Structural transformation and dynamical heterogeneity in Germania melt under compression: molecular dynamic simulation

2021 ◽  
pp. 1-9
Author(s):  
N.T.T. Ha ◽  
M.T. Lan ◽  
N.V. Hong ◽  
P.K. Hung
Keyword(s):  
Structural Transformation ◽  
Ambient Pressure ◽  
Low Density ◽  
Transformation Mechanism ◽  
Melt Structure ◽  
Structural Domains ◽  
Dynamical Heterogeneity ◽  
Cluster Function ◽  
Domain Structures ◽  
Compression Mechanism

The structural transformation and dynamical heterogeneity in Germania (GeO2) are investigated via molecular dynamics (MD) simulation. The MD model with 5499 atoms was constructed under pressure up to 150 GPa and at a temperature of 3500 K. The structural transformation mechanism has been studied by observing domain structures and boundary oxygen atoms. The simulation result reveals that GeO2 consists of separate domains and boundaries in its melt structure. Under compression, the structure of GeO2 changes gradually and represents many types of structures. The melt structure exhibits many structural domains Dx, and polymorphism appears at pressures of 12 and 20 GPa. The change of tetrahedral structure to octahedral structure in germanium coordination occurred in parallel with the process of merging and splitting of domain structure. Moreover, the existence of high- and low-density phases in GeO2 melt is indicated. The high-density phase is D6 domain and boundary oxygen while the low-density phase is D4 and D5 domain. The compression mechanism in GeO2 melt mainly is a reduction of average Voronoi volume of oxygen and Voronoi volume of D6, boundary atoms oxygen. Furthermore, we find the dynamical heterogeneity at ambient pressure. The separate “fast” regions and “slow” regions in GeO2 are detected via link-cluster function.

Effect of ambient pressure on low-density nozzle plumes

1995 ◽  
Author(s):  
Chan-Hong Chung ◽  
Kenneth D ◽  
Robert Stubbs
Keyword(s):  
Ambient Pressure ◽  
Low Density

scholarly journals X-ray studies of the transformation from high- to low-density amorphous water

2019 ◽  
Vol 377 (2146) ◽  
pp. 20180164 ◽  
Author(s):  
Daniel Mariedahl ◽  
Fivos Perakis ◽  
Alexander Späh ◽  
Harshad Pathak ◽  
Kyung Hwan Kim ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Structural Evolution ◽  
High Energy ◽  
Real Space ◽  
High Density ◽  
Low Density ◽  
X Ray ◽  
Amorphous Ice ◽  
Density State ◽  
Amorphous States

Here we report about the structural evolution during the conversion from high-density amorphous ices at ambient pressure to the low-density state. Using high-energy X-ray diffraction, we have monitored the transformation by following in reciprocal space the structure factor S OO ( Q ) and derived in real space the pair distribution function g OO ( r ). Heating equilibrated high-density amorphous ice (eHDA) at a fast rate (4 K min –1 ), the transition to the low-density form occurs very rapidly, while domains of both high- and low-density coexist. On the other hand, the transition in the case of unannealed HDA (uHDA) and very-high-density amorphous ice is more complex and of continuous nature. The direct comparison of eHDA and uHDA indicates that the molecular structure of uHDA contains a larger amount of tetrahedral motives. The different crystallization behaviour of the derived low-density amorphous states is interpreted as emanating from increased tetrahedral coordination present in uHDA. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Synthesis and Effect of DCCA on the Ambient Pressure Dried, TEOS-Based Silica Aerogel

2014 ◽  
Vol 1044-1045 ◽  
pp. 119-123 ◽  
Author(s):  
Song He ◽  
Xu Dong Cheng ◽  
Hai Jiang Bi ◽  
Hui Yang
Keyword(s):  
Ambient Pressure ◽  
Mesoporous Structure ◽  
High Specific Surface Area ◽  
Low Density ◽  
Chemical Additive ◽  
Control Chemical ◽  
Microstructure Morphology ◽  
Ft Ir ◽  
Drying Control Chemical Additive ◽  
Hydrophilic Gel

In this paper, we report the experimental results on the synthesis of low-density tetraethoxysilane (TEOS)-based silica aerogels prepared under ambient pressure. The drying control chemical additive N, N-Dimethylformamide (DMF) was introduced to the experiments. Before dring, the water within alcogel was exchanged with ethanol and n-hexane. Trimethylchlorosilane (TMCS) was used to modify the hydrophilic gel surface to make sure the final aerogel is hydrophobic. The effects of solvent EtOH and DMF on the properties of the resulting aerogels were investigated. The microstructure, morphology and other properties of the aerogels were studied by FT-IR, TEM and BET measurement. The resulting aerogels have a well-developed mesoporous structure (mean pore size of ~15 nm) with low density (0.08g/cm3), a high specific surface area (1267m2/g) super hydrophobicity (Ө=165o) and high transmissivity (~90%).

