| Microwave stealthy materials have a wide application in the military field and have become a research hotspot in the field of military stealth. In this paper, firstly, polyaniline (PANI) and polypyrrole (PPY) with controllable conductivity and good environmental stability was synthesized by chemical oxidation polymerization, in which FeCl3 was used as dopant and deputy oxidizing agent, and ammonium persulfate (APS) as primary oxidizing agent. The morphology, composition and structure were observed by SEM, EDS and XRD. By using the four-point probe method, the change rule of the conductivity of PANI and PPY were obtained as the change of initial FeCl3, meanwhile, the conductivity of stability of the PANI and PPY were studied at room temperature. The molar ratios of n (An):n (FeCl3)= 1: 0.6 and n (Py):n (FeCl3)= 1:0.4 were chosen as a fixed ratio for synthetic PANI and PPY in composites respectively. Secondly, the flake powder LaCrCrO3 and NiFe2O4 were prepared by polyacrylamide sol-gel method. Through the study of TG-DTA of precursors and chaging calcination temperature, the best crystallization temperatures were explored. The complex permittivity and permeability of them were investigated by vector network analyzer, meanwhile, the microwave absorbing properties were simulated in centimeter wave band. Wherein, the best reflection loss of LaCrCrO3 and NiFe2O4 reached -4.2 dB (5.5 mm) and -2.3 dB (5.5 mm) under coating thickness less than 6 mm. In addition, LaCrO33 and NiFe2O4 were tested among the millimeter wave band, especially microwave response for 94 GHz. It was found that they had high reflectivity under this frequency point. Then, LaCrO3 and NiFe2O4 were modified by silane coupling agent and called GLCO and GNFO respectively. The different mole ratio of GLCO/PANI, GLCO/PPY, GNFO/PANI and GNFO/PPY were synthesized by situ emulsion oxidation mothed. The morphology and structure were observed by SEM, TEM and XRD and it was concluded that the thermal-behavior change law and compound ratio of the composite powders by TG analysis. The microwave stealth performance was simulated in centimeter wave band. It was found that GLCO/PANI (n (GLCO):n (An)=1:3) had maximum reflection loss of-16.5 dB in centimeter wave band and effective bandwidth of 5.4 GHz. When n (GLCO):n (Py) was 1:1 or 1:2, their synthetic GLCO/PPY have the reflection loss less than-10 dB under different thickness (< 5.5 mm), but the maximum reflection loss appeared in different positions. The molar ratio of GNFO and An was 1:0.5,1:1 or 1:2, the maximum reflection loss of synthetic GLCO/PPY composites was in unceasing increase, but not reached-10 dB. The reflection loss of GNFO/PANI (1:3) had reached-10 dB under the same thickness compared with GNFO/PANI (1:0.5), GNFO/PANI (1:1) and GNFO/PANI (1:2), and the maximum effective bandwidth appeared when the coating thickness was 4 mm. The reflection loss of GNFO/PPY (1:0.5) had less than-10 dB in 5-18 GHz under different coating thickness. And GNFO/PPY (1:1) had the maximum reflection loss of-42 dB (8 GHz,3.5 mm) and the effective band was 3.3 GHz. When the mole ratio of GNFO and Py was increased sequentially, the reflection loss of synthetic GNFO/PPY came to decline. Moreover, the synthetic GLCO/PANI, GLCO/PPY, GNFO/PANI and GNFO/PPY with different mole ratio were tested in the response of millimeter wave band, and it was found that they have lower reflectivity compared with single LaCrO3 or NiFe2O4. Finally, CF/PANI and CF/PPY composite fibers were synthized by chemical oxidation method after surface treatment of CF. It was found that attenuation effects of compound fibers were relevant with the chage of conductivity, but no corresponding proportion relationship. When CF/PANI was compared with CF/PPY, the maximum attenuation effect of CF/PPY at millimeter wave (94 GHz) was better than that of CF/PANI, which indicated CF with PPY could more effectively improve millimeter wave attenuation effect (94 GHz) of composite fibers. |
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