CN108328615B - High-purity cubic perovskite structure compound Mn4C and preparation method thereof - Google Patents

Abstract

The invention discloses a high-purity manganese-carbon binary compound Mn with a cubic perovskite structure₄C and a preparation method thereof. With Mn₄N is relatively stableAlso, Mn having this structure₄C is in a metastable state at normal temperature and can be decomposed at high temperature, so that high-purity Mn is obtained in practical experiments₄The synthesis of C has never been successful. This results in the fact that Mn is present in₄The physical properties of C are poorly understood. Although there is a theoretical work on Mn₄The performance of C was predicted, but the predicted results could not be verified experimentally. There is no Mn in the X-ray powder diffraction database₄The structural parameter data of C does not have Mn in a manganese-carbon binary phase diagram₄C. The invention mixes, melts and cools the high-purity manganese and the carbon according to a certain stoichiometric proportion to obtain the Mn with higher purity₄C compound, Mn is produced by magnetic separation process₄The purity of the product C was further improved and the powder diffraction pattern of the product is shown in figure 2.

Description

High-purity cubic perovskite structure compound Mn4C and preparation method thereof

Technical Field

The invention relates to the technical field of high-purity magnetic compounds and preparation thereof, in particular to a high-purity metastable magnetic compound Mn₄C, a synthetic technology and a magnetic separation and purification technology thereof, and application of the compound in the field of thermodynamic regulation and control of magnetization intensity of magnetic materials.

Background

Manganese-carbon binary compounds can form various stable crystal structures according to different preparation conditions and atomic proportions, and the manganese-carbon binary compounds which are successfully synthesized at present have cubic Mn₂₃C₆Mn of hexagonal or trigonal structure₇C₃Mn of monoclinic structure₅C₂Mn of orthorhombic structure₃C, Mn of hexagonal structure₁₅C₄. Theoretical research shows that Mn₄C and Mn₄N has a similar cubic perovskite crystal structure, as shown in FIG. 1, but Mn was found experimentally₄C is unstable at normal temperature and high temperature, particularly, the C is difficult to synthesize due to high-temperature decomposition, and has a lot of Mn historically₄C Synthesis effort, but phase-pure Mn in the experiment₄The synthesis of C has never been successful. It has been desired to obtain Mn₄The synthesis experiments of the C phase generally finally obtained are all thermodynamically more stable compositions close to Mn at room temperature₄Mn of C₂₃C₆Instead of Mn₄C. Although Mn is present₄C seems to be a very simple compound, but its sample is difficult to prepare and makes Mn quite different₄The synthetic principles and physical properties of C are poorly understood, even without Mn in the X-ray powder diffraction database₄Structural data of C, Mn is not present in the manganese-carbon binary phase diagram₄The presence of C. The invention obtains high-purity Mn in experiments for the first time₄And C, providing possibility for the subsequent research and application development of the related compound.

Thermodynamic regulation of the magnetism of materials is one of the fields where magnetic research is most attractive and application value is also the most difficult to realize. The saturation magnetization of most substances decreases with increasing temperature, and the decrease of the magnetic order caused by thermal disturbance has many negative effects, which is a problem that most magnetic materials must consider during use. For example, the performance of the ndfeb strong magnet decreases rapidly with increasing temperature, which greatly limits the maximum use temperature range of the ndfeb magnet, mostly below 80 ℃ and a few below 200 ℃. In magnetic recording media, the thermal stability of the information magnetic storage bit cell is critical to the security of the stored information. In disk information read head noise, magnetization fluctuations due to temperature changes are a major source of noise. Thermal stability of information and readout noise are key issues in the field of magnetic storage. We found high purity Mn for the first time by magnetic testing₄The saturation magnetization of C is increased linearly with the increase of temperature, the thermomagnetic behavior different from most substances is very meaningful, the thermomagnetic behavior can be used for overcoming the thermal disturbance of the magnetization, the problem that the magnetization of the traditional material is reduced along with the increase of the temperature is compensated, and the possibility is provided for maintaining the thermal stability of the magnetic material.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a high-purity magnetic material Mn₄A compound C having a cubic perovskite structure (fig. 1), which has been confirmed by X-ray powder diffraction results of the compound (fig. 2). Main diffraction peaks and Mn in FIG. 2₄The C structure is highly inosculated, and the perovskite structure lattice parameter on the surface is calculated asa ₀ =3.8682 angstroms. Mn₄C unit cell of (111), (200), (220), (311)And (222) the diffraction intensities of the diffraction peaks of the crystal planes are decreased in sequence. The very low background peak in FIG. 2 indicates that the product has very low Mn₄The content of impurities other than C. The Mn is₄The C compound has a physical property that the saturation magnetization increases with an increase in temperature over a wide temperature range, which is a characteristic different from most substances. The product has a saturation magnetization of 6 Am or more at a temperature of 50K or less²Per kg; saturation magnetization of 7 Am or more at room temperature of 300K²Per kg; saturation magnetization of 8 Am or more at 400K²In terms of/kg. Above the 590K interval the saturation magnetization of the material starts to decrease. The XRD pattern of the initial product in FIG. 1 shows Mn₄C has high purity and trace Mn₂₃C₆And Mn were not separated, demonstrating that our process is preparing pure phase Mn₄The C aspect is very effective.

