JPH02175668A - Calcinator - Google Patents

Abstract

PURPOSE:To obtain a calcinator, especially equipped with a controlling means for O2 partial pressure near a material to be calcined in a calcining furnace body and capable of controlling a calcining atmosphere according to respective steps of calcination and improving superconductive characteristics of superconducting material compositions. CONSTITUTION:The interior of a calcining furnace 1 is evacuated to a prescribed vacuum degree with a gas discharge system 2 and a mixed gas of O2 and N2 is fed into the interior of the furnace 1. That is the O2 is introduced from a gas cylinder (3A) into a gas mixer 5 and the N2 is introduced from a gas cylinder (4A) thereinto, mixed and then introduced into the furnace 1. In this case, the quantity of O2 near a material to be calcined is sensed with an oxygen sensor 7 provided in the vicinity of the material to be calcined in the furnace 1. The above-mentioned sensed signal is then inputted to an oxygen densitometer 8 and the O2 concentration signal is further inputted to an oxygen partial pressure controller 9. On the other hand, O2 partial pressure previously memorized in a temperature controller 10 of the furnace 1 is compared with the O2 concentration signal from the densitometer 8 in the controller 9 to control opening and closing of control valves (3F) and (4F) so as to provide a prescribed value of the O2 partial pressure near the material to be calcined. Thereby, an oxide superconductor containing, e.g. Ag2O added to LaBa2Cu3O7-delta, is produced by using the above-mentioned calcinator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a firing apparatus used for firing various ceramics, oxide superconductors, and the like.

[Prior Art] Oxide superconductors with high superconducting transition temperatures, including Y-Ba2-Cu3-07-6, have been discovered and announced. The production of these oxide superconductors requires a firing process that includes sintering and annealing to generate a superconducting phase. The superconducting properties of oxide superconductors are greatly influenced by firing conditions, and controlling the atmosphere during each firing process is particularly important.

[Problems to be Solved by the Invention] However, no apparatus has been proposed so far that can strictly control the oxygen partial pressure near the object to be fired in accordance with each firing process.

SUMMARY OF THE INVENTION An object of the present invention is to provide a firing apparatus that can control the firing atmosphere according to each firing process so that the object to be fired can exhibit its best characteristics.

[Means for Solving the Problems] The present invention includes a firing furnace body, a heating means, and a temperature control means for controlling the heating means so as to change the temperature of the object to be fired according to a predetermined time-temperature curve. , a gas supply means for supplying oxygen and an inert gas to the firing furnace, 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 near the object to be fired. Then, a predetermined oxygen partial pressure-time curve is memorized, and based on the detection result of the oxygen detection means, oxygen and inert gas are The invention is characterized by comprising means for controlling the supply amount of.

[Function] According to the present invention, during firing, the total pressure in the furnace and the oxygen partial pressure in the vicinity of the object to be fired can be controlled, so that the fired object can exhibit the excellent characteristics inherent to the material.

[Example] Fig. 1 schematically shows an example of the firing apparatus according to the present invention, and its operation will be explained. First, inside the firing furnace 1, an exhaust system 2 including a rotary pump 2A, a vacuum solenoid valve 2B, an exhaust filter 2C, a leak valve 2D, and a vacuum gauge 2E is used.
Evacuate to the specified degree of vacuum. Next, a mixed gas of oxygen and nitrogen (or argon) is supplied to the firing furnace 1. Oxygen passes from the pump 3A to the stop valve 3B, needle valve 3G, mass flow controller 3D, Chutsuki valve 3E, and control valve 3F, and nitrogen (or argon) passes from the pump 48 to the stop valve 4B, needle valve 4G, and mass flow controller. 4D, enters the gas mixer 5 via Chatsuki valve 4E and control valve 4F, respectively.
mixed. The mixed gas (or a single gas) is introduced into the firing furnace 1 through the gas introduction valve 6 . 3G and 4G are each a primary pressure gauge. An oxygen sensor 7 is placed near the object to be fired in the firing furnace 1 to detect the amount of oxygen near the object 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 manually input to the oxygen partial pressure controller 9. On the other hand, a temperature controller 1 that controls the temperature of the firing furnace 1
0 stores a predetermined oxygen partial pressure according to each firing process, and this predetermined oxygen partial pressure and the oxygen concentration signal from the oxygen concentration meter 8 are sent to the oxygen partial pressure controller 9.
The oxygen partial pressure controller controls the opening and closing of the control valves 3F and 4F so that the oxygen partial pressure near 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 transmitted by a compound meter 11.
is input. 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,
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, Ag2 was added to LaBa2cu30t J.
An oxide superconductor to which O was added was fabricated.

