JPH0422880B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an aluminum borate whisker and a method for producing the same. The whiskers of the present invention have excellent chemical resistance, heat insulation properties, heat resistance, neutron absorption ability, and electrical insulation properties, and can be used not only as insulation materials, heat-resistant materials, and corrosion-resistant materials, but also as thermoplastic resins, thermosetting resins, cement, and ceramics. , useful as a reinforcing material for metals, etc. (Prior art) Ceramic whiskers with excellent thermal and mechanical properties have been industrially manufactured in recent years.
It is being researched. Ceramic whiskers are broadly classified into non-oxide type and oxide type, with the former containing SiC, Si ₃ N ₄ , etc., and the latter containing CaSO ₄ ,
K ₂ O・6TiO ₂ (Special Publication No. 55-25157),
2MgO・B ₂ O ₃ (Japanese Unexamined Patent Publication No. 60-204697), etc. belong to this category. Non-oxide whiskers generally have a high melting point (above 1900℃) and are excellent in heat resistance, but because they require atmosphere adjustment during production, they are expensive in terms of equipment and raw materials, and the resulting whiskers Its uses will be limited. On the other hand, oxide whiskers do not have as high a melting point as non-oxide whiskers (1000-1600
℃), so the heat resistance is poor, 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 aluminum. The phase diagram of aluminum borate, a general term for aluminum borates, under normal pressure has already been completed, and [PJMGielisse; Nature, 4836, 69]
70 (1962)], the existence of the compound 2Al ₂ O ₃ .B ₂ O ₃ has been revealed, but the whisker substance 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 compositions of aluminum and boron that are 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℃ and then slowly cooling them, 3Al ₂ O ₃・B ₂ O ₃ and
It is known that whiskers with the composition 9Al ₂ O ₃・B ₂ O ₃ can be obtained, and the U.S. Department of the Interior's Bureau of Mines has reported that whiskers can be obtained by heating aluminum oxide, sodium tetraborate, and lithium chloride to 1200°C.
A whisker with a composition of 2.5Al ₂ O ₃・B ₂ O ₃ ,
By heating aluminum oxide, sodium tetraborate, and boron oxide to 1400℃,
It has been reported that whiskers with the composition 4.8Al ₂ O ₃・B ₂ O ₃ can be obtained [RC Johnson
“Bureau of Mines Report of
Investigations 6575'' (1965)]. According to US Pat. No. 3,350,166, the latter is produced 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 with the composition ₃・B ₂ O ₃ can be obtained. (Problems to be solved by the invention) Oxidation of CaSO ₄ , K ₂ O・6TiO ₂ , 2MgO・B ₂ O ₃ , etc. Physical whiskers can be manufactured at low cost using a liquid phase method, and the use of whiskers is expected to expand. However, they have the disadvantage of poor chemical resistance, especially acid resistance, and when used as reinforcing materials. However, it is clear that aluminum borate of the 2Al ₂ O ₃ /B ₂ O ₃ type has excellent chemical resistance [JWMeller; Comprehensive Treatisc on
Inorganic and Theoretica] Chemistry, vol V
Part A.599p]. As mentioned above, aluminum borate whiskers have already been synthesized, but their molecular formula is
3Al ₂ O ₃・B ₂ O ₃ , 2.5Al ₂ O ₃・B ₂ O ₃ , 4Al ₂ O ₃・
B ₂ O ₃ , 4.8Al ₂ O ₃・B ₂ O ₃ and 9Al ₂ O ₃・B ₂ O ₃ , and 2Al ₂ O ₃・ which is a well-known aluminum borate.
