I'm putting this in a new thread, so it's easier to find.
My current goal is plating a robust layer of platinum onto a titanium substrate. So far, I have found more treatments that serve only to further
passivate titanium, than treatments than activate the surface.
First off, fire and acid suck. Fire works nicely to build a heavy layer of TiO2 / Ti2O3 of iridescent color. Titanium is stable in air up to at
least 900C, reaching a dark gray color in the process. Hydrochloric acid appears to have no effect whatsoever, at least on this alloy (CP4). It has
a weak effect on 6Al4V. Boiling sulfuric acid attacks titanium, resulting in a white to blue to purple encrustation. Boiling NaOH solution has
little or no effect.
The only things that I have found suitable are: molten NaOH and HF.
To clean oxides from titanium, cover the surface with strong NaOH solution or solid granules. Heat until the water boils off and the NaOH melts.
Around 400C or so, the molten NaOH will attack the metal, moving around in an interesting way and giving off hydrogen bubbles. The metal will turn a
clean gray color, as the surface is etched and cleaned. Use caution around molten alkali!
To activate the surface, after washing off the alkali, a solution of HF is added. The solution I'm using is about 20% HCl solution, 5%wt NH4HF2.
Spread the solution over the surface and heat lightly. Just as it passes 50C or so, the titanium should darken in waves as the solution grows into
thick white foam. Do not wash! Place directly into the plating bath. Some wiping action may be desirable, to clean the white and black gunk off the
metal, which tends to result from all this.
With any luck, you will soon discover a deposit which is sort of adherent. If not, strip it off and try again. The bond might be strengthened by
annealing to 800-900C for several minutes. If the coating survives a hard wire brushing, it should be okay for service. There is no guarantee, as
far as I know, that it won't later blister off the surface.
Thin platings seem to work better, probably because there is less stress in the layer. More plating might be possible on top of a good strike layer.
I have tried strike plating with copper, even adding copper to the HF treatment. When the titanium surface is activated, instead of turning into
white foam it turns to a dark red color, as colloidial copper is deposited. It does not adhere appreciably. A lower current density is necessary to
do that, but it may not adhere as well.
I currently have a slab of titanium, plated with a few microns of platinum, working away on some sodium chlorate. It has been going for about a day
so far, showing no sign of blistering as the first anode did. Current is reading as relatively low (about 20A, compared to the 35A the earlier anode
started at), though the cell temperature is quite warm. Cell voltage is 4 or 5V, come to think of it I haven't measured it exactly.
Timdann2 - 12-1-2008 at 12:26
Hello,
What do you mean by "HCl sucks".
Do you mean it will not etch the surface clean or will not activate it?
I know nothing about 'activating' Ti surface BTW.
Warm/hot HCl will etch the stuff easily.
Do not put the Ti into the HCl when cold and then warm up. Heat the acid first and then place Ti into it.
Dann212AX7 - 12-1-2008 at 13:59
Quote:
Originally posted by dann2
What do you mean by "HCl sucks".
"Hydrochloric acid appears to have no effect whatsoever, at least on this alloy (CP4)."
Quote:
Warm/hot HCl will etch the stuff easily.
Do not put the Ti into the HCl when cold and then warm up. Heat the acid first and then place Ti into it.
What's the difference?
Timsolo - 12-1-2008 at 14:22
Seems like this guy has that problem solved, maybe you can write to him and he can tell you how as a science hobbyist with a project.....solo
"One of the difficulties with plating titanium is that it is difficult to "activate". Traditional methods use high concentrations of nitric acid,
hydrofluoric acid, hydrochloric acid, and hydrogen peroxide. Our new proprietary process makes it very simple to remove the oxide layer present on
titanium and replace it with a new coating that has excellent adhesion properties. Electroplating of the titanium creates a strong bond that won't
chip or flake. "
[Edited on 12-1-2008 by solo]Xenoid - 12-1-2008 at 14:31
Quote:
Originally posted by 12AX7
What's the difference?
Hmmm.. Nothing, my Ti (I assume it's CP) etches OK both ways. I just use the 290g/L stuff from the hardware shop. I put the sanded Ti rod in it and
slowly heat up until the reaction starts, then leave it for about 10 mins (actually I think this may be overkill, even 5 mins would be OK. The Ti
turns dark grey and the HCl turns violet!
