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Tacho
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The AgS dark coating does not seem conductive. If this H2S thing works at all, certainly is NOT spetacular! Maybe I’ll do some further tests. Maybe
not.
Solutions of AgNO3 and/or CuSO4 mixed with hydroquinone and ammonia, give a thick black solution. and some fine, slow-depositing precipitate. I
believe the black liquid (actually dark brown) is colloidal metal, and the precipitate is fine metal powder.
I could not make wood or paper conductive after many layers of that black liquid, but I have hope on the precipitate.
Why didn’t I stick to the hydroquinone/AgNO3/water/ethanol/(light?) clean silver precipitate? Because the I had the black liquid by accident,
decided to research it before I go back to that silver. Besides, a good conductive copper powder would be much cheaper and readily available.
About hydroquinone: I use it because I have a lot of it. Probably other reducers can be used. In fact, I should try Kodak D-76 developer. It has
about 5% hydroquinone in it, and is internationally available under the same D-76 denomination.
I’ll be traveling for a couple days, and won’t be able to continue my tests.
Cyrus,
Yes, I believe drying and mixing with non-polar solvents would work, if the powder don’t cake too badly, but I’ll try other options first.
Would the oxalate thing work wet? I mean, boil the water solution and silver precipitates as CO2 bubbles away? Sorry, I don’t have time to research
now.
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Cyrus
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-From this webaddress
http://64.233.167.104/search?q=cache:ipsKj2uCrqwJ:www.intox.org/databank/documents/chemical/oxalicac/cie358.htm+decomposition+of+silver+oxalate&hl
=en&ie=UTF-8
-I got (for oxalic acid)
Melting Point: 101.5 deg C (215 deg F) (dihydrate); 187 deg C (369 deg F) (anhydrous) melts and decomposes; sublimation begins at 100 deg C.
Boiling Point: Range 149-160 deg C (300-320 deg F) (dihydrate); sublimes with partial decomposition.
-And the following-
Incompatibility - Materials to Avoid:
BASES - vigorous reaction may occur, yielding heat and pressure
OXIDIZING AGENTS (eg. sodium chlorite, sodium hypochlorite) - may react violently or explosively
SILVER - May form explosive silver oxalate.
-so no, I doubt it will work in soln.
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Tacho
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I am trying to get a surface resistance smaller than a few dozen ohms/mm.
My failures:
I could not make a conductive paint using silver or copper precipitates. The strips of paper or woodsticks painted with this precipitates (with or
without binders) result in very high surface resistance in the best cases. Hundreds of kOhms/mm.
H2S makes a paper treated with AgNO3 (exposed to sunlight, in case it makes any difference) turn from brown to black in an impressive way. But the
resistance of the surface is the same hundreds of kOhms/mm. Graphite powder rubbed on the surface does the same and is not a deadly poison.
Strips of paper soaked with AgNO3+gelatin, exposed to sunlight and “developed” using hydroquinone or Kodak developer show no impressive results.
This is pure madscience: tin heated to orange-hot on a Ni-Cr wire does not deposit in a near graphite electrode even if I make a 15kV discharge
between the two. Yes, I did that.  Please, don’t mention vacuum, I know, I
know.
My hope:
Silver halides. I hope to cover a surface with silver halide somehow and expose it to sunlight. My idea is to make a gelatin with AgNO3 and, after
dry, expose it to sodium bromide. Or the other way around. If anybody knows a solvent for a silver halide, let me know.
I remember seeing some b&w photos with silvery spots in the blacks due to, I presume, bad fixing bath. If I can fix the halide badly enough, maybe
it will be conductive.
I have an idea about electroforming a retort:
Cover a paraffin mold with very thin aluminum foil (they used to have those in some candies, haven’t seem them recently) , electroplate it quickly,
melt the paraffin, dissolve the al away with NaOH.
