DE1590215A1 - Process for the production of an electrically conductive surface on an insulator - Google Patents

Description

The invention relates to insulator bodies that have a surface layer made of a semiconducting material, and is directed in particular on spark-generating devices with spaced electrodes, which are connected to a semiconducting Surface layer of an insulator in connection, as it is for example for jet engine ignition devices the case is.

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ORlQiNAL ^ '3PECTED

It is common practice to be a semiconducting material. to be provided between and in contact with the electrodes of a jet engine ignition device to reduce the threshold or threshold voltage necessary to induce a spark between the electrodes. In some cases a disk of semiconducting material was used which was inserted between and in abutment with the electrodes, while in still other cases a thin coating, also known as a cast coating, was used on an electrical insulator body such that a thin semiconducting layer was used of the coating hits the gap between the electrons of the igniter and bridges it. The insulator bodies used essentially in all cases contained approximately 85 to 95% aluminum oxide and were burned to hard, erosion-resistant bodies, which, however, had a few percent defects is spoken of, percentages by weight fczw. Parts by weight are meant. The cast coatings previously used had an oxide of either iron or copper as an electrically conductive component. These components were usually mixed with one or more other oxides. Bines the most commonly used

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Materials contained copper oxides mixed with a lesser percentage of either chromium oxide or Iron oxide or a mixture of both. In some cases copper powder was mixed with chromium oxide or iron oxide mixed and processed to a suspension and applied as such to the insulator body and fired in an oxidizing atmosphere to produce copper oxide in situ.

If semiconducting material is used to bridge the spark gap on an ignition device, then This material naturally erodes away. Discs of noticeable density contain so much material on that it takes a comparatively long time for them to be eroded, but it has been shown that the thickness of the discs required for a long service life does not affect the flow of electricity The surface area of the semiconductor is limited, so that an excessively high current flow is required before ignition. It was also found that the casting coatings used so far begin to become soft, so that they erode faster without resulting in a useful operating time

The invention is therefore based on the object of having a new and improved insulator body

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to create a semiconducting surface layer that, when spaced with the Electrodes is connected, is much more resistant to ignition erosion.

The invention is also intended to provide a new and improved insulator body of the type described above that is a semiconducting layer on and slightly below the surface of a fired insulating body which is formed by diffusion of semiconducting oxydes into the structure of the insulator body.

In the case of the insulator body according to the invention with a semiconducting surface layer, a minimum should also be achieved of the material from the original insulator body to the outside of the insulator body during the time diffuse, in which the conductive material diffuses into the surface of the insulator body.

Preferably, the semiconducting material consists of a conductive aluminate which is produced in situ by reaction between the materials of the insulator body and another oxide that is in the surface of the insulator body is diffused.

The invention is also intended to be made of aluminum oxide existing insulator body created,

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in the case of copper oxide in the crystal lattice of aluminum oxide near the surface of the insulator body diffused to form a dense aluminate without noticeable To generate migration of the aluminum oxide from the surface of the aluminum oxide body.

The object of the invention is also a new and improved method for producing an insulator body with overlying semiconducting surface layer, where the surface of the aluminum oxide insulator body with a fine layer of a smaller amount of aluminum oxide and a larger amount of an oxide is coated which together form an electrically conductive aluminate form the insulator body, wherein the coated body then to form a tight electrically conductive Aluminate in the insulator near its surface is heated.

The invention is thus based on a method for producing an electrically conductive surface on an insulator consisting essentially of aluminum oxide, especially for jet engine ignition devices, and is characterized by the fact that a copper-containing The coating is applied by the time and temperature of contact between the coating and the surface of the isolator are regulated that under

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the surface of which creates an electrically conductive phase.

The method according to the invention is preferably carried out using copper oxide as the coating material carried out.

In a further embodiment of the invention, a mixture with a larger proportion is applied to the insulator applied to copper oxide and a smaller proportion of aluminum oxide and by temperature treatment the surface layer in an electrically conductive one containing Cu Al O and aluminum oxide Layer converted.

A mixture with a larger proportion of copper oxide and a smaller one can also be applied to the insulator Apply a portion of chromium sesquoxide and transform it into an electrically conductive one through heat treatment Surface layer made of converted copper oxide, Convert aluminum oxide and chromium sesqu * oxide.

