JP5870325B2 - Initial activation method and hydrogenation method of hydrogen storage metal or alloy - Google Patents

Description

  The present invention, for example, irradiates a plate-like hydrogen storage (occlusion) metal with a plasma of a rare gas such as helium and removes an oxide film on the surface thereof to activate the hydrogen storage metal or alloy surface. Alternatively, the present invention relates to an initial activation method of an alloy and a hydrogenation method in which hydrogen is injected by irradiation with hydrogen plasma.

  In general, the initial activation of a hydrogen storage metal or alloy means that a hydrogen storage metal or alloy heated to a high temperature of about 500 ° C. is exposed to gaseous hydrogen at a high pressure of several atmospheres and then cooled to hydride near the surface. This is to cause fine cracks (microcracks) on the surface by the internal stress, to secure sufficient cracks by repeating the process, and to prepare the surface state for subsequent hydrogenation. However, this initial activation is sensitive to differences in conditions such as heat treatment in the manufacturing process of the same kind of alloy, not to mention dissimilar alloys. For this reason, initial activation is inadequate and reproducibility is poor, and thus the use of hydrogen storage metals or alloys has been limited so far.

Specifically, the behavior of hydrogen absorption and release with respect to titanium at a temperature of 450 to 800 ° C. has been studied (for example, see Non-Patent Document 1). In this case, the activation energies for hydrogen absorption and release were 74 KJ / mol and 25 KJ / mol, respectively.
Journal of Nuclear Materials 96 (1981) 227-232

  By the way, the reaction between metal and hydrogen gas placed in a closed system reaches a thermodynamic equilibrium state determined by given temperature and pressure. That is, the hydrogen concentration in the metal at a certain temperature is determined by the external pressure of the hydrogen gas. For example, when metal hydrogenation is carried out in a closed reaction system, the external hydrogen pressure decreases with hydrogen absorption by the metal and eventually reaches an equilibrium pressure. Once this equilibrium state is reached, the hydrogen concentration in the metal (hydrogen absorption amount) cannot be increased any further, so it is necessary to add hydrogen gas to increase the external pressure. At that time, impurities such as oxygen may enter, and if the metal surface is oxidized by the oxygen, it is necessary to perform initial activation again. As described above, the conventional hydrogenation method in which a high-temperature and high-pressure hydrogen gas is brought into contact with a high-temperature hydrogen storage metal or alloy is very inefficient and lacks reproducibility. In addition, when the thermodynamic equilibrium state is reached, it is necessary to add hydrogen gas, and as a result, there is a problem that initialization must be performed again.

  The present invention has been made in view of such problems of the prior art, and its object is to perform initial activation of a hydrogen storage metal or alloy sufficiently efficiently and with good reproducibility. It is an object of the present invention to provide an initial activation method of a hydrogen storage metal or alloy that can be used and a hydrogenation method that can increase hydrogen absorption.

To achieve the above object, the initial activation method of the hydrogen storage metal or alloy of the first aspect of the present invention, the hydrogen to the hydrogen storage metal or alloy on the assumption that perform hydrogen implantation by irradiating hydrogen plasma This is an initial activation method of a hydrogen storage metal or alloy that is activated by irradiating with a rare gas plasma not containing oxygen, removing the oxide film on the surface thereof, and having a plasma density of 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ , and the hydrogen storage metal or alloy is at least one selected from iron-titanium alloy, pure titanium, titanium-nickel alloy, and magnesium-titanium alloy.

  The method for initial activation of a hydrogen storage metal or alloy according to a second aspect of the invention is characterized in that, in the invention according to the first aspect, an electron temperature during the plasma irradiation is 3 eV to 10 eV.

  The hydrogen storage metal or alloy hydrogenation method according to the third aspect of the invention is the hydrogen storage metal or alloy after the initial activation method of the hydrogen storage metal or alloy according to the first or second aspect. It is characterized in that hydrogen implantation is performed by irradiating with hydrogen plasma.

  The hydrogen storage metal or alloy hydrogenation method according to a fourth aspect of the present invention is the method according to the third aspect, wherein the hydrogen plasma irradiation is performed under a condition that the temperature of the hydrogen storage metal or alloy is 100 to 300 ° C. It is characterized by being performed.

