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Thread: Reaction between Aluminum and my Chlorinated pool water?

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    Reaction between Aluminum and my Chlorinated pool water?

    Hi! New here but signed up b/c I have a rare question that I can find little about through Google. Long story but a swim up bar was installed in my pool last summer. (It is removable.) It was constructed out of aluminum so it wouldn't be too heavy but it appears that the aluminum reacted with the chlorine in the pool water and crystalized. These crystals are stuck to the aluminum itself and also fell off into the water. When the pool bar was removed for winterization, water, dish soap, and a sponge actually got a good deal of it off b/c the crystals are not that hard. If I were to use the swim up bar again this year, do you know of any chemical I can use to clean the crystals off the aluminum thoroughly? And, any ideas of how I could prevent this from happening...? Like if I could treat it with something? My house is on the market so it would not be worth it to me to switch over to a treatment other than Chlorine.
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    Administrator JasonLion's Avatar
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    What color are these crystals? Chlorine would not be my first guess for a possible cause, but no way to know without more info.
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    white

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Aluminium is possibly a poor choice for immersion in chlorinated water. It's possibly aluminium oxide. anodizing the aluminium would help with the corrosion but its a sacrificial thing, once the oxide forms it protects the aluminium underneath, cleaning it off just allows fresh oxidation to occur.

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    And how does one go about anodizing aluminum?
    The problem with leaving it is that parts of the crystals fall off into the pool and I don't want to damage the liner or anything.
    And yes, aluminum was clearly the wrong choice of material!

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    From : http://astro.neutral.org/anodise.shtml
    "Chemically speaking, aluminium is an extremely reactive metal. We are familiar with the action of the environment on iron. It oxidises quite readily to produce iron oxide - or rust as it's more commonly known. Aluminium is more reactive than iron, and, as such, will rust more readily. However, with aluminium a rough layer of aluminium oxide forms which strongly inhibits further oxidation. This is why aluminium is known for its resilience in corrosive environments - eg car radiators or boats. After a period of time the aluminium "rusts" - slowly producing a white powdery coat.

    Thankfully for the aluminum industry there is a technique which overcomes the inherent softness of the metal and protects against further oxidation. Using chemical processes it is possible to build a carefully controlled layer of aluminium hydroxide on the surface of the metal which is extremely hard - much harder and more durable than the rough natural oxidised layer that normally forms. The process involves suspending the aluminium in and acid bath and passing an electric current through the it. This is known as anodizing - so called because the aluminium part forms the anode in the electrolysis bath.

    The other advantage of anodizing aluminium is the potential of coloured anodizing dye. Coloured dye seeps into the microscopic pores of the anodized layer and colours it. The layer is then sealed and the colour appears as part of the aluminium metal itself. This can be used to great artistic effect, producing aluminium parts with strikingly tasteless colours to adorn your motor bike or, more topically, telescope. With optical applications, black is the most popular anodizing colour to reduce internal reflections. Typically of course, black is supposed to be one of the most difficult colours to achieve and commercial black anodizing dye fetches the highest price.

    Anodizing aluminium (or indeed anodizing aluminum) is a fairly simple process, and providing you can lay your hands on the correct chemicals (ie sulfuric acid) it is fairly straightforward to do simple diy anodizing aluminium in the home. I would limit yourself to anodizing aluminium in fairly small amounts - if you want to anodize a large object you need a lot of electrical power and a lot of acid, so if you want to do an entire bike frame in one go, I suggest you contact an aluminium anodizing company. "

    Don't think anodizing is going to be a possibility... the bar is much larger than a bike frame! So I'll have to go the protective rust coat route.
    Thanks for your help!

  7. #7
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Any commercial anodisers around you? it is such a popular finish large pieces are pretty common.

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Actually it looks very similar to what happens to aluminum pans that have been left sitting in water. Can you post a current set of test results, especially your current calcium level?
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    I haven't opened the pool yet... right now it's sitting in gravel outside of the water!

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    I'm with zea3, I think it's calcium.
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Ok... do you think my calcium levels may actually be too high or that the level of calcium that my pool requires happens to react with aluminum? I guess I'll just keep a real close eye on my calcium levels this year and find out!