This process can be modified in such a way that the mixture changes the insulator surface in a layer of aluminates and chromates of copper oxide a small amount of aluminum oxide contains.

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The process is preferably characterized by The use of a mixture of 5-30 percent by weight Chrome sesquioxide, 10-30 weight percent Aluminum oxide and the rest copper in a form that can be used at the temperature of treatment with oxygen is in equilibrium, with treatment time and Treatment temperature are chosen so that no noticeable migration of the aluminum oxide from the Insulator body takes place.

The coating mixture and the insulator body are advantageous for a period between heated to a temperature between about 13 ^ 5 and about 1485 for approximately 10 and approximately 6 minutes.

As a modification of the invention, a coating can be used Mixture of approx. 90 percent by weight copper in one Form which at elevated temperatures results in an equilibrium with oxygen and approx. 10 percent by weight Use Cr 0 and place the mixture and insulator in an oxidizing agent for a period of between approx. 10 and 6 minutes Atmosphere to a temperature between approx. 13 * 5 and heat approx. 1435.

You can also lead the process so that a mixture of about 75 percent by weight of copper in one

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Form that results in equilibrium with oxygen at elevated temperatures, approx. 16.5 percent by weight Aluminum oxide and approx. 8.5 percent by weight chromium sesquioxide are used and at one temperature of approx. 1315 for approx. 10 min. is heated.

An insulator body having electrically sliding surface of the invention is in accordance characterized by a Aluniiniumoxydkorper which is burned to approximately 95% of the theoretical density and a surface layer between O _t O25 mm and having 0.25 mm thickness, with the alumina of the insulator to form of Cu Al 0 » _{contains Cu 2} 0 combined.

Preferably, the layer contains the aluminum oxide of the insulator to form a stabilized Electrically conductive layer in the insulator body combined copper oxide and chromium sesquioxide.

Although the invention is useful in a variety of applications where it is desired is to make the surface of an insulator electrically conductive, it has particular advantages in use on jet engine ignition devices where the electrically conductive material is heavy mechanical and thermal shock loads,

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as well as corosive atmospheres and is exposed to alternating reducing and oxidizing conditions. To the A better understanding of the invention is intended first in connection with a jet engine ignition device will be described, followed by the description of some modifications of the invention.

As already mentioned, a preferred field of application of the invention is a jet engine ignition device. The jet engine ignition device shown in the drawing is denoted by the reference numeral 11 and has a thin electrical design semiconducting layer, which bridges the two electrodes around a path for the discharge of one to deliver high-energy spark. The ignition device 11 includes a metal sleeve 12 with a Screw thread 13 for insertion into the combustion chamber for example a jet engine and with a screw thread 14 for attaching a Ignition cable · A ceramic insulator 15 attached to a second ceramic insulator 16 is in the Metal sleeve 12 sealed, while a center electrode 17 is sealed in the insulator 15 * Sine

according to the invention produced electrically semi-

Conductive layer sits on the nose end of the isolator 15 and is denoted by the reference number 18.

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The electric semiconductor layer 18 provides one of the nose end 19 of the center electrode 17 and one Electrical path connecting ground electrode 20 to sleeve 12 · Becomes a comparatively low one Voltage having charge on the center electrode of the ignition device 11, for example from a Capacitor applied, then one is created high-energy electrical discharge along the

Surface of the semiconducting layer 18. The electrical resistance of the layer 18 generally depends on its thickness, as well as on the aterial from which
it is made. The resistance decreases as the layer thickness increases. The thickness of the layer 18 can be controlled by the manner in which it is made.

The present invention is mainly concerned with the composition of the semiconducting layer 18 as well as with the process with which such a layer can be produced. As a result, should one of the best known methods of making this Schult by means of the following example to be explained in more detail

Example I ;
A preferred embodiment of an ignition device

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• Was produced using a previously fired ceramic insulator 95 from approximately 92% Al ₀ 0 ", which had been fired to approximately 95% of the theoretical density. A coating of the following materials was prepared by mixing with an equal amount of water and brushing onto the lower end surface of the insulator 15.

