CA1287507C - Method for producing rare earth alloy - Google Patents

Abstract

ABSTRACT

A rare earth alloy for producing permanent magnet comprised of 15-65 atomic % R1, 35-83 atomic % Fe, and 0-15 atomic % B, where R1 represents at least one of heavy rare earth elements Gd, Tb, Dy, Ho, Er, Tm and Yb. This alloy is produced by reducing a mixture of corresponding rare earth oxides, Fe, and a boron containing material by Ca, contacting the reduced mass with water, and treating the resultant slurry with water. Using this alloy, Fe-B-R base magnets wherein R1 is substituted for part of R (R representing lanthanide and/or Y) having a high performance are produced with a reduced cost.

Description

~.2~7~0~

SPECIFICATION

` Title of the Invention METHOD FOR: PRODUCING RARE EARTH ALLOY

Fiel~ of ~he Invention ~ The~present~ lnventlon relates to Fe-B-R ~ase rare earth :magnet~material~s :having a~hi~gh-performance, particularly, method for:producing~thè ~same,~:wherein~ F~ represents at least ~ one~of~Nd,~Pr~ La,~Ce,~Tb~, ~Dy,~Ho,~ Er,~: Eu,~ Sm, Gd,;Pm, Tm, Yb,~
La~ and;Y.
Backqround:~of ~the Invention ~The~.Fe-B~ base ;~;magnets~ have~ ~attr:acted public~
: ~ attent~lon~a~s~a~novel~.permanent magnet~: w~ith~ a high-performance ~ us`ing r`a:re-,~ear~th,el~em~ents~ (R)~::represented by Mdr Pr etc. They :~10 ~ hav`é'promlnent advantages that~:~they~exhlblt~the characterlstics compa~rable~ to.:those;~o~ a;oonventional~ hlgh-performance magnet, e.~g.:~ the,~ 5m-~o ~ba~se~;magnet,~ do ~not~require eXpensive arld :scarce~Sm.~as~R~and~do;~n`ot.~necéssarily use expensive Co which is ~1 2~37~07 difficult to be procurea steadily, as disclosed in JP Patent Kokai No. 59-46008 or EP 0101552~ P~rticularly, N~ has been hitherto regarded as having no utility value. Thereore~ it is very v&luable for industry that Nd can be use~ as a principal element.
Recently, it has been attempted to provide high magnetic characteristics for the Fe~ ase magnets and to produce them at lower costs. For éxample, the ~pplicants' company developed a high-performance r,lagnet using, as R, Nd and~or Pr mainly, and partly at least one of Gd/ Tb, Dy, Ho, Er, Tm an~ Yb (hereinafter, these elements are referred to as Rl)r and filed a patent application thereon (JP Application No. 58-140590 ~ now JP Patent Kokai No. 60-32306 or EP 0134305).
In the JP Patent Kokai No. 60-32306, it was proposed that the superior Rl-R2-Fe-B base rare earth magnets ~wherein Rl represents the same as hereinabove mentioned, an~ R2 represents that the~sum of Nd and/or Pr is at least 80 atomic and the balance in R2 is at least one of rare earth elements ~R other than P~l~ are pr~oduced by substituting at least one of heavy rare earth elements Rl for at most 5 atomic % of rare~ earth element such~ as Ndl Pr, etc. in the R-Fe-B base or R-Fe-Co-E ba~se rare earth magnets. These ` ~
superior ~Rl-~2-Fe-B base rare earth màgnets enable to .
prominently~raise~the~ coerclve force (lHc) to 10 kOe or more and~ to be~used~at~l00 - 150Cr i.e., temperatures hiyher than room temperature, while maintaining a high energy product of -~

(BH)~ max~ of;at least~20 MGOe. ~s st rting materials for the ~ ~ 2 :

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production of Rl-R2-Fe-~ base rare earth magnets, primarily there are used expensive bulk or lump metals having little impurities, such as electrolytic iron with a purity of at least 99.9%, and rare earth metals with a purity of at least 99.5%
prepared by an electrolysis or a heat reduction.
Summary oE the Disclosure Therefore, any of these raw materials is the high quality material having little impurities previously refined from ores~ Using these materials, the resultant magnets become considerably expensive in spite of the efforts for lowering the cost by using of Nd, Pr, etc. The content of the heavy rare earth metals Rl such as Gd, Tb, Dy, Ho, Er, Tm, Yb, etc.
which are effective for increasing the coercive force, is at most 7% ln the ore~ that is, less than the content of Nd which is 15~. Actually, such heavy rare earth metals~are expensive, since thelr production requires hlgh separatiny-refining technics and their production efflciency is low. Consequently~
Rl-R2-Fe-B ~base permanent magnets having a high-performance and~ a high iHa are very valuable as the practical permanent magnet materials,~but have a drawback in their high cost.

