Modulation of size and viscosity of Ni/Zn ferrites: Effect of doping with βCD and chemical treatment with HNO3 and NaOH

• Fe–Ni/Zn/βCD ferrite was synthesized by coprecipitation method in presence of βCD.
• Stoichiometry found for Fe–Ni/Zn/βCD was (Ni0.57Zn0.42Fe2O3.99)·(H2O)1.33·(βCD)0.05.
• Fe–Ni/Zn/βCD showed greater amorphicity and lower particle size than Fe–Ni/Zn.
• Fe–Ni/Zn suspension was pseudoplastic/thixotropic while Fe–Ni/Zn/βCD was Newtonian.
• HNO3/NaOH affected the charge, size and viscosity due to the reaction with FeOOH.

In this work, we have studied the rheological properties of nickel–zinc and nickel–zinc-β-cyclodextrin (Fe–Ni/Zn and Fe–Ni/Zn/βCD) ferrite suspensions as a function of temperature, solids content, shear rate and NaOH/HNO3 concentration. The goal was to investigate the conditions where the particle size and viscosity are both lower. In both suspensions, temperature had insignificant impact on viscosity, suggesting no destructive effect on the particles. The Fe–Ni/Zn/βCD suspension exhibited lower viscosity, Newtonian profile and lower dependence of viscosity upon the solids content in comparison with Fe–Ni/Zn, which was pseudoplastic and thixotropic. These differences were ascribed to the lower particle size caused by incorporation of βCD. Considering both ferrites, HNO3 was more efficient in reducing the particles size and viscosity than NaOH, which affected only the Fe–Ni/Zn. This behavior was rationalized in terms of chemical equilibrium of FeOOH at the surface of particles, which was supported by structural characterization as well as elementary analysis.

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