JP6790880B2 - Method for analyzing foreign substances in metal oxide powder - Google Patents

Description

The present invention is a method for analyzing a foreign substance contained in a powder of a metal oxide, and particularly relates to a case where the foreign substance is a metal.

In the production of metal compounds such as metal oxides, metal sulfides, and metal carbonates, metals or metal compounds may be mixed as foreign substances in these compounds. The mixed metal or metal compound may be derived from a manufacturing apparatus, a raw material, or a reagent, but it is important for quality control to identify the mixed foreign matter and understand the cause of its occurrence.

Patent Document 1 discloses a method of separating and analyzing nickel species of nickel salt, metallic nickel, and nickel oxide mixed in carbonate, and according to the analysis method, impurities that become foreign substances in the metallic form are removed. By using a bromine-methanol solution that selectively dissolves, metal impurities that become foreign substances in the sample are quantified.

Japanese Unexamined Patent Publication No. 2001-221726

In the method disclosed in Patent Document 1, the separation operation is performed using bromine methanol, but when quantifying a metal in a metal compound such as a metal oxide, a metal sulfide, or a metal carbonate, it is appropriate. It is necessary to select a reagent, and the selection work requires time and labor.

The present invention has been made under the above circumstances, and the problem to be solved is a method for analyzing a foreign substance in a metal oxide powder, which saves time and labor, particularly when the foreign substance is a metal. Is to provide.

Here, in order to solve the above-mentioned problems, the present inventors have conducted research and have come up with the idea of applying a fully automatic mineral analyzer (Mineral Liberation Analyzer, which may be referred to as "MLA" in the present invention). ..
The MLA is an analyzer for identifying inorganic compound particles such as mineral particles, and is a scanning electron microscope equipped with an energy dispersive X-ray analyzer (sometimes referred to as "EDX" in the present invention). In the present invention, it may be described as "SEM"). Then, it is an analyzer equipped with a control PC that automatically controls the SEM / EDX, performs image processing and spectrum matching, and performs an operation for identifying inorganic compound particles such as mineral particles.

The measurement principle of MLA will be briefly described.
In MLA, a sample in which particles to be measured and a resin are mixed and solidified is polished, and the obtained polished surface is measured. In the measurement of MLA, first, an electron beam is irradiated to the polished surface to obtain a reflected electron image (sometimes referred to as "BSE image" in the present invention), and an inorganic compound such as mineral particles appearing on the polished surface is obtained. Acquire data on particle position, size, and polished surface shape. Next, the energy dispersive X-ray spectrum of the particles (may be referred to as "EDS" in the present invention) is acquired. Then, for each particle appearing on the polished surface, these data acquisitions are sequentially performed by automatic measurement.

In the method for identifying inorganic compound particles using MLA, information on the elements constituting the inorganic compound particles is acquired and identified. Therefore, it is possible to easily analyze and identify the particles by using the MLA and performing spectral matching using a database in which elemental information of various inorganic compound particles is covered in advance. Further, in the MLA, since the element information of the particle to be measured is acquired and analyzed, the element to be measured is narrowed down in advance, and the measurement is performed using the filtering function of extracting the mineral particle to be measured by the characteristic X-ray intensity. It is also preferable. As a result, particles containing a predetermined element present in a trace amount in the object to be measured can be efficiently extracted and analyzed.
In MLA, it is possible to automatically perform analysis work on an extremely large number of particles such as 1 million or 1 billion particles, so once the work is started, almost no man-hours are required. Therefore, it became possible to complete the analysis of the foreign metal particles in the metal oxide particle sample.

Next, the present invention for analyzing foreign substances contained in the powder of the metal oxide using the above-mentioned MLA will be described.

