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Re: nitrile rubber rings, or?
James Lerch
Dominic,
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Nitrile appears to be the same thing as Buna-N, which is what I use for my main chamber seals. so Yea, I'd say they will work. If it helps, the o-rings for my electrical pass troughs were found at the plumbing store, and originally used to repair water faucets (btw, my latest chamber vent valve is a simple brass garden hose bib faucet with whatever they used for a rubber seal) Of course there is always a difference between "what's best" and "what works", I tend to go with things that work, even if they are not the best :) So far I've only found two things that I couldn't pull a good vacuum on. #1 Wet painted wood #2 Petroleum jelly based ointment that found itself onto my filaments (which held a good vacuum until the heat was applied) Take Care, James Lerch (My telescope construction,testing, and coating site) "Anything that can happen, will happen" -Stephen Pollock from: "Particle Physics for Non-Physicists: A Tour of the Microcosmos" ----- Original Message -----
From: "Dominic-Luc Webb" <dlwebb@...> To: "VacuumX mailing list" <VacuumX@...> Sent: Tuesday, December 16, 2003 13:22 Subject: [VacuumX] nitrile rubber rings, or?
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nitrile rubber rings, or?
On the continuing saga of the electrode-through-chamber story...
I now secured some green TIG welding rods and see that this is the material for my first aluminizing attempt. For feed-throughs I plan to use glass as insulator with a hole drilled through it for a conductive rod to pass through, using o-rings to seal the vacuum. There is a decent assortment of sizes, but I have no idea about best material. The shops here have nitrile rubber. Is this OK material, or someone know this will not work (outgassing, etc)? Dominic-Luc Webb |
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Re: aluminizing chamber electrodes queery
On Mon, 8 Dec 2003, Gomez wrote:
Not knowing welding, are all TIG electrodes tungsten, or shouldSo far as I know, they are all Tungsten. Some are alloyed with a OK, I looked around on the Net and did some quick learning about TIG electrodes. As one member already suggested, green does appear the best choice, being essentially pure tungsten (99.97%). This type has letter symbol designations such W, WP, YWP and EWP, but all are color coded green. Other types have small traces of La, Th, Zr or Ce and have their respective character designations indicate the added metal, like EWCe or EWLa, etc. Even these are 97-99.3 tungsten. Interestingly, while TIG electrodes seem to be more expensive over here in Sweden (5 USD each), they are a lot longer, typically 300 mm, about 12" US units. Here is the link to a place that has a decent-looking table of codes and compositions for TIG electrodes: Dominic-Luc Webb |
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Re: aluminizing chamber electrodes queery
Hello All,
? In my experince of vacuum coating, we should use tungsten filament for evaporating the aluminum.
Ismail
Darald Bantel wrote: Greetings Do you Yahoo!? |
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Re: aluminizing chamber electrodes queery
¿ªÔÆÌåÓýYou may recheck your Kanthal catalog as nichrome may be good for 1450 F as compared to C. A cigarette lighter will vaporize the aluminum but then you will alloy the aluminum with the nichrome and decrease it's life as a heating element considerably.. A relatively cheap source of tungsten is an electrode for a TIG welder (TIG...Tungsten Inert Gas ) it is a very stiff wire about 6" long of various diameters under 1/8". A beer can which is 99.9% Al. bent over the tungsten will vaporize enough Al. to coat most mirrors.
