JP6509668B2 - Method of manufacturing aluminum borate whisker - Google Patents

Description

  The present invention relates to a method of making aluminum borate whiskers.

Whiskers (double oxide represented by the chemical formula of such _{9Al 2 O 3 · 2B 2 O} 3) Aluminum borate has excellent mechanical strength and heat resistance, is used as a reinforcing material of various materials.
Conventionally, a flux method using a melting agent is known as a method of producing such aluminum borate whiskers, but there is a problem that it takes time to finally separate the melting agent and the whiskers.
Therefore, for example, in Patent Document 1, “The powder of an aluminum compound and the powder of a boron compound are uniformly mixed, and then heated to form aluminum borate whiskers, and the like. A method is described in which an additive having the function of promoting the growth of aluminum whiskers is added to the raw material mixture ([claim 1]).

JP 10-203879 A

  In the method described in Patent Document 1, although aluminum borate whiskers are produced by heating a precursor obtained by mixing solid powder raw materials, the operation of uniformly mixing the powder raw materials is complicated, and particularly, a large amount This problem is more pronounced when producing.

  The present invention has been made in view of the above points, and provides a method for producing aluminum borate whiskers in which aluminum borate whiskers can be obtained by a simple method.

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said objective was achieved by employ | adopting the following structure, as a result of earnestly examining. That is, the present invention provides the following [1] to [4].
[1] Alcohol, metal aluminum and halide are mixed to adjust pH to 3 or less to obtain composition A1, or alcohol is mixed with metal aluminum to adjust pH to 11 or more The step of obtaining the composition A2, the composition A1 or the composition A2, the boron compound, and water are mixed, the pH is adjusted to 4 to 5, and the precipitate C is precipitated, A process for producing an aluminum borate whisker comprising the step b of collecting the precipitate C, and the step c of firing the precipitate C to obtain an aluminum borate whisker.
[2] In the step b, first, the composition B containing the boron compound and the water is prepared, and then the composition A1 or the composition A2 is mixed with the composition B, [1] ] The manufacturing method of the aluminum borate whisker as described in [].
[3] When preparing the above composition B, the above composition B so that the pH after mixing the above composition A1 or the above composition A2 and the above composition B will be in the range of 4 to 5 The manufacturing method of the aluminum borate whisker as described in said [2] which adjusts pH of 5.
[4] The method for producing aluminum borate whiskers according to any one of the above [1] to [3], wherein the precipitate C is fired at a firing temperature of 800 ° C. or more in the step c.

  According to the present invention, it is possible to provide a method for producing aluminum borate whiskers in which aluminum borate whiskers can be obtained by a simple method.

FIG. 1 is a potential-pH diagram of aluminum. FIG. 2 is a potential-pH diagram of boron. FIG. 3 is an XRD pattern when the firing time is fixed to 0.5 hours and the firing temperature is changed. FIG. 4 is an XRD pattern when the firing temperature is fixed at 1100 ° C. and the firing time is changed. FIG. 5 (a) is a SEM image when firing is performed at 1100 ° C. for 2 hours, and FIG. 5 (b) is a SEM image when firing is performed at 1300 ° C. for 2 hours. FIG. 6 is a graph showing the relationship between the aspect ratio and the firing conditions.

  The method for producing an aluminum borate whisker according to the present invention (hereinafter, also simply referred to as the “production method of the present invention”) comprises mixing an alcohol, metallic aluminum and a halide to adjust the pH to 3 or less A step of obtaining composition A1 or mixing alcohol and metal aluminum and adjusting the pH to 11 or more to obtain composition A2, the above composition A1 or the above composition A2 and a boron compound Water, and adjusting the pH to 4 to 5 to precipitate out the precipitate C, and the step b of collecting the precipitate C, and calcining the precipitate C to obtain aluminum borate whiskers A process for producing an aluminum borate whisker comprising the step c).

  According to the manufacturing method of the present invention, in obtaining the precursor (precipitate C) of the aluminum borate whisker, there is no complicated operation of uniformly mixing the solid powder raw material, and only by mixing the liquid containing the raw material Since it is good, aluminum borate whiskers can be produced by an extremely simple method. At this time, high purity aluminum borate whiskers can be obtained by using a raw material with few impurities.

