JP5509731B2 - Rare earth nitride, method for producing the same, magnetic refrigeration material and cold storage material - Google Patents
Rare earth nitride, method for producing the same, magnetic refrigeration material and cold storage material Download PDFInfo
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- 229910052761 rare earth metal Inorganic materials 0.000 title claims description 81
- -1 Rare earth nitride Chemical class 0.000 title claims description 65
- 239000000463 material Substances 0.000 title claims description 25
- 238000005057 refrigeration Methods 0.000 title claims description 24
- 239000011232 storage material Substances 0.000 title claims description 13
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 239000002245 particle Substances 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 17
- 239000012298 atmosphere Substances 0.000 claims description 16
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 13
- 229910052799 carbon Inorganic materials 0.000 claims description 13
- 239000002923 metal particle Substances 0.000 claims description 13
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 229910052688 Gadolinium Inorganic materials 0.000 claims description 5
- 229910052689 Holmium Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052692 Dysprosium Inorganic materials 0.000 claims description 4
- 229910001873 dinitrogen Inorganic materials 0.000 claims description 4
- 238000004438 BET method Methods 0.000 claims description 3
- 229910052691 Erbium Inorganic materials 0.000 claims description 3
- 229910052779 Neodymium Inorganic materials 0.000 claims description 3
- 229910052771 Terbium Inorganic materials 0.000 claims description 3
- 239000013078 crystal Substances 0.000 claims description 3
- KBQHZAAAGSGFKK-UHFFFAOYSA-N dysprosium atom Chemical compound [Dy] KBQHZAAAGSGFKK-UHFFFAOYSA-N 0.000 claims description 2
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 claims description 2
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 claims description 2
- KJZYNXUDTRRSPN-UHFFFAOYSA-N holmium atom Chemical compound [Ho] KJZYNXUDTRRSPN-UHFFFAOYSA-N 0.000 claims description 2
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 claims description 2
- 229910052706 scandium Inorganic materials 0.000 claims description 2
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 claims description 2
- GZCRRIHWUXGPOV-UHFFFAOYSA-N terbium atom Chemical compound [Tb] GZCRRIHWUXGPOV-UHFFFAOYSA-N 0.000 claims description 2
- 229910052727 yttrium Inorganic materials 0.000 claims description 2
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 2
- 239000012798 spherical particle Substances 0.000 description 13
- 238000011156 evaluation Methods 0.000 description 8
- 239000001257 hydrogen Substances 0.000 description 7
- 229910052739 hydrogen Inorganic materials 0.000 description 7
- 230000007704 transition Effects 0.000 description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- 229910000765 intermetallic Inorganic materials 0.000 description 6
- 238000005259 measurement Methods 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 150000004767 nitrides Chemical class 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000005338 heat storage Methods 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000011049 filling Methods 0.000 description 2
- 238000009689 gas atomisation Methods 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000009257 reactivity Effects 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000003507 refrigerant Substances 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 239000012300 argon atmosphere Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- KYKAJFCTULSVSH-UHFFFAOYSA-N chloro(fluoro)methane Chemical compound F[C]Cl KYKAJFCTULSVSH-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000005347 demagnetization Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000007429 general method Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 150000004678 hydrides Chemical class 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000005339 levitation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000003252 repetitive effect Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical class O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000008207 working material Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
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- Ceramic Products (AREA)
Description
本発明は、希土類窒化物およびその製造方法、さらには、そのような希土類窒化物を含有する磁気冷凍材料（または磁気冷凍作業物質）、その磁気転移温度付近の大きな比熱を利用した蓄冷材料に関する。 The present invention relates to a rare earth nitride, a method for producing the same, a magnetic refrigeration material (or magnetic refrigeration working material) containing such a rare earth nitride, and a cold storage material using a large specific heat near the magnetic transition temperature thereof.
水素は、近未来社会の新エネルギーとして有用であり、その利用に際しては、社会的インフラ設備が必要である。水素を燃料として効率よく貯蔵・運搬するには水素の液化技術が必須である。そこで、液化に必要なエネルギー効率を、現在のアンモニアまたはフロンガスを使用する気体冷媒による冷却より大幅に改善することが望まれている。そのような改善に、磁気冷凍システムを用いることが提案されているが、そのシステムを有効ならしめるために、システムに使用できる最適な磁気冷凍材料を開発することが望まれている。 Hydrogen is useful as a new energy in the near future society, and social infrastructure facilities are necessary for its use. In order to efficiently store and transport hydrogen as a fuel, hydrogen liquefaction technology is essential. Therefore, it is desired to significantly improve the energy efficiency required for liquefaction over the current cooling with a gaseous refrigerant using ammonia or chlorofluorocarbon gas. It has been proposed to use a magnetic refrigeration system for such improvement, but in order to make the system effective, it is desired to develop an optimal magnetic refrigeration material that can be used in the system.
