Acid decomposition method for ceramic sample

Abstract

To suitably decompose a ceramic sample including aluminum nitride as a main component.SOLUTION: An acid decomposition method for a ceramic sample including AlN as a main component includes: a step S11 of putting, into a sealed container, a mixture of a decomposition liquid including sulfuric acid and a powdery ceramic sample including AlN as a main component (that is, AlN sample); and a step S12 of irradiating the mixture with a microwave to heat the mixture at a processing temperature of 200°C ore more and 250°C or less, and thereby decomposing the AlN sample to generate a sample solution. Consequently, the AlN sample can be suitably decomposed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for acid decomposition of a ceramic sample containing aluminum nitride as a main component. [Background technology]

[0002] A conventional method for chemical analysis of ceramic samples whose main component is aluminum nitride (AlN) is the "Method for chemical analysis of aluminum nitride fine powder for fine ceramics (JIS R1675)." In this chemical analysis method, a sample whose main component is AlN is dissolved using a sulfuric acid pressure acid decomposition method, and the resulting solution is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to quantify impurities such as silicon (Si), iron (Fe), and calcium (Ca).

[0003] When preparing a sample solution using the sulfuric acid pressure acid decomposition method, a powdered sample and an aqueous sulfuric acid solution are placed in a resin container, which is then placed inside a stainless steel pressure vessel. The pressure vessel is then heated to 200°C in an air bath or the like and maintained at this temperature for 16 hours. After the pressure vessel is cooled to room temperature, it is opened, and a sample solution in which the sample is dissolved in the aqueous sulfuric acid solution is obtained.

[0004] In the sulfuric acid pressure acid decomposition method described above, the sample and sulfuric acid aqueous solution inside are indirectly heated by heating the pressure vessel, which requires a long heating time of 16 hours. In addition, because the stainless steel pressure vessel is relatively large and heavy, the heating and cooling times also require a total of about 8 hours.

[0005] On the other hand, Patent Document 1 proposes a method for decomposing a sample whose main component is AlN by placing a mixture of a sample whose main component is AlN and a solution containing hydrochloric acid in a Teflon (registered trademark) inner container, placing the inner container in an airtight container, and then microwave-heating the mixture at outputs of 250 W, 400 W, and 500 W in that order for 5 minutes each. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3241213 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, the method of Patent Document 1 requires less time to heat the sample than the sulfuric acid pressure decomposition method of "JIS R1675," but does not necessarily decompose the sample effectively. For example, when the sample is a mixture of commercially available AlN raw material powder and additives, the method of Patent Document 1 results in the sample not being completely decomposed and remaining in the solution. In particular, when the additive is an organic substance, the amount of undissolved sample is significant. Furthermore, when the sample is a calcined powder obtained by calcining the above-mentioned AlN raw material powder or mixture, the method of Patent Document 1 also results in the sample not being completely decomposed and remaining in the solution.

[0008] The present invention has been made in view of the above-mentioned problems, and has as its object to suitably decompose a ceramic sample containing aluminum nitride as its main component. [Means for solving the problem]

[0009] The invention of aspect 1 is a method for acid decomposition of a ceramic sample whose main component is aluminum nitride, comprising the steps of: a) storing a mixture of a decomposition liquid containing sulfuric acid and a powdered ceramic sample whose main component is aluminum nitride in a sealed container; and b) irradiating the mixture with microwaves to heat it at a processing temperature of 200°C or higher and 250°C or lower, thereby decomposing the ceramic sample and producing a sample solution.

[0010] A second aspect of the invention is the acid decomposition method for a ceramic sample according to the first aspect, wherein the sulfuric acid concentration in the decomposition solution is 15 mass % or more and 50 mass % or less.

[0011] A third aspect of the invention is the method for acid decomposition of a ceramic sample according to the first aspect (which may be the first or second aspect), wherein the ceramic sample contains less than 10 mass % of an additive.

[0012] A fourth aspect of the invention is the acid decomposition method for a ceramic sample according to the third aspect, wherein the additive includes an organic substance.

