Papers by Author: Jun Jie Qi

Abstract: In-doped ZnO nanodisks were successfully fabricated by thermal evaporation Zn, In2O3 and graphite powder mixture without catalyst. Morphology, structures and components of ZnO nanodisks were investigated by SEM, HRTEM, EDS and X-Ray diffraction. ZnO nanodisks have perfect hexagonal shape, with 1~3μm size and 40~100 nm in thickness. The nanodisks are single-crystalline ZnO with wurtzite structure and In content of nanodisks reaches 2.2%. The growth along [0001] is suppressed leading to the formation of ZnO nanodisks. Room temperature photoluminescence spectra of the nanodisks shows that the UV emission peak blueshifts and becomes broader after doping.

Abstract: Antibacterial titanate nanotubes were synthesized by alkali digesting of metatitanic acid via hydrothermal route, following by cation-exchanged and immobilized with Ag+, Zn2+ and Cu2+. The conditions for nanotube synthesis and ion exchange were investigated; the microstructures of as-synthesized nanotubes were characterized by XRD, SEM, XPS and DTA/TG. The antibacterial performance of cation-doped titanate nanotubes was tested and evaluated by Escherichia Coli. and staphylococcus aureus.

Abstract: A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

Abstract: Quantitative characterization of microstructural development during deformation enhanced transformation in a low carbon steel was investigated on a Gleeble 1500 machine. General conclusions of the features of austenite transformation kinetics during deformation-enhanced transformation were formulated. It was shown that the process of deformation-enhanced transformation can be divided into three stages according to the characteristics of transformation kinetics: The kinetics equations of two early stages fitted well in J-M-A equation. The kinetics of the first stage obeys Cahn’s site saturation mechanism, with the value of kinetics parameter n of 4. Ferrite nucleates at austenite grain boundaries and triple points during the first stage. Kinetics of the second stage doesn’t obey Cahn’s theory, with the value of kinetics parameter n of 1-1.5, corresponding to ferrite nucleation repeatedly at areas with high stored energy in front of the ferrite/austenite interface. The kinetics doesn’t obey the law of J-M-A equation any more in the final stage, and only few nucleation sites left at this moment.

Abstract: The concept of deformation-enhanced transformation of ferrite in plain low carbon steel is introduced. The characteristics are presented. Systematic works conclude that deformation significantly enhances the ferrite transformation of undercooled austenite in plain low carbon steel. Nucleation is the dominant process of the transformation. Until the completion of the transformation, nucleation is always repeated, especially at the zone in front of the newly formed ferrite grains, which restrict the grain growth and lead to formation of very fine ferrite grains. Three stages of kinetics are clearly shown from the experimental measurement, which correspond to nucleation at grain boundaries, at the zone in front of newly formed ferrite grains and within residual austenite.