CN1312706C - Rare earth iron-base room-temp mangnetic refrigerant material and preparation method thereof - Google Patents

Abstract

The present invention relates to the field of magnetic materials and discloses a rare earth-iron base magnetic refrigeration material at room temperature and a preparation method thereof. The general chemical formula of the magnetic refrigeration material is Pr [2]Fe [17-x]Co [x], wherein X is bigger than and is equal to 0 but is smaller than 0.1. The preparation method for the magnetic refrigeration material comprises the following steps: raw materials are mixed and then are put in a vacuum arc furnace or an induction heating furnace; the furnace is evacuated and alloy casting ingots are smelted under the protection of high-purity argon gas; the alloy casting ingots are quenched into water after the vacuum annealing procedure. The principal raw material Fe used by the present invention has low price and has abundant storage capacity in nature; the prepared product Pr [2]Fe [17-x]Co [x] indicates second order phase change in the magnetization process and has larger magnetic entropy change within the temperature range of 270 to 350K. Moreover, the Curie point can be continuously regulated along with the compositional variation; the preparation method uses conventional electric arc or induction melting; a Pr [2]Fe [17-x]Co [x] compound can be synthesized after the annealing procedure is carried out after the smelting procedure. The present invention has simple process and low cost and is suitable for industrial production.

Description

A kind of rare earth-iron base room temperature magnetic refrigerating material and preparation method thereof

Technical field

The present invention relates to a kind of magnetic material, particularly a kind of rare earth-iron base room temperature magnetic refrigerating material and preparation method thereof.

Background technology

At current science and technology and sphere of life, Refrigeration Technique is essential.Because fluorine Lyons (Freon) refrigeration working medium especially is on the rise to the destruction that atmospheric ozone layer causes to biological environment, according to the Montreal agreement, international community has determined worldwide progressively to forbid to produce and has used fluorine Lyons to make cold-producing medium.For replacing fluorine Lyons some cold-producing medium such as R134a newly developed, they still bring greenhouse effect though do not damage the ozone layer, and the shortcoming that its refrigerating efficiency is low and energy consumption is big makes it can't replace fluorine Lyons fully.Therefore, seek refrigerating working material and corresponding Refrigeration Technique novel, efficient, environmental protection, become the most urgent research topic of various countries scientists and engineers.In some New Refrigerating technology such as semiconductor refrigerating, absorption/absorption refrigeration and magnetic refrigeration, the magnetic refrigeration is energy-efficient with it, environmental protection and advantage such as reliable, has place of gas compression refrigeration fully and receives much concern.

The basic principle of magnetic refrigeration is to utilize the magneto-caloric effect of ferromagnetic substance, promptly changes making that its generation is put, endothermic effect freezes by the magnetic entropy that applies and remove external magnetic field control ferromagnetic substance.Wherein, magnetic refrigerating working material is one of technology of magnetic refrigeration most critical, the Curie point that requires this working material near room temperature, add that controlling magnetic field is little, magnetic entropy becomes big, low price.

1976, the Brown of the U.S. at first adopted Metal Gd as magnetic refrigerating working material, has realized room temperature magnetic refrigerating under the superconducting intense magnetic field of 7T, and the mangneto temperature difference reaches 38K.For a long time, the simple substance rare metal Gd is considered to unique material that can be used for room temperature magnetic refrigerating, though near its magneto-caloric effect room temperature is big, it costs an arm and a leg, unstable chemcial property, work magnetic field is big (needing superconducting magnet) too, is difficult to practicability as room temperature magnetic refrigerating working.1997, people such as U.S. Pecharsky are at Phys.Rev.Lett., 78 (1997): report in 4494, the magnetic entropy variate of GdSiGe compound is higher than gadolinium, though this compound has huge magneto-caloric effect, but it is in close relations with material purity that its magnetic entropy becomes, and the alloy of preparing with industrial pure material does not have huge magnetic entropy change at present; And this compound warm area is narrow, directly influences its industrialization; In addition, Gd, Ge in this compound cost an arm and a leg, and chemical stability is also poor, and difficult preparation still needs superconducting magnet, so this compound is difficult to industrialization as room temperature magnetic refrigerating working during work.In recent years, found that in perovskite with huge magneto-resistor (CMR) effect and perovskite-like Mn oxide big magnetic entropy changes, caused the extensive concern of numerous scholars thus to such material, compare with the GdSiGe series alloy with Gd, the major advantage of this series compound is that cost reduces significantly, stable chemical performance, coercive force is little and resistivity is big, China Nanjing University has carried out a large amount of research to this series compound, find that this series compound can mix its Curie temperature of adjusting to required scope by trace element, but doping can cause magnetic entropy to become to decline by a big margin, and practicality reduces.

