JPH0575713B2

JPH0575713B2 -

Info

Publication number: JPH0575713B2
Application number: JP62179577A
Authority: JP
Inventors: Yasushi Oonishi; Fumiaki Kikui; Keisuke Kageyama
Original assignee: Sumitomo Special Metals Co Ltd
Current assignee: Proterial Ltd
Priority date: 1987-07-17
Filing date: 1987-07-17
Publication date: 1993-10-21
Also published as: JPS6424066A

Description

[Detailed description of the invention]

利用産業分野この発明は、BaO−Y₂O₃−CuO系超電導セラ
ミツクス用原料粉末の製造方法に係り、特に
BaO源の原料粉末としてBa（NO₃）₂を用いて、斜
方晶の低温安定相からなる仮焼原料粉末を得る超
電導セラミツクス用原料粉末の仮焼方法に関す
る。背景技術従来、BaO−Y₂O₃−CuO係超電導セラミツク
スを製造するための出発原料の仮焼方法として
は、出発原料として、粒度3μｍ以下、純度99.9％
以上のBaCO₃、Y₂O₃、CuO粉末を、所要の組成
比に応じて配合、混合した後、大気中で、900℃
〜1000℃の温度にて仮焼されていた。出発原料として、Ba源にBaCO₃を用いるため、
BaCO₃BaO＋CO₂↑の分解温度が850℃以上の
ため、仮焼温度は900℃以上にする必要があるが、
仮焼温度が950℃でも完全なる脱炭酸は行われず、
一方、焼結反応は徐々に進行し、仮焼温度と焼結
温度が重複するようになり、そのため、下記の如
き問題があつた。すなわち、前記配合原料粉末の仮焼が不十分な
場合は、仮焼粉末に微量のBaCO₃が残留し、前
記仮焼粉末を用いて焼結すると、焼結体は異常収
縮あるいはひび割れ等が生ずる恐れがあつた。また、仮焼を十分に行うと、焼結反応が進行し
て所要の微細粉末は得られず、従つて、粉末の粒
成長が起こると、仮焼後の降温時に、斜方晶の低
温安定相への転移が前記粒子内部にまで及び難
く、粒子内に超電導相と非超電導相との混合組織
が生成される恐れがあつた。発明の目的この発明は、かかる現状に鑑み、従来の仮焼方
法における問題を解消し、すぐれた超電導性を有
するBaO−Y₂O₃−CuO系セラミツクスを製造す
るために最適な斜方晶の低温安定相組織からなる
仮焼原料粉末を得ることができる超電導セラミツ
クス用原料粉末の仮焼方法を目的としている。発明の概要発明者は、従来法のかかる問題を解決するた
め、BaO−Y₂O₃−CuO系超電導セラミツクスの
製造において、出発原料の原料粉末及び仮焼条件
について種々検討した結果、出発原料としてBa
源に、Ba（NO₃）₂を使用することにより、従来の
BaCO₃を用いる場合の仮焼温度より200℃低い温
度での仮焼が可能となる点、また、真空中での昇
温後、O₂雰囲気での仮焼条件にて仮焼を行うこ
とにより、生成されるBaOが大気中のCO₂と可逆
的に反応してBaCO₃が生成されることが防止さ
れ、かつ仮焼後の降温時、酸素吸収により超電導
相への転移を完全に行うことができる点を知見
し、この発明を完成した。すなわち、この発明は、出発原料として、Ba（NO₃）₂、Y₂O₃、CuO粉
末を所要量配合混合後、真空中で700℃まで昇温し、その後、O₂100vol％雰囲気中にて 700℃〜850℃に１時間〜20時間保持して仮焼
し、その後、２℃／分以下の冷却速度で徐冷するこ
とを特徴とする超電導セラミツクス用原料粉末の
仮焼方法である。発明の好ましい実施態様この発明において、出発原料粉は、純度99.9％
以上、粒度3μｍ以下が好ましく、かかる性状の
Ba（NO₃）₂、Y₂O₃、CuOの出発原料を、所要の
組成比に配合し混合する。次に、１×10^-2Torr以下の真空中で、原料粉
末中Ba（NO₃）₂を完全に分解するため、700℃ま
で昇温する。さらに、雰囲気をO₂100vol％雰囲気に切換え
て、700℃〜850℃に１時間〜20時間保持して仮焼
する。その後、O₂100vol％雰囲気で、２℃／分以下
の冷却速度にて冷却して、斜方晶の低温安定相か
らなる仮焼原料粉末を得る。限定理由この発明において、配合後の原料粉を、１×10^-2Torr以下の真空中で、700℃まで昇温
するが、これは雰囲気中のCO₂を完全に除去する
ためである。前記真空中の昇温に続いて、雰囲気を真空より
O₂100％雰囲気に変更する理由は、真空中の仮焼
では酸素の欠如したものしか得られず、すなわ
ち、低温安定相（超電導相）である斜方晶は高温
安定相の正方晶より酸素含有量が多く、このため
超電導相へ転移するには酸素を吸収する必要があ
るためである。また、仮焼温度を700℃〜850℃に限定した理由
は、700℃未満では、仮焼による反応に長時間を
要するため好ましくなく、850℃を超えると焼結
が進行し、次の焼結温度が高くなり、CuOが分解
するため好ましくない。また、仮焼温度での保持時間は、十分な仮焼反
応を得るために、少なくとも１時間保持する必要
があるが、20時間を超えると、仮焼反応が飽和し
て量産的でなくなるため、１時間〜20時間とす
る。好ましくは、10〜20時間である。仮焼温度よりの冷却速度は、２℃／分を超える
と、正方晶から斜方晶へ相転移が不十分となるた
め好ましくなく、さらに好ましくは、１℃／分以
下がよい。冷却雰囲気は、O₂100vol％が好まし
い。発明の効果この発明方法により、原料粉末中のBa（NO₃）₂
を真空中にて完全に分解した後、O₂100vol％雰
囲気中にて仮焼、並びに室温までの徐冷を行なう
ため、生成仮焼粉中には非超電導相は残存せず、
すべて超電導相からなる均一な粉体が得られる。得られた仮焼粉を所要の粒度に微粉砕した微粉
砕仮焼粉を、Ｘ線回析法にて結晶構造を調査した
結果、斜方晶の低温安定組織からなることが分つ
た。この発明方法により得られた微粉砕仮焼粉を、
O₂20vol％以上の雰囲気中で、900℃で焼結した
後、炉冷することにより、焼結体全体が斜方晶の
低温安定相からなるすぐれたBaO−Y₂O₃−CuO
系超電導性セラミツクスを得ることができる。実施例純度99.9％以上、粒度1μｍ以下のBa（NO₃）₂、
Y₂O₃、CuO粉末を、組成比２：１：３のモル比
にて配合して、アルコールを収容したボールミル
中で６時間混合した。１×10^-2Torr以下の真空中で、700℃まで２
℃／minの昇温速度で昇温後、700℃に４時間保
持した。その後、O₂100vol％雰囲気に切換えて、700℃
から800℃まで、２℃／minの昇温速度で昇温し
た。その後、800℃に４時間保持し、さらに、前記
O₂雰囲気中で、２℃／minの冷却速度で常温まで
冷却した。得られた仮焼粉を微粉砕して粒度1μｍ以下の
仮焼粉を得た。これをＸ線回析法にて結晶構造を
測定した結果、斜方晶からなる低温安定相であつ
た。その後、前記仮焼粉を、寸法径20mm×高さ30mm
の材質SiCのダイスを用いて、圧力1000Kg／cm²で
成形した後、900℃にて10時間保持した。その後、２℃／分の冷却速度で冷却して、寸法
径20ｍ×高さ５mmの焼結体を得た。得られた焼結体をＸ線回析方法及び顕微鏡にて
組織、結晶構造を調査した結果、焼結体は斜方晶
の低温安定相を有し、Tcが90〓でマイスナー効
果を示す超電導セラミツクスが得られた。比較例実施例１と同一組成比の純度99.9％以上の粒度
