KR100530872B1 - Preparation method for transition metal pnictide powder by reaction milling - Google Patents

Abstract

The present invention relates to transition metal powders such as titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) and phosphorus ( The present invention relates to a method of producing a transition metal pnictide powder by reacting a group VB element powder such as P) and arsenic (As) by a reaction milling method.

According to the present invention, the step of mixing the transition metal powder and the group VB element powder in an atomic mixing ratio of 0.5: 1 to 4: 1; Injecting the mixture into a reaction vessel with a diameter of 5 to 30 mm; Filling the reaction vessel with argon (Ar); In addition to the high-energy ball milling of the mixture, if necessary, the present invention provides a method for preparing a transition metal nickide powder by a reaction mill comprising a heat treatment step of a reaction powder for removing stress and defects in the powder.

Therefore, the present invention can be prepared from the transition metal powder and the group VB element powder as a raw material and the reaction milling to produce the transition metal nickide powder in a short time at room temperature.

Description

Preparation method for transition metal pnictide powder by reaction milling

The present invention relates to transition metal powders such as titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) and phosphorus ( The present invention relates to a method of producing a transition metal pnictide powder by reacting a group VB element powder such as P) and arsenic (As) by a reaction milling method.

Recently, with the discovery of various metal compounds with a large magnetocaloric effect, interest in magnetic coolers that can use refrigerants that are more efficient than current cooling methods using gas compression cycles and does not cause any air pollution problems is increasing. have.

The core of this self-cooling technology is to find a material having a high magnetic heat effect. Especially, the development of a material having a high magnetic heat effect near room temperature has been applied to various products such as refrigerators and air conditioners using gas compression cycle cooling methods which have been widely used until now. It will be possible to apply the magnetic cooler, so the ripple effect will be very large throughout the industry.

Among the few materials currently known to have high magnetic thermal effects at room temperature, the most widely known is Gd ₅ (Si _x Ge _1-x ) ₄ , which has been studied for a long time at the Ames Institute in the United States. Cooler prototypes have been developed [KA Gschneidner, Jr. and VK Pecharsky, "Magnetocaloric Materials," Annual Review of Materials Science, 30, (2000) 387-429].

However, given that gadolinium (Gd) reserves on the planet are very limited, it is also very important to pay attention to other materials with high room temperature magnetothermal effects. In this respect, transition metal nickides such as MnFeP _1-x As _x are very promising because of their excellent self-heating effect and abundant raw materials and low price [O.Tegus, E. Bruck, KHJ Buschow and FR de Boer, "Transition-Metal-Based Magnetic Refrigerants for Room-Temperature Applications," Nature, 45, (2002) 150-152].

However, the transition metal nickide has a disadvantage that it is not suitable for mass production because P or As has a problem of gradually reacting for several days to several weeks at a high temperature in a vacuum-sealed state due to the property of sublimation above 600 ° C.

Accordingly, the present invention is to solve the above problems, the present invention is a novel method for producing a transition metal nickide powder using high-energy ball milling (transition metal powder and group VB element powder) The purpose is to economically prepare the transition metal nickide powder by reacting in a short time of about several hours at room temperature.

As a technical idea for achieving the above object of the present invention

Mixing the transition metal powder and the group VB element powder in an atomic mixing ratio of 0.5: 1 to 4: 1;

Injecting the mixture into a reaction vessel with a diameter of 5 to 30 mm;

Filling the reaction vessel with argon (Ar);

In addition to the high-energy ball milling of the mixture, if necessary, it provides a method for producing a transition metal nickide powder by reaction milling comprising a heat treatment step of a reaction powder for removing stresses and defects in the powder.

Hereinafter, with reference to the accompanying drawings, the configuration and operation of the embodiment of the present invention will be described in detail.

1 is a process flowchart showing the manufacturing process of the present invention.

First, a transition metal powder having a purity of 95% or more and a particle size of 1 mm or less and a group VB element powder having a purity of 95% or more and a particle size of 1 mm or less are mixed at an atomic mixing ratio of 0.5: 1 to 4: 1 (S10).

At this time, the transition metal is Ti, V, Cr, Mn, Fe, Co, Ni, Cu or a state in which two or more thereof are mixed, the group VB element is P, As or P and As and a state of mixed. In addition, the reason for limiting the atomic mixing ratio of the transition metal powder and the group VB element powder to 0.5: 1 to 4: 1 is that the transition metal and group VB element powder that does not participate in the reaction other than the transition metal nickide if it is out of this composition range. Because this happens too much.

The mixture is placed in a reaction vessel (tool) made of tool steel, stainless steel, cemented carbide, silicon nitride, alumina or zirconia. ball) and 1: 1 to 1: 100 in a weight ratio (S20). At this time, the reason for limiting the diameter of the ball to 5 ~ 30 mm is that if the diameter of the ball is 5 mm or less, the strength of milling is weak This is because the reaction does not proceed, and if the thickness is 30 mm or more, the strength of milling is so strong that the material of the ball is mixed into the synthetic powder as impurities by the wear of the ball.

