JPH0328230A - Production of magnesium complex polymer and magnesia fiber or film - Google Patents

Abstract

PURPOSE:To obtain the subject complex polymer useful for obtaining a serviceable magnesia film or fiber at a low cost by selecting a specified magnesium complex polymer. CONSTITUTION:A magnesium complex polymer of the formula (wherein L is a neutral ligand selected between water and an alcohol) is selected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnesium complex polymer, and more particularly to a method for producing magnesia fibers or magnesia films obtained using the magnesium complex polymer.

(Prior Art) Magnesia is characterized by being lighter and having better heat resistance than alumina and zirconia, which are typical industrialized inorganic oxides. Therefore, magnesia can be preferably used as a heat-resistant material, a reinforcing material, a filler, and an insulating material.

Furthermore, since the coefficient of thermal expansion of magnesia is almost equal to that of metal, magnesia fibers are extremely promising as FRM.

Furthermore, it can also be preferably used as a base material for oxide superconductors because there is little interdiffusion reaction with other substances at high temperatures.

Here, 1. magnesia film, and 2. This article will discuss the current technology and problems associated with producing magnesia fibers.

1. Magnesia film In order to obtain the magnesia film, Suba sotering,
Possible methods include vacuum evaporation, CvD1 ion plating, or a method in which a magnesium organometallic compound or magnesium alkoxide is mixed with a suitable liquid and applied to a substrate, followed by heat treatment.

Sputtering, vacuum evaporation, and CvD1 ion plating require large-scale vacuum equipment. Furthermore, since the film formation rate is extremely slow, films produced by these methods have the disadvantage of being expensive.

On the other hand, in the method of mixing a magnesium organometallic compound or magnesium alkoxide with a suitable liquid, applying it to a substrate, and then heat-treating it, the starting material is expensive and is relatively difficult to handle (in the atmosphere). There were problems with spontaneous combustion, hydrolysis, etc.

2. Magnesia fiber: Typical inorganic oxide fibers currently in practical use are:
They are alumina fiber and zirconia fiber, and there is no commercially available magnesia fiber. Regarding magnesia fiber,
There are only a few proposals for manufacturing methods 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 component that becomes magnesia after sintering is contained in the spinning stock solution in an amount of only 8.5 w t % at most. Therefore, the volumetric shrinkage during the process of firing the precursor fibers is extremely large, and the fiber morphology is not necessarily maintained sufficiently, making it 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 it is possible that the metal alkoxide or the hydrolyzate of the metal alkoxide takes the form of precursor fibers through some kind of chemical bonding. None. Therefore, the fibers obtained by this method are not necessarily dense and often have fiber bends and voids, making it difficult to put them into 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,
The need to use a substituted metal alkoxide makes the process complicated and increases the cost. 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, so it has been 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 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 a practically usable magnesia membrane or magnesia fiber, and a raw material thereof. The purpose of the present invention is to provide a magnesium complex polymer, a stock solution for molding, and a method for producing the same.

(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) Formula [ [Mg (OOCCH3)・4L] (
CH,COO)] Magnesium complex n polymer.

However, L is a neutral ligand selected from water or alcohol.

■Formula [[Mg (OOCCH3)・4L] (CH
3COO)] n A stock solution for molding containing a magnesium complex n polymer and having a viscosity of 2 to 10,000 poise.

However, L is a neutral ligand selected from water or alcohol.

(3) Concentrate the magnesium acetate solution and/or the magnesium compound acetic acid solution to a viscosity of 2 to 10,000.
A method for producing a stock solution for molding characterized by forming it into poise.

<4) Concentrate the magnesium acetate solution and/or the magnesium compound acetic acid solution to a viscosity of 2 to 100
1. A method for producing magnesia fibers or films, which comprises heat-treating a molded product obtained by spinning or forming a film using a liquid made to 00 poise.

(5) The method for producing magnesia fibers or films according to (3) or (4), wherein the magnesium acetate solution is an aqueous magnesium acetate solution and/or an alcoholic magnesium acetate solution.

e) The method for producing magnesia fibers or films according to (3) or (4), wherein the magnesium compound is at least one selected from magnesium hydroxide, magnesium chloride, and magnesium acetate.

The present invention will be explained in detail below.

It is known that saturated aqueous solutions of magnesium acetate have a high viscosity.