そのような磁気冷凍システムに使用できる磁気冷凍材料として、希土類元素と遷移金属との金属間化合物が種々提案されている。そのような金属間化合物には、例えばＤｙＮｉ２、ＨｏＡｌ２、ＥｒＣｏ２、ＤｙＡｌ２、（Ｄｙ，Ｈｏ）Ａｌ２等がある（下記非特許文献１〜４参照）。このような金属間化合物は、水素貯蔵合金にも利用できることから理解できるように、水素との反応性が高く、水素化物となって磁気転移温度等の磁気的性質が変化する。水素を液化する場合、磁気冷凍材料は、その熱効率を上げるため、水素と直接接触するように使用することが望ましい。しかしながら、直接接触する場合には、上述の反応性のため、磁気冷凍材料を長期にわたって繰り返し安定して所望の温度範囲で作動する磁気冷凍材料として使用することができなくなる。また、ＥｒＣｏ２などの一部の金属間化合物は一次相転移を起こし、磁気転移温度で結晶構造までが変化する。従って、励磁・消磁に伴って磁気転移温度を経る温度変化に反復的にさらされることによって材料が脆化し、磁気冷凍材料としての機能が低下してしまう（下記非特許文献５〜８参照）。Various magnetic intermetallic compounds of rare earth elements and transition metals have been proposed as magnetic refrigeration materials that can be used in such a magnetic refrigeration system. Examples of such intermetallic compounds include DyNi 2 , HoAl 2 , ErCo 2 , DyAl 2 , (Dy, Ho) Al 2 (see Non-Patent Documents 1 to 4 below). As can be understood from the fact that such an intermetallic compound can also be used for a hydrogen storage alloy, the reactivity with hydrogen is high, and it becomes a hydride and changes magnetic properties such as a magnetic transition temperature. When liquefying hydrogen, it is desirable to use the magnetic refrigeration material in direct contact with hydrogen in order to increase its thermal efficiency. However, in the case of direct contact, due to the above-described reactivity, the magnetic refrigeration material cannot be used as a magnetic refrigeration material that operates stably in a desired temperature range over a long period of time. In addition, some intermetallic compounds such as ErCo 2 undergo a primary phase transition, and the crystal structure changes at the magnetic transition temperature. Therefore, the material becomes brittle due to repetitive exposure to a temperature change through the magnetic transition temperature accompanying excitation and demagnetization, and the function as a magnetic refrigeration material is reduced (see Non-Patent Documents 5 to 8 below).
ところで、液体ヘリウム温度のような極低温をエネルギー効率よく実現する装置として、蓄冷機能を有する蓄冷材式冷凍機が提唱され、すでに市販されている。この冷凍機は医療機器のＭＲＩや磁気浮上車両など、強力な磁場を発生させるための超伝導コイルの冷却に用いられる。蓄冷材には大きな比熱が求められるが、一般に２０Ｋ以下の極低温では、物質の比熱は冷媒として用いられるＨｅに比べ極めて小さくなる。このため、２０Ｋ以下でも大きな比熱をもつ材料が調査され、希土類元素を含有する金属間化合物が開発され、現在市販されるに至っている。これらの金属間化合物は極低温で磁気転移し、その転移温度付近で大きな磁気比熱を示す。この大きな磁気比熱を蓄熱に利用している。 By the way, a cold storage material type refrigerator having a cold storage function has been proposed as an apparatus for efficiently realizing a cryogenic temperature such as a liquid helium temperature, and is already on the market. This refrigerator is used for cooling superconducting coils for generating a strong magnetic field, such as MRI of medical equipment and magnetic levitation vehicles. Although a large specific heat is required for the regenerator material, the specific heat of the substance is extremely small as compared with He used as a refrigerant at an extremely low temperature of 20K or less. For this reason, materials having a large specific heat even at 20K or less have been investigated, and intermetallic compounds containing rare earth elements have been developed and are now on the market. These intermetallic compounds undergo a magnetic transition at an extremely low temperature and exhibit a large magnetic specific heat near the transition temperature. This large magnetic specific heat is used for heat storage.
