Letter 38087

Titanium heaters in chromic acid

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We use titanium sheathed heaters in 122-15% chromic acid containing free iron radicals. Temperature maintained is 70 Deg C.

We experience rapid corrosion of the wetted titanium tubes. Life experienced is 4-5 months when continuously immersed.

Kindly suggest ways to improve life.

regards

MANOJ M DESAI
HEATER MANUFACTURER - MUMBAI, INDIA

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According to the chemical resistance charts and prior experience the only electric heater shells that stand up to chromic acid/sulfate plating solutions are those with an outer shell of Quartz or Teflon (PTFE).

Gene Packman
- Great Neck, NY

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Hi Manoj

Wouldn't PVDF be a better material? Superb in acids. OK for max l40 C ... but doesn't like high pH.

Freeman Newton
- White Rock, B.C. Canada

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As we all know, chromic acid is disgusting stuff that creeps everywhere and attacks just about everything. Gene and Freeman are right in suggesting a polymeric or ceramic coating to protect the heaters - pH will not be an issue because chromic acid has such a low pH that is almost falls off the scale!

Trevor Crichton
R&D practical scientist - UK

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Use lead bonded heater for chrome solution.

Salim
- Saudi Arabia

First of two simultaneous responses -- +++++

From the life of your Ti heaters, I will guess that you are using full rated heat in your heaters. For longer life, use derated heaters and for even longer life, use double derated heaters.

James Watts
- Navarre, Florida

Second of two simultaneous responses -- +++++

Trev.

I didn't infer a 'coated' pvdf heat exchanger ... but a solid PVDF unit.

Disadvantages? Heat transfer is slower than metals. Advantages....ENORMOUS ....I sold one to a chrome customer who, as far as I know, is still using it.

Ptfe costs an arm and a leg. Mind you, Salim's suggestion of lead sounds very good ... and probably less expensive than pvdf.

Freeman Newton
- White Rock, B.C. Canada

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