JP2004161839A - Cooling storage material using rare earth element vanadium oxide ceramic and production method therefor and cooling storage apparatus - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、希土類バナジウム酸化物を用いた蓄冷材とその製造方法、及びこの蓄冷材を用いた蓄冷器に関する。さらに詳しくは、赤外線センサーの分解能の向上、あるいは超伝導線材の臨界電流特性の大幅な向上をもたらすために必要とされる、２Ｋ付近の極低温領域で高い熱容量を有し、さらに冷凍機運転中において、摩耗粉が生じない高機能性蓄冷材やその製造方法、及びそれを充填した蓄冷器に関する。
【０００２】
【従来の技術とその課題】
赤外線センサーや超伝導マグネットなどは、より低温化させることによって、特性を向上させることができる。例えば宇宙衛星に搭載される赤外線センサーは、より高度な情報を得るために、センサーの冷却が行われている。その冷却方法としては、現在のところ、衛星内に搭載した超流動ヘリウム（絶対温度２．２Ｋ以下）を宇宙空間に徐々に放出しながら、一定期間温度を保持する方法がとられている。しかしこの方法では、赤外線センサーの寿命が残っているのにも関わらず、超流動ヘリウムが無くなった時点で、赤外線センサーの使用が困難となる。そのため、長期間にわたり繰り返し使用可能で宇宙衛星に搭載可能な、小型極低温冷凍機が注目されている。
【０００３】
【特許文献１】特許２６０９７４７
【０００４】
小型冷凍機の冷却能力や最低到達温度などは、冷凍機に組み込まれている蓄冷器を構成する充填物質である蓄冷材に大きく依存し、蓄冷材は大きな熱容量をもちかつ熱交換効率が高いことが必要である。Ｐｂなどの金属蓄冷材では、１０Ｋ以下で熱容量が急激に低下するため、１０Ｋ以下での冷却効率が低下する。そこで、より液体ヘリウム温度（４．２Ｋ）に近い極低温領域において、大きな熱容量を有する蓄冷材が開発されている。このような蓄冷材には、例えばＨｏＣｕ２やＥｒＮｉなどの希土類金属間化合物（上記特許文献１，対応米国特許ＵＳＰ５４４９，４１６）がある。また出願人は、ＧｄＡｌＯ３（特願２０００−１７５１２８）あるいはＧｄ２Ｏ２Ｓ（特願２００２−１６９７３２）を蓄冷材とすることを先願で提案した。しかし図１に示すように、ＨｏＣｕ２、ＧｄＡｌＯ３ 、Ｇｄ２Ｏ２Ｓ は２Ｋ付近の熱容量は小さく、２Ｋ付近の極低温での冷却能力の向上は期待できない。
【０００５】
【発明の課題】
本発明の課題は、超流動ヘリウム温度等の約２Ｋ付近で大きな熱容量を有し、かつ熱衝撃や振動に対する耐久性の高い蓄冷材と、その製造方法、及びこれを用いた蓄冷器とを提供することにある。
【０００６】
【発明の構成】
この発明の蓄冷材は、一般式 ＲＶＯ４ （Ｒは Ｙを含むＬａ， Ｃｅ， Ｐｒ， Ｎｄ， Ｓｍ， Ｅｕ， Ｇｄ， Ｔｂ， Ｄｙ， Ｈｏ， Ｅｒ， Ｔｍ， Ｙｂ及びＬｕから選択される１種類又は２種類以上の希土類元素を表す。） で表される希土類バナジウム酸化物セラミックスを用いたものである（請求項１）。セラミックスの形状は、粒状やハニカム状、あるいは粒状の粒子をネットワーク状に多孔質に焼結したものなどとする。また希土類バナジウム酸化物等の筒状セラミックス内に、粒状の希土類バナジウム酸化物の粒子を充填したものなどでも良い。粒状の場合、蓄冷材の平均粒径は０．０５〜２ｍｍが好ましい。
【０００７】
好ましくは、希土類バナジウム酸化物蓄冷材に、両性金属元素、アルカリ土類金属元素及び遷移金属元素の少なくとも一員の元素の添加物を、金属元素として５０〜１０００重量ｐｐｍ添加し、蓄冷材を強化する（請求項２）。添加時の形態は、酸化物などの化合物が好ましい。
好ましくは、前記添加物をＡｌ及びＧａからなる群の少なくとも一員の両性金属元素の添加物とする（請求項３）。
また好ましくは、前記添加物をＭｇ、Ｃａ、Ｓｒ、Ｂａ、からなる群の少なくとも一員のアルカリ土類金属元素の添加物とする。（請求項４）。
好ましくは、前記添加物を元素番号が２２（Ｔｉ）〜３０（Ｚｎ）及び４０（Ｚｒ）、７２（Ｈｆ） の少なくとも一員の遷移金属元素の添加物とする（請求項５）。
【０００８】
蓄冷材の相対密度は９６％以上が好ましく、より好ましくは９８％以上とし、理論密度に近づけることが好ましい（請求項６）。これは蓄冷材の強度を向上するためである。
蓄冷材の平均結晶粒径は１００μｍ以下が好ましく、より好ましくは５０μｍ以下とし、さらに好ましくは１０μｍ以下とする（請求項７）。これも同様に、蓄冷材の強度を向上するためである。
蓄冷材は２〜３Ｋに、熱容量の極大値を有することが好ましい（請求項８）。即ち４Ｋ付近に熱容量の極大値を有するものとしては、ＧｄＡｌＯ３やＧｄ２Ｏ２Ｓ等の蓄冷材が既にあり、より低温で熱容量の極大値を持つことが重要である。
【０００９】
本発明の希土類バナジウム酸化物蓄冷材の製造方法では、一般式ＲＶＯ４の粉体を、１５００〜１７００℃の温度範囲に１〜１０時間保持するように焼成する（請求項９）。この条件で、相対密度が例えば９６％以上（好ましくは９８％以上）で、平均結晶粒径が１００μｍ以下（通常は５０μｍ以下）の希土類バナジウム酸化物蓄冷材が得られる。
蓄冷材の製造では例えば、ＲＶＯ４粉末をボールミル等で粉砕し、９００〜１２００℃程度で仮焼する。得られた希土類バナジウム酸化物粉末体を、例えば転動造粒法、押し出し法と転動造粒法との組み合せ、流動造粒法、噴霧乾燥法、型押し法等によって、顆粒状に造粒する。あるいは所望の形状に成型する。これらを、１５００〜１７００℃で１〜１０時間保持するように焼成する。焼成雰囲気は例えば大気中でよいが、他の雰囲気でも良い。得られた蓄冷材の平均粒径は０．０５〜２ｍｍが好ましい。
【００１０】
蓄冷材の焼成条件は、焼成後の蓄冷材の相対密度が９６％以上、より好ましくは９８％以上となるようにし、平均結晶粒径が１００μｍ以下、より好ましくは５０μｍ以下、最も好ましくは１０μｍ以下、となるようにすることが好ましい（請求項１０）。
またＲＶＯ４には、両性金属、アルカリ土類金属及び遷移金属の少なくとも一員の元素を、金属元素として５０〜１０００重量ｐｐｍ添加することが好ましい（請求項１１）。両性金属は例えばＡｌやＧａで、アルカリ土類金属は例えばＭｇ、Ｃａ、Ｓｒ、Ｂａとし、遷移金属は例えば原子番号２２（Ｔｉ）〜３０（Ｚｎ）及び４０（Ｚｒ）、７２（Ｈｆ）からなる群の少なくとも一員とする。これらの添加物を加える場合、例えば仮焼前の粉体に添加することが好ましいが、仮焼後の粉体に添加して焼成過程で添加物を拡散させても良い。これらの添加物は、蓄冷材の相対密度を向上させ、かつ平均結晶粒径を小さくする。
【００１１】
本発明の極低温蓄冷器は、上記の希土類バナジウム酸化物セラミックス蓄冷材を、適宜の筒などに充填したものである（請求項１２）。さらに前記蓄冷器には、蓄冷材を高温用蓄冷材から中間温度用蓄冷材、低温用蓄冷材への順で層状に充填し、高温用蓄冷材を希土類金属間化合物蓄冷材、例えばＨｏＣｕ２、中間温度用蓄冷材を希土類酸化物または希土類オキシ硫化物蓄冷材、例えばＧｄＡｌＯ３やＧｄ２Ｏ２Ｓ、低温用蓄冷材を希土類バナジウム酸化物蓄冷材とすることが好ましい（請求項１３）。これは１０Ｋ弱から２Ｋ程度まで蓄冷器が連続した熱容量を持つようにし、冷凍効率を高めるためである。
【００１２】
【発明の作用と効果】
本発明の希土類バナジウム酸化物（以下ＲＶＯ４と示す。）蓄冷材は、２〜３Ｋに磁気相転移温度を持ち、熱容量は２Ｋ付近の温度領域で０．３Ｊ／ｃｃ・Ｋ以上である。このように本発明の蓄冷材では２Ｋ付近で高い冷凍効率が得られるので、例えば宇宙衛星に搭載する赤外線センサー用の小型冷凍機や、超伝導マグネット用の冷凍機などに適している。
