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topic 7904

Make Glass Surface Conductive


Q. Dear specialists,

This web-site database contains a lot of questions/answers on the plating the metals on the glass. But restrictions of my task force me to ask about this again. For laboratory research I need to make the inner surface of fused silica capillary (360 um OD, 100 um ID, 0.5 m length) conductive. In literature and on this web-site I have found a lot of information about metal plating on the glass. But I encountered great problems when tried to realize any of the methods described.

The capillaries are covered outside by polyamide protecting film, therefore plating process cannot be hot, to avoid the film destruction. The inner diam is so small and the length is so big, that it is impossible to use vacuum deposition. The silver mirror having good adhesive property and strength, which could be created without any problem on the outer surfaces by two-nozzle spray, cannot be created at the inner surface (I tried to reduce the speed of silver deposition by diluting and lowering pH in order to allow solution to fill the capillary before the silver starts to deposit. But silver layer never appeared to be strong and adhesive and always exfoliates and clogs the capillary).

I also cannot create the tin oxide film, because this process needs too high temperatures.

Now I try to plate the gold, but experience the same problem - gold layer is not adhesive. My current process includes 1) glass surface etching by HF, 2) sensitizing by NiCl2/borane-tertbutylamine reducer (not by SnCl2/PdCl2) - similar, but not equal to as described by Feldstein in 3993799 US patent (1975) , and 3) plating in KAuCl4 + borane trimethylamine mixture, pH=12 (adjusted by NaOH) (similar although not equal composition to as described by Burke et al, US patent 4142902, (1979) ). Temperature is always room temperature. Rinsing in distilled water is done after each step. For first experiment I try to plate on the glass stick, not inside the capillaries. I use double distilled water for solutions preparation, not deionized water. I needed to modify the recipes from patents because I could not find all chemicals described.

What I do wrong? What is the main direction of search could you recommend?

I would appreciate for any comments on my question and also for any information how to make the glass surface conductive by other methods, different from metal plating?


Sergei Aksyonov
Arizona State University - Tempe, Arizona, USA


A. Do you want to invent a patentable way to coat your product, or do you want to coat your product?

Have you exhausted the possibility of using proprietary chemistry? Many of the problems from a patent to a useful product have been worked out.

Or at least use proprietary chemistry first, then try to equal or do better with a novel chemistry, then file the patent!

Best Wishes,

tom pullizzi portrait
Tom Pullizzi
Falls Township, Pennsylvania


Q. Dear Tom Pullizzi,

Now I need to make conductive (only from inside) fused silica capillaries only for laboratory needs. I didn't think about inventing something new, but I feel I go that direction.

You are right, there are a plenty of patents about the electroless plating. I searched through several dozens of them. But close view reveal, that all of them use two-three basic approach with slight modifications.

Particularly, I didn't found any information about good _one_solution_ method for silvering. All of them use _two_spray_ - this is because of the demand that silver salt and reducer must meet together only on the plated surface. Really, if one place two droplet (silver salt and reducer) on the glass and slowly connect them, then excellent bright silver appears _on_the_boundary between two droplets, and never - _under_the_droplets. The sludge is formed in the volume of mixed silver salt+reducer deposits on the glass, making the growing silver layer (formed under droplet volume) porous and non-adhesive :-(. This is an essentials of two-spray method.

For my purpose (thin capillary) I essentially need one-solution method. It should contain some sludge inhibitor, which nevertheless allow silver to deposit on the glass.

Actually I found one well described one-solution silvering method in one book on glass blowing from 1950's, but close analysis showed, that sludge effect is overcome by _thick_ silver deposition, thus making silver layer strong enough, although allowing some sludge to be incorporated in the layer. This will not work for me because capillary is too narrow.

Feldstein in one his patent describes the additives (Pb, Sn etc. salts) which, as he claimed reduce the sludge formation. But nevertheless he used two-spray method. I tried this approach, but sludge appeared in volume _before_ the silver began to deposit on the glass.

I see one way to overcome sludge-in-volume this by adding some silver-chelating agent or micell-formator. But what could it be? It should be some substance, that cover the silver suspension particles as they appear and prevent their further growth but does not prevent extended silver layer to grow.


Sergei Aksyonov
Arizona State University - Tempe, Arizona


A. Here in Israel there are quite a few plating shops for plating decorative glass items. They all use conductive paint that is sprayed on the glass. On top of the paint layer they plate acidic copper and cyanide silver, both at room temperature.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel


Q. Thank you, Sara, but probably it is not what I am looking for. Nobody can spray inside 0.1 mm inner diameter capillary with length ~0.5 m.

Sergei Aksyonov
Arizona State University - Tempe, Arizona


A. Instead of trying to coat the inside of a long capillary, make the capillary of metal and coat the outside with glass or another insulating material.

jim treglio portrait
Jim Treglio
- Vista, California


! Dear Jim Treglio,

Thank you for the idea which is a real inventor's approach! I thought about something like this but other restrictions of my task do not allow to use this method.

Anyway, thanks!

P.S. All manufacturers able to make such coating are welcome.

Sergei Aksyonov
Arizona State University - Tempe, Arizona, USA


A. I'm sorry if this sounds like an advertisement, but we have been coating the inside of fused silica and metal capillary tubing with metals, semiconductors and dielectrics, for years.

Please drop us a line. I am certain we can help you out.

Dale Woika
Surface Conversion Sciences- Bellefonte, Pennsylvania, US

Ed. note: We will be delighted to retract this notice if we are advised otherwise, but we believe that Surface Conversion Sciences is not in business anymore.


Q. Dear Sergei Aksyonov,

I have the similar problem to coat the inside surface of the microcapillary to make it conductive. Also, the metal coating need to be thinner than 800 nm to make sure the visual light could go through. I read your question and all the follow-up answers here. Did you get any solution for your problem?

Any suggestion is welcome.

Limin Liu
Tulane university - New Orleans, Louisiana

Ed. note: Our FAQ on metallizing non-metallic materials lists a number of different metallizing approaches and may be of some help to the readers. Although we have no experience to bear it out, in theory it would seem that a silver nitrate solution should be reducible electrochemically or with some sort of "time release" reducing solution to obviate the problems that Sergei is seeing with two-part silvering.


Q. I like to produce/print as if a printed circuit on glass with transparent but optically conductive tracks for putting LEDs on it and sandwiching the same between two glasses by single component, UV curable adhesive to produce laminated safety glass. The same shall be electrically connected from outside to light up the LEDS. It would give appearance of LEDs light up without wire being seen from out side.
Second, application is to put invisible tracks on automobile glass/house glass to heat them up for fog control. I am looking for a method which can be employed without much infrastructure, comparatively safe in handling. economical in price. Can some one provide the solution with name and addresses of manufacturers of the involved materials

hobbyist and product designer - NASIKROAD, MAHARASTRA, INDIA

April 6, 2010

A. If the conductive surface does not have to be very long maybe you could use a microchip. This could be assembled with conductive layers. You could insert length of capillary into the ends to make it longer

nick schlensky
- denistone, nsw, australia

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