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Bill Lang |
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Re: aluminizing chamber electrodes queery
Gomez
On Monday, December 8, 2003, at 11:29 AM, Dominic-Luc Webb wrote:
On Mon, 8 Dec 2003, Gomez wrote:So far as I know, they are all Tungsten. Some are alloyed with a small amount of Thorium, which makes the arc easier to start. I assume we don't want that.Try TIG welding electrodes. |
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Re: aluminizing chamber electrodes queery
James Lerch
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From: "arcstarter" <arcstarter@...> Last time I bought abox of 0.020 inch rods price was about $12 forThe bulk wire is just as brittle has the Tig electrodes :0 I still find it pretty amazing that a material with such a high melting point, has a Brittle to Ductile transition temperature starting as low as 100C. Take Care, James Lerch (My telescope construction,testing, and coating site) "Anything that can happen, will happen" -Stephen Pollock from: "Particle Physics for Non-Physicists: A Tour of the Microcosmos" |
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Re: Electrodes and aluminizing
arcstarter
--- In VacuumX@..., Dominic-Luc Webb <dlwebb@c...> wrote:
actually. I hadI was thinking about car cigarette light in these terms idea to use a nozzle arrangement as an outlet above the heatsource, such that the vapor would be forced to rise upward before encounteringthe nozzle which points downward in my tentative design.As I understand - unless the walls of the nozzle are held at a temperature akin to that of the evaporating aluminum - the aluminum will stick to the nozzle walls and will not make the curve. Most references show line of sight propagation from the molten surface outwards, with no 'reflection' or other flow properties. The atoms stick to the first cold surface they reach. If your pressure is too high the hot freshly evaporated atoms will either react with or lose heat with (via collision) the other gas molecules, and one way or another will not stick to the target. As far as low pressure - the lower the better with 10e-6 Torr being a common goal for evaporation. That's about 1 billionth of atmospheric! -Bill |
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Re: aluminizing chamber electrodes queery
arcstarter
--- In VacuumX@..., Dominic-Luc Webb <dlwebb@c...> wrote:
On Mon, 8 Dec 2003, Gomez wrote:I think that if have decided to wind your own W filaments - youTry TIG welding electrodes. would be better off buying wire from www.smallparts.com as recently posted. Now about welding rods. Your welding supplier will carry all sorts of TIG welding electrodes. Typically the pure tungsten rods will have a green end (paint), and are used for TIG welding aluminum. Other types are 2% thoriated as well as types including other rare earch alloying ingredients. These ingredients increase electron emission during the welding proces, but are probably not wanted for evaporation. Last time I bought abox of 0.020 inch rods price was about $12 for 10 rods. 6 inches long. As someone has pointed out they are brittle unless properly warmed. I would think that bulk wire purchased from smallparts would't have this problem (but I could be wrong). Lesker.com carries all sizes and shapes of pre-spiraled tungsten filaments. -Bill Dominic-Luc Webb |
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Re: aluminizing chamber electrodes queery
Gomez
On Monday, December 8, 2003, at 07:31 AM, Dominic-Luc Webb wrote:
Tungsten is strong for its thickness, but generally is very, veryTry TIG welding electrodes. However, the nichrome and kanthal wiresThe issue is whether one wishes to evaporate pure aluminum, or also evaporate aluminum and some of your heating element with it, contaminating your mirror coating. Tungsten's extremely low vapor pressure even at high temperatures makes this very unlikely. The same cannot be said for Nichrome. I don't know what is in Kanthal and I'm too lazy to Google for it, but I do know you don't want to sputter your mirror with nickel (an ingredient of nichrome). |
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Re: Electrodes and aluminizing
On Mon, 8 Dec 2003, James Lerch wrote:
Perhaps someone knows there is in fact a reason to not use theseSeveral things to consider: I was thinking about car cigarette light in these terms actually. I had idea to use a nozzle arrangement as an outlet above the heat source, such that the vapor would be forced to rise upward before encountering the nozzle which points downward in my tentative design. #2 Chemistry Great! That was the kind of value (821 C) I knew existed somewhere. NiCr has a melting point of 1395C, while at the same time it appears to This sublimation temp is indeed inferior to tungsten. So if your chamber is at 10-6 torr, you'll need to keep the NiCr wire below 987C Exactly! And this might even be highly reflective and less prone to oxidation. Kanthal is another interesting species, its made from FeCrAl, the Al forms anKanthal = Swedish product, so we we hear about it alot up here. There are different grades of this wire. I recall some very high temp versions when I was interested