Simulation of structural characteristics of Mullite melt at high pressure

2018 ◽  
Vol 32 (24) ◽  
pp. 1850271
Author(s):  
Mai Thi Lan ◽  
Toshiaki Iitaka ◽  
Nguyen Van Hong
Keyword(s):  
Short Range ◽  
Md Simulation ◽  
Structural Characteristics ◽  
Periodic Boundary Conditions ◽  
Degree Of Polymerization ◽  
Nonbridging Oxygen ◽  
Visualization Technique ◽  
Silica Network ◽  
Intermediate Range Order ◽  
Local Environments

Molecular dynamics (MD) simulation is applied to investigate the structural characteristics of Al2O3–SiO2 system with the Al2O3 content at 60 mol.% (Mullite — 3Al2O[Formula: see text]2SiO2). MD models containing 5250 atoms in cubic box with periodic boundary conditions are constructed at 3500 K in 0–100 GPa pressure range. The Born–Mayer–Huggins potential is applied in this study. Based on the cluster analyzes and MD data visualization technique, the structural characteristics of Mullite melt, such as the short-range and intermediate-range order, the local environments of oxygen and network structure will be clarified. Under compression, the Al–O bonds are broken, leading to incorporation of Al atoms into Si–O subnet through both nonbridging oxygen (NBO) and bridging oxygen (BO), forming –Al–O–Si-network (Al–O–Si, Si–O–Al2, Si2–O–Al, Si–O–Al3, Si2–O–Al2 and Si3–O–Al). The degree of polymerization (DOP) of the silica network and alumina network increase with pressure and the DOP of SiOx-network is lower than that of AlO[Formula: see text]-network under compression. The statistics of corner, edge and face-sharing bonds between two adjacent TO[Formula: see text] units (T is Si, Al; x = 3–7) as well as characteristics of all type OT[Formula: see text] linkages (y = 2–6) are investigated in detail. Structural and compositional heterogeneities are clarified via analysis of structure and size distribution of TO[Formula: see text]-clusters.

GLASS STABILITY EFFECT OF IRON OXIDE ADDED TO ALKALINE EARTH BORATE GLASSES

2007 ◽  
Vol 21 (05) ◽  
pp. 731-736
Author(s):  
V. SIMON ◽  
P. RIEDL ◽  
E. TATARU
Keyword(s):  
Iron Oxide ◽  
Short Range ◽  
Alkaline Earth ◽  
Structural Changes ◽  
Opposite Effect ◽  
Glass Stability ◽  
Intermediate Range Order ◽  
Alkaline Earths ◽  
Stability Effect

Glass stability and the structural role of iron oxide in x Fe 2 O 3(100-x)[ B 2 O 3– MO ] systems ( M=Ca , Sr or Ba , 0≤x≤30 mol%) were estimated from differential thermal analysis. The results suggest structural changes characteristic for the transition from short range to intermediate range order as the cationic field strength of the alkaline earths increases. In contrast, the iron addition has an opposite effect and determines a higher glass stability of these systems.

scholarly journals Antioxidant and Fluorescence Properties of Hydrogenolyzised Polymeric Proanthocyanidins Prepared Using SO42−/ZrO2 Solid Superacids Catalyst

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2445 ◽  
Author(s):  
Liwen Ni ◽  
Fanbin Zhao ◽  
Bolun Li ◽  
Tong Wei ◽  
Hang Guan ◽  
...  
Keyword(s):  
Structural Characteristics ◽  
Antioxidant Properties ◽  
Solvent Polarity ◽  
Degree Of Polymerization ◽  
Fluorescent Properties ◽  
Solid Superacids ◽  
Fluorescent Marker ◽  
Oligomeric Proanthocyanidins ◽  
Reducing Ability ◽  
Ic50 Values

Larix bark oligomeric proanthocyanidins (LOPC) were prepared from larix bark polymeric proanthocyanidins (LPPC) by catalytic hydrogenolysis using SO42−/ZrO2 solid superacid as the catalyst. The catalyst to polymeric proanthocyanidins ratio was 0.2:1 (m/m). The LOPC, obtained after hydrogenolysis at 100 °C for 4 h under 3 MPa hydrogen pressure, retained the structural characteristics of proanthocyanidins. The average degree of polymerization was reduced from 9.50% to 4.76% and the depolymerization yield was 53.85%. LOPC has good antioxidant properties and, at the same concentration, the reducing ability of LOPC was much higher than that of LPPC. The IC50 values of LOPC for scavenging DPPH• and ABTS•+ radicals were 0.046 mg/mL and 0.051 mg/mL, respectively. LOPC is biocompatible and has fluorescent properties that are affected by external factors, such as solvent polarity, pH and the presence of different metal ions. These features indicate that LOPC could be developed as a new biological fluorescent marker. The depolymerization of low-value polymeric proanthocyanidins to provide high-value oligomeric proanthocyanidins and the development of new applications for proanthocyanidins represent significant advances.

scholarly journals Short-Range Structure of Vitreous P2O5 by MD Simulation

2001 ◽  
Vol 42 (11) ◽  
pp. 2242-2246 ◽  
Author(s):  
Yoshihiro Suzuki ◽  
Keiichi Takase ◽  
Isao Akiyama ◽  
Kentaro Suzuya ◽  
Norimasa Umesaki ◽  
...  
Keyword(s):  
Short Range ◽  
Md Simulation ◽  
Short Range Structure

scholarly journals Genoprotective Effect of Some Flavonoids against Genotoxic Damage Induced by X-rays In Vivo: Relationship between Structure and Activity

