Method for the production of a composite body from a basic body of opaque quartz glass and a tight sealing layer

A method for producing a composite body having a basic body of opaque quartz glass and a dense sealing layer, the method comprising:

• (a) producing the basic body from a first slip, said first slip containing a first dispersion liquid and first amorphous SiO2 particles having particle sizes of not more than 500 μm, wherein the first amorphous SiO2 particles that have particle sizes in a range between 1 μm and 60 μm constitute a largest fraction of a total volume of solids in the first slip, wherein the first slip contains a first concentration of SiO2 nanoparticles with particle sizes of less than 100 nm by weight based on a total solids content of the first slip, and wherein the first slip has a first vitrification temperature;
• (b) providing a second slip that contains a second dispersion liquid and second amorphous SiO2 particles having particle sizes of not more than 100 μm, wherein the second amorphous SiO2 particles that have particle sizes in a range between 1 μm and 40 μm constitute a largest fraction of a total volume of solids in the second slip, the second slip having a composition that differs from a composition of the first slip at least in that the second slip contains a second concentration of SiO2 nanoparticles with particle sizes of less than 100 nm in a range between 0.2% by wt. to 15% by wt. of a total solids content of the second slip, the second concentration being greater than the first concentration, and wherein the second slip has a second vitrification temperature lower than the first vitrification temperature;
• (c) producing a slip layer from the second slip on a surface of the basic body, and drying the slip layer;
• and
• (d) vitrifying the slip layer so as to form the dense sealing layer.