Glass formation in amorphous SiO2 as a percolation phase transition in a system of network defects

JETP Letters (Impact Factor: 1.36). 01/2004; 79(12):632-634. DOI: 10.1134/1.1790021

ABSTRACT Thermodynamic parameters of defects (presumably, defective SiO molecules) in the network of amorphous SiO2 are obtained by analyzing the viscosity of the melt with the use of the Doremus model. The best agreement between the experimental
data on viscosity and the calculations is achieved when the enthalpy and entropy of the defect formation in the amorphous
SiO2 network are H

=220 kJ/mol and S

=16.13R, respectively. The analysis of the network defect concentration shows that, above the glass-transition temperature (T

), the defects form dynamic percolation clusters. This result agrees well with the results of molecular dynamics modeling,
which means that the glass transition in amorphous SiO2 can be considered as a percolation phase transition. Below T

, the geometry of the distribution of network defects is Euclidean and has a dimension d=3. Above the glass-transition temperature, the geometry of the network defect distribution is non-Euclidean and has a fractal
dimension of d

=2.5. The temperature T

can be calculated from the condition that percolation arises in the defect system. This approach leads to a simple analytic
formula for the glass-transition temperature: T



+1.735R). The calculated value of the glass-transition temperature (1482 K) agrees well with that obtained from the recent measurements
of T

for amorphous SiO2 (1475 K).

Download full-text


Available from: Michael I. Ojovan, Sep 29, 2015
544 Reads
  • Source
    • "It can be used for some special glass applications. However, this is not very common due to silica's high glass transition temperature of over 1200 °C (2192 °F) ( M. I. Ojovan (2004). Normally, other substances are added to simplify processing. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Brand equity is a phrase used in the marketing industry which describes the value of having a well-known brand name, based on the idea that the owner of a well-known brand name can generate more money from products with that brand name than from products with a less well known name, as consumers believe that a product with a well-known name is better than products with less well-known names. Some marketing researchers have concluded that brands are one of the most valuable assets a company has, as brand equity is one of the factors which can increase the financial value of a brand to the brand owner, although not the only one. We, in this paper have conducted the research about the Glass Industry in India with particular reference to Saint-Gobain Glass India Ltd in Chennai, India.
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work k0-INAA (via IAEAk0-software) has been applied on glass samples to determine major, minor and trace element concentration. As many as 50 elements were detected and quantified with 3–5 mg of 0.1 % AuAl comparator monitor (0.1 % gold–99.9 %Alumimum wire). The average concentration of SiO2, Na2O, CaO, Al2O3 and MgO ranged between 76–96 %, 11.15–12.66 %, 5.26–10.71 %, 1.13–2.73 % and 3.51–6.23 % respectively. The relative concentrations of impurity elements; Cr, Fe, Mn and Co determined from the glass samples were used to match the physical appearance (color) of the glass based on general knowledge of colored glass production. The analytical procedure was validated using SRM 610 (glass matrix) and SRM GBW07106 (rock matrix) both as control samples which indicated a relative uncertainty of 15 and 6 % respectively for SRM 610 and SRM GBW07106. The relative sensitivity at which some of the elements were detected in major, minor and trace levels have indicated, that the k0-method in instrumental neutron activation analysis using low power research reactor is a useful technique in glass analysis and could equally be used for forensic and archeological glass characterization.
    Journal of Radioanalytical and Nuclear Chemistry 03/2012; 295(3). DOI:10.1007/s10967-012-2249-1 · 1.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An isothermal kinetic diagram for the beginning of homogeneous nucleation is constructed using the molecular-dynamics model of an instantaneously supercooled iron melt near the icosahedral percolation transition temperature identified with the glass transition temperature T g . This diagram is compared with the theoretical one calculated using quantitative information obtained by analyzing the kinetics of the initial stage of growth of supercritical nuclei at temperatures higher than T g . A satisfactory coincidence of the theoretical curve with computer simulation data at temperatures higher than T g and substantial disagreement with these data below T g , where crystallization is necessarily preceded by the formation of an icosahedral percolation cluster, demonstrate the substantive influence of an icosahedral substructure on the nucleation rate predicted by the classical theory.
    Physics of the Solid State 05/2006; 48(5):815-820. DOI:10.1134/S1063783406050015 · 0.82 Impact Factor
Show more