一般に磁気比熱は、磁場雰囲気中では、無磁場雰囲気と比べると、著しく減少する傾向がある。従って、磁場が存在する雰囲気において低温を発してそれを維持する場合、磁場雰囲気中において大きい比熱を有する蓄冷材が必要となる。例えば、先にも述べたように、極低温用冷凍機は多くの場合、強磁場を発生する装置の近傍で使用されるので、ある程度の漏洩磁場に晒されるため、そのような蓄冷材が望まれる。尚、希土類窒化物の一部（例えば、ＥｒＮ、ＤｙＮ等）の極低温における比熱が評価されている（下記非特許文献９参照）が、磁場の影響については、教示も示唆もされていない。 In general, the magnetic specific heat tends to decrease significantly in a magnetic field atmosphere as compared to a non-magnetic field atmosphere. Therefore, when a low temperature is emitted and maintained in an atmosphere in which a magnetic field exists, a cold storage material having a large specific heat in the magnetic field atmosphere is required. For example, as mentioned above, a cryogenic refrigerator is often used in the vicinity of a device that generates a strong magnetic field, so that it is exposed to a certain amount of leakage magnetic field. It is. Although specific heat at a very low temperature of a part of rare earth nitrides (for example, ErN, DyN, etc.) has been evaluated (see Non-Patent Document 9 below), there is no teaching or suggestion about the influence of a magnetic field.
上述のような課題に対して、希土類窒化物を用いた磁気冷凍材料および蓄熱材料が提案されている。（特許文献１〜２参照）これら希土類窒化物に共通する問題点として、大気中での安定性に乏しいということが挙げられる。希土類窒化物は大気中に存在する酸素や水分により容易に酸化され、磁気冷凍材料および蓄熱材料としての特性が低下してしまう。 In response to the problems as described above, magnetic refrigeration materials and heat storage materials using rare earth nitrides have been proposed. (See Patent Documents 1 and 2) A problem common to these rare earth nitrides is that they are poorly stable in the atmosphere. Rare earth nitride is easily oxidized by oxygen and moisture present in the atmosphere, and the characteristics as a magnetic refrigeration material and a heat storage material are degraded.
特許文献２には、大気中での酸化を抑制するために、希土類窒化物の表面を樹脂で被覆する技術が開示されている。しかしながら、希土類窒化物の表面を樹脂で被覆するまでは不活性雰囲気中で取り扱わなければならず、工業生産性の点で問題を有している。 Patent Document 2 discloses a technique for coating the surface of rare earth nitride with a resin in order to suppress oxidation in the atmosphere. However, until the surface of the rare earth nitride is coated with a resin, it must be handled in an inert atmosphere, which is problematic in terms of industrial productivity.
本発明が解決しようとする課題は、上述のような希土類窒化物の問題点を解消しうる、大気中での安定性に優れた希土類窒化物およびその製造方法を提供することである。また、本発明が解決しようとする別の課題は、各種冷凍システムに使用可能な、希土類窒化物を含有する磁気冷凍材料および蓄冷材料を提供することである。 The problem to be solved by the present invention is to provide a rare earth nitride excellent in stability in the air and a method for producing the same, which can solve the problems of the rare earth nitride as described above. Another problem to be solved by the present invention is to provide a magnetic refrigeration material and a regenerator material containing rare earth nitride that can be used in various refrigeration systems.
発明者らは、希土類窒化物の組成、形状、製造方法について鋭意検討を行った結果、希土類窒化物をアスペクト比３．０以下の略球状にし、かつ炭素の含有量を０．３質量％以下とすることにより、希土類窒化物の大気中における安定性を飛躍的に向上させることができることを見出した。また、そのような希土類窒化物は、希土類元素の球状金属粒子を窒化することにより得られることを見出した。さらには、そのような希土類窒化物は、磁気冷凍材料および蓄冷材料として、好ましく使用できることを見出した。 As a result of intensive studies on the composition, shape, and manufacturing method of the rare earth nitride, the inventors have made the rare earth nitride substantially spherical with an aspect ratio of 3.0 or less and the carbon content is 0.3 mass% or less. Thus, it has been found that the stability of rare earth nitrides in the atmosphere can be dramatically improved. It has also been found that such rare earth nitrides can be obtained by nitriding spherical metal particles of rare earth elements. Furthermore, it has been found that such rare earth nitrides can be preferably used as magnetic refrigeration materials and cold storage materials.
