Powder of particles, more than 95% by number of said particles exhibiting a circularity greater than or equal to 0.85, wherein said powder contains more than 99.8% of a rare earth oxide and/or of hafnium oxide and/or of yttrium aluminum oxide, as percentage by weight relative to the oxides, and has: a median particle size D 50 of between 10 and 40 microns and a size dispersion index (D 90D 10)/D 50 of less than 3; a percentage by number of particles having a size less than or equal to 5 m which is less than 5%; an apparent-density dispersion index (P<50P)/P of less than 0.2, the cumulative specific volume of the pores which have a radius of less than 1 m being less than 10% of the apparent volume of the powder, in which the percentiles Dn of the powder are the particle sizes corresponding to the percentages, by number, of n %, on the curve of cumulative distribution of the particle size of the powder, the particle sizes being classified in increasing order, the density P<50 being the apparent density of the fraction of particles having a size less than or equal to D50, and the density P being the apparent density of the powder.

Provided are oil-based fuel additive compositions that, when combusted with a fuel containing vanadium in a gas turbine, inhibit vanadium hot corrosion in the gas turbine. The oil-based fuel additive compositions include at least one rare earth element compound or alkaline earth element compound that retards vanadium corrosion resulting from combustion of vanadium rich fuel.

Ceria particles contain molybdenum. In the ceria particles, the molybdenum may be unevenly distributed in a surface layer of the ceria particles. A crystallite diameter of a [100] plane of the ceria particles may be 250 nm or more. A crystallite diameter of a [101] plane of the ceria particles may be 300 nm or more. A median diameter D.sub.50 of the ceria particles calculated by a laser diffraction/scattering method may be 5.00 ?m or more and 1000.00 ?m or less. A method for producing the ceria particles includes calcining a cerium compound in presence of a molybdenum compound. The molybdenum compound may be at least one compound selected from a group including molybdenum trioxide, lithium molybdate, potassium molybdate and sodium molybdate. In the method for producing the ceria particles, a calcination temperature may be 800? C. or higher and 1600? C. or lower.

Ceria particles contain molybdenum. In the ceria particles, the molybdenum may be unevenly distributed in a surface layer of the ceria particles. A crystallite diameter of a [100] plane of the ceria particles may be 250 nm or more. A crystallite diameter of a [101] plane of the ceria particles may be 300 nm or more. A median diameter D.sub.50 of the ceria particles calculated by a laser diffraction/scattering method may be 5.00 ?m or more and 1000.00 ?m or less. A method for producing the ceria particles includes calcining a cerium compound in presence of a molybdenum compound. The molybdenum compound may be at least one compound selected from a group including molybdenum trioxide, lithium molybdate, potassium molybdate and sodium molybdate. In the method for producing the ceria particles, a calcination temperature may be 800? C. or higher and 1600? C. or lower.

This invention relates to azirconium solution or sol comprising: (a) zirconium, (b) nitrate, acetate and/or chloride ions, and (c) one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group, wherein the molar ratio of components (a):(b) is 1:0.7 to 1:4.0, the molar ratio of components (a):(c) is 1:0.0005 to 1:0.1, and the pH of the zirconium solution or sol is less than 5. The invention also relates to a process for preparing a zirconium solution or sol, the process comprising the steps of: (a) dissolving a zirconium salt in nitric, acetic and/or hydrochloric acid, and (b) adding one or more complexing agents to the resulting solution, the one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group, and (c) heating the solution or sol to a temperature of at least 75? C. In addition, the invention relates to products formed from the zirconium solution or sol or obtainable by the process.

