Equilibria concentrations in the oxidation of SiCl₄and GeCl₄for optical fibers

A computational fluid dynamics model for co-deposition of silica and germania in the MCVD process

“…However, due to the challenges of direct measurement, thermodynamic calculations have been used to elucidate the type and quantity of these intermediate species. Thus McAfee et al [13,14] showed that both GeO and GeOCl 2 are also present (besides GeO 2 ) in significant quantities when the temperature is above 1700 K. Indeed their calculations showed that GeOCl 2 could be more prevalent than GeO at temperatures up to around 2600 K. Although no other study has suggested (or confirmed) the importance of GeOCl 2 , the existence of GeO is agreed upon by all experimental and theoretical studies. Less certain, however, is the temperature at which its formation becomes significant.…”

“…In fact, most MCVD modeling literature quotes the same limited set of sources (French et al [10], Wood et al [5,11] and Kim and Pratsinis [12]), although it must be said that other researchers (McAfee Jr. et al [13,14], Wood et al [15] and Zhang et al [16] have explored the chemistry further via thermodynamic calculations aimed at predicting the composition of the relevant species under equilibrium conditions. Only two experimental studies (French et al [10] and Atkins and Hoban [17]) have examined the forward reaction rate kinetics for GeCl 4 oxidation.…”

“…Less certain, however, is the temperature at which its formation becomes significant. Calculations carried out by McAfee et al [13,14], Yan et al [18] and Wood et al [5] showed that GeO becomes a significant product in GeCl 4 oxidation at temperatures above 1700, 1800 and 1900 K, respectively. Unfortunately, even though limited data are available for the GeO M GeO 2 equilibrium reaction [5,19], no forward or backward reaction rate data could be found in the literature, as also noted recently by Tandon and Murtagh [20].…”

Advancements in semiconductor core optical fiber

“…Firstly, the thermodynamic free energy driving the oxidation of silicon is lower (i.e., there is a greater driving force) than that for the oxidation of germanium and so silicon oxidizes ''easier" than germanium; this can be further observed by comparing the Ellingham diagrams for the oxidation of silicon and germanium. Secondly, germanium oxide is volatile at high temperatures [21,22]. In this case, oxidation of the germanium melt yields a volatile species which should fine out of the molten core given the very low viscosity of the germanium melt [23].…”

Impact of chlorine dissociation for modified chemical vapor deposition

“…It should be noted that a variety of other chemical species are known to be present [5][6][7]. However, the associated reactions need not be considered in a modeling context as the concentrations of these species are expected to be very low under MCVD operating conditions [8].…”