Effect of carrier gases on the entrainment defects within AZ91 alloy castings

An entrainment defect(also known as a double oxide film defect or bifilm) acts a void containing an entrapped gas when submerged into a light-alloy melt, thus reducing the quality and reproducibility of the final castings. Previous publications, carried out with Al-alloy castings, reported that this trapped gas could be subsequently consumed by the reaction with the surrounding melt, thus reducing the void volume and negative effect of entrainment defects. Compared with Al-alloys, the entrapped gas within Mg-alloy might be more efficiently consumed due to the relatively high reactivity of magnesium. However, research into the entrainment defects within Mg alloys has been significantly limited. In the present work, AZ91 alloy castings were produced under different carrier gas atmospheres(i.e., SF6/CO2, SF6/air).The evolution processes of the entrainment defects contained in AZ91 alloy were suggested according to the microstructure inspections and thermodynamic calculations. The defects formed in the different atmospheres have a similar sandwich-like structure, but their oxide films contained different combinations of compounds. The use of carrier gases, which were associated with different entrained-gas consumption rates, affected the reproducibility of AZ91 castings.

Mo_(3)Nb_(14)O_(44): A New Li^(+) Container for High-Performance Electrochemical Energy Storage

Intercalating Nb-based oxides are promising anode compounds for lithiumion batteries since they have both good safety and large capacities.However,the research in this field is still limited.Here,Mo_(3)Nb_(14)O_(44)with a large theoretical capacity of 398 mAh g^(–1)(Mo^(64)←→Mo^(4+)and Nb^(5+)←→Nb^(3+))is exploited as a new Nb-based oxide anode compound,and Mo_(3)Nb_(14)O_(44)micron-sized particles(Mo_(3)Nb_(14)O_(44)-M)and Mo3Nb14O44 nanowires(Mo_(3)Nb_(14)O_(44)-N)are demonstrated.Mo3Nb14O44 owns a tetragonal shear ReO_(3)crystal structure(high-symmetric 14 space group)constructed by 4×4×∞(Mo,Nb)O_(6)octahedron blocks linked by Mo O4 tetrahedra,forming an A–B–A layered structure with a large interlayer spacing.This interesting structure allows fast Li+storage within the interlayers and significant intercalation-pseudocapacitive behavior,leading to the high rate performance of Mo_(3)Nb_(14)O_(44)-M/Mo_(3)Nb_(14)O_(44)-N with a large 10 C versus 0.1 C capacity retention percentage of 38.1/54.2%.Mo_(3)Nb_(14)O_(44)-M/Mo_(3)Nb_(14)O_(44)-N further exhibits a safe operating potential of 1.72/1.68 V,large reversible capacity of 323/321 m Ah g^(–1)at 0.1 C,high initial coulombic efficiency of 92.2/90.0%,and good cycling stability with 71.8/75.8%capacity retention after 1000 cycles at10 C.Additionally,a Li Mn_(2)O_(4)/Mo_(3)Nb_(14)O_(44)-N full cell also performs well.Therefore,Mo_(3)Nb_(14)O_(44)holds great promise as a fast-charging,safe,largecapacity,high-efficient,and long-life Li^(+)anode container.

Diminishing ether-oxygen content of electrolytes enables temperature-immune lithium metal batteries

The reversibility of lithium(Li) metal anodes is highly susceptible to temperature,owing to the aggravated side reactions at high temperatures and serious Li dendrite growth at low temperatures.Thus it is extremely challenging to simultaneously realize the high Li reversibility in both low and high temperature scenarios.Herein,an oxygen-free solvent(n-hexane,HEX) assisted with the hexyl methyl ether and 1 mol L^(-1)lithium bis(fluorosulfonyl)imide is proposed to constitute an electrolyte for temperatureimmune lithium metal batteries.It demonstrates that the HEX not only greatly suppresses the solvent reduction even at high temperatures but also weaken the Li~+-solvent interaction for the facile Li-ion desolvation,leading to high Li Coulombic efficiencies(99.59% at 25℃,99.30%at 60℃ and 98.75% at -30℃) and the dendrite-free Li plating from -30℃ to 60℃.Benefitting from the low density and temperature-immune properties of our electrolyte,the sulfurized polyacrylonitrile(3.8mAh cm^(-2))||Li(60 μm) pouch-cells deliver 278 Wh kg^(-1)energy density and maintain the stable performance over 50 cycles,and retain 248 and 320 Wh kg^(-1) energy density at -30℃ and 60℃,respectively.This work provides a new perspective on the electrolyte design for wide-temperature Li metal batteries.

Influence of Deformation on the Microstructure and Low-temperature Refining Behavior of Al-3.5P Master Alloy

In this paper,the influence of deformation on the microstructure and low-temperature refining behavior of Al-3.5P master alloy was investigated.The results show that the average size of AIP particles can be reduced obviously from 15.3 μm to about 2.1 μm by deformation.However,it exhibits entirely opposite influence on refining performance when A1-3.5P master alloy was deformed at room temperature and high temperature,respectively.Only when Al-3.5P master alloy was subjected to thermal deformation,can an improvement of low-temperature refining performance be obtained.In this condition,primary Si in A390 alloy can be refined from 137 to 21 μm,making it a potential candidate for die casting production.A mechanism associated with the transformation of particle-matrix interface during deformation has been proposed and further experiment has been designed to validate it.

Morphologically templated nucleation of primary Si on AlP in hypereutectic Al-Si alloys

AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction.It is found that AlP collected from an Al-0.03 P melt could be divided into two categories:spinel twin crystals and non-twin crystals.During the nucleation process,these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase,resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals,respectively.As such,the percentage of primary Si twin crystals in the experimental Al-18 Si alloy was also increased obviously after the morphologically templated nucleation via Al P.The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si,forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism.The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.