Flexible Fe3Si/SiC ultrathin hybrid fiber mats with designable microwave absorption performance

Flexible Ceramic Fibers: Recent Development in Preparation and Application

Flexible ceramic fibers (FCFs) have been developed for various advanced applications due to their superior mechanical flexibility, high temperature resistance, and excellent chemical stability. In this article, we present an overview on the recent progress of FCFs in terms of materials, fabrication methods, and applications. We begin with a brief introduction to FCFs and the materials for preparation of FCFs. After that, various methods for preparation of FCFs are discussed, including centrifugal spinning, electrospinning, solution blow spinning, self-assembly, chemical vapor deposition, atomic layer deposition, and polymer conversion. Recent applications of FCFs in various fields are further illustrated in detail, including thermal insulation, air filtration, water treatment, sound absorption, electromagnetic wave absorption, battery separator, catalytic application, among others. Finally, some perspectives on the future directions and opportunities for the preparation and application of FCFs are highlighted. We envision that this review will provide readers with some meaningful guidance on the preparation of FCFs and inspire them to explore more potential applications.

Implications from Broadband Microwave Absorption of Metal-Modified SiC Fiber Mats

Understanding the physical requirements for a broad bandwidth is vital for the design of high-efficiency microwave absorber. Our recent works on silicon carbide (SiC) fiber mats-based absorbers imply that metal modification (e.g., Fe or Hf) could benefit their bandwidth effectively. For verification, we fabricated a Co/SiC fiber mat via a similar electrospinning process and subsequent pyrolysis at 1400 °C in Ar atmosphere. The results indicate that after Co modification, the SiC fiber mats show elevated permittivity and tangent loss. With a proper amount of Co adding, the mats could exhibit a wide bandwidth of around 8 GHz (ranging from 10 to 18 GHz) for effective absorption (reflection loss (RL) less than -10 dB) at 2.8 mm thickness. This is similar to our previous findings, confirming that metal modification could be an effective approach to extend the bandwidth of SiC mat absorbers. Explanations can be found through theoretical analysis with the quarter wavelength (λ/4) cancellation theory. It suggests that the declining permittivity (with the increase of frequency) is the key to keep the wavelength in material (λ_m) nearly unchanged within a frequency range. As a result, in this range, λ/4 cancellation could still be satisfied without changing thickness, which could explain the reasons for the broad bandwidth of metal-modified SiC fiber mats. With this model, it is further predicted that the effective absorption bandwidth could be even extended to be around 12 GHz with appropriate tangent loss. It should be emphasized that the implications obtained in this study could also be applicable to other dielectric absorbers. The requirement of permittivity and the proposed approach could serve as guidelines to achieve a wide bandwidth on a dielectric absorber relying on the λ/4 cancellation principle.

Control of the Length of Fe73.5Si13.5Nb3Cu1B9 Microwires to Be Used for Magnetic and Microwave Absorbing Purposes

A combination of high-energy ball milling, vacuum filtering, and sedimentation processes has been demonstrated to be a useful approach to reduce, in a controlled way, the length of as-cast Fe_73.5Si_13.5Nb₃Cu₁B₉ amorphous magnetic microwires (MWs) and annealed material at 550 °C in nitrogen conditions. Homogeneous compositional microstructures with fairly narrow size distributions between 1300 and 11.7 μm are achieved, exhibiting tunable response as a soft magnetic material and as a microwave absorber. From the magnetic perspective, the soft magnetic character is increased with smaller length of the MWs, whereas the remanence has the opposite behavior mainly due to the structural defects and the loss of the shape anisotropy. From the microwave absorption perspective, a novel potential applicability is tested in these refined microstructures. This innovation consists of coatings based on commercial paints with a filling percentage of 0.55% of MWs with different lengths deposited on metallic sheets. Large attenuation values around -40 dB are obtained in narrow spectral windows located in the GHz range, and their position can be varied by combining different optimized lengths of MW. As an example of this powerful mechanism for absorbing microwaves at specific frequencies, MW lengths of 2 mm and 50 μm are chosen, where precise tailoring of the minimum reflection loss (R_L) is obtained in a range between 8.85 and 13.25 GHz. To confirm these experimental results, an effective medium standard model proposed for electrical permittivity is used. Experimental and theoretical results are consistent and these novel composites are also proposed as a feasible candidate for designing frequency-selective microwave absorbers on demand, with low filling percentages and high absorption intensity values.