It~ is a primary~ object of the present invention to provide higher m~agnetic characteristics for the Fe-B-R base magnets and to~ enable the lne~pensive production.

~ Uore~speclflcally, the present invention relates to a ~heavy~ rare; earth alloy~ ~or powder thereof) for magnet raw materlals~for~use ln-the high-performance rare earth magnets of Rl-R2-Pe-e~ base (Rl represents at least one of rare earth ~ ~ 3 ~

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elements includiny Gdr Tb~ DY, HO, Er/ TM and Y~, and R2 represents that the sum Of Nd and/or Pr is a~ least 80 atGmic %
and the balance in R2 is at least one of rare earth elements including Y other than P~l) and to a method for producing them.
Thus a further object of the present invention is to provide an P~l base rare earth alloy with a reducec~, cost in an industrial scale, That is, a concrete object of the present invention is to eliminate the various drawbacks above-mentioned and to inexpensively provide a high-quality rare earth alloy containing the P~l-element in a mass-production scale.
In an aspect, the present inv:ention relates to a rare earth alloy characterizecl in an alloy consistiny essentially of Rl : 15-65 atomic ~, Fe : 35-83 atomic ~, and B : 0-15 atom1c~%, in which Rl represents at least one of Gd, Tb, Dy, Ho, Er, Tm and Yb, with an o~:ygen content being at most 7000 ppm, and a carbon content being at most lO00 ppm.
~0 In another aspect, the present invention relates to a method for produc1nJ a rare earth alloy having said alloy composition w1th~ an oxyger~ content being at most 7000 ppm, and a ca:rbon content~being at most lO00 ppm, characterized in steps of: :~
~25 ~ ~ preparing a mixed raw material powder comprisiny at least one~of the oxides of rare earth elements Rl, an iron po~7~er an~: a boron containincJ powder selectecl from the sroup : ':
: - 4 -~.Z~7~07 consisting of boron, ferroboron and boron oxide in a manner such that the resultant alloy product consists essentially o~: -15-65 atomic % Rl, 35-83 atomic ~ Fe, and 0-15 atomic ~ ~, in which Rl represents at least one of heavy rare earth ele-ments selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm and Yb; said mixed raw material powder further com-prising metallic Ca and/or Ca hydride in an amount of 1.2-3.5 times by weight of the amount stoichoimetrically required for reducing oxygen in said raw material powder and at least one of the oxides of said rare earth elements Rl, and 1-15 % by weight of calcium chloride based on ~he oxides of said rare -earth elements Rl;
lS compacting the resultant mixture;
subjecting:the resultant compacted mixture to reduc-tion-diffision treatment under a nonoxidizing atmosphere at a temperature of 950-1200C;
: ~ brlng the reduced mass to a particle size of 8 mesh to ~ 20 35 mesh; ~; ~
-` contacting the resultant:reduced mass with water to ~orm a slurry-like:substance;:and ~ ~ ~ treating:said slurry-like substance with water by `~ stirrLng the slurry and: removing~water to recover the resultant alloy powder;:
whereby:said alloy:powder has an oxygen content of at ` ~most 7000~ppm~, and: a~carbon content o at most 1000 ppm.
For~both aspects,~Said R1 ls prefarably 15-50 atomic~;%,~ more preferably ~at least 35 atomic %, and B is preferably 2-15 atomic %.
~ :In a further~embodiment, said mixed raw matarial .. -- ~ ,. .. , : : ~ : -.' ~ . !
, . . . .. , ., ' ,' . , . , , ' ' , .
,, . ~ . ': . .: , , :
' ' ; :'` ' .' ' ' . " ', ' ,: ' ' ' . " .' ' .' '. ` ' ' :. .~, i ' . ' ' `,, ' , : ' , , ' ' ' ,"' ', ': ' ' ~1.2~37507 powder is prepared so that said alloy product consists essentially of:
25-40 atomic % Rl, 50-71 atomic ~ Fe, and 4-10 atomic % B.
The reduction-diffusion treatment provides direct reduction of o~ides in the startiny materials.
The reduced mass is preferably brought to a particle size from 8 mesh to 35 mesh prior to contacting with water~ The contacting witn water may be effected by bringing the reduced -~
mass (or crushed or pulverized mass) in water. The reduction-diffusion treatment may be effected after compacting the resultant mixture, ~ however, the compacting may be .
eliminated. As~the heavy rare earth elements Rl use of Ho, Tb and/or Dy is preferre~, while most preferred is Dy. Tm and Yb~ mlght encounter 60me~di~f~ficulty in procurement in a large amount an~ cost~ Withln this~preferr~ed ranye the~alloy product may include R-Fe~-E~tetragonal~crystal structure expressed by the formula R2Pel4~ in an; amount of, e.g., at least 50 vol ~, more~preferably~at least 80~vol % of~the entire~alloy. -Detailed DescriPtion~of the Preferred~Embodiments ~ n~ the~folLowlng the preferred embodiments of the present~invention will be~described in detail.
By~ uslng~the~ R1-Fe-B alloy~ powder of the present 25` ~ i~nvent1on,~ t~ s~ ;possible~ to~ provide the ~inexpensive Rl-R2-Pe-E ~base~rare~earth ~magne~tc which are used in a suffic1ently~stable~ state at~temperatures higher than room ... .: : ~ ...... - :
. , . ~ . , ,. . :. . .; :. .. , .. : .: : .. : . ..

