【発明の詳細な説明】[Detailed description of the invention]
本発明は水素貯蔵合金、さらに詳しくは少なく
とも一部がLaNi5とNiとの共晶組織からなり、
水素吸収・放出操作の際の合金の微粉化を抑制な
いし防止したLa−Ni水素貯蔵合金に関する。
発明の背景
水素は将来のクリーンエネルギーの中核をなす
と思われるが、水素の貯蔵および輸送形態として
高圧ガス、液体水素、さらに金属水素化物による
固形化が挙げられる。このうち安全性および取扱
い易さから金属水素化物を利用する方法が注目さ
れている。その理由として、
(1) 単位体積当たりの水素貯蔵密度が高く気体水
素の1000倍以上を有し、また液体水素のそれと
同程度である
(2) 水素の貯蔵に高圧容器を必要とせず、従つて
容器の耐圧や水素脆性の点では問題はない
(3) 金属水素化物は熱力学的に安定であるために
液体水素のように蒸発による損失はなく長時間
の貯蔵が可能である
(4) 金属水素化物の解離圧はほぼ一定であり解離
温度を決めれば一定圧の水素ガスが得られる
などが挙げられる。従つて金属水素化物を利用し
た水素貯蔵容器をはじめ燃料電池、内燃式エンジ
ン用ボンベはもとより水素精製装置、冷暖房器、
コンプレツサー、冷凍器に至るまで幅広い用途が
考えられており、安全性の向上、装置の簡略化、
特性の向上などの面で従来のものに比べ多くの利
点を有する。
このように水素の貯蔵および輸送形態として金
属水素化物による水素の固形化が注目を浴びてい
るが、水素貯蔵材料として実用化されるために
は、
(1) 水素の吸収・放出に伴い合金が微粉化しない
こと
(2) 安価であること
(3) 活性化が容易であること
(4) 水素吸蔵能力がすぐれていること
(5) 水素の吸収・放出のくり返しによる合金性能
の劣化が少ないこと
(6) 常温近傍での金属水素化物の生成平衡圧や解
離平衡圧が数気圧であること
(7) 金属水素化物の生成および解離平衡圧曲線の
ヒステリシスが小さいこと
(8) 平衡圧曲線が明瞭なプラトーを有すること
などが挙げられ、従来より種々の水素貯蔵用材料
が提唱されてきた。さらに、これらの実用的諸問
題のうち水素吸収・放出の繰り返し使用により材
料が微粉化する問題は、実用化に対する最大の障
壁となつているのが現状であり、その解決が大き
な命題である。
合金の微粉化は性能劣化に直接関係するのみな
らず、熱伝導率の低下に起因する合金容器設計の
複雑化や水素の吸収・放出に伴う容器からの合金
の飛散やフイルター、バルブの目詰まり等維持管
理上の問題にも関係するため、多くの研究の一焦
点が微粉化しにくい合金開発へ絞られている。し
かし現在の合金製造方法では微粉化の回避は困難
であり、視点を変えた材料の製造方法の研究が必
要である。
このような趨勢の中で、本発明者らは共晶反応
により組織を制御する技術を水素貯蔵合金の製造
に適用することによつて微粉化し難い水素貯蔵合
金の製造が可能であることを見出した。
すなわち、LaとNiとを所定量配合し溶解後凝
固する過程において共晶反応により少なくとも一
部をLaNi5とNiとの共晶組織として凝固させる
ことにより、水素の吸収・放出操作の繰り返し中
にも合金の微粉化が抑制ないし防止できることを
見出し本発明の合金に到達した。
発明の概要
本発明はLaxNi100-x（但しｘは14〜21重量％）
で表される組成からなり、溶解凝固後、少なくと
も一部がLaNi5とNiとの共晶組織を呈すること
を特徴とする耐微粉化性に優れた水素貯蔵合金に
ある。
発明の詳細な記述
以下、本発明の水素貯蔵合金について説明す
る。
本発明の基本的技術思想は多量の水素を吸収・
放出（水素化反応）する金属間化合物である
LaNi5と殆ど水素を吸収・放出しないが水素化反
応の触媒作用を有し且つ延性を有するNiとの共
晶組織により合金の微粉化を抑制するにある。
本発明によるLaとNiとの配合割合は水素の吸
収・放出能力と水素貯蔵合金の微粉化抑制能力と
を考慮して決定される。すなわち、水素吸収放出
能力を有するLaNi5相をできるだけ多く晶出させ
ることが望ましいが過度にLaNi5相が多くなると
Ni相による微粉化抑制能力が低下するために
LaNi5相の微粉化が起こり、本発明による所望の
効果を達成することはできない。すなわちLaが
14重量％より少ないとNi相が多くなつて合金の
微粉化は抑制されるが、LaNi5相が少なくなるた
めに水素吸蔵量が減少する。Laが21重量％より
なるとLaNi5相が多くなるために水素吸蔵量は多
くなるがNi相が少なくなるために合金の微粉化
が起こり易い。従つてLa含有量は14〜21重量％
に限定される。水素吸蔵量と微粉化抑制能力を考
慮して第３図の共晶点よりもLaNi5側の組成にす
ることが好ましい。
合金の溶解は酸化を防止するために真空または
不活性ガス（例えばアルゴン）中で合金の融点以
上の温度に温度上昇できる任意の溶解炉を使用し
て実施できるが、ただ、水素貯蔵合金自体が不純
物、特に酸素を極端にきらうために「るつぼ」の
材質の選定が重要なキーポイントとなる。例えば
水冷アルミナるつぼを使用して行なわれる。
溶解した合金成分を凝固させれば、第３図から
明らかなように、凝固過程で晶出する初晶および
共晶組織の量はLaとNiの含有量によつて決定さ