This may be tricky, since al may react with the electroplating bath. It sure reacts with CuSO4, but if you are quick... Or use a thicker al foil...
I may try this in the near future.
[Edited on 27-5-2004 by Tacho]
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Cyrus
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I don't see the problem with high resistance coatings- as soon as you start plating it shouldn't be a problem
The real goal in my opinion is adhesion of the layers (for my application) - graphite powder rubbed on may have the same electrical resistance, but it
doesnt have much adhesion. Which is a good thing for electroforming though.
I like your high tech method of tin sputtering. I was thinking about using the
Al metal vaporized by sparks from a large battery to make mirrors though.
Maybe if you put it in helium...
IIRC, to electroplate on Al, you need to first zincate it- dip the Al piece in a bath with Zn2+ and NaOH. Then electroplate onto the relatively
smooth Zn coat.
Here's a random idea- to make a copper test tube fill a glass one with copper oxide and strongly heat, then dissolve the glass in NaOH.
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axehandle
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| Quote: |
I don't see the problem with high resistance coatings- as soon as you start plating it shouldn't be a problem
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It's actually very difficult when you come to the inevitable endpoint: plating Ti with Pt. If anyone could give me pointers, I'd be
eternally grateful -- I want to plate a big Ti plate with Pt using nothing but water, HCl and hexachloroplatinic acid.
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BromicAcid
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How about a low melting alloy, most take advantage of gallium, one, the gallium-indium-tin melts at 10C, just keep your electolyte solution lower then
this and it should stay solid and conduct, afterward you could easily melt it out. But gallium and indium tend to contribute to the high prices which
make this unreasonable. How about something like Wood's metal, it has a Mp of 70C but that is a little high to put it over something like wax.
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axehandle
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| Quote: |
How about a low melting alloy, most take advantage of gallium, one, the gallium-indium-tin melts at 10C, just keep your electolyte solution lower then
this and it should stay solid and conduct, afterward you could easily melt it out. But gallium and indium tend to contribute to the high prices which
make this unreasonable. How about something like Wood's metal, it has a Mp of 70C but that is a little high to put it over something like wax.
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Makes sense, but as I've understood it, electroplating Ti with Pt is VERY difficult (since Ti passivizes in almost any atmosphere), and I've
found little to no info about it  .
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Tacho
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Cyrus,
My experience with plating high resistance surfaces is that the metal deposits in the contact with “wire” and keeps depositing there because its
the path of least resistance. Literally.
Industry circumvents that somehow. That’s why I used a mesh of thin copper wire backing my styrene-graphite mold, all insulated with a layer of pure
plastic goo.
People say metal sputtering can be done with a lower vacuum, but what do they call a lower vacuum? Compared to what? Sam Barros at the Powerlabs page
claims he made a sort of plasma ball using a refrigerator pump. Would that be enough? If I get obsessed enough with this, I may try.
http://www.powerlabs.org/plasmaglobe.htm
Thanks for the Zn tip. Do you think a dip in a ZnCl solution would do the trick?
Hey everybody! This is a good idea here!
Sorry, Cyrus, but I didn’t understand the copper tube thing.
Sorry axehandle, but I’ve never seen a piece of pure Ti or Pt in my life (only your pictures) and I can barely plate copper. Can’t help you.
Bromic Acid,
Why not tin? Most low melting point alloys are expensive or have cadmium. Or both. Tin melts pretty easy under a blowtorch or in an oven. I once
bought relatively pure tin in a welders supply.
Common solder has lead, but what the hell, just be carefull, recicle and don't use the kitchen oven.
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Cyrus
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I think you will need NaOH too, IIRC it exposes the Al metal so that the reaction can take place.
The copper idea is a little wierd I admit, but because 2CuO-> 2Cu + O2
I was thinking that if you heated CuO in a test tube it might deposit Cu in a film, but it would pobably be a powder.
