JPH02277822A - Production of magnesia fiber - Google Patents

Abstract

PURPOSE:To obtain the title dense fiber excellent in mechanical properties and useful as a base material fiber for reinforcing materials, filler, electrical insulating materials and oxide superconductors by heat treatment of precursor fiber produced by mixing a magnesium compound, acid and alcohol followed by concentration and then carrying out spinning. CONSTITUTION:The objective fiber can be obtained by baking at pref. 500 -2800 deg.C precursor fiber which is produced by mixing (1) a magnesium compound (pref. magnesium hydroxide or magnesium alkoxide), (2) an acid (pref. acetic acid, lactic acid, hydrochloric acid, nitric acid, formic acid or sulfuric acid) and (3) an alcohol (e.g. methanol, ethanol) followed by concentration and then carrying out spinning.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing magnesia fiber.

More specifically, the present invention relates to a method for producing magnesia fibers that are preferably used as reinforcing materials, fillers, insulating materials, or base fibers for oxide superconducting wires.

(Prior art) Inorganic oxide fibers can be used at high temperatures or in high-temperature oxidizing atmospheres, so they can be used as heat-resistant reinforcing materials in the aviation and space fields, or as reinforcing filling materials for resins, metals, fibers, etc. It is used in various industrial fields.

Typical inorganic oxide fibers currently in practical use include alumina fibers and zirconia fibers.

For example, Japanese science and technology (Table 1. p, 28゜3
-4. No. 24. Vol. 23, 1982), alumina is lightweight and has relatively excellent heat resistance, while zirconia has a high density but has excellent heat resistance.

However, in recent years, the heat resistance of inorganic oxide fibers,
The demand for weight reduction is unstoppable, and the current situation is that inorganic oxide fibers that have better heat resistance and are lighter than alumina fibers and zirconia fibers are required.

On the other hand, among inorganic oxides, magnesia is characterized by low density and excellent heat resistance. Therefore, if we can supply magnesia fiber that can withstand practical use, it will not only be an alternative fiber to alumina fiber and zirconia fiber, but it will also be possible to open up a new field as a high-performance inorganic oxide fiber, which will greatly contribute to the development of the industrial world. It seems to be. However, unfortunately, no magnesia fibers have been commercialized, and only a few proposals for manufacturing methods have been made in patent publications. This clearly shows how difficult it is to turn magnesia into fibers.

For example, Example 1 of Japanese Patent Publication No. 48-567 discloses a method for obtaining magnesia fibers by using an aqueous solution containing hydrous magnesium acetate and a polymer as a starting material, obtaining precursor fibers, and firing the precursor fibers. has been done. However, the magnesia contained in hydrated magnesium acetate is only 19 wt 1% at most, and furthermore, hydrated magnesium acetate dissolves only 66 wt% in water at 68°C, so the weight part of magnesia contained in the precursor fiber is becomes extremely low. Therefore, the volumetric shrinkage during the firing process of the precursor fiber is extremely large.
The fiber morphology is not necessarily maintained sufficiently, and it has been extremely difficult to obtain magnesia fibers that can withstand practical use.

Further, JP-A-58-91823 proposes a method for obtaining a metal oxide molded body from a metal alkoxide and a viscosity imparting agent. Unfortunately, since this method uses a viscosity-imparting agent, there is a problem in that the volumetric shrinkage of the precursor fiber during firing becomes large. Furthermore, in this method, the metal alkoxide is merely kneaded into the viscosity imparting agent, and does not take the form of fibers due to some kind of chemical bond between the metal alkoxides or the hydrolysates of the metal alkoxides. Therefore, the fibers obtained by this method are not necessarily dense, and the fibers have bending,
They often have voids and the like, making it difficult to put them to practical use.

Furthermore, JP-A No. 62-230643 discloses that an aqueous solution consisting of a mixture of a metal alkoxide and a substituted metal alkoxide is hydrolyzed to form a sol and then concentrated, and the viscosity of the concentrated sol is in the range of 10 to 500 poise. A method of spinning to obtain precursor fibers is disclosed.

However, in this method, in addition to the metal alkoxide,
Since it is necessary to use a substituted metal alkoxide, there is a problem that the process becomes complicated and the cost becomes high.

