JPS63319299A - Aluminum borate whisker and production thereof - Google Patents

Abstract

PURPOSE:To obtain long acicular crystals having a compsn. represented by a formula 2Al2O3.B2O3 (Al4B2O9), superior heat insulating property and superior resistance to hot mineral acids and hot alkalis by treating components for feeding Al and boric acid together with a flux at a relatively low temp. CONSTITUTION:Al hydroxide or an inorg. salt of Al is selected as a component for feeding Al. Boron oxide, an oxyacid of boron or an alkali metal salt thereof is selected as a component for feeding boric acid. Both the components are brought into a reaction by heating to 600-1,000 deg.C in the presence of a flux and produced aluminum borate is grown to obtain whiskers having a compsn. represented by a chemical formula 2Al2O3.B2O3 (Al4B2O9), 0.05-5mum diameter, 2-50mum length and 10-100 aspect ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an aluminum borate whisker and a method for producing the same.

The whisker of the present invention has excellent chemical resistance, heat insulation, heat resistance, neutron absorption ability, and electrical insulation, and can be used as a heat insulating material, a heat resistant material,
In addition to corrosion-resistant materials, thermoplastic resins, thermosetting resins, cement,
It is useful as a reinforcing material for ceramics, metals, etc.

(Prior Art) Ceramic whiskers having excellent thermal and mechanical properties have been industrially manufactured and researched in recent years. Ceramic whiskers are broadly classified into non-oxide type and oxide type, and the former include SiC, 5i3N
a, etc., and the latter is Ca504.

K2O・6Ti02 (Special Publication No. 55-25157)
, 2Mg0.B2O3 (Japanese Unexamined Patent Publication No. 60-204697).

Non-oxide whiskers generally have a high melting point (1900
°C or higher), and has excellent heat resistance, but because the atmosphere must be adjusted during production, the costs for equipment and raw materials are high, and the uses of the resulting whiskers are limited.

On the other hand, the melting point of oxide whiskers is not as high as that of non-oxide whiskers (1000-1600°C).
Therefore, the heat resistance is inferior, but since it can be manufactured by a liquid phase method using a melting agent in the atmosphere, the equipment and raw material costs are low. Therefore, it can be used in general-purpose fields that do not require very high heat resistance, such as reinforcing materials for plastics and reinforcing aluminum.

The phase diagram of aluminum borate, a general term for aluminum borates, under normal pressure has already been completed, and [
P, J, M, Gielisse; Nature, 483
6.69-70 (1962)], 2A as a compound
Although the presence of I203.B2O3 has been revealed, the whisker material of this compound has not been obtained. Several attempts have been made to synthesize whiskers in the past, but all that have been obtained are whiskers with a composition of aluminum and boron that is not shown in the phase diagram.

For example, according to US Pat. No. 3,080,242,
By heating aluminum hydroxide and boron oxide to 1400°C and then slowly cooling them, 3A]2C13・B2O3 and 9
It is known that whiskers with a composition of AI203.B2O3 can be obtained, and the U.S. Department of the Interior's Bureau of Mines has reported that whiskers with a composition of 2.5AI20 can be obtained by heating aluminum oxide, sodium tetraborate, and lithium chloride to 1200'0.
Whiskers with the composition 3.B2O3, and aluminum oxide, sodium tetraborate, and boron oxide at 1400%
By heating to °C, 4.8AI2D3・B2O
It has been reported that whiskers with a composition of 3 can be obtained.
f Mines Report of Invest
igations6575'' (1965)].

Furthermore, according to US Pat. No. 3,350,166, the latter is converted into 4 by a gas phase reaction method in which water vapor is passed through aluminum fluoride and boron oxide in the gaseous state at 1000 to 1400°C.
It has been reported that whiskers having the composition A1203.B2O3 can be obtained.

(Problem to be solved by the invention) CaSOa, ni20・6Ti02,2Mg0・B2O3
Oxide whiskers such as oxide whiskers can be manufactured at low cost using a liquid phase method, and the use of whiskers can be expected to expand. It is thought that problems will arise in long-term reliability when used. On the other hand, 2AI203・
B2O3 type aluminum borate has been shown to have excellent chemical resistance [J, W.

Meller; Comprehensive Tre
atisc on Inorganicand The
oretical chemistry, vol.
V Part A.

599pl.

As mentioned above, aluminum borate whiskers have already been synthesized, but their molecular formula is 3AI203・B
2O3,2,5AI203・B2O3,4A1203・
B2O3.

4.8AI203・B2O3 and 9AI203・B
2O3 and 2A1 which is a known aluminum borate
203.B2O3 whiskers were not synthesized at all.

