JP7205399B2 - Powder shape analysis method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for analyzing powder shape, a method for evaluating fluidity of powder, and a method for evaluating fluidity of resin in which powder is dispersed.

In the manufacture of fine powders, the fluidity of the powder product may be one item of quality control. There are many factors related to fluidity, and each factor has a complex influence to characterize the fluidity of powder. One of the factors is the powder shape.

When a powder product is produced by pulverization, the shape may change depending on the pulverization method and conditions, resulting in a large change in fluidity. At that time, it becomes necessary to evaluate the powder shape. Sensory evaluation is generally performed by observation using an optical microscope or a scanning electron microscope (hereinafter also referred to as SEM). On the other hand, as a method of quantifying the shape, there is a method of obtaining, for example, circularity and aspect ratio by binarizing the observed image and performing image analysis (see, for example, Patent Document 1). In addition, there is also a method of measuring using an image analysis type particle size distribution meter and obtaining various shape indexes for evaluation (see, for example, Patent Document 2).

Japanese Patent No. 4822826 JP-A-11-326177

However, since optical microscopes and image analysis type particle size distribution analyzers have insufficient resolution, it is difficult to accurately analyze the shape of the powder when the size of the target powder is several microns.

In addition, although SEM has high resolution and can analyze the shape of fine powder, the analysis is sensory, and minute differences in shape that affect powder fluidity are quantified and evaluated. is difficult.

On the other hand, it is conceivable to digitize and evaluate the shape of fine powder by image analysis of a backscattered electron image obtained by SEM. In image analysis, the shape of the powder can be analyzed after the backscattered electron image is divided into the powder portion and the background portion (resin portion) by binarization processing and the powder particle image is extracted.

However, when the powder is fine, the powder particle image obtained by image processing is displayed in a state where the powder is agglomerated, making it difficult to distinguish the particles individually. Therefore, it is difficult to accurately analyze the shape of the entire powder from the shape of the particles.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique for accurately analyzing the shape of powder even when the powder aggregates.

The present inventor obtained a powder particle image by acquiring a backscattered electron image of a resin-embedded sample prepared by embedding powder in a resin and subjecting the image to binarization. However, in the powder particle image, the powder is displayed as agglomerated, and it was confirmed that each particle could not be identified individually and its shape could not be analyzed accurately.

Therefore, the present inventor appropriately changed the gray level gradation for distinguishing between pixels corresponding to powder and pixels corresponding to resin, which is a processing condition when binarizing a backscattered electron image. Study was carried out. As a result, the inventors have found that the gray level gradation can be set to a range in which the powder particles are displayed in a monodispersed state in the powder particle image. That is, by binarizing with a predetermined gradation, it is possible to convert a backscattered electron image displayed in a state in which powder is aggregated into a powder particle image in which the powder is monodisperse. According to this powder particle image, the shape of the powder as a whole can be accurately analyzed from the shape of each particle.

However, it was confirmed that if the image analysis of the entire powder displayed in the powder particle image is performed as it is, the analysis results of the powder shape will vary. As a result of examining this point, the present inventor found that the variation in the analysis results is caused by the inclusion of particles (fine powder) that are displayed minutely in the powder particle image in the analysis target.

In general, when analyzing the shape of a powder, a plurality of particles are randomly extracted from the powder displayed in the powder particle image, image analysis is performed, and the obtained shape data are number-averaged to determine the overall powder shape. You will get the shape data as The powder particle image includes not only relatively large particles but also fine particles whose shape cannot be accurately analyzed. Therefore, if the powder particle image is subjected to image analysis as it is, fine particles are included in the analysis target, and the analysis result of the shape of the powder is far from the original shape. Moreover, the number of fine particles contained in the analysis target may vary for each measurement, and the variation causes variations in the analysis results.

Therefore, the present inventors investigated the size of particles to be analyzed. As a result, it was found that when the particle size (particle diameter) is less than 0.5 μm, the accuracy of analyzing the particle shape is significantly lowered. For this reason, from the viewpoint of maintaining high accuracy in analyzing the shape of the powder, among the powder displayed in the powder particle image, fine particles with a particle diameter of less than 0.5 μm are excluded from the analysis target. However, the inventors have found that it is preferable to analyze the shape of particles having a particle diameter of 0.5 μm or more, and have created the present invention.