temperature maintaining magnetic characteristics haviny a (BEI)max of at least 20 ~IGOe and iHc of at least 10 kOe. The inexpensive heavy rare earth metal oxide as one of the starting materials used in the present invention includes Ho203, Tb30~ and the like, which are present as the intermediates in the prestep for the preparation of rare earth metals. Since the rare earth alloy of the present invention is produced by using as starting materials such inexpensive heavy rare earth metal o~ide, Fe-powder and at least one of pure boron powder, Fe-B po~der and boron-containing powder (e.g., B203)~ by using as reducing material a metallic calcium powder and by usin~ calcium chloride for easy collapse or disintegration of reduction-diffusion-reaction product, an inexpensive, improved alloy powder containing Rl as the raw materials of Rl for the Rl-R2-Fe-E base ma~nets may be obtained easily in an industrial scale -Therefore, the method of the present invention is much superior in efficiency and economical effect, as compared with the conventional method using the produced Rl-rare earth metal of~ the~bulk form.
~20 Hereupon, if the mixed powder of the Rl-rare earth metal oxide and metal powders such as Fe-powder, Fe-~ powder, etc. as ~tbe~ ~starting materials is subjected to reduction-diffusion-reaction by metallic Ca, the rare earth metal~ln molten state at the reaction temperature in situ forms an alloy~very easily and uniformly, toyether with Fe-powder or Fe-B powder. In this case, the R1-rare earth alloy powder is recovered in a high~ yield from the Rl-rare earth metal oxide, :

.
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37~i07 and hence the Rl-rare earth metal o~ e may be utiliz~d effectively.
The B (boron) content in the raw material powc'er serves to effectively drop the reaction temperature at the reduction-diffusion-reaction of the P~l-Fe-B alloy powder, and facilitates the reduction-diffusion-reaction of the alloy based on the present invention. Thererore, in orc~er to procluce Rl-heavy rare earth raw materials for the Rl-R2-Fe-~ base magnets in an industrial scale from the inexpensive heavy r~re earth metal o~;ide, the inventors considere~ as most effective to produce the alloy powder from the heavy rare earth metal oxide, Fe which constitutes the main in~redient of the ~agnets and is produced inexpensively in a mass-production system, and B.
From such points of view, the inventors have come.to find the Rl-Fe-~ base alloy in a specific composition-range of the present invention and the method for producing them.
Moreover, the ~rare :earth~ alloy of the present invention has been developed for; the purpose of producing the alloy for the above Rl-~2-Fe-E base permanent magnet. However, the po~der of the present invention is not limited to this purpose, :
and is applicable: not only for the productlon of a wide range of Fe-B-R~base magnets, but also for: the production of various raw materials~ uslng;Fe~ as a constituent lngredient.
~ : The~ r~are;earth alloy of the present invention may be produced~by~the:fol:lcwincJ steps, and are usable to the alloys - ,.: .
.

. ~ . ., . . ~, , . . -~ ~fi~7 50~

for the Rl-R2-Fe-B base ~ermanent magnets. The mixed raw material powder of at least one of various heavy rare earth metal oxides such as Ho oxide (Ho23)' Tb oxide (Tb407), etc., an~ an iron powder, and at least one of pure boron powder, ferroboron (Fe-B) powder and boran trioxide ~B203) powder is prepared in order to form the alloy product consisting essentially o~:
Rl : 15 ~ 65 atomic ~, Fe : 35 - 83 atomic ~, and B : 0 - 15 atomic ~
in whlch Rl represents one of heavy rare earth elements including Gd, Tb, Dy, Ho, Er, Tm and Yb. To the mixed raw material powder are added metallic calcium and/or calcium hydride as a reducing agent~ of the heavy rare earth metal oxide and CaC12-powder for promoting the collapse of the reaction product tbrlquette) after the reduction, consequently obtaining the incorporated materials. The amount of calcium ~metallic or as hydri~e) required is 1.2 - 3.5 times ~by weight) as much as -the amount stoichiometrlcally required for the reduction of oxygen content~of the~mixed~raw materlal powder. The amount . of CaC12~ lS 1 - 15%~by weight, based on the rare earth metal oxide~raw~materials. Mixing of all the materials may be done at once~or~seq~uentlally. ;~ ~
The~above mixed~materials including each raw material 2S powd~er~such a~s~heavy rare~ear~th mètal oY.ide powder, Fe-powder, ferroboron~powder~,~Ca~as~ a reducing agent and the like, is (occas~ionally compacted an~) subjected to reduction-diffusion -: : : ~ ~ : :
: ~ : -, . . .: - , . ; . . , , . . : . .

