Ruthenium/Iridium coated Titanium anodes

A. Hi Matias. We appended your inquiry to a thread about anodes of this sort. It should give you a start on the selection. In addition there is a very interesting posting from Tom Baker on thread 11754 which you might want to review.

Luck & Regards,

A. Applying 60kV for 20 microseconds is likely to produce intense plasma close to the electrode which is likely to result in physical processes such as sputtering, chemical etching etc. I wonder if such situations are considered in electroplating, for the plasma may influence the chemical processes.
Titanium can be coated with gold and many other metals, metal nitrides, carbides etc by PVD processes.

? Hi Ed. Apologies but I'm getting no mental picture -- why you can't passivate the whole surface, what these edges are, what it is you want to stop grinding off and how passivation will save grinding it, whether you're talking about anodes or some other topic. Unfortunately, 'passivation' is one of the more confusing words in the finishing lexicon because it applies to so many processes in so many ways (passivation of stainless steel, passivation of carbon steel in boilers, passivation of zinc plating with chromates, passivation of phosphatizing with final rinses). Please tell us what you're building and what problems it is presenting. Thanks.

Luck & Regards,

A. Hi again. If the anode cannot be shortened, is it not possible to mask the ends either with a polymer or by installing a mylar or similar sheet between the anode and cathode to act as a shield? I admit that I don't fully understand your arrangement, but it seems to me that rendering the ends of the cathode non-conductive would just slightly reduce the width of the plated strip without solving too-thick at the edges plating problem.

Luck & Regards,

A. Platinum or Graphite. Platinum clad mesh materials go for about US$5.00/square inch. The Metal Finishing Guidebook lists several sources for both materials.

Good Luck,

A. You can try activated titanium electrodes, this is titanium covered by ruthenium and/or iridium oxide. This is also known as DSA (dimensionally stable anode) material.

Another possibility is Ebonex.

Regards,

Q. I've heard that titanium covered with ruthenium and/or iridium oxide is a very expensive technology. I'm looking for an anode with a surface area of about 200 square cm.

A. Hello Nick,

Typically this process is done via vacuum methods, or by plating of Ir then thermal oxidization. Do you actually want reduced Iridium or the Oxide exposed? I am interested in understanding why you choose the Oxide? Also, are these platinum anodes that you will replace with IrOx/Ti located in your high-speed cells or your low speed flood cells? Using it in your high speed cells may introduce a severe design constraint into your cell tooling designs. I am sure if you contacted Technic, Inc. they will put you in contact with someone that they supply Ir to.

Regards,

A. The electrical resistivity of our IrO2 films is about 40 micro-ohm-cm (which compare well with that of single-crystal bulk IrO2). this particularly answers the questions of Jean-Michel.DESVIGNES from Lab. CHARLES FABRY de l'INSTITUT d'OPTIQUE and Paul R. Kerr.

-We have developed a new physical process to coat virtually any surface (Titanium is an excellent substrate with highly conductive and dense IrO2 films with an excellent adherence (Appl. phys. Lett. 69, (1996) 2027) . So this is a direct response to the Nick Lim - Malaysia.

- These iridium oxides have been tested for some specific corrosion studies and they have exhibited excellent corrosion resistant behaviors. Other applications are currently under evaluation.

A. Platinum group metals are deposited on titanium via thermal decomposition methods. For the most part, any form into which you can fabricate titanium, can be coated.

Depending on application requirements, the coating composition and loading can be altered for better performance.

Iridium oxide or iridium oxide/tantalum oxide mixes are quite common and perform well in a broad variety of applications.

For chlorine generation, mixtures containing ruthenium oxides are typically preferred due to higher yield (i.e. better specificity).

A. RuO and IrO are what we refer to as DSA (Dimensionally Stable Anodes). They are used when one or all of the following conditions exist.

1) Very high current densities (greater than 5 amps/SF up to 12 amps/SF)

2) Concern for good UV durability on cationic acrylic tanks. As you experience soluble iron contamination greater than 20 ppm from parts or iron dissolution from stainless steel anodes that leak or overflow from plugged return lines, the UV durability will drop off rapidly.

