JP5570011B2 - Method for producing yttrium oxide precursor aqueous sol and yttrium oxide precursor aqueous sol - Google Patents

Description

  The present invention relates to a method for producing an yttrium oxide precursor aqueous sol in which yttrium oxide is generated by heat treatment, and an yttrium oxide precursor aqueous sol produced by the production method.

  In a metal or alloy casting process, a container for storing molten metal (molten metal), a handle rod-like or bowl-shaped member used for transporting or transferring the molten metal, is easily damaged by contact with the molten metal. Therefore, in recent years, ceramic materials excellent in heat resistance and corrosion resistance, such as aluminum titanate ceramics, alumina ceramics, and mullite ceramics, are used as members that contact the molten metal instead of conventional cast iron (see, for example, Patent Document 1). .

  However, since aluminum and magnesium are highly reducible, metal ions in the matrix are reduced and eroded by contact with molten aluminum, molten aluminum alloy, and molten magnesium alloy even in the case of ceramic materials as described above. The Further, even a member that does not directly contact the molten metal is eroded by exposure to a gas containing a highly reducing metal. Therefore, a material that is more excellent in reduction resistance or a material that can improve reduction resistance by coating a conventionally used material is desired.

  As described later, the present inventors have found that yttrium oxide is promising as a refractory material excellent in reduction resistance, and have reached the present invention. Yttrium oxides are used in stabilized zirconia stabilizers, red phosphors, solid-state laser oscillators, etc. used as gas sensors and high-strength structural materials. Material.

  Here, in order to be able to form a coating film in addition to the generation of yttrium oxide, the precursor is preferably a sol or a solution. As a general method for producing a metal oxide precursor sol, there is a method in which a metal alkoxide is dissolved in an organic solvent and hydrolyzed. However, in recent years, the industry has been required to reduce the emission of VOC (volatile organic compounds), and it is desirable that the liquid medium be aqueous.

  Therefore, in view of the above circumstances, the present invention provides a method for producing an yttrium oxide precursor aqueous sol with reduced environmental load, and the provision of an yttrium oxide precursor aqueous sol produced by the production method. It is what.

In order to solve the above-mentioned problems, the method for producing an aqueous yttrium precursor precursor sol according to the present invention is described as follows. A step of separating from a solvent, and stirring without mixing the separated yttrium hydroxide with acetic acid as a carboxylic acid at a ratio of 1.5 mol or more and less than 3 mol of carboxyl group to 1 mol of yttrium ion And a step of obtaining a colorless and transparent sol ”.

  In the present invention, “aqueous” means that the dispersion medium of the sol is water and an organic solvent such as alcohol is not contained in the dispersion medium.

  As the “yttrium salt”, for example, chloride, nitrate, sulfate, carbonate, oxalate, and acetate can be used. Moreover, as an additive for adjusting the aqueous solution of yttrium salt to be alkaline, for example, ammonia water, aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and aqueous tetramethylammonium hydroxide solution can be used.

As “carboxylic acid” , acetic acid is used in the present invention . The “ ratio of less than 3 moles of carboxyl groups per mole of yttrium ions” means that when the carboxylic acid is a monocarboxylic acid, the carboxylic acid is less than 3 moles and the carboxylic acid is a dicarboxylic acid per mole of yttrium ions. in some cases the carboxylic acid is less than 1.5 mole of yttrium ion 1 mole, less than 1 mole carboxylic acid to yttrium ions per mol when the carboxylic acid is a tricarboxylic acid, makes sense der that, carboxylic acid acetate In the case of the present invention, the acetic acid is less than 3 moles per mole of yttrium ions .

  In the present invention, the grounds for considering yttrium oxide as a promising refractory material with excellent reduction resistance are as follows. FIG. 7 shows an Ellingham diagram in which the standard generation energy ΔG for oxide generation is calculated based on the literature value of the constant pressure specific heat and shown in relation to the temperature. As a result of calculating the standard generation energy ΔG for various metal oxides, the present inventors have noticed that yttrium is more stable as an oxide than aluminum or magnesium. That is, in the Ellingham diagram, the lower the position, the more stable the oxide. As shown in FIG. 7, the Y oxide line is located below the Al oxide line and the Mg oxide line. Therefore, a member coated with yttrium oxide or a member formed with yttrium oxide is hardly reduced even when it comes into contact with a molten aluminum or magnesium, and is expected to be stable as an oxide over a long period of time.

