DE19817680A1 - Silicon boronitride ceramic powder is produced - Google Patents

Abstract

Silicon boronitride ceramic powder is produced from a mixture of bis-trichlorosilylaminodichloroborane, bis-trimethylsilylaminodichlorosilane and optionally a novel chloride-containing silicon-boron-nitrogen polymer. A silicon boronitride ceramic powder, of formula SixByNz (x = 1 to 15, y = 3 to 10 and z = 7 to 15), is produced by (a) converting a mixture (1) of 20-80 wt. % bis(trichlorosilylamino) -chloroborane (TACB) and 20-80 wt. % bis(trimethylsilylamino)- dichlorosilane at \- 50 deg C for 72 hr. into a mixture (2) of 50-70 wt. % TACB, 10-30 wt. % bis(trimethylsilylamino)- dichlorosilane and 15-30 wt. % trichloroborazine, subjecting this mixture (2) to ammonolysis with ammonia at -200 to +1400 deg C and then calcining under protective gas at 800-1550 deg C; or (b) converting the above mixture (2) into a mixture (3) of 25-40 wt. % TACB, 2-10 wt. % bis(trimethylsilylamino)- dichlorosilane, 2-10 wt. % trichloroborazin and 40-60 wt. % chloride-containing SiBN polymer at \-70 deg C, subjecting this mixture (3) to ammonolysis with ammonia at -200 to +1400 deg C and then calcining under protective gas at 800-1550 deg C to an amorphous silicon boronitride ceramic powder. Independent claims are also included for (i) production of the silicon boronitride ceramic powder described above by refluxing a trichlorosilylaminodichloroborane (TADB) sump mixture at 78-110 deg C for 2 hr. to 4 days, distilling off the light boiling components, mixing the residual product with an inert non-polar aprotic solvent, isolating the precipitated chloride-containing SiBN polymer by filtration, reacting the polymer with ammonia at -200 to 1400 deg C and calcining at 800-1550 deg C to an amorphous silicon boronitride ceramic powder; (ii) a chloride-containing SiBN polymer which is obtained in the above process (i) and which has been vacuum dried after filtration; and (iii) a molding obtained by pressing the above SiBN polymer after ammonolysis.

Description

The present invention relates to a method for producing an amorphous silicon citric boron nitride ceramic powder of the general formula

Si _x B _y N _z

in which
x represents the numbers 1 to 15,
y stands for the numbers 3 to 10 and
z stands for the numbers 7 to 15, with which moldings can be produced which are characterized by high thermal resistance, high oxidation resistance, high dimensional stability and low carbon content.

From Baldus et al, Mat. Res. Soc. Symp. Proc., Vol. 271 (1992) 821-826 it is known that these powders are usually used for the production of Si ₃ N ₄ / BN composite ceramics. The advantage of using silicon boron nitride ceramic powders over conventional powder mixtures made of Si ₃ N ₄ and BN powders lies in their better sintering activity.

From DE-A-11 93 485 and US 3,676,343 it is known that amorphous silicon boron nitride can be produced via the coammonolysis of the element chlorides BCl ₃ and SiCl ₄ with ammonia in an electric arc or by subsequent pyrolysis in NH ₃ / N ₂ .

According to JP 05 320 356, the synthesis is also via the coammonolysis of dihalosilanes and trihaloboranes in the presence of Lewis bases possible.

Another access to silicon boron nitride powders (SiBN powders) results from Misawa et al (J. of Non-Crystalline Solids 95 & 96 (1987) 1119-1126) by the conversion of SiCl ₄ , B ₂ H ₆ and H ₂ in Presence of ammonia at temperatures between 1100 and 1300 ° C (CVD process).

An alternative way of producing the silicon boron nitride ceramic is described in EP-A-0 424 082. Here, a soluble polysilazane is polymerized with a soluble boron compound in a solvent under moderate conditions and pyrolyzed under NH ₃ / N ₂ .

Sneddon et al (Chem. Mater. 7 (11) (1995) 2203-12) leads the copolymerization of tris (trimethylsilylamino) silane (TTS) with borazine with subsequent pyrolysis up to 1400 ° C. to amorphous Si-BN ceramics with variable silicon content by crystallization at 1800 ° C leads to semi-crystalline products. Crystalline phases are Si ₃ N ₄ and SiC, BN is amorphous.

According to JP 04 272 227, chloroborazines with chain or cyclic Copolymerized polysilazanes, which are then in silicon boron nitride ceramics (fibers or copmposite) can be converted by thermal treatment.

