Abstract: A method for producing a barium titanate-based powder, the method including: step a of spraying a raw material including a barium titanate-based compound into a high-temperature field heated to a temperature equal to or higher than a melting point of the compound to form barium titanate-based particles; and step b of heating a powder including the barium titanate-based particles formed in step a at 700 to 1300° C.

Abstract: The alumina powder contains: a first alumina particle having an average particle diameter of 0.1 µm or more and less than 1 µm; a second alumina particle having an average particle diameter of 1 µm or more and less than 10 µm; and a third alumina particle having an average particle diameter of 10 µm or more and 100 µm or less, wherein each of the average particle diameters is a particle diameter measured using laser light diffraction scattering particle size distribution analyzer, average sphericity of first alumina particle having projected area equivalent circle diameter of 0.1 µm or more and 1 µm or less as determined by microscopy is 0.80 or more and 0.98 or less, a specific surface area of first alumina particle is 1.9 m2/g or more and 20.0 m2/g or less, and content ratio of an ? crystal phase is 80% by mass or more.

Abstract: An alumina powder containing alumina particles, wherein among the alumina particles, an average sphericity of an alumina particle having a projected area equivalent circle diameter of 50 nm or more as determined by microscopy is 0.80 or more, a content ratio of an alumina particle having a particle diameter of 75 ?m or more is 0.05% by mass or less, an average particle diameter of the alumina powder is 0.2 ?m or more and 15 ?m or less, the average particle diameter is a particle diameter measured using a laser light diffraction scattering particle size distribution analyzer, and an amount of water included in the alumina powder measured by a specific measurement method is 30 ppm or more and 500 ppm or less.

Abstract: A carbon-containing alumina powder containing a carbon-containing alumina particle having a projected area equivalent circle diameter of 1 ?m or more and 100 ?m or less as determined by microscopy, wherein an average sphericity of the carbon-containing alumina particle is 0.85 or more, and a specific surface area is 0.05 m2/g or more and 1.0 m2/g or less, and a ratio B/A of a carbon content ratio B to a carbon content ratio A in the carbon-containing alumina powder calculated by using a specific measurement method is 0.20 or more and 0.90 or less.

Abstract: An alumina powder containing: a first alumina particle having average particle diameter from 0.1 ?m to 1 ?m; a second alumina particle having average particle diameter from 1 ?m to 10 ?m; and a third alumina particle having average particle diameter from 10 ?m to 100 ?m, wherein the particle diameters are measured using laser light diffraction scattering particle size distribution analyzer, average sphericity of first alumina particle having projected area equivalent circle diameter from 0.1 ?m to 1 ?m as determined by microscopy is from 0.80 to 0.98, and a ratio of D90/D10 of first alumina particle is from 2.0 to 8.0 wherein the ratio of D90/D10 is a ratio when particle diameter at cumulative value of 10% from fine particle side of cumulative particle size distribution on volume basis is D10 and particle diameter at cumulative value of 90% from fine particle side is D90.

Abstract: Provided is an external additive for toner, which is suitable for producing a toner having excellent storage stability and chargeability. A silica fine powder suitable for being added to the external additive for toner is also provided. The silica fine powder has a specific surface area of 15 m2/g or more and 90 m2/g or less, a loose bulk density of 0.09 g/cm3 or more and 0.18 g/cm3 or less, a carbon content of 0.25 wt % or more and 0.90 wt % or less, and a hydrophobicity of 60% or more and 75% or less. It is preferable that a ratio (A)/(B) of the loose bulk density of the silica fine powder after surface treatment (A) to a loose bulk density of the silica fine powder before the surface treatment (B) be 1.05 or more and 1.60 or less.

Abstract: Provided is an external additive for toner, which is suitable for producing a toner having excellent storage stability and chargeability. A silica fine powder suitable for being added to the external additive for toner is also provided. The silica fine powder has a specific surface area of 15 m2/g or more and 90 m2/g or less, a loose bulk density of 0.09 g/cm3 or more and 0.18 g/cm3 or less, a carbon content of 0.25 wt % or more and 0.90 wt % or less, and a hydrophobicity of 60% or more and 75% or less. It is preferable that a ratio (A)/(B) of the loose bulk density of the silica fine powder after surface treatment (A) to a loose bulk density of the silica fine powder before the surface treatment (B) be 1.05 or more and 1.60 or less.