JP2014132114A - Corrosion-resistant magnesium binary alloy - Google Patents
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本発明は、食塩水に対して優れた耐食性を示し、かつ起電力が大きく、かつ生体に無害な元素のみから構成されるマグネシウム2元合金に関する。 The present invention relates to a magnesium binary alloy that shows excellent corrosion resistance against saline, has a large electromotive force, and is composed only of elements that are harmless to a living body.
マグネシウムは、軽量で比強度が大、資源量が膨大、細胞毒性・発がん性がないなどの優れた特性を有している。しかし、食塩水に代表される中性塩溶液に対する耐食性の悪いことが用途を拡大する上での大きな障害となっている。 Magnesium has excellent properties such as light weight, high specific strength, enormous amount of resources, and no cytotoxicity / carcinogenicity. However, the poor corrosion resistance to neutral salt solutions typified by saline is a major obstacle to expanding applications.
例えば、マグネシウムの期待される用途にマグネシウム電池がある。マグネシウムは水溶液電解質を使える金属の中で、発生可能な電気量(Ah/g)とエネルギー密度(Wh/g)は最大であるため、電池の負極活物質として非常に有望な材料である。さらに、マグネシウムは軽量であり、生体毒性がないので使用時、使用後に環境問題を起すことのない材料として大きな可能性を有している。 For example, there is a magnesium battery as an expected use of magnesium. Magnesium is a very promising material as a negative electrode active material for batteries because it has the largest amount of electricity (Ah / g) and energy density (Wh / g) among metals that can use aqueous electrolytes. Furthermore, since magnesium is lightweight and has no biotoxicity, it has great potential as a material that does not cause environmental problems after use.
しかしながら、大容量電池材料としてのマグネシウムの使用実績はほとんどない。その原因は、マグネシウム合金の食塩水に対する耐食性がきわめて悪く、使用中に溶解して性能を十分に発揮できなかったことに関係している。電池の電極材料としてマグネシウム合金の使用を検討する場合は、材料自体の食塩水に対する耐食性を増すとともに、エネルギー密度や電気量などの電気特性を考慮した合金組成とする必要がある。なお本願において、「マグネシウム電池」とは、マグネシウム空気電池、マグネシウム水電池等を含む、「マグネシウムを負極活物質とする電池」の総称を示すものとする。 However, there is almost no record of using magnesium as a large capacity battery material. The cause is related to the fact that the magnesium alloy has extremely poor corrosion resistance to salt water and has not been able to exhibit its performance sufficiently by dissolving during use. When considering the use of a magnesium alloy as an electrode material of a battery, it is necessary to increase the corrosion resistance of the material itself to salt water and to have an alloy composition that takes into account electric characteristics such as energy density and electric quantity. In addition, in this application, a "magnesium battery" shall show the general term of "battery which uses magnesium as a negative electrode active material" including a magnesium air battery, a magnesium water battery, etc.
マグネシウム電池の負極活物質に求められる重要な特性は、(1)耐食塩水性が良いこと、(2)起電力が大きい、の二点である。(1)の耐食塩水性が悪い材料を電極に使用すると、電解液として使用される食塩水に対して自然溶解(自己放電)してしまうために十分な発電を行うことができない。これまでのマグネシウム合金の中では難燃マグネシウム(Mg-6Al-2Ca)が中性電解液である食塩水に対して優れた耐食性を示すとして特許出願されているが(特許文献1)、(2)の起電力に関して、難燃マグネシウムは標準電極電位がマグネシウム(−2.37V)よりも劣るアルミニウム(−1.66V)を6%程度含むので、電池として取り出せる電力が減少する問題がある。 The important characteristics required for the negative electrode active material of a magnesium battery are two points: (1) good salt water resistance and (2) high electromotive force. When the material having poor saltwater resistance (1) is used for the electrode, the material is naturally dissolved (self-discharged) in the saline used as the electrolytic solution, so that sufficient power generation cannot be performed. Among conventional magnesium alloys, flame-retardant magnesium (Mg-6Al-2Ca) has been applied for a patent (Patent Document 1) and (2) as exhibiting excellent corrosion resistance against saline, which is a neutral electrolyte. ), The flame retardant magnesium contains about 6% of aluminum (−1.66 V) whose standard electrode potential is inferior to magnesium (−2.37 V), so that there is a problem that the power that can be taken out as a battery is reduced.