According to the present invention, the following effects can be exhibited.
In the initial activation method of the hydrogen storage metal or alloy according to claim 1, the hydrogen storage metal or alloy is irradiated with a rare gas plasma not containing hydrogen to activate the surface of the hydrogen storage metal or alloy. The plasma density is 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ . For this reason, the oxide film present on the surface of the hydrogen storage metal or alloy is irradiated with a rare gas plasma not containing high-density hydrogen, and the oxide film is removed by the sputtering action. Therefore, the initial activation of the hydrogen storage metal or alloy can be performed sufficiently efficiently and with good reproducibility.

  In the initial activation method of the hydrogen storage metal or alloy of the invention according to claim 2, the electron temperature at the time of plasma irradiation is set to 3 eV to 10 eV, and the plasma intensity of the inert gas is sufficiently exhibited. The effect of the invention according to claim 1 can be improved.

  In the hydrogen storage metal or alloy hydrogenation method according to claim 3, after the initial activation method of the hydrogen storage metal or alloy is performed, the hydrogen storage metal or alloy is irradiated with hydrogen plasma to perform hydrogen injection. Is to do. Hydrogen is injected by irradiation with hydrogen plasma in a state where the oxide film on the surface of the hydrogen storage metal or alloy is removed by the initial activation method of the hydrogen storage metal or alloy. Therefore, hydrogen injection can be performed effectively, and the amount of hydrogen absorption can be increased based on the non-equilibrium nature of the hydrogen plasma.

  In the hydrogen storage metal or alloy hydrogenation method according to the fourth aspect of the invention, the hydrogen plasma irradiation is performed under the condition that the temperature of the hydrogen storage metal or alloy is 100 to 300 ° C. Therefore, the effect of the invention according to claim 3 can be sufficiently exerted at a temperature lower than that of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments that are considered to be the best of the present invention will be described below in detail with reference to the drawings.
An apparatus used for initial activation and hydrogenation of the hydrogen storage metal or alloy (hereinafter also simply referred to as hydrogen storage metal) of this embodiment is a rare gas such as helium (He) or argon (Ar), hydrogen (H _2). It is an apparatus for generating a plasma of gas applied to a vacuum system containing gas. FIG. 1 is an explanatory view schematically showing an apparatus 10 for generating a rare gas or hydrogen gas plasma and performing initial activation and hydrogenation of a hydrogen storage metal in the present embodiment. As shown in the figure, a turbo-molecular pump 12 is connected to a stainless steel vacuum chamber 11 having a square box shape via a communication pipe 13, and the inside of the vacuum chamber 11 is evacuated to a level of 10 ⁻⁵ Pa. It has become so.

  Examples of the hydrogen storage metal or hydrogen storage alloy include those generally used as hydrogen storage metals such as iron-titanium alloy, pure titanium, titanium-nickel alloy, magnesium-titanium alloy. The shape of the hydrogen storage metal is preferably a block shape such as a plate shape or a rod shape, and a powder shape is not preferred. As the rare gas, neon (Ne), krypton (Kr), or xenon (Xe) is used in addition to helium and argon.

  An electrically insulated plate-like resistance heating type heater 14 is cantilevered in the vacuum chamber 11, and its tip is positioned at the center in the vacuum chamber 11. A crucible 15 is held on the upper surface of the tip of the heater 14, and a plate-like hydrogen storage metal 16 is set in the crucible 15. One end of a thermocouple 17 is connected to the crucible 15 and the temperature of the hydrogen storage metal 16 is measured. A pressure gauge 18 is connected to a side position of the vacuum chamber 11 to measure the pressure in the vacuum chamber 11.

  Above the vacuum chamber 11, an electron cyclotron resonance (ECR) plasma generator 21 is disposed via a connecting pipe 22, and plasma generated by the plasma generator 21 is placed in a crucible 15 in the vacuum chamber 11. The set hydrogen storage metal 16 is irradiated. Here, plasma means that gas molecules dissociate and become atoms when the temperature of the gas rises, and electrons around the nucleus move away from the nucleus and ionize into positive ions and electrons as the temperature rises further. It means a gas containing the generated charged particles. The irradiation particle bundle of the plasma irradiated on the hydrogen storage metal 16 is determined by the output of the plasma generator 21. A gas introduction pipe 23 as a gas introduction part is connected to the plasma generator 21 side of the connection pipe 22, and a rare gas such as helium or a gas containing hydrogen is introduced into the connection pipe 22 and generated by the plasma generation apparatus 21. A plasma column 24 of rare gas or hydrogen gas is generated by the plasma to be generated.

