JPH045770B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to refractory alumina fibers. Various types of inorganic fibers that can be used at high temperatures are known or proposed. A typical example is glass fiber obtained by melt-spinning siliceous and/or alumina raw materials, which are already widely used. However, glass fibers lose their strength due to recrystallization at high temperatures, so the maximum operating temperature is said to be about 1200°C. Therefore, it has been proposed to use crystalline fibers for higher temperature applications. Crystalline alumina fibers are mainly composed of aluminum oxide (Al ₂ O ₃ ) with a melting point of 205° C., and are inherently resistant to high temperatures. However, conventionally known crystalline alumina fibers cannot necessarily be said to have sufficient performance for use at high temperatures. For example, in Japanese Patent Publication No. 47-37215, a reaction mixture obtained by mixing an inorganic oxide sol such as alumina sol or aluminum chloride sol with a fiber-forming organic polymer is drawn or extruded, and the resulting fibrous A method is disclosed in which precursors are calcined at temperatures of about 300-1000°C to obtain inorganic oxide fibers, such as alumina fibers. Although the alumina fibers obtained by this method are made of α-alumina, they show considerable shrinkage even at temperatures of about 1000°C. Furthermore, the crystal growth rate of α-alumina increases significantly at temperatures above 1200°C. This is not a problem in applications with high surface area and porous fibers, such as catalysts used at relatively low temperatures, but with small fiber diameters and non-porous dense structures, such as insulation materials used at high temperatures. In applications where performance is required, the crystallization tendency tends to become even more pronounced and can become a major problem. That is, when used as a fibrous heat insulating material, exposure to high temperatures causes the fibers to shrink, resulting in problems such as opening of the joints. Shrinkage during use can be reduced if the firing temperature during manufacture is set as high as possible to sufficiently advance shrinkage. This is because the fibers become brittle at high firing temperatures.
It has the fatal disadvantage of becoming easily powdered and difficult to handle. The present inventors focused on the strong demand for heat shrinkage resistance when used as a high-temperature insulation material, and conducted extensive studies from the viewpoint of the basic structure of aluminum oxide in alumina fibers and its effect on the physical properties of the fibers. As a result, the inventors have discovered that the above-mentioned problems can be solved by a novel method for stabilizing the crystalline phase, and have arrived at the present invention. That is, an object of the present invention is to provide an alumina fiber suitable for use _at high temperatures. O ₃ ), silicon oxide (SiO ₂ ), and zirconium oxide (ZrO ₂ ) in a proportion of Al ₂ O ₃ 70 to 98.9% by weight, SiO ₂ 1 to 29.9% by weight, ZrO ₂ 0.1 to 3% by weight, and oxidized. The silicon content C _si (wt%) and the zirconium oxide content C _zr (wt%) satisfy the following relational expression: C _si ≦−20log C _zr +10, and the powder X-ray diffraction spectrum (anticathode :Cu−K〓)
The degree of delta-ization of alumina, defined as the ratio I〓/I〓 of the intensity I〓 of the δ-alumina peak (2θ67.5°) to the intensity I〓 of the α-alumina peak (2θ66.5°) at 0.5~ Refractory alumina fiber, characterized in that it is within the range of 1.5. The present invention will be explained in detail below. To produce the refractory alumina fiber of the present invention,
First, a spinnable aqueous liquid containing an Al compound, a Si compound, a Zr compound, and an organic polymer compound is prepared. As the Al compound, various Al compounds that generate Al ₂ O ₃ upon firing are used, and specific examples include inorganic aluminum (Al) salts such as aluminum chloride, aluminum oxychloride, aluminum sulfate, and aluminum nitrate; and organic aluminum (Al) salts such as aluminum acetate. These Al compounds are treated in an aqueous solution under suitable conditions to form a solution or sol deficient in acid anions, and used in such a form in an aqueous liquid. Examples of the treatment for forming a solution or sol lacking in acid anions include, for example, a method of partially hydrolyzing the above Al salt in an aqueous solution;
A method in which an appropriate amount of metallic aluminum is added and dissolved in an aqueous solution of an acid that forms Al or its anion, and an anion of the acid is prepared from an aqueous solution of the Al salt by physical or physicochemical means such as heating and electrolysis. Examples include a method of partially removing. As an example, to explain a system using aluminum chloride as a raw material, an aqueous solution lacking chloride ions is prepared by dissolving metallic aluminum particles or thin plates in an aluminum chloride aqueous solution or hydrochloric acid while stirring with heating. At that time, the molar ratio of aluminum atoms to chlorine atoms (Al/Cl) in the aqueous solution is 1 to 1.
