Cyclosilazane als Precursoren für Si₃N₄‐Keramiken

Abstract

Die Produktbildung in der Reaktion von 1‐Trimethylsilyl‐2,2,4,4,6,6‐hexamethylcyclotrisilazan 1 mit Butyllithium und Fluorsilanen ist durch die Reaktionsbedingungen steuerbar. Lithiiertes 1 reagiert mit F3SiN(SiMe3)2 bei tiefen Temperaturen unter Bildung der Mono‐ und Disubstitutionsverbindungen 2, 3 sowie des 1,3,5,7‐Tetraaza‐2,4,6,8‐tetrasilabicyclo [4.2.0] octans 4. Ein permethylierter Bicyclus (5) entsteht in analoger Reaktion mit MeSiF2N(SiMe3)2. Bei Raumtemperatur reagiert das Monolithiumsalz von 1 mit F3SiN(SiMe3)2 unter Kontraktion zum Cyclodisilazan 6. 6 bildet mit Butyllithium das Lithiumderivat 7. 7 reagiert mit F3SiN(SiMe3)2 zu 8, dem zu 3 isomeren Cyclodisilazan. In der Reaktion von lithiiertem 1 mit Me2SiF2 wird das silylverbrückte Cyclodisilazan 9 erhalten, das in Pyrolysereaktionen ein geeignetes Ausgangsmaterial für Si3N4‐Keramiken darstellt. Die Resultate der Röntgenstrukturanalyse von 7 und der Pyrolyse von 9 werden mitgeteilt.

Silicon-Based Polymer-Derived Ceramics: Synthesis Properties and Applications-A Review

“…Silicon-Based Polymer-Derived Ceramics: Synthesis Properties and Applications-A Review péÉÅá~ä fëëìÉ Äó dìÉëí bÇáíçêëW lêÖ~åáÅ-íç-fåçêÖ~åáÅ`çåîÉêëáçå mêçÅÉëë Ñçê mçäóãÉê-aÉêáîÉÇ`Éê~ãáÅë polyorganosilazanes [39][40][41][42][43][44][45][46][47][48][49][50] and polysiloxanes [51][52][53][54] as preceramic polymers have been reported.…”

Cyclosilazanes and borazines: polymer precursors to silicon- and boron-containing ceramics

“…In recent years oligo-and poly-silazanes were investigated as precursors for Si 3 N 4 -based ceramics. 1,2,12,[17][18][19][20][21][22][23] Thermal decomposition under atmospheric pressure of the silazanes yields Si 3 N 4 ceramics and Si 3 N 4 /SiC composites, depending on the pyrolysis atmosphere. [24][25][26] The six-and eightmembered cyclosilazanes which are used as starting material can be easily synthesized by ammonolysis of chlorosilanes.…”

“…LiF elimination forces a ring closure of a third cyclodisilazane (II) (Eqn [12] and The silyl-coupled rings are stable up to 650°C and react with NH 3 at 1100°C to give Si 3 N 4 . 23 The advantages of this method are that the preparation of Si 3 N 4 is at relatively low temperatures, the Si 3 N 4 obtained is free of chlorine, and variation of the pyrolysis atmosphere (Ar/NH 3 ) allows the synthesis of Si 3 N 4 /SiC powders with definite C contents (Fig. 5).…”

“…In course of our work with cyclosilazanes, we also investigated molecular boron-containing silazanes as precursors for the formation of materials in the quaternary system Si-B-C-N. 14,15,23 Hexamethylcyclotrisilazanes and their lithium derivatives react with F 2 BN(SiMe 3 ) 2 to give the corresponding mono-, bis-and tris-fluoroborylbis-(trimethylsilyl)amino]hexamethylcyclotrisilazanes (III). 14,15,32 The six-membered N 3 Si 3 ring adopts a distorted boat conformation with normal Si-N distances and planar-coordinated boron atoms 14,15 (Eqn [16]).…”

Dehydrocoupling of tris(hydridosilylethyl)boranes with ammonia or amines: a novel route to Si–B–C–N preceramic polymers

“…Precursor thermolysis is a process by which suitable polymers with an inorganic skeleton are converted into a wide variety of amorphous ceramics. [1][2][3][4][5] In particular, silicon-based polymers, such as polysilanes, [6][7][8][9][10][11] polycarbosilanes, [12][13][14][15][16][17][18] polysilazanes, [19][20][21][22][23][24][25][26][27][28][29][30][31] and polysiloxanes (for an overview, see , have proven to be promising precursors for the production of technologically important ceramic components, such as fibers, coatings, infiltrated porous media, or complexshaped bulk parts.…”