Gotcha, saw the same thing looking myself. Tungsten doesn't like air (either main gas) but it
really doesn't like water when hot. Takes the stuff apart, makes hydrogen, the oxide evaporates off the filament, condenses on the walls, gets reduced by the hydrogen there, which then makes water -- rinse and repeat. But, "it's not that bad" if you're reasonably careful and don't try to run this at high pressures.
If Edison had had tungsten wire, he couldn't have used the stuff -- vacuum not good enough (dry) then for things like that. I got a record here of about 20 hours with 1 mil wire as a yellow hot filament with a really good 2 stage vane pump and tight bell jar chamber.
It's worse at higher heats than lower, hence thoria, which reduces the work function a bunch. From what I can tell, yttria (we apply it catephorically, it's easy) does about as well, reducing the temps needed to get emission; the one in there gets low-yellow hot, and at similar temperatures, we got 10 ma off a nominal 6.3v, 2a bulb filament with the coating, but running it at 3v and about half an amp. Hmmm. The one in there, which is a wire in a circle about an 3/4 inch diameter, is running at 2.6v and 3.3 amps now -- and the calculated resistance is going down, as it's regulated for a certain emission (1 ma) and things are cleaning up over the last few hours. It's not having to get as hot as it and the rest clean up. Still a lot more power in than we got off the bulb we used as a test filament -- but it's less compact, so probably radiates more heat per degree above ambient.
Tungsten/rhenium is mentioned in Kohl as being more resistant to the nasty water cycle, and...I've got some, I got at
Nanmac. The rhenium raises the electrical resistance of the tungsten too. They aren't the easiest to deal with -- large minimums, but are nice people -- their gift "calibrated hot sauce" is really good, no kidding.
Type C thermocouples are W/5%Re, and W/26%Re wire. It is very %$&#$% hard to weld, but good stuff once you do. Joe, did I show you my jig for the TIG welder for that? Really works great.
Better than the spot welder I built (the normal one from Harbor freight doesn't work on this stuff unless you want to just weld it to the welder).
Scratches head.
No way I'm going to invest 3 bills in a stock filament for this at the moment. That would kinda ruin the gloat -- this thing cost about the same as shipping and paperwork on the new one I got from Pfeiffer -- and seems about as good, besides. It's not like the Pfeiffer doesn't eat some power -- has a fast computer in it, and needs another for display. Makes a goodly amount of warm air out the vent itself. I kinda dig the green screen...I used to design and build stuff like this when it was the hottest tech there was. It was certainly a great leap forward from the ASR-33 teletypes we were stuck with just before that.
Here's what it looks like now.
- After some running and baking, in analog and 4 decade span mode
I can make it dwell longer and see deeper into the noise if I reduce the scan range. It will go to 15 divs per amu if you want. I think the downward spikes to the baseline are basically some magic nulls you get in this type gear, and that some of the mass one is "zero blast" you also get with quadrupoles. This is just good old gear telling the truth (no faking out the hardware limitations), or so it looks to me.
I haven't calibrated the gains on this yet. My other gage is reading half this thing's total pressure (couple e-6) and they had jacked up the gain to make the peaks read in torr instead of amps, or something like that. But, this stuff tends to be a bit relative, but I'll work on making it hard numbers for fun and giggles anyway. At least I got water on-scale after some hard baking. This is an all viton (many linear inches) sealed system with a tiny (60lps) turbo/drag on it - about the same as the turbo-only I'm also working up a good controller for. Not so bad, considering.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.