[0013] A fifth aspect of the invention is the acid decomposition method for a ceramic sample according to the fourth aspect, wherein the ceramic sample is a spray-dried powder, and the decomposition solution contains 0.6% by mass or more and 10% by mass or less of nitric acid.

[0014] A sixth aspect of the invention is the acid decomposition method for a ceramic sample according to any one of the first to fourth aspects, wherein the ceramic sample is a calcined powder or a fired powder. [Effects of the Invention]

[0015] In the present invention, ceramic samples containing aluminum nitride as a main component can be suitably decomposed. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a front view showing a decomposition apparatus used in an acid decomposition method according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the container assembly. [Figure 3] FIG. 1 is a diagram showing the flow of acid decomposition of an AlN sample. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 is a front view showing an example of a decomposition apparatus 1 used in an acid decomposition method according to one embodiment of the present invention. In the decomposition apparatus 1, a powdered ceramic sample (a so-called refractory ceramic sample) containing aluminum nitride (AlN) as its main component is acid-decomposed to form a solution. The solution (hereinafter also referred to as "sample solution") produced in the decomposition apparatus 1 is used for analysis by, for example, inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0018] A ceramic sample containing AlN as a main component (hereinafter also referred to as an "AlN sample") is a sample containing 80 mass% or more of AlN. The AlN content in the AlN sample is preferably 90 mass% or more. The AlN sample may be, for example, a commercially available AlN powder (hereinafter also referred to as an "AlN raw material"). The AlN raw material is, for example, AlN powder with a purity of 99.99% or more. The AlN sample may contain additives other than AlN. When the AlN sample contains an additive, the content of the additive is preferably less than 10 mass%. The additive may be an inorganic substance such as a metal, or an organic substance.

[0019] The AlN sample may be, for example, a mixture of AlN raw material and additives granulated using a spray dryer (hereinafter also referred to as "spray-dried powder" or "SD powder"). SD powder may be, for example, a powder heated to 80°C or higher using a spray dryer. The AlN sample may also be an AlN raw material or a mixture of AlN raw material and additives that has been calcined at, for example, 300°C or higher (hereinafter also referred to as "calcined powder"). Alternatively, the AlN sample may be an AlN raw material or a mixture of AlN raw material and additives that has been calcined at, for example, 1000°C or higher (hereinafter also referred to as "calcined powder").

[0020] The decomposition apparatus 1 is a substantially rectangular parallelepiped apparatus having a substantially rectangular parallelepiped storage space 11 therein, and irradiates microwaves onto an object stored in the storage space 11. In FIG. 1 , the front door of the decomposition apparatus 1 is not shown so that the interior of the storage space 11 of the decomposition apparatus 1 can be viewed. In the example shown in FIG. 1 , a plurality of container assemblies 20, each including a sealed container 21, are stored in the storage space 11. Specifically, a rotor 12 is rotatable about a rotation axis extending in the vertical direction, and a plurality of container assemblies 20 are attached to the rotor 12, which is rotatable about the rotation axis, and the plurality of container assemblies 20 are arranged in a substantially circular shape around the rotation axis in a plan view (i.e., as viewed from above). The plurality of container assemblies 20 are stored in the storage space 11 together with the rotor 12. The plurality of container assemblies 20 have substantially the same shape and structure. The number of sealed containers 21 stored in the storage space 11 of the decomposition apparatus 1 may be one or may be varied as appropriate within a range of two or more.

[0021] FIG. 2 is a cross-sectional view showing one container assembly 20. The container assembly 20 includes a sealed container 21, a shield 22, and a jacket 23. The sealed container 21 includes a container body 211 and a lid 212. The container body 211 is a substantially cylindrical member with a bottom and centered on a central axis that extends substantially parallel to the vertical direction. The lid 212 is a substantially disk-shaped member centered on the central axis. The lid 212 closes the top opening of the container body 211 from above. This forms the sealed container 21, which has an internally formed substantially cylindrical sealed space 213 centered on the central axis. The container body 211 and the lid 212 are made of, for example, a resin with high chemical resistance. In this embodiment, the container body 211 and the lid 212 are made of Teflon (registered trademark).

