JPH0372724B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing refractory alumina fibers suitable for use at high temperatures.

Various manufacturing methods have been devised for inorganic fibers used at high temperatures. The representative ones are
Glass fibers made by melt-spinning siliceous and alumina raw materials are widely used. However, the maximum operating temperature of this fiber is said to be around 1200°C, and crystalline fibers are used for higher temperature applications. Crystalline fibers containing aluminum oxide as a main component are known to have excellent heat resistance.

Crystalline alumina fibers are mainly composed of aluminum oxide with a melting point of 2050°C and are inherently highly heat resistant. However, in the method of firing a fibrous precursor as described in Japanese Patent Publication No. 47-37215, the resulting fiber is heated to about 1000℃ because it transforms into α-Al ₂ O ₃ through intermediate alumina. Contraction also occurs in

Furthermore, α-Al ₂ O ₃ has a high crystal growth rate above 1200℃, and in applications where small fiber diameter is required for performance, such as fibrous insulation materials, crystals tend to grow to a size that cannot be ignored. There is.
Therefore, for example, when used as alumina fiber for insulation materials, it is exposed to high temperatures during use, so
The fibers tend to shrink, causing problems such as opening of the joints.

For this reason, it is desirable to set the firing temperature during manufacturing as high as possible to allow sufficient shrinkage to occur and to reduce shrinkage during use.However, if the firing temperature is too high, the fibers become brittle and become powdery, making them difficult to handle. There is a contradiction.

Japanese Patent Publication No. 46-2147 describes a heat-resistant felt-like web consisting of 80-95% by weight of Al ₂ O ₃ and 5-20% by weight of SiO ₂ , 80-90% by weight of Al ₂ O ₃ and 5-15% by weight of SiO ₂ and 3 to 10% by weight of Cr ₂ O ₃ are described.

However, according to the inventors' study,
Alumina fibers made of two components, Al ₂ O ₃ and SiO ₂ , have a large linear reheating shrinkage rate, as shown in the comparative example below. In addition, if it contains Cr ₂ O ₃ , there is a risk that the Cr component will vaporize at high temperatures and cause pollution.
Fibers also become brittle.

As a result of various studies with the above points in mind, the present inventors have found that the above problem can be overcome by using a specific amount of ZrO ₂ components in addition to Al ₂ O ₃ components and SiO ₂ components. completed.

That is, the gist of the present invention is a method for producing refractory alumina fibers by forming a liquid material containing an organic polymer and a metal compound into fibers to obtain a fibrous tip and then firing the metal compound.
At least: (a) 99 to 70 parts by weight of an inorganic or organic salt of aluminum that provides the Al ₂ O ₃ component as the Al ₂ O ₃ component; (b) 1 to 30 parts by weight of the silicon compound that provides the SiO ₂ component as the SiO ₂ component; and (c) 0.1 to ₃ parts by weight of an inorganic salt or an organic salt of zirconium which provides ₂ ZrO components per 100 parts by weight of 3 Al ₂ O and ₂ SiO components as the ₂ ZrO components. It consists in a method for producing fire-resistant alumina fiber.

The present invention will be specifically explained below.

Inorganic salts or organic salts of aluminum that provide the Al ₂ O ₃ component of the present invention include aluminum chloride,
Mention may be made of aluminum compounds such as aluminum oxychloride, aluminum sulfate, aluminum nitrate or aluminum acetate. These are then used by a known method, such as hydrolysis, or by adding metal aluminum and dissolving it to form a solution or sol deficient in acid ions of the aluminum compound.

As an example, regarding an aluminum chloride system, metal aluminum particles or thin plates may be dissolved in hydrochloric acid or an aqueous solution of aluminum chloride while heating and stirring. In this case, the atomic ratio of aluminum to chlorine is preferably adjusted to 1:1 to 2:1.

Silicon compounds that provide the SiO ₂ component include silica sol such as "Snowtech-O" (manufactured by Nissan Chemical), silicon tetrachloride, tetraethoxy silicon ((C ₂ H ₅ O) ₄ Si), tetramethoxy silicon (( Examples include organic silicon compounds containing CH ₃ O) ₄ Si), siloxane, silanol, or silanolate groups and having the ability to dissolve in water, and are used after being appropriately treated such as hydrolysis.

In 100 parts by weight of the Al ₂ O ₃ component and SiO ₂ component, the metal compound that provides the Al ₂ O ₃ component and SiO ₂ component is
99 to 70 parts by weight as Al ₂ O ₃ component, preferably 95 to 70 parts by weight and 1 to 30 parts by weight as SiO ₂ component, respectively.
Parts by weight are used, preferably in the range of 5 to 25 parts by weight.

