Baphomet
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PVD at home
Hi guys
I am embarking on another out-there attempt at recreating hitech at home. This time it is Physical Vapour Deposition - which would be rather neat to
try out as I know someone who uses the equipment at work for plating, and they said it is great.
What I have envisaged so far is a small crucible at the bottom of a cone-shaped container used to direct the particles. No vacuum at this stage but
who knows, maybe later.
The crucible would have two graphite electrodes separated by a spark gap for the generation of heat to vapourise the feedstock.
The base of the crucible has another cathode (launch cathode) on a different circuit, and maybe 10 - 15cms away is a plate that is the
opposite anode for that circuit - this is what attracts the particles to the target.
Now already I have a lot of questions:
- Is a transformer sufficient for the circuit separation? Last thing I want is for arcing between heating anode and the launch cathode!
- Perhaps a special design is required to prevent arcing within the transformer itself?
- I'm assuming that at least rudimentary results will be achievable, or is vacuum a neccessity for some reason?
- Is terra cotta a suitable refractory material or am I living in dreamland?
If you have answers or any ideas please chime in as I am all ears. Thanks!
\"Who ARE you? You\'re like the drummer from REO Speedwagon - nobody knows who you are\" from \'Employee of the Month\'
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Twospoons
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What do you want to deposit?
Instead of a crucible and arc electrodes you could use a tungsten or tantalum boat : http://www.tungsten.com/mtsprod.html which is heated simply by passing a current through it. Good for low boiling materials like Al.
If you don't run under vacuum you run into three problems: reaction of your coating material with air; rapid condensation of your vapor due to
conduction cooling; and very short mean free path for the vapor molecules which will make coating larger areas very difficult.
Pulling even a poor vacuum will improve your chances considerably. Refrigeration service pump go down to a few millitorr, are not that expensive,
and would be a good starting point for this exercise.
[Edited on 13-5-2008 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
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Baphomet
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Good idea! I like it since the crucible could fit in a vac chamber and it is electrically conductive too
Do we really need to boil the material? I think hight heat is enough is it not? I am depositing random metals at the start (iron, copper, zinc etc.
though I will try aluminium first)
Now I just need to figure out how to get the power cables into the vac unit 
Or... helium filled chamber instead?
Thanks for your help.
\"Who ARE you? You\'re like the drummer from REO Speedwagon - nobody knows who you are\" from \'Employee of the Month\'
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not_important
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What Twospoons said. Reducing the pressure also increases the boil-off rate at a given temperature.
For some evaporated coating you need to clean the surface in an inert gas, or even under vacuum.
Terra-cotta is pretty low melting, someone I know used it as the basis for a glaze. Typical firing temperatures for common ceramics are:
terra-cotta - cone 06 to 2
Stoneware - cone 6 to 10
Porcelain - cone 7 to 12
High mullite ceramics - cone 8 to 14
and to turn cone numbers into degrees
http://www.bigceramicstore.com/Information/ConeChart.html
cones are not precise, fixed temperature points; they react to the firing environment in the same way the ceramic body does. Rate of temperature
change and gases in the kiln atmosphere affect when a ceramic will be properly fired, not some exact temperature reading.
| Quote: | | Do we really need to boil the material? I think hight heat is enough is it not? I am depositing random metals at the start (iron, copper, zinc etc.
though I will try aluminium first) |
You need the material being evaporated to have a high enough vapour pressure to give reasonable transfer rates. For some materials this means
boiling, although ay a low pressure. You have to get enough energy into the target to kick loose atoms or molecules ofit; heat, energetic electrons,
plasmas, are all ways to do this.
[Edited on 13-5-2008 by not_important]
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12AX7
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Maybe your first exploration should start with CuO + Al. Packed tightly, I've seen this thermite mixture burn smoothy like a fountain, producing a
spray of copper vapor. I once found a metallized acorn after burning a charge...
Tim
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Twospoons
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| Quote: | Originally posted by Baphomet
Now I just need to figure out how to get the power cables into the vac unit
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Sparkplugs. They are cheap, pressure / vacuum tight, have a nice insulator section for HV, come with a standard threaded end to screw into your
equipment.
Helicopter: "helico" -> spiral, "pter" -> with wings
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kilowatt
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| Quote: |
Is terra cotta a suitable refractory material or am I living in dreamland? |
Maybe; people have done some surprising things with flower pot crucibles (like cast iron), but much better alumina and zirconia crucibles are
available on the internet from several companies, just do a google search and shop around. I got a 500mL alumina crucible for about $50 and a 50mL
zirconia one from $40. They are really worth the money especially for something like this, but you have to be careful with materials that can reduce
or dissolve them. Graphite crucibles (which are quite cheap and might be a good place to start) and tungsten crucibles are available too, or you
could make your own graphite crucible from a solid piece. Keep in mind that graphite is fairly volatile at over 2000°C especially in a vacuum, and
both it and tungsten can easily burn away in air at such temperatures. There are refractory coatings like ITC-213 that can protect graphite or metal
parts from oxidation, but the composition is proprietary.
The mind cannot decide the truth; it can only find the truth.
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tentacles
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Tungsten and tantalum boats aren't too expensive on ebay, do some searches..
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Texium
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Thread Moved
19-11-2023 at 12:28 |
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