  Therefore, as a result of investigations to realize a new sol that can be used not only as yttrium oxide but also as a coating agent for forming a coating film of yttrium oxide, a manufacturing method having the above-described configuration The yttrium oxide precursor water-based sol was successfully produced. That is, according to the present invention, a sol which is a precursor of yttrium oxide is obtained by an extremely simple method of simply precipitating yttrium hydroxide by making an aqueous solution of an yttrium salt alkaline, mixing the yttrium hydroxide with a carboxylic acid and stirring. Can be manufactured.

  Here, it is one of the features of the present invention that yttrium hydroxide is mixed with carboxylic acid “without drying” and stirred. When yttrium hydroxide is separated from the solvent and then dried, a transparent sol cannot be obtained even when mixed with carboxylic acid and stirred. Further, even if a commercially available yttrium hydroxide powder material is suspended in water, mixed with carboxylic acid and stirred, a transparent sol cannot be obtained. Although these reasons are not clear, it is considered that yttrium hydroxide just formed is small in crystal and unstable as a hydroxide.

  In addition, since yttrium ions are trivalent ions, when mixing yttrium hydroxide and carboxylic acid, the proportion of carboxylic acid should be such that the carboxyl group is 3 moles per mole of yttrium ions. This is the normal concept of those skilled in the art. Or in order to make it react more reliably, it may be a general idea of those skilled in the art that the ratio of the carboxyl group to 1 mol of yttrium ions is 3 mol or more. On the other hand, the present invention is characterized in that a stable sol can be produced by adding a carboxylic acid in a proportion of less than 3 moles of carboxyl groups per mole of yttrium ions. Thereby, since the carbon dioxide which generate | occur | produces in the case of the heat processing for producing | generating a yttrium oxide reduces, the load given to an environment can be reduced. In addition, when the sol to be produced is used as a coating agent, it is expected that a uniform film can be formed with less shrinkage and loss of the coating film due to the small amount of components that disappear during the heat treatment.

  Furthermore, since this manufacturing method does not use an organic solvent, it meets social demands for reducing VOC emissions, and the load on the environment can be reduced in this respect as well.

  Also, an aqueous solution containing yttrium ions can be conceived as a precursor for forming a coating film of yttrium oxide. However, when an aqueous solution of yttrium chloride, nitrate, or sulfate is used, heating to generate yttrium oxide is possible. During processing, harmful gases containing chlorine, nitrogen and sulfur are generated. On the other hand, the sol of the present invention produced from yttrium hydroxide and carboxylic acid is composed only of elements of yttrium, carbon, hydrogen, and oxygen. In addition, even when using yttrium chloride, nitrate, and sulfate as the starting yttrium salt, it becomes a sol through the yttrium hydroxide precipitate, so in the step of separating the precipitate from the solvent, Chloride ion, nitrate ion and sulfate ion are separated from yttrium hydroxide together with the solvent. Therefore, according to the present invention, it is possible to produce a sol in which the risk of generating harmful gases during heat treatment is reduced, and the load on the environment can be further reduced.

  It should be noted that ions derived from an additive for adjusting the aqueous solution of yttrium salt to alkaline are also separated together with the solvent in the step of separating the yttrium hydroxide precipitate from the solvent. As a result, when ammonia water is used as an additive, a gas containing nitrogen may be generated during heat treatment of a sol that generates yttrium oxide, or when sodium hydroxide or potassium hydroxide is used as an additive. In addition, the possibility that the heat resistance of the yttrium oxide produced from the sol is lowered due to the presence of sodium or potassium is reduced.

  The method for producing an yttrium oxide precursor aqueous sol according to the present invention has the above-described configuration, wherein “the ratio of the carboxylic acid to the yttrium hydroxide is 1.5 mol to 2.5 mol of the carboxyl group with respect to 1 mol of the yttrium ion. Can be.

  As a result of investigations aimed at obtaining a transparent sol by further reducing the ratio of carboxyl groups to yttrium ions, a transparent sol is formed from yttrium hydroxide when the ratio of carboxyl groups to yttrium ions is large. Although the speed is large, it has been clarified that a transparent sol can be obtained at a sufficiently high speed even if the ratio of the carboxyl group to 1 mole of yttrium ions is reduced to at least 1.5 moles to 2.5 moles. In other words, the sol can be obtained from almost the whole amount of yttrium hydroxide even if the ratio of the carboxyl group to 1 mol of yttrium ions is reduced to 1.5 mol to 2.5 mol. Therefore, according to the present invention, carbon dioxide generated when heat-treating the sol to produce yttrium oxide can be further reduced, and the components disappeared by heating can be reduced. When is used as a coating agent, it is expected that a more uniform coating film is formed.