Copper metal powder 70.2%

Chromium oxide 7 _f 8%

Aluminum oxide 20.0%

pure kaolin 2.0%

The insulator with the coating of the above-described layer was passed through an oven, the internal temperature of which was maintained at 1370 in such a way that the insulator could be kept in the hot zone of the oven for 10 minutes. The coated insulator is then read cool to room temperature, daubed another coating of 'the material described above, and burned again the coated insulator for the same time and at the same temperature. The coated insulator was allowed to cool again to room temperature and a third coating made from this suspension was applied. This third coating was also made in the same way

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Fired in the same way as the two previously described coatings .

In a development program for the inventive Ignition device, it is necessary that a large number of test items tested for its ignitability and that a standard test specimen and a test arrangement for the ignition test of each insulator body with semiconducting layer is present. The specimens used were tubular bodies with a length of 3ij75 now and an outer diameter of approx. 9 mm, and an inner diameter of approx. 2.7 mm. These insulator bodies were made of the same material manufactured as the insulator body 15 and contained approximately 92? o aluminum oxide. It became stripes various materials are brushed onto the lower ring surface of the test insulators, which you then put on burned at a predetermined temperature. Each insulator was cooled to room temperature and second and third strips have been applied, as described above. The test specimens with the applied and burned strips were then placed in a spark plug mount with a center electrode used, the head pressed under spring tension against the end having the fired strip

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became. This arrangement was then placed in a test housing inserted with a shoulder that rested on the outer edge of the fired strip of the sample. There was a gap of approximately 1.2 mm between the head of the center electrode, the spark plug mount and the edge of the shoulder of the coated body and the test samples were made with the The burnt, coated end was installed in a blasting machine, pointing upwards *! One dripped every minute JP4 jet engine fuel on the test tube end with the burned strip and generated two ignitions per second over that end with the burned strips between the electrodes. These ignitions were made by discharging a 10 microtfarafi capacitor charged with 2000 volts was so that 20 joules of energy was consumed during each ignition.

Five examinees, aie using the same Strips made and burned at 1370 °, gave an average life, time of 57 »7 hours. The burning of the above Strip "took place in an oxidizing atmosphere, so that the copper metal transformed into a copper oxad, which at approximately 1093 primarily Copper oxide is »Above this firing temperature

Copper oxide evidently reacts with chromium oxide and aluminum oxide to form aluminates and chromates. An examination of the specimens after firing shows that very little remains of the order and that has penetrated a black Eindringband of cuprous oxide in the Aluminiumoxydisolatorkörper in different depths amounting mm in some cases up to 0.8. There is a slight swelling of the insulator body, and a sipectographic analysis shows that a large amount of the copper oxide is present in the surface layer of the insulator in a form combined with aluminum oxide and chromium oxide. The electrical resistance across the electrodes to the test specimen. «Varies between 30 and 40,000 ohms, as initially generated» The samples were ignited in the test machine described above for 7 hours at room temperature; the samples were then at. 538 sintered to remove the carbon deposits. Then new electrodes were applied to these specimens and the response voltage was determined. An error appeared in the sample and the tests were interrupted when the response voltage required to initiate ignition was 1800 volts with a capacity of 0.1 mfd. exceeded.

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The time and temperature at which an insulator body coated with a coating compound is fired determines the depth to which the copper oxide of the potting compound diffuses into the insulator »and determines the proportion of aluminate that is formed from relatively non-conductive material which the insulator body is made. By ragein the '"ext and the temperature of the firing process layers of different resistance can therefore be created, and if the one covered with the potting compound Insulator body at a temperature below approximately

is fired, then a cast overlay is formed on the insulator body without noticeable diffusion of the copper oxide into the insulator body. For the in most igniter applications it is desirable when a relatively close copper oxide concentration in a thin, dense layer adjacent the outer surface of the insulator is present, so that the surface has a fairly high conductivity and thus dense and is resistant to erosion. Apparently there is a noticeable diffusion of the copper oxide into the insulator body Ranter formation of aluminates and chromates does not occur below approximately I316 C. as a result, arises when firing below this temperature, a casting compound coating on the surface of the IsdLator «

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body. When burning above this critical temperature, diffusion takes place in the insulator body at a rate that increases with temperature A satisfying diffusion speed results at approx. 1370, while too high a diffusion rate above approximately 1480 occurs. If a casting size coating instead of an aluminate or chromate layer within the surface of the insulator body, this then results in a significantly reduced service life of the ignition device. The casting size covers in the form described above are relatively porous and soft and have a Lifespan that is only a fraction of that of an insulator body with a good seal Has layer of aluminates and chromates in the vicinity of the surface of the insulator body. This was shown by the following procedure, which was for the purpose of comparison and not in agreement was carried out with the invention.

