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Antwain
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[*] posted on 6-11-2007 at 03:26
Platinum plated titanium


The always present dilemma... do I make a new thread or go off topic in an existing one :D

Already I am unhappy with my platinum electrode. It leaks from the bottom and initially released bromine into the confined space within the pipette. The platinum seems ok, but the tin/lead has gone white. It still conducts though. I have wax :( stuck at the bottom and that has stopped the leak for now but is slowly turning into crap in my solution, it floats at least. I'm not going to throw it out but I am looking for a new option and will decide if if needs to be resealed if and when I need pure platinum (It has been heated very hot 4 times now, and the platinum wire has gone as soft as solder). Anyhow.... about this new topic....

Recently Xenoid mentioned in the PbO2 thread that he had acquired one of these:

http://www.palloys.com.au/category7_1.htm

a platinum coated titanium anode.

Now obviously this wont stand up to as much abuse per unit area as pure Pt, but it has a lot more area.

Xenoid also mentioned that there was some corrosion starting near the edges. (@Xenoid- is that the non coated edges where they cut it off?)

I was thinking that if you got one of these it may be possible to expoxy, or otherwise seal the edges and the spot welded connection (and half of the rod). In this way it could be completely submerged and erosion would not occur.

Is this possible? More specifically, is there some hard, strong substance which is chemically unreactive which could be coated on to metal well?

I like the look of this anode on the basis that it is not as flexible or flimsy as anything else I had envisioned using. I could put it close to the cathode without fear that they would touch. Also, even if it is not as good as platinum it would still take many amp-hours to burn out.
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hashashan
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[*] posted on 6-11-2007 at 04:39


60 bucks for that crap? i bet it doesnt contain even 1 gram of Pt.
why wont you just make it yourself?
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Antwain
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[*] posted on 6-11-2007 at 05:16


Maybe because I have no titanium, several hundreds to a thousand dollars worth of platinum to dissolve to make a plating solution, a reliable temperature control unit to keep a constant temperature, any information of the current density, temperature, concentration or duration of electroplating, and finally I have never come close to making a cohesive coating when electroplating in the past. Just to name a few ;)


You can bet your life it doesn't have a gram of platinum, if it did I would buy them and salvage it, making a slight profit.
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[*] posted on 6-11-2007 at 05:55


profit?
the market price of one gram of Pt is 45$ so no profit there.
and IIRC you dont need a lot of platinum to make a plating solution, one gram would be sufficient, Ti is quite cheap, you can buy it on e-bay heating .. well i think that is the smallest problem .. the plating will not take much time .. for that hour that it will you can babysit the solution
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Antwain
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[*] posted on 6-11-2007 at 07:30


This is all in AU$.... And WTF?????

Is the US sucking these days or is Australia unsucking? last time I checked it was more than AU$55/g. You are right, it is now only ~AU$47/g. And so yes I was exadurating (no I can't spell and that one is too far gone for the spellchecker) slightly before about making a profit. But as of a month ago, not by much.

I realise that the concentration of platinum must be low, but I almost certainly don't have a reaction vessel the right shape, so that means making a large excess of solution. I also will be hard pressed to weigh things that accurately when making the solution. I can always sneak into uni and use their tenth-milligram balances and as long as I only do the measuring there they wont be too pissed if I get caught. Also, don't you need a platinum anode unless you want to contaminate your solution? If you have data about this or can point me in the right direction then I will seriously consider it.

Unfortunately it is usually closely guarded trade secrets as to how to electroplate properly, my father found that out when he wanted to plate gold a decade or two ago. Fortunately we now have the internet with a good knowledge base of intelligent people (as well as oh so many more stupid ones, but we can ignore those).

Finally, pretending you don't need a platinum anode which I believe you should have, you need symmetry of anodes with respect to the cathode or it wont plate evenly. And you have trouble with large surfaces because of 'depletion' where the center of the cathode has a lower concentration because of the platinum being used up by deposition at the edges. I know the above two because my godmother's housemate is an electroplating operator, but only does silver and gold of the precious metals.

And sorry if I am waffling, I have been up for 48hrs, mostly not doing my assignment. :o
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[*] posted on 6-11-2007 at 10:51


Plating platinum is stupid easy. It works from weak solutions of PtCl6(2-).

Tim




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[*] posted on 6-11-2007 at 13:13


Hello,

Just guessing but the above mentioned anode was probable plated after the Ti mesh was cut and attached to the other (flat piece) of Ti. Therefor there there should be no bare Ti in soluton when put into use.
Ti will "self seal" itself if it is uncoated and protect itself.

