JPH0868735A - Method of acid decomposition of undecomposable sample using microwave heating - Google Patents

Abstract

PURPOSE: To efficiently and quickly obtain an optimum solution as a sample for analyzing the composition of an undecomposable sample used for absorption spectrochemical analysis of atoms and induction coupling plasma light emission spectral analysis. CONSTITUTION: An undecomposable sample is housed in a Teflon container along with a solution containing at least one type of hydrofluoric acid, nitric acid, sulfuric acid, and hydrochloric acid, the Teflon container is housed in a pressure-resistance enclosure, and microwave heating is performed successively for at least 250W, 400W, and 500W or 600W for five minutes each to a mixture of the undecomposable sample and solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a method of solubilizing a sample for composition analysis used for instrumental analysis such as atomic absorption analysis and inductively coupled plasma optical emission spectroscopy. The present invention relates to an acid decomposition method for a decomposable sample.

[0002]

2. Description of the Related Art In recent years, the progress of measuring instruments has been remarkable, but especially when quantitatively analyzing the target element of a solid sample with an analytical instrument, it is a major problem to make the solid sample into an optimum solution for analysis. It was

Conventionally, as a method of decomposing a solid sample, the solid sample is melted by adding, for example, sodium carbonate, potassium hydrogen sulfate, sodium hydrogen sulfate, or an oxidizing agent such as sodium peroxide or potassium nitrate. A melting method in which the agents are mixed, heated to melt, and converted into a substance that easily decomposes into water or acid, or the solid sample and the acid or alkali solution are stored in a Teflon container, which is then placed in a closed container and heated. There is also a pressurized acid decomposition method in which decomposition is promoted in combination with an increase in internal pressure.

However, in the melting method, the crucible used is eroded by the flux, and the crucible is contaminated by the material of the crucible, a large amount of salts used as the flux and the complexity of the operation, and the decomposition treatment is performed once. An error is likely to occur in the analytical measurement value, such as the maximum possible amount being about 0.5 g. On the other hand, in the pressure acid decomposition method, it takes a long time to decompose the solid sample, and thus the composition analysis sample cannot be rapidly processed. It is difficult to prepare, and the amount that can be decomposed at one time is a maximum of about 0.5 g as in the melting method. Therefore, there is a large variation in analytical measurement values.

Therefore, there is a method of thermally decomposing a solid sample by using microwave heating of a microwave oven, which is widely used in general households, by using a liquid reagent which is relatively easier to purify than a solid reagent such as the flux. However, unlike the conventional external heating, the object to be heated itself becomes a heating element and is heated from the inside, so that it is attracting attention as a very efficient decomposition method.

In recent years, if the heating method using the microwave is adopted in a closed system, the contamination from the outside can be prevented and the decomposition is further promoted by the stirring and mixing action of the liquid reagent by the microwave. A microwave thermal decomposition method that decomposes various solid samples with time has been reported.

[0007]

However, in the above-mentioned microwave thermal decomposition method, animal standard samples, plant standard samples, metals, coal, rocks, etc. have been studied variously as the samples to be analyzed. The decomposition conditions, that is, the amount of the sample to be analyzed, the acid and its combination, the decomposition container, the output condition of the microwave, the heating time, etc., are set to the hard-to-decompose sample typified by ceramics, cermet, etc., such as alumina (Al ₂ O ₃ ), oxide ceramics typified by zirconia (ZrO ₂ ) and silicon nitride (Si ₃ N
₄ ), SIALON, aluminum nitride (AlN), silicon carbide (SiC) and other non-oxide ceramics, cermet, cemented carbide, etc. There is a problem that it is difficult to decompose, it is difficult to prepare a solution as a sample for composition analysis used for atomic absorption analysis, inductively coupled plasma emission spectroscopic analysis, etc., there is a large error in analysis accuracy, and it is not suitable for microanalysis.

Further, in order to prevent a rapid reaction between the sample to be analyzed and the acid, the decomposition container must be housed in a beaker containing water and microwave-heated, which requires an extremely complicated operation. There was another task to do.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to analyze a composition using a hardly decomposable sample represented by ceramics, cermet or the like for atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis. To provide an acid decomposition method for a hardly decomposable sample represented by ceramics, cermet, etc. by microwave heating, which can be simply and optimally prepared as a sample for use, can obtain high analytical accuracy, and is suitable for microanalysis. is there.