Specifically, the invention prepares a magnetic manganese-carbon binary compound which has a perovskite structure and can exist in a metastable state at room temperature, wherein the carbon content atomic ratio is about 20 percent, the manganese content atomic ratio is about 80 percent, one sample is tested by an electron energy scattering spectrometer arranged on a scanning electron microscope to obtain the manganese-carbon atomic ratio of the magnetic manganese-carbon binary compound which is 80.62:19.38, as shown in figure 3, the value is very close to a theoretical value of 4:1 in consideration of errors of experimental instruments, and the further proves that the obtained sample is Mn₄And C phase. The manganese-carbon binary alloy composition deviates from Mn to some extent₄C causes the manganese atoms to be absent or excessive, and the crystal structure of the product can still maintain the cubic perovskite structure but the lattice parameters are slightly changed as long as the deviation is not large.

The invention provides a method for preparing high-purity cubic perovskite structure Mn₄A process for preparing the compound C. The technical scheme adopted by the process comprises the following steps: 1) proportioning manganese and carbon in proportion → 2) putting the proportioned materials under inert atmosphere → 3) heating the proportioned materials until all the proportioned materials are melted → 4) cooling the melt until the melt is solidified → 5) collecting the product → 6) grinding and refining → 7) separating the magnetic material by using a magnet to remove the nonmagnetic material → 8) repeating the grinding and magnetic separation process to improve the purity.It is noted that the stoichiometric atomic ratio of manganese to carbon may deviate from 4 to 1, but not by more than 1%. The batching reaction cavity is vacuumized to be below 0.001 pascal, and then high-purity argon is introduced. The ramp-up and ramp-down rates for the batch warming melting process and the melt cooling process are between one thousand and twenty degrees per second per minute. The obtained magnetic Mn has a certain purity₄Compound C requires multiple iterations of the process of milling the pulverized magnet separation to increase purity, leaving only the magnetic phase.

Drawings

FIG. 1 Mn with cubic perovskite Structure₄C is a schematic unit cell structure. Mn_ⅠAtom occupies the cell apex angle, Mn_ⅡThe atoms occupy the face-center position of the unit cell, and the C atoms occupy the body-center position of the unit cell.

FIG. 2 is an X-ray powder diffraction pattern of the product showing that the product consists essentially of high purity Mn₄C, the composition is shown. Mn₄And marking the crystal face indexes of all diffraction peaks of the C perovskite structure together.

FIG. 3 Mn₄And obtaining the manganese-carbon atomic ratio of 80.62:19.38 by the electron microscope picture morphology of the product C and the electron energy scattering spectrogram of element components in the corresponding region.

FIG. 4 Mn₄And C, the XRD pattern of the product obtained by heat treatment of the product at 700K and 923K. Both of which are composed of Mn₄C、Mn₂₃C₆Mn and manganese oxide phases. Mn at higher temperatures₂₃C₆The more.

Detailed Description

The invention will be further explained with reference to the drawings.

Melting and cooling manganese carbon according to a certain proportion at a certain temperature rise and fall speed to obtain Mn with certain purity₄C sample, grinding and crushing the sample product, and separating the magnetic phase and the non-magnetic phase for 8 times in a gradient magnetic field to obtain high-purity Mn with a perovskite structure₄C。

To observe Mn of perovskite Structure₄C structural change at elevated temperature, heat-treating the above product at 700K and 923K, respectively, and subjecting the obtained powder to X-ray powder diffraction experiment, wherebyThe results are shown in FIG. 4. It can be seen that part of the Mn after 700K treatment₄C is decomposed by heating to form Mn₂₃C₆And manganese, the manganese portion formed being oxidized again in air to form manganese oxide, indicating Mn₂₃C₆Is specific to Mn₄C a phase with higher thermal stability. As the heat treatment temperature reached 923K, a larger amount of Mn was added₄Decomposition of C to Mn₂₃C₆And manganese, wherein manganese is further naturally oxidized in air to form manganese oxide. From Mn₄The manganese particles precipitated from C are very small, so the manganese particles are easy to absorb oxygen and oxidize in the air. The Mn is₄The phase change process of C at high temperature further illustrates that the sample we originally obtained is Mn of high purity₄C。

Claims (1)

1. Preparation of Mn₄A method for producing a binary compound C, characterized by:

firstly, proportioning manganese and carbon in proportion, heating the mixture in an anaerobic space to melt the mixture at a high temperature, and cooling the molten liquid mixture in the anaerobic space to obtain the Mn-containing material₄The product of C phase is continuously separated by the gradient magnetic field, and the obtained Mn₄The purity of the C product can be further improved; repeating the magnetic field separation process for multiple times to finally obtain high-purity Mn₄C；

Wherein the batching reaction cavity is vacuumized to be below 0.001 pascal, then high-purity argon is introduced, the heating rate and the cooling rate of the batching heating and melting process and the melt cooling process are between one thousand DEG per second and twenty DEG per minute, the stoichiometric atomic proportion of manganese and carbon can deviate from 4 to 1, but the deviation range is not more than 1%.

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