Preparation And Microwave Permittivity Researching Of SiC-C Nanotubes And Micro-Coiled SiC-C Fiber

Nanotubes and micro-coiled fiber has special properties and combined easy with the matrix, Micro-coiled fiber are very interesting in relation to their novel functionality, for example, chirality, elasticity and combined easy with the matrix. So it has potential versatile applications as microwave absorbent, micro sensitivity energy absorbent, electromagnetism shield materials and high temperature resistance fillers. SiC fiber has high specific strength, high specific module, excellent high temperature stability, oxidation resistance and causticity resistance; it’s a proper reinforcement for high property composite materials. If SiC fiber has chiral structure, which may to be an excellent microwave absorbent. In this paper, preparation and microwave absorbing property of SiC-C nanotubes and micro-coiled SiC-C fiber absorbent were processed.Regular micro-coiled carbon fiber were prepared by chemical vapor deposition(CVD), C2H2as the carbon sources, Ni and S compound as the catalyses. The function of Ni in the experiments was researched.Four SiC-C nanaotubes (10-20nm,20-40nm,40-60nm, and60-100nm) were prepared by high temperature vapor phase siliconizing. The best experiment condition was1200℃,200ml/min flux N2and50ml/min H2with SiC14, and the silicon was5.59wt%. XRD patterns shows β SiC were prepared. Then micro-coiled SiC-C fiber were prepared by high temperature vapor phase siliconizing. Carbon fiber was easier siliconized than carbon nanotubes, the silicon was9.99wt%. XRD patterns shows α and β SiC were prepared.Siliconizing improved the oxidation resistance of carbon fiber and CNTs from the Tg patterns. After siliconizing, the start oxidation temperature of CNTs improved to662℃from550℃, while the stop oxidation temperature improved to810℃from706℃; the start oxidation temperature of micro-coiled carbon fiber improved to680℃from565℃, while the stop oxidation temperature improved to707℃from772.8℃.The permittivity and microwave absorbing properties of SiC-C nanotubes and micro-coiled fiber were researched. The microwave absorbing properties characters of SiC-C nanotubes was narrow frequency and double peaks, and the microwave absorbing properties improved with the increase of CNTs diameter. The5wt%SiC-C nanotubes composed with paraffin wax with10mm thickness,10-20nm SiC-C nanotubes almost have no ability to absorb microwave; the reflective loss of20-40nm SiC-C nanotubes less than-5dB in12.8-14.8GHz, and the peak was-31.79dB in13.6GHz; the reflective loss of40-60nm SiC-C nanotubes less than-5dB in6-7.4GHz,10.4-12.4GHz and15-17.2GHz; the reflective loss of60-100nm SiC-C nanotubes less than-5dB in9.4-10.8GHz,15.6-18GHz and16.2-17.2GHz. Siliconizing improved the microwave absorbing properties of the micro-coiled carbon fiber. The5wt%composed with paraffin wax with2mm thickness, the reflection loss of micro-coiled carbon fiber less than-5dB was in7.8-10.6GHz, the peak was-5.29dB in8.6GHz, after siliconizing, the reflection loss less than-5dB was in7.0-11.4GHz, while the peak was-6.11dB. The result proved that the SiC-C absorbent have potential usage in microwave absorbing field.