Microstructural development in porous β-Si₃N₄ ceramics prepared with low volume RE₂O₃–MgO–(CaO) additions (RE = La, Nd, Y, Yb)

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• 作者：Kevin P. Plucknett ; Mervin Quinlan ; Liliana Garrido ; Luis Genova
• 关键词：Porous ceramics ; Silicon nitride ; Silicon oxynitride ; Grain growth ; Scanning electron microscopy
• 刊名：Materials Science and Engineering: A
• 出版年：2008
• 出版时间：20 August 2008
• 年：2008
• 卷：489
• 期：1-2
• 页码：337-350
• 全文大小：2383 K

文摘

Porous β-Si₃N₄ ceramics have a wide range of potential applications, including filters for hot gases or molten metals, bioreactor supports and lightweight structural components. In the present study, a new approach is taken for the production of porous β-Si₃N₄ ceramics based on compositional design. A low volume fraction of multiple sintering aids is employed, where each additive is designed to play one or more specific roles in the sintering behavior and microstructural development of β-Si₃N₄ (e.g. densification, - to β-Si₃N₄ transformation, anisotropic β-Si₃N₄ whisker growth, debonding aid). The primary aim of this work was to develop β-Si₃N₄ ceramics with a more porous microstructure than in prior work (ideally with 20–40 vol. % porosity), while developing high grain aspect ratios (i.e. >10:1) such that good mechanical performance can be expected. Compositions are based on various ratios of RE₂O₃:MgO, where RE = La, Nd, Y or Yb, with selected materials also prepared with small CaO additions. Sintering has been conducted in a nitrogen atmosphere (0.1 MPa), at temperatures between 1400 and 1700 °C. The influence of sintering aid composition and sintering temperature has been assessed. Particular attention was paid to microstructure development, including: densification behavior, retained pore size, the extent of - to β-Si₃N₄ transformation, and the evolution of β-Si₃N₄ grain aspect ratios.