Boron-modified silazanes for synthesis of SiBNC ceramics

Patent metadata

Field	Value
Publication number	US-9453111-B2
Application number	US-201314377123-A
Country	US
Kind code	B2
Filing date	Feb 7, 2013
Priority date	Feb 7, 2012
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

New methods for synthesizing boron-modified silazanes, their use as polymer-derived ceramic precursors, and polymer-derived ceramics and composites formed therefrom are disclosed. The polymeric ceramic precursors comprise a boron-modified silazane that is a room temperature liquid-phase polymer comprising a backbone having recurring monomeric repeat units comprising boron-nitrogen bonds. Nanocomposites comprising polymer-derived ceramics and carbon nanotubes are also disclosed.

First claim

We claim:

1. A boron-modified silazane useful as a polymeric precursor for a polymer-derived ceramic, wherein said boron-modified silazane is a room temperature liquid-phase polymer.

2. The boron-modified silazane of claim 1 , wherein said boron-modified silazane comprises a backbone having recurring monomeric repeat units comprising boron-nitrogen bonds.

3. The boron-modified silazane of claim 2 , wherein said monomeric repeat units further comprise boron-oxygen bonds.

4. The boron-modified silazane of claim 2 , said monomeric repeat units comprising alternating silicon and nitrogen atoms in said backbone, wherein said boron-nitrogen bonds are selected from the group consisting of:
boron pendant from said nitrogen in said backbone;
boron-substituted nitrogen groups pendant from said silicon in said backbone; and
combinations thereof.

5. The boron-modified silazane of claim 2 , wherein said monomeric repeat units comprise —Si—N—B(R 5 ) 2 bonds, where each R 5 is individually —OCH 3 or —C 2 H 4 Si(R)H, where R is —H or —CH 3 .

6. A structure comprising:
a substrate having a surface; and
a layer of a polymer-derived ceramic adjacent said substrate surface, said polymer-derived ceramic formed from a boron-modified silazane according to claim 1 .

7. The structure of claim 6 , said ceramic further comprising a plurality of nanofillers dispersed therein.

8. The structure of claim 6 , wherein said layer of ceramic is formed from a powder coating comprising said boron-modified silazane and a plurality of nanofillers, wherein said boron-modified silazane is bonded with said nanofillers.

9. The structure of claim 6 , wherein said layer is resistant to:
oxidation in flowing air at a temperature of up to about 1000° C.; or
laser irradiation up to about 15 kWcm −2 at a wavelength of about 10.6 μm, for about 10 seconds without burning, delamination, or deformation of said layer.

10. The structure of claim 6 , wherein said substrate is selected from the group consisting of metal and non-metallic: natural or synthetic woven or non-woven cloth, carbon nanotube mats, cellulose mats, fibers, wires, tubing, pump shafts, cylinders, spindles and/or sleeves, induction coils, and combinations thereof.

11. A nanocomposite comprising:
a plurality of carbon nanotubes having respective sidewalls; and
a layer of a polymer-derived ceramic adjacent said sidewalls, said ceramic being formed from a boron-modified silazane according to claim 1 , wherein said polymer-derived ceramic is bonded to said sidewalls forming a protective shell thereon.

12. The nanocomposite of claim 11 , wherein said nanocomposite is resistant to oxidation in flowing air at a temperature of up to about 1000° C.

13. The nanocomposite of claim 11 , wherein said nanocomposite is selected from the group consisting of nanowires, nanorods, nanosheets, and combinations thereof.

14. A method of making a boron-modified silazane, said method comprising forming a reaction mixture comprising trimethyl borate and a room temperature liquid-phase silazane, and mixing under ambient conditions for at least about 12 hours, wherein said reaction mixture is optionally heated from room temperature up to about 85° C. during said mixing such that said mixture is dried during said mixing.

15. The method of claim 14 , wherein said reaction mixture further comprises a nanofiller selected from the group consisting of carbon nanotubes, metal nanoparticles, graphene ribbons, molybdenum disulfide, carbon fiber, 2-D nanosheets, fullerenes, and mixtures thereof.

16. The method of claim 14 , wherein said room temperature liquid-phase silazane comprises monomeric repeat units comprising alternating silicon and nitrogen, of the formula:

where each of R 1 and R 2 are individually —H, alkyls, alkenyls, or alkynls, and R 3 is —H, alkyl, aryl, or allyl.

17. The method of claim 14 , wherein said room temperature liquid-phase silazane comprises monomeric repeat units of the formula:

where R 1 and R 2 are individually —H, alkyls, alkenyls, or alkynls, R 3 is —H, alkyl, aryl, or allyl, R 4 is O or S, and at least one of R 3 is —H.

18. A method of forming a polymer-derived ceramic, said method comprising:
providing a boron-modified silazane according to claim 1 ;
crosslinking said boron-modified silazane to yield a cured polymeric precursor; and
converting said cured polymeric precursor to a ceramic.

19. The method of claim 18 , wherein said converting comprises pyrolyzing said cured polymeric precursor, by heating said cured precursor to a temperature of at least about 700° C. for at least about 4 hours.

20. The method of claim 18 , further comprising mixing a plurality of nanofillers with said boron-modified silazane prior to said crosslinking, said nanofillers being selected from the group consisting of carbon nanotubes, metal nanoparticles, carbon fiber, 2-D nanosheets, fullerenes, and mixtures thereof.

21. The method of claim 18 , further comprising:
providing a substrate having a surface and forming a layer of said boron-modified silazane adjacent said substrate surface prior to said crosslinking;
providing a mold and filling said mold with said boron-modified silazane prior to said crosslinking; or
providing a fibrous reinforcement structure and impregnating said structure with said boron-modified silazane prior to said crosslinking.

22. The method of claim 18 , further comprising grinding said cured polymeric precursor into a powder prior to said converting, and providing a substrate having a surface and forming a coating of said powder adjacent said substrate surface prior to said converting.

23. The method of claim 22 , further comprising dispersing said powder in a solvent system or binder before forming said coating.

24. The method of claim 18 , further comprising grinding said ceramic into a powder, and providing a substrate having a surface and forming a coating of said powder adjacent said substrate surface.

Assignees

• Univ Kansas State

Inventors

• Singh Gurpreet
• Bhandavat Romil

Classifications

• C04B2235/9607

  Thermal properties, e.g. thermal expansion coefficient · CPC title

• C04B35/62886

  by wet chemical techniques · CPC title

• C04B2235/3409

  Boron oxide, borates, boric acids, or oxide forming salts thereof, e.g. borax · CPC title

• B05D7/24

  for applying particular liquids or other fluent materials · CPC title

• Y10T428/31678

  Of metal · CPC title