JP7585670B2 - X-ray diffraction measurement method - Google Patents

Description

The present invention relates to an X-ray diffraction measurement method and a sample for X-ray diffraction measurement.

In materials development, detailed analysis of the physical properties of materials is important for understanding the mechanism by which characteristics are expressed. In recent years, in order to express the desired material characteristics, it has become common to change the crystal structure by doping with various elements or by heat treatment. X-ray diffraction measurement is often used to easily analyze such crystal structures (see, for example, Patent Document 1).

X-ray diffraction measurement involves irradiating a sample with X-rays and detecting the diffracted X-rays, which allows a wide range of information about the sample to be obtained, such as the structure of the constituent materials, lattice constant, crystallite size, crystallinity, distortion, and more.

In X-ray diffraction measurements, the height of the sample's measurement surface is important in terms of maintaining measurement accuracy. Therefore, if the sample to be measured is, for example, in powder form, it is necessary to prepare a sample stage with a recess, fill this recess with the powder sample, and level it to ensure that the height of the measurement surface is constant.

JP 2018-66652 A

However, some samples may deliquesce and change their crystalline state due to a reaction with moisture in the air. In the case of such deliquescent samples, the crystalline state of the sample may change due to the sample deliquescing and changing quality before the measurement is completed, or the height of the measurement surface may fluctuate even if the height is adjusted to be constant, making it impossible to maintain high measurement accuracy.

To measure such anaerobic samples using X-ray diffraction, it is best to use a special sample holder that can block the atmosphere. In this case, it is necessary to seal an inert gas (such as Ar) inside the sample holder before placing the sample in it and measuring it.

However, when an inert gas is sealed in this way, when X-rays are irradiated onto the sample, the X-rays are absorbed by the inert gas. As a result, the intensity of the detected diffracted X-rays decreases, making it difficult to maintain high measurement accuracy. Furthermore, when the sample is placed in a special sample holder, it is difficult to control the height of the sample surface, which can easily lead to a decrease in measurement accuracy.

The present invention was made in consideration of the above problems, and aims to provide a technique for accurately analyzing samples that are deliquescent using X-ray diffraction measurement.

In order to solve the above problem, the present inventors have investigated a method for reducing the effect of moisture on a deliquescent sample. As a result, they have found that it is effective to mix a moisture-absorbing material with a sample and subject the mixture to X-ray diffraction measurement. The moisture-absorbing material absorbs moisture around the sample from the time the sample is loaded onto the sample stage until the X-ray diffraction measurement is completed, and thus it is possible to prevent the sample from deliquescing due to moisture. In addition, since the deliquescent state of the sample can be suppressed, the crystalline state can be maintained without being altered, and the height of the measurement surface of the sample can be kept constant. Moreover, since the atmosphere around the sample is not an inert gas atmosphere, it is possible to suppress the absorption of X-rays by the inert gas. As a result, even a deliquescent sample can be analyzed with high accuracy by X-ray diffraction measurement.

That is, the first aspect of the present invention is
A step of mixing a powdered or lumpy deliquescent sample with a water-absorbing material capable of absorbing moisture to form a mixed sample;
and performing X-ray diffraction measurement on the mixed sample.
This is an X-ray diffraction measurement method.

A second aspect of the present invention is a method for producing a composition comprising the steps of:
The mixed sample is subjected to X-ray diffraction measurement in air.

A third aspect of the present invention is the first or second aspect,
The water absorbent material is mixed in the deliquescent sample in an amount of 10% by volume to 50% by volume.

A fourth aspect of the present invention is the method according to any one of the first to third aspects,
The deliquescent sample contains a metal.

A fifth aspect of the present invention is a method for producing a composition according to any one of the first to fourth aspects,
The water absorbent material is at least one of silica gel, silica alumina gel, synthetic zeolite, natural zeolite, calcium chloride, quicklime, bentonite clay, magnesium oxide, and magnesium chloride.

