Abstract: An improved material in the form of rare-earth borate, its precursor(s) and a luminophore made thereof is provided. The material is characterizable as comprising spherical, cubic or parallelepipedal particles having an average particle size not more than 10 &mgr;m, over a narrow particle size distribution (dispersion index not greater than 0.8). The material may comprise a rare earth element having that lacks luminescence in combination with a dopant.

Abstract: The present invention relates to a process for treating gases to reduce emissions of oxides of nitrogen. This process is of the type in which a catalytic composition is used which comprises a catalytic phase on a support and is characterized in that the support is based on silica and titanium oxide in an atomic proportion Ti/Ti+Si of between 0.1 and 15%. The process of the invention applies more particularly to the treatment of the exhaust gases from diesel engines or from lean burn engines.

Abstract: The present invention relates to a compound of the LaMO3 type, M being aluminum, gallium or indium, in the form of a powder or in sintered form, its process of preparation and its use as an oxygen conductor. The compound in powder form is capable of achieving, by pressureless sintering, a density of at least 93% of the theoretical density and of giving a sintered compound substantially free of any electrically active secondary phase of the grain boundaries. The compound in powder form is obtained by the reaction of the salts of lanthanum and of the element M with a base, and then the separation and calcining of the precipitate obtained. It may also be obtained by mixing, in a liquid medium, salts of lanthanum, and of the element M and, optionally, of a base, and then spray-drying and calcining the precipitate obtained. The sintered compound may be used in any application requiring an oxygen-conducting material in oxide form, such as solid-oxide fuel cells.

Abstract: The composition is based on a samarium sesquisulphide, it exhibits a samarium purity with respect to other rare earth metals of greater than 99% and it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide. According to another embodiment, the composition is based on a sesquisulphide of samarium and of at least one rare earth metal which is solely trivalent and it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide. According to a third embodiment, the composition exhibits a samarium purity such that the cerium content is less than 1%. The process consists in reacting samarium, trivalent rare earth metal and alkali metal or alkaline earth metal compounds with a gaseous mixture of hydrogen sulphide and of carbon disulphide.

Abstract: The present invention relates to a rare-earth borate, to a precursor thereof, to processes for their preparation and to the use of this borate as a luminophore.

Abstract: The present invention provides a process for preparing a rare earth borate by reacting together at least one rare earth salt, boric acid and a base. The process is characterized in that the reaction is carried out using an excess of acid with respect to the stoichiometry and under conditions such that the pH of the reaction medium at the end of the reaction is in the range of 6 to 8. The precipitate formed is then recovered and calcined. The phase purity of the borate obtained is good and it can be used as a luminophore.

Abstract: The invention concerns the use of a beta rare earth sulphide as coloring pigment and its method of preparation. A beta rare-earth sulphide is used, the rare earth being lanthanum, cerium, praseodymium, samarium or neodymium. The sulphide consists of whole crystallites forming medium-sized aggregates of not more than 1.5 &mgr;m. The method of preparation of this rare earth sulphide is characterized in that a rare earth compound is reacted with at least one sulphidizing gas selected among hydrogen sulphide or carbon sulphide. The pigment can be part of compositions of the following types: plastic, paint, surface coating, rubber, ceramic, glazing, paper, ink, cosmetic products, dyes, leather, laminated coating or other types of compositions with a base of at least one mineral binder or obtained therefrom.

Abstract: Thermally/chemically stable and nontoxic inorganic pigments/colorants, characteristically green and well suited for the coloration of a wide variety of materials and substrates, for example, plastics, ceramics, etc., comprise at least one mixed oxide of the formula: R2MxM′yO5 in which R is at least one element selected from among yttrium and a rare earth having an atomic number ranging from 62 to 71, inclusive, M and M′, which may be identical or different, are each at least one metallic element exhibiting at least one valence state of +2, and x and y are numbers, the sum x+y of which is equal to 2.

Abstract: The present invention relates to a compound based on an alkaline-earth metal, on sulphur and on aluminium, on gallium or indium, to its process of preparation and to its use as luminophore. The compound of the invention corresponds to the formula AB2S4, in which A represents an alkaline-earth metal and B aluminum, gallium, or indium and it is characterized in that it is provided in the form of a powder with a residual oxygen content of not more that 1.5% and composed of particles with a mean size of not more than 10 &mgr;m. This compound is obtained by a process which contains the following stages: a solution or a suspension comprising salts of the elements A and B is formed, the solution or the suspension is dried by atomization and the product obtained in the preceding stages is reacted with carbon disulphide or with a mixture of hydrogen sulphide and or carbon disulphide. The compound of the invention can be used as a luminophore, in particular in cathodoluminescence.

Abstract: The present invention relates to a rare-earth borate, to a precursor thereof, to processes for their preparation and to the use of this borate as a luminophore. The rare-earth borate and the precursor thereof are characterized in that they are in the form of cubic, parallelepipedal or spherical particles and in that they have a dispersion index of not more than 0.8. According to one embodiment of the invention, the borate is a red luminophore. The process for the preparation of the precursor is characterized in that a rare-earth carbonate or hydroxycarbonate is reacted with boric acid, the reaction medium being in the form of an aqueous solution. The borate is obtained by calcination of the precursor.

Abstract: The present invention concerns a sulfide of a rare earth and an alkali, a process for its preparation and its use as a colored pigment. The sulfide is characterized in that it has the formula ABS2 where A represents at least one alkali and B represents at least one rare earth and in that it is constituted by grains with an average size of 1.5 &mgr;m at most. The preparation process for the sulfide is characterized in that at least one rare earth carbonate or hydroxycarbonate is brought into the presence of at least one gas selected from hydrogen sulfide or carbon disulfide. The product obtained is optionally deagglomerated. The sulfide can be used as a pigment in plastics, paints, finishes, rubbers, ceramics, glazes, paper, inks, cosmetics, dyes, laminated coatings and materials based on or obtained from at least one inorganic binder.