From EP-A-0 502 399 it is known that homogeneous, amorphous silicon boron nitride powder by ammonolysis of TADB (trichlorosilylaminodichloroborane), a single-source precursor, with solid, liquid or gaseous ammonia and subsequent calcination and pyrolysis in NH ₃ / N ₂ can be produced.

A disadvantage of the processes in the prior art is that high-quality amorphous sili ciumboron nitride ceramics only by ammonolysis of elaborately manufactured mono mer compounds (single source precursors) or pure Si and B containing Aus materials can be synthesized. As a further possibility, the Ver linking of the three elements Si, B, and N only through the copolymerization of costs dig prepared silazane prepolymers with low molecular weight boron starting compound be realized.  

The syntheses of the starting compounds lead to environmental and health hazardous feedstocks that require sensitive handling. In most cases there remain residues that have to be disposed of at great expense.

Another disadvantage is the sensitivity to air and hydrolysis of the manufactured precursor molecules and polymers as well as the pure educts (e.g. BCl ₃ , SiCl ₄ ), their complex manufacturing and purification steps in their synthesis and the associated educt and auxiliary costs .

The task was to create a simple and environmentally friendly process considering economic aspects for the production of a silicon boron Provide nitride ceramic powder that is not used by single source precursors based on a chlorine-rich polymer and which has the disadvantages of single Source precursors does not have. As a result, there is no need for time-consuming disposal a waste, the TADB swamp (TADB = trichlorosilylaminodichloroborane).

The invention and thus the solution to the problem relates to a method for the produc- tion of an amorphous silicon boron nitride ceramic powder of the general formula

Si _x B _y N _z

in which
x represents the numbers 1 to 15,
y stands for the numbers 3 to 10 and
z stands for numbers 7 to 15,
characterized in that either with a mixture of substances
20 to 80 wt .-% bis (trichlorosilylamino) chloroborane (TACB) and
20 to 80% by weight bis (trimethylsilylamino) dichlorosilane
(Mixture 1) at least 50 ° C over a period of 72 hours in a mixture of the composition
50 to 70 wt% TACB
10 to 30 wt .-% bis (trimethylsilylamino) dichlorosilane and
15 to 30% by weight trichloroborazine
(= Substance mixture 2) transferred, this substance mixture 2 is either lysed without thermal pretreatment with ammonia at temperatures between -200 ° C and + 1400 ° C and calcined under protective gas at temperatures between 800 ° C and 1550 ° C, or substance mixture 2 if necessary in a further step at temperatures greater than or equal to 70 ° C
in a mixture of substances of the composition
25 to 40 wt% TACB
2 to 10% by weight bis (trimethylsilylamino) dichlorosilane
2 to 10 wt .-% trichloroborazine and
40 to 60 wt .-% chloride-containing SiBN polymer
(= Substance mixture 3) thermally transferred and this substance mixture 3 then ammonolyzed with ammonia at temperatures between -200 ° C and + 1400 ° C and calcined under protective gas at temperatures between 800 ° C and 1550 ° C, the respective sum of the percentages by weight always results in 100%.

The process according to the invention is particularly suitable for producing an amorphous silicon boron nitride ceramic powder of the general formula

Si _x B _y N _z

in which
x represents the number 3,
y stands for the numbers 8 or 9 and
z stands for the numbers 12 or 13.

The process according to the invention can be used to produce silicon boron nitride ceramic powders whose BN content (B = boron, N = nitrogen) can be set between 15 and 47% by weight and whose Si ₃ N ₄ content can be set between 53 and 85% by weight and which also have a low carbon content.

According to the method according to the invention, substance mixture 2 can also be used directly, without thermal pretreatment which is subjected to ammonolysis and calcination, without the method according to the invention being restricted thereby.

Preferred in the sense of the present invention for the production of the amorphous silicon umbornitride ceramic powder is the use of substance mixture 3, that of substance mixture 2 can be prepared as described above. Ammonolysis and Calcination of mixture 3 is carried out analogously to that of mixture 2.

The duration of the pyrolysis is between 0 minutes and 24 hours, preferably between 15 minutes and 12 hours.

The pressure of the atmosphere is between 0.9 and 1.5 bar.

The duration of the calcination is between 0 minutes and 24 hours, preferably between 15 minutes and 12 hours. The calcination can also be done directly after the Pyrolysis take place without intermediate cooling.

The pressure of the atmosphere is between 0.9 and 1.5 bar.

