CN103205590A - Preparation process of magnetic refrigeration material - Google Patents

Abstract

The invention provides a preparation process of a magnetic refrigeration material. The chemical general formula of the magnetic refrigeration material is Mn(2-x)Fe(x)P(1-y)Ge(y), wherein x ranges from 0.8 to 0.9, and y ranges from 0.2-0.27. The preparation process is characterized by comprising the following steps of: (1) continuously ball-milling raw materials, namely manganese, iron and phosphorus powder and germanium fragments which have the purity of 99.9-99.9999 percent by weight, for 0.5-4 hours; (2) pre-annealing ball-milled powder at 400-600 DEG C in vacuum or at a protective atmosphere for 2-30 minutes, sintering the powder by adopting a discharge plasma sintering technology, wherein the sintering vacuum degree is higher than 6Pa, the temperature increasing speed is 60-120 DEG C/minute, the preserved sintering temperature is 880-950 DEG C after the temperature is increased to sintering temperature, the sintering pressure is 10-40 MPa, and the heat preserving time is 2-30 minutes; and cooling to room temperature with a furnace after the sintering is finished. The preparation process provided by the invention can be used for controlling the grain size of the material by carrying out pre-annealing before the sintering, is more uniform in component distribution, outstandingly enhances the magnetic entropy change and enhances the magnetocaloric effect.

Description

A kind of preparation technology of magnetic refrigerating material

Technical field

The present invention relates to a kind of novel preparation process of magnetic refrigerating material.

Background technology

The magnetic refrigeration is novel Refrigeration Technique, relates to huge refrigeration markets such as refrigerator, air-conditioning.Adopt magneticsubstance as refrigeration working medium, freeze by magnetothermal effect, namely emit heat to the external world during magnetic refrigerating material isothermal magnetization, and reach refrigeration from extraneous draw heat during adiabatic demagnetization.Because it is efficient, energy-conservation, does not produce Greenhouse effect and become the following technology that is hopeful to substitute traditional gas compression refrigeration most.Obviously, the magnetic Refrigeration Technique of energy-conserving and environment-protective all will have very important meaning to society, environment and economy.

In recent years, many materials with room temperature magnetothermal effect have obtained developing faster and studying.Ferromanganese phosphorus germanium (MnFePGe) based compound is because not only there is huge magnetothermal effect in it, and has characteristics such as abundant raw, low production cost and non-environmental-pollution and become the novel magnetic refrigerating material that is hopeful to obtain practical application most.First-order phase transition takes place in the MnFePGe based compound near Curie temperature (Tc), magnetic phase transition can be induced by externally-applied magnetic field, when applying magnetic field near Curie temperature, changes ferromagnetic phase mutually into by paramagnetic, the material heat release; Remove externally-applied magnetic field, by the ferromagnetic paramagnetic phase that changes into mutually, the material heat absorption.Produce huge magnetothermal effect thus, material exists bigger magnetic entropy to become.By regulating Mn/Fe ratio and P/Ge than the Curie temperature Tc that can regulate the MnFePGe based material, make it to be close to or higher than room temperature and be beneficial to practical application.Preparing the MnFePGe based material at present both at home and abroad all is the method that adopts ball mill ball milling+sintering, adopts the simple substance powder to carry out ball milling, forms Fe ₂The P phase, sintering obtains magnetic heating performance MnFePGe compound preferably then.But we discover, the powder behind the ball milling is nano particle, does not have magnetic heating performance substantially, though and the compound crystal grain behind the sintering has been grown up, but still have the nanocrystal can't produce magnetic phase transition, influence the raising of magnetic heating performance.

The present invention carries out preannealing under the certain temperature with ball-milled powder before by sintering, make the grain size of material controlled, and composition profiles is more even, is conducive to the transformation between paramagnetic and the ferromagnetic phase, magnetic entropy is become enlarge markedly, improved the magnetothermal effect of material greatly.Can be applicable in the magnetic Refrigeration Technique.

Summary of the invention

The purpose of this invention is to provide a kind of working temperature near room temperature, Curie temperature is adjustable continuously; In the magnetic field range that permanent magnet can provide, there is big magnetic entropy to become, can be widely used in the novel preparation process of the magnetic refrigerating material of magnetic Refrigeration Technique.

The chemical general formula of magnetic refrigerating material involved in the present invention is: Mn _(2-x)Fe _(x)P _(1-y)Ge _(y), the scope of x is: 0.8～0.9.The scope of y is: 0.2～0.27.

