FR2673201A1 - Inorganic fibres based on silicon, carbon, nitrogen and oxygen - Google Patents

Abstract

Inorganic fibres essentially based on silicon, carbon, nitrogen and oxygen, characterised in that their elemental composition expressed as atomic ratios is the following: - the atomic ratio r1 corresponding to the number of nitrogen atoms over the number of silicon atoms is between 0.01 and 0.6, - the atomic ratio r2 corresponding to the number of carbon atoms over the number of silicon atoms is between 0.01 and 2, - the atomic ratio r3 corresponding to the number of oxygen atoms over the number of silicon atoms is between 0.01 and 0.15. Use of the fibres as reinforcing agents in composite materials with a glass, metal or ceramic matrix.

Description

INORGANIC FIBERS BASED ON SILICON,
OF CARBON, NITROGEN AND OXYGEN
The present invention relates to novel inorganic fibers essentially based on silicon, carbon, nitrogen and oxygen.

 It also relates to a process for obtaining such fibers.

 Finally, it relates, as an application, to the use of these fibers in the manufacture of composite materials whose matrix consists of glass, metal or ceramic.

 Inorganic fibers are well known materials and are generally used as reinforcing materials.

 Many inorganic fibers are thus known essentially based on silicon, carbon, nitrogen and oxygen.

However, these fibers have the disadvantage of losing their mechanical properties when they have been treated at high temperatures, generally at temperatures above 1200 C.

 The object of the invention is therefore to provide new inorganic fibers having a maintenance of their mechanical properties after treatment at high temperatures.

 This and other objects are achieved by the present invention which relates in fact to inorganic fibers essentially based on silicon, carbon, nitrogen and oxygen, characterized in that their elementary composition expressed in atomic ratios is as follows: the atomic ratio r 1 corresponding to the number of nitrogen atoms over the number of silicon atoms is between 0.01 and 0.6, the atomic ratio r 2 corresponding to the number of carbon atoms over the number of atoms silicon is between 0.01 and 2, the atomic ratio r3 corresponding to the number of oxygen atoms on the number of silicon atoms is between 0.01 and 0.15.

 The fibers according to the invention preferably correspond to r1 between 0.1 and 0.6, r2 between 0.5 and 1.5 and r3 between 0.01 and 0.1.

 Even more preferably, R 1 is between 0.4 and 0.55, R 2 is between 0.7 and 1.3 and R 3 is between 0.03 and 0.07.

 Thus, it is from the very composition of the fibers according to the invention that the purpose indicated above is obtained.

 The fibers according to the invention are obtained in particular by a process, which will now be described, constituting the second object of the present invention.

et de 75 à 25 % molaire de motifs de formule

formules dans lesquelles R1 et R2, identiques ou différents, représentent un atome d'hydrogène ou un radical hydrocarboné substitué ou non, saturé ou insaturé ;
2. Thermolyse des copolymères obtenus en 1. à des températures comprises entre 250 et 5000C sous atmosphère inerte ;
3. Filage des polymères obtenus en 2. This process for obtaining inorganic fibers essentially based on silicon, carbon, nitrogen and oxygen is characterized in that it consists of five stages
1. Synthesis of copolymers consisting of 10 to 90 mol% of units of formula

and from 75 to 25 mol% of units of formula

formulas in which R1 and R2, identical or different, represent a hydrogen atom or a substituted or unsubstituted hydrocarbon radical, saturated or unsaturated;
2. Thermolysis of the copolymers obtained in 1. at temperatures of between 250 and 5000 ° C. under an inert atmosphere;
3. Spinning of the polymers obtained in 2.

4. Crosslinking the fibers obtained in 3. by treatment with γ-radiation or electronic radiation under high vacuum or, preferably, under a neutral atmosphere at a temperature below the softening point of the spun polymer, preferably at room temperature;
5. Heat treatment of the fibers obtained in 4. in a non-oxidizing atmosphere, provided that when the temperature reached is greater than about 13000C, preferably greater than or equal to 14000C, one operates under a nitriding atmosphere.

et de 90% à 10% molaire d'un silane de formule
(R2)2sicl2 (2) formules dans lesquelles R1 et R2 ont la définition donnée ci-dessus, R représente un atome d'halogène, de préférence le chlore.The copolymers consisting of the units of formulas (A) and (B) are especially obtained by the process described in the patent
EP-A-0296028 and more specifically corresponds to the copolymerization of 10 to 90 mol% of a disilazane of formula

and 90% to 10 mol% of a silane of formula
(R 2) 2sicl 2 (2) wherein R 1 and R 2 are as defined above, R is a halogen atom, preferably chlorine.

 Preferably, the copolymers synthesized during step 1.

consist of 25 to 75 mol% of units of formula (A) and 75 to 25 mol% of units of formula (B).

 According to a preferred embodiment of the process of the invention, R 1 and R 2 represent the methyl radical.

 By inert atmosphere in step 2. is meant according to the invention, an atmosphere inert vis-à-vis reagents present such as argon or nitrogen.