  A donut limiter 25 having a circular hole 25a having a constant opening diameter (for example, 3.5 cm) is arranged in the connecting pipe 22 so as to be orthogonal to the plasma column 24, and the diameter of the plasma column 24 is set by the opening diameter. The Around the plasma generator 21, the connecting pipe 22, the vacuum chamber 11, and the turbo molecular pump 12, three circular electromagnets 26 are arranged at regular intervals, and the plasma column 24 generated by the plasma generator 21 is arranged. It is guided to the hydrogen storage metal 16 on the crucible 15. A plasma density measuring probe 27 is disposed at substantially the center of the connection pipe 22 and is supported so as to be movable back and forth. The tip of the plasma density measuring probe 27 is supported so as to reach the plasma column 24, and the density and electron temperature (electron volt, eV) of the plasma column 24 are measured. The irradiation particle bundle is calculated from their density and electron temperature.

Next, the initial activation method and hydrogenation method of the hydrogen storage metal using the above apparatus will be described.
In the initial activation method of the hydrogen storage metal 16, a rare gas is introduced into the connection pipe 22 from the gas introduction pipe 23, and a plasma column 24 of a rare gas such as helium is formed by the plasma generator 21. The plasma column 24 is guided to the hydrogen storage metal 16 in the crucible 15 by the linear magnetic field of the three electromagnets 26. The surface of the hydrogen storage metal 16 is activated by irradiating the hydrogen storage metal 16 with the plasma column 24 of a rare gas.

In this case, in order to perform the initial activation of the hydrogen storage metal 16 sufficiently and efficiently, the plasma density of the rare gas is set to 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ . When the plasma density is less than 10 ¹⁶ / m ³ , the plasma density is low, and the removal of the oxide film on the surface of the hydrogen storage metal 16 cannot be performed efficiently, and eventually initialization takes a long time. . On the other hand, if it exceeds 10 ¹⁸ / m ³ , the thermal load due to plasma irradiation is too large, and the sample may melt. Further, the pressure of the rare gas is preferably 1.33 × 10 ⁻¹ Pa to 1.33 × 10 ⁰ Pa. When the pressure of the rare gas is less than 1.33 × 10 ⁻¹ Pa, since the pressure is low and the plasma ignitability by ECR is poor, the purpose of initial activation of the hydrogen storage metal 16 cannot be sufficiently achieved. On the other hand, when it exceeds 1.33 × 10 ⁰ Pa, the pressure is too high, and the ECR plasma ignitability deteriorates.

Moreover, in order to perform the initial activation of the hydrogen storage metal 16 more efficiently, the electron temperature at the time of plasma irradiation is desirably 3 eV to 10 eV. When this electron temperature is less than 3 eV, it becomes difficult to maintain a plasma density of 10 ¹⁶ / m ³ or more. When the electron temperature exceeds 10 eV, the heat load due to the plasma becomes high and the sample may be melted.

Further, the irradiation particle bundle of the rare gas plasma is desirably 10 ¹⁶ ions / sec.m ² or more in order to increase the density of the rare gas plasma and to exert its strength. When the irradiation particle bundle is less than 10 ¹⁶ ions / sec.cm ² , the density of the rare gas plasma is low, and the intensity cannot be fully exhibited. The upper limit is not particularly limited, but is desirably 10 ¹⁸ ions / sec.cm ² or less. When the irradiation particle bundle exceeds 10 ¹⁸ ions / sec.cm ² , the heat load due to the plasma becomes high and the sample may be melted.