Furthermore, simply setting the viscosity of the concentrated sol to 10 to 500 poise does not necessarily result in a viscous liquid that can be spun.
It was extremely difficult to obtain the precursor fiber itself. Therefore, with this method, it was impossible to obtain magnesia fibers that could be put to practical use.

Although the problems related to the method for producing magnesia fibers have been pointed out in the patent publications above, the present situation is that a method for producing magnesia fibers with characteristics that can be put to practical use has not yet been established.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the problems of the prior art, and to provide a method for inexpensively producing magnesia fibers that can be put to practical use. be.

(Means for Solving the Problems) To achieve the above object, the inventors of the present invention have finally arrived at the present invention after many years of intensive study. The outline is as follows.

(1) A method for producing magnesia fiber, which comprises heat-treating a precursor fiber obtained by mixing and concentrating a magnesium compound, an acid, and an alcohol, and then spinning the mixture.

(2) Claim (1) wherein the magnesium compound is magnesium hydroxide and/or magnesium alkoxide.
The method for producing magnesia fibers described in .

(3) The method for producing magnesia fibers according to claim (1), wherein the acid is at least one selected from acetic acid, lactic acid, hydrochloric acid, nitric acid, formic acid, and sulfuric acid.

The present invention will be explained in detail below.

Generally, in a liquid containing a metal alkoxide and an alcohol, a method of hydrolyzing the alkoxide is used to directly or indirectly bind the metals to each other. For example, in the method for producing heat-resistant fibers based on alumina or titanium oxide silica, disclosed in Japanese Patent Publication No. 52-47052, alcohol is added to alcoholate, which is mixed and reacted, and then left to stand in the atmosphere. A method is described in which a viscous, spinnable liquid is obtained by slow hydrolysis.

The present inventor also attempted to leave a liquid prepared by adding alcohol to magnesium alkoxide in the air at room temperature for a period of several minutes to a month. Unfortunately, although the viscosity of the liquid increased over time, the liquid did not become viscous and spinning was impossible.

They also tried adding water to a liquid containing magnesium alkoxide and alcohol and concentrating it while heating.

However, in this case as well, although the viscosity of the liquid increased as it was concentrated, it could not be made into a viscous liquid and spinning was impossible.

Although it may not be necessary to explain it again here, it is necessary to note that it is not always possible to judge whether spinning is possible or not based only on the parameter of viscosity. For example, when clay is dried, the viscosity of the clay increases as it dries, and eventually it solidifies, but as is well known, spinning clay at any viscosity is difficult.
It is extremely difficult.

Therefore, it is extremely difficult to obtain precursor fibers by simply hydrolyzing a liquid in which alcohol is added to a metal alkoxide and adjusting the viscosity of the liquid, as disclosed in JP-A-62-230643.

That is, in order to obtain magnesia fibers that can be put to practical use, it is not enough to adjust the viscosity appropriately; it is necessary to make the liquid viscous and spinnable. In reality, it is difficult to quantitatively define a ``viscous and spinnable liquid,'' and here we refer to a liquid that does not cause drips during spinning and can yield substantially continuous precursor fibers. It is defined as At this time, it is desirable that the viscosity of the liquid be 10 to 1000 poise.

As mentioned above, in order to obtain a viscous and spinnable liquid without using a viscosity-imparting agent, it is not sufficient to simply hydrolyze a liquid in which alcohol is added to magnesium alkoxide; It is necessary to link magnesium molecules directly or indirectly through a reaction.

Due to the lack of specific guidelines, it was extremely difficult to obtain a viscous spinning solution that was capable of being spun using a liquid prepared by adding alcohol to magnesium alkoxide as a starting material. It was also possible to obtain a viscous spinning dope. It was first obtained by mixing magnesium alkoxide, acid, and alcohol and then concentrating the mixture.

The reason why a viscous and spinnable liquid is obtained by adding an acid is not always clear, but the inventors of the present invention speculate as follows.

Mg (OR) 2 +2H20 →Mg (OH)2 +2ROH■n M g
(OH) 2 → HO(Mg-0)nH + (n 1) H20■ Here, R is an alkyl group.

