JPH01280022A - Aluminum nitride fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title fiber having high thermal conductivity and high strength by spinning a solution consisting of an Al compound and an organic binder to give precursor fiber, adding carbon powder to the precursor fiber and calcining the blend in a nitrogen atmosphere under a specific condition. CONSTITUTION:A solution consisting of an aluminum compound (e.g., aluminum oxychloride) and an organic binder (e.g., PVA) is spun to give precursor fiber or alumina fiber, to which carbon powder is added and which is calcined in a nitrogen atmosphere at a calcination temperature for calcination time in a range on or higher than a curve passing point A (1,500 deg.C, 7 hours), point G (1,600 deg.C, 2 hours) and point L (1,700 deg.C, 0.5 hour) to give the aimed fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum nitride fiber having high thermal conductivity and high strength, and a method for producing the same.

[Conventional technology]

Regarding aluminum nitride fiber, for example, JP-A-61-
124626 and Japanese Patent Application Laid-Open No. 62-53417, the manufacturing method thereof is described.

As these methods, ■ a method of nitriding aluminum metal fibers, and ■ a method of nitriding an alumina precursor fiber obtained by spinning a solution consisting of an aluminum compound and a carbon-containing substance (organic binder) are disclosed. .

When aluminum nitride powder is obtained by nitriding alumina, carbon powder is generally used as a reducing agent for alumina.

That is, when alumina and a carbon source are mixed and fired in a nitrogen atmosphere, aluminum nitride is obtained by the following reaction.

At203+3C+N2→2AtN+3CO The principle is almost the same in the method of nitriding the alumina precursor fibers described above. At the initial stage of firing the weft precursor weft fibers, carbon-containing substances (organic binders) are carbonized to produce carbon, and aluminum compounds are decomposed to become alumina. Next, the above reaction At203+3C+N2→2A
tN+3 Co progresses to produce aluminum nitride fibers.

Therefore, in this case, carbon, which is a reducing agent for alumina, utilizes carbon in the organic matter contained in the precursor fiber. This organic binder is essential for imparting spinnability to the spinning solution.

[Problem to be solved by the invention]

However, when carbon in the organic matter contained in the precursor fiber is used as a reducing agent for alumina, the reaction formula At
As can be seen from 203+3C+N2→2AΔ+3CO, a large amount of organic matter is theoretically required. As mentioned above, this organic substance also serves as a binder that gives spinnability to the spinning solution, so consideration must be given to degreasing the binder during firing by lengthening the degreasing time. To some extent, it becomes difficult to determine firing conditions such as temperature increase.

Furthermore, the organic binder portion in the precursor fibers tends to remain as pores, and from this point of view as well, it is not preferable to add a large amount of organic matter. As described above, there are various problems when using only an organic binder as a reducing agent.

Furthermore, as a result of repeated research by the present inventors, a car for reducing alumina? However, the carbon in the organic matter contained in the precursor fiber is not sufficient for this purpose, and the X-ray diffraction image of the resulting fiber confirms the formation of AtX0YN2, which is an intermediate product during the AtO+3C+N2→2 AtN+3CO reaction. However, the formation of aluminum nitride is hardly confirmed.

AtxOWNz defined here is the aluminum nitride production reaction λt203+3C+N2→2AtN+3C'O
Refers to the intermediate product between α-At203 and AΔ, for example, At1, Oj 5N #At27039”
9602B8N4 (δ-4AtN, 96At2o3)
.

It is a compound of the form AAON (At(8A+x/A)04-XNX). Aluminum nitride is a substance with high thermal conductivity, but it is well known that the thermal conductivity decreases significantly if oxygen remains in aluminum nitride. (For example, Ceramics Association Journal 86 (4) 1978 rA
Effect of impurity oxygen on sintering of M and thermal conductivity, etc.) Remaining of the intermediate product defined by AtxOYN2 above is undesirable because it causes a decrease in thermal conductivity.

That is, one of the problems that this application attempts to solve is At20
It is an object of the present invention to provide aluminum nitride fibers that are substantially composed only of aluminum nitride and in which no intermediate products defined by AtX0YN2 or AtX0YN2 remain.

Furthermore, in order to further increase the strength of this aluminum nitride fiber, another challenge is to make the sintered structure of the aluminum nitride particles constituting the fiber more dense.