また、難燃マグネシウム(Mg-6Al-2Ca)を電極とするマグネシウム電池は、使用中に負極の金属イオンが溶出し、正極で酸化されることで電流を発生する。従って、使用後の廃棄物は主成分の水酸化マグネシウム(Mg(OH)2)の他に、副成分として水酸化アルミニウム(Al(OH)3)を含む。これらの水酸化物は加熱すると容易に酸化マグネシウム(MgO)と酸化アルミニウム(Al2O3)に変化する。マグネシウムとアルミニウムの水酸化物、あるいは酸化物混合粉末を、両方の成分に分離することは困難である。酸化マグネシウムはフェロシリコンを還元剤とするピジョン法などによって、容易に金属マグネシウムに還元できる。しかしながら、酸化アルミニウムの熱還元は不可能に近いので、マグネシウム電池廃棄物処理の障害になる。このように難燃マグネシウム(Mg-6Al-2Ca)は耐食性は良いが、添加元素であるアルミニウムの作用として、発生電位が低下することと、廃棄物の処理効率を低下させる問題が生じる。 In addition, a magnesium battery using flame retardant magnesium (Mg-6Al-2Ca) as an electrode generates a current when the metal ions of the negative electrode elute during use and are oxidized at the positive electrode. Therefore, the waste after use contains aluminum hydroxide (Al (OH) 3 ) as a minor component in addition to magnesium hydroxide (Mg (OH) 2 ) as a main component. These hydroxides are easily converted into magnesium oxide (MgO) and aluminum oxide (Al 2 O 3 ) when heated. It is difficult to separate magnesium and aluminum hydroxide or mixed oxide powder into both components. Magnesium oxide can be easily reduced to magnesium metal by the Pigeon method using ferrosilicon as a reducing agent. However, the thermal reduction of aluminum oxide is almost impossible, which becomes an obstacle to the disposal of magnesium battery waste. As described above, flame retardant magnesium (Mg-6Al-2Ca) has good corrosion resistance, but as an effect of aluminum as an additive element, there are problems that the generated potential is lowered and the waste processing efficiency is lowered.
従来のマグネシウム合金は食塩水に対する耐食性が悪いことが問題とされており、我々の実験によれば、純度99.95%の純マグネシウム板は室温、10%食塩水中での1時間の腐食減量率は6.7%であり、2時間後には44.3%まで、腐食減量が加速的に増加する。また、一般のマグネシウム合金の中で耐食塩水性が優れているとされるAM60合金(Mg-6%Al-0.3%Mn)でも、室温の10%食塩水に25時間漬けると1.2%の腐食減量率を示す。この腐食への対策として表面処理法が検討されてきた。特許文献2は純度99.9%以上の純マグネシウムを酸化雰囲気530℃で9時間加熱することによって、表面に強固な酸化マグネシウム(MgO)の皮膜を形成することで、生体材料としての耐食性を高めている。また特許文献3はMg-Al-Mn合金あるいはMg-Al-Zn-Mn合金を射出成型した後に、酸素濃度を30〜99%まで高めた雰囲気中、400℃で4〜5時間加熱して強固な酸化マグネシウム(MgO)皮膜を作る方法である。一方、特許文献4はマグネシウム合金を水により蒸気養生して厚さ10〜200μmの水酸化マグネシウム膜を表面に形成することで、耐食性を高めている。これらは表面皮膜で耐食性を高める方法であって、電池電極のようにマグネシウム全体が溶解する用途には適用できない。
The conventional magnesium alloy has been considered to have a problem of poor corrosion resistance to saline solution, and according to our experiment, a pure magnesium plate having a purity of 99.95% has a corrosion weight loss rate of 1 hour in room temperature and 10% saline solution. Is 6.7%, and the corrosion weight loss increases at an accelerated rate to 44.3% after 2 hours. In addition, AM60 alloy (Mg-6% Al-0.3% Mn), which is considered to have excellent saltwater resistance among general magnesium alloys, is 1.2% when immersed in 10% saline at room temperature for 25 hours. Indicates the corrosion weight loss rate. Surface treatment methods have been studied as countermeasures against this corrosion.
表面処理に加えて、組成を制御することでマグネシウム合金の耐食性を増す発明が多くなされてきた。たとえば特許文献5は主要な合金元素として5〜12%のアルミニウムを含み、これにイットリウムとセリウムを添加している。また、特許文献5と同程度のアルミニウムを含むマグネシウム合金を基地組織とする耐食マグネシウム合金は数多く特許出願されている。アルミニウム以外の合金元素によって耐食性を高めた耐食性マグネシウム合金として特許文献6がある。これは0.1〜10%の亜鉛、0.1〜2%のジルコニウム、0.1〜8%の希土類元素を含み、亜鉛と希土類元素の金属間化合物の比率を30%以下とすることで良好な耐食性が得られるとしている。
Many inventions have been made to increase the corrosion resistance of magnesium alloys by controlling the composition in addition to the surface treatment. For example,
以上の先行発明は、耐食性の向上のみを目的として開発された材料、方法であって、電極として使用する場合の起電力や廃棄物処理は考慮されていない。しかし本発明が目的とする耐食塩水性マグネシウム合金は、マグネシウム電池の電極材料の用途において、中性食塩水溶液に対する耐食性と電気的な特性の両方を課題としている。したがって皮膜生成などの表面処理ではなく、合金成分と基地組織を制御することにより、合金自体の耐食性と起電力をはじめとする電気的特性の向上を目指した。このような理由から本合金が必要とする諸性は以下の4点である、(1)マグネシウム電池は電解液として濃度が数%から20%程度の飽和食塩水を使うので、食塩水に対する耐食性が良い。(2)電池としての起電力がアルミニウム含有合金よりも高い、(3)生体や環境に有害な元素を含まず、廃棄物処理の障害にならない。(4)大気中で加熱しても発火することなく取り扱いが安全であること。 The above prior inventions are materials and methods developed only for the purpose of improving corrosion resistance, and do not take into account electromotive force or waste treatment when used as electrodes. However, the salt-resistant aqueous magnesium alloy targeted by the present invention has problems in both corrosion resistance and electrical characteristics with respect to a neutral saline solution in the use of an electrode material for a magnesium battery. Therefore, we aimed to improve the corrosion resistance of the alloy itself and the electrical characteristics such as electromotive force by controlling the alloy components and the matrix structure instead of surface treatment such as film formation. For these reasons, the alloy requires the following four points: (1) Magnesium batteries use saturated saline with a concentration of several percent to 20% as the electrolyte, so corrosion resistance to saline Is good. (2) The electromotive force as a battery is higher than that of an aluminum-containing alloy. (3) It does not contain elements harmful to living bodies and the environment, and does not hinder waste disposal. (4) Handling is safe without ignition even when heated in the atmosphere.
