An advanced solid reducing agent, i.e., a CaO/SiO2 composite has been optimized to improve the hydrogen fluoride (HF; a green house gas) elimination in semiconductor-based industrial applications. To avoid the Ca(OH)2 formation and enhance the HF removal efficiency of CaO, the hydrophobic properties of silica (SiO2) have used as a catalyst materials to enhance the stability of CaO/SiO2 solid reducing agent in the present investigation. The novel composite structure based on CaO/SiO2 was prepared using various concentrations of hydrophobic nano-silica sol and Ca(OH)2. The composite was characterized by contact angle goniometry, thermogravimetry analysis, and scanning electron microscopy. The water contact angle of the CaO/SiO2 composites significantly increased with increasing SiO2 content. In particular, angles of 61.6°, 73.7°, 84.8°, and 84.9° were obtained for SiO2 concentrations of 20, 40, 60, and 80 wt.%, respectively. These results suggest that the hydrophobic nature of the composites was improved with the addition of 60 and 80 wt.% of SiO2. Moreover, the surface properties were measured using the nitrogen Brunauer–Emmett–Teller method for obtaining the weight ratios (wt.%) and calcinations times. The determined specific surface areas (SSAs) were 16.19, 27.25, 32.86, and 40.56 m2/g for 80:20, 60:40, 40:60, and 20:80 CaO/SiO2 composites, respectively. From the water contact angle and SSA analysis, the optimum hydrophobic nature of CaO/SiO2 composites for HF removal was achieved at a weight ratio of 40:60 (Ca(OH)2/SiO2) at the calcination temperature of 650 °C. The perfluorinated compound (PFC) removal rate is 80 and 88% for a common regenerative catalytic system (RCS) catalyst and the CaO/SiO2 reaction-enhanced (RE)-RCS catalyst, respectively. In addition, higher amount of HF elimination is successfully achieved using CaO/SiO2 solid reducing agent. During the RE-RCS process, SiO2 acts as a catalyst to prevent the formation of Ca(OH)2 when CaO is exposed to water.

In this study, an Electromagnetic (EM) wave-absorbing composite structure design is proposed. The conventional composite EM wave absorber contains lossy fillers for dielectric characteristics, and thus the fillers affect the mechanical properties, which determine the structural performance of the composite itself. The newly proposed EM wave absorber uses a combination of the following two components: the load-bearable composite structure as the ‘shell’ and the EM wave-absorbing back layer as the ‘absorber.’ The shell type absorber does not use any additional fillers in the composite structure. However, the absorbing layer that is designed with a periodic patterned layer and low lossy foam exhibits good EM wave-absorbing performance. Design, analysis with computational simulation, and measurement of EM characteristics are performed to verify the advantages of the shell type absorber. Furthermore, the EM wave absorber is adopted in the leading edge of an aircraft to identify the contribution of Radar Cross Section reduction. This type of absorber has various applications in aerial vehicles, and the EM characteristics are widely tunable for specific purposes without changing the original shell structure.