JP7245656B2 - Alumina fiber and gripping material for automotive exhaust gas purification equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to alumina fibers and gripping materials for automotive exhaust gas purifiers.

Alumina fiber, which is mainly composed of alumina and silica, exhibits high durability even at high temperatures exceeding 1500 ° C, so it is used as a high temperature refractory insulation material in a wide range of fields such as steel, metals, ceramics, and automobiles. there is
An example of the application of such a high-temperature refractory insulation material is a gripping material in the casing of an automobile exhaust gas purifier. The holding material is provided for the purpose of fixing the catalyst carrier to prevent damage due to vibration and for the purpose of an exhaust gas sealing material (see, for example, Patent Document 1).

JP-A-7-286514

A casing of an automobile exhaust gas purifier expands due to the heat of the exhaust gas, and every time the automobile repeats running and stopping, a load is applied to the gripping material housed in the casing. For this reason, the gripping material is required to have the ability to retain the catalyst carrier for a long period of time even if it continues to be subjected to repeated loads. On the other hand, gripping members are required to have performance that does not cause damage such as longitudinal cracks even when subjected to repeated loads, and that they exhibit good reliability over a long period of time.
The level required for such performance is increasing year by year, and further improvement is required for conventional alumina fibers. Even in applications other than gripping materials, there is a demand for higher levels of various properties of alumina fibers when used at high temperatures. Specifically, there is a demand for an alumina fiber that can exhibit higher strength and maintain a high level of reliability when used in a high-temperature environment.
Based on the above, the present invention provides an alumina fiber that exhibits sufficient strength and can maintain reliability over a long period of time.

According to the present invention, an alumina fiber containing 70% by mass or more and 98% by mass or less of alumina and 2% by mass or more and 30% by mass or less of silica,
In the unloading curve in the load-displacement curve with the displacement on the horizontal axis and the load on the vertical axis, obtained by performing the nanoindentation method with the alumina fiber as the measurement object under the following conditions,
The displacement at the time of 10% unloading from the maximum load is h1,
The displacement at the time of 20% unloading from the maximum load is h2,
The displacement at the time of 80% unloading from the maximum load is h3,
The displacement at the time of 90% unloading from the maximum load is h4,
The slope of the line connecting the point (displacement h2, load P(80)) and the point (displacement h1, load P(90)) is S1 (mN/μm), the point (displacement h4, load P(10)) and the point When the slope of the line connecting (displacement h3, load P (20)) is S2 (mN/μm),
Alumina fibers having a slope ratio S2/S1 of 0.4 or more and 0.8 or less are provided.
(conditions)
・Implement an indentation test in accordance with ISO14577.
・Equipment: Shimadzu dynamic microhardness tester DUH-211
・Indenter elastic modulus: 1.14×10 ⁶ N/mm ²
・Measurement indenter: 115 degree angle between edges, diamond triangular pyramid indenter ・Maximum load: 5 mN
・Load speed: 0.2926 mN/sec ・Maximum load holding time: 5 seconds

Further, according to the present invention, there is provided a gripping material for automobile exhaust gas purifiers formed using the alumina fibers described above.

ADVANTAGE OF THE INVENTION According to this invention, while exhibiting sufficient intensity|strength, the alumina fiber which can maintain reliability for a long period of time can be provided.

FIG. 2 is a schematic diagram of a load-displacement curve obtained by the nanoindentation method;

Hereinafter, embodiments of the present invention will be described in detail.

