DE2408122B2 - PROCESS FOR MANUFACTURING FEDES FROM ALUMINUM OXIDE OR ALUMINUM OXIDE-SILICON DIOXIDE WITH A SILICON DIOXIDE CONTENT OF 60 PERCENT BY WEIGHT - Google Patents

Description

in which Y is a halogen atom, an alkyl, alkoxy, is acyloxy, hydroxy or an optionally substituted

Alumina gchalt =

denotes phenoxy group, or a mixture of the polyaluminoxane and one or more silicon compounds in an organic solvent, which may also contain one or more lithium, beryllium, boron, sodium, magnesium, phosphorus, potassium, comprising calcium, titanium, chromium, manganese, yttrium, zirconium, barium, lanthanum, or tungsten compounds and calcined spinning the filaments obtained at temperatures from 700 to 2000 ⁰ C.

2. The method according to claim 1, characterized in that a polyaluminoxane with a Aluminum oxide content of at least 20 percent by weight is used, according to the following equation is calculated:

51

where Y has the meaning given in claim 1 and if Y is two or more groups, the molecular weight of the basic building block is an average value.

3. The method according to claim 1, characterized in that a polyaluminoxane is used in the Y is an alkyl radical with 1 to 15 carbon atoms, an alkoxy radical with 1 to 14 carbon atoms, an acyloxy group having at most 20 carbon atoms, a phenoxy group or a substituted one Phenoxy group with a maximum of 8 carbon atoms in the substituent or in a mixture of means at least two of the groups.

4. The method according to claim 1, characterized in that a polyaluminoxane is used, at which the organic radical contains 1 to 20 mol percent stearoyloxy and / or palmitoyloxy groups.

5. The method according to claim 1, characterized in that a polyaluminoxane with a Degree of polymerization of 10 to 200 begins.

6. The method according to claim 1, characterized in that there is a silicon compound Polysilicic acid esters with basic components of the general formula

OR ³
- Si — O—

OR ⁴

is used in which R ³ and R ^{4 are} identical or different and denote hydrogen atoms, alkyl radicals with 1 to 6 carbon atoms, alkenyl radicals with 2 to 6 carbon atoms, phenyl groups or chlorine atoms.

7. The method according to claim 1, characterized in that during or after the spinning obtained precursor thread treated with steam or an acidic reacting solution.

The latest developments in various technical fields, e.g. B. Space, requires work \ ^Y I

materials with excellent mechanical properties, e.g. B. high strength and heat resistance.

A common method of improving the properties of materials is through use of carbon fibers, metal fibers, e.g. B. made of tungsten, molybdenum or steel, or composite fibers or threads made by coating the surface of a

, o obtained tungsten filament with boron or silicon carbide polycrystalline fibers such as aluminum oxide fibers or zirconium oxide fibers or whiskers such as silicon carbide, as a reinforcement material.

Alumina and alumina-silica fibers are used as reinforcing materials for laminates known. However, they are also suitable for other purposes, since they are oxidizing Atmosphere at high temperatures can be used for which the conventional Carbon fibers or metal fibers are not suitable. They also lose their excellent mechanical properties Properties such as high strength even at high temperatures because of their high melting point (above 1590 ° C) not.

These inorganic fibers such as alumina-silica fibers are commonly used produced by melt spinning an alumina-silica compound. For this procedure however, special devices are required for melting because the starting material is high Has melting point. Furthermore, it is difficult to produce alumina-silica fibers by this method with an aluminum oxide content of at least 70 percent, which is better Distinguish heat resistance because such masses are very difficult to spin. The one after this Filaments or fibers obtained by processes are short and usually contain 30 to 50% by weight granular material. Furthermore, it is unavoidable that the product is caused by alkaline compounds is contaminated, which cause a reduction in the strength properties of the product.

As an alternative process for the production of fibers from aluminum oxide or aluminum oxide-silicon dioxide processes have been described in which a precursor fiber from an aqueous solution of a Aluminum compound is produced, into which a silicon compound can be incorporated. The manufac-

Treatment of the precursor fibers takes place according to the dry spinning process, and then the resulting Calcined product. In some of these known methods, only short fibers or the Processes cannot be carried out on an industrial scale. In other of these processes, the starting material is Not only is it expensive, but it requires numerous cumbersome stages of treatment to turn it into one to transfer spinnable state. After all, spinning has been fraught with difficulties so far could not be resolved. All known methods have the decisive disadvantage that the fibers from Alumina or alumina-silica does not have a sufficient density and only an unsatisfactory one Have strength because the precursor fiber has a low content of aluminum oxide or aluminum oxide-silicon dioxide, z. B. of at most about 25 percent by weight.