A ceria-zirconia composite oxide includes at least one of lanthanum, yttrium, and praseodymium. A rate of a total content of the at least one rare earth element to a total content of cerium and zirconium is 0.1 at % to 4.0 at %. A content of the rare earth element present in near-surface regions, which are at a distance of less than 50 nm from surfaces of primary particles of the ceria-zirconia composite oxide, accounts for 90 at % or more of the total content of the rare earth element. An average particle size of the primary particles of the ceria-zirconia composite oxide is 2.2 m to 4.5 m. After a predetermined durability test, the intensity ratio I(14/29) of a diffraction line at 2=14.5 to a diffraction line at 2=29 and the intensity ratio I(28/29) of a diffraction line at 2=28.5 to the diffraction line at 2=29 respectively satisfy the following conditions:
I(14/29)0.02, and
I(28/29)0.08.

This invention relates to a cerium-zirconium based mixed oxide having: (a) a Ce:Zr molar ratio of 1 or less, and (b) a cerium oxide content of 10-50% by weight, wherein the composition has (i) a surface area of at least 18 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.11 cm.sup.3/g, after ageing at 1100? C. in an air atmosphere for 6 hours, and (ii) a surface area of at least 42 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.31 cm.sup.3/g, after ageing at 1000? C. in an air atmosphere for 4 hours. The invention also relates to a catalytic system comprising the cerium-zirconium based mixed oxide, as well as to a process 10 for treating an exhaust gas from a vehicle engine comprising contacting the exhaust gas with the cerium-zirconium based mixed oxide. In addition, the invention relates to a process for preparing a cerium-zirconium based mixed hydroxide or mixed oxide as claimed in any preceding claim, the process comprising the steps of: (a) dissolving a zirconium salt in an aqueous acid, (b) adding one or more complexing agents to the resulting solution, the one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group, (c) heating the solution or sol formed in step (b), (d) adding a cerium salt, and adding a sulphating agent either before or after the addition of the cerium salt, and (e) adding a base to form a cerium-zirconium based mixed hydroxide.

Provided is a complex oxide that has a high hydrogen content, contains almost no impurity phase, and is suitable for proton conductivity. The complex oxide is represented by a chemical formula Li.sub.7-xH.sub.xLa.sub.3M.sub.2O.sub.12 (M represents Zr and/or Hf, and 3.2<x7) and is a single phase of a garnet type structure belonging to a cubic system. A method for producing the complex oxide includes an exchange step of bringing a raw material complex oxide represented by a chemical formula Li.sub.7-xH.sub.xLa.sub.3M.sub.2O.sub.12 (M represents Zr and/or Hf, and 0x3.2) and a compound having a hydroxy group or a carboxyl group into contact with each other to exchange at least some of lithium of the raw material complex oxide and hydrogen of the compound having a hydroxy group or a carboxyl group.

A composite material comprising an amorphous, porous material with nanocrystalline material in its pores has been found to be a UV absorber. The porous material is a matrix of pores that act as a scaffold for the nanocrystalline material. The particles of the nanocrystalline material are isolated, which mean that they do not connect to each other. In some embodiments, the nanocrystalline material is completely inside the pores of the porous material. In some embodiments, the nanocrystalline material may stick out of some or all of the pores of the porous material. In some embodiments, the nanocrystalline material is a cerium oxide material. In some embodiments, the nanocrystallite ranges in size from 2 to about 100 nm on its longest axis, with an aspect ratio from about 1 to about 1.5.

Provided is a method for manufacturing a sintered body for an electrolyte and an electrolyte for a fuel cell using the same. More particularly, the following disclosure relates to a method for preparing an electrolyte having a firm thin film layer by using a sintered body having controlled sintering characteristics, and application of the electrolyte to a solid oxide fuel cell. It is possible to control the sintering characteristics of a sintered body through a simple method, such as controlling the amounts of crude particles and nanoparticles. In addition, an electrode using the obtained sintered body having controlled sintering characteristics is effective for forming a firm thin film layer. Further, such an electrolyte having a firm thin film layer formed thereon inhibits combustion of fuel with oxygen when it is applied to a fuel cell, and thus shows significantly effective for improving the quality of a cell.