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Subliming, or evaporating polymers

  1. Dec 11, 2007 #1
    I have an application where I need to bond various materials together, perform certain machining, cutting, forming operations on this matrix - then - with the matrix in position, gradually heat & then drive off the polymer until only the metallic component remains in place.

    I had in mind a polymer-based substance due to its inherent strength.

    If anyone has information on subliming, or evaporating polymer substances I'd be most grateful. Alternatively, if someone has alternative suggestions - thanks indeed.

    This is a research/commercial application.

    Many thanks,
    mw...
     
  2. jcsd
  3. Dec 11, 2007 #2
    I don't really understand what you're asking.

    Are you saying that you need a material that bonds two metals together? Like an adhesive?

    And that it needs to perform certain mechanical operations and then upon heating, the adhesive sublimates and the metals separate?

    If I have this wrong, let me know.

    There are two subdivisions of polymers. Thermoplastic and thermosetting. What you would want is a thermoplastic polymer. These types of polymers soften when heated (and eventually liquefy). I'm assuming that if you raise the temperature enough that that liquid would also evaporate.

    Let me know if this helps or if I can help you more (which is probably a long shot).
     
  4. Dec 11, 2007 #3
    Many thanks for your kind reply.

    Essentially hold metals apart for initial machining.

    Upon heating, the spacer activity of the polymer would cease as it sublimates, or evaporates - leaving only the metallic components.

    Yes. Absolutely - unless the material were able to first sublimate. How exactly it disappears would not be too much of a problem - I'd expect the melting/evaporation route to take longer. The final objective would be to have no residue remaining.
     
  5. Dec 12, 2007 #4
    I guess you could use a polymer, but what type of polymer will depend on the distance between the two metals and if you want it to be rigid or flexible (among other properties I'm sure).

    If it is a large distance, I'm not sure that a thermoplastic polymer will have the mechanical properties to withstand the stress/strains associated with the design. However, a thermosetting polymer may be strong enough to hold the metals together. With a thermosetting polymer though, you would not be able to get it to sublimate because it will not soften upon heat treatment.

    What type of application is it? How much structural support does the polymer attribute to the design?
     
  6. Dec 12, 2007 #5
    Thanks so much for your comments

    The polymer-metal matrix would need to be 'fairly' rigid during cutting, & machining operations - too much slop would create inconsistencies on the metallic surfaces.

    Inter-metallic distances approx 0.1-1.0mm. This spacing in itself, would probably stiffen the polymer-metal matrix.

    Other than a polymer substance, I wonder what other materials could be considered? Essentially, the polymer is only necessary for initial cutting/machining, positioning of the component during assembly & support during much of the heating phase. After that it is a liability & needs to exit the system as cleanly as possible.
     
    Last edited: Dec 12, 2007
  7. Dec 12, 2007 #6
    Support during much of the heating phase?

    I'm not sure you can accomplish this and also have the polymer exit the system via evaporation. The support will decrease with increasing temperature if it is thermoplastic.

    Perhaps you could use a fiber reinforced polymer (a composite material) that would be stronger during the heating phase up until a certain temperature. At this temperature (melting temp), the polymer matrix will break down and hopefully exit the system. The melting temperature will depend on what kind of fiber you use.

    What temperature do you reach during the heating phase?

    You will have to determine the amount of heat you are willing to add to the operation after the heating phase has been accomplished so as to break down the polymer composite. This will increase the amount of energy input to the system, which increases cost. You will want to minimize the cost. Therefore try to select a composite that will break down at a temperature just slightly over the heating phase final temperature.

    I imagine there is an easier solution to this than what were are starting to get into. Clearly my lack of engineering experience precedes me in this discussion.
     
  8. Dec 12, 2007 #7
    Thanks for your input & brain-storm.

    The polymer support can be phased out fairly early if correct material tolerances & a level of interference fit is accommodated - so this portion can probably be neglected. In this sense, the polymer's major role would be sufficient up to say even less that 100'C, or maximum machining temperature. After that, once the polymer-metal matrix is in place, it can begin exiting the system - by whatever means.

    Now, what type of thermoelastic/thermoplastic polymers could fit into that role? Suppliers/manufacturers?
     
  9. Dec 12, 2007 #8
    I would suggest looking up information on thermoplastics, amorphous polymers, etc. I really don't know myself. good luck
     
  10. Dec 12, 2007 #9
    Thanks so much - you have been extremely helpful.

    Regards,
    mw...
     
  11. Dec 13, 2007 #10

    chemisttree

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    It sounds like you are drifting toward powder metallurgy. Wiki has a pretty good article about the process. If you could use a metal/ceramic composite rather than just a metallic piece, you might consider that route. In that example, the binder for your metallic powder would be a preceramic polymer. Upon heating the preceramic polymer would harden into a ceramic/metal composite. You would have what is referred to as a near net shape ceramic/metallic composite. The silicon carbide SCC composite used on the space shuttle is manufactured in this way. A carbon fiber/amorphous carbon preform is infiltrated with molten silicon and heated to convert the skin to a silicon carbide. No metal remains in that example because high temperature stability in a triplet oxygen environment (i.e. re-entry conditions) is the ultimate goal, however there is nothing to prevent you from using more silicon on a more porous substrate yielding a rigid silicon-carbide reinforced silicon metal composite. Alternatively, you could use a porous metal preform or even a slurry of metallic particles in a preceramic polymer matrix. In these examples, the binder (preceramic polymer) never leaves the system.
     
  12. Dec 19, 2007 #11
    ^ Thanks for your excellent post.

    Oddly-enough, my original thoughts for this thread were more around a 'lost-wax' type concept leaving metallic objects in place, whilst binder-spacer disappeared, but, your post has triggered an 'Ahah moment' & has shunted me along an alternative path.

    I had been investigating, in parallel, a superfine powder metallurgical concept. This path now suddenly seems to be a lot more plausible.

    Thanks so much for your input - I love the 'Ahah moments'. o:)
     
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