JPH0256320B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel method for producing aluminum orthophosphate crystals (hereinafter abbreviated as AlPO ₄ crystals), sometimes AlPO ₄ single crystals. Since AlPO ₄ has a crystal structure similar to crystalline quartz (SiO ₂ ), it is seen as a promising piezoelectric material for surface acoustic wave (SAW) devices. Also, like SiO ₂ , it has excellent fire resistance, so it is used as a raw material for various ceramics. (Prior Art) The following method was generally used to obtain AlPO ₄ crystals. That is, (1) a method in which a water-soluble phosphate and an aluminum salt are reacted in an aqueous medium to obtain AlPO ₄ as a precipitate (precipitation method). (2) A method of mixing aluminum hydroxide or aluminum oxide and orthophosphoric acid and firing the mixture (calcination method). (3) A method in which AlPO ₄ is dissolved in an aqueous phosphoric acid solution and crystals are precipitated and grown using the difference in saturation solubility depending on temperature (hydrothermal synthesis method). However, in the precipitation method (1) above, the AlPO ₄ obtained is amorphous according to X-ray diffraction, so it is necessary to sinter this precipitate at a high temperature of about 1000°C in order to obtain AlPO ₄ crystals. . In the firing method (2) above, the solidified product obtained by reacting aluminum hydroxide or aluminum oxide with phosphoric acid at a temperature of about 130 to 270°C is
It is necessary to bake at a high temperature of 1300℃ for 5 to 20 hours.
Moreover, the reactor also requires expensive materials that are resistant to corrosion by high-temperature phosphoric acid. In addition, along with the precipitation method (1), it is inevitable that impurities are mixed into the product due to corrosion of the equipment material during the firing process, which is unsatisfactory especially for recent electronic industry materials that require high purity. The hydrothermal synthesis method (3) above obtains AlPO ₄ crystals by the so-called crystallization method, and is a suitable method for obtaining single crystals, but the amount of AlPO ₄ precipitated can only be obtained by the solubility difference. Large-scale equipment is required for mass production. Furthermore, since the temperature gradient of saturated solubility of AlPO ₄ is negative, it is necessary to gradually raise the temperature, the operation time is long at least 2 days, and temperature control becomes complicated accordingly. Furthermore, since the temperature gradient of saturation solubility is negative,
Generally, it is necessary to heat the device to a high temperature of 200°C or higher, and the equipment must be made of materials that can withstand the phosphoric acid aqueous solution at this temperature, and there are other problems such as consuming a large amount of thermal energy. As described above, the conventionally known methods have various problems, and the actual situation is that the utilization of AlPO ₄ crystals, which have excellent properties, is greatly hindered. (Problems to be Solved by the Invention) The present inventors first reacted an aqueous solution of phosphoric acid with an aluminum hydroxide or oxide in an organic solvent capable of forming two phases with water to form AlPO ₄ crystals. I applied for a method to obtain the. (Japanese Unexamined Patent Publication No. 58-104007) However, although this method is an economical method for obtaining AlPO ₄ crystals, it is extremely difficult to obtain single crystals. (Means, Actions, and Effects for Solving the Problems) As a result of intensive studies on how to economically obtain high-quality AlPO ₄ single crystals, the present inventors found that an organic solvent that can be uniformly mixed with water , especially at atmospheric pressure 60
The present invention has been completed in which phosphoric acid and aluminum hydroxide or oxide are reacted in the presence of one or more organic solvents having a boiling point of .degree. C. or higher. That is, the present invention is a method for producing aluminum orthophosphate crystals, which comprises: in the presence of an organic solvent that can be uniformly mixed with water, particularly one or more organic solvents having a boiling point of 60° C. or higher at atmospheric pressure; Regarding a technology characterized by reacting an aqueous phosphoric acid solution with an aluminum hydroxide or/and an aluminum oxide (hereinafter simply referred to as aluminum raw material), according to this technology, the temperature at 190°C or lower under normal pressure is It is possible to produce AlPO ₄ crystals at relatively low temperatures. To describe one embodiment of the method of the present invention, first, a phosphoric acid aqueous solution, an aluminum raw material, and an organic solvent are charged into a reaction tank and heated. The order in which the raw materials and organic solvents are charged into the reaction tank is generally as described above, but is not necessarily limited to this. A cooler is connected to the top of the reaction tank.
