Study On Mechanical-Chemistry And Physical Properties Of Mechanically Ground Fly Ash

Since the first years of the 1980s, mechanico-chemistry, the study of chemical reactions and relevant chemical properties of materials subjected to mechanical forces, has experienced a significant development with consequence of a wider variety of grinding objects, grinding techniques and analytical methods. In the present research, mechanico-chemical basic principles have been employed to explore changes in chemistry and physical properties of fly-ashes, on which extensive academic studies and application researches remain to be of great interests, by using advanced analytical techniques such as particle size analysis, thermal analysis and SEM, especially NMR and HR/MAS NMR. Also the new research results have been made applicable to other novel materials or research areas under development.This thesis firstly gives an overview on fly-ashes and mechanico-chemistry, including fly-ash's basic properties, its applications and milling technologies. It can be seen that some potentially important studies concerned with changes in microstructure and thermal properties of fly-ashes after milling treatment were not yet reported so far in literatures published at home or abroad.After an establishment of research program, the kinds of fly-ashes, milling equipment, milling conditions and analytical methods were determined. The main research conclusions based on a great deal of experiments are outlined as follows:The density, particle size distribution and specific surface area of fly-ashes were found to be influenced by the type of milling equipment, milling conditions (wet- or dry- processes), milling temperature and the loading ratio of grinding medium to water and materials. It was shown that 1) stronger milling force leads to higher density and smaller sizes of fly-ashes; 2) thermal effect by milling is one of the main causes for the agglomeration of fine fly-ash particles. Moreover, the milling operation at constant temperature results in the gradual decrease in particle size of fly-ashes aswell as the elimination of thermal effect with an increasing mechanical force; 3) the finer particles of fly-ashes milled in wet conditions, as observed by SEM, often adhere to the surface of bigger particles to form flocculent masses while the particles in a dry-milling process are quite dispersed.DTA results showed that the temperatures at which the release of adsorbed water, isomorphism of quartz, charcoal burning and decomposition of CaCO3 in fly-ashes start to take place are relatively cut down after a milling treatment. In the thesis, these phenomena have been discussed and accounted for in terms of the theory of physical chemistry.To analyze the structural changes with fly-ashes, trimethylsiliane (TMS) method for detecting polymerization of Si-O tetrahedra and solid 1D and 2D NMR for Al and Si were utilized in the study. It is the first time for solid NMD to be applied to in-depth study of fly-ashes. The NMR data revealed that [A104] and [AlO6] polyhedra underwent a remarkable structural change after a milling process while a slight one was detected with Si-O tetrahedra. This result suggests that the flocculation of fly-ash particles after a long-time milling is the macro-scopical reflection of a structural change of [AlO6] hexahedra of a single symmetry to ones of multiple asymmetries.2D MQMAS NMR, which was first used to study fly ashes, has revealed that [AlO4] may exist in three structural forms, whereas [AlO6] exists in two forms originally and then turns to three forms after milling. The SEM results were also in good agreement with that of NMR for the fly-ashes milled either in wet or in dry conditions.To develop the effective applications of fly-ashes, the finely-milled fly-ashes were used as a filling of resin-based composite materials to study the variation of their properties including viscosity, thermo-solidifying temperature and time, gel-forming time and bending strength. It has been found that with the fly-ash content increasing,the resinous matrix composite materials showed a higher viscosity, lo...