Preparation And Properties Of Asphalt-based Carbon Materials And Their Composites

Carbon/metal nanocomposites are a kind of novel carbon functional composite materials. Because those materials possess special structures and properties, they might obtain the widespread application in areas such as high-density magnetic data storage, oxidation-reduction catalyst and biomedical-materials. Carbon fiber reinforced cement composites (CFRC) has the widespread application prospect for structural health monitoring and the shield of electromagnetic wave due to its superior structural and functional properties. Deoiled asphalt (DOA), as a carbon-rich by-product of petroleum industry, is a favorable option as the carbon source for synthetic process of advanced carbon composites. Utilization of DOA to prepare carbon functional composite materials should provide a new approach for both the expansion of the product chains of petroleum processing and the comprehensive utilization of petroleum resource.This thesis innovatively synthesized carbon-encapsulated metal nanoparticles (CEMPs) with the lower temperature pyrolysis and vacuum heat treatment methods and DOA as the carbon source. The product structures and formation rules with different reaction conditions were investigated systematically; The products'magnetic properties were tested; The growth model of CEMPs was extensively studied and it's growth mechanism was proposed. Furthermore, vapor grown carbon fibers (VGCFs) were prepared from DOA by chemical vapor deposition (CVD) and the preparation procedures and mechanical properties and electricity performance of VGCFs cement-matrix composites were investigated. Conductivity mechanism of the composites was also discussed.The main results are as follows:1. Synthesis of carbon/iron nanocomposites with lower temperature pyrolysis of the mixture of DOA and ferrocene. With the increase of ferrocene content from 10 wt. % to 30wt. % under the reaction temperature of 450℃, the morphology of the product had a transformation from CEMPs towards carbon-encapsulated metal nanorods (CEMRs). The encapsulated metal cores were mainly singleα-Fe and the carbon shells were amorphous structure. The possible formation mechanism of CEMPs with this method was condensation and polymerization of the two components in a vapor-liquid bi-phase with the aid of catalysis under certain pressure, and the catalytic mechanism of iron nanoparticles to aromatic molecule was the dissolution-precipitation procedure. By carbonization at 1100℃, the size of CEMPs became larger and the carbon shells were converted from the disordered into graphitic structure with the catalysis of nano-sized iron core. Both primary-grown CEMPs and the carbonized product had high coercivity and a small ratio of remanent magnetization (Mr) to saturation magnetization (Ms). It indicated that CEMPs possess the combined magnetic characteristic of ferromagnetic and paramagnetic materials.2. VGCFs with diameters ranging from 500nm to1.5μm were prepared with CVD method utilizing DOA as carbon source and ferrocene as catalyst under the atmosphere of argon. The VGCFs, exhibited a tree annual ring type of structure and had a hollow core. CMSs with diameters ranging from 1~2μm were produced in the absence of catalyst. There were large amount of residue coke with VGCFs and CMSs preparation.3. Carbon/nickel composites were synthesized with the vacuum heat treatment methods and utilizing CMSs or DOA residue coke as carbon source and nickel as catalyst. Ni/CMSs composites, in which nickel microparticle with 200~400nm in diameter were coated with 30~100nm graphitic carbon layers with vacuum heat treatment at 1600℃. Ni-containing carbon nanoonions (CNOs) were obtained by vacuum heat treatment using DOA residue coke as carbon source and nickel as catalyst at 1800℃~ 2000℃for 60min. Ni-containing CNOs possessed the sizes ranging from10 to 30 nm and had core/shell structure with 5nm carbon shell and nickel core. The formations of graphitizing carbon shell with these two products were due to the formation and decomposition of the metal carbide Ni3C. The two carbon/nickel composites had a small coercivity and ratio of remanent magnetization to saturation magnetization and exhibited superparamagnetism and soft-magnetic properties.4. Based on the measurements of the resistivity, the variation coefficient and scanning electron microscopy (SEM) fractographs for the specimen, the influence of different preparation procedures on the dispersion of carbon fiber in cement reinforced with VGCFs was investigated. The studies indicated that by using dispersant and defoamer for pre-dispersion, together with proper manufacturing technology, the dispersion of VGCFs in cement got the best results, in comparison to the dry-mixture and wet-mixture methods.5. Preparation of VGCFs reinforced cement-matrix composites with different VGCFs weight fraction with pre-dispersion method were investigated. The VGCFs were prepared from de-oiled asphalt (DOA) by chemical vapor deposition (CVD) and then the cement-matrix composites were prepared with the VGCFs. Results indicated that compressive strength and electrical conductivity of VGCFs reinforced cement-matrix composites with lower fiber content were significantly enhanced. The resistivity decreases and compressive strength increased when the cement-matrix composites with weight fraction of VGCFs increasing from 0 to 0.6% fiber in the paste. A fiber content of 0.4% by mass of cement gave the best result: with the resistivity of 1.49×103?cm, which was lower by two orders of magnitude the value of 3.25×105 ?cm for the same paste without VGCFs. And with increases of the compressive strength by 28.8% as the VGCFs content increases from 0 to 0.4% by mass of cement. The good electricity property of the VGCFs cement-matrix composites resulted from the electrical conductivity of electron and cavity in the VGCFs and quantum mechanics tunneling effect.The above research provided a novel and effective route for the preparation of various carbon and carbon composites. This research should have significant influence in the promotion of the practical applications of carbon function composites and in the expanding of the petroleum process product chains and realizing comprehensive utilization of the natural resource.