A sixth aspect of the present invention is the method according to any one of the first to fifth aspects,
When X-ray diffraction measurement is performed on the water absorbent material, the water absorbent material has an X-ray diffraction pattern that does not overlap with the X-ray diffraction pattern caused by the components contained in the deliquescent sample.

A seventh aspect of the present invention is the method according to any one of the first to fifth aspects,
a second measurement step of performing X-ray diffraction measurement only on the water absorbent material, when the step of performing X-ray diffraction measurement on the mixed sample is defined as a first measurement step;
The method further includes a correction step of subtracting the diffraction intensity of the X-ray diffraction pattern obtained in the second measurement step from the diffraction intensity of the X-ray diffraction pattern obtained in the first measurement step.

An eighth aspect of the present invention is a method for producing a composition comprising the steps of:
The sample for X-ray diffraction measurement includes a powdered or lump deliquescent sample to be analyzed, and a water-absorbent material capable of absorbing moisture.

According to the present invention, even samples that are deliquescent can be analyzed with high accuracy by X-ray diffraction measurement.

FIG. 1 is a schematic diagram showing a cross section of a sample stage. FIG. 2 is a diagram for explaining the filling of the mixed sample onto the sample stage.

<One embodiment of the present invention>
Hereinafter, a method for preparing an analytical sample according to one embodiment of the present invention will be described.

(Preparation process)
First, a powder or lump deliquescent sample is prepared as an analysis target. An example of the deliquescent sample is a metal-containing compound having a crystal structure and deliquescent properties. The size of the deliquescent sample is not particularly limited, but is, for example, 1 μm to 50 μm.

Also, prepare a water-absorbing material to be mixed with the deliquescent sample. The water-absorbing material is not particularly limited as long as it can absorb moisture and does not react with the deliquescent sample. However, if the X-ray diffraction patterns due to the components contained in the water-absorbing material and the deliquescent sample overlap, it becomes difficult to analyze the X-ray diffraction pattern. Therefore, from the viewpoint of performing X-ray diffraction measurement easily and accurately, it is preferable for the water-absorbing material to have an X-ray diffraction pattern that does not overlap with the X-ray diffraction pattern due to the components contained in the deliquescent sample when X-ray diffraction measurement is performed. Here, the X-ray diffraction pattern does not overlap means that a predetermined peak (diffraction line) constituting the X-ray diffraction pattern of the component contained in the deliquescent sample and a predetermined peak (diffraction line) constituting the X-ray diffraction pattern of the component contained in the water-absorbing material do not match and are different. In other words, it is preferable for the water-absorbing material to have a diffraction line that does not overlap with the diffraction line due to the component contained in the deliquescent sample. Note that, as described later, even if the X-ray diffraction patterns (or diffraction lines) overlap, the measurement accuracy can be improved by correcting the X-ray diffraction pattern.

The shape of the absorbent material is not particularly limited, but it is preferably granular or lumpy. Absorbent materials having these shapes are easy to mix uniformly with the deliquescent sample, and when the mixed sample is mixed with the deliquescent sample and filled into the recesses of the sample stage and rubbed off, a flatter measurement surface can be formed.

The size of the absorbent material is not particularly limited, but from the viewpoints of ease of mixing with the deliquescent sample and ease of leveling the surface when grinding the mixed sample, it is preferable that the size be smaller than that of the deliquescent sample. Also, from the viewpoint of absorbency, it is preferable that the particle size is small. Specifically, it is more preferable that the maximum particle size is 1 μm to 50 μm.

Specific examples of the water-absorbing material that may be used include at least one of silica gel, silica alumina gel (allophane), synthetic zeolite (molecular sieve), natural zeolite, calcium chloride, quicklime (calcium oxide), bentonite clay (montmorillonite), magnesium oxide, and magnesium chloride.

(Mixing process)
Next, the deliquescent sample and the water-absorbing material are mixed to form a mixed sample. The mixing method is not particularly limited, and a conventionally known method can be adopted. For example, these may be mixed manually using a mortar or the like, or may be mechanically mixed uniformly using a ball mill or the like.

