Experimental study of radiative transfer in semi-transparent composite materials at different temperatures

This study deals with the analysis of the propagation of radiation within a diffusing semi-transparent composite medium with rough boundaries. The two-phase medium (resin matrix and glass fibers reinforcement) is treated as an equivalent homogeneous medium characterized by volumetric radiative properties (extinction coefficient, albedo and phase function) and boundary scattering properties. The aim is to identify the radiative properties at different temperatures ranging from room temperature to 200°C. The identification method (Gauss-Newton) uses bidirectional reflectance and transmittance values. The experimental results are obtained using a spectrophotometer equipped with a goniometer and a heated sample holder. The Monte Carlo method is used to solve the Radiative Transfer Equation (RTE) in order to obtain the theoretical values.

A thin and optically transparent infrared-radar compatible stealth structure with low emissivity and broadband absorption

In this paper, an optically transparent structure that combines broadband absorption and low infrared emissivity for dual-band stealth is proposed. The whole structure includes two functional layers. The periodic resistive film of the upper functional layer acts on infrared stealth. Its emissivity in the infrared band of 8-14μm is lower than 0.3. Another functional layer achieves greater than 90% wide absorption from 6 to 18.5 GHz. The whole optically transparent composite structure has a low profile of 0.141λ0, where λ0 is the wavelength of free space at the center frequency. It has an absorptivity that greater than 90% in the region of 5.7-16.5 GHz and has wide angular stability. Measured result is consistent with the simulation which verify the performance of the proposal. The infrared-radar compatible stealth structure proposed in this paper has potential application in the field of multi-spectrum compatible stealth.

Fabrication of Transparent Composites from Pinaceae Wood Packaging Residues

In the 21st century, mankind has witnessed the rapidly development of all industries with a lot of new products in a variety of types and designs. However, this development has been also causing many problems with the society and the ecological environment such as a wasteful excess of products, exhaustive exploitation of natural resources, indiscriminate deforestation, and waste pollution affecting the living environment, ecosystem, and human health. Many organizations and governments are calling for environmental protection, limit waste emissions, and find good solutions to use the recycled materials as raw materials in production plants. This study would like to provide a solution which not only utilizes waste packaging Pinaceae wood for recycling as raw material but also supplies to the market with a green product responding to the durability requirements in fact. Pinaceae wood packaging residues were chemically processed through two stages. The amount of lignin extract from Pinaceae was determined by the method of Tappi 222 om-02 which was significantly influenced by the extraction parameters such as temperature, time and concentration of the treatment solution. Morphological modification of wood materials was analyzed by SEM micrographs. In particular, the mechanical properties of the Epoxy/TPW2 composite green material have been significantly improved with increasing up to 206–540 % compared to the original Pinaceae wood. The optical properties of the wood have completely changed from opaque pine wood with the optical transmittance of 8 % into transparent composite material with the optical transmittance up to 85 % using UV-vis spectroscopy analysis.

IR-transparent MgO-Gd2O3 composite ceramics produced by self-propagating high-temperature synthesis and spark plasma sintering

A glycine-nitrate self-propagating high-temperature synthesis (SHS) was developed to produce composite MgO-Gd2O3 nanopowders. The X-ray powder diffraction (XRD) analysis confirmed the SHS-product consists of cubic MgO and Gd2O3 phases with nanometer crystallite size and retains this structure after annealing at temperatures up to 1200 °C. Near full dense high IR-transparent composite ceramics were fabricated by spark plasma sintering (SPS) at 1140 °C and 60 MPa. The in-line transmittance of 1 mm thick MgO-Gd2O3 ceramics exceeded 70% in the range of 4–5 mm and reached a maximum of 77% at a wavelength of 5.3 mm. The measured microhardness HV0.5 of the MgO-Gd2O3 ceramics is 9.5±0.4 GPa, while the fracture toughness (KIC) amounted to 2.0±0.5 MPa·m1/2. These characteristics demonstrate that obtained composite MgO-Gd2O3 ceramic is a promising material for protective infra-red (IR) windows.