  In addition, in order to increase the sputtering rate of the rare gas plasma and increase the efficiency of initial activation of the hydrogen storage metal 16, it is preferable to apply a DC voltage of 50 to 300 V to the hydrogen storage metal. When this DC voltage is less than 50 V, the impact force of the rare gas plasma cannot be sufficiently improved, which is not preferable. On the other hand, when the voltage exceeds 300 V, arc discharge occurs during the generation of the plasma column, which results in unexpected damage to the surface of the hydrogen storage metal.

  Next, the hydrogen storage metal 16 is hydrogenated by performing the initial activation method of the hydrogen storage metal 16 described above and then irradiating the hydrogen storage metal 16 with hydrogen plasma to inject hydrogen. In this case, the irradiation with hydrogen plasma is preferably performed by controlling the temperature and the pressure of hydrogen, and is preferably performed under the condition that the temperature of the hydrogen storage metal is 100 to 300 ° C. When the temperature is lower than 100 ° C., the temperature becomes too low and the diffusion rate becomes low, and the efficiency of hydrogen injection into the hydrogen storage metal 16 is lowered. On the other hand, when the temperature exceeds 300 ° C., the efficiency of hydrogen injection with respect to the hydrogen storage metal 16 does not increase even at such a high temperature, but hydrogen is released due to heating.

Now, the operation of this embodiment will be described. In the apparatus 10 shown in FIG. 1, the hydrogen storage metal 16 is set on the crucible 15 in the vacuum chamber 11 in the initial activation of the surface of the hydrogen storage metal 16. Then, a rare gas is introduced from the gas introduction pipe 23, a rare gas plasma column 24 is formed by the plasma generator 21, and the hydrogen storage metal 16 is irradiated. At this time, at least the density of the plasma column 24 is set to 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ , and preferably the electron temperature is set to ³ eV to 10 eV. With such a condition setting, rare gas ions (or neutral atoms of the rare gas) flying from the rare gas plasma column 24 reach the surface of the hydrogen storage metal 16. The floating potential at this time is determined in particular by the electron temperature of the plasma column 24, and the rare gas ions bombard the surface of the hydrogen storage metal 16 according to this potential. This impact force removes the oxide film on the surface of the hydrogen storage metal 16 so that a clean metal surface is exposed and the hydrogen storage metal 16 is initially activated.

  Subsequently, in hydrogenating the hydrogen storage metal 16 subjected to the initial activation treatment, the surface of the hydrogen storage metal 16 is irradiated with hydrogen plasma. At this time, the temperature of the hydrogen storage metal is preferably set to 100 to 300 ° C. By setting such conditions, the hydrogenation can be effectively performed with the surface of the hydrogen storage metal 16 being clean, and the hydrogen absorption amount can be increased. As described above, the rare gas is turned into plasma, and the plasma is brought into direct contact with the hydrogen storage metal 16, whereby the initial activation of the hydrogen storage metal 16 is performed, and then hydrogenation is continuously performed with hydrogen plasma. In this method, hydrogen plasma is continuously irradiated, and there is no saturation point as in the prior art due to plasma non-equilibrium, and the amount of hydrogen absorption continues to increase.

The effects exhibited by the embodiment described in detail above will be collectively described below.
In the initial activation method of the hydrogen storage metal or alloy in the present embodiment, the hydrogen storage metal 16 is irradiated with a rare gas plasma to activate the surface of the hydrogen storage metal 16, and the plasma density is 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ . For this reason, the oxide film present on the surface of the hydrogen storage metal 16 is irradiated with high-density rare gas plasma, and the oxide film is removed by the sputtering action. Therefore, the initial activation of the hydrogen storage metal 16 can be performed sufficiently efficiently and with good reproducibility.

Furthermore, since the electron temperature at the time of plasma irradiation is set to 3 eV to 10 eV, the above effect can be improved.
-In the hydrogenation method of the hydrogen storage metal 16, after the initial activation method of the hydrogen storage metal is performed, the hydrogen storage metal 16 is irradiated with hydrogen plasma to perform hydrogen injection. In this case, by the initial activation of the hydrogen storage metal 16, the oxide film on the surface of the hydrogen storage metal 16 is removed, and hydrogen implantation is performed by irradiation with hydrogen plasma with the clean metal surface exposed. As a result, hydrogen injection is effectively performed, and the amount of hydrogen absorption can be increased based on the non-equilibrium nature of the hydrogen plasma.

