Carbonization of polyaniline – nanodiamond hybrid structure achieved 6-18 GHz UWB electromagnetic wave absorption
Since the application of the scale everyday electronic products, electrical and industrial areas, industrial equipment and military weapons and equipment in the field and not expanding the scope of electromagnetic radiation it can be said to be everywhere, and therefore, how to effectively prevent electromagnetic radiation on humans the normal operation of the health hazards and equipment, which has become an important problem to be solved Cheng. In order to effectively solve the electromagnetic radiation hazards, research and development of different composition, structure and morphology of the electromagnetic wave absorbing material is one of the most effective solutions and the most widely studied. Ideal absorbing material requires thin, light weight, absorbing frequency band, a strong absorption performance characteristics. In order to meet the absorbing material \”thin light intensity width\” needs, many lightweight construction of the absorbing material, such as carbon nanotubes, graphene, Mxenen,, a conductive polymer, a light absorbing material has been many research extensive research scholars. Course of the study found that the type of light absorbing material can effectively enhance the absorption intensity of the electromagnetic waves, but can not effectively meet the requirement for impedance matching, microwave absorption bandwidth is extremely limited. To improve the poor impedance matching characteristics, the most effective way is to add a magnetic absorbing material, a magnetic absorbing material often contains large amounts of metal ions, which would increase the weight as well as a substantial difference in the characteristics of stability of metal ion absorbing material will limit its application in real life. In recent years, from a large number of experiments, it has been observed, nitrogen-doped carbon nanomaterial can induce a magnetic response, and theoretical studies have shown that the elements tend to form N-doped hybrid structure on the surface of the carbon material; in addition, theoretically and experimentally confirmed the non-plasma-doped carbon nano material is ferromagnetic; on this basis, recently, School of transportation Engineering, Dalian Maritime University Chen Xiangnan (first communication author) research team , the polyaniline / diamond (PANi / ND) N doping ND hybrid manner carbide structure was prepared FIG. 1 (a) Fig. Firstly, aniline (Ani) in situ polymerization of dispersed well into the ND PANi matrix, during PANi can stabilize and protect against ND reunited, N and serves as a source to achieve carbonization of N-doped ND then, the PANi / ND precursor is at different temperatures (600,700,800,900 ℃), and finally the structure, shapeAnalysis appearance, composition and performance. Experimental results show that the surface of the sp ND PANi of 2 C atom forming a carbonized N = N = C … Q groups (Q representative of a quinone active N atoms between the unsaturated groups on the Q type of functional group). Hybrid carbide body C … N hybrid structure can not only enhance the interfacial polarization, it can also produce ferromagnetism, ultra wideband EM absorption. The results show that the absorption of electromagnetic waves, the effective bandwidth (less than 10 dB, the absorption rate of> 90%) can reach 12 GHz, covering 6-18 GHz. to the research entitled \”Ferromagnetic carbonized polyaniline / nanodiamond hybrids for ultrabroad-band electromagnetic absorption\” of papers published in \” Carbon \” on (see the text description link).
1. Analysis of morphology and structure
1, carbonizing, PANi / ND precursor complex showed a close-packed spheres. After carbonization 700 ℃, the hybrid surface is obviously more granular projections. This change in morphology was mainly due to dehydrogenation and decomposition of the polymer due, resulting in collapse of the surface of hybrids. From the high-resolution TEM thin coating can be clearly observed around the ND precursor, which layer spacing of 0.374 nm, and PANi (111) plane in good agreement, indicating the successful synthesis of polyaniline. After carbonation, we found ND (111) planar lattice fringes confirmed after carbonization can be obtained NDGood to save. Its alignment performed by XRD structural analysis, for PANi, C-PANi600 and C-PANi700, at 43 ° at a clear peak was not observed, indicating that only the carbonization in the presence of a temperature higher than 700 ° C and ND, or will not form ordered arrangement of PANi. And, as the carbonization temperature rises, the peak intensity of PANI increases, and moves higher point (23 ℃), described carbonization temperature is raised effectively enhance the graphitization of PANI. With the increase of carbonization temperature, the true density of the sample is increasing, and further confirms the high degree of carbonization and graphitization degree. In these samples, C-PANi / ND700 minimum porosity, and the C-PANi / ND800 and porosity C-PANi / ND900 further increase may be due to decomposition of the amorphous carbonized and PANi increased PANi defect results.