Antioxidants ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Miguel Alcaraz ◽  
Amparo Olivares ◽  
Daniel Gyingiri Achel ◽  
José Antonio García-Gamuz ◽  
Julián Castillo ◽  
...  
Keyword(s):  
Chemical Structure ◽  
Structural Characteristics ◽  
Micronucleus Assay ◽  
Degree Of Polymerization ◽  
Structural Factors ◽  
X Rays ◽  
Before And After ◽  
Flavonoid Monomer ◽  
Structure And Activity

Flavonoids constitute a group of polyphenolic compounds characterized by a common gamma-benzo- pyrone structure considered in numerous biological systems to possess antioxidant capacity. Among the different applications of flavonoids, its genoprotective capacity against damage induced by ionizing radiation stands out, which has been related to antioxidant activity and its chemical structure. In this study, we determined the frequency of appearance of micronucleus in vivo by means of the micronucleus assay. This was conducted in mice treated with different flavonoids before and after exposure to 470 mGy X-rays; thereafter, their bone marrow polychromatophilic erythrocytes were evaluated to establish the structural factors enhancing the observed genoprotective effect. Our results in vivo show that the presence of a monomeric flavan-3-ol type structure, with absence of carbonyl group in position C4 of ring C, absence of conjugation between the carbons bearing the C2 = C3 double bond and the said ring, presence of a catechol group in ring B and characteristic hydroxylation in positions 5 and 7 of ring A are the structural characteristics that determine the highest degree of genoprotection. Additionally, a certain degree of polymerization of this flavonoid monomer, but maintaining significant levels of monomers and dimers, contributes to increasing the degree of genoprotection in the animals studied at both times of their administration (before and after exposure to X-rays).

Structural properties of liquid aluminosilicate with varying Al2O3/SiO2 ratios: Insight from analysis and visualization of molecular dynamics data

2017 ◽  
Vol 31 (05) ◽  
pp. 1750036 ◽  
Author(s):  
N. V. Yen ◽  
M. T. Lan ◽  
L. T. Vinh ◽  
N. V. Hong
Keyword(s):  
Molecular Dynamics ◽  
Random Network ◽  
Md Simulations ◽  
Degree Of Polymerization ◽  
Distribution Functions ◽  
Molar Ratio ◽  
Nonbridging Oxygen ◽  
Structural Units ◽  
Self Diffusion ◽  
Continuous Random Network

Molecular dynamics (MD) simulations and visualizations were explored to investigate the changes in structure of liquid aluminosilicates. The models were constructed for four compositions with varying Al2O3/SiO2 ratio. The local structure and network topology was analyzed through the pair of radial distribution functions, bond angle, bond length and coordination number distributions. The results showed that the structure of aluminosilicates mainly consists of the basic structural units TO[Formula: see text] (T is Al or Si; y = 3, 4, 5). Two adjacent units TO[Formula: see text] are linked to each other through common oxygen atoms and form continuous random network of basic structural units TO[Formula: see text]. The bond statistics (corner-, edge- and face- sharing) between two adjacent TO[Formula: see text] units are investigated in detail. The self-diffusion coefficients for three atomic types are affected by the degree of polymerization (DOP) of network characterized by the proportions of nonbridging oxygen (NBO) and Q[Formula: see text] species in the system. It was found that Q4 and Q3 tetrahedral species (tetrahedron with four and three bridging oxygens, respectively) decreases, while Q0 (with four nonbridging oxygen) increase with increasing Al2O3/SiO2 molar ratio, suggesting that a less polymerized network was formed. The structural and dynamical heterogeneities, micro-phase separation and liquid–liquid phase transition are also discussed in this work.

scholarly journals Structural Aspects of the Superionic Transition in AX2 Compounds With the Fluorite Structure

2021 ◽  
Vol 9 ◽  
Author(s):  
Paul C. M. Fossati ◽  
Alain Chartier ◽  
Alexandre Boulle
Keyword(s):  
Structural Changes ◽  
Structural Characteristics ◽  
Fluorite Structure ◽  
Atomic Scale ◽  
Small Scale ◽  
Empirical Potentials ◽  
Structure Changes ◽  
Local Environments ◽  
Binary Compounds ◽  
Liquid States

Some AX2 binary compounds with the fluorite structure (space group Fm3̄m) are well-known examples of materials exhibiting transitions to ionic superconducting phases at high temperatures below their melting points. Such superionic states have been described as either highly defective crystals or part-crystal, part-liquid states where the A ions retain their crystalline order whilst the X ions undergo partial melting. However, no detailed description of the structure of these phases exists. We present here the results of our investigation of the structural changes that occur during these transitions and the structural characteristics of the resulting superionic materials. This work is based on atomic-scale molecular dynamics modelling methods as well as computational diffraction techniques. We employed a set of empirical potentials representing several compounds with the fluorite structure to investigate any potential-dependent effect. We show the importance of small-scale structure changes, with some local environments showing a hexagonal symmetry similar to what is seen in the scrutinyite structure that has been documented for example in UO2.

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