From DT-AS 16 69 380 a process for producing the mother solution containing an aluminum compound and silicon oxide for producing calcined heat-resistant fibers for a service ^{temperature of about 1370 0} C is known, which is characterized in that metallic aluminum is in a solution of Aluminum chloride is dissolved by adding a liquid, preferably acetic acid, which lowers the surface tension, adding the silicon oxide in the form of an inorganic silicon-containing compound and adding a small amount of an acidic oxide from the group consisting of boron oxide, phosphorus pentoxide and titanium oxide, the components Aluminum, silicon and acidic oxide are used in amounts such that the calcined fiber contains in weight percent 6-3 to 80 percent aluminum oxide, 14 to 30 percent silicon dioxide and 1 to 10 percent acid oxide.

Calcine those obtainable from this mother liquor Fibers have the following physical properties:

Tensile strength (on average)

After heating
to 1010 ⁰ C

After heating
to 137O ⁰ C

Fiber length

Fiber diameter

430 to 500 kg / cm '

180 to 255 kg / cm *

up to 255 mm

3.0 to 5.0 microns

The invention has for its object to provide yarns of alumina and alumina-silica with a silica Anleil of at most 60 weight percent having excellent heat resistance, mechanical strength and Fascrstruklur, which can be prepared by a simple seduction slightly from ^s available starting compounds. This object is achieved by the invention.

The invention thus relates to the subject matter characterized in the claims.

The main chain of the process used

tu polyaluminoxane consists of basic building blocks that Contain aluminum and oxygen atoms. Therefore this compound has a high content of aluminum oxide. For example, polyethylene aluminoxane contains about 71 percent by weight aluminum oxide. The silicon compound which is optionally mixed with the polyaluminoxane, may have a high silica content exhibit. For example, dimethylpolysiloxane contains about 81 weight percent silicon dioxide. From the leave compounds used according to the method

μ easily filaments of alumina and alumina-silica produce with extremely high density, which are non-porous and a very high mechanical Have strength.

The polyaluminoxane used according to the process is a polymer with basic building blocks of the general formula

- Al-O-

in which Y is an alkyl radical, such as the methyl, ethyl, propyl or butyl group, an alkoxy group such as ethoxy, propoxy or butoxy group, an acyloxy group such as the formyloxy, acetoxy, propionyloxy or butyryloxy group, or an optionally substituted one Means phenoxy group. As substituents for the phenoxy group, for. B. methyl, ethyl or Propyl groups in question. The radical Y in the polymer can be selected from one or more of the foregoing Groups exist. Part of the Y groups can be a halogen atom, such as a fluorine or chlorine atom, or a Mean hydroxyl group.

In the process according to the invention, preference is given to using polyaluminoxanes with an aluminum oxide content of at least 10, in particular at least 20 percent by weight are used. The aluminum oxide content is calculated according to the following equation:

Alumina content =

51

Molecular weight of the basic building block ( —Al — O— )

100%

If Y represents two or more groups of the type mentioned above, this means the molecular weight the average molecular weight. When using a polyaluminoxane with an aluminum oxide content of less than 10 percent by weight, it is very difficult to find usable threads made of alumina or To produce alumina-silica with excellent strength, although this is not impossible.

If the radical Y is an alkyl radical, this radical can generally have 1 to about 33 carbon atoms, but preferably contain at most about 15 carbon atoms. If the rest of Y is a Alkoxy radical, this radical can generally have a maximum of about 32 carbon atoms, preferably but contain at most 14 carbon atoms. If the radical Y is a carboxy radical, then contains this radical is preferably not more than 31 carbon atoms, in particular not more than 20 carbon atoms. Particularly preferred polyaluminoxanes for: Processes according to the invention contain 1 to 2 ( Mole percent, especially 1 to 10 mole percent, de; Radical Y, which is a palmitoyloxy and / or stearoyl

ds oxyrest, since such polyaluminoxam Can be spun excellently. If the radical Y is a (substituted phenoxy group, then dei Substituent preferably no more than 26 carbon

atoms, especially not more than 8 carbon atoms ^ Particularly preferred radicals Y are alkyl, alkoxy and acyloxy radicals each having a maximum of 4 carbon atoms, since these polyaluminoxane have a high aluminum oxide content and those made from them Connections made by precursor threads can easily be formed in the manner described below; hydrolyze permit.