[0010]

The method for acid decomposition of a hardly decomposable sample by microwave heating according to the present invention comprises:
At least hydrofluoric acid, nitric acid, stored in a Teflon container together with a solution containing one of sulfuric acid and hydrochloric acid, after housing the Teflon container in a pressure-resistant closed container, to the mixture of the persistent sample and the solution, at least Output of 250W is 5
Microwave heating conditions of sequentially heating for 400 minutes, then 400 W for 5 minutes, and further adding 500 W or 600 W for 5 minutes are repeated until the hard-to-decompose sample decomposes. It is suitable for cermet and cermet.

[0011]

According to the method for acid decomposition of a hardly decomposable sample by microwave heating of the present invention, the heating energy is intermittently increased by applying for a short time while gradually increasing the microwave heating condition from a small output to a large output. Since the acid solution can be safely and efficiently heated because it is added to the decomposable sample, and because the closed pressure container is used, the decomposition action is promoted by the increase in the internal pressure, and the heat generated from the inside of the hardly decomposable sample and the acid The molecular vibration of the solution becomes active, and the solution is decomposed in a short time.

[0012]

EXAMPLES The method for acid decomposition of a hardly decomposable sample by microwave heating according to the present invention will be described in detail below.

(Example 1) 0.3 g of an alumina (Al ₂ O ₃ ) powder sample was weighed, and (2 + 1) to (1 + 1) sulfuric acid 9
ml and hydrochloric acid 1 ml are put in a Teflon container having a capacity of 100 ml, then the Teflon container is put in a polypropylene pressure-resistant closed container, and then attached to a microwave decomposition apparatus.

Next, microwave heating is first performed at a power of 250 W for 5 minutes, and then at a power of 400 W for 5 minutes, and further 5 minutes.
After microwave heating at an output of 00 W for 5 minutes in the same manner, microwave heating is performed again in the order of 250 W, 400 W, and 600 W for 5 minutes each, and then the pressure-resistant airtight container is taken out of the apparatus and water-cooled for 15 minutes or more.

Usually, with the above-mentioned sample amount, the microwave heating and the water cooling can be carried out twice for complete decomposition, and the time required for decomposition at that time was about 1 hour.

After cooling with water, the decomposed sample was made up to a volume of 50 ml with water, elemental analysis of Ca and Fe was carried out by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and the alkali melting method and the pressurized acid were respectively used in the same sample amount. Compared with the decomposition method.

In the alkali melting method and the pressurized acid decomposition method of Comparative Example, the required decomposition time was about 1.5 hours and 16 hours, respectively.

[0018]

[Table 1]

As is clear from the results shown in Table 1, in the acid decomposition method by microwave heating according to the present invention, the variation in the analytical measurement value is extremely smaller than that in the comparative example.

(Example 2) 0.5 g of a zirconia (ZrO ₂ ) sample was weighed, and 1 ml of hydrofluoric acid and 5 ml of (1 + 1) sulfuric acid or 2.51 m of (1 + 1) hydrofluoric acid.
1 and hydrochloric acid 2.51 ml, in the case of YSZ (1+
1) Treat 10 ml of sulfuric acid as in Example 1 to give 250
Microwave heating is performed in the order of W, 400 W, and 500 W for 5 minutes each, and the pressure-resistant airtight container is taken out of the apparatus and cooled with water for 15 minutes or more.

Usually, with the above sample amount, the microwave heating can be completely decomposed in one time, and the time required for the decomposition at that time is about 3
It was 0 minutes.

Thereafter, the decomposed sample was adjusted to a volume of 50 ml with water, and elemental analysis of Al and Fe was performed by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and compared with the alkali melting method and the pressurized acid decomposition method. However, in the case of YSZ in which yttrium is present, hydrofluoric acid is volatilized and then the volume is adjusted to 50 ml with water.

In the alkali melting method and the pressurized acid decomposition method of Comparative Example, the required decomposition time was about 2.5 hours and about 4 hours to 24 hours with the same sample amount.

[0024]

[Table 2]

Example 3 La (Ca, Mg) CrO ₃
0.5 g of the sample, or 0.4 g in the case of LaCaMnO ₃ , was weighed, treated with 5 ml of nitric acid in the same manner as in Example 1, and microwave-heated in the order of 250 W, 400 W and 500 W for 5 minutes each, and the pressure Remove the closed container from the device and cool with water for 15 minutes or longer.

However, in the case of the La (Ca, Mg) CrO ₃ sample, the microwave heating can be completely decomposed in one time with the above sample amount, and the time required for the decomposition at that time is about 30 minutes.
In the case of aCaMnO ₃ , microwave heating was usually required 3 times, and the time required for decomposition was about 1.5 hours.

