Another warning.

[tonyfoale]

I suspect that like me other machinists keep some caustic soda for things like removing stuck aluminium from carbide milling cutters etc. it really works well.

I had some stored in a plastic jar that started life as a container for honey, jam, coffee or something in that line. A month or so back I wanted to use it, the first time in months. This is what I found.

Click on thumbnails for full size images.

We tend to think of plastic as capable of holding most liquids save for organic solvents, I did but I was wrong.
Glass can be dangerous in a workshop but I keep my caustic soda in it now.

[MeJasonT]

Is this a good time to mention material science, The great thing about plastic recycling at home and 3D printing is that we can now identify different plastics.
PET plastic Polyethylene terephthalate don't ask - is really crap for keeping acid or strong alkaline such as Caustic soda in (Sodium hydroxide https://en.wikipedia.org/wiki/Sodium_hydroxide). isn't sodium salt.
Polypropylene is the baby for chemical jars where your average ABS and PLA 3D printer stuff are not so good. However you can smooth 3D prints by putting them in a container with superglue, the fumes decay the surface smoothing your part also superglue vapour is damn good for lifting latent fingerprints if you watch CSI.


https://en.wikipedia.org/wiki/Plastic
https://www.ryedale.gov.uk/attachmen...ymer_types.pdf

[Drew1966]

I suspect that like me other machinists keep some caustic soda for things like removing stuck aluminium from carbide milling cutters etc. it really works well.

I had some stored in a plastic jar that started life as a container for honey, jam, coffee or something in that line. A month or so back I wanted to use it, the first time in months. This is what I found.

Click on thumbnails for full size images.

We tend to think of plastic as capable of holding most liquids save for organic solvents, I did but I was wrong.
Glass can be dangerous in a workshop but I keep my caustic soda in it now.

Tony, Sodium Hydroxide is an organic solvent naturally found at low concentration in seawater.

[JTG]

As a chemist, it is my duty to inform you that literally every aspect of your description of sodium hydroxide is incorrect.

Sodium hydroxide, commonly known as lye, is an inorganic compound which is a white solid at room temperature. As a strong base it completely ionizes in water, so claiming that it is found in sea water is misleading at best; sodium ions are certainly present in large quantities (3.1-3.8% of seawater by mass), but the concentration of hydroxide ions is orders of magnitude lower, and evaporating seawater would only give trace quantities of sodium hydroxide.

For anyone interested, high-density polyethylene (HDPE) is the recommended storage medium for strong alkali, both in solid and liquid form. Concentrated alkali solutions will slowly etch glass, and over significant periods of time (years) can cause the failure of glass bottles.

[Drew1966]

I’m sorry? One of the companies I have worked for over the years used to process seawater, by evaporation and vacuum concentration, mostly to obtain table salt, but one of the byproducts was Sodium Hydroxide.

[JTG]

Are you certain that the sodium hydroxide wasn't the result of a chloralkali process? Electrolysis of sodium chloride brine is the primary production route for sodium hydroxide, and it also produces hydrogen and chlorine gas. However, this process involves the electrochemical oxidation of the chloride ions in solution, and the simultaneous reduction of water, thus producing hydroxide ions as hydrogen gas is liberated.

If it was obtained through a chloralkali process, then the process itself generated the necessary hydroxide ions from water, instead of them being present in the sea water originally. Perhaps I'm being too pedantic about the specifics -- I would similarly take issue if someone claimed that water was made of hydrogen and oxygen gas; it is absolutely made of hydrogen and oxygen atoms, but it takes a great expenditure of energy to convert them to their elemental forms.

[Drew1966]

I’m pretty sure all that was used was solar dehydration and vacuum dehydration. Although some salt from salt lakes was mixed into the seawater, and I remember one of the seriously techno-geeks saying it was to increase the density so that the water would release less heat.

[MeJasonT]

This is becoming a very informative and interesting thread.
Having turned my hand at anodising im well aware of the potency of the little 1ltr bottle of Caustic Soda. Its being used to clean the aluminium prior to being electrificated in sulphuric acid to open up the pours in the metal surface to allow the die to be absorbed.
The caustic is mixed to 1 tablespoon to 2 litres water and it really does get the metal clean, i've also used the same concentration for light rust removal and it has brought the metal up like new.