2. The composition analysis and hybrid interfaces
As shown in FIG 3 before carbonization, IR analysis PANi / ND show that , it appeared typical PANi bands were 1563 cm -1 (C = C stretching vibration of the quinoid), 1483 cm -1 (benzene ring C = C stretching vibration), 1294 cm -1 (CNC imine stretching vibration), 1238 cm -1 (CNC quinone imine stretching vibration) and 1108 cm -1 (N = Q stretching vibration, and Q represents a quinone group), was successfully synthesized polyaniline described. When the carbonization temperature is 600 ℃, IR analysis showed that the PANI moiety, indicating incomplete carbonization occurs PANI; and when the carbonization temperature is higher than 600 ℃, only two bands were observed: a 1630cm -1 (C = C, quinones stretching vibration energy groups) and one in 1084 cm -1 (N = Q = N stretching vibration), described in carbonizing dehydrogenation reaction process occurs. In addition, C PANi / ND600, C-PANi / ND700, C-PANi / ND800 of N = Q = N stretching vibration characteristic bands and PANi / ND significant compared to red shift, ND indicates that the surface of the sp [123 ] 2 C and after the carbonization PANi N = Q = N unsaturated groups on the N-atom form a N-doped diamond nano structure. Raman analysis also showed a broad peak at 2798 cm -1 and at the small peak at 591 cm – 1 is due to the chemical interaction between ND and PANi carbon due to the interaction of functional groups hybrid phenomenon. When the carbonization temperature is 700-900 C, only 1350 cm -1 (D band) and 1580 cm -1 (G band) with two. 2840 and 591 cm -1 further evidence of deletions band PANi carbonization and surface ND sp 2 carbon atom N = Q = strong hybrid structure between a group N presence. As the carbonization temperature rises, ID / IG ratio increased, indicating a defect content is increased. Briefly, can be found from the results of FTIR and Raman spectroscopy, surface ND sp 2 PANi C and the carbonized N = Q = N there is a strong hybridization between the groups. During carbonization, the generated Q = N group of the unsaturated N atoms enter the surface of the high activity of ND. X-ray photoelectron spectroscopy found that, as shown, the C content after carbonization increases to 85.06% from 75.34, and 12.24 O content reduced from 4 to 8.87%, indicating that the carbonization process containing group dissociation occurs group. For C-PANi / ND700, CN and CO peak showed a significant blue shift in FIG. 4 (b), the change indicating that the carbonization ND and the hybridization between the PANi form, the hydrogen bond interactions becomes C … N hybridization, which will further alter the chemical CN and C = O groupssurroundings. N spectral analysis showed that after carbonization of the ring structure appeared PANi N = Q group (398.3 eV, 2.2%, pyridine-N) at the interface between C and ND and carbonization PANi … N = Q hybrid structure (400.7 eV, 3.9%, graphitization N). It is noted that with the increase in the carbonization temperature, N content of the two types of atoms are gradually decreased (for pyridine N, decreased from 3.9% to 3.1%; for graphitization N, decreased from 2.2% to 1.0%). This phenomenon indicates that, at higher carbonizing temperature, Q = N group and the C PANi … N hybridized ND gradually destroyed and eliminated, with RAMAN and FTIR results are very consistent.