[0022] The shield 22 is a substantially cylindrical member centered on the central axis. The shield 22 is disposed radially outward of the container body 211 of the sealed container 21 (i.e., radially outward from the central axis) and contacts the outer surface of the container body 211 from the outside. The shield 22 is formed from a resin such as PEEK (polyether ether ketone).

[0023] The jacket 23 is a member having a substantially rectangular frame shape. The thickness of the jacket 23 in the direction perpendicular to the paper surface in Fig. 2 is, for example, slightly larger than the outer diameter of the sealed container 21. In other words, the jacket 23 has a shape obtained by removing the central substantially rectangular parallelepiped portion from a substantially rectangular parallelepiped member having a thickness slightly larger than the outer diameter of the sealed container 21 and providing a through-hole in the direction perpendicular to the paper surface.

[0024] The sealed container 21 with the shield 22 attached thereto is placed in the through hole of the jacket 23. The bottom surface of the sealed container 21 is supported from below by the lower part of the jacket 23. The lid part 212 of the sealed container 21 is pressed downward by a protrusion provided on the upper part of the jacket 23, and is urged against the upper end of the container body 211. The jacket 23 is formed of a resin such as PE (polyethylene). Note that a substantially disk-shaped thin plate made of, for example, PEEK may be placed on a portion of the upper surface of the lid part 212 of the sealed container 21 that comes into contact with the jacket 23.

[0025] The shapes and materials of the decomposition apparatus 1, the sealed container 21, the shield 22, and the jacket 23 are not limited to the above examples and may be modified in various ways. The structure of the container assembly 20 is also not limited to the above example and may be modified in various ways.

[0026] Next, with reference to FIG. 3, the flow of acid decomposition of an AlN sample using the decomposition apparatus 1 will be described. When acid decomposition of an AlN sample 91 is performed, first, a decomposition liquid 92 and the above-described powdered AlN sample 91 are placed inside the container body 211 of the sealed container 21 shown in FIG. 2, and the upper opening of the container body 211 is closed with the lid 212. As a result, a mixture of the AlN sample 91 and the decomposition liquid 92 is contained in the sealed space 213 inside the sealed container 21 (step S11). In FIG. 2, for convenience of illustration, the AlN sample 91 is drawn larger than it actually is. The amount of the AlN sample 91 contained in the sealed container 21 is, for example, 0.1 g to 1.0 g, and the median diameter (D50) of the AlN sample 91 is, for example, 10 μm (micrometers) to 500 μm. The amount of the decomposition liquid 92 contained in the sealed container 21 is, for example, 5 ml (milliliters) to 20 ml.

[0027] The decomposition liquid 92 is a liquid containing sulfuric acid (H2SO4). The decomposition liquid 92 may contain components other than sulfuric acid. For example, the decomposition liquid 92 may be a sulfuric acid aqueous solution obtained by diluting sulfuric acid with water, or may be a sulfuric acid aqueous solution to which nitric acid (HNO3) or another liquid has been added. The sulfuric acid concentration in the decomposition liquid 92 is, for example, 10 mass% or more, preferably 15 mass% or more, and more preferably 20 mass% or more. The sulfuric acid concentration in the decomposition liquid 92 is, for example, 50 mass% or less, preferably 40 mass% or less, and more preferably 30 mass% or less. When the decomposition liquid 92 contains nitric acid in addition to sulfuric acid, the nitric acid concentration in the decomposition liquid 92 is, for example, 0.6 mass% or more, and preferably 1.5 mass% or more. The nitric acid concentration in the decomposition liquid 92 is, for example, 13.8 mass% or less, and preferably 10.0 mass% or less.

