WO2008138554A1

WO2008138554A1 - Spinning mass for producing aluminum oxide and mullite fibers

Info

Publication number: WO2008138554A1
Application number: PCT/EP2008/003734
Authority: WO
Inventors: Norbert Roesch
Original assignee: Clariant Finance (Bvi) Limited
Priority date: 2007-05-15
Filing date: 2008-05-09
Publication date: 2008-11-20
Also published as: DE102007022821B4; DE102007022821A1; TW200912060A

Abstract

The invention relates to a spinning mass for producing aluminum oxide and mullite fibers. Said spinning mass comprises and acid-modified aminosilane, in addition to the typical AI<SUB>2</SUB>O<SUB>3</SUB> precursors in the form of aluminum salts, and optionally polymers and other additives. Said acid-modified aminosilane brings about improved phase stability of the ceramic fibers.

Description

description

Dope for the production of alumina and mullite fibers

The present invention relates to the use of modified aminosilanes for the production of oxide-ceramic fibers.

Ceramic fibers have been produced for many years and used in various fields. They are characterized by high chemical resistance, high thermal stability and remarkable mechanical properties. While short fibers have gained tremendous importance in high-temperature insulation as a substitute for asbestos, the available filament fibers are niche products which, due to the high price, are only used to a limited extent for special applications.

As insulating material, the ceramic fibers based on alumina and alumina / silica (mullite) are used in furnace construction, in the aerospace and automotive industries.

In the production of these alumina fibers and Mullitfasem serve as

Starting materials corresponding precursors of metal oxides. Silica is often used to stabilize the crystal phases and to suppress crystal growth (EP 0 318 203 and EP 0 206 634). Further additives for influencing the crystal structure and the crystal growth in the fibers, such. As MgO and iron oxide, are described in EP 0 294 208th

As precursors for the production of aluminum oxide and Mullitfasem aluminum salts such as aluminum chlorohydrate (EP 0 318 203) or aluminum formate acetate mixed salts (EP 0 294 208) are used. In contrast, in US Pat. No. 3,808,015 mixtures of aluminum oxide particles (13-80% proportion) and corresponding binders, such as, for example, are used. B. aluminum chlorohydrate. The aluminum oxide particles used according to US Pat. No. 3,808,015 are intended to be Corundum size distribution of 99.5% less than 5 microns, 98% less than 3 microns and 50% greater than 0.2 microns.

To improve the rheology and spinnability of the masses are often water-soluble polymers such. As polyethylene oxide or polyvinyl alcohol added.

After production of the fibers by appropriate spinning processes, these must be converted into the ceramic fiber. This is done by thermal treatment in suitable ovens. It is usually worked with temperature gradients, wherein in the lower temperature range, depending on the precursor usually water and the corresponding decomposition products of the precursors are released. At higher temperatures, the phase transformations take place to form the desired crystal structure.

The stabilization of the crystal phases and the suppression of

Silica used in crystal growth or the silica content in alumina-silica mixed fibers (mullite) is usually added in the form of colloidal silica. This method has the decisive disadvantage that in the aluminum salt solutions nano-particles are introduced from silica, which usually does not succeed homogeneous. When forming the mixed phases then domains can form, which adversely affect the mechanical properties of the oxide fibers.

It has now been found that the disadvantages can be avoided by using acid-modified aminosilanes to stabilize the crystal phases and to suppress crystal growth.

The invention therefore relates to a spinning composition for the production of aluminum oxide and mullite fibers, which contains an aluminum percursor and optionally a polymer and further auxiliaries, wherein these

Spinnmasse additionally contains one or more acid-modified aminosilanes. Suitable silanes in this case are preferably the following types: Compounds of the formulas

Organosilanes of the type (RO) ₃ Si (CH 2) m R 'R = alkyl, such as methyl, ethyl, propyl m = 0.1-20

R- = .NH ₂ , -NH-CH ₂ -CH ₂ -NH ₂ , -N- (CH ₂ -CH ₂ -NH ₂ ) ₂

-NH-COO-CH ₃ , -NH-COO-CH ₂ -CH ₃ , -NH- (CH ₂ ) ₃ Si (OR) ₃

As these formulas show, the term "aminosilanes" includes not only those compounds bearing primary, secondary or tertiary amino groups, but also those compounds containing nitrogen atoms in carbonamido structures.

Furthermore, well-known aminosilicone oils from Wacker, Dow Corning, Bayer, Rhodia, etc. are used, which carry randomly distributed (cyclo) -alkylamino groups on their polymer chain on the polysiloxane chain.

Preferred silanes are the following silanes:

3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane, Triaminofunctional propyltrimethoxysilanes (DYNASYLAN ^® triamino Fa. Degussa),

N- (n-butyl) -3-aminopropyltrimethoxysilanes, 3-aminopropylmethyldiethoxysilanes.

These silanes are reacted with acids with the preferred molar ratio of silane to acid being 1: 1.

