Hi Sumit,

alumina probably can stand the temperature, and is a excellent insulator up to a few kV depending on the coating thickness.

Alumina is good choice. You can use it up to 2000ºC or more, if is a 99,99% alumina. Alumina is also used to manufacture eletric ceramic insulators.

I agree with all.

Materials made of clay are good thermal and electrical insulators, especially when reinforced with pure alumina in a very moderate quantity (about 8%), It will conveniently go beyond 1,400 degree C. If higher temperature (above 1,400) operation is desired, the clay may be purified hydrometallurgically in order to lower the Fe content which is the element responsible for lowering the refractoriness of clay.

Sorry, at temperatures higher than 1200 oC alumina is not an insulator (!). Be sure I have got a very special experience in this area. That is why we cannot apply it in ion rocket engines... and were forced to design some special materials (see my publications). However, the consideration of Sumit's question, in my opinion, has to be accompanied by the consideration of exploitation condition gas atmosphere (partial pressures, gas exchange rate etc) otherwise it is not serious...

Mix of the powders AlN and Al2O3 is difficult processed mechanically in the pressed look. It is desirable to press an insulator at once under the demanded sizes.

There is only one type of high-temperature electrical insulators, which could be machined by common instruments, that is BN-graphene-like containing ceramic-ceramic composites, also called "high-E - low-E composites" or "hetero-modulus ceramics". Sure you can find something useful among my publications/presentations on ResearchGate...

I agree with Shabalin

Well, in first place, you must determine how you will use the insulating material. If it should be flexible or may be rigid properties.

In the first case, there are rubber and polymers having good insulating action.

In the second case, ceramics are the best choice.

But remember that the electrical insulation characteristics of dielectric properties depends of the material, and these, by the way, do not obey Ohm's law.

You should review the range of voltage and current that will work and compare with the functional chart of the chosen material.

You can try Beryllium Oxide which has a melting point  ~2470 degree centigrade.

However, there are at least two serious disadvantages:

(1) BeO is an ionic conductor (!) at higher temperatures and

(2) BeO has very high hardness, so its machining by common tools is impossible...

Also we cannot ignore the facts that BeO is an extremely dangerous hazard and not stable in the wet atmosphere even at room temperature...

You can try Pyrophyllite - hydrous aluminium silicate. This is machinable. You can also look at machinable ceramics.Macor can be used upto 850 C.

Sorry, but my question to Mr. C. Divakar: How can you use pyrophilite under atmospheric pressure (not under high and ultra-high pressures!) at such high temperature, if its decompostion process (at 0.1 MPa) initiates at 300-500 oC?

The parameters of interest are vague. What do you means by electrical insulators? High K or low k materials? What is the operational voltage? AC or DC field? Most insulators I know in that region do not have any adhesive properties at all. I believe that the author of the question should rethink his needs for such an contradicting criteria for his material. I would suggest Silicon nitride or silica based on the gases in the operation environment. But i think Dr. Shahabin's opinion is the best here. 

What about  99.8% Alumina? The volume resistivity is still high enough to be an insulator at 1200C- 1E7 ohm cms.

They asked for machinable ceramics! This is exactly not about alumina...

I do not see machinable in his requirements?

99.8% alumina will be best for your application. It has breakdown voltage around > 5 KV for even 1 mm thickness and also can be used up to 1600 Degree Centigrade. But alumina can not have adhesive property. Sintered ground alumina can be fitted in your set up with modification.

IF YOU USE PRESSING THE EXPLOSION YOU CAN GET THE THREE-LAYER SYSTEM OF METAL-ALUMINA-METAL WITH GOOD INSULATION PROPERTIES

I would suggest that you try a high alumina cement. It can easily adhere to any ceramic surface (if that is the case) providing a suitable heat treatment is employed.

Regards,

Fernando Oliveira

Concerning adhesion properties, Dr. F. Oliveira is absolutely true.

Thank you all for your much needed valuable input..

Mr. Alex ..

The intended specification are absolutely fine....As per my ineterest of application I need both i.e., good electrical insulation and high temeparature resistant....

taking that into view I tried  out with Alumina mixed with sodium silicate and is working fine...giving me both Adhesive property as well as needed electrical insulation. But I am not sure whether it can resist high temperature..

Please do a test firing for your selected materials before you run the sample for high temperature application to check for melting or bubble formation. Keep the test firing parameters as close as possible to your intended high temperature operation environment. 

Thank you so much Mr. Alex for the valuable input ..will surely take care of this ...

We produce and supply high purity nuclear grade beryllium oxide, beryllium fluoride, Sodium fluoride.  my email address: [email protected].

you can use ceramic insulator materials such as alumina....

Dear Jose,

Maybe, you will wonder, but in the range of temperatures higher than 1300-1400 oC alumina is a conductor...

Alumina mixed with sodium silicate is a mix of a acid and basic oxides, this fact can reduce its point of fusion (euthetic point). Did you try use a silico-aluminate material? The point of fusion is high. There is a calcium silicates (Ca2SiO4 or Ca3SiO5) which fusion point around 2130 °C (3866ºF), and it is a relactive electrical insulator. These oxide compounds are generated in a blast furnace slag.

At higher temperatures all the ceramics with ionic bonding, including all the alumosilicates, are conductors. To solve the problem mentioned above a researcher has to employ ceramics with covalent bonding, such as boron and silicon nitrides, sialons etc

I found this discussion interesting as I am working on an electrical insulation at very high temperatures (up to 1700 °C). As I understood boron nitride is a good candidate for this type of application while alumina is not (which I already found out to be not good for my case). I was wondering if one of the BN forms is better than the other one (a,h,c,w) and if the commercial Shapal is still a good candidate. Is anyone able to give me any clue? thank you

Resistivity (at RT):

for graphite-like h-BN >10(power12) Ohm cm,

for diamond-like c-BN (strongly depends on contamination) 10(power7)-10(power9).

I had some doubts about the hexagonal due to the van der waals forces between the layers but it seems to be not relevant to the resistivity. I will keep searching for Shapal but in the meanwhile I will go for h-BN. Thank you for your help

Graphite is an amazing material in both "black" and "white" forms! Be sure...

machinable ceramics h-BN and SiAlON-BN are highly recommended