Abstract: A method of making a polycrystalline Mn containing ferrite body composed of crystallites which have the (111)-crystallographic planes thereof oriented substantially parallel with each other. The method involves providing a manganese compound, forming a body of a mixture made up of the manganese compound and other ferrite constituents, and heating the body made of the mixture into a polycrystalline Mn containing ferrite body of a spinel structure, wherein the manganese compound is in the form of thin platelets which have substantially parallel major surfaces oriented substantially in one direction in the body of the mixture. The ferrite body made thereby is a dense polycrystalline ferrite body having improved resistance to crumbling, improved wear characteristics and suitable physical properties for e.g. magnetic heads.

Abstract: On disposing of an acidic aqueous waste including ferrous ions, the ferrous ions are oxidized to produce iron compound precipitate in a remaining waste liquid. With the temperature of the waste kept between 50.degree. C and 75.degree. C and with pH of the waste liquid adjusted between 3.5 and 5.2, fine particles of the iron compound otherwise produced agglomerate into large polycrystalline particles. The large particles are readily separated from the waste liquid, which is now substantially neutral and transparent.

Abstract: Fine crystalline powder, from 0.02 to 0.2 micron in average particle size, of a composition Pb(Zr.Ti)O.sub.3. Parts of Zr and Ti of the composition may be substituted for with Mn and Sb, Nb, and/or Ta. The powder is produced by preparing an acidic aqueous solution of the constituent metallic ions, neutralizing the solution to provide a suspension of hydroxides of the metals, and subjecting the suspension to hydrothermal reaction at 150.degree.-300.degree.C. The powder provides piezoelectric ceramics of a high sintered density without resorting to hot pressing.