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  1. #1
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    caustic lye and alloy (last time I ask this, I swear)

    I just want to know if the caustic lye (NaOH) will mess up my choice cro-mo steel frame when I put it in there to dissolve the aluminum seat post that is royally stuck inside her. Buddy says alloy is different than elemental metal but a jar of draino, which contains NaOH says to keep away from chrome, and as we know there is a fair bit of chrome in that steel frame. But is she locked away chemically inside that iron, or will she be lured by the temptuous and exciting sodium hydroxide, corrupting the structure of my beloved Japanese Lugged Mountain Frame? Any inorganic chemists in the house? Please share. Many thanks, and sorry for bringing this up again but the search engine isn't even giving me a straight answer (people who had gone the way of Lye did so on high-tensile frames which of course contain no cromium).

  2. #2
    Senior Member DannoXYZ's Avatar
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    Uh... NaOH is a base and will only dissolve the oxides of aluminium. Namely the surface anodization. Once it eats up the surface, it'll stop working. You'll need an acid next to eat away the bare aluminium (oxidation).

    And no, NaOH won't hurt chromoly steel.

    And there are also easier ways to remove a stuck seatpost...

  3. #3
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    Quote Originally Posted by DannoXYZ View Post
    Uh... NaOH is a base and will only dissolve the oxides of aluminium. Namely the surface anodization. Once it eats up the surface, it'll stop working. You'll need an acid next to eat away the bare aluminium (oxidation).

    And no, NaOH won't hurt chromoly steel.

    And there are also easier ways to remove a stuck seatpost...
    very wrong, it will dissolve the aluminum (reduced metal Al) and quick
    making H2 gas

    dont know much more chemistry other than that, but if I had to guess I would think it would not do much damage to the steel
    keep a bottle of vinegar handy

  4. #4
    2-Cyl, 1/2 HP @ 90 RPM slvoid's Avatar
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    This might explain why my aluminium cookware gets f**ked up in the dishwasher...

  5. #5
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by special View Post
    very wrong, it will dissolve the aluminum (reduced metal Al) and quick
    making H2 gas

    dont know much more chemistry other than that, but if I had to guess I would think it would not do much damage to the steel
    keep a bottle of vinegar handy
    You are correct. The sodium hydroxide will react with the aluminum until there is no more NaOH left. The problem is going to be keeping the NaOH solution in contact with the aluminum and venting the hydrogen. You get a fair amount of hydrogen (not as much as with some other metals), llamer, and it is flammable. Make sure you do this with lots of ventilation. You'd probably do better with potassium hydroxide than sodium. Here's the reaction:



    It's not that fast and you'll chew up a lot of KOH to do it. If you have 100 g of seat post, you'll need 5000 mL of 1.5M KOH to do it. (Ratio is 1g Al to 50 ml of 1.5M KOH) You'll need about 500 g of KOH in water. If you can buy the KOH, it'll cost you around $22. But the real problem will be holding 5 L of solution in a 50 mL tube...kinda can't be done

    But be very careful with it. Making the solution isn't trivial. 500g takes a while to dissolve and it makes a lot of heat doing so. Any hydroxide solution of that concentration can do nasty stuff to you! Bare skin exposed to it will saponify...turn the underlying fat tissue to soap. I've worked with chemists who have pulled the skin off their hands when they took a leaky glove off...not pretty If you get it on your skin, it will feel 'soapy'. Rinse with cool water until the soapy feeling goes away. And you have to figure out how to dispose of it.

    It would probably be easier to take the bike to a machine shop and have them bore out the post. At the very least, try to reduce the mass of aluminum in the frame with a file or some kind of hone before you try the KOH.

    As for reacting with the steel, it probably won't. Iron hydroxides aren't terribly water soluble nor that easy to form. But you are going to want to rinse with copious amounts of water and that might cause problems.

    All-in-all, you might want to find some other way.
    Stuart Black
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    I wouldn't even think of trying to dissolve the seat post out of the seat tube. As cyccomute says, keeping the base solution in contact with the seat tube would be difficult unless you wanted to dip the frame upside down in a tub of strong base.

    The reaction equation posted by cyccomute appears to be an overall equation for a multistep process, with base and acid steps. Strong bases like KOH by themselves will react with aluminum metal without the acid (the H2SO4 in the equation) to make, for example, KAl(OH)4, which is soluble.

    This might work - First cut off the seat post with a hacksaw, leaving 1/4" or so extending above the seat tube, enough to grip with pliers. Then take the hacksaw blade out of the saw frame, wrap a rag around one end as a handle, and cut a groove on the inside of the the stuck seat post, taking care to keep the blade flat so that you only cut the seat post stub and not the seat tube. To cut completely through the stub, you may scratch up the inside of the seat tube a little, but make sure you don't cut into the seat tube enough to weaken it. Once you get a groove cut through the stub, grip it with pliers next to the groove and try to bend it inward to loosen it. If that doesn't work, try cutting another groove opposite the first one and take the stub out in two pieces.

    Use a good, sharp hacksaw blade with 24 or 32 teeth per inch. If you need to buy one, get a bimetal blade, which might cost twice as much but will last more than twice as long as a regular blade.

    Or, as suggested, take it to your LBS and let them bore it out. What I just wrote seems like a lot of work.