  -In addition, in the hydrogenation method, the irradiation of hydrogen plasma is performed under the condition that the temperature of the hydrogen storage metal is 100 to 300 ° C, so that the above effect can be sufficiently exerted at a temperature lower than conventional. it can.

Hereinafter, although the embodiment will be described more specifically with reference to examples and comparative examples, the present invention is not limited to these examples.
(Examples 1 and 2)
Using the apparatus 10 shown in FIG. 1, the surface of the hydrogen storage metal 16 was activated according to the above-described initial activation method. In Example 1, an iron-titanium alloy containing 90 atomic% iron and 10 atomic% titanium was used as the hydrogen storage metal 16. In Example 2, pure titanium was used as the hydrogen storage metal 16. The shape of the hydrogen storage metal 16 was a disk having a diameter of 28 mm and a thickness of 2 mm. Further, helium was used as a rare gas to form helium plasma, and the diameter of the helium plasma column 24 was set to 3.5 cm.

The initial activation conditions were an applied voltage (DC voltage) of 100 V, a plasma irradiation time of 10 minutes, and a temperature of the hydrogen storage metal 16 of 600 ° C. The density of helium plasma was set to 3 × 10 ¹⁶ / m ³ , the electron temperature was set to 3 eV, and the irradiation particle bundle of the helium plasma was set to about 5 × 10 ²⁰ He-ions / m ² .sec.

Here, in the case of pure titanium, since the sputtering rate is about 0.046, about 1.4 × 10 ¹⁸ titanium atoms per cm ² were removed from the surface from the helium plasma particle bundle. When this is converted into the thickness of titanium, it becomes about 2000 mm. Similarly, when converted into the thickness of iron, it is about 3000 mm. Since these values are considered to apply to oxides (TiO ₂ , FeO, Fe ₂ O ₃ ) approximately, the thickness is sufficient for surface oxide film removal in terms of metal phase (metal structure). I can say that.

  The hydrogen storage metal 16 subjected to the initial activation treatment in this way was irradiated with hydrogen plasma under the following conditions to perform hydrogenation. That is, the temperature was set to 300 ° C. No DC voltage was applied. The reason is that, when a DC voltage is applied, the hydrogen injection rate increases, but the temperature of the hydrogen storage metal 16 also increases, so that the hydrogen absorption amount may decrease due to the release. And the hydrogen absorption amount (the number of hydrogen atoms) with respect to the hydrogen gas exposure time (minute) by hydrogen plasma was measured by the following method.

That is, after the hydrogenation is completed, the introduction of hydrogen gas is stopped, the inside of the vacuum chamber 11 is again evacuated to the 10 ⁻⁵ Pa level, the hydrogen storage metal 16 is heated to about 600 ° C. with a heater, and hydrogen is released. The pressure inside the vacuum chamber 11 was measured with a pressure gauge 18. Then, from the exhaust velocity catalog value (150 L / sec) of the turbo molecular pump 12, the total discharge amount Q, that is, the total absorption amount was obtained using the following formula (1).

ここで、Ｐ１（ｔ）は時間ｔ（例えばｔ１）における水素の分圧、Ｐ^０はバックグラウンド水素分圧及びＳはポンプの排気速度を表す。

Here, P1 (t) represents the partial pressure of hydrogen at time t (eg, t1), P ⁰ represents the background hydrogen partial pressure, and S represents the pumping speed of the pump.

FIG. 2 shows the relationship between the hydrogen gas exposure time (minutes) and the hydrogen absorption amount (number of hydrogen atoms) thus obtained. As shown in FIG. 2, in Examples 1 and 2, the initial activation of iron-titanium alloy or pure titanium using helium plasma followed by hydrogenation using hydrogen plasma resulted in the original non-equilibrium of the plasma. As a result, the hydrogen absorption did not reach saturation and the result increased in proportion to the hydrogen gas exposure time.
(Comparative Examples 1 and 2)
In Comparative Example 1, an iron-titanium alloy of 90 atomic% iron and 10 atomic% of titanium was used as the hydrogen storage metal 16, and pure titanium was used as the hydrogen storage metal 16 in Comparative Example 2. The shape of the hydrogen storage metal 16 was set to the same shape as in Example 1 in both Comparative Examples 1 and 2. Then, the hydrogen storage metal 16 was hydrogenated under the following conditions by a conventional method of pressurizing hydrogen gas without using plasma. That is, the temperature was set to 600 ° C. After the hydrogenation was completed, the relationship between the hydrogen gas exposure time (minutes) and the amount of absorbed hydrogen (number of hydrogen atoms) was determined in the same manner as in Example 1, and is shown in FIG.

