Microstructure and complex magnetic permeability of thermally sprayed NiZn ferrite coatings for electromagnetic wave absorbers

摘要

Ferrites are iron containing, non-conducting ceramics, which exhibit magnetic properties. One of the most common is (Ni,Zn)1Fe2O4. Bulk ferrites are typically made by conventional ceramic sintering. However, manufacture of thick coatings is of growing interest, and deposition by thermal spraying is potentially attractive. The present paper reports work on the development of (Ni_(0.549)Zn_(0.333)Co_(0.028)Mn_(0.049))O_(0.958)Fe_2O_3 based powder feedstock by self-propagating high temperature synthesis and coating deposition by both air plasma and high velocity oxy-fuel spraying. The results obtained show that some decomposition of the ferrite material occurred with the loss of zinc and oxygen. The Zn loss is dependent to a large extent on the surface/volume ratio of the powder used in spray deposition. The influence of the spraying technique on the electromagnetic properties was also measured and compared to bulk ferrite materials. The air plasma sprayed coatings showed similar absorption coefficient compared to the bulk ferrite material at high frequencies (～3 GHz).