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Q&As since 1989


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Acid based electrolytic cleaning

Q. I'm in the process of learning more about surface cleaning, finishing, and coating. I'm using the ASM Volume 5 for reference. I was wondering if anyone ever used acid for cathodic electro cleaning of carbon steel. Cathodic cleaning uses hydrogen ions for the scrubbing action instead of hydroxyl ions, so I was wondering why a basic solution is recommended for both anodic and cathodic cleaning.

Keith Davis
fuel cells - Danbury, Connecticut, USA
2005

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2005

A. Bases or alkalies are preferred because they are effective in dissolving greases and oils. Acids are not, also some unwanted metallic species may be present dissolved in the cleaning baths. Cleaning in forward polarity may result in their reduction and consequent deposition over the surface of the part instead of leaving the bare metal clean. For that and other reasons, like the brittleness of high strength steels, acid cleaning is preferred as a mid or final step after alkaline cleaning and mostly used on reverse. G. Marrufo-Mexico Guillermo Marrufo Monterrey, NL, Mexico A. In addition to the scrubbing action of the generated gasses, alkaline cleaners are able to saponify oils and greases. Acids generally have no effect on oils and greases. Jeffrey Holmes, CEF Spartanburg, South Carolina 2005 "Practical Guide to Industrial Metal Cleaning" by David S. Peterson on AbeBooks or eBay or Amazon (affil links) A. The scrubbing action is only one aspect of the cleaning process. All things being equal, it's a lot easier to remove organic soils with alkaline cleaner formulations than with acidic products. An acidic product also has the potential of attacking the steel surface, while you can pack the caustic into an alkaline cleaner and not do any harm to the surface. George Gorecki - Naperville, Illinois 2005

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Q. My particular application for electrolytic cleaning is to remove rust and scale, therefore the breaking down of soils with an alkaline solution isn't paramount. Acid dipping is another method for attacking the oxides and I was wondering if acid in either an anodic or cathodic environment would be most effective.

Keith Davis [returning]
fuel cells - Danbury, Connecticut, USA
2005

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2005 A. US patent 6294072 seems to be relevant to your enquiry. But one must ask - if you wish to use acid, why add the complexity of an external electrical system? - just let the acid dissolve the oxides, as is done in countless thousands of pickling tanks around the world. Electrolytic descaling has the advantage of not needing anything as aggressive as the usual pickling acids, but it swaps one set of operating problems for a different set. To superimpose an electrolytic system on an acid system seems to force on you the difficulties of both, for no overall benefit. Bill Reynolds [deceased] consultant metallurgist - Ballarat, Victoria, Australia We sadly relate the news that Bill passed away on Jan. 29, 2010. A. Not enough information and far too many variables for a finite answer. Anodic acid might work great for a while and then the amount of iron or copper or chloride ions reach a magic point and the parts would be pitted beyond use. Temperature is a factor as is the voltage applied. In acid cathodic, you reach a point where crud will plate out on the part which can be difficult to get off. For heavy rust and mill scale, abrasive blasting is probably the best option. Approach free advice with great caution. James Watts - Navarre, Florida 2005

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Q. The reason I was contemplating using electrolytic cleaning in conjunction with the acid is to get the benefit of the scrubbing action of hydrogen/oxygen. I can't use abrasive blasting because it will not reach internal cavities. These internal cavities have rust (cast iron manifolds, pump housings). Normal passivation does not actively remove the scale, and I've had good luck doing both acid cleaning, and alkaline electrolytic cleaning, and I was just wondering if the combination would add some benefit. Maybe I'll check out that patent.

Keith Davis [returning]
- Danbury, Connecticut USA
2005

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Neutral pH Electrolytic Cleaning

November 14, 2015

Q. Hi

Is anyone aware of a pH neutral chemical that can be used in lieu of acid or alkali to take advantage of the scrubbing action alone?

Not a silly question - I am copper plating ceramic coated steel (plating areas not covered by ceramic) the ceramic is resistant to acids but not resistant to strong alkalis and attacked more vigorously when the solution is hot as you would expect.

It is not possible to apply the after the plating operation on account of the temperatures involved in applying the ceramic materials.

Desirable qualities should include non-toxic gases so sodium chloride is out, I looked into sodium carbonate / washing soda [affil links] (soda crystals) not sure about that - it does apparently dissociate into sodium hydroxide and carbolic acid in water but manufacturers don't use this as a method of producing sodium hydroxide so it may be a weak effect and not a concern.

I already have a cleaning routine that is effective for situations where I do not need to apply the ceramic but when I am working with the ceramic I cannot use the strong alkali electrolysis to clean hence this question.

Grease is not a major issue as the steel has been heated to 850 °C (red heat) so I figure all being equal I will get some of the benefits I seek with a pH neutral scrub.

I do have degree of smut to deal with - it seems to come from the silicon carbide sand blast, I suspect minute particles get lodged in pores.

Whilst waiting hopefully for an answer I figure I will just try a very small quantity of sulfuric - just enough to get a reasonable conduction going.