That is, the first aspect of the present invention is
A method for analyzing the shape of powder, comprising:
A resin embedding step of embedding powder in resin to form a resin-embedded sample;
A cross-section forming step of forming a cross-section in which the powder is exposed with respect to the resin-embedded sample;
an acquiring step of irradiating the cross section with an electron beam to acquire a backscattered electron image displayed in gray levels having a plurality of gradations;
For the backscattered electron image, setting a predetermined gradation for distinguishing between pixels corresponding to the powder and pixels corresponding to the resin, and binarizing each pixel using the predetermined gradation as a threshold. an image processing step of obtaining a monochrome two-tone powder particle image in which the powder is displayed as being uniformly dispersed;
an analysis step of analyzing the shape of the powder by performing image analysis on particles having a size of 0.5 μm or more among the powder displayed in the powder particle image;
A method of powder form analysis is provided.

A second aspect of the present invention is the powder shape analysis method of the first aspect,
The backscattered electron image is displayed with 256 gray levels,
In the image processing step, if the gradation of each pixel in the backscattered electron image is smaller than the predetermined gradation, it is converted into a gradation of 0 indicating black or a gradation of 255 indicating white. If the gradation is equal to or higher than the predetermined gradation, it is binarized by converting to a gradation that indicates a color opposite to that for the case that the gradation is smaller than the predetermined gradation.

A third aspect of the present invention is the powder shape analysis method of the second aspect,
In the image processing step, the predetermined gradation is set within a range of 20 to 250.

A fourth aspect of the present invention is the powder shape analysis method of the second or third aspect,
In the acquisition step, in the backscattered electron image, the gradation of the pixels corresponding to the resin is 0 indicating black, and the gradation of the pixels corresponding to the powder is 255 indicating white. to adjust brightness and contrast.

A fifth aspect of the present invention is the powder shape analysis method according to any one of the first to fourth aspects,
In the acquiring step, the electron beam is irradiated with an acceleration voltage set in a range of 0.5 kV or more and 10 kV or less.

A sixth aspect of the present invention is the powder shape analysis method according to any one of the first to fifth aspects,
In the obtaining step, the electron beam is irradiated with an acceleration voltage set in a range of 3 kV or more and 7 kV or less.

A seventh aspect of the present invention is the powder shape analysis method according to any one of the first to sixth aspects,
In the analyzing step, the circularity and angularity of the powder are calculated to analyze the shape.

An eighth aspect of the present invention is the powder shape analysis method according to any one of the first to seventh aspects,
The acquiring step, the image processing step and the analyzing step are performed by a fully automatic mineral analyzer.

According to a ninth aspect of the present invention,
Evaluating the fluidity of the powder based on the circularity and the angularity calculated by the powder shape analysis method according to the seventh aspect,
A powder fluidity evaluation method is provided.

According to a tenth aspect of the present invention,
Evaluating the fluidity of the resin in which the powder is dispersed based on the circularity and the angularity calculated by the powder shape analysis method according to the seventh aspect,
Provided is a method for evaluating fluidity of a resin in which powder is dispersed.

According to the present invention, it is possible to accurately analyze the powder shape even when the powder aggregates.

FIG. 1 is a process diagram of a powder shape analysis method according to an embodiment of the present invention. FIG. 2 is a backscattered electron image of a cross section of a resin-embedded sample. FIG. 3 is a powder particle image obtained by extracting the powder portion from the backscattered electron image of FIG. 2 and binarizing it. FIG. 4 is a diagram for explaining angularity.

<One embodiment of the present invention>
A powder shape analysis method according to an embodiment of the present invention will be described using a fully automatic mineral liberation analyzer (hereinafter simply referred to as "MLA") as an example.

MLA is an analysis device that identifies inorganic compound particles such as mineral particles, and is a scanning electron microscope (hereinafter simply (also called "SEM") is the platform. The analyzer is equipped with a control PC that fully automatically controls the SEM/EDS, performs image processing and spectrum matching, and identifies inorganic compound particles such as mineral particles.

