Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1999-03-05
2003-02-25
Wyszomíerskí, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S302000, C075S349000, C164S122000
Reexamination Certificate
active
06524399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to permanent magnetic materials of RE—TM—B alloys, and, more particularly, to methods of producing alloyed Nd/Pr—Fe—B alloyed powders.
BACKGROUND OF THE INVENTION
This invention relates to magnetic Materials comprising one or more transition metals, one or more rare earth elements and iron. A variety of such materials are known. See, for example, U.S. Pat. Nos. 4,374,665, 4,402,770, 4,409,043 and 4,533,408 of Koon which disclose magnetic alloys comprising iron, lanthanum and a lanthanide, and boron; U.S. Pat. Nos. 4,802,931 and 4,851,058 to Croat which disclose single phase TM—RE—B alloys, U.S. Pat. No. 4,935,074 of DeMooij et al. which discloses a material including iron, a relatively high percentage of boron, and Nd and/or Pr; U.S. Pat. No. 5,071,493 to Mizogochi et al., and U.S. Pat. No. 4,770,723 to Sgawa et al. Methods of preparing such magnetic materials are taught in U.S. Pat. Nos. 4,867,785 and 5,116,434 to Keem et al., and U.S. Pat. Nos. 4,715,891 and 4,753,675 to Ovshinsky et al.
In general, the magnetic material is prepared in two-steps. The first step is to prepare a substantially homogeneous master alloy of the desired composition of the various components, and then to break the alloy into relatively large, e.g., 1 cm pieces, that can be easily remelted for later processing. The second step is to remelt the alloy in a crucible, and then to quench and rapidly solidify (e.g., 25-30 micron and not over 50 microns thick) homogeneous ribbon. Typically the quenching and rapid solidification is accomplished by passing the melted material through a small (e.g., 1 mm in diameter) orifice onto a moving chill surface, e.g., a rotating chill surface such as that shown in aforementioned U.S. Pat. No. 4,867,785.
Typically, the ribbon is then crushed into fine powder, the powder is then heat treated and magnetically separated (e.g., as disclosed in U.S. Pat. No. 5,116,434) to separate powder having high magnetic parameters from that having lower magnetic parameters, and the high magnetic parameter powder is made into permanent magnets.
The above described procedure, and particularly the quenching and rapid solidification, is expensive and subject to a number of potential problems and difficulties. For example, unsatisfactory product may result from variations in the flow from the crucible caused by alloy/crucible reaction products, slag or products of reaction between the atmosphere and the molten alloy at the crucible orificd that can clog or impede flow through the small crucible orifice, or for relatively small variations in the chill surface temperature or speed that affect the quench rate and/or ribbon thickness.
There has been, and remains, a need for a process that is less expensive and has fewer difficult-to-control parameters.
SUMMARY OF THE INVENTION
According to the present invention, a class of alloyed magnetic materials, i.e., materials having a relatively high boron content, are prepared in a single step procedure. A molten mixture of the desired composition is cooled at a rate slower that about 10
5
degrees Celsius per second, and preferably more than about 10
4
degrees Celsius per second. Without the need for conventional rapid quenching, a powder of the slow-cooled material may then be heat treated, and, optionally, magnetically separated. Surprisingly, such slow cooled material has been found to have magnetic properties superior to those of material of identical composition made in the conventional two-step, rapid quenching procedure.
In some preferred practices of the invention, the molten mixture is solidified by depositing it on a heat conducting surface such that it forms a layer between about 120 and about 300, and preferably between about 120 and about 150, microns thick, and the relatively thick layer of slow-cooled material is then crushed into powder before heat treating. In these and other preferred practices of the invention, the molten mixture contains more than about 10 (and most preferably not less than about 20) atomic percent boron and not more than about 10 atomic percent of a rare earth. Preferably at least 90 percent by weight of the rare earth content is Nd, Pr or a mixture thereof and any other rare earth constitute less than 10 percent of the total rare earth content. In most preferred practices, the molten mixture includes at least 60 atomic percent, and preferably at least 70 atomic percent, Fe.
REFERENCES:
patent: 4374665 (1983-02-01), Koon
patent: 4402770 (1983-09-01), Koon
patent: 4409043 (1983-10-01), Koon
patent: 4533408 (1985-08-01), Koon
patent: 4715891 (1987-12-01), Ovshinsky et al.
patent: 4753675 (1988-06-01), Ovshinsy et al.
patent: 4770723 (1988-09-01), Sagawa et al.
patent: 4792368 (1988-12-01), Sagawa et al.
patent: 4802931 (1989-02-01), Croat
patent: 4851058 (1989-07-01), Croat
patent: 4867785 (1989-09-01), Keem et al.
patent: 4935074 (1990-06-01), De Mooij et al.
patent: 4994109 (1991-02-01), Willman et al.
patent: 5071493 (1991-12-01), Mizoguchi et al.
patent: 5116434 (1992-05-01), Keem et al.
patent: 5597425 (1997-01-01), Akioka et al.
patent: 6019859 (2000-02-01), Kanekiyo et al.
patent: 6022424 (2000-02-01), Sellers et al.
patent: 0542529 (1993-05-01), None
patent: 01 171209 (1989-07-01), None
patent: 08 264363 (1996-10-01), None
Kanekiyo, H. et al.: “Thick FE3B/ND2FE14B Nanocomposite Permanent Magnet Flakes Prepared by Slow Quenching,” Journal of Applied Physics, U.S., American Institute of Physics, New York, vol. 83, No. 11, Part 2, Jun. 1, 1998, pp. 6265-6267.
Hale and Dorr LLP
Pioneer Metals and Technology, Inc.
Wyszomíerskí George
LandOfFree
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