in higher melting point glass and ceramic materials years ago. The "Kanthal D" is likely the most famous (max temp 1300 C), but there is also "Kanthal Super", which has max temp 1700-1800 C. I'll attach the Kanthal Handbook in a private post (to James). BTW, I did find this interesting, Tungsten appears to sublimate at 2407C @ 10-6Immediate thought: If you need such high temperature, there is something seriously wrong with either the temperature reading or the pressure reading or the material you think is (reduced) aluminum. I see no hope for tungsten on the mirror to contribute positively. I am not totally committed on this statement, either. I am suspicious that rate of vaporization could be a factor, in which case your heat excess is an unavoidable consequence of achieving a desirable instant vaporization. To that end, perhaps the lower pressures I am getting, like below 10e-7 could be favorable. Any idea if there is a pressure that is too low (within reason for a diffusion pump)? Dominic-Luc Webb |
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Re: Digest Number 81
Hans Summers
I would think that once proper vacuum has been reached thereTrue enough; I think it's quite likely that the degree of vacuum attained by H P Friedrichs wasn't too high. Friedrichs has used tungsten light bulb filaments in homemade triodes Ohho sounds like I'll have to buy this book!I can confirm it's a great read! Hans |
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Re: Digest Number 81
arcstarter
--- In VacuumX@..., Hans Summers <Hans.Summers@t...>
I would think that once proper vacuum has been reached there won't be enough o2 left to cause any appreciable wear. Seems that for aluminum the classic format is that of the heavy gauge spiral tungsten filament. Aluminum in particular will alloy with the tungsten prior to evaporation. Choice of wire size is somewhat important as if your gauge is too fine the AL will dissolve through the filament and casue it to break. The site www.lesker.com contains TONS of useful vacuum information, including suggested filament materials to be used with target evaporants. The chart at: irements_Boats7.cfm? CFID=218535&CFTOKEN=45377807§ion=tspttboats&init=skip describes the voltage, amperage, power, max temperature relations for their thermal evaporation sources. The old evap I'm resurrecting uses a tungsten 'boat', specifically the EV31A010W model, at: oat_EVS29000_35000.cfm? CFID=218535&CFTOKEN=45377807§ion=tsboats&init=skip You can't beat the price - each boat is $5 or such. Peak temperature is listed at 1800 C. Friedrichs hashis book Instruments of AmplificationOhho sounds like I'll have to buy this book! -Bill |
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Re: Electrodes and aluminizing
James Lerch
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From: "Dominic-Luc Webb" <dlwebb@...> Well, if you want pre-finished ready to go Tungsten, try : Alternativly, I cut and form my own tungsten using bulk 0.032" wire from here: Another easy to scrounge source of Tungsten is from the Tig Welding Industry. (however it only comes in 150mm lengths, and can be somewhat expensive.) If you go with either the bulk Tungsten wire, or Tig Rod, before you try to Cut/Form the wire, you'll need to heat it past the "Ductile to Brittle Transition Tempature" At room temps, Tungsten is surprisingly brittle and any attempts to cut/bend will just snap it like a lead pencil. Fortunatly the ductile transition tempature starts at around 100c, once the wire is above this tempature it will bend / cut easily. I use a 2400watt hot air gun to pre-heat the tungsten before inserting into my filament mold. Perhaps someone knows there is in fact a reason to not use theseSeveral things to consider: #1 Wetting Action If you plan on using a wire filament, if the Al won't wet onto the filament material, it will just melt and fall off, and if the blob of liquid Al lands on a glass surface, it WILL FRACTURE the glass (been there, done that, makes for a VERY BAD DAY!) If your going to use a Boat / Box thermal source, then wetting action isn't important anymore. #2 Chemistry Al is amazingly reactive stuff, even when used with Tungsten, some of the Tungsten will disolve into the molten Al (cause of the wetting action?) As the Al evaporates, the Tungsten is re-deposited back onto the filament. If the filament is too small in diameter (compared to the amount of Al) dissolution of the tungsten into the Al will cause the filament to separate into two pieces, and evaporation quickly stops :-0 I tried using a heating element material used for HVAC (no idea what it was but probably not NiCr) and as soon as I applied power, the filament went "poof" into two rather small pieces. Based on the Al deposition data chart from Lesker's ( ) for a coil /wire thermal source, they only recomend Tungsten, for a boat they recomend Tungsten or Titanium-Boride. If you try NiCr or Kanthal, here are few thinkgs to consider. Al has a melting point of 660C, and a evaporation temp of 821C @ 10-6 torr. NiCr has a melting point of 1395C, while at the same time it appears to sublimate at 987C @ 10-6 torr. So if your chamber is at 10-6 torr, you'll need to keep the NiCr wire below 987C and above 660C, or you will end up with some form of NiCrAl film? Kanthal is another interesting species, its made from FeCrAl, the Al forms an Aluminum oxide which protects the FeCr from oxidation when used as a heating element. No data is listed for Kanthal's melting point or vapor pressure, so who knows what will happen :) BTW, I did find this interesting, Tungsten appears to sublimate at 2407C @ 10-6 torr, and of late, after the Al has evaporated off the Tungsten, I've been running the filament power up untill the Tungsten was white hot (why, no reason other than it's entertaining in an odd way). I mention this as I suddenly wonder if perhaps I might be sublimating a very thin film of Tungsten over the Al coat. If that's a good idea or not, I don't know.... James |
