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Polymer‐derived ceramic materials exhibit adjustable composition, microstructure, and dielectric properties and are widely used as high temperature microwave absorption materials in the aerospace field. In this study, polymer‐derived SiCN ceramic aerogels with excellent electromagnetic wave absorption (EMA) properties were successfully fabricated through a combination of the sol‐gel, freeze‐ drying, and polymer precursor conversion methods. The hydrosilylation reaction between the Si‐H bond in polysilazane (a polymer ceramic precursor) and the C = C bond in divinylbenzene (a cross‐linking agent) occurs to form a wet gel. The effects of the molar ratios of the two bonds (C = C/Si‐H) on the microstructure and EMA properties of the SiCN ceramic aerogels were systematically studied. At a C = C/Si–H molar ratio of 1.25:1, the minimum reflection loss of the SiCN ceramic aerogels is −37.57 dB at 10.88 GHz. Moreover, the corresponding effective absorption bandwidth covers almost the entire X‐band, showing excellent EMA properties. [ABSTRACT FROM AUTHOR]

Ti2AlCx ceramic was produced by reactive hot pressing (RHP) of Ti:Al:C powder mixtures with a molar ratio of 2:1:1–.5 at 10–20 MPa, 1200–1300°C for 60 min. X‐ray diffraction analysis confirmed the Ti2AlC with TiC, Ti3Al as minor phases in samples produced at 10–20 MPa, 1200°C. The samples RHPed at 10 MPa, 1300°C exhibited ≥95 vol.% Ti2AlC with TiC as a minor phase. The density of samples increased from 3.69 to 4.04 g/cm3 at 10 MPa, 1200°C, whereas an increase of pressure to 20 MPa resulted from 3.84 to 4.07 g/cm3 (2:1:1 to 2:1:.5). The samples made at 10 MPa, 1300°C exhibited a density from 3.95 to 4.07 g/cm3. Reaction and densification were studied for 2Ti–Al–.67C composition at 10 MPa, 700–1300°C for 5 min showed the formation of Ti–Al intermetallic and TiC phases up to 900°C with Ti, Al, and carbon. The appearance of the Ti2AlC phase was ≥1000°C; further, as the temperature increased, Ti2AlC peak intensity was raised, and other phase intensities were reduced. The sample made at 700°C showed a density of 2.87 g/cm3, whereas at 1300°C it exhibited 3.98 g/cm3; further, soaking for 60 min resulted in a density of 4.07 g/cm3. Microhardness and flexural strength of Ti2AlC0.8 sample were 5.81 ±.21 GPa and 445 ± 35 MPa. [ABSTRACT FROM AUTHOR]

This study reports on the synthesis of hafnium diboride (HfB2)‐based nanofibers via electrospinning of polyhafnoxanesal (PHO)‐based solution followed by pyrolyzing hafnium‐boron containing polyvinylpyrrolidone precursor fibers by a moderate heat treatment at 1500°C under argon atmosphere. The influence of the molar ratios of C/Hf and B/Hf in preceramic polymer method is investigated on the final phase of HfB2‐based nanofibers. Structural, thermal, microstructural, and physical properties of the hafnium‐based fibers are evaluated using Fourier transform infrared spectra (FTIR), thermogravimetry and differential scanning calorimetry (TG/DSC), X‐ray diffractometer (XRD), high‐temperature X‐ray diffraction (HT‐XRD), field‐emission scanning electron microscope/energy‐dispersive spectrometer (FE‐SEM/EDS), and Brunauer‐Emmett‐Teller (BET). The results unveiled that the acidic pH was the optimal condition needed for obtaining the single phase of HfB2 nanofibers. The precursor fibers with the stoichiometric ratio of 1:4:5 of Hf:B:C prepared under the acidic conditions converted into pure HfB2 nanofibers having rough and porous surface after pyrolysis at 1500°C for 2 hour in argon, whereas HfB2‐HfC composite nanofibers with smooth surface were produced in the neutral conditions. The HfB2 nanofibers with a mean diameter of ~100 nm prepared under the acidic conditions showed a higher specific surface area compared to HfB2‐HfC composite nanofibers with a diameter of ~121 nm derived in the neutral conditions. [ABSTRACT FROM AUTHOR]