JPH0543270A - Glass-ceramic li-al-si-o composition and its preparation - Google Patents

Abstract

PURPOSE: To provide a glass-ceramic composition which has a low thermal expansion coefficient and is reinforced by fibers.

CONSTITUTION: A gel is prepared by performing hydrolysis and polycondensation to a metal raw material compound in a solvent. The metal raw material is composed of a silicon alcholate, an aluminium alcholate, a lithium compound, a magnesium compound, BaO, Nb₂O₅ and BaO. In the prepared gel, the solvent is removed. Next, the gel is dehydrated and oxidized under heat treatment. Then, compression and ceramicization treatments are applied. As a result, the composition substantially becomes the form of ceramic solid solution like β-spodumene, cordierite and mullite.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to glass-ceramic compositions based on silica, alumina and lithium oxide. The lithium oxide can be completely or partially replaced with magnesium oxide.

[0002]

2. Description of the Prior Art Compositions of this type have hitherto been obtained by melting oxides and / or carbonates. Several years ago, another method was discovered, called "sol-gel." This method is based on a hydrolysis reaction and a polycondensation reaction in a dissolution medium of a precursor compound, in which at least aluminum and a silicon compound of the precursor compound are alcoholates in a sol state, and then converted into a gel state. After that, the temperature was raised and heat treatment was performed.

This sol-gel method is superior to conventional methods in that
There are various advantages. The product is purer and more homogeneous, and is a more compact composition with no evaporation loss. Also, since the applied temperature is low, energy consumption is low. The composition obtained is
It is crushed if necessary to remove lumps, producing a large specific surface area and highly activated powder. Then, in order to facilitate production, a dense fragment having a low porosity or a porosity of 0 is produced.

It is an object of the present invention that the glass-ceramic composition obtained by the sol-gel process has a low coefficient of thermal expansion and allows large or abrupt temperature changes (temperature shock) when made into dense pieces. It is to provide things. Another object of the invention is to provide a composition of this type which is particularly suitable for forming a matrix of fiber reinforced ceramic composition material. Hereinafter, in the specification, unless otherwise specified, the numbers used after the element symbols represent the numbers of the respective elements, and the numbers used after the mathematical formulas and units represent the “power” numbers. ..

[0005]

According to the present invention, the main component is SiO 2.
Provided is a composition which is 2, Al2O3, Li2O and / or MgO and is obtained by a sol-gel method from silicon alcoholates, aluminum alcoholates, lithium compounds and / or magnesium compounds. This composition is characterized in that it is substantially in the form of a ceramic solid solution such as β-spodumene, cordierite and mullite.

When the glass-ceramic composition is substantially in the form of such a solid solution, the coefficient of thermal expansion of the composition is low, and it also undergoes a phase transition except that the glass phase is transformed by increasing temperature. I knew it wouldn't happen. The glass phase remains in the solid solution but has a low coefficient of thermal expansion as a whole. Also, the low coefficient of thermal expansion and other properties are suitable for synthetic materials with fiber reinforcement,
Exhibits good thermochemical properties.

[0007] The main components of β-Yupite, Quinseite and Mullite are Al2O3 ・ Li2O ・ 4SiO2,2MgO ・ 2Al2O3 ・ 5SiO2,
It is 2SiO2 / 3Al2O3. Since they are solid solutions, compositions of these phases are of course obtained from these components.

In addition to the above main components, the composition of the present invention comprises
It contains at least one component selected from BaO, Nb2O5 and B2O3, but should not be limited to these components. Such additives, depending on the function of the intended application,
It is particularly effective in improving certain properties of the composition and / or the synthetic material obtained from this composition.

The production of the substance according to the invention depends on various factors. One, of course, is the chemical constituent of the composition. This chemical constituent should be compatible with the main constituent and another is the stability of at least one solid solution. The person skilled in the art can easily determine from the phase diagram of the system in question whether the components used are suitable in this respect.

Li2O is ax-b moles, SiO2 is c moles, BaO is b moles, and MgO per mole of Al2O3.
Are a (1-x) moles, where a, b, c and x are 0.4 to 1, 0 to 0.1, 3 to 8 and 0, respectively.
It has been found that compositions in the range from 1 to 1 are particularly suitable.