1μｍ以下のBa（NO₃）₂、Y₂O₃、CuO粉末を混合
後、第１表に示す真空中昇温条件、O₂雰囲気中
の仮焼条件、冷却条件にて仮焼して、得られた仮
焼粉を微粉砕して、粒度1μｍ以下の仮焼粉を得
た。これをＸ線回析法及び顕微鏡にて調査した仮焼
粉の性状を第２表に示す。 Field of Application This invention relates to a method for producing raw material powder for BaO-Y ₂ O ₃ -CuO-based superconducting ceramics, and in particular,
The present invention relates to a method for calcination of raw material powder for superconducting ceramics, which uses Ba(NO ₃ ) ₂ as a raw material powder for a BaO source to obtain a calcination raw material powder consisting of an orthorhombic low-temperature stable phase. BACKGROUND ART Conventionally, as a method for calcination of starting materials for producing BaO-Y ₂ O ₃ -CuO-based superconducting ceramics, the starting materials have a particle size of 3 μm or less and a purity of 99.9%.
The above BaCO ₃ , Y ₂ O ₃ , and CuO powders were blended and mixed according to the required composition ratio, and then heated at 900°C in the atmosphere.
It was calcined at a temperature of ~1000℃. Since BaCO ₃ is used as a Ba source as a starting material,
Since the decomposition temperature of BaCO ₃ BaO + CO ₂ ↑ is over 850°C, the calcination temperature needs to be over 900°C.
Even at a calcination temperature of 950℃, complete decarboxylation does not occur.
On the other hand, the sintering reaction progresses gradually, and the calcination temperature and sintering temperature come to overlap, resulting in the following problems. That is, if the blended raw material powder is insufficiently calcined, a trace amount of BaCO ₃ remains in the calcined powder, and when the calcined powder is used for sintering, the sintered body may shrink abnormally or crack. I was afraid. In addition, if calcination is performed sufficiently, the sintering reaction will progress and the required fine powder will not be obtained. Therefore, if grain growth of the powder occurs, the orthorhombic crystals will become stable at low temperatures when the temperature is lowered after calcination. It was difficult for the phase transition to reach the inside of the particles, and there was a risk that a mixed structure of a superconducting phase and a non-superconducting phase would be generated within the particles. Purpose of the Invention In view of the current situation, the present invention solves the problems in the conventional calcination method and develops an orthorhombic crystal that is optimal for producing BaO-Y ₂ O ₃ -CuO ceramics having excellent superconductivity. The object of the present invention is to provide a method for calcination of raw material powder for superconducting ceramics, which can yield raw material powder for calcination having a low-temperature stable phase structure. Summary of the Invention In order to solve the problems of the conventional method, the inventor conducted various studies on the starting material powder and calcination conditions in the production of BaO-Y ₂ O ₃ -CuO-based superconducting ceramics. Ba
By using Ba(NO ₃ ) ₂ as a source, the conventional
