|MadSci Network: Chemistry|
(Posting all uppercase is SHOUTING. SHOUTING is impolite.)
Brittle materials fail in tension. Cracks propagate when they are pulled open. Glass is a disordered matrix of alternating ionically bonded silicon and oxygen in three dimensions, with some capping by added metal oxides (sodium, calcium) to lower the degree of polymerization.
| | -O-Si-O-Si-O- | | O O | | -O-Si-O-Si-O- | | O O | |When you open a crack you break some bonds and leave them dangling, grabbed by whatever is nearby. Silicon very avidly grabs ionic oxygen. When you cut glass under water the water rushes in, caps the newly broken bonds, and this packing expands the crack, making it propagate.
Is this true? You cut the glass under mostly neutral pH water. Does the experiment work as well conducted in vinegar (mild acid), baking soda solution (mild base), borax solution (stronger base), or corn syrup (viscous)? Does it work immersed in salad oil instead of water?
After the experiments you will know something about the mechanism of cutting glass under water - or what is irrelevant to the mechanism!
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