Investigations On The Activation And The Synthesis Of Nanometer-Sized Titanic Carbide During Mechanical Alloying

The materials with metastable structures, e.g., nanostructure and supersaturated solid solutions, have unique physic, chemical and mechanical properties, and get extensive application in many fields. For the reason of rigorous preparation requirement, the research of convenient and low-cost preparation method for materials with non-equilibrium structures has been a hotspot in materials field. Since 1970s', mechanical alloying (MA) has attracted research interesting. MA is a dry and high energy milling process with some notable advantages, such as in the preparation of advanced materials and the inducement of phase transformation, which is focused attention upon. In this thesis, the author reviews the development and application of MA, and comments on the method for nanometer-sized powder. By using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC) and optical microscopy, mechanical activation is investigated. And during the study, two new innovative processes or thoughts, "dual activation reactive milling" and "in situ synthesis in salt bath activated by MA" has been presented for the synthesis of nanometer-sized powder. The phase transformation and oxidation control of Cu-Cr system during MA is also investigated.The mechanism of dual activation reactive milling is discussed. According to the mechanism, the mechanical activation from MA and thermal activation from the second high-exothermic reaction system (Ti-C) are utilized for synthesizing of nanometer-sized TiC powder from low-cost TiO2 powders. In the process, the mechanical activation is a fundamental. The thermal activation by reason of the mechanical activation has promoting effect on the mechanical activation. Furthermore, the mechanical activation assures the final powders are in nanometer-size. Otherwise, for the first attempt of MA in the reaction system of metal-macromolecule or oxide-metal-macromolecule, author investigates the synthesis of nanometer-sized TiC from petroleum coke by using reactive milling and dual activation reactive milling.The process of in situ synthesis in salt activated by MA is discussed, and the separation of activation and reaction during MA is investigated. The Ti-C mixtures with elevated system energy from mechanical activation occur due to thermal activation from in salt bath. The action between molten salt and precipitated TiC particles has an effect on the size of final TiC particles, which is around 10nm.Moreover, the investigation for the MA of Cu-Cr indicates that: with using of protective atmosphere, active carbon has a good effect on the oxidation controlduring milling; the structure refining and increasing of interface and defect result in the formation of non-equilibrium phase.