Preparation of low-density porous silica thin films by ambient pressure drying

2004 ◽  
Author(s):  
Lanfang Yao ◽  
Jun Shen ◽  
Guangming Wu ◽  
Xingyuan Ni ◽  
Jue Wang ◽  
...  
Keyword(s):  
Thin Films ◽  
Ambient Pressure ◽  
Porous Silica ◽  
Ambient Pressure Drying ◽  
Low Density ◽  
Silica Thin Films

Super Thermal Insulating SiO2 Cryogels Prepared by Vacuum Freeze Drying

2010 ◽  
Vol 105-106 ◽  
pp. 851-854 ◽  
Author(s):  
Li Fen Su ◽  
Lei Miao ◽  
Gang Xu ◽  
Sakae Tanemura
Keyword(s):  
Freeze Drying ◽  
Ambient Pressure ◽  
Supercritical Drying ◽  
Silica Aerogels ◽  
Base Catalysis ◽  
Low Density ◽  
Solvent Exchange ◽  
Acid Base ◽  
Thermal Insulating ◽  
Silica Precursor

Traditionally, silica aerogels with low thermal conductivity are prepared by supercritical drying, however, the process is expensive and hazardous due to it run in autoclaves. In order to overcome these disadvantages, a cheaper and safer process, drying at ambient pressure has been developed for decades, but tedious repetitive gel washing and solvent exchange steps are involved. Therefore, in the present study, a novel vacuum freeze-drying was utilized to prepare the super thermal insulating SiO2 cryogels. The wet gels were synthesized via acid-base catalysis using tetraethoxysilane (TEOS) as a silica precursor and ethanol as a solvent. After vacuum freeze drying, nanoporous SiO2 cryogels with low density in the range of 0.08-0.15 g/cm3 were obtained.

Nanoporous Silica for Low k Dielectrics

1996 ◽  
Vol 443 ◽  
Author(s):  
Teresa Ramos ◽  
Kevin Roderick ◽  
Alok Maskara ◽  
Douglas M. Smith
Keyword(s):  
Thin Films ◽  
Dielectric Constant ◽  
Film Thickness ◽  
Pore Size ◽  
Ambient Pressure ◽  
Porous Solids ◽  
Nanoporous Silica ◽  
Low Density ◽  
Trade Offs ◽  
Small Pore

AbstractConsiderable progress has been made in development of thin films of nanoporous silica (also known as aerogels or low density xerogels) for ILD and IMD applications. Advantages of these materials include high thermal stability, small pore size, and similarity to conventional deposition processes, precursors and final material (silica). We have previously reported success in synthesizing low density, low dielectric constant (K<2) thin films using ambient pressure processing. However, processing of those films was complicated due to large number of process steps and difficulties in independently controlling both film thickness and film porosity.Nanoglass has now developed a new process which considerably reduces the number of process steps and allows independent control of both film thickness and porosity. The dielectric constant of the films can be tailored between 1.3 and 2.5. These films have improved mechanical properties due to controlled pore size and narrow pore size distribution and also because of higher density. The trade-offs between density, mechanical strength and dielectric constant for these types of porous solids will be elucidated. The known properties of the film and the process flow for deposition and post-deposition curing and the role of the relative rates of reaction, gelation, aging, and drying will be presented.

Distribution of sodium and dynamical heterogeneity in sodium silicate liquid

2019 ◽  
Vol 33 (05) ◽  
pp. 1950013 ◽  
Author(s):  
N. T. T. Ha ◽  
N. V. Hong ◽  
P. K. Hung
Keyword(s):  
Sodium Silicate ◽  
Mobile Network ◽  
Nonbridging Oxygen ◽  
Silicate Liquid ◽  
Dynamical Heterogeneity ◽  
Cluster Function ◽  
Sodium Atoms ◽  
Simulation Results ◽  
The One ◽  
Dynamics Method

The structural and dynamical properties in sodium silicate liquid were investigated by molecular dynamics method. To clarify the distribution of sodium atoms in model, characteristics of simplex have been investigated. The simulation results reveal that Na2O⋅4SiO2 (NS4) liquid has a lot of simplexes with four sodium atoms inside but about half of simplexes do not have sodium. The spatial distribution of sodium is nonuniform, sodium tends to be in the nonbridging oxygen-simplexes and in larger-radius simplex. Moreover, the sodium density for nonbridging oxygen region is significantly higher than the one for Si-region. Namely, link-cluster function F[Formula: see text](r, t) has been used to clarify dynamical heterogeneity in NS4 liquid. The F[Formula: see text](r, t) for sets of random, immobile and mobile network atoms is quite different, which indicates that the dynamics of network atoms is heterogeneous. The Si–O network has the structure with two separated domains (immobile and mobile domains). These types of domain are significantly different in local microstructure, mobility of atoms and chemical composition.

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