JP2019044265A - MANUFACTURING METHOD OF MnAl ALLOY - Google Patents

Abstract

To manufacture a MnAl alloy without melting a raw material nor conducting a long term treatment using a high energy ball mill device.SOLUTION: A method has a process (S2) for generating a mixture by mixing Mn oxide, Al oxide and a Ca-based reductant, a process (S3) for generating MnAl alloy and CaO by heating the mixture at 550°C or higher and less than 1200°C, and a process (S5) for removing CaO. Since the MnAl alloy is manufactured by using a Ca reduction diffusion method, the MnAl alloy can be manufactured at a temperature of 550°C or higher and less than melting point of Mn (1246°C) such as less than 1200°C. Since a mixture Ca and Al becomes liquid in the case of 550°C or higher, the MnAl alloy can be formed with short time treatment at good efficiency, different from the case when a high energy ball mill treatment is used.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of manufacturing a MnAl alloy, and more particularly to a method of manufacturing a MnAl alloy using a Ca reduction diffusion method.

  MnAl alloys have long been known as magnetic materials. The conventional MnAl magnet manufacturing method comprises a step of alloying a raw material with an atomic ratio of Mn: Al of 55:45 by arc melting or high frequency melting, and the obtained alloy by heat treatment at 1100 ° C. and a quenching step A step of forming an MnAl phase and a step of performing a phase transformation from an ε-MnAl phase to a τ-MnAl phase which is a ferromagnetic phase by heat treatment at 600 to 800 ° C. are included.

Preparation In the liquid quenching method devised after that, the molten metal of the raw material which adjusted the atomic ratio of Mn: Al to 55:45 is cooled rapidly, and the heat treatment step of 1100 ° C. and the quenching step are not performed, An MnAl phase can be obtained (see Patent Document 1). Also, a mechanical alloy method (see Patent Document 2) in which Mn metal and Al metal are alloyed by a high energy ball mill (see Patent Document 2), and Mn metal and Al are mixed by mixing Mn oxide, Al oxide and Ca metal by a high energy ball mill. The mechanochemical method (refer nonpatent literature 1) which obtains an epsilon-MnAl phase is not known without passing through the process which melts a metal.

Unexamined-Japanese-Patent No. 1-22007 gazette Japanese Patent Application Laid-Open No. 7-11301

JOM, Vol. 67, no. 6 (2015)

  However, in the liquid quenching method described in Patent Document 1, it was necessary to heat the raw material to about 1300 ° C. to obtain a molten metal. Moreover, the mechanical alloy method and the mechanochemical method described in Patent Document 2 and Non-Patent Document 1 require long-time processing using a high energy ball mill apparatus.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a method for producing an MnAl alloy which does not require melting raw materials and which does not require long-time treatment using a high energy ball mill. I assume.

  As a result of intensive studies by the present inventors, it was found that the MnAl alloy can be formed without melting the raw material and without performing high energy ball milling, if the Ca reduction diffusion method is used. The present invention has been made based on such technical knowledge, and a method of producing a MnAl alloy according to the present invention produces a mixture by mixing Mn oxide, Al oxide and a Ca-based reducing agent. It comprises the steps of: producing a MnAl alloy and CaO by heating the mixture to a temperature of at least 550 ° C. and less than 1200 ° C .; and removing CaO.

  According to the present invention, since the Ca reduction and diffusion method is used, it is possible to form an MnAl alloy at a temperature of 550 ° C. or more and less than 1200 ° C. and a temperature less than the melting point of Mn (1246 ° C.). In particular, in the step of reducing and diffusing Ca, since an alloy of Ca and Al having a melting point of about 550 ° C. is formed, the MnAl alloy is formed at a temperature lower than the melting point of Ca (842 ° C.) or the melting point of Al (660 ° C.) It is also possible to create. In addition, since the mixture of Ca and Al becomes liquid at 550 ° C. or higher, the MnAl alloy can be efficiently formed in a short time process unlike the case of using the high energy ball milling process.

In the present invention, the Ca-based reducing agent may contain CaH ₂ . Since CaH ₂ is easy to process into a fine powder, it is possible to make a more uniform MnAl alloy.

  The method of manufacturing a MnAl alloy according to the present invention may further include the step of heat treating the MnAl alloy at a temperature of 300 ° C. or more and 600 ° C. or less. According to this, since the MnAl alloy phase-transforms from the ε-MnAl phase to the τ-MnAl phase, it is possible to obtain stronger magnetism.

  Thus, according to the present invention, it is possible to produce a MnAl alloy without melting the raw material and without performing the high energy ball milling process.

FIG. 1 is a flowchart showing a method of manufacturing a MnAl alloy according to an embodiment of the present invention. FIG. 2 is a schematic view for explaining the mechanism of formation of the MnAl alloy by the Ca reduction diffusion method.