By adding the SiO ₂ component, mullite (3Al ₂ O ₃ .2SiO ₂ ) is formed during firing, which strengthens the bonds between alumina particles and increases the strength of the fiber. If the SiO ₂ component is added in an amount of 1 part by weight or less, this effect will not appear and strong fibers will not be obtained.

On the other hand, if 30 parts by weight or more of _SiO2 component is present,
_SiO2 components exceeding the mullite composition form cristobalite at high temperatures of 1200°C or higher, but this cristobalite has a large volume change and large coefficient of thermal expansion during formation, making the fiber extremely brittle.

Next, as the inorganic or organic salt of zirconium that provides the ZrO ₂ component, zirconium oxychloride is inexpensive and easy to use, but other water-soluble zirconium salts such as zirconium oxyacetate can also be used.

In the present invention, ZrO ₂ component is Al ₂ O ₃ component and
It is used in an amount of 0.1 to 3 parts by weight, preferably 0.2 to 2 parts by weight, based on a total of 100 parts by weight of the SiO ₂ component.

The ZrO ₂ component has the effect of promoting α-Al ₃ O ₃ formation and suppressing the growth of crystal grains during firing. However, if the ZrO ₂ component is less than 0.1 part by weight, the effect of promoting α-Al ₂ O ₃ is not observed and high temperature firing is required.
If the ZrO ₂ component is 3 parts by weight or more, excessive gelatinization occurs, grain boundary precipitates increase, and the strength of the fiber decreases.

As the organic polymer used in the present invention, any natural or synthetic material having fiber-forming ability can be used. Natural products include starch or soluble cellulose and its derivatives, such as acetated starch,
Examples include hydroxyethyl starch, methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose.

Examples of the synthetic organic polymer include soluble polyvinyl alcohol, polyurethane, polyacrylate, polyacrylamide, and polyethylene oxide. In particular, polyvinyl alcohol (PVA)
is preferred.

Such an organic polymer is used in an amount of 5 to 5 parts by weight based on a total of 100 parts by weight of the ₃ Al ₂ O components, the ₂ SiO components, and the ₂ ZrO components.
It is used in an amount of 30 parts by weight, preferably in the range of 10 to 15 parts by weight.

In the present invention, a liquid material containing the above organic polymer and metal compound is prepared according to a known method. The liquid material in the present invention refers to a liquid consisting of a solution, sol, colloid, or a mixture thereof of these organic polymers and metal compounds.

A spinning solution is prepared by appropriately concentrating the liquid material. There are differences depending on the organic polymer used, the spinning method, etc., but in general, the viscosity of the spinning solution is 1 to 1000.
Each component is blended and adjusted so that it becomes a poise.

For fiberization, ordinary fiber manufacturing equipment and manufacturing methods used industrially can be applied. For example, there are methods such as blowing out a trickle of the spinning solution, extruding it through a narrow opening, drawing a continuous filament extruded through a narrow opening, or creating fibers using centrifugal force similar to sugar cotton candy manufacturing equipment to obtain a fibrous end drive. be.

When the refractory alumina fiber of the present invention is used as a heat insulating material, it is preferable that the shrinkage rate during high-temperature use is small, and the reheating linear shrinkage rate should normally be 2% or less.

The shrinkage rate of the obtained fibers is influenced by the firing temperature of the fibrous tip, but in the present invention, it is usually 1220 to 1270°C, preferably 1240°C.
Bake at ~1260℃ for about 30 minutes to 2 hours.

Below 1220℃, the effect of ZrO ₂ components is not expressed,
Since α-Al ₂ O ₃ conversion is insufficient, fibers with a small shrinkage rate cannot be obtained. On the other hand, at temperatures above 1270°C, conversion to α-Al ₂ O ₃ proceeds regardless of the amount of ZrO ₂ component added.
Fibers become brittle.

In the present invention, the Al ₂ O ₃ component is completely converted to α-Al ₂ O ₃
It is preferable to include a portion of intermediate alumina instead of adding alumina, since flexible fibers can be obtained. Since the promoting effect of α-Al ₂ O ₃ changes depending on the amount of the ZrO ₂ component, it may be adjusted by appropriately selecting the firing temperature within the above range. For example, as _shown in Figure ₁ below, the α-
The desired degree of gelatinization can be achieved by appropriately combining the amount of the _two ZrO components and the firing temperature so that the degree of gelatinization expressed with the Al ₂ O ₃ powder X-ray diffraction peak as a reference (100) is kept at a level of 250 or less. It is possible to obtain fibers having

The refractory alumina fiber of the present invention can be produced by the method described above.

