DEP0055730DA - Method of manufacturing a sintered ceramic body - Google Patents

Description

United Insulator Company Limited,

Oakcroft Road, Tolworth, Surbiton, Surrey / England.

■ ία dio il un procedure

The invention relates to ceramic bodies which are suitable for use as dielectric material in capacitors and other articles and which contain as the main component barium titanate which makes up 90 or more percent by weight of the body. Such ■ body are mainly due to the high value of the permeability ^ he ^^^ J ^ m ^ ^m of importance, which can be obtained with them.

These bodies are usually made by a process in which the ingredients well mixed together in a suitable degree of fine subdivision, pressed, given them the appropriate shape and dimensions and then subjected them to heating, to sinter the particles and make a sufficiently strong and rigid, non-porous ceramic To create bodies. The shapes commonly used are thin-walled tubes and thin, flat discs or rectangular plates. The greatest thickness of the pipe walls and washers or panels (hereinafter referred to as wall thickness) normally does not exceed about 5 mm.

The heating is usually carried out so that a large number of the bodies, if necessary on suitable carriers, together in

is introduced an oven, then closed, the furnace, the temperature is then gradually increased to the Sinterungsbereich, which is approximately between 1200 and 1JOO ⁰ G and then allowed to cool the material to a relatively low temperature before the oven is opened. Such a treatment can allow the temperature to rise to its maximum value over a period of. 10 to 12 hours or longer and the cooling from the maximum temperature down to 900 ° extend over a period of 2-3 hours or more.

It has been found that the bodies produced, while possessing verhältniamässig high permeability (500 and up), not a sufficiently high value of insulation resistance at ordinary room temperature au £ §a "- ^<H * ^< 'and a very considerable dete-

alteration of this property er] »* b'OT'M'Mli-ei * if the

Temperature is increased to 100 ⁰ C and also suffer a deterioration when they are subjected to an endurance test at this and a lower temperature. This deficiency seriously affects the usefulness of the body.

& OTfffi * Voler invention are improved ceramic bodies of the specified composition obtained, which have such an internal structure that their insulation resistance with ordinary Room temperature has a high value.

They also have satisfactory insulation resistance values at 100 and higher temperatures and suffer no great deterioration in this ^ (in some cases none at all) if they are exposed to an applied voltage at this temperature for a long time. The improved bodies also have high levels of permeability, generally higher than those with bodies of the same composition

but can be obtained by the previously known method. For example, you can use permeability values from 150 to 4000.

The main factor in achieving the

improved structure isw & ie reduction ⁰ of time for increasing the temperature of 900 ° to the maximum temperature and reducing the time for cooling from the area of maximum temperature to 900 ⁰ G down. The heating from 900 ° to the maximum temperature and the subsequent cooling to 900 ° can take place, for example, in about 25 minutes, of which about 1/4 hour is the time to cool the body from the sintering temperature to 900 °. It has been found that the improved structure is obtained when the total time that the article is held at a temperature above 900 is less than 3 hours. This time can advantageously be reduced to 1 hour for bodies with a wall thickness of not more than 0.5 mm.

From the foregoing it will be seen that the improved body is obtained when the fresh articles are heated to the maximum temperature to effect sintering and then cooled from that temperature, but both are done in a rapid manner. Similar results can sometimes be obtained with articles which γ already obtained through the long-lasting previous JM JLJuju ^ process but then a short heat treatment

be subjected, in which they are quickly heated to sintering temperature and quickly cooled will. Accordingly, the determining step in the treatment is the relatively rapid heating and cooling in the range of 900 ° upwards to the maximum temperature of 1200 to 1300 ° and from the maximum temperature down to 900 °.

The ones obtained with the improved bodies

Values of the force factor are not higher than those produced by the previous processes Body, and in some cases they are much lower.

The improved Aärmebeh and treatment can suitably be carried out in a tube furnace through which the body to be treated either gradually or gradually promoted will. They reach the full sintering temperature in the middle part of the Pipe length and the cooling zone at the outlet end. By controlling the degree of movement of the Body through the tube, suitable rapid heating and cooling can be achieved.