~ 7 treatment under the atmosphere of an inert gas (e.g., argon) for 1 to 5 hours preferably at a temperature ranging 950 to 1200C, more preferably 950 to 1100C, and then i5 cooled to room temperature to result in a reduction-reaction product.
This reaction product is usually pulverized to a particle size of at most 8 r.lesh (at most 2.4mm), and is brought into water, in which calcium oxide (CaO), CaO.2CaC12 and excess Ca in the reaction product are converted into calcium hydroxide [CatO~)2] etc. while the reaction product itself collapses to form a slurry mixed with water. From this slurry, the Ca contained is throughly removed with water, consequently obtaining a rare earth alloy powder having a particle size of 5~m - lmm according to the present invention. Considering the workability in a magnet production step and the magnetic characteristics, the particle size of the powder of the present invention lS preferably 20~m - l~m, more preferably 20~m -500~m. At a temperature below g50C the reduction~diffution reaction becomes insuffiGient, while above 1200C wear of furnace becomes;ser1ous.
~ When the reduction-reaction product is brouyht into water without pulverization to a part1cle slze of at most 8 mesh, that is, as such or as a particle size of more than 8 mesh,~lt~ mlght become occasionally unsuitable for the ~ industr~lal production~due to slow collapse and reaches a high :, - 25 temperature due to the accumulated destruction-reaction heat in its product~if~blocks are too large, so that the obtained rare -^
earth alloy powder might have an o~ygen content of more than ~ ~ .
, ~ : :'"

:

7, jC~7 7000 ppm and hence become unsuitable for use in the subsequent magnet-production step. If the reduc~ion-reaction product has a particle size of less than 35 mesh, it starts to burn due to vigorous reaction. Preferably, water used in the present invention is ion-exchanged water or distilled water, considering the little oxygen content in the alloy powder, high yield in the magnet-producing step and good magnetic characteristics.
Thus obtained alloy powder for the magnetic materials consists essentially of the following composition:
Rl : 15-65 atomic % Ipreferably 15-50 atomic %), Fe : 35-83 atomic %, and B : 0-15 atomlc % (preferably 2-15 atomic %), in which Rl represents at least one of heavy rare earth elements including Gd, Tb, Dy, Ho, Er, Tm and Yb, with an oxygen content being at most 7000 ppm, and a c~rbon content being at most 1000 ppm. Using this alloy powder, the P~l-R2-Fe-B base permanent magnet may be produced, as described hereafter.
:
More preferred c = position range of the~rare earth alloy po~7der~0f the present invention is as follows:
Rl : 25~- 40 atomic %, Pe : 50 - 71 atomic ~, and B : 4 -~lO atomic ~.
.:
~ In this composition, the oxygen content of the alloy powder comes~ to at most 4000~ppm, and the carbon content thereof come~s to at most 600 ppm.~ This facilitates formation . : : -- 11 -- , ;:
. : :
,. . .- ~: . . : , . .

- ~ . . . :. . " . ~ . , ~ ~f37507 of the alloy, causes less generation of slay, increases yield of the alloy product and makes the effective use of the alloy powder possible, in the course of melt-alloying of the Rl-R2-Fe-B magnetic alloy. If the alloy powder as such is used by being added in the pulverization step, the amounts of the oxides and the carbides are reduced in the permanent magnet, so that the Rl-~2-Fe-B permanent magnet achieves a high coercive force and excellent magnetic characteristics.
Further, the reducing temperature becomes 950 - 1100CI which facilitates the production in an industrial scale. The rare earth alloy powder of the present invention can be used either by adding a required amount of the alloy powder of the present invention as a compact or sintered mass upon melt-alloying the Rl-R2-Fe-B magnetic alloy, or by adding a required amount of the alloy powder of the present invention as such to a separately prepared ~2-Fe-B alloy powder in the pulverization-step to obtain the mixed Rl-R2-Fe-B alloy powder. In any caser the method of the present invention has advantages that it shortens the process for the production of the magnets and lowers the costs of the produced magnet due to the use of inexpensive raw materials. Further, it has advantageous economical effects since it facilitates the mass-productlon of practical permanent magnets.
The oxygen in the alloy powder of the present invention is combined with the rare earth element to be most easily oxidized to form rare earth metal oxide. Therefore, if the o~ygen content fs more than 7000 ppm, the meltlng of the .: , . :, . . .

- . .. . . . , , ~ . ...
.. . . . . . . . . .