It is possible to perform calcination at a temperature 200°C lower than the calcination temperature when using BaCO ₃ , and by performing calcination under the conditions of calcination in an O ₂ atmosphere after raising the temperature in vacuum. , the produced BaO is prevented from reversibly reacting with CO ₂ in the atmosphere to produce BaCO ₃ , and when the temperature is lowered after calcination, the transition to the superconducting phase is completely carried out by oxygen absorption. This invention was completed based on the knowledge that this can be done. That is, in this invention, after mixing the required amounts of Ba(NO ₃ ) ₂ , Y ₂ O ₃ , and CuO powder as starting materials, the mixture is heated to 700°C in vacuum, and then placed in an atmosphere of 100 vol% O ₂ . This is a method for calcination of raw material powder for superconducting ceramics, which is characterized by holding the powder at 700°C to 850°C for 1 to 20 hours to calcinate it, and then slowly cooling it at a cooling rate of 2°C/min or less. Preferred embodiment of the invention In this invention, the starting raw material powder has a purity of 99.9%.
Above, the particle size is preferably 3μm or less, and with such properties
Starting materials Ba(NO ₃ ) ₂ , Y ₂ O ₃ , and CuO are mixed in a desired composition ratio. Next, in a vacuum of 1×10 ⁻² Torr or less, the temperature is raised to 700° C. in order to completely decompose Ba(NO ₃ ) ₂ in the raw material powder. Further, the atmosphere is changed to an O ₂ 100 vol % atmosphere, and the temperature is maintained at 700° C. to 850° C. for 1 hour to 20 hours for calcination. Thereafter, it is cooled in an O ₂ 100 vol % atmosphere at a cooling rate of 2° C./min or less to obtain a calcined raw material powder consisting of an orthorhombic low-temperature stable phase. Reason for limitation In this invention, the raw material powder after blending is heated to 700° C. in a vacuum of 1×10 ⁻² Torr or less, and this is to completely remove CO ₂ in the atmosphere. Following the temperature increase in vacuum, the atmosphere is changed from vacuum to
The reason for changing to a 100% O ₂ atmosphere is that calcining in a vacuum only yields a product that lacks oxygen.In other words, orthorhombic, which is a low-temperature stable phase (superconducting phase), has less oxygen than tetragonal, which is a high-temperature stable phase. This is because the content is large, and therefore it is necessary to absorb oxygen in order to transition to a superconducting phase. In addition, the reason why the calcination temperature was limited to 700°C to 850°C is that if it is less than 700°C, it will take a long time for the reaction due to calcination, which is undesirable, and if it exceeds 850°C, sintering will progress and the next This is not desirable because the temperature becomes high and CuO decomposes. In addition, it is necessary to hold the calcination temperature for at least 1 hour in order to obtain a sufficient calcination reaction, but if it exceeds 20 hours, the calcination reaction will become saturated and it will not be suitable for mass production. 1 hour to 20 hours. Preferably it is 10 to 20 hours. If the cooling rate from the calcination temperature exceeds 2° C./min, the phase transition from tetragonal to orthorhombic crystals will be insufficient, which is not preferable, and more preferably 1° C./min or less. The cooling atmosphere is preferably O ₂ 100vol%. Effects of the invention By the method of this invention, Ba(NO ₃ ) ₂ in the raw material powder can be reduced.
After being completely decomposed in a vacuum, it is calcined in a 100vol% O ₂ atmosphere and slowly cooled to room temperature, so no non-superconducting phase remains in the calcined powder produced.
