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I read that to make a dipped tantalum capacitor, they make tantalum powdered stick together with a binder and then sinter, which makes it porous.

But why do the pores form? It seems that if they are compressed then it would remove pores. Is it air bubbles?

Thanks

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Anything sintered has a sponge like structure with pores. That's what sintering is. For example, oil-impregnated bronze for use as self-lubricating bushings.

You're compressing the metal powder so that adjacent particles are applying pressure against each other, but they are not liquified. More like a putty, if anything I believe. They only deform slightly and fuse at the contact boundaries between particles. The empty space between the particles are still there.

Also, do not mislead yourself to believe it necessarily needs to look like a sponge to the naked eye. The particles can be powders after all when they are, the pores may be so small that it might just look like a solid mass. For example, sintered bronze bushings looks just like a solid piece of bronze.

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  • $\begingroup$ fuse at the contact boundaries between particles. What does "fusing" in this case mean? $\endgroup$
    – MeltedStatementRecognizing
    Commented Nov 28, 2022 at 20:16
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    $\begingroup$ @MeltedStatementRecognizing I believe it's basically the same as cold-welding, except they heat it up to facilitate the process so that less pressure is required. They do not heat it up so much that it turns too liquid. $\endgroup$
    – DKNguyen
    Commented Nov 28, 2022 at 20:23
  • $\begingroup$ Sintered items can have visible particles, too -- I've used sintered brass filters that are made out of small brass balls that are visible to the naked eye. $\endgroup$
    – TimWescott
    Commented Nov 28, 2022 at 22:14
  • $\begingroup$ @TimWescott Oh yeah, I guess the porous air filters really would look porous. I have some of those. I forget they're sintered. $\endgroup$
    – DKNguyen
    Commented Nov 28, 2022 at 23:15

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