Abstract: Storage-stable colloidal organic sols comprise suspended tetravalent metal oxide particulates in an organic diluent medium, notably cerium dioxide particulates, the tetravalent metal oxide particulates having a particle size d90 no greater than 200 nanometers and being complexed with at least one amphiphilic organic acid, and either said tetravalent metal oxide particulates comprising agglomerates of crystallites, the d80 of which being no greater than 5 nanometers and at least 90% of said agglomerates comprising from 1 to 5 crystallites, and/or said at least one amphiphilic organic acid has from 11 to 50 carbon atoms and is branched in at least one of the &agr;-, &bgr;-, &ggr;- or &dgr;-positions relative to the atom bearing the acidic hydrogen.

Abstract: The present invention relates to a compound based on an alkaline-earth metal, on sulphur and on aluminium, on gallium or indium, to its process of preparation and to its use as luminophore. The compound of the invention corresponds to the formula AB2S4, in which A represents an alkaline-earth metal and B aluminum, gallium, or indium and it is characterized in that it is provided in the form of a powder with a residual oxygen content of not more that 1.5% and composed of particles with a mean size of not more than 10 &mgr;m. This compound is obtained by a process which contains the following stages: a solution or a suspension comprising salts of the elements A and B is formed, the solution or the suspension is dried by atomization and the product obtained in the preceding stages is reacted with carbon disulphide or with a mixture of hydrogen sulphide and or carbon disulphide. The compound of the invention can be used as a luminophore, in particular in cathodoluminescence.

Abstract: The present invention relates to a composition based on a sulphur compound, zinc and optionally a transparent oxide, to a process for its preparation and to its use as a dye pigment. The composition of the invention is characterized in that it comprises a support based on at least one sulphur compound, and a zinc compound, deposited on the support and obtained by reaction of a zinc precursor with aqueous ammonia and/or an ammonium salt. The composition may also comprise a layer based on at least one transparent oxide deposited at the surface of the support and/or fluorine atoms. It may be prepared in particular by a process in which the support, a zinc precursor, aqueous ammonia and/or an ammonium salt and, if necessary, a transparent oxide precursor and a fluorinating agent are placed in contact and the zinc compound is deposited on the support and, where appropriate, the transparent oxide is precipitated on the said support.

Abstract: A method for processing soot containing one or more rare earths, wherein said soot is contacted with an oxygen-containing gas, is disclosed. The method comprises (a) preparing an aqueous phase comprising a dispersion of at least one oxygenated metal compound; (b) simultaneously or consecutively contacting a suspension from step (a) with an organic phase including at least one amphiphilic agent and preferably an organic mixture or compound as the solvent; and c recovering the organic phase. Said oxygenated metal compound is produced by means of a method according to which a solution including at least one soluble rare-earth salt, usually an acetate and/or a chloride, is prepared; the solution is contacted with a basic medium and the resulting reaction mixture is maintained at a basic pH; and the precipitate formed by atomization or freeze-drying is recovered. Said method is useful in inorganic synthesis and catalysis.

Abstract: Unique colorant compositions, well suited for the pigmentation of a wide variety of coatings and substrates, e.g., cosmetics, plastics, paints and rubbers, comprise (1) at least one crystalline rare earth metal sulfide or sesquisulfide, for example cubic cerium sesquisulfide Ce.sub.2 S.sub.3, and (2) a dopant amount of at least one alkali metal, and wherein the at least one rare earth metal sulfide or sesquisulfide comprises whole (unground) monocrystalline grains thereof having a mean particle size of at most 1.5 .mu.m.

Abstract: Alkaline-earth metal- and copper- and optionally titanium-based silicates in the form of agglomerates consisting either of monocrystalline grains or of aggregates themselves consisting of monocrystalline particles.These silicates are prepared by a process including the following stages: a silica sol or a silicate and optionally a titanium sol is mixed with salts of the other constituent elements of the silicate with the exception of oxygen; the mixture thus obtained is dried, preferably by spraying, and the product obtained is calcined. The silicates may be employed as colored pigments in plastics, paints, varnishes, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes and laminated coatings.

Abstract: Oxygen-rich exhaust gases, for example those emanating from internal combustion engines, e.g., diesel engines, are catalytically treated/converted to reduce emissions of NO.sub.x, in the presence of a catalytically effective amount of a spinel mass oxide essentially having the formula ZnAl.sub.2 O.sub.4 which was prepared by forming a solution or suspension of the salts of the constituent elements of the mass oxide, drying by atomizing the solution or suspension and calcining the salts of the constituent elements of the mass oxide so as to result in the spinel mass oxide.

Abstract: Unique colorant compositions, well suited for the pigmentation of a wide variety of coatings and substrates, e.g., cosmetics, plastics, paints and rubbers, comprise (1) at least one crystalline rare earth metal sulfide or sesquisulfide, for example cubic cerium sesquisulfide Ce.sub.2 S.sub.3, and (2) a dopant amount of at least one alkali metal, and wherein the at least one rare earth metal sulfide or sesquisulfide comprises whole (unground) monocrystalline grains thereof having a mean particle size of at most 1.5 .mu.m.

Abstract: The present invention concerns a process for the preparation of a rare-earth sulphide characterized in that a rare-earth halide is brought into the presence of an alkaline or aluminum halide and heated in the presence of hydrogen sulphide at a temperature which is sufficient to volatilize the halides.More particularly, the halide is a chloride, the rare-earth is cerium and the alkali is sodium.