I need to etch some stainless steel for a project. I found some instructions that only require household chemicals (it's kind of hard to acquire chemicals here). It required 30% HCl and 3% H2O2. I tried different variations of this with different concentrations (i could not get 30% HCl so i initially used 10% and then boiled it down to approximately 20% but not much changed). Interestingly, etching does appear to occur after submerging a piece of stainless steel in the solution but not in the expected way. The exposed area slightly darkens (some sort of chromium oxide i would guess, as the solution takes a turquoise colour) but not much else happens. However the edges of the masked off area appear to be properly etched, even though further in the metal is completely intact (as expected)
I added a picture of the best test piece i've made so far.
Is there a specific thing that's causing this and what should i do to solve it?
Thanks in advance
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4$\begingroup$ Very doubtful you got 20% $\ce{HCl}$ by boiling a dilute solution at 10%, so you probably have the story of "what's going on here" muddied by that, at least. $\endgroup$– Todd MinehardtCommented Jun 11 at 19:00
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1$\begingroup$ Are stripes across the detail and marks around the perimeter traces of welding or stamping (is a duct tape stripe in the middle)? Do you know the SS grade? Have you degreased the surface prior to acidic treatment (if yes, how?)? I think I've never seen a recipe like this: usually I'd use either phosphoric/sulfuric acid, or iron(III) chloride, or blue instead. $\endgroup$– andselisk ♦Commented Jun 11 at 19:05
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2$\begingroup$ @andselisk that piece was cut with a sheet metal shears so that's where the marking originates from. The stripe in the middle was the exposed area. The sides were masked off (including the areas with the actual deep etching) Unfortunately i don't really know the ss grade but i'll check if i can find it. The surface was cleaned with a penetrating oil, then degreased with acetone. For a different test i also tried sanding the surface down. Also i tried some high concentration sulfuric acid (i don't remember if it was 96% or 98%) and i only got discoloration. $\endgroup$– HristosCommented Jun 12 at 8:24
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1$\begingroup$ @ToddMinehardt Shouldn't i be able to concentrate it by boiling it down until it reaches an azeotrope? $\endgroup$– HristosCommented Jun 12 at 8:27
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2$\begingroup$ @andselisk I still haven't found the actual ss grade but it's either 300 or 400 series $\endgroup$– HristosCommented Jun 12 at 9:08
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1 Answer
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You could etch most stainless steels in far safer chemicals, e.g. $\ce{NaCl}$ in $\ce{H2O}$, i.e. salt water, using electricity.
- Prepare a bath of salt water at room temperature. You can experiment with different concentration, but a saturated solution is ~360g/L, and would likely etch fastest.
- Clean the piece to be etched scrupulously. Any oils or fingerprints will show up afterwards.
- Mask off the area to be preserved.
- Wash the work piece again.
- Connect the positive lead of a DC power source of between 3 and 12 volts, capable of supplying a few amperes. A DC power supply, battery charger or battery can be used.
- Connect the negative lead to bare scrap metal (almost any metal except aluminum, which has a surface oxide film should work). The scrap piece should be larger than the work piece.
- Adjust the pieces to be near each other, but not touching, because that would damage a battery or unprotected power supply. Move the pieces to make bubbling (and etching) uniform.
It's that simple!
Cautions
- Toxic chlorine gas is evolved, so this is best done outdoors.
- The resulting solution after etching contains toxic iron, nickel and chromium compounds. Do not let it contact eyes, skin, clothing, etc. Use eye protection and rubber gloves. Dispose of the chemicals safely and responsibly, even if small amounts. Adding some baking soda, $\ce{NaHCO3}$, should precipitate much as carbonates, before disposal.
answered Jun 11 at 21:24
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$\begingroup$ According to wikipedia water and HCl form an azeotrope at 20.24% HCl shouldn't that mean that by boiling a low concentration solution i should be able to get it to 20% essentially? Also i considered doing electrolytic etching but as far as i know you cannot get actual deep etching with a reasonable amount of work. I may be mistaken though. $\endgroup$– HristosCommented Jun 12 at 8:43