Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1991-07-31
1994-11-22
Sheehan, John P.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148108, H01F 102
Patent
active
053665660
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for preparing very high quality magnetic materials, and more particularly solid magnetic materials obtained from a solidification of a liquid phase or a solid diffusion close to melting temperature.
BACKGROUND OF THE PRIOR ART
The manufacturing of very high quality magnetic materials encounters problems which impair the material quality after solidification, among which can be mentioned the influence of the walls and convection phenomena in the liquid phase. These problems are inherent in the coexistence of, on the one hand, composition, temperature or density gradients and, on the other hand, the gravity field. Sedimentation and stratification phenomena also occur in liquids including solid suspensions, or non-miscible liquid suspensions; the heaviest suspensions move downwardly. These various effects are responsible for the lack of homogeneity in composition and defects in the magnetic material after solidification.
To overcome these various problems, it has been proposed to manufacture materials in satellites or during free fall in order to obtain a zero gravity or microgravity condition. But this implies very powerful and expensive means.
SUMMARY OF THE DISCLOSURE
An object of the invention is to provide a method for manufacturing magnetic materials while ensuring in a simple way conditions, partially or entirely similar to those encountered in microgravity.
To achieve this object, the invention provides a method for preparing a sample of a magnetic compound having a magnetic susceptibility .chi. comprising the following steps:
a) providing a vertical magnetic induction B which has a magnetic induction gradient dB/dz and which is such that B.dB/dz has a sign opposite to that of the weight of the sample in a selected reference axes and such that the magnetic force (.chi..B.dB/dz)/.sub..mu.0 is higher than the weight, and
b) heating at a temperature close to the melting temperature.
According to a characteristic of the invention, step (b) is followed by a step consisting in cooling the sample in the presence of the magnetic induction B and magnetic induction gradient dB/dz.
According to a first embodiment of the invention, the sample is heated during step (b) at a temperature higher than the melting temperature.
According to a second embodiment of the invention, the sample is heated during step (b) at a temperature lower than the melting temperature and adapted to enhance the internal diffusions of atoms.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments as illustrated in the accompanying figures wherein:
FIG. 1 is a perspective view of an assembly illustrating a first implementation of the method according to the invention;
FIG. 2 shows the intensity of the magnetic induction generated by a coil along its axis and the product of the induction by the gradient of this magnetic induction as a function of the position on this axis in the assembly of FIG. 1; and
FIG. 3 is a cross-sectional view of another assembly illustrating a second implementation of the method according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an assembly illustrating a first embodiment of the method according to the invention. The assembly comprises a coil 1. A system of Cartesian coordinates (x, y, z) has its origin at the center of the coil, equally spaced from its two extremities. The coil is placed so that its axis, which corresponds to the axis z of the reference axes, is oriented along the gravity field, this orientation being hereafter called "vertical".
A cylindrical crucible 2, in which a magnetic material 3 in solid or compact powder form is introduced, is so positioned in coil 1 that the crucible axis is in coincidence with the axis of the coil and that bottom 4 of the crucible is above position z=0. The material initially lies on the bottom of the crucible at a height -z.
REFERENCES:
patent: 2686864 (1954-08-01), Wroughton et al.
patent: 3887401 (1975-06-01), Hetzel
patent: 4950335 (1990-08-01), Couderchon
Peifer, "Levitation Melting-A Survey of the State of the Art", Journal of Metals. May 1965 pp. 487-493.
Patent Abstracts of Japan, vol. 9, No. 180 (C-293)(1903) Jul. 25, 1985.
Centre National de la Recherche Scientifique
Sheehan John P.
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