GB2310432A

GB2310432A - Hydrogenation/dehydrogenation treatment of rare earth magnetic powder

Info

Publication number: GB2310432A
Application number: GB9603878A
Authority: GB
Inventors: Yoshinobu Honkura; Hironari Mitarai; Takenobu Yoshimatsu
Original assignee: Aichi Steel Corp
Current assignee: Aichi Steel Corp
Priority date: 1996-02-23
Filing date: 1996-02-23
Publication date: 1997-08-27
Anticipated expiration: 2016-02-23
Also published as: GB2310432B; GB9603878D0; DE19607747A1; DE19607747C2

Description

2310432

TITLE OF THE INVENTION

PRODUCTION METHOD, PRODUCTION APPARATUS, AND HEAT TREATMENT APPARATUS FOR ANISOTROPIC MAGNET POWDER BACKGROUND OF THE INVENTION

Field of the Invention

1 1 The present invention relates to production method and its apparatus tor anisotropic rare earth magnet materials which are produced by means of HDDR treatment. HDDR stands for hydrogenationg disproportionation. desorption and recombination.

i Description of the Related Art

In the process rare earth alloy Is first prepared. then hydrogen Is occluded into the alloy by holding the mater 1al at a temperature from 500 t to 1000 t either in an atmosphere of hydrogen gas or mixture of hydrogen and Inert gases.Subsequently the alloy Is subjected to dehydrogenation at a temperature from 500t. to 1000 t until the pressure 2 - of hydrogen in the atmosphere is reduced tono greater than 1 x 10-1 torr. and is subjected to cooling.

Up to now rare earth magnet powder is widely used for bonded magnets. The shortcoming of the bonded magnets is their lower levels of magnetic properties compared to sinterd magnets because of its low density and isotropic property.

To Improve the bonded magnet anisotroic powders. which has much better magnetic property than that of isotropic powder. have been under developing. HDDR treatment is well known for preparation of anisotroplc magnet powder.

In the treatment the magnetic property deteriorates significantly if the treating temperature of hydrogenation or desorption slightly deviates from very narrow optimum temperature range. Hydrogenation Is exothermic reaction, and desorption is endothermic. It is difficult to keep a constant temperature of rare earth magnet material in hydrogenation and desorption process. It is more difficult to carry out production in large scale because the heat increases proportionally with the the mass of the magnet material.

Thermal reservoir which Is inserted together with the material Into reactive vessel is generally used to keep desired temperature, but the temperature control ability of such reservoir Is not satisfactory for mass production.

In Japanese patent application Laid-open (Kokai) No. 5163510. radiation heating is proposed to improve follow-up 3 temperature control. But still the temperature control abilit y is not satisfactory for mass production and causes deterioration of magnet powder.

In Japanese patent application Laid-open (Kokai) No. 5171203 and 5-171204. using a hydrogen absorbed alloy as source of hydrogen is proposed in hydrogenation and desorption processes. The endothermic reaction of the alloy oancels the heat generated by exothermicreacti-on of magnet and vise versa to keep a constant temperature. But still the temperature control ability is not satisfactory for mass production and causes deterioration of magnet powder.

Prior inventions have not succeeded to compensate the heat generatedlabsorbed by exothermic/endothermio reaction with hydrogen in HDDR treatment. Consequently mass production of HDDR treated powder has not achieved.

Summary of the Invention

An object of the present Invention is to offer a method to keep the temperature within a desired range in HDDR treatment by means of compensating the heat accompanied with hydrogenation and desorption.

The principle of the present invention is to oompensa te the heat accompanied with exothermic/endothermic reaction by counter reaction of dummy material." The apparatus has a set of a processing vessel.and a heat compensating vessel - 4 in contact and can control their temperature like ordinary furnace. Raw material is inserted in the processing vessel in which hydrogen pressure can be contro14ed. Dummy material is inserted in the compensating vessel also in which hydrogen pressure can be controlled independently with the processing vessel.

When exothermic reaction occurs and the material generates heat in the processing vessel, the hydrogen pressure of the compensating vessel is decreased to start endothermic reaction and to compensate for the generated heat In the processing vessel.