耐食性マグネシウム合金に必要とされる上記(1)〜(4)の特性を持つ合金組成について鋭意研究を重ねた結果、カルシウムの添加量を適度に調節したマグネシウム―カルシウム2元合金は、これら4つの特性をすべて兼ね備えた合金であるとの結果を得ることが出来た。 As a result of earnest research on the alloy composition having the characteristics (1) to (4) required for the corrosion-resistant magnesium alloy, the magnesium-calcium binary alloy in which the amount of added calcium is appropriately adjusted is It was possible to obtain the result that the alloy had all the characteristics.
本発明は、マグネシウムとカルシウムから構成される2元合金であって、カルシウム含有率が0.18質量%以上、2.26質量%以下であることを特徴とする耐食性マグネシウム合金材料である。 The present invention is a corrosion-resistant magnesium alloy material which is a binary alloy composed of magnesium and calcium and has a calcium content of 0.18% by mass or more and 2.26% by mass or less.
カルシウム含有率が0.46質量%以上、1.65質量%以下であることを特徴とする耐食性マグネシウム合金材料であるとより好ましい。 More preferably, it is a corrosion-resistant magnesium alloy material having a calcium content of 0.46 mass% or more and 1.65 mass% or less.
この材料を一定温度で加熱・保持し、その後急冷する熱処理を加えることにより、さらに耐食性を増すことができる。 Corrosion resistance can be further increased by applying a heat treatment in which this material is heated and held at a constant temperature and then rapidly cooled.
その熱処理の際には、加熱温度を450℃以上、516.5℃(Mg-Ca合金の溶融温度)未満とすることが好ましい。 In the heat treatment, the heating temperature is preferably set to 450 ° C. or higher and lower than 516.5 ° C. (Mg—Ca alloy melting temperature).
また、加熱温度を500℃以上、516.5℃(Mg-Ca合金の溶融温度)未満とすることがより好ましい。 The heating temperature is more preferably 500 ° C. or more and less than 516.5 ° C. (Mg—Ca alloy melting temperature).
上記熱処理における急冷処理においては1秒以内に材料表面温度を40℃以下にまで急冷することが望ましい。 In the rapid cooling treatment in the heat treatment, it is desirable to rapidly cool the material surface temperature to 40 ° C. or less within 1 second.
上記急冷処理は、40℃以下の冷却液に被加熱材料を投入することによって行われることが望ましい。 The rapid cooling treatment is desirably performed by introducing a material to be heated into a cooling liquid of 40 ° C. or lower.
電解質として食塩水を使用している電池においては、この耐食塩水性マグネシウム合金材料を負極活物質として利用することにより高性能な電池とすることができる。 In a battery using saline as an electrolyte, a high-performance battery can be obtained by using this saline-resistant magnesium alloy material as a negative electrode active material.
また、マグネシウムとカルシウムから構成され、カルシウム含有率が0.18質量%以上、2.26質量%以下であることを特徴とする2元合金を加熱して一定温度で保持し、その後急冷する熱処理を加えて耐食性を増すことによって目的とする耐食性マグネシウム合金材料を製造することが可能である。 Also, a heat treatment comprising a binary alloy that is composed of magnesium and calcium and has a calcium content of 0.18% by mass or more and 2.26% by mass or less, and is maintained at a constant temperature and then rapidly cooled. It is possible to produce a target corrosion-resistant magnesium alloy material by increasing the corrosion resistance.
また、カルシウム含有率が0.46質量%以上、1.65質量%以下として、目的とする耐食性マグネシウム合金材料を製造することがより好ましい。 Moreover, it is more preferable to manufacture the target corrosion-resistant magnesium alloy material with a calcium content of 0.46 mass% or more and 1.65 mass% or less.
得られた材料を一定温度で加熱・保持し、その後急冷する熱処理を加えることにより、さらに耐食性を増した耐食性マグネシウム合金材料を製造することができる。 The obtained material is heated and held at a constant temperature, and then subjected to a heat treatment for rapid cooling, whereby a corrosion-resistant magnesium alloy material with further enhanced corrosion resistance can be produced.
