JPH0222164A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To obtain an oxide superconducting material having high superconducting transition temperature by adding ammonia to an acidic aqueous solution containing salts of Bi, Sr, Ca and Cu, adding a specific organic solvent to the aqueous solution to give precipitate, drying, molding and calcining. CONSTITUTION:Salts of Bi, Sr, Ca and Cu are blended in the ratio of Bi:Sr:Ca: Cu of about 2:2:3:4 to give a mixture, which is dissolved in an aqueous solution (e.g., aqueous solution of nitric acid) adjusted to pH of acidic side to give a solution. Then ammonia is added to the solution, adjusted to pH 4.5-6.6, an extremely excess amount of acetone, ethanol, propyl alcohol or mixture thereof as an organic solvent is added to the aqueous solution and the formed precipitate is filtered off and dried. Then the prepared powder is calcined, ground, mixed with a small amount of binder, molded and sintered in air at 770-880 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing oxide superconducting materials with high superconducting transition temperatures.

Conventional technology Superconducting materials have properties not found in other materials, such as ■) zero electrical resistance, 2) complete diamagnetism, and 3) Josephson effect, and are useful for power transport and power generation. It is expected to have a wide range of applications, including nuclear reactors, fusion plasma confinement, magnetic levitation trains, magnetic shields, and high-speed computers. However, with conventional metallic superconductors, the highest superconducting transition temperature is around 23°C, and in actual use they must be cooled using expensive liquid helium and large-scale insulation equipment, making it difficult for industrial use. It was a big problem.

For this reason, research has been underway to find materials that become superconductors at higher temperatures.

In January 1988, an oxide-based superconducting material B i-8r-Ca-Cu-0 having a high superconducting transition temperature was discovered. This material has a high superconducting transition temperature of about 110°C, can use inexpensive liquid nitrogen (boiling point 77K) for cooling, and has a compact cooling device, so it is expected that the range of applications will expand. . For this reason, many studies are currently being conducted on the manufacturing method, physical properties, applications, etc. of this material.

Two types of methods are generally used to produce oxide superconducting materials using ceramic methods: a solid phase method and a coprecipitation method. The solid phase method is a method in which solid raw materials such as oxides or carbonates of each component metal are mechanically mixed and then heat treated. On the other hand, the coprecipitation method is a method in which salts of each component metal are dissolved in water to form a uniform aqueous solution, a precipitate such as oxalic acid is added to this to form a precipitate, and the powder recovered from this is heat-treated. . The sintered body is produced by molding and firing the powder synthesized in this way.

Problems to be Solved by the Invention Among these synthesis methods, in the former solid phase method, the raw materials are solid powders of each component, so the reaction does not occur at low temperatures.
In addition, since carbonate is generally used as the raw material powder for S r + Ca etc., the decomposition temperature of this carbonate is high, and heat treatment at a temperature of at least 800°C is required to generate a superconducting phase. Met. In addition, in order to obtain a high superconducting transition temperature, it was necessary to sinter for a long time just below the melting point.

On the other hand, in the latter coprecipitation method, the powder produced as a precipitate is fine particles, but since oxalic acid or other precipitant is used, this precipitant decomposes during heating to produce carbonate. Therefore, the temperature at which the superconducting phase is formed during heat treatment is only slightly lower than that in the solid phase method, and the same problems as the solid phase method remain.

Means to solve the problem pH salts of bismuth, strontium, calcium and copper
Dissolve it uniformly in an acidic aqueous solution, add ammonia to adjust the pH to 4.0-6°5, and then add a large excess of acetone, ethanol, propyl alcohol, or a mixture thereof to dissolve the resulting The precipitate is filtered and dried, molded, and then heat-treated at a temperature of 770° C. or higher and 880° C. or lower to produce an oxide superconducting material.

Effect Inventors B 1203. SrcO3+C
We investigated the phase formation process when a mixture of aCO3°CuO is heated and found that the decomposition of strontium carbonate and calcium carbonate has a dominant influence on the formation of the superconducting phase. In the method of the present invention, each metal component is precipitated as a hydroxide or oxide, so carbonate is not involved in the generation of a superconducting phase, and since the method is a coprecipitation method from a homogeneous liquid phase, The particle size of the powder is fine and highly uniform.

Therefore, a superconducting phase is generated at a lower temperature than in the solid phase method. Moreover, when heat-treated at the same temperature, superconducting ceramics with even better properties can be obtained.

Example The present invention will be explained below with reference to Examples.

Bismuth nitrate pentahydrate, strontium nitrate, calcium nitrate tetrahydrate, and copper nitrate trihydrate were used as starting materials. These powders were divided into Bi: Sr: Ca: Cu=
Each powder was weighed so that the ratio was 2:2:3:4 and the total weight of the powder was 20g, and dissolved in 25ml of water to which a small amount of nitric acid was added to make a homogeneous solution. Aqueous ammonia was added to this solution while stirring to adjust the pH to 5.
．． 5 and continued stirring for an additional hour. The aqueous solution containing the obtained precipitate was added to 3000 ml of ethanol and further mixed for 1 hour. After the mixing was completed, the precipitate was filtered and dried in a dryer at 120°C. The obtained powder was heated to 750°C.
After calcining in oxygen for 2 hours, the mixture was pulverized for 30 minutes in a grinder. Further, calcination and pulverization were repeated twice. When the composition of the obtained powder was analyzed by ICPC photoemission spectroscopy, it was found that Ca was slightly decreased compared to the blended composition. For comparison, B 1203+ S rCC with the same composition
h+ CaCO3 and CuO were weighed and mixed in a ball mill (normal solid phase method), and the powder was also calcined and pulverized in the same manner. Add a small amount of binder to these powders, granulate them, take 1 g of the powder, and granulate it in a mold with a diameter of 12 mm.
Molded at a pressure of 0 kg/cm2, 750-9
Baked in air for 40 hours at each temperature of 00°C,
'C/hour. The temperature change in electrical resistance of the obtained sintered body was measured using the usual four-terminal method. The measurement results are shown in Table 1.

(Left below) Table 1゜Superconducting transition temperature is that superconducting transition is not observed up to 77 K, and
This is because the sintered body melts at temperatures exceeding 80°C. Further, the reason why the pH after adding ammonia of the present invention is set to 4.0 to 6.5 is because Cu tends to precipitate outside this range.

Effects of the Invention Ceramics obtained by the production method of the present invention easily exhibit a higher superconducting transition temperature than those produced by conventional methods.

Claims (1)

[Claims] Bismuth, strontium, calcium, copper salts are
H is uniformly dissolved in an aqueous solution adjusted to the acidic side, ammonia is added to this to adjust the pH to 4.0-6.5, and a large excess of acetone, ethanol, propyl alcohol, or a mixture thereof is added. A method for producing an oxide superconducting material, which comprises filtering and drying the resulting precipitate, shaping it, and then heat-treating it at a temperature of 770°C or higher and 880°C or lower.