FR2698366A1 - Cyclic precursors for prepn. of silicon nitride - Google Patents

Abstract

Cpd. of formula (I) is new, R1, R2=H, 1-6C alkyl or alkenyl, 6-10C aryl or 7-18C alkylaryl or arylalkyl; R3=H, 1-6C alkyl, 6-10C aryl or 7-18C alkylaryl or arylalkyl; Hal=F, Cl or Br; and p=1-3.Pref., cpds. of formula (II) and polymer intermediates of formula (III) are disclosed as novel: R4, R5=H, 1-6C alkyl or alkenyl, 6-10C aryl or 7-18C alkylaryl or arylalkyl; R6=H, 1-6C alkyl, 6-10C aryl or 7-18C alkylaryl or arylalkyl; R1=H, 1-6C alkyl, aryl, alkylaryl or arylalkyl; x=1 or 2; and n=deg. of polymerisation.Cpds. (I) and (II) are prepd. by reacting a halosilane of formula R1R2Si(Hal)2 with a hydrazine of formula HR3N2H2 in the presence of a tert. amine, pref. NEt3 in a solvent, at 0-25 deg.C. The number of moles of HR3N2H2 and NEt3 per mole of R1R2Si(Hal)2 is 0.5-1 and 1 resp. in the prepn. of (I) and 2 and 0.8-1 resp. in the prepn. of (II).

Description

CYCLIC PRECURSORS OF SILICON NITRIDE
The subject of the present invention is cyclic precursors of silicon nitride, and their use in a process for synthesizing Si3N4 silicon nitride.

 Si3N4 belongs to the family of technical ceramics. The particular properties of silicon nitride make it a particularly suitable material for the manufacture of objects intended for use at high temperatures, typically from 1000 to 1200 ° C. The objects made from silicon nitride are obtained by sintering at high temperature, under a nitrogen atmosphere, a silicon nitride powder, in the form a, to which is conventionally added an additive promoting densification The mechanical properties of objects made from silicon nitride are mechanical strength, strength to thermal shocks, hardness, high wear resistance and therefore these objects are widely used in all types of industry. As examples, silicon nitride is used for the production of rocker pads, turbocharger rotors , pre-combustion chambers for diesel engines in the automotive industry, ball bearings, nozzles, res extrusion and cutting tools.

The known processes for synthesizing silicon nitride on an industrial scale are as follows:
The first method consists of direct nitriding of silicon

This reaction is very exothermic, difficult to control and leads to coarse powders which it is necessary to grind before sintering.

The second method consists in thermal decomposition of a silicon imide, for example according to the diagrams

This reaction leads to a very fine but nevertheless amorphous powder, which is necessary to crystallize at a temperature of 1300 to 1500 ° C.

The third method consists of carbonitriding of silica

This process has the major advantage of using low-cost starting materials and not leading to any effluent other than CO, easily burned.

Nevertheless, carbonitriding has disadvantages. The reaction temperature must be perfectly controlled. Beyond 1470 ° C, there are risks of formation of SiC.

Below 1400 ° C, there is a risk of formation of a poorly crystallized product containing a lot of oxygen During the process, there is competition between the formation of two crystalline forms of Si3N4, the forms a and p The shape a is the desired form, because it is this which leads to the sintered bodies having the aforementioned properties In addition, the particle size of the powder is critical for the implementation of the sintering, a perfectly controlled particle size is therefore necessary. Since the process is carried out under a stream of nitrogen, entrances of materials often occur. These entrainments are due to the formation of an intermediate SiO gas, abbreviated as SiO, which can either be disproportionate to one another. temperature of 1000 to 1200 ° C in SiO2 and Si resulting in fouling of the installation, leading to the formation of Si3N4 rods crystals (w) r so-called whiskers "unsuitable for sintering.

 Other methods of manufacturing Si3N4 have been proposed. These use precursors, in particular polysilazanes and more specifically polysilazanes derived from hydrazine or polysilylhydrazine. These are obtained by reaction of halosilane or disilane with hydrazine, optionally substituted. A tertiary amine may be added to the reaction medium EP-A-0351262 and the application FR-90-15670 describes such a process.

 None of the above documents teaches or suggests the present invention.