[Means to solve the problem]

As a result of intensive research against the background of the current situation described above, the present inventors have found that when alumina precursor fibers are fired in a nitrogen atmosphere to produce aluminum-enriched fibers, there is a problem in the spinning of the fibers. It has been discovered that by adding aluminum nitride powder, a highly thermally conductive aluminum nitride fiber consisting essentially of aluminum nitride can be obtained, and that by limiting the firing conditions, a high strength aluminum nitride fiber can be obtained, and the present invention has been made. reached. That is, the gist of the present invention is an aluminum nitride fiber consisting essentially only of aluminum nitride, and furthermore, the average particle diameter of each particle of each aluminum nitride fiber constituting this fiber is 1 μm or less, and the porosity is 10%. The aluminum nitride fiber is as follows.

Here, it means that it consists essentially only of aluminum nitride.
In the process of nitriding alumina precursor fibers or alumina fibers to produce aluminum nitride, virtually the entire view is turned into nitride alumina fibers, including At2o3 and intermediate products AtxO and N2.
There is virtually no remaining.

The method for this confirmation will be explained. That is, X-ray diffraction t9
A & , (!-At20. and its intermediate product AtxOYN2, respectively 20-33.2°,
The heights of the peaks at 433° and 45.3° to 45.5° are respectively a, b, and e, and the aluminum nitride ratio is (
When defined as a/(a+b+c) ) X 100,
This value is substantially 1o o (%).

The present invention also provides a method for producing aluminum nitride fibers, which comprises adding carbon powder to precursor fibers or alumina fibers obtained by spinning a solution consisting of an aluminum compound and an organic binder, and firing the mixture in a nitrogen atmosphere. Monodeashi,
Aluminum nitride fibers made of substantially only aluminum nitride can be produced using the method described above, with the firing temperature and firing time set at point A (1500°C, 7 hours) and point G (1600°C, 7 hours) in Figure 1.
℃, 2 hours), and the range K is greater than the curve passing through point L (1700℃, 0.5 hours).

FIG. 1 is a diagram showing firing temperature (horizontal axis) and firing time (vertical axis), which are firing conditions for precursor fibers or alumina fibers. On the other hand, the average particle diameter of each particle constituting the fiber is 1#
? For aluminum nitride fibers with high strength, which have a porosity of 10 cm or less and a porosity of 10 cm or less, in addition to the above-mentioned conditions for the firing temperature and time,
℃, 7 hours), by limiting the range below the curve passing through point K (1700℃, 2 hours). That is, the first
The fibers obtained under the firing conditions within the range of curves A, G, L and E in the figure are extremely dense, with an average particle diameter of each particle constituting the fiber of 1 μm or less and a porosity of 10% or less. Since it is a fiber with a tensile strength of 50 kgf/- or more. Aluminum nitride fibers having such characteristics can be used in fields that require electrical insulation and high thermal conductivity.

Hereinafter, the aluminum nitride fiber of the present invention will be explained in detail, focusing on its manufacturing method. First, the composition of the precursor fiber and the spinning solution will be described. The spinning solution requires an aluminum compound that thermally decomposes to form alumina when heated to 1000° C. or higher, and an organic binder to impart spinnability to the spinning solution. Examples of the aluminum compound include aluminum oxychloride, aluminum chloride, and aluminum acetate. Further, examples of the organic binder include polyvinyl alcohol and polyethylene oxide. In the conventional method for producing aluminum nitride fibers, carbon produced when the organic binder is fired is used as is in the production of aluminum nitride. In this case, since the carbon in the organic binder acts as a reducing agent for alumina, it was necessary to add a large amount of the organic binder to promote the nitriding reaction. However, in the production method of the present invention, the organic binder need only be added to the spinning solution to impart spinnability, and only a small amount of needles can be added.

The ratio of the aluminum compound as a starting material to the organic binder is, for example, the aluminum compound in terms of alumina and the organic binder in terms of polyvinyl alcohol.The ratio of alumina:polyvinyl alcohol is preferably 95=5 to 50:50. The ratio is approximately 90:10 to 60:40 (parts by weight).

If the amount of polyvinyl alcohol is less than 5 M parts, the spinnability of the spinning solution will be poor, the spun fibers will not be thick, and the resulting fibers will have low strength.

