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

提案编号伊利诺伊大学厄巴纳-香槟分校：John Kieffer提出了采用实验和计算相结合的方法来研究凝胶的致密化行为。提出的研究目的是更好地理解分子尺度上的致密化机制，特别是在溶胶-凝胶衍生陶瓷的干燥和烧结阶段。布里渊光散射将用于测量在不同化学条件下制备的平衡凝胶结构的高频复杂机械模块，以及在其致密化路径的不同阶段。该模量的弹性成分评估凝胶骨架的结构刚度，并允许沿着致密化路径监测结构发展。损失分量主要反映了凝胶骨架与流经其孔隙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，建立凝胶-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它们的性质，并建立凝胶结构与其动力学行为之间的关系。网络松弛和溶剂-网络摩擦的相对贡献将通过含有盐掺杂溶剂的样品的互补交流电导率测量来评估。该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的基本理解。这样可以更好地控制这种加工方法。此外，将设计一种直接测量凝胶粘度和渗透率的技术，这些参数很难通过其他方式获得。

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.