Grain boundary segregation of P and its interaction with Cr and Mo in Ni-base alloys

The behaviour of phosphorus (P) segregation to grain boundary during cooling and aging and its interaction with chromium (Cr) and molybdenum (Mo) in Ni-base alloys have been investigated using transmission electron microscopy. P segregation takes place during cooling and aging. The segregation width was several nanometres, much wider than the grain boundary thickness. This indicated a non-equilibrium mechanism. The effect of grain boundary misorientation angle and grain size on the segregation level has been investigated. The grain boundary P concentration increased with increasing misorientation angle until about 45°. A further increase in the grain boundary misorientaion angle resulted in a decline of the segregation level. Compared with random high angle grain boundaries, special grain boundaries displayed much lower segregation. This can be related to the free volume dependence on the misorientation angle. When the effective time during cooling is shorter than a certain critical time, increasing grain size reduced the grain boundary segregation level because of the higher mass transfer coefficient close to the grain boundary in samples with smaller grain size. Segregation level during cooling at different rates and after aging for different times was obtained. A critical cooling rate and aging time existed where the grain boundary P concentration reached a maximum, indicating a non-equilibrium segregation pattern. Calculations based on Faulkner’s [1, 2] and Xu’s [3] and Wu’s [4] theory were conducted and compared with the experimental results. As regard the effect of grain size, the results based on Wu’s theory were consistent with our experimental results. The elemental interaction between P and Cr or Mo was investigated. On samples without P addition, no segregation of Cr and Mo was observed after cooling and aging due to the low binding energy between vacancies and Cr or Mo. With P addition, P segregated to the grain boundary while Cr and Mo were depleted at the grain boundary. With increasing P concentration, the grain boundary Cr and Mo concentrations decreased in a linear manner due to the repulsive relative interaction coefficient between P and Cr or Mo in Ni-base alloys

Aerosol vertical distribution and optical properties over China from long-term satellite and ground-based remote sensing

The seasonal and spatial variations of vertical distribution and optical properties of aerosols over China are studied using long-term satellite observations from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) and ground-based lidar observations and Aerosol Robotic Network (AERONET) data. The CALIOP products are validated using the ground-based lidar measurements at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The Taklamakan Desert and Tibetan Plateau regions exhibit the highest depolarization and color ratios because of the natural dust origin, whereas the North China Plain, Sichuan Basin and Yangtze River Delta show the lowest depolarization and color ratios because of aerosols from secondary formation of the anthropogenic origin. Certain regions, such as the North China Plain in spring and the Loess Plateau in winter, show intermediate depolarization and color ratios because of mixed dust and anthropogenic aerosols. In the Pearl River Delta region, the depolarization and color ratios are similar to but higher than those of the other polluted regions because of combined anthropogenic and marine aerosols. Long-range transport of dust in the middle and upper troposphere in spring is well captured by the CALIOP observations. The seasonal variations in the aerosol vertical distributions reveal efficient transport of aerosols from the atmospheric boundary layer to the free troposphere because of summertime convective mixing. The aerosol extinction lapse rates in autumn and winter are more positive than those in spring and summer, indicating trapped aerosols within the boundary layer because of stabler meteorological conditions. More than 80 % of the column aerosols are distributed within 1.5 km above the ground in winter, when the aerosol extinction lapse rate exhibits a maximum seasonal average in all study regions except for the Tibetan Plateau. The aerosol extinction lapse rates in the polluted regions are higher than those of the less polluted regions, indicating a stabilized atmosphere due to absorptive aerosols in the polluted regions. Our results reveal that the satellite and ground-based remote-sensing measurements provide the key information on the long-term seasonal and spatial variations in the aerosol vertical distribution and optical properties, regional aerosol types, long-range transport and atmospheric stability, which can be utilized to more precisely assess the direct and indirect aerosol effects on weather and climate

Dealloying of an amorphous TiCuRu alloy results in a nanostructured electrocatalyst for hydrogen evolution reaction

Abstract Development of an electrocatalyst that is cheap and has good properties to replace conventional noble metals is important for H2 applications. In this study, dealloying of an amorphous Ti37Cu60Ru3 alloy was performed to prepare a free‐standing nanostructured hydrogen evolution reaction (HER) catalyst. The effect of dealloying and addition of Ru to TiCu alloys on the microstructure and HER properties under alkaline conditions was investigated. 3 at.% Ru addition in Ti40Cu60 decreases the overpotential to reach a current density of 10 mA cm−2 and Tafel slope of the dealloyed samples to 35 and 34 mV dec−1. The improvement of electrocatalytic properties was attributed to the formation of a nanostructure and the modification of the electronic structure of the catalyst. First‐principles calculations based on density function theory indicate that Ru decreases the Gibbs free energy of water dissociation. This work presents a method to prepare an efficient electrocatalyst via dealloying of amorphous alloys

DataSheet1_Regional organic matter and mineral dust are the main components of atmospheric aerosols over the Nam Co station on the central Tibetan Plateau in summer.docx

The transport of air pollutants from areas surrounding the Tibetan Plateau (TP) has recently been studied. However, the major sources of atmospheric total suspended particulate matter (TSP) on the central TP remain unclear due to a lack of in-situ observations on aerosol physico-chemical properties. Therefore, to quantitatively investigate the physico-chemical properties and reveal the major sources of atmospheric aerosols, a comprehensive field campaign was conducted at the site of Nam Co from August 6 to September 11, 2020. Aerosol loading was low during the campaign with average TSP mass concentration, scattering coefficient at 550 nm, and absorption coefficient at 670 nm being 10.11 ± 5.36 μg m−3, 1.71 ± 1.36 Mm−1, and 0.26 ± 0.20 Mm−1, respectively. Organic matter (63.9%) and mineral dust (27.8%) accounted for most of the TSP mass concentrations. The average scattering Ångström exponent of 0.59 ± 0.14 reflected the influence of mineral dust, and the elemental fractions and the results of enrichment factor illustrated that crustal materials were the main contributors of mineral dust. The organic to elemental carbon ratio of 15.33 is probably caused by the aging that occurs during the transport of aerosols. The strong correlation between organic carbon and Ca2+ and the results of the electron microscopy analysis of single particles indicated that organic carbon and mineral dust had the same sources; however, the weak relation between mineral dust and wind speed indicated that local wind erosion was not the main contributor to the mineral dust. The potential source contribution function further illustrated that the summertime TSP in the central TP was mainly characterized by background biomass and mineral dust aerosols originating regionally from the ground within the TP.</p