A uniform powder consisting entirely of superconducting phase is obtained. The resulting calcined powder was finely pulverized to a desired particle size, and the crystal structure of the finely pulverized calcined powder was investigated by X-ray diffraction, and it was found that it consisted of an orthorhombic low-temperature stable structure. The finely pulverized calcined powder obtained by the method of this invention is
By sintering at 900℃ in an atmosphere containing 20 vol% or more of O ₂ and then cooling in a furnace, the entire sintered body becomes an excellent BaO−Y ₂ O ₃ −CuO consisting of an orthorhombic low-temperature stable phase.
system superconducting ceramics can be obtained. Example Ba(NO ₃ ) ₂ with a purity of 99.9% or more and a particle size of 1 μm or less,
Y ₂ O ₃ and CuO powder were blended at a molar ratio of 2:1:3 and mixed for 6 hours in a ball mill containing alcohol. In a vacuum of 1×10 ^-2 Torr or less, up to 700℃2
After raising the temperature at a temperature increase rate of °C/min, it was held at 700 °C for 4 hours. Then, switch to O ₂ 100vol% atmosphere and heat at 700℃.
The temperature was raised from 1 to 800°C at a rate of 2°C/min. Thereafter, the temperature was maintained at 800°C for 4 hours, and the
It was cooled to room temperature in an O ₂ atmosphere at a cooling rate of 2° C./min. The obtained calcined powder was finely pulverized to obtain calcined powder with a particle size of 1 μm or less. The crystal structure of this was measured by X-ray diffraction, and the result was that it was a low-temperature stable phase consisting of orthorhombic crystals. After that, the calcined powder is
After molding at a pressure of 1000 Kg/cm ² using a die made of SiC material, the molding was held at 900°C for 10 hours. Thereafter, it was cooled at a cooling rate of 2° C./min to obtain a sintered body with dimensions of 20 m in diameter and 5 mm in height. The microstructure and crystal structure of the obtained sintered body were investigated using X-ray diffraction and a microscope, and it was found that the sintered body had an orthorhombic low-temperature stable phase and was a superconductor exhibiting the Meissner effect with a Tc of 90〓. Ceramics were obtained. Comparative example Particle size with purity of 99.9% or more with the same composition ratio as Example 1
After mixing Ba(NO ₃ ) ₂ , Y ₂ O ₃ , and CuO powders of 1 μm or less, they were calcined under the conditions of heating in vacuum, calcining in O ₂ atmosphere, and cooling conditions shown in Table 1. The obtained calcined powder was finely pulverized to obtain calcined powder with a particle size of 1 μm or less. The properties of the calcined powder, which were investigated using X-ray diffraction and a microscope, are shown in Table 2.

【表】【table】

【table】

Claims

[Claims] 1. Ba(NO ₃ ) ₂ , Y ₂ O ₃ , CuO as starting materials
After mixing the required amount of powder, heat it to 700℃ in a vacuum, then heat it to 700℃ to 850℃ in an O ₂ 100vol% atmosphere.
1. A method for calcination of raw material powder for superconducting ceramics, which comprises calcination by holding at a temperature of 1 to 20 hours at a temperature of 1 to 20 hours, and then slowly cooling at a cooling rate of 2°C/min or less.