If a liquid containing alcohol added to magnesium alkoxide is simply left in the atmosphere or hydrolyzed by adding water, the reaction will almost complete at step ①, making it impossible to obtain a viscous and spinnable liquid. I don't think it will be possible.

On the other hand, when an acid is added to a liquid in which alcohol is added to magnesium alkoxide, the reaction (■) occurs, and Mg-
A viscous spinning dope may be obtained due to the formation of zero chains. However, the bonding mechanism is completely unknown, such as why the reaction (2) occurs when an acid is used, and how magnesium and oxygen are bonded.

Magnesium hydroxide is dissolved in water at room temperature about 8 x 10. □-4w
The fact that it dissolves only in t% and dissolves in acids may be linked to the mechanism of reaction (■). Alternatively, since the liquid obtained by adding alcohol to magnesium methoxide can be considered alkaline, adding an acid is equivalent to neutralizing it, and this neutralization reaction may be linked to the mechanism of reaction ■. However, the details are unknown. Future research is awaited, including confirmation of the existence of Mg-0 chains.

Furthermore, the present inventors substituted magnesium alkoxide,
We succeeded in obtaining a viscous spinning dope by using magnesium hydroxide. The results of this study are detailed below.

If a more viscous liquid can be obtained than in reaction (1), a viscous spinning stock solution should be obtained by using magnesium hydroxide as a starting material without using magnesium alkoxide. The present inventor attempted various studies. It has been found that a viscous, spinnable liquid can be obtained by mixing the magnesium hydroxide, acid and alcohol and then concentrating the liquid. However, it was difficult to obtain a viscous spinning stock solution even if any one of acid, alcohol, and magnesium hydroxide was missing.

When using magnesium hydroxide in carrying out the present invention, commercially available magnesium hydroxide can be used. Alternatively, it is of course possible to obtain magnesium hydroxide by reacting hot water with magnesium. There are no particular limitations on the alcohol added to magnesium hydroxide. For example, methanol and ethanol can be preferably used. The amount of alcohol is preferably about 10 to 300 parts by weight based on magnesium hydroxide.

When using magnesium alkoxide, there are no particular limitations on the types of magnesium alkoxide and alcohol. In general, magnesium alkoxide easily reacts with the atmosphere and is often difficult to handle, but if magnesium and alcohol are allowed to react at a certain temperature, it is possible to obtain a liquid mixture of magnesium alkoxide and alcohol. The mixed liquid has the characteristics of being stable in the atmosphere and easy to handle. The reaction at this time is shown by formula (■).

M g + 2ROH → M g (OR) 2 + H2 ■ Particularly when methanol or ethanol is used as the alcohol, ■ quickly at a relatively low temperature.
This reaction is suitable for industrial production. When methanol is used, it is preferable to carry out the reaction at a temperature of about room temperature to 100°C, and when ethanol is used, it is preferable to carry out the reaction at a temperature of about room temperature to 150°C. If methanol is used here,
Needless to say, magnesium methoxide can be obtained, and when ethanol is used, magnesium ethoxide can be obtained. As is clear from the formula (■), “at least 2 moI for 1 mol of magnesium
! It is desirable to add and react the above alcohols.

There are no particular limitations on the acid used, but at least one selected from acetic acid, lactic acid, nitric acid, formic acid and sulfuric acid is used. These acids are preferred because they provide a viscous, spinnable liquid relatively quickly. The amount of acid used may be appropriately selected depending on the type of alkoxide and alcohol, but it is preferably about 10 to 300 parts by weight based on magnesium hydroxide or magnesium alkoxide.

In addition, after mixing magnesium hydroxide or magnesium alkoxide, acid, and alcohol, it is preferable to stir for about 1 minute or more in order to allow the reaction to proceed sufficiently.

A viscous, spinnable liquid is obtained by mixing the magnesium compound, acid and alcohol and then concentrating the liquid. There are no particular limitations on the concentration method. The liquid may be left in the atmosphere and a portion of the liquid may naturally evaporate,
If the liquid is concentrated using an evaporator or the like, it is possible to perform the concentration more quickly. The reason why a viscous spinning dope can be obtained by concentration is probably that the alcohol and water produced in reaction (2) are quickly removed. The processing temperature during concentration should be selected appropriately depending on the type of magnesium alkoxide, alcohol, acid, etc. For example, when using methanol as the alcohol, it is desirable to set it at room temperature to about 100°C; In use, it is desirable that the temperature be from room temperature to about 150°C.