In general, a lot of materials are because temperature or STRESS VARIATION have phase transformation to take place, and the phase transformation of phase variation firsts and seconds, the magnetic refrigeration principle is exactly reversible magnetic phase transition.Compare with the first order phase change material system, the material system with second-order phase transistion does not have heat stagnation, and it is comparatively smooth that its magnetic entropy becomes the peak, meets the requirement of magnetic refrigeration to the refrigerating working material characteristic.According to research, R ₂Me ₁₇Near the magnetic phase transition that the type compound takes place Curie temperature is second-order phase transistion mostly, has refrigeration preferably, is current research focus.

Summary of the invention

The objective of the invention is to overcome the shortcoming that exists in the prior art, the stable and environmental protection of a kind of with low cost, chemical property is provided, has the rare earth-iron base room temperature magnetic refrigerating material of big magneto-caloric effect.

Another object of the present invention is to provide the preparation method of above-mentioned rare earth-iron base room temperature magnetic refrigerating material.

Purpose of the present invention is achieved through the following technical solutions:

Rare earth-iron base room temperature magnetic refrigerating material provided by the invention, its chemical general formula is: Pr ₂Fe _17-xCo _x, 0≤x in the formula＜0.1.

The preparation method of rare earth-iron base room temperature magnetic refrigerating material provided by the invention comprises the steps:

(1) presses Pr ₂Fe _17-xCo _xThe chemical formula weighing mixes rare earth metal Pr, transition-metal Fe and Co raw material, and wherein, the excessive interpolation 5～7.5% of rare earth metal Pr (atomic percent) compensates volatilization and the scaling loss in the fusion process;

(2) the above-mentioned raw material for preparing is put into arc furnace or induction heater, be evacuated to 10 ^-1More than the Pa, clean burner hearth with high-purity argon after, charge into be lower than 1 atmospheric high-purity argon gas and under its protection melt back obtain the uniform alloy cast ingot of composition;

(3) with the vacuum annealing 0～200 hour under 1123K～1273K of above-mentioned melted alloy cast ingot, take out in the entry of quenching fast then, can make rare earth-iron base room temperature magnetic refrigerating material Pr ₂Fe _17-xCo _x

The present invention compared with prior art has following advantage and effect: (1) primary raw material Fe of the present invention is cheap and abundant at the occurring in nature reserves; (2) prepared Pr ₂Fe _17-xCo _xIn magnetization process, show second-order phase transistion, reach 65～73% of Metal Gd in the low change of (H=2.0T) magnetic entropy after the match, (H=5.0T) magnetic entropy becomes under the High-Field also 63～68% of Metal Gd, in 270～350K temperature range, have bigger magnetic entropy and become, and Curie point changes adjustable continuously with composition; (3) preparation method adopts conventional electric arc or induction melting, and the melting after annealing can synthesize Pr ₂Fe _17-xCo _xCompound, technology is simple, with low cost, be suitable for suitability for industrialized production.

Description of drawings

Fig. 1 is the Pr of embodiment preparation ₂Fe _17-xCo _xThe room temperature x-ray diffractogram of powder of (x=0,0.02,0.04,0.06,0.08,0.1).

Fig. 2 is Pr ₂Fe _17-xCo _xNear the isothermal magnetization curve of compound Curie temperature:

Fig. 2 (a) represents the Pr of x=0 ₂Fe _17-xCo _xThe isothermal magnetization curve;

Fig. 2 (b) represents the Pr of x=0.02 ₂Fe _17-xCo _xThe isothermal magnetization curve;

Fig. 2 (c) represents the Pr of x=0.04 ₂Fe _17-xCo _xThe isothermal magnetization curve;

Fig. 2 (d) represents the Pr of x=0.06 ₂Fe _17-xCo _xThe isothermal magnetization curve;

Fig. 2 (e) represents the Pr of x=0.08 ₂Fe _17-xCo _xThe isothermal magnetization curve.