[0028] After the mixture of the AlN sample 91 and the decomposition liquid 92 is placed in the sealed container 21, a shield 22 and a jacket 23 are attached to the sealed container 21 to form a container assembly 20. The container assembly 20 is placed in the storage space 11 of the decomposition apparatus 1 (see FIG. 1 ). In the decomposition apparatus 1, after the front opening of the storage space 11 is closed, microwaves are irradiated onto the mixture (i.e., the AlN sample 91 and the decomposition liquid 92) in the sealed container 21. This increases the temperature of the decomposition liquid 92 in the sealed container 21, and the pressure inside the sealed container 21 also increases, causing acid decomposition of the AlN sample 91. In the decomposition apparatus 1, microwave irradiation is continued, so that the temperature of the decomposition liquid 92 is raised to a predetermined processing temperature and maintained at that processing temperature for a predetermined processing time. This causes acid decomposition of the AlN sample 91 to proceed, and a sample solution containing the decomposed AlN sample 91 is produced (step S12).

[0029] The processing temperature in step S12 is 200°C or more and 250°C or less. Setting the processing temperature to 200°C or more ensures that the AlN sample 91 is decomposed appropriately. Setting the processing temperature to 250°C or less prevents the Teflon (registered trademark) sealed container 21 from being damaged by heat or the like. The processing time in step S12 is, for example, 10 minutes or more and 80 minutes or less. Setting the processing time to 10 minutes or more ensures that the AlN sample 91 is decomposed appropriately. Setting the processing time to 80 minutes or less prevents the time required for the decomposition process of the AlN sample 91 from becoming excessively long. From the viewpoint of more appropriately decomposing the AlN sample 91, the processing time may be 60 minutes or more. From the viewpoint of shortening the time required for the decomposition process of the AlN sample 91, the processing time may be 40 minutes or less.

[0030] In the decomposition apparatus 1, the sealed container 21, which is a decomposition container for accommodating the mixture of the AlN sample 91 and the decomposition liquid 92, is made of resin, and therefore microwaves pass through the sealed container 21 to directly heat the mixture. This allows the time required to heat the mixture and the time required to cool it (for example, by allowing it to cool naturally) to be shortened. Specifically, in the decomposition apparatus 1, the time required to heat the mixture is about 10 minutes, and the time required to cool it is about 60 minutes. In addition, in this embodiment, the treatment time during which the mixture is maintained at the treatment temperature (for example, 200°C to 250°C) is 50 minutes. That is, in the decomposition apparatus 1, the time required from the start of heating the mixture of the AlN sample 91 and the decomposition liquid 92 to the completion of cooling it is about 2 hours.

[0031] On the other hand, in the sulfuric acid pressure acid decomposition method (hereinafter also referred to as the "JIS method"), which does not use microwaves and is specified in the "Methods for Chemical Analysis of Aluminum Nitride Powder for Fine Ceramics (JIS R1675)," a stainless steel pressure vessel is heated, thereby indirectly heating the resin inner container inside the pressure vessel and the mixture of AlN sample and decomposition liquid inside the inner container. Therefore, the temperature rise time of the mixture is about 4 hours, and the temperature fall time is about 4 hours. Furthermore, the treatment time for the mixture to be maintained at the treatment temperature (e.g., 230°C) is 8 hours. In other words, in the JIS method, the time required from the start of temperature rise to the completion of temperature fall of the mixture of AlN sample and decomposition liquid is about 16 hours.

[0032] In the decomposition apparatus 1, all of the components of the container assembly 20 (i.e., the sealed container 21, the shield 22, and the jacket 23) are made of resin, which prevents metals and other substances from the container assembly 20 from being mixed into the generated sample solution. In addition, the container assembly 20 is lightweight and easy to handle. Furthermore, since the container assembly 20 does not rust due to adhesion of the decomposition liquid 92, cleaning of the container after decomposition of the AlN sample 91 is also easy.

[0033] On the other hand, the JIS method uses a stainless steel pressure vessel, which may result in the sample solution being contaminated with metals such as iron (Fe), chromium (Cr), and nickel (Ni). Furthermore, stainless steel pressure vessels are heavy and difficult to handle. Furthermore, rust may form on the pressure vessel due to adhesion of the decomposition solution, which means that cleaning the vessel after decomposition of the AlN sample takes a long time and increases the burden on the workers who perform the cleaning.

