Silicic Acid in phosphoric acid solution

[JohnP]

Consider the following reaction:
3Si₃N₄ + 27H₂O + 4H₃PO₄ --> 4(NH₄)₃PO₄ + 9H₂SiO₃ --> ^4NH₃(g) + 4H₃PO₄ + 9H₂SiO₃ --> 4H₃PO₄ + ??

The phosphoric acid solution is 85%wt.

In your fella's opinion, what happens to the Meta Silicic Acid (H₂SiO₃)? Is the solution to acidic to form a polysilicic acid?
Will this occur: H₂SiO₃ --> H₂O + SiO₂ and form a gelatinous poly silica? Something else?
I do know that at relatively low concentrations of this silicate based product (~100PPM @ 155C) the product will come out of solution.
Appreciate your thoughts, thanks guys.

 

[Matcon]

I would expect a gelatinous amorphous hydrated silica. It would be a polymer composed of Si(OH) and SiO units, not the stoichiometric dissociation that your equation suggests