La2O3, Ba(OH)2H8H20 and CuO
were weighed, dry mixed, and pulverized so that the ratio of La:Ba:Cu was 1:2:3. The mixed powder was heat-treated at 800-900°C for 10 hours. The heat treatment atmosphere may be air, oxygen, or nitrogen.

After heat treatment, it is re-ground and passed through a 30 μm sieve.
A powder of aBa2Cu+0t-s was obtained.

For 1 mole of this powder, 20 wt% Heg20 powder (
purity 99.99%), 1-2 ton/cm2
A pellet with a diameter of 15 mm and a thickness of 1.5 mm was created by applying a pressure of . This pellet was placed in a crucible and fired while controlling the temperature and heating atmosphere, that is, the total pressure and oxygen partial pressure.

FIG. 2 shows an example of a time-temperature curve during firing.

As shown in the figure, the firing process is a process of increasing the temperature to the sintering temperature,
Sintering process at a constant temperature, cooling process to the annealing temperature,
and a superconducting phase generation process by annealing at a constant temperature.

In the example below, the heating and cooling rates are each 200℃/
hr and 60°C/hr. Sintering temperature is 93
The temperature was appropriately selected within the range of 0°C to 950°C, and the sintering time was kept constant for 5 hours. The annealing temperature was kept constant at 300°C, the holding time was set for 5 hours or 10 hours, and the firing process was performed as shown in FIG.

The atmosphere during firing was controlled in four segments, b, c, and d. Segment a is a process of increasing the temperature to 700°C, and segment b is mainly a sintering process, including a process of increasing the temperature to 700°C or more and a process of decreasing the temperature to 900°C. Segment C corresponds to a temperature decreasing process of 900° C. or less, and segment d corresponds to annealing, that is, a superconducting phase generation process. In the present invention, while controlling the total pressure in the furnace, the oxygen partial pressure near the object to be fired was detected, and firing was performed while controlling the oxygen partial pressure in each segment.

The superconducting transition temperature and critical current density were measured for the various samples prepared. The superconducting transition temperature is determined by measuring the DC resistance using the four-probe method and determining the Tcend at which the electrical resistance becomes O.
Furthermore, the superconducting transition temperature TCI was measured from the temperature change in AC magnetic susceptibility using a Hartshorn bridge.

The critical current density Jc is determined by passing a large current pulse through the sample under liquid nitrogen and finding the maximum current value at which the superconducting state is maintained.
c.

Superconducting transition temperature T el! of each sample prepared with different heg20 concentrations and firing conditions. □, Tel, and critical current density Jc are shown in Table 1. As is clear from the table, even for oxides with the same composition, their superconducting properties, especially their critical current density, vary greatly depending on the firing conditions.

When the total pressure in the furnace is 1.2 kg/cm2 and the oxygen partial pressure near the sample in each process of heating, sintering, cooling, and annealing is 20.0.100 and 100%, the critical current density is 390 A. It showed a high value of /cm2.

Table 1 [Effects of the Invention] As explained above, according to the present invention, the oxygen partial pressure near the object to be fired can be controlled in accordance with each stage of the firing process, so the superconducting properties of the superconducting material composition can be improved. can be improved.

The firing apparatus according to the present invention can be widely applied to firing not only oxide superconductors but also various ceramic compositions that require control of oxygen partial pressure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the firing apparatus according to the present invention, and FIG. 2 is a diagram illustrating a firing method using the apparatus according to the present invention. DESCRIPTION OF SYMBOLS 1... Firing furnace, 7... Oxygen sensor 8... Oxygen concentration meter, 9... Oxygen partial pressure controller, 10... Temperature controller. 14...Resistance heating element. 4-line diagram that explains everything

Claims (1)

[Scope of 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 the object to be fired according to a predetermined time-temperature curve, and oxygen in the firing furnace. and a gas supply means for supplying 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 near the object to be fired; The oxygen partial pressure-time curve obtained is stored, and based on the detection result of the oxygen detection means, the supply amount of oxygen and inert gas is adjusted so that the oxygen partial pressure near the object to be fired becomes a predetermined value. A firing device characterized by comprising: means for controlling.