RU2531393C1 - METHOD OF OBTAINING SOLID MAGNESIUM MATERIAL Sm2Fe17NX - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining the solid magnesium material Sm₂Fe₁₇N_x includes mixing Sm and Fe powders, their mechanical activation and the following nitration. First, mechanical activation in a high-energy-voltage grinder is carried out in the inert atmosphere without content of moisture for 2-3 hours. For nitration in the grinder reactor introduced is ammonia and hydrogen in a ratio of NH₃ - 85-95%, H₂ - 5-15% and mechanical activation is continued for 5-7 hours. After that, a highly-molecular compound polymethylmetacrylate (PMMA) is introduced in a quantity of 2-4% of the weight of the initial powder mixture and the process of mechanical activation is continued for than 10-15 minutes.

EFFECT: invention makes it possible to reduce the time of obtaining the solid magnesium material and increase its coercive force.

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Description

The invention relates to the field of production of hard magnetic materials used in electrical engineering and mechanical engineering.

A known method of producing magnetically hard material [Magnetic properties of Sm-Fe (Ti) -C (N) / α-Fe alloys prepared by mechanical alloying, J. Phys. D: Appl. Phys. 36 (2003) 375-379]. Purity powders of 99.9% Sm, Ti, Fe and 99.7% purity graphite are mixed into various compositions, sealed in argon atmosphere in cylindrical banks of hardened steel. Hardened steel balls have a diameter of 12 mm. The grinding is carried out in a high-energy ball mill for 5 hours. Next, the powders are annealed at 1123 K and 30 min in a vacuum oven. Nitriding is carried out immediately after annealing for 5 hours at a temperature of 673 K. Disadvantages: the duration and multi-operation process of obtaining magnetically hard material. The nitrogen content of the material is reduced, resulting in a powder whose dimensions cannot be controlled, which has a negative effect on magnetic properties.

A known method of producing powders Sm ₂ Fe ₁₇ N _x -α-Fe [Mikio Ito Sm ₂ Fe ₁₇ N _x -α-Fe anisotropic composite powders prepared by Sm evaporation and mechanical grinding in NH ₃ Scripta Materialia, 46 (2002), 695- 698]. The method includes preparing an alloy of Sm _12.8 Fe _{87.2 by} induction melting a mixture of Sm and Fe powders and subsequent crushing to 45-150 lm. The powders were subjected to heat treatment at 1273 K for 3.6–18.0 ks in a quartz tube. The atmospheric pressure of NH ₃ when used in a rotary ball mill is 18.0 ks, and then nitriding was carried out in flowing gas N ₂ at a temperature of 723 K for 21.6 ks.

The disadvantage of this method is the inability to obtain a nitrogen content of 3%, as well as the duration and complexity of the process.

A known method of producing a hard magnetic alloy based on rare-earth metal (in particular samarium) and iron [Patent No. US8329056]. In this method, the starting components (samarium and iron) are mixed in the ratio of 11 at.% Sm and 89 at.% Fe, mechanical alloying is carried out, and then the resulting alloy Sm ₂ Fe _{17 is} nitrided. The particle size of Sm ₂ Fe ₁₇ N ₃ is 1-10 nm. Then, to improve the magnetic characteristics, the particles are coated with an epoxy oligomer layer at a temperature of 70-76 ° C. The thickness of this layer is 30-100 nm.

The disadvantage of this method is the complexity of the process of coating particles, as well as the inability to obtain a nitrogen content of 3%, which significantly affects the magnetic characteristics of the alloy.

As a prototype, a method for producing magnetic material based on the Sm-Fe-N system [US Patent No. 5288339A] was selected. The Sm ₂ Fe ₁₇ alloy was obtained by mechanical alloying, while the intensity, material, and diameter of the mill balls were varied. As initial components, powders of samarium and iron with a purity of at least 99.5% were selected. X-ray phase analysis after mechanical alloying showed the presence of an amorphous phase and an alpha-iron phase. In order to obtain a crystal structure, heating is carried out to 700 ° C. Next, nitriding of the obtained alloy was carried out in two stages. At the first stage, the following parameters were used: temperature - 300-400 ° C, duration - 10-1000 hours, nitrogen content - 1.5%. Parameters of the second stage: temperature - 500 ° C, duration - 16 hours, nitrogen content about 3%. Thanks to the two-stage nitriding process, stable nitride was obtained.

The disadvantage of this method is the complexity of the process due to the two-stage nitriding, large time costs and the inability to achieve a nitrogen content of about 3%, which leads to a deterioration in the coercive force of 17-22 kA / cm

The task is to develop a simple and quick way to obtain a hard magnetic material Sm ₂ Fe ₁₇ N _x , increasing the coercive force.

