Aqueous colloidal processing of carriers for delivering silica nanoparticles in iron matrix nanocomposites

Concentrated aqueous suspensions of iron powder were developed to produce carriers for delivering silica nanoparticles, which may act as inoculants in cast iron during solidification. Those iron matrix nanocomposites may present higher strength and hardness due to enhanced nucleation and grain refinement. Moreover a nanosized dispersed ceramic phase may improve chemical and wear resistance of the metal matrix. In this work, colloid stability and the rheological behavior of iron aqueous suspensions have been studied. Under acidic conditions, iron readily dissolves, but no dissolution takes place at basic pH. Zeta potential studies showed that the isoelectric point occurs at pH ∼ 7. Concentrated iron and iron–silica suspensions were prepared to solids loading up to 40 vol% using ultrasound and ball mill homogenization. Deflocculant content, mixing time and SiO2 nanoparticles content were optimized. Stable suspensions were achieved using an ammonium salt of a polyacrylic acid-based polyelectrolyte as a dispersant, KOH for adjusting the pH at 10, and SiO2 nanoparticles solids loading from 1.0 to 12.5 vol%. Those suspensions were processed via slip casting and microstructures of the shaped carriers were characterized through FE-SEM.