# Products of silicate synthesis

I'm attempting to make a hard refractory cement to apply over kiln brick made of sodium silicate and Perlite. This creates a very good kiln brick, however they are susceptible to abrasion. I've been making my own sodium silicate, and thought I might be able to make it harder with the addition of some oxides.

I added silica gel and water; then I added magnesium oxide and sodium hydroxide. There was a extremely strong exothermic reaction.

What would this be called? I imagine it's called something like $$\ce{Na2SiO4Mg}$$. Tomorrow I will try some combinations of sodium silicate with Aluminum Oxide, and magnesium oxide. What would these be called?

If you have a recipe for a hard refractory cement to protect the Perlite mix from abrasion I would appreciate the input.

• im curious, did you find a solution? I could used an abrasion resistant refractory coating as well – Francis L. Aug 8 '20 at 1:43

I imagine it's called something like $$\ce{Na2SiO4Mg}$$. Tomorrow I will try some combinations of sodium silicate with Aluminum Oxide, and magnesium oxide. What would these be called?

Much simplier than that. Sodium hydroxide dissolves incredibly exothermally:

$$\ce{NaOH (s) -> NaOH (aq)}\qquad{\mathrm{\Delta} H = \pu{-44.5 kJ mol-1}}$$

This is what heated your mixture.

Expanded perlite is a bubbly glass, so if a kiln brick has a rough surface, there is insufficient fine material in the mix. Impacts of anything on the surface will break the thin glass bubbles. Of course, adding lots of fine material to the mix will strengthen it, but also increase its thermal conductivity, so that may not be a good way to improve abrasion resistance.

The surface can be improved by painting on a mix of finely ground perlite (previously expanded, so as to remove bound water) with sodium silicate to fill in surface imperfections. If you adjust the sodium silicate to perlite ratio, and paint 5 of the 6 sides, you can set the painted brick on its unpainted side and heat it in your kiln to a bit above your service temperature, whereupon the surface paint will melt and set, as opposed to dry and react. Adding $$MgO$$ or portland cement to the paint will give a higher melting final product, although you may be able to get an initial melting that then stiffens up during the heating. Now whether this smooth, but brittle coating is more abrasion resistant will depend on the impacts it must withstand - the brick is still not really tough, just stronger.