JPH03140509A - Production method of beta alumina fiber - Google Patents

Abstract

PURPOSE:To produce an inexpensive and high efficient beta aluminum fiber, by spinning fibers from a viscous sol obtained from a solution chiefly composed of aluminum nitrate and sodium nitrate and crystallizing it with heat. CONSTITUTION:A solution including specified volume of 100 parts of aluminum nitrate, 2-60 parts of aluminum powder and 2-70 parts of sodium nitrate in weight respectively is heated to produce a viscous sol. Next, fibers are spinned from this viscous sol and the fibers are crystallized with heat to obtain beta aluminum fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention provides a method for producing beta alumina fibers having ionic conductivity. Beta-alcoholic acid 7-iper is also a useful substance used in applications such as force sensors, composite materials, and solid electrolytes.

[Problems that Furukawa tries to solve]

Beta alumina is known to be produced by sintering a mixed powder of sodium carbonate and alumina. Therefore,
Previously known beta aluminas have been provided in bulk or powder form. However, a gas sensor that utilizes the ionic conductivity of beta alumina, 111 composite material,
When it comes to applications such as solid electrolytes, there has been a strong desire to provide them in the form of fibers.

[Means to solve the problem]

The present inventors have conducted extensive research into the production of beta alumina fibers. As a result, by using a solution containing nitric acid (nitric acid) and aluminum nitrate as the main components, fibers can be easily spun, and beta alumina fibers can be obtained by heating the 7-iper. They discovered this, continued their research, and came to propose the present invention.

That is, 1. The present invention is a method of obtaining a viscous sol from a solution containing sodium nitrate and aluminum nitrate as main components, spinning fibers from the viscous sol, and heating and crystallizing the fibers. This is a method for producing alumina fiber.

In order to produce beta-alumina fibers, one essential requirement is to produce fibers whose crystals can easily be converted to the beta type, which serve as a precursor thereof. In order to obtain fibers with the above properties, the problem is how to select raw materials for forming a sol for spinning the fibers.

The raw materials for sol formation in the present invention include sodium nitrate and aluminum nitrate as necessary components. The above-mentioned aluminum component and sodium component are necessary elements constituting beta alumina, which is the target product. The reason for using the above nitrate is that Nitokuma salt is soluble in water and can form a sol with excellent spinnability, and the resulting fiber becomes 100% beta-type crystals when heated. The point is that it can be converted to

The raw material for forming the sol is nitric acid, which is prepared as a solution containing IJium and aluminum nitrate. Such a solution may be any solution as long as it can dissolve the sodium component and the aluminum component, but generally water or an aqueous nitric acid solution is industrially most suitable. When the nitric acid aqueous solution is used, it is a preferred embodiment because the sol has particularly excellent stringability, and the temperature at which the fiber is heated and crystallized is lower, making crystallization of beta-alumina crystals more efficient. The nitric acid concentration of the above nitric acid aqueous solution is not particularly limited, but as the concentration becomes higher than nitric acid, the generation of nitrous acid gas tends to increase. It is preferable to set an upper limit on the amount of water added.

The solution forming the sol in the present invention is generally prepared by dissolving sodium nitrate and aluminum nitrate in water or an aqueous nitric acid solution, or further, if necessary, aluminum powder of about 0.50 to 0.01 m. To do this. The aluminum powder is not only consumed as the aluminum component of the target product, but also effectively acts to form a transparent sol. For this purpose, when preparing a solution containing ordinary sodium nitrate and aluminum nitrate, it is most preferable to use aluminum nitrate and aluminum powder as the aluminum components. The skeleton aluminum component and sodium component are Na components of the fiber described later.
There is no particular limitation as long as it is selected within the range of 2O.XAI,03 (where X is 3 to 11). The most industrially suitable composition ratio is, for example, 10011 parts of aluminum nitrate to 1 part of aluminum powder and 2 to 7 parts of aluminum powder and 2 to 7 parts of nitric acid.
It is preferable to choose from the range of 0i groin.

The cap of the solvent used to prepare the solution depends on the ratio of the raw materials used, especially the aluminum concentration, and cannot be generally specified.

Therefore, it is preferable to use the above-mentioned raw materials after determining them in advance according to their usage ratios. - As a standard for boat fishing, as will be described later, the obtained sol is generally used after being filtered, so the sol should be
It is preferable to determine the concentration of the solvent so that it has an appropriate viscosity, for example, 2 to 3 centipoise.

