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Good choice of chemically resistant filament

Discussion in 'General Questions' started by DavidR, Feb 18, 2019.

  1. DavidR

    DavidR Member

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    I would like to make an electrochemical cell. I was wondering if anybody might have good recommendations for chemically inert filaments. Ideally, it would not be prone to corrosion via acid/base interactions or redox. Polypropylene has this property but is supposed to be virtually impossible to print with.
     
  2. Geof

    Geof Volunteer Moderator
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    PP is about the only material I can think of and it all depends on your acid. I'd grab a few manufacturers MSDS and see what shakes.

    I print PP on my Ultimaker with zero issues.
     
  3. DavidR

    DavidR Member

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    @Geof Interesting, I read awhile back that it warped worse than ABS. Also at that time I could only find it in 3mm but it appears now to be available in 1.75. The standard used to store chemical reagents is HDPE but I can only find one manufacturer and they are sold out.

    I was more interested in the base resistance than mineral acid as I would be using it to make hydroxides. Although sometimes I will make sulfuric acid by electrolyzing copper sulfate solution. I had wanted to use it to isolate group I metals by electrolyzing their salts but that can't be done in solution---you have to electrolyze the molten salt itself which requires temps on the order of 300 C. I quickly realized the filaments couldn't sustain that temperature.

    I will note that according to this (possibly sticky worthy) chart:

    https://kuhnke.kendrion.com/attachment/ICS/ics_pdf_brochure/ics_pdf_chemical-resistance-2015_en.pdf

    PVDF takes the cake for anything except bases (better even than PP). Its even resistant to chlorine gas! I will note that it appears to have very minimal resistance when it comes to inorganic bases. Seems to be more expensive but not outrageously so.

    I've also thought of using ceramic clay-based PLA, which supposedly maintains its structure if you debind the PLA by heating it in a kiln, and then applying an inert glaze. Would then have temp resistance up to 1000 C. Have you used this latter filament before?
     
    #3 DavidR, Feb 19, 2019
    Last edited: Feb 22, 2019
  4. Geof

    Geof Volunteer Moderator
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    I do have an enclosure on my Ultimaker- but the top is off and door is open when I print PP-
     
  5. Geof

    Geof Volunteer Moderator
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    More in depth into the chemical science of materials than I get, so I wont be of much more help than its possible to run PP lol.
     
  6. Geof

    Geof Volunteer Moderator
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    Never seen it before, but I seriously (SERIOUSLY) doubt any material will hold up to 1000 C after being printed. Anything is possible I spose :D
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The ceramics would. Remember you are extruding the base ceramic (think -- the clay) which then gets oven cured and can be quite sturdy :)
     
    WheresWaldo and Geof like this.
  8. DavidR

    DavidR Member

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    @Geof As Mark said what is advertised is after you heat the ceramic filament the PLA is completely removed (maybe vaporized?) and all that remains is the clay. With regards to the sciency bit...

    Electrolysis refers to the process of running a current through a liquid material (generally water-based ionic/electrolyte solutions). It can be used to drive reactions that normally would not occur. For instance, when making sulfuric acid in the process above I will use a copper cathode and an inert anode (I use platinized titanium) and dip them in a copper sulfate solution and then subject them to a potential difference (e.g. connect them to a battery). Copper (II) sulfate (CuSO4) is an an ionic compound consisting of a positively-charged copper cation Cu^2+ and a polyatomic sulfate anion SO4^2- that are "stuck together" because of their opposite charges. When dissolved in water it breaks apart into these component ions. The following process then occurs (Note: e- here refers to an electron)

    At the anode: Note when several species are present at the anode only the one most easily oxidized (i.e. the one most willing to give up its electrons) will participate. In this instance we have sulfate and water. It turns out that water has the higher reduction potential and so the sulfate remains untouched:

    2H2O ---> O2 + 4e- + 4H^+ (giving off oxygen gas)


    at the cathode: 2Cu^2+ + 4e- ----> 2Cu (solid copper plates at the cathode)


    Thus the process amounts to a removal of the copper ions an addition of hydrogen ions (the latter coming from the splitting of water).
    The species that remains is hydrogen sulfate (H2SO4) which is referred to as sulfuric acid when dissolved in water.


    Group 1 metals correspond to the left-most column of the periodic table. They are not found in their pure form in nature as they are so reactive. The issue in obtaining these metals via electrolysis in water, like with the copper above, is that they immediately react with water to form hydroxides. For instance, sodium hydroxide (aka lye) is commercially obtained by electrolysis of sodium chloride (aka table salt, NaCl) solutions (this is called the chlor-alkali process):

    At the anode: 2Cl- ------> Cl2 + 2e- (giving off chlorine gas)

    At the cathode: 2e- + 2Na+ -----> 2Na (giving sodium)

    However the sodium then immediately reacts with water to give sodium hydroxide and hydrogen gas:

    2Na + 2H2O ------> 2NaOH + H2.

    In order to obtain sodium metal you can't have water present. Instead, you melt the sodium chloride and electrolyze that. Ionic compounds like sodium chloride tend to have high melting points. Most filaments are organic compounds and tend to melt at relatively lower temperatures.
     

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