It is well known that polyalumino; «. Ane are replaced by partial Hydrolysis of organoaluminum compounds such as triethylaluminum, triisopropylaluminum, tributylaluminum, Aluminum triethoxide or aluminum tributoxide, or by substitution of the remaining group of Polyaluminoxane made by other suitable groups. The organoaluminum compound is preferred first or the silicon compound, which may also be used, by distillation cleaned.

The degree of polymerization of the polyaluminoxanes used according to the process can be relatively wide range. One degree of polymerization is sufficient of at least 2. In view of the ease of the polymerization reaction Compounds with a degree of polymerization of at most 1000 are preferred. Are particularly preferred Compounds with a degree of polymerization from 10 to 200.

A polyorganosiloxane is preferably used as the silicon compound with basic building blocks of the general formula

R ¹

—Si — O—
R ²

used, in which R ¹ and R ^{2 are} identical or different and are hydrogen atoms, alkyl radicals with 1 to 6 carbon atoms, such as the methyl, ethyl, propyl and butyl groups, alkenyl radicals with 2 to 6 carbon atoms, such as the vinyl group, alkoxy radicals with 1 to 6 carbon atoms, such as the ethoxy group, phenyl groups or chlorine atoms. Furthermore, polysilicic acid esters with basic building blocks of the general formula

OR ³

—Si —O—

OR ⁴

preferred in which R ³ and R ^{4 are} identical or different and are hydrogen atoms, alkyl radicals with 1 to 6 carbon atoms, such as the methyl, ethyl, propyl and butyl groups, alkenyl radicals with 2 to 6 carbon atoms, such as the vinyl group, phenyl groups or chlorine atoms mean. Organosilanes of the general formula are also used

R?, Si (OR ⁶ ) ₄ _ "

preferred in which R ⁵ and R ^{6 are} identical or different and hydrogen atoms, alkyl radicals with 1 to 6 carbon atoms, such as the methyl and ethyl group, alkenyl radicals with 2 to 6 carbon atoms, such as the vinyl group, phenyl groups or chlorine atoms and / i mean a whole Is a number with a value from 1 to 4. Finally, preference is given to silicic acid esters of the general formula Si (OR ') ₄ , in which R ^{7 is} a hydrogen atom, an alkyl radical having 1 to 6 carbon atoms S or a phenyl group. Other silicon compounds can also be used.

The silicon compound is preferably dissolved homogeneously in the solution of the polyaluminoxane. she can however, they can also be dispersed in the solution, ίο A silicon compound is preferably used, which gives a spinnable solution when dissolved in the solution of the polyaluminoxane. However, this is not critical.

The maximum amount of silicon compound that can be incorporated into the polyaluminoxane solution, depends on the spinnability of the silicon compound itself. If a non-spinnable silicon compound is used in too large an amount, the spinnability of the solution deteriorates so much that the solution cannot be spun into threads by any of the conventional spinning processes. The aforementioned Silicon compounds are used in such a maximum amount that the silicon dioxide content after calcining the alumina-silica fibers is 60 weight percent. Possibly two or more silicon compounds can be incorporated into the solution of the polyaluminoxane.

As an organic solvent in the process of the invention, for example, diethyl ether, tetrahydrofuran, Dioxane, benzene, toluene, xylene or mixtures thereof can be used. A viscous solution is obtained which can be spun well with appropriate concentration. The relationship between the concentration and the spinnability of the solution depends on the type of polyaluminoxane, the degree of polymerization, the type of Solvent and the type and amount of any silicon compound used. Preferably, a spinning solution with a viscosity of 1 to 5000 poise, measured at room temperature, used.

Preferably, the spinning solution is also a small amount of a lithium, beryllium, boron, Sodium, magnesium, phosphorus, potassium, calcium, titanium, chromium, manganese, yttrium, zirconium, barium, Lanthanum or tungsten compound or a mixture of at least two of these compounds incorporated in order to improve various properties of the threads or fibers. The spinning one Solution of the polyaluminoxane or a mixture of

the polyaluminoxane and the silicon compound is preferably carried out according to the dry spinning process, however, other conventional spinning processes, such as the centrifugal spinning process, can also be used or the blow spinning process can be used. The spinning is usually done at room temperature carried out. If necessary, the spinning solution can also be brought to a temperature below the boiling point of the solvent used are heated. Preferably the spinning is carried out under such conditions carried out that the solvent contained in the spun thread during or after Spinning can be separated. However, such a separation is not absolutely necessary, when very thin threads are spun.

