PAN基炭纤维皮芯结构的高温演变规律

Evolution of the skin-core structure of PAN-based carbon fibers with high temperature treatment

以T300聚丙烯腈(PAN)炭纤维为研究对象,在1500℃～2500℃进行石墨化处理,采用元素分析、XRD、TEM和Raman测试手段从成分含量、聚集态结构、碳化学结构、微晶结构等方面分析研究PAN炭纤维在高温热处理过程中皮芯结构的演变规律及机理。结果表明,随热处理温度的升高,氮元素含量和d002逐渐减少,碳含量和石墨微晶网面宽度(La)不断增加。超过1900℃后La增加显著。由径向4点的Raman结果可知,皮层的G峰强度比芯层强(1700℃时G峰位置无变化)。然而,2500℃热处理后,从纤维芯向皮层的G峰位置从1 588.2移至1582.2 cm-1处,G峰和D峰的半峰宽强度分别从46.3降至28.9cm-1,46.9降至36.7cm-1处。不同热处理后皮芯微观结构的差异与氮元素的脱除和温度有密切关系。低于1900℃时,由于较短的分散通道和较高的皮层温度,接近皮层的氮元素更易脱除,这导致随温度的升高,皮层比芯层的La增加缓慢。超过1900℃时,氮元素完全脱除,皮层石墨化快于芯层,导致皮芯差异加剧,皮层呈较高的模量和芯层呈较高强度。

PAN-based carbon fibers were subjected to high temperature heat treatment（HTT） at 1 500-2 500 ℃ and the evolution of the skin-core structure of the carbon fibers was investigated by elemental analysis,XRD,TEM and Raman spectroscopy.Results showed that nitrogen content and d002 decreased,and carbon content and La increased with HTT temperature.La increased sharply with temperature above 1 900 ℃.The Raman spectra taken at four points in radial directions indicated that the intensity of the G band at the skin was stronger than at the core with no change in peak position at 1 700 ℃.However,the G peak position decreased from 1 588.2 to 1 582.2 cm-1,the width of the G band at half maximum intensity decreased from 46.3 to 28.9 and that of D band from 46.9 to 36.7 cm-1 from core to skin after HTT at 2 500 ℃.The differences of microstructure in the core and skin at different temperatures are related closely to the differences in nitrogen removal efficiency and temperature.At temperatures below 1 900 ℃,nitrogen near the skin is more easily removed due to a shorter diffusion path and a higher temperature on the skin,leading to a slower increase of La with temperature on the skin than in the core.At temperatures above 1 900 ℃,nitrogen is removed completely and graphitization on the skin is more rapid than in the core,leading to a large skin-core difference with the skin portion having a high modulus and the core portion a high strength.