    My two cents,

    tcpasley

  7. #7
    biked well well biked's Avatar
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    Quote Originally Posted by tcpasley View Post
    ........This might work - First cut off the seat post with a hacksaw, leaving 1/4" or so extending above the seat tube, enough to grip with pliers. Then take the hacksaw blade out of the saw frame, wrap a rag around one end as a handle, and cut a groove on the inside of the the stuck seat post, taking care to keep the blade flat so that you only cut the seat post stub and not the seat tube. To cut completely through the stub, you may scratch up the inside of the seat tube a little, but make sure you don't cut into the seat tube enough to weaken it. Once you get a groove cut through the stub, grip it with pliers next to the groove and try to bend it inward to loosen it. If that doesn't work, try cutting another groove opposite the first one and take the stub out in two pieces........
    What you have written is pretty much what Sheldon describes as the "last resort," step #16, in his article on stuck seatposts. http://sheldonbrown.com/stuck-seatposts.html

    It does seem very likely that this would work as a last resort, but I'm pretty sure I've heard reports here of galvanic corrosion so bad that even this wouldn't work because the seatpost and seat tube had bonded so completely. I have no first hand experience with that techique, I've been lucky in that any stuck seatposts I've encountered I've been able to get loose by installing a junk saddle on the post and then beating the saddle on the nose, first one side and then the other, with a hammer.
    Last edited by well biked; 10-20-07 at 12:24 PM.

  8. #8
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    No plagiarism intended. I wasn't aware of Sheldon's article on the subject. Once again, he's way ahead of most folks on the journey through "been there, done that" land.

    The sacrificial saddle and hammer is a good idea. Maybe also some torque on the seat post with a strap wrench of vise grips while hammering, too, if you have enough hands available.

    tcpasley

  9. #9
    biked well well biked's Avatar
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    Quote Originally Posted by tcpasley View Post
    No plagiarism intended. I wasn't aware of Sheldon's article on the subject.

    No, I didn't mean it that way. More like "great minds think alike."

  10. #10
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by tcpasley View Post
    I wouldn't even think of trying to dissolve the seat post out of the seat tube. As cyccomute says, keeping the base solution in contact with the seat tube would be difficult unless you wanted to dip the frame upside down in a tub of strong base.

    The reaction equation posted by cyccomute appears to be an overall equation for a multistep process, with base and acid steps. Strong bases like KOH by themselves will react with aluminum metal without the acid (the H2SO4 in the equation) to make, for example, KAl(OH)4, which is soluble.
    Oops I gave the reaction for making alum from aluminum. KOH reaction with the aluminum is the first step and it's the one that makes hydrogen. The sulfuric acid isn't needed at all. Sorry.
    Stuart Black
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  11. #11
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    Quote Originally Posted by cyccommute View Post
    Oops I gave the reaction for making alum from aluminum. KOH reaction with the aluminum is the first step and it's the one that makes hydrogen. The sulfuric acid isn't needed at all. Sorry.
    Hey! I remember making alum a few years back in high school chem
    I was a good student, but Ive just about forgotten most of it now
    I am suddenly encouraged to "get back into" chemistry and sign up for a course next semester
    anyone think I should do general or organic?

  12. #12
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by special View Post
    Hey! I remember making alum a few years back in high school chem
    I was a good student, but Ive just about forgotten most of it now
    I am suddenly encouraged to "get back into" chemistry and sign up for a course next semester
    anyone think I should do general or organic?
    General first. A little more fun. Organic is rather cerebral with lots of reactions to memorize.
    Stuart Black
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    An Good Ol' Fashion Appalachian Butt Whoopin'.

  13. #13
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    well thanks for your advice everyone, including cyccommute. i had a feelling that this wouldn't work, and knowing that it will take at least a pound of KOH (and I have NaOH so likely more is needed) maybe i ought to quit. I went ahead and did it anyways, just for fun. Currently I would rate the temperature of the seat post at something like 100 degrees, but it's hard to tell because of the duct tape around it. and i would have done more stuff like the saddle-whacking idea but the god damned piece of seat post which holds the saddle came out (unglued) when i realized the thing was in there for good -- likely the result of the previous owner torquing away at it.

    so maybe a machine shop, or if i find someone with an adjustable reamer. i'm just worried a machine shop will ream ME for it (fiscally) or possibly damage the tube. a friend did recommend something he's done a couple of times, which was cut off the last remaining bit of post and then use a very hot torch to MELT the tube out (but i like the paint job so that's a no-go). Or also drill a hole in the bottom of the BB and then insert a long piece of steel and then pound out the tube from the bottom.

  14. #14
    South Denver Commuter Leiniesred's Avatar
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    Stuck post

    PB Blaster. Just spray it every day. Whack the post with a hammer (like you mean it) before you spray every day.

    If you have the time, it'll work. If you want it out now, hacksaw blade. get a quality blade. big difference.
    200? Bianchi Milano (main commuter)
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  15. #15
    sch
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    One other bad thing lye does is remove paint. It is an excellent paint remover.
    It also has minor effects of dissolving skin, does horrible things to eyes, and
    converts fat to soap, if your skin dissolves away. The protein dissolving effect
    is why lye feels so slippery when it gets on your hands, and why it takes a ton
    of water to get it off. It is also why it works nicely as a drain cleaner, it dissolves
    the hair and fat in the drain clog.

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