When spun in air, the polyaluminoxane component are gradually hydrolyzed in the precursor thread by the humidity. on This way, organic ingredients can gradually

lost, whereby the content of aluminum oxide in the precursor thread increases and the mechanical Properties of the threads after calcining can be improved. Accordingly, if it is also used A silicon compound is preferably used a compound that is easy to hydrolyze like a polysilicic acid ester. The precursor thread is preferably also used during or after the Spinning treated with steam or an acidic reacting aqueous solution to hydrolysis accelerate.

The precursor thread initially produced in the method according to the invention can have an average Have a diameter of 1 to 100 μ, but it is not limited to this range. Of the Precursor thread made of aluminum oxide or aluminum oxide-silicon dioxide is in a homogeneous and continuous state in which the alumina and silica are in high concentration, respectively is included. Therefore, threads made of aluminum oxide can be made from such a precursor thread by calcining or to produce alumina-silica with excellent properties. Also the precursor thread has excellent strength. If he z. B. processed into textile fabrics and is then calcined, the corresponding sheet-like structures are obtained.

The precursor thread obtained by contacting with moisture is not melted by heating. It can therefore be used in a gas atmosphere containing oxygen or free oxygen, e.g. B. in air, can be calcined without losing its thread shape. Containing atmosphere by calcining at temperatures of about 700 ⁰ C in an oxygen free, such as air, is obtained from the precursor thread a transparent alumina or alumina-silica-thread, be prepared by calcining at temperatures of about 1000 ⁰ C with transparent threads excellent strength obtained.

When calcining the precursor thread in a gas atmosphere containing free oxygen, e.g. B. in air, he loses water and the organic components at temperatures of about 600 ⁰ C, and the strength of the thread increases with increasing calcination temperature. When calcining a thread which contains pure aluminum oxide, the thread-forming y-aluminum oxide phase is converted into the <x-aluminum oxide ^{phase at temperatures of about 1000 to HOO 0 C.} This results in a significant reduction in the strength of the thread. On the other hand, when calcining a filament containing alumina as well as silica, the transition temperature can be shifted to a higher temperature range as the silica content increases. In a Siliciumdioxldgehalt 25 to 28 weight percent of the transition temperature at about 155o C. is ⁰ Further increases Siliciumdloxidgehalt the transformation temperature decreases again. In a Siliciumdioxldgehalt of about 40 weight percent, it is about HOO ⁰ C and ° at a Siliciumdloxidgehalt of about 50 weight percent at about 1200 C.

For the production of threads from aluminum oxide or aluminum oxide-silicon dioxide with excellent strength, the calnation temperature can be below the aforementioned transformation temperature. In this case, the aluminum oxide filaments have practically no reflections in the X-ray diffraction diagram that indicate α-aluminum oxide, and the aluminum oxide-silicon dioxide filaments have no reflections that indicate cristobalite. For certain purposes, e.g. B. for thermal insulation, where the heat resistance of the threads is more important than their mechanical properties, the threads are preferably sintered at a higher temperature in order to avoid further shrinkage. In this case the

ίο The temperature of the heat treatment are above the aforementioned transformation temperature, and it can be around 50 ⁰ C lower than the melting point, which is at temperatures of 1700 to 2050 ° C, depending on the ratio of aluminum oxide to silicon dioxide in the thread.

In this case, the alumina filament shows α-alumina reflection. The heat treatment temperature and calcination may thus be in the range of about 700 to 2000 ⁰ C.

Upon heating of yarns to temperatures of about 1000 ⁰ C up to the transition point, the y-Aiuminiumoxidphase and the mullite phase may form when the Siliciumdloxidgehalt is at most 28 percent by weight. With a silicon dioxide content of more than 28 percent by weight, amorphous silicon dioxide and mullite phase are formed. These phases can be converted into the α-aluminum oxide phase and the mullite phase or the cristobalite and mullite phase at or above the conversion temperature.

Accordingly, threads made of aluminum oxide or aluminum oxide-silicon dioxide with high thread strength, which contain 100 to 72 percent by weight of aluminum oxide and 28 to 0 percent by weight of silicon dioxide, practically no reflections in the X-ray diffraction diagram

.15 that indicate α-alumina. Further are said to have threads made of alumina-silica that are less than 72 percent by weight alumina and Contains more than 28 percent by weight silicon dioxide, practically no reflections in the X-ray diffraction diagram that indicate cristobalite.

