Just so everyone knows, and to save them from making the same mistake i have, the commonly available 'just add water' casting product containing alumina and calcium oxide (there are many brands, secar 71 being what i got) is NOT suitable for either vacuum or high voltage applications. the reason is that some of the hydrates formed on addition of water decompose above 20deg C releasing there water and making the material porous.
The freshly cured substance is pretty hard, but when baked out becomes rather like chalk. it seems the only use for this stuff is for its refractory properties, which are rather good.
It may be possible to cast the desired shape and then fire it to form a ceramic. if i ever get/make a suitable kiln i shall attempt this and report back.
Oliver.
high alumina casting cement/ceramic
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Todd Massure
- Posts: 443
- Joined: Thu Mar 11, 2004 12:38 am
- Real name: Todd Massure
Re: high alumina casting cement/ceramic
Too late for me!
I got some of the two part stuff instead of the just add water kind only to find that it too is quite porous and brittle. I was going to use it for vacuum applications and I found a sealer that may work to make it vacuum tight, but I gave up on it and instead I am now planning on using a machinable ceramic similar to Macor, but cheaper.
-Todd
I got some of the two part stuff instead of the just add water kind only to find that it too is quite porous and brittle. I was going to use it for vacuum applications and I found a sealer that may work to make it vacuum tight, but I gave up on it and instead I am now planning on using a machinable ceramic similar to Macor, but cheaper.
-Todd
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HighVoltageFox
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- Real name:
Re: high alumina casting cement/ceramic
I have tried out alot of ceramics, not for vacuum apps. but I believe that you do need to heat the alumina to at least 10 cone other wise it will be worthless. And I think that you can make high alumina ceramics by adding pure alumina and a little high-fire clay. I have access to a very large kiln and once I get some alumina or some of this mix you got I will tell you how it came out. By the way where did you get this mix?
AH
AH
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Roberto Ferrari
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- Real name: Roberto Ferrari
- Location: Argentina
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Re: high alumina casting cement/ceramic
Fellows,
I suggest to reconsider the poor-man approach with respect to some materials.
You will spend a lot of time to avoid to spend a little money. Used feedthroughs and high voltage insulators pops-up periodically in eBay and surely in the US there are plenty of surplus stores able to provide them. As a matter of fact, you live in the most technologically driven country. Take advantage of that!
Some strategic pieces are a must, not only from the time/money point of view but also by safety issues. Don´t mess with doubtful vacuum pumps, high voltage insulators and cables, vacuum parts and chamber materials.
I wondered many times why US amateurs don't joint efforts and spare money.
In case of long distances between two teams, even to consider to use the fusor half-of-the year each party.
Regards,
Roberto
I suggest to reconsider the poor-man approach with respect to some materials.
You will spend a lot of time to avoid to spend a little money. Used feedthroughs and high voltage insulators pops-up periodically in eBay and surely in the US there are plenty of surplus stores able to provide them. As a matter of fact, you live in the most technologically driven country. Take advantage of that!
Some strategic pieces are a must, not only from the time/money point of view but also by safety issues. Don´t mess with doubtful vacuum pumps, high voltage insulators and cables, vacuum parts and chamber materials.
I wondered many times why US amateurs don't joint efforts and spare money.
In case of long distances between two teams, even to consider to use the fusor half-of-the year each party.
Regards,
Roberto
Re: high alumina casting cement/ceramic
indead, Roberto has a point. i wasn't so much interested in just makeing a feedthrou, as in the possability of custom ceramic parts for ion guns, e guns, supports etc. alough i had an idea to make a small custom feedthrough and imerse the outside conection in oil, with a metal tube covering it, so an RF tight join could be made with sheilded HV cable. if i just used a normal lower voltage feedthrou for this, the vacuum side would not be rated for the voltage
i got the stuff from here, if anyones interested:
http://www.tiranti.co.uk
Oliver
i got the stuff from here, if anyones interested:
http://www.tiranti.co.uk
Oliver
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Steven Sesselmann
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- Joined: Wed Aug 10, 2005 9:50 pm
- Real name: Steven Sesselmann
- Location: Sydney - Australia
- Contact:
Re: high alumina casting cement/ceramic
Has anyone experimented with extruded ceramic tubes. They are very
cheap and easy to work with. They come in standard sizes and lengths,
my supplier says up to one meter.
Just find a way to get a good vacuum seal at each end and you effectively
have a feedthrough. As it has a straight shape, rather than corrugated like
the commercial bushings, it would have to be longer by about three times.
I am experimenting at the moment with an 8mm outside diameter tube,
using Swagelok fittings at either end. I am also trying to get special
graphite ferrules to replace the S/S ferrules, so I can get a better seal.
http://www.cof.com.au/Index.shtml
Steven
cheap and easy to work with. They come in standard sizes and lengths,
my supplier says up to one meter.
Just find a way to get a good vacuum seal at each end and you effectively
have a feedthrough. As it has a straight shape, rather than corrugated like
the commercial bushings, it would have to be longer by about three times.