The material according to the present invention prevents the amorphous glass phase from remaining and prevents the crystal phase such as cristobalite from being damaged. Obtained by a fully converting manufacturing process.

Therefore, the present invention proposes a method for producing a composition as described above. The method is as follows: a) preparing a gel by hydrolyzing and polycondensing a raw material metal in a solvent solution, b) removing the solvent, c) crushing the gel as necessary, and d) heating. This comprises dehydration and oxidation of the gel with compression and ceramisation (converting the gel into a ceramic).

The raw materials used are preferably silicon alcoholates, aluminum alcoholates, lithium inorganic compounds and / or magnesium inorganic compounds. Barium and niobium are added as needed. Tetraethyl orthosilicate is particularly preferable among silicon alcoholates, aluminum second butoxide (sec-butoxide) is preferable among aluminum alcoholates, lithium nitrate is particularly preferable among lithium inorganic compounds, and magnesium inorganic compound Among them, magnesium nitrate is particularly preferable, barium nitrate is particularly preferable among barium, and niobium chloride is particularly preferable among niobium.

It is preferable to divide the step a into the following steps. a1) The silicon alcoholate is previously hydrolyzed with a part of the entire hydrolyzed water, and a2) the product of the phase a1 is reacted with other raw materials and the remaining hydrolyzed water. Also, the step d can be divided into two steps. d1) oxidize by raising the temperature to about 500 ° C. in air over a period of several hours, and d2) first compress and ceramize at a temperature just above the melting temperature of the composition.

The dehydrated and oxidized phases, after grinding, produce powders with a large specific surface area. This powder is very active and can be compacted easily and effectively.

This compaction is achieved by compacting the composition in powder form during the ceramization process.

When the debris exhibits a glassy phase after compaction and ceramization, this phase is converted to a ceramic solid solution by a second heat treatment just below the melting temperature of the composition.

In order to obtain a fiber-reinforced synthetic material with a refractory ceramic matrix, before compression heat treatment,
Fibers are incorporated into the powder of the glass-ceramic composition. This operation is carried out in particular on fibers based on silicon carbide.

When the silicon carbide fibers contain suitable amounts of oxygen and carbon on their surface, the glass-ceramic composition preferably contains at least one compound other than SiO2, Al2O3, Li2O, for example Nb2O5. Nb2O5
Suppresses the composition from adhering to the fibers.

Other features and advantages of the present invention will be apparent from the detailed description of several examples set forth below.

First, a method for preparing a gel will be described. material
Only the type of precursor and its amount depend on the components of the composition prepared between the examples.

These raw materials are tetraethyl orthosilicate Si (OC2H5) 4 (TEOS) aluminum second butoxide Al (OCH (CH3) C2H5) 3.
(ASB) Lithium nitrate LiNO3 and, if necessary, magnesium nitrate Mg (NO3) 2.6H2O 4 per weight of water
Barium nitrate Ba (NO3) 2 Niobium chloride NbCl5 containing 2.2%.

The solvent of choice is isopropanol, which is concerned with the raw material and the hydrolyzed water.

Nitric acid is added at 70% by weight, based on the aqueous solution. Nitric acid acts to prevent precipitation of AlOOH as a result of hydrolysis and is involved in the formation of micro-porous gels that exhibit high activity during sintering.

Isopropanol is used in an amount of 10 mol per 1 mol TEOS and nitric acid is based on 1 mol TEOS.
Used in an amount of 0.2 mol.

The amount of water to be hydrolyzed in advance is 1 mol based on 1 mol of TEOS, including those contained in isopropanol and nitric acid. The remaining amount of hydrolyzed water is 3 mol per 1 mol ASB and 4 mol per 1 mol TEOS, including those contained in isopropanol and optionally added magnesium nitrate. ..

TEOS, half the solvent, pre-hydrolyzed water,
And nitric acid, equipped with heating mantle, stirrer and distillation column 3
It was charged into the neck reactor while stirring. The mixture is 30
Refluxed for min (82 ° C).

