Low-temperature Synthesis Of Silicon Nitride, Aluminum Nitride Nanomaterials

On the basis of comprehensive and thorough investigation of literatures concerning the developments of silicon nitride (Si3N4) and aluminum nitride (AlN) nanomaterials synthesis and applications, in the dessertation, we dedicated to explore the low-temperature synthesis of high-temperature resistant materials such as silicon nitride and aluminum nitride in autoclaves. The morphologies of the as-prepared products were characterized and the properties were investigated. The main contents are summarized as follows:1. The preparation method of silicon nitride nanomaterials in stainless steel autoclaves at low-temperature was developed. (1) The mixture ofβ-Si3N4 nanorods andα-Si3N4 nanoparticles were produced by using silicon powder, sodium azide and N-aminothiourea at 170℃for 10 hours. (2) By adding iodine to the above system, the mixture ofβ-Si3N4 nanorods andα,β-Si3N4 nanoparticles were produced at 60℃for 10 hours.X-ray powder diffraction pattern results indicated that the products obtained at 170 and 60℃were both composed ofα-Si3N4 (JCPDS card no.41-0360) andβ-Si3N4 (JCPDS card no.33-1160). Transmission electron microscopy photographs showed the product obtained at 170℃mainly composed of nanoparticles with diameters of 160-250nm and nanorods with diameters of 60-90nm, lengths up to hundreds of nanometers. The results of HRTEM showed the high crystality of products, the d-spacing of 0.266 nm and 0.254 nm are consistent with (101) lattice spacing ofβ-Si3N4 nanorods and (210) lattice spacing ofα-Si3N4 nanoparticles respectively. The silicon nitride nanomaterials obtained at 60℃are mainly composed of Si3N4 nanorods and nanoparticles. The nanorods with diameters of 60-150nm, lengths up to 1μm, and the diameters of nanoparticles are in the range of 25-50nm. From the HRTEM results of silicon nitride nanorods, the d-spacing of 0.267 nm is consistent with (101) lattice spacing ofβ-Si3N4. The d-spacings of 0.436 nm and 0.266 nm of nanoparticle correspond well to the (101) lattice spacing ofα-Si3N4 andβ-Si3N4, respectively. The possible reaction mechanism of the low-temperature synthesis of Si3N4 nanomaterials was also discussed.2. The preparation method of aluminum nitride nanomaterials in antoclaves at low-temperature was developed. AlN nanomaterials were produced by using Al powder as aluminum source, N2H4-2HC1 and NaN3 as synactic nitrogen source, and Mg powder as additive at 150℃for 10 hours. X-ray powder diffraction pattern results indicated that the product was hexagonal AlN with lattice constants a=3.115 and c=4.978 (?), which are near the reported values (a=3.111, c=4.979 (?), JCPDS, card No.25-1133). Transmission electron microscopy and Scan electron microscopy photographs showed the sample was mainly consists of nanodendrites with diameters ranging from 100-150 nm and lengths up to several micrometers. The possible reaction mechanism and the effect of different nitrogen source and metal powder on the morphology and reaction temperature were discussed. The thermal stability of the sample was tested and the result was also analyzed.