Oxidation behavior of ferritic/martensitic steels in flowing supercritical water

The oxidation behavior of two Ferritic/Martensitic(F/M)steels including novel SIMP steel and commercial P91 steel were investigated by exposure to flowing deaerated supercritical water(SCW)at 700℃for up to 1000 h.The kinetic weight gain curves follow parabolic and near-cubic rate equations for SIMP and P91 steels,respectively.X-Ray Diffraction analysis showed the presence of magnetite and a spinel phase in flowing SCW for both steels.The morphology and structure of the oxide scales formed on these two steels were analyzed.The relationship between the microstructure and oxidation behavior and the reason that SIMP steel showed better oxidation resistance than P91 steel were discussed.

Fast CO_(2) Retrieval Using a Semi-Physical Statistical Model for the High-Resolution Spectrometer on the Fengyun-3D Satellite

China’s Fengyun-3D meteorological satellite launched in December 2016 carries the high-resolution greenhouse-gases absorption spectrometer(GAS)aimed at providing global observations of carbon dioxide(CO_(2)).To date,GAS is one of the few instruments measuring CO_(2) from the near-infrared spectrum.On orbit,the oxygen(O_(2))A band suffers a disturbance,and the signal-to-noise ratio(SNR)is significantly lower than the nominal specification.This leads to difficulties in the retrieval of surface pressure and hence a degradation of the retrieval of the column-averaged CO_(2) dry air mole fraction(XCO_(2))if a full physics retrieval algorithm is used.Thus,a fast CO_(2) inverse method,named semi-physical statistical algorithm,was developed to overcome this deficiency.The instrument characteristics,the semi-physical statistical algorithm,and the results of comparison with ground-based measurements over land were introduced in this paper.XCO_(2) can be obtained from three bands,namely,the O_(2) A,weak CO_(2),and strong CO_(2) bands,with compensation from the Medium Resolution Spectral Imager-2(MERSI-2)products,ECMWF Reanaly-sis v5(ERA-5)data,and Total Carbon Column Observing Network(TCCON)data.The eigenvectors of covariance matrices and the least square fits were used to derive retrieval coefficients and yield cloud-free solutions.In addition to the GAS radiance,some key factors necessary for the accurate estimations of XCO_(2) were also taken as input information(e.g.,air mass,surface pressure,and a priori XCO_(2)).The global GAS XCO_(2) restricted over land was compared against the simultaneously collocated observations from TCCON.The retrieval algorithm can mitigate the issue caused by the low SNR of the O_(2) A band to a certain extent.Overall,through site-by-site comparisons,GAS XCO_(2) agreed well with the average precision(1σ)of 1.52 ppm and bias of−0.007 ppm.The seasonal variation trends of GAS XCO_(2) can be clearly seen at TCCON sites on the 1-yr timescale.

Effects of Thermal Aging on the Oxidation Behavior of 316L Austenitic Steel in 600℃Supercritical Fired Boiler:Mechanism Based on Interface Features

The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of high angle grain boundaries(HAGB)increased in the steel after thermal aging process,with the observation of micro-textures.The weight gain rate of the steel after aging process increased,presenting the decreased Cr_(2)O_(3)contain in the oxide layer,which resulted in the increasing diffusion rate of Fe and O ions in oxide layer.The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.