Effects of Oxygen Impurities on Glass-Formation Ability in Zr2Cu Alloy.

Using ab initio molecular dynamics simulations, we show that oxygen (O) impurities have a noticeable influence on the glass-formation ability (GFA) in Zr2Cu alloy. Cu-centered icosahedral clusters and Zr-centered Kasper polyhedra are the dominate short-range orders in undercooled Zr2Cu liquid which are most likely to be responsible for the glass formation in Zr2Cu systems. When O is introduced, a Zr octahedron is formed around the O impurity. Most of the Zr atoms in the octahedron also serve as the bridging atoms for cross-linked Kasper polyhedral network, resulting in an O-centered medium range order (MRO) structure. Meanwhile, Cu atoms are moved away from the first shell of O-centered octahedral clusters. With 1 at. % O impurities, the fractions of Zr-centered clusters are less affected, while the increase of ideal icosahedral order and decrease of distorted icosahedral order lead to a more stable atomic structure. This result suggests that a low concentration of O impurities would improve the GFA in Zr2Cu alloy. However, when ∼5 at. % O impurities are included, the ideal icosahedral clusters and Zr-centered Kasper polyhedra are seriously suppressed by the formation of O-centered MRO, which can lead to deterioration of GFA. Our analyses provide useful insight into glass formation behavior in O-doped metallic alloy systems.

Local structure order in Pd78Cu6Si16 liquid.

The short-range order (SRO) in Pd78Cu6Si16 liquid was studied by high energy x-ray diffraction and ab initio molecular dynamics (MD) simulations. The calculated pair correlation functions at different temperatures agree well with the experimental results. The partial pair correlation functions from ab intio MD simulations indicate that Si atoms prefer to be uniformly distributed while Cu atoms tend to aggregate. By performing structure analysis using Honeycutt-Andersen index, Voronoi tessellation, and atomic cluster alignment method, we show that the icosahedron and face-centered cubic SRO increase upon cooling. The dominant SRO is the Pd-centered Pd9Si2 motif, namely the structure of which motif is similar to the structure of Pd-centered clusters in the Pd9Si2 crystal. The study further confirms the existence of trigonal prism capped with three half-octahedra that is reported as a structural unit in Pd-based amorphous alloys. The majority of Cu-centered clusters are icosahedra, suggesting that the presence of Cu is benefit to promote the glass forming ability.

Effects of strontium impurity on the structure and dynamics of Al88Si12 liquid.

The effects of strontium modification on the structure and dynamics of Al88Si12 liquid are studied by means of ab initio molecular dynamics simulations. By replacing 0.5% and 4.0% of Al with Sr, we show that the addition of Sr lowers the self-diffusion of Al and Si of the liquid and reduces the nearest-neighbor correlation between Si atoms. The simulation provides an explanation for the change in morphology of the eutectic phases observed in rapidly solidified Al-Si alloys modified with Sr.

Development of a new animal model of liver cirrhosis in swine.

This study aimed to develop a new experimental model of liver cirrhosis in swine by using carbon tetrachloride (CCl(4)) and ethanol. Liver cirrhosis was induced by intraperitoneal injection of CCl(4) twice a week for 9 weeks. Maize flour was the only food provided and the animals drunk a 5% alcohol-water mixture. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), albumin, bilirubin and portal venous pressure (PVP) levels were determined throughout CCl(4) treatment. The animals were sacrificed under general anesthesia at week 9 and liver samples were collected for histological analysis. 83.3% of the swine had liver cirrhosis and 33.3% had died. There was no change of body weight during the course of the experiment (p > 0.05). The AST and ALT levels increased significantly in the early stage of the study but had a trend to decrease during the late phase. The level of bilirubin increased greatly and albumin decreased during the whole experiment (p < 0.05). PVP levels decreased in the early stage in CCl(4)-treated swine, but increased significantly at the late phase. In conclusion, this study was successful in producing liver cirrhosis and offers an ideal experimental model for observing surgical therapeutic efficacy.