A transparent molded article for optical applications made from silicon nitride and a coating thereon of oxidic silicon nitride formed by chemical reaction of the silicon nitride with oxygen. The moldings can be shaped, depending on the area of application, to give various articles, for example optical waveguides, prisms, sensor elements or lenses, and are used in all areas where high optical demands are made.

The invention relates to fiber composite materials and a process for their preparation. The process comprises impregnating fibers with a molten polysilazane in a first step, converting the polysilazane in the fibers into the non-fusible state in a second step, and heating the impregnated fibers to 800.degree. to 2000.degree. C. in a nitrogen, noble gas or ammonia atmosphere in a third step.

The invention 1204 to a process for the preparation of .alpha., .omega.-chlorosilazanes which comprises reacting an oligohydridoorganylsilazane of the formula [--RSiH--NH--].sub.n in which n is from about 3 to about 12 with at least one of the chlorosilanes R.sup.1 HSiCl.sub.2, R.sup.2 R.sup.3 SiCl.sub.2, R.sup.4 SiCl.sub.3, Cl.sub.2 R.sup.5 SiCl.sub.2 CH.sub.2 SiR.sup.5 Cl.sub.2 and Cl.sub.3 SiCH.sub.2 CH.sub.2 SiR.sup.6 Cl.sub.2 where R is C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl and,independently of one another, R.sup.1 -R.sup.6 are H, C.sub.1 -C.sub.6 alkyl, or C.sub.2 -C.sub.6 -alkenyl, at from -20.degree. C. to +50.degree. C. In addition, the invention relates to the novel .alpha., .omega.-chlorosilazanes obtainable by this process.