Water and solvent vapor evaporated by heating can be condensed and refluxed to the reaction tank or discharged outside the system.
When the raw materials and organic solvent are completely charged, the contents of the reaction tank are heated while being stirred. The heating temperature is boiling, and the reaction is completed within 2 hours. After heating, the generated AlPO ₄ crystals are in the form of a slurry, and if this is separated and dried using a commonly known method, AlPO ₄ crystals can be obtained. However, in the present invention, water and an organic solvent are first removed. If the method of evaporation and distillation followed by separation is adopted, it is preferable to obtain single crystal AlPO ₄ , which is the object of the present invention, and it is possible to obtain AlPO ₄ crystals with higher purity. In addition, when water and organic solvent are distilled off, water is removed from the reaction system while replenishing the reaction tank with a volume of organic solvent corresponding to the distilled amount, and after the water is substantially removed, the organic solvent and This is done by separately separating AlPO ₄ crystals. The aluminum raw materials used in the method of the present invention include various aluminum hydroxides such as gibbsite, viarite, nordstrandite, boehmite, diaspore, α-, γ-, δ-, θ
-, ρ-, ξ-, χ-, η-, κ-, and various types of alumina are used. The higher the purity of the aluminum raw material and phosphoric acid aqueous solution used, the easier it is to obtain a highly purified product, which is preferable, but there are no particular limitations. Raw materials with appropriate purity may be selected depending on the intended use of AlPO ₄ . Generally, industrial grade aluminum raw materials and phosphoric acid aqueous solutions can be used satisfactorily. In the method of the present invention, the reaction molar ratio of phosphoric acid and aluminum raw material is _0.8 to _P2O5 / _{Al2O3 .}
It is in the range of 1.8, preferably in the range of 1.0 to 1.3, and within this range AlPO ₄ crystals can be synthesized with good yield. In AlPO ₄ , the theoretical molar ratio of phosphorus to aluminum is 1.0 as P ₂ O ₅ /Al ₂ O ₃ , so _the actual reaction should be 1.0 _.
The reaction progresses more easily when P ₂ O ₅ is added in excess. However, if the molar ratio is 1.8 or more, the degree of crystallinity of AlPO ₄ decreases, which is undesirable, and the dispersibility of crystals in the reaction tank deteriorates, resulting in the formation of solids, resulting in poor operability. On the other hand, if the molar ratio is less than 1.0, unreacted aluminum raw materials will remain in the reaction product, which is undesirable, but if it is 0.8 or more, AlPO ₄ crystals of acceptable quality may be produced for some applications. can get. The concentration of the aqueous phosphoric acid solution used in the method of the present invention is suitably 64% by weight or less as P ₂ O ₅ (hereinafter, % means % by weight unless otherwise specified). Originally, the reaction between phosphoric acid and aluminum raw material is
For example, Al ₂ O ₃ +2H ₃ PO ₄ →2AlPO ₄ +3H ₂ O As is clear from this, it is a dehydration reaction, so generally, the higher the concentration of the phosphoric acid aqueous solution, the faster the reaction is desirable. However, in the method of the present invention, P ₂ O ₅
The use of highly concentrated phosphoric acid exceeding 64% is not preferred because the reaction products tend to solidify during the reaction, making it difficult to stir the reaction system. on the other hand,
There is no particular limitation on the lower limit of the appropriate value of the phosphoric acid concentration. However, if extremely low concentration phosphoric acid is used, the reaction rate will decrease and the capacity of the reaction apparatus will have to be increased, which naturally limits its practical use. The organic solvent used in the method of the present invention is
Any material that mixes uniformly with water is fine. Although the suitability of the above organic solvents may differ depending on the selection of state variables, generally suitable organic solvents include cellosolves such as methyl cellosolve, ethyl cellosolve, isopropyl cellosolve, and butyl cellosolve; methyl carbitol and diethyl carbitol. Various carbitols such as toll; methyl ethyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, ethylene glycol, 2-methyl-2,4-penntadiol, furfuryl alcohol, tetrahydrofluoryl alcohol, propylene Alcohols such as glycol; Amines such as n-butylamine, n-amylamine, isobutylamine, sec-butylamine, dibutylamine, 2-aminopentane, ethylenediamine, propylene diamine, cyclohexylamine, pyridine, ethanolamine; diacetone alcohol, Examples include ketones such as acetylacetone and acetonitrile acetone; other organic solvents that mix uniformly with water such as dimethylformamide, acetonitrile, and dimethyl sulfoxide.