【００１３】
蓄冷材には充分なセラミックス強度が要求され、このためには例えば、両性金属元素やアルカリ土類金属元素、あるいは遷移金属元素などの添加物を、金属元素として５０〜１０００重量ｐｐｍ加える。これらの添加物により、蓄冷材の熱容量のピーク値が若干低下するが、２Ｋ付近の温度領域の熱容量は０．３Ｊ／ｃｃ・Ｋ以上に保たれ、無添加のＲＶＯ４蓄冷材とほとんど変わらない。このような添加物を加えたＲＶＯ４の結晶粒径は、無添加のＲＶＯ４よりも小さく、結晶粒の成長は抑制され、かつ蓄冷材はより緻密になる。一般的にセラミックスの強度は気孔率や結晶粒径に依存するため、緻密で結晶粒径が小さいセラミックスほど高強度となる。このため上記の添加物を金属換算で５０〜１０００重量ｐｐｍ添加すると、冷凍機を連続運転した際の微粉の発生が少なくる。
【００１４】
添加物が金属元素として５０重量ｐｐｍ未満しか添加されていない場合、平均結晶粒径は無添加のものとほとんど同じで、冷凍機を長時間運転した際の微粉の発生状況も同じであった。一方、添加物が、金属元素として１０００重量ｐｐｍを超えると、結晶粒成長を抑制するよりも、むしろ結晶粒成長を促進させるようになり、蓄冷材の耐久性の向上に寄与しなかった。従って添加量は、金属換算で５０〜１０００重量ｐｐｍに限られる。
【００１５】
本発明では、金属換算で５０〜１０００重量ｐｐｍの、両性金属元素や、アルカリ土類金属元素、遷移金属元素の添加物を添加することによって、結晶粒成長を抑制し、高強度の蓄冷材を得ることができる。そのため、冷凍機を長時間稼動させても、蓄冷材の破壊が生じず、冷凍機のシール部分等を損傷させることはない。また添加物を金属元素として５０〜１０００重量ｐｐｍ加えたＲＶＯ４蓄冷材は、無添加のＲＶＯ４蓄冷材と比較して熱容量のピークが若干低下するが、２Ｋ付近の温度の熱容量は０．３Ｊ／ｃｃ・Ｋ以上で、無添加のＲＶＯ４蓄冷材の冷凍特性とほとんど変わらない。
【００１６】
上記のように、蓄冷材の強度を定める要素は相対密度と平均結晶粒径である。相対密度が９６％未満では蓄冷材の強度は低く、９８％以上とすると強度は極めて高くなる。しかし蓄冷材の相対密度が９８％以上でも、平均結晶粒径が１００μｍを越えると、強度は低下する。そこで相対密度が９６％以上で、かつ平均結晶粒径が１００μｍ以下で、蓄冷材としてほぼ実用的な強度が得られる。また相対密度が９８％以上で、かつ平均結晶粒径が５０μｍ以下、最も好ましくは１０μｍ以下で、長時間冷凍機を運転しても微粉の発生がない蓄冷材が得られる。
【００１７】
２Ｋ付近までの冷凍を行うには、１０Ｋ程度から２Ｋ程度まで、蓄冷器の熱容量がほぼ連続しており、熱容量の小さな温度領域がないことが重要である。そこで、蓄冷器に、高温用蓄冷材の希土類金属間化合物蓄冷材、中間温度用の希土類酸化物または希土類オキシ硫化物の蓄冷材、低温用の希土類バナジウム酸化物蓄冷材の順で、層状に蓄冷材を配置すると、２Ｋ付近まで効率的に冷凍できる。
【００１８】
【実施例】
以下実施例について説明するが、本発明はこれらに限定されるものではない。
【００１９】
【実施例１ ＧｄＶＯ４ ディスクの作製】
市販の酸化ガドリニウムＧｄ２Ｏ３（平均粒径：０．５１μｍ）３６．２ｇと五酸化バナジウムＶ２Ｏ５（平均粒径：０．５９μｍ）１８．２ｇの化学量論比の混合物をボールミルに入れ、超純水を溶媒として４８時間混合した。なお、平均粒径はマイクロトラック測定装置から得られた粒度分布から算出した。得られたスラリーを乾燥させて混合粉末とし、その後アルミナルツボに入れて大気雰囲気で１１００℃、３時間仮焼した。得られた仮焼粉をＸ線回折で測定したところ、ＧｄＶＯ４のみのピークしか認められなかった。その仮焼粉を３０ＭＰａで１２ｍｍ直径の円盤状に成形し、２００ＭＰａ圧力下で静水圧プレスした後、大気雰囲気中で１６００℃に６時間保つように焼成をおこなった。
【００２０】
得られたＧｄＶＯ４焼結体の相対密度は、アルキメデス法により理論密度の９８．８％であり、平均結晶粒径は以下の式から算出すると１２．１μｍであった。
ｄ＝ １．５６Ｃ／（ＭＮ）
（ｄ：平均粒径、Ｃ：ＳＥＭ等の高分解能画像で任意に引いた線の長さ、Ｎ：任意に引いた線上の結晶粒の数、Ｍ：画像の倍率Ｍ）
【００２１】
得られたＧｄＶＯ４焼結体の熱容量を図１に示す。ＧｄＶＯ４焼結体は２．４Ｋに磁気相転移温度をもち、その温度の熱容量は０．８５Ｊ／ｃｍ３・Ｋである。また約１．７〜２．５Ｋ付近の温度の熱容量は、０．３Ｊ／ｃｃ・Ｋ以上を有する。ＧｄＶＯ４焼結体の２Ｋ付近の熱容量は、ＨｏＣｕ２の熱容量の約５〜６倍、Ｇｄ２Ｏ２Ｓの熱容量の約３〜４倍、ＧｄＡｌＯ３の熱容量の約２〜３倍で、２Ｋ付近の蓄冷材として用いることができる。
【００２２】
【実施例２ ＴｂＶＯ４及びＤｙＶＯ４ ディスクの作製】
平均粒径が０．６９μｍの酸化テルビウム又は平均粒径が０．５５μｍの酸化ジスプロシウムを用いた以外は、実施例１と同様の条件で、ＴｂＶＯ４及びＤｙＶＯ４のディスク状焼結体を作製した。理論密度及び平均結晶粒径は、実施例１（ＧｄＶＯ４）の場合とほぼ同様であった。ＴｂＶＯ４，ＤｙＶＯ４，及びＧｄＶＯ４の熱容量を図２に示す。図２から、ＴｂＶＯ４の磁気相転移温度はＧｄＶＯ４と比較して若干高温側に移行しているのに対し、ＤｙＶＯ４の磁気相転移温度は若干低温側に移行していることが判る。以上の結果から、希土類元素を変えることによって、２Ｋ付近で任意の磁気相転移温度と熱容量を得ることができる。
【００２３】
【実施例３ Ａｌの添加効果】
実施例１で得たＧｄＶＯ４の仮焼粉とＡｌ２Ｏ３粉末とをボールミルに入れ、エタノールを溶媒として、２４時間混合した。得られたスラリーを乾燥し再度仮焼（９００℃×３時間）し、実施例１と同様にして焼成し（２００ＭＰａで静水圧プレス後、大気中１６００℃で６時間保つように焼成）、Ａｌを含むＧｄＶＯ４セラミックス（Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４）を作製した。得られたＡｌ−ｄｏｐｅｄ ＧｄＶＯ４に対する、Ａｌとしての添加量と焼結体の平均結晶粒径との関係を図３に示す。また添加量を一定（５００重量ｐｐｍ）にした際の、焼成温度と焼結体の相対密度との関係を図４に示す。さらに添加量を５００重量ｐｐｍに固定し、焼成時間を６時間に固定した際の、焼成温度と焼結体の平均結晶粒径との関係を図５に示す。なお、それぞれの図には、参考として無添加のＧｄＶＯ４焼結体についても示す。
【００２４】
これらの結果から、Ａｌの添加によって、粒成長抑制効果と焼結促進効果をもたらされ、焼結助剤のＡｌの添加量は、金属換算で５０〜１０００重量ｐｐｍとすることが好ましいことが判る。表１には、Ａｌとしての添加量に対する、磁気相転移温度とその時の熱容量及び、２Ｋの熱容量を示す。Ａｌの添加によって磁気相転移温度での熱容量はわずかに低下するが、２Ｋでの熱容量は０．３Ｊ／ｃｃ・Ｋ以上である。熱容量が０．３Ｊ／ｃｃ・Ｋを越えていれば冷凍機の冷却特性に大きな影響はないため、上記の程度の添加量であれば、２Ｋ付近に関する冷凍特性にほとんど影響を及ぼさない。
【００２５】
【表１】
【実施例４ ＣａＯの添加】
Ａｌ２Ｏ３をＣａＯに変更し、他は実施例３と同様の条件で、金属換算で５０〜１０００重量ｐｐｍのＣａＯを添加したＧｄＶＯ４セラミックスディスク（Ｃａ−ｄｏｐｅｄ ＧｄＶＯ４）を作製した。ディスクの直径は１２ｍｍ、焼成条件は大気中１６００℃に６時間保つものとした。得られたＣａ−ｄｏｐｅｄ ＧｄＶＯ４の密度はアルキメデス法により理論密度の９８．７〜９９．１％であり、平均結晶粒径は７．１〜８．５μｍであった。またそれらの蓄冷材の磁気相転移温度とその時の熱容量及び２Ｋの熱容量は、実施例３と同様であった。
【００２７】
【実施例５ 他のアルカリ土類の添加】