Alumina or alumina-silica filaments with a filament diameter of 10 μ, the meet these conditions have the following mechanical properties:

Fiiücn- tensile strenght Tensile strength collect- module ¹¹¹ ) scl / ung % SiO ₂ i / an ² t / cm ²

0 about 10-15 about 1000-1500

10-25 about 25-30 about 2500 - 3500

50 - 60 about 30 - 35 about 1000 - 1300

100 about 35 about 700

Note: *) Young's module when pulling in the direction of the fiber lling lynx.

For the production of the threads from aluminum oxide or Aluminum oxide-silicon dioxide can be obtained from Precursor-Fa

according to the invention either in an inert

Gas atmosphere or under reduced pressure

calcined and then in a free Sauersiof containing atmosphere

(> 5 whereby organic or carbonaceous substancesi

to be burned down.

The thread made of aluminum oxide is preferred or alumina-silica further into one

700 B28 / 2I

reducing atmosphere. calcined to different Improve properties of the thread. Finally, during the calcination step, the thread can be underneath Tension can be maintained to obtain a thread with excellent mechanical properties.

The threads made of aluminum oxide or aluminum oxide-silicon dioxide which can be produced according to the invention are suitable due to their excellent heat resistance and mechanical strength to reinforce Synthetic resins such as thermoplastic synthetic resins and thermosetting synthetic resins, as well as reinforcing agents Threads or fibers for metals.

The threads that can be produced according to the invention are also valuable as heat insulators at high temperatures, e.g. above 1000 ^° C., because they can be used in air at these high temperatures.

Examples illustrate the invention.

example 1

1 mol of monoisopropoxydiethylaluminum is dissolved in 600 ml of diethyl ether. The mixture is heated ^{to 40 °} C. in an oil bath. The diethyl ether distilling off at this temperature is condensed in a condenser, introduced into a container containing 1 mol of water, moistened thereby and then returned to the reaction vessel. 1 mol of water is consumed within 8 hours and the partial hydrolysis of the monopropoxydiethylaluminum is complete. A polyisopropoxyaluminoxane with a degree of polymerization of 130 is obtained. The polymer solution is evaporated to a concentration of 70 percent by weight of polyaluminoxane. The viscosity in the solution obtained is 500 poise, measured at room temperature.

The solution obtained is used as a spinning solution. After degassing, the solution is extruded at room temperature through a spinneret with a diameter of 100 μ, and the extruded thread is wound up in air at a speed of 50 m / min. A transparent precursor thread with a diameter of 15 μ is obtained. The thread is calcined in air at a temperature which is increased from room temperature to 95O ⁰ C at a rate of 300 ° C / hour. A transparent thread made of aluminum oxide with extremely high strength is obtained. The thread diameter is 10 μ, the ^{tensile strength 15.1 t / cm 2} and the tensile strength ^{module 1480 t / cm 2} . Because of the X-ray diffraction diagram, the thread is made of γ-aluminum oxide.

Example 2

1 mol of THa ¹ ethylaluminum is dissolved in 600 ml of dioxane and a solution of 100 ml of dioxane containing 1 mol of water is added dropwise over the course of 2 hours. As a partial hydrolysis product to obtain a polyether äthylaluminoxan with a degree of polymerization of 40. The temperature of the reaction mixture is adjusted during the reaction to 5O ⁰ C. 0.3 mol of stearic acid is then added to the reaction mixture, as a result of which 0.3 mol of ethyl groups in the polyethylaluminoxane are replaced by stearoyloxy groups. A 60 percent by weight solution of the polymer has a viscosity of 230 poles, measured at room temperature. The solution is spun according to Example 1 to form a precursor thread with a diameter of 12 μ. The thread is completely stable, even when standing in the air. The thread is calcined in air with increasing temperature from room temperature to 95O ⁰ C at a rate of 600 ° C / hour. A transparent thread made of aluminum oxide with extremely high strength is obtained. After calcining, the thread diameter is 8 μ, the tensile strength 16.8 t / cm ² and the tensile strength module 1550 t / cm ² . Based on the X-ray diffraction diagram, the thread consists of γ- aluminum oxide.