以下、本発明を実施するための形態について説明する。本発明の希土類窒化物は組成式：ＭＮで表され、そのアスペクト比が３．０以下の略球状の粒子であり、かつ炭素の含有量が０．３質量％以下である。組成式中のＭはＹ（イットリウム）とＳｃ（スカンジウム）を含む希土類元素から選択される１種以上の元素を表す。Ｍとして選択される希土類元素の種類、量、組合せは、その用途により要求される特性、コスト等を考慮して適宜選択できる。Ｍとしては、Ｎｄ（ネオジム）、Ｇｄ（ガドリニウム）、Ｄｙ（ジスプロシウム）、Ｈｏ（ホルミウム）、Ｔｂ（テルビウム）、Ｅｒ（エルビウム）が好ましく挙げられる。Ｍは、２種以上であることが好ましい。Ｍが２種の場合のＭＮとして、ＧｄＸＤｙ１−ＸＮ、ＧｄＸＴｂ１−ＸＮおよびＨｏＸＴｂ１−ＸＮ（いずれの式においても、ｘは０より大きく、１未満の数値である）が好ましく例示される。ＭとしてＮｄ、Ｇｄ、Ｄｙ、Ｈｏ、Ｔｂ、Ｅｒから選択される１種以上（Ｍ１とする）とＭ１以外の希土類元素から選択される１種以上（Ｍ２とする）を含む場合、Ｍ１は、Ｍ２より多く含むことが好ましい。Hereinafter, modes for carrying out the present invention will be described. The rare earth nitride of the present invention is a substantially spherical particle represented by the composition formula: MN, having an aspect ratio of 3.0 or less, and the carbon content is 0.3 mass% or less. M in the composition formula represents one or more elements selected from rare earth elements including Y (yttrium) and Sc (scandium). The type, amount, and combination of rare earth elements selected as M can be appropriately selected in consideration of characteristics, costs, and the like required by the application. Preferred examples of M include Nd (neodymium), Gd (gadolinium), Dy (dysprosium), Ho (holmium), Tb (terbium), and Er (erbium). M is preferably two or more. As MN when M is two kinds, Gd X Dy 1-X N, Gd X Tb 1-X N and Ho X Tb 1-X N (in any formula, x is a value greater than 0 and less than 1) Is preferred). When M includes one or more selected from Nd, Gd, Dy, Ho, Tb, Er (referred to as M1) and one or more selected from rare earth elements other than M1 (referred to as M2), M1 is: It is preferable to contain more than M2.
なお、本発明の希土類窒化物は、基本的にはＭＮで表されるＭ（希土類元素）とＮ（窒素）の１：１の希土類窒化物であるが、ＭＮで表される希土類窒化物が本来有する特性を損なわない範囲で、この比率からずれた組成を有するものであってもよい。また、ＭとＮ以外の元素についても、同様の理由により含有してもよい。本発明の希土類窒化物は、ＮａＣｌ型結晶構造であることが好ましい。 The rare earth nitride of the present invention is basically a 1: 1 rare earth nitride of M (rare earth element) and N (nitrogen) represented by MN, but the rare earth nitride represented by MN is It may have a composition deviating from this ratio as long as the inherent properties are not impaired. Further, elements other than M and N may be contained for the same reason. The rare earth nitride of the present invention preferably has a NaCl type crystal structure.
本発明の希土類窒化物は、炭素の含有量が０．３質量％以下である。炭素が希土類窒化物中に存在すると、大気中における安定性が低下する。特に酸化の進行が促進されるため好ましくない。従って、本発明の窒化物中の炭素の含有量は好ましくは０．１質量％以下、さらに好ましくは０．０５質量％以下である。本願において炭素の含有量は、ガス分析装置により行う。 The rare earth nitride of the present invention has a carbon content of 0.3% by mass or less. If carbon is present in the rare earth nitride, the stability in the air is reduced. In particular, it is not preferable because the progress of oxidation is promoted. Therefore, the carbon content in the nitride of the present invention is preferably 0.1% by mass or less, more preferably 0.05% by mass or less. In the present application, the carbon content is determined by a gas analyzer.
