DE19530390A1 - Infusible polyborosilazanes for prodn of ceramic powders, fibres and mouldings - Google Patents

Abstract

Infusible polyborosilazanes (I) and their preparation by reaction of fusible polyborosilazanes with borane-amine adducts are claimed.

Description

The invention relates to infusible polyborosilazanes, processes for their preparation and their use for the production of ceramic powders, fibers and Molded articles.

DE-OS 41 07 108 and EP-A 659 806 produce oligomers and polymeric borosilazanes from molecular precursors. You will be through Implementation of the molecular precursor compounds Cl₃Si-NH-BCl₂ (TADB) or (Cl₃Si-NH) ₂-BCl (TACB) or a mixture of chlorosilanes SiCl (R₁, R₂, R₃) [R₁, R₂, R₃ = Cl, H, C₁-C₆-alkyl, vinyl, alkylamino, alkylsilyl] with primary or secondary amines obtained. The products obtained can be obtained by subsequent Pyrolysis to ceramic material in the form of powders, fibers or moldings be implemented.

This causes the oligomer or polymer to melt during the pyro disadvantageously noticeable. With powders and moldings, it leads to a Foaming of the material since the pyrolysis gases do not escape unhindered can; during fiber production, the green fibers stick together.

It has now been found that by reacting meltable polyborosilazanes can produce infusible polyborosilazanes with borane-amine adducts.

The meltable polyborosilazanes used are in DE-OS 41 07 108 and EP-A 659 806. They can be achieved by implementing (Trichlor silylamino) dichloroborane, bis (trichlorosilylamino) chloroborane or mixtures thereof Compounds with chlorosilanes SiCl (R₁, R₂, R₃) [R₁, R₂, R₃ = Cl, H, C₁-C₆-alkyl, Produce vinyl, alkylamino, alkylsilyl], and primary or secondary amines. The products of the reaction with methylamine are preferably used, the product of the reaction of (trichlorosilylamino) dichloro is particularly preferred borane with methylamine. The meltable polyborosilazanes used can be liquid at room temperature or have a melting point <200 ° C.  

Borane-amine adducts which can be used according to the invention are complexes of borane with N-containing Lewis bases, such as ammonia, primary, secondary or tertiary Amines, N-aromatics or N-containing heterocycles. Examples are the complexes of borane with ammonia, dimethylamine, trimethylamine, triethylamine, ethyldi isopropylamine, tert-butylamine, N, N-diethylaniline, pyridine, 2,6-lutidine, piperidine, Piperazine, morpholine, N-methylmorpholine, N-ethylmorpholine etc. Preferred complexes of borane with amines are used, particularly preferably borane-ammonia complex and borane-dimethylamine complex.

The meltable polyborosilazanes can be either in bulk or in solution be reacted with the borane-amine adduct. This can either be in Substance (solid, liquid or gaseous), in dissolved form, as a suspension be used. Per kilogram of meltable polyborosilazane, 0.5 to 20 mol of borane-amine adduct can be used, depending on the one used meltable polyborosilazane and the intended use of the manufacture seldom infusible polyborosilazane. If you assume at room temperature liquid polyborosilazanes, so you will larger amounts of borane-amine adduct add, for example 5 to 20 mol / kg of meltable polyborosilazane. In the case of polyborosilazanes with a higher melting point, even a smaller amount can of borane-amine adduct are sufficient to obtain an infusible product, for example 0.5 to 10 mol / kg of meltable polyborosilazane. While at one Use of the infusible polyborosilazane for the production of ceramic Powder or molded body, the material should be as completely infusible as possible for fibers, it is often sufficient to have a sufficiently thick layer on the Surface is infusible. Therefore, in this case it may be enough a smaller amount of the borane-amine adduct, e.g. B. melt 0.5 to 7 mol / kg bares polyborosilazane.

The reaction can be carried out at a temperature in the range of about 0 ° C to 250 ° C be performed. You will choose the higher the temperature, depending the borane-amine adduct used is less reactive. When implementing in Sub You will punch a temperature above the melting point of the used select meltable polyborosilazane if a complete implementation to un meltable polyborosilazane should be ensured. You want infusible Produce fibers from meltable green fibers, so of course you become the reaction below the melting point of the green fiber.

Suitable solvents are aprotic organic solvents, e.g. B. hexane, Petroleum ether, toluene, tetrahydrofuran, methylene chloride.  

The invention also relates to the use of the invention infusible polyborosilazanes for the production of ceramic powders, Fibers and molded articles. For this purpose, the infusible ones according to the invention Polyborosilazanes in a reactive gas or inert gas atmosphere to ceramic Material are pyrolyzed. For example, in argon or nitrogen pyrolyzed atmosphere, a silicon boron nitride ceramic is obtained, at Pyrolysis in ammonia and subsequent annealing in nitrogen or argon you get a silicon boron nitride ceramic. In pyrolysis you become ordinary Select heating rates from 0.1 ° C / min to 10 ° C / min. With pyrolysis in reactive gas atmosphere in the first step you will reach a final temperature of approx. 600-1100 ° C heat. For complete ceramization of the material it is necessary in Heat inert gas atmosphere to temperatures <1000 ° C. You become ordinary choose a final temperature in the range of about 1300 ° C to 1600 ° C.