To solve the problem, a method for producing a magnetically solid compound Sm ₂ Fe ₁₇ N _{x is} proposed, which consists in mixing the initial powder components Sm and Fe and their mechanical activation in a high-energy-intensive vibratory mill for 2-3 hours. Mechanical activation is carried out in an inert atmosphere without moisture content. Next, ammonia and hydrogen are introduced into the reactor in the ratio of NH ₃ - 85-95% and Н ₂ - 5-15% and the process of mechanical activation is continued for another 5-7 hours. After that, a high molecular weight compound, polymethyl methacrylate, is introduced into the reactor in an amount of 2-4% by weight of the initial powder mixture and mechanical activation is continued for another 10-15 minutes. Argon, helium, etc. can be used as an inert atmosphere.

Mechanical activation under certain conditions eliminates the interaction with the environment and the oxidation of the starting components. Dilution of ammonia with hydrogen increases the nitrogen potential of the atmosphere and thereby accelerates the nitriding process.

Continuous mechanical activation accelerates the nitriding process and improves the magnetic characteristics of the material.

The introduction of polymethylmethacrylate (PMMA) allows you to get fine powders with their uniform distribution in size.

The combination of distinctive features is necessary and sufficient to solve the problem.

When the mechanical activation time is less than 2 hours, we do not get the Sm ₂ Fe ₁₇ phase. Carrying out mechanical activation for more than 3 hours is impractical due to the strong oxidation of the components.

The ratio of ammonia / hydrogen gases in the range of NH ₃ -85 - 95% and H ₂ -5 - 15%, as well as further mechanical activation for 5-7 hours, allow obtaining a nitrogen content of 2.5-3%, which leads to the formation of Sm ₂ Fe ₁₇ N ₃ . The amount of hydrogen more than 15% and ammonia less than 85% in the ammonia / hydrogen mixture does not allow to increase the nitrogen potential of the atmosphere due to the small amount of ammonia, and, accordingly, to accelerate the nitriding process. The amount of hydrogen less than 5% and more than 95% ammonia is impractical, because is insufficient to increase nitrogen potential. A time of mechanical activation of less than 5 hours is not enough to obtain the compound Sm ₂ Fe ₁₇ N ₃ , and more than 7 hours is impractical.

The introduction of a high molecular weight polymethyl methacrylate compound (PMMA) in an amount of 2-4% of the amount of the initial powder mixture and further grinding for 10-15 minutes result in a dispersion of the powder of less than 40 microns. The introduction of PMMA in an amount less than 2% is insufficient to achieve uniformity and the required dispersion of the powder, the addition of PMMA in an amount greater than 4% is impractical.

Grinding less than 10 minutes will not lead to uniform dispersion of the powders, a grinding time of more than 15 minutes is impractical, because the process of forming the necessary dispersion is already completed.

To obtain a hard magnetic material Sm ₂ Fe ₁₇ N _x , a powder mixture of Sm and Fe was selected to form the Sm ₂ Fe ₁₇ compound. We carry out mechanical activation in a highly energized mill in an inert atmosphere without moisture content for 3 hours. To form an inert atmosphere, argon gas (examples 1-3) and helium (examples 4-5) are purified, for which gas is passed through titanium and copper shavings in a furnace at low temperatures and introduced into a mill. Silica gel is used to remove moisture in the mill. For nitriding, ammonia and hydrogen are introduced into the mill reactor in the ratio: NH ₃ - 85% and Н ₂ - 15%. The process of mechanical activation occurs continuously. We continue mechanical activation for 6 hours. We introduce a high molecular weight polymethyl methacrylate compound (PMMA) in an amount of 3% by weight of the initial powder mixture (11% Sm and 89% Fe). We continue the process of mechanical activation for another 12.5 minutes. The amount of nitrogen in the material is 2.95% (table)

No. Mechanical activation time 1, hour. The ratio of NH ₃ / H ₂ Mechanical activation time 2, hours. The number of PMMA,% Mechanical activation time 3, min. The amount of nitrogen,% one 3 85/15 6 3 12.5 2.95 2 2 85/15 5 2 10 2,50 3 2,5 95/5 5 four 12.5 2.60 four 2 85/5 7 3 fifteen 2.74 5 3 90/10 6 2 fifteen 2.98

The time to obtain hard magnetic material is reduced due to the one-step process of nitriding and the continuous process of mechanical alloying.

Through the use of a mixture of ammonia and hydrogen and the continuity of the mechano-alloying process, we obtain a nitrogen content of ~ 3%, which leads to an increase in the coercive force of the material - 22-25 kA / cm.

Claims (1)

A method of obtaining a magnetically hard material Sm ₂ Fe ₁₇ N _x , which consists in mixing powders Sm and Fe to form the compound Sm ₂ Fe ₁₇ , their mechanical activation followed by nitriding, characterized in that at the initial stage the mechanical activation is carried out in a high-energy-stressed mill in an inert atmosphere without moisture content for 2-3 hours for nitriding mill reactor is added ammonia and hydrogen in a ratio of NH ₃ - 85-95% and h ₂ - 5-15% mechanoactivation continue for 5-7 hours followed by introducing a high molecular compound packing f methacrylate (PMMA) in an amount of 2-4% by weight of the initial powder mixture and continue the process of mechanical activation for 10-15 minutes.