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Author: Subject: A high-temperature mini-furnace for temperatures above 2000 C.
metalresearcher
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[*] posted on 13-12-2021 at 01:04


Quote: Originally posted by macckone  
Magnesia is easily synthesized.
Start with sorel cement, heat until all the HCl is given off.To make it impermeable you can treat it with milk of magnesia (use the low sodium variety).
Then treat with linseed oil, which will crosslink and carbonize under heat.
At the working temperature you are hoping to achieve, the carbon with graphitize.
This yields a magnesia/graphite composite that is very durable and capable of withstanding all but the highest temperatures (> 2500C) and is more resistant to oxidizing conditions.

I thought cement is basic so it never can contain HCl ?
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[*] posted on 13-12-2021 at 14:35


Quote: Originally posted by macckone  
Magnesia is easily synthesized.
Start with sorel cement, heat until all the HCl is given off.
To make it impermeable you can treat it with milk of magnesia (use the low sodium variety).
Then treat with linseed oil, which will crosslink and carbonize under heat.
At the working temperature you are hoping to achieve, the carbon with graphitize.
This yields a magnesia/graphite composite that is very durable and capable of withstanding all but the highest temperatures (> 2500C) and is more resistant to oxidizing conditions.


I find the idea very interesting - Thank you! I'll be ordering a technical grade MgO fired from magnesite and MgCl2 hydrate. Maybe a cleaner chemical grade MgO would be much better, because I don't know what sodium content the one extracted from magnesite normally has? But this technical MgO is very cheap...
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[*] posted on 15-12-2021 at 09:50



ZrO2 becomes conductive when heated up above 800C or so. That complicated a furnace made from these bricks even more.

The MgO may be the way to go.

https://news.thomasnet.com/fullstory/magnesium-oxide-ceramic...

Lanthanum Chromite

A heating module for service in oxidizing gas media at temperatures up to 1700°C is proposed. Results of an analysis of the thermally stressed state of lanthanum chromite-based heaters designed in various configurations for use in the heating module are reported.

Paper attached. Not terribly useful IMO but interesting reading.

Yob

[Edited on 15-12-2021 by yobbo II]

[Edited on 15-12-2021 by yobbo II]

Attachment: La_Chromite.pdf (144kB)
This file has been downloaded 86 times

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macckone
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[*] posted on 16-12-2021 at 07:04


metalresearcher,

Sorel cement is not the same as regular cement.
It is an oxychloride and I assure you it gives off HCl when heated above the required temperature.
Calcined magnesium oxide is quite unreactive to HCl.
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yobbo II
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[*] posted on 28-12-2021 at 18:27



Has this device a thermocouple ( or perhaps a thermopile(a numbe of thermocouples connected in series )) inside as the 'working' element with just a lense directing the heat?

Can they be made successfully in the garage.?

https://www.ebay.co.uk/itm/284502206779?hash=item423da7293b:... *

Yob

* nearly needed the 8 ball....
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[*] posted on 28-12-2021 at 21:14


Quote: Originally posted by yobbo II  

Has this device a thermocouple ( or perhaps a thermopile(a numbe of thermocouples connected in series )) inside as the 'working' element with just a lense directing the heat?

Can they be made successfully in the garage.?

https://www.ebay.co.uk/itm/284502206779?hash=item423da7293b:... *

Yob

* nearly needed the 8 ball....


Well that's how some IR spectrophotometer detectors work xD.
I had the idea of using a PIR detector from a cheap motion sensing unit, at a first glance it looks like it is made to detect a temperature difference more than an exact value.

Quickly reading how old pyranometers worked there is one that is pretty simple. Just a tube with a filament in the middle, you look at the inside of the furnace through the tube and crank up the current of the filament until it "disappears" since it is the same color of the furnace, aka the same temperature.
It needs to be calibrated in order to correlate current to temperature, and right now i have no idea how to do that, maybe looking at a metal while it melts so you can assume that is the melting temperature of the metal (aluminium, copper and silver, 3 points for a pretty crappy calibration curve)
https://en.m.wikipedia.org/wiki/Disappearing-filament_pyrome...





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[*] posted on 30-12-2021 at 05:39




I have one of those devices, a Hartmann & Braun, which was purchased from a German flea market.
It goes up to 2000C. A three volt battery works OK in it. A two volt battery would probably do. It is quite old, forties or fifties?

I have just crancked it up for the first time. I need an open fire to test it on. Most lights are too white and therefor give a false impression that they are at a very hight temperature (I think).

Here is one the exact same (amazing internets).
http://www.deprez.org/folio_0024_en.html

The description of operation is not correct (I think). There are two scales. One is for when the red filter is in the line of view (the higher temperatures) and the other when the red filter is not in line. The filiment must be easier to see (harder to make disappear) when the red filter is in line and therefor you must dial up more current to make it disappear?

If anyone can shed any light on how to operate the device I would be grateful.

There is a pyrometer below which uses a thermocouple with thermocouple still attached. If you look at the 'batch No.' on the instrument it says
Pt/Pt.Rh. Is that a Platinum Rhenium thermocouple that in still attached I wonder? They are mighty expensive.

https://www.ebay.co.uk/itm/Portable-CAMBRIDGE-PYROMETER-0-14...

Here is an example of another disappearing filiment from ebay.

https://www.ebay.co.uk/itm/363668752251?hash=item54ac58c77b:...
and here
https://www.ebay.co.uk/itm/124439566941?_trkparms=amclksrc%3...

A real beauty here for $ale:
https://www.ebay.co.uk/itm/333111230230?hash=item4d8ef9ff16:...


Yob



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[*] posted on 26-4-2022 at 10:28


I was thinking on something like this to a high temperature heater: a tube made of high alumina or magnesia filled with compacted graphite on center to increase the electrical resistance and graphite rods on the extremities as contact tips

will it work?




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