Fig. 3 is Pr ₂Fe _17-xCo _xThe isothermal magnetic entropy change-temperature relation curve of compound under different magnetic field changes

Fig. 3 (a) represents the Pr of x=0 ₂Fe _17-xCo _xIsothermal magnetic entropy change-temperature curve;

Fig. 3 (b) represents the Pr of x=0.02 ₂Fe _17-xCo _xIsothermal magnetic entropy change-temperature curve;

Fig. 3 (c) represents the Pr of x=0.04 ₂Fe _17-xCo _xIsothermal magnetic entropy change-temperature curve;

Fig. 3 (d) represents the Pr of x=0.06 ₂Fe _17-xCo _xIsothermal magnetic entropy change-temperature curve;

Fig. 3 (e) represents the Pr of x=0.08 ₂Fe _17-xCo _xIsothermal magnetic entropy change-temperature curve;

Fig. 4 is Pr ₂Fe _17-xCo _xThe magnetic entropy at compound Curie temperature place becomes (Δ S _M) to H ^2/3Dependence

"-■-" represents the Pr of x=0.02 ₂Fe _17-xCo _xThe magnetic entropy at compound Curie temperature place becomes (Δ S _M) to H ^2/3Dependence

"-●-" represent the Pr of x=0.04 ₂Fe _17-xCo _xThe magnetic entropy at compound Curie temperature place becomes (Δ S _M) to H ^2/3Dependence

"-△-" represents the Pr of x=0.06 ₂Fe _17-xCo _xThe magnetic entropy at compound Curie temperature place becomes (Δ S _M) to H ^2/3Dependence

"--" represents the Pr of x=0.08 ₂Fe _17-xCo _xThe magnetic entropy at compound Curie temperature place becomes (Δ S _M) to H ^2/3Dependence

Fig. 5 is embodiment 1,2, the Pr of 3,4,5 preparations ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature (the Δ S of (x=0,0.02,0.04,0.06,0.08) and comparative example rare metal Gd _M～T) the contrast of curve, wherein:

"-■-" represents the Pr of x=0 ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature curve;

"-●-" represent the Pr of x=0.02 ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature curve;

"-▲-" represent the Pr of x=0.04 ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature curve;

"--" represents the Pr of x=0.06 ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature curve;

"-◆-" represent the Pr of x=0.08 ₂Fe _17-xCo _xIsothermal magnetic entropy change～temperature curve;

"-◇-" represents the isothermal magnetic entropy change～temperature curve of comparative example rare metal Gd.

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention is done further detailed description, but embodiments of the present invention are not limited thereto.

Embodiment 1

Step 1: Pr, Fe are pressed Pr ₂Fe ₁₇The ratio batching of (atomic ratio), the excessive as required interpolation 5% of rare earth metal Pr (atomic percent) compensates volatilization and the scaling loss in the fusion process;

Step 2: the raw material that step 1 prepares is put into arc furnace, be evacuated to 10 ^-1More than the Pa, with filling a little less than 1 atmospheric high-purity argon gas behind the high-purity argon cleaning burner hearth, melt back is 4 times under the high-purity argon gas protection, becomes the uniform button-type ingot casting of composition after the cooling;

Step 3: the ingot casting after the melting is encased with the tantalum paper tinsel, be sealed in the quartz glass tube that vacuumizes, annealing in process is 168 hours under the 1173K temperature, in the entry of quenching fast afterwards.

The sample that makes like this proves water chestnut side Th through X-ray diffraction _2Zn ₁₇The type structure be similar to single-phase material, its matrix is the Pr of 2:17 type ₂Fe ₁₇Phase has a spot of 1:7 type second to have (seeing shown in Figure 1) mutually simultaneously.With near the isothermal magnetization curve (see Fig. 2 (a)) of SQUID magnetometer survey Curie temperature, near the intensification step-length the Curie temperature is 5K, and all the other warm area intensification step-lengths are 10K, and field scan speed is slowly to the condition that is enough to satisfy isothermal.