(1) Rivette, Journal of the Chemical Society, page 1063, 1926; (2) Goode et al., page 1950, 1928 (^.C.D.
Ribell, Journal ol the Che
Mical Society 1063 (1926);
E. A. Goode, el. al ibid. 1
950 (1928)) discloses an experiment to investigate solubility by adding magnesium acetate tetrahydrate to water.
There are reports that supersaturated aqueous magnesium acetate solutions exhibit a viscosity of about 1.5 poise.

This publication proposes polymerization of magnesium acetate as the reason for the increase in viscosity, and proposes a model of the following formula (I).

Magnesium complexes generally have hexacoordination. Therefore, the formula (
In the model I), it is thought that one H20 is arranged at the top and bottom of the paper.

Of course, it is possible to obtain magnesia by heat-treating this supersaturated magnesium acetate solution. However, since the content of magnesium and oxygen in the solution is low, the viscosity is also low, and there is no spinnability, it is difficult to form it into a fiber or film form, and it is difficult to obtain a magnesia fiber or film that can withstand practical use. There was nothing I could hope for.

By the way, it is well known that the amount of a compound dissolved in a particular liquid depends only on the temperature and does not depend on the dissolution process.

For example, NaCA' is up to 26.3 for water at 20°C.
It is possible to dissolve up to 8 wt%.

At this time, whether NaC/ is gradually added to the water, NaCl
Even if a dilute aqueous solution is concentrated, solubility remains constant regardless of the process of creating the solution.

However, surprisingly, when the present inventor concentrated an unsaturated aqueous magnesium acetate solution, the above publication (
Even if it exceeds the saturation concentration expected from Fig. 1 in 1),
No crystallized substances appeared in the concentrated liquid. For example, at 25° C., a concentrated solution containing 60 wt % or more of anhydrous magnesium acetate could be obtained. According to the experimental results of the above-mentioned publication, when the content of anhydrous magnesium acetate is increased to 44 wt% or more, crystallized substances should appear.

Even more surprisingly, upon concentration, the viscosity of the liquid increased to 2 poise or more, and it exhibited extremely good stringability.

This experimental result shows that the solubility of magnesium acetate depends on the process of making the solution.

This strongly suggests that the structure of this concentrated magnesium acetate solution is different from that of a dilute solution.

The present inventors have discovered that concentration of a magnesium acetate solution brings it into a state suitable for spinning or film formation, and furthermore, the present inventors have discovered that a magnesium acetate solution can be made into a state suitable for spinning or film formation. By heat-treating the material, we succeeded in obtaining dense magnesia fibers or films with excellent mechanical properties.

The idea of the present invention is completely different from conventional ones.

That is, the present invention does not simply add magnesium acetate to water until it becomes supersaturated to obtain a solution with a high magnesium acetate content, but rather concentrates the solution to contain magnesium acetate in a solution above the normal saturation concentration. The experiment described in the above-mentioned publication is based on the principle,
Their points of view and ideas are different. Of course, special public service
As in Example 1 of Japanese Patent Publication No. 67, a polymer may be added as a thickener, or as in JP-A No. 58-91823,
This method is completely different from the method for producing magnesia using a metal alkoxide, as disclosed in Japanese Patent Application Laid-Open No. 61-230643.

The reasons why an extremely dense sintered body can be obtained using the concentrated liquid according to the present invention are as follows: 1) Magnesium is uniformly dispersed in the solution at the atomic level, and 2) The composition that becomes magnesia (Mg and This is due to the high concentration of O). Table 1 shows an example of the MgO yield (wt%) of the magnesia/a condensed solution obtained when the concentrated solution was heat-treated.

Table 1 Note) Magnesium 7A: H2 0/M g (C2 H3
02) 2●4H20 Magnesium 7B: CH3 0H/Mg (C2H3
0,)●4H20 As shown in Table 1, the MgO yield is 15.0% to 17.5%, which is higher than the example (8.5%) in the Japanese Patent Publication No. 1987-567. It can be seen that the yield is

Furthermore, the present inventor has succeeded in experimentally determining the structure of a polymer in polymerization in a concentrated magnesium acetate solution.

Below, we will discuss the investigation process that led to the determination of the structure of the magnesium complex polymer, using an aqueous magnesium acetate solution and a methanol solution of magnesium acetate as examples.

