JPH09134836A - Manufacture of rare earth permanent magnet and hydrogen crushing processing oven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable necessary alloys to be crushed into powder prescribed in grain diameter only through a hydrogen treatment without using a mechanical crushing method by a method wherein rare earth-rich phase forming alloy powder which is subjected to a hydrogen absorption treatment and a dehydrogenation treatment and obtained by crushing and main-phase forming alloy powder are mixed together as rolled, molded in a magnetic field, and baked. SOLUTION: Rare earth-rich phase forming alloy b which contains 40% or more rare earth element by weight is introduced together with a heat storing material c into a capsule a as a crushing chamber. The capsule (a) can be filled with hydrogen gas and provided with a pressure control opening (i) which is used for controlling an oven in hydrogen pressure. The capsule (a) is hermetically closed, but an oven tube (d) is provided taking the probability of hydrogen leakage into consideration, and inert gas is filled into the oven tube (d). A heater (c) and an heat insulator (f) are provided around the periphery of the oven tube (d). The capsule (a) is rotated at a speed of 200rpm or below, the rare earth-rich phase forming alloy (b) is subjected to a hydrogen absorption treatment and a dehydrogenation treatment into rare earth-rich phase forming alloy powder, and the rare earth-rich phase forming alloy powder and main-phase forming alloy powder are mixed together, molded in a magnetic field, and sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crushing device for a rare-earth-rich phase-forming alloy, among alloy raw materials for permanent magnets obtained by mixing a main-phase-forming alloy fine powder and a rare-earth-rich phase-forming alloy fine powder. By using a processing furnace having a crushing chamber which can be held in a hydrogen atmosphere and can be rotated, fine powder having a low oxygen content and a sharp particle size distribution can be efficiently and stably produced.

[0002]

_2. Description of the Related Art At present, with respect to the production of sintered magnets having R ₂ T ₁₄ B as a main phase, the amount of R (rare earth element) is slightly higher than that of R ₂ T ₁₄ B.
A method of pulverizing a single alloy containing a large amount of components as a starting material and a method of dividing into two alloys, a main phase containing R ₂ T ₁₄ B as a main component and a rare earth-rich alloy containing a large amount of rare earth components in advance, and then finely powdered and mixed. Either way you are done.
In the former case, the excess rare earth component generated during crushing serves as a liquid phase in the sintering process. On the other hand, in the latter case, since the main phase has a composition close to stoichiometry of R ₂ T ₁₄ B as much as possible, the liquid phase at the time of sintering is mainly responsible for the fine powder of the rare earth-rich phase. In any case, since it contains rare earth elements, its crushing is extremely difficult, and there is even a risk of causing ignition during crushing. The cause of this is largely influenced by the equipment used for pulverizing the fine powder. Generally, a jet mill that uses an inert gas is used, but since it is pulverization that uses mechanical impact force, the heat generated at that time activates the powder and it is unavoidable in the atmosphere or in the equipment. Oxidation is unavoidable due to reaction with oxygen. Thus, the crushing method using mechanical stress is inevitable even if the surroundings are covered with an inert atmosphere, and extremely time-consuming atmosphere management is required. Further, ball mill grinding in an organic solvent has been carried out to prevent oxidation, but carbon is left in the fine powder and the amount of effective rare earth is reduced like oxidation, which is not preferable. The sintered magnet made of the raw material obtained by the above method naturally causes an increase in oxygen content. Since oxygen preferentially reacts with rare earths, it reduces the rare earth components originally required for liquid phase sintering. In other words, it means a substantial decrease in the effective rare earth amount. On the other hand, as a pulverization method for preventing an increase in oxygen, a treatment using hydrogen, which utilizes the phenomenon of volume expansion and contraction of an alloy, is widely performed. However, as a result of observing the individual alloys closely, the outer peripheral portion of the alloy is greatly affected by hydrogen absorption and is excellent in pulverizability, but its effect is diminished as it progresses to the central portion. Therefore, finally, the pulverized powder has a wide particle size distribution.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
_{2 In the} method for producing a rare earth permanent magnet, in which the main phase forming alloy containing T ₁₄ B as a main component and the rare earth rich forming alloy phase containing a large amount of rare earth elements are finely pulverized, and then mixed, molded and sintered, particularly in the pulverization. Focusing on the pulverization of rare-earth rich phase forming alloys with remarkable oxidation, a method for producing a rare-earth permanent magnet that pulverizes to a predetermined particle size only by hydrogen treatment without using any mechanical pulverization method such as jet mill or ball mill. Is to provide. Another object of the present invention is to provide a hydrogen crushing treatment furnace capable of gradually collapsing the outer periphery of the initially crushed alloy in the hydrogen crushing treatment and crushing evenly to the inside of the alloy.