Example 3

The Polyäthylaluminocan prepared according to Example 2 is 0.1 mol of stearic acid and 0.9 mol Isopropanol added. As a result, a total of 1 is mol of ethyl groups are replaced by stearoyloxy groups and Isopropoxy groups replaced in the polyethylaluminoxane. The mixture is in 51 g of ethyl silicate of the formula

C ₂ H ₅ O-

OC ₂ H ₅
-Si-O
, OC ₂ H ₅

-IC ₂

dissolved and evaporated to a concentration of 60 percent by weight polyaluminoxane. The viscosity of the solution obtained is 200 poise, measured at room temperature. This solution is spun according to Example 1 to form a transparent precursor thread with a diameter of 15 μ. The obtained precursor yarn is treated for 3 hours at 60 ⁰ C with saturated steam and then calcined with increasing temperature from room temperature to 1200 ⁰ C at a rate of 300 ° C / hour in air. A transparent thread of alumina-silica containing 20 percent by weight silica is obtained. This thread has a diameter of 10 μ, a tensile strength of 30.1 t / cm ² and a tensile strength module of 3320 t / cm ² . Even when heated to 1500 ^° C., the thread still remains transparent and retains its high mechanical strength.

The method described above is repeated, but the precursor thread is left untreated

-ls calcined with steam. The thread obtained has a tensile strength of 16.3 t / cm ² and a tensile strength module of 2540 t / cm ² .

The threads obtained according to the two embodiments exist due to the X-ray diffraction diu-

so gramms from) '· aluminum oxide and mullite.

Example 4

A solution of the polyisopropoxyaluminoxane prepared according to Example 1 in diethyl ether is mil

Benzene added. The diethyl ether is distilled off from the mixture until the solution is a polyaluminoxane ' has a concentration of 35 percent by weight. 27 g of polydimethylsiloxane are added to the solution according to Example 1 to a transparent precursor Fo

fio den spun with a diameter of 15 μ. The precursor thread is calcined with increasing temperature from room temperature to 1200 ⁰ C at a speed of 300 ° C / hour in air. It becomes a transparent thread made of aluminum oxide-silicon dioxide

obtained with 30 weight percent silica. These Thread has a diameter of 10 u, a tensile strength of 23.2 t / cm 'and a tensile strength module vot 2780 t / cm '. In the X-ray diffraction diagram of the thread:

. «■

becomes the main mullite reflection and practical no reflection attributable to amorphous silica was observed. Even with When heated to 1550 ° C, the thread remains transparent.

Example 5

A solution of a polyaluminoxane, in which 0.1 mol percent of the organic radicals are stearoyloxy radicals and 0.9 mol percent isopropoxy radicals (degree of polymerization 40), in dioxane is mixed with γ-methacryloyloxypropyl-trimethoxysilane in such a weight ratio that the calcined thread 10 ¹ percent by weight silicon dioxide contains. The mixture is evaporated to a polyaluminoxane concentration of 50 percent by weight and left to stand for 12 hours at room temperature. Then the γ-methacryloyloxypropyl-trimethoxysilane is polymerized. A viscous solution is obtained which is excellent for spinning. The viscosity is 200 poise at room temperature. The solution obtained is spun according to Example 1 to form a transparent precursor thread with a diameter of 10 μ.

The precursor yarn is calcined with increasing temperature from room temperature to 600 ⁰ C at a rate of 300 ° C / hour under nitrogen as protective gas. Then, the calcination is continued in air with increasing temperature up to 1200 ⁰ C. A transparent thread made of alumina-silica with high mechanical strength and a diameter of 6 μ is obtained. Based on the X-ray diffraction diagram, the thread consists almost entirely of γ-aluminum oxide. However, a faint reflection is observed which is indicative of amorphous silica.

Example 6

The solution of polyaluminoxane in dioxane used in Example 5 is mixed with tetraethoxysilane in such a proportion that the calcined thread contains 50 percent by weight of silicon dioxide. The solution is evaporated to a concentration of polyaluminoxane of 60 percent by weight and then spun into a precursor thread with a diameter of 15 μ. The obtained precursor yarn is treated for 2 hours at 6O ⁰ C with steam and then calcined with increasing temperature from room temperature to 1150 ° C at a rate of 300 ⁰ C / hour in air. A thread of alumina-silica with a diameter of 10 μ is obtained. This thread has a tensile strength of 27.8 t / cm ² and a tensile strength module of 1260 t / cm ² . In the X-ray diffraction diagram, only the reflections from mullite and amorphous silicon dioxide are observed.

Claims (1)

24 122 claims: 1. Process for making the filaments from alumina or alumina-silica with a silicon dioxide content of at most 60 percent by weight, characterized in that, that one is a solution of a polyaluminoxane with basic building blocks of the general formula —Al - O -