The alumina fiber according to the embodiment contains alumina (Al ₂ O ₃ ) in an amount of 70% by mass or more and 98% by mass or less, and silica (SiO ₂ ) in an amount of 2% by mass or more and 30% by mass or less.
In the unloading curve in the load-displacement curve with the displacement on the horizontal axis and the load on the vertical axis, obtained by performing the nanoindentation method with the alumina fiber as the measurement object under the following conditions,
The displacement at the time of 10% unloading from the maximum load is h1,
The displacement at the time of 20% unloading from the maximum load is h2,
The displacement at the time of 80% unloading from the maximum load is h3,
The displacement at the time of 90% unloading from the maximum load is h4,
The slope of the line connecting the point (displacement h2, load P(80)) and the point (displacement h1, load P(90)) is S1, the point (displacement h4, load P(10)) and the point (displacement h3, load P(20)), the slope ratio S2/S1 is 0.4 or more and 0.8 or less.
(conditions)
・Implement an indentation test in accordance with ISO14577.
・Equipment: Shimadzu dynamic microhardness tester DUH-211
・Indenter elastic modulus: 1.14×10 ⁶ N/mm ²
・Measurement indenter: 115 degree angle between edges, diamond triangular pyramid indenter ・Maximum load: 5 mN
・Load speed: 0.3 mN/sec ・Maximum load holding time: 5 seconds

By simultaneously controlling the content of alumina and silica and the above-described slope ratio S2/S1, the alumina fiber of the present embodiment exhibits sufficient strength and can maintain reliability over a long period of time.

Hereinafter, the alumina fiber of this embodiment will be described in detail.
(component of alumina fiber)
Alumina fibers of this embodiment comprise alumina and silica. The lower limit of the content of alumina in the alumina fiber of the present embodiment is 70% by mass or more, and more preferably 72% by mass or more. On the other hand, the upper limit of the content of alumina in the alumina fibers according to the embodiment is 98% by mass or less, more preferably 97% by mass or less.

By setting the alumina content in the alumina fiber to 70% by mass or more, the heat resistance can be improved, and in particular, when used as a gripping material for an automobile exhaust gas purification device, the alumina fiber deteriorates due to high-temperature exhaust gas. can be suppressed. In addition, by setting the alumina content in the alumina fiber to 98% by mass or less, the strength of the alumina fiber can be made sufficient. power can be sufficient.

In addition, the lower limit of the content of silica in the alumina fibers according to the embodiment is 2% by mass or more, and more preferably 3% by mass or more. On the other hand, the upper limit of the content of silica in the alumina fibers according to the embodiment is 30% by mass or less, more preferably 28% by mass or less.

By setting the lower limit of the silica content in the alumina fibers to 3% by mass or more, the strength can be increased. On the other hand, by setting the upper limit of the silica content in the alumina fibers to 30% by mass or less, the heat resistance can be enhanced.

In the alumina fiber of the present embodiment, the lower limit of the alumina content with respect to the total mass of alumina and silica is 70% by mass or more, more preferably 72% by mass or more. On the other hand, the upper limit of the content of alumina with respect to the total mass of alumina and silica is 98% by mass or less, more preferably 97% by mass or less.

By setting the lower limit of the content of alumina to the total mass of alumina and silica to 70 mass or more, heat resistance can be improved. Degradation of alumina fibers can be suppressed. In addition, by setting the content of alumina to 98% by mass or less relative to the total mass of alumina and silica, the strength of the alumina fiber can be made sufficient, especially when used as a gripping material for an automobile exhaust gas purification device. The strength and holding power of can be made sufficient.

(Indices stipulated by the Nanoindentation Law)
In this embodiment, the following indicators are defined for alumina fibers from the load-displacement curve obtained under the above-described measurement conditions by the nanoindentation method.
FIG. 1 is a schematic diagram of a load-displacement curve obtained by the nanoindentation method. Load P(90), load P(80), load P(20), and load P(10) are loads removed by 10%, 20%, 80%, and 90%, respectively, from the maximum load Pmax.
The slope S1 (mN/μm) of the straight line connecting the point (displacement h2, load P(80)) and the point (displacement h1, load P(90)) on the unloading curve is expressed by the following formula (1). be.
(P(90)-P(80))/(h1-h2) (1)
The slope S2 (mN/μm) of the straight line connecting the point (displacement h3, load P(20)) and the point (displacement h4, load P(10)) on the unloading curve is given by the following formula (2): expressed.
(P(20)-P(10))/(h3-h4) (2)
In the alumina fiber of the present embodiment, the lower limit of the slope ratio S2/S1 is 0.4 or more, preferably 0.45 or more, and more preferably 0.5 or more. Moreover, the upper limit of the slope ratio S2/S1 is 0.8 or less, preferably 0.75 or less, and more preferably 0.7 or less.