The purpose of this pre-hydrolyzing phase is TEOS,
When SBA and water are added at the same time, the activity of TEOS is low, so that the hydrolysis of ASB accompanied by the precipitation of ALOOH does not occur in advance. By this phase, TEOS is partially hydrolyzed according to the following reaction formula, and Si (OR) 4 + H2O → Si (OR) 3OH + ROH partially hydrolyzed products are Reacts with raw materials.

At the end of the above 30 minutes, the temperature of the reactor was reduced by 10 ° C. to finish the reflux. Then fluidized AS diluted with a small amount of isopropanol
A small amount of B was added (4-5 parts). Then the reflux is 4
It lasted 5 minutes. Then, the heating was stopped, and lithium nitrate dissolved in the remaining isopropanol and, if necessary, magnesium nitrate were added while continuing stirring.

When the mixture is at room temperature, hydrolyzed water is added and, if necessary, barium nitrate is added for another 5 minutes to 10 minutes so that a homogeneous sol is obtained.
It was stirred for a minute. The mixture was then placed in a sealed container. The gel was formed at 45 ° C. for several hours or at room temperature overnight. After the gelation was complete, the container was opened and kept in the oven at 90 ° C. for 24 to 48 hours to evaporate the solvent. The gel is then optionally crushed to reduce agglomeration and placed in a circulating oven (th
In a rough-circulation oven) it was subjected to an oxidation step to produce a glass-ceramic composition.

The following thermal cycle is particularly suitable for this step: Heating from room temperature to 250 ° C at 3 ° C / min and from 250 ° C to 500 ° C at 10 ° C / min. 250 ° C to 500 ° C
Maintained at 50 ° C intervals for up to 4 hours. Then, cool to room temperature at a rate of 20 ° C. per minute. However, this cycle can be simplified by omitting the temperature maintenance step. This produced a very active amorphous powder with a specific surface area of about 300 square meters / g.
This powder was successfully redispersed in a mill containing zirconium oxide beads, the agglomerates of individual grains were crushed and sieved so that only grains with a diameter of 50 μm or less remained.

[0032]

【Example】

Example 1: Composition A Li2O-Al2O3-SiO2 gel was prepared, followed by dehydration and oxidation. The resulting composition was ground and screened as described above. The amount of raw material used was 0.45 Li as the final component.
It corresponded to 2O-Al2O3-SiO2. The obtained powder was subjected to compression and ceramization heat treatment in the solid state in order to obtain a compressed ceramic sintered piece. It was then placed in a vacuum to completely remove the water and the powder was pressed at a pressure of 3.5 MPa. The following heat treatment was applied. It was heated to 500 ° C. at 20 ° C./min and held at this temperature for 60 minutes. 500 ° C to 1300 ° C
Was heated at 10 ° C. per minute. On the way, it was maintained at 780 ° C. for 20 minutes. Then, it was cooled to room temperature at 30 ° C. per minute.

The product obtained has a density of 2.5 and a closed porosity measured by immersion in water.
) Was 1%. The composition consists of β-Yupite and mullite and has an average expansion coefficient between 20 ° C. and 1000 ° C.

[Equation 1] Is.

The fracture stress σ, elastic deformation rates E and K 1 C measured by the three-point bending test in the polynomial standard of Paris are as follows.

[Equation 2]

[Equation 3]

[Equation 4] At σ and E, a force was applied at right angles to the pressing direction of the powder. The support interval is 16 mm, and the ratio of length to thickness is 15. In K1 C, a force was applied at right angles to the pressing direction. The support spacing is 15 mm, the notch depth is 0.9 mm, and its width is 70 μm. The height to notch ratio is 4 and the support to height ratio is 4.17. The descent rate is 0.2 mm per minute. These tests are the same in the following examples unless otherwise specified.

Example 2: Composition Li2O-Al2O3-SiO2-Nb2O
5 The amount of reactants was the same as in Example 1 and niobium chloride was added so that the final product contained 3% by weight of Nb2O5. The compression and ceramization heat treatment was performed above the melting temperature of the composition. Nb2O5 has the morphology of a solid solution and the homogeneous recrystallization properties after partial and total melting of the crystalline phase produced after the first heat treatment without the addition of nucleic acid agents. It is necessary to completely remove this water beforehand in order to prevent the formation of pores due to the presence of the remaining water that was introduced during the melting.