その熱処理の際には、加熱温度を450℃以上、516.5℃(Mg-Ca合金の溶融温度)未満とすることが好ましい。 In the heat treatment, the heating temperature is preferably set to 450 ° C. or higher and lower than 516.5 ° C. (Mg—Ca alloy melting temperature).
また、加熱温度を500℃以上、516.5℃(Mg-Ca合金の溶融温度)未満とすることがより好ましい。 The heating temperature is more preferably 500 ° C. or more and less than 516.5 ° C. (Mg—Ca alloy melting temperature).
上記熱処理における急冷処理においては1秒以内に材料表面温度を40℃度以下にまで急冷することが望ましい。 In the rapid cooling treatment in the heat treatment, it is desirable to rapidly cool the material surface temperature to 40 ° C. or less within 1 second.
上記急冷処理は、40℃以下の冷却液に被加熱材料を投入することによって行われることが望ましい。 The rapid cooling treatment is desirably performed by introducing a material to be heated into a cooling liquid of 40 ° C. or lower.
本発明のマグネシウム-カルシウム2元合金は純マグネシウムやアルミニウム含有マグネシウム合金に勝る耐食塩水性と、マグネシウム電池の負極活物質としての優れた電気特性を有し、併せて難燃マグネシウム(Mg-6Al-2Ca)と同等の難燃性を有する。 The magnesium-calcium binary alloy of the present invention has a salt water resistance superior to pure magnesium and aluminum-containing magnesium alloys, and excellent electrical properties as a negative electrode active material for magnesium batteries. 2Ca) has the same flame retardancy.
以下、図1〜図11によって本発明を実施する形態を説明する。 Hereinafter, embodiments of the present invention will be described with reference to FIGS.
マグネシウムに0.18、0.46、1.13、1.65、2.26、3.02、5.01質量%のカルシウムを含む2元合金を溶解、鋳造した。これらの試験片、各4組を35×35×5mmに成型した。このうち一組は鋳放しのままで腐食試験に供し、他は電気炉中、400℃、450℃、500℃で一時間空気中加熱をした後、25℃の水中に投入して急冷した。なお、一般のマグネシウム合金を空気中400℃〜500℃で加熱すると発火し、これを水中に投入することは水素爆発を起こす危険性が大きい。しかし本発明の合金はカルシウムの燃焼防止効果によって、加熱時の発火も、急冷時の水素発生も生じない。加熱・急冷後の試験片表面の外見は鋳放し材と同様であって、明らかな酸化物(白色の酸化マグネシウム膜)の付着は認められなかった。これらの試験片を、(1)10%食塩水による腐食試験、(2)10%食塩水を電解液とする起電力測定、(3)マグネシウム空気電池電極としての発電特性試験に供して、それらの特性を評価した。 A binary alloy containing 0.18, 0.46, 1.13, 1.65, 2.26, 3.02, 5.01 mass% calcium in magnesium was melted and cast. Four sets of these test pieces were molded into 35 × 35 × 5 mm. One of them was subjected to a corrosion test as it was, and the other was heated in air at 400 ° C., 450 ° C., and 500 ° C. for 1 hour in an electric furnace, and then put into 25 ° C. water and rapidly cooled. In addition, when a general magnesium alloy is heated in air at 400 ° C. to 500 ° C., it ignites, and throwing it into water has a high risk of causing a hydrogen explosion. However, the alloy of the present invention does not cause ignition during heating nor hydrogen generation during rapid cooling due to the effect of preventing combustion of calcium. The appearance of the test specimen surface after heating and quenching was the same as that of the as-cast material, and no obvious oxide (white magnesium oxide film) was observed. These test pieces were subjected to (1) corrosion test with 10% saline solution, (2) electromotive force measurement using 10% saline solution as electrolyte, and (3) power generation characteristic test as magnesium air battery electrode. The characteristics were evaluated.
次に本発明の詳細を実施例に基づいて説明する。なお、本発明は明細書の全体に記載される技術思想によって限定されるものであり、本実施例によってのみ限定されるものでないことは理解されるべきことである。 Next, details of the present invention will be described based on examples. In addition, it should be understood that the present invention is limited only by the technical idea described in the entirety of the specification, and is not limited only by this embodiment.