A casting size in the following "referred to as" casting size No. 2 ^H and consisting of 93% copper, 5 S "chromium oxide and 2% kaolin was brushed onto an aluminum oxide test insulator of the type described in more detail above, which contained 2% aluminum oxide.

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The isulator was coated with this casting compound

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and then fired at II50. The isulator body was then cooled and the process repeated to apply two more additional coats of grout for a total thickness of approximately 0.15 mm (0.006 inches). A visual inspection showed that the isulator had a coating of casting compound with essentially no diffusion of the material of which the casting compound was made into the insulator. This isulator body with the casting compound thus formed was tested in the manner described above and had a service life of only approximately 6 hours.

An optimal ignition life is obtained if a extremely dense concentration of electrically conductive copper chromates dispersed in aluminates in close to the surface of the IsdLator with minimal diffusion of the insulating material from the surface of the Isolator are generated. The temperature given above must be high enough to produce aluminates and chromates and the burning time must be long enough for the oxide to be deposited on the outer surface of the insulator body is exhausted by diffusion into the insulator to such an extent that a porous area poor in aluminates and chromates This can be shown by the following experiments.

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Numerous XL ^ Pj insulators of the type described above are coated with a casting compound of 88.3 % copper, 9 »8 A chromium oxide and 1.9 % kaolin, which will later be referred to as" casting compound No. 3 ". The coated insulators are heated in the time and temperature shown in Table I. Then each isolator is cooled. A second coating of casting compound is applied and the insulator is baked again at the same temperature for the same time as when the first coating was stoved. This procedure is repeated a third time and the finished insulator body is then tested in the manner described above. Although there is a considerable difference in life between the samples fired at some of the higher temperatures, a comparison of the average life of the insulators fired at the different times and temperatures shows what life expectancy can be expected for an isolator body at a given temperature and time.

Table I now follows from the English text Be 13. Namely, (l) table I, (il) means triple application and triple firing, (III) hourly ignition until failure at different firing temperatures. (4) Brer.n-

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ORIGINAL INSPECTED

time, (5) average.

It has been shown that the consistency of the casting compound affects the furnace enatiao sphere and other variables affect the service life for samples produced at a given time »So that correct comparisons can be made, it is therefore necessary to drive control specimens, the times and temperatures calculated in advance were fired, if one set of test objects manufactures.

Table II shows the results of other series of tests on insulator bodies performed in the same manner as siid mentioned above in connection with the test items according to Table I, but for the times and temperatures according to Table II were fired. Table II shows that improved results are obtained when the insulator bodies have been fired for only approximately 7 minutes but at a temperature of 1 ^ 82.

Other experiments have shown that a single application and firing of a casting compound leads to a lifetime leads, which is approximately 2/3 of the service life that can be achieved when applying a triple application and Bringing a triple firing of the casting compound to produce the insulating body.

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In a number of other attempts it has been found beneficial to use the same material which the insulator consists in the copper-containing material which is applied to the insulator body. Copper oxide is very fluid at approx. 1370 and the viscosity of the material applied to the insulator increases considerably with the addition of aluminum oxide. The addition of aluminum oxide and chromium sulfate oxide contributes Therefore, the copper oxide to promote a uniform penetration into the insulator body on his Hold place. In addition, the addition of aluminum oxide additives to the cast mass increases the density of the Materials that lie on the Obeflüclie Isola uoricbodya remain, and thus their resistance to erosion.

You have test objects by applying coatings Appropriate casting moisture on insulator bodies in dor above prepared manner, they are fired at the temperatures given in Table XlI for 10 minutes and the Coating and firing steps repeated a total of 3 times. The coverings were composed of the "Begußnasso No. 3" and · "Casting compound No. 3+" with different amounts of aluminum oxide. The compositions used and the Average lease times in hours are given in table Ι1Ϊ reproduced.

