Centre National De La Recherche Scientifique

Université Paul Sabatier (toulouse Iii)

Universite Paul Sabatier

Paul Mollard

Abel C Rousset

Philippe Tailhades

Christiane B Salvaing

Daniel Fruchart

Salvatore Miraglia

Rene Perrier De La Bathie

Michel Gougeon

Robert Fruchart

Alain Manoux

Christian Sarda

There is disclosed a process for optimizing the magnetic properties of a multiphase product of composition rare earth/iron/boron endowed with permanent magnet properties at ambient temperature. This composition serves as a precursor, which is first subjected to a decrepitation treatment by hydrogenation under low pressure at low temperature to obtain an intermediate hydride in pulverulent form. The pulverulent intermediate hydride is subsequently subjected to a first heat treatment under vacuum for partial dehydrogenation at a temperature below its element separation temperature. The non-separated product thereby obtained is subjected to a second heat post-treatment under an initial primary vacuum and extensively dehydrogenated until the primary vacuum is reestablished at a temperature close to 600.degree. C. The precursor can be an isotropic material obtained by fast quenching, such as wheel quenching or hot welding with a forging ratio of at least 10. According to another aspect of the invention the dehydrogenated product obtained is subjected to a third heat post-treatment under a neutral atmosphere or under vacuum, at a temperature of between 450.degree. and 1000.degree. C. The two post-treatments are optionally separated by a thermal plateau.

Treatment of pulverant magnetic materials and products thus obtained

A process for preparing hexaferrite particles of the type M'Fe.sub.12 O.sub.19 wherein M' represents principally an alkaline earth metal involves preparing a particulate mixture of a ferrous salt of an organic acid and a salt of an organic acid with at least one metal M', optionally with at least one dopant agent, the particles of the mixture having a size not greater than about 0.5 .mu.m and the said mixture containing a stoichiometric excess of the salt of metal M'. This mixture is heated up to the decomposition of the organic salts and the resulting product is submitted to a thermal treatment at a temperature at least equal to 700.degree. C. but not greater than 1000.degree. C. and is maintained at this temperature for a period of time sufficient to form hexaferrite. After cooling the resulting particles are washed with an aqueous solution of an acid capable of dissolving formed monoferrites of the type M'Fe.sub.2 O.sub.4 to remove them.

Process for the preparation of hexaferrites

Compositions of particulate magnetic oxides with a defect spinel

Particulate compositions of ferromagnetic metal oxalates in the form of

Growing community of inventors

Domene, France

Paul Mollard