Lots of (bedtime) reating on Pt at the link at the bottom of this page:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

Pt metals review journal.



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[*] posted on 6-11-2007 at 14:45


Quote:
Originally posted by dann2
Just guessing but the above mentioned anode was probable plated after the Ti mesh was cut and attached to the other (flat piece) of Ti. Therefor there there should be no bare Ti in soluton when put into use.
Ti will "self seal" itself if it is uncoated and protect itself.
Dann2


Actually, "... that crap" as hashashan so eloquently describes it, is made from a large sheet of Tl mesh which has been plated (coated?) with Pt. The mesh appears to have been sand blasted or etched first as it has a frosted appearance. The large sheet is then cut with a guillotine into smaller pieces and spot welded onto a Ti strip. The Pt thickness on these anodes is quoted as about 2 - 20 microns from memory. I'm not sure if this refers to the variation on any one anode, between anodes or that anodes are available with that range of thickness. I don't know what thickness the coating is on my anode. I don't think that the thickness is as important as the superb bonding that is achieved. This is the key, and we amateurs haven't mastered this yet.

Seeing there seems to be some doubt about the efficacy of these anodes, I am about to start another perchlorate run, so we will see how it holds up. Even if it fails, as Dann2 pointed out in the LDO anode thread, it can still be used as a substrate for making ones own anodes of various persuasions. So it's not a total waste of money!

I think the key to sucess with platinised Ti is to avoid halogens/halides like the plague. Others may have had early failures because they tried to use them in chlorate cells. Even industry does not do this, they use MMO anodes. In my opinion platinised anodes should only be used in perchlorate cells where the chlorate has been repeatedly recrystallised to remove chloride traces. The fabled lead dioxide anode might be suitable for going all the way but not platinised Ti.

Regards, Xenoid
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[*] posted on 6-11-2007 at 15:29


That is preciesly what concerned me about electroplating. A cohesive coating is very hard to achieve. I expect you don't want the titanium to be passive, rather you want it active as all hell. Maybe if you give it strong curry as an anode in HCl first and then make it the cathode in an electroplating solution without letting it see oxygen. Alternatively, you could just plate it with a full gram of platinum and let it etch as it may. Ive just decided to buy another Pt coin anyway. My electrode is shite but I know how to improve it. I can rebuild it... I can make it better than it was :D

From my aweful experience with the softening of my electrode + some lit I saw which mentioned this (annealing right?) I believe I can make it thinner and then cold work it to make it strong again. Perhaps heating and slow cooling ine the relatively cold range of 0-200*C could help, we shall see. When I have that I will dissolve my old one (I want some Pt compounds anyway) and maybe I will do a trial electroplate and see how it holds up. I'm going to do some serious reading first. I'm sure that making a cohesive layer can't be simple... it isn't for any other metal...
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[*] posted on 6-11-2007 at 19:25


Strong HCl doesn't seem to be a good combination with Ti. At room temperature, it doesn't react quickly, and I think I may've tried anodizing in it -- resulting in anodization, who would've thought. Maybe as cathode it might reduce some, I don't know.

It really is a bitch to dissolve...

The only way I've dissolved any quantity (at room temperature) is by soaking with H2SO4 for weeks. I obtained a deep purple solution with some insoluble salt present (what's the solubility of titanous sulfate hydrate?). Having removed the metal and let it out exposed, it has since oxidized to a colorless titanyl solution, which is orange from a small amount of peroxide that happened to get in.

I haven't tried boiling in HCl or H2SO4.

My experience with plating Pt on Ti, so far, is as long as the metal is clean and silvery, it will plate. It seems to adhere well enough, having heated the material to dull orange heat (700-750C or so).

Tim

[Edited on 11-6-2007 by 12AX7]




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Antwain
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[*] posted on 6-11-2007 at 19:51


@ 12AX7- That's an interesting thought. Perhaps heating it - rather than having potential to damage it - would instead allow some atom migration and essentially sinter the coating into the titanium. This would mean that the oxide film would spread in both directions (out and in) and pose less resistance. And there would be a small region where the metals were essentially alloyed, which surely would help and not hurt the platinum film stay on.

When you say silvery, do you mean scrubbed down or nice and polished, ie would a very fine abrasive cream be the go?

Don't suppose you know how much platinum you deposited either in terms of thickness or mass and surface area?

And while I will research this myself from literature before proceeding, what do you call a weak solution of [PtCl6]2-? Was this prepared by aqua regia and if so did you neutralise the acid before using it?

