Manufacturing Fully-dense MgO Nanocrystalline Ceramics By SHS/QP And Investigating On The Desification Mechanism

Self-propagating High-temperature Synthesis plus Quick Pressure (SHS/QP) which is the combination of conventional SHS process and additional mechanical pressure, is a new method of manufacturing materials. SHS/QP has the characters as followed:1.High heating rate(about 1600 K/min); 2.High pressure(about 120MPa).As a result, SHS/QP is not only suitable for manufacturing nano-materials for the while of the character of high heating rate in the process of SHS, but also fit for effectively overcoming the drawbacks of relatively low density of traditional SHS products, so as to manufacture bulk materials of high density with the help of added high mechanical pressure.The experiment utilized appropriate composites of SHS reaction system as the "Chemical Oven" to provide thermal for the combustion synthesis and successfully manufactured MgO nano-materials with the help of high mechanical pressure. This method effectively restrained grain growth that would exist in conventional process of ceramics-synthesis, and was verified to be an efficient way for manufacturing nano-ceramics of high density. As the result of the short synthesis period, severe reaction qualifications and the fact that the grain growth got restrained sharply, the traditional diffusion theory failed for providing convincing explanation, which indicated the existence of distinctive mechanism for densification.The content of this thesis can be divided into three parts:Firstly, introduction and experiment, describe the process of SHS/QP in the experiment and test methods; Secondly, investigation of the influence of temperature and pressure on the grain size and density of synthesized nano-materials,respectively; Thirdly, research on the mechanism of densification in the process of SHS/QP.On the basis of traditional sintering theory, preparing nano-materials of high density in high temperature requires the general factors as followed:1.High heating rate; 2.Short holding time of sintering temperature; 3.High pressure. Although the existing synthesis methods have some features, there are some distinct shortcomings when compared with SHS/QP, which predicts good blueprint of theory for manufacturing nano-materials by SHS/QP.Selecting from different SHS reaction systems and adjusting the component of each system so as to get the temperature schedule proper for manufacturing nano-materials, and then analyzing for the influence of temperature on the micro-phenomenon of grain growth, investigating for the impact that temperature exerted on macro- phenomenon of density; Adopting classic sintering model to simulate the densification process under the effect of pressure, and comparing the experiment results to that calculated from classic sintering theory to testify the theory based on presumption.Under the factor of SHS/QP process as followed:top sintering temperature of 1350℃and added pressure of 120MPa, the SHS/QP process could manufacture nanoscale MgO ceramics, with density above 95% while without visible grain growth. The result of simulation in the model verifies that: The mechanism of grain plastic deformation rather than the mechanism of diffusion, is the dominating densification mechanism in the process of SHS/QP.