カルシウム含有率が異なる鋳放し、および熱処理試験片を、それらの底面が容器底面から5mm離れるように固定し、濃度10質量%の食塩水70ml中に室温で25時間静置した。食塩水の濃度である10質量%は、マグネシウム電池の電解液の食塩水濃度を想定し、その電解液中における耐食性を確かめることを目的として設定しているが、この濃度での耐食塩水性が確かめられれば、より塩分濃度の低い生体内においても十分な耐食塩水性があることを確かめることができる。各試験片は微量の水素を発生しながら溶解して、腐食の程度に応じて表面に腐食孔と腐食生成物である水酸化マグネシウムを生じた。腐食試験終了後に試験片表面をブラシで軽くこすって付着物を除去し、乾燥後に重量変化率を測定した。その結果を図1の表に示す。この図のマイナスの値は重量減少を示し、プラスの値は重量が増加したことを示している。この重量増加は腐食生成物の付着による。図1の測定値の中から、鋳放し(As Cast)材について、全部の試験片のカルシウム含有率と腐食減率の関係を図2に示す。腐食減量率は2.26質量%カルシウムから急に増加している。そこで、カルシウム量2.26質量%以下の腐食減量率が小さい範囲を見やすく拡大した、鋳放し材と熱処理材の腐食減量率を図3に示す。 The as-cast and heat-treated test pieces having different calcium contents were fixed so that their bottom surfaces were 5 mm away from the bottom surface of the container, and were allowed to stand at room temperature for 25 hours in 70 ml of 10% strength by weight saline. The salt solution concentration of 10% by mass is set for the purpose of confirming the corrosion resistance in the electrolyte solution assuming the salt solution concentration of the magnesium battery electrolyte solution. If confirmed, it can be confirmed that there is sufficient saline resistance even in a living body having a lower salinity. Each test piece dissolved while generating a trace amount of hydrogen, and produced corrosion holes and corrosion product magnesium hydroxide on the surface according to the degree of corrosion. After completion of the corrosion test, the surface of the test piece was lightly rubbed with a brush to remove deposits, and the weight change rate was measured after drying. The results are shown in the table of FIG. A negative value in this figure indicates a decrease in weight, and a positive value indicates an increase in weight. This weight increase is due to adhesion of corrosion products. FIG. 2 shows the relationship between the calcium content of all the test pieces and the corrosion reduction rate of the as-cast material among the measured values of FIG. Corrosion weight loss rate increases rapidly from 2.26 mass% calcium. Accordingly, FIG. 3 shows the corrosion weight loss rates of the as-cast material and the heat-treated material, in which the range where the corrosion weight loss rate with a calcium content of 2.26% by mass or less is small is easily seen.
図1、図2が示すように、Mg−Ca合金試験片の鋳放し材は、カルシウム含有率が1.65質量%以下の試験片は腐食減量率が1%以下であるが、カルシウム含有率が2.26質量%を超えるあたりから、食塩水による腐食が増え始め、5.01質量%では腐食率が30%を超えて、食塩水に対する腐食量が著しく増加する。よって、カルシウム含有率を0.18質量%以上、2.26質量%以下としたマグネシウムーカルシウム2元合金とすることで、耐食塩水性の高いマグネシウム合金とを得ることができ、より好ましくは、カルシウム含有率を0.46質量%以上、1.65質量%以下とすることにより、さらに耐食塩水性のすぐれたマグネシウム合金とすることができる。 As shown in FIG. 1 and FIG. 2, the as-cast material of the Mg—Ca alloy test piece has a calcium content of 1.65% by mass or less, and the corrosion weight loss rate is 1% or less. When the amount exceeds 2.26% by mass, corrosion due to the salt solution starts to increase, and at 5.01% by mass, the corrosion rate exceeds 30%, and the amount of corrosion with respect to the salt solution increases remarkably. Therefore, by using a magnesium-calcium binary alloy having a calcium content of 0.18% by mass or more and 2.26% by mass or less, a magnesium alloy with high salt water resistance can be obtained, and more preferably, By setting the calcium content to 0.46% by mass or more and 1.65% by mass or less, a magnesium alloy having further excellent salt water resistance can be obtained.
熱処理の効果を示す図1の結果のように、熱処理材の腐食特性は加熱温度によって大きな差が生じた。400℃熱処理材では、カルシウム含有率が0.18質量%および0.46質量%の試験片が腐食減量を示したが、他は腐食によって重量が増加している。これは、深い腐食孔が生じて、その中の腐食生成物(水酸化マグネシウム)が除去できなかったことによると考えられる。3.02質量%の試験片は12%以上の大きな重量増加を示した。これは試験片端面に腐食割れが生じて、内部に多量の腐食生成物が生じた結果による。また、450℃熱処理試験片は、0.18質量%の試験片のみが鋳放し試験片よりも大きな腐食減量を示し、他は鋳放し試験片の腐食減量のほぼ半分程度に改善されている。3.02質量%の試験片のみは腐食減量が鋳放し材の20分の一に減っている。さらに500℃熱処理試験片は450℃熱処理試験片よりも、すべてのカルシウム含有率組成において腐食減量が減っている。 As shown in the result of FIG. 1 showing the effect of heat treatment, the corrosion characteristics of the heat treated material varied greatly depending on the heating temperature. In the heat-treated material at 400 ° C., the specimens having a calcium content of 0.18% by mass and 0.46% by mass showed a weight loss by corrosion, but the others were increased in weight by corrosion. This is probably because deep corrosion holes were formed and the corrosion products (magnesium hydroxide) therein could not be removed. The 3.02 mass% specimen showed a large weight gain of 12% or more. This is due to the result of corrosion cracking on the end face of the specimen and a large amount of corrosion products inside. Further, in the 450 ° C. heat-treated test piece, only 0.18% by mass of the test piece shows a larger weight loss than the as-cast test piece, and the others are improved to about half of the corrosion weight loss of the as-cast test piece. Only 3.02% by weight of the test piece has a corrosion weight reduction of 1/20 that of the as-cast material. Further, the 500 ° C. heat-treated test piece has a reduced corrosion weight loss at all calcium content compositions than the 450 ° C. heat-treated test piece.
