Methods of using boron-containing additives as silicon carbide crosslinking agents

Patent metadata

Field	Value
Publication number	US-9359479-B2
Application number	US-201313905732-A
Country	US
Kind code	B2
Filing date	May 30, 2013
Priority date	May 30, 2013
Publication date	Jun 7, 2016
Grant date	Jun 7, 2016

Abstract

The present disclosure generally relates to methods of using boron-containing additives for crosslinking polysilazane green fibers, which are precursors to silicon carbide fibers. These methods provide a controllable process for crosslinking silicon carbide fibers while providing a simple way for the introduction of boron as a sintering aid into the polymer structure.

First claim

What is claimed is:

1. A method of forming a polydisilazane resin comprising reacting in an oxygen-free and moisture-free system:
a) at least one methylchlorodisilane;
b) at least one organochlorosilane comprising at least one vinyl or allyl group, wherein the concentration of olefin in the polydisilazane resin is greater than 1 mol/kg;
c) an additive of formula I

wherein
Y is (C 2 -C 3 )alkylene; and
R 4 , R 5 , and R 6 are each independently selected from phenyl, (C 1 -C 12 )alkyl, chlorine, and bromine;
wherein at least one instance of R 4 , R 5 , and R 6 must be selected from chlorine and bromine; and
d) at least one nitrogen-containing additive selected from hexamethyldisilazane, tetramethyldisilazane, divinyltetramethyldisilazane, methylamine, and ammonia.

2. A method of forming a polydisilazane resin according to claim 1 , wherein said nitrogen-containing additive is hexamethyldisilazane.

3. A method of forming a polydisilazane resin according to claim 1 , wherein R 4 , R 5 , and R 6 are each independently selected from methyl, phenyl and chlorine.

4. A method of forming a polydisilazane resin according to claim 1 , wherein
Y is selected from —CH 2 CH 2 —, —CH(CH 3 )—, —CH 2 CH 2 CH 2 —, and —CH 2 —CH(CH 3 )—; and
each instance of R 4 , R 5 , and R 6 is methyl, phenyl, or chlorine.

5. A method of forming a polydisilazane resin according to claim 1 , wherein said organochlorosilane is of formula

wherein
R a is selected from hydrogen, (C 1 -C 12 )alkyl, phenyl, vinyl, allyl or a combination thereof; and
R b is selected from chlorine, hydrogen, (C 1 -C 12 )alkyl, phenyl, vinyl, allyl or a combination thereof.

6. A method of forming a polydisilazane resin according to claim 5 , wherein R a is selected from (C 1 -C 4 )alkyl, phenyl, vinyl, allyl and vinylbenzyl.

7. A method of forming a polydisilazane resin according to claim 5 , wherein R b is selected from chloro, (C 1 -C 4 )alkyl, phenyl, vinyl, allyl and vinylbenzyl.

8. A method of preparing a silicon carbide fiber, comprising:
a) forming a polydisilazane resin in an oxygen-free and moisture-free system, said forming comprising reacting:
i) at least one methylchlorodisilane;
ii) at least one organochlorosilane comprising at least one vinyl or allyl group wherein the concentration of olefin in the polydisilazane resin is above 1 mol/kg;
iii) at least one nitrogen-containing additive selected from hexamethyldisilazane, tetramethyldisilazane, divinyltetramethyldisilazane, methylamine and ammonia; and
iv) an additive of formula I

wherein
Y is (C 2 -C 3 )alkylene; and
R 4 , R 5 , and R 6 are each independently selected from phenyl, (C 1 -C 12 )alkyl, phenyl, chlorine, and bromine;
wherein at least one instance of R 4 , R 5 , and R 6 must be selected from chlorine and bromine;
b) spinning said polydisilazane resin to form a polydisilazane fiber;
c) exposing said polydisilazane fiber to oxygen, air, or the mixture of air with inert gas such as nitrogen, and optionally moisture, to form a cross-linked polydisilazane fiber; and
d) heating said cross-linked polydisilazane fiber.

9. A method of preparing a silicon carbide fiber according to claim 8 , wherein said exposing a polydisilazane fiber step is performed at a temperature between 20° C. and 200° C.

10. A method of preparing a silicon carbide fiber according to claim 8 , wherein said heating of the cross-linked polydisilazane fiber is performed in an inert gaseous atmosphere to a temperature of at least 800° C. to form an amorphous SiCNO fiber.

11. A method of preparing a silicon carbide fiber according to claim 10 , wherein said amorphous SiCNO fiber contains boron at a concentration between 0.02 wt % and 2 wt %.

12. A method of preparing a silicon carbide fiber according to claim 10 , further comprising converting said amorphous SiCNO fiber into a crystalline SiC fiber by heating in an inert gaseous atmosphere in a temperature range from 1400° C. to 2000° C.

Assignees

• Gen Electric

Inventors

• Rubinsztajn Slawomir
• Littlejohn Matthew Hal
• Mills Ryan Christopher
• Davis Peter Kennedy

Classifications

• C01B32/977

  Preparation from organic compounds containing silicon · CPC title

• C04B2235/9661

  Colour · CPC title

• C04B2235/483

  Si-containing organic compounds, e.g. silicone resins, (poly)silanes, (poly)siloxanes or (poly)silazanes · CPC title

• C08G77/60

  in which all the silicon atoms are connected by linkages other than oxygen atoms · CPC title

• D01F9/10

  by decomposition of organic substances (D01F9/12 takes precedence) · CPC title