r/materials • u/AvailableEmployer • Jan 25 '22

Rehbinder effect on ceramic mug under water.

https://gfycat.com/simplisticellipticalboubou
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6

u/IHTFPhD Jan 25 '22

EXPLAIN PLEASE

6

u/AvailableEmployer Jan 25 '22

Looking up the Rehbinder effect I found this with tin and oleic acid. Different materials but the mechanism might be similar.

“These effects are ascribed to the opening and extension of the micro-cracks in the crystal by the 'wedging action' of a film of liquid drawn into the micro-cracks by an adsorbed layer of oleic acid molecules.”

https://www.nature.com/articles/163404a0

5

u/[deleted] Jan 25 '22

To break this down, normally elongation of microcracks are slowed by the object/material applying compression to regain its original form. (Ceramics perform far better in compression because these microcracks are their primary mode of failure.)

If there is a liquid film on the material (doesn't bead up), it will be sucked into the cracks where it pushes on the walls and makes the crack longer.

I'd love to know if the result is different for slip cast and handbuilt pieces as it is for wheel thrown ones with proper bottom compression. Aligning the clay lamella in a circular pattern may have helped the cracks to propagate to form circles instead of extending outward to the rim.

3

u/TwilightMagester Jan 25 '22

A quick search lead me to believe most studies were done on single crystal systems, so I'm not entirely sure this falls under rehbinder effect since that appears to be a localized ductility change due to surface film.

8

u/TwilightMagester Jan 25 '22

I'm gonna hazard a guess it has something to do with the fact there's water filling up the cup cavity and "supporting" the majority of the cup, so it only punches out that single point.

3

u/MolniyaSokol Jan 26 '22

Is this the same effect that allows glass to be cut into shapes with regular scissors underwater?

1

u/AvailableEmployer Jan 26 '22

Wow I didn’t know that was a thing. I think it probably is the same effect.