KR20010094374A - Apparatus for heating ceramic materials through preheating and heat generation by means of the electric resistance of materials and thereof method - Google Patents

Abstract

PURPOSE: An apparatus and a method for heating a ceramic material are provided to measure a fusing point of material without a hot chamber by heating the center of the ceramic material with high temperature and the outside thereof with low temperature. CONSTITUTION: An apparatus for heating a ceramic material is comprised of a vacuum chamber(1), a preheating electric furnace(2), an electrode(3), a power supplying and controlling unit(4) of the preheating electric furnace(2), a power supplying and controlling unit(5) for the electrode(3), an observation and measurement window(7), and a temperature measuring sensor(8). The preheating electric furnace(2) is installed in the vacuum chamber(1). The electrode(3) is installed in the preheating electric furnace(2). The electrode(3) is installed in the vacuum chamber(1) to a cross direction or a vertical direction and a ceramic material(9) is mounted between the electrodes. The preheating electric furnace(2) is composed of a heating element and a heat insulating material. The preheating electric furnace(2) measures a temperature of the heating element and controls the heating element through the power supplying and controlling unit(4) of the preheating electric furnace(2).

Description

Apparatus for heating ceramic materials through preheating and heat generation by means of the electric resistance of materials and details method}

SUMMARY OF THE INVENTION An object of the present invention is to provide a device for heating a ceramic material using self-heating caused by electrical resistance by preheating the ceramic material by using an electric furnace in the heating device of the ceramic material and then flowing electricity to the ceramic material. To provide.

Ceramic materials are widely used as high-temperature materials because they have a very high melting point and stable to oxidation at high temperatures compared to metal materials. An electric furnace is widely used as a heating device for ceramic materials, and this method is characterized in that the heating element of the electric furnace generates heat to uniformly heat the material inside the electric furnace. Electric furnaces are widely used for heat treatment and sintering of materials below about 2000 ° C. However, it is difficult to use for applications requiring higher temperatures.

For example, if a ceramic material is to be heated and melted, the material must be contained in a container and heated above the melting point. In the method of heating the ceramic material using an electric furnace, it is very difficult to reach a high temperature of 2000 ° C. or higher, and there is a disadvantage in that the melt containing the ceramic material and the melt react with each other even if the melting of the ceramic material occurs. Therefore, the temperature measurement becomes inaccurate when measuring the melting point of the material. The container containing the ceramic material must also use a high melting point material, for example tungsten. Therefore, the prior art of heating the ceramic material to an extremely high temperature has the disadvantage that the power consumption is large and the price of the container used is expensive.

Some ceramic materials are specially used under conditions where the core temperature of the material is much higher than the outside temperature. In order to test the performance of the material under these conditions, the same temperature conditions must be established. The conventional heating apparatus that supplies heat from the outside has a disadvantage in that the interior of the ceramic material cannot be heated to a much higher temperature than the outside. .

For example, ceramic uranium dioxide (UO ₂ ) fuel used in nuclear power plants is processed into rods and used in nuclear reactors, and heat is generated inside the material by uranium nuclear fission and the heat is removed by cooling water flowing around the rod. And is delivered to the steam generator. Thus, the core of the fuel material is hot and the outside is cold, with a temperature gradient of about 200 ° C./mm.

In the event of an accident in a nuclear reactor, the temperature of the fuel material may rise excessively and the core may reach melting, and the fuel material may deform or degrade material performance due to a larger temperature difference between the inside and the outside. Since this material behavior is necessary for the safe design of the reactor, the data can be obtained directly from nuclear fuel in small test reactors. However, these tests are not only costly, but also limit the data that can be obtained by not being able to mount the instrument.

Realization of temperature conditions similar to those of reactor fuel materials outside the reactor can save test costs and provide a wide range of test data, but so far no suitable test equipment is known.

The present invention provides a heating device that facilitates melting point measurement of ceramic materials by heating the interior of the ceramic material to a much higher temperature than the outside in order to solve the disadvantages of the prior art. It is intended to provide a heating apparatus and heating method suitable for performance testing of high ceramic materials.

BRIEF DESCRIPTION OF THE DRAWINGS The longitudinal cross-sectional view which shows the principal part of the heating apparatus of the ceramic material which concerns on this invention.

