Where the
world gathers for metal finishing
Q&As since 1989


-----

Coating ID of capillary tubes with polysiloxane / silicone

1998

We are attempting to coat the inside of brass and stainless steel capillary tubes (approximately 250 Microns I.D.) with a polysiloxane (silicone) coating. We are having difficulty getting a uniform coating and am looking for a procedure to produce same without defects. We currently do not use and pretreatment or passivation of the metals (brass and stainless) and have been attempting to coat by drawing a dilute 3% solids polysiloxane coating through the tubes under vacuum and exhausting the residual solvents to complete the coating/curing process.

Can you recommend a process for cleaning and passivating the surfaces of the brass and stainless that would give satisfactory results with subsequent coating. Capillary tubes are for gas chromatography column use.

Any assistance would be appreciated.

Dave Reim
- Columbus, Ohio

Not all polysilaxanes are currently being marketed. The ones that are not must typically be licensed from a patent holder. On the web you can find abstracts of many of these patents and can contact the patent holder after getting the phone number of the patent holder from the Patent & Trademark Office. Currently I am looking at one particular polysilaxane for our project that has a clear optical finish (our requirement) but requires no fillers, thus the chemical has a higher modulus, goes on differently, and is even harder than others once cured. I am not a chemist, but it could be that fillers are interfering with adhesion in your application.

Christina Duncan
- Dallas, Texas
2000