ＣａＯをＭｇＯ、ＳｒＯ及びＢａＯに変更し、他は実施例３，４と同様の条件でＧｄＶＯ４ディスクを作製した。Ｍｇ−ｄｏｐｅｄ ＧｄＶＯ４、 Ｂａ−ｄｏｐｅｄ ＧｄＶＯ４及びＢａ−ｄｏｐｅｄ ＧｄＶＯ４では、実施例４と同等の結果が得られた。
【００２８】
【実施例６ 遷移金属元素の添加】
Ａｌ２Ｏ３を遷移金属化合物のＣｒ２Ｏ３（金属換算で５０〜１０００重量ｐｐｍ添加）に変更し、他は実施例３と同様の条件で、Ｃｒ２Ｏ３を含むＧｄＶＯ４セラミックス（Ｃｒ−ｄｏｐｅｄ ＧｄＶＯ４）を作製した。得られたＣｒ−ｄｏｐｅｄ ＧｄＶＯ４の密度はアルキメデス法により理論密度の９８．７〜９９．２％であり、平均結晶粒径は７．５〜８．３μｍであった。またそれらの蓄冷材の磁気相転移温度とその時の熱容量及び２Ｋの熱容量は、実施例３と同様であった。
【００２９】
【実施例７】
Ｃｒ２Ｏ３をＭｎＯ（金属換算で５０〜１０００重量ｐｐｍ添加）に変更し、他は実施例３と同様の条件で、ＭｎＯを含むＧｄＶＯ４セラミックス（Ｍｎ−ｄｏｐｅｄ ＧｄＶＯ４）を作製した。得られたＭｎ−ｄｏｐｅｄ ＧｄＶＯ４の密度はアルキメデス法により理論密度の９８．７〜９９．２％であり、平均結晶粒径は７．３〜８．３μｍであった。それらの蓄冷材の磁気相転移温度とその時の熱容量及び２Ｋの熱容量は、実施例３と同様であった。
【００３０】
【実施例８】
Ｃｒ２Ｏ３やＭｎＯ以外の、ＴｉやＺｒ、Ｃｏ等の遷移金属の化合物に添加物を変更し、他は実施例６，７と同様の条件で、ＧｄＶＯ４セラミックス蓄冷材を作製した。この蓄冷材では、実施例６，７と同様の結果が得られた。
【００３１】
【実施例９】
金属換算で５０〜１０００重量ｐｐｍのＡｌ２Ｏ３を添加した以外は、実施例２と同様の条件（１６００℃焼成で最高温度に６時間保持）で、Ａｌ２Ｏ３を含むＴｂＶＯ４及びＤｙＶＯ４セラミックス（Ａｌ−ｄｏｐｅｄ ＴｂＶＯ４及びＡｌ−ｄｏｐｅｄ ＤｙＶＯ４）を作製した。これらの平均結晶粒径及び相対密度は、実施例３と同様であった。添加量が５０〜１０００重量ｐｐｍでは平均結晶粒径が１０μｍ以下で、相対密度はＡｌ２Ｏ３無添加の場合もＡｌ２Ｏ３を添加した場合も９８％以上であった。また磁気相転移温度での熱容量は、Ａｌの添加によりわずかに低下する程度で、２Ｋの熱容量は０．３Ｊ／ｃｃ・Ｋ以上であるため、２Ｋ付近での冷凍特性にほとんど影響を及ぼさない。さらに、希土類元素の種類をＨｏやＮｄ等に変えた場合でも、同様の傾向が見られた。
【００３２】
【実施例１０ 顆粒状蓄冷材の作製】
実施例１で得たＧｄＶＯ４粉体を転動造粒法により球状に成形し、得られた造粒物を異なる２種類のフィルターネット（Ａメッシュ（目開き５９７μｍ）とＢメッシュ（目開き４３５μｍ））によって篩い分けした。篩い分けた造粒物を約２５°に傾けた鉄板（鏡面に研磨したもの）上に転がし、転がり落ちた造粒物を回収して形状分級した。顆粒１００個の平均粒径は０．５ｍｍであった。なお、ＧｄＶＯ４造粒物の平均粒径は、ビデオハイスコープシステムを用いて撮影した画像から測定した。
【００３３】
得られたＧｄＶＯ４造粒物をアルミナ製のルツボの中に充填し、焼成温度を１６００℃とし、この温度に６時間保持するように焼成して、平均粒径が０．４ｍｍ、平均アスペクト比が１．１のＧｄＶＯ４セラミックス蓄冷材を得た。なおＧｄＶＯ４蓄冷材の平均粒径及び平均アスペクト比は、ビデオハイスコープ画像から測定した。ＧｄＶＯ４蓄冷材の密度はピクノメーター法により理論密度の９８．７％で、平均結晶粒径は１２．１μｍであり、実施例１と同等の値であった。
【００３４】
ナイロン系メディアと１０ｗｔ％濃度のアルミナスラリーを加工槽内に装入し、そこにＧｄＶＯ４蓄冷材を入れ、回転バレル加工法により表面加工処理を行った。このようにして得られたＧｄＶＯ４蓄冷材の強度を知るために、１００個のＧｄＶＯ４蓄冷材を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、ＧｄＶＯ４蓄冷材の粉砕状況を調べた。その結果、ＧｄＶＯ４蓄冷材の破壊や微粉の発生は確認されなかった。次にＧＭ冷凍機の蓄冷器に最密充填に近い充填率で充填した後、消費電力３．４ｋＷの２段式ＧＭ冷凍機を連続１０００時間及び１５００時間継続し、各時間における蓄冷材の２Ｋの冷凍特性を調査し、連続１５００時間後の蓄冷材の破壊状況を確認した。なお、冷媒ガスとしては３Ｈｅを使用した。その結果を表２に示す。なお、高温側の１段目の蓄冷器にＰｂを使用し、２段目の蓄冷器の高温側から順にＨｏＣｕ２、ＧｄＡｌＯ３又はＧｄ２Ｏ２Ｓ、そしてＧｄＶＯ４を充填した。各蓄冷材の充填体積比率は表２に示す。ＧｄＶＯ４蓄冷材を使用することによって、ＨｏＣｕ２のみの場合の約２．５倍、ＨｏＣｕ２とＧｄＡｌＯ３又はＧｄ２Ｏ２Ｓの場合の１．３〜１．５倍に、初期冷凍能力が向上することが判った。そして連続１５００時間運転を行っても冷凍能力の低下は認められなかったが、ＧｄＶＯ４蓄冷材から僅かであるが微粉の発生が見られた。
【００３５】
【表２】
【実施例１１ Ａｌ２Ｏ３添加蓄冷材の作製】
Ａｌ２Ｏ３を添加した以外は、実施例１０と同様の条件（１６００℃に６時間保持して焼成）で、蓄冷材を作製した。Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の強度を知るため、それぞれのＡｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。すべての蓄冷材からの微粉の発生は確認できなかった。次に実施例１０と同様の方法で２Ｋの冷凍特性と蓄冷材の破壊状況を調査し、その結果を表３，４に示す。表３には、２段目の蓄冷器に高温側から順にＨｏＣｕ２、ＧｄＡｌＯ３、Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４に充填し場合の結果を示し、その充填体積比率は、ＨｏＣｕ２：ＧｄＡｌＯ３：Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４＝２：１：１とし、表４には、２段目の蓄冷器に高温側から順にＨｏＣｕ２、Ｇｄ２Ｏ２Ｓ、Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４に充填した場合の結果を示し、その充填体積比率はＨｏＣｕ２：Ｇｄ２Ｏ２Ｓ：Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４＝２：１：１とした。２段目の蓄冷器にＡｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材を使用しても、無添加のＧｄＶＯ４蓄冷材と同等の冷凍能力を有することが判った。またＡｌとしての添加量が５０〜１０００重量ｐｐｍの場合は、連続１５００時間運転を行っても微粉の発生は確認されず、無添加のＧｄＶＯ４蓄冷材よりも耐久性に優れていることが判った。一方、Ａｌとしての添加量が５０重量ｐｐｍ未満、あるいは１０００重量ｐｐｍを超えた場合、若干ではあるが微粉の発生が見られた。以上のことから添加量は、５０〜１０００重量ｐｐｍが好ましい。
【００３７】
【表３】
【表４】
【実施例１２】
Ａｌ２Ｏ３に代えてＣａＯを添加した以外は、実施例１１と同様の条件で蓄冷材を作製した。Ｃａ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の強度を知るため、それぞれのＣａ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ｃａ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。その結果、実施例１１と同様の傾向が認められた。次に実施例１１と同様の方法で、冷凍特性と蓄冷材の破壊状況を調査した。その結果、実施例１１と同様の傾向が見られた。
【００４０】
【実施例１３】