Experiment 1 180g of H20 (10mo
1) Mg (C2 H3 02 ) 2 ●4H2
The solution was concentrated by dissolving 21.44 g (0.1 mol) of 0.0 and heating. The concentration temperature in this case is 90°C.

Heating was discontinued when the solution became very viscous.

When the solution was observed several hours later, the viscosity of the concentrated solution was so high that it showed almost no fluidity even when the beaker was tilted.

The concentrated solution was left standing in the atmosphere in order to drive off free water. After 2 days, a part of the concentrated solution had changed to crystallized material, and 3
After a few days, almost all of the concentrated solution had become a crystallized product. What is the change over time in the mass m of the liquid remaining in the beaker (later becoming a crystallized substance)? is shown in Figure 1.

Experiment 2 Mg(C2H302)2.4H2021.44g (0
．． 1mo 1) to CH3 0H 1 2 8 g (4
mol) and concentrated using an evaporator.

The concentration temperature is 60°C. The concentrated liquid was left standing in the atmosphere for one month in order to evaporate free methanol.

The liquid did not solidify and was viscous.

The liquid applied to the partially stabilized zirconia substrate was
When baked at ℃ for 20 hours, 15
Magnesia corresponding to wt% was obtained.

From Experiment 1 (Figure 1), the mass of the residual liquid is observed to increase somewhat after 2 to 5 days after concentration, but after 7 days it remains almost constant at about 22.35 g. I understand.

On the other hand, Mg (C2 H30
■) 2.4H20 is approximately 21.45 g, which shows good agreement with the mass of the residual liquid.

Therefore, it is considered that in the magnesium acetate polymer, four water molecules are coordinated with one magnesium acetate polymer. In this case, the difference of about 0.9 g may be due to water trapped in the crystallized product.

If we follow the model of the above-mentioned publication, the mass of the residual liquid is 1
It should be 7.85 g, and it is extremely difficult to explain the experimental results using the model in the above-mentioned publication.

The viscous liquid in Experiment 2 was Mg (C2 H3 02
)2.4 (CH30H), magnesia equivalent to 4.9% of the liquid should be obtained by calcination, which shows good agreement with the experimental results. Therefore, it is reasonable to assume that in this system as well, four methanol molecules are coordinated with one magnesium molecule.

When four neutral ligands L are coordinated to magnesium, the polymer of the magnesium complex takes the structure shown in the following formula (II).

[ [Mg (OOCCH3)-4L] (CH3C
00)], one acetate ion is within the coordination sphere of the Mg ion so as to satisfy the main atom n valence and the sub valence, and firmly binds Mg-Mg. One more
The acetate ions are outside the coordination sphere.

Acetate ions outside the coordination sphere also play a role in binding Mg-Mg, but their force is thought to be much weaker than that of the acetate ions inside the coordination sphere. The two O's in the acetate ion are in a resonance state. At this time, Mg-0
The bond between Mg and Mg...O is also in a resonance state and is considered to be equivalent. This resonance is thought to be a major reason why magnesium complex polymers can be stably handled in air.

By the way, when magnesium acetate is dissolved in a liquid, the following two cases can be considered for the development mechanism of a magnesium complex polymer.

1) Once the acetate ion dissociates, it combines with the magnesium ion again to form a polymer.

2) The acetate ion does not dissociate, but two water molecules dissociate to form a polymer.

In order to determine which of the above-mentioned expression mechanisms of the magnesium complex polymer, the present inventors investigated magnesium acetate 4
The conductivity was measured for the hydrate solution and the magnesium chloride hexahydrate solution.

The solution concentration is 2% of the solution per 0.001 mol of magnesium acetate tetrahydrate (or magnesium chloride hexahydrate).
．． The amount was set to 5 mol. The measurement temperature was 28°C. Table 2 shows the measurement results.

Table 2? ) Magnesia A: H20/Mg (C2H3 0■)
2.4H20 Magnesia B: CH30H/Mg (C2 H3
02),・4H20 Magnesia C: H,0/MgCQ2' 6H20 Magnesia D: CH30H/MgCQ2・6H20 Same as the experimental results shown in the above publication, the conductivity of the magnesium chloride hexahydrate solution is higher than that of magnesium acetate tetrahydrate. The electrical conductivity is higher than that of the hydrate. However, compared to the conductivity of magnesium acetate tetrahydrate (or magnesium chloride hexahydrate) solution, that of H201 or CH,OH is three to four orders of magnitude higher. From the experimental results, it is thought that acetate ions are dissociated in a dilute solution of magnesium acetate tetrahydrate, similar to a solution of magnesium chloride hexahydrate.

