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Quince
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[*] posted on 25-6-2005 at 00:07
Vacuum furnace?


If something needs to be heated at 1100*C in vacuum or inert atmosphere, obviously a glass vessel can't be used (Googling for melting point of Pyrex/borosilicate I'm getting numbers from 850*C to 1400*C, so I'm assuming the worst, especially that even unmelted glass would probably be too weak to withstand vacuum). What can be used to contain the vacuum, given that this is a DIY thing for a single use, so I'm not asking what expensive commercial solution to buy (cheapest vacuum furnace on eBay is a small old dental machine already at $1500).

[Edited on 25-6-2005 by Quince]




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[*] posted on 25-6-2005 at 00:20


Are you heating it internally or externally, and for what contents?

Heating a vacuum vessel is suicide. Your best bet would be refractory metals or HIPed ceramic products. The first issue is maintaining strength at elevated temperatures, the second is porosity. Certainly, no matter what, you will have substantial vacuum leakage at that temperature, though "substantial" depends if you're trying to make a sputtering gun or just putting "negative" pressure on something hot.

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[*] posted on 25-6-2005 at 02:12


What I need is such heating in an inert atmosphere for the process in patent US4240878. Also, I'm assuming this procedure would work for tungsten instead of tantalum, so if anyone thinks I'm wrong, please comment here.



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[*] posted on 25-6-2005 at 04:24


I don't see why just ordinary argon wouldn't work for this application.

My two cents about this vacuum furnace business: Quartz would be good choice. Quartz should have a continuous working temperature in this range, as its melting point is ~1800*C. You could get a test tube made of quartz, place the thing you’re heating in the bottom, attach a vacuum pump to the opening, and put a damp rag around there to prevent the vacuum tubing from melting. (Quartz is very resistant to thermal shock.) Then just heat the bottom with a blowtorch for a while.

The problem here is that you’d have to get an appropriately sized test tube from the beginning, as you can’t soften quartz even with an oxyacetylene torch. Bigger tubes can be somewhat expensive ($20 for 15x125mm).
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[*] posted on 25-6-2005 at 10:58


Quote:
Originally posted by 12AX7
Are you heating it internally or externally, and for what contents?

Heating a vacuum vessel is suicide. Your best bet would be refractory metals or HIPed ceramic products. The first issue is maintaining strength at elevated temperatures, the second is porosity. Certainly, no matter what, you will have substantial vacuum leakage at that temperature, though "substantial" depends if you're trying to make a sputtering gun or just putting "negative" pressure on something hot.

Tim


Uhm... I take it you have never seen any kind of vacuum system for metallurgical processes. No offense, but what you just said, is complete crap. I use high temp vacuum / inert gas systems on a daily basis, and there are so many different kinds. Maybe you should do some searching?

Quince. pure quartz will withstand temps up to 1500C(1700 is the mp, but 1500 will start to collapse). A thin walled enclosure will start to sag around 1200 C though. The thicker stuff can be heated up to 1400-1500 without leaking. The idea here, is to take a quartz tube or enclosure and pump it down with a vacuum. Then backfill it with an inert gas (or just leave it in the vacuum) then seal it with a hot flame (methane, propane, acetylene / with O2 will work. Note that sealing it under a slight vacuum makes it easier) It might be best to have someone seal it up for you, if you dont have the tools on hand. Its pretty cheap.

I make certain not-so machinable alloys this way. Since they will be difficult to swage or work, I just find the right diameter quartz tube, place the correct proportions of metals inside (metals that will either melt below the 1500C mark, or the % on the phase diagram below that mark. (yes, you can get away with melting metals which have higher MPs this way)
*edit. Then I throw the sealed tube, into a furnace (of your choice) and heat it up to whatever temp. Let it stay in there for an hour or so, come back, shake the tube (carefully), lay it so it all runs to one end (so its in the right shape). come back a little while later and quench it in what.
Quartz will not have the thermal shock you might be used to with glass, so you can actualy take it from white hot and quench it in water without it fracturing at all.

That would be the easiest I think. Otherwise there are a few other possibilities that are realistic for you. (that you can msg me about)

[Edited on 25-6-2005 by uber luminal]
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[*] posted on 25-6-2005 at 12:21


Quote:
Originally posted by neutrino
I don't see why just ordinary argon wouldn't work for this application.

Because I don't have any, of course, nor a vessel to contain it. Else I wouldn't be posting here now, would I!