..
, , - . - '. ~ : : ' ' alloy in the melting-step of the Rl-R2-Fe-B magnetic alloy becomes difficult, which does not form an alloy, causes a considerable generation of slag, lowers the yield of the alloy product and hence prevents the effective use of the alloy powder based on the present invention.
If the carbon content is more than 1000 ppm, carbides are left in the final permanent magnet product, which leads to an undesirable decrease of magnetic characteristics, particularly a decrease of the coercive force below 10 kOe and deteriorates the ~loop squareness of the demagnetization curve of the magnet.
If the oxygen content is more than 7000 ppm and the carbon content is more than l000 ppm in the case where the alloy powder as such is used by adding in the pulverization-step, both ingredients are lef~t as oxides and carbides (R3C, R2C3~ RC2) in the resultant permanent magnet, which lowers the coercive force remarkably.
If the Ca content as the reducing agent of the raw materials of the present 1nvention exceeds 3.5 times as much as the amount required stoichiometrically, vigorous chemical reaction occurs in ~he reduction-diffusion-reaction, which causes prominent heat generation and brings about serious wear of a reaction vessel by the highly reductive Ca, and hence makes the steady mass-production impossible. Further, in this case, ~the residual Ca content in the alloy powder produced in -`~ the reductio~-step becomes hlgh, which wears out the furnace in the heat-treating-step of magnet production due to generation ~ - 13 -. ~
:` :

- . ... . . . .
.: . .. . , : ., .

. : . . : . .

375C~7 of much Ca vapor and deteriorates the magnetic characteristics due to the high Ca content in the magnet product. If the Ca content is less than 1~2 times as much as that required stoichiometrically, the reduction-diffusion-reaction is incomplete and non-reduced substances are left in a large amount, so that the alloy powder o the present invention is not obtained. The amount of Ca is preferably 1.5-2.5 times, most preferably 1.6-2.0 times of the stoichiometric amount.
If the amount of CaC12 exceeds 15% (by weight), the Cl (Chlorine ion) in water increases remarkably in the treatment of the reduction-diffus1on-reaction product with water, and reacts with the produced rare earth alloy powder, so that the oxygen content of the powder attains more than 7000 ppm. and the powder can not be utilized as raw materials for the Rl-R2-Fe-B magnets. Besides, in case of less than 1 weight % of CaC12, the collapse does not occur even if the reduction-diffusion-reaction product is put into water, thus its treatment by water becomes impossible.
The reasons for limitiny the range of the composition .
of the rare earth alloy powder of the present invention are as .
follows. Where the ~Rl element (at least one of Gd, Tb, Dy, : Ho, Er,~ Tm and Yb), which is indispensable for improving the coerciv~e~ force (iHc) of the Rl-R2-Fe-B ~ase rare earth magnets, ~ ~lS~ less than lS atomic %, the residual Fe content increases~an~ ~the oxygen content in the alloy powder attains more th~an 7000 ppm, the melting of the Rl-R2-Fe-B base magnetic alloy in the melt production becomes dlff1cult, which ~ - 14 --: . :, . .. :,, : , :. . . .

~ ~7~7 does not form the alloy, causes slag formation, and lowers the yield of the melt-formed alloy.
If the Rl element is more than 65 atomic %, the amount of the rare metal oxide in the raw materials for the reduction is too large to be reduced sufficiently or to form the rare earth metal oxide adequately. In this case, the oxygen content of the alloy powder is more than 7000 ppm, which brings about, as is the case with the previous case, the difficult alloy formation and the drop in the alloy yield.
Thus the Rl element of no more than 50 atomic % is preferred.
Fe is an indispensable element for directly obtaining the rare earth alloy of the present invention, which is inexpensive and of good quality, by the process wherein the Rl rare earth element obtaineù by the reduction of the heavy rare earth metal oxide with metallic calcium diffuses immediately. In the case of less than 35 atomic % or more than 83 atomlc % of the Fe content~ the oxygen content of the alloy powder becomes more than 7000 ppm, and~ the carbon content thereof becomes more than lOOO ppm, so that the production of a ~O superior maqnet from the al~loy becomes difficultl the yield of the melt-proauced a11Oy decreases and the alloy powder is unabLe~ to be used~for the~magnetic alloys.
~ ~ ~B~ (boron)~ ~lS preferred~ element for lowering the reduction-diffusl~on temperature of the alloy based on the present invention.~ B is~effe~tive at 0.1 atomic ~ or more. In the~case of less than~2~atom~ic % of~E content, the reduction temperature ~of ~more~ than;1200C is occaslonally required, and ~ : `
., .... . . , , . , . , - . . ..