By setting the upper limit of the slope ratio S2/S1 obtained by the nanoindentation method to the above range, the alumina fiber can exhibit sufficient strength and maintain reliability over a long period of time. In particular, when the alumina fibers of the present embodiment are used as the gripping material, even when subjected to repeated loads, the holding performance and reliability of the catalyst carrier can be exhibited in a well-balanced manner over a long period of time.

In the alumina fiber of the present embodiment, the lower limit of the slope S1 is preferably 30 mN/μm or more, more preferably 35 mN/μm or more, and even more preferably 40 mN/μm or more. On the other hand, the upper limit of the slope S1 is preferably 75 mN/μm or less, more preferably 70 mN/μm or less, and even more preferably 65 mN/μm or less.
By setting the slope S1 within the above range, the alumina fibers can be given appropriate elasticity, and for example, when used as a holding material, the holding performance of the catalyst carrier can be further enhanced.

In the alumina fiber of the present embodiment, the lower limit of the slope S2 is preferably 20 mN/μm or more, more preferably 25 mN/μm or more, and even more preferably 30 mN/μm or more. On the other hand, the upper limit of the slope S2 is preferably 50 mN/μm or less, more preferably 45 mN/μm or less, and even more preferably 40 mN/μm or less.

By setting the slope S2 within the above range, the suppleness and cushioning properties of the alumina fibers can be moderated. This makes it difficult for damage such as vertical cracks to occur even if it continues to receive repeated loads. It can be made difficult.

(Method 1 for producing alumina fiber)
Alumina fiber production method 1 according to the embodiment is a method for producing bulk alumina fibers (cotton-like fibers), and includes a stock solution preparation step, a spinning step, a cotton collection step, and a firing step. Details of each step will be described below.

(Undiluted solution preparation process)
As the alumina source, for example, an aluminum oxychloride aqueous solution, alumina sol, etc. are used, and as the silica source, for example, silica sol, polysiloxane, etc. are used. Polyvinyl alcohol, polyethylene glycol, and the like can be used as spinning aids as necessary. A spinning dope is obtained by mixing these in a desired ratio and concentrating under reduced pressure.

(Spinning process)
The spinning stock solution prepared in the stock solution preparation step is extruded into the atmosphere through pores using a spinning device to form an alumina fiber precursor. The spinning device to be used is not particularly limited, and a blowing spinning device, a rotating disk spinning device, or the like can be used. From the viewpoint of preventing fusion of fibers extruded from pores and producing alumina fibers having a high surface pressure, the rotating disk spinning method described in JP-A-2010-31416 is preferably used.

By adjusting the pore size and extrusion conditions, it is possible to control the average fiber diameter and fiber diameter distribution of the obtained alumina fibers, as well as the content of non-fiberized substances called shot. Typically, the average fiber diameter of alumina fibers is adjusted in the range of 3 μm or more and 8 μm or less. The content of shots with a length of 50 μm or longer is preferably less than 1%.

(Cotton collection process)
The alumina fiber precursor obtained in the spinning step is collected by sucking from the lower part of the net conveyor installed in the cotton collection chamber, thereby obtaining an aggregate of the alumina fiber precursor. By adjusting the speed of the net conveyor, the thickness and surface weight of the resulting assembly are adjusted.

(Baking process)
The alumina fiber precursor obtained in the cotton collection step is fired in the firing step. In the firing process, a degreasing process and a crystallization process are performed in this order using a firing device.

The baking rate in the degreasing step is preferably 3° C./min or less. In the degreasing step, decomposition reactions of moisture, hydrochloric acid, and organic matter contained in the precursor occur, and firing products are generated, and the volume of the alumina fiber precursor rapidly shrinks. By setting the baking rate in the degreasing process to 3° C./min or less, volume shrinkage occurs in a state in which moisture, hydrochloric acid, and organic substances are sufficiently decomposed. As a result, an alumina fiber with suppressed generation of defects can be obtained, and the surface pressure can be sufficiently increased. For example, in the degreasing step, firing is performed at a firing rate of 3°C/min or less until the temperature reaches 800°C.