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[*] posted on 25-6-2005 at 14:07


How about buying a used muffle furnace or potter's clay firing furnace. Then drill a small hole through the bottom (missing all electrical parts, of course). Fit this hole with a pipe to introduce an inert gas from a cylinder (say N2 or Ar) at a low flow rate. Allow the gas to leak out at the door gap.



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[*] posted on 25-6-2005 at 17:33


Quote:
Originally posted by uber luminal
Uhm... I take it you have never seen any kind of vacuum system for metallurgical processes.


My understanding is all metallurgical processes are remotely heated, as by induction or arc (I guess the vacuum is soft enough to allow a discharge?).

Since tool steel is produced in quantity in a vacuum melting process, it would make sense to use a heated vacuum crucible, but still, the cost of manufacturing and maintaining something that hot while sealing while withstanding several tons of force wouldn't be nice.

Quote:
No offense, but what you just said, is complete crap.


Well that's a rather ignorant word to say so.

Quote:
I use high temp vacuum / inert gas systems on a daily basis, and there are so many different kinds. Maybe you should do some searching?


Probably should some day, but I don't have much personal interest in the process since I don't have a HIP machine and the two hundred thousand dollars to do the other things in the process...

[snip fused quartz]

Well and good on a small scale, I'll remember that If I ever need it.

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neutrino
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[*] posted on 25-6-2005 at 18:34


Quote:
Originally posted by 12AX7
I guess the vacuum is soft enough to allow a discharge?


Actually, discharges are easier in a vacuum than in air. Air acts as an insulator of sorts.

uber: quartz is not that cheap to the home experimenter. Unless you know of a good source?:)

[Edited on 26-6-2005 by neutrino]
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[*] posted on 25-6-2005 at 19:59


What does the discharge travel over then? I seem to recall vacuum capacitors have a nice high voltage rating.

Cold electron emission doesn't count, that's in the xray eV range anyway :o

Tim




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[*] posted on 25-6-2005 at 21:48


What are you guys talking about? A discharge requires some sort of medium to be ionized between the electrodes. You can't have a discharge in vacuum, though of course the cathode will emit an electron beam if it's heated or the voltage is high enough. I think the confusion here comes from the fact that it is much easier to get a visible disharge at very low pressure, even near vacuum. But below some point, there's nothing left to ionize.

Have you ever seen vacuum relays? The gap the relay contact switches is usually on the order of a millimeter for a 5 kV relay (I'm looking at one right now). The whole point of a vacuum relay is that you can switch high voltage without worrying about discharges.

So can inert gases be bought cheaply? The only thing I see is argon cartridges for wine preservation, but I haven't found them in Canada and importing compressed gas would probably not work.

[Edited on 26-6-2005 by Quince]




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[*] posted on 25-6-2005 at 22:29


Look in your phone book for welding supplies. Go to the place (note the lack of my adding an "if there is a place", it WILL be there) and ask for a cylinder of argon. It gets cheaper in bulk but you have a larger cost to put down, obviously. I'm guessing a typical expense of between $20-50 for a refill to $200 for a new tank.

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[*] posted on 25-6-2005 at 23:31


- air does act as an insulator. but some gas is needed to strip electrons from. No ions/electrons, no bombardment, no kinetic energy transfer, no useful heat produced. I run plasma in closed systems from -15 to -20 psi, backfilled with (HighP) argon with great results.

- Magpie has a point. you could run a furnace (take your pick), semi-enclose it with a single input and output. then set up an inert purge to run the whole time. Such that at room temp, what goes in, goes out at the same rate. put a buffer between the two chambers. As the gas inside is heated, it will increase in volume and escape, drawing more gas in from the buffer, which is is replenished by a cylinder. This would work in place of a vacuum setup. I think I have done something like that for sampling infrared analysis. Nitrogen is used because it is dirt cheap, and while it may react with the samples, it may not be a concern.

- most of the induction systems I use or have seen, are under vacuum/inert. sometimes its a quartz container inside the coils, or a containment around the entire thing.
direct arc or plasma melting is done directly and under argon, etc. some things are old fashioned methods, stuffed into special oversized glove boxes. HIP and CIP devices also fit this. I dont have these either ;(. but for powder metallurgy, they are quite nice. most research grade metal production, or metal fabrication, is done under vacuum or inert to maintain purity.

-If quartz wont work, you can also use stainless, Inconel, Ta, etc. to serve the same purpose as quartz.

-Another note about the quartz, some metals may compete for the oxygen in the SiO2, so it may be a good idea to wrap the sample is something.

