Studies On The Preparation And Properties Of Composite Absorbing Coatings With Hydrotalcite, Graphite, SiC And Ferrite

It is an important approach to utilize new materials and multi-layer composite structure for improving microwave absorbing properties, especially in the full frequency range of 2~18GHz. A minimum surface reflection can be obtained via changing impedance characteristic by controlling dosages of absorbing reagents and coatings thicknesses of multi-layer materials. At present most researches are focused on double-layer and tri-layer composite absorbing coatings. In this paper, three types of composite absorbing coatings are prepared with different absorbing reagents in epoxy resin matrix.1. Ferrite/SiC/ graphite tri-layer composite absorbing coatingsThe tri-layer composite absorbing coatings with impedance-graded structure are prepared by using ferrite, carborundum and graphite as absorbing reagents. The influence of dosages of absorbing reagents, thicknesses of coatings and particle sizes of SiC on microwave absorption properties are studied in detail.①The peak value of the reflection loss shifts to lower frequency with increased dosages of absorbing reagents and thicknesses of absorbing coatings.②The reflection loss and absorption bandwidth are improved with increased dosages of ferrite. The amount of 60 wt.% ferrite is adopted considering the reduction of adhesion and increase of density with increased dosages of ferrite.③Two types of tri-layer composite absorbing coatings are prepared with amount of 60 wt.% ferrite 1# in the bottom layer, 46 and 50 wt.% SiC 320mesh in the middle layer, and 23 wt.% graphite in the surface layer. The absorption bandwidths are 6.52GHz and 5.16GHz respectively below -5dB, 3.52GHz and 2.84GHz respectively below -10dB. The maximum reflection losses corresponding to the absorption bandwidths reach -35.74dB and -39.25dB. A tri-layer composite absorbing coating is also prepared with amount of 60 wt.% ferrite 1# in the bottom layer, 33 wt.% SiC 1000mesh in the middle layer, and 23 wt.% graphite in the surface layer. The absorption bandwidths are 8.68GHz below -5dB and 4.08GHz below -10dB and the maximum reflection loss reaches -18.78dB. ④The microwave absorption properties can be improved by increasing the thicknesses of the coatings. The reflection loss and absorption bandwidth are enhanced by increasing the thicknesses of the bottom, the middle and the surface layer of the sample with amount of 60 wt.% ferrite 1#, 33 wt.% SiC 320mesh, and 23 wt.% graphite. The reflection loss and absorption bandwidth are prominently enhanced by increasing the thickness of the bottom. The absorption bandwidths are 4.72GHz below -5dB and 2.48GHz below -10dB, and the maximum reflection loss reaches -37.88dB.2. Hydrotalcite/graphite double-layer composite absorbing coatingsThe double-layer composite absorbing coatings are prepared by adopting hydrotalcite, graphite 2#and 3# as absorbing reagents. The influence of dosages of absorbing reagents, thicknesses of coatings and types of hydrotalcite on microwave absorption properties are studied in detail.①The peak value of the reflection loss shifts to lower frequency with increased dosages of absorbing reagents and thicknesses of absorbing coatings.②A composite absorbing coating, whose thickness and area density are 0.88mm and 0.2g·cm-2 respectively, is prepared with amount of 11 wt.% Zn-Al hydrotalcite in the bottom layer and 16 wt.% graphite 2# in the surface layer. The absorption bandwidths are 5.36GHz below -5dB and 3.12GHz below -10dB and the maximum reflection loss reaches -22.27dB.③The microwave absorption properties can be improved by increasing thicknesses of the coatings. The coatings has no microwave absorption property with amount of 11 wt.% Zn-Al hydrotalcite in the bottom layer and 16 wt.% graphite 3# in the surface layer. But the maximum reflection loss reaches -32.60dB when the thickness increases from 0.84mm to 2.14mm. The reflection loss reaches -47.00dB when the thickness continues increasing to 2.52 mm, and the absorption bandwidths are 3.56GHz below -5dB and 1.92GHz below -10dB.④Three types of hydrotalcite combined with graphite have absorption to radar wave in different certain degree, but Zn-Al hydrotalcite is the best absorber.3. Carborundum/graphite double and tri-layer composite absorbing coatings The double-layer composite absorbing coatings are prepared by using carborundum, graphite 2#and 4# as absorbing reagents. The influence of the structure of coatings, dosages of absorbing reagents and particle sizes of SiC on microwave absorption properties are studied in detail.①The peak value of the reflection loss shifts to lower frequency with increased dosages of absorbing reagents and numbers of the layer. Little influence is found for particle sizes on displacement of the peak value②A thinner double-layer composite absorbing coating is prepared with amount of 32 wt.% SiC 320mesh in the bottom layer and 16 wt.% graphite 2# in the surface layer. The maximum reflection loss reaches -25.64dB, and the absorption bandwidths are 5.12GHz below -5dB and 3.28GHz below -10dB. A thicker double-layer composite absorbing coating is prepared with amount of 34 wt.% SiC 1500mesh in the bottom layer and 16 wt.% graphite 4# in the surface layer. The maximum reflection loss reaches -46.68dB, and the absorption bandwidths are 3.76GHz below -5dB and 1.96GHz below -10dB. The reflectivity curves have absorption in lower and higher frequency range when the thicknesses of the coating is between 2.86 and 3.10mm.③A tri-layer composite absorbing coating is prepared with amount of 42 wt.% SiC 150mesh in the middle layer and 16 wt.% graphite 2# in the bottom and surface layers. The maximum reflection loss reaches -47.70dB, and the absorption bandwidths are 4.28GHz below -5dB and 2.32GHz below -10dB.No evident changes are discovered on the surface of the coatings after soaked in natural seawater, but the maximum reflection losses minish universally. The reflection losses and absorption bandwidths change prominently only for few samples. The peak values of the reflection loss shift to lower frequency after the coatings are soaked in natural seawater.