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A chemical coating for a copper coil

I need a chemical coating for a copper coil that is used in a hot water furnace . There is some flame impingement on the coil. The material needs to be heat conductive. The coil loads up with a green scale that stops heat conductivity.

Robert Boop
thermal custom design - Clearfield, Pennsylvania, USA
2007

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2007

The green scale perhaps forms after the flame shuts off, allowing combustion products to cool and condense. Have the green scale tested for chloride, sulphate, etc. to learn the origin of the problem.

Industrial boilers with blower combustion air often purge the combustion chamber with air for 15-30 seconds before & after combustion cycles to remove any gas or vapor. Perhaps you can do so.

As to possible coatings, see the article 'High-Temperature Oxidation of Nickel-Plated Copper vs. Pure Copper' by U.V. Aniekwe and T.A. Utigard, Canadian Metallurgical Quarterly, Vol. 38(No. 4) pages 277-281 (1999), abstract available on-line. It states that
"Thin layers of nickel were plated onto copper to improve oxidation resistance at high temperatures. Pure copper and nickel-plated copper were oxidized at 600-800 °C in air for various lengths of time. The degree of oxidation was determined by the mass gain. It was found that the nickel-plated copper oxidizes at a rate of about 1/20 of that pure copper..."

If nickel plating, specify a ~pure, engineering nickel (without brighteners). Also, have the plated coil annealed in a protective atmosphere furnace for diffusion bonding between copper & nickel; lessens the chance of plating spalling at the first flame impingement.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.