After that, argon (Ar) is filled into the reaction vessel (S30), and then shaker shaker (shaker mill), vibratory mill (vibratory mill), planetary mill (planetary mill) or attritor (attritor mill) using a high It consists of a process (S40) for the energy ball milling.

Here, the reason for limiting the weight ratio of the raw material powder and the ball from 1: 1 to 1: 100 is that when the weight ratio of the raw material powder and the ball is 1: 1 or less, milling is not effectively made in a short time, and 1: 100 or more. This is because the amount of impurities mixed by wear of the ball and the container increases.

The reason why the reaction vessel is filled with Ar is to prevent oxidation and nitriding of the raw powder in the air during milling. Balls used in high energy ball milling may have one diameter or may be used in a combination of balls having two or more diameters.

Thereafter, the temperature of the surface of the reaction vessel is measured and recorded using a non-contact infrared thermometer (S50). In the milling process, as shown in FIG. 2, a sharp increase in the surface temperature can be observed.

Here, the sudden rise in temperature is caused by the heat generated when the transition metal nickide is formed by reacting the raw material powder in the reaction vessel, and then the temperature decreases slowly after the reaction is completed to escape the heat out of the vessel through heat transfer. Because.

The rapid temperature rise is influenced by the weight ratio of the raw material powder and the ball, but is generally observed between 1 to 3 hours after the start of milling. By stopping the milling between 1 minute and 24 hours after the rapid temperature rise and recovering the synthesized powder (S60), the transition metal nickide powder is prepared in a short time at room temperature (S70). The reason for limiting to minutes to 24 hours is that unreacted raw material powders (transition metals, group VB elements) that the reaction did not proceed completely when the recovery time of the powder is 1 minute or less, and wear of the ball when 24 hours or more This is because the material of the balls is mixed with impurities.

In addition, stopping the high energy ball milling within a certain time after the rapid exothermic reaction is to prevent the mixing of impurities in the ball and the container. If necessary, the powder obtained by milling is heat-treated at 400 to 1200 ° C. for 1 to 24 hours. At this time, the heat treatment temperature is limited to 400 to 1200 ° C. The reason is that if the temperature is 400 ° C. or less, diffusion does not occur actively, so that the inside of the powder This is because there is no effect of removing stress and defects, and if the temperature is 1200 ° C or higher, there is a fear that the phosphorus (P) and arsenic (As) of the nickide may rise. Similarly, the reason for limiting the heat treatment time to 1 to 24 hours is that there is no effect of removing internal stresses and defects when the heat treatment time is less than 1 hour, and phosphorus (P) or arsenic (As) of nickide is more than 24 hours. The temperature increase rate during the heat treatment is maintained at 0.5 ~ 5 ℃ per minute to prevent sublimation of unreacted P or As, the cooling rate is maintained at 0.5 ~ 5 ℃ / minute or quenching do. At this time, the temperature rising temperature and the cooling rate during the heat treatment do not significantly affect the preparation of the transition metal nickide.

<Example 1>

Mn powder having a purity of 99.6%, a particle size of 8 micrometers and a P powder having a purity of 99.5% or more and a particle size of 150 micrometers was an atomic mixing ratio of 2: 1. The mixture was charged together with a 7.9 mm diameter ball made of tool steel and a weight ratio of 10: 1 in a reaction vessel made of tool steel, and then charged with argon into the reaction vessel, followed by high energy ball milling using a shaker mill. The temperature of the reaction vessel surface was measured and recorded using a non-contact infrared thermometer. Milling was stopped 2 hours after the sudden exothermic reaction and the powder was recovered.

Figure 3 shows the X-ray diffraction pattern of the powder before and after high energy ball milling. It can be seen that Mn and P before milling reacted with hexagonal Mn ₂ P after milling.

<Example 2>

Purity 99.6%, Mn powder with a particle size of 8 micrometers, Purity 99.9%, Fe powder with a particle size of 4 micrometers, Purity 99.6%, P powder with a particle size of 10 micrometers and 99% purity, As, with a particle size of 3 micrometers The powder was used for an atomic mixing ratio of 1: 1: 0.5: 0.5.

The mixture was charged together with a 7.9 mm diameter ball made of tool steel and a weight ratio of 10: 1 in a reaction vessel made of tool steel, and then charged with argon into the reaction vessel, followed by high energy ball milling using a shaker mill.

The temperature of the reaction vessel surface was measured and recorded using a non-contact infrared thermometer. Milling was stopped for several hours after the rapid exothermic reaction and powder was recovered. The recovered powder was heat treated at 900 ° C. for 2 hours. The temperature increase rate during the heat treatment was 1 ℃ per minute, the cooling rate was maintained at 1 ℃ per minute. The heat-treated powder was measured for temperature-magnetization curves using a physical property measurement system.

