Cobalt ferrite prepared employing powder technology, the potential applications, the preparation and characterisation

The phenomenon of magnetostriction takes place where there is a change in dimensions that spontaneously occurs in ferromagnetic and ferrimagnetic materials when an external magnetic field is applied. Cobalt ferrite, being a ferromagnetic material, has been proposed as a suitable magnetostrictive material for some applications in the area of sensors and actuators. In such applications, speed of response with accurate displacements is important. Although cobalt ferrite has been shown to have a small magnetostrictive coefficient, which is a disadvantage, it also has a very small hysteresis characteristic. It follows that the results of using this material should be a smaller amount of energy loss and higher accuracy at high frequencies, and these benefits may outweigh this disadvantage. In this thesis, making cobalt ferrite powder with nano sized particles is suggested as a first step in a solution to overcoming the disadvantage mentioned above, if the particles are small enough to have only one magnetic domain. Powders were prepared employing the sol–gel technique. A particular emphasis is devoted to an understanding of the role of the chemical parameters involved in the sol–gel technique, and of the effect of the heat treatment on the structures and morphologies of the powders obtained. These were investigated by varying the initial parameters of the experiment in addition to the heat treatment temperature. The magnetic characteristics of the optimum nanoparticles were measured. The heat treatment process was simulated and optimised by means of DoE. The optimal heat treatment conditions, which facilitate the attainment of cobalt ferrite nanoparticles under low electrical operating costs, were defined. Nanoparticles obtained employing the optimal solution were uniaxially pressed to form standard disc samples, and sintered under continuous ramp rate and single dwell time conditions. A study of the powder behaviour during this process, the density variation with pressing applied pressure, sintering temperature and dwell time, was conducted