The infusible material according to the invention can be used to produce ceramic powders Polyborosilazane be crushed before pyrolysis. For making mold can form a molding from this polymer powder by known methods prepared and then pyrolyzed in the manner mentioned above.

For the production of fibers, it may be expedient to first make a green fiber to produce meltable polyborosilazane. The material of the green fiber is then by reaction with a borane-amine adduct at least superficially in the infusible polyborosilazane according to the invention converted. It can be beneficial be liable to carry out this step so that the borane-amine adduct in the Gas phase transferred and the green at temperatures below the melting point fiber can react with this.

The infusible green fibers obtained can then be as above wrote to be pyrolyzed.

Examples

All process steps were carried out in the absence of air and moisture guided

example 1

200 g of 700 ml of liquid methylamine were added at -78 ° C. in the course of 4 hours Cl₃Si-NH-BCl₂ added dropwise in 1000 ml of hexane. They were left within 12 hours warm to room temperature and then heated for 2 hours to Boil. After cooling, the reaction mixture was filtered, the residue washed with hexane and the filtrate under reduced pressure of solution free medium and excess methylamine. The residue was under reduced pressure heated to 90 ° C to add volatile components remove. 160 g of highly viscous polyborosilazane remained.

14.4 g of this polyborosilazane were placed in 100 ml of tetrahydrofuran. At Room temperature was a solution of 3.01 g BH₃ · NH₃ in 400 ml Tetrahydrofuran added dropwise. The mixture was kept at room for 12 hours temperature stirred, then heated to boiling and at boiling temperature for 24 hours touched.

The reaction mixture was filtered, the solvent under reduced pressure Pressure distilled off. 16.4 g of colorless, infusible Polyboro remained silazane.

A compact made of this material was placed in a nitrogen atmosphere at 1 ° C / min heated to 1450 ° C. The material did not melt during pyrolysis; it no foaming of the compact was observed. It became a ceramic Obtained molded articles from silicon boron carbonitride; the ceramic yield was 55.7%.

Example 2

14.4 g of the meltable polyborosilazane from Example 1 were in 100 ml of toluene dissolved, and at 40 ° C to a solution of 0.58 g BH₃ · H (NH₃) ₂ in 100 ml of toluene dripped. The mixture was heated to boiling and added for 12 hours Boiling heat stirred.  

The reaction mixture was filtered, the solvent under reduced pressure Pressure distilled off. The residue was heated to 180 ° C in vacuo Remove residual solvent. There remained 11.6 g of colorless, infusible Polyborosilazane.

The material was crushed in a mortar, in an ammonia atmosphere at 2 ° C / min heated to 1000 ° C and aged at this temperature for 1 hour. While no foaming of the material was observed during pyrolysis.

The powder obtained was then at 5 ° C / min in a nitrogen atmosphere 1450 ° C heated. Powdered silicon boron nitride was obtained; the kerami The yield was 57.4%.

Example 3

In a solution of 80 g Cl₃Si-NH-BCl₂ and 58.8 g SiCl₄ in 1.5 l hexane was Methylamine initiated at -10 ° C for 6 hours. The reaction mixture was briefly heated to boiling. After cooling, it was filtered, the precipitate was washed with hexane. The solvent was removed from the filtrate distilled off under reduced pressure; then the residue was still for 1 Heated to 180 ° C in a vacuum. 81.3 g of a colorless solid were obtained obtained, which showed a melting point of about 60 ° C.

From the polymer obtained were spun using a small melt apparatus and a winding head at a temperature of 90 ° C, a spinning pressure of 1 MPa and a take-off speed of 50 m / min green fibers with a 25 µm diameter spun.

10 g of green fibers were transferred to a reactor loaded with 0.5 g BH₃ · NH₃. This was evacuated and heated to 80 ° C for 1 hour. Then were heated the fibers to 1450 ° C in a nitrogen atmosphere at 2 ° C / min. The fibers kept their shape and did not stick together. The received ceramic fibers had a diameter of approx. 15 µm and had one smooth surface.

Claims (4)

1. Infusible polyborosilazanes, obtainable by reacting melt baren polyborosilazanes with borane-amine adducts. 2. Process for the preparation of the infusible polyborosilazanes according to Claim 1 by implementing fusible polyborosilazanes with Borane amine adducts. 3. Use of the infusible polyborosilazanes according to claim 1 for Manufacture of ceramic powders, fibers and moldings. 4. Process for making infusible meltable polyborosilazanes by reaction with borane-amine adducts.