Silicic Acid in phosphoric acid solution

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The discussion centers on the reaction involving silicon nitride, water, and phosphoric acid, leading to the formation of ammonium phosphate and meta silicic acid (H2SiO3). Key points include the behavior of H2SiO3 in an 85% phosphoric acid solution and whether the acidity is sufficient to prevent the formation of polysilicic acid. Participants speculate that H2SiO3 may dissociate into water and silica (SiO2), potentially resulting in a gelatinous form of hydrated silica. There is consensus that the product is likely a polymer consisting of Si(OH) and SiO units, rather than a simple stoichiometric dissociation. Additionally, it is noted that at low concentrations (around 100 PPM at 155°C), the silicate product tends to precipitate from the solution.
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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.
 
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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
 

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