このように450℃以上に加熱・保持後、急冷熱処理を施すと、マグネシウム-カルシウム2元合金の耐食塩水性を大幅に改善することができ、特に500度を超えた温度(ただし融点(=516.5℃)未満の温度であること)での熱処理には大きな効果があることがわかった。0.18質量%カルシウム試験片の熱処理効果が他試験片よりも少なかった原因は、カルシウム量が少なくて試料自体の耐酸化性が悪かったためと考えられる。 Thus, when a rapid cooling heat treatment is performed after heating and holding at 450 ° C. or higher, the salt-water resistance of the magnesium-calcium binary alloy can be greatly improved, particularly at temperatures exceeding 500 degrees (however, the melting point (= 516). It was found that the heat treatment at a temperature of less than 5 ° C.) has a great effect. The reason why the heat treatment effect of the 0.18% by mass calcium test piece was less than that of the other test pieces is considered to be that the amount of calcium was small and the oxidation resistance of the sample itself was poor.
次に、図4に示すマグネシウム-カルシウム状態図によって、熱処理の効果を考察する。図4によればMg-Ca合金は516℃において0.82原子%Ca(1.36質量%Ca)の時に、もっとも広範囲なマグネシウム単一相となる。従って450℃以上の加熱によってカルシウムの全量がマグネシウム相に固溶して、この状態が水冷によって室温までもたらされたと考えられる。単一相の場合は食塩水中での局部電池形成がないので、耐食塩水性は向上する。しかし400℃以下ではカルシウムの一部が結晶粒界に金属間化合物(Mg2Ca)として析出した結果、耐食塩水性が低下したと考えられる。なお本明細書において、室温とは一般的な生活環境にて想定される温度を示し、具体的には0℃〜40℃程度の範囲を示すものとする。 Next, the effect of the heat treatment will be considered using the magnesium-calcium phase diagram shown in FIG. According to FIG. 4, the Mg—Ca alloy becomes the most extensive magnesium single phase at 0.82 atomic% Ca (1.36 mass% Ca) at 516 ° C. Therefore, it is considered that the total amount of calcium was dissolved in the magnesium phase by heating at 450 ° C. or higher, and this state was brought to room temperature by water cooling. In the case of a single phase, there is no formation of local batteries in saline solution, so that the saltwater resistance is improved. However, at 400 ° C. or lower, it is considered that a part of calcium is precipitated as an intermetallic compound (Mg 2 Ca) at the crystal grain boundary, and as a result, the salt resistance is lowered. In addition, in this specification, room temperature shows the temperature assumed in a general living environment, and shall specifically show the range of about 0 degreeC-40 degreeC.
次に、カルシウム含有率による起電力の変化を、6質量%のアルミニウムを含む難燃マグネシウムと比較した。腐食特性と異なり、起電力は合金組成に依存する量であり、熱処理の影響は少ないので鋳放し材のみについて測定した。実施例1と同じサイズの試験片に対して、10%食塩水を電解液、炭素を正極、マグネシウム合金を負極として、開放状態の起電力を各試験片について測定した。対比試験片の難燃マグネシウム(Mg-6Al-2Ca)の起電力1.80V(基準)に対して、カルシウム含有率(質量%)が1.13%、2.26%および3.02%に増すと、起電力は1.85V(+2.8%)、および1.91V(+6.1%)に増加した。しかしカルシウムを5.01%に増すと起電力は1.83V(+1.7%)の増加にとどまった。この結果を図5に示す。このように2%までのカルシウム添加は6質量%アルミニウムを含む難燃マグネシウム合金よりも高い起電力が得られた。 Next, the change in electromotive force due to the calcium content was compared with flame retardant magnesium containing 6% by mass of aluminum. Unlike the corrosion characteristics, the electromotive force depends on the alloy composition, and the influence of the heat treatment is small, so only the as-cast material was measured. An electromotive force in an open state was measured for each test piece using 10% saline as an electrolyte, carbon as a positive electrode, and magnesium alloy as a negative electrode for the test piece having the same size as that of Example 1. Calcium content (mass%) is 1.13%, 2.26% and 3.02% against the electromotive force of 1.80V (standard) of flame retardant magnesium (Mg-6Al-2Ca) Increasing the electromotive force increased to 1.85V (+ 2.8%) and 1.91V (+ 6.1%). However, when calcium was increased to 5.01%, the electromotive force increased only to 1.83V (+ 1.7%). The result is shown in FIG. Thus, the addition of calcium up to 2% gave a higher electromotive force than the flame retardant magnesium alloy containing 6% by mass aluminum.
