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Optical Fibers
Published in Johan Meyer, Justice Sompo, Suné von Solms, Fiber Lasers, 2022
Johan Meyer, Justice Sompo, Sune von Solms
The MCVD is an improved version of OVD developed at Bell Laboratories in 1974 (MacChesney et al. 1974). Unlike the OVD, the reaction takes place on the inner surface of a glass tube. The glass of the original tube will ultimately become the cladding of the drawn fiber. In this process, vapour reactants (chlorides and oxygen) are blown inside a rotating silica substrate tube. A source of heat moves back and forth on the external surface of the tube as illustrated in Figure 2.22. On the action of the heat, chlorine reacts with oxygen to form silica soot, which is deposited inside the tube. The first reaction involves Silicon tetrachloride (SiCl4) with Oxygen to form Silicon Dioxide (SiO2), and the last Germanium tetrachloride (GeSl4) reacting with Oxygen to form Germanium Dioxide (GeO2) and increase the refractive index. After the deposition is completed, the temperature is increased to values between 1700°C and 1900°C. The tube is then collapsed to give a solid preform, which may then be drawn into a fiber.
Synthesis of Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
The process uses volatile silicon tetrachloride, which can be easily purified, for example, by fractional distillation. Additives such as germanium tetrachloride are incorporated into the center of the fibre to give a higher refractive index. The process starts by making a ‘preform’. A silica tube, which forms the outer low refractive layer, known as the cladding of the fibre, is heated to about 1600°C by a flame passing up and down the outside of the tube as it is rotated (Figure 3.12). SiCl4 and O2 pass down the tube and react together to form SiO2, which deposits evenly along the tube wall as soot. Small amounts of GeCl4 and other chemicals are gradually added into the process to deposit as oxides on the wall in the inner layers to increase the refractive index. The flame burner is then used to melt the soot deposit onto the glass preform. After cooling, the cylindrical preform is heated in a drawing tower to about 1900°C until it melts sufficiently to fall under gravity into a fine thread, which is slowly pulled and wound onto a spool. One preform can produce 2 km of fibre.
Optical Materials
Published in Christoph Gerhard, Optics Manufacturing, 2018
Depending on the process parameters, the deposited silicon dioxide (i.e., the fused silica) features high purity and homogeneity. Flame pyrolysis can also be applied for the deposition of multicomponent glasses. This approach is one of the most important manufacturing methods for the production of blanks for optical step index fibers. Here, a thin layer of fused silica is first deposited on the tube wall. Subsequently, a further process gas is used and another solid-state phase is deposited onto the previously deposited silicon dioxide layer. For example, the use of gaseous germanium tetrachloride (GeCl4) results in the formation of germanium dioxide (GeO2), which features a higher index of refraction than does silicon dioxide. After depositing such different layers at the inner surface of the tube, it is finally heated and drawn (“collapsed”) to an optical fiber.
A Review on Germanium Resources and its Extraction by Hydrometallurgical Method
Published in Mineral Processing and Extractive Metallurgy Review, 2021
Thi Hong Nguyen, Man Seung Lee
A mixture of four trialkyl phosphine oxides (Cyanex 923) was used to extract Ge(IV) from concentrated acid solutions owing to their poor aqueous solubility and high extraction power (Gupta and Mudhar 2006). Cyanex 923 has been employed to extract Ge(IV) from HCl solutions with moderate to strong acidity. HCl solution is the most effective medium for Ge(IV) extraction by Cyanex 923 at high acid concentration. The extracted species of Ge(IV) from concentrated HCl solution can be represented as GeCl4⋅2R (Eq. (9)). The extraction of Ge(IV) by Cyanex 923 from HCl solution might be related to the formation of neutral germanium tetrachloride up to 4 M HCl, while no data is available for sulfate, nitrate and phosphate neutral complexes of Ge(IV) (Wood and Samson 2006). Complete stripping of Ge(IV) from Cyanex 923 was easily obtained using moderate HCl solution (Gupta and Mudhar 2006). The main advantage of Cyanex 923 was high extraction efficiency and easy stripping but solvent extraction of Ge(IV) by Cyanex 923 should be carried out from concentrated HCl solution due to the formation of neutral germanium tetrachloride. Like Cyanex 923, tributyl phosphate (TBP) can extract Ge(IV) from 3 M HCl solution in the presence of chloride salts such as chlorides of lithium, sodium, potassium magnesium, and aluminum through the solvating mechanism and the extracted species can be represented as GeCl4⋅2TBP (Kalyanaraman and Khopkar 1977). It can be concluded that the extraction efficiency of Ge(IV) by neutral extractants such as TBP and Cyanex 923 depends on the concentration of both HCl and chloride ion. In order to extract Ge(IV) from moderate acid solutions (pH = 1–3), oxalic acid was added as a ligand which converts germanium to neutral species, H2Ge(C2O4)3 (Haghighi et al. 2019). The extracted species, H2Ge(C2O4)3–⋅4 R was identified by the slope analysis method and the Ge(IV) was stripped from the loaded organic using NaOH solution (Haghighi et al. 2019).