Tim, are you sanding your Ti thoroughly first!dann2 - 12-1-2008 at 16:22
Hello,
I have CP Grade one (ebay).
When this Ti is placed (with no sanding ) into cold acid (let it Oxalic, Sulphuric, or HCl) and the acid + metal heated up it will not etch/react. I
presume that the Oxide coating is capable of getting thicker/thougher as the challange gets slowly greater. I have thrown out good Oxalic and
Sulphuric acid thinking they were 'dead' as they would not etch.
The problem was as described: Heating up from cold with Ti in the acid.
When the Ti in put straight into hot acid it etched OK.
Sanding guarantees a start to the reaction.
I use 12% hardware store HCl.
EDIT.
To add to the above. I tried etching in cold HCl after sanding my Ti and it passivated after a few minutes in the HCl. Not too sure of conc. of HCl as
it has been boiling for hours and hours with a top up of 12% going into it when it gets low. It would be approching 20% (azetope) but the Ti etching
it is doing will lower its conc. I guess.
I tried connecting + voltage to the Ti in the cold HCl. It passivate at lowish voltages, when voltage is high enough current will flow but it seems to
be all concentrated where the Ti is at the surface of the liquid. It close to cut through the Ti strip at the surface. When the Ti is viewed with a
microscope at the place where it was very much etched away the Ti looks like pumice stone. A mass of holes into the Ti. It would sure be a good
surface for coatings to key into if you could have it alll over the surface.
If you were to portect the Ti at the surface of the liquid with some insulation tape then it may etch the Ti under the liquid more evenly. Perhaps
not.
Dann2
Dann2
[Edited on 13-1-2008 by dann2]chloric1 - 12-1-2008 at 18:05
First time I tried to etch, I got uneven mottled surface. I did not sand. I want to try sand with coarse (80 grit) followed by fine(400 grit)
sandpaper and try a HF in situo etchant.12AX7 - 12-1-2008 at 19:14
Without the molten NaOH cleaning, especially on well passivated (annealed, etc.) stock, the HF only serves to pit and pinhole the surface. Trying a
platinized anode in a bromate cell had a similar, much more dramatic effect...
Timchloric1 - 13-1-2008 at 07:10
Well I wanted more detailed information on titanium etching and machining as well. My etchant will be ammonium bifluoride acidulated with nitric
acid.
I did cut some Ti6Al4V with a diamond cuttoff wheel the other day. Pretty light show with the sparks and all. After reading a titanium machining
page from a www.titanium.com , I realized using the highest speed was not recommoned DOH! Anywho next time I will increase feed rate while using a lower
cutting speed. At least the titanium will not react with diamond buy I cannot say about the bonding agent for diamond tools.
See also, chemistry index, in my sig (but what's new is indicated on the index index).
TimRosco Bodine - 23-1-2008 at 22:38
You can use platinum to greater effect as an interface coat on titanium , and then apply a baked spinel MMO coating
containing Ta oxide as the wearing outer layer .
See US4086157 attached
Hydriding the Ti substrate as a preplating treatment should result in good adhesion .
I've tried running the titanium as cathode in an alkaline solution. All I get is a cruddy deposit that easily rubs off. Exactly not what I need.
TimRosco Bodine - 24-1-2008 at 09:59
Quote:
Originally posted by 12AX7
I've tried running the titanium as cathode in an alkaline solution. All I get is a cruddy deposit that easily rubs off. Exactly not what I need.
Tim
Yeah but that is not the same condition as is used for
a preplating hydriding treatment , which can be done
in dilute H2SO4 . jpsmith123 was reporting good adhesion for cobalt to the hydrided Ti and the same should occur for Pt . A bonus with Pt is that
on baking the TiH2 would readily
decompose without delaminating the Pt because the Pt is itself such an adsorbent material for the hydrogen which the
TiH2 will begin offgassing at about 200C . What should result
is an essentially Ti to Pt bimetal elemental interface .
Another pipe dream..........
dann2 - 26-1-2008 at 15:18
Hello,
Looking up Ferric Oxalate on Google and came across the Pt printing process (Photography).
Wondered could it be used to deposit metallic Pt onto Ti?