According to the method according to the invention, the amorphous silicon obtained can boron nitride ceramic powder by a subsequent heat treatment between  1500 ° C and 2200 ° C are partially or completely crystallized. As x-ray Graphically detectable crystalline phases primarily form α and β silici umnitride. The formation of hexagonal BN is kinetically inhibited and only occurs in higher temperatures and longer holding times. In addition, the formation of SiC can be observed. The density of the silicon increases during the crystallization umborn nitride ceramic powder and the specific surface is reduced.

The crystallization is carried out under protective gas or inert gas such as N ₂ and / or argon.

The pressure of the atmosphere is between 0.9 bar and 100 bar, preferably 1 bar to 10 bar.

The duration of the aging is between 5 minutes and 4 days, preferably 10 minutes to 24 hours.

The crystallization of the silicon boron nitride ceramic powder can also be carried out directly after the Calcination done without intermediate cooling.

For the purposes of the present invention, particular preference is given to using the TADB sump as a starting material mixture for the preparation of the invention Ceramic powder instead of mixture 1 and / or mixture 2 and / or substance mix 3.

The TADB swamp falls during the manufacture of the single source precursor mentioned TADB (trichlorosilylaminodichloroborane) as a residue that normally occurs on would have to be disposed of quickly.

By ammonolysis of the raw sump or the purified sump with ammonia (solid, liquid, gaseous) at temperatures between 800 ° C and 1400 ° C and on closing pyrolysis and calcination up to a maximum of 1550 ° C can be done by amorphous silici umbornitride ceramic powder can be produced in the sense of the present invention.  

The TADB sump is cleaned according to the invention in that the sump mixture with an inert, non-polar, aprotic solvent or solvent is mixed. Hydrocarbons such as pentane and hexane are preferred used, particularly preferably petroleum ether.

The precipitated polymeric solid, according to the invention, containing chloride-containing SiBN poly mer, is obtained in 11-70% yield (based on the sump mixture used).

Depending on the application, the precipitated SiBN polymer can be filtered off and dried or continue to be used in a precipitated form.

The amorphous silicon boron nitride powder according to the invention can be produced by ammonolysis of the chloride-containing SiBN polymer, also in combination with substance mixture 1 and / or substance mixture 2 and / or substance mixture 3 and subsequent pyrolysis and calcination, which has a BN content between 15 and 47% and an Si ₃ N ₄ content between 53 and 85%. Crystallization leads to semi-crystalline silicon boron nitride powder.

In a particularly preferred embodiment in the sense of the present invention the TADB swamp mixture at a temperature between 78 ° C and 110 ° C, preferably between 88 ° and 100 ° C, for a period of 2 hours to 4 days below Kept reflux. The low boilers are then distilled off and the residue is left behind product with an inert, non-polar, aprotic solvent such as carbon Hydrogen, particularly preferably with petroleum ether.

According to the invention, the chloride-containing SiBN polymer is then produced to produce the Ceramic powder in 90% yield.

If the chloride-containing SiBN polymer is reacted further in the precipitated form or another application can be used to isolate the product tes can be dispensed with.  

The preferred work-up step is to isolate the precipitated chloride-containing SiBN polymer by filtration and its reaction with Ammo niak (solid, liquid, gaseous) at temperatures between -200 ° C and + 1400 ° C. The subsequent calcination at temperatures between 800 ° C and 1550 ° C leads to the amorphous silicon boron nitride powder in the sense of the present invention. Crystalline sation leads to partially crystalline silicon boron nitride powder.

For the reaction with NH ₃ , all known ammonolysis processes of silicon tetrachloride can be used; this relates to the reaction with solid or liquid ammonia at low temperatures (US-A-4 196 178), the reaction with gaseous ammonia in an organic solvent (US-A-4 959 446) or the reaction with NH ₃ in one High temperature reaction with elimination of hydrogen chloride (US-A-4 145 224).

The ammonium chloride obtained is separated off in accordance with the invention by known methods such as sublimation or washing with liquid ammonia. The salt in the ammonia stream is particularly preferred by pyrolysis of the ammono lysed product removed in an oven between 400 and 1000 ° C. Subsequently the material becomes special in a nitrogen stream between 800 ° C and 1550 ° C but preferably calcined at 1500 ° C to amorphous nitridic ceramics. As above Crystallization leads to partially crystalline product.

The amorphous ceramic material represented in this way consists in the main components made of Si, N and B and can also contain C, Cl, H and O in traces.