れる。凝固の一態様として凝固パラメーターとな
る温度勾配や凝固速度を調節することからなる指
向性凝固を行なうことにより第１図に示すような
LaNi5相またはNi相の整列組織相間隔および大
きさを任意に変えることができる。
発明の実施例
以下、実施例に基づき本発明を説明する。
実施例 １
純度99.8％ランタン（La）と純度99.95％ニツ
ケル（Ni）を用いて金属間化合物LaNi5とNiと
の共晶合金（第１表中符号１）および一部共晶組
織を有する合金（第１表中符号２−４）を溶製し
た。さらに一部共晶組成を有する合金（第１表中
符号５，６）およびLaNi5のみからなる合金（第
１表中符号７）を比較材として溶製した。Laお
よびNiの調合割合と合金組成の関係を下記第１
表に示す。
まず、各割合で調合した原材料500ｇを水冷ア
ルミナるつぼに入れ、10-3〜10-1トルまで排ガス
後、プラズマアーク（Arガス中）にて溶解して。
次いで溶湯状態から冷却すると各試料の凝固後の
組成および初晶量（初晶／全組織）は第１表に示
す通りである。
このようにして得た各合金試料を１cm角に小割
し、高温高圧水素ガス雰囲気中で温度、圧力自動
制御可能な自動天秤装置にセツトして、250℃で
排気後純度99.99999％の水素を導入し30分間保持
した後、再び排気した。その後室温にて40気圧の
水素を加圧したときの水素化反応に伴う合金重量
の変化から、合金が吸収・放出した水素量を求
め、第１表に示した。
さらに、本発明合金および比較材について室温
における水素吸収量、水素吸収速度、さらに室温
度で水素を10気圧の条件で吸収させた後100℃で
水素圧10気圧の条件で水素を放出する操作で50回
くり返した試料について、微粉化の状況を第１表
に示した。
The present invention relates to a hydrogen storage alloy, more specifically, at least a part of which is composed of a eutectic structure of LaNi 5 and Ni,
This invention relates to a La-Ni hydrogen storage alloy that suppresses or prevents pulverization of the alloy during hydrogen absorption and release operations. BACKGROUND OF THE INVENTION Hydrogen is likely to be central to the future of clean energy, and forms of storage and transportation for hydrogen include high pressure gas, liquid hydrogen, and solidification with metal hydrides. Among these methods, methods using metal hydrides are attracting attention because of their safety and ease of handling. The reasons for this are: (1) the hydrogen storage density per unit volume is high, more than 1000 times that of gaseous hydrogen, and is comparable to that of liquid hydrogen; (2) hydrogen storage does not require a high-pressure container; Therefore, there is no problem in terms of pressure resistance and hydrogen embrittlement of the container (3) Metal hydrides are thermodynamically stable, so unlike liquid hydrogen, there is no loss due to evaporation and they can be stored for a long time (4) The dissociation pressure of metal hydrides is almost constant, and if the dissociation temperature is determined, hydrogen gas at a constant pressure can be obtained. Therefore, hydrogen storage containers using metal hydrides, fuel cells, cylinders for internal combustion engines, hydrogen purification equipment, air conditioners, heaters, etc.