As a result, in Comparative Examples 1 and 2, when an iron-titanium alloy or pure titanium is not irradiated with hydrogen plasma and hydrogen is injected only by exposure to hydrogen gas, a thermodynamic equilibrium state is reached after 100 to 150 minutes. As a result, the amount of absorbed hydrogen was saturated and no longer increased.
(Example 3)
In Example 3, initial activation and hydrogenation of the hydrogen storage metal 16 were performed in the same manner as in Example 1 except that argon plasma was used as a rare gas and argon plasma was formed. Argon plasma has the same density and irradiated particle flux characteristics as helium plasma. The relationship between the obtained hydrogen plasma irradiation time (minutes) and the amount of absorbed hydrogen (number of hydrogen atoms) is shown in FIG. As shown in FIG. 2, in the case of Example 3, a result that the hydrogen absorption amount was increased as compared with the case of Comparative Example 1 was obtained.

It should be noted that the embodiment described above can be modified and embodied as follows.
In the initial activation of the hydrogen storage metal 16, the density of the rare gas plasma is higher than 10 ¹⁶ / m ³ , the irradiation particle flux of the rare gas plasma is much higher than 10 ¹⁶ ions / sec.m ² or more, and the plasma irradiation The electron temperature at the time can be set sufficiently higher than 3 eV or more to shorten the initialization time.

Next, the technical idea that can be grasped from the embodiment will be described below.
The method for initial activation of a hydrogen storage metal or alloy according to claim 1 or 2, wherein a DC voltage of 50 to 300 V is applied to the rare gas plasma. According to this method, in addition to the effect of the invention according to claim 1 or 2, the efficiency of initial activation can be increased.

  The method for initial activation of the hydrogen storage metal or alloy according to claim 1 or 2, wherein the hydrogen storage metal or alloy is in a lump shape. According to this method, the effect of the invention according to claim 1 or claim 2 can be exerted on the surface of the hydrogen storage metal or alloy forming a lump.

Schematic explanatory drawing which shows the apparatus used for the initial activation and hydrogenation of a hydrogen storage metal. The graph which shows the relationship between the hydrogen gas exposure time (minutes) and hydrogen absorption amount (number of hydrogen atoms) in Examples 1-3 and Comparative Examples 1 and 2. FIG.

Explanation of symbols

  16 ... Hydrogen storage metal, 24 ... Plasma column.

Claims (4)

The initial stage of the hydrogen storage metal or alloy that is activated by irradiating the hydrogen storage metal or alloy with a rare gas plasma that does not contain hydrogen on the assumption that hydrogen injection is performed by irradiating the hydrogen plasma and removing the oxide film on the surface. An activation method comprising:
The plasma has a density of 10 ¹⁶ / m ³ to 10 ¹⁸ / m ³ ;
The method for initial activation of a hydrogen storage metal or alloy, wherein the hydrogen storage metal or alloy is at least one selected from iron-titanium alloy, pure titanium, titanium-nickel alloy, and magnesium-titanium alloy. The method for initial activation of a hydrogen storage metal or alloy according to claim 1, wherein an electron temperature at the time of plasma irradiation is 3 eV to 10 eV. A hydrogen storage metal or a hydrogen storage metal or alloy characterized by performing hydrogen injection by irradiating the hydrogen storage metal or alloy with hydrogen plasma after performing the initial activation method of the hydrogen storage metal or alloy according to claim 1 or 2. Alloy hydrogenation method. The method of hydrogenating a hydrogen storage metal or alloy according to claim 3, wherein the irradiation of the hydrogen plasma is performed under the condition that the temperature of the hydrogen storage metal or alloy is 100 to 300 ° C.

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