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Tacho
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I made six gels, using gelatin, agar and alginate. three with AgNO3, three with NaBr. Only agar became a really solid gel. I wetted the NaBr gels and
goos with AgNO3 and vice-versa. Exposed to sunlight to dryness, tested for conductance, “developed” with Kodak photograph developer, dried, and
tested again. All failed.
Thin aluminum foil is corroded away in my attempts to plate it with copper. I tried to do the ZnCl/NaOH thing with no good results. By the way, ZnCl
reacts with NaOH making a white insoluble, so you have to wash the Al between baths.
Failures, failures, failures...
However,
My crude attempts to plate Sn with copper were not fruitless. No, I could not make anything impressive, but the copper was there. Irregularly
distributed on the surface, like oil and water paints mixed, but was plated. A black powder (?) formed where copper was not deposited.
I believe is a matter of preparing the surface of tin. Some acid dipping, maybe. Or the proper alloy...
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chemoleo
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Bromic: there are certain waxes that have a much higher MP than 70 deg C. Any modelling shop will have them.
Most likely they will have Woods metal too.
Tacho: Sorry I didnt have time to reread the whole thread - but how about Cu plating on iron? Have done that many times, works well. A CuSO4 solution
suffices
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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IvX
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Sort of off topic perhaps but for the Ti thing the new(ish) procces for Ti manufacture from TiO2 is electrlysing it out of molten CaCl.
I tried this once(ages ago) but I had to cut the experiment short(external circumstances).The Ti formed a small mass around the copper mesh and had
small buble like hollows in it.
Perhaps you coukld try something like that to make the basic structure, sand it down ,and the electroplate?
Ps.
A factory made Ti ring costs about 50 bucks :p
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Tacho
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| Quote: | Originally posted by chemoleo
(snip)
Tacho: Sorry I didnt have time to reread the whole thread - but how about Cu plating on iron? Have done that many times, works well. A CuSO4 solution
suffices |
The idea here is to plate on a conductive mold that can be easily made and removed (washed, dissolved or molten).
You gave me an Idea! Fe or Zn powder in agar matrix. Expose it to CuSO4 solution, copper cristals grow and touch each other making the whole thing
conductive. Better yet: copper powder and silver solution.
I'll try it and post.
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Tacho
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Who told me how to use FTP right? Organikum!
Who gave me good information on yeast reactions (and booze as a bonus)? Organikum!
Who is always there with good answers and a helping hand? Organikum!
Who told me to use zinc spray to get a conductive coat? Organikum!
Did I listen? NO! Did I say thank you? NO! Why? Has to be that damn mercury poisoning!
Bad Tacho! Bad Tacho!
What did I get when I stained my fingers with silver nitrate and poisoned my body with ominous chemicals? NOTHING!
What did I get when I followed Organikum's advice and sprayed a zinc “cold galvanizing” paint on my mold?
Well, we have to slow down here...
The zinc spray sold here as “cold galvanizing” (they claim "over 95% zinc powder" does not make a conductive coat by itself (I can't understand why), but makes a surface that gets coated with
copper if dipped in a strong copper sulfate solution. It’s by far my best result until now. Just a few dozen ohms per centimeter in my first
attempts! I’m sure it can be improved vastly.
I have never seen nothing like this procedure described anywhere, so I guess Mad Science is, again, in the cutting edge of kitchen chemistry!
Whip me Orgy! Whip me hard!
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Organikum
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Someones calling me?
Uuups here I am!
The zinc spray makes no conductive coating at once as the zinc particles are covered with a very thin layer of epoxide or such for adhesion reasons.
The copper sulfate etches this away and so it works.
But meanwhile I found something whats probably better:
Dipping the mold into a solution of SnCl2 should form a conductive layer on plastic and even glass - an transparent layer too. This can be electroless
or electrolytically plated (a thin layer of copper deposited from the sulfate might be advantageous - its to be tried).
SnCl2 is the way it is done in industry - it replaces the rather expensive treatment with Pd-salts which was used before.