B ₂ O ₃ whiskers have not been 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 have very high mechanical strength, but the larger they get, the more defects there are. Become,
In some cases, a 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 a whisker with a fiber diameter of about 1 μm that has a tensile strength of 5000 MPa decreases to 700 MPa when the fiber diameter becomes 5 μm. The above-mentioned aluminum borate whiskers synthesized in the past have a fiber diameter of about 5 to 100 .mu.m and have extremely low mechanical strength, and whiskers with a fiber diameter of about 1 .mu.m 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., fine fiber diameter, and high strength. 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 inorganic salts of aluminum as the aluminum supply 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 fibers have a composition represented by the chemical formula 2Al ₂ O ₃ B ₂ O ₃ (Al ₄ B ₂ O ₉ ), have a fiber diameter of 0.05 to 5 μm, a length of 2 to 50 μm, and a fiber diameter of 10 to 100 μm. An aluminum borate whisker is provided having an aspect ratio of . According to the invention, aluminum hydroxide,
and at least one aluminum supplying component selected from aluminum inorganic salts, and at least one boric acid supplying component selected from boron oxides, oxyacids, and alkali metal salts thereof. Aluminum borate whiskers, which are reacted and grown by heating to a temperature of 600 to 1000°C in the presence of at least one type of melting agent selected from alkali metal sulfates and alkali metal carbonates. A manufacturing method is provided. (Function) The aluminum borate whisker of the present invention is
Its distinctive feature is that it consists of a needle-like single crystal of 2Al ₂ O ₃ .B ₂ O ₃ . As already mentioned, aluminum borate with the formula 2Al ₂ O ₃ B ₂ O ₃ has superior chemical resistance compared to other aluminum borates, and the whiskers of the present invention also have this property. I keep it as is. The aluminum borate whiskers of the present invention are the first
It has the fiber shape shown in the X-ray diffraction data shown in the table and the electron micrograph in FIG. According to this Table 1, in the whisker of the present invention, 2Al ₂ O ₃ .
It consists of a single phase of B ₂ O ₃ , and its crystal structure is extremely developed in the C-axis direction (fiber axis direction).
Furthermore, from FIG. 1, it can be seen 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 are obtained by reacting an aluminum supplying component and a boron supplying component in the presence of a melting agent.
One feature is the use of aluminum hydroxide or an aluminum inorganic salt as the aluminum supply component. 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 _.
It is recognized that the tendency of the components to be eliminated and decomposed is prevented, and the 2Al ₂ O ₃ .B ₂ O ₃ whiskers having the single composition are produced. (Preferred Embodiment of the Invention) As the aluminum supply component of the present invention, aluminum hydroxide such as aluminum hydroxide and aluminum sulfate, such as aluminum sulfate, aluminum sulfate 14-18 hydrate, aluminum potassium sulfate, aluminum sulfate 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 acid hydroxides of aluminum, such as boehmite, diaspore, todite, etc., 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 aluminum borate whiskers grown are characterized by their fineness. Next, boron oxides such as boron oxide and boron oxyacids such as orthoboric acid (H ₃ BO ₃ ), tetraboric acid (H ₂ B ₄ O ₇ ), and metaboric acid (HBO ₂ ) Alternatively, alkali metal salts thereof such as sodium tetraborate, sodium pyroborate, potassium pyroborate, sodium metaborate, etc. may be mentioned, and these may be used alone or in combination of two or more kinds. 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 mixed in a molar ratio of aluminum to boron ranging from 1:9 to 6:4, and a melting agent is added at a ratio of 10 to 95% of the total weight. 2Al ₂ O ₃ .
Aluminum borate whiskers with the composition B ₂ O ₃ can be produced. At this time, if the heating temperature is less than 600℃, the reaction will be insufficient or
Formed in the presence of a melting agent at temperatures exceeding 1000℃
This is not preferable because a decomposition reaction occurs in which the B _{2 O 3 component in the 2Al 2 O 3 .B 2} O ₃ whisker is gradually eliminated. For the aforementioned aluminum borate 3Al ₂ O ₃・B ₂ O ₃ and 2.5Al ₂ O ₃・B ₂ O ₃ , whose synthesis has already been reported, the reaction temperature was lowered to lower the viscosity of the melt and increase the whisker growth rate. It is thought that this decomposition reaction is occurring because the temperature is high, 1200-1400°C.
