高温下含硅气相介质与多壁碳纳米管的作用机理

Reaction Mechanism Between Silicon-Containing Gaseous Species and Multi-walled Carbon Nanotubes at High Temperature

采用单质硅粉、铝粉和二氧化硅微粉(Al+SiO2),以及硅粉和二氧化硅微粉(Si+SiO2)作为3种不同硅源,在埋碳床中于1 000～1 500℃处理多壁碳纳米管(multi-walled carbon nanotubes,MWCNTs),研究了不同含硅气相介质与MWCNTs的作用机理。结果表明:不同温度条件下以Si为硅源时,Si(g)分压最高;Si+SiO2为硅源时SiO(g)分压最高;而以Al+SiO2为硅源时,SiO(g)和Si(g)分压均最低。硅源决定了含硅气相介质与MWCNTs的作用机理:以Si为硅源时,Si(g)在MWCNTs表面反应并沉积,使得MWCNTs在1 400℃处理后表面出现2～4 nm厚的SiC涂层,在1 500℃时,大部分MWCNTs转化为实心SiC纳米线;以Si+SiO2为硅源时,SiO(g)不断沉积,1 300℃处理后MWCNTs表面出现了无定形SiO2涂层,随处理温度升高,涂层厚度增加。在上述沉积过程中,含硅气相介质在MWCNTs顶端催化剂Ni中不断发生溶解反应并形成纳米SiC晶粒。

The reaction mechanism between different silicon-containing gaseous species and multi-walled carbon nanotubes（MWCNTs） was investigated in a coke bed in a temperature range from 1 000 ℃ to 1 500 ℃ using a silicon powder（Si）,a mixture of aluminum and silica powders（Al ＋ SiO2）,a mixture of silicon and silica powders（Si ＋ SiO2） as silicon sources,respectively.The results show that at different temperatures,Si（g） partial pressure in the system is highest for silicon source,and SiO（g） partial pressure is the highest for Si ＋ SiO2 silicon source.In the case of Al ＋ SiO2 as silicon source,Si（g） and SiO（g） partial pressures are both the lowest.Reaction mechanism between silicon-containing gaseous species and MWCNTs was determined by different silicon sources.When Si was used as a silicon source,SiC coating with a thickness of 2–4 nm formed on the surface of MWCNTs after treated at 1 400 ℃ due to the deposition and reaction of Si（g）.Most of MWCNTs transformed into solid SiC nanowires at 1 500 ℃.However,for Si ＋ SiO2 as a silicon source,amorphous SiO2 coating formed on the surface of MWCNTs at 1 300 ℃ and the thickness increased with the increase of temperature,which was attributed to the deposition of SiO（g）.Also,SiC nanocrystals were formed in the Ni-rich area at the tip of MWCNTs due to the dissolution and reaction of silicon-containing gaseous species.