本発明の希土類窒化物は略球状の粒子の形態を持ち、そのアスペクト比は３．０以下である。同一体積の粒子の表面積は、その形状が真球であるとき（アスペクト比が１のとき）に最も小さくなるため、アスペクト比は１に近い方がよい。表面積が小さいと、大気中での酸化が抑制されるため、大気中での安定性が高い。また、アスペクト比が３．０以下である場合、希土類窒化物を磁気冷凍材料や蓄冷材料として容器内に充填して使用する際に、流動性、充填性が高く、充填後の希土類窒化物間には、適度な空隙が形成され、容器内に熱交換媒体を供給、排出する際に熱交換媒体の圧力損失が減少する。従って、本発明の希土類窒化物のアスペクト比は好ましくは２．０以下、さらに好ましくは１．５以下、最も好ましくは１．３以下である。本願においてアスペクト比の測定は、希土類窒化物を良く混合した後、四分法により採取した試料について、光学顕微鏡を用いて任意の１００個の粒子のアスペクト比を計測し、それらの平均値を算出した。これを３回繰り返し、３回の平均値をアスペクト比とした。 The rare earth nitride of the present invention has a substantially spherical particle shape, and its aspect ratio is 3.0 or less. Since the surface area of particles having the same volume is the smallest when the shape is a true sphere (when the aspect ratio is 1), the aspect ratio is preferably close to 1. When the surface area is small, oxidation in the air is suppressed, and thus stability in the air is high. In addition, when the aspect ratio is 3.0 or less, when the rare earth nitride is filled in a container as a magnetic refrigeration material or a cold storage material, the fluidity and filling properties are high, and between the rare earth nitrides after filling. In this case, an appropriate gap is formed, and the pressure loss of the heat exchange medium is reduced when the heat exchange medium is supplied to and discharged from the container. Therefore, the aspect ratio of the rare earth nitride of the present invention is preferably 2.0 or less, more preferably 1.5 or less, and most preferably 1.3 or less. In this application, the aspect ratio is measured by measuring the aspect ratio of 100 arbitrary particles using an optical microscope and calculating the average value of samples collected by the quadrant method after mixing rare earth nitrides well. did. This was repeated three times, and the average of the three times was defined as the aspect ratio.
また、本発明の希土類窒化物は、表面が滑らかな略球状の粒子の形態であることが好ましい。表面が滑らかな場合、表面積が小さく、大気中における安定性が高い。本発明の希土類窒化物の平均粒径ｄ、粒子の理論密度ρより算出した比表面積６／ρｄとＢＥＴ法により測定した比表面積Ｓとの比ρｄＳ／６は２０以下が好ましく、さらに好ましくは１０以下であり、最も好ましくは５以下である。本発明において、平均粒径ｄは、希土類窒化物の粒子をよく混合した後、四分法を用いて１００個程度を採取し、ＳＥＭ像を撮り、これを画像解析して投影面積円相当径を算出した値とする。 The rare earth nitride of the present invention is preferably in the form of substantially spherical particles having a smooth surface. When the surface is smooth, the surface area is small and the stability in the atmosphere is high. The ratio ρdS / 6 between the specific surface area 6 / ρd calculated from the average particle diameter d of the rare earth nitride of the present invention and the theoretical density ρ of the particles and the specific surface area S measured by the BET method is preferably 20 or less, more preferably 10 Or less, most preferably 5 or less. In the present invention, the average particle diameter d is obtained by thoroughly mixing rare earth nitride particles, then collecting about 100 pieces using the quadrant method, taking an SEM image, analyzing this, and analyzing the image to obtain a projected area equivalent circle diameter. Is the calculated value.