These are only examples of organic solvents that can be used in the method of the present invention, and are not limited thereto. The appropriate amount of organic solvent to be added varies depending on the type of organic solvent, the concentration of the phosphoric acid aqueous solution, and the stirring conditions during the reaction, but under all conditions, AlPO ₄
It is desirable that the crystal slurry concentration is 50% or less, and that the amount of slurry used is at least the same weight as the water in the system at the initial stage of the reaction, as shown in Examples below. For the above reasons, conventional production of AlPO ₄ crystals required many days, whereas in the present invention, the reaction is carried out in the presence of an organic solvent and the obtained AlPO ₄ crystals are dried separately. Manufacturing time is shortened, thermal energy consumption is low, and manufacturing equipment made of ordinary glass or stainless steel is sufficient. As described above, the present invention has made it possible to produce AlPO ₄ crystals, especially single crystals, at low cost, which was conventionally difficult to do, and has made it possible to manufacture AlPO 4 crystals, especially single crystals, at low cost. worth it. (Examples) Hereinafter, the present invention will be explained more clearly using Examples. Example 1 145 g of phosphoric acid aqueous solution (P ₂ O ₅ concentration 54%), 78 g of aluminum hydroxide (gibbsite type), and 250 g of ethylene glycol were placed in a flask, and the temperature was raised with stirring to give a reaction temperature of about 1 After heating for a period of time, water and ethylene glycol in the reaction system were evaporated, and dehydration was carried out while adding ethylene glycol in a volume equivalent to the distilled ethylene glycol and water to the system. As dehydration progresses, the internal temperature rises, and when the internal temperature exceeds 160℃, heating is stopped and after cooling, the product (precipitate) is separated from the solvent and dried to form white fine particles. I got something. The X-ray diffraction pattern of this product is shown in FIG. As is clear from Figure 1, the diffraction angle 2θ = 26.4°,
Has main peaks at 28.0° and 49.7°, ASTM card 10
This coincided with the characteristic diffraction peak of berlinite-type AlPO ₄ described in -423. Furthermore, Fig. 2 shows an electron micrograph of this berlinite type AlPO ₄ . As is clear from Figures 1 and 2, the obtained product is AlPO ₄
It is a crystal. Example 2-5 Aluminum hydroxide (kibsite type), aluminum oxide (gelatinization rate of Al ₂ O ₃ 85%), phosphoric acid aqueous solution (P ₂ O ₅ 54%) and organic solvent were used under the conditions shown in Table 1. AlPO ₄ crystals were obtained by the same procedure as in Example 1 except for the conditions shown in Table 1. The yield and analysis results of the obtained AlPO ₄ crystals are shown in Table 2. As is clear from Tables 1 and 2, the present invention allows AlPO ₄ to be produced at relatively low temperatures of 190°C or less.
Crystals were obtained almost quantitatively.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a traced scaled-down X-ray diffraction pattern of AlPO ₄ crystal obtained according to the present invention.
Figure 2 is a micrograph of this object (magnification: 1740
times).

Claims (1)

[Claims] 1. In the presence of one or more organic solvents that are uniformly miscible with water, a phosphoric acid aqueous solution and an aluminum hydroxide or/and oxide are mixed so that the molar ratio of phosphorus to aluminum is P ₂ O. A method for producing aluminum orthophosphate crystals, which comprises reacting in a slurry state at 0.8 to 1.8 as ₅ /AI ₂ O ₃ . 2. The method according to claim 1, wherein the organic solvent is a compound having a boiling point of 60° C. or higher at atmospheric pressure.