[0034] Next, the decomposition results of the AlN sample 91 using the decomposition apparatus 1 will be described with reference to Tables 1 to 3. Examples 1 to 6 and Comparative Examples 1 and 2 shown in Table 1 show the relationship between the processing temperature in the decomposition apparatus 1 and the decomposition results of the AlN sample 91.

[0035] [Table 1]

[0036] In Examples 1 to 6 and Comparative Examples 1 and 2, a mixture of 0.5 g of AlN sample 91 and 10 ml of decomposition liquid 92 was placed in a sealed container 21, which was then placed in the storage space 11 of the decomposition device 1 as shown in FIG. 1, and the mixture was then irradiated with microwaves. The AlN sample 91 was a calcined powder having a median diameter (D50) of approximately 200 μm that was calcined at approximately 300°C. The AlN content in the AlN sample 91 was 90 mass %, and the additive content was 10 mass %. The decomposition liquid 92 was a sulfuric acid aqueous solution with a concentration of 20 mass % obtained by diluting sulfuric acid with water, and did not contain nitric acid.

[0037] In Comparative Example 1 and Comparative Example 2, the treatment temperatures of the mixture in the decomposition apparatus 1 were 180°C and 190°C, respectively. In Examples 1 to 6, the treatment temperatures were 200°C, 210°C, 220°C, 230°C, 240°C, and 250°C, respectively. Note that, to prevent damage to the sealed container 21, experiments were not conducted at treatment temperatures above 250°C. In Examples 1 to 6 and Comparative Examples 1 and 2, the treatment time of the mixture at the above treatment temperatures was 50 minutes. Furthermore, in Examples 1 to 6 and Comparative Examples 1 and 2, the time required to heat the mixture from room temperature (25°C in this embodiment) to the above treatment temperature was 10 minutes, and the time required to cool the mixture to room temperature by natural cooling after the treatment time had elapsed was 60 minutes.

[0038] In Table 1, the decomposition result "excellent" indicates that the AlN sample 91 in the sealed container 21 was completely dissolved in the decomposition liquid 92. "Poor" indicates that the AlN sample 91 in the sealed container 21 remained dissolved or that the AlN sample 91 was barely dissolved. When the decomposition result is "excellent," the generated sample solution can be suitably used for analysis by ICP-AES, etc. On the other hand, when the decomposition result is "poor," the generated sample solution is not suitable for analysis by ICP-AES, etc. The decomposition results of Examples 1 to 6 (i.e., treatment temperatures of 200°C to 250°C) were "excellent." On the other hand, the decomposition results of Comparative Examples 1 and 2 (i.e., treatment temperatures of 180°C to 190°C) were "poor."

[0039] When sintered powder with a median diameter (D50) of 500 μm sintered at approximately 1000°C was used as AlN sample 91, the decomposition results at treatment temperatures of 200°C to 250°C were similar to those described above, with the result being "excellent" and the decomposition results at treatment temperatures of 180°C to 190°C being "unacceptable." Furthermore, when SD powder with a median diameter (D50) of approximately 100 μm formed at approximately 80°C or higher was used as AlN sample 91, the decomposition results at treatment temperatures of 200°C to 250°C were similar to those described above, with the result being "excellent" and the decomposition results at treatment temperatures of 180°C to 190°C being "unacceptable." The sintered powder and SD powder both had an AlN content of 90% by mass and an additive content of 10% by mass, similar to the calcined powder described above.

[0040] When an AlN raw material with an AlN content of 99.99 mass% and a median diameter (D50) of approximately 100 μm was used as AlN sample 91, the decomposition results at a processing temperature of 200°C to 250°C were "excellent," while the decomposition results at a processing temperature of 180°C to 190°C were "unacceptable."

[0041] Examples 7 to 12 shown in Table 2 show the relationship between the sulfuric acid concentration in the decomposition solution 92 and the decomposition results of the AlN sample 91.