The difference in electrical conductivity between the aqueous solution system of magnesium acetate tetrahydrate and the aqueous solution system of magnesium chloride hexahydrate should be interpreted as being due to the sizes of chloride ions and acetate ions. In a dilute aqueous system of magnesium acetate tetrahydrate, magnesium exists in the form of [Mg 6 (H20)] 2'', and the inventor speculates that 2(H20) is eliminated as the concentration progresses. ing.

The present inventors also succeeded in obtaining a viscous liquid by concentrating the Mg (OH) 2 /CH 3 COOH system. However, the structure of the polymer is not necessarily clear. This is due to the complex behavior of a concentrated solution in that if it is left standing in the air for a day or night, it dries and becomes powdery, but if it is left standing for an even longer period of time it becomes a viscous liquid.

There are no particular limitations on the solvent used in preparing the magnesium acetate solution. It is possible to preferably use water or alcohol in which magnesium acetate can be easily dissolved. Among alcohols, methanol is particularly preferred since it can increase the yield of magnesia. For example, at room temperature, magnesium acetate can be sufficiently dissolved by adding 100 g of water (or alcohol) to 10 g of magnesium acetate.

In carrying out the present invention, when an acetic acid solution of a magnesium compound is used, there is no particular limitation on the magnesium compound used. Any magnesium compound can be used as long as it is soluble in acetic acid, and for example, inexpensive magnesium hydroxide, magnesium chloride, and magnesium acetate can be preferably used. Furthermore, regarding the concentration before concentration, a higher concentration is desirable because a concentrated solution can be obtained more efficiently. Of course, it is desirable to sufficiently dissolve the magnesium compound before concentration. For example, at room temperature, 1 g of magnesium hydroxide can be sufficiently dissolved in 100 g of acetic acid.

When concentrating a solution to obtain a highly viscous concentrated solution,
Any known method may be used.

The liquid may be left in the atmosphere and a portion of the liquid may naturally evaporate, but it is possible to concentrate more quickly by concentrating the liquid by heating with an evaporator or gas burner. Note that there is no particular limitation on the liquid temperature for concentration.

There is no problem even if the concentration is performed at room temperature.

When using the magnesium complex polymer as a film raw material or after straining the spinning dope, it is preferable that the concentrated solution contains 5 Qwt% or more of the magnesium complex polymer. This is because the yield of magnesia increases and dense and smooth magnesia can be obtained. Furthermore, the viscosity of the concentrated solution is adjusted to 2 to 10,000 boads, preferably 100 to 2
000 bores, film formation by concentrated solution,
This is preferred because spinning becomes easier. Especially spinning? In this case, by adjusting the viscosity within the above-mentioned range, it is possible to impart spinnability to the spinning dope, which is very preferable. Of course, there is no problem in adding a solution of water, alcohol, acetic acid, etc. to the concentrated solution for the purpose of adjusting the viscosity of the concentrated solution.

There are no particular limitations on forming the concentrated solution into a film, but methods such as bar coating, roll coating, spray coating, and gravure coating can be preferably used. As for the base material, a film made of magnesia alone can be obtained by using a material that is carbonized during sintering and eventually burns out, such as a film of PET or nylon.

Alternatively, if ThO2, UO2, etc. having a high melting point are used as the base material, it is possible to obtain a composite material in which a magnesia film is formed on the base layer.

When spinning a concentrated solution, 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.

The viscous and spinnable liquid is commercially available magnesium acetate 4.
It can also be obtained by leaving the hydrate in the atmosphere for a long time (for example, about two weeks at room temperature). In this case as well, it is thought that bolimerization of magnesium acetate tetrahydrate occurs, but adjusting the viscosity is not always easy and it takes time to become a viscous liquid.
A method of obtaining a viscous liquid by leaving the hydrate in the atmosphere is not very preferable.

