CN109266951B

CN109266951B - LaFeSiCu magnetic refrigeration alloy and preparation method thereof

Info

Publication number: CN109266951B
Application number: CN201811113587.1A
Authority: CN
Inventors: 王敬民; 杨洋; 蒋成保
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2018-09-25
Filing date: 2018-09-25
Publication date: 2020-05-22
Anticipated expiration: 2038-09-25
Also published as: CN109266951A

Abstract

The invention discloses a lanthanum-iron-silicon-copper magnetic refrigeration material with excellent magnetocaloric property and short preparation period and a preparation method thereof, wherein the general chemical formula of the lanthanum-iron-silicon-copper magnetic refrigeration material is (La)_yFe_13‑zSi_z)_100‑xCu_x，0<x is less than or equal to 50, y is less than or equal to 2 and is less than or equal to 1, and z is less than or equal to 10 and is more than or equal to 0. The preparation method comprises the following steps: (1) mixing La, Fe, Si and Cu according to the mass percentage of each element in the general formula; (2) under the protection of high-purity argon, repeatedly smelting, cooling and turning the prepared raw materials in a vacuum electric arc furnace for four times; (3) and carrying out high-temperature heat treatment on the cast ingot in a high-purity argon atmosphere and then quenching the cast ingot in cold water. The material disclosed by the invention has a simple preparation process, the preparation period of the lanthanum-iron-silicon magnetic refrigeration material is greatly shortened, and the prepared magnetic refrigeration material has large magnetic entropy and small hysteresis and thermal hysteresis loss.

Description

LaFeSiCu magnetic refrigeration alloy and preparation method thereof

Technical Field

The invention relates to a magnetic material, in particular to a novel low-cost magnetic refrigeration lanthanum-iron-silicon-copper material without harmful elements, and a rapid preparation method and application thereof.

Background

The traditional gas compression refrigeration technology is widely applied to the technical field of refrigeration, but has the defects of low refrigeration efficiency, high energy consumption, damage to atmospheric environment and the like. The magnetic refrigeration technology is a novel refrigeration technology which uses a magnetic material with a magnetocaloric effect as a refrigeration working medium. Compared with the traditional gas compression refrigeration, the magnetic refrigeration technology adopting the solid refrigeration working medium has a plurality of advantages, such as: high refrigerating efficiency (the Carnot cycle efficiency can reach more than 60 percent), no toxicity, no pollution, low noise, good stability and the like. Based on the advantages, the room temperature magnetic refrigeration has great application prospect in magnetic refrigeration refrigerators, air conditioners, space technology, nuclear technology and the like, and becomes a high and new technical field which is strongly competitive in various countries at present.

The research of the magnetic refrigeration technology mainly focuses on the development of high-performance room-temperature magnetic refrigeration materials, and the magnetic refrigeration materials which are found at present mainly comprise heavy rare earth and alloy thereof: la (Fe, Si)13 series, Gd5(Ge, Si)4 series, MnFePAs type alloy series, Ni2MnGa alloy series, perovskite type compound and other material systems. Each of these magnetic refrigeration materials has advantages and disadvantages. The large amount of magnetic entropy change of the material caused by the change of the magnetic field is the premise of realizing large magnetic refrigeration capacity, and the ideal magnetic refrigeration material should contain more than 80 percent of transition group metal elements with large magnetic moment, such as Fe, Co, Mn and the like; also comprises some elements of the third, fourth and fifth main groups to regulate performance indexes such as Curie temperature and the like, such as Al, Si, P and the like. Most of the problems of the magnetic refrigeration materials at present are concentrated on: high cost, toxic elements, high component requirement, complex preparation process, long time consumption and the like; the La (Fe, Si) 13-based material becomes a solid magnetic refrigeration working medium with great development potential due to the advantages of low cost and no toxicity of raw materials, simple preparation process, large magnetic entropy and the like, but has some defects to limit practical application, firstly, peritectic solidification generated in the traditional smelting and casting process is incomplete, so that the preparation of the material can require high-temperature heat treatment for more than 30 days to obtain a single phase, and the material is time-consuming and energy-consuming; secondly, the material has a first-order phase change which causes large hysteresis thermal hysteresis loss. When Co is used for replacing Fe by people, the Curie temperature is increased, but the entropy change is reduced, the Mn element replaces Fe to generate antiferromagnetic coupling, and the Tc is reduced. Therefore, finding suitable alloying elements and shortening the preparation time, and preparing the magnetic material with reversible large magnetic entropy change and high magnetic refrigeration capacity near room temperature is the key point for promoting the application of the magnetic refrigeration technology.

Disclosure of Invention

The invention aims to provide a preparation method of a lanthanum-iron-silicon-copper magnetic refrigeration material with high efficiency, and the LaFeSiCu compound with stable performance and giant magnetocaloric effect is quickly prepared by using the method.