Thanks for the flowers 
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Tacho
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| Quote: | Originally posted by Organikum
Uuups here I am!
The zinc spray makes no conductive coating at once as the zinc particles are covered with a very thin layer of epoxide or such for adhesion reasons.
The copper sulfate etches this away and so it works.
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Interesting, I just worshiped you and now I totally disagree with you! I think the zinc is partially exposed and is displaced by the copper as it
happens when you dip iron in copper sulfate. It just grows in fractal crystals, touching each other and making the whole thing conductive.
| Quote: |
But meanwhile I found something whats probably better:
Dipping the mold into a solution of SnCl2 should form a conductive layer on plastic and even glass - an transparent layer too. This can be electroless
or electrolytically plated (a thin layer of copper deposited from the sulfate might be advantageous - its to be tried).
SnCl2 is the way it is done in industry - it replaces the rather expensive treatment with Pd-salts which was used before.
Thanks for the flowers |
Eeeeh! Disagree again... The tin or palladium bath is used to create some sort of nucleating points for electroless deposition (maybe electrolytic
too) but doesn't make the surface conductive.
(remark sniped by edit)
[Edited on 10-6-2004 by Tacho]
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Organikum
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Ehem.
If you use zinc-spray of higher concentration it will be conductive - mine was.
Of course the copper replaces partly the zinc and if you let it in the bath very long it will be displaced almost completely - not absolute completely
as the copper grows on the zinc and protects it in parts. Called "zinc promoted copper".
Oh, that SnCl2 doesnt produce conducting tranparent surfaces on glass and plastics this is not only new to me but also to the Kirk-Othmer and a whole
industry producing products by this method.
You are right, there exists the method of forming nucleating points with Pd and tin salts. And there exists the method for forming conducting layers.
One doesnt exclude the other, actually the first is necessary for the other to work.
I believe we have to train this "worshipping" a little bit better, I am NOT REALLY SATISFIED! 
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Tacho
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Sorry mighty Organikum. Once again you showed me the path and once again I went in the wrong direction.
I'm still uncomfortable with the SnCl2 idea though.
I guess HCl+H2O2+tin will make me some SnCl2.
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Polverone
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Skip the H2O2 if you want SnCl2. I've found that aqueous HCl attacks at least high-tin alloys (lead free solder) at a reasonable pace. Does it
not do the same for your tin?
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Organikum
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| Quote: |
Skip the H2O2 if you want SnCl2. I've found that aqueous HCl attacks at least high-tin alloys (lead free solder) at a reasonable pace.
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As long the alloys contain some copper thats true.
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Cyrus
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Zinc paint is great so long as you don't care about adhesion. I've tried
and the immersion plating that results doesn't adhere. Oh well, thats my problem, not yours. Just finished finals, the experimenting level is
getting kicked up a couple notches.
I don't get the SnCl2 method- could some one explain it to me. SnCl2 is a good reducing agent, but what is it going to do to glass? It is
depositing tin? Is the reaction something like 2SnCl2 --> Sn + SnCl4. Sorry, this is a completely random guess. And if it doesn't form
conductive coatings/nucleating points withoud Pd, why are we even trying?
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Tacho
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A paste of zinc powder mixed with gypsum, after hard, also develops a conductive copper layer when dipped in CuSO4 solution. The surface is not very
smooth though. I’m waiting for samples made with zinc powder and sodium silicate to dry. My quest now is for a smooth very
conductive surface. I’m thinking of making zinc pastes with shellac, gelatin, agar, alginate, ceramic etc. And try other copper salts, specially
acetate, in various solvents.
“Cold galvanizing” zinc spray is, after all, a bit conductive, but in the same range as graphite powder or silver sulfide. Too high a resistance
for me.
I have pure tin, and could only make the salt electrolytically. HCl did not react even with H2O2. At least not fast enough. None of the tests I made
showed a hint of low resistance neither on glass nor plastics nor organic substrates.