* Explanation of symbols for main parts of the drawings

(1): vacuum chamber

(2): preheating furnace

(3): electrode

(4): Power supply and control device for preheating electric furnace

(5): electrode power supply and controller

(6): vacuum pump

(7): window for observation and measurement

(8): Temperature measuring sensor

(9): ceramic material

(10): gas supply

(11): support

Ceramic materials are generally electrical insulators with high electrical resistance at room temperature, but as the temperature increases, the electrical resistance rapidly decreases and turns into electrical conductors. The device provided by the present invention uses this principle. The ceramic material is preheated from room temperature to a specific temperature using an electric furnace to change the ceramic material into a conductor, and then the current is flowed through the ceramic material to heat the material using self-heating caused by electrical resistance.

FIG. 1 illustrates an "apparatus for heating a ceramic material combining preheating and electrical resistance heating" provided in the present invention. The heating device comprises a vacuum chamber (1), a preheating furnace (2), an electrode (3), a power supply and control device (4), a power supply and control device (5) for the preheating furnace, It consists of a vacuum pump (6), observation and measurement window (7), temperature measuring sensor (8), an electric furnace is installed in the chamber, and the electrode is installed inside.

In the chamber, the electrodes are installed in the transverse or longitudinal direction, and the ceramic material 9 is mounted between the electrodes. A compressive force acts between the electrodes to support the ceramic material, and the spacing between the electrodes can be adjusted. A high melting point metal is used as the electrode material, and tungsten or graphite is preferable. It is preferable to process a ceramic material into rod shape, and several materials of short length are laminated | stacked and mounted between electrodes.

The electric furnace is composed of a heating element and a heat insulating material, and measures the temperature of the heating element and controls the temperature of the heating element through the power supply and control device for the electric furnace. The temperature of the furnace is controlled through the program.

The electrode power supply and control device is characterized by supplying a low voltage and a high current, the voltage is less than 100V, the current is less than 100A. In addition, the voltage can be adjusted and has the function of adding voltage in the form of a pulse. If the ceramic material is heated using electrical resistance heating from room temperature without preheating, additional high voltage (thousands of V) and low current power supplies are needed and the voltage adjustment is very difficult and not practical.

During preheating, the ceramic material is heated evenly, and the preheating temperature may vary depending on the ceramic material, but may be as high as 300-1200 ° C. When the self-heating caused by the electrical resistance starts, a part of the generated heat escapes to a low temperature environment. In particular, since the ceramic material has a very low thermal conductivity, the center of the ceramic material has a high temperature and a low external temperature. Therefore, the ceramic material is heated with a temperature deviation between the center and the outside.

A method of heating a ceramic material using the above apparatus will be described. The ceramic material is sandwiched between the electrodes and supported by the ceramic material support 11, and then a vacuum pump is operated to discharge the air in the chamber, and then the inert gas is filled in the chamber by the gas supply 10. The ceramic material is preheated using an electric furnace, and the preheating temperature should be determined in a range in which the electrical resistance of the ceramic material can be appropriately reduced, and thus may vary slightly depending on the electrical properties of the material. The ceramic material has a resistance of hundreds to thousands of kΩ at room temperature, so there is almost no current flow even at high voltage, and as the temperature rises, the electrical resistance decreases to several Ω to several tens of Ω, and a considerable current flows even at low voltage. When the preheating temperature reaches 300-1200 ° C, a current is passed through the ceramic material using the electrode power supply. At this time, the ceramic material starts to generate heat by itself due to the electrical resistance and the temperature becomes high.

Once the internal heating of the ceramic material begins, the temperature is adjusted to either stop the operation of the electric furnace or to maintain the external temperature of the ceramic material at the desired temperature.

Heat generated by the electrical resistance is generated in the whole ceramic material, and part of the generated heat escapes to a low temperature environment. Therefore, the temperature of the center of the ceramic material is high and the surface temperature is low. In particular, the ceramic material has a very low thermal conductivity, thereby increasing the temperature difference. Accordingly, since the resistance of the center of the ceramic material is further reduced than the resistance of the outside of the material, more heat is generated in the center and the temperature of the center of the ceramic material rises rapidly. The temperature difference between the center and the outer reaches several 100 ℃-1000 ℃.