本発明の希土類窒化物の粒子径は、０．０１ｍｍ以上、５ｍｍ以下であることが好ましく、さらに好ましくは０．１ｍｍ以上、３ｍｍ以下である。粒径が小さすぎる場合、大気中での安定性を損ない、希土類窒化物を磁気冷凍材料や蓄冷材料として容器内に充填して使用する際に、充填後の希土類窒化物間に適度な空隙が形成されず、容器内に熱交換媒体を供給、排出する際に熱交換媒体の圧力損失が増大する恐れがある。また、粒径が大きすぎる場合、後述する本発明の希土類窒化物の製造方法において、製造が困難となる恐れがあり、また、希土類窒化物を磁気冷凍材料や蓄冷材料として容器内に充填して使用する際に、充填密度が上がらず、容器内に熱交換媒体を供給、排出する際に希土類窒化物と熱交換媒体の接触面積が小さくなり、熱交換性能が低下する恐れがある。 The particle diameter of the rare earth nitride of the present invention is preferably 0.01 mm or more and 5 mm or less, more preferably 0.1 mm or more and 3 mm or less. If the particle size is too small, the stability in the air is impaired, and when the rare earth nitride is filled in a container as a magnetic refrigeration material or a cold storage material, there is an appropriate gap between the filled rare earth nitrides. There is a risk that the pressure loss of the heat exchange medium may increase when the heat exchange medium is supplied to and discharged from the container. Also, if the particle size is too large, there is a risk that the production will be difficult in the rare earth nitride production method of the present invention described later, and the container is filled with rare earth nitride as a magnetic refrigeration material or a cold storage material. When used, the packing density does not increase, and when the heat exchange medium is supplied to and discharged from the container, the contact area between the rare earth nitride and the heat exchange medium becomes small, which may reduce the heat exchange performance.
本発明の希土類窒化物の製造方法は、希土類元素の球状金属粒子を窒化する。希土類元素の球状金属粒子の作製方法は特に限定されず、一般的な球状金属粒子の作製方法を採用することができる。金属粉末を球状に造粒した後、粉末冶金的手法を用いて球状金属粒子を得ることも可能である。また、溶湯から直接球状金属粒子を得られるガスアトマイズ法やディスクアトマイズ法、比較的粒度のそろった大きな球状金属粒子の得られる均一液滴噴霧法や回転電極法なども採用することができる。 The method for producing a rare earth nitride of the present invention nitrides spherical metal particles of rare earth elements. The method for producing rare earth element spherical metal particles is not particularly limited, and a general method for producing spherical metal particles can be employed. After granulating the metal powder into a spherical shape, it is possible to obtain spherical metal particles using a powder metallurgical technique. In addition, a gas atomizing method and a disk atomizing method that can obtain spherical metal particles directly from a molten metal, a uniform droplet spraying method and a rotating electrode method that can obtain large spherical metal particles with relatively uniform particle sizes can be employed.
上述した希土類元素の球状金属粒子は、ほほそのままの形態で窒化されるため、希土類金属の球状粒子のアスペクト比は３．０以下、好ましくは２．０以下、さらに好ましくは１．５以下、最も好ましくは１．３以下である。粒子径は、０．０１ｍｍ以上、５ｍｍ以下であることが好ましく、さらに好ましくは０．１ｍｍ以上、３ｍｍ以下である。粒子径が小さすぎたり、大きすぎたりすると、希土類窒化物の粒子径について述べた問題が生じる恐れがある。 Since the rare earth element spherical metal particles described above are nitrided in an almost intact form, the aspect ratio of the rare earth metal spherical particles is 3.0 or less, preferably 2.0 or less, more preferably 1.5 or less, most preferably Preferably it is 1.3 or less. The particle diameter is preferably 0.01 mm or more and 5 mm or less, more preferably 0.1 mm or more and 3 mm or less. If the particle size is too small or too large, the problem described for the particle size of the rare earth nitride may occur.
希土類元素の球状金属粒子は、例えば、窒素ガス雰囲気中、Ｈｏｔ Ｉｓｏｓｔａｔｉｃ Ｐｒｅｓｓ（ＨＩＰ）法により窒化する。温度、圧力、処理時間は、用いる球状金属粒子に合わせ、適宜選択して行うことができる。 The rare earth element spherical metal particles are nitrided by, for example, a hot isostatic press (HIP) method in a nitrogen gas atmosphere. The temperature, pressure, and treatment time can be appropriately selected according to the spherical metal particles to be used.
特許文献２の希土類窒化物の球状粒子は、希土類酸化物を出発原料とし、炭素と混合した後、窒素雰囲気中で加熱する炭素熱還元法により作製されるが、この方法で作製した希土類窒化物は、炭素を多く含有しており好ましくない。 The rare earth nitride spherical particles of Patent Document 2 are produced by a carbothermal reduction method in which a rare earth oxide is used as a starting material, mixed with carbon, and then heated in a nitrogen atmosphere. The rare earth nitride produced by this method is used. Is not preferable because it contains a large amount of carbon.