マグネシウム-カルシウム2元合金を負極とする電池の発電特性を、難燃マグネシウム負極(Mg-6Al-2Ca)と比較した。10%食塩水を電解液として、正極は多孔質の炭素極(7cm×18cm)を用い、これから0.5cm離してマグネシウム電極を固定した。図6に難燃マグネシウム(Mg-6Al-2Ca)を負極として、負荷抵抗が1.57Ωの場合に発生する電圧と、負荷抵抗に流れる電流を24時間(1440分間)測定した結果を示す。測定開始13時間(780分)までは発生電圧1.2V、電流0.8A程度のほぼ一定値を保ったが、その後、11時間で電圧は1Vに、電流は0.65Aに徐々に低下した。この時に測定された電気量(負極1gが発生した総電流)は1.03Ah/gであり、エネルギー密度(負極1gが発生した総電力)は1.19Wh/gであった。 The power generation characteristics of a battery using a magnesium-calcium binary alloy as a negative electrode were compared with those of a flame retardant magnesium negative electrode (Mg-6Al-2Ca). A porous carbon electrode (7 cm × 18 cm) was used as the positive electrode with 10% saline as an electrolyte, and a magnesium electrode was fixed at a distance of 0.5 cm from this. FIG. 6 shows the results of measuring the voltage generated when flame resistance magnesium (Mg-6Al-2Ca) is used as the negative electrode and the load resistance of 1.57Ω and the current flowing through the load resistance for 24 hours (1440 minutes). Up to 13 hours (780 minutes) from the start of measurement, the generated voltage was kept at 1.2 V and the current was about 0.8 A, but after that, the voltage gradually decreased to 1 V and the current gradually decreased to 0.65 A in 11 hours. . The amount of electricity (total current generated by the negative electrode 1g) measured at this time was 1.03 Ah / g, and the energy density (total power generated by the negative electrode 1g) was 1.19 Wh / g.
次に負極として、マグネシウムーカルシウム合金(Mg-1.13Ca)を500℃―1時間加熱後に水冷した電極を使用し、負荷抵抗の値を4段階で変化させた以外は実施例3と同じ条件でマグネシウム電池の発電特性を測定した。この測定では最長141時間(8460分)の連続実験を行なった。電池の発電特性は負荷抵抗の値によって大きく変化するので、この実験では負荷抵抗を0.68、1.18、2.40、19.9Ωの4段階に変化させて実験を継続した。この4回の実験における電圧測定の結果を図7に示す。また、各測定において発生した電圧の平均と、電流の平均の関係を図8に示す。さらに、各測定で得られた電気量(Ah/g)とエネルギー密度(Wh/g)の関係を図9に示す。 Next, as the negative electrode, an electrode obtained by heating a magnesium-calcium alloy (Mg-1.13Ca) at 500 ° C. for 1 hour and then water-cooling was used, and the load resistance value was changed in four steps. The power generation characteristics of the magnesium battery were measured. In this measurement, a continuous experiment was conducted for a maximum of 141 hours (8460 minutes). Since the power generation characteristics of the battery greatly change depending on the value of the load resistance, in this experiment, the experiment was continued by changing the load resistance in four stages of 0.68, 1.18, 2.40, and 19.9Ω. The results of voltage measurement in these four experiments are shown in FIG. FIG. 8 shows the relationship between the average voltage generated in each measurement and the average current. Furthermore, the relationship between the amount of electricity (Ah / g) and energy density (Wh / g) obtained in each measurement is shown in FIG.
図7に示すように、負荷抵抗が高い場合は発生電圧は高く、その持続時間も長い。しかし負荷抵抗が小さくなると、発生電圧は低下し、その持続時間も短くなっている。0.68、1.18、2.40、19.9Ωの実験開始時近傍の発生電圧はそれぞれ、1.06V、1.18V、1.27V、1.38Vであったが、その持続時間は約1000分、4000分、5500分、8500分以上と負荷抵抗の値とともに大きく変化している。
19.9Ωと高い場合は抵抗を流れる電流が少なくて、負極の溶解量も少ないので、発生電圧は測定全期間の間1.38Vとほぼ一定であった。
As shown in FIG. 7, when the load resistance is high, the generated voltage is high and the duration is long. However, as the load resistance decreases, the generated voltage decreases and the duration is shortened. The generated voltages in the vicinity of the start of the experiment of 0.68, 1.18, 2.40, and 19.9Ω were 1.06V, 1.18V, 1.27V, and 1.38V, respectively. About 1000 minutes, 4000 minutes, 5500 minutes, 8500 minutes or more, the values greatly change with the load resistance.
When the voltage was as high as 19.9Ω, the current flowing through the resistor was small and the amount of dissolution of the negative electrode was small, so that the generated voltage was almost constant at 1.38 V during the entire measurement period.
各測定における平均電圧と、平均電流の関係を示す図8によれば、負荷抵抗が0.68〜2.40Ωの間での平均電流は0.43〜0.53Aと大きな差はない。負荷抵抗が19.9Ωになると平均電流は0.07Aと著しく少なくなり、この時の発生電圧は図7に示されるようにほぼ一定になる。このように発生電圧が電流によって大きく変化した原因として、電解液である塩水の電気抵抗の影響が考えられる。今回の実験では濃度10%の食塩水を用いた。食塩水の濃度を上げると電気抵抗は減少して抵抗による損失は減るが、負極の腐食速度が増す問題がある。 According to FIG. 8 showing the relationship between the average voltage and the average current in each measurement, the average current when the load resistance is between 0.68 and 2.40Ω is not so large as 0.43 to 0.53A. When the load resistance is 19.9Ω, the average current is remarkably reduced to 0.07 A, and the generated voltage at this time becomes almost constant as shown in FIG. As a cause of the large change in the generated voltage due to the current in this way, the influence of the electrical resistance of the salt water, which is the electrolyte, can be considered. In this experiment, a saline solution having a concentration of 10% was used. Increasing the concentration of the saline solution reduces the electrical resistance and reduces the resistance loss, but has the problem of increasing the corrosion rate of the negative electrode.