Edit- Just a quick interlude-
I am about to have the problem of trying to clean platinum, whether I want to use it as an electrode or a reagent, it will need to be cleaned up.

Now there are damn white crystals growing up inside the glass housing, but I don't care because I am confident that I can get rid of those. They are growing on the wire and there is no solution there any more but there may be catalytic water and salts. My bigger problem is that lead and platinum apparently form an alloy.

I have never worked with alloys in a chemistry capacity so I have no idea how they generally behave. Will conc. nitric acid on its own bring the lead out given time. If so will it attack the normally resistant platinum, or more likely IMO will it leave the platinum completely stuffed or cause it to fall apart?

[Edited on 7-11-2007 by Antwain]
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[*] posted on 6-11-2007 at 20:18


Antwain, do you rabbit on as much in real life as you do in these forums..:D

How the hell did lead get into the platinum?

Regards, Xenoid
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[*] posted on 6-11-2007 at 22:10


The bits of titanium I plated were cleaned in base and acid. I didn't prepare the surface in any way, it was metallic gray as titanium tends to be.

I was given a gram of K2PtCl6, of which I dissolved a teensy bit in water with some HCl (out to maybe 1M acid). So that's like 0.1g / 300ml H2O, pretty weak. I used a graphite anode (mind the chlorine gas) and plated with no particular current density. Full voltage (around 5V I think) may be beneficial in reducing the titanium's surface (in a solution this weak, prodigious amounts of hydrogen bubble off), I don't know. I let it sit for a number of hours with a 20 ohm resistor (about 3/20 = 0.15A then?).

After plating, I annealed the pieces as mentioned, which resulted in a somewhat smutty appearance. (Under the flame, the metal showed the irridescent redox behavior familiar from copper metal. Say, that reminds me, I think there was a minor copper impurity in this solution.) After dipping in the acidic bath, the plates were clean again.

The plated surface appears to be shinier than the base metal started. Of course, bare titanium surfaces are now colored iridescent with thicker titanium oxide. I didn't measure thickness. I have a micrometer, I'll keep track of it next time.

Tim




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[*] posted on 6-11-2007 at 22:42


12AX7 - you'll need a hell of a good micometer to measure a few microns.

Quote:
with no particular current density. Full voltage (around 5V I think) may be beneficial in reducing the titanium's surface (in a solution this weak, prodigious amounts of hydrogen bubble off), I don't know. I let it sit for a number of hours with a 20 ohm resistor (about 3/20 = 0.15A then?)


Er, I am not sure I'd use you in my plating shop. Or to write technical notes...

Regards,

Der Alte
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[*] posted on 6-11-2007 at 22:51


The following from my abridged Mellors;

"Platinum is attacked by alkalis, nitrates, cyanides, and phosphates under reducing conditions. With phosphorus it forms platinum phosphide; with sulphur it forms platinum sulphide; with sulphur and dry alkali it forms platinum disulphide; with arsenic it forms platinum arsenide. Platinum also alloys directly with metals such as lead, silver, zinc etc. but not mercury. Hence Pt crucibles must not be heated with these metals. Carbon alloys with Pt forming brittle platinum carbide, and hence Pt crucibles should not be heated in a smoky flame."

I had a student once who carried out two or three alkaline fusions of some base metal ores, (mixed sulphides, arsenides, etc.). We had to scrap the Pt crucible, the bottom was crystalline and brittle and fell off when poked with a finger! Admittedly it was a fairly old crucible, but it doesn't take much to ruin Pt ware. Always insure oxidising (oxygen rich) conditions with Pt.

Regards, Xenoid
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[*] posted on 6-11-2007 at 23:44


Quote:
Originally posted by DerAlte
12AX7 - you'll need a hell of a good micometer to measure a few microns.


I have a micrometer that does tenths. 0.0001" = 0.00254 mm = 2.54 um. Microns are actually kind of large, as small measures go. :)

Quote:
Er, I am not sure I'd use you in my plating shop. Or to write technical notes...


:P

I prefer to think my complete lack of data implies how foolproof this process is...

I could take measurements, but why bother? Science just slows down chemistry. :D

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[*] posted on 7-11-2007 at 14:30


Besides, it's not like it was your platinum anyhow :-). This time around I think it'll be chloroplatinic acid, and I will want to know how thick the deposit is, and all the details as I'll be sending 5-10X what I sent the first time around.