7~7 the utilization of the equipment of an industrial scale becomes difficult since the extremely high reductive Ca is used.
Further, in the case of more than 15 atomic % of the ~ content, the oxygen content of the rare earth alloy powder obtained reaches more than 7000 ppm since boron is subjected to oxidation easily, so that, as the previous case, the magnet production from the alloy becomes difficult, the yiela of the melt-formed alloy decreases and the alloy powder is not effective as the alloy powder for magnetic materials.
As mentioned previously, the alloy product of the present invention includes ones having an Fe-B-R tetragonal crystal structure within the preferred alloy composition, while the presence of such crystal structure is not essential for the entire compositional scope of~ the present invention. ~owever, even the alloy product havlng no FeBR tetragonal crystal structure may be utilized to prepare the PeBRlR2 alloy having the saiù crystal structure. Generally the directly reduced alloy product of the present invention is of the crystalllne nature (e.g., crysta} sraln size of 20-120 ~ m). i;

2~ In order to produce a FeBRlR2 sintered magnet a mixture ~or preferably an alloy thereof) of said alloy product and appropriate FeBR2 alloy (e.g.,~ FeB~d) is prepared and pulverized to prefer~bly 1-20 ~m in size, then compacted and sintered,~usually ~followed by aging. For preparing the :: ~ : :
FeBRlR2 ~alloy, ~said FeBRl alloy proauct is preferably consolidated~ by compactiny, melting and/or sintering, or hot presslng~ or the llke manner, then melted together with the ~ ~ - 16 -- :

- . : . . ...................... ... . .......... . .

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37~

FeBR2 alloy. This consolidation provldes easy alloying by high frequency melting. The resultant permanerlt magnet is generally of the FeER tetragonal crystal structure (i.e., at least 80 vol % of the entire magnet), the crystal grain being preferably 1-40~m (most preferably 3-20~m) for e~:cellent permanent magnet properties~ The detailed disclosure about the FeBR tetragonal crystal structure is disclosed in EP 0101552 and herewith referred to.
It should be noted that the inventive alloy product may be utilized in producing FeCoBRlR2 type permanent magnet (refer to EP 0134304) wherein Co is present to be substituted for a part of Fe in the FeBRlR2 type magnet.
Furthermore, the alloy powder of the present invention may contaln at most 2 % by weight of impurities inevitabIe i~n the technically available raw materials or in the manufacturing steps, or eYamples, A1/ Si, P, Ca, Mg, Cu, S, Nbl Ni, Ta, V, Mo, Mn, ~, Cr, Hf, ~Ti/ Co etc., howeYer the impurities should be as less as possible, e.g., at most 1 % by weight, or ev~en at most 0.5 % by weight. Cu, S and P are particularly~not preferred. ~
~ When the calcium content e~ceeds 2000 pFm, a large , amount ~of~ ~strongly ~reducing Ca ;vapor is generated in the interme~iate~ sintering step of the subsequent steps for making ~ magnets~;f~rom~;the; alloy powders of the present invention. The a vapor contaminates the heat-treatment furnace used to a consiaerable ~extent and, in some cases, give rise to serious damage~to the~wall thereo~, such that it becomes impossible to ~i 2~75~

effect the industrially stable proc-iuction of maynets. In addition, if the amount of Ca contained in the alloy powders formed by reduction is so large that a large amount of Ca vapor is generated at the time o~ heat treatment involved in the subsequent steps for making magnets to give damage tG the heat treatment furnace used. This also leads to a large amount of Ca remaining in the resulting magnets, entailing deteriorations in the magnet properties thereof as a result. Thus a calcium content of 2000 ppm or less is preferred, most preferred is lO00 ppm or less.
Usual1y, the amount of rare earth elements in the rare earth metal oxides as the starting materials is calculated in consideriny the yield, and may be, e.g., 1.1 times of the amount in the alloy product.
Examples Various rare earth alloy powders will now be described in deta11 with reference to the followin~ es.amples.
Example 1.
Tb407 powcier : 75-29 Fe powder : 35.1g ~ ~
Eerroboron powder (19.5 wt% B-Fe alloy powder) : 2.2g MetalIic Ca : 72.4g (2.5 times as much as the amount required stoichiometrically) ~ CaCl2~ : 3.89 ~5.1 wt~ based on the rare earth metal ~ os~ide materials) 188.7g of ~al1 the raw~ materia1s above-described were m1xed~1n~a~V-type mixer,~ a1mi.ng at an a11Oy composed of 35~ Tb ~ 18 -.
~ : ~
..

.. ~ . - . . .

375C~7 - 61% Fe - 4% ~ (atomic ~) (61.72 wt% Tb - 37.80 wt % ~e - 0.48 wt % B). Then, compacts of the mixed raw tnateri~ls were charged in a stainless steel vessel, then placed in a mufle furnace, and heated in argon gas flow. After having been held constant at 1075C for 3 hours, the furnace was cooled to room temperature. The resultant reductive reaction product was pulverized to a particle size of 8 mesh-throuyh, then was introduced into an ion-exchanged water/ in which calcium o~id~
(CaO), CaO.2CaC12 an~ unreacted residual calcium were converted into calcium hydrozide allowing the reaction products to collapse to form a slurry-like product. After stirring for 1 hour, the pLoduct was allowed to stand for 30 minutes, and then the suspension of calcium hydroxide was removed. The product was again diluted with water. The Steps of stirring, standing and suspension-removing were repeated many times.
Thus separated and withdrawn Tb-Fe-B base alloy powder was dried under vacuum. In this manner, there were obtained 76g of the heavy rare earth~alloy powder for the magnet raw materials of a 20 - ~300~m~ particle~ size accordlng to the present ~0 invention.
The elementary analysis values of this powder were as follows~
: Tb : 6 0.11 wt~
:
~ ;~ Fè~ 39.45~wt%

