Abstract: A method as well as an apparatus for manufacturing a tube according to the EFG-method. To manufacture tubes with a desired even wall thickness, it is proposed to draw the tube from a melt whose temperature can be controllably adjusted section by section.

Abstract: There is provided a heating element and an arrangement of heating elements, respectively, for heating crucibles, in particular for LEC devices for growing semiconductor single crystals, with a tulip-shaped bottom heater (20) being built such that the heater legs of the main heater (40) positioned thereabove can barely be guided towards the bottom. Such arrangement of bottom and main heater enables multi-heater arrangements without having to interfere with a lateral insulation (18) which, thus, need not be cut out or pierced.

Abstract: A process for measuring the oxygen potential in a silicon melt uses an electrochemical potential probe which dips into the melt. The probe voltage is measured using this potential probe which is made of an SiO.sub.2 glass tube in which graphite is in direct contact with SiO.sub.2 glass. The graphite has a wire making contact with it at the graphite upper end. The probe is dipped into the silicon melt only to an extent such that the graphite/wire contact point contained in the SiO.sub.2 glass tube lies above the silicon melt.

Abstract: A method for measuring and controlling the oxygen concentration in silicon melts which are contained in a silica glass crucible or which can be touched by a silica glass surface can especially be used for achieving a defined, uniform axial and radial oxygen concentration in a growing silicon crystal. The measurement of the oxygen concentration is realized by an electrochemical solid ionic sensor dipped into the melt; the voltage is measured between the sensor and the growing silicon crystal. The oxygen concentration in the melt is controlled by applying a voltage between crystal and silica glass crucible. The apparatus for putting the method into practice includes an electrochemical solid ionic sensor formed of a silica glass tube which encloses a metal/metal oxide mixture, contacted by a metal wire.