3) Cationic color control tanks. Cationic tanks whether or not they are acrylic or epoxy can benefit in color control if you minimize the potential for dissolved iron from entering the paint bath from fallen parts or iron dissolution from stainless steel anodes that leak or overflow from plugged return lines. RuO is about twice the price of stainless steel and IrO is even higher yet. The RuO and IrO material are brushed on to a titanium anode. These hold up extremely well, but they can be prone to corrosion if the RuO layer is scratched.

A. Ruthenium and Iridium Oxide coated mesh type anode is suitable for electrolysis of chlorates and caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] anodes. It weighs light and surface area is more. You can operate 2KA/m2 suitable. Coating adherence is not a problem for mesh type anodes. Iron will deposit in the anode while power cut and will inactivate your UV system.

A. Expanded metal is a very efficient form of titanium to use in developing an anode. For example, if the mesh pattern has about 50% void area, the surface area is the same as for a solid sheet, even though half the titanium material is used. The cost of expansion is markedly less than the material savings for an expensive material like titanium.

The coatings are applied as salt solutions and the baked in an oven to convert to oxides. Various proprietary methods are used by manufacturers to prepare the surface for the coating and to control the thickness and uniformity of the coating to assure proper quality. Coating uniformity is not perfect, but depending on the manufacturing method, it can be quite good.

Coating loading effects life, but unless the area effected is large, the current discharge would shift to a nearby site that is still active. The titanium would form a passive film that would not breakdown and pass current. In most applications, the majority of the coating would have to fail before titanium substrate failure began.

A. Hi Chuck. Chrome should not immersion plate on your anodes because iridium is a noble metal. Although such anodes can be used as auxiliary anodes to reach low current density areas, I'm not familiar with doing zinc plating with only such anodes. Where does the zinc come from if not from zinc anodes?

But chrome can really mess up a plating process. I'd suggest doing some Hull Cell testing to see if the plating solution has been successfully decontaminated and will plate properly. Good luck.

Regards,

A. Hi, Howard. I don't think there is a formula for amount of hydrogen per square inch -- I think that's an empirical number based on the construction details. But I think that the amount of hydrogen per amp-sec should be predictable by Faraday's Law of Electrolysis, which says that 96,485 amp-seconds will release 1 gram equivalent weight.

Regards,

A. The substrate is sand blasted and pickled for the removal of scales. A paint of isopropyl alcohol with the metal chlorides along with titanium tetra chloride is painted by brush with no metal parts. It is baked in oven at 400 to 600 degrees. Painting and baking done many times to achieve the desired thickness. If wear resistance is needed iridium chloride is added, if catalytic action is needed ruthenium chloride is added, for water electrolysis, more platinum chloride is added. If high current density is required niobium is added. As far as I know.

My understanding is that one applies the Ru or Ir to the CLEAN Ti surface as the appropriate nitrate. By CLEAN I mean totally free of oxides. One does this by treating the Ti with a nitric/HF or nitric/NH4HF2 pickle. Right after rinsing, you paint the precious metal nitrate on. Then, bake, to something like 400 °C.

After baking, you may with to add more nitrate solution, you might wish to do this a few times. On the final baking cycle, cool the coated metal electodes rapidly. One wants a certain amorphous nature in the coating; that helps the catalytic activity.

There's lots of literature out there about this technology. Such electrodes are commercially known as DSA - dimensionally stable anodes.

My knowledge of this is rusty. This is some stuff I did 20 years ago. I tried, not having any Ru or Ir, to coat my anodes with a mixed oxide of Ni and Co. I got a nice adherent coating, but the catalytic activity was disappointing.

A. Hi Eshan. If you introduce yourself and your situation and a rather specific problem that you are encountering, this forum will generally help you address the specific problem. But if you are looking for a technical paper addressing the subject, scholar.google.com or surfacequery.com is probably a better idea.

Dave gave the general idea of how th process is done 23 years ago, and others have offered miscellaneous hints in the intervening years, but it seems that despite many people asking a similar question before you, nobody has yet offered to write a paper on this subject for us :-(

Regards,