Whiskers are acicular single crystals with a high aspect ratio, and they have no grain boundaries and fewer crystal defects than polycrystals, so they are characterized by extremely high mechanical strength, but as they grow larger, they tend to have more defects. In some cases, the single crystal becomes a polycrystal that gathers around the fiber axis, so its strength is extremely reduced, and the use of whiskers becomes meaningless. As an example of the above measurement, it has been reported that even a whisker with a fiber diameter of about 1 gm having a tensile strength of 5000 MPa decreases to a strength of 700 MPa when the fiber diameter reaches 5 gm. The above-mentioned aluminum borate whiskers synthesized in the past have a fiber diameter of about 5 to 1100 JL and have extremely low mechanical strength, and whiskers with a fiber diameter of about 1 gm are desirable for use as reinforcing materials.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of conventional aluminum borate whiskers, to have excellent chemical resistance, heat insulation, heat resistance, neutron absorption ability, electrical insulation, etc., to have fine fiber diameter, and to have high strength. An object of the present invention is to provide an excellent aluminum borate whisker and a method for producing the same.

(Means for Solving the Problems) In view of the above circumstances, the inventors of the present invention have conducted extensive research, and as a result, have selected aluminum hydroxide and aluminum rhamno inorganic salt as an aluminum supplying component. It has been found that this objective can be achieved by reacting a given boric acid supply component with a melting agent at a given temperature.

That is, according to the present invention, the chemical formula 2A I 203·B2
Aluminum borate whiskers are provided having a composition represented by O3 (AI4B209).

According to the present invention, there is also provided an aluminum supplying component, at least one aluminum supplying component selected from aluminum inorganic salts, and at least one aluminum supplying component selected from boron oxides, oxyacids, and alkali metal salts thereof. reacting with a boric acid supply component by heating to a temperature of 600 to 1000 ° C. in the presence of at least one melting agent selected from alkali metal chlorides, alkali metal sulfates, and alkali metal carbonates, Provided is a method for producing aluminum borate whiskers, which comprises growing aluminum borate whiskers.

(Function) The aluminum borate whisker of the present invention is 2AI203
・The remarkable feature is that it consists of a needle-shaped single crystal of B2O3. As already mentioned, the aluminum borate of the formula 2A1203.B2O3 has better chemical resistance than other aluminum borates, and the whisker of the present invention also retains this property.

The aluminum borate whiskers of the present invention have the X-ray diffraction data shown in Table M1 and the fiber shape shown in the electron micrograph of FIG. According to Table 1, the whisker of the present invention is composed of a single phase of 2AI203.B2O3, and its crystal structure is extremely developed in the C-axis direction (fiber axis direction). It is understood that the fiber diameter is extremely fine and uniform, resulting in a fiber structure that is highly desired in terms of strength.

The aluminum borate whiskers of the present invention can be obtained by reacting an aluminum supply component and a boron supply component in the presence of a melting agent, but it is preferable to use aluminum hydroxide or an aluminum inorganic salt as the aluminum supply component. It is a characteristic of This specific component is converted into active aluminum oxide during reaction and growth, and due to its high reactivity, there is no problem of unreacted alumina remaining and it has the effect of reducing the diameter of the generated whiskers.

Another feature is that the reaction is carried out at a relatively low temperature in the presence of a melting agent, especially a low-viscosity melting agent, which prevents the tendency of the B2O3 component in the generated whiskers to desorb and decompose. , the single composition 2A l 203·B
It is recognized that 2O3 whiskers are generated.

(Preferred Embodiment of the Invention) As the aluminum supply component of the present invention, aluminum hydroxides, such as aluminum hydroxide and aluminum sulfates, such as aluminum sulfate, aluminum sulfate 14 to 18 eternal, aluminum potassium sulfate, aluminum M acid Potassium dodecahydrate, sodium aluminum sulfate, sodium aluminum sulfate dodecahydrate, ammonium aluminum sulfate, ammonium aluminum sulfate dodecahydrate, and aluminum nitrates, such as aluminum nitrate, aluminum nitrate nonahydrate, and aluminum chlorides, such as , aluminum chloride, aluminum chloride hexahydrate or aluminum acid hydroxide, e.g.
Examples include boehmite, diaspore, and todite, which may be used alone or in combination of two or more. All of these aluminum supply components decompose when heated in the atmosphere to generate active aluminum oxide, and because they are extremely reactive, there is the problem of unreacted alumina remaining when alumina is used as an aluminum supply component. The grown aluminum borate whiskers are characterized by their fine size.

Next, as the boric acid supplying component, boron oxides such as boron oxide, boron oxyacids such as orthoboric acid (H3BO3), tetraboric acid (H2ELO7), metaboric acid (HBO2), or alkali metal salts thereof, Examples include sodium tetraborate, pyroborate, potassium pyroborate, sodium metaborate, etc., and these may be used alone or in combination of two or more.

