Mr. Kai Li Profile

Kai Li

at Institute of NBC Defense

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Publications (4)

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Proceedings Article | 7 August 2024 Paper

Preparation and characterization of barium ferrite by self-propagating method

Ming Wu, Wenjie Dong, Luoguo Wang, Weizhao Yao, Kai Li

Proceedings Volume 13229, 1322907 (2024) https://doi.org/10.1117/12.3038171

KEYWORDS: Crystals, Barium, Absorption, Vibration, Magnetism, Particles, Iron, Ions, Heat treatments, FT-IR spectroscopy

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With the development of various precision-guided weapons, new radars, and detection means, stealth technology and stealth materials are paying more and more attention. Stealth materials have been widely used in aircraft, missiles, ships, UAVs, and other military fields. Barium ferrite (BaFe₁₂O₁₉) is a hexagonal crystalline ferromagnetic oxide that has good chemical stability, corrosion resistance, and uniaxial magnetic crystal energy anisotropy. The easy magnetization axis parallel to the C-axis makes it have a large involuntary force and magnetic energy product, so it has been widely used in the field of stealth technology and electromagnetic shielding. In this paper, pure ferrite barium nanoparticles were prepared by sol-gel self-combustion technique. The reaction mechanism and the critical temperature of the solid-state reaction of the dried gel were studied by TG/differential scanning calorimetry (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). The structure and properties of barium ferrite were studied by scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and X-ray diffraction (XRD). The results show that the particle size of the products increases gradually with the increase of calcination temperature and is greater than the critical particle size of a single domain. When the precursor was held at 400℃ for 2h and calcined at 1200℃ for 3h, the maximum particle size of 82.7 nm was obtained, greater than the critical particle size of the single domain. The maximum saturation magnetization of the product was 64.72 emu•g⁻¹ , and the minimum coercivity was 1181.07 Oe•g⁻¹.

Proceedings Article | 21 March 2023 Paper

Preparation of nickel/iron/cobalt-coated graphene and infrared interference performance

Kai Li, Weizhao Yao, Xuanyu Wang, Wenjie Dong, Kang Ai

Proceedings Volume 12595, 1259508 (2023) https://doi.org/10.1117/12.2666853

KEYWORDS: Infrared radiation, Particles, Graphene, Absorption, Mass attenuation coefficient, Refractive index, Displays, Instrument modeling, Plating, Statistical modeling

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Graphene, as a new two-dimensional nano carbon material, has a high potential application value in the military field. At present, exploratory research has been carried out on graphene materials in infrared interference, and it has shown good near-infrared interference performance. However, its far-infrared interference performance needs to be improved, and the poor dispersion caused by its easy agglomeration also needs to be solved urgently. In this paper, Reduced Graphene Oxide (RGO) was prepared by oxidation-reduction method, and then RGO/Ni/Fe/Co composite was prepared by chemical plating method. The RGO and RGO/Ni//Fe/Co samples were characterized by SEM, TEM, XPS, EDS, XRD, etc. The complex refractive index of the samples in 2~14μm infrared wavebands was measured by ellipsometry method, and the infrared absorption characteristic was calculated by DDA method. Then, the infrared interference performance was tested by the method of Fourier transform spectrometer connected with smaller smoke box, and the dispersity was also comprehensively evaluated by Carr index method. It is found that electroless nickel-iron-cobalt plating not only can ease the secondary agglomeration between the RGO layers, improve its dispersity, but also can change the electromagnetic properties of graphene surface and significantly improve its infrared absorption. As shown in results, the average mass extinction coefficient of RGO smoke for 3~5 μm infrared was increased from 2.56m² /g to 2.75m²/g, and the average mass extinction coefficient for 8~14 μm infrared was increased from 1.8m² /g to 2.16m²/g. In particular, the far-infrared extinction performance has been obviously improved. It further indicates that the surface modification of electroless nickel-iron-cobalt plating can effectively improve the infrared interference performance of RGO smoke.

Proceedings Article | 18 March 2021 Paper

Research progress on composite interference of infrared/millimeter smoke material and its extinction performance

Yueyue Sun, Xuanyu Wang, Weizhao Yao, Huiying Li, Zhilong Liu, Kai Li

Proceedings Volume 11780, 1178018 (2021) https://doi.org/10.1117/12.2590225

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Passive interference from smoke screen is an important part of optoelectronic countermeasure. With the rapid development of photoelectric weapons, the status of the smoke screen aerosol is increasing day by day, and multi- spectrum composite jammers have become the top priority of smokescreen passive interference technology. In order to promote the research and application transformation of smoke screen materials, understand the research status of composite interference materials and improve the jamming performance of smoke screens on infrared/millimeter wave band, this paper finishes the analysis of the system from the interference of material composition, extinction mechanism, problems and development trend under the condition of selecting composite interference of infrared/millimeter wave smoke materials as the main research object. The research results show that: the combined interference material and the integrated interference material have their own advantages and disadvantages. New types of composite interference materials with better composite interference effects and a complete range are constantly emerging. The status quo of the current research is mainly manifested in the different limitations of different smoke screen materials and the poor systemicity of the compound extinction mechanism. Smoke screen materials are generally developing in the direction of excellent dynamic characteristics, low cost, easy survival and environmental protection.

Proceedings Article | 12 March 2021 Paper

Measurement of complex refractive index of graphene in infrared bands by reflection spectra

Kai Li, Xuanyu Wang, Zeqian Wu, Wenjie Dong, Yueyue Sun

Proceedings Volume 11763, 117630I (2021) https://doi.org/10.1117/12.2585754

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Graphene is a new type of infrared interference carbon Nano-material. The complex refractive index is an important parameter to study its extinction performance. The reflection spectra in 2.5 to 25 m wavebands of graphene pellets were measured by Fourier infrared spectrometer, and the complex refractive index was calculated by Kramers-Kronig ( K-K) relation, and calculation deviations were analyzed. The calculation results show that the real part of complex refractive index is 3.5 to 4.9 and the imaginary part is 0.3 to 2. The results of error analysis indicate that, the difference between the measured reflectivities of 22 degrees angle of incidence and the reflectivities of normal incidence is 10^-4 , the oblique incidence can be used to represent the normal incidence condition, and the different extrapolation of the reflectivities outside the test wavebands have little effect on the results. The data of complex refractive index has some reference value for the study of the infrared extinction characteristics of graphene.

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