In the same manner the hydrogen pressure is increased to compensate for absorbed heat by endothermic reaction in the processing vessel.

The kind and amount of dummy material is chosen according to processed material to have equivalent latent heat.

The notable characteristic of the apparatus is that the processing vessel and the compensating vessel comprises single system and requires no energy transport between the system and the outside. The heat compensation can be controlled only by hydrogen pressure in the compensating vessel.

Now the apparatus of the present invention will be described in detail.

It consists of the processing vessel in which raw material is inserted, heater for the processing vessel. hydrogen supplier to the processing vessel. evacuating i 1 - 5 system to evacuate the hydrogen from the vessel, the compensating vessel in which a dummy material is inserted:, and control system for the hydrogen pressure of the compensating vessel. The processing vessel and the compensating vessel are placed in contact to form a set of vessels.

Hydrogen pressure control system consists of a temperature sensor placed in the processing vessel to- detect the generation or absorption of heat. electromagneticthreeway valve for hydrogen. and electronic control unit.

The apparatus can have multiple sets of vessels. The number of the sets can be from two to as much as several hundreds. The vessels are made of materials which have good heat conduction and small heat capacity, preferably stainless steel because the heat transportation between the vessels is made easy.

Raw material for the present invention has magnetic property which is enhanced by HDDR treatment. The kinds of material are R-T-B type magnet. R-T-M type magnet and 50Fe-N type where R stands for rare earth element such as Y, La, Ce. Pr. Nd. Smg Gdy Tby Dy, Ho, Er. Tm, Lu; T stands for ferrus metal such as Fe, Co, Ni; and M stands for elements which form tetragonal ThMnl2 type compounds such as TI, V, Cr, Mo. More than 50 % of R must be Nd or Pr or both. also more than 50 $ of T must be Fe.

The examples of the magnet are Nd-B-Fe type3 Nd-Ga-B-Fe types Nd-Co-Ga-BFe type, Nd-Fe7T1 type, Nd-Fe-TI-C type and Nd-Fe-V-C type magnet.

The dummy material must have either exothermic or endothermic reaction, preferably both of them. It is preferable to choose the same type as the processed raw material.

The present invention which utilizes compensation.effect of the dummy material with controlled hydrogen pressure enables the temperature control of HDDR treatment within a desired range and brings out the maximum property from the material constantly. The controllability of the method is independent of the production scale so that mass production by the HDDR treatment can be set into practice.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a construction of the invented apparatus.

Figure 2 Is a magnified view of a set of processing and compensating tubes.

Figure 3 shows heat pattern for HDDR treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments according to the presentinvention will be described as follows with reference to the figures 1 to 3.

The construction of the-apparatus is shown in figure 1.

The processing vessels 1 made of stainless steel are consists of multiple tubes 10 apart from each other and contains raw material 2 inside of them.

Dummy material 25 has exothermic and endothermic reaction with hydrogen. Same alloy as the processed material is used for dummy material 25. It is inserted in the compensating tubes 27 made of stainless steel. The compensating tubes are placed inside each processing tube1O coaxially. Processed material 2 and the dummy material 25 are placed In close distance separated by the tube wall.

Through junction 3 the hydrogen supply line 31 turns out into branch lines 30 which are connected to each processing tube 10 for supply and evacuation of hydrogen. In this example each set of tube and line is equivalent In dimension andmaterIal to keep same temperature among tubes., .

Through junction 7 the dummy hydrogen supply line 11 turns out into branch lines 70 which are connected to each compensating tube 10 for. supply and evacuation of hydrogen. In this example each set of tube and line is equivalent In dimension and material to keep same temperature among tubes.

Heater 4 Is for heating of processed material 2 and dummy material 25. The temperature of heat chamber 40 Is controlled by control unit 45.

Hydrogen supply unit 5 is for supplying hydrogen to both processed material and dummy material. It consists of a hydrogen gas cylinder 50p purifier 51 for purification of raw hydrogen gas, and two.hydrogen supply lines. The first - 8 line is for the processing tubes and the second line Is for the compensating tube.

The first line consists of hydrogen accumulator 53, electromagnetic threeway valve 52, line 54 to connect them. The second line consists of hydrogen accumulator 57. ' electromagnetic threeway valve 56, line 58 to connect.them.