Furthermore, examples of the melting agent include chlorides of alkali metals such as sodium chloride and potassium chloride, sulfates of alkali metals such as sodium sulfate and potassium sulfate, and carbonates of alkali metals such as sodium carbonate and potassium carbonate. They may be used alone or in combination of two or more.

According to the method of the present invention, the aluminum supplying component and the boric acid supplying component are combined in a molar ratio of aluminum to boron of 1:9.
to 6:4, and further a melting agent is added in a range of 10 to 95% by weight of the total weight, 600 to 100% by weight.
Aluminum borate whiskers having the composition 2A1203.B2O3 can be produced by reacting at a temperature in the range of 0 DEG C. for typically 30 minutes to 8 hours.

At this time, if the heating temperature is less than 6006C, the reaction is insufficient, and if it exceeds too'oo'c, 2A I 203 B? 03 B in Winukah
This is not preferable because a decomposition reaction occurs in which the 2O3 component is gradually eliminated. The aforementioned aluminum borate 3A1203・B2O3 and 2.5A12o3 whose synthesis has already been reported
-8203TE, the reaction temperature was set at 1200-1400°C to reduce the viscosity of the melt and increase the whisker growth rate.
It is thought that this decomposition reaction is occurring because of the high In the present invention, in order to prevent such a phenomenon, a melting agent having a low melt viscosity is used and the reaction temperature is set to 1000°C or less.

In order to isolate whiskers from this reaction product, first, it is treated with hot water, hot hydrochloric acid, hot sulfuric acid, hot nitric acid, etc. to remove the melting agent and other water-soluble components. The purpose of using an inorganic acid is to improve the dissolution rate, and the treatment time can be shortened to 1/10 to 1/20 compared to using hot water. If water-insoluble by-products are present due to the composition of the raw materials used, the fibrous materials are separated from the residue by means such as decantation, water plating, and bubble separation. The crude aluminum borate whiskers thus obtained are then thoroughly washed with water to remove impurities, yielding pure aluminum borate whiskers having a composition of 2A1203.B2O3.

In powder X-ray diffraction, the aluminum borate whiskers thus obtained had a [220] plane with a d value of 5.30 and a d value of 3.34 A compared to ASTM powder X-ray diffraction card 29-10. [231] plane, d value 2.65 O
The diffraction intensity of the [440] plane and [341] plane of A is strong, and all the diffraction peaks are 2AI203・B2O3
It is assigned to the crystal structure of

In addition, after melting and decomposing with sodium pyrosulfate, the aqueous solution obtained by the above method was 2AI203.
- Can be identified as aluminum borate whiskers consisting of a single phase of B2O3.

(Effect of the invention) The aluminum borate whiskers isolated as described above have a fiber diameter of 0.05 to 571 m, particularly 0.1 to 3 pm.
, length 2-100 μm, especially 2-50 Ji.

m, colorless and transparent long acicular crystals with an aspect ratio of 10 to 100, and have excellent resistance to hot saw acid and hot alkalis. There is no decrease and no change in appearance is observed. Furthermore, it is impossible to easily dissolve the whiskers in hot aqua regia, and the only way to decompose and dissolve the whiskers is to melt them with sodium pyrosulfate, sodium hydroxide, or the like.

The aluminum borate whiskers of the present invention have acid resistance, alkali resistance, chemical resistance, heat insulation, heat resistance, neutron absorption ability,
It has excellent electrical insulation properties and is extremely useful as a heat insulator, heat resistant material, corrosion resistant material, and as a reinforcing material for thermoplastic resins, thermosetting resins, cement, ceramics, metals, etc.

(Example) The present invention will be explained in detail below using examples.

Example 1 7 g of aluminum sulfate (Al1(SO4)3), 3.7 g of orthoboric acid (H3BO3), and 7 g of potassium chloride (KCI) as a melting agent were thoroughly ground and mixed in a mortar, and placed in an alumina crucible. Electric furnace medium 850'03
Allow time to react. After slowly cooling the reaction mixture, 200 cc of I
Crude aluminum borate is obtained by boiling with N hydrochloric acid to dissolve and remove the melting agent. Subsequently, trace amounts of non-fibrous by-products are separated by decantation with water to obtain 1.0 g of aluminum borate whiskers. The whiskers thus obtained had an anharmonic melting point of 1050°C, and the molar ratio of Al2O3 to B2O3 determined by quantitative analysis of aluminum and boron was 1.97:1.00.

The aluminum borate whiskers obtained by this method have a fiber diameter of 0.2 to 0.5 pm and a length of 2 to 15 gm. A scanning electron micrograph is shown in Fig. 1, and powder X-ray diffraction data are shown in accordance with ASTM 29-1. The data are also shown in Table 1. In Table 1, [2201 [231 pieces] [440 pieces]
and [The intensity of the diffraction plane such as 3411 is high,
The 1a fiber axis can be estimated to be parallel or nearly parallel to these planes.

