KR100896454B1 - Method for manufacturing magnesium based hydrogen storage alloy powder with fine-crystalline phase showing fast dehydriding kinetic and magnesium based hydrogen storage alloy powder with fine-crystalline phase showing fast dehydriding kinetic made of the method - Google Patents

Abstract

The present invention is a step of rapidly solidifying the molten magnesium-based alloy, heat-treating the solidified magnesium-based alloy to produce a magnesium-based alloy having a fine crystal phase, ball milling the heat-treated fine crystalline magnesium-based alloy as a fine powder It relates to a method for producing a fine magnesium hydrogen storage alloy powder having a fine crystal phase composed of a grinding step.

According to the present invention, using a low-cost magnesium as a main raw material to produce a fine magnesium-based hydrogen storage alloy powder having a fine crystal phase can improve the dehydrogenation rate at 300 ℃.

Hydrogen storage alloy, magnesium, hydrogen absorption rate, rapid solidification, activation

Description

METHOD FOR MANUFACTURING MAGNESIUM BASED HYDROGEN STORAGE ALLOY POWDER WITH FINE-CRYSTALLINE PHASE SHOWING FAST DEHYDRIDING KINETIC AND MAGNESIUM BASED HYDROGEN STORAGE ALLOY POWDER WITH FINE-CRYSTALLINE PHASE SHOWING FAST DEHYDRIDING KINETIC MADE OF THE METHOD}

1 is a transmission electron microscope microstructure photograph of 76.5% by weight Mg ~ 23.5% by weight Ni alloy heat-treated after rapid solidification.

The present invention relates to a method of manufacturing magnesium-based hydrogen storage alloy powder having an improved dehydrogenation rate at 300 ° C. or lower, more specifically, rapidly solidifying a magnesium-based alloy in a molten state and heat-treating the solidified magnesium-based powder. The present invention relates to a method for producing a fine magnesium hydrogen storage alloy powder having a fine crystal phase consisting of a step of manufacturing a magnesium-based alloy having a fine crystal phase, and milling the heat-treated magnesium-based alloy into a fine powder.

Hydrogen storage techniques include compressed gas storage, liquid hydrogen storage, and hydrogen storage alloys. Compressor storage method has a relatively low storage density per volume and there is a risk of using a high pressure gas container.In the case of liquid hydrogen storage method, the storage density per volume is larger than the compressor storage method, but it is below the liquefaction point of hydrogen below minus 235 ℃. Special insulation systems are required because of the need to maintain and are unsuitable for long term storage. On the other hand, the storage method using the hydrogen storage alloy has the advantages of high storage density per volume, easy storage for a long time, and high pressure storage, which is a safe storage method. Hydrogen storage alloys include FeTi, LaNi, V-Ti-Cr, magnesium, etc., but the theoretical hydrogen storage capacity is the highest magnesium-based, light and rich raw materials. Despite the advantages of magnesium-based hydrogen storage alloys, however, magnesium has strong ionic bonds with hydrogen, which makes it difficult to absorb and release hydrogen because of its high hydride stability and low hydrogen diffusion rate. As a result, research on the optimal production process to be applied to the production of magnesium-based alloys is insufficient.

As a study for increasing the hydrogenation reaction rate to magnesium, there has been a study to increase the hydrogen absorption rate by adding an oxide. However, in this trial, the absorption rate increases at a temperature in the range of 320 ° C. to 350 ° C., but the hydrogen release rate is low at 300 ° C. or lower. This is uneconomical due to the long milling time required.

On the other hand, the hydrogen-sintered alloy powder may be prepared by casting and grinding a magnesium-nickel-based alloy, but there are limitations in increasing hydrogen absorption rate and release rate due to segregation and coarse phases during casting. Amorphous alloys prepared by rapid solidification of a molten magnesium-nickel-based alloy for the purpose of suppressing segregation have a disadvantage in that the hydrogen release rate is low because there is little or no interfacial interface between phases that are easy for hydrogen diffusion.

The present invention has been made to solve the above problems, an object of the present invention is to provide a fine magnesium hydrogen storage alloy powder having a fine crystal phase with a high hydrogen release rate even at 300 ℃ as magnesium-based alloy powder.

In order to achieve the above object, a method for preparing a magnesium alloy powder having a high hydrogen absorption rate according to the present invention includes the steps of rapidly solidifying a magnesium alloy in a molten state, and heat treating the solid magnesium powder to have a fine crystal phase. Manufacturing a magnesium-based alloy, characterized in that it comprises a step of milling the heat-treated magnesium-based alloy into a fine powder.

Hereinafter, the present invention will be described in detail.

