THE STUDY IN DIFFUSION MECHANISM BY VORONOI POLYHEDRON IN SODIUM TETRA-SILICATE MELT

2021 ◽  
Vol 66 (3) ◽  
pp. 52-60
Author(s):  
Lich Duong Thi ◽  
San Luyen Thi ◽  
Yen Nguyen Hai
Keyword(s):  
Chemical Composition ◽  
Molecular Dynamic Simulation ◽  
Molecular Dynamic ◽  
Dynamic Simulation ◽  
Diffusion Mechanism ◽  
Nonbridging Oxygen ◽  
Free Oxygen ◽  
Voronoi Polyhedron ◽  
Motion Type ◽  
Motion Types

Molecular dynamic simulation is carried out for Sodium tetra-silicate (NS4) melt at 1873 K and pressure of 0.1 MPa. The diffusion mechanism of Na atoms is investigated in terms of Voronoi polyhedron around network former and displacement of Na atoms between them. The simulation shows that Na atoms are not uniformly distributed through polyhedrons, but they mainly gather in nonbridging oxygen (NBO) and free oxygen (FO) polyhedrons. More than 75.22% of total Na atoms are place in NBO polyhedrons, although the number of NBO polyhedrons is only 22.27%. The two motion types give mainly contribution to Na diffusion: hopping of isolated Na atom or collective displacement. During 150 ps, the system comprises two separate regions: Na-poor regions formed by Si-O subnets and Na-rich regions formed by O2 clusters. The two regions have strongly different chemical composition, the density of Na atoms as well as motion type of Na atoms.

About the diffusion mechanism in the silica liquid

2016 ◽  
Vol 30 (10) ◽  
pp. 1650059
Author(s):  
N. T. T. Nhan ◽  
P. H. Kien ◽  
P. K. Hung ◽  
N. V. Hong ◽  
L. T. San
Keyword(s):  
Spatial Distribution ◽  
Molecular Dynamic Simulation ◽  
Molecular Dynamic ◽  
Dynamic Simulation ◽  
Diffusion Mechanism ◽  
Diffusion Time ◽  
Large Cluster ◽  
Collective Movement ◽  
Cluster Reaction ◽  
And Diffusion

In this paper, we have numerically studied the diffusion mechanism in silica liquid based on the idea that the collective movement of particles is controlled by reactions [Formula: see text] and [Formula: see text]. Four models at temperatures from 2600 K to 3500 K have been constructed by molecular dynamic simulation. The simulation shows that the liquid has a small amount of defect-cells which are of importance for the diffusion. In particular, the majority of reactions happen via defect-cells SiO5 and OSi3. Moreover, the defect-cells do not uniformly distribute in the liquid, but they have a tendency to locate nearby forming large cluster. Further, it is revealed that the spatial distribution of reactions is heterogeneous. We found two distinct clusters. First cluster (none-reaction cluster) consists of particles on which no reaction happens. The second cluster (reaction cluster) includes particles where the reactions happen. The size of clusters found is dependent with temperature and diffusion time. Moreover, the mobility of particles in none-reaction cluster is significantly smaller than in reaction cluster. This indicates the dynamics heterogeneity in the liquid. We suggest that the dynamics slowdown is originated from the percolation of none-reaction cluster.

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