Study On Preparation Of Carbon Nanotubes Using Catalytic Chemical Vapor Pyrolysis And Their Applications

Carbon nanotubes (CNTs), as one of the new carbon materials, have extensive applications due to their particular structures and excellent physical/chemical characteristics. Study of CNTs has achieved great success since their discovery in 1991, but some problems in their preparation are still needed to solve, and their applications are to be further developed.In order to provide the scientific bases to produce CNTs industrially using the catalytic pyrolysis equipment, this dissertation studied the effects of experimental parameters on the yields, structures and morphologies of the products, and also investigated the modification of CNTs and their application systematically. The contents are summarized as follows.(1) CNTs were prepared by the catalytic pyrolysis method using verticalequipment, and the effects of the parameters such as carbon source, hydrogen flow rate, catalyst concentration on the yields, structures and morphologies were investigated. The results showed that: 1) CNTs withvarious morphologies could be prepared by changing the carbon source; the products were consisted of straight CNTs when using pure benzene as carbon source, while curl CNTs were synthesized when using the mixtures of benzene and toluene as carbon source; furthermore, branched CNTs were formed when using pure toluene as carbon source; 2) nearly all of the products were carbon-encapsulated-iron particles when the H2 flow rate was lower than 3000sccm, and the straight CNTs were the main products when the H2 flow rate was larger than 5400sccm, while the products were curled CNTs if the H2 flow was between 3000sccm and 5400sccm; 3) the products were mainly carbon particles with few CNTs at O.Olg/ml of the catalyst concentration, and carbon nanofibers were synthesized if the catalyst concentration was about O.lg/ml, while CNTs could only be prepared at about 0.05g/ml of the catalyst concentration.By high temperature treatment, CNTs' structural disfigurements and impurities were removed effectively, and the regularity was improved with improvement of the anti-oxidation property. CNTs could be shortened and with releasing of the inner pores by the ball-mill. And the longer the ball-mill time was, the shorter CNTs were.(2)CNTs and graphitic nanotubes (GNTs) were activated with KOH as activation agent. The results showed that the activation could effectively enhance the specific surface area (SSA) of CNTs, and release the inner pore structure; meanwhile the pore structures were formed in the wall with the formation of oxygen-containing functional groups. With the increase of the activation temperatures, SSAs and pore volumes were all enhanced monotonically; while SSAs increased with increasing of the KOH/CNTsratio, and reached a maximum at 7 : 1; The activation of GNTs had a similar rule. The optimal parameters were 900 °C of the activation temperature and 7 : 1 of the KOH/nanotubes ratio. SSA of the activated CNTs under these conditios was 360m2/g, which was about 14 times larger than that of the non-activated CNTs; besides, the total pore volume was improved from 0.051cc/g to 0.791cc/g; however, SSA of the activated GNTs was increased just from 40.9m2/g to 61.2m2/g.The CNTs' activation mechanism was also investigated. The results indicated that during activation process, the activation agents etched CNTs from different positions, and the potassium could intercalate into the space of CNTs' walls and formed the 1-stage, 2-stage and 3-stage K/CNTs intercalation compounds. The existence of K promoted the activation process, and the decomposition of the K/CNTs intercalation compounds leaded to the secondary oxidation during washing process.The microwave absorbing properties of the non-activated CNTs and the activated CNTs were studied. In the range of 5.3 GHz to 18 GHz, the reflectivity of the activated CNTs was lower than -5dB, while that lower than -lOdB in the range of 6.48 GHz to 10.88 GHz. The maximum absorbing peak of the activated CNTs could reach 22.58 dB at 8.08 GHz. These results suggested that activation was a very effective method to enhance the microwave absorbing property of CNTs.(3)The activated CNTs were used as catalyst support to prepared carbon coils, whose carbon yield was higher than that used Ni or Ni/non activated CNTs as catalyst systems. The selective capability to catalyze formation of carbon coils was also better than that of the other two catalyst systems.The reaction temperature had great effect on the product. Nearly all products were CNTs when the temperature was lower than 600 °C; carbon nanocoils and carbon microcoils were formed at 650°C; while nearly only carbon microcoils were produced with very high purity at 750°C; when reaction temperature increased to 800°C, the product contained a great deal of CNTs and lots of double carbon microcoils. The effects of the Ni concentration in the catalyst system on the products were also investigated. The results showed that only CNTs were prepared at 1% of Ni concentration with carbon yield larger than 70000%; while the products contained CNTs and carbon microcoils at 10% of Ni concentration; products were nearly all carbon microcoils at 20% of Ni concetration, but carbon yield decreased to about 13000%. The H2 flow rate was also one of the key parameters to synthesize carbon coils. CNTs and carbon microcoils were synthesized with 16254% of the carbon yield at 450sccm of the total H2 flow rate, while products were nearly all carbon microcoils with 11418% of the carbon yield if the H2 flow rate increased to 600sccm. Furthermore, when using graphitic boat to place the catalysts, some particular carbon materials such as coiled carbon nanotubes, super-long carbon coils, fish-bone carbon fibers and carbon nanotubes having variational inner diameter were found in the products.(4)The CNTs/rubber nano-composites were prepared. The results showed that: 1) the solid vulcanizing agent (Dicumyl peroxide) was better than the liquid vulcanizing agent (2, 5 Dimethyl-2, 5-ditbutyl peroxy hexane) since CNTs could adsorb the liquids; 2) using the master batch of CNTs and low molecule liquid hydrogenated HNBR (LHNBR), CNTs could disperse in...