Process for manufacture of a component made of opaque synthetic quartz glass

#The present invention relates to a process for the manufacture of a component made of opaque synthetic quartz glass. Moreover, the invention relates to a quartz glass tube manufactured in accordance with said method.

#Quartz glass tubes, rods, panels, and blocks, either as semi-finished or finished goods, are important components for heat engineering applications, in which good thermal insulation along with high temperature stability and thermal fatigue resistance are essential. Applications of the semi-conductor industry put ever increasing demands on the purity of the opaque quartz glass tubes and components used. Reactors, diffusion tubes, thermal shields, cones or flanges are but a few examples. These applications require the glass components to be opaque mainly in the infrared region of the spectrum. The impurities present in low-purity quartz glass contribute to the opacity of the glass. However, quartz glass manufactured from pure starting materials is transparent, and must be made opaque by artificially introducing pores into the glass.

#In this context, the manufacture of thin-walled opaque quartz glass tubes or tube sections by reshaping an opaque blank in a thermal reshaping process poses a formidable problem because of the low wall thickness such tubes or tube sections have, which causes these parts to easily become transparent while heated in the reshaping process, especially if highly pure starting materials are used for manufacture. This invention relates to the manufacture of components, above all of thin-walled tubes, of opaque quartz glass manufactured from pure starting materials.

#FIG. 1 the process step of vitrification (melting) of granulated material by means of an arc under formation of a hollow cylinder,

#FIG. 2 the manufacture of a quartz glass tube by extending and top blowing a quartz glass cylinder in a horizontal drawing process,

#FIG. 3 a first embodiment of the SiO2 granulates according to the invention, shown as a cross section through an individual SiO2 grain,

#Further details on the manufacture as well as the chemical and physical properties of a granulated material suitable for the purposes of the process according to the invention are given below.

#FIG. 1 shows a schematic depiction of the process according to the invention for manufacture of a hollow cylinder 12 from opaque quartz glass by vitrification of the initially porous form body 1. The manufacture of form body 1 shall be described in detail in the following:

#A wet granulation process is used to manufacture SiO2 granulated material from synthetic SiO2. The granulated material is treated with a Cl2/HCl gas mixture for cleaning. The following contaminant contents are detected in the cleaned material (in units of wt-ppb): lithium <10; sodium 40; potassium 36; iron 30. The specific BET surface of the granulated material and the compacted bulk density of the material are adjusted to 34 m2/g and 1.1 g/cm3, respectively, by thermal compaction in a rotating tubular kiln at a temperature of 1,200° C.