  The method for producing an aqueous yttrium oxide precursor sol according to the present invention includes, in addition to the above-described configuration, “having a step of washing the yttrium hydroxide precipitate with water after the step of separating yttrium hydroxide from the solvent”. be able to.

  By providing a step of washing with water, from the solvent adhering to the yttrium hydroxide precipitate, the anion derived from the yttrium salt and the ion derived from the additive used to adjust the liquidity of the aqueous solution of the yttrium salt It becomes possible to remove almost completely. Thereby, there is almost no fear that harmful gas is generated during the heat treatment of the sol that generates yttrium oxide and there is a possibility that impurities that affect the properties of the generated yttrium oxide exist.

Next, the yttrium oxide precursor aqueous sol according to the present invention contains “acetate ions of 1.5 mol or more and less than 3 mol per mol of yttrium ions, and does not contain nitrate ions, chloride ions, and sulfate ions. In addition, it is colorless and transparent .

  This is a sol produced when acetic acid is used as the carboxylic acid in the above-described method for producing an yttrium oxide precursor aqueous sol. Since acetic acid has a structure with a small number of carbon atoms, less carbon dioxide is generated during the heat treatment for producing yttrium oxide. Moreover, since there are few components lose | disappeared by heat processing, it is anticipated that a uniform coating film can be formed. In addition, unlike formic acid and oxalic acid, which have the same number of carbon atoms, it is not a deleterious substance, and therefore has an advantage of easy handling.

  Further, as a precursor for forming a coating film of yttrium oxide, an aqueous solution of yttrium acetate tetrahydrate which is easily soluble in water can be conceived. In this case, 3 mol of acetate ions per 1 mol of yttrium ions Exists. On the other hand, since the acetic acid ion contained in the sol of the present invention is less than 3 mol per 1 mol of yttrium ion, the heat treatment for generating yttrium oxide is more than when an aqueous solution of yttrium acetate tetrahydrate is used. It is considered more promising in that the amount of carbon dioxide generated at the time is small and a uniform coating film is formed.

  As described above, as an effect of the present invention, there is provided a method for producing an yttrium oxide precursor aqueous sol with reduced environmental load, and provision of an yttrium oxide precursor aqueous sol produced by the production method. be able to.

It is process drawing of the manufacturing method of the yttrium oxide precursor aqueous sol which is one Embodiment of this invention. The Y-1.5 dried product and the Y-2 dried product, which are yttrium oxide precursor aqueous sols of the present embodiment manufactured by the manufacturing method of FIG. It is the figure contrasted with the Japanese thing. It is the figure which contrasted the X-ray-diffraction pattern measured while raising temperature about (a) sample Y-1.5 dried material, (b) dried sample Y-2, and (c) yttrium acetate tetrahydrate. . It is the graph which compared the result of the differential thermogravimetric analysis about the dehydrate of (a) sample Y-1.5 dried material, (b) sample Y-2 dried material, and (c) yttrium acetate tetrahydrate. . It is a figure which shows the X-ray-diffraction pattern of the sample which heat-processed each sample Y-1.5 dried material at 400 degreeC, 500 degreeC, and 600 degreeC for 2 hours. It is the figure which showed the melt | dissolution equilibrium in the water of yttrium oxide by the relationship between a density | concentration and pH. It is an Ellingham figure created based on calculation of the standard production energy of a metal oxide.

  Hereinafter, a method for producing an yttrium oxide precursor aqueous sol according to an embodiment of the present invention and an yttrium oxide precursor aqueous sol of this embodiment produced by the production method will be described with reference to FIGS. 1 to 5. To do.

  As shown in FIG. 1, the production method of the yttrium oxide precursor aqueous sol of the present embodiment (hereinafter simply referred to as “production method”) includes a step S1 of adjusting an aqueous solution of yttrium salt and an alkaline solution of the aqueous solution of yttrium salt. Step S2 for producing a precipitate of yttrium hydroxide, Step S3 for separating the produced yttrium hydroxide from a solvent, Step S4 for washing the separated yttrium hydroxide with water, and yttrium hydroxide washed with water after separation Step S5, which is mixed with carboxylic acid and stirred at a ratio of less than 3 mol of carboxyl groups per 1 mol of yttrium ions without drying.