It is desirable to adjust the conditions so that a reducing atmosphere is not obtained inside the pipe. This can evoke a small one Require air flow through the tube.

It has now been found that the method of the invention is particularly suitable for bodies of the type is as described and claimed in de $ #riiv Patent / 586 802. Of these Corpses show those which euorides of the metals of group II of the Feriodisc system contain the most noticeable wear and tear in the volume line resistance.

The following examples illustrate the use of the invention in manufacture sintered bodies of different shape and composition and compare the new bodies with those produced by the known methods.

3a
3b

5a
5b

Put together
tongue

Form total time

above 900 ⁰ Q

Volume-line maximum resistance according to the Teuxu.
Ohm / ccm Bauer test G

W. A. in minutes 25 ° G 3 10O ⁰ G 25th ⁰ G 10O ⁰ G 1250
1225 1a
1b W. A. 26th
4 $ 0 11
2x10 ''
5x1 o ⁹ 1 .4x10 ™
2x10 ⁸ 1250
1225 2a
2 B 26th
480 5.2X10 ¹¹
5.2X10 ¹⁰ 6x1O ¹⁰
.7x1O ⁸ 2.
1. 11
8x10 ''
1x10 ¹⁰

26th

480

80 480

1.5x10

^12th

1.6x10

^12th

3.1x10

^11th

1?
1.4x10 ^ 1.4x10

11th

5x10

10

, 6x10

1238 '1200

4a
4b Y B. 26th
480 1.1x10 '^
2.7x10 ¹⁰ 8.4x1O ¹⁰
1.4x1O ¹⁰ 1300
1200 5a
5b Z A. 26th
540 3.6x10 ¹²
1.9x10 ¹¹ 1.6x10 ' ^!
9x10 ¹⁰ 1350
1325

1250 1225

In these examples, the bodies tested were all tubular and of the following dimensions: shape length outer diameter wall thickness

A 10 mm 3 now 0.3 21 m

B 27 mm 4 mm 0.5 mm

G 15 mm 3 mm 0.7 mm

In example 1 (a), the body had already been subjected to the known heat treatment process sintered for 8 hours before receiving the rapid heat treatment.

The compositions in parts by weight (denoted by W X Y Z) were as follows:

W. Ba TiO, 100 Bentonite 1 X BatiO, 98.5 Mg F ₂ 1.0 Zn 0 0.5 Y H ₃ BO ₃
Bentonite
Ba TiO,
Mg ZrO, 1.0
98
2 Bentonite 1 Z Ba TiO ₃ 95 Mg TiO ₃ 5 Bentonite 1 The endurance test mentioned was that the Body subject to a load of 800 volts per mm

was subjected at 75 ° C for 170 hours, the following table explains how the permeability (K) and the force factor are improved in some cases.

example K Force factor
(tan χ 10) 2a
2 B 1200
1100 300
300 3a
3b 3000
1600 300
400

Claims (4)

Claims. 1. Process for the production of a sintered ceramic, suitable for dielectric purposes and 90 or more weight percent barium titanate-containing body characterized by the Step of increasing the temperature of the body to the sintering temperature or a higher temperature and then lowering the temperature to 900 °, the total time for increasing and Lowering the temperature of the body does not exceed 3 hours. 2. Process for the production of a sintered ceramic body with a maximum wall thickness of not more than 0.5 mm, which for dielectric Purposes and contains 90 or more weight percent barium titanate, characterized by the step of increasing the temperature of the body to the sintering temperature or higher Temperature and then lowering the temperature to 900 °, whereby the total time for raising and lowering the temperature of the body is 1 hour does not exceed. 3. The method according to claim 1, characterized in that the body 0.5-10% of a fluoride, one Contains metal of Group II of the Periodic Table. 4. The method according to claim 2, characterized in that the body contains 0.5-10 % of a fluoride of a metal of Group II of the Periodic Table.