The amount of absorbent material added is not particularly limited, but from the viewpoint of more reliably suppressing deterioration of the deliquescent sample, it is preferable to add 10% by volume or more of the deliquescent sample. On the other hand, if the amount added is excessively large, the deliquescent sample will be diluted, and the intensity of the spectrum caused by the deliquescent sample will decrease, which may result in a decrease in measurement accuracy. In this regard, from the viewpoint of maintaining high measurement accuracy, it is preferable to add 50% by volume or less of the absorbent material.

(Filling process)
Next, a sample stage is prepared for X-ray diffraction measurement of a sample. Fig. 1 is a cross-sectional view of the sample stage 1. The sample stage 1 has, for example, a rectangular or circular shape in a plan view, and as shown in Fig. 1, a recess 2 recessed to a predetermined depth is provided on the upper surface 1a. This recess 2 becomes a space into which the sample is filled.

Next, the mixed sample is filled into the sample stage. At this time, as shown in FIG. 2, for example, a large amount of the mixed sample 3 is poured in so that it rises slightly. Then, the surface of the mixed sample 3 is flattened based on the top surface 1a of the sample stage 1. Specifically, a glass plate or the like is moved horizontally along the top surface 1a of the sample stage 1, so that the edge of the glass plate cuts through the mixed sample 3, flattening the surface of the mixed sample 3. This results in a sample 4 for X-ray diffraction measurement. In the sample 4 for X-ray diffraction measurement, the mixed sample 3 is filled into the recess 2 so that the surface 3a of the mixed sample 3 is flush with the top surface 1a of the sample stage 1. Note that, during X-ray diffraction measurement, the top surface 1a of the sample stage 1 serves as the reference plane for height, and the surface 3a of the mixed sample 3 serves as the measurement surface.

(Measurement process)
Next, the X-ray diffraction measurement sample 4 is subjected to measurement. Specifically, the X-ray diffraction measurement sample 4 is set in an X-ray diffraction measurement device. Next, X-rays are irradiated onto the mixed sample 3 in the X-ray diffraction measurement sample 4. Then, X-ray diffraction measurement is performed by relatively changing the positions of the X-ray source, detector, etc. while maintaining the relationship between the incident angle θ and the diffraction angle 2θ. In this way, an X-ray diffraction pattern is obtained.

The obtained X-ray diffraction pattern contains information on the deliquescent sample and the water-absorbing material. To obtain information on only the deliquescent sample from this information, for example, the following procedure may be performed. For example, in the case of a combination in which the X-ray diffraction patterns of the deliquescent sample and the water-absorbing material do not overlap, the previously obtained X-ray diffraction pattern of the water-absorbing material may be referenced, and among the peaks constituting the X-ray diffraction pattern, those other than those attributable to the water-absorbing material may be identified as peaks attributable to the deliquescent sample. Then, based on the X-ray diffraction pattern attributable to the deliquescent sample, information on the structure, lattice constant, crystal grain size, crystallinity, etc. of the deliquescent sample may be obtained.

Using the above, X-ray diffraction measurements are performed on the deliquescent sample.

In this embodiment, as shown in FIG. 2, a deliquescent sample is mixed with a water-absorbing material to form a mixed sample 3, which is then filled into the sample stage 1 to prepare a sample 4 for X-ray diffraction measurement. With such a sample 4 for X-ray diffraction measurement, the water-absorbing material can absorb moisture from the time the mixed sample 3 is filled until the measurement is completed, so that the deliquescent sample can be suppressed from deliquescing. This allows the crystal state of the deliquescent sample to be maintained without alteration during the measurement. In addition, the height fluctuation of the surface 3a (measurement surface) of the mixed sample 3 due to deliquescent can be suppressed. Furthermore, by performing X-ray diffraction measurement in the atmosphere, the intensity of the diffracted X-rays can be detected without decreasing, compared to when the measurement is performed in an inert gas. Thus, with the sample 4 for X-ray diffraction measurement of this embodiment, even if the sample is a deliquescent sample, the alteration of the sample can be suppressed and the height of the measurement surface can be maintained, allowing accurate X-ray diffraction measurement in the atmosphere.