By applying the apparatus and heating method provided by the present invention, it is possible to easily measure the melting point of the ceramic material. The ceramic material is processed into rods, and a thermocouple is inserted up to the center of the material. When the ceramic material is heated, it melts only in the center and the outside remains solid, so the outside serves as a container for the melt. Therefore, the melting point of the ceramic material can be measured without a separate hot container. Above 2200 ° C, where thermocouples cannot measure temperature, an infrared pyrometer is used. In this case, the material is heated in the state of having previously drilled the center of the ceramic material, and the temperature of the melt in the center is measured through the hole.

By using the heating apparatus and heating method provided by the present invention, it is possible to heat with a temperature deviation at the center and the outside of the material of the ceramic material. For example, performance tests can be performed at temperatures similar to those of reactor nuclear fuel reactors. Ceramic nuclear fuel (UO ₂ ) has a columnar shape with a diameter and length of about 10 mm, which are stacked longitudinally and mounted between longitudinal electrodes and preheated to 400-1200 ° C using an electric furnace. When a current flows between the electrodes using a power supply, the fuel material generates heat. At this time, part of the generated heat is transferred out of the material, so that the central portion of the nuclear fuel material having low thermal conductivity is high in temperature and the outside is low in temperature. By controlling the rate of increase of the voltage of the power supply, it is possible to control the heating temperature and heating rate of the fuel material. Applying a voltage or current in the form of a pulse can rapidly heat up the ceramic material. The temperature around the fuel material can also be controlled by cooling or heating the gas in the chamber.

Using the heating apparatus and heating method provided by the present invention it is possible to heat treatment or sintering the ceramic material.

(Variants, applications and legal interpretations)

The present invention is not limited to the above specific preferred embodiments and modifications, and any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims can make various design changes. Of course, such changes are within the scope of the claims.

In the heating apparatus and the heating method provided by the present invention, the center of the ceramic material can be heated at a high temperature and the outside at a relatively low temperature, so that the melting point of the material can be measured without a hot container when measuring the melting point of the ceramic material. It also enables simple and very low cost performance testing of nuclear fuel materials used in nuclear reactors.

Claims (9)

Apparatus for heating ceramic materials, vacuum chamber, preheating furnace, electrode, preheating electric power and temperature control device, power supply and control device for electrode, vacuum pump, gas supply, temperature measuring sensor, observation and measurement It consists of a window for preheating in the chamber, and then installs the electrode therein. The preheating furnace and the electrodes are installed in one combination in the vertical or horizontal direction, and the ceramic material is mounted between the electrodes. , The heating device of the ceramic material combined with preheating and electrical resistance heating, characterized in that the elasticity between the electrode and the electrode to maintain the contact when energized and at the same time accommodate the expansion and contraction of the ceramic material. The method of claim 1, An apparatus for heating a ceramic material combining preheating and electrical resistance heating, characterized in that a metal having a high melting point such as tungsten, molybdenum or graphite is used as the electrode material. The method of claim 1, A device for heating a ceramic material combining preheating and electrical resistance heating, characterized in that the distance between the electrodes is adjustable. The method of claim 1, The gas supply unit has a cooling function of the gas, the heating device of the ceramic material combined with preheating and electric resistance heating, characterized in that the temperature in the chamber can be constantly adjusted. A method of heating a ceramic material, comprising mounting a ceramic material between two electrodes, preheating the material to change the material from a nonconductor to a conductor, and applying a voltage between the electrodes to flow a current through the material, wherein The method of heating a ceramic material in combination with preheating and electrical resistance heating, characterized in that the central portion of the material is heated to a high temperature and the outside to a relatively low temperature using self-heating by electrical resistance. The method of claim 5, The ceramic material is a method of heating a ceramic material combined with preheating and electrical resistance heating, characterized in that one or several laminated. The method of claim 5, The method of heating a ceramic material combined with preheating and electrical resistance heating characterized in that the temperature of the ceramic material can be controlled by controlling the voltage between the electrodes. The method according to claim 5, And heating the ceramic material rapidly by applying a voltage or current between the electrodes in a pulse form. The method of claim 5, The heating method of the ceramic material combined with preheating and electrical resistance heating characterized in that the heating atmosphere of the ceramic material is maintained in a vacuum or inert gas.