It is preferable to set it to 2. As the above-mentioned Si compounds, various Si compounds that produce SiO ₂ upon firing are used. Specific examples include water-dispersible silica gel, inorganic Si compounds such as silicon tetrachloride, and ethyl orthosilicate and orthosilicate. Examples include organic Si compounds such as acid methyl, siloxanes, silanols, and silanolates. Among the above-mentioned Si compounds, those other than silica gel are desirably treated with appropriate treatment such as hydrolysis to improve their water dispersibility before use. Furthermore, the Zr compound can be
Various Zr compounds are used to produce ZrO ₂ , including inorganic compounds such as zirconium oxychloride.
Examples include Zr compounds and organic Zr compounds such as zirconium oxyacetate. Now, the above-mentioned three compounds, Al compound, Si compound, and Zr compound, must be present in a specific quantitative ratio in the aqueous liquid. In other words, these three are the weight percentages of the corresponding oxides of each compound based on the total weight of the corresponding oxides (Al ₂ O ₃ , SiO ₂ and ZrO ₂ ) of each compound (hereinafter referred to as the "oxide equivalent content rate"). ”) and must be within the following ranges. Al compound: 70 to 98.9% by weight Si compound: 1 to 29.9% by weight Zr compound: 0.1 to 3% by weight A more preferable quantitative ratio of the above three is expressed as an oxide equivalent content and is within the following range. Al compounds 70-95% by weight Si compounds 5-25% by weight Zr compounds 0.2-2% by weight Here we discuss the use of Si and Zr compounds in the method of the invention, and therefore the concentration of SiO ₂ and ZrO ₂ in the alumina fibers of the invention. Explain the effects of its presence. Due to the presence of Si compounds together with Al compounds, mullite (3Al ₂ O ₃ 2SiO ₂ ) is formed during firing of the fibrous precursor, which strengthens the bonds between Al ₂ O ₃ particles and increases the strength of the fibers. It has the effect of increasing When the amount of the Si compound used is less than 1% by weight in terms of oxide content, this effect hardly appears and fibers with sufficient strength cannot be obtained.
On the other hand, the amount of Si compound used is 30% in terms of oxide content.
If the SiO2 content exceeds the mullite composition when the fibrous precursor is fired, _cristobalite is formed at a high temperature of 1200℃ or higher, but this is because the volume change and thermal expansion coefficient during its formation are large. , which makes the alumina fibers produced extremely brittle. When the fibrous precursor is calcined, the _Zr compound _is
- It has the effect of promoting aluminization and suppressing excessive growth of crystal grains. When the amount of Zr compound used is less than 0.1% by weight in terms of oxide content, almost no effect of promoting α-alumina formation is observed.
Firing at the same high temperature as when no Zr compound is used is required. If the amount of Zr compound used exceeds 3% by weight in terms of oxide content, Al ₂ O ₃
α-alumina formation is transiently promoted, the amount of grain boundary precipitates increases, and the strength of the final alumina fiber decreases. Next, in order to obtain a good alumina fiber as the object of the present invention, it is necessary that the Si compound and the Zr compound in the aqueous liquid have a specific quantitative relationship. That is, depending on the quantitative relationship between the Si compound and the Zr compound, a phenomenon of clouding or gelation may occur during the preparation of the aqueous liquid material used as the spinning stock solution, making spinning impossible. Although the quantitative ratio at which these phenomena occur depends to some extent on the type and properties of the organic polymer compound used to prepare the aqueous liquid, for example, gelation occurs when polyvinyl alcohol is used as the organic polymer compound. The relationship between the amounts of Si compounds and Zr compounds at the time of generation is expressed in terms of oxide content as shown in the following table.
