RU2326091C2 - Method of obtaining electroconductive ceramic on beryllium oxide base - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention pertains to the method of obtaining a ceramic on a beryllium oxide base with doping, influencing the properties of the obtained ceramic, and can be used in different electrochemical devices, as detectors of ionising radiation, as well as in radio devices operating in the microwave range, where a microwave radiation absorbing ceramic is required. Such a ceramic has high thermal conductivity and defined values of electro-conductivity. The proposed method of obtaining an electro-conductive ceramic on a beryllium oxide base with a percentage mass ratio of titanium oxide of 5-35%, involves obtaining a mixture of the initial oxides, forming the product through organic bond and burning, following agglomeration, in which agglomeration is done in an atmosphere of carbon monoxide at excess pressure of mm Hg and temperature of approximately 1500°C. The obtained products have semiconductor properties with electron conduction and have electro-conductivity of 8-10^-13 -4-10^-1 Ohm^-1 cm^-1.

EFFECT: wider range of electro-conductivity of the obtained material with retention of high level of operational characteristics; provision for safety during the process.

2 ex

Description

The invention relates to a method for producing ceramics based on beryllium oxide with the addition of impurities that affect the properties of the resulting ceramics, and can be used in various electrochemical devices (where high-temperature electrically conductive ceramics are required), dosimetry of ionizing radiation (as detectors), and also in radio engineering devices microwave range, which requires microwave absorbing ceramics with high thermal conductivity and certain values of electric wire range.

A known method for producing ceramics of the BeO-TiO _{2 system} in ratios of 1: 1.2: 1.3: 1 using titanium dioxide in the form of anatase and rutile and beryllium oxide or titanium hydroxide and beryllium hydroxide as starting materials. The starting materials were passed through a sieve, the mixtures were ground in an agate mortar, first in a semi-liquid state (moistened with water), then in a dried state and pressed under pressure of 7000 N / cm ² . Samples were fired in the temperature range 1400–1750 ° С (E.K. Keller, E.N. Isupova, “Investigations of solid phases in the BeO-TiO _{2 system} ”, journal “Inorganic chemistry”, volume V, issue 2, 1960 ., p. 433-436).

The disadvantages of this method is the low conductivity of the mixture, which at room temperature does not exceed 1 · 10 ^-14 -1 · 10 ^-13 Ohm ^-1 · cm ^-1 .

A known method for producing ceramics based on beryllium oxide with the addition of titanium dioxide, in which beryllium oxide and titanium dioxide are used as starting materials. The method is carried out by semi-dry pressing of the starting oxides with an organic binder followed by its burning, sintering in vacuum at temperatures of 1560 ° C and additional firing in a hydrogen atmosphere at a temperature of 1030 ° C (BCKiyko, S.N. Shabunin, Yu.N. Makurin " Obtaining, physicochemical properties and transmission of microwave radiation by BeO-based ceramics ", Refractories and technical ceramics, No. 10, 2004, pp. 8-17).

Ceramics obtained in a known manner (depending on the amount of introduced TiO ₂ ) have a sufficiently high thermal conductivity, varying within 200-60 W / m · K along with good electrical conductivity, varying within

8 · 10 ^-10 -4 · 10 ^-2 Ohm ^-1 · cm ^-1 .

However, the disadvantages of the method are not wide enough to vary the electrical conductivity of the resulting material, which limits its scope, as well as increased requirements for process safety, since an explosive gas — hydrogen — is used as the reducing atmosphere.

Thus, the authors were faced with the task of developing a method for producing ceramics based on beryllium oxide, which makes it possible to extend the range of changes in the electrical conductivity of the resulting material while maintaining a high level of performance characteristics, as well as process safety.

The problem is solved in a method for producing conductive ceramics based on beryllium oxide, including obtaining a mixture of the starting oxides, molding using an organic binder with its burning and subsequent sintering, in which sintering is carried out in an atmosphere of carbon monoxide at a residual pressure of 1 · 10 ^-2 · 5 · 10 ^-2 mmHg and temperature no more than 1500 ° С.

Currently, there is no known method for producing conductive ceramics based on beryllium oxide, in which sintering is carried out in an atmosphere of carbon monoxide in the claimed range of parameters.

In the known method, the conductivity values in the range of 8 · 10 ^-10 -4 · 10 ^-2 Ohm ^-1 · cm ^{-1 are} achieved provided that additional firing in a hydrogen atmosphere at a temperature of 1030 ° C, which is carried out after sintering in vacuum at a temperature of 1560 ° FROM. As the studies conducted by the authors showed, the use of carbon monoxide CO during sintering of the reducing atmosphere provides a wider range of electrical conductivity values, while maintaining both electrical conductivity and thermal conductivity at a high level. In addition, working conditions are not only improved by increasing the safety of the process, which is carried out in the absence of an explosive atmosphere of hydrogen, but the process of producing ceramics is also simplified, since sintering in the atmosphere of carbon monoxide eliminates the operation of additional annealing. It should be noted that the technical result is achieved only if the entire set of conditions proposed by the authors is observed, which along with the use of a certain reducing atmosphere are certain intervals of the residual pressure of CO and temperature. With an increase in sintering temperature above 1500 ° C, the degree of restoration of ceramics decreases due to the formation of a certain amount of an impurity in its composition - titanium carbide, which negatively affects the conductivity. When the residual pressure is higher than 1 · 10 ^-2 mm Hg, or lower than 5 · 10 ^-2 mm Hg, a decrease in the degree of ceramic recovery is also observed.

