Synthesis of (Ba4Zn2-xMnxFe36O60) U-type hexaferrite pigments and studying their influence on the protective performance, mechanical behavior and microwave absorption properties of polyurethane paint coatings

A series of U-type hexaferrite ceramic powders Ba4Zn2-xMnxFe36O60 (x= 0.5, 1, and 1.5) were synthesized through the solid-state reaction (SSR) method and used as electromagnetic (EM) waves absorbing inorganic pigments to fabricate radar absorbing paint (RAP) coatings containing polyurethane matrix and talc as a filler. The colour properties and chemical stability of powder pigments were determined. Also, the crystalline structure and morphology of the synthesized pigments were characterized by X-ray diff ;raction (XRD) and scanning electron microscope (SEM) analysis. The effect of addition of these pigments to the polyurethane (PU) matrix on mechanical properties, corrosion performances and microwave absorption performances was investigated. The EM parameters and microwave absorbing properties of the RAP coatings applied on the aluminum substrate were measured in the X-band (8.2-12.4 GHz) frequency range by using vector network analyzer (VNA) and the scattering parameters method. The results showed that the mechanical properties such as microhardness, wear resistance and roughness were increased due to the addition of Mn content in the Zn-U type pigment. Also, the impact resistance was seen to increase with addition of Zn (decreasing x). The corrosion performance and adhesion strength of the coatings were examined using the salt spray and tape adhesion test, which exhibited that both of them were higher than non-pigmented polyurethane (NPPU) matrix coatings. The pigment composition with x = 1 led to an optimum microwave absorption of 97.55 % (or reflection loss RL = - 16.10 dB) at 9.82 GHz and 1.5 mm thickness. In addition, this composition coating displays a broad frequency bandwidth (- 4.03 GHz) for RL <=-10 dB (90 % MW absorption), in 8.2-12.4 GHz. This type of RAP coating, due to its small required thickness, light weight, wide band absorption and cost-effectiveness can be used for suppressing EM interferences and stealth applications.