**3.4 Effect of additional Si**

Addition of Na2SiO3H2O into the solutions was selected to see the effect of Si on iron oxide crystallization. In precipitation of magnetite crystals, Na2SiO3H2O was added to a solution of 4M NaCl, pH 7.5 at a temperature of 60°C. The presence of Si affected crystal size, which became smaller, from 30 to 26 nm, and unit cell parameter decreased from 0.8392 to 0.8380 nm.

Addition of 0.0135 g Na2SiO3H2O to the solutions at the initial crystallization stage hindered crystal growth of goethite crystals (**Figure 11**). Elevated amounts of Si added as 0.135 g Na2SiO3 and 1.35 g caused formation of short-range ordered phases (suggested name singerite) [12].