  Hereinafter, preferred embodiments of the present invention will be described. The present invention is not limited by the contents of the embodiments and examples described below. In addition, the components shown in the embodiments and examples described below may be combined as appropriate or selected as appropriate.

  FIG. 1 is a flowchart showing a method of manufacturing a MnAl alloy according to an embodiment of the present invention.

In the present embodiment, first, Mn oxide and Al oxide which are raw materials are weighed (step S1), and these raw materials are mixed using a ball mill or the like (step S2). Although not particularly limited, MnO, Mn ₃ O ₄ , Mn ₂ O ₃ , and MnO ₂ can be used as the Mn oxide, but the amount of Ca necessary for reduction of Mn oxide to Mn metal is It is preferred to use less MnO. Further, it is preferable to use _Al 2 _{O 3} (aluminum oxide) as the Al oxide. The Mn oxide and the Al oxide are weighed so that the atomic ratio Mn: Al of Mn and Al is in the range of 45:55 to 60:40, preferably 55:45. The size (particle size) of each of the Mn oxide and the Al oxide is preferably smaller. This is because the smaller the size of the Mn oxide, the finer the powder of the MnAl alloy finally obtained can be, and the smaller the size of the Al oxide, the uniformity of the finally obtained MnAl alloy The reason is because In addition, when mixing these raw materials, it is preferable to fully mix by adding an ethanol solvent and a ceramic ball | bowl to a ball mill. By sufficiently mixing, it is possible to obtain a more uniform MnAl alloy.

Next, after drying the mixed raw material, a Ca-based reducing agent is mixed (step S2). As the Ca-based reducing agent, Ca metal or CaH ₂ can be used, but it is most preferable to use CaH ₂ which can obtain a finer powder. The input amount of the Ca-based reducing agent is preferably the same as the amount capable of reducing Mn oxide and Al oxide. This is because if the input of the Ca-based reducing agent is smaller than the reducible amount, the Mn oxide and the Al oxide can not be completely reduced, and if the input of the Ca-based reducing agent is too large, the β- This is because the proportion of the MnAl phase increases and the magnetism decreases. Further, C (carbon) may be added as an additive.

  Next, a mixture of Mn oxide, Al oxide and Ca-based reducing agent is heated to a temperature of 550 ° C. or more and less than 1200 ° C. to reduce and diffuse the Mn oxide and the Al oxide. The heat treatment time during reduction diffusion is about 1 hour to 2 hours per 10 g of the mixture. Thereby, the Mn-based oxide and the Al-based oxide are reduced by the Ca-based reducing agent to form a MnAl alloy (step S3). The mechanism by which the MnAl alloy is formed by heat treatment is as follows.

First, as shown in FIG. 2 (a), before heat treatment, MnO which is Mn oxide, Al ₂ O ₃ which is Al oxide, and Ca metal or CaH ₂ which is a Ca-based reducing agent are mixed. It is in. In the example shown in FIG. 2A, the particle size of the Ca-based reducing agent is the largest, and the particle size of Al ₂ O ₃ is the smallest. When heat treatment is performed on such a mixture, as shown in FIG. 2 (b), MnO and Al ₂ O ₃ are reduced by the Ca-based reducing agent. That is, MnO starts to change to Mn metal and Al ₂ O ₃ starts to change to Al metal. The Ca-based reducing agent obtained by reducing MnO or Al ₂ O ₃ changes to CaO.

  The melting point of Al metal is 660 ° C. However, when Al and Ca are mixed, a Ca-Al mixture having a lower melting point is formed. Since the melting point of the Ca-Al mixture is about 550 ° C., by setting the reduction diffusion temperature to 550 ° C. or more, a Ca-Al liquid phase is obtained. In the example shown in FIG. 2 (b), most of the reduced Al is present in the form of a Ca-Al liquid phase, but a part of Al is present in the form of a Ca-Al solid phase.

  Since the Ca-Al liquid phase is a liquid, it is easily in contact with the reduced Mn metal and diffusion forms an MnAl alloy (see FIG. 2 (d)).

  Further, when the reduction diffusion temperature is set to 660 ° C. or higher, which is the melting point of Al, Al metal becomes a melt as shown in FIG. 2C, and Al metal and Mn metal are more easily diffused. Thereby, as shown in FIG. 2D, the MnAl alloy is rapidly formed. The higher the reduction diffusion temperature, the more uniform the MnAl alloy formed by the above process. However, when the reduction diffusion temperature reaches 1200 ° C., the proportion of the β-MnAl phase increases even after rapid cooling. Therefore, if it is necessary to make the MnAl alloy have magnetism, it is necessary to set the reduction diffusion temperature to less than 1200 ° C. When the reduction diffusion temperature is low, a Ca-Al solid phase which is an impurity is generated. However, when the reduction diffusion temperature is set to 1087 ° C. or more, the Ca-Al solid phase is not generated. In consideration of these points, it is most preferable to set the reduction diffusion temperature to 1100 ° C. or more and 1150 ° C. or less.

