物理学报. 2020, 69(11): 117701.
摘要: 通过在碳化硅中添加高纯度近零膨胀质料β-锂辉石, 回收无压液相烧团结成了锂辉石/碳化硅复相陶瓷. 研究表白: 适当添加β-锂辉石能促进碳化硅烧结, 复相陶瓷体密度和杨氏模量随β-锂辉石含量的添加呈先升高后低落趋势, 并在–150—480 ℃温度区间得到较低的热膨胀系数. 研究功效对付开拓烧膨胀系数小、烧结温度较低的碳化硅复相陶瓷具有重要的参考意义.
Preparation and properties of spodumene/silicon carbide composite ceramic materials
18 February 2020
22 March 2020
05 June 2020
Abstract: Silicon carbide (SiC) is widely used due to the lower coefficient of thermal expansion (CTE), high thermal conductivity and excellent mechanical properties. However, the self-diffusion coefficient of SiC relative to that of oxide ceramics is very low, it is difficult to sinter at lower temperature. The β-spodumene has ultra low or even negative thermal expansion coefficient combined with good thermal and chemical durability, which melts at 1423 ℃. Accordingly, the present study focuses on the use of β-spodumene as a flux at lower sintering temperature and the preparation of lower CET composite ceramics. The effects of spodumene on the sintering behavior, phase relations, thermal expansion and mechanical properties of spodumene/silicon carbide composites are discussed.A high pure β-spodumene LiAlSi2O6 compound with nearly zero thermal expansion coefficient is synthesized via solid phase sintering. Spodumene/silicon carbide composites are fabricated by the adding 25, 30, 35 and 40 mass% synthesized β-spodumene powder to 75, 70, 65 and 60 mass% α-SiC matrix, respectively. Both β-spodumene and SiC are fabricated by conventional pressureless liquid sintering technique, and the batches are uniaxially pressed into discs and rectangular bars, then sintered at 1550 ℃ for 2 h in an Ar atmosphere.The results show that the SiC and β-spodumene do not react during sintering, and the β-spodumene changes from tetragonal phase into hexagonal phase, the cell volume has a considerable shrinkage. A certain amount of liquid phase can help to enhance the density, improve Young’s modulus and promote the sintering behavior of SiC. When the feedstock contains 35% β-spodumene, the Young’s modulus reaches to (204.2 ± 0.5) GPa. Excess porosity is formed when liquid phase is too much during sintering, The Young's modulus of the sample 40SP is (119.6 ± 0.5) GPa. It is determined that the Young’s modulus of these materials are affected by porosity and internal microcracks. This study indicates that the content of β-spodumene and porosity are the dominant factors to control the CET of composites, but the porosity has a stronger effect. Besides, the microcracks, which are formed by the interaction of various internal stresses, are also an impotant factor. The materials with nearly zero thermal expansion are developed in a lower temperature range from –150 ℃ to 25 ℃, the spodumene content in the most stable composite reaches 40 mass%, and the CET of composite is close to that of Si (α25 ℃ = 2.59 × 10–6 ℃–1) in a temperature range of 25–480 ℃.
Li2O·Al2O3·SiO2(LAS)玻璃陶瓷体系具有热膨胀系数低、尺寸不变性高、耐热攻击强和化学机能不变等利益, 在很多技能应用中具有非凡的重要性, 一些较常利用的LAS体系成员热膨胀系数如所列[-].
System/material CET/10–6 ℃–1 Temperature range/℃
Li2O·Al2O3·2SiO2 (LiAlSiO4, Eucryptite) –6.2 25—800
Li2O·Al2O3·3SiO2 (Solid solution of eucryptite) Negative near zero CET 25—1000
Li2O·Al2O3·4SiO2 (β-LiAlSi2O6, β-Spodumene) 0.9 25—1000
Li2O·Al2O3·6SiO2 (LiAlSi3O8, Virgilite) 0.5 25—1000
Li2O·Al2O3·8SiO2 (LiAlSi4O10, Petalite) 0.3 25—1000
Li2O·Al2O3·10SiO2 0.5 25—1000
LAS + TiO2 (Pyroceram) –0.07—0.30
LAS + TiO2 + ZrO2 (Cer-Vit) 0.05—0.30
Hercuvit (LAS-based transparentlow expanding glass-ceramic) 0—0.3
Average linear thermal expansion coefficient (CET) of some important materials based on LAS system.