CN103205590B - 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

Magnetic refrigeration is novel Refrigeration Technique, relates to the refrigeration market that refrigerator, air-conditioning etc. are huge.Adopt magneticsubstance as refrigeration working medium, freezed by magnetothermal effect, namely outwardly release heat during magnetic refrigerating material isothermal magnetization, and reach refrigeration from extraneous draw heat during adiabatic demagnetization.Because it is efficient, energy-conservation, do not produce Greenhouse effect and become the following technology being hopeful alternative traditional vapor 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 obtain and develop faster and study.Not only there is giant magnetio-caloric effects due to it in ferromanganese phosphorus germanium (MnFePGe) based compound, and has the features such as abundant starting material, low production cost and non-environmental-pollution and become the New Magnetic Field Controlled refrigerating material being hopeful to obtain practical application most.There is first-order phase transition in MnFePGe based compound, magnetic phase transition can be induced by externally-applied magnetic field near Curie temperature (Tc), when near Curie temperature applies magnetic field, is ferromagnetic phase by paramagnetic phase in version, material exothermic; Removing externally-applied magnetic field, is paramagnetic phase by ferromagnetic phase in version, and material absorbs heat.Producing giant magnetio-caloric effects thus, there is larger magnetic entropy and becomes in material.By regulating Mn/Fe ratio and P/Ge than the Curie temperature Tc that can regulate MnFePGe based material, making it to be close to or higher than room temperature and being beneficial to practical application.Preparing MnFePGe based material at present is both at home and abroad all the method adopting ball mill ball milling+sintering, adopts elemental powders to carry out ball milling, forms Fe ₂p phase, then sintering obtains the good MnFePGe compound of magnetic heating performance.But our research finds, the powder after ball milling is nano particle, does not substantially have magnetic heating performance, although and compound crystal grain after sintering has been grown up, but still there is the nanocrystal that cannot produce magnetic phase transition, affect the raising of magnetic heating performance.

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

Summary of the invention

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

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 comprises the following steps successively:

(1) raw materials is business manganese, iron, phosphor powder, germanium fragment, purity is 99.9 ~ 99.9999wt%, adopt the method for mechanical alloying by starting material continuous ball milling 0.5 ~ 4 hour, material is made tentatively to 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, basically forms Fe ₂p crystalline structure phase, the average grain size of powder is approximately 30 nanometers.

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

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 to scan sample, obtain composition profiles figure; Adopt Netzsch204F1 differential scanning calorimeter (DSC) to test sample, utilize the heat flow versus 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 calculated.The thermal capacitance that wherein Cp is magnetic field when being 0.

Experiment proves, the Mn prepared by the method _(2-x)fe _(x)p _(1-y)ge _(y)magnetic refrigerating material, sample composition is evenly distributed, and is conducive to the transformation of the cis-ferromagnetic phase of near Curie temperature, the Entropy Changes of material is increased, improves the refrigeration capacity of material, can be applicable in magnetic Refrigeration Technique.

Accompanying drawing illustrates:

Fig. 1: Mn _1.2fe _0.8p _0.73ge _0.27the XRD figure of ball-milled powder;

Fig. 2 a: Mn in embodiment 1 _1.1fe _0.9p _0.8ge _0.2the scanning electron microscope (SEM) photograph of direct sintering sample;

Fig. 2 b: Mn in embodiment 1 _1.1fe _0.9p _0.8ge _0.2the scanning electron microscope (SEM) photograph of powder vacuum preannealing then sintered sample in SPS;

Fig. 2 c: Mn in embodiment 1 _1.1fe _0.9p _0.8ge _0.2the Entropy Changes figure of direct sintering and powder vacuum preannealing then sintered sample in SPS;

Fig. 3 a: Mn in embodiment 2 _1.2fe _0.8p _0.73ge _0.27the scanning electron microscope (SEM) photograph of direct sintering sample;

Fig. 3 b: Mn in embodiment 2 _1.2fe _0.8p _0.73ge _0.27powder is first at atmosphere (N ₂) protect lower preannealing and then the scanning electron microscope (SEM) photograph with SPS sintered sample;

Fig. 3 c: Mn in embodiment 2 _1.2fe _0.8p _0.73ge _0.27direct sintering and powder are first at atmosphere (N ₂) protect lower preannealing and then the Entropy Changes figure with SPS sintered sample.

