NO179365B - Process for joining parts of ceramic high temperature superconductor materials - Google Patents

Abstract

For joining parts of ceramic high-temperature superconductive material of the composition Bi(2+a-b)(Sr(1-c)Cac)(3-a)PbbCu(2+d)Ox, a being 0 to 0.3, b being 0 to 0.5, c being 0.1 to 0.9 and d being 0 to 2, and x having a value depending on the oxidation state of the metals present, the end faces of the parts, located at a mutual distance amounting to a gap, are heated by means of a fuel gas/oxygen flame to temperatures from 750 to 875 DEG C. At the same time, a rod of the same material is heated above the distance amounting to a gap until the melt thereof drips between the end faces of the two parts into the gap, completely filling it. At least the joint region between the two parts is then heat-treated for 7 to 100 hours at temperatures between 780 and 850 DEG C.

Description

The present invention relates to a method for connecting parts of ceramic high-temperature superconductor material with the composition (2+a-b)^<r>(1-c)^<a>c^(3—a)~ PtobCu(2+d) °X' where a is from 0 to 0.3, b from 0 to 0.5, c from 0.1 to 0.9, d from 0 to 2 and x has a value that depends on the oxidase;] onst Ustanden to the containing metals.

From the unpublished German patent application P 38 30 092.3, a method is known for the production of a high-temperature superconductor with composition Bi2(Sr, Ca^CugOx with values for x from 8 to 10. There, stoichiometric mixtures of oxides or carbonates of bismuth, strontium, calcium and copper heated to temperatures from 870 to 1100°C to form a homogeneous melt. The homogeneous melt is poured into a metal mold and solidified there. The castings removed from the mold are tempered from 6 to 30 hours at 780 to 850°C and then treated for at least 6 hours at 600 to 830°C in an oxygen atmosphere. In this way, it is possible to produce plates with up to several cm edge length, respectively diameter, as well as rods up to 50 cm long and 10 mm diameter, each of which consists of the phaser compound.

A disadvantage is that the above-described ceramic high-temperature superconductors are so brittle that for transport in the form of long current conductors they cannot be rolled on a drum with a large diameter (e.g. 2 m) without breaking, or suffer from cracking, especially when the high-temperature superconductors are to be used for high-current transport.

There are also already filled ceramic high-temperature superconductors in powder form in silver tubes and the tubes have been lengthened by round hammering and deep drawing, until there were "wires" of the desired diameter, whereby the inner space of the silver tube contains high-temperature superconductor powder which can be sinterable by heat treatment into a continuous column. The oxygen which is necessary for the formation of the superconductor thus diffuses through the wall of the silver tube.

The aforementioned "powder tube" conductors can withstand a certain degree of bending, so that they can in principle be used as a transport current conductor. The disadvantage, however, is that they can only be bent to small diameters without interference and they cannot be connected to complicated systems.

It is therefore a task for the present invention to specify a method for connecting parts of ceramic high-temperature superconducting material to complicated and extensive structures, where the connection points are also superconducting. The invention relates more specifically to a method for connecting parts of ceramic high-temperature superconductor material with composition ^*(2+a—b )^r(l-c)Cac)(3_a)PbbCu(2+d)°X' where a is from 0 to 0.3, b from 0 to 0.5, c from 0.1 to 0.9, d from 0 to 2 and x has a value that depends on the oxidation state of the containing metals, characterized by heating the front floats of the parts located at a gap-like distance from each other by means of a fuel gas-oxygen flame to temperatures from 750 to 875"C and at the same time heating a rod of the same material across the gap-like distance until the melt therefrom drips into the gap between the front faces of the parts during complete filling of the gap, and that the connection area between the parts is then heat treated for 7 to 100 hours at temperatures between 780 and 850°C.

The method according to the invention can optionally also be carried out by

a) you heat treat at temperatures from 815 to 830°C,

b) heat treatment time depends on joint thickness, whereby a thicker joint requires a

longer heat treatment time and vice versa,

c) the front faces of the connecting parts are arranged parallel to each other, d) the front surface of the connecting parts is arranged wedge-shaped to each other, e) the connecting parts of ceramic high-temperature conductor material are enveloped by a silver tube.

The compounds used according to the invention, e.g. Bi2(Sr ,Ca)3C\i20x (with x from about 8.2), melt incongruously, i.e. they show no melting point, but instead a melting point range. Furthermore, the surface tension in this melt in relation to the solid phase in air is so great that the melt does not quickly flow from that phase. Both properties are good prerequisites for a relationship, which resembles connections of metals in autogen welding.

Melting of the compounds Bi2(Sr,Ca)3Cu20x (with x from approx. 8.2) takes place e.g. above 875 °C during oxygen loss, whereby the melting temperature at x from approx. 7.5 decreases to approx. 780° C. The present solid after solidification of this melt is no longer superconducting. However, it can again by heat treatment at approx. 800"C in air be transferred to the superconducting state.

In the method according to the invention, it is to be noted that the front surfaces of the joined parts are so hot that they cannot be connected with the dripping melt of the heated rod.

In the method according to the invention, a thin joint is heat treated for 8 to 15 hours, while a thicker joint is heat treated for up to 100 hours. The heat treatment of the connection points between the parts can take place by subjecting the assembled new mold part in an oven during heat treatment. The heat treatment can also take place locally by arranging the connection points in an electric miniature furnace with precise temperature measurement and regulation, or by local high-frequency induction heating or by direct heating with arranged electrodes at an angle to the connection point or by laser pulses.

