Accelerating Cementite Precipitation during the Non-Isothermal Process by Applying Tensile Stress in GCr15 Bearing Steel.

In this work, the non-isothermal process of GCr15 bearing steel after quenching and tempering (QT) under different tensile stress (0, 20, 40 MPa) was investigated by kinetic analysis and microstructural observation. The Kissinger method and differential isoconversional method were employed to assess the kinetic parameters of the microstructural evolution during the non-isothermal process with and without applied stress. It is found that the activation energy of retained austenite decomposition slightly increases from 109.4 kJ/mol to 121.5 kJ/mol with the increase of tensile stress. However, the activation energy of cementite precipitation decreases from 179.4 kJ/mol to 94.7 kJ/mol, proving that tensile stress could reduce the energy barrier of cementite precipitation. In addition, the microstructural observation based on scanning and transmission electron microscopy (SEM and TEM) shows that more cementite has formed for the specimens with the applied tensile stress, whereas there is still a large number of ε carbides existing in the specimens without stress. The results of X-ray diffraction (XRD) also verify that carbon in martensite diffuses more and participates in the formation of cementite under the applied tensile stress, which thus are in good agreement with the kinetic analysis. The mechanisms for the differences in cementite precipitation behaviors may lie in the acceleration of carbon atoms migration and the reduction of the nucleation barrier by applying tensile stress.

[Removal of mixed waste gases by the biotrickling filter].

A biotrickling filter (BTF) was designed for treating mixed waste gases, which contained hydrogen sulfide (H2S), tetrahydrofuran (THF) and dichloromethane (DCM) at the start-up and steady states. The removal efficiency of H2S and DCM could maintain about 99% and 60%, respectively, and the removal efficiency of DCM was reduced from 90% to 37% with the shortening empty bed retention time (EBRT) form 50 to 20 seconds when the inlet concentrations were 200, 100, 100 mg x m(-3) of H2S, THF, DCM, respectively. In the theoretical study, the biodegradation efficiency of contaminants was H2S > THF > DCM by analyzing the Michaelis-Menten Dynamic model.

[Removal of hydrogen sulfide by plate type-biotrickling filter].

A plate type biotrickling filters (plate type-biotrickling filter, PTBTF) in which three layers are separately sprayed by nutrient solution of pH 2.5, 4.5 and 6.5, relatively, was designed for H2S removal at the start-up and steady states. The biofilm formation of PTBTF was completed within 14 d, and the removal efficiency of 100% was achieved at the inlet H2S concentration of 188.6 mg x m(-3). Afterwards, H2S removal efficiency remained above 99% with the inlet concentration between 100 mg x m(-3) and 1 000 mg x m(-3) and empty bed residence time (EBRT) between 28 s and 4 s. When removal efficiency was 90%, the maximum elimination capacity of PTBTF increased with EBRT (3.3-6 s), e. g. 1 019.0 g x (m3 x h)(-1) for EBRT 6 s. The elimination capacity of the upper, middle and lower layer varied with the inlet H2S loading. It was found that the microorganisms onto the packing carriers in upper, middle and lower layers increased significantly at the start-up state, and reached 1.29 x 10(7), 5.47 x 10(8), and 1.07 x 10(9) cells x g(-1), respectively, in 125 d by the means of fluorescence staining. The bacilliform and filamentous microorganisms were the dominants in the upper and lower layer, respectively, observed by scanning electron microscopy. The biological community analysis by denaturing gradient gel electrophoresis was also conducted in this study. The main products of SO4(2-) and sulfur were determined for H2S degradation.