  In Step 1, when an yttrium salt does not have an element that generates a harmful gas by heating, such as halogen, nitrogen, or sulfur, such as when an acetate, oxalate, or carbonate is used as an yttrium salt, It is possible to omit the step S4 of washing the separated yttrium hydroxide with water. However, even when using an yttrium salt that does not become a source of harmful gas, by performing step S4 of washing with water, anions in water adhering to the precipitate of yttrium hydroxide are almost completely removed. Generation of carbon dioxide when the produced sol is heat-treated can be reduced.

  Yttrium chloride hexahydrate (manufactured by Kanto Chemical Co., Ltd., high purity reagent 99.99%) was dissolved in water to obtain a 0.1 M aqueous solution (step S1). FIG. 6 shows the dissolution equilibrium of yttrium hydroxide in water in relation to the concentration and pH of the aqueous solution. If the aqueous solution is alkaline, yttrium hydroxide precipitates almost without being affected by the concentration. Here, in the case of a 0.1 M aqueous solution, hydroxide is generated in a region having a pH of about 7 or more, as indicated by a broken line in the figure. In this example, aqueous ammonia (made by Nacalai Tesque, 28% reagent grade) prepared to 1.5 M was added to 20 ml of a 0.1 M aqueous solution of yttrium chloride to adjust the pH to 9.5, and white yttrium hydroxide was added. Precipitated (step S2). Here, a glass electrode type hydrogen ion concentration meter (manufactured by Iwaki Glass, AC-50) and a pH electrode (manufactured by Terumo, Orion 81-72) were used for pH measurement.

  The aqueous solution containing the precipitate was centrifuged with a centrifuge (Tomy Seiko, TD-65) (rotation speed: 3000 rpm, 15 minutes) to separate yttrium hydroxide from the solvent (step S3). When the yttrium concentration of the supernatant (solvent) was measured with an inductively coupled plasma emission spectrometer (ICP-AES ULTIMA2 manufactured by Horiba, Ltd.) and the yield of yttrium hydroxide was calculated, it was 96.8% to 99.4%. Met. As a standard solution for inductively coupled plasma emission spectroscopic analysis, a 1000 ppm yttrium standard solution (manufactured by Kanto Chemical) for atomic absorption analysis was used.

  Pure water was added to the centrifuged yttrium hydroxide and stirred, followed by a water washing operation of centrifuging under the same conditions as described above. This washing operation is intended to remove chloride ions derived from yttrium chloride hexahydrate and ammonium ions derived from aqueous ammonia, and the electrical conductivity of the supernatant liquid is 0.1 S / m or less. As a guide, this was repeated four times (step S4). In addition, the electrical conductivity was measured using a glass electrode type hydrogen ion concentration meter (manufactured by Horiba, Ltd., D-24) and an electrical conductivity electrode (manufactured by Horiba, Ltd.).

  Acetic acid (manufactured by Nacalai Tesque, reagent special grade 99.7%) was added to the gel-like yttrium hydroxide washed with water, mixed and stirred (step S5). Stirring was performed at a shaking speed of 260 rpm using a shaker (manufactured by Tokyo Science Instruments, Multi-shaker MMS BASE-L50) while measuring the time until the mixture became colorless and transparent. As shown in Table 1 below, this process is performed with five types of samples Y-3, Y-2.5, Y-2, Y with different ratios of the acetic acid to be added to the yttrium ions (the ratio of carboxyl groups). -1.5, Y-1 was performed, and the change due to stirring of the mixed solution was compared.

  As a result, as shown in Table 1, 3 mol of acetic acid sample Y-3 per 1 mol of yttrium ions and 2.5 mol of acetic acid sample Y-2.5 per 1 mol of yttrium ions were added with acetic acid. Immediately became a colorless and transparent sol. Sample Y-2 with 2 moles of acetic acid per 1 mole of yttrium ions was clouded when acetic acid was added, but the transparency increased with the passage of time. became. Similarly, sample Y-1.5 having 1.5 moles of acetic acid with respect to 1 mole of yttrium ions also turned into a colorless and transparent sol by stirring for 4 days from the cloudy state when acetic acid was added. Thus, for samples Y-3, Y-2.5, Y-2, and Y-1.5, since a colorless and transparent sol was obtained, the sol was generated from almost the entire amount of yttrium hydroxide. it was thought. These colorless and transparent sols were stable in dispersion state even when half a year or more passed.