本発明の希土類窒化物は、磁気冷凍材料および蓄冷材料として使用することができる。本発明の希土類窒化物を含有する本発明の磁気冷凍材料および蓄冷材料は、大気中での安定性に優れるため、特性が低下せず、工業生産性に優れる。本発明の磁気冷凍材料および蓄冷材料は、各種冷凍システムに用いることができる。 The rare earth nitride of the present invention can be used as a magnetic refrigeration material and a cold storage material. The magnetic refrigeration material and the regenerator material of the present invention containing the rare earth nitride of the present invention are excellent in stability in the air, and therefore have no deterioration in characteristics and excellent in industrial productivity. The magnetic refrigeration material and the cold storage material of the present invention can be used in various refrigeration systems.
次に実施例により本発明を詳述する。 Next, the present invention will be described in detail by way of examples.
金属Ｄｙをアルゴン雰囲気中で高周波溶解した後、ガスアトマイズ法により球状金属粒子を得た。得られた希土類元素の球状金属粒子を１４０ＭＰａの高純度窒素ガス雰囲気中（純度９９．９９９９％）で１６００℃に２時間加熱するＨＩＰ法により窒化し、球状形態有する希土類窒化物を得た。ＨＩＰ法には神戸製鋼所製の０２−Ｄｒ．ＨＩＰを用いた。この希土類窒化物を目開き２ｍｍと０．３ｍｍのふるいを用いて分級し、粒子径０．３〜２ｍｍとした。 After metal Dy was melted at high frequency in an argon atmosphere, spherical metal particles were obtained by a gas atomization method. The obtained rare earth element spherical metal particles were nitrided by the HIP method of heating to 1600 ° C. for 2 hours in a 140 MPa high-purity nitrogen gas atmosphere (purity 99.9999%) to obtain a rare earth nitride having a spherical form. In the HIP method, 02-Dr. HIP was used. This rare earth nitride was classified using a sieve having openings of 2 mm and 0.3 mm to obtain a particle diameter of 0.3 to 2 mm.
得られた希土類窒化物のアスペクト比を測定した。測定方法は、得られた球状粒子を良く混合した後、四分法により採取した試料について、光学顕微鏡を用いて任意の１００個の粒子のアスペクト比を計測し、それらの平均値を算出した。これを３回繰り返し、３回の平均値をアスペクト比とした。結果を表１に示す。 The aspect ratio of the obtained rare earth nitride was measured. The measurement method was carried out by mixing the obtained spherical particles well, then measuring the aspect ratio of 100 arbitrary particles using an optical microscope, and calculating the average value of the samples collected by the quadrant method. This was repeated three times, and the average of the three times was defined as the aspect ratio. The results are shown in Table 1.
得られた球状粒子のρｄＳ／６を算出した。平均粒径ｄは、得られた球状粒子を良く混合した後、四分法を用いて１００個程度の粒子を採取し、日本電子株式会社製ＪＸＡ８８００を用いてＳＥＭ画像を撮り、これを画像解析して投影面積円相当径を算出した。理論密度ρは、株式会社リガク製ＲＩＮＴ Ｕｌｔｉｍａ＋を使用し、Ｃｕ−Ｋαを用い、得られた回折ピークより算出した。比表面積Ｓは、カンタクローム社製ＮＯＶＡ２０００を用いて測定した。結果を表１に示す。 ΡdS / 6 of the obtained spherical particles was calculated. The average particle diameter d is obtained by mixing the obtained spherical particles well, then collecting about 100 particles using the quadrant method, taking an SEM image using JXA8800 manufactured by JEOL Ltd., and analyzing this. The projected area equivalent circle diameter was calculated. The theoretical density ρ was calculated from the obtained diffraction peak using RINT Ultimate + from Rigaku Corporation and using Cu-Kα. The specific surface area S was measured using NOVA2000 manufactured by Cantachrome. The results are shown in Table 1.
上述のように得られた希土類窒化物のＸ線回折の測定を行ったところ、得られた回折パターンはいずれも窒化物由来のピークのみであり、他のピークは確認できなかった。 When the X-ray diffraction of the rare earth nitride obtained as described above was measured, all of the obtained diffraction patterns were only peaks derived from nitride, and other peaks could not be confirmed.