In the degreasing step, exhaust is performed at a rate of 0.1 Nm ³ /h or more and 3 Nm ³ /h or less per 1 kg of alumina fiber precursor. By setting the exhaust amount to 0.1 Nm ³ /h or more, the convection of the cracked gas in the sintering device becomes sufficient, and the cracking reaction is promoted to produce fibers with suppressed defect generation, which in turn increases the surface pressure. be able to. In addition, by setting the exhaust rate to 3 Nm ³ /h or less, it is possible to suppress an excessive increase in the amount of heat carried away by the exhaust gas, thereby facilitating temperature control in the furnace and, in turn, facilitating uniform heating. The pore structure of the alumina fibers can be controlled by controlling the sintering rate and exhaust rate in the degreasing process. For example, it is possible to produce alumina fibers having a fine structure with a total pore volume of 0.0055 ml/g or less.

By changing the maximum firing temperature in the crystallization process, it is possible to control the mineral composition of the alumina fibers.

In the crystallization step, firing may be performed under normal conditions (temperature and holding time) that cause crystallization of the inorganic fiber source. and excellent surface pressure, it is preferable to adopt a step of maintaining the highest firing temperature of 1000° C. or higher and 1230° C. or lower for 5 minutes or longer and 60 minutes or shorter. By setting the crystallization temperature to 1000° C. or higher, the heat resistance of the alumina fiber is improved, and it can be adapted to the operating temperature of the gripping material of the exhaust gas purifying device. On the other hand, by setting the crystallization temperature to 1230° C. or lower, it is possible to suppress the decrease in fiber strength due to excessive crystallization of alumina fibers such as mullite formation, and to keep the contact pressure at a sufficient value. By setting the holding time at the maximum temperature to 5 minutes or more, crystallization proceeds sufficiently, so that the occurrence of uneven baking is suppressed, and the surface pressure of the alumina fibers can be maintained at a sufficient value. By setting the holding time to 60 minutes or less, it is possible to suppress excessive crystal growth of alumina fibers and decrease in surface pressure.

In addition, when the alumina fiber is used for a purpose other than the gripping material of the exhaust gas purifier (for example, an industrial furnace such as a heating furnace or a calcining furnace), the degree of crystallinity of the alumina fiber may be increased by mullite formation or the like. The upper limit of the curing temperature may be 1400°C.

As long as the sintering speed and exhaust conditions for the degreasing step and the crystallization step described above can be satisfied, the sintering apparatus used for sintering is not particularly limited. For example, batch furnaces such as Kanthal furnaces and siliconit furnaces, and continuous furnaces such as roller hearth furnaces and mesh belt furnaces can be suitably used. Moreover, it is also possible to use these sintering apparatuses in combination as needed.

(Method 2 for producing alumina fiber)
Alumina fiber production method 2 according to the embodiment is a method for producing blanket-like alumina fibers (a laminate of cotton-like alumina fibers, usually having a thickness of 5 mm or more and 25 mm or less), and includes a stock solution preparation step, a spinning step, and cotton collection. process, a needling process and a firing process. Among these steps, the stock solution preparation step, spinning step, cotton collecting step, and firing step are the same as in the above-described manufacturing method 1.

In this production method, the needling step described below is performed between the cotton collection step and the firing step.

(needling process)
In the needling step, a needle is pierced into an aggregate made of the alumina fiber precursor. In the needling step, it is preferable to simultaneously or sequentially pierce the stack downward from the top surface and pierce the stack upward from the bottom surface. By carrying out the needling step, the thickness of the blanket-shaped molded body can be controlled, and the properties of the blanket-shaped molded body, such as surface pressure, tensile hardness, and peel strength, can be enhanced.

