Advanced Materials Research Vols. 295-297

Abstract: The mechanism of the formation of active nitrogen atoms and the function of hydrogen molecules for the dissociation of the mixture of nitrogen and hydrogen in the plasma nitriding process are discussed in this paper. The results show that the nitrided case thickness of nitrided samples become thinner and the surface hardness decreases with the increase of cathode voltage. Active nitrogen atoms mainly result from non-elastic collision between positive ions H₂⁺ and neutral particles N₂ for N₂-H₂ mixture plasma nitriding at 550V cathode voltage, the volume percent of e-Fe₃N and the superficial nitrogen concentration of plasma nitrided case decrease with the increase of the mixture ratio of N₂/H₂. However, active nitrogen atoms mainly result from non-elastic collision between energetic positive ions H₂⁺, N₂⁺and neutral particles N₂ for N₂-H₂ mixture plasma nitriding at 650V cathode voltage. The existence of a few of nitrogen molecules makes critical energy of positive ions H₂⁺ dissociating neutral N₂ molecules drop to 26.06eV and the cathode voltage threshold value become 490V.

Abstract: Ductile iron specimen with dimensions of Φ590mm×800mm were prepared by treating the melt with an yttrium-containing nodulizer. Cooling curves at four locations____the center location, the location 85mm distant from the center, the location 170mm distant from the center and the location 255mm distant from the center of the heavy ductile iron casting Φ590mm×800mm was obtained. The effect of yttrium and magnesium on microstructure and mechanical properties was investigated, and the factors on the distribution of chunky graphite in the specimen were discussed as well. The results show that the largest amount of chunky graphite and the lowest mechanical properties appear at the location 170mm distant from the center. Excessive yttrium and magnesium content at the location 170mm distant from the center is the main factor for the large amount of chunky graphite. The characteristics of the solidification mode^____pasty solidification and the considerably long solidification of the casting are the basic reasons for the distribution of chunky graphite of the heavy ductile iron casting Φ590mm×800mm.

Abstract: Jet shape of submerged nozzle (SEN), flowage, fluid level fluctuation and the superheat on bath surface in mold under the static electromagnetic field were 3-D simulated by using the CFX, commercial software. The results showed that electromagnetic brake (EMBR) can alter jet shape of SEN and fluid flow in the mold. And on the premise of controlling fluid level fluctuation of mold bath effectively, higher superheat of bath surface is obtained.

Abstract: Based on law of Beer-Lambert, a novel optical fiber gas sensing system is designed to determine the concentration of gas. The narrow-band filtering characteristic of optical fiber Bragg grating is used by this system to produce the narrow spectrum light signal which is wanted in difference absorption measuring. The system has full optical fiber structure, which is mainly composed by super luminescent emitting diode (SLED), optical fiber of 10km, optical fiber gas detector, optical fiber isolator, optical fiber coupler network, optical fiber detecting grating, photoelectric detector and data processing unit. The aspheric objective optical fiber collimator is adopted by this system to compose optical fiber gas sensing detector, which enhances the optic stability of the detector, diminishes the injection loss and makes the echo signal of the optical fiber detector greatly diminished. Experimental data and results show that this system has its feasibility and it can be used for real time monitoring of gas concentration in the domains of colliery and natural gas station, etc.

Abstract: Generalized particle dynamics method (GP) is a kind of new multi-scale analysis approach which relates various scales naturally through cohering small scale lattice to large-scale lattice. In this paper, a method named nearby condensation method is proposed to lump small scale lattice to large-scale lattice keeping topology structure and mass distribution. The method provides a theoretical support to the GP method. It is indicated that, after cohesion BCC (Body-Centered Cubic) crystal structure possessed the same topological structure and mass distribution, and FCC (Face-centered cubic) crystal structure possessed the same topological structure, but the mass distribution gradually converges to a steady state.

Abstract: A novel photochromic diarylethene bearing a six-membered aryl unit, 1-[2-methyl-5-(3-fluorophenyl)-3-thienyl]-2-(2-methoxylphenyl)perfluorocyclopentene (1o), was synthesized and its photochromic properties, fluorescence switch and optical recording were investigated in detail. This compound exhibited remarkable photochromism, changing from colorless to blue after irradiation with 297 nm UV light both in solution and in PMMA film, respectively. The new diarylethene also exhibited excellent fluorescence intensity and fluorescence switches by photoirradiation in hexane solution. Finally, photo-mode rewritable optical storage using 1o was performed. The images demonstrated that the compound as optical storage material was very sensitive responding to 633 nm recording laser, and the recorded-signals were provided with high S/N ratio.

Abstract: A new unsymmetrical photochromic diarylethene 1-(2,5-dimethylisoxazolyl)-2-[(2-n-butyl-5-formylthiophenyl)] perfluoroncyclopentene (1a), was synthesized and its optoelectronic properties, such as photochromism in solution as well as in poly-methylmethacrylate (PMMA) amorphous films, and the fluorescence spectra of diarylethene 1a was investigated. The photochromic reaction kinetics indicated that the cyclization process of 1a belongs to the zeroth order reaction and the cycloreversion process belongs to the first order reaction.Using diarylethene 1/PMMA film as recording medium and a linearly polarized 633 nm laser diode for recording and readout, polarization multiplexed image recording can be carried out in this film, which illustrated that the diarylethene can be potentially used as holographic optical recording medium.

Abstract: Crystal structures of Bi₂Mo₃O₁₂ and Bi_1.8Ln_0.2Mo₃O₁₂ (Ln = Ce, Nd, Dy, Er) were studied using Rietveld structural refinements of X-ray powder diffraction data. Substitution of 10 mol% Ln for Bi produced changes in lattice parameters, bond lengths and distances between metal ions. These changes such as decreases in average bond lengths of Mo1O4 tetrahedra and variations in the distances between adjacent metal ions on the same plane could be ascribed to different ionic radii and electronegativty of Bi and rare earth atoms, and might be related to catalytic activity of bismuth molybdate for the selective oxidation and ammoxidation of alkenes.

Abstract: The electron paramagnetic resonance (EPR) technique was employed to investigate the point defects in barium strontium titanate ceramics. All samples showed a strong EPR signal with g = 2.000, which was indexed as intrinsic Ti-vacancy defects. In (Ba_0.85Sr_0.15)TiO₃ ceramic, which showed a tetragonal symmetry and consisted of the crystallites with average size of ~ 220 nm, a novel EPR powder spectrum was observed - the g-factor of the g = 2.000 signal evolved into a g-tensor, and the two weak signals with g₃ = ~ 2.6 and g₁ = ~ 1.6 gradually shifted toward the g2 = 2.000 signal and approached to each other with increasing temperature.

Abstract: This paper analyses and studies control of nitrogen on Al- killed steel using the methods of production experiment in the flow of molten iron pretreatment - 180t converter - LF refining – continuous caster. Results show that adding aluminum final deoxidization should be divided into two steps: Firstly, putting some aluminum into molten steel after adding alloy in the process of tapping of molten steel, making the [O] reduce to 6 ~ 7ppm. Secondly, adding aluminum wire in LF-refining making [O] and [N] reach the required values. LF-refining should try to shorten operating time and original mission ought to be finished ahead. Desulfurization should be completed in the flow of molten iron pretreatment and the tapping of molten steel. Process of removal inclusions should be accomplished by adding slag during tapping of molten steel and blowing-mixing. LF-refining has scarcely any slagging task, it only needs to complete adjustment ingredient task. Alloy and carburant which contains extremely low nitrogen should be choosed, so that nitrogen in molten steel can be steadily controled below 30ppm.