  On the other hand, the mixed solution of sample Y-1 containing 1 mol of acetic acid per 1 mol of yttrium ions was not completely colorless and transparent even after stirring for 3 months. However, since the supernatant was cloudy, it was considered that the sol was partially formed even if not the total amount of yttrium hydroxide.

  From the above results, at least in the range of 1.5 to 2.5 moles of acetic acid per mole of yttrium ions, the sol is made from yttrium hydroxide at a sufficiently practical rate and at a high rate (almost all). It is possible to produce a sol in which the ratio of components that can be produced and disappear during the heat treatment for producing yttrium oxide is reduced.

  For the purpose of identifying the produced sol, X-ray diffraction patterns were measured at room temperature for the dried sols of Samples Y-1.5 and Y-2. The sol was dried at 150 ° C. for 12 hours using a room temperature dryer (DRN-420DA). As a control, a commercially available yttrium acetate tetrahydrate (manufactured by Kanto Chemical Co., Ltd., high-purity reagent 99.99%) was similarly measured for an X-ray diffraction pattern at room temperature. Here, an X-ray diffractometer (manufactured by Mac Science, MXP18) is used for X-ray diffraction, the source CuKα ray, measurement time 1.00 sec, step width 0.02 degree, output 8.000 kW (voltage 40.00 kV, Measurement was performed under the condition of a current of 200.00 mA.

  The measured X-ray diffraction pattern is shown in FIG. For the sample Y-1.5 dried product and the Y-2 dried product, values consistent with the lattice constant read from the measured diffraction pattern were not found in JCPDS, and the crystal phase could not be identified. However, the dried sample Y-1.5 and the dried sample Y-2 are different in crystal phase from yttrium acetate tetrahydrate, and the dried sample Y-1.5 and dried sample Y-2 are also The crystal phases were thought to be different.

  Therefore, organic elemental analysis was performed on the dried sample Y-1.5 and the dried sample Y-2. For the analysis, an organic trace element analyzer (manufactured by Yanaco Analytical Industry, CHN coder MT-6) was used. Moreover, the organic elemental analysis was similarly performed about the yttrium acetate tetrahydrate. The results are shown in Table 2.

The analysis results for the commercially available yttrium acetate tetrahydrate were relatively consistent with the molar ratio calculated from the chemical formula (Y: C: H = 1: 6: 17). For sample Y-1.5 dried product, Y (OH) _1.5 (CH 3 COO) _1.5 is considered as the chemical formula from the result of elemental analysis, and for sample Y-2 dry product, chemical formula is derived from the result of elemental analysis. Y (OH) (CH3COO) ₂ can be considered. Thereby, it can be considered that the novel sol which has not been confirmed so far is manufactured by the manufacturing method of the present embodiment.

  Furthermore, as shown below, the sol of this embodiment obtained by the above production method is confirmed to be a yttrium oxide precursor that generates yttrium oxide by heat treatment, by measuring an X-ray diffraction pattern. It was. Here, the measurement of the X-ray diffraction pattern is performed by storing the dried sample Y-1.5 and the dried sample Y-2 in a platinum sample holder and increasing the temperature at a heating rate of 5 ° C./min. Except for the above, the same apparatus and measurement conditions as described above were used. The same measurement was performed for yttrium acetate tetrahydrate. The result is shown in FIG.

  When compared with the lattice constant described in JCPDS, a broad peak of yttrium oxide was observed from 400 ° C., and it was considered that yttrium oxide having poor crystallinity or small crystallites was formed. . The peak became clearer at 700 ° C. and sharper at 800 ° C. Therefore, it was considered that yttrium oxide having high crystallinity was generated from any sample by heating to 800 ° C. while gradually raising the temperature.

  As is clear from FIG. 3, the crystal structure greatly changes between 300 ° C. and 400 ° C. in any sample. Regarding this, as shown in FIGS. 4 (a), (b), and (c), considering that an exothermic peak and weight loss were measured between 300 ° C. and 400 ° C. in differential thermogravimetric analysis, It was thought that acetate ions disappeared in this temperature range and yttrium oxide began to be generated. Here, the differential thermogravimetric analysis is performed using a differential thermogravimetric simultaneous measurement apparatus (manufactured by SII, EXSTAR TG / DTA6300), and FIGS. 4 (a) and 4 (b) show sample Y-1.5 dried products, respectively. And the results of the dried sample Y-2. FIG. 4C shows the measurement results for a sample obtained by previously drying yttrium acetate tetrahydrate at 150 ° C. for 12 hours to remove hydrated water. The conditions for removing the water of hydration were determined based on the results of differential thermogravimetric analysis (not shown) based on the observation of weight loss and endothermic peaks that were thought to be due to desorption of water of hydration near 100 ° C It is.