Ａｌ２Ｏ３に代えてＣｒ２Ｏ３を添加した以外は、実施例１１と同様の条件で蓄冷材を作製した。Ｃｒ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の強度を知るため、それぞれのＣｒ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ｃｒ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。その結果、実施例１１と同様の傾向が認められた。次に実施例１１と同様の方法で、冷凍特性と蓄冷材の破壊状況を調査した。その結果、実施例１１と同様の傾向が見られた。
【００４１】
【実施例１４】
焼成温度を１４００℃、焼成時間を６時間に変更した以外は、実施例１０と同様の条件で蓄冷材を作製した。得られたＧｄＶＯ４蓄冷材の相対密度は９４．１％であった。そのうち１００個のＧｄＶＯ４蓄冷材を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、ＧｄＶＯ４蓄冷材の粉砕状況を調べた。すると蓄冷材から微粉が発生していた。そのため冷凍特性試験を実施しなかった。
【００４２】
【実施例１５】
焼成温度を１４００℃、焼成時間を６時間に変更した以外は、実施例１１と同様の条件で蓄冷材を作製し、得られたＡｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の平均粒径は９４〜９５％であった。それぞれの蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、ＧｄＶＯ４蓄冷材の粉砕状況を調べた。するとすべての蓄冷材から微粉が発生していた。そのため冷凍特性試験を実施しなかった。
【００４３】
【実施例１６】
焼成温度を１７５０℃、焼成時間を２０時間に変更した以外は、実施例１０と同様の条件で蓄冷材を作製した。得られたＧｄＶＯ４蓄冷材の平均結晶粒径は１２２μｍであった。そのうち１００個のＧｄＶＯ４蓄冷材を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、ＧｄＶＯ４蓄冷材の粉砕状況を調べた。すると蓄冷材から微粉が発生していた。そのため冷凍特性試験を実施しなかった。
【００４４】
【実施例１７】
焼成温度を１７５０℃、焼成時間を２０時間に変更した以外は、実施例１１と同様の条件で蓄冷材を作製し、得られたＡｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の平均粒径は１０５〜１２５μｍであった。それぞれの蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。するとすべての蓄冷材から微粉が若干発生していた。そのため冷凍特性試験を実施しなかった。
【００４５】
【実施例１８】
焼成温度を１５００℃、焼成時間を０．５時間に変更した以外は、実施例１０と同様の条件で蓄冷材を作製し、得られたＧｄＶＯ４蓄冷材の相対密度は９４．２％であった。そのうち１００個のＧｄＶＯ４蓄冷材を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、ＧｄＶＯ４蓄冷材の粉砕状況を調べた。すると蓄冷材から微粉が発生していた。そのため冷凍特性試験を実施しなかった。
【００４６】
【実施例１９】
焼成温度を１５００℃、焼成時間を０．５時間とし、Ａｌ２Ｏ３添加料を金属換算で５００重量ｐｐｍに変更した以外は、実施例１１と同様の条件でＡｌ２Ｏ３添加の蓄冷材を作製した。得られたＡｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の相対密度は９４．５％であった。それぞれの蓄冷材の各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ａｌ−ｄｏｅｐｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。するとすべての蓄冷材から微粉が発生していた。そのため冷凍特性試験を実施しなかった。しかし１５００℃に保持する時間を１．５時間とすると、相対密度は９６．８％となり、振蕩機で１２０回／分の振蕩を５分間経験しても、微粉は発生しなかった。
【００４７】
【実施例２０】
平均粒径が０．６９μｍの酸化テルビウム又は平均粒径が０．５５μｍの酸化ジスプロシウムを用い、Ａｌ２Ｏ３等の添加物を加えなかったこと以外は、実施例９と同様の条件（１６００℃に６時間保持して焼成）で、ＴｂＶＯ４蓄冷材及びＤｙＶＯ４蓄冷材を作製した。得られた蓄冷材のそれぞれ１００個の蓄冷材を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、それらの蓄冷材の粉砕状況を調べた。その結果、どちらの蓄冷材にも破壊や微粉の発生は確認されなかった。次に実施例９と同様に２Ｋの冷凍特性と蓄冷材の破壊状況を調査し、その結果を表５に示す。２段目の蓄冷器の高温側から順にＨｏＣｕ２、ＧｄＡｌＯ３又はＧｄ２Ｏ２ＳそしてＴｂＶＯ４あるいはＤｙＶＯ４を充填した。各蓄冷材の充填体積比率は表５に示す。表５の結果から、ＧｄＶＯ４蓄冷材とほぼ同等の結果を得られた。
【００４８】
【表５】
【実施例２１】
Ａｌ２Ｏ３を添加した以外は、実施例２０と同様の条件で作製したＡｌ−ｄｏｐｅｄ ＴｂＶＯ４蓄冷材及びＡｌ−ｄｏｐｅｄ ＤｙＶＯ４蓄冷材の強度を知るため、それぞれの蓄冷材を各々１００個を一辺が約５ｃｍで他辺が約１０ｃｍのビニール袋に入れ、１２０回／分の振蕩機で５分間振った後に、Ａｌ−ｄｏｐｅｄ ＧｄＶＯ４蓄冷材の粉砕状況を調べた。その結果、すべての蓄冷材で微粉の発生を確認されなかった。次に実施例９と同様の方法で２Ｋの冷凍特性と蓄冷材の破壊状況を調査した。その結果、冷凍特性については、実施例２０と同様の傾向が見られ、また蓄冷材の破壊状況は、実施例１１と同様の傾向が見られた。
【図面の簡単な説明】
【図１】ＨｏＣｕ２、ＧｄＡｌＯ３ 、Ｇｄ２Ｏ２Ｓ及びＧｄＶＯ４蓄冷材の熱容量を示す特性図
【図２】ＧｄＶＯ４、ＴｂＶＯ４及びＤｙＶＯ４蓄冷材の熱容量を示す特性図
【図３】Ａｌとしての添加量とＧｄＶＯ４焼結体の平均結晶粒径との関係図
【図４】添加量を一定にした際の焼成温度とＧｄＶＯ４焼結体の相対密度との関係図
【図５】添加量を一定にした際の焼成温度とＧｄＶＯ４焼結体の平均結晶粒径との関係図[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a regenerator using a rare earth vanadium oxide, a method for producing the regenerator, and a regenerator using the regenerator. More specifically, it has a high heat capacity in a cryogenic region around 2K, which is required to improve the resolution of an infrared sensor or to significantly improve the critical current characteristics of a superconducting wire. The present invention relates to a high-performance regenerative material that does not generate wear powder, a method for producing the same, and a regenerator filled with the material.
