray pyrolysis device (10) by injecting the composition (A) and the oxygen-containing gas (G) until aggregates of cerium oxide of formula (I) are obtained; and then c. In a second chamber (30) of said flame spray pyrolysis apparatus (10) in fluid communication with said first chamber (20), element M' or a compound of formula (II) injecting a composition (B) containing one or more precursors of element M' until a top coating layer (2) composed of an oxide of element M' is obtained on the surface of said cerium oxide aggregates; Including; The method wherein the flame spray pyrolysis apparatus (10) is isolated from the ambient air so that the amount of oxygen present within the apparatus is controlled.

10. 10. The method of claim 9, wherein composition (A) comprises at least two flammable solvents selected from 2-ethylhexanoic acid, toluene, absolute ethanol, and diethylene glycol monobutyl ether.

11. The method described in claim 9, characterized in that composition (A) contains at least 5 volume % of 2-ethylhexanoic acid, at least 5 volume % of toluene, at least 5 volume % of anhydrous ethanol, and at least 5 volume % of diethylene glycol monobutyl ether, relative to the total volume of flammable solvents in composition (A).

12. 10. The method of claim 9, wherein the element M' is selected from selenium, titanium, aluminum, and elements of column 14 of the periodic table of the elements.

13. Together or separately: Molar atomic ratio (Ce / M') ｉｎｊｅｃｔｅｄ is greater than or equal to 0.25; and / or Composition (B) comprises one or more solvents selected from polar protic solvents other than water; and / or The molar amount of oxygen-containing gas (G) injected during step b is strictly less than the molar amount of oxygen-containing gas required to react composition (A) with oxygen in a stoichiometric ratio.

10. The method according to claim 9.

14. 10. The method according to claim 9, characterized in that the flame spray pyrolysis device (10) is pressurized with an inert gas (G2) selected from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia.

15. Particles according to any one of claims 1 to 8, characterized in that they are obtainable via a method according to any one of claims 9 to 14.

16. A composition comprising one or more particles according to any one of claims 1 to 8.

17. 17. The composition according to claim 16, for use in protecting human skin from visible and / or ultraviolet radiation, UV-A and / or UV-B.

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