  In addition, as described above with reference to FIG. 3, according to the X-ray diffraction pattern measured while increasing the temperature at a rate of 5 ° C./min, a sharp peak of yttrium oxide is observed by heat treatment up to 800 ° C. However, it has been found that when heat treatment is performed at a predetermined temperature for a predetermined time, yttrium oxide having high crystallinity is generated at a lower temperature. FIG. 5 illustrates the result of measuring the X-ray diffraction pattern at room temperature after the sample Y-1.5 dried product was heat-treated at a predetermined temperature for 2 hours. A considerably sharp yttrium oxide peak was observed by the heat treatment at 500 ° C., and the yttrium oxide peak became clearer by the heat treatment at 600 ° C.

  Therefore, it was confirmed that yttrium oxide was produced from the sol of the present embodiment obtained by the above production method by heat treatment at 500 ° C. to 600 ° C. for 2 hours. In general, when an attempt is made to coat a ceramic material or a metal member with a precursor sol of an oxide ceramic, the target temperature for the formation of the oxide ceramic is below 1000 ° C. In view of this, the sol of this embodiment in which yttrium oxide is generated at 500 ° C. to 600 ° C. is expected to be extremely useful as a coating agent.

  As described above, according to the present embodiment, a sol that is a precursor of yttrium oxide, which is considered to be promising as a refractory material having excellent reduction resistance, can be manufactured by an extremely simple manufacturing method. The produced sol is stable in a dispersed state for a long time, and yttrium oxide is generated at a low temperature of 500 ° C. to 600 ° C.

  In addition, according to the production method of the present embodiment, it is possible to produce a stable sol by reducing the ratio of acetate ions to 1 mol of yttrium ions to at least 1.5 to 2.5 mol. Thereby, the sol of the present embodiment is expected to have a component that disappears by heating and can form a uniform coating film.

  In addition, the sol of this embodiment has a low ratio of acetate ions to 1 mol of yttrium ions, and does not contain an organic solvent in the dispersion medium. Since it does not have, it can produce | generate an yttrium oxide extremely reducing the load given to an environment. Furthermore, since it is produced through a step of washing the precipitate of hydroxide with water, chloride ions derived from the starting material yttrium chloride and ammonium ions derived from aqueous ammonia used as an additive for adjusting liquid properties Is almost completely eliminated, and the load on the environment is more reliably reduced.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above-described embodiments, and various improvements and design changes can be made without departing from the scope of the present invention. It is.

  For example, the sol produced by the production method described above is a sol that produces yttrium oxide by heat treatment alone, but by mixing with a precursor of another metal oxide and performing a heat treatment, It is considered possible to generate double oxides of yttrium and other metals.

  In addition, the sol produced by the production method described above is expected to be useful as a coating agent for forming a coating film of yttrium oxide, but of course, a material containing a bulk body of yttrium oxide or an oxide of yttrium oxide. It can also be used as a precursor for producing a bulk body.

Special table 2003-506217 gazette

Claims (4)

Making the aqueous solution of yttrium salt alkaline and producing a precipitate of yttrium hydroxide;
Separating the produced yttrium hydroxide from the solvent;
Without drying the separated yttrium hydroxide, by mixing and stirring with acetic acid as a carboxylic acid at a ratio of 1.5 mol or more and less than 3 mol of carboxyl group to 1 mol of yttrium ion , colorless and transparent And a step of obtaining a sol . A method for producing an aqueous sol of yttrium oxide precursors. 2. The yttrium oxide precursor aqueous sol according to claim 1, wherein the ratio of the carboxylic acid to the yttrium hydroxide is a ratio of 1.5 mol to 2.5 mol of carboxyl groups with respect to 1 mol of yttrium ions. Production method. The method for producing an yttrium oxide precursor aqueous sol according to claim 1 or 2, further comprising a step of washing the precipitate of yttrium hydroxide with water after the step of separating yttrium hydroxide from the solvent. Containing 1.5 mol or more and less than 3 mol of acetate ion to 1 mol of yttrium ion ,
Contains no nitrate, chloride, and sulfate ions,
An aqueous sol of yttrium oxide precursor characterized by being colorless and transparent .

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