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• Carbon aerogels with porosity in the range of 35.8–92.7 % are prepared, and the amount of reactants and catalysts is found to be the key parameter for regulating the porosity of carbon aerogels. • The mass extinction coefficients of carbon aerogels in infrared band show a trend of increasing initially and then decreasing with the increase of porosity. • Compared with the literature's results, the mass extinction coefficients of the samples prepared in this study increased by 157–189 % in 3–5 μm IR band and by 104–124 % in 8–14 μm IR band, respectively. Porosity is an important factor affecting the infrared (IR) extinction performance of porous materials. In this paper, seven kinds of bulk carbon aerogels with different porosities have been prepared based on sol-gel method and their physical parameters such as microstructure, porosity, specific surface area and apparent density have been systematically characterized. Then, the infrared extinction properties of the ultrafine powders prepared by bulk carbon aerogel were studied in smoke chamber. The results show that the IR mass extinction coefficients (MECs) of the carbon aerogel increase initially and then decrease with the increase of porosity, and the maximum value of MEC in 3–5 μm IR band appears at 75.2 % porosity, while it appears at 86.7 % porosity in the 8–14 μm IR band. The maximum values of MEC are 2.62 m2/g in the 3–5 μm band and 1.23 m2/g, in 8–14 μm band, respectively, showing excellent infrared extinction performance. [ABSTRACT FROM AUTHOR]

Nonoxide ceramics microspheres with multiple compositions are attractive for wide applications especially in thermal insulation science. The flower-like Fe-doped Si–C–N ceramic microspheres with the average size of about 1 μm were fabricated from polyvinylsilazane and ferrocene precursor through polymer-derived ceramics technology combined with emulsion polymerization method. The properties of the resultant microspheres were characterized by FTIR, SEM-EDX, VSM, TGA, and XRD. The morphology and size of the microspheres could be tuned by changing of ferrocene content, cross-linking time, and pyrolysis temperature. The ceramic microspheres were estimated to be composed of SiC/Si3N4 and α-Fe/Fe2O3 crystal phase, and the folding sheets on the surface induced the flower-like morphology due to phase separation and crystal rearrangement. The effective extinction coefficient of silica aerogels opacified with 10 wt% of Fe-doped Si–C–N microspheres increased with rising pyrolysis temperature, the maximum value of e* reached 27.5 cm2/g at 1300 °C. Moreover, the microspheres showed weak room temperatures ferromagnetism, which was facilitated to alignment in fabrication and recycle, make them an ideal candidate for aerogels in infrared shielding application. Highlights: Novel Fe-doped Si-C-N ceramic microspheres with flower-like morphology were prepared by polymer-derived ceramics technology combined with the emulsion polymerization method. The morphology and size of microspheres could be tuned by changing conditions. Microspheres were composed of multiple crystals. Microspheres showed weak room temperature ferromagnetism. [ABSTRACT FROM AUTHOR]

Carbon nanofibre is a new kind of materials with good capability of electromagnetic wave absorption. To explore the infrared extinction performance of carbon nanofibres as smoke particle in passive interference, based on the electromagnetic field theory, the integral equation model of induced current for carbon nanofibres is established. The method of Moment is used to solve the integral equation and the formulae of scattered field, absorption and scattering cross section of carbon nanofibres are derived. The relationships between infrared extinction cross section of carbon nanofibre and the angle of incidence, the fibre length, the wavelength and diameter are analysed and simulated. The simulation results show that the method is valuable and provides a theoretical basis for the application of nanocarbon fibre in infrared smoke interference. [ABSTRACT FROM AUTHOR]

Using method of moment, the calculating model of electric current distributing and scattered electric field for carbon nanofibers is established in this paper. Based on it, the expression of absorption cross section, scattering cross section and extinction cross section are got. The relationship between infrared extinction cross section of carbon nanofiber and electrical conductivity is analyzed and calculated by using Matlab. The results show that the infrared extinction cross section increases with electrical conductivity increase and peak value appeares when wavelength is longer than the length of carbon nanofiber. The electrical conductivity on peak value is related to wavelength.

Abstract: We construct a model of interstellar dust in which H-rich amorphous carbon is deposited on silicate substrates in the interstellar medium, and is annealed to form H-poor amorphous carbon. The model grains are stratified spheres composed of hollow silicate cores coated with two carbonaceous layers, the inner layer of sp 2 carbon and the outer layer of sp 3 carbon. Using an accurate method of computing the optical properties of such layered grains, we explore the consequences of varying the core-grain size distribution and the thicknesses of the carbonaceous layers on the resulting infrared extinction. We find a wide dispersion in the curve morphology that reflects the grain size distributions and the chemical composition of dust materials. [Copyright &y& Elsevier]

Simultaneous size distributions and Fourier transform infrared (FTIR) extinction spectra have been measured for several representative components of mineral dust aerosol (quartz, calcite, and dolomite) in the fine particle size mode (D=0.1–1μm). Optical constants drawn from the published literature have been used in combination with the experimentally determined size distributions to simulate the extinction spectra. In general, Mie theory does not accurately reproduce the peak position or band shape for the prominent IR resonance features in the 800–1600cm−1 spectral range. The resonance peaks in the Mie simulation are consistently blue shifted relative to the experimental spectra by ∼20–50cm−1. Spectral simulations, derived from a simple Rayleigh-based analytic theory for a “continuous distribution of ellipsoids” particle shape model, better reproduce the experimental spectra, despite the fact that the Rayleigh approximation is not strictly satisfied in these experiments. These results differ from our previous studies of particle shape effects in silicate clay mineral dust aerosols where a disk-shaped model for the particles was found to be more appropriate. [Copyright &y& Elsevier]