Concern according to Maxwell: $\mathrm{\ΔS}(T,H)=-{\∫}_0^H{\left(\frac{\∂M(T,H)}{\∂T}\right)}_H\mathrm{dH}$ , can become from isothermal magnetization curve calculation magnetic entropy.The magnetic entropy that calculates becomes the relation of Δ SM and temperature T and sees Fig. 3 (a).Obviously, (Δ SM)～T curve is typical λ shape, and magnetic entropy becomes peak value near Curie temperature (Tc=293K), and the Pr of x=0 is described ₂Fe _17-xCo _xCompound belongs to second-order phase transistion in the phase transformation that Curie point takes place.

Measurement result sees Table 1, by table 1 as seen, the magnetic entropy at this sample Curie temperature place under 2T and the effect of 5T external magnetic field become be respectively-Δ SM=2.78J/ (kgK) ,-Δ SM=5.27J/ (kgK).

Embodiment 2

Step 1: Pr, Fe, Co are pressed Pr ₂Fe _16.98Co _0.02The ratio batching of (atomic ratio), the excessive as required interpolation 5% of rare earth metal Pr (atomic percent) compensates volatilization and the scaling loss in the fusion process;

Step 2 and step 3 are with embodiment 1, and the sample that makes like this proves Th through X-ray diffraction ₂Zn ₁₇Type water chestnut square structure, its matrix are the Pr of 2:17 type ₂(Fe, Co) ₁₇Phase has a spot of 1:7 type second to have (seeing shown in Figure 1) mutually simultaneously.With near the isothermal magnetization curve (see Fig. 2 (b)) of SQUID magnetometer survey Curie temperature, according to the Maxwell relation, the magnetic entropy that calculates becomes the relation of Δ SM and temperature T and sees Fig. 3 (b).Obviously, (Δ SM)～T curve is typical λ shape, and magnetic entropy becomes peak value near Curie temperature, and measurement result sees Table 1.By table 1 as seen, the Pr of x=0.02 ₂Fe _17-xCo _xThe magnetic entropy at compound sample Curie temperature place under 2T and the effect of 5T external magnetic field become be respectively-Δ SM=2.88J/ (kgK) ,-Δ SM=5.51J/ (kgK).

Embodiment 3

Pr, Fe, Co are pressed Pr ₂Fe _16.96Co _0.04The ingredient composition of (atomic ratio), preparation technology is with embodiment 2, and the sample that makes like this proves water chestnut side Th through X-ray diffraction ₂Zn ₁₇The type structure be similar to single-phase material, its matrix is the Pr of 2:17 type ₂(Fe, Co) ₁₇Phase has a spot of 1:7 type second to have (seeing shown in Figure 1) mutually simultaneously.With near the isothermal magnetization curve (see Fig. 2 (c)) of SQUID magnetometer survey Curie temperature, wherein near the intensification step-length the Curie temperature is 5K, and all the other warm area intensification step-lengths are 10K, and field scan speed is slowly to the condition that is enough to satisfy isothermal.

Concern according to Maxwell: $\mathrm{\ΔS}(T,H)=-{\∫}_0^H{\left(\frac{\∂M(T,H)}{\∂T}\right)}_H\mathrm{dH}$ , can calculate the Pr of x=0.04 from the isothermal magnetization opisometer of Fig. 2 (c) ₂Fe _17-xCo _xThe magnetic entropy of compound sample becomes, and the result who obtains is shown in Fig. 3 (c).The magnetic entropy change that the Curie temperature place measures under 2T and the effect of 5T external magnetic field the results are shown in table 1.

Embodiment 4

Pr, Fe, Co are pressed Pr ₂Fe _16.94Co _0.06The ingredient composition of (atomic ratio), preparation technology is with embodiment 2, and the sample that makes like this proves Th through X-ray diffraction ₂Zn ₁₇Type water chestnut square structure, its matrix are the Pr of 2:17 type ₂(Fe, Co) ₁₇Phase has a spot of 1:7 type second to have (seeing shown in Figure 1) mutually simultaneously.With near the isothermal magnetization curve (see Fig. 2 (d)) of SQUID magnetometer survey Curie temperature, the magnetic entropy that calculates becomes the relation of Δ SM and temperature T and sees Fig. 3 (d).Obviously, (Δ SM)～T curve is typical λ shape, and magnetic entropy becomes peak value near Curie temperature, and the Pr of x=0.06 is described ₂Fe _17-xCo _xCompound belongs to second-order phase transistion in the phase transformation that Curie point takes place.