Traces of carbon with an upper limit of 1.5% by weight are preferred, in particular traces of carbon of less than or equal to 0.25% by weight are particularly preferred.

The calcination is carried out under protective gas. Particularly suitable as protection gas are nitrogen, argon and / or ammonia.  

The process according to the invention is illustrated by the following examples, without being limited to them.

The silicon boron nitride ceramic produced by the method according to the invention powders are characterized by high thermal resistance and high sensitivity to oxidation out. Shaped body made of the silicon ceramic powder by pressing have high dimensional stability, breaking strength and impact toughness.

Embodiments

All work was carried out in a protective gas atmosphere (N ₂ or argon) using Schlenk technology.

example 1 Ammonolysis of mixture 1 or mixture 2

500 ml of liquid ammonia (99.999%) are condensed in a 3000 ml three-necked flask and 1100 ml of petroleum ether are added. 180 g of mixture 1 and / or mixture 2 are then slowly added dropwise (1 drop per second) at a temperature of -78 ° C. with vigorous stirring. Then the suspension of polymeric ammonolysis product, NH ₄ Cl, liquid ammonia and petroleum ether is stirred for another hour and the excess ammonia is allowed to evaporate. The mixture is heated under reflux for one hour to remove residual ammonia from the reaction mixture. After filtration and drying in vacuo, a white, saline, polymeric solid remains.

Example 2 Ammonolysis of mixture 3 or TADB raw sump

100 g of substance mixture 3 and / or TADB- are placed in a 2000 ml three-necked flask. Submitted to the sump in 1000 ml of hexane. Then ammonia (99.999%) is added -78 ° C initiated to saturation. The reaction mixture is within 48 h warmed to room temperature and heated to reflux for one hour. The ent standing white polymeric solid is filtered off and dried in vacuo.  

Example 3 Cleaning the TADB raw sump

1000 g of TADB raw sump are placed in a three-necked flask. With vigorous stirring, the amount of petroleum ether is added to the sump at room temperature, which can be 1: 1 to 1:10 to the amount of sump weighed in. The precipitated, high chloride SiBN polymer is isolated by filtration and dried under vacuum. It can also be implemented directly from the precipitation solution.
Yield: 11-70%
Composition (in percent by weight):
C 2.3%; Cl 45.5%; N 25.8%; O 1.5; B 12.7%; Si 11.4%

Example 4 Refurbishment of the TADB raw sump

1000 g of TADB raw sump are placed in a 2000 ml three-necked flask and heated to boiling under reflux. The mixture is kept at a temperature between 78 ° C and 110 ° C for a period of 2 hours to 4 days. The viscosity of the contents of the flask increases sharply in the course of the reflux. The low boilers are distilled off and the remaining viscous, cream-colored residue is mixed with an appropriate amount of petroleum ether. The precipitated, white, chloride-containing SiBN polymer is isolated by filtration and dried under vacuum.
Yield: <90%
Composition (in percent by weight):
C 2.97%; H 1.85%, N 18.8%; O 0.66%; Cl 53.9%; B 9.77% Si 12.7%

Example 5 Ammonolysis of the chloride-containing SiBN polymer

300 g of the chloride-containing SiBN polymer are weighed into a 1000 ml three-necked flask. An inert, non-polar, aprotic solvent or solvent mixture can be added in any ratio or not. The flask is cooled to -78 ° C and the introduction of NH ₃ (99.999%) started with vigorous stirring. The introduction is ended after 5 hours. The excess ammonia is evaporated and the remaining white solid is freed from residual ammonia in vacuo.

Example 6 Ammonolysis of the chloride-containing SiBN polymer

500 ml of ammonia (99.999%) and 1100 ml are placed in a 2000 ml three-necked flask Hexane submitted at -78 ° C. 150 g of the chloride are then stirred vigorously containing SiBN polymer slowly metered in via a solids metering funnel. The The reaction mixture is warmed to room temperature over a period of 24 h and heated to reflux for an hour. The white solid is filtered off and dried in vacuo.

Example 7 Conversion of the ammonolysis product from Examples 1, 2, 5 and 6 into the amor phe silicon boron nitride ceramic powder

The polymeric ammonolysis product obtained according to Examples 1, 2, 5 and 6 is heated in a quartz glass frit in an ammonia stream to 1000 ° C. and tempered at this temperature for one hour in order to drive off any NH ₄ Cl still present. The material is then heated in a carbon crucible under nitrogen to 1500 ° C. (10 K / min) and calcined there for a further hour.