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Electrodes and aluminizing
Note I changed the subject heading to reflect the present topic:
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OK, what I am learning is that other electrode types might be prefered due to increased longevity, as per my original concern and now voiced by others. From the Merck Index: Specific melting/boiling properties of Al are mp 660 C, bp 2327 C. The boiling point is presumably @ 1 atm and, like water, with reduced pressure (i.e., 10e-7 Torr) this drops a great deal. Al normally never goes to vapor, but I suspect this is exactly what one accomplishes by using the vacuum chamber. Perhaps herein is the problem as well. For instance, is the rate of vaporization a matter for concern and does tungsten heat up more quickly than nichrome or kanthal? Dominic-Luc Webb On Mon, 8 Dec 2003, Hans Summers wrote:
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Re: Digest Number 81
Hans Summers
Nichrome is also used in every day household toasters! The average household
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toaster holds two slices of bread. From my reading, it contains about 5m of nichrome wire and the power consumption is about 1 KW (UK mains 240V ac). Note that these ratings are applicable in air. I do not know how this is likely to change in a vaccuum. I suspect the problem with Tungsten might be oxidation. H P Friedrichs has used tungsten light bulb filaments in homemade triodes etc. See his book Instruments of Amplification . He found the lifetime was only of the order of 15 minutes, when he removed the tungsten wire from a light bulb and reused it in his valves. This was extended to a matter of hours when he retained the entire lightbulb assembly i.e. did not handle the tungsten wire. Personally I would like to have a go at making some valves (lack of time at the moment) and am wondering if nichrome would be suitable rather than tungsten, and be much more convenient and easy to obtain. Hans -----Original Message-----
From: gjnelson@... [mailto:gjnelson@...] Sent: 08 December 2003 14:39 To: VacuumX@... Cc: dominic-Luc Webb Subject: Re: [VacuumX] Digest Number 81 According to telescope making volume 3, the filament materials in order of merit are tungsten, tantalum, molybdenum and columbium. Nichrome may also work as Nickel is a possible material. Nichrome may be more easily available if you work in an industry that uses furnaces as it is used for furnace elements . Electrical pass throughs can also be constructed by drilling a hole and then making sure that contact does not touch the sides and use a neoprene or similar insulating material to insulate. Also from telescope making vol3. Geoff ------------------------ Yahoo! Groups Sponsor To unsubscribe from this group, send an email to: VacuumX-unsubscribe@... Your use of Yahoo! Groups is subject to |
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Re: Digest Number 81
According to telescope making volume 3, the filament materials in
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order of merit are tungsten, tantalum, molybdenum and columbium. Nichrome may also work as Nickel is a possible material. Nichrome may be more easily available if you work in an industry that uses furnaces as it is used for furnace elements . Electrical pass throughs can also be constructed by drilling a hole and then making sure that contact does not touch the sides and use a neoprene or similar insulating material to insulate. Also from telescope making vol3. Geoff ------------------------ Yahoo! Groups Sponsor |
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Re: aluminizing chamber electrodes queery
Tungsten is strong for its thickness, but generally is very, very
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thin, as in light bulbs. However, the nichrome and kanthal wires are commonly much thick so are quite strong. Reduced form of aluminum goes to melts at slightly above 500 degrees. It is not clear to me that the temperature ratings you mention are the determining factor in choice. I rather like the strength of highly re-usable things like car cigarette lighters and kanthal wires. Perhaps there are specific tungsten electrodes one would suggest? Perhaps someone knows there is in fact a reason to not use these other options? Dominic-Luc Webb On Mon, 8 Dec 2003, Darald Bantel wrote:
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