A wide range of applications are being considered, from compressors to refrigerators, to improve safety, simplify equipment,
It has many advantages over conventional ones in terms of improved characteristics. As described above, the solidification of hydrogen using metal hydrides is attracting attention as a form of hydrogen storage and transportation, but in order to be put to practical use as a hydrogen storage material, (1) the alloy must be formed as hydrogen is absorbed and released; Not pulverized (2) Cheap (3) Easily activated (4) Excellent hydrogen storage capacity (5) Less deterioration of alloy performance due to repeated absorption and release of hydrogen (6) The equilibrium pressure for production and dissociation of metal hydrides at room temperature is several atmospheres.(7) The hysteresis of the equilibrium pressure for production and dissociation of metal hydrides is small.(8) The equilibrium pressure curve is clear. Various hydrogen storage materials have been proposed in the past. Furthermore, among these practical problems, the problem of material becoming pulverized due to repeated use of hydrogen absorption and release is currently the biggest barrier to practical application, and its solution is a major challenge. The pulverization of alloys is not only directly related to performance deterioration, but also complicates the alloy container design due to a decrease in thermal conductivity, as well as scattering of the alloy from the container and clogging of filters and valves due to the absorption and release of hydrogen. Many studies have focused on the development of alloys that are less likely to be pulverized. However, it is difficult to avoid pulverization with current alloy manufacturing methods, and it is necessary to research methods for manufacturing materials from a different perspective. In light of these trends, the present inventors have discovered that it is possible to produce hydrogen storage alloys that are difficult to pulverize by applying technology that controls the structure through eutectic reactions to the production of hydrogen storage alloys. Ta. In other words, in the process of blending a predetermined amount of La and Ni and solidifying after melting, at least a portion of LaNi is solidified as a eutectic structure of LaNi 5 and Ni due to a eutectic reaction, and during repeated hydrogen absorption and release operations, The inventors have also discovered that the pulverization of the alloy can be suppressed or prevented, and have arrived at the alloy of the present invention. Summary of the invention The present invention uses LaxNi 100-x (where x is 14 to 21% by weight)
This hydrogen storage alloy has a composition represented by the following formula and exhibits a eutectic structure of at least a portion of LaNi 5 and Ni after melting and solidification, and has excellent pulverization resistance. DETAILED DESCRIPTION OF THE INVENTION The hydrogen storage alloy of the present invention will now be described. The basic technical idea of the present invention is to absorb and absorb a large amount of hydrogen.
It is an intermetallic compound that is released (hydrogenation reaction)
The eutectic structure of LaNi 5 and Ni, which hardly absorbs or releases hydrogen but has a catalytic effect on the hydrogenation reaction and is ductile, suppresses the pulverization of the alloy. The blending ratio of La and Ni according to the present invention is determined by taking into consideration the ability to absorb and release hydrogen and the ability to suppress pulverization of the hydrogen storage alloy. In other words, it is desirable to crystallize as much LaNi 5 phase as possible, which has the ability to absorb and release hydrogen, but if the LaNi 5 phase increases too much,
Because the ability to suppress pulverization by the Ni phase decreases.
Micronization of the LaNi 5 phase occurs and the desired effect according to the invention cannot be achieved. In other words, La
If it is less than 14% by weight, the Ni phase will increase and the pulverization of the alloy will be suppressed, but the amount of LaNi 5 phase will decrease and the amount of hydrogen storage will decrease. When La exceeds 21% by weight, the amount of hydrogen storage increases because the LaNi 5 phase increases, but the Ni phase decreases, which tends to cause the alloy to become pulverized. Therefore, the La content is 14-21% by weight.
limited to. In consideration of hydrogen storage capacity and ability to suppress pulverization, it is preferable to set the composition to be closer to LaNi 5 than the eutectic point in FIG. 3. Melting of the alloy can be carried out using any melting furnace capable of raising the temperature above the melting point of the alloy in a vacuum or inert gas (e.g. argon) to prevent oxidation, but only if the hydrogen storage alloy itself In order to avoid impurities, especially oxygen, the selection of the material for the crucible is an important key point. For example, it is carried out using a water-cooled alumina crucible. When the melted alloy components are solidified, as is clear from FIG. 3, the amounts of primary crystals and eutectic structures that crystallize during the solidification process are determined by the contents of La and Ni. As a form of solidification, directional solidification is performed by adjusting the temperature gradient and solidification rate, which are the solidification parameters.