  The MnAl alloy is formed by the mechanism described above.

After the reduction diffusion by heat treatment is completed, the sample is quenched (step S4). As a result, an MnAl alloy including the powdery ε-MnAl phase, the や -MnAl phase, the? ₂ -MnAl phase and the? -MnAl phase which is not the ferromagnetic phase and the? -MnAl phase which is the ferromagnetic phase can be obtained.

  Next, pure MnAl alloy is taken out by removing CaO (step S5). The method for removing CaO is not particularly limited, but can be carried out by washing with water or the like.

  Finally, the MnAl alloy is heat-treated at a temperature of 300 ° C. or more and 600 ° C. or less to transform the ε-MnAl phase into the ferromagnetic phase τ-MnAl phase (step S6). The heat treatment time is about 0.5 to 1 hour. In the present invention, although the heat treatment is not essential, the heat treatment increases the proportion of the τ-MnAl phase. Since the MnAl alloy of the τ-MnAl phase obtained in this manner is in the form of powder, it is possible to obtain an arbitrary product shape by compression molding.

  As explained above, since the manufacturing method of the MnAl alloy according to the present embodiment uses the Ca reduction and diffusion method, the MnAl alloy at a temperature of less than the melting point (1246 ° C.) of Mn of 550 ° C. or more and less than 1200 ° C. Can be created. In particular, in the heat treatment step for reducing and diffusing Ca, since an alloy of Ca and Al having a melting point of about 550 ° C. is formed, the MnAl alloy is formed at a temperature lower than the melting point of Ca (842 ° C.) or Al It is also possible to create In addition, since the mixture of Ca and Al becomes liquid at 550 ° C. or higher, an MnAl alloy is formed in a short time, unlike the case of using high energy ball milling.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. It is needless to say that they are included in the scope.

<Preparation of MnAl alloy>
(Comparative example 1)
Raw materials Mn metal and Al metal were weighed so as to be 55 atomic% of Mn and 45 atomic% of Al, heated to 1300 ° C. by arc melting method, and cooled to obtain a MnAl alloy. The obtained MnAl alloy was heat-treated at 1100 ° C. and then quenched to give an ε-MnAl phase. Furthermore, it was made to be a τ-MnAl phase by performing heat treatment at 600 ° C. for 1 hour. Thus, a sample of Comparative Example 1 was obtained.

(Comparative example 2)
The raw materials Mn metal and Al metal are weighed so that Mn is 55 atomic% and Al is 45 atomic%, and mechanical alloy processing is performed using a high energy ball mill to obtain a MnAl alloy of ε-MnAl phase. The The treatment time is 15 hours per 10 g, and the treatment temperature is normal temperature (25 ° C.). The obtained MnAl alloy was heat-treated at 600 ° C. for 1 hour to change the ε-MnAl phase to the τ-MnAl phase. Thus, a sample of Comparative Example 2 was obtained.

(Comparative example 3)
Raw materials MnO, Al ₂ O ₃ and Ca metal are weighed so as to be 55 atomic% of Mn and 45 atomic% of Al, and mechanochemically treated using a high energy ball mill to obtain MnO and Al ₂ O Reduced ₃ Thereafter, CaO was removed by washing with water (H ₂ O) to obtain a MnAl alloy of ε-MnAl phase. The time required for the mechanochemical treatment is 10 hours per 10 g, and the treatment temperature is normal temperature (25 ° C.). The obtained MnAl alloy was heat-treated at 600 ° C. for 1 hour to change the ε-MnAl phase to the τ-MnAl phase. Thus, a sample of Comparative Example 3 was obtained.

Example 1
Raw materials MnO and Al ₂ O ₃ were weighed so that Mn was 55 atomic% and Al was 45 atomic%, and these raw materials were mixed in a ball mill. The ethanol solvent and ceramic balls were added to the ball mill and mixing was performed for 24 hours. Next, after drying the mixed raw material, it was transferred to a mortar and charged with Ca metal, which is a Ca-based reducing agent. The input amount of Ca metal was equal to the amount that can reduce MnO and Al ₂ O ₃ .

Next, a mixture consisting of MnO, Al ₂ O ₃ and Ca metal was introduced into a molybdenum crucible and heated to 550 ° C. in an Ar atmosphere to reduce and diffuse MnO and Al ₂ O ₃ . The heat treatment time during reduction diffusion was 1 hour per 10 g of the mixture. After reduction diffusion by heat treatment, the sample in the crucible was quenched with Ar gas to make the sample powdery. Next, CaO was removed from the sample by washing with water (H ₂ O) to extract the MnAl alloy.