Figure 4 shows the change of the X-ray diffraction pattern with the high energy ball milling time. From the X-ray diffraction pattern of the mixed raw material powder before milling, it can be seen that all the raw material powders except P are made of fine polycrystalline powder of 100 nm or less as crystalline, and P is amorphous.

Until about 100 minutes after the start of milling, only the grain size of Fe, Mn and As was reduced, but no reaction product was formed yet. After 120 minutes, hexagonal MnFeP _0.5 As _0.5 was observed. As the milling continued, no change in structure was observed.

5a to 5c are scanning electron micrographs showing the shape of the powder after milling for 4 hours and 24 hours immediately after the rapid exothermic reaction, respectively. The powder immediately after the rapid exothermic reaction is in the form of agglomerated fine particles of about 1 micrometer or less. After 4 hours of milling, the size and shape of the powder were not significantly different from that of the rapid exothermic reaction, but the particles were more spherical. After 24 hours of milling, the shape of the particles was not significantly different from that of the rapid exothermic reaction or milling for 4 hours, but sometimes coarse particles of several micrometers or more were observed.

Figure 6 shows the change in the average particle size of the powder according to the high energy ball milling time, the average particle size of the powder before the rapid exothermic reaction is about 10 micrometers coarse than the raw material powder, but after the rapid exothermic reaction The average particle size became fine at about 0.3 to 0.4 micrometers and the average particle size did not change significantly even if the milling time increased.

7 shows the temperature-magnetization curve of the powder subjected to heat treatment after high energy ball milling for 4 hours. At 250K near room temperature, it can be seen that a sudden decrease of magnetization value occurs due to ferromagnetic-paramagnetic transformation. A sharp decrease in magnetization indicates that the transformation is a primary transformation.

8 shows the change in entropy calculated from the temperature-magnetization curve. A very large entropy change is observed, indicating that MnFeP _0.5 As _0.5 synthesized by reaction milling exhibits a high magnetocaloric effect.

As described above, according to the production method of the present invention, the transition metal powder and the group VB element powder as a raw material and the reaction milling it can be produced in a short time at room temperature transition metal nickide powder. Compared to the high temperature synthesis method, which is a method for preparing a transition metal nickide powder, it is very economically effective in terms of manufacturing facilities and live cost.

1 is a process flowchart showing the manufacturing process of the present invention.

2 is a graph showing the temperature change of the surface of the reaction vessel according to the high energy ball milling time.

3 is a graph showing the X-ray diffraction pattern change of the powder before and after the high energy ball milling.

4 is a graph showing the change of the X-ray diffraction pattern according to the high energy ball milling time.

Figures 5a to 5c are scanning electron micrographs showing the shape after milling 4 hours and 24 hours immediately after the rapid exothermic reaction, respectively.

Figure 6 is a graph showing the change in the average particle size of the powder with high energy ball milling time.

7 is a view showing a temperature-magnetization curve of the powder subjected to heat treatment after high energy ball milling for 4 hours.

8 shows the change in entropy calculated from the temperature-magnetization curve.

Claims (9)

Mixing the transition metal powder and the group VB element powder in an atomic mixing ratio of 0.5: 1 to 4: 1; Injecting the mixture into a reaction vessel with a diameter of 5 to 30 mm; Filling the reaction vessel with argon (Ar); Preparation of transition metal nickide powder by reaction milling comprising a high energy ball milling of the mixture with rapid exothermic reaction and a heat treatment step of the reaction powder for removing stresses and defects in the powder obtained by the milling. Way. The method of claim 1, wherein the transition metal is Ti, V, Cr, Mn, Fe, Co, Ni, Cu or a mixture of two or more thereof, the Group VB element is P, As or a mixture of P and As Method for producing a transition metal nickide powder by reaction milling, characterized in that. The method of claim 1, wherein the material of the reaction vessel and the ball is any one of tool steel, stainless steel, cemented carbide, silicon nitride, alumina or zirconia. The method of claim 1 or 2, wherein the ratio of the mixture and the ball to be added to the reaction vessel ranges from 1: 1 to 1: 100 by weight ratio. The method of claim 1, wherein the high energy ball milling method uses a shaker mill, a vibration mill, a planetary mill, or an attritor mill. The method of claim 1, wherein the temperature of the surface of the reaction vessel is measured by using a non-contact infrared thermometer to determine whether there is a sudden exothermic reaction and time. 7. The method of claim 1 or 6, wherein the high energy ball milling is stopped and the reaction powder is recovered between 1 minute and 24 hours after the rapid exothermic reaction. The method of claim 1, wherein the powder obtained by milling is subjected to a heat treatment for 1 to 24 hours at a temperature range of 400 to 1200 ° C. delete