Then, the decomposed sample was adjusted to a volume of 50 ml with water, and elemental analysis of Mg was performed by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and compared with the alkali melting method.

In the alkali melting method of Comparative Example, the time required for decomposition was about 1.5 hours with the above sample amount.

[0029]

[Table 3]

(Example 4) 0.6 g of a ferrite sample was weighed, treated with 1 ml of nitric acid and 3 ml of hydrochloric acid in the same manner as in Example 1, microwave-heated in the order of 250 W, 400 W and 500 W for 5 minutes each, and then Remove the pressure tight container 15
Cool with water for at least one minute.

With the above-mentioned sample amount, the microwave heating condition was usually repeated three times to completely decompose it, and the time required for decomposition was about 1.5 hours.

Then, the decomposed sample was made up to 50 ml with water and subjected to elemental analysis of Cr and Cu by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and compared with the alkali melting method with the same sample amount.

In the alkali melting method of Comparative Example, the time required for decomposition was about 1.5 hours.

[0034]

[Table 4]

Example 5 Barium titanate (BaTi)
O ₃ ) 0.2 g of the sample was weighed, and a solution containing 10 ml of hydrochloric acid was treated in the same manner as in Example 1 to obtain 250 W, 400 W,
After microwave heating for 5 minutes each in the order of 500 W, the pressure-resistant airtight container is taken out and water-cooled for 15 minutes or more.

With the above-mentioned sample amount, the microwave heating condition was usually repeated three times to completely decompose it, and the time required for decomposition was about 1.5 hours. In addition, yellow needle crystals (B
When aCl ₂ · H ₂ O) is generated, water is added to dissolve it.

Then, the decomposed sample was adjusted to a volume of 50 ml with water, and elemental analysis of Al and Si was performed by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and the same sample amount was compared with the alkali melting method.

In the alkali melting method of Comparative Example, the time required for decomposition was about 2.5 hours.

[0039]

[Table 5]

Example 6 Aluminum Nitride (AlN)
0.6 g of the sample was weighed, and a solution containing 10 ml of hydrochloric acid was treated in the same manner as in Example 1 to obtain 250 W, 400 W, 500
After microwave heating for 5 minutes in the order of W, the pressure-resistant airtight container is taken out and water-cooled for 15 minutes or more.

With the above sample amount, the microwave heating condition was usually repeated twice for complete decomposition, and the time required for decomposition was about 1 hour.

Thereafter, the decomposed sample was made up to a volume of 50 ml with water, and elemental analysis of Ca and Fe was carried out by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis. Compared.

In the alkali melting method and the pressurized acid decomposition method of the comparative example, the time required for decomposition is about 1.5 hours and 6 hours, respectively.
It was time.

[0044]

[Table 6]

(Example 7) As a silicon nitride (Si ₃ N ₄ ) sample, a standard sample JCRM-R of the Japan Ceramic Society.
After weighing 2.2 g of -005 and treating with 9 ml of hydrofluoric acid and 3 ml of nitric acid in the same manner as in Example 1, 250
After microwave heating for 5 minutes in the order of W, 400 W, and 600 W, the pressure-resistant airtight container is taken out and water-cooled for 15 minutes or more.

The above sample amount can be completely decomposed by repeating the microwave heating condition three times, but when the decomposition amount is small, it is almost decomposed in one time, and the maximum decomposition time is about 1.5. It was time.

After cooling with water, 1 ml of sulfuric acid was added to the decomposed sample,
After evaporating to dryness in a platinum dish, add 3 ml of 10 ml of (1 + 1) hydrochloric acid.
Heat extraction for 0 minutes, make up to a volume of 50 ml with water, and use the system for high salt concentration of inductively coupled plasma optical emission spectrometry
Elemental analyzes of 1, Ca, Fe and Mg were performed and compared with the alkali melting method and the pressurized acid decomposition method with the same sample amount.

In the alkali melting method and the pressurized acid decomposition method of Comparative Example, the required decomposition time was about 2 hours and 16 hours, respectively.

[0049]

[Table 7]

As is clear from the results shown in Table 7, in the measurement sample prepared by the acid decomposition method by microwave heating according to the present invention, the analytical value was in good agreement with the displayed value of the standard sample, and the variation was lower than the displayed value. , Shows extremely high analysis accuracy.