Jon Light
- Saltum Denmark

November 15, 2015 Q. Just an update to my previous posting regards pH neutral scrubbing. I tried Sodium Sulphate and this worked just fine, a small quantity gave me conduction sufficient to pass something like 30% of my usual plating amperage, I warmed the solution a little. It was interesting to note that because I am plating the interior of bowls I needed to use the same conforming anode principle to do the cleaning as well as the plating. Indeed I took it to be a useful tool for visualising the likely current distribution in plating as I was able to play around with different anode shapes and see their effect on where bubbles originated from. Even with a stainless steel "wand" entering the interior of the bowl it was difficult to prevent the majority of bubbling originating in the region around the rim, it might be necessary to make a wand which has only a conducting tip (insulating sleeve) so that it can be directed to any region selectively. Seems to me that a logical path is to get the anode right for (pH neutral*) scrubbing first using bubble formation density/rate patterns as a guide and then to move onto creating the conforming anode for plating based on what was seen. Ok I cannot count bubbles per second but as an approximate visual guide I find it interesting and potentially very useful - easier than going through the disappointment of unsuccessful platings and, of course, the same article can be used over and over until the "scruubbing anode" is right whereas clean up after a fully or partially trial & error plating is likely to be more costly in time or money. Of course if I were using a hot caustic scrub solution I would not really want to be around breathing in ambient air and looking at bubble formation but the neutral Sodium Sulphate solution presents no hazards as far as I am aware other than the usual issues of small quantities of hydrogen and oxygen being released. * I included this pre-emptive to alert the casual reader to the dangers of peering over a vat of caustic scrub solution when bubbling which I would not choose to do. Jon Light [returning] - Saltum Denmark Jon Ultrasonic cleaning might be an option. Willie Alexander - Colorado Springs, Colorado November 16, 2015

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November 24, 2015

Hi Geoff, thanks for the reply.

Yes the steel is de-greased before heating to 850, like with electroplating the ceramic adhesion is dependent on cleanliness. I have not experimented to see which is more "fussy" I simply apply the best cleaning methods available to me throughout. A waterbreak free test is part of my visual inspection routine.

The hot alkaline bath is part of my steel degrease routine, first a solvent then hot alkali with electrolytic cleaning; the texts I have on the subject seem to recommend a double barreled approach here. Being artisan level I don't have access to specialist solvents and vapour equipment -- the double barrel approach works for me well and adhesion tests on flat non-ceramic samples (no heat stage) show that the plate is slowly worn away with no lift or peel. I am confident in saying that all complications for me arise out of shape (covered in other postings) and the aftermath and processes involved in applying the ceramic whilst protecting the metal destined for plating.

Yes I understand that conventional acid plating onto steel will result in immersion deposition I use a flash plate first although I do not use cyanide.

In an ideal world I would simply use the alkali cleaner before the ceramic taking advantage of both its grease removing and physical scrubbing action. I would then use the same process after the ceramic is applied (pre-plate) taking advantage of its scrubbing action but regarding its grease removing properties as being hopefully redundant. The reason I cannot adopt this simple re-use of an existing process is the fact that the ceramic does not stand up particularly well to hot alkalis so I am looking for the same scrub action but without the alkali.

What am I trying to scrub off ?
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The steel that requires plating has been protected from gross oxidation by a paste which is a ball milled mixture of sand (safety note below), specialist clays, wood ash and so on. The anti scale mixture is very good but it is not perfect, there are still thin oxide films in places (blue haze not hard black crust). Even though the anti-scale is doing a very good job and leaves shiny steel in places it is not perfect and I watch out for particles hiding in pores and pits, the steel is used as supplied (cold rolled) and magnification at only 40x shows within the apparently smooth surface there are plenty of places for particles to hide. I could resort to full on blasting but I consider that a last resort as it brings along its own issues and complications, my judgement is that an acid pickle, electrolytic scrub and a very light hand applied abrasion should be sufficient - at least thats the direction I am trying to pursue before resorting to blasting indeed the effort gone into the anti-scale reflects the wish to sidestep blasting as a process.

Jon

Postnotes
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Safety Note: Since I mention ball milling of sand. For the unaware experimenter please make sure you are familiar with the dangers of ball milling, sand and silicosis. Ball mills can/do produce ultra fine powders. There are substances which are considered benign in larger grain size which are potentially hazardous to health when milled ultra fine - glass for instance, freshly WASHED large grain frit is not usually considered hazardous but ball milled ultra fine glass frit can easily go airborne.

Anti-scale Note: The anti-scale mix I have experimentally developed is based on what westerners "think" Japanese sword makers are/were doing - by this I mean that master craftsmen tend to be a bit cagey about whats in their mix. I avoid certain anti-scale products sold in the west because they tend to cause pitting (borax and so on) so I use only specialist clays, ash and sand. The effectiveness of these pastes is highly dependent on particle size - clay is already composed of very fine particles but sand is not - in addition ultra thorough mixing is required (stirring paste with a spoon does not cut it here).

Jon Light [returning]
- Salum, Denmark

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Sorry Geoff, I can see my previous wording very reasonably led you to question if I was relying on red heat to remove grease. The answer is no -- I am afraid coming from a scientific background I have a kind of "Doubting Thomas" approach that tends towards belt and braces. I betray my doubting mind by lining up three processes (solvent, alkali, heat) and then suggesting that the third would be a safety net for the first two - its more of the "no such thing as 100% only 99.99999%" if you catch my drift :-) Either way from your response I see that you think that heat treatment would only convert one problem (grease) into another (hard to remove carbon) - makes me think of my first plain steel wok so my take on that is "don't lean on the third process as a catch all" - thanks.

Sorry Ted, if I had been more on the ball I would have sensed my previous mis-direction to Geoff and got it all in one posting instead I have posted twice today.

Jon Light [returning]
- Saltum Denmark
November 24, 2015