The preparation method of above-mentioned magnetic refrigerating material provided by the present invention adopts mechanical alloying and discharge plasma sintering technique thereafter.It may further comprise the steps successively:

(1) used starting material are commercial manganese, iron, phosphor powder, germanium fragment, purity is 99.9～99.9999wt%, the method that adopts mechanical alloying was with the continuous ball milling of starting material 0.5～4 hour, make material tentatively become phase, its material phase analysis adopts X-ray diffractometer to carry out, Fig. 1 is X-ray diffraction (XRD) collection of illustrative plates of 0.5 hour ball-milled powder, has basically formed Fe ₂P crystalline structure phase, the average grain size of powder is approximately 30 nanometers.

(2) with ball-milled powder preannealing 2～30min under 400～600 ℃ of vacuum or protective atmosphere; adopt discharge plasma sintering technique that powder is carried out sintering; sintering vacuum tightness is higher than 6Pa; heat-up rate is 60～120 ℃/min; be incubated after being warming up to sintering temperature, sintering temperature is 880～950 ℃, and sintering pressure is 10～40MPa; soaking time is 2～30min, cools to room temperature with the furnace after sintering is finished.

Preannealing can carry out at independent annealing furnace or in discharging plasma sintering equipment SPS system.

Discharging plasma sintering equipment specifically adopts (DR.Sinter SPS-3.2-MV).

Adopt FEI quanta200 scanning electron microscope that sample is scanned, obtain composition profiles figure; Adopt Netzsch204F1 differential scanning calorimeter (DSC) that sample is tested, utilize the hot-fluid-temperature curve of gained to adopt equation

$\mathrm{\ΔS}=S_{T_2}-S_{T_1}=\underset{T_1}{\overset{T_2}{\∫}}\frac{C_p}{T}\mathrm{dT}$

The entropy that calculates.Wherein Cp is that magnetic field is 0 o'clock thermal capacitance.

Experiment showed, the Mn with this method preparation _(2-x)Fe _(x)P _(1-y)Ge _(y)Magnetic refrigerating material, sample composition is evenly distributed, and is conducive near the transformation of suitable Curie temperature-ferromagnetic phase, and the Entropy Changes of material is increased, and has improved the refrigeration capacity of material, can be applicable in the magnetic Refrigeration Technique.

Description of drawings:

Fig. 1: Mn _1.2Fe _0.8P _0.73Ge _0.27The XRD figure of ball-milled powder;

Mn among Fig. 2 a: the embodiment 1 _1.1Fe _0.9P _0.8Ge _0.2The sem photograph of direct sintering sample;

Mn among Fig. 2 b: the embodiment 1 _1.1Fe _0.9P _0.8Ge _0.2Powder is the vacuum preannealing sem photograph of sintered sample then in SPS;

Mn among Fig. 2 c: the embodiment 1 _1.1Fe _0.9P _0.8Ge _0.2Direct sintering and powder be the vacuum preannealing Entropy Changes figure of sintered sample then in SPS;

Mn among Fig. 3 a: the embodiment 2 _1.2Fe _0.8P _0.73Ge _0.27The sem photograph of direct sintering sample;

Mn among Fig. 3 b: the embodiment 2 _1.2Fe _0.8P _0.73Ge _0.27Powder is earlier at atmosphere (N ₂) the following preannealing and then with the sem photograph of SPS sintered sample of protection;

Mn among Fig. 3 c: the embodiment 2 _1.2Fe _0.8P _0.73Ge _0.27Direct sintering and powder are earlier at atmosphere (N ₂) the following preannealing and then with the Entropy Changes figure of SPS sintered sample of protection.

Mn among Fig. 4: the embodiment 3 _1.2Fe _0.8P _0.76Ge _0.24Direct sintering and powder be preannealing and then with the Entropy Changes figure of SPS sintered sample under atmosphere (Ar) protection earlier

Embodiment

Below in conjunction with drawings and Examples the present invention is described in further details.

It is manganese powder that example 1. adopts starting material, iron powder (purity 〉=99.99%), red phosphorus powder (purity 〉=99.9999%) and germanium wafer (purity 〉=99.9999%).Be Mn according to nominal composition _1.1Fe _0.9P _0.8Ge _0.2Stoicheiometry with starting material ball milling 4 hours in ball mill, again ball-milled powder is placed the SPS system under 400 ℃ of vacuum conditions, to be incubated 30min, carry out sintering then, again insulation.Sintering vacuum tightness 5Pa, sintering temperature is 880 ℃, and sintering pressure is 10MPa, and heat-up rate is 60 ℃/min, is incubated 30min after being warming up to 880 ℃, cools to the demoulding after the room temperature with the furnace, obtains the cylindrical block sample.Respectively direct sintering sample and powder preannealing sample are scanned under the surface sweeping Electronic Speculum.The sem photograph of sample and Entropy Changes curve are respectively as Fig. 2 a, and 2b is shown in the 2c.