In addition to the above, K and Na can be analyzed by atomic absorption spectrometry.
B is a hydrofluoric acid system of an inductively coupled plasma optical emission spectrometer, which includes Ba, Co, Cr, Cu, Mn, Mo and N.
It was confirmed that i, Sr, Ti, V, W, Zn, Zr, etc. can be measured with good reproducibility and small variation in the high salt concentration system of the inductively coupled plasma emission spectroscopic analyzer.

(Example 8) 0.4 g of a cermet sample was weighed and treated with 1 ml of hydrofluoric acid and 5 ml of nitric acid in the same manner as in Example 1, then 250 W, 400 W, 500 W
After microwave heating for 5 minutes in this order, the pressure-resistant airtight container is taken out and cooled with water for 15 minutes or more.

It should be noted that, with the above-mentioned sample amount, it is possible to completely decompose by usually performing microwave heating once, and the time required for decomposition is about 3
It was 0 minutes.

After cooling with water, the volume of the decomposed sample was adjusted to 50 ml with water, and elemental analysis of Fe and Ni was carried out by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and the same sample amount was compared with the alkali melting method.

In the alkali melting method of Comparative Example, the time required for decomposition was about 1.5 hours.

[0056]

[Table 8]

Example 9 0.5 g of a silicon carbide (SiC) sample was weighed and treated with 3 ml of hydrofluoric acid, 3 ml of nitric acid and 6 ml of sulfuric acid in the same manner as in Example 1, and then 250
Microwave heating in the order of W, 400W, 500W for 5 minutes, followed by microwave heating in the order of 250W, 400W, 600W for 5 minutes, and then 40 minutes at 600W every 3 minutes rest.
After microwave heating for 3 seconds is repeated 3 times, the pressure tight container is taken out and cooled with water for 15 minutes or more.

With the above sample amount, it was possible to completely decompose by usually performing microwave heating twice, and the time required for decomposition was about 1.5 hours.

After cooling with water, the decomposed sample was treated with white smoked sulfuric acid in a platinum dish and then adjusted to a volume of 50 ml with water, or evaporated to dryness in a platinum dish and then heat-extracted with 10 ml of (1 + 1) hydrochloric acid for 30 minutes. To 50 ml with water, and then use atomic absorption spectrometry or inductively coupled plasma emission spectrometry to analyze Al, Ca,
Elemental analysis of Fe was performed and compared with the alkali melting method and pressurized acid decomposition method with the same sample amount.

In the alkali melting method and the pressurized acid decomposition method of the comparative example, the time required for decomposition is about 2.5 hours and 4 hours, respectively.
It was 8 hours.

[0061]

[Table 9]

Example 10 0.4 g of a titanium carbide (TiC) sample was weighed, and 1 ml of hydrofluoric acid and 5 ml of nitric acid were added.
Alternatively, after treating with 5 ml of nitric acid and 5 ml of sulfuric acid in the same manner as in Example 1, microwave heating is performed in the order of 250 W, 400 W, and 500 W for 5 minutes, and then the pressure tight container is taken out and cooled with water for 15 minutes or more.

It should be noted that, with the above-mentioned sample amount, the microwave heating was usually able to completely decompose it once, and the time required for the decomposition was about 30 minutes.

After cooling with water, the volume of the decomposed sample was adjusted to 50 ml with water, and elemental analysis of Al and Ca was carried out by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and the same sample amount was compared with the alkali melting method.

In the alkali fusion method of Comparative Example, the time required for decomposition was about 1.5 hours.

[0066]

[Table 10]

(Example 11) 0.5 g of a cemented carbide sample was weighed, and Example 1 was used together with 3 ml of hydrofluoric acid and 3 ml of nitric acid.
After the same treatment as above, microwave heating is performed in the order of 250W, 400W, 500W for 5 minutes, and then 250W, 400W.
After microwave heating in the order of W and 600 W for 5 minutes, the pressure-resistant airtight container is taken out and cooled with water for 15 minutes or more.

With the above sample amount, microwave heating is usually performed four times for complete decomposition, and the time required for decomposition is about 2
It was time.

After cooling with water, the volume of the decomposed sample was adjusted to 50 ml with water, and elemental analysis of Al and Fe was performed by atomic absorption analysis or inductively coupled plasma emission spectroscopic analysis, and the results were compared with the alkali melting method with the same sample amount.

In the alkali melting method of Comparative Example, the time required for decomposition was about 1.5 hours.

[0071]

[Table 11]

From the above results, it is clear that in the acid decomposition method by microwave heating of the present invention, even if the decomposition treatment amount is the same as that of the conventional decomposition method, the variation in the analytical measurement value is extremely small. Became.

