Reactor Problems in Modified Chemical Vapour Deposition (II). The Mean Viscosity of Quartz Glass Reactor Tubes

Abstract

A new inethod is developed for deducing viscosity data from collapse experiments with quartz glass reactor tubes. These data involve informations on temperature differences between outer and inner tube surface which are of great importance t o the MCVD procedure. The present investigations supported by some deposition experiments yield the surprising result t h a t a considerable temperature gradient exists also at rather low torch speeds. The reason for this effect is discussed.Eine neue Methode zur Ableitung von Viskositiitsdaten aus Kollabierexperimenten niit Quarzglasreaktorrohren wird entwickelt. Diese Daten enthalten Informationen uber Temperaturdifferenzen zwischen innerer und iiuBerer Rohroberfliiche, die fur die Durchfuhrung des MCVD-Verfahrens von grol3er Bedeutung sind. Die vorliegenden Untersuchungen liefern, gestutzt durch einige Beschichtungsversuche, das uberraschende Ergebnis, daR auch bei verhaltnismiil3ig kleinen Brennergeschwindigkeiten ein betriichtlicher Temperaturgradient existiert. Die Ursachen fur diesen Effekt werden diskutiert.

Collapsing of glass tubes: analytic approaches in a hydrodynamic problem with free boundaries

“…Such an elementary process is called collapsing (see, e.g., [1][2][3][4][5][6][7][8]). We will exclusively focus on collapsing with a uniformly moving heat source, where an observer comoving with the heat source becomes aware of a steady-state collapsing profile narrowed against the direction of motion [2][3][4][5][6][7]. Of course, this only occurs if the comoving observer measures, at the same time, an accompanying steady-state temperature field.…”

“…For clarity, the mathematical description chosen throughout in this paper will strictly adopt the arrangements for viscosity measurements through collapsing described in [2][3][4]. In particular, we will assume that the cold ends of the glass tube are fixed in the laboratory frame.…”

“…This paper is motivated by the concern to have a well-founded analytical base for data evaluation, if systematic and contactless measurements of viscosity and surface tension of molten glasses are carried out through collapsing with a moving heat source [3,4]. In addition, both collapsing and drawing are fundamental technological steps in manufacturing of optical fibers (see, e.g., [1][2][3][4][5][6][7][8][9][10][11][12]). Always for reasons of economy in time, conditions should be predicted to assure the fabrication of optical fibers where, at least, the desired properties are approached (see, e. g. [12,13]).…”

“…One of the most important premises is, of course, that the governing material parameters, in particular, the temperature-dependent viscosity and the surface tension of the special glasses, are known precisely enough. Vice versa, a correct modeling is the base to exploit collapsing and drawing to measure the material parameters in question (see, e.g., [3,4,8,14]). …”

“…There is a large series of papers on analytic approaches of the drawing problem since the 1970s (e.g., [9,10,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]), but only fewer papers involve an analytic treatment of collapsing [1][2][3][4][5][6][7][8] since the 1980s. The approaches on drawing (axial symmetry assumed) favor a perturbation analysis with the prerequisite of a dominating axial viscous flow and axial viscous flow gradient, small axial viscosity dependence, and small inclination of the rod boundary (or tube boundaries) against the rotation axis, as typical for capillary geometries.…”