Fusor Forums

Hi all,

Some preliminary experiments with yttria coating on tungsten:

The result on the picture uses:
a) an yttria colloid (10nm particles, water + acetic acid)
b) a graphite anode (so we don't get any metallic contamination in the colloid, just Kolbe electrolysis)
c) a 2% duty cycle -150V, 5A electrophoresis signal for about 300 seconds

We didn't do any sintering yet, but the layer doesn't fall off easily, so that's good, we will do some sintering en emission tests soon.

We do see one problem, the yttria layer is not smooth, this is because of the H2 bubbles forming during the process.

So, next we will try introducing more movement en vibration during the process, we tried with a pager motor, but that wasn't enough.

Question 1:
Does anyone here know a surfactant which would loosen the H2 bubbles from the cathode?

Question 2:
We are using tungsten now, but would anyone here know a good source of iridium or rhenium wire/ribbon?

Could you try a slight vacuum to enlarge the bubbles so that more buoyant force results?

Hi Jeroen

For wires check http://www.sisweb.com/

What about depositing a Y carbonate, decomposing it later under vacuum, as the classical procedure for coating oxide cathodes?

Regards

Roberto

Oh, I would be interested in knowing how you did the yttrium coating. My RGA uses yttria coated filaments and they are incredibly expensive.

Dennis: I think vacuum would just make more bubbles.

Roberto: thanks, I did know sisweb is selling it, but they don't have any prices on their site, bit afraid of the "request pricing", but I will ask them.

Jerry: the basic procedure is in this post, we don have more for now. But as soon as we have "proven endurance and emission" I will post a more detailed version.
Attached is a picture of our setup. (very simple, mosfet switch, 150V, grafite anode).
We used this water based colloid: http://www.nyacol.com/products/yttrium/

Jeroen
SIS domestic prices are approx 100 dollars for 10 feet W/Re (0.0132").
But international requests may be charged double than the domestic price.

Roberto, W/Re is indeed not that expensive usually.

But (as far as I understand), I would need pure rhenium wire.
The "enemy" is the tungsten-water cycle. Does tungsten-rhenium also suffer from this problem?

This shows teh emission of yttria coated pure rhenium:
http://www.sisweb.com/referenc/applnote/app-92.htm

Jeroen

This paper states that rhenium resists well the water cycle.

Gordon B. Gaines,
Chester T. Sims,
and Robert I. Jaffee

The Behavior of Rhenium in Electron Tube Environments

J. Electrochem. Soc. 1959 106(10): 881-885.

Even tungsten COATED with rhenium.

Roberto,

thank you, that was exactly what I was looking for, I was thinking about electroplating tungsten with rhenium. Just don't know how yet...

Jeroen

Think this will help you:

Electrodeposition of rhenium on tungsten hot plate used in Q plasma source
P. J. Paris
Citation: Review of Scientific Instruments 60, 2802 (1989); doi: 10.1063/1.1140664

How much did the Nyacol yttria colloid cost you?

I see an unanswered question in the OP that I may field.

I have used surfactants in electrolysis before, and in one case it was precisely for this reason (prevent gas bubble adhesion to avoid pitting).

It was a different application though so take this with a grain of salt.

I used Triton X-100, a nonionic surfactant, at 0.5% concentration. It gave reasonable results. The application was coating of a graphite anode with a layer of lead dioxide. The electrolysis conditions were vastly different (DC 4V, about 800mA for ~20min). The Triton degrades slowly over these conditions so its surfactant properties decrease over time but it should be good enough for runs of up to 1h. I don't know how it would fare under your conditions though.

Another method that I used to deal with bubbles in this particular system was centrifugal force. Essentially the piece to be coated is spun during electrolysis by a small electric motor. I used a 6V 20000rpm motor that I undervolted to 1.5V; this combined with the inertia of the piece+connecting shaft and the friction with the electrolyte resulted in a rotation speed of about 300rpm. That is enough to knock off bubbles as they form. Caution if you use surfactant at the same time as it can lead to a significant amount of foaming.

(edit) Here's a short video that I made during that process.
https://www.dropbox.com/s/lpuqob9fl9ruj ... t.mp4?dl=0

Ian,

I ordered a sample of the yttria colloid.
It was for free.