In addition, by setting the amount of absorbent material to be added in the range of 10% to 50% by volume of the deliquescent sample, it is possible to further suppress deterioration of the deliquescent sample while maintaining a high spectral intensity by adjusting the dilution ratio appropriately, thereby maintaining a high measurement accuracy.

The absorbent material is preferably granular or lumpy, with a maximum particle size of 1 μm to 50 μm. By using an absorbent material with such a shape and size, it can be mixed uniformly with a powdered or lumpy deliquescent sample, and the mixed sample can be filled more evenly into the recesses of the sample stage. Moreover, the specific surface area of the absorbent material can be reduced to obtain high absorbency, so that deterioration of the deliquescent sample and fluctuations in the height of the measurement surface can be more reliably suppressed.

<Other embodiments>
Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

In the above embodiment, a case where the X-ray diffraction patterns of the deliquescent sample and the water-absorbing material do not overlap has been described, but the present invention is not limited to this, and it is possible to perform accurate analysis even with combinations in which the X-ray diffraction patterns overlap. This will be explained in detail below.

In the case of a combination in which the X-ray diffraction patterns of a deliquescent sample and a water-absorbing material overlap, it is not possible to identify each X-ray diffraction pattern individually from the X-ray diffraction pattern obtained from the mixed sample. Therefore, it is preferable to provide a correction process in which the X-ray diffraction pattern obtained from the mixed sample is corrected by subtracting the X-ray diffraction pattern obtained from the water-absorbing material alone.

Specifically, first, a second measurement step is performed on only the absorbent material, separate from the first measurement step in which X-ray diffraction measurement is performed on the mixed sample. The X-ray diffraction pattern obtained in the first measurement step contains information on the deliquescent sample and the absorbent material. In contrast, the X-ray diffraction pattern obtained in the second measurement step contains information on only the absorbent material. Next, the diffraction intensity of the X-ray diffraction pattern obtained in the second measurement step is subtracted from the diffraction intensity of the X-ray diffraction pattern obtained in the first measurement step. This removes the information on the absorbent material, making it possible to obtain an X-ray diffraction pattern containing information on only the deliquescent sample. Then, based on the X-ray diffraction pattern obtained by this correction, information on the structure, lattice constant, crystal grain size, crystallinity, and the like of the deliquescent sample can be obtained.

1 Sample stage 1a Upper surface of sample stage 2 Recess 3 Mixed sample 3a Measurement surface 4 X-ray diffraction measurement sample

Claims (4)

A mixing step of mixing a powdered or lumpy deliquescent sample with a water-absorbing material capable of absorbing moisture to form a mixed sample;
a first measurement step of filling the mixed sample into the recess so that a surface of the mixed sample is flush with an upper surface of a sample stage having the recess, and performing an X-ray diffraction measurement on the mixed sample;
A second measurement step of performing X-ray diffraction measurement only on the water absorbent material;
a correction step of subtracting the diffraction intensity of the X-ray diffraction pattern obtained in the second measurement step from the diffraction intensity of the X-ray diffraction pattern obtained in the first measurement step ,
In the mixing step, the water absorbent is mixed with the deliquescent sample in an amount of 10% by volume or more and 50% by volume or less,
In the first measurement step, X-ray diffraction measurement is performed while suppressing a height variation of a measurement surface, which is a surface of the mixed sample.
X-ray diffraction measurement method. The mixed sample is subjected to X-ray diffraction measurement in air.
The X-ray diffraction measurement method according to claim 1 . The deliquescent sample contains a metal.
The X-ray diffraction measurement method according to claim 1 or 2 . The water absorbent is at least one of silica gel, silica alumina gel, synthetic zeolite, natural zeolite, calcium chloride, quicklime, bentonite clay, magnesium oxide, and magnesium chloride;
The X-ray diffraction measurement method according to any one of claims 1 to 3 .

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