1.

[Table] In order to form fibers from an aqueous liquid in good condition, it is not enough that the phenomenon of clouding or gelation does not occur, and Si compounds and Zr compounds are more effective. It is necessary to maintain a strict quantitative ratio relationship. That is, in order for the aqueous liquid to have good fiber forming properties that meet the purpose of the present invention, the oxide equivalent content C _si (weight%) of the Si compound and the oxide equivalent content of the Zr compound in the aqueous liquid are required. It is necessary that C _zr (weight %) satisfies the following relational expression: C _si ≦−20log C _zr +10. As the organic polymer compound used for preparing the aqueous liquid, various water-soluble organic polymer compounds having fiber-forming ability are used. Specifically, natural organic polymer compounds such as starch, starch acetate, hydroxyethyl starch, methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; polyvinyl alcohol;
Examples include synthetic organic polymer compounds such as polyurethane, polyacrylate, polyacrylamide, and polyethylene oxide. Among these, polyvinyl alcohol is particularly preferred. The amount of the organic polymer compound used is expressed as a weight percentage (hereinafter referred to as "oxide based percentage") based on the sum of the weights of the corresponding oxides of Al compound, Si compound, and Zr compound in the aqueous liquid. The amount is usually 5 to 30% by weight, preferably 10 to 15% by weight. In the present invention, the above Al compound,
An aqueous solution or sol containing a Si compound, a Zr compound, and an organic polymer compound is prepared and, if necessary, concentrated until an appropriate viscosity is obtained to obtain a stringable aqueous liquid. The suitable viscosity for fiberization depends to some extent on the method of fiberization, but is usually 1 to 1000 poise, preferably 5 to 100 poise. The aqueous liquid thus prepared is subjected to a suitable fiberizing operation to form a fibrous precursor.
The fiberizing operation to be used is not particularly limited, but suitable spinning methods include, for example, a method of extruding an aqueous liquid through pores, a method of blowing an aqueous liquid out of pores using compressed air, a method of blowing an aqueous liquid through centrifugal force, etc. means are available. Although the thickness of the fibrous precursor will also depend on the specific use of the final alumina fiber, suitable fiber diameters for use as high temperature insulation materials are about 1-10 .mu.m, more preferably 1-5 .mu.m. The alumina fibers of the present invention are produced by firing the fibrous precursor at high temperatures. It is preferable to perform a preheating treatment to remove volatile components prior to the firing treatment. The temperature of the preheating treatment is usually 800°C or lower, preferably 700°C or lower.
The preheating treatment may be carried out as an independent process, or may be carried out in conjunction with the firing treatment as an integrated process. The refractory alumina fiber that is the object of the present invention has a long-term
The shrinkage rate (hereinafter referred to as "reheat linear shrinkage rate") needs to be extremely small. The reheat linear shrinkage rate of alumina fibers also depends on the firing temperature of the fibrous precursor. For the purpose of the present invention, good results can be obtained by setting the maximum firing temperature in the range of usually 1210 to 1280°C, preferably 1220 to 1270°C, and performing firing at this temperature for about 20 minutes to 2 hours. I can see it. 1210℃
Below, the above-mentioned effect due to the presence of ZrO ₂ is not manifested, and since α-alumina conversion of Al ₂ O ₃ is insufficient, it is difficult to obtain alumina fibers with a sufficiently small reheating linear shrinkage rate. On the other hand, above 1280℃
Even if the amount of Zr compound is within the above range, α
- Alumina fibers tend to become brittle due to excessive alumina formation. In the alumina fiber of the present invention, Al ₂ O ₃ must not be completely in the form of α-alumina, but must partially exist as alumina in an intermediate state such as δ-alumina. The presence of intermediate alumina imparts flexibility to the alumina fibers. Therefore, the aforementioned effect of promoting α-aluminization due to the presence of ZrO ₂ depends on the amount of ZrO ₂ present.