The measurement principle of MLA will be briefly described.
In MLA, the surface of a resin-embedded sample obtained by mixing and solidifying a powder to be measured and a resin is ground, and the obtained cross section is measured. In the MLA measurement, first, a backscattered electron image (hereinafter also simply referred to as a "BSE image") is obtained by irradiating a cross section with an electron beam, the resin portion is removed by image processing, and mineral particles, etc. Acquire data on the position, size, and cross-sectional shape of the powder. Then, backscattered electron images of cross sections at different locations are acquired and image processing is repeated to automatically perform measurement. For example, in MLA, it is possible to perform these tasks fully automatically for an extremely large number of powder particles such as 1 million, so once the work starts, almost no human man-hours are required. It is possible to complete the powder shape data measurement.

Next, a powder shape analysis method according to the present embodiment will be described with reference to FIG. FIG. 1 is a process diagram of a powder shape analysis method according to one embodiment of the present invention. As shown in FIG. 1, the powder shape analysis method of this embodiment includes a resin embedding step S1, a cross-section forming step S2, an acquisition step S3, an image processing step S4, and an analysis step S5. Each step will be described in detail below.

(Resin embedding step S1)
First, powder to be subjected to shape analysis is prepared. Examples of powder include metal powder, metal oxide powder, and composite oxide powder.

Moreover, liquid or solid resin can be used as the resin for embedding the powder. A thermosetting or photo-setting resin can be used as the liquid resin. As the thermosetting resin, for example, a room-temperature-setting or heat-setting epoxy resin can be used. As the photocurable resin, for example, an acrylic resin, an epoxy acrylate resin, or the like can be used. A thermosetting resin such as a phenolic resin can be used as the solid resin.

In the resin embedding step S1, when a liquid resin is used, powder is preferably added and mixed with the liquid resin and the liquid resin is cured by light or heat. When a solid resin is used, the powder is added and mixed with the solid resin. It is preferable to melt and harden with heat. As a result, a resin-embedded sample in which the powder is dispersed and embedded in the resin is produced.

(Cross-section forming step S2)
Subsequently, a cross-section of the resin-embedded sample is obtained. For example, using a buffing machine, the resin-embedded sample is subjected to rough polishing, intermediate polishing and mirror polishing to form a smooth cross section exposing the powder. In addition to buffing, ion polishing such as cross-section polisher or focused ion beam processing may be performed. This cross-section becomes an observation surface that is irradiated with an electron beam and observed in an acquisition step S3, which will be described later. In addition, in order to suppress charge-up due to electron beam irradiation, a conductive film may be provided on the cross section by vapor-depositing a conductive material such as carbon, if necessary.

(Backscattered electron image acquisition step S3)
Subsequently, the resin-embedded sample is introduced into the MLA, and the cross section of the resin-embedded sample is irradiated with an electron beam in the MLA to acquire a backscattered electron image (hereinafter also referred to as a BSE image) of the cross section. In the BSE image, the composition distribution in the cross section is displayed with gray levels (black and white shades) having a plurality of gradations. In the BSE image of the cross section of the resin-embedded sample, for example, as shown in FIG. Each is displayed as a bright portion (white) with a relatively large gradation. In this BSE image, a plurality of particles forming the powder are displayed densely, and it is difficult to accurately analyze the shape of each particle.

Although the gradation of the gray level is not particularly limited, the point of view is to clearly distinguish the pixel corresponding to the powder (hereinafter also referred to as the powder portion) and the pixel corresponding to the resin (hereinafter also referred to as the resin portion) by the gray level. is preferably 256 gradations from 0 to 255.

In the acquisition step S3, from the viewpoint of improving the processing efficiency in the image processing step S4 described later, when acquiring the BSE image, the gray level gradation of the resin portion is set to 0 (black), and the powder portion is set to 0 (black). It is preferable to adjust the brightness and contrast so that the gray level gradation is 255 (white). The reference for setting the gradation to 0 is preferably the pixel with the lowest gradation among the pixels corresponding to the resin, and the reference for setting the gradation to 255 is the pixel with the highest gradation among the pixels corresponding to the powder. pixels.

In the acquisition step S3, the electron beam irradiation conditions are not particularly limited, but from the viewpoint of accurately reflecting the shape of the powder in the BSE image, it is preferable to set the acceleration voltage of the electron beam to a low value. Specifically, the acceleration voltage is preferably 0.5 kV or more and 10 kV or less, more preferably 3 kV or more and 7 kV or less.