[0042] [Table 2]

[0043] In Examples 7 to 12, the experimental conditions and the like were the same as in Examples 1 to 6 and Comparative Examples 1 and 2, except that the treatment temperature in the decomposition apparatus 1 and the sulfuric acid concentration of the decomposition liquid 92 were changed. In Examples 7 to 12, the treatment temperature of the mixture in the decomposition apparatus 1 was 250°C. In Example 7, an aqueous sulfuric acid solution with a sulfuric acid concentration of 10 mass% was used as the decomposition liquid 92. In Examples 8 to 12, aqueous sulfuric acid solutions with sulfuric acid concentrations of 15 mass%, 20 mass%, 30 mass%, 40 mass%, and 50 mass%, respectively, were used as the decomposition liquid 92. Note that in Examples 7 to 12, the decomposition liquid 92 did not contain nitric acid.

[0044] The decomposition result "excellent" in Table 2 indicates the same state as in Table 1. The decomposition result "good" in Table 2 indicates that, when multiple experiments were performed, there was a mixture of states in which the AlN sample 91 was completely dissolved and states in which the AlN sample 91 was almost completely dissolved but a very small amount of undissolved particles remained. The decomposition result "fair" in Table 2 indicates a state in which the AlN sample 91 was dissolved but a small amount of undissolved particles remained. When the decomposition result is "good," the resulting sample solution can be suitably used for analysis by ICP-AES, etc. When the decomposition result is "fair," the resulting sample solution can be used for analysis by ICP-AES, etc., but the accuracy of the analysis results may be lower than when the decomposition results are "excellent" or "fair."

[0045] The decomposition results of Examples 8 to 11 (i.e., sulfuric acid concentrations of 15% by mass to 40% by mass) were "excellent." The decomposition results of Example 12 (i.e., sulfuric acid concentration of 50% by mass) were "good." The decomposition results of Example 7 (i.e., sulfuric acid concentration of 10% by mass) were "fair."

[0046] When a calcined powder with a median diameter (D50) of 500 μm calcined at approximately 1000°C was used as AlN sample 91, the decomposition results at sulfuric acid concentrations of 15% to 40% by mass were "excellent," the decomposition results at a sulfuric acid concentration of 50% by mass were "good," and the decomposition results at a sulfuric acid concentration of 10% by mass were "passable." Furthermore, when an SD powder with a median diameter (D50) of 100 μm formed at 80°C was used as AlN sample 91, the decomposition results at sulfuric acid concentrations of 15% to 40% by mass were "excellent," the decomposition results at a sulfuric acid concentration of 50% by mass were "good," and the decomposition results at a sulfuric acid concentration of 10% by mass were "passable." The calcined powder and SD powder both had an AlN content of 90% by mass and an additive content of 10% by mass, similar to the calcined powder described above.

[0047] When an AlN raw material having an AlN content of 99.99% by mass and a median diameter (D50) of 100 μm was used as AlN sample 91, the decomposition results at sulfuric acid concentrations of 15% by mass to 40% by mass were "excellent," and the decomposition results at sulfuric acid concentrations of 10% by mass and 50% by mass were "good."

[0048] Table 3 shows the relationship between the nitric acid concentration in the decomposition solution 92 and the decomposition results of the AlN sample 91 in Examples 13 to 18 and Comparative Example 3.

[0049] [Table 3]

[0050] In Examples 13 to 18 and Comparative Example 3, the experimental conditions were the same as in Examples 7 to 12, except that the type of AlN sample 91 and the sulfuric acid and nitric acid concentrations of the decomposition solution 92 were changed. In Examples 13 to 18 and Comparative Example 3, the AlN sample 91 used contained an organic substance. The AlN content in the AlN sample 91 was 90 mass% or more, and the organic binder content was 2 mass% or less. Examples of organic binders used included polyvinyl alcohol, vinyl acetate, acrylic copolymer resin, polyethylene, polypropylene, polystyrene, water-soluble cellulose derivatives, polyvinylpyrrolidone, polyvinyl acetate, water-soluble polyester, and ethylene / vinyl acetate copolymer, which are commonly used as ceramic binders. The AlN sample 91 was SD powder granulated at approximately 80°C and had a median diameter (D50) of approximately 200 μm.

