Trying to make an anodize stripping solution for some headlight bezels. If I mix 2lbs. of crystal lye with 3 gallons of water, what % of caustic solution will I have?

 

I don't know the mix %, but be careful with aluminum parts and lye. Lye and aluminum equals hydrogen.

 

I've never heard of stripping anodizing with lye.
Most of the time aluminum trim parts are repaired, polished, and re-anodized.
The polishing removes the anodizing.

 

8% NaOH solution (908g NaOH/11340g H2O)
Where 908g = weight of 2 lbs NaOH (solute); 11340g = weight of 3 gals H2O (solvent)

 

Thanks for the reply! How much more lye do I need to add to obtain 30% caustic solution?

 

Solving for x

x/11340g = 30% (0.30)
x = 11340g X 0.30g = 3402g

3402g - 908g = 2494g
You will need to add an additional 2494g NaOH to 11340g (3gals) H2O to achieve a 30% NaOH solution

x/y = z
Where x = g NaOH; y= g H20; z = %
x = 908g NaOH; y = 11340g H2O; then, 908g/11340g = 8% (0.08)
x = 3402g NaOH; y = 11340 H2O; then 3402g/11340g = 30% (0.30)

 

EZ Off oven cleaner in the yellow can works. Sounds a lot easier.

 

I prefer to use grams to pounds, but this equation is simple if you remain in pounds (or you can make the equivalent adjustments in ounces if you like). Simple stuff, you just need(ed) to get your equivalents.

1gal H2O = 8.34lbs; therefore, 8.34lbs X 3 (gals H2O) = 25.02lbs (H2O)

2lbs NaOH/25.02lbs H2O = 8% (0.08) NaOH solution
Again, simply solve for x

x/y = z
If z = 30% (0.30) what is x?
x = y X z (25.02lbs X 0.30) = 7.5lbs NaOH

Therefore, 7.5 lbs - 2 lbs = 5.5 lbs. You'll need to add an additional 5.5lbs to a known 8% NaOH solution to achieve a 30% NaOH solution. Think about it logically & you can quickly do the math in your head. If 2lbs NaOH in 25lbs H2O = 8%, you know you'll need roughly x4 times that amount to achieve a 32% NaOH solution.

 

Thanks Norm, impressive math skills For anyone following, the anodize is a very hard surface and very hard to just sand or polish off. 10 minutes in caustic solution and you can start polishing after any repair work.

 

Again, I've had success with EZ off.

 

Thanks for the tip, I will give it a try.

 

Other than providing you with answer(s) to your question(s) regarding % NaOH solution, two caveats to consider in EZ-Off application(s):

(1) Do not use the EZ-Off Fume Free product as it contains no NaOH; and,
(2) Easy Off Heavy Duty Oven Cleaner Aerosol contains ≤10% NaOH. So a little less than the 30% solution you were after but should work effectively none-the-less. I use the Easy Off Heavy Duty Over Cleaner Aerosol to clean engine parts (intake manifold etc. made of iron). I've never used it to remove the Al anodized layer.

JoeP told be Wal-Mart sells an oven cleaner much less expensive than Easy Off. I'll see if it I can find it.

Easy Off Heavy Duty Oven Cleaner Aerosol MSDS
EASY-OFF®Fume Free Oven Cleaner

 

I found the post where JoeP told me about the WalMart oven cleaner, but I never bought any. I'll see if I can find it.

Post>>> 9

 

Us common folk call oven cleaner Sodium Hydroxide, used in bluing salts for bluing guns and a bunch of other cleaning tasks, and it will make any aluminum you have mistakenly left in the salts disappear..Tedd

 

I guess us even more common folks call Lye Sodium Hydroxide since it has been used in making soap before they made oven cleaners.

 

This common folk just uses soapy paper towels to clean all the oven he can, then runs the cleaning cycle and gets the ash later. That serious of an oven cleaner makes me wonder about the grease fire in waiting that needed it in the first place.

 

We've gone from making a caustic NaOH solution to cleaning ovens. LOL

 

Make sure it's the good ol yellow can of EZ Off, the blue doesn't work.

 

Post #12

 

All this oven cleaning talk makes me want to clean the wife's oven....not

 

Not to be a jerk (although it does come easily), that mix would be a 7.41% solution. 908g/(11,340g + 908g) = 908g/12,248g = 0.0741.

More fun is the negative heat of solution of NaOH. 50g NaOH dissolved in 117g 68F water (a 30% solution) would go to 211F (assuming no heat loss).

 

I was amazed at how warm it got when I mixed in the first 2 lbs. of lye. Getting ready to add 2 more lbs. ,is it going to get even hotter?

 

You are absolutely correct & you're not being a jerk. I was trying to keep it as simple as possible w/in reasonable terms of a weight-weight ratio which most could follow in an automotive forum.

I trust we aren't next going to determine heat of enthalpy of this Rxn?

 

Dissolving lye (NaOH = Sodium Hydroxide = solute) into H2O (solvent) is a highly exothermic Rxn releasing energy in the form of heat. You should always add the solute (NaOH) to the solvent(H2O) slowly. Just as you would with a strong acid such as HCl (Hydrochloric Acid = Muriatic Acid). You would never want to add water to NaOH or water to HCl. You add the solute (e.g. NaOH) to the solvent (e.g. H2O).

In chemistry we say: "Do as you oughta, add acid to water". This provides a simple mental cue to assist in abiding by safety rules when dealing with strong bases and strong acids, but it should be used whenever you're mixing solvents and solutes to create a solution.

 

Next two pounds will give you a little less temperature increase, only because your solution is now 27-lbs, versus the 25-lbs of water you began with. Be careful, and eye protection is a must!

 

There's obviously no manner to tell what someone's background is when working with nearly anything - albeit, I just answer questions. As F-85 stated wear gloves & eye protection - always.
To be clear. A strong base (NaOH) solution burn is FAR, FAR more damaging to your body (especially mucous membranes) than a strong acid burn. Bases will literally eat away your adipose (fat) tissue in a heart beat and continue eating (dissolving) it deeper and further. You'd much prefer to have an acid burn than a base burn. None-the-less, with that said:
(1) Clearly label the NaOH solution container - VERY CLEARLY IN LARGE PRINT
(2) NEVER store a strong base (NaOH) solution or strong acid solution above ground. ALWAYS store them at ground level.
(3) Both strong acid solutions and strong base solutions REQUIRE a lid.

 

I guess I'm not really beating it to death if I'm referring to safety - so, I'll rant one more time in the name of safety.

Accidents happen. If yourself or anyone should spill Sodium Hydroxide solution on themselves, IMMEDIATELY run large copious amounts of COOL water (not warm, not hot) over the area of skin. Bases (e.g. NaOH solution) like bleach (Sodium Hypochlorite) are slippery to the touch. Continue running cool water over the area of skin during the 1st hour - every 15' to 20'.

 

Got the first one stripped. Had to add another gallon of water to keep bezel submerged so now I have 4 gallons of solution. Added 3 lbs. more of lye so according to my calculation I now have around 15% solution. The bezel below was submerged for 15 minutes and it appears to be stripped pretty good. Now the hard part, sanding and removing factory flaws, then polishing before anodizing.

 

Looks good.

 

First lesson learned when stripping anodize, sand or brush the black trim paint off first. Where the black gets left anodize remains and you have to dip it again in the solution.