  In the following, the case where the step a is a step of mixing the alcohol, the metal aluminum and the halide, adjusting the pH to 3 or less, and obtaining the composition A1 is referred to as the “first embodiment”. The case where the step a is a step of mixing an alcohol and metal aluminum and adjusting the pH to 11 or more to obtain the composition A2 may be referred to as a "second embodiment".

  Hereinafter, each process with which the manufacturing method of this invention is equipped is demonstrated in detail. At this time, first, the first aspect will be described first, and then the second aspect will be described focusing on differences from the first aspect.

[First aspect]
[Step a (First Embodiment)]
The step a is a step of mixing an alcohol, metal aluminum and a halide, adjusting the pH to 3 or less to obtain a composition A1.
That is, step a ionizes (Al ³⁺ ) metal aluminum in an alcohol such as ethanol to obtain a composition A1 containing an aluminum alkoxide such as aluminum ethoxide (Al (OC ₂ H ₅ ) ₃ ). It is a process.
The metal aluminum is simply not soluble only added to alcohol (not ionized), chloride ion (Cl ^-) surface coating (aluminum oxide) by halide ion or the like is removed, further, that pH3 or less It ionizes by strong acid conditions (it becomes Al ³⁺ ion).

<Metal aluminum>
The metal aluminum (Al) is not particularly limited, but in order to suppress contamination of the final product aluminum borate whisker, it is preferable to have high purity.
In addition, the aspect of metal aluminum is not specifically limited, For example, granular form, sand form, powder form etc. are mentioned.

<Halide>
The halides, fluoride ion (F ^-), chloride ion (Cl ^-), bromide ion (Br ^-), iodide ion (I ^-) is not particularly limited as long as it can give a halide ion such as, For example, ammonium chloride, aluminum chloride and the like can be mentioned, but aluminum halide (aluminum halide) is preferable, and aluminum chloride is more preferable, because ionized cations do not need to be removed in a later step.

<alcohol>
As the alcohol, an alcohol which is miscible with water is preferable because water is added to hydrolyze the aluminum alkoxide in step b described later. Specifically, alcohols having 1 to 3 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol and the like are preferable, and methanol and ethanol are more preferable.

<PH 3 or less>
FIG. 1 is a potential-pH diagram of aluminum. As shown in FIG. 1, in order for aluminum to be present as Al ³⁺ , it is necessary to at least adjust the pH to about 3 or less.
Therefore, in the process a, in the process of obtaining the composition A1, the pH of the alcohol to which metal aluminum is added is adjusted to 3 or less, preferably 1 to 3. At this time, although a conventionally known acid component can be used as a pH adjuster, the above-mentioned halide may double as the pH adjuster. For example, aluminum chloride is a strong Lewis acid.
In addition, since a pH meter having a pH electrode (such as a glass electrode) can not generally be used for alcohol, in the present invention, the pH changes according to the pH of the liquid. Product) (following, the same).

<mixture>
In step a, metal aluminum and a halide are added, and an alcohol whose pH is adjusted to 3 or less is mixed.
The mixing conditions are not particularly limited, and the mixing may be continued using a known stirring device or the like while heating as necessary until metal aluminum is ionized to form an aluminum alkoxide, for example, alcohol It is preferable to carry out mixing for about 6 to 24 hours at a temperature not higher than the boiling point of At this time, an aluminum alkoxide is produced, whereby a viscous off-white liquid is obtained as the composition A1.
In addition, although the addition order of each component is not specifically limited, For example, when using aluminum chloride as a halide, after dissolving aluminum chloride in ethanol, it is preferable to add and mix metal aluminum.

[Step b (First Embodiment)]
In step b, the composition A1 obtained in step a, a boron compound, and water are mixed, the pH is adjusted to 4 to 5, a precipitate C is deposited, and the precipitate C is collected. It is.
That is, in step b, the aluminum alkoxide contained in the composition A1 is hydrolyzed with water to form aluminum hydroxide (Al (OH) ₃ ) as the precipitate C, and boric acid derived from the boron compound ( H ₃ BO ₃ ) is also a step of forming as a precipitate C.
At this time, aluminum hydroxide and boric acid are mixed in a liquid and dispersed uniformly.