B ~: 0.37 wt%

~ Ca :~ 0.08 wt%
.
O2 :~1900 ppm~ ~

~ ~ :
:. ~ , ; -.. . : - : . . .. .: . , . :

- - : . . . ~

~ ~:137'~

C : 250 ppm As a result, the desired alloy powder was obtained.
A sintered body was pre~ared by treating the above alloy po~7der at 1150C ~or 2 hours in order to prepare a magnetic alloy composed of 14 Nd - 1.5 ~b - 77.5 Fe - 7 B
(atomic %). This sintered body as the raw material of Tb was melted with the beforehand prepared metallic Md, ferroboron alloy and Fe material. The resultant melt-formed alloy piece was pulverized to a powder having an average particle size of 2.70~m, then was compacted in a magnetic field o~ 10 kOe under a pressure of 1.5 t/cm2, thereafter was sintered at 1120C
for ~ hours, and was aged at 600C for 1 hour to produce a permanent magnet specimen.

The obtained magnet specimen ~e)~hibited excellent magnetic characteristics as follows:

~Br = 11.5 kG
iHc~=~l9 kOe ~ (BH)~max = 31.3 MGOe~

Example 2 ~ Tb40~: 22-99 O3~ ~ 5-HO2O3~ ;16.3g~
Fe~pow~der;:~42.6;g Ferroboron~powder ~20.4 wt~ B-Fe alloy powder) : 8.0y ~ Metal1~ic~Ca ~ 26.6g tl.5 times as much as the amount requlF~ed stolchlometr1aally)~ ~ ~
C~Cl2~ 2.7g (5.9~wt~base on the rare earth metal : :: : , . . .. .. . .. . . . .. .

37~

oxide materials) 122.3g of all the raw materials above-described were treated in the same manner as in Example 1 eY.cept that this example aimed at obtaining an alloy composition of 8% Tb - 5%
Ho - 2% Dy ~ 73% Fe 12% B (atomic %)(19.18% Tb - 12.44% Ho -4.90~ Dy - 61.51% Fe - 1.96% B, by weight %). There was obtained 86g of an alloy powder having a 50 - 500 ~m particle size.
The elementary analysis values of this powder were as follows:
Tb : 19.74 wt%
Dy : ~ 4.23 wt%
Fe : 50.73 wt%
Ho : 13.28 wt%
B : 1.86 wt%
Ca : 0.16 wt%
.
2 : 5500 ppm .
C : 750 ppm As~a result, the rèquired alloy powder was obtained.
~ A compact was prepared by compacting the~above alloy powder under~ a pres6ure of 2 t/cm2 for preparing a magnet1c alloy composed of 14 Nd - 0.2 Tb - 0.15 ~lo - 0.05 Dy - 78.6 Fe - 7 B~(atomic %~ The; compact as the raw materlal of Tb-Elo-Dy was melted with~metall~lc Mdl ferroboron alloy and Fe material.
~ 25 The resultant~melt-produced alloy ~piece was pulverized to a ; powder h~avlng ;an avera~e~ particle size of 2.67~m, then wascom~act~ed in a magnetic flelc~of 1~0 kOe under a pressure of 1.5 f~ ~t~f3~0~7 t/cm , thereafter WAS sintered at 1120C for 2 hours and was aged at 600C for 1 hour to produce a permanent magnet.
The obtained magnet exhibited excellent magnetic characteristics as follows:
Br = 12.4 kG
iHc = 11.5 kOe (~H)maY. = 35.8 MGOe Example 3 Mixed heavy rare earth metal o~,ides : 91.4g The composition of the mixed heavy rare earth metal oxides is as follows:
Dy2o3 : 80 wt~ :
Tb407 : 10 wt~
Ho23 3 wt%
Er2O3 : < 0.5 wt~o : :
. .
T~l12O3 : < 0.5 wt% :.
Gd2O3 : 6 ~1t%
Yb2O~: < 0.5 wt%
~ , Fe powder : 22.1g Ferroboron:powder (20.0 wt% B-Fe~alloy powder) : 1.8g ~.
:: : ` :
:Metallic Ca : 97.3g (3.3 times as much as the amount required stoichiometrical-ly) ~ CaC12~: 11.09 ~(12.0: wt% based on the rare earth metal~ ox~lde:materlals)~
~ 223;.6g~of all~the raw materials above-described were treated ~in;the~ same manner as in Example 1 except that this example ~almed. at obtalning ~an alloy composition o~ 50% Rl -~ 22 -~ ....
' ~ ~ - -, : . - . :