[0004]

Means for Solving the Problems As a result of focusing on the relationship between the production phase of various rare earth-rich phase forming alloys containing 40 wt% or more of rare earth components and the pulverizability by hydrogen treatment, the present inventors It was found that the pulverizability can be greatly improved by absorbing the heat amount of the exothermic reaction due to the occlusion with the heat storage material. Furthermore, this alloy and heat storage material can be pressure-controlled in a hydrogen atmosphere, and the outer periphery is inserted into a crushing chamber covered with an inert gas. The hydrogen crushing process is performed while rotating the main crushing chamber at a rotation speed of 200 rpm or less. It was also found that by using a furnace, it is possible to obtain fine powder having a fine crushed particle size and sharpness. 40 rare earth elements
As a rare earth-rich alloy containing more than wt%, RT ₃
The phases base - scan to RT ₃ M or base the RT ₂ phase, - scan to RT ₂ M (wherein R: rare earth component, T: transition metals,
Typical examples are alloys such as M: Al, Cu, Ga, Mn, Zn, or an additive element consisting of a combination of two or more thereof.

As a general property of the rare earth-rich phase forming alloy with respect to hydrogen, hydrogen is rapidly occluded from around room temperature and its volume expands. By gradually heating the alloy, dehydrogenation occurs naturally, causing volume contraction and crushing progress. At the time of dehydrogenation, it may be forcedly exhausted by a rotary pump or the like.
The alloy is accompanied by an exothermic reaction when hydrogen is absorbed. With this amount of heat, the entire alloy is warmed up, and as it approaches the temperature at which dehydrogenation begins, the occlusion tendency weakens, gradually becoming an equilibrium state, and occlusion ends. Therefore, when a heat storage material having excellent hydrogen embrittlement resistance is used together with the alloy, a thermal gradient is generated between the alloy and the alloy that has generated heat in the region in contact with the alloy. The thermal stress due to this thermal gradient promotes crushing. The heat storage material may be a metal material such as steel, tungsten or molybdenum, or a ceramic material.

By crushing a rare earth-rich phase forming alloy together with a heat storage material by hydrogen storage and dehydrogenation, the crushed particle size becomes sufficiently fine, but the difference in particle size between the outer peripheral part and the inner peripheral part of the alloy becomes slightly large. I also understood. This is because
This is because when the hydrogen absorption starts from the outer peripheral portion of the alloy and gradually progresses to the inside, the alloy generates heat as a whole, so that the thermal gradient inside the alloy becomes small. Therefore, when the alloy and the heat storage material were put in the crushing chamber and crushed in the same manner while rotating the crushing chamber, fine powder having a fine particle size and an extremely sharp distribution could be obtained. This is because the relative positions of the alloy and the heat storage material are changed by rotation, so that the outer peripheral portion of the alloy in which hydrogen absorption has already progressed can be collapsed, and the inside of the alloy and the heat storage material are newly contacted. Although the crushing chamber has a hydrogen atmosphere whose pressure is controlled, it is better to cover the outer periphery of the crushing chamber with an inert gas in consideration of the risk of hydrogen leakage. If the rotation speed of the crushing chamber is too fast, the contact between the alloy and the heat storage material is interrupted in a short time or the crushing chamber rotates together with the crushing chamber. It is also possible to have a structure having a grinding auxiliary tool which becomes an obstacle such as a protrusion or a vane in the grinding chamber when the outer peripheral portion of the alloy is collapsed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Example 1) FIG. 1 shows the basic structure of a processing furnace developed for hydrogen crushing of rare earth-rich alloys. In FIG. 1, a sample (rare earth rich phase forming alloy) b is inserted into a capsule a which is a crushing chamber together with a heat storage material c. This capsule can be maintained in a hydrogen atmosphere and has an atmosphere control port i for controlling the pressure in the furnace.
It is a structure that can rotate at the following rotation speeds. Although this capsule is hermetically sealed, a furnace core tube d is provided in consideration of a hydrogen leak, and the inside of the furnace core tube d is set to an inert gas atmosphere. Core tube d
A heater e and a heat insulating body f are arranged on the outer circumference, and the structure is such that the sample held in the capsule a can be heated.
Further, as shown in FIGS. 2 and 3, the inside of the capsule a is
A structure having protrusions g or vanes h may be used.