Furthermore, for the purpose of obtaining magnesia containing alumina, silica, calcia, etc., it is perfectly acceptable to add aluminum, silicon, calcium, compounds thereof, etc. to the concentrated solution.

When heat-treating the product formed from the concentrated solution, it may be fired at a temperature slightly lower than the usual temperature for producing magnesia or at a temperature slightly lower than that at which magnesia powder is sintered. The reason why firing is possible at a relatively low temperature is that magnesium is extremely uniformly dispersed in the solution. Specifically, 500℃
As mentioned above, it is preferable to perform the firing at 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) Example 1 Weighed 180 g of water in a beaker,
Magnesium acetate tetrahydrate Mg (C2 f{302
) 22.4g of 2.4H20 was dissolved. Heat with a gas burner and concentrate until the viscosity becomes 300 poise.
It was used as a spinning stock solution. The spinning dope was viscous and exhibited good spinnability. The spinning stock solution was discharged from a monohole mouthpiece with a diameter of 100 μm under nitrogen pressure. Draft temperature is 150
℃. The taken precursor fibers were heated at 150°C for 2 hours.
After holding, the temperature was raised to 2000°C and held for 10 hours to obtain white magnesia continuous fibers. The fibers are polycrystalline and have a diameter of 10 μm. It was extremely dense, had no bends, had a smooth surface, and had excellent mechanical properties.

? Example 2 The spinning dope obtained in Example 1 was applied onto a PET film to a thickness of 50 μm and dried. The coating method is a bar coating method. The film was fired at 1800°C for 10 hours. The obtained magnesia film was dense and had a smooth surface.

Example 3 Magnesium acetate tetrahydrate Mg (C2 H3 02
)2.4H,0 22.4g methanol 200g
The mixture was dissolved in water and concentrated using an evaporator until the viscosity reached 500 poise to obtain a spinning stock solution. The spinning stock solution was blown out from a nozzle with a high-speed air stream to form a sheet. The sheet-like material obtained consisted of short precursor fibers. By firing the sheet material, the average fiber length is 30 m.
A fabric composed of short magnesia fibers with a diameter of 20 μm was obtained.

Example 4 The spinning dope obtained in Example 3 was applied onto a ThO2 substrate to a thickness of 20 μm. The coating method is a roll coating method. By baking the substrate at 2000° C. for 20 hours, a composite material in which a magnesia film was formed on the thoria substrate was obtained.

Example 5 3 g of magnesium hydroxide Mg (OH) was dissolved in 180 g of acetic acid CH3COOH and concentrated in an evaporator until the viscosity reached 200 poise. The liquid was applied onto a PET film in the same manner as in Example 2, and then the film was baked at 1500° C. for 15 hours to obtain a dense and smooth magnesia film.

(Effects of the Invention) According to the present invention, it is possible to produce dense and smooth magnesia films and magnesia fibers at low cost.

The magnesia film and magnesia fiber obtained according to the present invention can be preferably used as a heat-resistant material, a reinforcing material, a filler, an insulating material, or a base material for an oxide superconductor.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between mass and time in a concentrated magnesium acetate solution.

Claims (6)

[Claims] (1) Formula [[Mg(OOCCH_3)・4L](CH_
3COO)] magnesium complex polymer represented by n. However, L is a neutral ligand selected from water or alcohol. (2) Formula [[Mg(OOCCH_3)・4L](CH_
3COO)] A stock solution for molding containing a magnesium complex polymer represented by n and having a viscosity of 2 to 10,000 poise. However, L is a neutral ligand selected from water or alcohol. (3) Concentrate the magnesium acetate solution and/or the magnesium compound acetic acid solution to a viscosity of 2 to 10,000.
A method for producing a stock solution for molding characterized by forming it into poise. (4) Concentrate the magnesium acetate solution and/or the magnesium compound acetic acid solution to a viscosity of 2 to 10,000.
A method for producing magnesia fibers or films, which comprises heat-treating a molded product obtained by spinning or forming a film using a poised liquid. (5) The method for producing magnesia fibers or films according to claim (3) or (4), wherein the magnesium acetate solution is an aqueous magnesium acetate solution and/or an alcoholic magnesium acetate solution. (6) The method for producing magnesia fibers or films according to claim (3) or (4), wherein the magnesium compound is at least one selected from magnesium hydroxide, magnesium chloride, and magnesium acetate.