Advanced Materials Research Vols. 295-297

Abstract: Mg-Al spinel has been synthesized by using industrial waste from ferroalloy plant, decomposed magnesite and used MgO-C brick as the main raw materials. The influence of decomposed magnesite and used MgO-C brick addition on crystalline structure, micro-morphology and properties of synthesized Mg-Al spinel are discussed. The synthesized product was characterized by XRD and SEM, and the crystallinity of each crystalline phase is calculated by relevant analytical software such as X'Pert plus and so on. The experimental result show the crystalline phase periclase increase with the increasing of decomposed magnesite and used MgO-C brick powder. The crystallinity of crystalline phase is highest when the addition of decomposed magnesite is 40wt%. Activity magnesia generated by decomposed magnesite powder decomposition has helped to improve the crystallinity of Crystalline phase. The energy provided by oxidization of the residual carbon promotes Mg-Al spinel grain growth.

Abstract: Silver nanowires were fabricated in a direct current electric field using a solid-state ionic method, and were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The reverse saturable absorption and optical limiting properties in silver nanowires, suspended in de-ionized water were investigated by using an EKSPLA (PL2143A) picosecond laser, which produced 30 ps laser pulses at 532 nm with a repetition rate of 2 Hz. Experimental results indicate silver nanowires have obvious optical limiting properties.

Abstract: Nanometer composite S₂O₈^2-/SnO₂-TiO₂, a novel solid superacid, was prepared by the sol-gel method and its structure was characterized by XRD, TEM, FT-IR and nitrogen adsorption. Results indicated that the composite S₂O₈^2-/SnO₂-TiO₂ had a narrow particle size distribution with an average particle diameter about 15~20nm. S₂O₈^2- combined with SnO₂-TiO₂ resulted in formation of strong acid sites on the surfaces. The surface area of catalysts obviously increased after incorporating SnO₂. Nanometer S₂O₈^2-/ SnO₂-TiO₂ composite was used as a catalyst for a-pinene isomerization and the influence of catalyst preparation conditions on its performances were investigated. The optimum condition for superacid catalyst preparation was found to be with 2:1 Sn/Ti mole ratio, S₂O₈^2- 1 mol · L^-1 of impregnation consideration and toasting temperature of 773K. With 3% of S₂O₈^2-/SnO₂- TiO₂ catalyst dosage at a reaction temperature at 403K for 2 h, the conversion of a-pinene was 98 % and the selectivity to camphene was 62 %.

Abstract: The composite specimens have been prepared using fused corundum, silicon and bauxite-based β-SiAlON powder as starting materials. The physical properties, high temperature modulus of rupture (HMOR), thermal shock resistance (TSR), phase composition and microstructure of the specimens after firing at 1500°C have been studied. The results show: (1) Al₂O₃-SiC-SiAlON composites are sintered well at 1500°C. (2) HMOR and TSR of the specimens increase with increase of Si content, high temperature properties are further increased with appropriate β-SiAlON addition. (3) The in-situ formed SiC and O’-SiAlON fill in the interstices of corundum skeleton structure, forming interlocking network structure, thus creating strengthening and toughening effects.

Abstract: Sulfate attack is one of several chemical and physical mechanisms of concrete deterioration. In actual situation, concrete structures always suffer from the coupled effects of multifactor such as wet-dry cycle and sulfate attack when exposed to tidal area or groundwater level change environment. Partial replacement of cement with mineral admixture is one of the efficient methods for improving concrete resistance against sulfate attack. In this regard, the resistance of concrete with fly ash and slag to sulfate attack was investigated by wet-dry cycle method. The degree of sulfate attack on specimens after different cycles was observed using scanning electron microscopy. The results of compressive strength and percentage of compressive strength evolution factor at various cycling times show an increase in the sulfate resistance of concrete with 60% of fly ash and slag than that only with 40% fly ash. The microstructural study indicates that the primary cause of deterioration of concrete under wet-dry cycle condition is swelling of the sulfate crystal rather chemical attack.

Abstract: CeO₂ nano-sized crystalline powders were prepared by sol-gel combustion method from ammonium cerium nitrate and citric acid, and the dependences of the particle size of synthesized powder on the precursor gel were investigated. The precursor gels and the synthesized powders were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray scattering (XRD). The colloid particle with nanometer size was firstly observed by FE-SEM, and its size variation had the same tendency as that of CeO₂ powders with the varying of the ratio of metal ions to citric acid. Furthermore, the probable reasons for the effect of gel structure on properties of nano-sized ceria powders prepared by sol-gel combustion were explained.

Abstract: The microstructure and the formation mechanism of martensite in W6Mo5Cr4V2 steel was studied by metallographic microscope and JEM-2100 transmission electron microscope after the samples were austenized between the temperatures of Ac₁~Ac_cm and then quenched. The results show that When heating W6Mo5Cr4V2 steel samples between the temperatures of Ac₁~Ac_cm and then quenching, the cryptocrystalline martensite will be obtained. The cryptocrystalline martensite is plate martensite actually. It is considered that the formation cause of the cryptocrystal martensite is extremely inhomogeneous chemical composition in the austenite grains and the difference of martensite starting point (Ms point) of every small area in austenite grains. Besides the high-density dislocation and the fine twin crystal, the substructure of the cryptocrystalline martensite includes the superfine stacking fault. The stacking fault is caused by the stacking misarrangement during the crystal lattice reconstruction of martensite phase transformation. The midrib exists in the cryptocrystal martensite of W6Mo5Cr4V2 steel, which is composed of the fine twin crystal plates. The shear mechanism can not account for the formation of the martensite midrib.

Abstract: Silica nanowires (NWs) were prepared on the Si wafer with a modified thermal evaporation of silicon monoxide and cryptophane-A was fixed to the surface of the silica NWs for methane sensing. Scanning electron microscopy equipped with EDS was used to characterize the morphology and composition of the sensitive material. A fiber optical device was designed to operate via luminescence reflection and the methane sensing properties were characterized at room temperature. The sensing material shows a stable and strong blue luminescence when excited by UV light source at wavelength of 380 nm, and it is efficiently quenched by molecular methane within the methane concentration range between 0.2% and 3.5% (v/v). This novel methane sensing material has significant advantages and might have application potential.

Abstract: By analyzing the randomicity and sensitivity of design parameters on fire resistance performance of RC structure, it indicates that the concrete thickness of covering layer is the most sensitive parameter to RC fire resistance performance in all given out parameters. And the stochastic finite element reliability analyzing method is briefly introduced too.

Abstract: The long-retention of antibiotics in Calcium Phosphate Cement (CPC) may induce the development of drug resistance. Fast-releasing CPC containing antibiotics (FRCPC) was proposed as a solution to this problem and studied in this work. The FRCPC containing different proportions of soluble component were prepared and characterized. The setting time, compressive strength, degree of the conversion, in vitro antibiotic release and fracture surface morphology of FRCPC were studied. The results showed that the setting time increased, the compressive strength decreased, the in vitro antibiotic release accelerated with increasing fraction of soluble component in FRCPC. The setting time and compressive strength of FRCPC containing 20 wt% soluble components were close to the requirements of clinical applications, and the in vitro release was completed within 7 d. These results mentioned above showed that the FRCPC with suitable proportions of soluble components may prevent the development of drug resistance and may find applications in clinics.