β–Si3N4晶种对注凝成型制备多孔Si3N4陶瓷的影响毕业论文
2022-01-13 08:01
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.m1/2。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
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