Boron compounds
The boron compound is not particularly limited. For example, oxo acids of boron such as boric acid (H ₃ BO ₃ ), tetraboric acid (H ₂ B ₄ O ₇ ), metaboric acid (HBO ₂ ), etc .; alkali metals thereof Salts; alkoxide compounds of boron such as boron ethoxide; and the like.
Among these, boron oxo acids are preferable, and boric acid is more preferable.

<water>
In step b, water is used for hydrolysis as described above, but such water is not particularly limited, and for example, ion exchanged water or the like is used.

<PH 4 to 5>
As described above, in step b, aluminum hydroxide (Al (OH) ₃ ) is precipitated by hydrolyzing the aluminum alkoxide contained in the composition A1. Here, referring to the potential-pH diagram of the aluminum of FIG. 1 described in the step a, in order to cause the aluminum to exist as aluminum hydroxide (Al (OH) ₃ ), the pH is at least about 4 or more (10 or less). ) It turns out that it is necessary to make it to a certain extent.

In addition, as described above, in step b, boric acid (H ₃ BO ₃ ) is also precipitated.
FIG. 2 is a potential-pH diagram of boron. As shown in FIG. 2, boron is generally in the ionic state (HB ₄ O ₇ ⁻ , B ₄ O ₇ ²⁻ , H ₂ BO ₃ ⁻ , HBO ₃ ²⁻ , BO ₃₎ when the pH is high. ^3- etc), which may be present as boric acid (H ₃ BO ₃ ) at lower pH. Referring to FIG. 2 as such, it can be seen that in order for the boron to be present as boric acid (H ₃ BO ₃ ), at least the pH needs to be about 5 or less.

Therefore, in the step b, the pH of the mixture of the composition Al containing the aluminum alkoxide, the boron compound and water is adjusted to 4 to 5. Thus, aluminum hydroxide (Al (OH) ₃ ) and boric acid (H ₃ BO ₃ ) both precipitate as precipitate C without aluminum and boron being in the ionic state.

In addition, since composition A1 is an acidic area of pH 3 or less, pH may be raised a little and it may be made to shift in the range of 4-5 by adding an alkali component.
The alkali component to be used is not particularly limited, but, for example, hydroxides such as sodium hydroxide and potassium hydroxide; inorganic alkalis such as aqueous ammonia, sodium carbonate and potassium carbonate; organic amines such as diethanolamine and triethylamine; Among them, ammonia water is preferred.

<Composition B>
Although the order of combination of the components in step b is not particularly limited, it is preferable to first prepare a composition B containing a boron compound and water, and then mix the composition B and the composition A1. At this time, when preparing the composition B, the pH of the composition B is set to the above-mentioned alkali component so that the pH after mixing the composition A1 and the composition B falls within the range of 4 to 5 It is more preferable to use and adjust.
As a result, hydrolysis of the aluminum alkoxide contained in the composition A1 (i.e., formation of aluminum hydroxide) and formation of boric acid are simultaneously performed, and aluminum hydroxide and boric acid are coprecipitated, so that both Distributed more evenly.

<Precipitate C>
The precipitate C is, as described above, aluminum hydroxide (Al (OH) ₃ ) obtained by hydrolyzing the aluminum alkoxide contained in the composition A1, and boric acid (H ₃ BO ₃ ) derived from a boron compound. And).
The precipitate C, aluminum hydroxide and boric acid, are mixed in the solution and dispersed uniformly.

<Collecting>
The means for collecting the precipitate C in the step b is not particularly limited. For example, known means such as filtration using filter paper, centrifugation and the like can be appropriately selected. In addition, in the case of collection of the precipitate C, you may dry the precipitate C as needed.

[Step c (First Embodiment)]
Step c is a step of calcining the precipitate C collected in step b to obtain an aluminum borate whisker. In the step b, since the precipitate C in which aluminum hydroxide and boric acid are uniformly dispersed is obtained, by firing the precipitate C, homogeneous high-grade aluminum borate whiskers can be obtained.

