VAPOR PHASE PREPARATION OF ELECTRIC CONDUCTIVE AND MICRO-COILED METAL NITRIDE FIBERS AND THEIR ELECTROMAGNETIC ABSORPTION PROPERTIES

采用气相渗氮金属碳化物线圈（间接法或两步法）和金属化/氮化碳线圈（一步法或直接法）制备了各种金属氮化物的微线圈或微管，并对其制备条件、机理、显微组织和性能进行了研究。所得结果可总结如下。(A)间接法或两步法：(1)在TiCl4 + H2气氛下，在800-1200℃的温度下气相钛化碳微线圈，形成TiC微线圈。采用常规碳圈制备的TIC微线圈具有微管状形貌。(2)在N2气氛下，在800-1200℃的温度下氮化TiC微线圈。将TiC微线圈在800℃下部分氮化，反应时间为6小时，形成TiN/TiC微线圈/管。(3)在1000℃的温度下将TiC微线圈完全氮化至芯部，反应时间为6小时，形成TiN微线圈/微管。(B)直接法：(1)采用MCI （M=Ti, Nb, Ta, Si）…More +N2+H2气氛处理碳卷，温度范围为800-1200ºC。(2)碳卷转变为金属氮化物，充分保留了卷取图案，没有形成金属碳化物中间层。(3)非常规则卷曲的碳纤维，随着反应温度和反应次数的增加，卷曲模式逐渐消失，然后完全消失，形成3 ~ 10 μ m直径的表观直纤维。(4)直纤维沿纤维轴具有直径为亚微米的连续孔。也就是说，这种由常规碳卷经金属化/氮化处理得到的直纤维是一种金属氮化微管。(5)在1000℃的温度下，将碳卷芯完全钛化/氮化6小时，在800℃的温度下，将碳卷芯表面部分钛化/氮化6小时。(6)碳卷比表面积大；根据反应温度和反应时间的不同，经金属化/氮化处理后，其含量约为100m^2/g ~ 10 ~ 20m^2/g。(7)金属氮化微线圈/微管的体积电阻率为0.1-0.01 "0"cm，取决于碳线圈与金属氮化物的体积密度和转化率。(8)在环氧树脂中，金属氮化微线圈/微管在800-900 MHz范围内的电磁波吸收率约为90%，吸收率为20wt%。少

Micro-coils or micro-tubes of various metal nitrides were prepared by the vapor phase nitriding of metal carbide coils (indirect process or two step process) and metalizing/nitriding of carbon coils (one step process or direct process), and the preparation conditions, mechanism, microstructure, properties were examined. The obtained results can be summarized as follows.(A) Indirect process or two step process :(1) The carbon micro-coils was vapor phase titianized at 800-1200ﾟC under TiCl4 + H2 atmosphere to form TiC micro-coils. Using regular carbon coils, the obtained TIC micro-coils have micro-tube like morphology.(2) The TiC micro-coils was nitrided at 800-1200ﾟC in N2 atmosphere. The TiC micro-coils was partly nitrided at 800ﾟC for 6-hr reaction times to form TiN/TiC micro-coils/tubes.(3) TiC micro-coils was fully nitrided to the core at 1000ﾟC for 6-hr reaction time to form TiN micro-coils/micro-tubes.(B) Direct process :(1) The carbon coils was treated with MCI (M=Ti, Nb, Ta, Si) … More +N2+H2 atmosphere in the temperature range of 800-1200ﾟC.(2) The carbon coils changed to metal nitride with full preservation of the coiling pattern, without the formation of intermediate layers of metal carbides.(3) Using very regular-coiled carbon fibers, the coiling pattern gradually disappeared with increasing reaction temperature and reaction times, and then fully disappeared to form apparent straight fibers of 3-10 mum diameter.(4) The straight fibers have a continuous pore of submicrom diameter through the fiber axis. That is, this straight fibers obtained by the metarizing/nitriding of the regular carbon coils is a micro-tube of metal nitride.(5) The carbon coils was fully titanized/nitride to the core at 1000ﾟC for 6 hrs, while partly titanized/nitrides from the surface at 800ﾟC for 6 hrs.(6) The large specific surface area of carbon coils ; about 100m^2/g, was decreased to 10-20m^2/g by the metalizing/nitriding, depending on the reaction temperature and reaction time.(7) The metal nitride micro-coils/micro-tubes have bulk electrical resistivities of 0.1-0.01 "0"cm depending on the bulk density and conversion ratio of the carbon coils to the metal nitride.(8) The electromagnetic wave absorption of the metal nitride micro-coils/micro-tubes was about 90% in 800-900 MHz region for 20wt% in an epoxy resin. Less