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

摘要提案编号：CTS-9407958伊利诺伊大学香槟分校P.I.：John Kieffer建议使用实验和计算技术相结合的方法来研究凝胶的致密化行为。布里渊光散射将被用来测量在不同化学条件下制备的、沿致密化路径处于不同阶段的平衡凝胶结构的高频复杂力学模数。该模数的弹性部分评估凝胶骨架的结构刚性，并允许监测致密化路径上的结构发展。损失成分主要反映了凝胶骨架和流经其毛孔的溶剂之间的粘性耗散。对实验结果的解释将通过分子动力学计算机模拟来完成。通过模拟，将生成凝胶-溶剂体系的模型，使人们能够在与非弹性光散射相同的时间和长度尺度上研究其性质，并建立凝胶结构与其动态行为之间的关系。网络松弛和溶剂-网络摩擦的相对贡献将通过互补的A.C.进行评估。含盐掺杂溶剂样品的电导率测量。这项研究的预期结果是对控制凝胶干燥和致密的分子尺度机制有一个基本的了解。这允许更好地控制该处理方法。此外，还将设计一种直接测量凝胶粘度和渗透率的技术，否则很难获得这些参数。

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.