Therefore, the firing temperature for achieving a suitable degree of α-aluminization of Al ₂ O ₃ in the final alumina fiber depends on the amount of ZrO ₂ present. That is,
Good results can be obtained when the maximum firing temperature T (° C.) satisfies the following relational expression: −20logC _zR +1220≦T≦−20logC _zr +1260. The refractory alumina fiber of the present invention produced by the method of the present invention described above will be explained below. The alumina fiber of the present invention is a metal oxide fiber whose main component is crystalline Al ₂ O ₃ , Al ₂ O ₃ , SiO ₂
and ZrO ₂ in the proportions of 70 to 98.9% by weight of Al ₂ O ₃ , 1 to 29.9% by weight of SiO ₂ , and 0.1 to 3% by weight of ZrO ₂ . Moreover, the content C _si (weight %) of SiO ₂ and the content C _zr (weight %) of ZrO ₂ satisfy the following relational expression: C _si ≦−20log C _zr +10. Now, as mentioned above, in the alumina fiber of the present invention, Al ₂ O ₃ is not completely converted into α-alumina, but partially exists as alumina in an intermediate state such as δ-alumina, and Therefore, the alumina fiber of the present invention has appropriate flexibility. The degree of α-aluminization mentioned above is δ as described below.
It is determined by the degree of In this specification, the "delta degree" refers to the delta-alumina peak (2θ
It is defined as the ratio I〓/I〓 of the peak intensity I〓 of the α-alumina peak (2θ66.5°) to the peak intensity I〓 of the α-alumina peak (2θ66.5°). Therefore, the degree of δ alumina in the alumina fiber of the present invention must be within the range of 0.5 to 1.5, and by having such a quantitative relationship between the α-alumina portion and the δ-alumina portion, the alumina fiber is given a certain degree of flexibility. FIG. 1 is a powder X-ray diffraction diagram of an example of the alumina fiber of the present invention (maximum firing temperature: 1210°C). The degree of δ conversion in this example is approximately 1.5. FIG. 2 is a powder X-ray diffraction diagram of another example of the alumina fiber of the present invention (maximum firing temperature: 1250°C).
The degree of δ conversion in this example is approximately 0.5. When the surface of the alumina fiber of the present invention is observed with a scanning electron microscope, it is observed that the surface state corresponds to a distribution of uniform and fine crystal grains. That is, the alumina fiber of the present invention has a non-porous, smooth surface and a dense structure. Furthermore, the alumina fiber of the present invention has a low degree of embrittlement and a low linear reheating shrinkage rate, so it is suitable for use at high temperatures. Furthermore, in the alumina fiber production method of the present invention, alumina fibers with sufficient performance can be produced at a lower firing temperature than conventional methods, so the thermal energy during firing can be reduced, making it suitable for industrial use. It is useful for Next, specific embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 Metal aluminum pieces (purity 99.5% or more) were added to 20% hydrochloric acid so that the Al/Cl molar ratio was 1.85,
After heating at 95℃ for 3 hours, remove the insoluble matter.