-I do know of a good source for quartz, but its still not that bad. granted a 20 mm od x 40 cm is like $8, its still a cheap alternative when you consider the time, labor and materials if you make something more complex.

-Inert gasses, is relative to what its inert to. Nitrogen is dirt cheap. CO2 is even cheaper, and can be purchased for paintball or pellet gun stuff. hell, you can make N or CO2. He can be purchased or rented from welding shops, or party places (for balloons) or from a neon/sign shop. Neon can be bought/rented from neon sign shops. Argon can be found at most welding distros. you can get a mix of Ar and CO2 for less than pure Ar, or HP Ar.

The tanks allways cost a lot. go online and search for the tank sizes before you call a welding / gas distro. they will use the tank lettering sizes, and you wont know what the hell it means. anyway, ask them about what it costs to rent or lease them. Sometimes there are good deals.

you can also help justify a small argon tank by buying a small mig welder :)

[Edited on 26-6-2005 by uber luminal]
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[*] posted on 26-6-2005 at 00:25


Quote:
Originally posted by uber luminal
Nitrogen is used because it is dirt cheap, and while it may react with the samples, it may not be a concern.


For the method in question (which reminds me, why doesn't anyone ever offer a link when mentioning a patent to discuss?!), it may well suffice. I know tantalum adsorbs hydrogen at moderate temperatures, and other gasses as well I believe - hence a small transmitter tube I have has no silver getter spot, but a suspiciously small anode for the power dissipation, driving it into the red hot range where tantalum getters best.

I don't remember how it responds to nitrogen.

Quote:
-Another note about the quartz, some metals may compete for the oxygen in the SiO2, so it may be a good idea to wrap the sample is something.


The patent mentions diffusing Pt into a Ta electrode (for the purposes of detecting breach of glass-lined steel tanks), so I don't think that's much of an issue. It just needs a vacuum or inert atmosphere and tight temperature control (tight to eyeball anyway, 1050-1150C).

Quote:
He can be purchased or rented from welding shops, or party places (for balloons) or from a neon/sign shop.(dont breath the He, unless you want Radon in your lungs forever)


Errr, wha?

Even if there were radon in the gas to begin with, it would decay to lead within a month of storage.

Quote:

you can also help justify a small argon tank by buying a small mig welder :)


Welding is always a worthwhile persuit to throw money at :D

Tim




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[*] posted on 26-6-2005 at 01:32


Quartz: I know that a lot of halogen lights have bulbs made out of quartz, but does that apply to all? I'm asking as a halogen bulb is $2 vs $8 test tube.

The patent: can I use tugnsten instead of tantalum? In the patent it's mentioned that a tantalum-tungsten alloy works, but pure tungsten sustrate is not mentioned. I have tungsten but not tantalum of the shape I need.

Temperature control: I've only got a propane torch. I can measureave the temperature with an S or R thermocouple I have, but for building a mini-kiln, is it OK to use concrete bricks? Someone told me that concrete can explode if heated to a very high temperature, which sounded like BS to me but I'd better ask here to make sure it's safe (I don't have any other bricks).




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[*] posted on 26-6-2005 at 07:51


Quote:

Errr, wha?
Even if there were radon in the gas to begin with, it would decay to lead within a month of storage.


Yea. actualy I was thinking of something else, as a byproduct of Helium isolation from natural gas wells, but in a way that isnt even possible. so yea... nevermind.

Quote:

Quartz: I know that a lot of halogen lights have bulbs made out of quartz, but does that apply to all? I'm asking as a halogen bulb is $2 vs $8 test tube.

The patent: can I use tugnsten instead of tantalum? In the patent it's mentioned that a tantalum-tungsten alloy works, but pure tungsten sustrate is not mentioned. I have tungsten but not tantalum of the shape I need.

Temperature control: I've only got a propane torch. I can measureave the temperature with an S or R thermocouple I have, but for building a mini-kiln, is it OK to use concrete bricks? Someone told me that concrete can explode if heated to a very high temperature, which sounded like BS to me but I'd better ask here to make sure it's safe (I don't have any other bricks).


-The quartz tube would need to be clean either way.
-please link the patent for us lazy people
-you plan to diffuse Pt to pure tungsten with a propane torch?
-the concrete exploding is not BS. PV=nRT. the moisture trapped inside while being made will expand, fracturing the concrete. It wont actualy explode, but it will pop apart. you can remedy this by replacing the aggregate with a something else that maybe acts like a refractory as well. Like pearlite(not the Fe :) or virmiculite. it should have enough holes in it to breath and dry out when fired.
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[*] posted on 26-6-2005 at 16:23


Halogen bulbs have no mercury. They have halogen gas that redeposits evaporated tungsten back onto the filament, extending life. So the only impurity on the quartz glass would be tungsten.