  Then, the sample of Example 1 was obtained by heat treating the MnAl alloy at a temperature of 400 ° C. for 0.5 hour.

(Examples 2-16, comparative examples 4-7)
Under the same conditions as in Example 1 except that the reduction diffusion temperature during Ca reduction diffusion was set to 500 ° C., 600 ° C., 700 ° C., 900 ° C., 1000 ° C., 1050 ° C., 1100 ° C., 1150 ° C. and 1200 ° C. The samples of Comparative Example 4, Examples 2 to 8 and Comparative Example 5 were obtained.

Furthermore, samples of Comparative Example 6, Examples 9 to 16, and Comparative Example 7 were obtained under the same conditions as Comparative Example 4, Examples 1 to 8, and Comparative Example 5 except that CaH ₂ was used as the Ca-based reducing agent. The

<Evaluation of magnetic characteristics>
The magnetic properties of the samples of Examples 1 to 16 and Comparative Examples 1 to 7 were measured in a magnetic field of 0 to 33000 Oe at room temperature using a vibrating sample magnetometer (VSM, manufactured by Tamagawa Seisakusho).

<Evaluation of crystal structure>
With respect to the samples of Examples 1 to 16 and Comparative Examples 1 to 7, the diffraction intensity is measured in the range of 20 ° to 80 ° at room temperature by Cuα1 radiation using an X-ray diffraction measurement apparatus (XRD, manufactured by Rigaku) I did

<Evaluation result 1>
The evaluation results are shown in Table 1.

  As shown in Table 1, the samples of Examples 1 to 16 and Comparative Examples 1 to 3 contained the τ-MnAl phase exhibiting ferromagnetism. On the other hand, the τ-MnAl phase could not be confirmed from the samples of Comparative Examples 4 to 7. Moreover, in preparation of the sample of Examples 1-16, while reduction diffusion temperature is 1150 degreeC or less, and the heat processing time per 10g is 1 hour, in preparation of the sample of the comparative example 1, it reduces. The diffusion temperature was 1300 ° C., and in the preparation of the samples of Comparative Examples 2 and 3, the heat treatment time per 10 g was 10 hours or more. Thereby, it was confirmed that the samples of Examples 1 to 16 showing ferromagnetism can be produced in a short time and at a low temperature.

Moreover, when the temperature at the time of reduction diffusion is the same when comparing Examples 1 to 8 using Ca metal as a Ca based reducing agent and Examples 9 to 16 using CaH ₂ as a Ca based reducing agent, The value of saturation magnetization was higher when ₂ was used. It is presumed that this is because the uniformity of the MnAl alloy is enhanced by using CaH ₂ as the Ca-based reducing agent.

(Examples 17 to 20, Comparative Example 8)
The sample of Example 17 was obtained under the same conditions as Example 7 except that the heat treatment of the MnAl alloy was not performed. Furthermore, samples of Examples 18 to 20 and Comparative Example 8 were obtained under the same conditions as in Example 7 except that the heat treatment temperatures of the MnAl alloy were set to 300 ° C., 500 ° C., 600 ° C., and 700 ° C., respectively.

<Evaluation of magnetic characteristics>
The magnetic properties of the samples of Examples 17 to 20 and Comparative Example 8 were measured in a magnetic field of 0 to 33000 Oe at room temperature using a vibrating sample magnetometer (VSM, manufactured by Tamagawa Seisakusho).

<Evaluation of crystal structure>
For samples of Examples 17 to 20 and Comparative Example 8, the diffraction intensity is measured in the range of 20 ° to 80 ° at room temperature by Cuα1 radiation using an X-ray diffraction measurement apparatus (XRD, manufactured by Rigaku), and phase identification is went.

<Evaluation result 2>
The evaluation results are shown in Table 2.

  As shown in Table 2, the MnAl alloy obtained by the Ca reduction and diffusion method contained a τ-MnAl phase that exhibits ferromagnetism without heat treatment, but heat treatment at a temperature of 300 ° C. to 600 ° C. Thus, it was confirmed that the τ-MnAl phase increased and the value of saturation magnetization was increased. The saturation magnetization value became the maximum value when the heat treatment temperature was 400.degree. On the other hand, when the heat treatment temperature was 700 ° C., the τ-MnAl phase could not be confirmed.

S1 to S6 steps

Claims (3)

Forming a mixture by mixing Mn oxide, Al oxide and Ca-based reducing agent;
Producing the MnAl alloy and CaO by heating the mixture to a temperature of at least 550 ° C. and less than 1200 ° C .;
And removing the CaO. The method according to claim 1, wherein the Ca-based reducing agent contains CaH ₂ .   The method for producing an MnAl alloy according to claim 1 or 2, further comprising the step of heat treating the MnAl alloy at a temperature of 300 ° C to 600 ° C.