According to the method of the present invention, refractory alumina fibers with a reheating linear shrinkage rate of 0.8 to 1.9% after heating at 1400°C for 24 hours and a thermal conductivity of 0.3 to 0.35 kcal/m・hr・°C at 1400°C can be easily obtained. It is useful as a heat insulating material.

EXAMPLES The present invention will be further explained in detail by giving examples below.

Example 1 Al metal piece (purity 99.5% or more) in 20% HCl aqueous solution
was added so that the Al/Cl molar ratio was 1.85.95
After heating at ℃ for 3 hours, insoluble matter was filtered and Al/
An aluminum oxychloride solution with a Cl molar ratio of 1.8 was obtained. This solution contains 20% SiO ₂ sol (Snowtex-O manufactured by Nissan Chemical), 10% ZrOCl ₂ solution, and 10% PVA.
(Nippon Gohsenol GH-17) Al ₂ O ₃ :
SiO ₂ :ZrO ₂ ; PVA (weight ratio) was added at a ratio of 95:5:1:10, concentrated at 50°C under reduced pressure, and the viscosity
A spinning solution of 30 poise with good spinnability was obtained.

The fibers were spun by blowing and fired at a maximum temperature of 1250° C. to obtain good fibers with a diameter of 2 to 3 μmφ.

Analysis by powder X-ray diffraction pattern shows that α-Al ₂ O ₃
The main component was δ-Al ₂ O ₃ and mullite.

The linear shrinkage rate of this fiber when reheated at 1400℃ for 24 hours is
It was extremely good at 0.8%.

Example 2 Al ₂ O ₃ :SiO ₂ :ZrO ₂ : was prepared in the same manner as in Example 1.
Prepare a solution of PVA (weight ratio) = 75:25:1:10,
It was concentrated under reduced pressure at 50°C to obtain a spinning solution with a viscosity of 27 poise.

The fibers were spun by blow spinning and fired at a maximum temperature of 1250°C to obtain good fibers with a diameter of 2 to 3 μmφ.

Analysis by powder X-ray diffraction revealed only a mullite peak.

The linear shrinkage rate of this fiber when reheated at 1400℃ for 24 hours is
It was extremely good at 0.9%.

Example 3 The precursor fiber produced in Example 1 was fired at 1230°C. The linear shrinkage rate of heating at 1400℃ for 24 hours is 1.90%.
It was a good fiber.

Example 4 Aluminum oxychloride solution with an Al/Cl atomic ratio of 1.8 obtained in the same manner as in Example 1, 20% SiO ₂ sol,
10% _ZrOCl2 aqueous solution, 10% PVA solution _{Al2O3 :}
Mix SiO ₂ :ZrO ₂ :PVA (weight ratio) = 95:5:2:10, concentrate at 50°C under reduced pressure, and reduce the viscosity.
A spinning solution of 22 poise was obtained. This spinning solution was spun by blow spinning and fired at 1240°C. 1400℃24
The linear shrinkage rate after heating for a period of time was 1.2%, which was good.

Refractory alumina fibers differing only in the amount ratio of ZrO ₂ were prepared according to the above example, and the relationship between the firing temperature and the degree of gelatinization as a result of changes in the amount of ZrO ₂ component is shown in FIG. 1 below.

In addition, the degree of gelatinization is that of the product fired at 1270℃ and without ZrO ₂ additive.
_-Al2O3 X _- ray diffraction peak was set as 100, and expressed as a ratio to that.

As can be seen from FIG. 1, the same degree of gelatinization is achieved at a lower firing temperature with the addition of the ZrO ₂ component. However, when the _ZrO2 component reaches 5% by weight, the effect of addition becomes small, and embrittlement (α
gelatinization degree of 250 or higher), and has an appropriate gelatinization degree,
Moreover, the firing temperature range for obtaining fibers that do not become brittle becomes narrower.

Comparative Example 1 A 10% ZrOCl ₂ solution and a 10% PVA solution were added to an aluminum oxychloride solution prepared in the same manner as in Example 1 to obtain Al ₂ O ₃ :ZrO ₂ :PVA (weight ratio)=
A 95:2:10 solution was prepared.

This was concentrated under reduced pressure at 50°C to obtain a spinning solution with a viscosity of 32 poise, which was spun using a blowing method and fired at 1250°C.

The obtained fiber had abnormal growth of α-Al ₂ O ₃ crystals, large shrinkage upon firing, and was brittle and unsuitable as a heat insulating material.

