论文总字数：23557字

摘 要

本文以低毒水溶性单体DMAA为凝胶体系，采用水基注凝成型制备多孔Si₃N₄陶瓷。系统研究了β–Si₃N₄晶种含量、尺寸及形貌对Si₃N₄浆料、生坯及烧结体性能的影响。结果表明，引入柱状β–Si₃N₄晶种更易导致浆料粘度增大。当晶种加入量为10 wt%时，浆料粘度达到最大值0.87 Pa.s。对于等轴状β–Si₃N₄晶种，Si₃N₄生坯抗弯强度随其含量的增加及粒径的减少呈现出单调递减的规律。而引入长柱状β–Si₃N₄晶种时，随其含量的增加，生坯抗弯强度表现为先增加后减小规律。在晶种含量为6 wt%时，生坯抗弯强度达到最大值32.06 MPa，在晶种含量为10 wt%时，强度出现最小值26.02 MPa。总体而言，本实验所制备的Si₃N₄生坯抗弯强度均在26 MPa以上，表现出优异的力学性能。在1750 °C无压烧结2 h后，α→β–Si₃N₄相变完全。Si₃N₄烧结体气孔率随着晶种 (包括等轴状和长柱状β–Si₃N₄) 粒径的增大及含量的增加，呈现出单调递增规律。相比于等轴状β–Si₃N₄晶种，引入柱状β–Si₃N₄晶种会赋予Si₃N₄陶瓷更高的气孔率，且当晶种含量为10 wt%时，气孔率达到最大值41.77%。Si₃N₄陶瓷抗弯强度和断裂韧性随晶种 (包括等轴状和长柱状β–Si₃N₄) 含量的增加呈现出先增大后减小趋势。相比于等轴状晶种，引入长柱状β–Si₃N₄晶种时，Si₃N₄陶瓷表现出更高的抗弯强度和断裂韧性。当晶种含量为2 wt%时，抗弯强度达到最大值378.5 MPa。当晶种含量6 wt%时，断裂韧性达到最大值8.54 MPa.m^1/2。在X波段 (8.2–12.4 GHz) 范围内，当引入2 wt%的柱状β–Si₃N₄晶种时，Si₃N₄陶瓷介电常数和介电损耗分别在4.6–4.8，0.04–0.05范围变化。

关键词：多孔Si₃N₄陶瓷；注凝成型；DMAA；β–Si₃N₄晶种；力学性能；介电性能

Effect of β–Si₃N₄ Seed on Porous Si₃N₄ Ceramics Prepared by Aqueous Gelcasting

Abstract

In this paper, porous Si₃N₄ ceramics were prepared by aqueous gelcasting using low–toxic water–soluble monomer DMAA as a gel system. The effects of seed content, size and morphology of β–Si₃N₄ on the properties of Si₃N₄ slurries, green and sintered bodies were systematically studied. The results show that when rod–like β–Si₃N₄ seed was introduced, the viscosity of slurries was significantly increased compared with the addition of the equiaxial one, and reached the maximum 0.87 Pa.s with 10 wt% seed content. Considering the equiaxial β–Si₃N₄ seed, the flexural strength of green bodies exhibited a monotonously decreasing tendency with the increase of content as well as decrease of seed size. But for the rod–like β–Si₃N₄ seed, the flexural strength of green bodies increased first and then decreased with the increase of the seed content. When the seed content was 6 wt% and 10 wt%, the corresponding flexural strength reached a maximum of 32.06 MPa and a minimum of 26.02 MPa, respectively. In general, the flexural strength of green bodies prepared in this work was above 26 MPa, showing excellent mechanical properties. After pressureless sintering at 1750 °C for 2 h, α→β–Si₃N₄ phase transformation was complete. The porosity of Si₃N₄ ceramics increased with the increase of seed size (including equiaxed and rod–like β–Si₃N₄ seeds), displaying a monotonously increasing pattern. In comparison to the equiaxed seed, the introduction of rod–like one led to a higher porosity. As the rod rod–like seed content was 10 wt%, the maximum porosity was 41.77%. Both flexural strength and fracture toughness increased first, followed by a decrease with an increase in seed content (including equiaxed and rod–like β–Si₃N₄ seeds). Nonetheless, The rod–like seed introduction conferred Si₃N₄ ceramic higher flexural strength and fracture toughness, which corresponded to 378.5 MPa and 8.54 MPa.m ^1/2, respectively, with the seed contents of 2 wt% and 6 wt%. In the X–band (8.2–12.4 GHz) range, as 2 wt% rod–like β–Si₃N₄ seed added, the dielectric constant and dielectric loss of Si₃N₄ ceramics varied from 4.6 to 4.8 and 0.04 to 0.05, separately,

Key words：Porous Si₃N₄ ceramics；Gelcasting；DMAA；β–Si₃N₄ seed；Mechanical properties；Dielectric properties

目录

摘 要 I

Abstract II

第一章 绪论 1

1.1 前言 1

1.1.1 Si₃N₄的结构与性能 1

1.1.2 多孔Si₃N₄陶瓷的制备方法 1

1.2 注凝成型制备多孔Si₃N₄陶瓷研究进展 2

1.3 多孔Si₃N₄陶瓷存在的主要问题 3

1.4 课题的提出与研究内容 4

第二章 实验 5

2.1 实验原料 5

2.2 实验设备 7

2.3 实验过程 8

2.4 表征与测试 9

第三章 结果与讨论 11

3.1 β–Si₃N₄晶种对浆料粘度的影响 11

3.2 β–Si₃N₄晶种对生坯显微结构和力学性能的影响 12

3.3 Si₃N₄生坯在空气气氛下的DSC–TG曲线 14

3.4 β–Si₃N₄晶种对多孔Si₃N₄陶瓷的影响 14

3.4.1 β–Si₃N₄晶种对多孔Si₃N₄陶瓷相组成的影响 14

3.4.2 β–Si₃N₄晶种对多孔Si₃N₄陶瓷显微结构的影响 15

3.4.3 β–Si₃N₄晶种对多孔Si₃N₄陶瓷孔结构的影响 17

3.4.4 β–Si₃N₄晶种对多孔Si₃N₄陶瓷气孔率的影响 18

3.4.5 β–Si₃N₄晶种对多孔Si₃N₄陶瓷力学性能的影响 19

3.4.6 β–Si₃N₄晶种对多孔Si₃N₄陶瓷介电性能的影响 21

第四章 结论 23

参考文献 24

成果 28

请支付后下载全文，论文总字数：23557字