The sol in the present invention is obtained by heating a solution in which the aluminum component and sodium component are dissolved. Since the heating has the role of promoting the dissolution of the aluminum component and the sodium component and the role of forming a sol, it is generally recommended to base the heating on an hourly basis, and it is usually preferable that the heating be transparent within a range of 5 to 30 hours. .

The heating temperature may be determined as necessary depending on various conditions, but it is generally in the range of 90 to 110°C, and preferably carried out under reflux.

The sol obtained as described above may be used for spinning after being concentrated or further concentrated, but generally it is preferable to filter the sol to obtain a homogeneous sol. As mentioned above, the filtration is usually carried out by 2
~3 cm viscosity is easiest, so
When the sol reaches the above viscosity, ? In order to use the homogeneous sol obtained by performing I11 filtration and prefiltration for spinning, it is preferable to further concentrate it by means of heating, for example, 30 to 90°C or vacuum degassing.

The viscosity of the sol is not particularly limited and varies depending on the spinning means, so it may be selected depending on the spinning means. Usually, the viscosity of the sol is selected from a range of several poise to the viscosity before solidification, but in general, a range of 5 poise to 1000 poise is best. The sol composition before spinning differs depending on the raw material composition, but is generally Na20.XAl2O.
It is preferable to prepare the oxide composition represented by 3 so that X is 3 to 11.

The present invention spins fibers from the above-mentioned viscous sol. The method for spinning fibers from the viscous sol is not particularly limited, and any known spinning method can be used. The spinning method can be selected depending on the shape of the desired fiber. If long fibers are desired, Senmon, which involves spinning by a 7-eye pull method from the surface of a viscous sol, is effective; When the target is fibers, a method of blowing out from a nozzle with an appropriate shape is preferably used. OiI viscous sol has excellent spinnability, so if it is spun using the above-mentioned pulling method, long fibers on the order of meters can be obtained. Therefore, it is possible to obtain fiber shapes ranging in length from micrometer order to meter order and diameters from several μm to several nanometers. The fibers obtained by the above spinning are dried as necessary and used for producing beta alumina fibers.

The fiber obtained by the above method becomes a beta alumina fiber by heating and crystallizing it. The lower the heating temperature is, the lower the conversion to beta alumina is, the more preferable it is from the viewpoint of energy cost and hu. The present invention has the feature that it can be converted to beta alumina at a significantly lower temperature than the conventional method, which required a high temperature of 1500° C. or more for crystallization into beta alumina. That is, the DU thermal temperature in the present invention depends on the oxide composition of the fiber,
Although it varies depending on the heating atmosphere etc., generally 900℃~1
Preferably, the temperature range is 300°C. In particular, when the above heating is carried out in a closed container under an Na 20 atmosphere, the above temperature is particularly preferably 950°C to 1200°C.
The gel-like fibers turn into beta alumina in a few minutes to a few minutes, for example 5 to 30 minutes, at a temperature of . 100% crystallized. Further, even if the above-mentioned heating is carried out in the air, beta alumina fibers, which are the object of the present invention, can be obtained, and this embodiment is industrially very advantageous. Moreover, the above-mentioned heating in the atmosphere can be carried out at a low temperature of 900'C to 1100C, preferably 950 to 1050C, by selecting the oxide composition of the gel fiber. That is, the oxide composition of the gel fiber is Na2O-YAl, 0. When expressed as 900°C to 110°C, when Y is prepared as a gel fiber of 3 to 6.
Beta alumina fibers can be obtained at 0°C. When heating is carried out in the above-mentioned atmospheric environment, m-alumina crystals may be formed in addition to the target beta-alumina crystals, but the m-alumina crystals will become saccharine as the heating time is increased. - When alumina crystals are formed, the heating time may be controlled. In addition, when heating in the above-mentioned atmosphere, the heating time requires a somewhat longer heating time compared to the above-mentioned closed system N&, 0 atmosphere atmosphere heating, for example, 1 hour to i
It is preferable to use a heating time of oo hours and ujb degrees as a reference.