In carrying out the present invention, it is equally acceptable to use magnesium alkoxide and magnesium hydroxide at the same time, and to mix alcohol and acid. Furthermore, to obtain magnesia fibers containing alumina, silica, calcia, etc., it is perfectly acceptable to add aluminum, silicon, calcium, compounds thereof, etc. to the spinning dope.

The viscosity of the spinning dope is preferably about 10 to 1000 poise. You can easily check whether the liquid is viscous and can be spun by, for example, dipping the tip of a glass rod into the spinning solution and seeing whether the spinning solution pulls threads like starch syrup. can.

Of course, there are no particular limitations on the spinning method. It is possible to extrude the precursor fibers from a die or to blow out short precursor fibers from a nozzle using a compressed air flow.

When heat-treating the precursor fiber, it may be fired at the usual temperature for producing magnesia, or at a slightly lower temperature. Specifically, it is preferable to bake at a temperature of 500° C. or higher and 2800° C. or lower.

Hereinafter, the present invention will be explained in more detail using Examples.
The validity of the present invention and the scope of rights are not limited or restricted thereby.

Rather, it brings about the next application and development.

Example 1 Magnesium hydroxide (Mg (OH) 2 ) 20
g, methanol (CH30H) 20g and acetic acid (CH3C
15 g of OOH) was added and thoroughly stirred to obtain a transparent liquid. Thereafter, the liquid was concentrated using an evaporator until the viscosity reached 300 poise (2. A viscous spinning stock solution was obtained. The bath temperature at this time was 80°C.

A spinning stock solution was discharged from a monohole [1 gold] with a diameter of 100 μm under nitrogen pressure. The draft temperature was 1,500C. After holding the taken precursor fibers at 150°C for 2 hours, the temperature was raised to 2000°C and held for 10 hours to obtain white continuous magnesia fibers. The fibers were polycrystalline, had a diameter of 10 μm, were extremely dense, had no bends, had a smooth surface, and had excellent mechanical properties.

Example 2 20 g of magnesium ribbon (Mg) was added to 100 g of methanol (CH30H), and the mixture was allowed to stand at 35°C for 5 hours. The liquid was then filtered and acetic acid (CH, COOH)
20 g was added and stirred for 30 minutes.

Thereafter, the liquid was concentrated using an evaporator until the viscosity reached 300 poise to obtain a viscous spinning stock solution.

At this time, the bath temperature was 50°C. The subsequent treatment was carried out in the same manner as in Example 1 to obtain magnesia fibers having the same characteristics as in Example 1.

Example 3 In Example 2, ethanol (C
,,H50H) 100g, add magnesium,
It was left standing at 50'C for 5 hours. The subsequent treatment was carried out in the same manner as in Example 1 to obtain magnesia fibers having the same characteristics as in Example 1.

Example 4 The spinning dope obtained in Example 1 was blown out from a nozzle using a high-speed air stream. The sheet-like material obtained consisted of short precursor fibers. By firing the sheet material, the average fiber length is 3 Onl nl and the diameter is 20 μm.
A fabric composed of short magnesia fibers was obtained.

(Effects of the Invention) According to the present invention, it is possible to inexpensively produce dense magnesia fibers with excellent mechanical properties.

The magnesia fibers obtained according to the present invention can be preferably used as reinforcing materials, fillers, insulating materials, base fibers of oxide superconductors, and the like.

Claims (3)

[Claims] (1) A method for producing magnesia fiber, which comprises heat-treating a precursor fiber obtained by mixing and concentrating a magnesium compound, an acid, and an alcohol, and then spinning the mixture. (2) Claim (1) wherein the magnesium compound is magnesium hydroxide and/or magnesium alkoxide.
The method for producing magnesia fibers described in . (3) The method for producing magnesia fibers according to claim (1), wherein the acid is at least one selected from acetic acid, lactic acid, hydrochloric acid, nitric acid, formic acid, and sulfuric acid.