When welding according to the invention with silver tube-sheathed shaped bodies that are high-temperature superconducting ceramic material, particular care must be taken to ensure that the fuel gas-oxygen flame does not come into contact with the silver sheath and this melts, as the melting point of silver and the high-temperature superconducting compound are not far apart . The silver-free connection area between both of the connected parts according to the invention can optionally be sheathed in silver afterwards.

In the accompanying drawings, application of the method according to the invention is shown schematically and in cross-section. They show: Fig. 1 connection of two round rods with parallel to

mutually arranged front surfaces,

Fig. 2 connection of two thicker round rods with wedge-shaped

mutually arranged front surfaces,

Fig. 3 connection of a thicker and a thinner round rod with

front surfaces arranged parallel to each other,

Fig. 4 connection of a thin disc with a round rod with

front surfaces arranged parallel to each other,

Fig. 5 device for local heat treatment of connections with round rods,

Fig. 6 temperature-resistance diagram.

In fig. 1, shading A represents the solidified, non-superconducting alloy and shading B represents the post-tempered, superconducting compound.

Image a shows the connection with the round rod immediately after solidification of the infused melt in the gap, while image b shows the connection point after 24 hours of heat treatment at 815°C.

In fig. 3, there are hollow areas in the longitudinal axis of the thicker and thinner round rod.

In fig. 5 is a ceramic heating carrier 1, in which there is a resistance heating coil 2, which is fixed over pipe diameter guide 4 in holder 3. 5 indicates the connection joint of two round rods of ceramic high-temperature superconductor material. A thermocouple 6 is arranged near the connecting joint 5.

In fig. 6 shows three measurements according to the method in example 1 of the connected parts; and each of curves 1 and 2 shows measurements on each of the connected parts and curve 3 shows measurement in the connection area of both parts above the welding point.

Example 1

Two of the manufactured round rods according to the method according to German patent application P 38 30 092.3 with a diameter of 5 mm and a length of 150 mm are pushed together on a ceramic substrate into a gap so that their front surfaces run parallel to each other. The front surfaces are heated by means of a natural gas-oxygen flame to a bright red glow. At the same time, a round rod of the same material is heated above the gap so strongly that the melt drips into the gap. By slowly turning both round rods, the gap is simultaneously filled with the melt

(cf. fig. 1, picture a). After 12 hours of heat treatment of the connected round bars at 815°C in an oven, the connection zone between both round bars was superconducting (cf. Fig. 1, picture b).

The burst temperature in the connection zone of both round rods was 85.5 K; on the left and right, the jump temperature is measured to 86.0 and 86.5 K (cf. Fig. 6).

Example 2

Two of the manufactured round rods according to the method according to German patent P 38 30 092.3 with 12 mm diameter and 300 mm length are arranged with their cone-shaped front surfaces in relation to each other. Using a propane gas-oxygen flame, the upper cone is heated and melted from the base, before the melt from a dripping round rod of the same material is dripped above into the cone and fills it completely (cf. fig. 2). The connected round bar is then heat treated in a furnace for 24 hours at 800°C.

As a check whether the connection zone between both round rods was no longer superconducting, the specific resistance of the connected round rods was measured.

Example 3

Example 2 was repeated with a change where a round rod of 5 mm diameter and 120 mm length and a round rod of 16 mm diameter and 40 mm length are clamped in a holding device so that their axes are centered and their front surfaces are arranged parallel to each other (cf. . Fig. 3).

The measurement of specific resistance of the connected rolls gave:

Example 4

Example 2 was repeated with the change that a round rod with a diameter of 5 mm and a length of 80 mm is vertically connected to a circular plate (20 mm diameter, 5 mm thickness) (cf. fig. 4). It is noted that the heating of the thin disc is less intensive than the round bars.

Example 5

Example 2 was repeated with the change that round rods with a diameter of 8 mm were connected to each other and the heat treatment took place by local heat treatment of the connection zone. In addition, an electric miniature furnace was used, which in the area of the connection zone is located around the round rod and is provided with a thermal insulation of aluminum oxide wool. An introduced thermocouple etc. served for temperature control. fig. 5).

Claims (6)

1. Method for bonding parts of ceramic high-temperature superconductor material with composition b)-(Sr(!_c )Cac )(3-a)Pl3bCu(2+d)0X' where a is from 0 111 °»3' b from 0 to 0.5, c from 0.1 to 0.9, d from 0 to 2 and x has a value that depends on the oxidation state of the containing metals, characterized by heating the front faces of the parts that are in the gap distance from each other by means of a fuel gas-oxygen flame to temperatures from 750 to 875°C and at the same time heats a rod of the same material over the gap-shaped gap until the melt from it drips into the gap between the front faces of the parts while completely filling the gap, and that one then heat-treats the connection area between the parts for 7 to 100 hours at temperatures between 780 and 850°C. 2. Method according to claim 1, characterized in that heat treatment is carried out at a temperature from 815 to 830°C. 3. Method according to claim 1 or 2, characterized in that the heat treatment time depends on the thickness of the connection point, where a thicker connection point requires a longer heat treatment time and vice versa. 4. Method according to any one of claims 1 to 3, characterized in that the front surfaces of the connecting parts are arranged parallel to each other. 5. Method according to any one of claims 1 to 3, characterized in that the front surfaces of the connecting parts are wedge-shaped to each other. 6. Method according to any one of claims 1 to 5, characterized in that the connecting parts of ceramic high temperature conductor materials are each enveloped by a silver tube.