On the other hand, if the amount is 50 parts by weight or more, the content of polyvinyl alcohol in the precursor fiber is too high, requiring a long time for degreasing as described above, and the fired fiber is porous and has poor strength. will be low.

The spinning solution is heated, stirred and matured, dehydrated and thickened until it reaches a viscosity suitable for spinning. The viscosity suitable for spinning is 500 to 3000 poise for long fibers, and 100 to 600 poise for short fibers. As the spinning method, the spinning method used in the production of general alumina fibers, etc. can be applied, the extrusion method can be applied in the case of long fibers, and the centrifugal spinning method can be applied in the case of short fibers.

Next, firing will be explained. The spun fibers are fired in a nitrogen atmosphere to produce aluminum nitride fibers.
At this time, carbon powder is added to the precursor fiber. Examples of carbon powder include carbon black, coke powder,
Any material that can react and supply the carbon source, such as calcined or graphitized carbon powder, may be used. This is extremely effective in reducing alumina and promoting the nitriding reaction. The amount to be added is preferably about 100,150 to 100/100 parts by weight of ht2o5/carbon in the precursor fiber.

Incidentally, applying a large amount of an organic binding agent to the filament at the time of filament winding during long fiber spinning is also an effective means, similar to adding carbon powder.

Examples of the organic binder include ethyl laurate dissolved in perchlorethylene or /IF roughin dissolved in a solvent such as toluene.

The firing temperature and time can be selected depending on the physical properties of the fiber to be obtained. For example, if you want to obtain a fiber made only of aluminum nitride, points A and G in Figure 1
, L. (In Fig. 1, the area is indicated by diagonal lines or cross lines.) Points A and G.

The curve connecting L indicates that the aluminum nitride ratio of the resulting fiber is 1.
00% borderline. Therefore, under the firing conditions of this line drawing, the fibers obtained have a low aluminum nitride percentage and α-A.
t203. Alternatively, a large amount of At-OYN2 (intermediate product) remains, and the thermal conductivity is correspondingly low. In addition, the firing conditions for obtaining high-strength fibers in which the aluminum nitride ratio is substantially 1001, the average particle diameter of each particle constituting the fiber is 1 μm or less, and the porosity is 101 or less are as shown in points A and G in Figure 1. , L and the curve connecting E and K. (In Figure 1, this is indicated by the cross-lined area.) If fl fibers are fired too much, the particles that make up the fl fibers will grow too much, and the porosity will be high, resulting in a decrease in strength. cause. The curve connecting points E and K in Figure 1 is the boundary line for obtaining fibers with an average particle diameter of 1 μm or less and a porosity of 10% or less, which can be obtained under higher firing conditions. The fiber has an aluminum nitride ratio of 1
Although it is 0.00cm, it does not meet the above conditions and the strength of the fiber is impaired.

Furthermore, similar results can be obtained by adding carnon to alumina fibers obtained by calcining the precursor fibers at 1100° C. and calcining the mixture in a nitrogen atmosphere.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the Examples.

(Example 1) Aluminum oxychloride (ht2(OH) 5Ct) and polyvinyl alcohol (hereinafter referred to as PVA) (polymerization degree 1
500) is mixed as a raw material. For aluminum oxychloride, we used ``1 Tachypain'' from Tamoto Kagaku Co., Ltd., and used PVA.
is dissolved in ion-exchanged water and used as a 10q6 aqueous solution. The blending ratio of aluminum oxychloride and PVA is the first
This is the table of contents. Aluminum oxychloride is At203
Displayed in terms of conversion. The mixed solution was concentrated under reduced pressure at 50°C to obtain a spinning solution with a viscosity of 1000 poise. Add this spinning solution to 1
Using a spinning nozzle with 48 moving holes of 00μ, the pressure was 2.
Extruded into dry air at 100°C at 0 kg/cIn”4
It was wound up at a speed of 00 m/min. The fiber diameter at this time is 12
It was μm. The precursor fibers obtained by these spinning were cut to a length of 150". In the obtained precursor fiber,
Precursor fiber Az2o3k/carbon powder 100
Carnon powder was added in an amount of 150!11 parts and fired. The carbon powder used was manufactured by Showa Kaget Co., Ltd.
Show Black N-326".

