Advanced Materials Research Vol. 624

Abstract: Silicon nitride (β-Si₃N₄) nano-belts had been synthesized by used silica bricks and carbon powder as raw materials through carbothermal reduction nitridation. The morphology and microstructure of β-Si₃N₄ nano-belts were characterized by scanning electron microscopy (SEM/HRSEM), energy disperse spectrum (EDS) and X-ray diffraction (XRD). Results showed that the well-crystallized β-Si₃N₄ nano-beltes were grown with thinness of 50-150nm and width of 3-5μm. The relatively purer β-Si₃N₄ were prone to be thin films with thinness of 150nm, while the as-grown SiCN (impurityβ-Si₃N₄with C elements) were presented as nanorods with cross section length of 150*150nm. Orientation growth mechanism by grain dislocation and vapor-solid (VS) mechanism were both involved in the growth of nanostructures of β-Si₃N₄ nano-beltes and SiCN nanorods.

Abstract: It has a relatively rapid reaction with self-propagating combustion method to synthesize Ti-Al-N powder. This can effectively avoid uneven phenomenon of aluminum melting reunion during the reaction of raw materials. So you can use lower-cost aluminum as raw materials. In addition, the combustion synthesis method also has a simple process and low-cost advantage. Thus this method has the potential to become the optimum process method to prepare Ti2AlN and Ti4AlN3. In this paper, Ti, Al elemental powders and N2 were used as raw materials. The powder of Ti2AlN was successfully prepared for the first time by combustion synthesis method. This substance is a nitrogen compound of single-phase and three yuan. The results from the XRD diffraction analysis and SEM show that synthetic product is high purity Ti2AlN with a small sample to combustion synthesis when the pressure of nitrogen is in 5 MPa, but the content of synthesis products Ti2AlN is small when the sample is magnified, and the TiN and AlN has a higher content. It can burn synthetic Ti2AlN to control the nitrogen pressure and add the amount of TiN, and the pressure of N2 is better 2 MPa, and the amount of TiN added is better 30 wt.%.

Abstract: The melting point of zirconium diboride is up to 3245 ° C. It is concerned widespread as a high-temperature structural materials because of high melting point, high hardness, excellent electrical conductivity and good thermal conductivity. In this paper zirconium diboride powder was prepared by the carbothermic reduction and precursor pyrolysis. XRD, SEM and DTA were used to characterize the performance of the two powders. Results show that the median diameter of zirconium diboride powder prepared by solid phase is about 6μm, round in shape, is not conducive to the sintering. Zirconium diboride powder prepared by precursor pyrolysis is massive, which is deposited by the layers of zirconium diboride crystals.

Abstract: Polycrystalline Cr₂AlC was fabricated by a solid reaction synthesis of a mixture of Cr, Al and graphite powders in a flowing or the atmosphere in the temperature range of 700 to 1450 °C. The products for identification and analysis were characterized by X-ray diffraction (XRD). The effects of the composition of the initial elemental powders and temperature of purity and formation of Cr₂AlC were examined. It is found that the co-existence of Cr₇C₃ with Cr₂AlC is attributed to the surplus of carbon in the starting powders at 1350 °C, selecting the starting materials with a Cr: Al: C molar ratio of 2: (1.1-1.6): 1. For sample obtained from the starting elemental powders with the Cr: Al: C molar ratio of 2: 1.2: 0.94, no other phases but Cr₂AlC were detected. In addition, the effect of temperature on the formation of Cr₂AlC ceramic powders was carried out.

Abstract: Mullite with puncheon-like grains was synthesized by sintering the mixtures of coal gangue and γ-Al₂O₃ at 1400 °C~1550 °C for 4 h. The phase and microstructure evolution of the mullitization behavior were investigated by XRD, SEM and EDS. Phases of the sintered specimens were mullite, corundum and cristobalite at 1400 °C to 1450 °C. Arise of temperature would enhance mullitization, and total consumption of cristobalite occurred from 1500 °C upward. The in-situ produced primary mullite from gangue upon heating may be seeds for the growth of enenly dispersed mullite puncheons. Specimen sintered at 1550 °C consists of puncheons with an aspect ratio of 2~4, regionally forming an interlocking structure.

Abstract: Pure Sm2Zr2O7 and Sm2(Zr0.7Ce0.3)2O7 nano powders were prepared by sol-gel method using zirconium nitrate and samarium nitrate as raw materials, citric acid as solvent and dispersant. The synthesized powders were characterized by XRD, Ft-IR, BET, SEM and Emission spectra. The effect of thermal temperature on particle size of the nano-powders were studied and single phases of Sm2Zr2O7 and Sm2(Zr0.7Ce0.3)2O7 were completely formed at 900°C. The obtained powders consist of abnormal particles with agglomerated structures in size range 7-10nm. Moreover, the strong fluorescent properties of the synthesized products show that these two kinds of powders are potential fluorescent emitted materials.

Abstract: Lanthanum aluminate powders were synthesized by sol-gel process with metal nitrates as raw materials, 2-methoxyethanol/water as solvent and citric acid as chelating agent. The influence of this techniques (the amount of citric acid, pH value, calcination temperature and the ratio of 2-methoxyethanol/water) on the lanthanum aluminate powders were studied. The XRD shows pure LaAlO3 powders could be obtained after calcining at 600-900 °C. The SEM analysis indicates that the LaAlO3 particles are uniform and nanosized with a range of about 40-70 nm, which is slightly larger than the estimated particle size using Scherrer formula.

Abstract: A series of Bi-doped BixLa1-xAlO₃ (x=0.0, 0.1, 0.2, 0.3, 0.4) powders have been prepared by sol-gel method at 800°C. The influences of Bi doping content on phase, morphology, particle size, surface area, infrared absorption spectrum are discussed. XRD results show that there is no second phase in powders when x≤0.3, however, there exist impure phases when x≥0.4. The SEM analysis indicates the particle size of powder is 50-150nm. The specific surface area is 5-13 m²/g.

Abstract: Bi2Al4O9 powders were prepared by sol-gel process. The precursors were heated at 500-800°C for 2h to obtain Bi2Al4O9 powder and X-ray diffraction (XRD), Differential thermal analysis (DTA), thermogravimetric analysis (TG), field emission scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize precursor and derived oxide powders. XRD analysis show that the powder is still amorphous after calcined at 500°C. The peaks of Bi2Al4O9 become sharp after calcined at 575°C though still existing some amorphous phase. After calcining at 675-800°C, the powder has fully turned into pure Bi2Al4O9 phase. The crystallization process can also be confirmed by DTA-TG and IR. Calcining the precursor at 575°C, the absorption bands at 527 cm-1, 738 cm-1, 777 cm-1, and 919 cm-1are observed, which are assigned to Bi2Al4O9 and becoming stronger and sharper with the increase of temperature.