Therefore, after dehydration and oxidation, the product is 5
Treated with ammonia at 00 ° C (milled and screened as needed). The powder was first kept at 320 ° C. under a nitrogen atmosphere for 4 hours in order to remove the water absorbed on the surface. Then ammonia was sprayed on. Then, in order to replace the residual OH groups with nitrogen compounds, the temperature was raised to 600 ° C. at a rate of 1 to 3 ° C. per minute. Heating under a nitrogen atmosphere was continued at a rate of 10 ° C per minute up to 1200 ° C. The powder was then placed in a press and heated to 1000 ° C at a rate of 10 ° C per minute. At this temperature, mechanical pressure of 16-35 MPa was applied while heating the powder at a rate of 5 ° C./min. Meanwhile, the thickness of the product is
nsducer).

When the temperature reaches 1330 ° C., the decrease in thickness indicates the onset of compression. The temperature was kept constant for 3 minutes, for example, until the thickness became stable. The viscosity of the composition is

[Equation 5] Met. The press was stopped and the product was cooled to ambient temperature.

The product obtained had few pores. It consisted mainly of Yu pyroxene and mullite with a small amorphous phase. Infrared spectroscopy showed the absence of water and the composition of Example 1 contained 224 ppm water, as determined by the same method. Also, nitrogen was not detected.

The characteristics of this product are

[Equation 6]

[Equation 7]

[Equation 8] And σ and E were measured by the same method as in the example.

As a result of reheating at 1250 ° C. for 5 minutes, the amorphous phase could be eliminated. Then, one having the characteristics of the mathematical formula was obtained.

[Equation 9]

[Equation 10]

[Equation 11]

Example 3: Composition Li2O-Al2O3-SiO2 + Short Fibers Prepared with 5% by volume, 10% by volume and 20% by volume of a three-component material, respectively, and a silicon carbide whisker sold by Sumitomo. ..

Dehydrated and oxidized glass-ceramic powders were prepared as in Example 1 and then dispersed with ultrasonication in an isopropanol bath containing 5% solution of nitric acid to stabilize the suspension. Was made The bath was vigorously stirred and the fibers ultrasonically dispersed in isopropanol were added. The resulting mixture was stirred under ultrasound for a further 15 minutes and then filtered on a filter consisting of glass fibers impervious to particles with a diameter greater than 0.5 μm.

The compression and ceramization process was carried out under the following conditions. 4 at 20 ° C / min in vacuum
The temperature was raised to 50 ° C. and maintained at this temperature for 45 minutes. 16 ° C / min up to 1000 ° C / min under nitrogen atmosphere
Heating was continued while applying a pressure of MPa. Along the way, the temperature was maintained at 780 ° C. for 20 minutes. The temperature was continuously raised to 1300 ° C. at 20 ° C./min under a nitrogen atmosphere, and the pressure at that time was 16 MPa.

The following table shows the properties of the resulting compositional material for a solution of fiber Vf.

[Table 1]

The expansion coefficient when Vf is 20% is 20 ° C.
Between ~ 1000 ° C,

[Equation 12] Met.

Example 4: Composition Li2O-Al2O3-SiO2-BaO
+ Short fibers A glass-ceramic powder was prepared as in Examples 1 and 3. However, the amount of lithium nitrate was reduced and barium nitrate was added so that the composition of the glass-ceramic composition was 0.05BaO-0.4Li2O-Al2O3-3SiO2. The addition of BaO is to prevent the formation of cristobalite and thus stabilize the composition above 1000 ° C. Cristobalite undergoes a phase transition at about 300 ° C. and induces cracks.