The magnetic entropy change that the Curie temperature place measures under 2T and the effect of 5T external magnetic field the results are shown in table 1, the i.e. Pr of x=0.06 ₂Fe _17-xCo _xThe magnetic entropy at compound sample Curie temperature place under 2T and the effect of 5T external magnetic field become be respectively-Δ SM=2.89J/ (kgK) ,-Δ SM=5.49J/ (kgK).

Embodiment 5

Pr, Fe, Co are pressed Pr ₂Fe _16.94Co _0.08The ingredient composition of (atomic ratio), preparation technology is with embodiment 2, and the sample that makes like this proves water chestnut side Th through X-ray diffraction ₂Zn ₁₇The type structure be similar to single-phase material, its matrix is the Pr of 2:17 type ₂(Fe, Co) ₁₇Phase has a spot of 1:7 type second to have (seeing shown in Figure 1) mutually simultaneously.With near the isothermal magnetization curve (see Fig. 2 (e)) of SQUID magnetometer survey Curie temperature.The magnetic entropy that calculates according to Maxwell relation becomes the relation of Δ SM and temperature T and sees Fig. 3 (e), and measurement result sees Table 1, i.e. the Pr of x=0.08 ₂Fe _17-xCo _xThe magnetic entropy at compound sample Curie temperature place under 2T and the effect of 5T external magnetic field become be respectively-Δ SM=2.7J/ (kgK) ,-Δ SM=5.35J/ (kgK).

Table 1:

The embodiment numbering	Atomic percent	Curie temperature Tc (K)	Magnetic entropy change-Δ S J/ (kgK) (T=Tc; H=2T)	Magnetic entropy change-Δ S J/ (kgK) (T=Tc; H=5T)
					1	Pr 2Fe 17	293	2.77	5.27
2	Pr 2Fe 16.98Co 0.02	295	2.88	5.51
					3	Pr 2Fe 16.96Co 0.04	300	3.02	5.82
4	Pr 2Fe 16.94Co 0.06	306	2.89	5.49
					5	Pr 2Fe 16.92Co 0.08	310	2.7	5.35

Utilize mean field approximation, near Curie temperature, the relation that magnetic entropy becomes (Δ SM) and external magnetic field can be expressed as (Δ SM)～H2/3, is also referred to as the H2/3 law that magnetic entropy becomes.Fig. 4 has provided Pr ₂Fe _17-xCo _x(the Δ SM) of compound is to the dependence of H2/3.(Δ SM) shows Pr to the good linear relation of H2/3 ₂Fe _17-xCo _xThe magnetic moment of the 3d element in the compound has the local feature.

Fig. 5 has provided Pr ₂Fe _17-xCo _xThe isothermal magnetic entropy of compound becomes the contrast with Gd.The magnetic entropy of Gd becomes under 2T and the 5T external magnetic field | Δ S _M| be respectively 4.15 and 8.5J/ (kgK), for Pr ₂Fe _17-xCo _xSeries compound, its magnetic entropy become that (H=0～2.0T) reaches 65～73% of Metal Gd under changing at low; But (H=0～5.0T) only reaches 63～68% of Metal Gd under High-Field changes.And cost is about 1/10 of Metal Gd, thus have the very high ratio of performance to price, and near Curie temperature refrigeration warm area broad.

Claims (2)

1, a kind of rare earth-iron base room temperature magnetic refrigerating material, its chemical general formula is: Pr ₂Fe _17-xCo _x, 0≤x in the formula＜0.1.

2, the preparation method of the described rare earth-iron base room temperature magnetic refrigerating material of claim 1 comprises the steps:

(1) presses Pr ₂Fe _17-xCo _xThe chemical formula weighing mixes rare earth metal Pr, transition-metal Fe and Co raw material, wherein, the excessive interpolation 5～7.5% of rare earth metal Pr, described percentage is atomic percent;

(2) the above-mentioned raw material for preparing is put into vacuum arc furnace ignition or induction heater, is evacuated to more than the 10-1Pa, clean burner hearth with high-purity argon after, charge into be lower than 1 atmospheric high-purity argon gas and under its protection melt back obtain the uniform alloy cast ingot of composition;

(3) with the vacuum annealing 0～200 hour under 1123K～1273K of above-mentioned alloy cast ingot, take out in the entry of quenching fast then, make rare earth-iron base room temperature magnetic refrigerating material Pr ₂Fe _17-xCo _x

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