In the present invention, when the gel fibers to be subjected to the heating crystallization are dried beforehand, the heating to the crystallization temperature may be appropriately selected. Since it is common to remove crystal water, it is preferable to determine the necessary heating rate in advance. Generally, in order to remove volatile substances such as water of crystallization under compatible conditions, it is preferable to raise the temperature slowly in a low temperature region, for example, 500° C. or less, and it is also possible to raise the temperature rapidly in a high temperature region. For example, in the normal low temperature range 2~10℃/
min, preferably 2-b, and in the high temperature range, 5-30°C/min, preferably 5-30°C/min.
b In the present invention, no special manufacturing equipment is required for each process for manufacturing beta alumina fibers,
All you have to do is select and use a material that can withstand the temperature and atmosphere in each process. In particular, it is best to use a known refractory crucible for the material to be heated and crystallized, which is a severe condition in the present invention, and gel fibers can be continuously formed using a tunnel kiln-type t-air furnace because the process can be carried out in an atmospheric atmosphere. It is clear that a method of heating can also be adopted.

The alumina fiber obtained in the present invention has a beta crystalline structure, Na2O.zAl! 20, (Z: 5~
11). These points are XfJ
This can be confirmed by first diffraction, infrared M absorption spectrum, etc.

The beta alumina fiber obtained by the present invention is nIJ
As is clear from the description, since the fiber is made of 100% beta alumina, it has excellent ionic conductivity and mechanical properties. Further, for the purpose of further improving these properties, commonly used technical applications can often be applied as effective means to the present invention.

For example, when mixing raw materials for the aluminum component and the sodium component, adding an appropriate amount of oxides such as lithium, magnesium, zirconium, etc. can be suitably used to improve ionic conductivity or mechanical properties.

〔effect〕

The present invention proposes the production of beta alumina fibers by a sol-gel method, and is intended to produce beta alumina fibers industrially at low cost and with high performance.

Further, with the completion of the present invention, it has become possible to use beta alumina in bulk or powder form obtained by conventional manufacturing methods for scum sensors, composite materials, etc., which were difficult to use. Also, by woven or bundled beta-alumina fibers, the surface species can be expanded, which can be used as a gas sensor [l! It can now be used as a battery electrolyte as an 11-body electrolyte, as a Kameike partition wall, as an electrode, etc.

〔Example〕

EXAMPLES In order to explain the present invention more clearly, the present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 The oxide composition of the gel fiber used for producing beta alumina fiber is Na2O.5.5120 in molar composition.
3 was prepared as follows.

Al(No3)3”9H2075,O,!?,NaNO
312.3 g of porcelain was melted in 10011/ml of water, then 16.2 g of aluminum powder was added and mixed well. This was then placed in a separable flask with a volume of M50 Qd, and a separately prepared concentrated 61'jll [( To this was added 1001 t of water containing 15 m (60%), and the mixture was heated under reflux and stirring at 100 to 110°C for 18 hours. The sol obtained by heating was suction-filtered with an aspirator using a porcelain Nutsche equipped with 1 m paper to obtain a homogeneous, transparent, and highly fluid sol with a viscosity of 2 to 37 inch poise at 25°C.

A portion of this sol was placed in a dryer kept at 60° C., and concentrated to about 1,731 ml of the first 8 sol to form a highly viscous sol. By dipping the tip of a glass pellet into this sol and pulling it up,
A large number of gel fibers each having a length of about 1 m were spun. These gel fibers were heated to 60°C and then tto'ct
It was heated and dried. This Gel 7 Eyeper was placed in a refractory crucible and heated to 550°C at a rate of 2°C/min in an electric furnace, then raised to 100°C at a rate of 5"C/min, and held at that temperature for 10 hours. The fibers obtained were white in color and had a diameter of 5 to 250 μm.
As a result, the powder was composed only of ionically conductive beta-alumina crystals. Note that the beta-alumina fiber obtained by this method had a uniform microstructure consisting of fine crystal grains with a size of 0.2 to 0.3 μm, according to a scanning electron microscope observation of its fractured surface. In addition, the AC electrical conductivity of beta alumina fiber is 1~2X 10-'5cx-r at room temperature and 1~2 at 300℃.
X 10-383-'.

Example 2 The oxide composition of the gel fiber used for producing baked alumina fiber was Na 20 .8.
8 Al 203 was prepared as a fertilizer.