(Example 2) The rare earth-rich alloy was actually crushed using the hydrogen crushing treatment furnace described in Example 1.
The composition of the rare earth-rich alloy is aimed at RT _3-phase Nd35.
Two types, 20Pr9.80Co52.60Al2.40 and Dy59.00Fe33.08Ga4.32Cu3.60 for the purpose of the RT ₂ phase, both of which have a rare earth content of 40 wt% or more. The homogenization treatment was performed in an argon atmosphere at a temperature at which the occupation ratio of each phase was maximized. The obtained alloy was crushed to a size of about 1 cm square and then placed in a normal hydrogen treatment furnace. First, the hydrogen pressure in the furnace was controlled to be in the range of 650 to 660 Torr, and the temperature was kept at room temperature for 3 hours. After allowing the alloy to absorb enough hydrogen 4
It was heated to 700 ° C. at a temperature rising rate of ° C./min, and its hydrogen resistance was examined. Since the pressure in the furnace decreases during hydrogen storage and rises in reverse during dehydrogenation, it is possible to determine the difference between the two by confirming the operating direction and frequency of control. From this preliminary study, it was found that the dehydrogenation completion temperature of the (NdPr) system is around 440 ° C. and that of the Dy system around 330 ° C. Then, a crushing experiment was conducted based on the final temperature of the dehydrogenation. FIG. 4 shows a hydrogen treatment pattern of the (NdPr) -based rare earth-rich phase forming alloy.

When a heat storage material is used, it is 30 with respect to the mass of the alloy.
It was inserted into a capsule shown in FIG. 1 together with a 0 wt% steel ball ball (diameter 9.5 mm). The inside of the capsule was once replaced with argon gas, and then the inside of the capsule was evacuated, and then a hydrogen atmosphere was created. The pressure inside the capsule was controlled to be within the range of 650 to 660 Torr and kept for 3 hours. After completion of hydrogen storage, the capsule was evacuated with a rotary pump and the temperature was raised to the dehydrogenation end temperature (about 440 ° C.) and kept for about 1 hour. This step was performed while rotating the capsule at a predetermined rotation speed from the start of hydrogen absorption to the end of dehydrogenation. After the treatment was completed, the atmosphere in the furnace was replaced with an argon atmosphere, the temperature was cooled to room temperature, and the pulverized powder was taken out. The same procedure was performed for the Dy system except that the dehydrogenation end temperature was about 330 ° C. Table 1 shows the measurement results of the residual gas amount and the average pulverized particle size of the obtained pulverized powder. In Table 1, No. Nd 35.2 from 1 to 6
No. 0 Pr9.80Co52.60Al2.40 7-12
Up to here are the results obtained for Dy59.00Fe33.08Ga4.32Cu3.60. In Table 1 in FIG. 1 and Comparative Example No. 1. 5 shows a pulverization fineness distribution by the hydrogen pulverization treatment of No. 5.

[0010]

[Table 1]

From Table 1, it can be seen that the average crushed particle size becomes finer when the heat storage material is used and the capsule is rotated regardless of which alloy is used. However, in No. In Nos. 6 and 12, a part of the alloy or the heat storage material rotated together without changing the relative position in the capsule, so that the grain size became coarse as a whole. In addition, the No. In Nos. 3 and 9, the amount of the heat storage material is 100 wt% and the particle size is fine although the amount is small. Therefore, it is understood that the outer periphery of the alloy is easily collapsed by providing the projection or the vane inside the capsule.

According to the present invention, among the sintered magnets composed of the main phase fine powder and the rare earth-rich alloy fine powder, the latter rare earth rich alloy is crushed into fine powder having a low oxygen content and a sharp particle size distribution. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a hydrogen pulverization processing furnace according to the present invention.

FIG. 2 is a schematic view of a grinding chamber having protrusions.

FIG. 3 is a schematic diagram of a grinding chamber having vanes.

FIG. 4 is a diagram showing an example of a heat treatment pattern.

FIG. 5 shows a pulverized powder particle size distribution obtained by hydrogen pulverization treatment.

[Explanation of symbols]

a capsule, b sample (rare earth rich alloy), c heat storage material d core tube, e heater, f heat insulator, g protrusion, h vane, i atmosphere control port

Claims (3)

[Claims] 1. A rare earth-rich phase forming alloy powder obtained by grinding and crushing a rare earth-rich phase forming alloy containing 40 wt% or more of a rare earth element with a heat storage material while rotating at a speed of 200 rpm or less and occluding hydrogen. A method for producing a rare earth permanent magnet, which comprises mixing with a phase forming alloy powder, molding in a magnetic field, and sintering. 2. A hydrogen pulverization treatment furnace comprising a pulverization chamber having an atmosphere control port capable of controlling the pressure of a hydrogen atmosphere and a heater for heating an object to be pulverized held in the pulverization chamber, the pulverization chamber being rotatable. A hydrogen pulverization treatment furnace characterized by: 3. The rare earth-rich alloy hydrogen crushing treatment furnace according to claim 2, further comprising a crushing assisting tool inside the crushing chamber.