(Image processing step S4 of backscattered electron image)
Subsequently, the obtained BSE image is binarized using a predetermined gradation as a threshold for each pixel by setting a gradation for distinguishing between pixels corresponding to powder and pixels corresponding to resin as a threshold. . As the threshold value, a gradation is selected so that the powder can be displayed as being monodisperse in the powder particle image. By this binarization, the powder is monodispersed, and a monochrome two-tone powder particle image is obtained in which the powder and the particles are displayed in black and white and opposite to each other. For example, by image-processing the BSE image shown in FIG. 2, a powder particle image as shown in FIG. 3 can be obtained. According to the powder particle image, the shape of the powder can be accurately and clearly reflected. In this embodiment, the term "single dispersion" means that the particles are dispersed to such an extent that each particle can be individually identified in the powder particle image.

Binarization is preferably performed as follows. For each pixel of the BSE image, the gray level is compared with a threshold value, and if it is smaller than the threshold value, it is converted to a gray level of 0 (black) or a gray level of 255 (white). Specifically, in the BSE image, pixels having a gradation smaller than the threshold value are determined to correspond to resin, and are converted to black or white. On the other hand, a pixel having a large gradation equal to or greater than the threshold value is determined to correspond to powder, and is converted to a color opposite to that of the resin portion. In other words, in the BSE image, the portion where the gray level does not satisfy the predetermined gradation is converted to black or white as a resin portion, whereas the portion where the gray level is higher than the predetermined gradation is converted to a powder portion as a resin portion. Convert to the opposite color. For example, in the binarization from FIG. 2 to FIG. 3, for each pixel, the gradation below the threshold is converted to 255 (white), while the gradation above the threshold is converted to 0 (black). A powder particle image is obtained in which the part is displayed in black and the resin part is displayed in white.

The threshold value is not particularly limited as long as it is a gradation that allows the powder to be uniformly dispersed and displayed. is more preferred.

(Powder particle image analysis step S5)
Subsequently, image analysis is performed on the powder particle image obtained in the image processing step S4. This provides data on the size and shape of particles in the powder. Specifically, using MLA, shape data is repeatedly obtained for different regions in the cross section of the resin-embedded sample, and average shape data of the powder is obtained based on the shape data of a plurality of particles.

In this embodiment, when obtaining shape data of a plurality of particles, particles having a particle diameter of 0.5 μm or more are selected in the powder particle image and the shape is analyzed. In other words, fine particles whose shape cannot be accurately analyzed are excluded from the analysis targets. As a result, the shape of the powder can be accurately analyzed, variation in analysis results can be suppressed, and the analysis accuracy of the powder shape can be maintained at a high level. The particles having a particle size of 0.5 μm or more as used herein refer to particles having a size of 0.5 μm or more among those displayed as particles in the powder particle image.

The number of particles to be analyzed is not particularly limited, but is preferably 5000 or more.

As for the shape, for example, circularity and angularity may be obtained. Circularity and angularity are defined as follows.

Assuming that the circularity of the powder particles in the powder particle image is C, the perimeter is L, and the area is S, the circularity C is obtained by the following formula (1). In this embodiment, the average sphericity of the powder can be calculated by totaling the circularities of all the powder particles by MLA and dividing by the number of particles.

_Angularity of a powder particle in a powder particle image is obtained by placing an ellipse inscribed in a rectangle circumscribing the powder particle as shown in FIG. This value focuses on the difference from the distance (D _e ) to the outer periphery of the particle. Specifically, as shown in the following formula (2), the angularity is the value obtained by squaring the difference between the distance D _p to the ellipse and the distance D _e to the outer periphery of the powder particles. It is calculated by dividing the distance D _e by the squared value, finding it over the entire circumference of the ellipse from 1° to 360°, and summing it up. In this embodiment, the average angularity of the powder can be calculated by totaling the angularities of all the powders by MLA and dividing by the number of particles.

As described above, the shape of the powder contained in the resin-embedded sample can be accurately analyzed.

Further, the fluidity of the powder can be evaluated based on the analysis results obtained for the shape of the powder, such as the circularity and angularity of the powder. Furthermore, the fluidity of the resin in which the powder is dispersed can also be evaluated. The fluidity correlates with the force applied per unit weight or unit volume to the powder or the resin in which the powder is dispersed. Qualitatively, in the case of the fluidity of the powder itself, when force is applied to the powder, if the powder flows in response to the force, the fluidity is high. If only the force contributes to powder flow, but the remaining force contributes to powder cohesion, the fluidity is evaluated as low. In the case of a resin in which powder is dispersed, the fluidity is evaluated to be high if the force required for fluidizing the resin is small, and the fluidity is low if the force required for fluidization is large.

