jonboy
06-29-2009, 01:08 PM
As a follow up to a previous thread I started here's the result of a bit of home passivating....Problem..localised small rust spots on perforated ss sheets when immersed in water and sometimes slight oxidising agents such as chlorine base bleach solutions...The standard procedures from various sources recommended 15% nitric acid HN O3... the results were ok in that the rust spots went, but the sheets and the ss shallow bath were left with a very slight greyish matt deposit which was a bugger to get off...Also a persistent residual low pH even after loads of rinsing. Expensive -ish and dangerous and not easy to find
2nd attempt with phosphoric acid....cheap, readily available in auto stores for bodywork de rusting. not good... turned the ss black in the localised rust areas and then could be easily removed leaving the ss to rust again...
3rd attempt 1% dilute hydrofluoric acid. HF..has worked perfectly , no deposits, no residual acidity, no recurring rust and super shiny ss...Readily available and cheap as a cleaning agent for aluminium pots and pans, in safe dilutions. Warning... HF is seriously nasty in concentration... more so than nitric due to toxicity levels through fumes and anaesthetic properties ...you don't feel the burns or notice the effects of inhalation... (there's no caustic acrid stink like other acids) till it's too late..which means too late as in dead.
Thanks again to the first thread respondents for the passivating pointers.
2nd attempt with phosphoric acid....cheap, readily available in auto stores for bodywork de rusting. not good... turned the ss black in the localised rust areas and then could be easily removed leaving the ss to rust again...
3rd attempt 1% dilute hydrofluoric acid. HF..has worked perfectly , no deposits, no residual acidity, no recurring rust and super shiny ss...Readily available and cheap as a cleaning agent for aluminium pots and pans, in safe dilutions. Warning... HF is seriously nasty in concentration... more so than nitric due to toxicity levels through fumes and anaesthetic properties ...you don't feel the burns or notice the effects of inhalation... (there's no caustic acrid stink like other acids) till it's too late..which means too late as in dead.
Thanks again to the first thread respondents for the passivating pointers.