<Firing (full firing)>
The composition and the shape of the shape of the obtained aluminum borate whisker may change depending on the baking temperature and the baking time when baking the precipitate C (main baking).
The firing temperature is, for example, at 800 ° C. or higher, preferably at least 900 ° C., acicular and columnar, from the viewpoint of obtaining aluminum borate whisker represented by the composition formula _{9Al 2 O 3 · 2B 2 O} 3, 1100 degreeC or more is more preferable, and 1200 degreeC or more is further more preferable. The upper limit of the firing temperature is not particularly limited and may be appropriately selected depending on the apparatus to be used, and, for example, 1500 ° C. or less may be mentioned.
The firing time is preferably 0.5 hours or more. Although the upper limit of baking time is not specifically limited, For example, it is 15 hours or less.

<Temporary baking>
In step c, it is preferable to perform pre-baking on the precipitate C at a temperature lower than the baking temperature of the main baking before performing the above-mentioned baking (main baking). For example, when aluminum chloride is used as the halide in step a, chlorine that is an impurity for the final product aluminum borate whisker can be removed by this calcination.
The temperature of the pre-baking is preferably less than 800 ° C. The lower limit of the pre-baking temperature is not particularly limited. For example, when ammonium chloride is used as a halide, since the sublimation temperature of ammonium chloride is 335 ° C., pre-baking may be performed at or above this temperature. Moreover, as temporary baking time, 0.5 to 3 hours are mentioned, for example.
From the viewpoint of removing impurities more effectively, it is preferable to grind the precipitate C after calcination, and it is more preferable to perform calcination and grinding twice or more.
In addition, the said baking (this baking) may serve as temporary baking.

Aluminum Borate Whisker
Aluminum borate is _{9Al 2 O 3 · 2B 2 O} 3, 2Al 2 O 3 · 2B 2 O 3, 10Al composite oxide represented by a composition formula such as _{2 O 3 · 2B 2 O 3} , firing temperature The composition formula may change depending on the baking time and the baking time.
Aluminum borate whiskers are needle-like particles as an example, but in the present invention, the shape is not particularly limited, and may be, for example, plate-like or columnar, and is appropriately selected according to the application and the like. The shape of the aluminum borate whisker can be changed depending on the baking temperature and the baking time.
Aluminum borate whiskers vary in their physical properties depending on their shape etc., but generally they have excellent properties such as mechanical strength, chemical resistance, heat insulation, heat resistance, neutron absorption ability and electrical insulation. In addition to heat insulation materials, heat-resistant materials, food-resistant materials, for example, organic materials such as thermoplastic resins and thermosetting resins; inorganic materials such as cement, glass and ceramics; metal materials such as aluminum alloys, magnesium alloys and titanium alloys Can be used as a reinforcing material for

[Second aspect]
[Step a (Second Embodiment)]
Step a of the second embodiment is a step of mixing an alcohol and metal aluminum, adjusting the pH to 11 or more, and obtaining a composition A2. In step a of the second embodiment, metal aluminum is ionized (AlO ²⁻ ) in an alcohol such as ethanol to obtain an alkoxide-containing composition A2. At this time, metal aluminum is not dissolved simply by adding to alcohol, but is ionized (becomes AlO ^{2 −} ion) under strong alkaline conditions of pH 11 or more.

  In addition, as metal aluminum and alcohol, the thing similar to a 1st aspect is mentioned suitably. The preferable conditions for mixing and the like are also the same as in the first embodiment, but it is preferable to keep the temperature around 70 ° C. from the viewpoint of increasing the dissolution rate during mixing.

<PH 11 or more>
As shown in FIG. 1 (potential-pH diagram of aluminum), in order for aluminum to be present as AlO ²⁻ , it is necessary to at least adjust the pH to about 11 or more.
Therefore, in the process a of the second embodiment, the pH of the alcohol to which metal aluminum is added is adjusted to 11 or more, preferably 11 to 14 in the process of obtaining the composition A2.
At this time, conventionally known alkali components can be used as a pH adjuster, and examples thereof include sodium hydroxide and potassium hydroxide.

[Step b (Second Embodiment)]
In step b of the second embodiment, the composition A2 obtained in step a, a boron compound, and water are mixed, the pH is adjusted to 4 to 5, and precipitate C is precipitated. Is a process of collecting
In step b of the second embodiment, boric acid (H) derived from a boron compound is produced while aluminum hydroxide (Al (OH) ₃ ) is formed as a precipitate C by hydrolyzing an alkoxide contained in the composition A2. ₃ BO ₃ ) is also a step of forming as precipitate C.