 Thus, the present invention relates to novel chemical compounds for use in the synthesis of Si3N4. These chemical compounds are cyclic primary intermediates on the one hand, then polymerized intermediates on the other hand. The present invention also relates to the use of these novel compounds in the synthesis of Si3N4.

où:
Rl est un atome d'hydrogène ou un groupe alkyle en C1 à
C6, alkényle en Cl à C6, aryle en C6 à C10, alkylaryle
ou arylalkyle en C7 à C
R2 identique ou différent de R1, est un atome d'hydrogène
ou un groupe alkyle en C1 à C6, alkényle en C1 à C6,
aryle en C6 à C10, alkylaryle ou arylalkyle en C7 à
C18;
R3 est un atome d'hydrogène, un groupe alkyle en C1 à C6,
aryle, alkylaryle, arylalkyle;
Hal est Cl, F, Br ou I;
p est compris entre 1 et 3, bornes incluses.Thus, the present invention provides novel cyclic compounds of formula I:

or:
R1 is a hydrogen atom or a C1 to C4 alkyl group
C6, C1 to C6 alkenyl, C6 to C10 aryl, alkylaryl
or C7 to C4 arylalkyl
R2 identical or different from R1, is a hydrogen atom
or C1-C6 alkyl, C1-C6 alkenyl,
C6-C10 aryl, C7-arylalkyl or arylalkyl
C18;
R3 is a hydrogen atom, a C1-C6 alkyl group,
aryl, alkylaryl, arylalkyl;
Hal is Cl, F, Br or I;
p is between 1 and 3 inclusive.

Preferably, p is about 2. The term "about" is used here statistically. A preferred compound then has the formula:

Preferably, Hal is chlorine.

Preferably, R3 is hydrogen, although any substituted hydrazine may be used in the synthesis of this precursor.

R1 and R2 are preferably C1 to C4 alkyl or alkenyl groups.

 According to one embodiment, R1 and R2 are both methyl while in another particularly preferred embodiment, R1 is methyl and R2 is vinyl.

dénommé en abrégé BC

(V = vinyle) dénommé en abrégé BCV
La présente invention fournit aussi de nouveaux composés cycliques de formule II:

où:
R4 est un atome d'hydrogène ou un groupe alkyle en C1 à
C6, alkényle en C1 à C6, aryle en C6 à C10, alkylaryle
ou arylalkyle en C7 à C18;
R est un atome d'hydrogène ou un groupe alkyle en C1 à
5
C6, alkényle en C1 à C6, aryle en C6 à C10, alkylaryle
ou arylalkyle en C7 à C18;
R6 est un atome d'hydrogène, un groupe alkyle en C1 à C6,
aryle, alkylaryle, arylalkyle. Two compounds are particularly preferred. Their formulas can be represented globally by (Ia) and (Ib)

abbreviated as BC

(V = vinyl) abbreviated as BCV
The present invention also provides novel cyclic compounds of formula II:

or:
R4 is a hydrogen atom or a C1 to C4 alkyl group
C6, C1 to C6 alkenyl, C6 to C10 aryl, alkylaryl
or C7 to C18 arylalkyl;
R is a hydrogen atom or a C1 to C4 alkyl group
5
C6, C1 to C6 alkenyl, C6 to C10 aryl, alkylaryl
or C7 to C18 arylalkyl;
R6 is a hydrogen atom, a C1-C6 alkyl group,
aryl, alkylaryl, arylalkyl.

This latter compound is derived from the compound of formula I, wherein p would be virtually equal to about 4, and where the extreme Si groups would be absent, particularly in the case where R4 = R5 = Me.

Preferably, R6 is hydrogen.

Preferably, R4 and R5 are C1-C6 alkyl and alkenyl groups
According to a preferred embodiment, R1 is a methyl group, R2 is a vinyl group.

