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A kinetic study of beta silicon nitride grown in yttrium-magnesium-aluminum-silicon-oxygen-nitrogen liquids.

机译：在钇-镁-铝-硅-氧-氮液体中生长的β-氮化硅的动力学研究。

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摘要

A fundamental study of the grain growth anisotropy of silicon nitride in liquids has been conducted in this thesis. The research employs a set of model experiments with dispersed silicon nitride crystals growing in different liquids. Through a systematic variation of the liquid compositions, the general growth behavior of β-Si3N4 has been identified and investigated. The results of a statistical analysis of the size distribution of β crystals, in length and width directions, have provided direct evidence that the kinetics is closely related to the successive phase transformations in the system, from α-Si3N4 to β-Si 3N4 and to β′-SiAlON. Velocity of crystal growth has also been calculated by analyzing the dynamics of crystal populations, which confirms that large crystals grow while small crystals shrink in the system at all time. The anisotropy in growth velocity is found to correlate to the ratio of Si to metal ions (Al, Mg and Y) in the system. In addition, electron microscopy has revealed a novel shape transition in silicon nitride crystals: the end caps evolve from a convex shape to a concave shape as the crystal width and length velocity increase. This leads to a newly proposed growth mechanism, which envisions transverse flux to aid length growth due to the inability of side surfaces to accommodate matter (i.e., under interface control). The shape transition is thus a result of long relaxation time at the end caps, which arises when the width is too wide and the length growth is too fast for the transverse flux to smooth out the end caps. Mathematical analysis of this shape transition, based on coupled surface diffusion equations, has been performed analytically and numerically (using finite element method, FEM). This analysis has identified a dimensionless parameter that governs shape transition and produced simulated crystal shapes that closely resemble the observed morphologies. From the above study, an improved understanding of the kinetics of silicon nitride, concerning phase transformation, growth dynamics, and interface processes, has been obtained.
机译：本文对液体中氮化硅的晶粒长大各向异性进行了基础研究。该研究采用了一组模型实验，其中分散的氮化硅晶体在不同的液体中生长。通过对液体成分的系统变化，确定并研究了β-Si 3 N 4 的一般生长行为。对β晶体在长度和宽度方向上的尺寸分布进行统计分析的结果直接提供了证据，证明动力学与系统中α-Si 3 N 4 到β-Si 3 N 4 和β' -SiAlON。还可以通过分析晶体种群的动力学来计算晶体生长的速度，这证实了大晶体生长，而小晶体始终在系统中收缩。发现生长速度的各向异性与系统中硅与金属离子（Al，Mg和Y）的比率相关。另外，电子显微镜揭示了氮化硅晶体的新型形状转变：随着晶体宽度和长度速度的增加，端盖从凸形演变成凹形。这导致了新提出的生长机制，该机制预见到横向通量将由于侧表面无法容纳物质（即在界面控制下）而有助于长度增长。因此，形状过渡是端盖处较长的松弛时间的结果，这是在宽度过宽且长度增长过快而使横向通量无法使端盖平滑时出现的。已经基于耦合的表面扩散方程对这种形状过渡进行了数学分析，并通过数值分析（使用有限元方法，FEM）进行了分析。该分析确定了控制形状过渡的无量纲参数，并产生了与观察到的形态非常相似的模拟晶体形状。从以上研究中，已经获得了对氮化硅动力学的更好理解，涉及相变，生长动力学和界面过程。

著录项

  • 作者

    Wang, Lingling.;

  • 作者单位

    University of Michigan.;

  • 授予单位 University of Michigan.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 212 p.
  • 总页数 212
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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