Valve 52 and junction 3 are connected by line 31. Valve 56 and junction 7 are connected by line 71.

Evacuation system 6 is to reduce the pressure of the processing tubes 10 and dummy tubes 27 for desorption of hydrogen from materials. It consists of two evacuating lines.

The first line is for the processing tubes and the second line Is for the compensating tube.

The first line consists of vacuum pump 60, electromagnetic threeway valve 52, line 61 to connect them. The second line consists of vacuum pump 65, electromagnetic. threeway valve 56, line 66 to connect them.

As seen in figure 1 temperature control unit 45, electromagnetic threeway valve 52, 56, vacuum pump 60,; 65 are governed by central control unit 98. Central control unit 98 controls the hydrogen pressure.of compensating vessel in accordance with the exo'thermiclendothermic reaction of the processed material. Thus the central unit 98 serves as moderator for heat compensation.

(Hydrogenation process) i 0 9 - Nd-Co-Ga-B-Fe type alloy with a chemical composition of Nd12.g Cogt.5, B6. ,,, Ga,.,iat% and balanced with Fe and inevitable impurities is melted into an ingot. It is crushed into coarse grain with the diameter of 2 to 4 mm by preliminary hydrogenation and desorption at 250 t. The prepared material is inserted to processing tubes 10 with equal quantity for each.

Same material as dummy 25 is inserted in the compensating tubes 27 under the hydrogen pressure of 1.2-1.5 atm. The sets of processing tube 10 and compensating tube 27 are inserted in heating chamber 40 of heater 4 so that the processed material and dummy material are heated to a set temperature.

The temperatures of the processed material and the dummy material are detected by thermocouple 4i and 4k. respectively as shown in figure 2.

The central control unit disconnects the line 61 from the line 31 and connects the line 54 to line 31 by electromagnetic threeway valve 52. Hydrogen is supplied to processing tubes 10 through line 54, valve 52, line 3h and line 30.

In hydrogenation process,, the"processed material absorbs hydrogen at elevated temperature in the processing tubes 10.

This hydrogenation is accompanied with heat generation. Hydrogenaton is carried out at a temperature of about 800.for 3 hours under a pressure of 1.2 to 1.5 atm.

At the same time with hydrogenation, the central control unit connects the line 66 to the line 71 and disconnects the line 58 from line 71 by electromagnetic threeway valve 56.

By vacuum pump 65 hydrogen Is evacuated from compensating tubes 27 through line 66, valve 56, line 71,, and line 70 to the vacuum of 10-5 to 10-9 torr. In desorption process, the dummy material desorbs hydrogen in the compensating tubes 27. This desorption Is accompanied with heat absorption.

The heat absorption in the compensating tubes 27 cancels the heat generation In the processing tubes 10 to k eep the temperature constant.

(Desorption Process) After hydrogenation desorption process is started.

The central control unit disconnects the line 54 from the line 31 and connects the line 61 to line 31 by electromagnetic threeway valve 52. By vacuum pump 60 hydrogen Is evacuated from processing tubes 10 through line to the vacuum of 10-5 to 10-9 torr. The processed material desorbs hydrogen in the processing tubes 10. This desorption is accompanied with heat absorption.

Desorption Is carried out at a temperature of 775 to 800 t for 30 minutes.

At the same time with desorption. the central control unit 98 disconnects the line 66 from the line 71 and connects the line 58 to line 71 by electromagnetic threeway valve 56. Hydrogen is supplied to compensating tubes 27 through line 58, valve 56, line 71, and line 70. The dummy material absorbs hydrogen. This absorption is accompanied with heat generation.

The heat generation In the compensating tubes 27 cancels the heat absorption in the processing tubes 10 to keep the temperature constant.

After desorption process the material is quenched with cooling gas such as argon or with cooling water as the final process. The cooling can be done directly to the material or from outside of the processing tube.

By the process described above an anisotropic magnet powder with improved magnetic property is manufactured.

The embodiment enables the temperature control,ofHDDR treatment within a desired range and brin gs out the maximum property from the material constantly. The controllability' of the embodiment is independent of the production scale so that mass production by the HDDR treatment can be set into practice.

