Chemical Garden, deeper conceptual explanation

[mishima]

Hey there, I am curious why certain metal salts grow faster in a chemical garden. As I understand, the growth is more of a physical process than a chemical one. The difference in density causes the metal silicate to rise in solution, and osmotic processes inflate the tubes.

However, at least initially, I suspect how quickly the metal salt dissolves in the sodium silicate is proportional to how quickly the tubes grow.

I have observed for example that cobalt (II) chloride hexahydrate grows faster than iron (II) sulfate heptahydrate. What could be the theoretical explanation for the difference in growth rate for these two substances?

There is not a lot of information on the actual process behind these gardens online. Thanks.

 

[Borek]

Just a personal opinion: probably the most important factor is the speed of water transport through the silicate membrane.

 

[mishima]

How would the type of metal affect this rate? Could it be proportional to the bond strength between the metal cation and the silicate? In other words a tighter lattice would slow the rate?

 

[Borek]

In other words a tighter lattice would slow the rate?

Yes, that's what I would expect, although I have no idea how to precisely quantify the "tightness". Different silicates can probably take different forms, arrangement of atoms in the membrane is probably to some extent ordered (as in crystals) and to some extent anisotropic, depending on the scale. These membranes are highly hydrated, so their properties are quite different from the crystalline silicates of respective metals.

Definitely mechanical strength and permeability of different membranes will vary, some combination of these will be responsible for how easily the membrane breaks and how fast the "branches" grow.