[0002]
[Prior art and its problems]
The characteristics of infrared sensors and superconducting magnets can be improved by lowering the temperature. For example, infrared sensors mounted on space satellites are cooled to obtain more advanced information. At present, as a cooling method, a method is used in which superfluid helium (absolute temperature of 2.2 K or less) mounted in a satellite is gradually released into outer space and the temperature is maintained for a certain period. However, this method makes it difficult to use the infrared sensor when the superfluid helium is exhausted, even though the life of the infrared sensor is left. Therefore, a small cryogenic refrigerator that can be repeatedly used for a long period of time and can be mounted on a space satellite has attracted attention.
[0003]
[Patent Document 1] Japanese Patent 2609747
[0004]
The cooling capacity and minimum temperature of a small refrigerator depend greatly on the regenerator material, which is the filling material that constitutes the regenerator built into the refrigerator, and the regenerator material has a large heat capacity and high heat exchange efficiency. is necessary. In the case of a metal regenerative material such as Pb, the heat capacity sharply drops below 10K, so that the cooling efficiency drops below 10K. Therefore, a regenerator material having a large heat capacity in an extremely low temperature region closer to the liquid helium temperature (4.2 K) has been developed. Such cold storage materials include, for example, HoCu 2 And rare earth intermetallic compounds such as ErNi (
[0005]
[Problems of the Invention]
An object of the present invention is to provide a regenerator material having a large heat capacity at about 2K such as superfluid helium temperature and having high durability against thermal shock and vibration, a method for producing the regenerator material, and a regenerator using the same. Is to do.
[0006]
Configuration of the Invention
The cold storage material of the present invention has a general formula of RVO 4 (R represents one or more rare earth elements selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y.) A rare earth vanadium oxide ceramic represented by the formula (1) is used. The shape of the ceramic is, for example, a granular shape, a honeycomb shape, or a shape obtained by sintering granular particles in a porous manner in a network shape. Further, a cylindrical ceramic such as a rare-earth vanadium oxide filled with granular rare-earth vanadium oxide particles may be used. In the case of granular, the average particle size of the regenerator material is preferably 0.05 to 2 mm.
[0007]
Preferably, the rare-earth vanadium oxide regenerator material is added with an additive of at least one member of an amphoteric metal element, an alkaline earth metal element and a transition metal element as a metal element in an amount of 50 to 1000 ppm by weight as a metal element to strengthen the regenerator material. (Claim 2). The form at the time of addition is preferably a compound such as an oxide.
Preferably, the additive is an additive of at least one amphoteric metal element in the group consisting of Al and Ga (claim 3).
Preferably, the additive is an additive of at least one member of the group consisting of Mg, Ca, Sr, and Ba. (Claim 4).
Preferably, the additive is an additive of at least one transition metal element having an element number of 22 (Ti) to 30 (Zn) and 40 (Zr), 72 (Hf) (claim 5).
[0008]
The relative density of the cold storage material is preferably 96% or more, more preferably 98% or more, and is preferably close to the theoretical density. This is to improve the strength of the cold storage material.
The average crystal grain size of the regenerator material is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 10 μm or less. This is also to improve the strength of the cold storage material.
It is preferable that the cold storage material has a maximum value of the heat capacity at 2 to 3K (claim 8). That is, as a material having the maximum value of the heat capacity near 4K, GdAlO 3 And Gd 2 O 2 It is important to have a cold storage material such as S already, and to have a maximum value of the heat capacity at a lower temperature.
[0009]
In the method for producing a rare earth vanadium oxide regenerator according to the present invention, the general formula RVO 4 Is calcined so as to be kept in a temperature range of 1500 to 1700 ° C. for 1 to 10 hours (claim 9). Under these conditions, a rare earth vanadium oxide regenerator having a relative density of, for example, 96% or more (preferably 98% or more) and an average crystal grain size of 100 μm or less (usually 50 μm or less) is obtained.
In the production of cold storage materials, for example, RVO 4 The powder is pulverized by a ball mill or the like and calcined at about 900 to 1200 ° C. The obtained rare earth vanadium oxide powder is granulated into granules by, for example, a tumbling granulation method, a combination of an extrusion method and a tumbling granulation method, a fluid granulation method, a spray drying method, an embossing method, or the like. I do. Alternatively, it is molded into a desired shape. These are fired so as to be maintained at 1500 to 1700 ° C. for 1 to 10 hours. The firing atmosphere may be, for example, the air, but may be another atmosphere. The average particle size of the obtained regenerator material is preferably 0.05 to 2 mm.
[0010]
The firing condition of the cold storage material is such that the relative density of the cold storage material after firing is 96% or more, more preferably 98% or more, and the average crystal grain size is 100 μm or less, more preferably 50 μm or less, and most preferably 10 μm or less. (Claim 10).
Also RVO 4 It is preferable that at least one element of an amphoteric metal, an alkaline earth metal, and a transition metal is added as a metal element in an amount of 50 to 1000 ppm by weight (claim 11). The amphoteric metal is, for example, Al or Ga, the alkaline earth metal is, for example, Mg, Ca, Sr, Ba, and the transition metal is, for example, from atomic numbers 22 (Ti) to 30 (Zn) and 40 (Zr), 72 (Hf). At least one member of the group When these additives are added, for example, it is preferable to add them to the powder before calcining. However, the additives may be added to the powder after calcining to diffuse the additives in the firing process. These additives improve the relative density of the cold storage material and reduce the average crystal grain size.
[0011]
The cryogenic regenerator of the present invention is one in which the above-mentioned rare earth vanadium oxide ceramic regenerator is filled in an appropriate cylinder or the like (claim 12). Further, the regenerator is filled with the regenerator material in layers in order from the high-temperature regenerator material to the intermediate-temperature regenerator material and the low-temperature regenerator material, and the high-temperature regenerator material is a rare earth intermetallic compound regenerator material, 2 The intermediate temperature regenerator material is a rare earth oxide or rare earth oxysulfide regenerator material such as GdAlO 3 And Gd 2 O 2 S, It is preferable that the low-temperature regenerator material is a rare-earth vanadium oxide regenerator material. This is because the regenerator has a continuous heat capacity from a little less than 10K to about 2K, and the refrigeration efficiency is increased.