In addition, since composition A2 is an alkaline area of pH 11 or more, pH may be lowered and it may be made to shift in the range of 4-5 by adding an acid component.
The acid component to be used is not particularly limited, and examples thereof include organic acids and inorganic acids. Examples of the inorganic acid include binary acids (hydrogen acids) such as hydrochloric acid and hydrofluoric acid; and oxo acids (oxygen acids) such as sulfuric acid, nitric acid, phosphoric acid and perchloric acid.

Other matters, for example, the boron compound and water used in step b are preferably the same as in the first embodiment. Further, in the step b, the meaning of setting the pH to 4 to 5 is also the same as in the first embodiment, and thus the description is omitted.
Furthermore, also in the second embodiment, it is preferable to first prepare a composition B containing a boron compound and water, and then mix the composition B and the composition A2. At this time, when preparing the composition B, the pH of the composition B is set to the acid component described above so that the pH after mixing the composition A 2 and the composition B is in the range of 4 to 5. It is more preferable to use and adjust.
And since it is the same as that of a 1st aspect also about the precipitate C obtained in the process b, and the means to extract | collect this, description is abbreviate | omitted.

[Step c (second aspect)]
The step c of the second embodiment is a step of calcining the precipitate C collected in the step b to obtain an aluminum borate whisker as in the first embodiment.
In step c of the second embodiment, the conditions for firing (main firing) and temporary firing, and the obtained aluminum borate whisker are the same as step c of the first embodiment, and thus the description thereof is omitted.

(Blended amount of each component)
In the first aspect and the second aspect, the blending amount of each component used in each step may be appropriately set in consideration of the stoichiometry.
For example, as the final product, when it is desired to obtain the aluminum borate whiskers represented by the composition formula _{9Al 2 O 3 · 2B 2 O} 3 is stoichiometrically, the _{9Al 2 O 3 · 2B 2 O} 3 It is sufficient to use metal aluminum which is an aluminum supply component, a boron compound which is a boron supply component, or the like in such an amount as to be obtained.
In addition, the alkali component and the acid component may be appropriately used in amounts to achieve the target pH.

  Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these.

<material>
In the following, aluminum powder (Al, purity: 98%, manufactured by Kanto Chemical Co., Ltd.), anhydrous aluminum chloride (AlCl ₃ , purity: 98.0%, manufactured by Wako Pure Chemical Industries, Ltd.), anhydrous ethanol (C ₂ H ₅ OH, Purity: 99.5%, Wako Pure Chemical Industries, Ltd., boric acid powder (H ₃ BO ₃ , purity: 99.5%, Wako Pure Chemical Industries, Ltd.), ion-exchanged water, ammonia water (NH ₃ , purity) 25%, manufactured by Wako Pure Chemical Industries, Ltd. was used.
In addition, pH test paper (made by As One Corporation) was used for pH measurement.

<Manufacturing>
(Step a)
10 g of anhydrous aluminum chloride was added to 100 mL of ethanol. After the anhydrous aluminum chloride was completely dissolved, 2.5 g of aluminum powder was added. The mixture was heated and stirred at 78 ° C. for 12 hours to obtain a viscous gray-white liquid composition A1. The pH of composition A1 was in the range of 1-2.

(Step b)
To 100 mL of ion-exchanged water, 5 g of boric acid powder and 10 mL of aqueous ammonia were added, and stirring was carried out for 30 minutes at room temperature to obtain Composition B, which was a colorless and transparent solution. The pH of composition B was 10.
Next, the whole of composition A1 obtained in step a was added little by little to composition B, and hydrolysis and pH adjustment were simultaneously performed. When the pH was in the range of 4 to 5, the viscosity increased and a gray precipitate C was obtained. The gray gel substance (precipitate C), which is a precursor of aluminum borate, was collected by separating into a solid phase and a liquid phase with a centrifuge (3500 rpm, 180 seconds).