It is manganese powder that example 2. adopts starting material, iron powder (purity 〉=99.99%), red phosphorus powder (purity 〉=99.9999%) and germanium wafer (purity 〉=99.9999%).Be Mn according to nominal composition _1.2Fe _0.8P _0.73Ge _0.27Stoicheiometry starting material were put into the ball mill ball milling 0.5 hour, again ball-milled powder is put into N ₂At 600 ℃ of insulation 2min, carry out sintering with SPS after adorning mould then, again insulation in the stove of atmosphere protection.Sintering vacuum tightness 6Pa, sintering temperature is 950 ℃, and sintering pressure is 40MPa, and heat-up rate is 120 ℃/min, is incubated 2min after being warming up to 950 ℃, cools to the demoulding after the room temperature with the furnace, obtains the cylindrical block sample.Respectively direct sintering sample and powder preannealing sample are scanned.The scintigram of sample and Entropy Changes are respectively as Fig. 3 a, and 3b is shown in the 3c.

It is manganese powder that example 3. adopts starting material, iron powder (purity 〉=99.99%), red phosphorus powder (purity 〉=99.9999%) and germanium wafer (purity 〉=99.9999%).Be Mn according to nominal composition _1.2Fe _0.8P _0.76Ge _0.24Stoicheiometry starting material were put into the ball mill ball milling 2 hours, the stove of again ball-milled powder being put into the Ar atmosphere protection is at 500 ℃ of insulation 15min, carries out sintering with SPS, insulation again after adorning mould then.Sintering vacuum tightness 6Pa, sintering temperature is 920 ℃, and sintering pressure is 25MPa, and heat-up rate is 90 ℃/min, is incubated 20min after being warming up to 920 ℃, cools to the demoulding after the room temperature with the furnace, obtains the cylindrical block sample.The Entropy Changes of sample as shown in Figure 4.

The Mn for preparing with example 1 _1.1Fe _0.9P _0.8Ge _0.2Sample is example, sem photograph by sample as can be known, powder preannealing sample is bigger than direct sintering sample grain-size, grain-size is relatively more even and composition profiles material is more even, from Entropy Changes-temperature curve as can be seen, the Entropy Changes of direct sintering sample and powder preannealing sample is respectively 22.2J/KgK and 26.5J/KgK, and the Entropy Changes of powder preannealing sample has increased by 19.4%.The Mn for preparing with example 2 _1.2Fe _0.8P _0.73Ge _0.27Sample is example, by sample is scanned as can be known, identical with example 1, powder preannealing sample is bigger than direct sintering sample grain-size, the composition profiles of even grain size and material is more even, from Entropy Changes-temperature curve as can be seen, the Entropy Changes of direct sintering sample and powder preannealing sample is respectively 22.4J/KgK and 29.4J/KgK, and the Entropy Changes of powder preannealing sample has increased by 31.2%.The Mn for preparing with example 3 _1.2Fe _0.8P _0.76Ge _0.24Sample is example, and is identical with preceding two examples, earlier through preannealing again the sample Entropy Changes that obtains of sintering obviously increase, the Entropy Changes of direct sintering sample and powder preannealing sample is respectively 20.2J/KgK and 23.6J/KgK, the Entropy Changes of powder preannealing sample has increased by 16.8%.

Claims (1)

1. a kind of preparation technology of magnetic refrigerating material, the chemical general formula of described magnetic refrigerating material is: Mn _(2-x)Fe _(x)P _(1-y)Ge _(y), the scope of x is: the scope of 0.8～0.9, y is: 0.2～0.27; It is characterized in that may further comprise the steps:

(1) used starting material were manganese, iron, phosphor powder, germanium fragment, and purity is 99.9～99.9999wt%, with the continuous ball milling of starting material 0.5～4 hour;

(2) with ball-milled powder preannealing 2～30min under 400～600 ℃ of vacuum or protective atmosphere; adopt discharge plasma sintering technique that powder is carried out sintering; sintering vacuum tightness is higher than 6Pa; heat-up rate is 60～120 ℃/min; be incubated after being warming up to sintering temperature, sintering temperature is 880～950 ℃, and sintering pressure is 10～40MPa; soaking time is 2～30min, cools to room temperature with the furnace after sintering is finished.

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