In the embodiment, by appropriately adjusting the type and blending ratio of each component contained in the alumina fiber and the manufacturing conditions of the alumina fiber, it is possible to obtain an alumina fiber that satisfies the above parameters.

In addition, as a method for producing blanket-shaped alumina fibers, it is used in general web production, such as a method of overlapping thin layer laminates made of alumina fiber precursors by a cross wrapper (see, for example, Japanese Patent Application Laid-Open No. 2000-80547). method can be adopted.

The alumina fibers described above exhibit sufficient strength and can maintain reliability over a long period of time.

(grasping material)
The alumina fiber according to the embodiment exerts a sufficient surface pressure and is less likely to be damaged such as vertical cracks even if it is repeatedly subjected to a load. It is suitably used as a gripping material for fixing and preventing damage due to vibration during running.

When the bulk alumina fibers obtained by the production method 1 described above are used as a raw material for papermaking, they can be processed into a gripping material by wet molding. Moreover, when using the alumina fiber of the blanket-like molded body obtained by the manufacturing method 2 mentioned above, it can be processed into a holding material by dry molding.

Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than those described above can also be adopted.

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

(Example 1)
5000 g of an aluminum oxychloride aqueous solution with an alumina concentration of 20.0% by mass and 1850 g of colloidal silica with a silica concentration of 20.0% by mass were mixed so that the alumina component was 73% by mass and the silica component was 27% by mass. Furthermore, 1096 g of a partially saponified polyvinyl alcohol aqueous solution having a polymerization degree of 1700 at a concentration of 10 mass % was mixed as a spinning aid, and dehydration and concentration under reduced pressure were carried out to prepare a spinning dope of 3300 mPa·s.
This spinning stock solution was spouted out radially from 300 holes with a diameter of 0.2 mmφ which were opened at regular intervals on the circumferential surface of a hollow disc with a diameter of 350 mmφ, by rotating the disc at a peripheral speed of 47.6 m/sec. rice field. The ejected undiluted solution was dried while floating and dropped in hot air of 150° C. to produce an alumina fiber precursor.
This alumina fiber precursor was fired in an air atmosphere using a roller hearth furnace. Firing is carried out by continuously raising the temperature at a rate of 2°C/min while exhausting 1.8 Nm ³ /h per 1 kg of the precursor in a degreasing process at an atmospheric temperature of up to 800°C, and crystallizing from over 800°C to 1200°C. The temperature was raised at a rate of 30°C/min, held at 1200°C for 30 minutes, cooled from 1200°C to 800°C at a rate of 40°C/min, and cooled from 800°C to 300°C at a rate of 125°C/min. Alumina fibers were produced by cooling at the cooling rate.

(Example 2)
Alumina fibers were produced in the same manner as in Example 1, except that the mixing ratio of the raw materials was changed so that the alumina component was 80% by mass and the silica component was 20% by mass.

(Example 3)
Alumina fibers were produced in the same manner as in Example 1, except that the maximum sintering temperature was 1230°C and the temperature was cooled from 1230°C to 800°C at a cooling rate of 40°C/min.

(Example 4)
After holding at 1200 ° C. for 30 minutes, it was cooled from 1200 ° C. to 800 ° C. at a cooling rate of 80 ° C./min and from 800 ° C. to 300 ° C. at a cooling rate of 250 ° C./min. Alumina fibers were similarly produced.

(Comparative example 1)
The same as in Example 1, except that the spouted stock solution was dried while floating and dropped in hot air at 500 ° C., held at 1200 ° C. for 30 minutes, and then naturally cooled from 1200 ° C. to produce an alumina fiber precursor. to produce alumina fibers.

(Comparative example 2)
Alumina fibers were produced in the same manner as in Example 1, except that the rate of temperature increase to 800°C was 15°C/min, and the temperature was maintained at 1200°C for 30 minutes, followed by natural cooling from 1200°C.

(Alumina and silica content)
The obtained alumina fiber was subjected to fluorescent X-ray analysis to measure the content of alumina and silica. Table 1 shows the results obtained.