[0051] In Comparative Example 3, an aqueous sulfuric acid solution with a sulfuric acid concentration of 20% by mass was used as the decomposition solution 92. In Comparative Example 3, the decomposition solution 92 did not contain nitric acid. In Example 13, a solution obtained by adding 0.1 ml of an aqueous nitric acid solution with a nitric acid concentration of 60% by mass to 10 ml of an aqueous sulfuric acid solution with a sulfuric acid concentration of 20% by mass was used as the decomposition solution 92. In Examples 14 to 18, a solution obtained by adding 0.25 ml, 0.5 ml, 0.75 ml, 1.0 ml, and 2.0 ml of an aqueous nitric acid solution with a nitric acid concentration of 60% by mass to 10 ml of an aqueous sulfuric acid solution with a sulfuric acid concentration of 20% by mass was used as the decomposition solution 92.

[0052] The nitric acid concentrations in the decomposition solutions 92 of Examples 13 to 18 were 0.6 mass%, 1.5 mass%, 2.9 mass%, 4.2 mass%, 5.5 mass%, and 10 mass%, respectively. The sulfuric acid concentrations in the decomposition solutions 92 of Examples 13 to 18 were 19.8 mass%, 19.5 mass%, 19.0 mass%, 18.6 mass%, 18.2 mass%, and 16.7 mass%, respectively. The ratios of the nitric acid concentration to the sulfuric acid concentration (i.e., nitric acid concentration / sulfuric acid concentration) in the decomposition solutions 92 of Examples 13 to 18 were 0.03, 0.08, 0.15, 0.23, 0.30, and 0.60, respectively.

[0053] The decomposition results indicated by "excellent" and "poor" in Table 3 are the same as those in Table 1. The decomposition results of Examples 13 to 18 (i.e., nitric acid concentrations of 0.6% by mass to 10% by mass) were "excellent." On the other hand, the decomposition result of Comparative Example 3 (i.e., nitric acid concentration of 0% by mass) was "poor." When a solution prepared by adding 3.0 ml of a nitric acid aqueous solution having a nitric acid concentration of 60% by mass to 10 ml of a sulfuric acid aqueous solution having a sulfuric acid concentration of 20% by mass (i.e., an aqueous solution having a nitric acid concentration of 13.8% by mass and a sulfuric acid concentration of 15.4% by mass) was used as the decomposition solution 92, the decomposition result was "excellent," but the nitric acid was adsorbed onto the sealed container 21, and the stability of temperature control in the decomposition device 1 sometimes decreased slightly.

[0054] The sample solutions prepared in Examples 1 to 18 were measured by ICP-AES. In all Examples, the measured values ​​of the impurity (e.g., Si, Fe, Ca, etc.) content were approximately the same as those measured when the sample solutions prepared according to the JIS method were used.

[0055] As described above, the acid decomposition method for a ceramic sample containing AlN as its main component includes the steps of: placing a mixture of a sulfuric acid-containing decomposition solution 92 and a powdered ceramic sample containing AlN as its main component (i.e., the AlN sample 91) in a sealed container 21 (step S11); and irradiating the mixture with microwaves at a temperature of 200°C to 250°C to decompose the AlN sample 91 and generate a sample solution (step S12). This allows the AlN sample 91, a difficult-to-decompose ceramic sample, to be decomposed effectively. For example, the acid decomposition method can decompose the AlN sample 91 as described above regardless of whether the AlN sample 91 has a thermal history (i.e., whether the AlN sample 91 is an AlN raw material, a calcined powder, a fired powder, or an SD powder). Furthermore, the acid decomposition method can decompose the AlN sample 91 as described above regardless of whether the AlN sample 91 contains additives other than AlN.

[0056] As described above, the sulfuric acid concentration in the decomposition solution 92 is preferably 15 mass % or more and 50 mass % or less, which allows the AlN sample 91 to be decomposed more suitably, as described above.

[0057] The AlN sample 91 preferably contains less than 10% by mass of additives. As described above, this acid decomposition method can decompose even AlN samples 91 containing additives that are difficult to decompose properly using JIS methods, etc. Therefore, this acid decomposition method is particularly suitable for decomposing AlN samples 91 containing less than 10% by mass of additives.