That is, the first invention for solving the above-mentioned problems is
A method for analyzing foreign substances contained in metal oxide powder.
Using a fully automated mineral analyzer (MLA),
A step of acquiring a reflected electron (BSE) image of the metal oxide powder sample, and
A step of image-analyzing the reflected electron (BSE) image to discriminate between the metal oxide particles and the foreign matter particles, and acquiring the position information of the discriminated foreign matter particles.
A step of acquiring an energy dispersive X-ray spectrum (EDS) at a position corresponding to the position information of the foreign particle particles, and
It is a method for analyzing a foreign substance contained in a powder of a metal oxide, which comprises a step of analyzing the foreign substance from the acquired energy dispersive X-ray spectrum (EDS).
The second invention is
The reflected electron (BSE) image is toned to obtain an image analysis result, and the gray level threshold of the metal oxide particles and the foreign matter particles is applied to the obtained image analysis result to obtain the metal. This is a method for analyzing a foreign substance contained in a powder of a metal oxide, which comprises discriminating between the oxide particles and the foreign substance particles.
The third invention is
The foreign matter is a method for analyzing a foreign matter contained in a powder of a metal oxide, which is characterized by being a metal.

According to the present invention, foreign substances contained in the powder of a metal oxide can be analyzed without a great deal of man-hours.

It is a BSE image of a powder of a metal oxide mixed with metal particles. It is a schematic diagram of the BSE image which concerns on FIG.

Hereinafter, regarding the steps of analyzing foreign substances contained in the powder of the metal oxide using MLA, (1) a step of acquiring a BSE image of a powder sample, and (2) an image analysis of the BSE image are performed. The process of discriminating between the metal oxide and the foreign matter and acquiring the position information of the discriminated foreign matter, (3) the step of acquiring the EDS at the position corresponding to the position information of the foreign matter, and (4) the foreign matter particles from the acquired EDS. The process of analysis will be described in detail in this order.

(1) Step of acquiring BSE image of powder sample Metal oxide powder that may contain foreign particles is mixed with an appropriate resin, and the metal oxide powder is embedded and consolidated. And obtain an embedded solidified body. Next, the embedded solidified body is subjected to rough polishing, intermediate polishing, and mirror polishing to obtain a consolidated metal oxide powder sample. The consolidated metal oxide powder sample that has undergone mirror polishing is placed in the MLA, and a BSE image is acquired using SEM for the particles exposed on the polished surface.

(2) Step of image analysis of BSE image to discriminate between metal oxide and foreign matter and acquire position information of the discriminated foreign matter The BSE image acquired in (1) above is image-analyzed to obtain metal. The oxide and the foreign matter are discriminated from each other. In this discrimination, it is utilized that there is a clear difference in brightness in the BSE image between the metal oxide particles and the metal particles which are foreign substances. That is, in the BSE image, the metal oxide particles appear dark, and the foreign metal particles appear bright.
Specifically, gradation processing is performed in the image analysis of the BSE image. For example, in the image analysis result of the gradation-processed BSE image of 256 gradations, when the gradation level of the metal oxide particles and the metal particles which are foreign substances is compared, the metal oxide particles have 0 gradation than the metal particles. The values are close, and the metal particles have a value closer to 256 gradations than the metal particle oxide particles. Here, the threshold value of the gray level for separating the metal oxide particles and the metal particles is appropriately set.

A gray level threshold value can be applied to the image analysis result of the tone-processed BSE image described above to discriminate between metal oxide particles and foreign matter particles.
Here, as an example of image analysis of the BSE image, FIG. 1 shows an image according to Example 1 described later, in which a threshold value is set so that a metal oxide and a foreign metal can be distinguished. In the image analysis result of the BSE image shown in FIG. 1, the region shown in gray is a metal oxide, and the region shown in white is a metal, that is, a foreign substance. Therefore, it can be seen that the metal oxide fine particles and the foreign matter fine particles that are metals can be distinguished.

(3) Step of acquiring EDS at a position corresponding to the position information of the foreign metal particles Since the position information of the foreign metal particles corresponding to the pixels can be obtained in the above-mentioned image analysis, the foreign matter determined by setting the threshold value. Positional information can be obtained for metal particles. In addition, information on the size, shape, and number of particles can be obtained as the image analysis result.

(4) Step of Analyzing Foreign Particles from Acquired EDS EDS is acquired from the pixels corresponding to the above-mentioned position information related to the foreign metal.
The foreign matter particles are analyzed from the acquired EDS. Specifically, the acquired EDS spectrum is collated with the EDS in the data list created in advance and mounted on the MLA. Then, the element corresponding to the acquired peak of EDS is specified. The peak of the EDS appears substantially corresponding to the type of heavy metal contained in the foreign metal. Therefore, the existing heavy metal element is identified corresponding to each pixel, and the type of heavy metal can be identified from the peak intensity.