[0012]
Function and Effect of the Invention
The rare earth vanadium oxide of the present invention (hereinafter referred to as RVO) 4 Is shown. ) The cold storage material has a magnetic phase transition temperature of 2 to 3K and a heat capacity of 0.3 J / cc · K or more in a temperature region around 2K. As described above, the regenerator material of the present invention can provide high refrigerating efficiency near 2K, and is suitable for a small refrigerator for an infrared sensor mounted on a space satellite, a refrigerator for a superconducting magnet, and the like.
[0013]
The regenerator material is required to have sufficient ceramic strength. For this purpose, for example, an additive such as an amphoteric metal element, an alkaline earth metal element, or a transition metal element is added in an amount of 50 to 1000 ppm by weight as a metal element. With these additives, the peak value of the heat capacity of the cold storage material slightly decreases, but the heat capacity in the temperature region around 2K is maintained at 0.3 J / cc · K or more, 4 Almost the same as cold storage material. RVO with such additives 4 The crystal grain size of 4 Smaller, the growth of crystal grains is suppressed, and the regenerator material becomes denser. In general, the strength of ceramics depends on the porosity and the crystal grain size, and therefore, the denser the ceramics, the smaller the crystal grain size, the higher the strength. For this reason, when the above additive is added in an amount of 50 to 1000 ppm by weight in terms of metal, the generation of fine powder during continuous operation of the refrigerator is reduced.
[0014]
When the additive was added as less than 50 ppm by weight as a metal element, the average crystal grain size was almost the same as that when no additive was added, and the state of generation of fine powder when the refrigerator was operated for a long time was also the same. On the other hand, when the amount of the additive exceeds 1000 ppm by weight as a metal element, the growth of the crystal grains is promoted rather than the growth of the crystal grains, and the additive does not contribute to the improvement of the durability of the cold storage material. Therefore, the amount of addition is limited to 50 to 1000 ppm by weight in terms of metal.
[0015]
In the present invention, by adding an additive of an amphoteric metal element, an alkaline earth metal element, and a transition metal element in an amount of 50 to 1000 ppm by weight in terms of metal, crystal grain growth is suppressed, and a high-strength cold storage material is obtained. Obtainable. Therefore, even if the refrigerator is operated for a long time, the regenerator does not break down, and the seal portion of the refrigerator is not damaged. RVO to which 50 to 1000 ppm by weight of an additive is added as a metal element 4 Cold storage material is RVO with no additives 4 The heat capacity peak is slightly lower than that of the cold storage material, but the heat capacity at a temperature near 2K is 0.3 J / cc · K or more, 4 Almost the same as the refrigeration characteristics of cold storage materials.
[0016]
As described above, the factors that determine the strength of the cold storage material are the relative density and the average crystal grain size. When the relative density is less than 96%, the strength of the cold storage material is low, and when the relative density is 98% or more, the strength becomes extremely high. However, even if the relative density of the regenerator material is 98% or more, the strength decreases when the average crystal grain size exceeds 100 μm. Therefore, when the relative density is 96% or more and the average crystal grain size is 100 μm or less, almost practical strength as a cold storage material can be obtained. Further, a regenerator material having a relative density of 98% or more, an average crystal grain size of 50 μm or less, most preferably 10 μm or less, and free from generation of fine powder even when the refrigerator is operated for a long time can be obtained.
[0017]
In order to perform refrigeration up to about 2K, it is important that the heat capacity of the regenerator is approximately continuous from about 10K to about 2K, and that there is no temperature region with a small heat capacity. Therefore, in the regenerator, the cold storage material of the rare earth intermetallic compound of the cold storage material for high temperature, the cold storage material of the rare earth oxide or rare earth oxysulfide for the intermediate temperature, and the cold storage material of the rare earth vanadium oxide for the low temperature are arranged in this order. By arranging the material, it can be efficiently frozen to around 2K.
[0018]
【Example】
Hereinafter, examples will be described, but the present invention is not limited to these examples.
[0019]
Example 1 GdVO 4 Production of disc]
Commercially available gadolinium oxide Gd 2 O 3 (Average particle size: 0.51 μm) 36.2 g and vanadium pentoxide V 2 O 5 (Average particle size: 0.59 μm) A mixture having a stoichiometric ratio of 18.2 g was placed in a ball mill, and mixed for 48 hours using ultrapure water as a solvent. The average particle size was calculated from the particle size distribution obtained from a Microtrac measuring device. The obtained slurry was dried to obtain a mixed powder, and then placed in an alumina crucible and calcined at 1100 ° C. for 3 hours in an air atmosphere. When the obtained calcined powder was measured by X-ray diffraction, GdVO 4 Only a peak was observed. The calcined powder was formed into a disk having a diameter of 12 mm at a pressure of 30 MPa, isostatically pressed under a pressure of 200 MPa, and then fired in an air atmosphere at 1600 ° C. for 6 hours.
[0020]
GdVO obtained 4 The relative density of the sintered body was 98.8% of the theoretical density according to the Archimedes method, and the average crystal grain size was 12.1 μm as calculated from the following equation.
d = 1.56C / (MN)
(D: average particle size, C: length of a line arbitrarily drawn in a high-resolution image such as SEM, N: number of crystal grains on the line arbitrarily drawn, M: magnification of image M)
[0021]
GdVO obtained 4 FIG. 1 shows the heat capacity of the sintered body. GdVO 4 The sintered body has a magnetic phase transition temperature at 2.4K, and the heat capacity at that temperature is 0.85 J / cm. 3 -It is K. The heat capacity at a temperature around 1.7 to 2.5K is 0.3 J / cc · K or more. GdVO 4 The heat capacity of the sintered body near 2K is HoCu 2 About 5-6 times the heat capacity of Gd 2 O 2 About 3 to 4 times the heat capacity of S, GdAlO 3 About 2 to 3 times the heat capacity of, and can be used as a cold storage material near 2K.
[0022]
Example 2 TbVO 4 And DyVO 4 Production of disc]
TbVO under the same conditions as in Example 1 except that terbium oxide having an average particle size of 0.69 μm or dysprosium oxide having an average particle size of 0.55 μm was used. 4 And DyVO 4 Was produced. The theoretical density and the average crystal grain size were determined in Example 1 (GdVO). 4 ) Was almost the same. TbVO 4 , DyVO 4 , And GdVO 4 FIG. 2 shows the heat capacity. From FIG. 2, TbVO 4 Has a magnetic phase transition temperature of GdVO 4 Although the temperature is slightly higher than that of DyVO, 4 It can be seen that the magnetic phase transition temperature has slightly shifted to a lower temperature side. From the above results, it is possible to obtain an arbitrary magnetic phase transition temperature and heat capacity around 2K by changing the rare earth element.
[0023]
Example 3 Effect of adding Al
GdVO obtained in Example 1 4 Calcined powder and Al 2 O 3 The powder was placed in a ball mill and mixed for 24 hours using ethanol as a solvent. The obtained slurry was dried, calcined again (900 ° C. × 3 hours), calcined in the same manner as in Example 1 (hydrostatic pressing at 200 MPa, and calcined at 1600 ° C. in the atmosphere for 6 hours in the air), and Al GdVO containing 4 Ceramics (Al-doped GdVO) 4 ) Was prepared. Obtained Al-doped GdVO 4 FIG. 3 shows the relationship between the amount of Al added and the average crystal grain size of the sintered body. FIG. 4 shows the relationship between the firing temperature and the relative density of the sintered body when the amount of addition was constant (500 ppm by weight). FIG. 5 shows the relationship between the firing temperature and the average crystal grain size of the sintered body when the addition amount was fixed at 500 ppm by weight and the firing time was fixed at 6 hours. In each figure, GdVO without additive is shown for reference. 4 The sintered body is also shown.
[0024]
From these results, it is preferable that the addition of Al brings about a grain growth suppressing effect and a sintering promoting effect. I understand. Table 1 shows the magnetic phase transition temperature, the heat capacity at that time, and the heat capacity of 2K with respect to the amount of Al added. With the addition of Al, the heat capacity at the magnetic phase transition temperature slightly decreases, but the heat capacity at 2K is 0.3 J / cc · K or more. If the heat capacity exceeds 0.3 J / cc · K, there is no significant effect on the cooling characteristics of the refrigerator. Therefore, if the amount of addition is in the above-mentioned range, the cooling characteristics in the vicinity of 2K are hardly affected.
