Thread Content
2.2 Bitumen without mesophase 2.2.1 Disadvantages of using bitumen with a mesophase as a binder The mesophase is formed during the modification (heat treatment) of bitumen. There are some controversies regarding the impact of the mesophase on the properties of binders; it is generally believed that the presence of a mesophase in the binder bitumen is detrimental, with the following disadvantages: Mesophase particles remain solid even at temperatures of 300°C. Therefore, the mesophase does not contribute to the binding effect during the raw material stage of producing shaped carbon materials (mixing and shaping), and must be regarded as part of the filler. The mesophase leads to the formation of a low-density, poor-quality mixture of asphalt aggregates. Moreover, mixtures containing mesophase pitch require higher extrusion pressure. The mesophase spheres break during mixing and coat the surface of the filler, having an adverse effect on the strength and reactivity of the calcined anode. The raw material paste made from pitch containing mesophase pitch has a higher viscosity than that without mesophase pitch, thus requiring a higher pitch content. 2.2.2 Production of intermediate-phase-free asphalt: The intermediate phase in asphalt is formed under high-temperature conditions. Therefore, the key to producing intermediate-phase-free asphalt lies primarily in using a low-temperature production process to control the formation and growth of secondary QI during the asphalt production process. The production of intermediate-phase pitch requires strict heating and reaction conditions, that is, a sufficient reaction time and avoidance of local overheating during heating. At the same time, the selection of raw materials for intermediate-phase-free asphalt production is very important. 2.2.3 Intermediate-phase-free asphalt prepared by physical separation: The pretreatment of raw materials for coal-based acicular coke production involves using soft asphalt as a starting material and employing solvent sedimentation to remove QI, thereby obtaining refined acicular coke raw material asphalt (free of QI); at the same time, heavy-phase asphalt rich in primary QI is produced as a by-product. By distilling this portion of asphalt to remove solvents and light components, intermediate-phase-free asphalt is obtained. Its parameters are: softening point of 81°C, coking value of 51.3%, QI of 11.33%, and TI of 31.33%.