Author Topic: What's needed to heat up 0.75 g of SiC (susceptor) mass until it turns dim-red??  (Read 884 times)

Egzoset

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Salutations,

Actually i have Silicon Carbide Foam in mind, more exactly a "tetrakaidecahedron" form known as "Duocel" apparently:





It turns out there's a manufacturer of ready-made 3rd-party commercially-available IH-drivers who's in-line "calculator" includes Silicon Carbide on a list of supported susceptors:



The trick here is that although SiC has excellent thermal properties i sense (e.g. using my story-teller crystal ball...) that it may exhibit lossy dielectric properties at some "magic" frequency which conveniently causes such fine Space-Age material to heat up, because of electromagnetic Induction Heat although it's not magnetic at all - not even metallic.  So, some more intuitive wandering warns me an IH-driver would have to work in the MHz range, perhaps below the TV/FM range...  Then go figure how much additional agravations awaits!

Well i though it's OKay to ask in case that's a valid question and it's in the correct forum section anyway.

 ;)

Good day, have fun!!   8)


« Last Edit: June 23, 2020, 10:38:59 PM by Egzoset »

Offline Twospoons

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I'd try a microwave oven.  It should have enough power to overcome the heat radiation from the SiC, to reach red heat.

Offline Twospoons

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My head still says 'microwave'.
200J in a few seconds should be easy.  So should modifying a microwave - pull the magnetron out, give it a waveguide with a terminator and a place for your susceptor. Maybe lined with refractory cloth to protect the waveguide.
Getting a couple hundred watts out of a 2kV battery driven inverter to power the magnetron should be reasonably straightforward. (Usually its around 4kV to get 1kW of microwave energy).

So long as you are aware of, and comfortable with, the hazards of microwave radiation.

Any other application details you'd care to share? Like the purpose of this device?  The more we know the better the advice will be.

Offline klugesmith

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Yes, what Twospoons said!
In the 1980's, most household MWO's used a conventionally fed rectangular waveguide to transfer power from magnetron probe to the cooker box, often with a mode-stirring "fan" at the outlet.  Not too long ago I scrapped one, but can't find the pictures.  I've seen newer MWO's with waveguides, like some which admit microwave power through a dielectric floor of the cooker box.

All you would need is a container of water in the box, as a power-absorbing load, and a little door into the waveguide for inserting your susceptor.    Or put susceptor into open end of the waveguide, like a nasal swab for COVID test, with view by mirror to see if it gets red hot.   I guess there are cases where a "susceptor" could cause enough return loss to stress the magnetron,  but we aren't talking about running for minutes at a time.
« Last Edit: June 26, 2020, 02:59:28 AM by klugesmith »

Offline Uspring

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A microwave oven works by exciting a vibrational resonance mode in water to which its frequency is tuned. There is probably no suitable frequency in the foam. Whether the MWO can be utilised as an induction heater depends on the electrical resistivity of the foam. It seems to lie at about 1k Ohm*m, which looks like a bit too high, even at the high operating frequency.

But it is better to experiment. Just put a chunk of the foam into the MWO and see whether it heats up.

Offline klugesmith

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The resonant frequencies of water molecules are all in the THz range. 
An Internet search for "microwave frequency water" found confirmation by dozens of writers.
Not that that means it's true.

Most MWO's have nominal frequency of 2450 MHz because it's the middle
of an RF spectrum band long allocated for ISM use (Industrial - Scientific - Medical).
https://en.wikipedia.org/wiki/ISM_band
and that ISM band is within a broad spectral range that could allow practical cooking by microwave.

The same ISM band has also come into use for unlicensed RF communication, including "Wi-Fi".
I have experienced Wi-Fi being jammed when a MWO operates, and found the RF leakage from MWO to be much lower than what's allowed by health rules as well as communication rules.  It's Wi-Fi that "must accept harmful interference".

Back to the SiC foam experiment: I bet the resistivity goes down as the temperature goes up.
Look at videos of people melting glass beer bottles in MWO, at places pre-heated with a torch.
Might be easier to get foam to red heat in a vacuum.
For example, inside a glass food-canning jar that's in the MWO and set up with hose to a vacuum pump. 
Pressure might need to be less than 1 torr (millibar) before air becomes thermally insulating -- look at the useful range of Pirani and thermocouple vacuum gauges.
« Last Edit: June 26, 2020, 04:22:11 PM by klugesmith »

Offline johnf

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I'm presently building a single mode microwave furnace
One of my options is the tube going through middle being SiC as a susceptor
I'm also now thinking of using the SiC foam for a frit in a boron nitride tube -all of this for carbonless reduction of ironsand into iron using superheated hydrogen to do the reduction ie 1350 degrees Celsius

yes you can use your domestic microwave to test materials in fact there are smelting kits available for melting metals for use in a non modified domestic microwave oven
https://www.instructables.com/id/microwave-smelter/

https://www.popsci.com/diy/article/2003-09/smelting-microwave/

Offline klugesmith

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Very cool project, John, in the figurative sense of the word.