3. Analysis of magnetic Analysis found hysteresis loop, shown in Figure 5, due to the interaction between the surface and the ND PANi, PANi / ND the PANi magnetically responsive coating can cause a significant decrease. On the other hand, C-PANi / ND700 shows more clearly than PANi / ND hysteresis loop, which is mainly due to the effects of doping on the N ND causes bonding defects and sp
2 / sp 3 mixing carbon. DESCRIPTION graphitized N atom to ferromagnetic critical, since the atomic proximity between the N and C, will exhibit a stronger electron cloud … C N overlapping and compression. Meanwhile, the empty p orbital of C atoms affect the electron cloud p N atom, which will lead to the N atom to produce induced dipole moment. 2p electrons exist three N atoms, and wherein two carbide PANi quinone ring structure bonded to a C atom, N atom, the remainder 2p electrons (dopingND) results in local spin, which may ferromagnetism. In addition, C-PANi / ND700 shows the maximum coercive force of 150 Oe, which will benefit the resonance frequency. Interestingly, with the increase in the carbonization temperature, coercive force CPANi / ND800 and CPANi / ND900 of the (Hc of) were reduced to 40 and 32 Oe. This is mainly because, when the carbonization temperature is higher than 800 deg.] C reduction, graphitized atom content of N, and formed of graphite crystallites and the introduction of defects PANi in more amorphous after carbonization will result in increased degree of disorder, and mixed to produce isomerization, and ultimately affect the change of ferromagnetic properties. As shown in FIG 6, ZFC carbonized sample / FC curves show more obvious differences phenomenon (TB = 125 K), shows the irreversible magnetization. This is confirmed by the ferromagnetic carbide sample is more obvious, mainly due to magnetic ordering generates additional, not just a ferromagnetic d0, because N atoms doped sp ND surface 2 [123 ] C. N has the highest content of graphitization (~ 3.9%) and a moderate degree of graphitization and defect levels C-PANi / ND700 point showed the greatest differences in ZFC / FC curve. MH curve
4. The electromagnetic wave absorption performance analysis
As illustrated, the permittivity real portion and the imaginary part with increasing the carbonization temperature is increased 7 . Wherein the C-PANi / ND900 exhibits the highest dielectric constant of the real and imaginary portions, but this would be detrimental to the impedance matching. Dielectric and magnetic loss characteristics analysis, C-PANi / ND700 and the 6-13 GHz14-18 GHz displayed in the vicinity of the dielectric response of two distinct broad peak. IF response peak (6-13 GHz) mainly from loss of dipole moment and the interface polarization relaxation polarization relaxation losses. C … N = Q radicals and Q = N group to act as a dipole center, to further enhance the dielectric relaxation. On the other hand, the high frequency response peak (14-18 GHz) may be due to resonance caused by the nanostructures. FIG. 7 (g) – (i), the three samples showed the three carbide relaxation semicircle, corresponding to a low frequency conductivity loss, loss of the intermediate frequency and high frequency polarization structure loss. As the carbonization temperature increases, the dielectric loss gradually from a low IF repolarization loss conductivity loss, which may be due to variations in the degree of graphitization and the increase caused by the hybrid process. As shown, the projection region other than the red 8 RL value 10dB below the effective area. Obviously, C-PANi / ND700 exhibit maximum effective area of the four samples, indicating that C-PANi / ND700 exhibited the widest effective bandwidth, which can effectively cover the 5-18 GHz. On the other hand, for the C-PANi / ND800 and C-PANi / ND900, effective area gradually converges to a lower frequency (FIG. 8 (c) and (d)). As the carbonization temperature rises, due to the low conductivity of the graphite crystallites loss gradually replaced the original dipole polarization and interfacial polarization relaxation losses. RL simulation results show that at 12.2 GHz, the optimal peak RL, up to 46.0 dB, and 10 dB at a bandwidth less staggering 12 GHz, covering 6-18 GHz. Of particular note is that, 20 dB or less bandwidth can reach 8.4 GHz, covering the 9.6-18 GHz. Compared with other carbon materials doped with nitrogen, This work was significantly increased effectively absorbing bandwidth achieves the same level of optimal values of RL.
6. Analysis of Absorbing Mechanism
binding analysis, foundcarbide PANi / ND is mainly due to the absorption of the hybrid, polarization and magnetic effect, FIG. 9 (c) shown in FIG. First, the scene is formed at the interface C … N = Q group; C … N = Q radicals and Q = N double polarization effects group can be effectively enhanced polarization relaxation, thereby significantly enhancing the dielectric loss. Second, since the N atoms substituted by suitable doping ND acting on the surface, and causes a synergistic ferromagnetic magnetic loss. Third, ND produced well dispersed homogeneously dispersed network interface is doped with nitrogen after carbonization, which causes multiple reflections interface between the reinforcing structure and the high frequency loss loss.