First, a magnesium alloy is cast, charged into a crucible, dissolved in a non-oxidizing atmosphere, and then rapidly solidified. In general, magnesium alloy is more than 66.5% by weight of magnesium component, the remainder is composed of one or more components of nickel, copper, iron, aluminum, zinc. At least one of the remaining components of nickel, copper, iron, aluminum, and zinc forms a process structure with magnesium and forms a second phase in addition to the magnesium phase. In the case of a hydrogen storage alloy, hydrogen decomposition is performed. Or it can act to increase the diffusion rate. Since magnesium, the main component, combines with hydrogen in the form of a compound to store hydrogen and is released when the hydrogenated compound is released, the magnesium content in the alloy can be stored at least 66.5% by weight or more to store a large amount of hydrogen.

The rapid solidification method is a melt spinning method in which a molten molten metal is dropped onto a wheel that rotates at high speed through a nozzle and rapidly cooled to prepare a ribbon-shaped specimen. The molten molten metal is sprayed through a nozzle to form nitrogen and argon. Gas atomization to produce rapidly solidified powder by cooling with the same inert atmosphere gas, or centrifugal gas atomization to prepare rapid solidified powder by centrifugal force by dropping dissolved molten metal on a rotating disk at high speed. Etc. If the above-mentioned rapid solidification method is used while the alloying components are well dissolved at the melting temperature, the rapid cooling rate suppresses segregation of the alloying components, forms an amorphous phase, and coarsens the formed phases even when the crystalline phase is formed. It is effective to prevent that.

After rapid solidification, the precipitated crystal phase size should be about 500nm or less. If the crystal phase size is about 500 nm or less, the interphase interfacial area is large, and the metal hydrate is decomposed to promote diffusion of hydrogen along the interphase interface, thereby increasing the rate of hydrogen release. The heat treatment temperature is appropriately performed for about 20 minutes to 5 hours at a temperature of about 150 ℃ to 400 ℃, if the temperature is low or short time, the amorphous phase of crystallization does not occur, if the temperature is too high or long time, the grains grow As the interface between phases decreases, the effect of increasing the rate of hydrogen release is small.

The heat treated alloy needs to have a powder size smaller than 45 m by ball milling. If pulverized or pulverized powder size exceeds 46μm, the distance of hydrogen atom to diffuse or diffuse to the center of powder increases when hydrogen is absorbed, and the distance to spread to the surface of powder is decomposed when hydrogen hydride is decomposed. Reduce the rate of absorption and release. Preferably it should be controlled to 45 μm or less which can pass through a 325 mesh sieve.

The milled alloy powder should be absorbed in a hydrogen atmosphere at an appropriate temperature to form metal hydrides on the surface of the powder, and the activation process is performed to break the oxide film locally by volume expansion and to easily diffuse hydrogen into the interior.

The activation treatment for the milled alloy powder is sufficiently reacted with hydrogen at a pressure between 260 ° C. and 400 ° C. and between 5 and 30 atm to form a metal hydride, and then the metal hydride is vacuumed at 300 ° C. to 400 ° C. It means performing one or more times of the process of dehydrogenating in hydrogen atmosphere or inert atmosphere of 1 atmosphere or less. If the hydrogenation reaction temperature is less than 260 ℃ it takes a long time to hydrogenate by pressurizing the hydrogen pressure, if the temperature exceeds 400 ℃ crystal growth occurs or the metal container containing the hydrogen storage alloy is not good to oxidize. In addition, if the pressing pressure is less than 5 atm during the hydrogenation reaction, the reaction time is long, and if the pressure exceeds 30 atm, it is difficult to use a welded stainless container.

The magnesium alloy powder thus prepared is a fine powder having a fine crystal phase and has a high hydrogen release rate even at 300 ℃.

Hereinafter, the present invention will be described in detail through comparative examples and examples. However, the following examples are only intended to illustrate the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not limited to the following examples in accordance with the gist of the present invention.

Comparative example  One

76.5 wt% Mg to 23.5 wt% Ni alloy is prepared by casting method. Pure Mg and Ni were charged into a stainless steel crucible so as to have this composition, and the mixed gas of CO ₂ and SF ₆ was heated up to 900 ° C. while being evenly flowed to the molten surface to dissolve it. Chips produced by drilling the molten Mg-Ni-based alloy were ball milled in a SPEX milling device for 15 minutes to obtain 76.5 wt% Mg-23.5 wt% Ni alloy powder. After pulverization, the powder was classified and passed through a 200 mesh sieve (75 mu m pore size) and failed to pass through the 325 mesh sieve (45 mu m pore size) to obtain only 46 mu m or more and 75 mu m or less powder.

