Novel NiZn-Ferrite Powders and Coatings for Electromagnetic Applications

Ferrites are iron-containing, ceramics which exhibit magnetic properties on the basis of a quantum mechanical effect. They are non-conducting and so are employed in high frequency applications. Most ferrites possess a spinel crystal structure and one of the most common is (Ni,Zn)₁Fe₂O₄. Traditionally, bulk ferrites are made by conventional ceramic powder processing. However, manufacture of thick coatings is of growing interest and deposition by thermal spray is potentially attractive. This paper will report work on the development of (Ni,Zn)₁Fe₂O₄ based powder feedstock materials and coating deposition by both air plasma and high velocity oxy-fuel spraying. Powders  of novel compositions and comprising nanosized grains were prepared using both self propagating high temperature synthesis and mechanical alloying. Powders and coatings were analysed by X-ray diffraction, optical and scanning electron microscopy so that grain size, microstrain, microstructure and phase composition could be investigated.  

The effect of processing parameters on powder size, morphology, grain size and chemistry was evaluated.
The influence of process parameters on coating development was studied for both air plasma and HVOF sprayed deposits up to 500 microns thick. Particular attention was paid to degradation of the spinel crystal structure , the formation of iron oxide phases and elemental loss during spraying. Grain size and microstrain were evaluated by high resolution X-ray diffraction and peak broadening effects. The results obtained will be reported in analysed in terms of thermal and chemical environments of the different spray processes.