Fig. 4: Mn in embodiment 3 _1.2fe _0.8p _0.76ge _0.24direct sintering and powder be preannealing and then the Entropy Changes figure with SPS sintered sample under atmosphere (Ar) protection first

Embodiment

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

Example 1. adopts starting material to be manganese powder, 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 by starting material ball milling 4 hours in ball mill, then ball-milled powder is placed in SPS system is incubated 30min under 400 DEG C of vacuum condition, then sinter, then be incubated.Sintering vacuum tightness 5Pa, sintering temperature is 880 DEG C, and sintering pressure is 10MPa, and heat-up rate is 60 DEG C/min, is incubated 30min after being warming up to 880 DEG C, cools to the demoulding after room temperature with the furnace, obtains cylindrical block sample.Respectively direct sintering sample and powder preannealing sample are scanned under surface sweeping Electronic Speculum.The scanning electron microscope (SEM) photograph of sample and Entropy Changes curve respectively as Fig. 2 a, shown in 2b, 2c.

Example 2. adopts starting material to be manganese powder, 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 are put into ball mill ball milling 0.5 hour, then ball-milled powder is put into N ₂at 600 DEG C of insulation 2min in the stove of atmosphere protection, then die-filling rear SPS sinters, then is incubated.Sintering vacuum tightness 6Pa, sintering temperature is 950 DEG C, and sintering pressure is 40MPa, and heat-up rate is 120 DEG C/min, is incubated 2min after being warming up to 950 DEG C, cools to the demoulding after room temperature with the furnace, obtains cylindrical block sample.Respectively direct sintering sample and powder preannealing sample are scanned.The scintigram of sample and Entropy Changes respectively as Fig. 3 a, shown in 3b, 3c.

Example 3. adopts starting material to be manganese powder, 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 are put into ball mill ball milling 2 hours, then stove ball-milled powder being put into Ar atmosphere protection is at 500 DEG C of insulation 15min, and then die-filling rear SPS sinters, then is incubated.Sintering vacuum tightness 6Pa, sintering temperature is 920 DEG C, and sintering pressure is 25MPa, and heat-up rate is 90 DEG C/min, is incubated 20min after being warming up to 920 DEG C, cools to the demoulding after room temperature with the furnace, obtains cylindrical block sample.The Entropy Changes of sample as shown in Figure 4.

With the Mn that example 1 is prepared _1.1fe _0.9p _0.8ge _0.2sample is example, known by the scanning electron microscope (SEM) photograph of sample, powder preannealing sample is larger than direct sintering sample grain-size, grain-size relatively evenly and the composition profiles of material evenly, as can be seen from Entropy Changes-temperature curve, 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 adds 19.4%.With the Mn that example 2 is prepared _1.2fe _0.8p _0.73ge _0.27sample is example, by known to Sample Scan, identical with example 1, powder preannealing sample is larger than direct sintering sample grain-size, even grain size and the composition profiles of material evenly, as can be seen from Entropy Changes-temperature curve, 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 adds 31.2%.With the Mn that example 3 is prepared _1.2fe _0.8p _0.76ge _0.24sample is example, identical with front two examples, and first sinter through preannealing the Sample entropy apparition obtained again and increase, the Entropy Changes of direct sintering sample and powder preannealing sample is respectively 20.2J/KgK and 23.6J/KgK, and the Entropy Changes of powder preannealing sample adds 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 comprising the following steps:

(1) raw materials was manganese, iron, phosphor powder, germanium fragment, and purity is 99.9 ~ 99.9999wt%, by starting material continuous ball milling 0.5 ~ 4 hour;

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