Metallophile
Hazard to Self
Posts: 87
Registered: 23-3-2018
Member Is Offline
Mood: No Mood
|
|
Conductive Sodium Silicate?
I've been attempting to make a stainless retort for making K, Rb, and Cs metals. Instead of using a tube furnace, I wanted to wind some Nichrome wire
around the pipe itself. I first slathered a layer of sodium silicate furnace cement on the pipe and baked it, to electrically insulate the Nichrome
from the stainless pipe. After winding the heating element, I added another layer of furnace cement to protect the wire.
During testing, I noticed that once it reached maybe 400C, the wattage would start to climb. I could turn down the variac to correct the wattage, but
it would still keep climbing. Eventually I'd see a dramatic power spike, and the element would quickly burn out. I re-built and tested this thing 3
times, with the same results. The highest temperature I measured was about 650C.
So this all leads to my question: Is it possible the sodium silicate cement is becoming conductive at a high enough temperature, and shorting out the
coils? This seems strange, but I honestly can't think of any other explanation.
|
|
|
Morgan
International Hazard
Posts: 1694
Registered: 28-12-2010
Member Is Offline
Mood: No Mood
|
|
There was this pdf article/title that maybe has something. Soda lime glass isn't very good for high voltage, borosilicate better and pure quartz a
good insulator. So maybe the sodium ion is "freeing up" even for your relatively low voltage and high heat. Seems like you have a very thin layer of
brittle silicate and the expansion of heated steel if the COE doesn't match, maybe along with the sodium, could be creating a pathway?
But I'm only guessing.
Selected properties of sodium silicate glasses and their structural significance - CORE
"The electrical resistivities of sodium silicate glasses ranging from 7.9 to 40.0 mole % Na20 were determined at 50 hz. and tempera tures fraa 360 to
480*C by Haven and Verkerk"
|
|
|
unionised
International Hazard
Posts: 5126
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Hot glass is a fairly good conductor.
https://www.youtube.com/watch?v=xwEQZw3KPWg
|
|
|
Metallophile
Hazard to Self
Posts: 87
Registered: 23-3-2018
Member Is Offline
Mood: No Mood
|
|
Thank you both! That pretty much confirms it then. I'll need to find a different cement, or change the design.
|
|
|
Morgan
International Hazard
Posts: 1694
Registered: 28-12-2010
Member Is Offline
Mood: No Mood
|
|
It's interesting unlike metals, glass becomes more conductive the hotter it gets. There was this article too using a lightbulb that lights when heated
glass starts to slump.
"Insulating glass becomes a conductor of electricity when heated red-hot with a blowtorch."
https://sciencedemonstrations.fas.harvard.edu/presentations/...
|
|
|
Fulmen
International Hazard
Posts: 1716
Registered: 24-9-2005
Member Is Offline
Mood: Bored
|
|
I did something quite similar using sodium silicate and talcum, it lasted for years at temps up to 900°C. This came from an old CRC handbook claiming
it could handle temperatures up to 1000°C.
We're not banging rocks together here. We know how to put a man back together.
|
|
|
macckone
Dispenser of practical lab wisdom
Posts: 2168
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline
Mood: Electrical
|
|
Sodium ions are mobilized at high temps in a silica matrix.
This leads to the ability to put a light bulb in salt and produce sodium inside the bulb.
This is a classic experiment: http://www.sciencemadness.org/talk/viewthread.php?tid=148098
|
|
|
Texium
|
Thread Moved
29-11-2023 at 22:12 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