The aligned structure phase spacing and size of LaNi 5 phase or Ni phase can be changed arbitrarily. Examples of the Invention The present invention will be described below based on Examples. Example 1 A eutectic alloy of the intermetallic compound LaNi 5 and Ni (symbol 1 in Table 1) using 99.8% pure lanthanum (La) and 99.95% pure nickel (Ni) and an alloy having a partial eutectic structure (Symbol 2-4 in Table 1) was melt-produced. Further, alloys having a partially eutectic composition (numbers 5 and 6 in Table 1) and alloys consisting only of LaNi 5 (number 7 in Table 1) were melt-produced as comparative materials. The relationship between the blending ratio of La and Ni and the alloy composition is shown in the following
Shown in the table. First, 500 g of the raw materials prepared in each ratio were placed in a water-cooled alumina crucible, and after exhausting gas to 10 -3 to 10 -1 Torr, they were melted in a plasma arc (in Ar gas).
Next, when the molten metal was cooled, the composition and amount of primary crystals (primary crystals/total structure) of each sample after solidification were as shown in Table 1. Each alloy sample obtained in this way was divided into 1 cm square pieces, set in an automatic balance device that can automatically control temperature and pressure in a high temperature and high pressure hydrogen gas atmosphere, and after evacuation at 250°C, hydrogen with a purity of 99.99999% was extracted. After being introduced and held for 30 minutes, it was evacuated again. Thereafter, when hydrogen was pressurized at 40 atmospheres at room temperature, the amount of hydrogen absorbed and released by the alloy was determined from the change in alloy weight due to the hydrogenation reaction, and is shown in Table 1. Furthermore, we investigated the hydrogen absorption amount and hydrogen absorption rate at room temperature for the present alloy and comparative materials, as well as the hydrogen absorption rate at room temperature and the operation of absorbing hydrogen at 10 atm and then releasing hydrogen at 100°C and at 10 atm. Table 1 shows the state of pulverization for the samples that were repeated 50 times.
【表】
本発明の合金は比較材、符号７（LaNi5単相）
に比べていずれの場合も水素吸収速度が速く、ま
た微粉化は生じていない。比較材、符号５の合金
はLaNi5相が多いために水素吸収量は多いが微粉
化した。また共晶組織のみの合金（符号１の合
金）の水素吸収量［0.3水素原子／金属原子
（Ｈ／Ｍ）］は比較材、符号７（LaNi5）の水素吸
収量（6.5H／Ｍ）に比べて約50％小さいが、
LaNi5とNiとの共晶反応の範囲を示す状態図で
ある第３図における共晶組成よりLaNi5側にずれ
るにつれて水素吸収量は増大し、例えば符号４の
合金（La28重量％−Ni72重量％）の水素吸収量
（4.9H／Ｍ）は比較材、符号７の約82％と大幅に
改善され、且つ水素吸収速度が比較材、符号７
（LaNi5）に比べて速く、さらに微粉化しない点
を考慮すると水素吸収量の不利は実用上問題とな
らない。なお比較材、符号６の合金はNi相が多
いために微粉化は起こらないが水素吸蔵量（Ｈ／
Ｍ）が少なく本発明の目的にそぐわない。
実施例 ２
実施例１の符号１と同様に調合したLaおよび
Niからなる試料を第２図に示した指向性凝固合
金製造装置１にセツトし10-3〜10-1トルまで真空
ポンプ（図示せず）により真空ポンプ接続管１１
から排ガスした。温度勾配をつくるために底部側
を冷却水（冷却水入口１２および冷却水出口１
３）で水冷しながら、SiC発熱体３から成る炉を
ゆつくりと上部へ引き上げることにより、溶融部
が下部から上部へ連続的に移動する間に、LaNi5
相およびNi相から成る指向性凝固合金を得た。
なお、第２図において４はアルミナるつぼ、５は
温度計、６は耐火レンガ、７はシリカチユーブ、
８はセラミツク管、９は銅棒、１０はＯリングで
ある。
本合金ではLaNi5相は凝固方向に連続であり、
任意の垂直断面で切断しても同様の様相を呈し
た。
このようにして製造した合金を前述の高温高圧
熱天秤装置を用いて水素の吸収・放出をくり返し
ても、全く微粉化は生じなかつた。
発明の効果
本発明の水素貯蔵合金は水素吸収作用を損なう
ことなく優れた耐微粉化性が得られる。
また、指向性凝固を採用することにより凝固方
向に長範囲で連続LaNi5相を得ることができるた
め、例えば水素フイルターや半透膜などの新用途
への適用も可能となる。[Table] The alloy of the present invention is a comparative material, code 7 (LaNi 5 single phase)
In all cases, the hydrogen absorption rate is faster than that of 1, and no pulverization occurs. The comparison material, alloy No. 5, had a large amount of LaNi 5 phase, so it absorbed a large amount of hydrogen, but was finely powdered. Also, the hydrogen absorption amount [0.3 hydrogen atoms/metal atom (H/M)] of the alloy with only eutectic structure (alloy numbered 1) is the hydrogen absorption amount (6.5H/M) of the comparative material, number 7 (LaNi 5 ). Although it is about 50% smaller than
In Fig. 3, which is a phase diagram showing the range of the eutectic reaction between LaNi 5 and Ni, the amount of hydrogen absorbed increases as the eutectic composition shifts toward LaNi 5 . %) hydrogen absorption amount (4.9H/M) was significantly improved to about 82% of the comparative material, code 7, and the hydrogen absorption rate was significantly improved compared to the comparative material, code 7.