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Table III

Coating material Beo: uß No. 2 Casting No. 2. Loo parts + 5 parts of aluminum oxide Casting No. 2, loo parts + Io parts Aluminum oxide casting No. 2, 100 parts + 15 parts aluminum oxide Casting No. 2, 100 parts + 20 parts aluminum oxide

Firing temperature 1425 °

1425

1400

1400

Lifespan 25.2

33.4 45.6 43.3

1370

57.7

Copper oxide is stable in air at temperatures up to approximately 1026 C, at which temperature it is in the copper justand dissociated. Copper oxide is stable above 1026 and melts at 1235 ° · Copper oxide combines with it Al "0_ with the formation of spinel, which below approx 900 ° C is stable ^. Above approximately 900 ° C forms

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BATH ORIGINAL

a copper aluminate with the formula CuAlO. It appears, therefore, that the presence of Al ₀ O lowers the temperature at which a transition from copper oxide to copper oxide takes place.

At temperatures above approximately II65 C a liquid is formed, which mainly consists of Cu ₃ O. Tuck liquid may be in equilibrium with ₂ CuAlQ namely abhänp-g ^ from the close of the Al ₀ O in the mixture. Above approximately 1260 ° C, CuAlO breaks down into / Al ₀ O and a melt rich in copper oxide. It therefore appears that Cu ₂ O flows ver with the aluminum oxide of the insulator body and quickly migrates under the surface of the insulator body.

It has been shown that the presence of Chronisesituioxyd when added to the material applied to the insulator body, the conductive phase that is formed is stabilized so that the resistance of the body thus formed does not noticeably increase when used at a temperature changes from approx. 870. It appears that chromium sesquioxide is one has a strong affinity for copper oxide, presumably with the formation of CuCrO, and that the large size of the chromium sesquioxide molecules the chromium oxide prevents it noticeably

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to diffuse or migrate into the alumina insulator body, and therefore the copper oxide on the surface and holds in place. It may also be that the chromium sesquicc jrd is the transition temperature of copper oxide reduced in copper oxide.

In any case, it has been found that somewhat more than a cast coating is formed when using copper or copper in any form which is in equilibrium with oxygen produces at elevated temperatures, applies to an aluminum oxide insulator body and at temperatures between approximately 1370 and 1485 in an oxidizing atmosphere burns for a controlled short period of time that reduces copper oxide diffusion to approximately 0.25 mm of the insulator surface and preferably less than 0.125 mm thereof Surface holds. It has also been shown that the presence of Chronisesquioxide markedly increases the resistance changes of the electrically conductive layers at temperatures above 87Ο and even at temperatures up to 1100 prevented.

To determine the effect of chromium and aluminum were 6 test specimens of the type described above were produced from the compositions according to Table IV. In any case, were

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2% kaolin incorporated, while the percentages of Cr ₀ O

or Al _o 0 “corresponded to those according to the table and the remainder was a copper powder.

Casting compounds from these compositions were in
a tape on the cylindrical outer surface of the
Aluminum oxide insulator bodies of the type described above were brushed on, and the coated bodies were then fired for 10 minutes at the specified temperature.
A second coating of the same casting compound was then applied over the first tape and the coated body was baked again at the specified temperature, whereupon a third coating was applied and baked in the same manner. Resistance was measured by sandwiching the treated surface of the samples between flat plates and measuring the resistance
in between with a 500 volt ohm measuring device. The average resistance measured for the 6 specimens
is shown in Table IV.

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TABLE IV

Resistance after the coating has been fired three times (K-Ohm) Casting compound addition firing temperature

1095 ° 1120 ° 1150 ° 1205 ° 1315 ° 1425 °

Pure copper

1% Cr ₉ O O 2% ^{2 3} * β "111 ' t » 5% CD 10% 20% _ » 30% cn 154 AJ O. ** ■ 2% • «a 3% 5% 10% 20% 30%

508 236 293 1.188 7,944 176 158 168 444 10,333 149 170 111 lol 3,000 81 112 104 119 5.611 53 61 85. II6 221 17th 18th 9 15th 21 8th 9 9 10 20th 4th 4th η 4 11 6th 593 204 188 1.959 8.389 280 224 231 2.131 II.889 346 208 172 rf 454 6.111 213 I58 142 1.467 7,500 125 117 91 3.561 9.333 81 74 74 3.889 12,866 88 77 70 133 15.ΟΟΟ

