NL8800740A - HARD-MAGNETIC MATERIAL FROM A RARE NATURAL METAL, IRON AND CARBON. - Google Patents

Description

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48 12482 1 N.V. Philips Incandescent lamp factories

Hard magnetic material from a rare earth metal iron and carbon.

The invention relates to a hard magnetic material containing neodymium, iron and carbon.

A known material of this type is the Md2Fe14B with tetragonal crystal structure. It is known that substitution of B by 5C in this compound leads to greater anisotropy (see, e.g., Journal de Physique Colloque C6, supplement au no. 9, T 46, Sept.

1985, page C6-305 / 308: "Magnetic Anisotropy of Carbon Doped Nd2Fe14B" by Bizonif Leccabue, Pareti et Sanchez). In this article it is reported on page 306 that it was not possible to obtain the tetragonal 10 phase if in the compound Nd2Fe14B boron was completely replaced by carbon. This is also noted in an article in Solid State Communications Vol. 64, no. 5 p. 639-644 (1987).

In this article "Synthesis and magnetic properties of ternary carbides R2Fe14C" by Gueramiom, Bezinge, Yvon and Muller on p. 640, it has been found that with recrystallizing annealing the tetragonal structure is not found with, inter alia, R = neodymium.

The object of the invention is now to provide a hard magnetic material with large crystal anisotropy, which only contains carbon instead of boron and also contains a relatively high content of neodymium.

It has been found that this task can be met with a tetragonal crystal structure material consisting of a recrystallizing annealed cast material having a composition that differs little or not from the stoichiometric composition of Nd2Fe ^ 4C, where Fe is a total of 6 atoms. %, based on the gross composition, can be replaced by Co. When more than 6 at. Fe is replaced by Co, the amount of hard magnetic material with a tetragonal crystal structure that can be obtained in the annealing treatment decreases markedly.

The hard magnetic material according to the invention can be obtained as follows. The starting materials neodymium, iron, cobalt (optional) and carbon are melted together in a substantially stoichiometric ratio, preferably under a protective gas atmosphere such as argon. The melt is poured into a mold. The material now has the Nd2Fe. | 7 structure and is not hard magnetic, the carbon is dissolved in the grid. It is suspected that the carbon in the lattice could take the place of one or more iron atoms. The structure is rhomboedric. The obtained casting can optionally be annealed at a temperature of 900 ° C or higher. The material is recrystallized and annealed at a temperature between 840 and 890 ° C. Only within this temperature range does recrystallization 10 appear to produce the tetragonal phase. Surprisingly, it has been found that when weighing the starting materials it is not desirable to deviate clearly from the stochimetric composition, as is necessary with the corresponding boron compounds. However, a small deviation of no more than 20% in a positive sense in the amount of neodymium and / or carbon with respect to the stoichiometric composition and of 15% in the amount of iron and any cobalt present appears to be permissible. Outside the indicated temperature range, the tetragonal phase is not formed (above 890 ° C) or if it is formed next to the tetragonal phase, predominantly a second phase with the Nd2Fe17 structure remains (below 840 ° C). When annealing in the indicated temperature range, the tetragonal phase is predominantly formed. A substantially single-phase material with optimum magnetic properties can be obtained when firing between 850 and 880 ° C, preferably at 870 ° C. If the material also contains cobalt, the recrystallizing annealing process should preferably take place at a temperature of about 850 ° C. The cobalt has been found to significantly increase the curie temperature of the hard magnetic material, which may be desirable for certain applications. The experiments that led to the invention were also carried out with praseodymium instead of neodymium, it turned out to be impossible to obtain a substantially single-phase material with tetragonal crystal structure.

Output Example 1: 35 As noted above, castings were made with the gross composition Nd2Fe14C. The material after casting had an Nd2Fe2 structure (Rhomboedrian). The resulting castings were immediately recrystallized for 500 hours at 870 ° C without prior homogenizing annealing for 8 hours. The material was now single-phase and had a tetragonal crystal structure. The lattice constants were measured. It was found: A * 8.814 A, C = 12.015 A.

The material according to the invention has a Curie temperature of 535 K. The saturation layer netization at 20 ° C = 130 EMU per gram.

Likewise, single-phase materials with tetragonal crystal structure were obtained with materials of gross composition ^ 12.1 ^ 81.8¾ and Nd11.8Fe81.1C7.1 · 10 ffityggi · ipgayoortbeelfl. 1;

A casting was made, the gross composition of which corresponded to the formula FeCoC. This casting was then directly exposed to a recrystallizing annealing process at 850 ° C for 150 hours without prior homogenizing annealing. The material is now substantially single-phase and has a tetragonal crystal structure. The material has a Curie temperature of € 20 K.

Magnets can be obtained by directly pouring the material according to the invention into the desired shape. After casting and recrystallizing annealing, the material can also be pulverized and subsequently sintered in the desired shape in a magnetic field or pressed into the desired shape mixed with plastic.

In the materials mentioned, it is possible to replace part of the iron and the possibly present cobalt with other 3 d metals and / or with aluminum, gallium, silicon and the like. Part of the neodynium can be replaced by one or more rare earth metals.

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Claims (7)

Hard magnetic material containing rare earth metal, iron and carbon, characterized in that the material consists of a recrystallizing annealed cast material with a tetragonal crystal structure with a composition which differs little or not different from the stoichiometric composition ^ Fe Fe C, in which Fe up to a total of 6 at.%, Based on the gross composition, can be replaced by Co. 2. A hard magnetic material according to claim 1, characterized in that the composition deviates no more than 20% in a positive sense from the stoichiometric composition in terms of neodymium and carbon and no more than 15% in a positive sense in terms of iron and the optional cobalt present. Hard magnetic material according to claim 2, characterized in that the grating constants A * 8.814 A and C = 12.015 A are for Nd2Fe14C. 4. Process for the production of a hard magnetic material containing neodymium, iron and carbon, characterized in that the starting materials neodymium, iron and carbon are melted together and poured into a mold in a quantity slightly different from the stoichiometric ratio RE2Fe. after which the casting is recrystallized and annealed at a temperature between 840 and 890 ° C. Method according to claim 4, characterized in that the material is annealed at a temperature between 850 and 880 ° C. Process for the production of a hard magnetic material containing neodymium, iron, cobalt and carbon, characterized in that the starting materials neodymium, iron, cobalt and carbon in a little of the stoichiometric ratio RE2Fe, j4_xCoxC (where x <1, 02) different amount are melted together and poured into a mold, after which the casting is recrystallized at about 850 ° C. 7. Magnetic moldings comprising a hard magnetic material according to claim 1 and / or obtained by a method according to claims 4, 5 and 6. 8800740