I am experimenting at the moment with an 8mm outside diameter tube,
using Swagelok fittings at either end. I am also trying to get special
graphite ferrules to replace the S/S ferrules, so I can get a better seal.
http://www.cof.com.au/Index.shtml
Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Todd Massure
- Posts: 443
- Joined: Thu Mar 11, 2004 12:38 am
- Real name: Todd Massure
Re: high alumina casting cement/ceramic
Roberto, there definitely is a such thing as "being too cheap for your own good" especially when high voltage etc. is concerned. I wish there was something I could get off the shelf that fits my needs, but there's not.
The two part compound I got was Cotronics Durapot 801. It's actually where McMaster Carr gets the stuff they offer, but this is supposed to be more pure. It is supposed to gain strength after firing and have increased electrical properties. I was a little mad at first, because they certainly didn't go out of their way to say that it was porous, as they didn't send me a catologue with full info until I actuall bought something, but on the other hand, they didn't say that it was vacuum tight either, as they do for many of their products. I'm still planning on ordering from them in the future, such as the machinable glass-ceramic I mentioned. Their products are pretty much all high temp applications, and they have a website which is worth a look.
Todd
The two part compound I got was Cotronics Durapot 801. It's actually where McMaster Carr gets the stuff they offer, but this is supposed to be more pure. It is supposed to gain strength after firing and have increased electrical properties. I was a little mad at first, because they certainly didn't go out of their way to say that it was porous, as they didn't send me a catologue with full info until I actuall bought something, but on the other hand, they didn't say that it was vacuum tight either, as they do for many of their products. I'm still planning on ordering from them in the future, such as the machinable glass-ceramic I mentioned. Their products are pretty much all high temp applications, and they have a website which is worth a look.
Todd
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Javier Lopez
- Posts: 141
- Joined: Wed Feb 22, 2006 3:32 am
- Real name: Javier L
Re: high alumina casting cement/ceramic
In space equipment it was used epoxi as cement but nowadays silicone is preferred.
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fedigrazia
- Posts: 1
- Joined: Wed Apr 19, 2006 10:46 am
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- Contact:
Re: high alumina casting cement/ceramic
Dear Sirs,
Looking into your needs I may have the solution for it.
I work at Saint-Gobain in Brazil and we are fabricators of ceramic technical parts.
I'll be glad to help you guys to find the best solution for yo process.
Email: fernando.brasileiro@saint-gobain.com
Site: www.saint-gobain-ceramicas.com.br
Oliver Greenaway escreveu:
> Just so everyone knows, and to save them from making the same mistake i have, the commonly available 'just add water' casting product containing alumina and calcium oxide (there are many brands, secar 71 being what i got) is NOT suitable for either vacuum or high voltage applications. the reason is that some of the hydrates formed on addition of water decompose above 20deg C releasing there water and making the material porous.
>
> The freshly cured substance is pretty hard, but when baked out becomes rather like chalk. it seems the only use for this stuff is for its refractory properties, which are rather good.
>
> It may be possible to cast the desired shape and then fire it to form a ceramic. if i ever get/make a suitable kiln i shall attempt this and report back.
>
> Oliver.
Oliver Greenaway escreveu:
> Just so everyone knows, and to save them from making the same mistake i have, the commonly available 'just add water' casting product containing alumina and calcium oxide (there are many brands, secar 71 being what i got) is NOT suitable for either vacuum or high voltage applications. the reason is that some of the hydrates formed on addition of water decompose above 20deg C releasing there water and making the material porous.
>
> The freshly cured substance is pretty hard, but when baked out becomes rather like chalk. it seems the only use for this stuff is for its refractory properties, which are rather good.
>
> It may be possible to cast the desired shape and then fire it to form a ceramic. if i ever get/make a suitable kiln i shall attempt this and report back.
>
> Oliver.
Looking into your needs I may have the solution for it.
I work at Saint-Gobain in Brazil and we are fabricators of ceramic technical parts.
I'll be glad to help you guys to find the best solution for yo process.
Email: fernando.brasileiro@saint-gobain.com
Site: www.saint-gobain-ceramicas.com.br
Oliver Greenaway escreveu:
> Just so everyone knows, and to save them from making the same mistake i have, the commonly available 'just add water' casting product containing alumina and calcium oxide (there are many brands, secar 71 being what i got) is NOT suitable for either vacuum or high voltage applications. the reason is that some of the hydrates formed on addition of water decompose above 20deg C releasing there water and making the material porous.
>
> The freshly cured substance is pretty hard, but when baked out becomes rather like chalk. it seems the only use for this stuff is for its refractory properties, which are rather good.
>
> It may be possible to cast the desired shape and then fire it to form a ceramic. if i ever get/make a suitable kiln i shall attempt this and report back.
>
> Oliver.
Oliver Greenaway escreveu:
> Just so everyone knows, and to save them from making the same mistake i have, the commonly available 'just add water' casting product containing alumina and calcium oxide (there are many brands, secar 71 being what i got) is NOT suitable for either vacuum or high voltage applications. the reason is that some of the hydrates formed on addition of water decompose above 20deg C releasing there water and making the material porous.
>
> The freshly cured substance is pretty hard, but when baked out becomes rather like chalk. it seems the only use for this stuff is for its refractory properties, which are rather good.
>
> It may be possible to cast the desired shape and then fire it to form a ceramic. if i ever get/make a suitable kiln i shall attempt this and report back.
>
> Oliver.