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Your calcium levels may or may not be too high. I suspect that aluminum is probably not the best material for pool use and that the calcium will precipitate onto it regardless of the level.
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    Mod Squad zea3's Avatar
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    I don't know if painting it will help or not. About the only metal I ever see used in pools is stainless steel or has had a powder coat finish baked on. Sometimes you can find local businesses that do powder coating. You may want to get an estimate and see if it is worth the cost.
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    You generally do not want to have aluminum in contact with pool water and if you do it most definitely should be anodized aluminum. If you want to continue to use this aluminum, then you can electrically connect (via a wire) a sacrificial anode to it. By any chance, do you have a saltwater chlorine generator (SWG) pool? Higher salt levels will exacerbate the problem. This is why salt pools with electric safety covers that have immersed aluminum headers usually use a sacrificial anode to slow down corrosion.
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    I don't know exactly what the substance is, but I recognize it. Anything aluminum that gets near a sailboat (at least one in salt water) is covered with it.

    That rail needs to be stainless steel, plastic of some sort, or you could try coating it with something, like that plastic-dip stuff. It works on the boat for a year or two.
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    Re: Reaction between Aluminum and my Chlorinated pool water?

    From a chemical perspective, although salt crystals may closely resemble what you are observing my hypothesis is that the white powder build-up is aluminum chloride.

    copied from:
    http://www.chemeddl.org/alfresco/servic ... guest=true
    "Aluminum and chlorine do not react rapidly at room temperature, but if the aluminum is heated, the reaction is vigorous. The product is aluminum chloride, a white powder that fumes in air, reacting with water to form HCl gas and aluminum oxide."

    That being said I would venture to suspect this build-up is observed more greatly in times when the sun heats the aluminum of your ladder.

    Without even emphasizing the harmful effects of the aluminum on the body (such as its direct correlation with Alzheimer's) since most water treatment processes include aluminum use anyway (not to mention any of the other plethora of products and methods exposing us to aluminum...) Considering the HCl mentioned in said quote would probably exceed in urgency.

    copied from:
    http://www.cdc.gov/niosh/docs/81-123/pdfs/0332.pdf "Occupational Health Guideline for HCl, Centers for Disease Control"
    (please note this is a PDF file so yes I did hand copy this passage and re-type it bc I believe it is important to share with you)
    "-Effects of overexposure
    1.Short-term exposure: when hydrogen chloride gas is inhaled, it may cause eye irritation, severe burns and permanent damage with loss of sight. Solutions of hydrogen chloride may cause severe burns of the skin unless the acid is washed off immediatly. Exposure of the skin to hydrogen chloride gas may cause skin inflammation or burns, swallowing hydrogen chloride solutions may cause burns of the mouth, throat, and stomach.
    2.Long-term exposure: Repeated or prolonged exposure to hydrogen chloride may cause erosion of the teeth. Repeated exposure of the skin to dilute solutions of hydrogen chloride may cause skin rash."

    To reiterate: aluminum chloride (white powder) reacts with water to form HCl gas... I hope this has been helpful to you, and I hope your pool is not in a sun room trapping any HCl gas. Please do consider taking precautions. Wishing you good tidings from your real estate agent, take care.

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    Re: Reaction between Aluminum and my Chlorinated pool water?

    Welcome to TFP!

    This thread is more than 2 years old and the information you provided is incorrect in the context of what is going on with aluminum corrosion in swimming pools. The reference you cited said "Aluminum foil heated to glowing red reacts vigorously with chlorine gas in a flask." We aren't using chlorine gas and the aluminum is not being heated to glowing red -- the chlorine in pools is dissolved in water and the active chlorine is hypochlorous acid (HOCl). HCl gas is not being produced. The HCl resulting from chlorine oxidation of aluminum dissolves readily in water to lower pH and to form chloride salt. Aluminum already reacts with oxygen in air to form a passivity layer of aluminum oxide. When some chlorine is able to penetrate defects in this layer to react with the underlying aluminum, it produces aluminum oxide and hydrochloric acid, but not as a gas since it is immersed in water.

    3HOCl + Al(s) ---> Al2O[sub]3[/sub(s)] + 3H+ + 3Cl-
    Hypochlorous Acid + Solid Aluminum ---> Solid Aluminum Oxide + Hydrogen Ion + Chloride Ion

    Because of the aluminum oxide passivity layer already on the aluminum, the above happens slowly, not vigorously, and is just metal corrosion that can be mitigated by using a zinc (or magnesium) sacrificial anode.
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