Synthesis and Characterization of Mesoporous Alumina via a Reverse Precipitation Method

Mesoporous aluminaΥ-AI203 with high specific surface area and large pore volume is prepared by using a facile reverse precipitation method from sodium aluminate and nitric acid. The effects of terminal pH value, aging time and thermal stability on the characterization of Υ-Al2Oa are studied by means of X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, Brunauer-Emmett-Teller （BET） method and scanning electron microscopy （SEM）. The results show that Υ-A1203 with better properties can be obtained by changing the preparation parameters. High BET surface area of 340 m2/g can be obtained by calcining at 500℃ for 4 h with large pore volume of 0.90 cm3/g and average pore size of 7.6 nm. After calcining at 1000°, the surface area is still 86 m2//g and the pore volume is 0.37 cm31/g.

Synthesis of γ-Al2O3 with High Surface Area and Large Pore Volume by Reverse Precipitation- azeotropic Distillation Method

γ-Al2O3 with high surface area and large pore volume combined with high thermal stability was synthe- sized by a reverse precipitation-azeotropic distillation method. The effects of azeotropic distillation on the characte- ristics of γ-Al2O3 were studied by means of X-ray diffraction（XRD）, Fourier transform infrared（FTIR） spectroscopy, transmission electron microscopy（TEM） and N2 adsorption-desorption. The results show that γ-Al2O3 dried by azeo- tropic distillation has excellent structure characteristics with a high surface area of 426 m2/g and a large pore volume of 2.56 cm3/g. After calcination at 1100 ℃, the surface area of γ-Al2O3 was still 92 mE/g with a large pore volume of 1.00 cma/g, indicating the potential application in catalyst and petroleum industry.

Microstructure and Mechanical Properties of 06Cr13Ni4Mo Steel Treated by Quenching–Tempering–Partitioning Process

A heat treatment process, quenching-tempering-partitioning （Q-T-P）, has been applied to a low carbon martensitic stainless steel 06Crl3Ni4Mo. By using this process, ultrafine reversed austenite can be obtained at room temperature. The microstructures of the reversed austenite and the martensite matrix were characterized by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS） in detail. The results show that the ultrafine reversed austenite is enriched in Ni resulting in the austenite stability at room temperature. Two new types of nano-scale carbide precipitates are found in the martensite matrix. Detailed analysis suggests that the two nano-scale precipitates can be identified as ω phase and λ phase carbides, respectively. The orientation relationship between the ω phase and matrix is [011]α [/[2110]ω and （211）α//（0110）ω, while that between the X phase precipitate and matrix is [011]α][[0001]λ and （200）α/（1210）λ. For the present steel, the ultrafine reversed austenite and carbide precipitates obtained by Q-T-P treatment provide a good combination of high strength and toughness.

Facile Synthesis of Mesoporous Si-containing γ-Al2O3 Nanofiber with Enhanced Thermal Stability

Mesoporous γ-Al2O3 nanofiber was prepared via a simple reverse precipitation route using Si-containing Al（OH）3 and HNO3 as raw materials. The resultant Si-containing mesoporous γ-Al2O3 nanofiber exhibited high surface area of 320 m^2/g, large pore volume of 1.17 cm^3/g and large pore size of 10.5 nm. The introduction of Si element remarkably enhanced the thermal stability of mesoporous γ-Al2O3. The as-prepared nanofiber could maintain relative high surface area（110 m^2/g） and pore volume（0.73 cm^3/g） up to 1100 ℃. The effects of various experimental conditions, such as pH value, reaction temperature and aging temperature on the structural properties of the mesoporous γ-Al2O3 were also investigated.