Densification Mechanisms During Drying and Sintering of Sol-Gel Derived Ceramics

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ABSTRACT Proposal No. CTS-9407958 University of Illinois Urbana-Champaign P. I.: John Kieffer The investigation of the densification behavior of gels, using a combination of experimental and computational techniques is proposed. The objective of the proposed research is develop a better understanding of the molecular scale mechanisms of densification, particularly during the drying and sintering phases of sol-gel derioedceramics. Brillouin light scattering will be used to measure the high-frequency complex mechanical modules of the equilibrium gel structures, prepared under different chemical conditions, and at different stages along their densification path. The elastic component of this modulus assesses the structural rigidity of the gel skeleton, and allows one to monitor structural developments along the densification path. The loss component predominantly reflects the viscous dissipation between the gel backbone and the solvent which flows throughout its pores. The interpretation of the experimental findings will be accomplished by means of molecular dynamic computer simulations. With simulations, models of the gel-solvent systems will be generated which allow one to study their properties on the same time and length scales as the inelastic light scattering, and to establish the relationship between the gel structure and is dynamic behavior. The relative contributions of network relaxation and solvent-network friction will be assessed by complementary a.c. conductivity measurements of samples containing salt-doped solvent. The expected outcome of the research is a fundamental understanding of the molecular scale mechanisms that control the drying and densification of gels. This permits a better control of this processing method. Furthermore, a technique for the direct measurement of gel viscosity and permeability, parameters which are difficult to access otherwise, will be devised.