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[*] posted on 14-11-2007 at 13:54


I bought platinum wire from an eBay jeweller. Then just dissove in HCl electrolytically.

The platinum plating is more rugged if processed by the method of US patent 4,240,878.




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[*] posted on 14-11-2007 at 20:05


Quote:
Originally posted by Xenoid
Antwain, do you rabbit on as much in real life as you do in these forums..:D

How the hell did lead get into the platinum?

Regards, Xenoid


Yes, of course :D

soldering, followed by heating the Pt wire to red heat 1.5cm away. The solder disappeared into the wire and it went a dull grey, but not like lead on its own. I expect there may be tin there too.
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[*] posted on 14-11-2007 at 22:00


12AX7 said:

Quote:
I prefer to think my complete lack of data implies how foolproof this process is...

I could take measurements, but why bother? Science just slows down chemistry


This must be the 12AX7 quote of the year! I love it! It happens to be true, too. Too much science does slow down chemistry. Being of a theoretical bent, I often mull over things like equilibrium constants, the exponentia;l effects of temperature on a reaction, etc., etc., while what I should have done is just get off my butt and tried the damned reaction. That's chemistry...

Regards,

Der Alte.
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[*] posted on 14-11-2007 at 23:52


Thanks! Think I'll put it in my sig then :D

Tim




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[*] posted on 21-11-2007 at 14:06


I'd like to think working problems slows down chemistry.. I can't wait to be done with Analytical.
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[*] posted on 2-2-2008 at 18:31


I found a supplier on Ebay that sells platinised titanium anodes as well as MMO Ti anodes.

http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&rd=1&it...

I am interested in purchasing them.

However, I have a few concerns.

1) The platinum plating is only 125u = 3 microns thick and the cape canaveral site recommends a minimum of 80 microns for Pt thickness.
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

2) The seller claims that the natural tendency for the chlorate cells to become basic over time (for a home setup at least) is not a problem for the MMO anodes but I have read that a basic cell can destroy a MMO anode in hours.

3) The surface area of the Platinised anode is 7.5 sq in = 48.4 sq cm but the seller recommends currents of 50A, this works out to 1.03 A/cm2 This is an outrageous current density!. I am not inclined to believe the recommendations of someone who promotes these types of current densities.

In short, is this a high quality anode that will last a very long time (several years) at modest 150-250 mA/cm2 current densities? or is it a ripoff?.

How about the MMO titanium anode? How long should I expect is to last if I treat it well 70-150 mA/cm2 and don't let it sit in the electrolyte unpowered.
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[*] posted on 2-2-2008 at 19:23


@ markgollum

At this stage I think it is a matter of "suck it and see". I don't think you will find many members of this forum who have used commercial electrodes for chlorate and perchlorate production.

I have used MMO electrodes from an old pool chlorinator which cost me nothng, whilst they worked OK there was nothing exceptional about their performance. I am concerned about the performance of MMO electrodes in the uncontrolled pH environment of home cells. Mind you, in an industrial environment these electrodes would be expected to last up to 8 years. If they last 2 or 3 years in a home cell, only you can tell if that is good value for money. I am afraid I haven't run them again yet to see what the wear rate is like, because I've got so many small cells running at the moment I can't be bothered.

I have made approximately 3Kg of K perchlorate with a platinised Ti anode, the coating is only a few microns, I'm not sure where Dann2 (Geocities Chlorate Site) got that figure of 80 microns from. I ran my anode at several amps, there is no apparent damage to it, I have no idea how long it will last. As you say, 50 amps is excessive, the heating effects would be a problem for starters. Up to 10,000 amps/m^2 is used in commercial mercury chlorine cells, but I wouldn't want to try this on a home cell.

I would say "go for it" especially if you are not committed to making lead dioxide or other types of anodes. It will probably work out cheaper in the long run. The prices do not seem unreasonable, given how much you might spend on chemicals and equipment trying to make your own. I for one would be interested in seeing how they perform!
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[*] posted on 3-2-2008 at 20:15


Hello,

The 'suck it and see' just about sums it up. :D:D:D

I can't remember where I got the 80 micron figure from. I think I sort of plucked it out of mid air (to be honest) as reports of light coating (electroplating anode) were poor. Wearing out, but the users were probably using them in the Chlorate cell that was turning into a Perchlorate cell. Bad thing to do AFAIK. May have seen the 80 Micron in an artical. I am often sorry I do not put in refs. for statements like that.

I used an MMO for a while. It seemed to be wearing a bit. There are many many types of MMO.

Dann2
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