Positive and Negative Oxygen Vacancies in Amorphous Silica

2019 ◽  
Vol 19 (2) ◽  
pp. 3-17 ◽  
Author(s):  
Anna Kimmel ◽  
Peter Sushko ◽  
Alexander Shluger ◽  
Gennadi Bersuker
Keyword(s):  
Amorphous Silica ◽  
Oxygen Vacancies

Modeling of the structure and properties of oxygen vacancies in amorphous silica

2004 ◽  
Vol 70 (19) ◽  
Author(s):  
Sanghamitra Mukhopadhyay ◽  
Peter V. Sushko ◽  
A. Marshall Stoneham ◽  
Alexander L. Shluger
Keyword(s):  
Amorphous Silica ◽  
Oxygen Vacancies ◽  
Structure And Properties

First-principles study of neutral oxygen vacancies in amorphous silica and germania

2004 ◽  
Vol 69 (19) ◽  
Author(s):  
Tomoyuki Tamura ◽  
Guang-Hong Lu ◽  
Ryoichi Yamamoto ◽  
Masanori Kohyama
Keyword(s):  
Amorphous Silica ◽  
First Principles ◽  
Oxygen Vacancies ◽  
First Principles Study

scholarly journals Diffusion and aggregation of oxygen vacancies in amorphous silica

2017 ◽  
Vol 29 (24) ◽  
pp. 245701 ◽  
Author(s):  
Manveer S Munde ◽  
David Z Gao ◽  
Alexander L Shluger
Keyword(s):  
Amorphous Silica ◽  
Oxygen Vacancies

scholarly journals Oxygen vacancies in amorphous silica: structure and distribution of properties

2005 ◽  
Vol 80 ◽  
pp. 292-295 ◽  
Author(s):  
P.V. Sushko ◽  
S. Mukhopadhyay ◽  
A.M. Stoneham ◽  
A.L. Shluger
Keyword(s):  
Amorphous Silica ◽  
Oxygen Vacancies

Amorphous silica coating on α-alumina particles

1995 ◽  
Vol 53 ◽  
pp. 210-211
Author(s):  
J. W. Mellowes ◽  
C. M. Chun ◽  
I. A. Aksay
Keyword(s):  
Amorphous Silica ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Silica Coating ◽  
Full Density ◽  
Optimal Conditions ◽  
Fine Grained ◽  
Alumina Particles ◽  
Complete Mullitization ◽  
Powder Compacts

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

Conditions for atomic imaging of mullite

1989 ◽  
Vol 47 ◽  
pp. 418-419
Author(s):  
T. A. Epicier ◽  
G. Thomas
Keyword(s):  
Oxygen Vacancies ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Work Conditions ◽  
Real Space ◽  
Potential Candidate ◽  
Silicate Mineral ◽  
Resolution Electron ◽  
The Subject ◽  
Aluminium Silicate

Mullite is an aluminium-silicate mineral of current interest since it is a potential candidate for high temperature applications in the ceramic materials field.In the present work, conditions under which the structure of mullite can be optimally imaged by means of High Resolution Electron Microscopy (HREM) have been investigated. Special reference is made to the Atomic Resolution Microscope at Berkeley which allows real space information up to ≈ 0.17 nm to be directly transferred; numerous multislice calculations (conducted with the CEMPAS programs) as well as extensive experimental through-focus series taken from a commercial “3:2” mullite at 800 kV clearly show that a resolution of at least 0.19 nm is required if one wants to get a straightforward confirmation of atomic models of mullite, which is known to undergo non-stoichiometry associated with the presence of oxygen vacancies.Indeed the composition of mullite ranges from approximatively 3Al2O3-2SiO2 (referred here as 3:2-mullite) to 2Al2O3-1SiO2, and its structure is still the subject of refinements (see, for example, refs. 4, 5, 6).

Mechanoactivation Of Rice Husk Ash In Laboratory Conditions

2019 ◽  
pp. 20-26
Keyword(s):  
Mechanical Activation ◽  
Rice Husk ◽  
Amorphous Silica ◽  
Silicon Oxide ◽  
Rice Husk Ash ◽  
Pozzolanic Activity ◽  
Maximum Solubility ◽  
Laboratory Conditions ◽  
Before And After ◽  
Mineral Additive

In many rice producing countries of the world, including in Vietnam, various research aimed at using rice husk ash (RHA) as a finely dispersed active mineral additive in cements, concrete and mortars are being conducted. The effect of the duration of the mechanoactivation of the RHA, produced under laboratory conditions in Vietnam, on its pozzolanic activity were investigated in this study. The composition of ash was investigated by laser granulometry and the values of indicators characterizing the dispersion of its particles before and after mechanical activation were established. The content of soluble amorphous silicon oxide in rice husk ash samples was determined by photocolorimetric analysis. The pizzolanic activity of the RHA, fly ash and the silica fume was also compared according to the method of absorption of the solution of the active mineral additive. It is established that the duration of the mechanical activation of rice husk ash by grinding in a vibratory mill is optimal for increasing its pozzolanic activity, since it simultaneously results in the production of the most dispersed ash particles with the highest specific surface area and maximum solubility of the amorphous silica contained in it. Longer grinding does not lead to further reduction in the size of ash particles, which can be explained by their aggregation, and also reduces the solubility of amorphous silica in an aqueous alkaline medium.

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