Posted by Gordon England on July 17, 2003 at 00:27:12:
In Reply to: dilluted H2SO4 corroding pump shaft coating posted by John Streeter on July 16, 2003 at 21:50:48:
: We are experiencing spalling of a plasma sprayed TiO2 coatings on to a 316 stainless steel shaft(mining industry.Temperature doesn't exceed 60C. Bonding material is NiAl or AlBronze applied via arc spraying.Coating thickness of TiO2 is 0.3mm and sealing is accomplished via Microseal.
: How would a NiCrCr2C3 type Tafa 1375VM work here?
: Any suggestions for improving the sealer?
: Thank you
Hi John
If you want to stick with plasma sprayed oxide ceramic coatings I would suggest changing to alumina or chromium oxide as titania can be attacked by sulphuric acid. Also, changing the underlay/bond coat material to something like Hastelloy C would also help.
HVOF coatings based on chromium carbide would certainly be worth trying.
Even with HVOF coatings, you can not guarantee 100% against permeation of the environment through the coating without sealing. If the environment contains no hydrocarbon solvents or oils and the max temperature is lower than 80 C I would consider using a microcrystalline wax sealer. Simple melt into the coating directly after application of coating (while still hot).
Regards Gordon
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