A titanium oxide powder of the present invention has a BET specific surface area of 5 m.sup.2/g or higher and 15 m.sup.2/g or lower and contains single-crystalline titanium oxide particles, in which a value (d10/d50) that is obtained by dividing a value (d10), which is obtained when a particle size distribution represented by a cumulative volume percentage of primary particle diameters of the titanium oxide particles is 10%, by a value (d50), which is obtained when a particle size distribution represented by a cumulative volume percentage thereof is 50%, is 0.3 or higher and 1 or lower, an amount of titanium oxide thereof is 99.0% by mass or more, and the titanium oxide powder has an anatase-type crystalline phase.

A titanium oxide powder of the present invention has a BET specific surface area of 5 m.sup.2/g or higher and 15 m.sup.2/g or lower and contains single-crystalline titanium oxide particles, in which a value (d10/d50) that is obtained by dividing a value (d10), which is obtained when a particle size distribution represented by a cumulative volume percentage of primary particle diameters of the titanium oxide particles is 10%, by a value (d50), which is obtained when a particle size distribution represented by a cumulative volume percentage thereof is 50%, is 0.3 or higher and 1 or lower, an amount of titanium oxide thereof is 99.0% by mass or more, and the titanium oxide powder has an anatase-type crystalline phase.

This powder satisfies requirements 1 and 2.

Requirement 1: |dA(T)/dT| satisfies 10 ppm/° C. or more at at least one temperature Ti in a range of −200° C. to 1200° C. A is (a-axis (shorter axis) lattice constant) of a crystal in the powder)/(c-axis (longer axis) lattice constant of the crystal in the powder), and each of the lattice constants is obtained by X-ray diffractometry of the powder. Requirement 2: a particle diameter D50 at a cumulative frequency of 50%, a particle diameter D10 at a cumulative frequency of 10%, and a particle diameter D90 at a cumulative frequency of 90% in a volume-based cumulative particle diameter distribution curve obtained by a laser diffraction scattering method satisfy conditions (I) and (II): (I) D10/D50 is 0.05 or more and 0.45 or less; and (II) 190 is 0.5 μm or more and 70 μm or less.

A solid composition contains a first material and a powder and satisfies requirements 1 and 2. Requirement 1: |dA(T)/dT| satisfies 10 ppm/° C. or more at least at −200° C. to 1,200° C. A is (an a-axis lattice constant of a crystal in the powder)/(a c-axis lattice constant of a crystal in the powder), obtained from X-ray diffractometry of the powder. Requirement 2: C is 0.04 or more. C is (a log differential pore volume when a pore diameter of the solid composition is B in a pore distribution curve of the solid composition)/(a log differential pore volume corresponding to a maximum peak intensity in the pore distribution curve of the solid composition). B is (a pore diameter giving a maximum peak intensity in the pore distribution curve of the solid composition)/2. The pore distribution curve of the solid composition shows a relationship between the pore diameter and the log differential pore volume.

The present invention relates to a method for converting and separating vanadium, titanium, and iron from the vanadium-titanium-iron concentrate in one step, which includes the steps as below. (1) The vanadium-titanium-iron concentrate is mixed and roasted together with addition agent and reducing, agent, and thereby vanadium-containing pig iron and vanadium enriched slag are obtained. (2) The vanadium titanium enriched slag is leached in water and filtered, and thereby vanadium-containing solution and titanium slag are obtained. The technical features of the present invention are as below. By the new process of sodium reduction coupling, a new system of low-temperature smelting multiphase reaction separation is constructed. The reduction of iron, sodiumizing of vanadium, and the melting separation process of the vanadium titanium enriched slag and the iron are achieved in one step. Three products, i.e., the vanadium-containing pig iron, the vanadium-containing solution, and the titanium slag are produced.

The present invention relates to a method for preparing uniform metal oxide nanoparticles. According to the preparation method of the present invention, it is possible to maintain the temperature and pressure inside the reactor in a stable and constant manner by removing water generated in the reaction step for forming metal oxide nanoparticles. Thus, the uniformity of nanoparticles formed is increased, and the reproducibility between batches can be increased even in a repeated process and and a large-scale reaction. Therefore, the preparation method of the present invention can be used to synthesize uniform nanoparticles reproducibly in large quantities.

With an aim to provide a method for producing an oxide particle with controlled color characteristics and also provide an oxide particle with controlled color characteristics, the present invention provides a method for producing an oxide particle, wherein the color characteristics of the oxide particle are controlled by controlling a ratio of an M-OH bond between an element (M) and a hydroxide group (OH) or an M-OH bond/M-O bond ratio, where the element (M) is one element or plural different elements other than oxygen or hydrogen included in the oxide particle selected from metal oxide particles and semi-metal oxide particles. According to the present invention, by controlling the M-OH bond or the M-OH bond/M-O bond ratio of the metal oxide particle or the semi-metal oxide particle, the oxide particle with controlled color characteristics of any of reflectance, transmittance, molar absorption coefficient, hue, and saturation can be provided.

With an aim to provide a method for producing an oxide particle with controlled color characteristics and also provide an oxide particle with controlled color characteristics, the present invention provides a method for producing an oxide particle, wherein the color characteristics of the oxide particle are controlled by controlling a ratio of an M-OH bond between an element (M) and a hydroxide group (OH) or an M-OH bond/M-O bond ratio, where the element (M) is one element or plural different elements other than oxygen or hydrogen included in the oxide particle selected from metal oxide particles and semi-metal oxide particles. According to the present invention, by controlling the M-OH bond or the M-OH bond/M-O bond ratio of the metal oxide particle or the semi-metal oxide particle, the oxide particle with controlled color characteristics of any of reflectance, transmittance, molar absorption coefficient, hue, and saturation can be provided.

Provided is a method for synthesizing TiO.sub.2 nanocrystal, comprising: adjusting the pH value of a colloidal suspension of tetratitanic acid nanosheet as a precursor to 5-13; and subjecting the precursor to a hydrothermal reaction to obtain the TiO.sub.2 nanocrystal. The TiO.sub.2 nanocrystal synthesized by the method is anatase-type, and the exposed crystal facet thereof is {010} crystal facet. The method has advantages of low cost, no pollution, simple synthesizing process, strong controllability, short production period and good reproducibility, and is suitable for industrial production.

According to one embodiment, there is provided an active material includes particles of a Na-containing niobium titanium composite oxide having an orthorhombic crystal structure. A peak intensity I.sub.1 of a strongest peak P.sub.1 within a range of 3350 to 3450 cm.sup.−1 is 1.6 or less in an infrared diffuse reflectivity spectrum of a surface of the particles, according to a diffuse reflectance Fourier transform spectrometry measurement.