In this embodiment the material is divided into small amount for each processing tube and is placed in close contact with the compensating tube. Each set of tubes are placed apart with sufficient distance to keep them without interaction.

Furthermore the latent heat of dummy material Is controlled to be the same-of the processed material so that the cancellation is done without any surplus heat.

Thus the temperature deviation caused by exothermiclendothermic reaction can be suppressed to very low level.

In figure 3 the heat pattern of the processed material 2 Is shown sohematically.

In the pattern the material is pre-treated from ingot by hydrogenation and desorption at 250 t to form cease-grain, then carried out hydrogenation and desorption at near 800 1C.

It is possible that the material is cooled to room temperature after pretreatment and subjected to hydrogenation and desorption at near 800 t.

13 -

Claims

What is claimed is:

1. A production method for anisotropic rare earth magnet powder, where the raw material of said magnet powder has magnetic properties enhanced by hydrogenation accompanied by heat generation and hydrogen desorption accompanied by heat absorption. comprising the steps of hydrogenation of said raw rare earth magnet material at a elevated temperature and hydrogen desorption at a elevated temperature where at least one of heat generation and heat absorption of said raw rare earth magnet material is compensated by the heat of a material which has heat absorption according to heat generation of said raw rare earth magnet material and heat generation according to heat absorption of said raw rare earth magnet material.

2. A production method as set forth claim 19 whercini.the material to compensate for heat generation or absorption Is a dummy material consisting essentially of the same type.of rare earth magnet as raw material of magnet powder.

3. A production method as set forth claim 2. wherein. both of the heat absorption compensating for the heat generation of said raw rare earth magnet material and heat generati on compensating for the heat absorption of said raw rare earth magnet material are provided by said dummy material.

4. A production method as set forth claim 3, wherein, the amount of the dummy material is to set off the heat generation of said raw rare earth magnet material by the heat absorption and the heat absorption of said raw rare earth magnet material by the heat generation.

5. An apparatus for producing rare earth magnet powder comprising processing vessels which contains the raw-rare earth magnet material of said magnet powder that magnetic properties enhanced by hydrogenation accompanied by heat generation and hydrogen desorption accompanied by heat absorption is contained; a heater to heat said raw rare earth magnet material in said processing vessels; hydrogen gas supply system which provides hydrogen to said processing vessels for the purpose of hydrogenation of said raw rare earth magnet material; evacuating system to reduce the pressure of said processing vessels for hydrogen desorption of said raw rare earth magnet material; compensating vessels placed near to said raw rare earth magnet material in the prooessing vessels and contains a material for heat compensation; and control unit which control the heat generation/absorption of compensating material according to heat absorption/generation of said rare earth material in said processing vessels.

6. An apparatus as set forth claim 51 wherein, the processing vessel comprises a plurality of tube In each of which a partition of raw rare earth magnet is contained..

7. An apparatus as set forth claim 6, wherein, equal numbers of compensating vessels to said processing tubes are equipped and each of said compensating vessel is placed inside the processing tube.

8. An apparatus as set forth claim 5, wherein, the material to compensate for heat generation or absorption Is a dummy material consisting essentially of the same type of rare earth magnet as raw material of magnet powder.

9. An heat treatment apparatus comprising heating vessel which forms heating room: heating device to heat said heating room, and temperature controlling device consisting hermetic. container which heat or cool said heating room placed inside the heating room. hydrogenated metal contained' Inside of said hermetic container and hydrogen pressure control system which controls the pressure inside said hermetic container.

10. An heat treatment apparatus as set forth claim wherein, said heating vessel Is a tube and said hermetic container Is another tube which is placed inside the first tube.

11. An heat treatment apparatus. as set forth claim 10, 16 - wherein. said heating device is a furnace which has a room having heat generator inside or periphery of it and said heating vessel is placed inside the room.

12. An heat treatment apparatus as set forth claim 11. wherein, a plurality of said heating vessel is placed in said room In the furnace.

13. A production method for anisotropic rare earth magnet powder, substantially as hereinbefore described with reference to the accompanying drawings.

14. A heat treatment apparatus substantially as described with reference to the accompanying drawings.