(Step c)
In order to remove chlorine of the gel-like substance (precipitate C), heat treatment (pre-baking) was performed at 700 ° C. for 2 hours in the atmosphere, and then ground. The powder obtained by repeating pre-baking and grinding twice is subjected to various baking times (900 ° C., 1000 ° C., 1100 ° C., 1200 ° C., or 1300 ° C.) at various baking temperatures (900 ° C., 1000 ° C., 1100 ° C. or 1300 ° C.) using an electric furnace. The baking (main baking) was performed for 0.5 hours, 1 hour, 2 hours, 5 hours, or 10 hours).

<Evaluation>
(XRD)
First, with regard to the powder when the firing time of the main firing is fixed and the firing temperature is changed, X-ray diffraction (X-ray diffraction, XRD) is performed using a tabletop powder X-ray diffractometer (Miniflex II, manufactured by Rigaku Corporation) Did). The results are shown in FIG.
FIG. 3 is an XRD pattern when the firing time is fixed to 0.5 hours and the firing temperature is changed. As shown in FIG. 3, the peak of _{9Al 2 O 3 · 2B 2 O} 3 becomes conspicuous with increasing firing temperature.
Next, the firing temperature of the main firing was fixed at 1100 ° C., and XRD was performed on the powder when the firing time was changed. The results are shown in FIG.
FIG. 4 is an XRD pattern when the firing temperature is fixed at 1100 ° C. and the firing time is changed. As shown in FIG. 4, the peak of _{9Al 2 O 3 · 2B 2 O} 3 was observed in any of the baking time. If the firing time is 0.5 hours and 1 hour, a peak of _{9Al 2 O 3 · 2B 2 O} 3 and _{2Al 2 O 3 · 2B 2 O} 3 was confirmed. If the firing time is 2 _{hours, 9Al 2 O 3 · 2B 2} O 3, 2Al 2 O 3 · 2B 2 O 3, and the peak of _{10Al 2 O 3 · 2B 2 O} 3 was confirmed. If the firing time is 5 hours and 10 _{hours, 9Al 2 O 3 · 2B 2} O 3, and the peak of _{10Al 2 O 3 · 2B 2 O} 3 was confirmed.

(SEM)
The powder after the main firing was observed with a scanning electron microscope (SEM). As SEM, "JSM-5310" manufactured by Nippon Denshi Co., Ltd. was used.
FIG. 5 (a) is a SEM image when firing is performed at 1100 ° C. for 2 hours, and FIG. 5 (b) is a SEM image when firing is performed at 1300 ° C. for 2 hours.
As shown in FIG. 5 (a), when firing is performed at 1100 ° C. for 2 hours, fine needle-like particles are obtained, and as the firing temperature rises, as shown in FIG. 5 (b), Plate-like particles and columnar particles appeared.

(aspect ratio)
The particles in the SEM image of the powder after main firing were visually measured to determine the aspect ratio (long side / short side).
FIG. 6 is a graph showing the relationship between the aspect ratio and the firing conditions. If the aspect ratio is large, needle-like particles, if small, columnar particles and plate-like particles, but as shown in FIG. 6, as the firing time becomes longer, the aspect ratio becomes smaller and the particles tend to become thicker .
Moreover, when the same baking time was compared, the tendency for particle | grains to become thick was seen, so that baking temperature was high.

Claims (4)

Alcohol, metal aluminum and halide are mixed to adjust pH to 3 or less to obtain composition A1, or alcohol and metal aluminum are mixed to adjust pH to 11 or more, Obtaining a composition A2;
A step b of mixing the composition A1 or the composition A2, a boron compound, and water, adjusting the pH to 4 to 5, depositing a precipitate C, and collecting the precipitate C;
Calcining said precipitate C to obtain aluminum borate whiskers c;
Method of producing aluminum borate whiskers comprising:   In the step b, first, a composition B containing the boron compound and the water is prepared, and then the composition A1 or the composition A2 and the composition B are mixed. Method for producing aluminum borate whiskers.   When preparing the composition B, the pH of the composition B is adjusted so that the pH after mixing the composition A1 or the composition A2 and the composition B is in the range of 4 to 5. The manufacturing method of the aluminum borate whisker of Claim 2 to adjust.   The method for producing aluminum borate whiskers according to any one of claims 1 to 3, wherein in the step c, the precipitate C is fired at a firing temperature of 800 ° C or higher.