The polymeric ammonolysis product has completely become a nitridic ceramic converted, which is X-ray amorphous. The surface was determined using BET.

example 1

Area: 304 m ²

/G
Composition (in percent by weight):
Si 37.2%; B 14.5%; O 1.5%; N 45.9%; C 0.1%; Cl <0.01%

Example 2

Area: 141 m ²

/G
Composition (in percent by weight):
Si 36.3%; B 16.2%; O 1.7%; N 44.5%; C 0.2%; Cl <0.01%

Example 5

Area: 56 m ²

/G
Composition (in percent by weight):
Si 24.5%; B 28.0%; O 0.7%; N 45.6%; C 0.06%; Cl <0.01%

Example 6

Area: 6 m ²

/G
Composition (in percent by weight):
Si 25.3%; B 25.8%; O 1.2%; N 47.2%; C 0.1%; Cl <0.01%

Claims (7)

1. A process for producing a silicon boron nitride ceramic powder of the general formula
Si _x B _y N _z
in which
x represents the numbers 1 to 15,
y stands for the numbers 3 to 10 and
z represents the numbers 7 to 15,
characterized in that either a mixture 1 with
20 to 80 wt .-% bis (trichlorosilylamino) chloroborane and
20 to 80% by weight bis (trimethylsilylamino) dichlorosilane
at least 50 ° C over a period of 72 hours in a mixture 2 of the composition
50 to 70 wt% TACB
10 to 30 wt .-% bis (trimethylsilylamino) dichlorosilane and
15 to 30% by weight trichloroborazine
transferred, this mixture of substances 2 ammonoly siert without thermal pretreatment with ammonia at temperatures between -200 ° C and + 1400 ° C and calcined under protective gas at temperatures between 800 ° C and 1550 ° C, or mixture of substances 2 if necessary in a further step Temperatures greater than or equal to 70 ° C
in a mixture of substances 3 of the composition
25 to 40 wt% TACB
2 to 10% by weight bis (trimethylsilylamino) dichlorosilane
2 to 10 wt .-% trichloroborazine and
40 to 60 wt .-% chloride-containing SiBN polymer
thermally transferred and then ammonolyzed with ammonia at temperatures between -200 ° C and + 1400 ° C and calcined under protective gas at temperatures between 800 ° C and 1550 ° C to an amorphous silicon boron nitride ceramic powder. 2. A method for producing a silicon boron nitride ceramic powder of the general formula Si _x B _y N _z according to claim 1, characterized in that
x represents the number 3,
y stands for the numbers 8 or 9 and
z stands for the numbers 12 or 13. 3. A process for producing a silicon boron nitride ceramic powder of the general formula Si _x B _y N _z according to claim 1, characterized in that a mixture of substances of the composition
50 to 70 wt% TACB
10 to 30 wt .-% bis (trimethylsilylamino) dichlorosilane and
15 to 30% by weight trichloroborazine
(Mixture 2) is assumed. 4. A method for producing a silicon boron nitride ceramic powder of the general formula Si _x B _y N _z according to claim 1, characterized in that a mixture of substances of the composition
25 to 40 wt% TACB
2 to 10% by weight bis (trimethylsilylamino) dichlorosilane
2 to 10 wt .-% trichloroborazine and
40 to 60 wt .-% chloride-containing SiBN polymer
(Mixture 3) is assumed. 5. A process for producing a silicon boron nitride ceramic powder of the general formula Si _x B _y N _z , in which
x represents the numbers 1 to 15,
y stands for the numbers 3 to 10 and
z represents the numbers 7 to 15,
characterized in that TADB bottom mixture is kept at a temperature between 78 ° C and 110 ° C for a period of 2 hours to 4 days under reflux, then the low boilers are distilled off, the remaining product is mixed with an inert, non-polar, aprotic solvent , the precipitated chloride-containing SiBN polymer isolated by filtration, reacted with ammonia at temperatures between -200 ° C and 1400 ° C and finally calcined at temperatures between 800 ° C and 1550 ° C to an amorphous silicon boron nitride ceramic powder. 6. Chloride-containing SiBN polymer obtainable from

• i) thermal treatment of TADB bottom mixture at a temperature between 78 ° C and 110 ° C for a period of 2 hours to 4 days under reflux,
• ii) distilling off the low-boiling fractions,
• iii) adding an inert, non-polar, aprotic solvent to the residue and
• iv) drying the chloride-containing SiBN polymer isolated by filtration in vacuo.

7. Shaped body obtainable by pressing the converted by ammonolysis ten Si BN polymer according to claim 6.