(Evaluation by nanoindentation method)
An indentation test was performed in accordance with ISO 14577 under the following conditions, and the slopes S1 and S2 and the slope ratio S2/S1 described above were calculated. Table 1 shows the results obtained.
・Equipment: Shimadzu dynamic microhardness tester DUH-211
・Indenter elastic modulus: 1.14×10 ⁶ N/mm ²
・Measurement indenter: 115 degree inter-ridge angle diamond triangular pyramid indenter ・Maximum load (Pmax): 5 mN
・Load speed: 0.3 mN/sec ・Maximum load holding time: 5 seconds

(surface pressure measurement)
A surface pressure measurement was performed in relation to the strength of the alumina fibers. Specifically, the alumina fibers of each of the above examples and comparative examples were compressed from 0.44 g/cm ³ to 0.5 g/cm ³ in bulk density using Autograph (manufactured by Shimadzu Corporation). After 1000 cycles, the contact pressure was measured.

(Presence or absence of vertical cracks)
In relation to the reliability of alumina fibers, the presence or absence of vertical cracks in alumina fibers after the endurance test was examined. Here, longitudinal cracks mean streaks and cracks that occur along the axial direction (or the major axis direction) of alumina fibers.
Specifically, for the alumina fibers of each of the above examples and each comparative example, after performing the compression-release of 1000 cycles as described above, arbitrary 10 alumina fibers were selected and longitudinal cracks were generated using an optical microscope. It was evaluated whether or not

(Evaluation result 1: Surface pressure measurement)
In Examples 1 to 4 and Comparative Example 1, the surface pressure is 9 N/cm ² or more, which is considered to be practically no problem as the surface pressure of alumina fibers, whereas in Comparative Example 2, the surface pressure is It was less than 9 N/cm ² .
(Evaluation result 2: Presence or absence of vertical cracks after durability test)
In Examples 1 to 4 and Comparative Example 2, no longitudinal cracks were observed in any of the 10 alumina fibers. Alumina fibers that do not develop longitudinal cracks after the endurance test are considered to exhibit stable reliability over a long period of time when used as a gripping material. On the other hand, in Comparative Example 1, one of ten alumina fibers was found to have longitudinal cracks, confirming that it is difficult to maintain reliability when used as a gripping material.

Claims (5)

Alumina fibers containing 70% by mass or more and 98% by mass or less of alumina and 2% by mass or more and 30% by mass or less of silica,
In the unloading curve in the load-displacement curve with the displacement on the horizontal axis and the load on the vertical axis, obtained by performing the nanoindentation method with the alumina fiber as the measurement object under the following conditions,
The displacement at the time of 10% unloading from the maximum load is h1,
The displacement at the time of 20% unloading from the maximum load is h2,
The displacement at the time of 80% unloading from the maximum load is h3,
The displacement at the time of 90% unloading from the maximum load is h4,
The slope of the line connecting the point (displacement h2, load P(80)) and the point (displacement h1, load P(90)) is S1, the point (displacement h4, load P(10)) and the point (displacement h3, load P(20)) is the slope of the line connecting P(20)),
Alumina fibers having a slope ratio S2/S1 of 0.4 or more and 0.8 or less.
(conditions)
・Implement an indentation test in accordance with ISO14577.
・Measurement indenter: 115 degree angle between edges, diamond triangular pyramid indenter ・Maximum load: 5 mN
・Load speed: 0.3 mN/sec ・Maximum load holding time: 5 seconds In the unloading curve,
2. The alumina fiber according to claim 1, wherein {load P(90)-load P(80)}/(h1-h2) is 30 mN/μm or more and 75 mN/μm or less. In the unloading curve,
3. The alumina fiber according to claim 1, wherein {load P(20)-load P(10)}/(h3-h4) is 20 mN/μm or more and 50 mN/μm or less. 4. The alumina fiber according to any one of claims 1 to 3, which is used for forming a gripping material of an automobile exhaust gas purifier. A gripping material for an automobile exhaust gas purifier, which is formed using the alumina fiber according to any one of claims 1 to 4.

Images