[0025]
[Table 1]
Example 4 Addition of CaO
Al 2 O 3 Was changed to CaO, and the other conditions were the same as in Example 3 and GdVO to which 50 to 1000 ppm by weight of CaO was added in terms of metal. 4 Ceramic disk (Ca-doped GdVO) 4 ) Was prepared. The diameter of the disk was 12 mm, and the firing conditions were kept at 1600 ° C. in the atmosphere for 6 hours. Obtained Ca-doped GdVO 4 Was 98.7 to 99.1% of the theoretical density by the Archimedes method, and the average crystal grain size was 7.1 to 8.5 μm. Further, the magnetic phase transition temperature, the heat capacity at that time, and the heat capacity at 2 K of those regenerator materials were the same as in Example 3.
[0027]
Example 5 Addition of other alkaline earths
CaO was changed to MgO, SrO and BaO, and GdVO was changed under the same conditions as in Examples 3 and 4 4 A disk was made. Mg-doped GdVO 4 , Ba-doped GdVO 4 And Ba-doped GdVO 4 In this example, a result equivalent to that of Example 4 was obtained.
[0028]
Example 6 Addition of transition metal element
Al 2 O 3 To the transition metal compound Cr 2 O 3 (Addition of 50 to 1000 ppm by weight in terms of metal). 2 O 3 GdVO containing 4 Ceramics (Cr-doped GdVO) 4 ) Was prepared. Obtained Cr-doped GdVO 4 Was 98.7 to 99.2% of the theoretical density by the Archimedes method, and the average crystal grain size was 7.5 to 8.3 μm. Further, the magnetic phase transition temperature, the heat capacity at that time, and the heat capacity of 2K of those regenerator materials were the same as in Example 3.
[0029]
Embodiment 7
Cr 2 O 3 Was changed to MnO (50 to 1000 ppm by weight in terms of metal), and the other conditions were the same as in Example 3 except that GdVO containing MnO was added. 4 Ceramics (Mn-doped GdVO) 4 ) Was prepared. Obtained Mn-doped GdVO 4 Was 98.7 to 99.2% of the theoretical density according to the Archimedes method, and the average crystal grain size was 7.3 to 8.3 μm. The magnetic phase transition temperature, the heat capacity at that time, and the heat capacity of 2K of those cold storage materials were the same as those in Example 3.
[0030]
Embodiment 8
Cr 2 O 3 The additives were changed to compounds of transition metals such as Ti, Zr, and Co other than GdVO and GdVO under the same conditions as in Examples 6 and 7, 4 A ceramic cold storage material was produced. With this cold storage material, the same results as in Examples 6 and 7 were obtained.
[0031]
Embodiment 9
50 to 1000 ppm by weight of Al in terms of metal 2 O 3 Under the same conditions as in Example 2 (sintering at 1600 ° C. and holding at the maximum temperature for 6 hours) except that 2 O 3 TbVO containing 4 And DyVO 4 Ceramics (Al-doped TbVO) 4 And Al-doped DyVO 4 ) Was prepared. The average crystal grain size and the relative density were the same as in Example 3. When the addition amount is 50 to 1000 ppm by weight, the average crystal grain size is 10 μm or less, and the relative density is Al. 2 O 3 Al without additive 2 O 3 Was also 98% or more. Further, the heat capacity at the magnetic phase transition temperature is slightly reduced by the addition of Al, and the heat capacity of 2K is 0.3 J / cc · K or more, so that the refrigerating characteristics near 2K are hardly affected. Further, the same tendency was observed when the type of the rare earth element was changed to Ho, Nd, or the like.
[0032]
Example 10 Preparation of granular cold storage material
GdVO obtained in Example 1 4 The powder was formed into a spherical shape by a tumbling granulation method, and the obtained granulated product was sieved with two different types of filter nets (A mesh (opening: 597 μm) and B mesh (opening: 435 μm)). The sieved granules were rolled on an iron plate (polished to a mirror surface) inclined at about 25 °, and the rolled granules were collected and classified. The average particle size of 100 granules was 0.5 mm. GdVO 4 The average particle size of the granules was measured from images taken using a video high scope system.
[0033]
GdVO obtained 4 The granulated material was filled in an alumina crucible, and baked at a firing temperature of 1600 ° C. and kept at this temperature for 6 hours to obtain an average particle size of 0.4 mm and an average aspect ratio of 1.1. GdVO 4 A ceramic cold storage material was obtained. GdVO 4 The average particle size and average aspect ratio of the cold storage material were measured from a video high scope image. GdVO 4 The density of the cold storage material was 98.7% of the theoretical density according to the pycnometer method, and the average crystal grain size was 12.1 μm, which was the same value as in Example 1.
[0034]
Nylon-based media and 10 wt% alumina slurry were charged into a processing tank, and GdVO was placed there. 4 A cold storage material was put in, and surface processing was performed by a rotating barrel processing method. GdVO obtained in this manner 4 In order to know the strength of cold storage material, 100 GdVO 4 Put the regenerator material in a plastic bag about 5 cm on one side and about 10 cm on the other side and shake it with a shaker for 120 minutes / minute for 5 minutes. 4 The crushing condition of the cool storage material was examined. As a result, GdVO 4 No destruction of the cold storage material or generation of fine powder was confirmed. Next, after filling the regenerator of the GM refrigerator with a filling rate close to the closest packing, the two-stage GM refrigerator with a power consumption of 3.4 kW is continuously operated for 1000 hours and 1500 hours, and 2K of the cold storage material at each time is continued. Was examined for the refrigerating characteristics, and the state of destruction of the cold storage material after continuous 1500 hours was confirmed. In addition, as a refrigerant gas, 3 He was used. Table 2 shows the results. Note that Pb was used for the first-stage regenerator on the high-temperature side, and HoCu was sequentially used from the high-temperature side of the second-stage regenerator. 2 , GdAlO 3 Or Gd 2 O 2 S and GdVO 4 Was charged. Table 2 shows the filling volume ratio of each cold storage material. GdVO 4 By using cold storage material, HoCu 2 About 2.5 times that of HoCu 2 And GdAlO 3 Or Gd 2 O 2 It was found that the initial refrigeration capacity was improved to 1.3 to 1.5 times the case of S. Although the refrigeration capacity did not decrease even after continuous 1500 hours of operation, GdVO 4 The generation of fine powder was slightly observed from the cold storage material.
[0035]
[Table 2]
Example 11 Al 2 O 3 Production of added cold storage material]
Al 2 O 3 A cold storage material was produced under the same conditions as in Example 10 (sintering at 1600 ° C. for 6 hours) except that was added. Al-doped GdVO 4 In order to know the strength of the cold storage material, each Al-doped
[0037]
[Table 3]
[Table 4]
Al 2 O 3 A cold storage material was produced under the same conditions as in Example 11 except that CaO was added instead of. Ca-doped GdVO 4 To know the strength of the cold storage material, each Ca-doped
[0040]
Embodiment 13
Al 2 O 3 Instead of Cr 2 O 3 A cold storage material was produced under the same conditions as in Example 11 except that was added. Cr-doped GdVO 4 To know the strength of the cold storage material, each Cr-doped
[0041]
Embodiment 14
A cold storage material was produced under the same conditions as in Example 10 except that the firing temperature was changed to 1400 ° C. and the firing time was changed to 6 hours. GdVO obtained 4 The relative density of the cold storage material was 94.1%. 100 of them GdVO 4 Put the regenerator material in a plastic bag about 5 cm on one side and about 10 cm on the other side and shake it with a shaker for 120 minutes / minute for 5 minutes. 4 The crushing condition of the cool storage material was examined. Then, fine powder was generated from the cold storage material. Therefore, the refrigeration property test was not performed.