Pipe diameter 5c for firing! The test was carried out in an IL Tammann furnace at a nitrogen gas flow rate of 1 t/min. The heating rate is 3 in both cases.
The temperature was set at 00°C/h. The firing temperature and time are as shown in Table 1.

Table 1 shows the aluminum nitride percentage when precursor fibers of various compositions were added with carbon powder and fired under various mild firing conditions.

Here, the aluminum perforation rate will be explained.

According to the X-ray diffraction image of the obtained fiber, AΔ, α-At203
and its intermediate product AtX0YN, the respective diffraction angles 2θ-33, 2°, 43.3° and 45.3° ~ 45
．． When the peak heights at 5° are respectively a, b, and c, aluminum nitride rate (%) = (a/(a+b+
c)) Defined by X100i. AtN, α-At20
3. The reason why each diffraction angle (2θ position) of AtxoYN2 is set as described above will be described below.

43.3° for α-At203 and 33.2° for AtN are the diffraction angles of the X-ray intensity ratio I/I and -Zoo, respectively.

Further, the intermediate product AtxO-N2 has several types of crystal systems as described above, and the intensity ratio (1/I) and interplanar spacing (dX) are as shown in Table 2.

Table 2 In Table 2, dX is shown in descending order of dX/■.

The peaks of the dX of intermediate products tend to overlap with those of AtN, but the peaks are different from those of AtN. was 45.3 to 4565°.

For the above reasons, the diffraction angle 2θ of AtxOYN2 is set to 45
．． The angle was 3 to 45.5°. Composition is AL20s/PVA
-70/30 firing conditions at 1500℃ for 7 hours (first
The X-ray diffraction images of the aluminum nitride fibers at point A) and 1500° C. for 0.5 hours (also point D) are shown in FIGS. 2 and 2, respectively.

The X-ray diffraction was performed at 25 KV and 10 mA using a copper anticathode and a nickel filter. Other conditions were: scanning speed 4°/min, divergence slit 1°, light receiving slit 0.
It is 30.

The aluminum nitride ratio of the aluminum nitride fibers in FIGS. 2(,) and (b) is as follows.

An example of calculation for the fiber in FIG. 2(a).

Calculation example for the fiber in Figure 2(b).

Table 1 shows the relationship between the composition of the starting materials, firing conditions, and aluminum nitride conversion rate. When the results in Table 1 are plotted on the diagram showing the firing conditions in Figure 1, the range where the aluminum nitride ratio is substantially 100% is at point A (1500') in Figure 1.
C57 hours), G (1600℃, 2 hours), L (
1700'C10.5 hours).

(Example 2) Based on the aluminum nitride fiber prepared in Example 1, the starting material S composition At205/1) MA = 70/30
(7) The porosity, average particle diameter, and tensile strength of those with a particularly high degree of firing were measured. These results are shown in Table 83.

The M3 surface porosity is determined from the amount of mercury intrusion measured by a porosimeter (“Autoscan 60” manufactured by Quantachrome). An example in which the porosity was determined from the pore distribution diagram of aluminum nitride fibers under firing conditions of 1700° C. for 2 hours will be described. Distribution map #) The amount of mercury that entered the fiber #pores was 0.03
6 cc/y-, and since the true specific gravity of aluminum nitride is 3.26, 0.036 Porosity-0,036+3.26'-"10"' 10
(%)

The average particle diameter is "' Lineal Intersept
Technique for Measuring G
rain 5ize 1n Tvro-PhaseC
+eramic” J, Am Soe 55 (1:
] 109 (1972) using the intercept method. The intercept method is a method of drawing several straight lines on a photograph of a fiber, measuring the number of grain boundaries that intersect with the straight lines (intercept number), and calculating the average particle diameter of the grains that make up the fiber using the following formula. It is.

Cod - 1,56X C/MN d, - Average particle diameter of fiber C - Total straight length M - Magnification of photograph N = number of intercepts
This was done based on 7601.

As shown in Table 3, the tensile strength of the fibers largely depends on the porosity and average particle size; the smaller both the porosity and average particle size, the higher the strength. Aluminum nitride rate 100%
As the firing degree is increased under the firing conditions (increasing the firing temperature and firing time), the particles that make up the fibers grow,
In the process shown in Table 3 (1700° C., 7 hours), the fibers grew to 3 μm and the porosity was 23%.As a result, the strength of the fibers corresponding to points I and J deteriorated significantly. Less strength deterioration 5
In Table 3, the firing conditions A, E, and F can maintain a strength of 0 kg 7 cm or more. In addition, in order to have a tensile strength of 50 kll/art 2 or more, the porosity must be 10% or less. It is necessary that the particle size is 1.0 μm or less.