I have to pick on the cited articles wrongly using the verb "to smelt" when they mean melting of metal.
Smelting implies chemical reduction of ore, as John intends to do using hydrogen instead of coal/coke.

Another metallurgical word often misunderstood is "to temper".
Right now I can't find one online article about words that are their own opposites.
Writer thought that "tempered steel", as in a knife, meant hardened.
Said that was opposite to the common meaning: tempered means not harsh, not strict and unyielding.
A topic on my mind after just reading about martensite and austenite.

Offline Uspring

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Hi klugesmith,

thank you for clearing up my misunderstanding about the resonant nature of water heating in a microwave. The resonant frequencies are indeed much higher, definitely above 1 THz, as you said.

Quote
Most MWO's have nominal frequency of 2450 MHz because it's the middle
of an RF spectrum band long allocated for ISM use (Industrial - Scientific - Medical).

Yes, but I thought, ISM use was reserved for that frequency, because MWOs work there well.

Quote
Back to the SiC foam experiment: I bet the resistivity goes down as the temperature goes up.

I've seen some diagrams which indicate that. The type I've quoted resistivity for was the one here: http://ergaerospace.com/materials/duocel-silicon-carbide-foam/
It seems to belong to the more resistive types. Silicon Carbide has more conductive ones. Skin depth gives a good indication of useful resistivity ranges. The skin depth should ideally correspond about to the linear dimensions of the sample.

Offline klugesmith

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>> Yes, but I thought, ISM use was reserved for that frequency, because MWOs work there well.

Now I just learned something from you. 
Heating by microwave had been developed enough that they requested 2450 MHz in 1947,
to get their foot in the door.  The previously cited Wikipedia article says this about history:

The ISM bands were first established at the International Telecommunications Conference of the ITU in Atlantic City, 1947. The American delegation specifically proposed several bands, including the now commonplace 2.4 GHz band, to accommodate the then nascent process of microwave heating;[4] however, FCC annual reports of that time suggest that much preparation was done ahead of these presentations.[5]

The report of the August 9th 1947 meeting of the Allocation of Frequencies committee[6] includes the remark:

"The delegate of the United States, referring to his request that the frequency 2450 Mc/s be allocated for I.S.M., indicated that there was in existence in the United States, and working on this frequency a diathermy machine and an electronic cooker, and that the latter might eventually be installed in transatlantic ships and airplanes. There was therefore some point in attempting to reach world agreement on this subject."


There are other ISM bands, like I think 13.56 and 27.12 MHz, used in things like glue curing devices and plasma-based process chambers.

While looking for this info I discovered shameful attempts in USA, this decade, to reallocate the entire TV broadcast spectrum to wireless digital services. Would have been the end of free TV here.
« Last Edit: June 27, 2020, 04:36:33 PM by klugesmith »

Offline Twospoons

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Well, that was very long winded and confusing. I still have no idea exactly what you are trying to achieve or what your constraints are.

Simple questions:
What is the final device and its purpose?
How big can it be?

One line answers please ...

If you are looking for curie point based temperature control, thats a whole other ball game.  My soldering iron uses the curie point of the metal tip for temperature control .. its inductively heated, not sure what frequency they use.

Offline Justin

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Offline ritaismyconscience

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Please explain in simple English what you are trying to do.

You are trying to heat up a piece of ceramic then use it to vape right?
« Last Edit: June 30, 2020, 09:09:02 PM by ritaismyconscience »

Offline T3sl4co1l

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Can't tell if this is actually over-unity power, or just garden-variety woo.  I can quite matter-of-factly state there is no such thing as "Bi-Energy"...

Regarding fine hairs, the easiest way to do that would probably be a plasma discharge.  An extremely fast (potentially microseconds) corona discharge can deliver high temperatures and low energies.  Potential downsides are, the vict\\\\target may not appreciate high voltages, electrostatic forces, ozone generation, pyrolysis products (smoke and burnt stuff), flashes of light, UV, etc.

Or a precision pointed laser, which can double as targeting laser to spot the hairs and burn them off precisely.  This can be done in say tens of microseconds at a time, so a full spider can be scanned, and... ablated, in under a second maybe.

I suspect this has nothing to do with the intended application, or, that there is any intended application, as such, for certain definitions of "application"...

Tim

Offline klugesmith

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Nice work, Bud!


Wonder if I could find my own sketches from about 1978, about electric devices for vaporizing free base alkaloids to inhale?


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