JPH0791115B2 - Oxide superconductor firing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a firing apparatus used for firing various ceramics and oxide superconductors.

[Prior _{Art] Y-Ba 2 -Cu 3 -O} 7 including - [delta, high oxide superconductor having a superconducting transition temperature, discovered one after another, have been published.
The manufacture of these oxide superconductors requires a firing process that includes sintering and annealing to produce a superconducting phase. The superconducting properties of oxide superconductors are greatly affected by the firing conditions, and it is particularly important to control the atmosphere in each firing process.

[Problems to be Solved by the Invention] However, hitherto, no apparatus has been proposed which can strictly control the oxygen partial pressure in the vicinity of the object to be fired to be an oxide superconductor according to each firing process. It is an object of the present invention to provide an oxide superconductor firing apparatus capable of controlling the firing atmosphere in accordance with each firing process so that the article to be fired can exhibit its best characteristics.

[Means for Solving the Problems] An apparatus for firing an oxide superconductor according to the present invention comprises a firing furnace body,
Heating means, temperature control means for controlling the heating means so as to change the temperature of the object to be fired to be an oxide superconductor according to a predetermined time-temperature curve, and oxygen and an inert gas are supplied to the firing furnace. Gas supply means, gas pressure control means for controlling the gas pressure in the firing furnace to a predetermined value, oxygen detection means for detecting the amount of oxygen in the vicinity of the object to be fired, and predetermined oxygen partial pressure-time A curve is stored, and based on the detection result of the oxygen detection means, the oxygen and inert gas supply amounts are adjusted so that the oxygen partial pressure in the vicinity of the fired product and the total pressure of the firing atmosphere become predetermined values at the same time. And a means for controlling.

[Operation] According to the present invention, the total pressure in the furnace and the oxygen partial pressure in the vicinity of the object to be fired can be controlled at the same time during firing, so that the fired oxide superconductor exhibits the excellent characteristics inherent to the material. You can

[Example] Fig. 1 schematically shows an example of the apparatus for firing an oxide superconductor according to the present invention, and the operation thereof will be described. First firing furnace 1
Inside, rotary pump 2A, vacuum solenoid valve 2B, exhaust filter
The exhaust system 2 equipped with 2C, a leak valve 2D and a vacuum gauge 2E exhausts to a predetermined degree of vacuum. Next, a mixed gas of oxygen and nitrogen (or argon) is supplied to the firing furnace 1. Oxygen passes from the cylinder 3A through the stop valve 3B, needle valve 3C, mass flow controller 3D, check valve 3E and control valve 3F, and nitrogen (or argon) similarly from the cylinder 4A through stop valve 4B, needle valve 4C, mass flow controller 4D. Then, they enter the gas mixer 5 via the check valve 4E and the control valve 4F and are mixed therein. The mixed gas (or a single gas) is introduced into the firing furnace 1 through the gas introduction valve 6. 3G and 4G are primary pressure gauges respectively. An oxygen sensor 7 is placed in the firing furnace 1 near the article to be fired to detect the amount of oxygen near the article to be fired. This detection signal is input to the oxygen concentration meter 8, and the oxygen concentration signal from the concentration meter 8 is input to the oxygen partial pressure controller 9. On the other hand, the temperature controller 10 for controlling the temperature of the firing furnace 1 stores a predetermined oxygen partial pressure according to each process of firing. Are compared by the oxygen partial pressure controller 9, and the oxygen partial pressure controller controls opening / closing of the control valves 3F and 4F so that the oxygen partial pressure in the vicinity of the object to be fired becomes a predetermined value.

On the other hand, the pressure signal of the gas introduced into the firing furnace 1 is a compound meter 11
Entered in. The compound gauge 11 operates the exhaust valve 12 so that the pressure inside the furnace is maintained at a predetermined value. 13 is a safety valve, and 14 is a resistance heating element. The furnace body of the firing furnace 1 can be water-cooled.

Using the device of the present invention, an oxide superconductor was prepared by adding Ag ₂ O to LaBa ₂ Cu ₃ O ₇ −δ.

La ₂ O ₃ , Ba (OH) ₂ · 8H ₂ O and CuO are added with a La: Ba: Cu ratio of 1:
Each was weighed to be 2: 3, mixed dry and crushed. The mixed powder was heat-treated at 800 to 900 ° C for 10 hours. The heat treatment atmosphere may be air, oxygen or nitrogen. After heat treatment, re-grind and pass through 30μm sieve
A powder of LaBa ₂ Cu ₃ O ₇ −δ was obtained.