In addition, the number of particles for each type of foreign metal (for each type of metal contained) can be obtained from the information on the number of particles as a result of the above-mentioned image analysis and the identification result of the type of the heavy metal.

Hereinafter, the present invention will be described in more detail with reference to Examples.
(Example 1)
A powder sample of metal oxide particles mixed with metal particles as foreign substances was prepared.
The powder sample and bakelite resin were mixed at a volume ratio of 1: 3.5 to obtain a mixed powder. The obtained mixed powder was compression-molded using a vise to obtain a cylindrical molded body having a diameter of 20 mm and a height of 3 mm. The obtained molded product was sealed in a hot embedding machine together with 2 g of phenol resin, and was hot-consolidated under the conditions of 180 ° C., 75 bar, and 5 minutes, and a columnar solidified piece having a diameter of 25 mm and a height of 6 mm. Got
The obtained solidified piece was subjected to cross-section polishing using a buffing machine to obtain a polished piece in which the cross section of the particles was exposed on the polished surface. Seven such polishing pieces were prepared from a powder sample of the same metal oxide particles.

Carbon vapor deposition was applied to the obtained polished piece, and this was placed in the MLA. Then, about 800 fields of view were set for each of the seven polishing pieces by the SEM installed in the MLA, and the BSE image was measured for each field of view. An example of the BSE image is shown in FIG.

Next, image analysis of the BSE image was performed.
Specifically, the BSE image was displayed in 256 gradations. Then, a threshold value was set between 100 and 200 gradations, particles having a gradation equal to or higher than the threshold value were treated as foreign metal particles, and particles having a gradation lower than the threshold value were treated as metal oxide particles. The threshold value is a value appropriately set in order to measure the BSE image of the metal oxide particles and the foreign metal particles in advance and discriminate between the two particles. For reference, FIG. 2 shows a schematic diagram in which foreign metal particles are hatched with dots and metal oxide particles are hatched with diagonal lines in FIG. 1 described above.

Then, from the above-mentioned image analysis results, the number of particles for each type and the position information of the foreign metal particles were obtained. The type of particle is whether it is a metal oxide or a metal. Furthermore, metals were classified according to their constituent elements. Next, the EDS was acquired in the pixels corresponding to the position information of the particles determined to be foreign metal particles.
In this way, approximately 10 million particles were analyzed by MLA in the total of the seven abrasive pieces.
Table 1 shows the total number of detected foreign metal particles for each type of analyzed foreign metal particles (for each type of metal contained).
On the other hand, Table 2 shows the results of quantitative analysis of the metal oxide material according to Example 1 by the bromine-methanol solution method according to the conventional technique.

From Table 1, according to the analysis method using MLA according to Example 1, the number of detected foreign metal particles for each type (for each type of metal contained) was found. Furthermore, we were able to obtain information on the shape and chemical morphology of foreign metal particles that cannot be obtained by the bromine-methanol solution method.

Claims (3)

A method for analyzing foreign substances contained in metal oxide powder.
Using a fully automated mineral analyzer (MLA),
A step of acquiring a reflected electron (BSE) image of the metal oxide powder sample, and
A step of image-analyzing the reflected electron (BSE) image to discriminate between the metal oxide particles and the foreign matter particles, and acquiring the position information of the discriminated foreign matter particles.
A step of acquiring an energy dispersive X-ray spectrum (EDS) at a position corresponding to the position information of the foreign particle particles, and
A method for analyzing a foreign substance contained in a powder of a metal oxide, which comprises a step of analyzing the foreign substance from the acquired energy dispersive X-ray spectrum (EDS). The reflected electron (BSE) image is toned to obtain an image analysis result, and the gray level threshold of the metal oxide particles and the foreign matter particles is applied to the obtained image analysis result to obtain the metal. The method for analyzing a foreign substance contained in a powder of a metal oxide according to claim 1, wherein the particles of the oxide and the particles of the foreign substance are discriminated from each other. The method for analyzing a foreign substance contained in a powder of a metal oxide according to claim 1 or 2, wherein the foreign substance is a metal.