After the powder was charged in a reaction tube, a Sievet's type hydrogen absorption / release measurement apparatus was used. After reacting with hydrogen at 300 ° C. and 20 atm for 20 hours, dehydrogenating at 350 ° C. and vacuum for 2 hours, and then reacting with hydrogen for 2 hours at 10 atm of hydrogen pressure at 350 ° C., and then at 350 ° C. And dehydrogenation for 2 hours in a vacuum atmosphere, followed by reaction with hydrogen for 2 hours at hydrogen pressure of 300 ° C. and 10 atm, and then dehydrogenation for 2 hours at 350 ° C. and vacuum atmosphere to complete the activation treatment. The activated powder was reacted with hydrogen at 300 ° C. and 10 atm for 2 hours, and then the weight of hydrogen in the powder released during 35 minutes of dehydrogenation at 300 ° C. and vacuum atmosphere was measured. The weight percent of heavy hydrogen was obtained by dividing the released hydrogen weight by the charged powder weight and multiplying by 100. In addition, the hydrogen release rate (% / min) per minute at 300 ℃ was calculated by dividing the weight of hydrogen in the powder released during 35 minutes dehydrogenation by 35 minutes.

Comparative example  2

76.5 wt% Mg to 23.5 wt% Ni alloy is prepared by casting method. Pure Mg and Ni were charged into a stainless steel crucible so as to have this composition, and the mixed gas of CO ₂ and SF ₆ was heated up to 900 ° C. while being evenly flowed to the molten surface to dissolve it. Chips produced by drilling the dissolved 76.5 wt% Mg-23.5 wt% Ni alloy were ball milled for 36 hours to obtain 76.5 wt% Mg-23.5 wt% Ni alloy powder. The ball milled powder was classified into a 325 mesh sieve to extract only powders of 45 µm or smaller.

The powder was activated in the same manner as in Comparative Example 1, and the powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C., and then dehydrogenated for 35 minutes in a vacuum atmosphere at 300 ° C. The hydrogen release rate (% / min) per minute at weight% and 300 ° C. was measured.

Comparative example  3

76.5 wt% Mg ~ 23.5 wt% Ni alloy prepared by casting method was charged into a high frequency induction furnace, dissolved in Ar atmosphere, and then sprayed at a pressure of 0.5kg / cm ² on a rotating copper wheel by melt-spinning method. A solidified ribbon was produced. The ribbon was ball milled for 15 minutes in a spec mill to obtain 76.5 weight% Mg-23.5 weight% Ni alloy powder. After milling, the powder was separated and passed through a 200 mesh sieve (pore size 75 μm) and failed to pass through the 325 mesh sieve (pore size 45 μm). The powder was activated in the same manner as in Comparative Example 1, and the powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C., and then dehydrogenated for 35 minutes in a vacuum atmosphere at 300 ° C. The hydrogen release rate (% / min) per minute at weight% and 300 ° C. was measured.

Comparative example  4

86.5% by weight Mg ~ 13.5% by weight Ni alloy manufactured by the casting method was charged into a high frequency induction furnace, dissolved in Ar atmosphere, and then sprayed at a pressure of 0.5kg / cm ² on a rotating copper wheel by melt-spinning method. A solidified ribbon was produced. The ribbon was ball milled for 15 minutes in a spec mill, thereby obtaining 86.5 wt% Mg-13.5 wt% Ni alloy powder. After milling, the powder was separated and passed through a 200 mesh sieve (pore size 75 μm) and failed to pass through the 325 mesh sieve (pore size 45 μm).

The powder was activated in the same manner as in Comparative Example 1, and the powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C. The hydrogen release rate (% / min) per minute at weight% and 300 ° C. was measured.

Comparative example  5

76.5 wt% Mg-23.5 wt% Ni alloy prepared by casting method was charged into a high frequency induction furnace, dissolved in Ar atmosphere, and then sprayed at a pressure of 0.5 kg / cm ² on a rotating copper wheel by melt-spinning method. A solidified ribbon was produced. The ribbon was subjected to isothermal heat treatment at 250 ° C. for 1 hour and then ball milled in a spec mill for 15 minutes to obtain 76.5 wt% Mg-23.5 wt% Ni alloy powder. After milling, the powder was passed through a 200 mesh (pore size 75 μm) and not passed through a 325 mesh body (pore size 45 μm) to obtain a powder of 46 μm or more and 75 μm or less.

The activation was performed in the same manner as in Comparative Example 1, and the powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C. The hydrogen release rate (% / min) per minute at weight% and 300 ° C. was measured.