[0042]
A regenerator material was prepared under the same conditions as in Example 11 except that the firing temperature was changed to 1400 ° C. and the firing time was changed to 6 hours, and the obtained Al-doped GdVO was obtained. 4 The average particle size of the cold storage material was 94 to 95%. 100 pieces of each regenerator material were placed in a plastic bag about 5 cm on one side and about 10 cm on the other side, and shaken for 120 minutes / minute with a shaker for 5 minutes. 4 The crushing condition of the cool storage material was examined. Then, fine powder was generated from all the cold storage materials. Therefore, the refrigeration property test was not performed.
[0043]
Embodiment 16
A cold storage material was produced under the same conditions as in Example 10 except that the firing temperature was changed to 1750 ° C. and the firing time was changed to 20 hours. GdVO obtained 4 The average crystal grain size of the cold storage material was 122 μm. 100 of them GdVO 4 Put the regenerator material in a plastic bag about 5 cm on one side and about 10 cm on the other side and shake it with a shaker for 120 minutes / minute for 5 minutes. 4 The crushing condition of the cool storage material was examined. Then, fine powder was generated from the cold storage material. Therefore, the refrigeration property test was not performed.
[0044]
Embodiment 17
A regenerator material was produced under the same conditions as in Example 11 except that the firing temperature was changed to 1750 ° C. and the firing time was changed to 20 hours, and the obtained Al-doped GdVO was obtained. 4 The average particle size of the cold storage material was 105 to 125 μm. 100 pieces of each regenerator material were placed in a plastic bag about 5 cm on one side and about 10 cm on the other side, and shaken with a shaker at 120 times / minute for 5 minutes, and then Al-doped GdVO. 4 The crushing condition of the cool storage material was examined. Then, fine powder was slightly generated from all the cold storage materials. Therefore, the refrigeration property test was not performed.
[0045]
Embodiment 18
A cold storage material was produced under the same conditions as in Example 10 except that the firing temperature was changed to 1500 ° C. and the firing time was changed to 0.5 hour, and the obtained GdVO was obtained. 4 The relative density of the cold storage material was 94.2%. 100 of them GdVO 4 Put the regenerator material in a plastic bag about 5 cm on one side and about 10 cm on the other side and shake it with a shaker for 120 minutes / minute for 5 minutes. 4 The crushing condition of the cool storage material was examined. Then, fine powder was generated from the cold storage material. Therefore, the refrigeration property test was not performed.
[0046]
Embodiment 19
The firing temperature was 1500 ° C., the firing time was 0.5 hour, and Al 2 O 3 Except that the additive was changed to 500 ppm by weight in terms of metal, Al was added under the same conditions as in Example 11. 2 O 3 An additional cold storage material was prepared. Obtained Al-doped GdVO 4 The relative density of the cold storage material was 94.5%. 100 pieces of each regenerative material were put in a plastic bag about 5 cm on one side and about 10 cm on the other side, and shaken with a shaker at 120 times / min for 5 minutes, and then Al-doepd GdVO. 4 The crushing condition of the cool storage material was examined. Then, fine powder was generated from all the cold storage materials. Therefore, the refrigeration property test was not performed. However, when the time of holding at 1500 ° C. was 1.5 hours, the relative density was 96.8%, and no fine powder was generated even when the shaker was subjected to shaking at 120 times / minute for 5 minutes.
[0047]
Using terbium oxide having an average particle diameter of 0.69 μm or dysprosium oxide having an average particle diameter of 0.55 μm, 2 O 3 Under the same conditions as in Example 9 (sintering by holding at 1600 ° C. for 6 hours) except that no additives such as TbVO were added. 4 Cool storage material and DyVO 4 A cold storage material was produced. 100 pieces of the obtained regenerator materials were put into a plastic bag of about 5 cm on one side and about 10 cm on the other side, and shaken for 120 minutes / minute with a shaker for 5 minutes. Was examined. As a result, destruction and generation of fine powder were not confirmed in either of the cold storage materials. Next, the refrigeration characteristics of 2K and the state of destruction of the cold storage material were investigated in the same manner as in Example 9, and the results are shown in Table 5. HoCu in order from the high temperature side of the second stage regenerator 2 , GdAlO 3 Or Gd 2 O 2 S and TbVO 4 Or DyVO 4 Was charged. Table 5 shows the filling volume ratio of each cold storage material. From the results in Table 5, GdVO 4 The result was almost the same as that of the cold storage material.
[0048]
[Table 5]
Embodiment 21
Al 2 O 3 Al-doped TbVO fabricated under the same conditions as in Example 20 except that was added. 4 Cool storage material and Al-doped DyVO 4 In order to know the strength of the cold storage material, 100 pieces of each cold storage material were placed in a plastic bag having a side of about 5 cm and the other side of about 10 cm, shaken for 120 minutes / minute with a shaker for 5 minutes, and then Al-doped. GdVO 4 The crushing condition of the cool storage material was examined. As a result, generation of fine powder was not confirmed in any of the cold storage materials. Next, the refrigeration characteristics of 2K and the state of destruction of the cold storage material were investigated in the same manner as in Example 9. As a result, the same tendency as in Example 20 was observed in the refrigerating characteristics, and the same tendency as in Example 11 was observed in the destruction state of the cold storage material.
[Brief description of the drawings]
FIG. 1 HoCu 2 , GdAlO 3 , Gd 2 O 2 S and GdVO 4 Characteristic diagram showing heat capacity of cold storage material
FIG. 2 GdVO 4 , TbVO 4 And DyVO 4 Characteristic diagram showing heat capacity of cold storage material
FIG. 3 Addition amount of Al and GdVO 4 Diagram of relationship with average crystal grain size of sintered body
FIG. 4 shows the firing temperature and GdVO when the addition amount is constant. 4 Diagram of relative density of sintered body
FIG. 5 shows the firing temperature and GdVO when the addition amount is constant. 4 Diagram of relationship with average crystal grain size of sintered body
Claims (13)
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2006242484A (en) * | 2005-03-03 | 2006-09-14 | Sumitomo Heavy Ind Ltd | Cold accumulating material, cold accumulator and cryogenic cold accumulating refrigerator |
| JP2010163510A (en) * | 2009-01-14 | 2010-07-29 | Institute Of Physical & Chemical Research | Heat storage material |
| WO2014068628A1 (en) * | 2012-10-29 | 2014-05-08 | 株式会社 日立製作所 | Heat storage system and power generation system |
| JP2015071795A (en) * | 2015-01-21 | 2015-04-16 | 独立行政法人理化学研究所 | Heat storage material |
| WO2018025581A1 (en) * | 2016-08-05 | 2018-02-08 | 神島化学工業株式会社 | Rare earth oxysulfide cold storage medium |
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Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006242484A (en) * | 2005-03-03 | 2006-09-14 | Sumitomo Heavy Ind Ltd | Cold accumulating material, cold accumulator and cryogenic cold accumulating refrigerator |
| JP2010163510A (en) * | 2009-01-14 | 2010-07-29 | Institute Of Physical & Chemical Research | Heat storage material |
| WO2014068628A1 (en) * | 2012-10-29 | 2014-05-08 | 株式会社 日立製作所 | Heat storage system and power generation system |
| JP5923619B2 (en) * | 2012-10-29 | 2016-05-24 | 株式会社日立製作所 | Thermal storage system, power generation system |
| JP2015071795A (en) * | 2015-01-21 | 2015-04-16 | 独立行政法人理化学研究所 | Heat storage material |
| WO2018025581A1 (en) * | 2016-08-05 | 2018-02-08 | 神島化学工業株式会社 | Rare earth oxysulfide cold storage medium |
| CN109312215A (en) * | 2016-08-05 | 2019-02-05 | 神岛化学工业株式会社 | Terres rares oxysulfide cold storage medium |
| JPWO2018025581A1 (en) * | 2016-08-05 | 2019-06-27 | 神島化学工業株式会社 | Rare earth oxy sulfide storage material |
| CN109312215B (en) * | 2016-08-05 | 2021-03-26 | 神岛化学工业株式会社 | Rare earth oxysulfide cold storage material |
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