In the present invention, in order to prevent such a phenomenon, a melting agent with a low melt viscosity is used and the reaction temperature is set to 1000°C or less. To isolate whiskers from this reaction product, first add hot water, about 1N hot hydrochloric acid, hot sulfuric acid,
The melting agent and other water-soluble components are removed by treatment with hot nitric acid or the like. The purpose of using inorganic salts is to improve the dissolution rate, and the processing time is 1/10 to 1/10 compared to hot water.
It can be shortened to 1/20. If water-insoluble by-products are present due to the composition of the raw materials used, the fibrous material is separated from the residue by means such as decantation, water droplet, and bubble separation. The crude aluminum borate whiskers thus obtained were then thoroughly washed with water,
By removing impurities, aluminum borate whiskers with the composition of pure 2Al ₂ O ₃ .B ₂ O ₃ can be obtained. In powder X-ray diffraction, the aluminum borate whiskers thus obtained were found to have a [220] plane with a d value of 5.30 Å and a [231] plane with a d value of 3.34 Å, compared to the ASTM powder X-ray diffraction card 29-10. , d value 2.650Å
The diffraction intensities of the [440] and [341] planes are strong, and all the diffraction peaks are attributed to the crystal structure of 2Al ₂ O ₃ .B ₂ O ₃ . In addition, after melting and decomposing with sodium pyrosulfate, the aqueous solution obtained by the above method was determined to be a single phase of 2Al ₂ O ₃ and B ₂ O ₃ . (Effects of the Invention) The aluminum borate whiskers isolated as described above have a fiber diameter of 0.05 to 5 μm, particularly 0.1 to 3 μm.
It is a colorless and transparent long acicular crystal with a length of 2 to 100 μm, especially 2 to 50 μm, and an aspect ratio of 10 to 100. It exhibits excellent resistance to hot mineral acids and hot alkalis. For example, it is resistant to hot mineral acids and hot alkalis. There was no weight loss at all even after 2 days of immersion in water, and no change in appearance was 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 properties, heat resistance,
It has excellent neutron absorption ability and electrical insulation, and is extremely useful as a reinforcing material for thermoplastic resins, thermosetting resins, cement, ceramics, metals, etc., as well as heat insulation materials, heat-resistant materials, and corrosion-resistant materials. (Example) The present invention will be specifically described below with reference to Examples. Example 1 7 g of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), 3.7 g of orthoboric acid (H ₃ BO ₃ ), and 7 g of potassium chloride (KCl) as a melting agent were thoroughly ground and mixed in a mortar and placed in an alumina crucible. Place it in an electric furnace at 850℃3
Allow time to react. After slowly cooling the reaction, 200 c.c.
Crude aluminum borate whiskers are obtained by boiling with 1N 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 Al ₂ O ₃ to B ₂ O ₃ 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 μm and a length of 2 to 15 μm. The scanning electron micrograph is shown in Figure 1, and the powder X-ray diffraction data is shown in ASTM29-10 data. They are also shown in Table 1. In Table 1, [220] [231]
The intensity of diffraction planes such as [440] and [341] is high, and the fiber axis can be estimated to be parallel or nearly parallel to these planes. In addition, powder X-ray diffraction data shows 2Al ₂ O ₃・B ₂ O ₃
No other diffraction peaks were observed, which, together with the results of elemental analysis, explains that whiskers with a single phase of 2Al ₂ O ₃ .B ₂ O ₃ were obtained in this example.

[Table] Comparative Example 1 As a comparison, aluminum borate whiskers were synthesized according to the method of US Patent Application No. 3,080,242, which does not use an alkali metal chloride, sulfate or carbonate as a melting agent. 1 g of aluminum hydroxide (Al(OH) ₃ ) and 4.0 g of boron oxide (B ₂ O ₃ ) were sufficiently pulverized and mixed in a mortar, placed in a platinum crucible, reacted at 1400°C for 30 minutes in an electric furnace, and then slowly cooled. 0.40 g of aluminum borate whiskers were obtained in the same manner as in Example 1. The whiskers obtained in this way have a fiber diameter of approximately 10 μm and a length of 100 μm.