* Less than 6 samples in this average value

25,721 24.610 8.6II 28.222 10.222

30,277 26,833 12.167 28,705 * 30,555 22,333 29,722

From the above and other experiments it was found that chromosesquioxide should make up between 33% weight percent of the solids applied to the insulators, the values preferably being between 5 and 20 % and, for economic reasons, preferably about 10 % should. These experiments also show that alumina additions improve the life of the finished article. Improved results are also achieved when the aluminum oxide contains between approximately 10% and 50% by weight of solids. It turns out, however, that there are no advantages if one uses more than approximately percent by weight of aluminum oxide and optimal results are apparently shown when the aluminum oxide makes up approximately 20% of the solid mixture. Lower percentages of other materials can be used without the Cu ₀ O - Al 0 _ _and Cu ₀ O - Cr ₀ O - shift phase ratio disadvantageously. In addition, it amounts considerable may use materials that do not shift the phase ratios without the Sinnergethische effect is blocked confirmation · was obtained by reacting large quantities of Alumiumoxyd may be used in the solid materials is applied to the Aluniiniumoxydisolatorkörpex ¹ without that the usefulness of the fired insulator is markedly reduced. Even though

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Although alumina is not inert, it is the same Material, such as the material from which the insulator is made is and acts, among other things, as a diluent.

Of course, you can make various changes, without leaving the scope of the invention ζτα.

Patent claims:

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Claims (1)

PATENT CLAIMS 1. A method for producing an electrically conductive surface on an insulator consisting essentially of aluminum oxide, in particular for jet engine ignition devices, d a. characterized in that a copper-containing coating is applied to the desired surface area and the time and temperature of the contact between the coating and the surface of the insulator are regulated in such a way that an electrically conductive phase is created under its surface. 2. Ve! Method according to claim 1, characterized 009819/1547 1530215 through the use of copper oxide as Coating material. 3. The method according to claim 1, characterized in that a mixture with a larger proportion of copper oxide and a smaller proportion of aluminum oxide is applied to the Isolai ^ o / and the surface layer is converted into an electrically conductive layer containing _{CuAlO 0 and aluminum oxide by heat treatment.} 4. The method according to claim 1, characterized that on the insulator a mixture with a larger proportion of KupferoxyddL and a smaller one Part of chromium sesquioxide applied and treated by heat into an electrically conductive surface layer is converted from converted copper oxide, aluminum oxide and and chromium sesquioxide. 5. The method according to claim 4, characterized that the mixture to change the insulator surface in a layer of aluminates and chromates of copper oxide contains a small amount of aluminum oxide. - 3 - 00 ^ 019/1547 Method according to claim 5 »characterized by using a mixture of 3 to 30 weight percent chromium sesquioxide, 10 to 30 weight percent Aluminum oxide and residual copper in a form that is in equilibrium with the treatment temperatures Oxygen results, with treatment time and treatment temperature are chosen so that there is no noticeable Wandemng of the aluminum oxide from the insulator body. 7. The method according to claim 6, characterized in that the coating mixture and insulator body for a period between approximately 10 and approximately 6 minutes to a temperature between 1315 C and approx. 1485 ° C. 8. The method according to claim 4, characterized that as a coating a mixture of about 90 percent by weight copper in a form that is at increased Temperatures an equilibrium with oxygen results, and about · 10 weight percent Cr0 "is used and mixture and isolator for a period of time between about 10 and 6 minutes in an oxidizing atmosphere on a temperature door be heated between approx. 1315 C and approx. 1485 β. 009819/1547 9 · Method according to one or more of Claims 4 to 6 characterized in that a mixture of approx. 75 percent by weight copper in a form which results in an equilibrium with oxygen at elevated temperatures, approx. 16.5 percent by weight aluminum oxide and about 3.5 weight percent chromium sesquioxide use takes place and at a temperature of approx. 1315 for approx. 10 Minutes. 10. Insulating body with an electrically conductive surface, characterized by an aluminum oxide body, which is burned to approx. 95% of the theoretical light and has a surface layer between 0.025 and 0.25 mm thick, the Cu _{2 combined with the aluminum oxide of the insulator to form CuAlO} 0 contains. 11r insulating body according to claim 10, characterized that the layer with the aluminum oxide of the insulator to form a stabilized electrically conductive layer in the insulator body contains combined copper oxide and chromium sesquioxide. 009819/1547 Blank page