Considering that it is faster than (LaNi 5 ) and does not become pulverized, the disadvantage in hydrogen absorption is not a practical problem. The comparison material, alloy No. 6, does not undergo pulverization because it has a large Ni phase, but the hydrogen storage capacity (H/
M) is too small to meet the purpose of the present invention. Example 2 La and La prepared in the same manner as code 1 of Example 1
A sample made of Ni was set in the directional solidification alloy manufacturing apparatus 1 shown in FIG .
Exhaust gas from. To create a temperature gradient, the bottom side is connected to cooling water (cooling water inlet 12 and cooling water outlet 1).
By slowly raising the furnace consisting of the SiC heating element 3 to the top while cooling with water in step 3), the LaNi 5
A directionally solidified alloy consisting of phase and Ni phase was obtained.
In addition, in Fig. 2, 4 is an alumina crucible, 5 is a thermometer, 6 is a refractory brick, 7 is a silica tube,
8 is a ceramic tube, 9 is a copper rod, and 10 is an O-ring. In this alloy, the LaNi 5 phase is continuous in the solidification direction,
A similar appearance was observed even when cut at an arbitrary vertical cross section. Even when the alloy produced in this manner was repeatedly subjected to hydrogen absorption and release using the aforementioned high-temperature, high-pressure thermobalance apparatus, no pulverization occurred. Effects of the Invention The hydrogen storage alloy of the present invention provides excellent pulverization resistance without impairing the hydrogen absorption effect. In addition, by employing directional solidification, it is possible to obtain five continuous LaNi phases over a long range in the solidification direction, making it possible to apply it to new applications such as hydrogen filters and semipermeable membranes.
【図面の簡単な説明】[Brief explanation of drawings]
第１Ａ図は本発明による指向性凝固合金の模式
図、第１Ｂ図は第１Ａ図に示す合金のマトリツク
スの組織を示す写真、第２図は指向性凝固合金製
造装置の概略断面図で、第３図はLaNi5とNiと
の共晶反応の範囲を示す状態図である。
１……指向性凝固合金装置、２……試料、３…
…SiC発熱体、４……アルミナるつぼ、５……温
度計、６……耐火レンガ、７……シリカチユー
ブ、８……セラミツク管、９……銅棒、１０……
Ｏリング、１１……真空ポンプ接続管、１２……
冷却水入口、１３……冷却水出口。
FIG. 1A is a schematic diagram of a directionally solidified alloy according to the present invention, FIG. 1B is a photograph showing the structure of the matrix of the alloy shown in FIG. 1A, and FIG. 2 is a schematic cross-sectional view of a directionally solidified alloy manufacturing apparatus. Figure 3 is a phase diagram showing the range of eutectic reaction between LaNi 5 and Ni. 1... Directional solidification alloy device, 2... Sample, 3...
...SiC heating element, 4...Alumina crucible, 5...Thermometer, 6...Firebrick, 7...Silica tube, 8...Ceramic tube, 9...Copper rod, 10...
O-ring, 11...Vacuum pump connection tube, 12...
Cooling water inlet, 13...cooling water outlet.