A powder / fiber mixture was prepared in the same way as the previous example in an amount of 20% by volume. The compression and ceramization process begins with the melting of the glass-ceramic composition, heating under vacuum at 10 ° C. per minute to 980 ° C., maintaining at 480 ° C. for 30 minutes, 780 ° C. and 980 ° C. for 15 minutes. 16MP under nitrogen atmosphere
It consists of continuously heating from 10 ° C./min to 1325 ° C. while pressurizing with a, maintaining this temperature for 5 minutes, and cooling to normal temperature at 30 ° C./min in a nitrogen atmosphere without applying pressure.

The resulting composition had a relative density of 0.99 (apparent density / density of the fully dense compound) and had excellent compressibility. As a result of X-ray analysis, Yuu pyroxene and mullite were predominant, and an amorphous phase was slightly present. At this stage the material had the following properties:

[Equation 13]

[Equation 14]

[Equation 15]

[Equation 16]

Subsequent heat treatment in air at a temperature of 1280 ° C. reabsorbs the glass phase and results in the absorption of the barium aluminosilicate (defined in ASTM Standard 12-926 under the name hexacelsian).
A new aspect of was revealed. The synthetic material thus treated has the following expansion coefficient between 20 ° C and 1000 ° C.

[Equation 17] And a density of 2.71 and the following notable mechanical properties

[Equation 18]

[Formula 19]

[Equation 20] It was equipped with

Example 5: Composition MgO-Li2O-Al2O3-SiO2
A glass-ceramic powder having the composition + long fibers 0.5MgO-0.5Li2O-Al2O3-4SiO2 was prepared.

The fibers used are long silicon carbide fibers manufactured by Nippon Carbon under product number NLM202 and sold by BROCHIER as product number E2140 bidirectional fibers. The acrylic based fiber coating was removed by dipping the fiber in a mixture containing equal amounts of acetone and isopropanol. The mixture was stirred for 15 minutes every 30 minutes with an ultrasonic bath. The fiber used two baths and was treated for 2 hours in each bath by this method.

Dehydrated and oxidized at 500 ° C. and 50 μm
70 grams of glass-ceramic powder deagglomerated through a No. 1 sieve was mixed with 5 grams of a viscous solution of polymethylmethacrylate in 100 cubic centimeters of chlorobenzene. The resulting suspension was applied to a paintbrush to impregnate the fibrous structure, and after immediate evaporation of the solvent it was assured by the polymer that the powder adhered to the fibers. While weighing, various methods were taken until a quantity of 80-90 mg of powder per square centimeter structure was obtained. 70 x
Five 70 mm sheets were cut from a portion of the tissue thus impregnated and laminated into a graphite mold of the same cross section for compression and ceramicization heat treatment to take place. Heat treatment is 2 minutes per minute under vacuum
The temperature was raised from 0 ° C to 960 ° C to 980 ° C, during which it was maintained at 350 ° C for 15 minutes to remove polymethylmethacrylate, and at 450 ° C for 45 minutes to perform the rearrangement, It was continuously heated at 20 ° C./min to 1310 ° C. under a nitrogen atmosphere, and this temperature was maintained for 5 minutes while applying a pressure of 11 MPa. The pressure was released and free cooling was performed under a nitrogen atmosphere.

The synthetic material obtained had a fiber solution ratio of 36.
%, The apparent density was 2.49 (relative apparent density 0.99). As a result of X-ray analysis, Yuu pyroxene and mullite were predominant, and an amorphous phase was slightly present.

The fracture resistance of a sample having a width of 10 mm and a thickness of 2.38 mm was measured by a three-point bending test at intervals of 50 mm as support points.
It was 0 ± 35 MPa.

The above embodiment does not impose any limiting meaning. Different combinations, or the above characteristics,
In particular, it is possible to change the composition of the glass-ceramic composition, the method of preparation of the gel, the heat treatment of dehydration and oxidation with ceramization, the presence or absence of fibers, and the chemical properties and physical structure. .. Furthermore, the use of silicon carbide fibers from raw materials other than those used in the examples, such as having different surface properties, should also be considered.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location C03C 14/00 6971-4G 27/00 7821-4G (72) Inventor Jihan Huaripou Monfu, France Eliere / Les, F-34980 Route de Mende 203 (72) Inventor Mitsusier Parrier Vouazan-le-Burtonneu, France, F-78960 Residence Chiyante So, Rieu Serpentin 46 (72) Inventor Marie-Elene Litchi F-91300, Avenyu Lamorph Garnier, Matissy, France 10 (72) Inventor Jijan Jame, F-33270, Abriene de la Bell Etoile, Briatsk, France 39

