Investigation On The Synthesis Of One Dimension Mullite By Molten Salts Synthesis

The specific crystals which grow along the linear chain are classified to one-dimension structured ceramic materials, which can exhibit special properties owing to the growth restriction in other directions. Owing to its great thermal shock resistance, creep resistance and stable room-temperature ?exural strength at high temperature, mullite has been applied in whisker technology, coating technology, filter membrane, high-temperature catalytic reactor, and so on. The molten salts synthesis (MSS) belong to a wet chemical method. In MSS, the resultant production without aggregation can be easily obtained, and has a higher quality when compared with other liquid phase methods. In this paper, the prepariton of one-dimension structured mullite by MSS was investigated.The investigation shows that high chemical activity and strong dissolve ability precursors were helpful to obtain isolated mullite crystal. The mullite was obtained when the sample with Al₂(SO₄)₃, amorphous-SiO₂, Na₂SO₄ (Al/Si/Na=2/1/8, atoms ratio) was heated at 1000℃for 3h after HF etching. XRD, EDS, and HR-TEM results show the Al-rich compostion in mullite, and photoluminescence results show the oxygen vacancies defects presence. The investigation on temperature schedule shows that rapid heating was helpful to form mullite, and mullite was transformed to NaAlSiO₄ at about 1100℃.The investigation on growth mechanism shows that supersaturation led to the mullite crystal nucleus formation in MSS. At the growth interface, the decomposition of mullite monomers was reversible, so the growth was revised continuously as energy minimum and along the c-axis. The new two-dimensional islands provided nucleations, which reqired large supersaturation because the nucleation barrier is high. The mullite crystal growth in MSS can be explained by liqiud-solid mechanism.With the B₂O₃ addition, the size of mullite crystal decreased. The mullite nanowires were obtained at B₂O₃/SiO₂ = 0.04. The phenomenon can be abscribed to the nucleation rate increase when B₂O₃ was added in MSS. With the mullite seeds addition, it was found that the yield of mullite was promoted and the the size of mullite crystal decreased. At the same time, the size distribution was narrower with higher seeds addition.