A particularly preferred compound is the compound of formula (IIa) below:

<tb><SEP> Me <SEP> V <SEP> Me <SEP> V <SEP> Me <SEP> V <SEP> Me <SEP> V
<tb><SEP> If <SEP> If <SEP> If <SEP> If
<tb> HN <SEP> N <SEP> / <SEP> N <SEP> / <SEP> N <SEP><<SEP> NH
<tb> I <SEP> N <SEP> N <SEP> I
<tb> HN <SEP> N <SEP> N <SEP> N <SEP> NH
<tb><SEP> If <SEP>Si'f<SEP> If <SEP> / e
<tb><SEP> Si
<tb><SEP> N <SEP> N
<tb><SEP> Me <SEP> V <SEP> Me <SEP> V <SEP> Me <SEP> V <SEP> Me <SEP> V
<tb><SEP> (IIa) <SEP> where <SEP> V <SEP> means <SEP> vinyl
<tb><SEP> named <SEP> in <SEP> abbreviated <SEP> CCV
<Tb>
These compounds of formula (I) or (II) are obtained by reaction of a halosilane of formula :: R1R2Si (Hal) 2 with a hydrazine HR3N2H2, in the presence of a tertiary amine, preferably NEt3. It is moreover the quantity of amine present which directs the reaction preferentially towards the compound of formula (I) or (II). A solvent is usually used, preferably it is chloroform. The temperature is from 0 to 25, preferably from -10 to + 30 ° C.

The reaction scheme is as follows:

In order to obtain the compound of formula (I), b is advantageously less than 2, preferably about 1. The number of moles of hydrazine a varies to a large extent, and is between 0.5 and 1. The number of mol of halosilane is taken as 1.

In order to obtain the compound of formula (II), b is approximately equal to 2. The number of moles of hydrazine is between 0.8 and 1. The number of moles of halosilane is taken to be 1.

 The compounds of formulas (I) and (II) above are useful as precursors of Si3N4. Indeed, a pyrolysis of the product, CCV for example, leads to a ceramization rate of about 70t. In parallel, the compounds of formula (I), insofar as they still contain Si-Hal reactive bonds, are advantageously converted into polymers. These polymers are obtained by reaction of the products (I) with appropriate reagents; they are then in turn pyrolyzed with ceramization rates of the order of 70%.

The compounds of formula (II) can be pyrolyzed in
Si3N4, by treatment at a temperature between 200 ° C and 1000 ° C, for a period of 8 to 14 hours. This process is another object of the present invention.

ou:
R1, R2 et R3 et p ont les significations ci-dessus;
x vaut 1 ou 2;
R' est un atome d'hydrogène, un groupe alkyle en C1 à C6,
aryle, alkylaryle, arylalkyle. Thus, the present invention also relates to these intermediate polymers of formula (III):

or:
R1, R2 and R3 and p have the above meanings;
x is 1 or 2;
R 'is a hydrogen atom, a C1-C6 alkyl group,
aryl, alkylaryl, arylalkyl.

 n is the degree of polymerization.

Preferably, R 1, R 2, R 3 and p have the preferred meanings as defined above.

Preferably, R 'is a hydrogen atom or a C1-C4 alkyl group.

où:
R' est un atome d'hydrogène ou un groupe alkyle en C1 à
C
4;
R1 et R2, identiques ou différents, sont un groupe alkyle ou
alkényle en C1 à C4.Thus, a preferred polymer has the formula (IIIa):

or:
R 'is a hydrogen atom or a C1 to C4 alkyl group
C
4;
R1 and R2, identical or different, are an alkyl group or
C1 to C4 alkenyl.

Particularly preferred compounds are the polymers of formulas (IIIb), (IIIc) and (IIId):

 The above polymers are obtained by reacting the compounds of formula (I) with the optionally mono or di-substituted hydrazine, or an optionally monosubstituted amine.

This reaction takes place, for example, at room temperature for a few hours. The reaction is carried out again in the presence of a tertiary amine, preferably NEt3, and in a solvent advantageously chloroform. The reaction can also be carried out with a dihalo silane containing different groups R 1 and R 2, for example more reactive.

The compounds of formula (III) can be pyrolyzed in
Si3N4 by treatment at a temperature between 200 and 1000 ° C for a period of 8 to 14 hours The pyrolysis process using new starting materials is yet another subject of the invention.

 The present invention is now described in more detail with the aid of the following examples given for illustrative and non-limiting purposes.

EXAMPLES
Example 1 - Synthesis of BC
In 200 ml of chloroform, 10.6 g (0.0815 mol) of Me2SiCl2 and 8.3 g (0.0815 mol) of NEt3 are introduced. The equimolar solution is cooled to 0 C. One equivalent of hydrazine (2.61 g, 0.0815 mol) is rapidly added over a short period (approximately 2 minutes). The resulting solution is stirred for 30 minutes at 0 ° C. and then brought to room temperature and left overnight with stirring. The product yield BC is 88%, based on the starting silane. The product is in the form of a thick oil.

Example 2
The procedure is as in Example 1, but with 0.85 equivalents (7.1 g, 0.0693 mol) of NEt3 and 0.5 equivalents (1.3 g, 0.04075 mol) of N2H4. . The yield of product-BC is 70% relative to the silane.

Example 3 - BCV Synthesis
The procedure is as in Example 1, but with Me (H 2 C = CH) SiCl 2 (11.57 g) in place of Me 2 SiCl 2.

The yield is 90% relative to the silane. The product is in the form of a viscous oil.

Example 4
The operation is carried out under the same conditions as in Example 3, but with 0.85 equivalents (7.1 g, 0.0693 mol) of NEt3 and 0.5 equivalents (1.3 g, 0.04075 mol) of hydrazine. The yield of BCV product is 77% relative to the silane.

Example 5 - Synthesis of CCV
The procedure is as in Example 1, but with Me (H 2 C = CH) SiCl 2 (11.57 g) and two equivalents (16.6 g, 0.163 mol) of NEt 3. The product obtained, with a yield of 90% relative to the silane, is in the form of a glue.

Example 6
The procedure is as in Example 5, but with 0.8 equivalents (2.09 g, 0.0652 mol) of hydrazine. The yield of CCV product is 93% relative to the silane.

Example 7
The CCV product is pyrolyzed at about 950 C under an argon inert atmosphere. The amount of residue, or ceramization rate is about 70%.

Example 8
A mixture of: one equivalent of BC, one equivalent of hydrazine, one equivalent of the following is reacted in chloroform at room temperature and for 10 hours
Me (H2C = CH) SiCl2, and four equivalents of NEt3. A white solid is obtained which leads to Si3N4 by pyrolysis.

Example 9
In a chloroform mixture, at room temperature and for 14 hours, a mixture of: one equivalent of
BCV, an equivalent of N2H4 in the presence of two equivalents of
NEt3. A white glue (yield 90%) is obtained which is transformed into a soluble glassy solid by heating at 200 ° C. for 1 hour under vacuum. There is a slight loss of weight (about 5).

 Pyrolysis of the solid obtained leads to a percentage of ceramization of 71.4%.

Example 10
A mixture of: one equivalent of the following is reacted in chloroform at room temperature and for 2 hours
BCV, an equivalent of n-PrNH2, two equivalents of NEt3. A thick oil is obtained which, after heating at 200 ° C. under vacuum for 2 hours, becomes a white solid.

Example 11
An equivalent of BCV with an excess of NH 3 is reacted in chloroform at 0 ° C. for 25 minutes. NH3 is bubbled into the chloroform solution of BCV. The mixture is stirred for a further 25 minutes at 0 ° C. and is then allowed to return to ambient temperature over a period of 30 minutes. It is filtered to remove NH4Cl hydrochloride. The solvent is removed under vacuum. A glue is obtained which, after heating at 220 ° C. under vacuum for 2 hours, is transformed into an insoluble glassy white solid.

 Pyrolysis of this solid leads to a ceramization rate of 70.6%.

 Thus good ceramization yields are obtained without having to use MeSiCl3.

Claims (7)

1.- Compound of formula:

 in which:  R1 is a hydrogen atom or a C1 to C4 alkyl group  C6, C1 to C6 alkenyl, C6 to C10 aryl, alkylaryl  or C7 to C18 arylalkyl;  R2 identical or different from R1, is a hydrogen atom  or C1-C6 alkyl, C1-C6 alkenyl,  C6-C10 aryl, C7-arylalkyl or arylalkyl  C18;  R is a hydrogen atom, a C1 to C6 alkyl group,  3  C6-C10 aryl, C7-C18 alkylaryl or arylalkyl;  Hal is F, Cl, Br;  p is between 1 and 3 inclusive.  2. The compound according to claim 1, wherein p is equal to about 2, said compound then having the formula:

 3. The compound of claim 1 or 2, wherein R1 and R2, which may be identical or different, are a C1-C4 alkyl or alkenyl group.  4. The compound of claims 1 to 3, wherein R3 is a hydrogen atom.  5. The compound of claims 1 to 4, wherein Hal is chlorine.  6. A compound according to claims 1 to 5, of formula:

 7. A compound according to claims 1 to 5, of formula:

 where V means vinyl.