As acids inorganic and organic acids can be used. Preference is given to using short-chain inorganic acids such as formic acid or acetic acid. The reaction is carried out by simply mixing the two components. In an exothermic reaction then forms the acid-modified aminosilane.

These acid-modified aminosilanes are then mixed with the aqueous solution of the aluminum precursors, which are usually used as starting material for the production of ceramic fibers based on Al ₂ O ₃ . Stirrers or dissolvers may be used to prepare the mixture. The use of ultrasound is also possible. Since the modified aminosilane decomposes to SiO ₂ in the final calcination in the process of producing the oxide fibers and as such remains in the fiber, the amount of added acid-modified aminosilane depends primarily on the desired level of SiO ₂ in the finished fiber , In general, one will choose the amount of acid-modified aminosilane so that the finished fiber contains 0.1 to 30 wt% SiO ₂ .

Suitable aluminum precursors are aluminum chlorides, aluminum sulphates, aluminum nitrates and the corresponding basic salts. Furthermore, aluminum alcoholates and aluminum salts of organic acids can be used. Particularly preferred is the aluminum chlorohydrate which has the formula Al ₂ (OH) _x Cl y, where x is a number from 2.5 to 5.5 and y is a number from 3.5 to 0.5 and the sum of x and y always 6. Preference is given to starting from 50% aqueous solutions, as they are commercially available.

It is also preferred to add a polymer to the aqueous mixture to adjust the rheology for bulk spinnability. Suitable polymers include polyvinyl alcohols, polyethylene oxides, polyvinylpyrrolidones, polyvinyl butyrals and other water-soluble, organic polymers, it being possible for the polymer content to be in the range from 0.2 to 40% by weight (based on the oxide content of the mixture). To increase the solids content, it may still be advantageous to extract water from the dope. This can be done under normal pressure or under vacuum. It continues possible to increase the solids content by adding solid aluminum precursor.

The spinning dope according to the invention is blown or expressed through nozzles, wherein the resulting green fibers are collected as short fiber. It is also possible to produce long fibers with the spinning composition according to the invention, in which case the thread is taken up and wound on bobbins. The green fiber thus obtained is converted into the desired ceramic fiber in a subsequent calcination step. This happens at the characteristic for the formation of the desired crystal phase temperature. During calcination, the silica forms by decomposition of the modified aminosilane. Since a homogeneous salt mixture was assumed, the effect of homogeneously distributed silica is very efficient.

It can be in this way also high quality fibers with high alumina content (97% Al ₂ O ₃ ) produced, as it is not possible with colloidal silica. It also shows that the fibers contain less amorphous or foreign phases, making the process more stable. In addition, the fibers usually show smaller crystallite sizes, denser microstructures and fewer defects in the crystal lattice. Macroscopically, this results in higher tensile strengths and improved fracture behavior.

The long fibers according to the invention are particularly suitable for the production of ceramic fiber fabrics and as starting material for the production of ceramic matrix and metal matrix composite materials.

example 1

To a 50% aqueous solution of aluminum chlorohydrate was added so much aminopropylmethyldiethoxysilane formate that after calcination the ratio of alumina to silica is 97: 3 wt%. After the solution was homogenized by stirring, an aqueous solution of polyethylene glycol polymer having a molecular weight of 1 million was added. After concentrating by evaporating water under vacuum, the dope was spun in a dry spinning method through a one-hole die. The obtained green fibers were heated in a chamber furnace at a heating rate of 10 ° C / min up to 1300 ⁰ C.

In the reference experiment, instead of modified aminosilane, colloidal silica (Klebosol 30 CAL50) was used as the source of silica. The direct comparison shows that the fibers obtained have improved flexibility, a reduced tendency to breakage and a smaller "shot" (droplets at the yarn end) when using the spinning composition according to the invention.

Claims

claims:

1. A dope for the production of alumina and mullite fibers, comprising an aluminum precursor and optionally a polymer and further auxiliaries, characterized in that the dope contains an acid-modified aminosilane.

2. A dope according to claim 1, characterized in that it contains an amino acid modified with an organic acid.

3. spinning mass according to claim 1, characterized in that it contains an amino acid modified with formic acid or acetic acid.

4. Dope according to claim 1, characterized in that it contains aluminum chlorides, aluminum sulfates, aluminum nitrates or the corresponding basic salts as aluminum oxide precursor.

5. spinning mass according to claim 1, characterized in that it contains an aluminum alkoxide or an aluminum salt of organic acids as the alumina precursor.

6. A dope according to claim 1, characterized in that it aluminum chlorohydrate of the formula Ab (OH) _x CIy, where x is a number from 2.5 to 5.5 and y is a number from 3.5 to 0.5 and the sum of x and y is always 6, as containing alumina precursor.

7. spinning mass according to claim 1, characterized in that it contains as polymer a polyvinyl alcohol, polyvinylpyrrolidone or polyvinyl butyral.

8. A process for the production of alumina and mullite fibers, characterized in that one spun a spinning composition according to claim 1 and the resulting fiber is calcined.