Comparative Example 2 A ZrO 2 -free solution of Al ₂ O ₃ :SiO ₂ :PVA (weight ratio) = 95:5:10 was prepared in the same manner as in Example ₁ , concentrated under reduced pressure at 50°C, and had a viscosity of 30. A poise spinning solution was obtained.

The fibers spun by the blowing method and fired at 1260°C have a diameter of 2 to 3 μmφ and a powder X-ray diffraction pattern of α-Al ₂ O ₃ and δ.
- It was a mixture of Al ₂ O ₃ and mullite. The linear shrinkage rate of this fiber by reheating at 1400° C. for 24 hours was 24%, which was higher than that of Examples 1 and 2.

Comparative Example 3 A 10% PVA solution was added to the aluminum oxychloride solution prepared in the same manner as in Example 1 to produce Al ₂ O ₃ :
A solution of PVA (weight ratio) = 100:10 was prepared. This solution was concentrated at 50° C. under reduced pressure to a viscosity of 30 poise to produce a spinning solution.

Fibers spun with blowing liquid and fired at 1250°C are extremely brittle and cannot be used as insulation materials.

Comparative Example 4 Al ₂ O ₃ :SiO ₂ :ZrO ₂ : by the same method as Example 1
A solution of PVA (weight ratio) = 65:35:1:10 was produced. The mixture was concentrated at 50° C. under reduced pressure to obtain a spinning solution with a viscosity of 30 poise, which was then spun using a blowing method.

Powder X-ray diffraction analysis of the fibers fired at 1250°C showed cristobalite peaks in addition to mullite, and the fibers were brittle and unsuitable for use as a heat insulating material.

Comparative Example 5 ₂₀ % SiO 2 sol was added to the aluminum oxychloride solution produced in the same manner as in Example 1 so that Al ₂ O ₃ :SiO _{2 :} ZrO ₂ :PVA (weight ratio) = 95:5:5:10. , 10% ZrOCl ₂ solution, and 10% PVA solution were cloudy, and the spinning solution with a viscosity of 35 poise obtained by concentrating at 50° C. under reduced pressure also had poor spinnability.

The fibers spun by the blowing method and fired at 1250°C were brittle and unsuitable for use as insulation materials.

Comparative Example 6 A 10% ZrOl ₂ aqueous solution and 10% Cr were added to an aluminum oxychloride aqueous solution prepared in the same manner as in Example 1.
_{( NO3} ) ₃ aqueous solution, 10% PVA aqueous solution with _Al2O3 :
ZrO ₂ :Cr ₂ O ₃ :PVA (weight ratio) = 95:2:5:10
Concentrate under reduced pressure at 50℃ to reduce the viscosity.
A spinning solution of 20 poise was produced.

It was spun using the blowing method and fired at a maximum temperature of 1240°C. The resulting fibers were brittle and unsuitable as insulation materials.

Comparative Example 7 20% SiO ₂ sol and 10% Cr(NO ₃ ) ₃ in aluminum oxychloride aqueous solution prepared by the same method as Example 1
solution _, 10% PVA solution _Al2O3 : _SiO2 : _{Cr2O3 :}
PVA (weight ratio) was added at a ratio of 90:5:2:10 and concentrated under reduced pressure at 50°C to produce a spinning solution with a viscosity of 25 poise.

Spun using the blowing method and fired at 1240°C to create a diameter of 2.
~3 μm fibers were obtained.

When this fiber was heated in air at 1400℃, Cr
16% was vaporized in 8 hours, and about 50% was vaporized in 166 hours.

[Brief explanation of drawings]

Figure 1 shows the firing temperature and α due to changes in the amount of ZrO ₂ components in the refractory alumina fiber of the present invention.
It is a graph showing the relationship between the degree of The horizontal axis represents the firing temperature, and the vertical axis represents the degree of gelatinization.

Claims (1)

[Claims] 1. A method for producing refractory alumina fibers by fiberizing a liquid material containing an organic polymer and a metal compound to obtain a fibrous precursor and then firing the metal compound, at least (a) Al ₂ O ₃
(b) 1 to 30 parts by weight of a silicon compound providing the SiO ₂ component as the SiO ₂ component; (c) Al ₂ O ₃ component of the inorganic or organic salt of aluminum that provides the component _; 1. A method for producing refractory alumina fibers, characterized in that _0.1 to _{3 parts by weight of a zirconium inorganic salt or an organic salt that provides a ZrO 2 component} is used as a ZrO ₂ component per 100 parts by weight of an O 3 component and a SiO 2 component.