Claims (17)

[Claims] 1. A ceramic composition in which fibers are immersed in a glass-ceramic matrix having SiO2, Al2O3, Li2O as a main component, wherein the matrix is silicon alcoholate, aluminum alcoholate, lithium compound,
And a ceramic composition obtained by a sol-gel method from at least one selected from BaO, Nb2O5 and BaO. 2. A ceramic composition obtained by immersing fibers in a glass-ceramic matrix containing SiO2, Al2O3, wherein the main components of the matrix are SiO2, Al2O3, MgO and, if necessary, Li2O, and the matrix is A ceramic composition obtained by a sol-gel method from a silicon alcoholate, an aluminum alcoholate, a magnesium compound, and optionally a lithium compound. 3. The ceramic composition according to claim 2, wherein the matrix additionally comprises at least one composition selected from Nb2O5, BaO. 4. The matrix according to claim 1, wherein the matrix is essentially one of the following formulas 0.05BaO-0.4LiO2-Al2O3-3SiO2 0.5 MgO-0.5LiO2-Al2O3-4SiO2. A ceramic composition according to item 4. 5. A method for producing the ceramic composition according to any one of claims 1 to 4, which comprises: a) hydrolyzing and polycondensing a metal raw material compound in a solution of a solvent. A gel is prepared by: b) removing the solvent; c) crushing the gel, if necessary; d) dehydrating and oxidizing the gel by elevating the temperature; e) adding fibers, and And f) comprising a step of compressing and ceramizing the matrix by raising the temperature.
Method. 6. The method according to claim 5, wherein the raw material used is composed of silicon alcoholate, aluminum alcoholate, lithium inorganic compound and / or magnesium inorganic compound, and optionally barium and niobium. Method. 7. The method according to claim 6, wherein the raw material is tetraethyl orthosilicate, aluminum secondary butoxide, and / or magnesium nitrate, and optionally barium nitrate and niobium chloride. 8. The method according to claim 5, wherein the solvent is isopropanol. 9. The above step a is followed by the following step a1) pre-hydrolyzing silicon alcoholate with a part of the total hydrolyzed water, and a2) the product of phase a1 and other raw materials and the remaining The method according to any one of claims 5 to 8, characterized by reacting with hydrolyzed water. 10. Steps d and f are in the following states: d) dehydrated and oxidized by raising the temperature to about 500 ° C. in air over a period of several hours, and f) just above the melting temperature of the composition. Method according to any one of claims 5 to 9, characterized in that it is carried out in compression and ceramicisation at temperature. 11. The method of claim 10, wherein the compressing and ceramization treatment is performed on the composition in powder form and comprises a press capable of performing compression. 12. The method according to claim 10, wherein the compression and ceramization treatment is performed at a temperature above the melting temperature of the composition and is accelerated by a dehydration treatment with ammonia. . 13. The compressing and ceramization process comprises a second step at a temperature slightly below the melting temperature of the composition.
Including a heat treatment as the next step, characterized in that the residual glass phase is converted into a ceramic solid solution,
The method of claim 12. 14. The fiber according to claim 5, characterized in that said fiber is based on silicon carbide.
The method according to any one of 3 above. 15. The fiber contains appropriate amounts of oxygen and carbon on its surface, and the matrix is formed of MgO, Nb2O5 to suppress adhesion between the composition and the fiber.
15. The method of claim 14 including at least one of: 16. A method according to claim 5, characterized in that the suspension of glass-ceramic powder and the suspension of short fibers are mixed and the liquid of the mixture obtained is removed by filtration.
The method according to any one of 5 above. 17. A suspension of glass-ceramic powder is formed in a viscous liquid, the structure of long fibers is impregnated into the suspension, and several sheets of impregnated structure are stacked to compress and ceramize. 16. A method according to any one of claims 5 to 15, characterized in that it is subjected to an application process.