Aiming at the defects of long preparation period, large thermal hysteresis, large magnetic hysteresis and the like of the existing La (Fe, Si)13 series materials, the invention prepares the LaFeSiCu room temperature magnetic refrigeration material with small thermal hysteresis and large magnetic entropy change by adding Cu element to accelerate the solid phase change rate in the heat treatment, and the general formula is as follows: (La)_yFe_13-zSi_z)_100-xCu_x，0<x≤50，1≤y≤2，0≤z≤10。

The magnetic refrigeration material has a NaZn13 type cubic crystal structure, and the space group is Fm3 c.

The technical scheme of the invention also comprises a preparation method of the magnetic refrigeration lanthanum-iron-silicon-copper alloy material, which comprises the following steps:

(1) the preparation method comprises the following steps of preparing materials according to the mass percentage of each element in a general formula: (La)_yFe_13-zSi_z)_100- _xCu_x，0<x≤50，1≤y≤2，0≤z≤10；

(2) Putting the raw materials prepared in the step (1) into a vacuum electric arc furnace, and vacuumizing to be equal to or less than 5 multiplied by 10^-3Pa, washing gas twice, finally repeatedly smelting under the condition of high-purity argon, and cooling and turning for four times to obtain an ingot;

(3) sealing the ingot prepared in the step (2) in a quartz tube, and vacuumizing to 3 x 10^-4Pa～1×10^-5And (3) introducing high-purity argon gas of 0.01-0.03 MPa after Pa, annealing the cast ingot at 1050 ℃ for 1-6 days, and quenching the cast ingot into liquid nitrogen or ice water for rapid cooling to obtain the magnetic refrigeration material with the content of the 1:13 magnetic thermal phase.

In the step (1), the rare earth element La is extremely easy to oxidize to compensate volatilization and burning loss in the preparation process, the rare earth element raw material La is excessively added by 4% according to atomic percentage, so that a single-phase material is obtained, and the single-phase material is sealed in alcohol or gasoline after the batching is finished and is taken out when the smelting is carried out.

In the step (2), the vacuum degree of the furnace chamber is 3 multiplied by 10^-3Pa; the smelting temperature is 1200-2000 ℃, and the time of single smelting is 60-80 seconds.

In the step (3), the degree of vacuum of the vacuum annealing treatment is 1X 10^-3Pa～1×10^-5Pa, the annealing temperature is 1050 ℃, and the annealing treatment time is 1-6 days.

The technical scheme of the invention provides application of a magnetic refrigeration lanthanum-iron-silicon-copper alloy material as a refrigeration material at room temperature.

Compared with the prior art, the invention has the following advantages and effects:

(1) the invention greatly shortens the time of high-temperature heat treatment, has simple and convenient equipment operation, lower cost, easy large-scale production and high economic value in the production and preparation process. Therefore, the invention has wide application prospect in the field of magnetic refrigeration.

(2) The lanthanum-iron-silicon-copper material prepared by the invention has a NaZn13 type cubic crystal structure, and has large magnetic entropy change and large magnetic refrigeration capacity due to the first-order phase change of cruise electronic transition of the material in the ferromagnetic-paramagnetic transition process, wherein (LaFe)_11.6Si_1.4)₉₆Cu₄And (LaFe)_11.6Si_1.4)₉₂Cu₈The magnetic entropy change peak values of the magnetic field reaches-22J/kg.K and-17J/kg.K respectively under the change of a 0-5T magnetic field.

(3) The Cu-containing compound provided by the invention has adjustable phase transition temperature, and the magnetic refrigeration material with small hysteresis loss and low price can be prepared by adjusting the proportioning process.

Drawings

FIG. 1 shows (LaFe) prepared under heat treatment conditions of 1-5 days in example 1 of the present invention_11.6Si_1.4)₉₈Cu₂The crystalline compound was measured for powder X-ray diffraction pattern at room temperature.

FIG. 2 shows (LaFe) prepared in example 1 of the present invention_11.6Si_1.4)₉₈Cu₂The thermomagnetic curves (0.03T and 5T applied magnetic field) were measured in the field-on (FC) mode for samples heat-treated for 1,3 and 5 days (fig. 2(a), 2(b), 2(c) correspond to heat-treated for 1,3,5 days, respectively).

FIG. 3 shows (LaFe) prepared in example 1 of the present invention_11.6Si_1.4)₉₈Cu₂Isothermal magnetization curves of the lifting magnetic field of the samples heat-treated for 1,3 and 5 days (fig. 3(a), 3(b), 3(c) correspond to heat-treated for 1,3,5 days, respectively).