For example, when the fluidity is evaluated by circularity and angularity, the fluidity of the powder or the fluidity of the resin in which the powder is dispersed is evaluated based on the following formula (3). In Equation (3), the coefficients A and B are obtained in advance from the correlation between the index representing fluidity and the degree of circularity and angularity. The index representing the fluidity is, for example, the distance that the powder moves per unit time and unit weight when the applied force is a predetermined constant value, and the distance that the resin moves in the case of a resin in which the powder is dispersed. However, it is not limited to this. After calculating the circularity and angularity of the target powder, an index representing the fluidity is obtained based on the following formula (3), and the fluidity of the powder or the fluidity of the resin in which the powder is dispersed is determined. Evaluate the degree of
(Indicator representing fluidity of powder, fluidity of resin in which powder is dispersed)=Coefficient A×(Circularity)+Coefficient B×(Angularity) (3)
The value of coefficient A in the above formula (3) is not necessarily the same value when corresponding to the fluidity of the powder and when corresponding to the fluidity of the resin in which the powder is dispersed. Similarly, the coefficient B does not always have the same value when it corresponds to the fluidity of the powder and when it corresponds to the fluidity of the resin in which the powder is dispersed.
Since the fluidity of powder and resin is considered to be related to the processability in the manufacturing process of these, the index representing the fluidity obtained by the above formula (3) is It can also be used as an indicator of workability in the manufacturing process of the resin that has been processed.

<Effects of this embodiment>
According to this embodiment, one or more of the following effects can be obtained.

In the present embodiment, a BSE image displayed in gray levels having a plurality of gradations, which can be obtained from a cross section of a resin-embedded sample, is binarized using a predetermined gradation as a threshold value for each pixel. A monochromatic two-gradation powder particle image is obtained in which is displayed as a single dispersion, and among the powder displayed in this powder particle image, particles having a particle diameter of 0.5 μm or more are subjected to image analysis. , are analyzing the powder shape. In the powder particle image, the powder is observed in a dispersed state and the shape of the powder is clearly reflected by binarization, so the shape of each particle can be accurately analyzed by image analysis. Moreover, since fine particles whose shape cannot be accurately analyzed are excluded from the analysis target, variations in analysis results can be suppressed, and high analysis accuracy of the powder shape can be maintained.

Also, by using MLA, it is possible to collect shape data for all powder particles and accurately analyze the average shape of the powder.

The backscattered electron image is displayed with 256 gray levels. In the image processing step S4, if the gray level of each pixel in the backscattered electron image is smaller than a predetermined gray level, the 0 level indicating black is displayed. It is possible to binarize by converting to 255 gradations that indicate grayscale or white, and if the gradation is equal to or higher than a predetermined gradation, convert it to a gradation that indicates the color opposite to when the gradation is lower than the predetermined gradation. preferable. As a result, even if the powder is aggregated and observed in the BSE image, the powder is displayed in a single dispersed state in the powder particle image, and by image analysis, each powder Shapes can be analyzed more accurately for body particles.

Further, in the image processing step S4, it is preferable to set the predetermined gradation as the threshold within the range of 20 to 250, more preferably within the range of 100 to 250. In the image processing step S4, if the threshold value is set to an excessively small gradation, the portion regarded as powder in the BSE image will increase, making it difficult to extract the powder portion so as to be monodisperse during binarization. . On the other hand, if the threshold value is set to an excessively large gradation, the part that is considered to be resin in the BSE image increases, and as a result, many pixels are missing from the powder part during binarization, resulting in a decrease in the analysis accuracy of the powder shape. easier. In this respect, by setting the threshold within the range of 20 to 250, more preferably within the range of 100 to 250, the powder portion is extracted so as to be monodisperse in the powder particle image, and Excessive omission due to binarization of the powder portion can be suppressed. As a result, the analysis accuracy of the powder shape can be maintained at a high level.