Applying the above to Figure 1, we find that the aluminum nitride percentage is essentially 100% and the average particle diameter of the particles constituting the fiber is 1#! Hereinafter, the firing range in which the porosity is 10 cm or less is the area surrounded by the curve connecting points A, G, and L and the curve connecting points E and K.

In addition, A (1500°C, 7 hours) and I (170°C) in Table 3
Scanning electron micrographs of aluminum nitride fibers produced under firing conditions of 0° C. and 7 hours are shown in FIGS. 3(&) and (b), respectively. Under both firing conditions A and I, the aluminum nitride percentage is essentially 100%, but it is clear that the aluminum nitride ratio in A is denser, and in the firing condition A, abnormal grain growth occurs and the fiber surface is broken. Deformation can be confirmed.

(Comparative Example 1) Three types of precursor fibers with different raw material compositions (At2o3/'Pv
A-90/10.70/30.60/40) carbon was fired at 1700° C. for 7 hours without additives. Table 4 shows the aluminum nitride percentage of the obtained fibers. The aluminum nitride ratio is low in all compositions, and unless Kagen (carbon powder) is added, n-fibers consisting essentially only of aluminum nitride cannot be obtained.

Table 4 (Example 3) Alumina fibers obtained by firing precursor fibers (At203/PVA-70/30) at 1100°C were used in Example 1.
As well as car? powder was added and fired under various conditions. Table 5 shows the aluminum nitride ratio and firing conditions of the obtained fibers.

Table 5 A', p', K' shows the curves AC, L in Fig. 1.
σ is above the curve and the aluminum nitride rate is 100%, but when σ is below the curve, the aluminum nitride rate is 10
It doesn't become 0chi.

〔effect〕

When producing aluminum nitride fibers by firing alumina precursor fibers or alumina fibers in a nitrogen atmosphere, it is extremely effective to add carbon powder, and the firing conditions (
By limiting the firing temperature and time, it is possible to produce fibers consisting essentially only of aluminum nitride.

Aluminum nitride fibers, which are obtained by nitriding alumina precursor fibers or alumina fibers, do not exhibit a glass-like structure like conventional commercially available short alumina fibers (for example, NICHIAS Co., Ltd. "Rupeel", etc.), and are made of fine nitrided particles. It becomes a structure in which aluminum particles are sintered.

Therefore, in order to provide strength as a fiber, it is necessary to make these sintered structures more dense.

This was made possible by limiting the firing conditions (specifically, the area marked by the cross line in FIG. 1).

As a high-strength, high-thermal-conductivity fiber material, this fiber is expected to have a wide range of applications in the electronic industry and other fields.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between firing conditions (firing time, firing temperature) and aluminum nitride ratio, and FIG. 2(a). Figure 3) is an X-ray diffraction diagram of aluminum nitride fiber.
a), ω) are micrographs (2500x magnification) showing the shape of aluminum nitride fibers. Applicant Showa Denko Co., Ltd. Agent Patent Attorney Tera 1) Real firing Onkaji C) Figure 3 (a) Figure 3 (b>

Claims (1)

[Claims] 1. Aluminum nitride fiber consisting essentially of aluminum nitride. 2. A method for producing aluminum nitride fibers, which comprises adding carbon powder to precursor fibers or alumina fibers obtained by spinning a solution consisting of an aluminum compound and an organic binder, and firing the fibers in a nitrogen atmosphere. 3. In the method of claim 2, the firing temperature and firing time are point A (1500°C, 7 hours) and point G (1600°C, 7 hours) in Figure 1.
C., 2 hours), and the range is equal to or greater than the curve passing through point L (1700.degree. C., 0.5 hours). 4. The aluminum nitride fiber according to claim 1, wherein each particle constituting the fiber has an average particle diameter of 1 μm or less and a porosity of 10% or less. 5. In the method of claim 3, the firing temperature and firing time are point E (1600°C, 7 hours) and point K (1700°C, 7 hours) in FIG.
C., 2 hours).