[0073]

EFFECT OF THE INVENTION The method for acid decomposition of a hardly decomposable sample by microwave heating according to the present invention is to store a hardly decomposable sample in a Teflon container together with a solution containing at least one of hydrofluoric acid, nitric acid, sulfuric acid and hydrochloric acid. Then, after the Teflon container is housed in a pressure-resistant closed container, at least 250 W, 400 W, 500 W or 600 W is sequentially microwave-heated to the mixture of the hardly decomposable sample and the solution for 5 minutes. Since it can decompose difficult-to-decompose samples, the amount of volatilization loss of the sample decomposition solution is small, high analysis accuracy is obtained, and it is suitable for trace analysis, and atomic absorption analysis and inductively coupled plasma emission spectroscopy are possible with simple equipment and operation. It is possible to efficiently obtain the optimum solution as a composition analysis sample used for analysis and the like in an extremely short time.

Claims (11)

[Claims] 1. A hardly decomposable sample and a solution containing at least one of hydrofluoric acid, nitric acid, sulfuric acid, and hydrochloric acid are housed in a Teflon container, and then the Teflon container is housed in a sealed container, and then the hardly decomposed. At least 250W, 400W, then 500W or 60
A method for acid decomposition of a hardly decomposable sample by microwave heating, which comprises decomposing the hardly decomposable sample by microwave heating for 5 minutes in the order of 0 W output. 2. The acid decomposition method for a hardly-decomposable sample by microwave heating according to claim 1, wherein the hardly-decomposable sample is any one of ceramics, cermet and cemented carbide. 3. The persistent sample is a sample containing Al ₂ O ₃ as a main component, and a solution containing sulfuric acid and hydrochloric acid is used, and microwave power is applied for at least 5 minutes in the order of 250 W, 400 W and 500 W, respectively. After heating, 250W, 400W,
The method for acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein microwave heating is performed for 5 minutes in the order of 600 W output. 4. The hardly-decomposable sample contains ZrO ₂ as a main component, and a solution containing sulfuric acid or sulfuric acid and hydrofluoric acid or hydrofluoric acid and hydrochloric acid is used.
The method of acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein microwave heating is performed for 5 minutes each in the order of W, 400 W, and 500 W. 5. The refractory sample is La (Ca, Mg) C.
rO ₃ or LaCaMnO ₃ as a main component, and using a solution containing nitric acid, at least 250
The method of acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein microwave heating is performed for 5 minutes each in the order of W, 400 W, and 500 W. 6. A solution containing nitric acid and hydrochloric acid, wherein the refractory sample is ferrite, and at least 250 W,
The method for acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein microwave heating is performed for 5 minutes in the order of 400 W and 500 W respectively. 7. The hardly-decomposable sample contains BaTiO ₃ or AlN as a main component, and a solution containing hydrochloric acid is used to perform microwave heating for 5 minutes at least in the order of 250 W, 400 W and 500 W in order. 3. The method for acid decomposition of a hardly decomposable sample by microwave heating according to claim 2. 8. The hardly decomposable sample is a sample containing Si ₃ N ₄ as a main component or cermet, and a solution containing hydrofluoric acid and nitric acid is used.
The microwave heating is performed for 5 minutes each in the order of 0 W and then 500 W or 600 W output.
A method for acid decomposition of a hardly decomposable sample by the microwave heating described. 9. The hardly decomposable sample contains SiC as a main component, and a solution containing hydrofluoric acid, nitric acid, and sulfuric acid is used, and at least 250 W, 400 W, and 500 W are output in this order for 5 minutes each. Microwave heated, then 250
After microwave heating for 5 minutes each in the order of W, 400W, and 600W, 600W output is applied every 3 minutes.
The method for acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein microwave heating is performed three times for 0 seconds. 10. The hardly decomposable sample contains TiC as a main component, and a solution containing hydrofluoric acid and nitric acid or nitric acid and sulfuric acid is used, and 250 W, 400 W and 500 W are used.
3. The method for acid decomposition of a hardly decomposable sample by microwave heating according to claim 2, wherein the microwave heating is performed for 5 minutes each in the order of the output. 11. The hard-to-decompose sample is a superhard material, and a solution containing hydrofluoric acid and nitric acid is used.
3. Microwave heating for 5 minutes each in the order of W, 400 W and 500 W, and then microwave heating for 5 minutes each in the order of 250 W, 400 W and 600 W. Acid decomposition method for persistent samples.