20 wt% of Ag ₂ O powder (purity 99.99
%), And a pressure of 1-2 ton / cm ² is applied to obtain a diameter of 15 m.
Pellets of m and 1.5 mm in thickness were prepared. The pellets were placed in a crucible and fired while simultaneously controlling the temperature and the heating atmosphere, that is, the total pressure and the oxygen partial pressure.

FIG. 2 shows an example of a time-temperature curve during firing. As shown in the figure, the firing process includes four processes including a temperature raising process up to a sintering temperature, a sintering process at a constant temperature, a temperature decreasing process to an annealing temperature, and a superconducting phase generation process by annealing at a constant temperature. .

In the following examples, the rate of temperature rise and temperature decrease were set to 200 ° C./hr and 60 ° C./hr, respectively. The sintering temperature was appropriately selected in the range of 930 ° C to 950 ° C, and the sintering time was constant for 5 hours. Annealing temperature is constant at 300 ℃, holding time is 5 hours or 1
It was 0 hours.

Further, as shown in FIG. 2, the firing process was divided into four segments a, b, c and d to control the atmosphere during firing. The temperature of segment a is 700 ℃, and that of segment b is mainly sintering process.
Including the process of cooling down to 00 ℃. The segment c corresponds to the temperature lowering process at 900 ° C. or lower, and the segment d corresponds to the annealing, that is, the superconducting phase forming process. In the present invention, while controlling the total pressure in the furnace, to detect the oxygen partial pressure in the vicinity of the object to be fired,
Firing was performed while controlling the oxygen partial pressure in each segment unit.

The superconducting transition temperature and the critical current density of each of the prepared samples were measured. For the superconducting transition temperature, the DC resistance was measured by the four-terminal method to measure Tcend at which the electric resistance became 0, and further, the superconducting transition temperature T _CI was measured from the temperature change of the AC magnetic susceptibility using a Hertzhorn bridge. The critical current density J _C was determined by applying a large current pulse to the sample under liquid nitrogen and determining the maximum current value at which the superconducting state was maintained, as J _C.

Table 1 shows the superconducting transition temperatures T _cend and T _CI and the critical current density J _C of each sample prepared by changing the Ag ₂ O concentration and the firing conditions. As is clear from the table, even with oxides of the same composition,
The superconducting property, especially the critical current density, greatly changes depending on the firing conditions. When the total pressure in the furnace is 1.2 kg / cm ² and the oxygen partial pressure in the vicinity of the sample during the temperature rising, sintering, temperature lowering and annealing processes is 20, 0, 100 and 100% respectively, the critical current density is 390 A / cm 2. ^It showed a high value of ² .

[Effects of the Invention] As described above, according to the present invention, not only the oxygen partial pressure in the vicinity of the object to be fired but also the total pressure of the firing atmosphere can be controlled at the same time according to each step of the firing process. The superconducting property of can be improved.

The firing apparatus according to the present invention is not limited to oxide superconductors and can be widely applied to firing various porcelain compositions that require control of oxygen partial pressure.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of a device for firing an oxide superconductor according to the present invention, and FIG. 2 is a diagram explaining a firing method using the device of the present invention. 1 ... Baking furnace, 7 ... Oxygen sensor, 8 ... Oxygen concentration meter, 9 ...
Oxygen partial pressure controller, 10… Temperature controller. 14 ... Resistance heating element.

Front page continuation (72) Izumi Hirabayashi Izumi Hirabayashi 2-4-1, Rokuno, Atsuta-ku, Nagoya-shi, Aichi International Superconductivity Industrial Technology Research Center Nagoya Laboratory (56) Reference JP-A-54-120210 (JP , A) Actual Development Sho 61-10492 (JP, U) Japanese Patent Sho 60-46357 (JP, B2)

Claims (1)

[Claims] 1. A firing furnace main body, a heating means, a temperature control means for controlling the heating means so as to change the temperature of an object to be fired which becomes an oxide superconductor according to a predetermined time-temperature curve, and the firing furnace. A gas supply means for supplying oxygen and an inert gas, a gas pressure control means for controlling the gas pressure in the firing furnace to a predetermined value, and an oxygen detection means for detecting the amount of oxygen in the vicinity of the object to be fired. A predetermined oxygen partial pressure-time curve is stored so that the oxygen partial pressure in the vicinity of the fired product and the total pressure of the firing atmosphere simultaneously reach a predetermined value based on the detection result of the oxygen detection means. A device for firing an oxide superconductor, characterized in that the device further comprises means for controlling the supply amounts of oxygen and an inert gas.