Further, when obtaining a backscattered electron image, the gradation of the pixel corresponding to the resin is 0, which indicates black, and the gradation of the pixel corresponding to the powder is 255, which indicates white. , brightness and contrast are preferably adjusted. This makes it possible to clarify the gray level gradation between the resin portion and the powder portion. As a result, it is possible to enhance the efficiency of image processing by adding contrast between the portion to be extracted and the portion to be removed in the BSE image.

In addition, in the acquisition step S3 for acquiring a backscattered electron image, the acceleration voltage is preferably set in the range of 0.5 kV to 10 kV, more preferably in the range of 3 kV to 7 kV. With respect to this point, knowledge obtained by the present inventors will be described below. In the resin-embedded sample, for example, another particle is positioned below the particle exposed in the cross section, so that the two particles may overlap vertically in the depth direction. When such a cross section is irradiated with an electron beam at a high acceleration voltage, not only the shape of the particles exposed on the cross section but also the shape of the particles located below it may be obtained. As a result, the obtained BSE image may be displayed in a state in which particles above and below are overlapped. In other words, the particles exposed on the surface may be displayed in a shape different from the original. In the present embodiment, the acceleration voltage is preferably set to 10 kV or less, more preferably 7 kV or less, and the electron beam is irradiated to make the penetration of the electron beam shallow, and the shape of the particles present on the extreme surface of the cross section. can be obtained. In other words, the particles exposed in the cross section can be displayed in a state close to their original shape. On the other hand, by setting the acceleration voltage to preferably 0.5 kV or higher, more preferably 3 kV or higher, the shape of the particles existing on the extreme surface of the cross section can be obtained favorably. According to the BSE image obtained by adjusting the acceleration voltage as described above, the shape of the powder can be analyzed more accurately.

Moreover, in this embodiment, it is preferable to perform acquisition process S3, image processing process S4, and analysis process S5 by MLA. According to the MLA, the acceleration voltage of the irradiated electron beam in the acquisition step S3, the brightness and contrast when acquiring the BSE image, and the gray level as the threshold value for the binarization processing in the image processing step S4 are set in advance. By doing so, it is possible to automatically acquire various data on the shape of the powder.

As for the shape of the powder, it is preferable to analyze the shape by calculating the circularity and angularity of the powder. Until now, the evaluation of powder fluidity generally used circularity. Angularity was also found to be important because of the large differences in the properties. However, the angularity needs to be analyzed with the powder particles dispersed, and it has been difficult to analyze the angularity with high accuracy. On the other hand, in the present embodiment, by performing image processing and image analysis so as to extract the powder portion, it is possible to obtain the angularity as well as the circularity of the powder and analyze it with high accuracy.

Further, according to the present embodiment, the fluidity of the powder or the fluidity of the resin in which the powder is dispersed can be evaluated based on the circularity and angularity calculated for the powder. As a result, it is possible to evaluate the fluidity, which could not be fully evaluated by circularity alone, by circularity and angularity.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be modified in various ways without departing from the gist of the present invention.

The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

(Example 1)
First, three types of powders with different fluidities were prepared. This powder is No. 1 to No. 3 powder. The particle diameter of the powder particles contained in the powder was approximately 2 to 3 μm.
Subsequently, 0.5 cc of the powder and 3 cc of a two-component room-temperature curing epoxy resin were weighed out, mixed in a cylindrical mold with a diameter of 25 mm, and allowed to stand still for curing. Approximately 7 cc of epoxy resin was added to the cured product and cured to obtain a cylindrical resin-embedded sample having a diameter of 25 mm and a height of approximately 15 mm. No. 1 to No. No. 3 powder was used. 1 to No. 3 resin-embedded samples (hereinafter simply referred to as samples) were prepared.

Next, the obtained sample was subjected to cross-sectional polishing using a buffing machine to obtain a cross-section (polished surface) where the powder was exposed. The polished surface was subjected to carbon vapor deposition and introduced into the MLA. In the MLA, first, the acceleration voltage, observation magnification and resolution were adjusted so that the powder particles were clearly projected on the BSE image using the SEM. Here, the acceleration voltage is 5 kV, the observation magnification is 6000 times, and the resolution is 1000×1000. Next, in the BSE image, the brightness and contrast are adjusted so that the gray level of the powder portion is 255 gradations and the gray level of the resin portion is 0 gradation, and a BSE image as shown in FIG. 2 is obtained. bottom.