Cyrus,
As I understand it, you are trying to make something like a sphere (almost) with a diameter of 47cm of... say... fiberglass, make it conductive,
electroplate the outside of it with copper and then with silver?
Ok, I’ll risk to sound like an idiot trying to teach someone who may know more than I, but here I have some observations connected to this idea:
1) the final surface has to be mirror polished to achieve higher voltages, right? Any grain on the surface and there goes the electrons into the air.
Well, every deposit I have seen until now (in my tests) is far from smooth.
2) the surface does not have to be very conductive, does it? I mean, only very, very low currents are involved, so charges will built even in a
polished graphite paint, won’t they? I really don’t know the dynamics of holding charges in a Van der Graff.
3) you will need a HUGE bath to plate this thing. Isn’t this a problem?
4) why are you so concerned about adhesion? If you have a metal layer on the fiberglass(?) substrate, who cares if it is very adherent or just hanging
there?
[Edited on 11-6-2004 by Tacho]
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Cyrus
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Yes, the surface needs to be EXTREMELY smooth otherwise all the charge dissapears- not even a dust grain.
That is why I have to sand the bondo (pretty close to fiberglass) layer for so long! And then put the conductive "paint" on top and make
sure that is perfectly smooth. And then the perfectly smooth copper plate. (which is why only BRIGHT copper works) And then the perfectly smooth
immersion plate of silver.
Nothing too hard, might take a couple of minutes or so.
I could have covered the whole thing in aluminum tape, but I am more than somewhat of a perfectionist.
I am obsessive about adhesion because the people at pupman.com have had problems with coatings flaking off of their toroids. (for tesla coils) But if
no other options are found, I might have to go with the zinc paint.
Thankfully, I don't have to use a 500 gallon plating bath! There is a method called brush plating- connect one wire to your object to be plated,
connect the other to a corrosion resistant brush- for copper plating it could be a copper brush with some chem. resistant fibers, dip the brush in the
plating solution, and paint and plate away, very useful for in situ. and large object plating.
Edit- just saw your question about how much conductivity even matters to a VDG.
The main reason is that when the lightning discharges from one point on the sphere, all the electricity has to race over the surface to that point,
and the less conductive the surface is, the smaller the discharges are.
Also, if the coating is too thin, ie gold foil or thin layers of graphite, the discharge tends to vaporize and burn holes in the conductive layer.
Here are some random things-
If I coat the sphere with a nickel plate, some sites say that during the discharge nickel carbonyl will form. Ahh, Healthy. 
Does anyone have info on this? It might be a way to make the useful but very toxic and flammable/explosive compound.
I love pottery stores! 227 g BaCO3, 227 g MnO2, 183 g Fe3O4, about 1L of fluffy MgCO3, and 30 g CrO3 (chrome plating), all for $4.53!
[Edited on 11-6-2004 by Cyrus]
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Nixie
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| Quote: | Originally posted by Cyrus
I've got a formula on this too.
1 oz/gal AgNO3
14 oz/gal Na2S2O3
10 oz/gal NH3 (Is it household strength ammonia or pure ammonia?!- probably household. Elsewhere you are supposed to add enough to make the silver
precipitate Ag2S2O3? that forms dissolve.) |
I'm interested in electroless silver plating for copper tracks on printet circuit boards, and would like to avoid buying a commercial solution. My
question regarding your recipe is where to get the Na2S2O3, or whether there's an easy to obtain or prepare substitute.
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Tacho
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Add a solution of table salt to a solution of AgNO3 and you have a white silver chloride precipitate.
Silver chloride powder, mixed with some table salt and a binder like kaolin can be used to plate copper. Just rub strongly the humid (almost dry)
powder on the clean copper surface and it takes a silver covering. You must rub strongly to obtain a shiny, resistant silver coating.
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