得られた希土類窒化物の炭素量をガス分析装置により測定した。測定には株式会社堀場製作所製ＥＭＩＡ−７２０を用いた。結果を表１に示す。 The carbon content of the obtained rare earth nitride was measured with a gas analyzer. EMIA-720 manufactured by Horiba Ltd. was used for the measurement. The results are shown in Table 1.
次に大気中での安定性評価のため、得られた希土類窒化物の酸素値とグローブボックス中で露点−６０℃の乾燥空気に１００時間さらした後の酸素値の分析を行った。結果を表１に示す。また、多湿環境下での安定性評価のため、得られた希土類窒化物をグロープボックス中、飽和水蒸気圧下で２０時間さらした際の重量増加量を測定した。重量増加量は、（評価後の重量−評価前の重量）を（評価前の比表面積×評価前の重量）で割った値とした。結果を表１に示す。ここでの比表面積は、ＢＥＴ法により測定した値を用いた。Next, in order to evaluate the stability in the atmosphere, the oxygen value of the obtained rare earth nitride and the oxygen value after exposure to dry air with a dew point of −60 ° C. in a glove box for 100 hours were analyzed. The results are shown in Table 1. In addition, in order to evaluate the stability in a humid environment, the amount of increase in weight was measured when the obtained rare earth nitride was exposed to a saturated water vapor pressure for 20 hours in a grope box. The amount of weight increase was a value obtained by dividing (weight after evaluation−weight before evaluation) by (specific surface area before evaluation × weight before evaluation). The results are shown in Table 1. As the specific surface area, a value measured by the BET method was used.
表１に示す比率となるように希土類元素を用いた以外は実施例１と同様の工程により希土類窒化物を作製した。実施例１と同様に各種測定、評価を行った。結果を表１に示す。 Rare earth nitrides were produced by the same steps as in Example 1 except that rare earth elements were used so that the ratios shown in Table 1 were obtained. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
原料の金属Ｄｙの炭素含有量が０．２質量％となるように炭素を添加した以外は実施例１と同様の工程により希土類窒化物を作製した。実施例１と同様に各種測定、評価を行った。結果を表１に示す。 Rare earth nitrides were produced in the same manner as in Example 1 except that carbon was added so that the carbon content of the raw material metal Dy was 0.2% by mass. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
実施例１で分級した粒径０．３ｍｍ未満の希土類窒化物について実施例１と同様に各種測定、評価を行った。結果を表１に示す。 In the same manner as in Example 1, various measurements and evaluations were performed on the rare earth nitride classified in Example 1 and having a particle size of less than 0.3 mm. The results are shown in Table 1.
Ｅｒの酸化物粉末を、炭素熱還元法による窒化に必要な化学量論量の２倍の炭素と混合した後、転動造粒機を用いて球状粒子を作製し、目開き２ｍｍと０．３ｍｍのふるいを用いて分級し、粒子径０．３〜２ｍｍの球状粒子を得た、この球状粒子を高純度窒素ガス雰囲気中で１５００℃に１２時間加熱して窒化物を作製した。実施例１と同様に各種測定、評価を行った。結果を表１に示す。 The Er oxide powder was mixed with carbon twice the stoichiometric amount necessary for nitridation by the carbothermal reduction method, and spherical particles were produced using a tumbling granulator. Classification was performed using a 3 mm sieve to obtain spherical particles having a particle diameter of 0.3 to 2 mm. The spherical particles were heated to 1500 ° C. for 12 hours in a high-purity nitrogen gas atmosphere to produce a nitride. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
実施例１の工程で得られた粒子径２ｍｍ以上の希土類窒化物球状粒子を乳鉢で粉砕した後、再度目開き２ｍｍと０．３ｍｍのふるいを用いて分級し、粒子径０．３〜２ｍｍの球状粒子を得た。実施例１と同様に各種測定、評価を行った。結果を表１に示す。 After pulverizing rare earth nitride spherical particles having a particle diameter of 2 mm or more obtained in the step of Example 1 with a mortar, the particles were classified again using a sieve having an opening of 2 mm and 0.3 mm, and a particle diameter of 0.3 to 2 mm. Spherical particles were obtained. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
表１から明らかなように、各実施例による希土類窒化物は、比較例と比べて、大気中における安定性が優れていることが確認された。 As is clear from Table 1, it was confirmed that the rare earth nitrides according to the respective examples were superior in stability in the atmosphere as compared with the comparative examples.
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