~.2~7~7 46% Fe - 4% B (atomic %)(75.7 wt~ Rl - 23.9 wt~ Fe - 0.4 wt%
- B). There was obtained 73g alloy powaer having a 10 - 650 ~m particle size.
The elementary analysis values of this powder were as follows: -Dy : 65.9 wt~, Tb : 4.0 wt%, Gd : 4.6 wt~, Ho : 1.2 wt%, Er : 0.2 wt%, Tm : 0.2 wt%, Yb : 0.1 wt%, Fe : 23.4 wt%, B : 0.35 wt~, Ca : 0.05 wt%, 2 : 3300 ppm, C : 650 ppm.
As a result, the required alloy powder was obtained.
This alloy powder having a particle size of at most 500~m (-35 mesh) and the Md-Fe-B alloy powder beforehand 15 prepared to a particle size of at most - 35 mesh after its melting were m~ixed, aimed at the production of an alloy composed of 14 Nd - 1.5 Rl - 77.5 Fe - 7 ~ (atomic %). The mixed powder was~pul;verlzed by means of a ball mill for 3.5 hours to produce a flne powder having~an average particle size 20 of 2.75~m.`
~ A permanent magnet spec1men was pro~uced from this fine po~7der~in the manner as in Example 1.
~ The obtained~ magnet specimen e~:hibited e~cellent magnetlc~char~acteristlcs as follows:
~ ~ ~Br = 11.4 kG
~ ~ iHc = 17.50 kOe :: ~
~ ` ~ (E~l)maY. = 30.9 MGOe ::
~ - 23 -~ :

~ 7 It should be understood that the present invention is not limited to the specific embodiments and modification is allowed without departing from the gist and scope of the present invention as disclosed and claimed.

:
; ~. ~ : ..

:

:
: , , ~ ~

Claims (13)

1. A method for producing a rare earth alloy which comprises:
preparing a mixed raw material powder comprising at least one of the oxides of rare earth elements R1, an iron powder and a boron containing powder selected from the group consisting of boron, ferroboron and boron oxide in a manner such that the resultant alloy product consists essentially of:
15-65 atomic % R1, 35-83 atomic % Fe, and 0-15 atomic % B, in which R1 represents at least one of heavy rare earth elements selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm and Yb; said mixed raw material powder further comprising metallic Ca and/or Ca hydride in an amount of 1.2-3.5 times by weight of the amount stoichiometrically required for reducing oxygen in said raw material powder and at least one of the oxides of said rare earth elements R1, and 1-15% by weight of calcium chloride based on the oxides of said rare earth elements R1;
compacting the resultant; mixture;
subjecting the resultant compacted mixture to reduction-diffusion treatment under a nonoxidizing atmosphere at a temperature of 950-1200°C;
bringing the reduced mass to a particle size of 8 mesh to 35 mesh;

contacting the resultant reduced mass with water to form a slurry-like substance; and treating said slurry-like substance with water by stirring the slurry and removing water to recover the resultant alloy powder;
whereby said alloy powder has an oxygen content of at most 7000 ppm, and a carbon content of at most 1000 ppm.

2 . The method according to claim 1, in which said mixed raw material powder is prepared so that said alloy product consists essentially of:

25-40 atomic % R1, 50-71 atomic % Fe, and 4-10 atomic % B.

3. The method according to claim 1, wherein the treating with water is effected until the amount of Ca becomes no more than 2000 ppm in the resultant alloy powder.

4. The method according to claim 1, wherein the reduction-diffusion treatment is effected at a temperature ranging from 950 to 1100°C.

5. The method according to claim 1, wherein the method further comprises consolidation of the resultant alloy powder.

6. The method according to claim 3, wherein said mixed raw material powder is prepared so that said alloy product contains at least 35 atomic % R1.

7. A rare earth alloy consisting essentially of:
15-50 atomic % R1, 35-83 atomic % Fe, and 2-15 atomic % B, wherein R1 represents at least one of rare earth elements selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm and Yb; and wherein oxygen is at most 7000 ppm, carbon is at most 1000 ppm and calcium is at most 2000 ppm.

8. The rare earth alloy according to claim 7, in which said alloy powder consists essentially of:
25-40 atomic % R1, 50-71 atomic:% Fe, and 4-10 atomic % B.

9. The rare earth alloy according to claim 7, in which said R1 is present in an amount of at least 35 atomic %

10. The rare earth alloy according to claim 7, in which said R1 is Tb and/or Dy.

11. The rare earth alloy according to claim 10, in which said R1 is Dy.

12. The rare earth alloy according to claim 7, in which the rare earth alloy is in the powder form.

13. The rare earth alloy according to claim 7, in which the rare earth alloy is in the consolidated form.