Example  One

76.5 wt% Mg-23.5 wt% Ni alloy prepared by casting method was charged into a high frequency induction furnace, dissolved in Ar atmosphere, and then sprayed at a pressure of 0.5 kg / cm ² on a rotating copper wheel by melt-spinning method. A solidified ribbon was produced. The ribbon was isothermally treated at 250 ° C. for 1 hour, and then ball milled in a hydrogen atmosphere with a planetary ball mill for 2 hours, and then powder was passed through a 325 mesh sieve (hole size 45 μm) to obtain 45 μm. Only the following powders were obtained. As shown in FIG. 1, the microstructure of 76.5 wt% Mg to 23.5 wt% Ni alloy heat treated after rapid solidification is composed of fine Mg and Mg ₂ Ni phases of 500 nm or less.

The activated powder was treated in the same manner as in Comparative Example 1, and the activated powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C. The hydrogen release rate (% / min) per minute at weight percent of hydrogen and 300 ° C. was measured.

Example 2

A pressure of 0.5kg / cm is applied to a copper wheel which is prepared by casting, 71.5% by weight Mg to 5.0% by weight Cu-23.5% by weight Ni alloy is charged into a high frequency induction furnace, dissolved in an Ar atmosphere, and then rotated by a melt-spinning method. Sprayed to ² to produce a ribbon quickly solidified. The ribbon was isothermally treated at 250 ° C. for 1 hour, and then ball milled in a hydrogen atmosphere with a planetary ball mill for 2 hours, and then powder was passed through a 325 mesh sieve (hole size 45 μm) to obtain 45 μm. Only the following powders were obtained.

The powder was activated in the same manner as in Comparative Example 1, and the powder was reacted with hydrogen for 2 hours at a hydrogen pressure of 10 atm at 300 ° C. The hydrogen release rate (% / min) per minute at weight% and 300 ° C. was measured.

Table 1 below is a chart showing the weight percent hydrogen released per minute (300 minutes) and hydrogen release rate per minute at 300 ℃ according to the comparative examples and examples described above.

division Main conditions (composition, manufacturing method, powder characteristics) Weight percentage of hydrogen released for 35 minutes at 300 ° C Hydrogen release rate per minute at 300 ° C (% / min) Comparative Example 1 Mg-23.5% Ni, casting, 75 μm or less 1.00% 0.0286 Comparative Example 2 Mg-23.5% Ni, casting, 45 μm or less 1.24% 0.0413 Comparative Example 3 Mg-23.5% Ni, rapid solidification, 75㎛ or less 1.4% 0.040 Comparative Example 4 Mg-13.5% Ni, rapid solidification, 75㎛ or less 1.4% 0.040 Comparative Example 5 Mg-23.5% Ni, rapid solidification + heat treatment + milling, 75 μm or less 1.4% 0.040 Example 1 Mg-23.5% Ni, rapid solidification + heat treatment + milling, 45 μm or less 4.3% 0.123 Example 2 Mg-5% Cu-23.5% Ni, Rapid Solidification + Heat Treatment + Milling, 45㎛ or less 4.8% 0.137

As can be seen in Comparative Examples 1 to 5 and Examples 1 to 2, it can be seen that the hydrogen release rate of the magnesium alloy powders obtained by the method according to the present invention is high. If the crystallization heat treatment after the rapid solidification to form a fine crystal phase and milling the powder to be fine, there is an advantage that the hydrogen release rate of the magnesium-based hydrogen storage alloy powder is excellent.

In the above description of the preferred embodiment of the present invention, the scope of the present invention is not limited to the conditions of the specific embodiment, and those skilled in the art within the scope of the claims of the present invention Changes may be made as appropriate.

As described above, according to the present invention, using a low-cost magnesium as a main raw material, a fine magnesium-based hydrogen storage alloy powder having a fine crystal phase can be prepared to improve the dehydrogenation rate at 300 ° C.

Claims (6)

Preparing a magnesium alloy ribbon by rapidly solidifying a molten magnesium alloy composed of at least 66.5% by weight of magnesium and the remainder of the nickel, copper, iron, aluminum, and zinc by melt spinning method; , Heat-treating the solidified magnesium alloy ribbon at a temperature of 150 ° C. to 400 ° C. for 20 minutes to 5 hours to have a fine crystal phase of 500 nm or less, Ball milling the heat-treated magnesium alloy ribbon into fine powder of 45 μm or less, and The ball milling powder is reacted with hydrogen at a pressure between 5 and 20 atmospheres at 300 ° C. to 400 ° C. and then dehydrogenated at 300 ° C. to 400 ° C. in a vacuum atmosphere or under 1 atm hydrogen atmosphere or an inert atmosphere. Method for producing a magnesium hydrogen-storage alloy powder having a fine crystal phase with a fast hydrogen release rate, characterized in that the step consisting of one or more steps. delete delete delete delete delete

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