FIG. 4 shows (LaFe) prepared in example 1 of the present invention_11.6Si_1.4)₉₈Cu₂And (3) a relation curve of magnetic entropy change and temperature T under the 5T magnetic field change near the Curie temperature of the crystalline compound.

FIG. 5 shows (LaFe) prepared by the present invention_11.6Si_1.4)_100-xCu_xPhotographs of the back-scattered electron morphology of crystalline compounds (x is 0,2,4,6 from left to right and from top to bottom, respectively),8,10)。

Detailed Description

The metallic materials such as La, Fe, Si and Cu used in the following examples were purchased from Cultiplex nonferrous metals technology development center and the purity of Fe and Cu was higher than 99.9%, La was higher than 99.5% and Si was higher than 99%, powder X-ray diffraction lines of the prepared crystalline compound were measured by a D/max2500PC multifunction X-ray diffractometer (Cu K α target), magnetic and magnetocaloric data of the prepared crystalline compound were measured by a PPMS-Dynacool type multifunction physical property measuring system of Quantum Design, and backscattered electron images and energy spectrum components were measured by a Japanese Electron JXA8100 electron probe.

Example 1: (LaFe)_11.6Si_1.4)₉₈Cu₂And (3) preparing and characterizing the magnetic refrigeration alloy.

1.(LaFe_11.6Si_1.4)₉₈Cu₂The preparation method specifically comprises the following steps:

step (1): is pressed (LaFe)_11.6Si_1.4)₉₈Cu₂Weighing the materials according to the mass percent of each element in the chemical formula, and mixing the raw materials of commercially available high-purity rare earth metal La, metal Fe, metal Cu and non-metal Si, wherein La is excessively added by 4% (atomic percentage);

step (2): putting the raw materials prepared in the step (1) into an electric arc furnace or an induction heating furnace for vacuumizing until the vacuum degree reaches 5 multiplied by 10^-3Pa～1×10^-3When Pa, cleaning with high-purity argon with the purity of 99.999 percent for 1-2 times, and vacuumizing to 5 multiplied by 10^-3Pa～1×10^-3When Pa is needed, high-purity argon is filled for protection, the pressure in the furnace chamber is 1 atmosphere, the furnace chamber is repeatedly turned and smelted for 4 times, the smelting time is 60-80 seconds each time, and the smelting temperature is 1600-2000 ℃;

and (3): cooling in a copper crucible to obtain an as-cast alloy, wrapping the as-cast alloy with tantalum foil, and sealing in a vacuum degree of 1 × 10^-3Annealing at 1050 deg.C for 1-5 days in Pa quartz tube, taking out, rapidly quenching in ice water to obtain high target phase content (LaFe)_11.6Si_1.4)₉₈Cu₂Crystalline compound samples.

2.(LaFe_11.6Si_1.4)₉₈Cu₂Performance measurement of

(1) X-ray diffraction lines

(LaFe) measured by a D/max2500PC multifunction X-ray diffractometer (CuK α target)_11.6Si_1.4)₉₈Cu₂The room temperature polycrystalline X-ray diffraction spectrum of (1) has an analytic structure of NAZn13 type cubic crystal structure and a space group of Fm3c, (LaFe)_11.6Si_1.4)₉₈Cu₂See table 1 for atomic occupancy. Measured with a D/max2500PC multifunction X-ray diffractometer (LaFe)_11.6Si_1.4)₉₈Cu₂The X-ray diffraction spectrum of the annealing treatment for 1 to 5 days is shown in figure 1. The Fe peak is sharply reduced after Cu doping, and a large amount of magnetocaloric phases are obtained after 3 days of annealing heat treatment, which shows that the Cu doping can effectively improve the heat treatment rate.

TABLE 1

(2) Thermomagnetic curve

Determined on the PPMS System (LaFe)_11.6Si_1.4)₉₈Cu₂The thermomagnetic (M-T) curve of the crystalline compound at a field strength of H300 oe is shown in fig. 2.

(3) Isothermal magnetization curve

FIG. 3 is (LaFe)_11.6Si_1.4)₉₈Cu₂Isothermal magnetization curves of the crystalline compound at the rising and falling fields around the curie temperature (measured every 3K over the temperature range 170K to 230K).

(4) Magnetocaloric effect and magnetic refrigeration capacity

Based on the results of fig. 3, maxwell's relation is continuously integrated into a discrete summation derivation formula in actual calculation:

according to the above formula can be selected fromThe temperature magnetization curve calculates the change in magnetic entropy. Calculated to obtain (LaFe)_11.6Si_1.4)₉₈Cu₂The plot of magnetic entropy versus temperature (- Δ S-T) around Tc is shown in FIG. 4. As can be seen from FIG. 4, the compound shows a large change in magnetic entropy around Tc, where under a 0-5T magnetic field change, (LaFe)_11.6Si_1.4)₉₈Cu₂The maximum magnetic entropy changes of the crystalline compounds are-24.6J/kg. K, respectively.

