Abstract: 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.

Abstract: A process for the preparation of optical materials from silicon nitride by pyrolysis of polymeric silazanes, by pressing the pulverulent polymeric silazanes to give moldings before the pyrolysis or first dissolving the polymeric silazanes in an organic solvent, drawing fibers from this solution and pyrolyzing these fibers after evaporation of the solvent, or by melting polymeric silazanes, casting, injection-molding or extruding this melt to give moldings and subsequently pyrolyzing the moldings. An oxidic coating is produced on the silicon nitride molding in an oxygen-containing atmosphere during or after the pyrolysis. The pyrolysis can be carried out at 800.degree.-1000.degree. C. in an atmosphere containing ammonia or an ammonia/inert gas mixture.

Abstract: 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.

Abstract: The invention relates to novel polysubstituted chlorine-containing silazane polymers, to their preparation, to their processing to form ceramic material containing silicon nitride, and to said material itself. The chlorine-containing silazane polymers are prepared by reating oligosilazanes of formula (I) ##STR1## in which at least one of the indices a or b and at least one of the indices c or d are not equal to 0 and n is about 2 to about 12, with at least one of the chlorosilanes Cl.sub.2 R.sup.6 Si--CH.sub.2 CH.sub.2 --SiR.sup.6 Cl.sub.2, Cl.sub.3 Si--CH.sub.2 CH.sub.2 --SiR.sup.7 Cl.sub.2, R.sup.8 SiCl.sub.3 or R.sup.9 SiHCl.sub.2 at 30.degree. C. to 300.degree. C., where the radicals independently of one another have the following meanings: R.sup.1, R.sup.2, R.sup.4 =H, C.sub.1 -C.sub.6 alkyl or C.sub.2 -C.sub.6 alkenyl and R.sup.3, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 =C.sub.1 -C.sub.6 alkyl or C.sub.2 -C.sub.6 alkenyl.

Abstract: The invention relates to novel polymeric hydridochlorosilazanes, to their preparation, to their processing to form ceramic materials containing silicon nitride, and to said materials themselves. The polymeric hydridochlorosilazanes are prepared by reacting oligohydridoorganosilazanes of the general formula (R.sup.1 SiHNH).sub.n, in which n is about 3 to about 12, with at least one of the chlorosilanes R.sup.2 SiHCl.sub.2, R.sup.3 SiCl.sub.3, Cl.sub.2 R.sup.4 Si--CH.sub.2 CH.sub.2 --SiR.sup.4 Cl.sub.2 or Cl.sub.3 Si--CH.sub.2 CH.sub.2 --SiR.sup.5 Cl.sub.2 at 30.degree. C. to 300.degree. C., where the radicals independently of one another have the following meanings:R.sup.1 =a C.sub.1 -C.sub.6 alkyl or C.sub.2 -C.sub.6 alkenyl group,R.sup.2 =a C.sub.2 -C.sub.6 alkenyl group if R.sup.2 SiHCl.sub.2 is reacted with the oligosilazanes by itself, orR.sup.2 =a C.sub.1 -C.sub.6 alkyl or C.sub.2 -C.sub.6 alkenyl group if R.sup.2 SiHCl.sub.2 is reacted with the oligosilazanes as a mixture with other chlorosilanes, andR.

Abstract: A process for the preparation of an Si.sub.3 N.sub.4 ceramic of high strength, wherein .alpha.-Si.sub.3 N.sub.4 powder is mixed with small amounts of at least one of the elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Y in form of an oxide or oxide precursor, the mixture is shaped to a shaped body and the shaped body is sintered under pressures of 1-100 bar in a nitrogen atmosphere at temperatures of 1,750.degree.-2,000.degree. C. is described.The sintered body is heated at temperatures of 1200.degree.-1500.degree. C. in an inert gas atmosphere for at least 10 hours and then cooled. During this procedure, crystalline apatites of the formula A.sub.4+x (SiO.sub.4).sub.3 N.sub.x, A denoting the element added in the form of the oxide or oxide precursor and x denoting a number which is greater than zero and not more than 1.

Abstract: The invention relates to novel polymeric chlorosilazanes, to their preparation, to their processing to form ceramic material containing silicon nitride, and to said material itself. The polymeric chlorosilazanes are prepared by reacting a mixture of oligosilazanes of formula (I) ##STR1## in which n is about 2 to about 12, and oligosilazanes of formula (II), (RSiHNH).sub.m, in which m is about 3 to about 12, with at least one of the chlorosilanes Cl.sub.2 R.sup.2 Si--CH.sup.2 --CH.sub.2 --SiR.sup.2 Cl.sub.2, Cl.sub.3 Si--CH.sub.2 --CH.sub.2 --SiR.sup.3 Cl.sub.2, R.sup.4 SiCl.sup.3 or R.sup.5 SiHCl.sub.2 at 30.degree. C. to 300.degree. C., where R and R.sup.1 to R.sup.5 are C.sub.1 -C.sub.6 alkyl or C.sub.2 -C.sub.6 alkenyl groups which can be identical or different.The polymeric chlorosilazanes according to the invention can be converted into polysilazanes by reaction with ammonia, and these in turn can be pyrolyzed to form ceramic materials containing silicon nitride.

