Electrokinetic properties of magnetite particles and cobalt ferrite obtained in the Fe0(St3)-H2O-O2 system and stability of their aqueous suspensions

We synthesized magnetite particles in the systems Fe 0 (St3)-H 2 O-O 2 ; Fe 0 (St3)-H 2 O-O 2 -FeSO 4 and Fe 0 (St3)-H 2 O-O 2 -Fe 2 (SO 4 ) 3 using St3 grade steel. The cobalt ferrite particles were obtained with the Fe 0 (St3)-H 2 O-O 2 system in the presence of cobalt(II) chloride. The samples were characterized by using XRD, SEM, microelectrophoresis, and nephelometry. By applying the Scherrer equation to the obtained XRD data, the dimensions of particle crystallites were determined. Possible mechanisms of formation the magnetite and cobalt ferrite particles were discussed for the systems under consideration. For the aqueous NaCl solution with the ionic strength 10 −3 mol/dm 3 as the dispersion medium, it was studied how the particle electrophoretic mobilities depend on the solution pH in the pH range 3–11. For both the particle types in such a solution, it was found that their Zeta Potentials changed its sign from the positive to negative value in the vicinity of pH = 7. The microelectrophoresis was also conducted for cobalt ferrite particles in the CoCl 2 electrolyte solution within the pH range 5–10. The measured Zeta Potential slightly changed and remained positive within the whole employed pH range. Possible mechanisms of the observed behavior were discussed. • Synthesis of magnetite and cobalt ferrite nanoparticles in Fe(Steel)-H 2 O-O 2 system. • Influence of electrokinetic potential from pH and electrolyte type. • Coagulation (contact-recrystallization) mechanism for nanoparticle formation. • Suspensions of particles are stable due to ionic-electrostatic and dispersion forces.