A Model Describing Solidification Microstructure Evolution in an Inoculated Aluminum Alloys

A population dynamics-cellular automaton(PD-CA)model is developed to describe the microstructure formation in an inoculated Al alloys.The model involves the dynamics behaviors of the inoculated particles and the nucleation,initial spherical growth of nuclei as well as the subsequent dendritic growth.The model was validated by using the experimental results for the Al-Cu alloys inoculated by Al–Ti–C refiner first,and then used to simulate the detailed solidification process in an inoculated Al–Cu alloy.The results indicate that the TiC is not stable in Al melt.The heterogeneous nucleation process consists of two stages:a very short initial stage dominated by the cooling rate and the later stage dominated by the number of the active TiC.It stops at the very moment the recalescence occurs.The average grains size d of the aluminum alloys aw))inoculated by the Al–Ti–C refiner can be calculated by d(μm)=a·exp(t/60·In(C_(0)/w)/(v_cool·^(t)^(1/3)w(1/3)+b·Int/Q·v^(1/2))cool where Q is the cool factor,C0(%)is the initial solutes composition,w(%)is the additive amount of Al–Ti–C refiner.t(min)is the holding temperature time since the Al–Ti–C refiner is added into the melt.a and b are the constants.

Design and Analysis of Terminal Guidance Law for Kinetic Interceptors based on Pulse Engine

A new terminal guidance law is proposed based on a solid propellant pulse engine and an improved proportional navigation method to address the terminal guidance issue for kinetic interceptors.On this basis,the start-stop curve of the pulse motor during the terminal guidance process is designed,along with its start-up logic.The effectiveness of the proposed guidance strategy is verified through simulation.

Adsorption and desorption characteristics of diphenylarsenicals in two contrasting soils

Diphenylarsinic acid （DPAA） is formed during the leakage of aromatic arsenic chemical weapons in soils, is persistent in nature, and results in arsenic contamination in the field. The adsorption and desorption characteristics of DPAA were investigated in two typical Chinese soils, an Acrisol （a variable-charge soil） and a Phaeozem （a constant-charge soil）. Their thermodynamics and some of the factors influencing them （i.e., initial pH value, ionic strength and phosphate） were also evaluated using the batch method in order to understand the environmental fate of DPAA in soils. The results indicate that Acrisol had a stronger adsorption capacity for DPAA than Phaeozem. Soil DPAA adsorption was a spontaneous and endothermic process and the amount of DPAA adsorbed was affected significantly by variation in soil pH and phosphate. In contrast, soil organic matter and ionic strength had no significant effect on adsorption. This suggests that DPAA adsorption may be due to specific adsorption on soil mineral surfaces. Therefore, monitoring the fate of DPAA in soils is recommended in areas contaminated by leakage from chemical weapons.

Efficient grain refinement of Al alloys induced by in-situ nanoparticles

Grain refinement of Al and Al alloys during the solidification remains a long-term challenge.Here we report a general strategy for efficient grain refinement through instantaneously in-situ forming abundant nanoparticles with concentrated size distribution.The Al-Zn-Mg-Cu alloy and commercial purity Al are respectively refined by using this proposed strategy and the traditional refinement method(adding AlTi-B alloy into Al melt),and the experimental and numerical results indicate that the TiBnanoparticles instantaneously form in the Al melt during the in-situ refinement process.Compared to the traditional refinement treatment method,the new approach not only can promote the high number density of the nucleation sites and narrow their size distribution,but also tremendously attenuates the agglomeration and settlement of the heterogeneous nucleation sites.It exhibits much better grain refinement ability and inhibits the decline of the grain refinement efficiency.This approach may have broad application prospect not only for the grain refinement of Al and Al alloys,but also for the grain refinement of other alloy systems,e.g.steel,magnesium,copper,and so on.

A tandem asymmetric oxidation-oxa-Michael sequence for dearomatization ofβ-naphthols

A catalytic asymmetric hydroxylative dearomatization reaction has been disclosed,and the products can smoothly transform into spiroannulation adducts by simply treated with a base under mild conditions.Novel in-situ generated magnesium catalytic methods are developed by application of combinational ligands.Related concise transformaitons of the spiroannulation adducts have been carried out.