マグネシウム電池の負荷抵抗を変化させた場合に取り出した電気量とエネルギー密度の間には、図9のようにほぼ直線的な正の比例関係が見られた。負荷抵抗が0.68Ωと低い場合の電気量とエネルギー密度はそれぞれ1.15Ah/g、0.87Wh/gであるが、負荷抵抗が19.9Ωに増すとそれは1.61Ah/gと2.17Wh/gに増加している。純マグネシウムから得られる理論電気量は2.29Ah/gなので負荷抵抗19.9Ωの場合は70.3%の電気量をとり出すことができた。 A substantially linear positive proportional relationship was seen between the amount of electricity taken out and the energy density when the load resistance of the magnesium battery was changed, as shown in FIG. When the load resistance is as low as 0.68Ω, the electric quantity and energy density are 1.15 Ah / g and 0.87 Wh / g, respectively, but when the load resistance increases to 19.9Ω, it is 1.61 Ah / g and 2. It has increased to 17 Wh / g. Since the theoretical amount of electricity obtained from pure magnesium is 2.29 Ah / g, when the load resistance is 19.9Ω, the amount of electricity of 70.3% can be extracted.
難燃マグネシウム(Mg-6Al-2Ca)と、本発明によるマグネシウムーカルシウム合金(Mg-1.13Ca)熱処理材を負極とするマグネシウム電池の電気量とエネルギー密度を比較した。難燃マグネシウム(Mg-6Al-2Ca)を負極とする測定は図6に示すように負荷抵抗1.57Ω、測定時間は電池特性がほぼ一定に保たれる24時間であった。一方、本発明によるマグネシウムーカルシウム合金(Mg-1.13Ca)熱処理材を負極とするマグネシウム電池の測定は図7に示すように負荷抵抗も、測定時間も難燃マグネシウムの場合とは異なる。そこで負荷抵抗の値に対して、電気量、エネルギー密度の変化がほぼ直線的に変化する0.68〜2.40Ωの間の測定値を難燃マグネシウムの測定値と比較した。電気量の比較を図10に示し、エネルギー密度の比較を図11に示す。図10によれば、本発明によるマグネシウムーカルシウム合金熱処理材の1.57Ω負荷での電気量は1.3Ah/g程度であるが、難燃マグネシウムの場合は1.03Ah/gと79%程度であった。また、図11によれば、本発明によるマグネシウムーカルシウム合金熱処理材の1.57Ω負荷でのエネルギー密度は1.22Wh/g程度であるが、難燃マグネシウムの場合は1.19Wh/gと97%程度であった。これらの結果から、本発明によるグネシウムーカルシウム合金熱処理材を負極とする電池の発電特性は、難燃マグネシウムを負極とする場合よりも優れた結果が得られることが明らかである。
The electricity quantity and energy density of the magnesium battery using the flame retardant magnesium (Mg-6Al-2Ca) and the magnesium-calcium alloy (Mg-1.13Ca) heat treatment material according to the present invention as a negative electrode were compared. As shown in FIG. 6, the measurement using flame retardant magnesium (Mg-6Al-2Ca) as a negative electrode was a load resistance of 1.57Ω, and the measurement time was 24 hours when the battery characteristics were kept almost constant. On the other hand, the measurement of the magnesium battery using the magnesium-calcium alloy (Mg-1.13Ca) heat treatment material according to the present invention as a negative electrode differs from the case of flame retardant magnesium in both load resistance and measurement time as shown in FIG. Therefore, the measured value between 0.68 and 2.40Ω, in which changes in the amount of electricity and energy density change almost linearly with respect to the value of load resistance, was compared with the measured value of flame retardant magnesium. A comparison of the quantity of electricity is shown in FIG. 10, and a comparison of the energy density is shown in FIG. According to FIG. 10, the heat quantity of the magnesium-calcium alloy heat treated material according to the present invention is about 1.3 Ah / g at 1.57 Ω load, but in the case of flame retardant magnesium, 1.03 Ah / g, about 79%. Met. Further, according to FIG. 11, the energy density of the heat-treated magnesium-calcium alloy material according to the present invention at a load of 1.57Ω is about 1.22 Wh / g, but 1.19 Wh / g and 97 in the case of flame retardant magnesium. %. From these results, it is clear that the power generation characteristics of the battery using the heat-treated material of gnesium-calcium alloy according to the present invention as a negative electrode are superior to those obtained when flame retardant magnesium is used as the negative electrode.
Claims (10)
The method for producing a corrosion-resistant magnesium alloy material according to claim 7 or 8, wherein the rapid cooling treatment in the heat treatment is performed by introducing a material to be heated into a cooling liquid of 40 ° C or lower.
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