Fe–Mn/MCM-41: Preparation,Characterization,and Catalytic Activity for Methyl Orange in the Process of Heterogeneous Fenton Reaction

Active Fe-and Mn-loaded MCM-41(Fe–Mn/MCM-41),which was synthesized via a hydrothermal reaction followed by impregnation,is used in the heterogeneous Fenton reaction to degrade methyl orange(MO) in aqueous solution. The synthesized samples were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,N_2 adsorption–desorption isotherm analysis,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy. Compared with Fe/MCM-41 and Mn/MCM-41,Fe–Mn/MCM-41 showed higher activity for MO degradation and mineralization. Effects of various operating parameters,such as pH,Mn content,and H_2O_2 dosage,on the degradation process were subsequently investigated. Results of experiments on the effect of radical scavengers revealed that the degradation of MO could be attributed to oxidation by HO_·. The synergy of Fe and Mn species in the Fenton oxidation process was also explained.

Microsegregation and Rayleigh number variation during the solidification of superalloy Inconel 718

The microstructure and composition of the residual liquid at different temperatures were investigated by scanning electron microscopy （SEM） and energy dispersive X-ray spectrometer （EDX） associated with the Thermo-calc software calculation of the equilibrium phase diagrams of Inconel 718 and segregated liquid. The liquid density difference and Rayleigh number variation during solidification were estimated as well. It is found that the heavy segregation of Nb in liquid prompts the precipitation of δ and Laves phase directly from liquid and the resultant quenched liquid microstructure consists of pro-eutectic γ＋eutectic,or complete eutectic according to the content of Nb from low to high. The liquid density increases with decreasing temperature during the solidification of Inconel 718 and the liquid density difference is positive. The largest relative Rayleigh number occurs at 1320°C when the liquid fraction is about 40vol%.

Surface Metallurgy of Nickle Base Superalloy

The Double Glow Plasma Surface Alloying Technique, the Xu-Tee Process, is a new method to produce high quality alloying layer on the surface of less expensive materials. By using thes technique, the surface alloying layer similar to superalloy Inconel 625 has been obtained on the surface of three kinds of melallic materials (low carbon steel, industrial pure iron, stainless steel Cr18Ni9). The results of the composition and microstructure analyzed by Scanning Electron Microscopy (SEM) and X-Ray Uffrachon (XRD) show that the alloying layer consistS of y matrix and several precipitates (Laves intermetallic phase and carbide etc.). The electrochemical corrosion results show that the surface alloying layer formed on the surface of stainless steel and industrial pure iron have better corrosion resistance than that of nickel base alloy inconel 625 and stainless steel Cr18Ni9 in 3.5%NaCl solution. The exper iments indicate that it is an effective way to obtain the gradient surface alloying layer on the surfaces of steels by using Double Glow Plasma Surface Alloying Technique.

Strengthening effect of Cu-rich phase precipitation in 18Cr9Ni3CuNbN austenitic heat-resisting steel

The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical （USC） power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP （three dimensional atom probe） have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging （less than 1 h）. Cu atoms gradually concentrate to Cu-rich particles and the other elements （such as Fe, Cr, Ni etc） diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ？ C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.

Phenomenon and Mechanism of High Temperature Low Plasticity in High-Cr Nickel-based Superalloy

Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.