Sodium Metasilicate — Frequently Asked Questions

Because the silicate passivates the metal. Sodium hydroxide attacks aluminium continuously, dissolving the metal and leaving a blackened etched surface. Sodium metasilicate provides comparable alkalinity, but the silicate anion adsorbs onto the aluminium and forms a thin protective film that stops the attack once the soil has been removed.

The molar ratio of silica to sodium oxide, and it determines behaviour. Metasilicate has a ratio near 1, which makes it strongly alkaline and a good detergent builder. Higher-ratio silicates are less alkaline and better film formers and adhesives. The ratio should be specified, since products sold generically as sodium silicate span a wide range.

Real cleaning performance. Silicate is an effective emulsifier and deflocculant for oily and particulate soil, keeping loosened dirt suspended so it does not redeposit, and it buffers strongly, holding the wash solution alkaline as acidic soil neutralises it. Those functions are additional to the corrosion inhibition it provides.

Yes. A solution at around pH 12.5 is corrosive to skin and eyes and requires goggles, gloves and protective clothing. As with caustic alkalis generally, contact may give limited immediate pain warning while tissue damage proceeds, so exposure should be flushed thoroughly rather than judged by discomfort.