Oxidation behavior of in-situ Al_2O_3/TiAl composites at 900°C in static air

In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2＋Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.

Prediction model of end-point phosphorus content for BOF based on monotone-constrained BP neural network

Dephosphorization is essential content in the steelmaking process,and the process after the converter has no dephosphorization function.Therefore,phosphorus must be removed to the required level in the converter process.In order to better control the end-point phosphorus content of basic oxygen furnace(BOF),a prediction model of end-point phosphorus content for BOF based on monotone-constrained backpropagation(BP)neural network was established.Through the theoretical analysis of the dephosphorization process,ten factors that affect the end-point phosphorus content were determined as the input variables of the model.The correlations between influencing factors and end-point phosphorus content were determined as the constraint condition of the model.200 sets of data were used to verify the accuracy of the model,and the hit ratios in the range of±0.005%and±0.003%are 94%and 74%,respectively.The fit coefficient of determination of the predicted value and the actual value is 0.8456,and the root-mean-square error is 0.0030;the predictive accuracy is better than that of ordinary BP neural network,and this model has good interpretability.It can provide useful reference for real production and also provide a new approach for metallurgical predictive modeling.

A new method for concentration analysis of bacterial endotoxins in perfluorocarbon

This communication demonstrates the feasibility of the gel-clot method for the analysis of bacterial endotoxins in water extracts of perfluorocarbon which is a water insoluble liquid medical device. Perfluorocarbon （10 mL） was shaken with 10 mL water for 15 min at 2000 r/min and the endotoxin present was extracted to the aqueous phase without interference inhibition/enhancement of the product and the recovery of endotoxin added to perfluorocarbon was determined, A validation study confirmed that endotoxins presented in perfluorocarbon pass over into the aqueous phase at concentrations of 20, 10 and 5EU/mL with recoveries from 86.8% to 96.8%. Therefore, the gel-clot test is suitable for detecting bacterial endotoxins in perfluorocarbon which is a water insoluble medical device.

Shortened duration and reduced area of frozen soil in the Northern Hemisphere

The changes in near-surface soil freeze-thaw cycles(FTCs)are crucial to understanding the related hydrological and biological processes in terrestrial ecosystems under a changing climate.However,long-term dynamics of soil FTCs at the hemisphere scale and the underlying mechanisms are not well understood.In this study,the spatiotemporal patterns and main driving factors of soil FTCs across the Northern Hemisphere(NH)during 1979–2017 were analyzed using multisource data fusion and attribution approaches.Our results showed that the duration and the annual mean area of frozen soil in the NH decreased significantly at rates of 0.13±0.04 days/year and 4.93104 km^(2)/year,respectively,over the past 40 years.These were mainly because the date of frozen soil onset was significantly delayed by 0.1±0.02 days/year,while the end of freezing and onset of thawing were substantially advanced by 0.21±0.02 and 0.15±0.03 days/year,respectively.Moreover,the interannual FTC changes were more drastic in Eurasia than in North America,especially at mid-latitudes(30
–45
N)and in Arctic regions(>75
N).More importantly,our results highlighted that near-surface air temperature(Ta)and snowpack are the main driving factors of the spatiotemporal variations in soil FTCs.Furthermore,our results suggested that the long-term dynamics of soil FTCs at the hemisphere scale should be considered in terrestrial biosphere models to reduce uncertainties in future simulations.