[0058] The additive preferably includes an organic substance. As described above, the acid decomposition method can decompose even AlN sample 91 containing an organic substance as an additive, which is difficult to decompose using the JIS method or the like. Therefore, the acid decomposition method is particularly suitable for decomposing AlN sample 91 containing an additive that includes an organic substance.

[0059] As described above, when the AlN sample 91 is a spray-dried powder (i.e., SD powder), the decomposition liquid 92 preferably contains 0.6 mass % or more and 10 mass % or less of nitric acid. This allows the AlN sample 91, which is an SD powder containing organic substances as additives, to be more effectively decomposed. Note that the decomposition liquid 92 may contain nitric acid even when used to decompose an AlN sample 91 that does not contain organic substances. Furthermore, the decomposition liquid 92 may contain nitric acid even when used to decompose an AlN sample 91 other than an SD powder (e.g., an AlN raw material powder, a calcined powder, or a fired powder).

[0060] The AlN sample 91 may be a calcined powder or a sintered powder. As described above, the acid decomposition method can suitably decompose the AlN sample 91 even if the AlN sample 91 is a calcined powder or a sintered powder, which is difficult to decompose suitably using the JIS method or the like. Therefore, the acid decomposition method is particularly suitable for decomposing the AlN sample 91 that is a calcined powder or a sintered powder.

[0061] The above-described method for acid decomposition of AlN samples can be modified in many ways.

[0062] The acid decomposition method may be carried out in a decomposition apparatus having a structure different from that of the decomposition apparatus 1 described above.

[0063] As described above, the AlN sample 91 may or may not contain additives other than AlN. If the AlN sample 91 contains an additive, the additive may be organic, inorganic, or a combination of organic and inorganic. The content of the additive in the AlN sample 91 may be 10 mass % or more.

[0064] As described above, the decomposition liquid 92 may contain a liquid other than sulfuric acid (for example, nitric acid) as long as it contains sulfuric acid. The sulfuric acid concentration in the decomposition liquid 92 may be less than 15% by mass or may be higher than 50% by mass. When the decomposition liquid 92 contains nitric acid, the nitric acid concentration in the decomposition liquid 92 may be less than 0.6% by mass or may be higher than 10% by mass.

[0065] The sample solution of the AlN sample 91 produced by the above-described acid decomposition method may be used for various purposes other than analysis by ICP-AES.

[0066] The configurations of the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory. [Industrial Applicability]

[0067] The present invention can be used to decompose various ceramic samples whose main component is AlN. [Explanation of symbols]

[0068] 21 Airtight containers S11~S12 steps

Claims

1. A method for acid decomposition of a ceramic sample containing aluminum nitride as a main component, comprising: a) placing a mixture of a sulfuric acid-containing decomposition liquid and a powdered ceramic sample containing aluminum nitride as a main component in a sealed container; b) irradiating the mixture with microwaves to heat it at a treatment temperature of 200°C or more and 250°C or less to decompose the ceramic sample and generate a sample solution; A method for acid decomposition of a ceramic sample, comprising:

2. The acid decomposition method for a ceramic sample according to claim 1, The acid decomposition method for a ceramic sample, wherein the sulfuric acid concentration in the decomposition solution is 15 mass % or more and 50 mass % or less.

3. The acid decomposition method for a ceramic sample according to claim 1, The method for acid decomposition of a ceramic sample, wherein the ceramic sample contains less than 10% by mass of an additive.

4. The method for acid decomposition of a ceramic sample according to claim 3, The additive is an acid decomposition method for a ceramic sample containing an organic substance.

5. The acid decomposition method for a ceramic sample according to claim 4, the ceramic sample is a spray-dried powder; The acid decomposition method for a ceramic sample, wherein the decomposition solution contains 0.6 mass % or more and 10 mass % or less of nitric acid.

6. 5. The method for acid decomposition of a ceramic sample according to claim 1, The method for acid decomposition of a ceramic sample, wherein the ceramic sample is a calcined powder or a fired powder.

Images