Characteristic Investigation Of Several Crystal Aggregate Morphologies With Diffrerent Symmetries

Traditional crystal morphology study only focused on the equilibrium morphology of the geometric polyhedron, but it was not sufficient about the studies of crystal dendritic aggregate morphology in the nature and production practice of crystal materials under a large number of non-equilibrium conditions. Study on crystal dendritic aggregate morphology can help us understand the causes of the special structure of certain crystals, but also learn more about microstructure and properties of ceramics and glass-ceramics, and indirectly accelerate the development of some non-linearity theory or non-equilibrium theory. Therefore, the studies of crystal dendritical aggregates morphology under non-equilibrium have great significance to the theory and utility.Through a large number of experimental studies, using solvent evaporation method, gel method, liquid-phase diffusion method, hydrothermal method, and mixed-alkalis process of different crystal growth methods, a variety of different crystal dendritic aggregate morphologies were growth (synthetic), with the help of various modern testing techniques to study their morphology and in accordance with dendrite, seaweed-like dendrite, spherulite of their classification system was classified. Crystallography orientations of a number of crystal dendritic aggregate morphologies were identified firstly using the EBSD technique. This dissertation focused on the effect of the crystal anisotropy in the crystal dendritic aggregate morphologies and the formation of aggregates. The formation mechanism of crystal dendritic aggregate morphologies was preliminary studied from the crystal structure, crystal growth conditions, etc.The main achievements of this dissertation:1.A series of crystal dendritic aggregate morphologies were prepared through a large number of experimental researches. According to the different characteristics and symmetrives, crystal dendritic aggregate morphologies were attributed to three types:dendrite, seaweed-like dendrite and spherulite.Compared and analysized crystal symmetry of crystalline materials and the formation type of dendritic morphology, it was found:for the higher the crystal symmetry of the internal structure of the crystal material, different types of crystal dendritic aggregate morphologies can be formed under different conditions; and for the lower symmetry of the crystal materials, the type of crystal dendritic aggregate morphology is less.Changing the conditions of crystal growth can be a significant impact on crystal dendritic aggregate morphology, in particular, the smaller the initial concentration, the more inclined to formate seaweed-like dendrite generated by small crystal particles.2.SrSO4 aggregate patterns have been successfully prepared by a simple diffusional reduction process including radial polycrystalline aggregate pattern and dendrite. EBSD and pole figures have been used to determine the directions of the branches in SrSO4 dendrites. The growth morphology of SrSO4 crystals is controlled by not only their crystal structure but also external growth conditions. The ultimate reason of radial SrSO4 aggregate pattern formation is the internal structure control. The growth morphology of SrSO4 dendrites is controlled by not only their internal structure but also external growth conditions. The internal structure of SrSO4 dendrites influences the character of the growth direction vertically<001>.The change of the ions concentration in the diffusion system leads to the evolution from<110> to<140> of the long main branches.3.The different forms and crystallography orientations of potassium sulfate dendrite and seaweed-like dendrite were tested with EBSD technique. It was found:for potassium sulphate (K2SO4) dendrite,the main trunks growth along the<111> direction; while for potassium(K2SO4) seaweed-like dendrite,there is the twin relationship of twin axis<011>and twin plane (053).4.EBSD testing techniques have been used to determine the growth direction of monomers in the radial CaSO4 aggregate patterns. Measurement results show that the monomers are one-dimensional crystals growth along the<001> direction. The possible formation mechanism of the CaSO4 bundle structure is the splitting growth mechanism.EBSD studies on NaCl spherulite have shown that the cells of these spherulites including some NaCl dendrites, the trunks of dendrite growth along the<111>direction.5.Two different morphologies of calcite CaCO3 microspheres were synthesized by adding a certain amount of vanadium oxide or boron oxide at 230℃.By means of scanning electron microscopy study of calcite crystal aggregates morphology, combined with the growth conditions of crystal morphology of branched aggregate, analysts believe that the formation main reason of different forms of calcite microspheres is due to mixed-alkali melts with different oxidation material formed a network of different oxygen-containing anion salt, changing the orientation of calcite crystals in different crystal plane crystallography surface activity to promote different forms of single crystal and the crystal formation of spherulites.This dissertation also discussed the formation mechanism of the hollow spherical hydromagnesite Mg5(CO3)4(OH)2·4H2O and the impacts of temperature, pressure and other experimental conditions on aggregate. It was found that the heating temperature and the filling amount of water and the quantity of added reactant material had a greater influence on their formation.