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

采用金属碳化物线圈气相氮化(间接法或二步法)和碳线圈金属化/氮化(一步法或直接法)的方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、组织、性能进行了测试。主要研究结果如下：(1)在TiCl4+H2气氛下，碳微线圈在800-1200ﾟ℃下进行气相滴定，生成TiC微线圈。在氮气气氛中，在800-1200ﾟC的氮气气氛下氮化，得到的TiC微线圈具有微管状的形貌。TiC微线圈在800ﾟC下部分氮化6小时，形成TiN/TiC微线圈/管。(3)TiC微线圈在1000ﾟC下完全氮化6小时，形成TiN微线圈/微管。(B)直接工艺：(1)碳线圈用mCI(M=Ti，Nb，Ta，Si)…处理在800-1200ﾟC的温度范围内，碳线圈转变为金属氮化物，完全保留了卷曲图案，没有金属碳化物中间层的形成。(3)使用非常规则的卷曲碳纤维，随着反应温度和反应时间的增加，卷曲图案逐渐消失，然后完全消失，形成直径3-10微米的明显直纤维。(4)直纤维沿纤维轴有一个连续的亚微米直径的孔。也就是说，通过金属化/氮化得到的这种直纤维是金属氮化物的微管。(5)碳线圈在1000ﾟC下完全钛化/氮化6小时，而在800ﾟC下表面部分钛化/氮化6小时。(6)大的比表面积；根据反应温度和反应时间的不同，金属氮化微线圈/微管的体电阻率为0.1-0.01“0”cm。(8)金属氮化微线圈/微管在800-900 MHz频率范围内的吸波能力约为90%，吸收率为20wt%。较少

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