The result analysis shows that the Cu doping can effectively improve the heat treatment forming efficiency of the compound; meanwhile, the thermal hysteresis and the Curie temperature have close relation with the content of Cu, the Curie temperature of the compound is rapidly increased along with the increase of the content of Cu, and the Curie temperature of the compound can be adjusted to the room temperature range by adjusting the proportion of Cu in the compound so as to be beneficial to practical application.

Example 2: (LaFe)_11.6Si_1.4)₉₂Cu₈And (3) preparing and characterizing the magnetic refrigeration alloy.

1.(LaFe_11.6Si_1.4)₉₂Cu₈The preparation method comprises the following steps:

step (1): is pressed (LaFe)_11.6Si_1.4)₉₂Cu₈Weighing the materials according to the mass percent of each element in the chemical formula, and mixing high-purity rare earth metal La, metal Fe, metal Cu and non-metal Si raw materials, wherein La is added in an excessive amount of 4% (atomic percent);

and (3): cooling in a copper crucible to obtain an as-cast alloy, wrapping the as-cast alloy with tantalum foil, and sealing in a vacuum degree of 1 × 10^-3Annealing in Pa quartz tube at 1050 deg.C for 6 days, taking out, and rapidly quenching in ice water to obtainHigh target phase content crystalline compound samples.

2.(LaFe_11.6Si_1.4)₉₂Cu₈Performance measurement of

Determined on a PPMS System as described in example 1 (LaFe)_11.6Si_1.4)₉₂Cu₈The thermomagnetic (M-T) curve of the crystalline compound at the magnetic field strength H of 300oe can be determined from the M-T curve of the temperature rise and fall (LaFe)_11.6Si_1.4)₉₂Cu₈The crystalline compound has a Curie temperature Tc of 200.8K. The Curie temperature of the Cu-doped sample is increased by about 15K relative to that of a ternary LaFe11.6Si1.4 compound, which shows that the phase transition temperature of the material is closer to room temperature, and the method is one test of the premise of the material for room-temperature magnetic refrigeration (LaFe)_11.6Si_1.4)₉₂Cu₈The isothermal magnetization curves of the rising field and the falling field of the crystalline compound near the Curie temperature (measured every 3K within the temperature range of 170K to 230K) are under the change of a 0-5T magnetic field, (LaFe)_11.6Si_1.4)₉₂Cu₈The maximum magnetic entropy changes of the crystalline compounds were-17.2J/kg. K, respectively.

The cooling capacity (RC) is another important parameter for measuring the practical value of a material. And calculating the relative refrigerating capacity RC of the sample by adopting the product of the temperature span at the half peak and the maximum isothermal magnetic entropy change. Under the condition of 0-5T magnetic field variation, (LaFe)_11.6Si_1.4)₉₂Cu₈The refrigerating capacity RC is 320J/Kg, and the excellent magnetocaloric performance is shown.

TABLE 2

From the analysis of the results, the thermal hysteresis and the Curie temperature of the compound have a close relationship with the content of Cu, the Curie temperature of the compound is rapidly increased along with the increase of the content of Cu, and the Curie temperature of the compound can be adjusted to the room temperature range by adjusting the proportion of Cu in the compound so as to be beneficial to practical application.

Claims

1. A preparation method of a magnetic refrigeration lanthanum-iron-silicon-copper alloy material is characterized by comprising the following steps:

(1) the preparation method comprises the following steps of preparing materials according to the mass percentage of each element in a general formula: (La)_yFe_13-zSi_z)_100-xCu_x，0<x≤50，1≤y≤2，0≤z≤10；

(2) Putting the raw materials prepared in the step (1) into a vacuum electric arc furnace, and vacuumizing to 3 multiplied by 10^-3Pa, washing gas twice, finally repeatedly smelting under the condition of high-purity argon, and cooling and turning for four times to obtain an ingot;

(3) sealing the ingot prepared in the step (2) in a quartz tube, and vacuumizing to 10 DEG^-3Introducing high-purity argon gas of 0.01-0.03 MPa after Pa, annealing the cast ingot at 1050 ℃ for 1-6 days, quenching the cast ingot in liquid nitrogen or ice water, and rapidly cooling to obtain a magnetic refrigeration material with the content of a 1:13 magnetic thermal phase;

in the step (1), the rare earth element raw material La is excessively added by 4% according to atomic percentage to make up for burning loss;

in the step (2), the smelting temperature is 1600-2000 ℃, and the time of single smelting is 60-80 seconds;

in the step (3), the annealing temperature is 1050 ℃, and the annealing time is 1-6 days.