The proposed method can be implemented as follows.

The starting materials for the preparation of beryllium ceramics with the composition BeO + TiO ₂ are: beryllium oxide of the qualification of chemically pure and titanium dioxide TiO ₂ powder is pretreated at a temperature of 1000 ° C to completely transform the anatase modification into the form of rutile. BeO powder is calcined at 1200 ° C to give it stable physicochemical properties. To obtain ceramics, the slip casting method using an organic binder is used. A mixture of BeO + TiO ₂ is prepared in a vibratory mill. An organic-based binder is prepared in the following composition: 82 wt.% Paraffin, 15 wt.% Beeswax and 3 wt.% Oleic acid. The amount of organic binder in this case varies in the range of 9.5-10 wt.%. The molded products are fed to the burning of the organic binder, which is carried out at a temperature of 1100 ° C. Then, the products are sintered in a CO atmosphere in graphite crucibles and in graphite filling at a temperature of not more than 1500 ° C at a residual pressure of 1 · 10 ^-2 ÷ 5 · 10 ^-2 mm Hg. with a heating rate of 200-250 degrees per hour and exposure at maximum temperature (depending on the amount of introduced TiO ₂ ) for 0.5 ÷ 1.0 hour. Get a dense conductive ceramic with water absorption of not more than 0.3%. The mechanical strength of the obtained products varies in the range of 180.5 ÷ 301.8 MPa. The electrical conductivity of the obtained ceramics varies within 8 · 10 ^-13 ÷ 4 · 10 ^-1 Ohm ^-1 · cm ^-1 .

Physico-chemical properties of the obtained ceramics:

- ceramics has an apparent density ranging from 2.89 to 3.35 g / cm ³ ;

- has semiconductor properties with an electronic type of conductivity, can change electrical conductivity in a wide range (8 · 10 ^-13 -4 · 10 ^-1 Ohm ^-1 · cm ^-1 ),

- thermal conductivity at 30 ° C varies in the range 200 ÷ 60 W / m · K.

The proposed method is illustrated by the following examples.

Example 1. Prepare a mixture of 98.4 g (95 wt.%) Beryllium oxide qualification H.H. and 1.6 g (5 wt.%) titanium dioxide odds The TiO ₂ powder is pre-heat treated at a temperature of 1000 ° C for 3 hours. The BeO powder is calcined at 1200 ° C for 1 hour. The initial charge is processed in a vibrating mill for 4 hours. Products are molded by slip casting with the addition of an organic binder in an amount of 9, 5 wt.% Of the total weight of the powder. The molded products are fed to the burning of the organic binder, which is carried out at a temperature of 1100 ° C for 4 hours. Sintering of products is carried out in graphite crucibles, in graphite filling in a CO atmosphere at a temperature of 1500 ° C at a residual pressure of 1 · 10 ^-2 mm Hg. with a heating rate of 200 ° C per hour and holding at 1500 ° C for 1.0 h. The electrical conductivity of the obtained ceramic is 8 · 10 ^-13 Ohm ^-1 · cm ^-1 .

Example 2. Prepare a mixture of 85.6 g (65 wt.%) Beryllium oxide qualification H.H. and 14.4 g (35 wt.%) titanium dioxide o.s.h. TiO ₂ powder is pre-heat treated at a temperature of 1000 ° C for 3 hours. BeO powder is calcined at 1200 ° C for 1 hour. The initial charge is processed in a vibrating mill for 4 hours. Products are formed by slip casting with the addition of an organic binder in an amount of 10 wt. .% of the total mass of powder. The molded products are burned to an organic binder, which is carried out at a temperature of 1100 ° C for 4 hours. Sintering of products is carried out in graphite crucibles, in graphite filling in a CO atmosphere at a temperature of 1500 ° C with a residual pressure of 5 · 10 ^-2 mm RT. Art. with a heating rate of 200 ° C per hour and holding at 1500 ° C for 1.0 h. The electrical conductivity of the obtained ceramic is 4 · 10 ^-1 Ohm ^-1 · cm ^-1 .

Thus, the authors propose a method for producing conductive ceramics based on beryllium oxide, which provides an extension of the range of changes in the electrical conductivity of the resulting material while maintaining a high level of performance, and also ensures process safety.

Claims (1)

A method of producing a conductive ceramic based on beryllium oxide, including obtaining a mixture of the starting oxides with a content of 5-35 wt.% Titanium oxide and beryllium oxide, the rest, molding products using an organic binder and burning it, sintering products in graphite crucibles in graphite filling in the atmosphere carbon monoxide at a residual pressure of 1 · 10 ^-2 -5 · 10 ^-2 mm Hg at a temperature of about 1500 ° C, and the resulting products have semiconductor properties with an electronic type of conductivity and have an electrical conductivity of 8 · 10 ^-13 -4 · 10 ^-1 Ohm ^-1 · cm ^-1 .