Pressure Field Assisted Polycondensation Nonaqueous Precipitation Synthesis of Mullite Whiskers and Their Application as Epoxy Resin Reinforcement.

Guo Feng,Qing Hu,Qian Wu,Jian Liang,Quan Zhang,Lifeng Miao,Jianmin Liu,Weihui Jiang,Zi Hu,Feng Jiang

doi:10.3390/polym11122007

Abstract

Mullite whiskers were novelty prepared via pressure field assisted polycondensation nonaqueous precipitation method. The precipitate phase transition in heating process, phase compositions and microstructure of samples calcined at different temperatures, effect of pressure field on precursors polycondensation and AlF3 amount on sample morphology, the structure and the growth mechanism of whiskers were investigated. The results indicate that pressure field caused by kettle treatment promotes the polycondensation reaction between AlF3 and tetraethyl orthosilicate (TEOS), the excess aluminum fluoride coordinates with the precipitate skeleton of the =Al–O–Si≡, which brings about the low mullitization temperature (900 °C). The sample prepared with the optimal amount of aluminum fluoride (1.3 of the theoretical amount) calcined at 1100 °C presents high yield and aspect ratio (>15, 100 nm in diameter) of mullite whiskers. Growth of whiskers prepared via pressure field assisted polycondensation nonaqueous precipitation method is attributed to a vapor-solid (VS) mechanism with the inducement of screw. These mullite whiskers with the structure of multi-needle whiskers connected in the same center can be distributed evenly in epoxy resin, which greatly improves the mechanical properties of epoxy resin.

Highlights

Mullite (3Al2 O3 ·2SiO2 ) materials are widely applied as high-temperature engineering and refractory materials, due to their unique excellent properties of high-temperature strength, low thermal conductivity, high creep resistance, relatively low thermal expansion coefficient, excellent chemical stability and creep resistance [1,2]
Well-developed mullite whiskers were prepared via nonaqueous precipitation in-situ synthesis
Well-developed mullite whiskers were prepared via nonaqueous precipitation in-situ synthesis method at 1100 ◦ C taking tetraethoxysilane (TEOS) as silicon source, anhydrous AlF as aluminum method at 1100 °C taking tetraethoxysilane (TEOS) as silicon source, anhydrous AlF33 as aluminum source and growth auxiliary for whisker

Summary

Introduction

Mullite (3Al2 O3 ·2SiO2 ) materials are widely applied as high-temperature engineering and refractory materials, due to their unique excellent properties of high-temperature strength, low thermal conductivity, high creep resistance, relatively low thermal expansion coefficient, excellent chemical stability and creep resistance [1,2]. Mullite has a stable crystal structure of orthorhombic. Its lattice constants (a, b and c) are of 7.545 Å, 7.689 Å and 2.884 Å (JCPDS Card # 15-0776). The crystal growth of mullite is generally more quickly in the c-axis direction than any other direction, which brings a high orientation degree to form mullite whiskers. Mullite whiskers have attracted much attention as the reinforcement for high-temperature materials [3,4,5].

Methods

Results

Conclusion