An aluminum oxychloride aqueous solution with an Al/Cl molar ratio of 1.8 was obtained. Add 20% aqueous silica sol (manufactured by Nissan Chemical: trade name Snotex-0) to this aqueous solution, 10%
% zirconium oxychloride aqueous solution and 10% polyvinyl alcohol (PVA) aqueous solution (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name Gohsenol GH-17) were added so that the component amount ratio would be the value shown in Table 2, and then under reduced pressure. The mixture was concentrated at 50°C to obtain an aqueous liquid. The properties (stability), viscosity, and stringiness of the obtained aqueous liquid are shown in Table 2. Each of the above aqueous liquids was made into fibers by blowing out from the pores using compressed air to obtain a fibrous precursor having a fiber diameter of 2 to 3 μm. After preheating each fibrous precursor at 600℃,
Firing treatment was performed at the maximum firing temperature shown in Table 2 to obtain alumina fibers with a fiber diameter of 2 to 3 μm. Table 3 shows the powder X-ray diffraction pattern findings, degree of δ-oxidation, reheating linear shrinkage rate upon heating at 1400° C. for 24 hours, and embrittlement findings by touch observation for each alumina fiber.

【table】

【table】

[Table] Example 2 Same as Example 1, aluminum oxychloride aqueous solution (Al/Cl molar ratio 1.8), 20% aqueous silica sol,
10% zirconium oxychloride aqueous solution and 10%
PVA aqueous solution is mixed with an Al:Si:Zr:PVA component ratio.
Mix at a ratio of 94:4:2:10 and 50% under reduced pressure.
It was concentrated at 0.degree. C. to obtain an aqueous liquid with a viscosity of 22 poise. The above aqueous liquid is blown out using centrifugal force to obtain a fibrous precursor, and then 1240
Alumina fibers were obtained by firing at ℃. The reheating linear shrinkage rate of this alumina fiber when heated at 1400°C for 24 hours was 0.7%, which was good. Next, the component ratio Al of the aqueous liquid in the above example:
Based on Si:Zr:PVA=94:4:2:10 as the standard for Zr=2.0%, only the amount of Zr compound added is 5.0% and 1.0%.
%, 0.75%, 0.25%, 0.1% and 0% (no additives) were prepared, and the fibrous precursors obtained from these were sintered at various maximum sintering temperatures to produce alumina fibers. I got it. The degree of gelatinization was determined for each alumina fiber by powder X-ray diffraction method. Here, the "degree of α-ization" in this example refers to the α-alumina peak (2θ
66.5°), where Zr=
0% (no additives) and the maximum firing temperature is 1270°C, which is set as 100. The obtained degree of gelatinization is shown in FIG. As is clear from FIG. 3, as the amount of Zr compound added increases, the same degree of gelatinization is achieved at a lower maximum firing temperature. However, when the amount of Zr compound added is 5%, the effect of addition becomes small, and the degree of gelatinization tends to be excessive (approximately 250 or more), and the firing temperature range for obtaining alumina fibers with low embrittlement becomes narrow.

[Brief explanation of drawings]

1 and 2 are powder X-ray diffraction patterns of examples of alumina fibers of the present invention. FIG. 3 is a graph showing the relationship between the amount of Zr compound added, the firing temperature, and the degree of gelatinization in the alumina fiber of the present invention. The horizontal axis represents the maximum firing temperature, the vertical axis represents the degree of gelatinization, and the numbers attached to each curve represent the amount of Zr compound added.

Claims (1)

[Claims] 1. A fiber made of a metal oxide whose main component is crystalline aluminum oxide, which contains aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), and zirconium oxide (ZrO ₂ ), They contain Al ₂ O ₃ 70 to 98.9% by weight, SiO ₂ 1 to 29.9% by weight, ZrO ₂ 0.1 to 3% by weight, and the silicon oxide content C _si (weight %) and the zirconium oxide content C _zr ( weight%) satisfies the following relational expression: C _si ≦−20log C _zr +10, and the powder X-ray diffraction spectrum (Anticathode: Cu−K〓)
Intensity I〓 of δ-alumina peak (2θ67.5°) and intensity I〓 of α-alumina peak (2θ66.5°) at
A refractory alumina fiber characterized in that the degree of δ of alumina defined as the ratio I〓/I〓 is within the range of 0.5 to 1.5.