Molecular simulations of the structure and thermal transport of high alumina aluminosilicate molten core glass fiber

Abstract

The atomistic structure and phonon transport in aluminosilicate glasses made via an interfacial mixing model of the Molten Core process were studied using molecular dynamics simulations. In the simulations, silica glass was brought in contact with different size alumina crystals (to afford core glasses with 4, 18, 24, 29, and 41 mole% alumina concentrations), followed by a melt‐quench process to enable mixing of the phases. The atomistic structure of the resulting glasses and radius of gyration calculations of resultant Al‐O‐Al connected clusters were evaluated. Variation in the 1‐dimensional thermal transport in each glass was also determined and showed that increased alumina concentration in the glasses resulted in increased transport of thermal energy. Results of the structural analyses showed a double peak in the Al‐Al pair distribution function, with the short‐distance peak indicative of edge‐sharing Al‐O‐Al‐O bonding and a longer distance peak of Al‐O‐Al bonding that is not indicative of edge‐sharing structures. The ratio of the first Al‐Al peak to the second Al‐Al peak varied inversely with the thermal transport behavior. An increased radius of gyration of Al‐O‐Al connectivity occurred with increasing alumina concentration, providing a mechanism for the increased thermal transport. Nanosegregation was also observed. Interconnectivity between Al ions created isolated Al‐O‐Al bonded clusters at low alumina concentrations with lower thermal transport than the high alumina glasses, whereas the latter showed a percolated network of Al‐O‐Al bonds that increased thermal transport.

Effect of calcium and potassium oxide addition on the viscosity and fragility of a calcium aluminosilicate melt

“…As the bond angle of Al–O BO –Al is normally narrower than those of the Si–O BO –Si and Si–O BO –Al bonds, 71 the formation of Al–O BO –Al species can decrease the viscosity of aluminosilicate melts in the low‐viscosity region. The signal of Al–O BO –Al was undetectable in the previous 17 O NMR spectrum of the CAS glass at room temperature 27 ; however, a non‐negligible amount of Al–O BO –Al exists in the molten calcium aluminosilicates at elevated temperatures (e.g., > 1673 K) 72–74 because its fraction generally increases with increasing temperature. In addition, the amount of Al–O BO –Al depends on the melt composition.…”

The uniqueness of glass for passive thermal management for optical fibers

“…89 Given the compositional limits of CVD processing, thermal conductivity is likely the least effective of the approaches noted. However, there have been indications of increased thermal transport, modeled atomistically and experimentally shown, at least at lower temperatures, in sesquioxide-containing silicate glasses 98 and fibers. 99…”

Observation and practical implications of nano‐scale phase separation in aluminosilicate glass optical fibers

“…That said, there are potential benefits of low loss, nano‐scale heterogeneous optical fibers. Of specific interest to the high‐power fiber laser applications to which these high alumina‐content glasses are directed, is the fact that the increasing concentration of Al–O–Al bonding seems also to correlate with enhanced thermal transport . This potentially is of value to mitigate the detrimental effects of fiber heating while lasing at high powers, such as transverse mode instabilities (TMI), which materially scale inversely with thermal conductivity, or pulling away heat generated by the quantum defect.…”

“…Recently, molecular dynamics (MD) simulations of binary aluminosilicate glass with similar compositions as the fibers presented in Ref. [4] indicated that phase separation should be present . The Ref.…”