Abstract: The object is to provide a high-purity magnesium oxide particle aggregate that is redispersible and can be supplied with keeping high purity, and a method for producing the same. A magnesium oxide particle aggregate that is an aggregate of magnesium oxide particles, wherein the magnesium oxide particles have an average particle size of 1 ?m or less, and comprises Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zr, B and Zn as impurities in their respective amounts of 10 ppm by mass or less, wherein the total amount of the impurities is 100 ppm by mass or less.

Abstract: Magnesium oxide powders having a large diameter of crystallite, and having a favorable crystallinity are provided. Magnesium oxide powders: having peak widths at half-height of the peaks on a (111) plane, a (200) plane and a (220) plane of each no greater than 0.20 degrees as determined with a powder X-ray diffraction method carried out using a Cu—K? ray; and having a crystallite diameter of no less than 700 ?.

Abstract: Magnesium oxide powders having a large diameter of crystallite, and having a favorable crystallinity are provided. Magnesium oxide powders: having peak widths at half-height of the peaks on a (111) plane, a (200) plane and a (220) plane of each no greater than 0.20 degrees as determined with a powder X-ray diffraction method carried out using a Cu—K? ray; and having a crystallite diameter of no less than 700 ?.

Abstract: The object is to provide a high-purity magnesium oxide particle aggregate that is redispersible and can be supplied with keeping high purity, and a method for producing the same. A magnesium oxide particle aggregate that is an aggregate of magnesium oxide particles, wherein the magnesium oxide particles have an average particle size of 1 ?m or less, and comprises Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zr, B and Zn as impurities in their respective amounts of 10 ppm by mass or less, wherein the total amount of the impurities is 100 ppm by mass or less.

Abstract: A composite metal hydroxide is produced by reacting magnesium-containing aqueous solution (X) including water soluble zinc compound wherein magnesium ion concentration is 0.01 to 1 mol/liter with alkaline material (Y) at a specific reaction equivalent ratio. Further, a composite metal hydroxide represented by the following general formula (1) is produced by hydrothermally treating thus obtained composite metal hydroxide within a temperature range of 100.degree. to 200.degree. C. for aging in chlorine-containing aqueous solution having a specific chlorine ion concentration:Mg.sub.1-x Zn.sub.x (OH).sub.2 (1)wherein x indicates a positive number within a range of 0.003.ltoreq.x.ltoreq.0.1. A uniform metallic solid solution can be obtained as a composite metal hydroxide by the above series of processes. Further, its crystal shape can be controlled thereby so as to restrain occurrence of secondary aggregation.

Abstract: By hydrating a metal oxide solid solution shown as the following formula (3), wherein an average primary crystal particle diameter is in the range of 1 to 10 .mu.m, in the presence of monocarboxylic acid and/or oxymonocarboxylic acid in aqueous medium,Mg.sub.1-z M.sup.2+.sub.z O (3)in which M.sup.2+ represents at least one divalent metal ion selected from the group consisting of Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+ and Zn.sup.2+, and z is in the range of 0.01.ltoreq.z<0.5, a metal hydroxide solid solution having a high aspect ratio shown as the following formula (1) can be obtained;Mg.sub.1-x M.sup.2+.sub.x (OH).sub.2 (1)in which M.sup.2+ represents at least one divalent metal ion selected from the group consisting of Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+ and Zn.sup.2+, and x is in the range of 0.01.ltoreq.x<0.5, characterized by that a crystal is a hexagonal plate in shape, 0.01 to 0.5 .mu.m in average thickness, 1 to 10 .mu.