Abstract: The invention relates to a process for the production of a ceramic/fiber composite.The process comprises impregnating fibers with a molten polysilazane in a first step, converting the polysilazane in the fibers into the infusible state in a second step and, in a third step, heating the impregnated fibers to 800.degree. to 2000.degree. C. in an atmosphere of nitrogen, noble gas, or ammonia.

Abstract: The invention relates to a novel sinterable ceramic powder, to its preparation and to its further processing to give a silicon nitride ceramic, and to this material itself and its use. The sinterable ceramic powder is produced by melting a polysilazane or dissolving it in an organic solvent, suspending a powdered sinter aid in this melt or solution, then pyrolyzing the melt, or the residue obtained after evaporation of the solvent, at 500.degree. to 1600.degree. C. in a protective gas atmosphere, the polysilazane eitherA) being obtainable by reacting at least one of the oligosilazanes of the formula (I) ##STR1## in which a, b, c and d are the mole fractions of the respective structural units and where 0.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.1, 0.ltoreq.c.ltoreq.0.7, 0.ltoreq.d.ltoreq.0.7, 0.3.ltoreq.a+b, c+d.ltoreq.0.7 and n is approximately 2 to approximately 12, with at least one of the chlorosilanes R.sup.6 R.sup.7 SiCl.sub.2, R.sup.8 SiCl.sub.3, Cl.sub.2 R.sup.9 Si--CH.sub.2 CH.sub.2 --SiR.sup.9 Cl.sub.

Abstract: The invention relates to a high-strength ceramic composite, in particular made from silicon nitride, a process for its preparation and its use. The process comprises impregnating an open-pore matrix with a molten polysilazane in a first step and, in a second step, heating the impregnated matrix to 800.degree. to 2500.degree. C. under a blanketing gas, such as nitrogen or a noble gas, or to 800.degree. to 1500.degree. C. under a gas containing ammonia. The high-strength ceramic composite prepared can be used as a component to be subjected to high thermal, mechanical or corrosive stress.

Abstract: The invention relates to a silicon nitride ceramic having a high strength both at low temperatures and at temperatures above 1000.degree. C., and to a process for its preparation.The silicon nitride ceramic contains, as the primary phase, .beta.-silicon nitride and, as a crystalline secondary phase, an yttrium compound which has been caused to crystallize out from the intergranular glass phase by thermal after-treatment. Teh yttrium-containing, crystalline secondary phase has the following d-values in an X-ray diffraction pattern using Cu-K.alpha. radiation: 4.69 .circle.; 4.05 .circle.; 3.48 .circle.; 3.20 .circle.; 3.06 .circle.; 2.81 .circle.; 2.40 .circle.; 2.07 .circle.; 2.03 .circle.; and 1.87 .circle., the most intense diffraction reflection having the d-value 3.06 .circle..+-.0.01 .circle.. A residue of amorphous glass phase is present in the ceramic as a further phase between the crystal grains.

Abstract: The invention relates to novel chlorine-containing silazane polymers, to their preparation, their further processing to ceramic material containing silicon nitride, and this material itself. In order to prepare the chlorine-containing silazane polymers, oligosilazanes of the formula (I) ##STR1## in which a >0, b.gtoreq.0 and n is about 2 to about 12, are reacted with at least one of the chlorosilanes Cl.sub.2 R.sup.4 Si--CH.sub.2 --CH.sub.2 --SiR.sup.4 Cl.sub.2, Cl.sub.3 Si--CH.sub.2 --CH.sub.2 --SiR.sup.5 Cl.sub.2, R.sup.6 SiCl.sub.3 or R.sup.7 SiHCl.sub.2 at 30.degree. C. to 300.degree. C., where, independently of one another,R.sup.1 and R.sup.2 =H, C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl,R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 =C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl andwhere if b=0 the reaction with R.sup.7 SiHCl.sub.2, if R.sup.7 =C.sub.1 -C.sub.6 -alkyl and none of the other chlorosilanes is present, is to be excluded.

Abstract: The invention relates to novel polysilazanes, the preparation thereof, the further processing thereof to form silicon nitride-containing ceramic material, and this material itself. In order to prepare the polysilazanes, dialkylaminoorganyldichlorosilanes of the formula RSiCL.sub.2 --NR'R' are reacted with ammonia. The polysilazanes can then be pyrolyzed to form silicon nitride-containing ceramic material. The polysilazanes according to the invention dissolve in customary aprotic solvents.