People have a tendency of worrying about acids but don't treat strong alkaline with the same respect, hence Tony's pot.

Fumes from such substances are also seriously hazardous to health and well being.

JTG will make it sound much more technical than I can - its great to find a Chemist amongst our members and going to be very useful.

[MeJasonT]

Whilst reading the comments between JTG and Drew i remembered a joke i came across years ago.
not directly linked at all but just the essence, Drew has obvioulsy worked in industry and has been told how to do his job and probably done it for years, then JTG i'm sure is very experienced in his field is passing on his expertise. Its actually the David and Goliath scenario that made me chuckle not the facts so please don't take any observation or insult from it. The conversation just surfaced an old memory.

A man is flying in a hot air balloon and realizes he is lost. He spots a man down below and lowers the balloon to shout: “Excuse me, can you help me? I promised my friend I would meet him half an hour ago, but I don’t know where I am.”

The man below says: “Yes. You are in a hot air balloon, hovering approximately 30 feet above this field. You are between 40 and 42 degrees N. latitude, and between 58 and 60 degrees W. longitude.”

“You must be an engineer” says the balloonist.

“I am” replies the man. “How did you know.”

“Well” says the balloonist, “everything you have told me is technically correct, but I have no idea what to make of your information, and the fact is I am still lost.”

The man below says “You must be a manager.”

“I am” replies the balloonist, “but how did you know?”

“Well”, says the man, “you don’t know where you are, or where you are going. You have made a promise which you have no idea how to keep, and you expect me to solve your problems. The fact is you are in the exact same position you were in before we met, but now it is somehow my fault.”

The link led me here
https://otfjokes.com/dirty-jokes/a-p...ppy-situation/
just be careful who seduces you.

[JTG]

Well now I've been reading about all kinds of brine mining techniques and the mineral composition of marine evaporite, and I still can't figure out how one would get sodium hydroxide (NaOH) as a byproduct without first adding something to drastically raise the pH of the brine. Generally speaking, when you evaporate untreated seawater you end up with calcium/magnesium carbonates, calcium sulfates, and a variety of chlorides including table salt.

You mentioned there was a pre-treatment process, and knowing more about what was added might explain the production of NaOH as a byproduct. If the end goal was pure table salt, you would need to remove most of the other cations (calcium, magnesium) and anions (sulfate, carbonate) before evaporation. Typically this would be done by adding calcium hydroxide (lime), which raises the pH and precipitates out CaSO4, CaCO3, and Mg(OH)2. I know that some desalination plants use NaOH to achieve a similar effect, but it's more expensive than lime and its use is usually limited to applications where any additional calcium would be detrimental (such as reverse-osmosis plants).

In any case, the number of techniques used industrially is large and I'm certainly not aware of all of them. It would be interesting to know specifically what the company was adding, but the pre-treatment is likely the source of the necessary hydroxide ions, as seawater itself isn't basic enough to produce significant quantities of sodium hydroxide on its own.

To bring this back closer to the original topic of the thread, sodium hydroxide is quite useful in dissolving aluminum because it reacts to form soluble sodium aluminate and releases a small amount of hydrogen gas in the process, but does not corrode cemented carbides nearly as quickly. It is similarly corrosive to copper- and zinc-containing metals, and becomes much more corrosive when concentrated and hot.

Thick HDPE and polypropylene (PP) are the best plastics for storing NaOH, whereas it will attack polyethylene terephthalate (PET/PETE), polystyrene (PS), and polycarbonate (PC) fairly quickly. Another thing to note is solutions should be kept in an airtight bottle -- not due to any fumes (of which there are essentially none over a pure NaOH solution, as it isn't volatile), but to prevent the solution from absorbing carbon dioxide from the air. CO2 reacts with the NaOH to give Na2CO3 (washing soda), which is what all of that white crust/powder is on the dead plastic jar. Washing soda is a weak base and is still somewhat corrosive to aluminum, but the strength of your NaOH solution will degrade over time if you leave the bottle open to the atmosphere.