AA'2(NO3)3'9H201115,! i', N
Dissolve aNO37,6F in 200311 water, then gradually add aluminum powder 13.6.9 and mix well. Put this into a separable flask with a capacity of 500 d, and add #J 100 ~ under reflux. The mixture was heated at 110° C. for 18 hours with stirring to obtain a sol.

Thereafter, the sol was suction-filtered with an aspirator using a porcelain nutsche equipped with standard MIIJII paper to obtain a homogeneous and obvious sol. A part of it was placed in a dryer kept at 60°C and concentrated, and the length was about 1+a by the same operation as described in Example (1).
A large number of fibers were spun. These gel fibers were dried at 60°C for 60 minutes and then at 110°C for 60 minutes.

This Gel 7 Eyeper has an oxide composition of N&20・5.5A.
Put it in a fireproof crucible with 4,03 ml of gel powder and heat at 5℃/
The mixture was heated to 1100° C. at a rate of 10 minutes, held at that temperature for 10 minutes, and then cooled at a rate of 3° C./minute. The beta alumina fibers obtained were white in color and had a diameter of 10-250 μm. According to X-ray diffraction and electron microscopy, the diameter of the beta-alumina fiber in the enclosure is 0.2 to 0.3μ.
It was composed of beta alumina crystals of m. The AC conductivity of beta alumina fiber is 5 at room temperature.
XIO-'5cR-', 1-2×1 at 300°C
It was 01.

Example 3 Gel fibers obtained in the same manner as in Example 1 were dried in the same manner as in Example 1. Gel fibers within the septum in a refractory crucible, the same composition, Na 20 5.5 A / 2
03 gel powder and heated to 550°C at a rate of 2°C/min. From 550°C to 1100°C under conditions different from Example (1), that is, 100°C higher than 1000°C.
℃ at a rate of 5° C./min and held at that temperature for 10 minutes to obtain white beta alumina fibers having a diameter of 5 to 250 μm and consisting only of beta alumina crystals. The electrical conductivity of the netabator alumina fiber obtained is 2 x 10-' S cm-' at room temperature, 30
It was 2 x 10"" S C1m-' at 0°C.

Example 4 The oxide composition of the gel fiber used for the production of beta alumina fiber is N a 20 ・5 in terms of molar composition.
A1203 was prepared, and an example of heating crystallization in an air atmosphere was carried out as follows. l (No.3
) 3・9H2075,0,9゜NaN0313.61
1 was dissolved in 100at water, and then aluminum powder 16.2.9 was added and mixed well.
oo* separable flask, and 100,111 liters of water containing 20 dttS of concentrated nitric acid (60%), which had been previously used, was added thereto, and the mixture was heated under reflux and stirring at 100 to 110° C. for 18 hours. The liquid obtained by heating is filtered by suction using a porcelain nutsche or glass filter equipped with a constant f1 filter paper,
A homogeneous transparent sol with a viscosity of 2-3 centipoise at 25°C was obtained.

A part of this sol is placed in a dryer kept at 60°C, and concentrated to about 173 of the first 8 sol to make a highly viscous sol. By dipping the tip of a glass rod into this sol and pulling it up, A large number of 1 m long 7-eye yarns were spun. These gel fibers were first heated at 60°C for 1 hour and then heated to 110°C, then arranged vertically on a refractory hearth board approximately 25 cm long, covered with a hearth board of the same size, and placed in an electric furnace. Heated.

Heating was carried out at a rate of 2°C/min up to 550°C, then at a rate of 5°C.
Raise the temperature to 1000'C at a rate of °C/min, and at that temperature
After holding for 0 hours, it was allowed to cool in the furnace. The resulting fibers were white in color, had a diameter of 5 to 200 μm, and were composed solely of ionically conductive beta-alumina crystals, as determined by X-ray powder diffraction.

Claims (2)

[Claims] (1) Production of beta alumina fibers, which is characterized by obtaining a viscous sol from a solution containing sodium nitrate and aluminum nitrate as main components, spinning fibers from the viscous sol, and heating and crystallizing the fibers. Method. (2) The viscous sol consists of 100 parts by weight of aluminum nitrate, 2 to 60 parts by weight of aluminum powder, and 2 to 7 parts by weight of sodium nitrate.
The method for producing beta alumina fibers according to claim (1), wherein the beta alumina fibers are produced by heating a solution containing 0 parts by weight.