Abstract: The invention relates to a novel sinterable ceramic powder, to its preparation, to its processing to form silicon nitride ceramic and to said material itself and its use. The sinterable ceramic powder is prepared by dissolving the polysilazane of formula (I)[CH.sub.3 SiHNH].sub.n [CH.sub.3 SiN].sub.nwhere n is about 10 to 12, in an organic solvent, suspending a pulverulent sinter aid in this solution and then evaporating the solvent and pyrolyzing the residue in an inert gas atmosphere at 500.degree. to 1600.degree. C.The resulting ceramic powder can be used to form a shaped article and then to manufacture silicon nitride ceramic by sintering. It is also possible, however, to form a shaped article from the as yet unpyrolyzed residue obtained after evaporation of the solvent, and then to pyrolyze and sinter said article.The ceramic obtained can be used to manufacture components subject to high mechanical, thermal and corrosive stress.

Abstract: The invention relates to novel polymeric hydridosilazanes, their preparation, their conversion into silicon nitride-containing ceramic material, and this material itself. To prepare the polymeric hydridosilazanes, polymeric hydridothiosilazanes are reacted with NH.sub.3. To prepare the silicon nitride-containing ceramic material, the polymeric hydridosilazanes are then pyrolyzed.

Abstract: The invention relates to a process for the production of ceramic material containing silicon nitride, such as fibers, coatings or moldings. In this process, polymeric hydridochlorosilazanes are rendered infusible at a temperature below their softening point by treatment with gaseous NH.sub.3 and are then pyrolyzed in an atmosphere containing NH.sub.3 at 700.degree. to 1500.degree. C. Fibers, coatings or moldings containing silicon nitride are produced by first producing appropriate structures from a melt of the polymeric hydridochlorosilazane and then rendering them infusible and pyrolyzing them.

Abstract: The invention relates to novel polymeric hydridosilazanes, processes for their preparation and their use for the preparation of ceramic material containing silicon nitride. To prepare the polymeric hydridosilazanes, polymeric hydridochlorosilazanes are reacted with NH.sub.3. To prepare the ceramic material containing silicon nitride, the polymeric hydridosilazanes are then pyrolyzed.

Abstract: A multi-phase ceramic which is resistant to high temperatures and contains 25-85 % by weight of crystalline .beta.-silicon nitride, 11 to 70% by weight of crystalline cubic HfO.sub.2 and an amorphous glass phase which, in addition to silicon, contains at least one of the elements magnesium, yttrium and/or the rare earths and if appropriate aluminum, has good mechanical properties.To prepare the ceramic, a mixture of 25-85% by weight of pulverulent a-silicon nitride, 11 to 70% by weight of monoclinic HfO.sub.2 and 5-20% by weight of at last one oxide of the elements magnesium, yttrium and/or the rare earths (from Sm to Yb) is shaped to a body and this is sintered to give a dense body at 1,700-2,000.degree. C.

Abstract: The invention relates to novel chlorine-containing silazane polymers, to their preparation, their further processing to ceramic material containing silicon nitride, and this material itself. In order to prepare the chlorine-containing silazane polymers, oligosilazanes of the formula (I) ##STR1## in which a>0, b.gtoreq.0 and n is about 2 to about 12, are reacted with at least one of the chlorosilanes Cl.sub.2 R.sup.4 Si--CH.sub.2 --CH.sub.2 --SiR.sup.4 Cl.sub.2, Cl.sub.3 Si--CH.sub.2 --CH.sub.2 --Sir.sup.5 Cl.sub.2, R.sup.6 SiCl.sub.3 or R.sup.7 SiHCl.sub.2 at 30.degree. C. to 300.degree. C., where, independently of one another,R.sup.1 and R.sup.2 =H, C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl,R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 =C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl and where if b=0 the reaction with R.sup.7 SiHCl.sub.2, if R.sup.7 =C.sub.1 -C.sub.6 -alkyl and none of the other chlorosilanes is present, is to be excluded.

Abstract: Polymeric ethylene-bridged chlorosilazanes, process for their preparation, ceramic materials which can be prepared from them containing silicon nitride, and their preparationThe invention relates to novel polymeric ethylene-bridged chlorosilazanes, their preparation, their further processing to a ceramic material containing silicon nitride, and this material itself. In order to prepare the polymeric chlorosilazanes, oligosilazanes of the formula (I) ##STR1## are reacted with at least one of the chlorosilanes ##STR2## in which R.sup.1 to R.sup.5 are C.sub.1 -C.sub.6 -alkyl or C.sub.2 -C.sub.6 -alkenyl groups, which may be identical or different.The polymeric chlorosilazanes according to the invention can be converted by reaction with ammonia into polysilazanes, which in their turn can be pyrolysed to ceramic materials containing silicon nitride.