Subsequently, for the obtained BSE images, the background subtraction function of the MLA control software was utilized to adjust the range of gray levels to be subtracted as background so that the powder was extracted monodisperse. In this embodiment, the threshold is set to 200 gradations for distinguishing between the powder portion and the resin portion. For each pixel of the BSE image, if the gray level is 0 or more and less than 200 gradations, it is removed as a resin portion, and if the gray level is 200 or more, it is extracted as a powder portion. A powder particle image shown in FIG. 3 was obtained by digitizing. Then, automatic MLA measurement was performed on the powder particle image, shape data of 10,000 particles was obtained, and circularity and angularity were calculated. At this time, particles having a particle diameter of 0.5 μm or more among the powder displayed in the powder particle image were subjected to shape analysis. In this example, two measurements were taken on different cross-sections of the sample.

Circularity and angularity determined in duplicate for each sample are shown in Table 1 below. These figures are average values of 10,000 particles. In this example, when the shape analysis was performed for each sample a plurality of times, the analysis results shown in Table 1 were obtained in each case, and it was confirmed that there was little variation in the analysis results. This is probably because, among the powder displayed in the powder particle image, fine particles whose shape cannot be accurately analyzed are excluded from the analysis target.

Also, No. 1 to No. A thin section sample was prepared from each of the 3 samples and observed with a transmission electron microscope. As a result, No. 1 is No. 2 and no. Although it was judged to be less angular and more circular than 3, these observations were found to correlate with the angularity and circularity in Table 1. Also, No. The fluidity of sample No. 1 is 2 and no. It was confirmed that the fluidity was greater than that of No. 3. Therefore, it was found that flowability correlates with angularity and circularity.

As described above, the powder part is extracted from the backscattered electron image of the cross section of the resin-embedded sample and binarized to obtain the powder particle image. It is possible to accurately analyze the powder shape that affects the powder flowability, such as the degree of hardness.

Claims (7)

A method for analyzing the shape of powder, comprising:
A resin embedding step of embedding powder in resin to form a resin-embedded sample;
A cross-section forming step of forming a cross-section in which the powder is exposed with respect to the resin-embedded sample;
an acquiring step of irradiating the cross section with an electron beam to acquire a backscattered electron image displayed in gray levels having a plurality of gradations;
For the backscattered electron image, setting a predetermined gradation for distinguishing between pixels corresponding to the powder and pixels corresponding to the resin, and binarizing each pixel using the predetermined gradation as a threshold. an image processing step of obtaining a monochrome two-tone powder particle image in which the powder is displayed as being uniformly dispersed;
an analysis step of analyzing the shape of the powder by performing image analysis on particles having a size of 0.5 μm or more among the powder displayed in the powder particle image;
The powder includes at least one of metal powder, metal oxide powder and composite oxide powder,
In the analysis step, the shape is analyzed by calculating the circularity and angularity of the powder,
Analysis method of powder shape. The backscattered electron image is displayed with 256 gray levels,
In the image processing step, if the gradation of each pixel in the backscattered electron image is smaller than the predetermined gradation, it is converted into a gradation of 0 indicating black or a gradation of 255 indicating white. If the gradation is equal to or higher than the predetermined gradation, it is binarized by converting it to a gradation that indicates the color opposite to that when it is lower than the predetermined gradation.
The method for analyzing a powder shape according to claim 1. In the image processing step, the predetermined gradation is set within a range of 20 to 250;
The method for analyzing a powder shape according to claim 2. In the acquisition step, in the backscattered electron image, the gradation of the pixels corresponding to the resin is 0 indicating black, and the gradation of the pixels corresponding to the powder is 255 indicating white. to adjust brightness and contrast,
The method for analyzing powder shape according to any one of claims 1 to 3. In the acquisition step, the electron beam is irradiated with an acceleration voltage set to a range of 0.5 kV or more and 10 kV or less.
The method for analyzing powder shape according to any one of claims 1 to 4. In the acquisition step, the electron beam is irradiated with an acceleration voltage set to a range of 3 kV or more and 7 kV or less.
The powder shape analysis method according to any one of claims 1 to 5. In the analysis step, the shape is analyzed by calculating the circularity and angularity of the powder,
The powder shape analysis method according to any one of claims 1 to 6.

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