The plumbing propane torch I have is labeled 1371*C. The patent calls from between 1050*C to 1150*C.

The patent can be downloaded as a PDF from http://free.patentfetcher.com/Patent-Fetcher.php?submit=Fetc...




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[*] posted on 26-6-2005 at 17:05


Torches don't have temperature except in marketing, BTW. One of those jet cig lighters does "white heat" but damned if you can burn your finger (>160F) with it! You just need power. A 1/2" (pipe; use a 0.02" orifice) burner will do that temperature inside a 6" cube, given reasonable refractory (cement block will not work, it crumbles at that temperature). Then do it slowly, over a period of an hour or three, plus as long as the diffusion takes, to keep the temperature stable.

You can also eyeball it with pyrometric cones.

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[*] posted on 26-6-2005 at 21:12


hah. The patent said 10w/percent tungsten alloy with the balance Ta.

10 w/percent W is about 8.7% of the volume in that alloy. you are talking about using just tungsten... which has way different properties. You need to get the W Pt phase diagram to see what temp is good for diffusion.
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[*] posted on 26-6-2005 at 21:38


http://www.platinummetalsreview.com/jmpgm/data/datasheet.do?...

If that doesn't work, http://www.platinummetalsreview.com/jmpgm/index.jsp | phase diagrams on sidebar.

As for Pt-Ta, I have it (far more intermetallics than Pt-W), in FactSage format, I forget where I downloaded it all from though (viewer and some 456 phase diagrams :D).

Tim




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[*] posted on 27-6-2005 at 03:05


12AX7, please post here the Ta-Pt and W-Pt diagrams from your source for comparison. I do have Ta, but it's the wrong shape and not enough volume to hammer into the right shapes.

According to the last comment in http://www.finishing.com/2800-2999/2819.shtml gold diffuses into tungsten at a mere 400*C. But the Na2S2O8 pretreatment mentioned, I don't have any of that. I see it's used for PCB etching, but as I didn't see it in the local electronics store, is there any synthesis procedure? I don't see one on the board or web search.

[Edited on 27-6-2005 by Quince]




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[*] posted on 27-6-2005 at 03:41
A cheap sorce of Argon gas.


Quote:
Originally posted by 12AX7
Look in your phone book for welding supplies. Go to the place (note the lack of my adding an "if there is a place", it WILL be there) and ask for a cylinder of argon. It gets cheaper in bulk but you have a larger cost to put down, obviously. I'm guessing a typical expense of between $20-50 for a refill to $200 for a new tank.

Tim


These Argon gas cylinders my allso be bought cheaply as disposible cylinders for about 15 Euro
(~ $19). This Argon gas, is however only pressurised, in exactly the same gas cylinders that I had discribed for CO2.

CO2 gas-cylinder as SO2 container.

Posted on 23-6-2005 by Lambda.
http://www.sciencemadness.org/talk/viewthread.php?tid=4061
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[*] posted on 27-6-2005 at 12:55


I don't see disposable tanks around here. The cheapest thing I've found is this http://www.coolstuffcheap.com/extra-gas-cartridges.html



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[*] posted on 27-6-2005 at 13:07
Disposable Argon gas cylinders


Come to Holland, you will like it here !

Disposable Argon gas cylinders:
(this is what I mean)

http://www.justoffbase.co.uk/s.nl/sc.9/category.748/.f

[Edited on 27-6-2005 by Lambda]
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[*] posted on 27-6-2005 at 14:37


I've been there. I couldn't manage to spend more than a few days in Amsterdam before the stench of marijuana drove me to hop back on the train out of there (and how about putting some brooms to the streets!). The TGV's 300 km/h couldn't carry me away fast enough... And what's with prices in Schiphol airport, you guys sure like to rip off foreign visistors! The pretty women are this place's only redeeming factor (note to Euro-bound Americans: unlike in North America, a fairly direct approach is recommended with European women; as many other things, this can be blamed on the malignant effect of Freud's nonsense on US society, and for any Euro people coming to North America, I recommend reading "Freudian Fraud" as preparation).

There now, I think I've managed nicely to offend everyone
Cheers :P

[Edited on 27-6-2005 by Quince]




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