It is large, ~500μm, and Al ₂ O ₃ and B ₂ O ₃ determined by quantitative analysis of aluminum and boron.
The molar ratio of was 2.76:1.00. Example 2 1.56 g of aluminum hydroxide (Al(OH) ₃ ), 4.94 g of orthoboric acid, and 3.0 g of sodium sulfate (Na ₂ SO ₄ ) as a melting agent were dissolved or dispersed in 100 c.c. of water to form a slurry. After that, the mixture was evaporated to dryness while stirring, and then placed in an alumina crucible and heated in an electric furnace for 900 m
React at ℃ for 8 hours. Thereafter, the reaction product was treated in the same manner as in Example 1 to obtain 0.4 g of aluminum borate whiskers (2Al ₂ O ₃ .B ₂ O ₃ ). This whisker had a fiber diameter of about 0.1 μm and a length of 5 to 10 μm. Example 3 Aluminum nitrate nonahydrate (Al(NO ₃ ) ₃ .
18.8 g of 9H ₂ O), 2.5 g of sodium tetraborate, and 13 g of an equimolar mixture of sodium chloride (NaCl) and potassium chloride (KCl) as a melting agent were thoroughly ground and mixed in a mortar, placed in an alumina crucible, and heated in an electric furnace. During ~
The reaction mixture was allowed to react at 800°C for 8 hours, and after being slowly cooled, it was boiled with 1000 c.c. of water to dissolve and remove the melting agent to obtain crude aluminum borate whiskers. Subsequently, after separating a trace amount of non-fibrous by-products by decantation, impurities were dissolved and removed with 1N hydrochloric acid to obtain 1.2 g of pure aluminum borate whiskers (2Al ₂ O ₃ .B ₂ O ₃ ).
This whisker had a fiber diameter of about 0.5 μm and a length of about 5 μm. Example 4 Aluminum sulfate 14-18 hydrate (Al ₂ (SO ₄ ) ₃ 14
~18H ₂ O), 3.7 g of orthoboric acid, and 5.3 g of sodium carbonate (Na ₂ CO ₃ ) as a melting agent were thoroughly ground and mixed in a mortar, placed in a platinum crucible, and reacted for 1 hour at 1000°C in an electric furnace. Thereafter, it was treated according to the procedure of Example 1 to obtain 2.5 g of aluminum borate whiskers (2Al ₂ O ₃ .B ₂ O ₃ ). The whiskers had a fiber diameter of 1 to 3 μm and a length of 20 to 30 μm. Example 5 12 g of aluminum sulfate (AlK(SO ₄ ) ₂ ), 2.5 g of boron oxide (B ₂ O ₃ ), and 10 g of sodium sulfate (Na ₂ SO ₄ ) as a melting agent were thoroughly ground and mixed in a mortar, and alumina Place in a crucible and heat at 900℃ in an electric furnace.
After reacting for 4 hours, it was treated according to the procedure of Example 1 to obtain 1.5 g of aluminum borate whiskers (2Al ₂ O ₃ .B ₂ O ₃ ). This whisker had a fiber diameter of approximately 1 μm and a length of 20 to 50 μm.

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph showing the fiber structure of aluminum borate (2Al ₂ O ₃ .B ₂ O ₃ ) whiskers obtained in Example 1 of the present invention.

Claims (1)

[Claims] 1. A fiber having a composition represented by the chemical formula 2Al ₂ O ₃ B ₂ O ₃ (Al ₄ B ₂ O ₉ ), a fiber diameter of 0.05 to 5 μm, a length of 2 to 50 μm, and a fiber diameter of 10 to 100 μm. Aluminum borate whiskers with aspect ratio. 2. At least one aluminum supplying component selected from aluminum hydroxide and aluminum inorganic salts, and at least one boric acid supplying component selected from boron oxides, oxyacids, and alkali metal salts thereof. and are reacted and grown by heating 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.