 The shaping of the polymers consists according to the invention in a spinning, and this by any means known per se, and in particular by a conventional die after melting or dissolution in a solvent of the polymer.

By high vacuum during step 4. according to the invention, the vacuum is understood whose pressure is at most equal to 1.33.10-2
Pascal.

 According to the invention, the neutral atmosphere in step 4 is understood to mean an atmosphere in which no gas present is capable of reacting with the reactants and the treating rays, such as in particular argon.

 The necessary dose of rays to crosslink the fibers, that is to say so that the fibers retain their physical integrity during the heat treatment of step 5., depends on the operating conditions. To fix the ideas, the necessary dose of rays is greater than or equal to 300 megarad (Mrad.).

 By non-oxidizing atmosphere is meant according to the invention any atmosphere free of oxygen and water. The operation is preferably carried out under a nitrogen or argon atmosphere.

 By nitriding atmosphere is meant according to the invention any atmosphere containing nitrogen atoms, such as in particular nitrogen or ammonia.

 Depending on the temperatures reached during the heat treatment of step 5 of the process according to the invention, the microstructure of the fibers varies.

 Thus, when the temperature reached in the heat treatment is less than about 15000C, the fibers according to the invention consist of an amorphous phase.

 When the temperature reached in the heat treatment is greater than about 15000C, the fibers according to the invention consist of an amorphous phase and ultrafine crystalline particles of -SiC whose average diameter does not exceed 5 nm and, more specifically, does not exceed not 3 nm.

 It is known that crystalline particles of the p-SiC type are one of the factors that causes fiber degradation at high temperatures (loss of mechanical properties). However, in the case of the present invention, the appearance of these crystalline particles is late (at about 15000C) and they have an average diameter not exceeding 5 nm.

 The pressure of step 5 of the process is, in general, the atmospheric pressure.

 It may, however, be advantageous to operate at pressures above atmospheric pressure.

 Quite unexpectedly, the Applicant has found that the general elemental composition of the fibers according to the invention relating to the essential elements mentioned above does not depend on the maximum temperature reached during the heat treatment of step 5. the operating conditions indicated above. This composition depends mainly on the copolymer obtained in step 1 of the process according to the invention.

 Depending on the operating conditions of the process for obtaining the fibers according to the invention, the fibers may have impurities in a small amount and hydrogen. The fibers may have, besides silicon, carbon, nitrogen and oxygen, hydrogen whose atomic ratio r4 of the number of hydrogen atoms on the number of silicon atoms is at most 0.4, and preferably at most 0.1.

 The fibers according to the invention find an important application in composite materials with a glass, metal or ceramic matrix, in which they are used as reinforcing agents.

 The following examples illustrate the invention without limiting its scope.

 In these examples, the elastic modulus E in gigapascal (GPa) was measured according to a method analogous to ASTM D 3379-75 on unit filaments at ambient temperature.

 The tensile strength tr also referred to as tensile strength is measured in megapascal (MPa) according to a method analogous to ASTM D 3379-75 on a single filament of 10 mm in length.

 The value of tr indicated is that obtained by making the arithmetic mean on 20 specimens, taken at random, at room temperature.

 Mw is the average molar mass by weight.

 THF is tetrahydrofuran.

EXAMPLE 1
In a 500 ml flask equipped with a magnetic stirrer, an isobaric dropping funnel, an inlet of inert gas (argon or nitrogen) and a condenser, are introduced toluene and sodium.

 The mixture is heated to reflux.

 When the dispersion of the molten sodium is sufficiently fine, the mixture dimethyldichlorosilane (50 mol%) and (Me 2 ClSi) 2 NH (50 mol%) are introduced dropwise.

 After a few hours of reflux, the mixture is allowed to cool under an inert atmosphere and is sintered in a glove box under an inert atmosphere. A clear and colorless solution is thus obtained.

The remaining blue solid is taken up in toluene and then filtered (operation carried out twice). The two filtrates thus obtained are added to the first, the whole is concentrated under reduced pressure. After distillation and drying, a copolymer soluble in most of the solvent is obtained.

 The polysilazane thus obtained is thermolysed by progressive heating of the flask using a fluidized sand bath to a temperature of 4000 ° C. A polycarbosilazane is obtained CMw = 15200).

 This polycarbosilazane is then melt-spun such that a continuous monofilament of 25 μm in diameter is produced.

 This monofilament is cut every 50 mm.

 These monofilaments of 50 mm polycarbosilazane are introduced in a dry container, under argon, in aluminum containers. These containers are sealed in the glove box and are then introduced into a chamber irradiated by a 60 Co source with a dose of 350 Mrad. at room temperature.

 After irradiation, the monofilaments are subjected to a heat treatment up to = 8500C under an argon atmosphere (rate of rise in temperature: 50 C / hour, plateau of 15 minutes at 8500C).

 The monofilaments thus treated are no longer sensitive to air and moisture.

 The yield is 80% by weight.

EXAMPLE 2
The monofilaments obtained in Example 1 are subjected to heat treatments under a nitrogen atmosphere up to different temperatures: t1 = 1000 ° C., t2 = 12000 ° C. t3 = 14000C and t4 = 16000C (rate of rise in temperature: 600C / minute, plateau of 15 minutes at respectively t1, t2, t3 or t4).

The results of Examples 1 and 2 are collated in the following Tables 1 and 2

<tb><SEP> to <SEP> t1 <SEP> t3 <SEP> t4
<tb> r1 <SEP> 0.46 <SEP> 0.46 <SEP> 0.46 <SEP> 0.48
<tb> r2 <SEP> 0.93 <SEP> 0.93 <SEP> 0.93 <SEP> 0.98
<tb> r3 <SEP> 0.05 <SEP> 0.05 <SEP> 0.05 <SEP> 0.05
<tb> j <SEP> microstructure <SEP> I <SEP> amorphous <SEP> j <SEP> amorphous <SEP> j <SEP> amorphous <SEP> j <SEP> amorphous <SEP> j <SEP>
<tb> ssSiC <SEP> (3nm)
<Tb>
Table 1
Table 1: Elemental composition and microstructure of the monofilaments obtained in Examples 1 and 2.

<Tb>

<SEP> I <SEP> I <SEP> I <SEP> I
<tb><SEP> I <SEP> t1 <SEP> I <SEP> t2 <SEP> | <SEP> t3 <SEP> I <SEP> t4 <SEP> 1
<tb> E <SEP> 185 <SEP> 215 <SEP> 215 <SEP> 220
<tb> (GPa) <SEP>
<tb> tr <SEP> 2400 <SEP> 2500 <SEP> 2250 <SEP> 2200
<tb> (MPa)
<Tb>
Table 2
COMPARATIVE EXAMPLE 3
The monofilaments obtained in Example 1 are subjected to heat treatments under an argon atmosphere up to t3 = 14000C.

 The breaking stress of the monofilaments thus obtained is equal to 1900 MPa.

 On the surface of these monofilaments there is also the onset of decomposition.

Claims (12)

1) Inorganic fibers mainly based on silicon, carbon,  of nitrogen and oxygen characterized in that their composition  elementary expressed in atomic ratios is as follows  . the atomic ratio r1 corresponding to the number of nitrogen atoms  on the number of silicon atoms is between 0.01 and 0.6,  . the atomic ratio r2 corresponding to the number of carbon atoms  on the number of silicon atoms is between 0.01 and 2,  the atomic ratio r3 corresponding to the number of oxygen atoms  the number of silicon atoms is between 0.01 and 0.15. 2) fibers according to claim 1, characterized in that  rl is between 0.1 and 0.6,  r2 is between 0.5 and 1.5 and  r3 is between 0.01 and 0.1. 3) Fibers according to claim 2, characterized in that  rl is between 0.4 and 0.55,  r2 is between 0.7 and 1.3 and  r3 is between 0.03 and 0.07. 4) fibers according to any one of the preceding claims,  characterized in that they consist of an amorphous phase. 5) Fibers according to claim 4 characterized in that  have ultrafine crystalline particles of ss-SiC whose  average diameter does not exceed 5 nm. 6) Fibers according to claim 5 characterized in that the  ultrafine crystalline particles of ss-SiC have a mean diameter not  not exceeding 3 nm. 7) Process for obtaining inorganic fibers essentially based  of silicon, carbon, nitrogen and oxygen is characterized in that  that it consists of five steps  1. Synthesis of copolymers consisting of 10 to 90 mol% of units  Formula

  and from 75 to 25 mol% of units of formula

 14000C, it operates under a nitriding atmosphere.  greater than about 13000C, preferably greater than or equal to  non-oxidising, provided that when the temperature reached is  5. Heat treatment of the fibers obtained in 4. under atmosphere  preferably at room temperature;  less than the softening point of the spun polymer, of  preferably under a neutral atmosphere at a temperature  y or under high vacuum electronic radiation or,  4.Reticulation of the fibers obtained in 3. by radiation treatment  3. Spinning of the polymers obtained in 2.;  between 250 and 5000C under an inert atmosphere;  2. Thermolysis of the copolymers obtained in 1. at temperatures  substituted or unsubstituted, saturated or unsaturated;  represent a hydrogen atom or a hydrocarbon radical  formulas in which R1 and R2, identical or different, 8) Method according to claim 7 characterized in that the synthesis  of Step 1. corresponds to the synthesis of copolymers consisting of  25 to 75 mol% of units of formula (A) and 75 to 25 mol% of  patterns of formula (B). 9) Method according to one of claims 7 and 8 characterized in that  the inert atmosphere of step 2 is nitrogen or argon. 10) Method according to one of claims 7 to 9 characterized in that  the neutral atmosphere of step 4 is argon. 11) Method according to one of claims 7 to 10 characterized in that  the pressure of step 5. is equal to the atmospheric pressure,  preferably, it is greater than the atmospheric pressure. 12) Use of the fibers according to one of claims 1 to 6 as  as reinforcing agents in matrix composite materials  glass, metal or ceramic.