In addition, powder X-ray diffraction data shows 2A I 203・B2
No diffraction peaks other than O3 were observed, and together with the results of elemental analysis, in this example, 2A I 203 B2O3 mono-
It is explained that phase whiskers are obtained.

Table 1 Comparative example 1 of powder X-ray diffraction data of Example 1 For comparison, alkali metal chloride as a melting agent,
No Sulfate or Carbonate U.S. Patent Application No. 3080
I attempted to synthesize aluminum borate whiskers according to the method of No. 242.

1 g of aluminum hydroxide (AI(OH)3) and 4.0 g of boron oxide (B203) were sufficiently pulverized and mixed in a mortar, placed in a platinum crucible, reacted in an electric furnace at 1400°C for 30 minutes, and then slowly cooled. 0.40 g of aluminum borate whiskers were obtained in the same manner as in Example 1. The whiskers thus obtained had a fiber diameter of 1101L and a length of 100~5
007hm, and the molar ratio of Al2O:+ and B2O3 determined by quantitative analysis of aluminum and boron was 2.76:1. It was OO.

Example 2 Aluminum hydroxide (A I (OH) 3) and orthoboric acid 4.94 g and sodium sulfate (as a melting agent)
After dissolving or dispersing 3.0 g of Na2SO4) in 100 cc of water to form a slurry, the slurry was evaporated to dryness with stirring, then placed in an alumina crucible and heated at 900° in an electric furnace.
React for C8 hours. Thereafter, the reactants were treated in the same manner as in Example 1, and aluminum borate whiskers (2AI203
-B203) 0.4 g was obtained. This whisker has a fiber diameter of 0. IILm, length 5~0JLm.

Example 3 Aluminum nitrate nonahydrate (Al(NO3)3.9H2
0) 18.8g and 2.5g of sodium tetraborate and sodium chloride (NaGI) and potassium chloride (as melting agents)
13 g of an equimolar mixture of KCI) was thoroughly ground and mixed in a mortar, placed in an alumina crucible, and placed in an electric furnace.

800'C! The reaction mixture was allowed to react for 8 hours, and after being slowly cooled, it was boiled with 1000 cc of water to melt and remove the melting agent to obtain crude aluminum borate. Subsequently, trace amounts of non-fibrous by-products were separated by decantation, and impurities were melted away with IN hydrochloric acid to obtain pure aluminum borate whiskers (2A l 2
03・B203) 1.2 g was obtained. This whisker had a fiber diameter of 0.5 gm and a length of about 5 gm. Example 4 Aluminum sulfate 14-18
) : 114-18H20) 12 g, orthoboric acid 3.7 g and sodium carbonate (Na2CO
3) Thoroughly pulverize and mix 5.3 g in a mortar, place in a platinum crucible, and react in an electric furnace at 1000°C for 1 hour.
The procedure of Example 1 was followed to obtain 2.5 g of aluminum borate whiskers (2AI203/B203). This whisker has a fiber diameter of 1 to 3 m and a length of 20 to 3 m.
It was 0pm.

Example 5 Aluminum sulfate (AIK(SO4)2) 12 g,
2.5 g of boron oxide (B203) and 10 g of sodium sulfate (NaSOn) as a melting agent were thoroughly ground and mixed in a mortar, placed in an alumina acid crucible, and heated in an electric furnace for 9 hours.
After reacting for 00°04 hours, it was treated according to the procedure of Example 1 to form borate alumina whiskers (2Al2O3.B
203) 1.5 g was obtained. This whisker had a fiber diameter of 1 pm and a length of 20 to 50 μm.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph showing the fiber structure of aluminum borate (2A 1 203/B203) whiskers obtained in Example 1 of the present invention. Patent applicant: Director-designated agent of the Institute of Industrial Science and Technology: Kazuhiko Suganami Agent: Patent attorney: Ikuo Tsuchi Suzuki

Claims (3)

[Claims] (1) Chemical formula 2Al_2O_3・B_2O_3(Al_
An aluminum borate whisker having a composition represented by 4B_2O_9). (2) The whisker according to claim 1, having a fiber diameter of 0.05 to 5 μm, a length of 2 to 50 μm, and an aspect ratio of 10 to 100. (3) At least one aluminum supply component selected from aluminum hydroxide and aluminum inorganic salts, and at least one boric acid selected from boron oxides, oxyacids, and alkali metal salts thereof. reacting and growing the feed components by heating them to a temperature of 600 to 1000°C in the presence of at least one type of melting agent selected from alkali metal chlorides, alkali metal sulfates, and alkali metal carbonates; A method for producing aluminum borate whiskers characterized by: