JP2022078759A - Method for evaluating metal powders, evaluation program for evaluating metal powders, and storage medium in which evaluation program is recorded - Google Patents

Abstract

To provide a method for evaluating metal powders.SOLUTION: The method for evaluation includes the steps of: drawing a scan electronic microscope image of metal powders; detecting the boundary of a metal particle by a threshold value method in the image; removing regions with a gray scale of a first threshold value or smaller from the image; calculating the aspect length-to-width ratio and the circularity of a first particle region surrounded by the boundary; and determining whether the metal particle in the first particle region is a single particle or a connected particle formed by connecting at least two fragment particles on the basis of the aspect length-to-width ratio and the circularity.SELECTED DRAWING: Figure 1

Description

One of the embodiments of the present invention relates to a powder evaluation method, an evaluation program and evaluation system for evaluating the powder, and a storage medium in which the evaluation program is recorded. For example, one embodiment of the present invention relates to an evaluation method for a metal powder containing metal particles, an evaluation program and evaluation system for evaluating the metal powder, and a storage medium in which the evaluation program is recorded.

One of the methods for evaluating powder, which is an aggregate of fine particles, is electron microscope observation. For example, by analyzing an image (SEM image) obtained by using a scanning electron microscope (SEM), the shape, particle size, and variation in shape and particle size of each particle can be evaluated. For example, Patent Documents 1 and 2 describe that by acquiring an SEM image of nickel powder containing nickel fine particles and visually observing the SEM image, the ratio of linked particles and coarse particles generated by the bonding of nickel particles can be evaluated. Has been done.

Japanese Unexamined Patent Publication No. 2019-173179 JP-A-2015-030886

One of the embodiments of the present invention provides a new method for evaluating a powder containing fine particles, an evaluation program and an evaluation system for carrying out the method, and a storage medium in which the evaluation program is recorded. That is one of the issues. For example, one of the embodiments of the present invention provides a method for evaluating a metal powder, an evaluation program and an evaluation system for carrying out the method, and a storage medium in which the evaluation program is recorded. Make it one of the issues.

One of the embodiments according to the present invention is a method for evaluating a metal powder containing a plurality of metal particles. This evaluation method captures a scanning electron microscope image of metal powder, detects the boundary of metal particles in the scanning electron microscope image using the threshold method, and the gradation is the first from the scanning electron microscope image. Eliminating the region below the threshold of 1, calculating the aspect ratio and circularity of the first particle region surrounded by the boundary, and the metal particles corresponding to the first particle region based on the aspect ratio and circularity. It involves determining whether it is a single particle or a linked particle in which at least two fragment particles are linked.

One of the embodiments according to the present invention is an evaluation program for evaluating metal powder. This evaluation program detects the boundaries of metal particles in a scanning electron microscope image of metal powder using the threshold method, and removes the region where the gradation is below the first threshold from the scanning electron microscope image. , Calculate the aspect ratio and circularity of the first particle region surrounded by the boundary, and the metal particle corresponding to the first particle region based on the aspect ratio and circularity is a single particle, or at least two. Have the computer perform a determination to determine if the fragment particles are concatenated particles.

One of the embodiments according to the present invention is a computer-readable storage medium in which the evaluation program is recorded.

The flow of the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. The schematic diagram of the SEM image acquired in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention, and the schematic diagram which shows the morphology of a metal particle. The schematic diagram which shows the data point after the boundary detection of the particle by the threshold method carried out in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention, and the schematic diagram which shows the particle region at the edge of an SEM image. The schematic diagram which shows the profound part of the SEM image acquired in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention, and the schematic diagram which shows the particle area division processing by applying a first-order differential filter. The schematic diagram which shows the water shed treatment in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. The schematic diagram which shows the expansion process in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. The schematic diagram which shows the convex hull deformation processing in the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. The flow of the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. The flow of the evaluation method of the metal powder which concerns on one of the Embodiments of this invention. An evaluation system for metal powder according to one of the embodiments of the present invention. SEM image showing each process in the examples. SEM image showing each process in the examples. SEM image showing each process in the examples.

Hereinafter, a method for evaluating a powder containing a plurality of particles according to one of the embodiments of the present invention will be described. There are no restrictions on the powder that can be applied to this evaluation method, and any tangible powder composed of a plurality of solid particles may be used. The powder may or may not have fluidity. For example, this evaluation method can be applied to a powder containing particles having a shape that can be regarded as spherical or substantially spherical, or a powder that can obtain an image to which individual particles can be discriminated. There are no restrictions on the materials contained in the particles, such as metals such as nickel, copper, titanium, and silver, alloys, metal compounds such as oxides and nitrides containing metals, and examples such as polystyrene, polyethylene, polypropylene, and polylactic acid. It may be a food such as artificial polymer, glass, titanium, or sugar. In the following description, a metal powder containing metal particles will be used as an example, but a powder containing metal compound particles can be handled in the same manner.

1. 1. Outline of evaluation method Figure 1 shows the flow of this evaluation method. As shown in FIG. 1, in this evaluation method, the acquisition of the SEM image of the metal powder (S1) is performed first, and then the particle region is specified (S2) by the boundary detection of the metal particles using the threshold method. Will be done. After that, the particle region at the end of the SEM image is excluded (S3), the particle region at the deep part of the SEM image is excluded (S4), the particle region is divided by the first derivative filter (S5), the water shed treatment (S6), and the expansion treatment (S6). At least one of S7) and the convex package deformation process (S8) is carried out. All of the above processes S3 to S8 may be performed, or a plurality of processes may be appropriately selected from these processes. Further, when a plurality of processes are performed, the order is not limited, and for example, the processes may be performed in the order shown in the flow of FIG. 1, or the execution order may be changed as appropriate.

2. 2. Acquisition of SEM image (S1)
An SEM image of the metal powder is obtained using a known method. FIG. 2A is a diagram schematically showing an SEM image, and a plurality of particle regions corresponding to metal particles are observed in the SEM image. The SEM image is acquired as gradation data of each of the data points (DP) arranged in a matrix. Hereinafter, the data points will be described as being arranged on the x-axis and the y-axis in m rows and n columns, respectively (m and n are natural numbers of 2 or more). Each data point is expressed as a gradation selected from a total of 256 gradations from the 0th gradation to the 255th gradation. When the SEM image is displayed on the screen of the display device, each data point corresponds to a pixel, and the gradation can be expressed as luminance. That is, the SEM image is visually recognized on the display device as an aggregate of pixels giving 256 different luminance levels. In this evaluation method, the microscope for acquiring the powder image is not limited to the SEM, and a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), an optical microscope, or the like may be used. Even when the powder image is displayed in color, the image may be converted into a gray scale of 256 gradations.

Usually, most of the metal particles contained in the metal powder have a shape that can be regarded as spherical or substantially spherical. Therefore, in the SEM image, the entire spherical or substantially spherical metal particles are observed, and as shown in FIG. 2B, the spherical or substantially spherical metal particles are also observed in an overlapping state. To. However, although it depends on the method for producing the metal powder, the metal powder may contain metal particles having a shape largely deviated from the spherical shape. A typical example thereof is a metal particle formed by collision and bonding of a plurality of metal particles in a high temperature state, and is a metal particle having a distorted shape called a connecting particle (FIG. 2 (C)). It is known that such linked particles can be produced, for example, by a vapor phase reduction method in which a metal chloride gas such as nickel chloride is reacted with a reducing gas such as hydrogen. Hereinafter, metal particles having a spherical shape or a shape close to a spherical shape are referred to as simple substance particles. On the other hand, metal particles formed by binding a plurality of metal particles and having a shape greatly deviated from a spherical shape or having a distorted shape are called connecting particles. In the linked particles, the individual metal particles bonded to each other may be referred to as fragment particles. As described in detail below, in the evaluation method according to one of the embodiments of the present invention, the shape of a huge number of metal particles observed by SEM can be grasped in a short time, and the metal particles can be divided into single particles and linked particles. Can be determined as.

3. 3. Boundary detection of particles by threshold method (S2)
In the process S2, the metal particles to which each data point constituting the acquired SEM image data belongs are determined, and the data points are binarized in order to detect the boundary of the metal particles. There are no restrictions on the method for binarization, and known methods such as the Niblack method, the Sauvola method, the p-tile method, and the discriminant analysis method may be adopted.

The data obtained by this binarization process is schematically shown in FIG. 3 (A). Here, matrix-like data points arranged in 12 rows and 12 columns on the x-axis and the y-axis, respectively, are shown, and the particle boundaries are shown by dotted circles. The data point DP1 constituting the particle boundary can be obtained by the above-mentioned binarization process. However, the data point DP2 determined to form the particle boundary may be detected within the particle boundary, that is, also in the particle region. Therefore, the data point DP2 that does not form a closed shape by a plurality of data points is excluded. By this process, the particle boundary can be accurately detected and the particle region and its shape can be determined.

4. Exclusion of particle region at the end of SEM image (S3)
As shown in FIG. 3B, the SEM image has four ends (sides). Since each data point can be represented by xy coordinates, the straight lines of x = 1, x = m, y = 1, and y = n are the ends of the SEM image. Since the particle region in contact with this end does not show the entire metal particle, its shape cannot be accurately evaluated. Therefore, in this evaluation method, after detecting the particle boundary by the threshold method, the process S3 for excluding the particle region at the end of the SEM image from the SEM image may be performed. Specifically, the data points included in the particle region in contact with any of the straight lines of x = 1, x = m, y = 1, and y = n are excluded from the evaluation target. This makes it possible to improve the accuracy of discriminating between single particles and connected particles. The method of determining single particles and connected particles will be described later.

5. Exclusion of particle region in deep SEM image (S4)
Conventionally, the distinction between a single particle and a connected particle has been performed by visually observing an SEM image of a metal powder. Usually, it is highly probable that the same level of results can be obtained regardless of which position (for example, different depth position) of the same lot is photographed and visually observed for the produced metal powder. It is assumed that metal particles existing at a position deep from the powder surface (for example, a position deeper than the powder surface by several hundred μm or more) may not be able to perform appropriate image processing due to the narrow gradation width in the captured image. .. Therefore, metal particles existing deep from the powder surface may be excluded from the evaluation target. Therefore, also in this evaluation method, a process for evaluating a metal powder existing in a region shallower than a certain position from the powder surface may be performed. For example, metal particles corresponding to a particle region having a low gradation may be excluded from the evaluation target.

Specifically, a region having a gradation equal to or lower than a certain threshold value is excluded from the SEM image. That is, as schematically shown in FIG. 4A, a data point having a gradation equal to or less than a certain threshold value although it is determined to constitute a particle region in particle boundary detection (S2) by the threshold method (FIG. 4 (A)). The data points that make up the hatched area in A) are excluded from the evaluation target. The threshold value may be selected from, for example, a range from the 60th gradation to the 70th gradation, and is typically the 65th gradation. As a result, metal particles having a narrow gradation width and deep positions in the captured image can be excluded, so that the discrimination accuracy between the single particles and the connected particles can be improved.

6. Processing for Improving Determination Accuracy In the particle boundary detection (S2) by the above-mentioned threshold method, it may not always be possible to extract a plurality of overlapping single particles as their respective particle regions. In this case, each process such as particle region division (S5), water shed process (S6), expansion process (S7), and convex hull deformation process (S8) by a first-order differential filter may be performed (see FIG. 1). ). Hereinafter, each of these processes will be described.

(1) Particle region division by a first-order differential filter (S5)
In this process, a first-order differential filter is applied to the data points constituting the SEM image. A known filter can be used as the first derivative filter, and for example, a Sobel filter, a Prewitt filter, or the like may be adopted. In this process, a constant constant is multiplied by the gradation of nine data points surrounding the data point of interest. This process is performed for all data points. For the aggregate of the obtained data points, the gradation change in the x direction and the y direction is calculated, and the portion where the gradation change is large is detected as an edge. For example, a portion of adjacent data points having a gradation difference of 10 or more may be regarded as an edge, and a portion having a gradation difference of 20 or more may be regarded as an edge. Divide the particle area by the detected edges.

By this processing, the contrast difference of the SEM image is emphasized. For example, two or more particle regions having a distorted shape that are misrecognized as one particle region only by the particle boundary detection (S2) by the threshold method are formed by the edge. Can be divided into regions of (see FIG. 4B). Each of the divided regions is treated as a particle region and evaluated. As a result, it is possible to prevent a plurality of overlapping single particles from being mistaken for one connected particle in the SEM image, and it is possible to more accurately discriminate between the single particles and the connected particles.

(2) Water shed treatment (S6)
This treatment can be performed on any particle region, but may be selectively performed on a particle region corresponding to a metal particle that has not been determined to be a single particle. For example, this process may be performed not only on the region not divided by the particle region division (S5) by the first derivative filter, but also on the divided region. Further, it may be performed on a region determined to be a connected particle by the determination process described later.

First, the data points of the SEM image in the target area are gradation-inverted. For example, the 127th gradation, which is the median value of the gradation value, is inverted at the center. After that, as shown in FIG. 5A, a plurality of data points having the local minimum gradation in the particle region are designated and adopted as markers. Focusing on one marker, since there is a region around the marker having a gradation higher than the gradation of the marker, contour lines of the gradation can be drawn around the marker. As a result, the contour lines are extended from each marker to the area having higher gradation, and the area surrounded by the contour lines is used as the occupied area of the marker. This operation is performed for each marker. By this operation, the occupied area of each marker is gradually expanded, and the point where the occupied areas with the adjacent markers as the base points are in contact with each other is set as a temporary boundary. Therefore, it is possible to make a temporary boundary line by connecting the points where the occupied areas are in contact with each other. FIG. 5B schematically shows the gradation change on the line connecting the contact point (CP) of the two occupied areas and the two markers (chain line AA'in FIG. 5A). As shown in FIG. 5B, the gradation is the minimum value in the two markers (here, the markers M _b and _Mc ), and one maximum value of the gradation exists in the contact CP between them. If the difference between the gradation of this contact CP and the gradation of the marker having the lower gradation of the two markers (here, marker _Mc ) is equal to or more than a predetermined threshold value, this contact CP is valid and two. It is regarded as a watershed, which is an effective boundary between two occupied areas. This process is performed for all markers in the target particle region. The threshold value can be selected from, for example, a range in which the gradation difference is 20 or more and 60 or less, 20 or more and 50 or less, or 35 or more and 45 or less.

When there is one or more valid boundaries (watersheds) in the target particle region, data with a sufficiently high gradation compared to the marker between adjacent markers in the gradation-inverted target particle region. It means that there is a point. That is, it means that there is a data point having a sufficiently low gradation between the data points having the local maximum gradation adjacent to each other in the particle region before the gradation inversion.

On the other hand, when there is no effective boundary in the target particle region, the gradation difference between adjacent markers in the gradation-inverted target particle region is small, and the gradation is remarkable between these markers. Means that there are no high data points in. That is, it means that there is no data point having a sufficiently low gradation between the data points having the local maximum gradation adjacent to each other in the particle region before the gradation inversion.

The curve representing the contour of the region corresponding to the connected particles formed by the collision and bonding of a plurality of fragment particles in a high temperature state has a portion where the slope changes abruptly. This portion is a groove formed between the fragment particles, and the groove is observed as a region having low gradation in the SEM image. In other words, if a groove is detected in the particle region, it can be determined that the metal particle corresponding to the particle region may be a connecting particle, and conversely, if the groove cannot be detected, the metal corresponding to the particle region is used. It can be determined that the particles are single particles. Watershed treatment is one of the methods for detecting grooves in linked particles, and the process described above examines grooves peculiar to linked particles. On the other hand, even if the shape deviates from the sphere, the groove seen in the connected particles cannot be detected if it is a single particle. Therefore, it is possible to improve the accuracy of distinguishing the connected particles from the simple substance particles by this treatment.

As described above, if an effective boundary can be confirmed in the target particle region by the water shed treatment, it can be understood that a low gradation region exists in the particle region. On the contrary, when an effective boundary cannot be confirmed, it is suggested that the low gradation region does not exist in the particle region. Therefore, by using this method, it is possible to determine the presence or absence of a groove in the target particle region, and it is possible to more accurately discriminate between a single particle and a connected particle.

In the watershed process described above, the gradation value of the data point is first inverted, and then the watershed is obtained, but in this evaluation method, the gradation value of the data point may not be inverted. In this case, the marker becomes a data point having a local maximum gradation, and the contour lines are extended from each marker to a region having a lower gradation.

(3) Expansion treatment (S7)
This treatment can also be performed on any particle region, but may be selectively performed on a particle region corresponding to a metal particle that is not determined to be a single particle. For example, this treatment can be performed on a particle region corresponding to a metal particle that has not been determined to be a simple substance particle by the watershed treatment (S6).

In this treatment, although the metal particles judged to be connected particles are actually single particles, are they judged to be connected particles because they are covered with other metal particles existing at a position shallower than these metal particles? Or, it can be performed to determine whether it is actually determined to be a connected particle without being covered with other metal particles. Specifically, binarization of data points, expansion treatment for the target particle region (first expansion treatment), and other particles overlapping with the expansion region obtained by the first expansion treatment (first expansion region). Expansion treatment (second expansion treatment) of the region (neighboring particle region), extraction of a region (superimposed region) where the target particle region and the expansion region (second expansion region) obtained by the second expansion treatment overlap. And the original gradation of the neighboring particle region and the original gradation of the superimposed region are compared. If the original gradation of the superimposed region is higher than the original gradation of the neighboring particle region, it is determined that the metal particles corresponding to the target particle region are not covered with the metal particles corresponding to the neighboring particle region. On the other hand, if the original gradation of the superimposed region is lower than the original gradation of the neighboring particle region, it is determined that the metal particles corresponding to the target particle region are covered with the metal particles corresponding to the neighboring particle region. The original gradation refers to the gradation before the binarization process.

A specific procedure will be described with reference to FIG. FIG. 6 schematically shows the particle region A of the metal particles to be evaluated and the neighboring particle regions B to D existing in the vicinity of the particle region A. The neighboring particle regions B to D may be a region corresponding to a single particle or a region corresponding to a connected particle. In this process, first, all data points are binarized. Therefore, all data points are represented by a gradation of 0 (black) or 1 (white). Next, the particle region A is subjected to an expansion treatment (first expansion treatment). A known method may be used for the expansion treatment itself. For example, focusing on one of the data points constituting the particle region A, among a plurality of data points (for example, 3 × 3 data points) centered on the data points. If there is even one data point with a gradation of 1, the gradation of the focused data point is set to 1. This operation is performed on all the data points constituting the particle region A. As a result, a first expansion region A'is obtained around the particle region A.

Next, among the other particle regions (here, the neighboring particle regions B and C) that overlap with the expansion region A', the same applies to the portion (neighboring particle regions B', C') that overlaps with the expansion region A'. The expansion process (second expansion process) is performed. By this operation, the second expansion regions B'and C'are obtained from the neighboring particle regions B'and C', respectively, and the overlapping region AB and the particle region A where the particle region A and the second expansion region B'overlap are obtained. A superposed region AC in which the second expansion region C'is overlapped with the second expansion region C'is obtained. It is not necessary to perform the expansion treatment on the particle region (here, the particle region D) that does not overlap with the expansion region A'.

After that, the original gradations of the neighboring particle region B and the superimposed region AB are compared. Similarly, the original gradations of the neighboring particle region C and the superimposed region AC are compared. Here, the superimposed regions AB and AC are portions of the target particle region A that are close to the neighboring particle regions B and C, respectively. Therefore, for example, the fact that the superimposed region AB has a higher gradation than the particle region B means that the portion of the particle region A that is closer to the particle region B has a higher gradation than the particle region B and is closer to the powder surface. It means that it exists in the position. That is, it means that the metal particles corresponding to the particle region A are not covered with the metal particles corresponding to the particle region B. On the contrary, the fact that the superimposed region AB has a lower gradation than the particle region B means that the portion of the particle region A closer to the particle region B has a lower gradation than the particle region B and is farther from the powder surface. It means that it is located. That is, it means that the metal particles corresponding to the particle region A are covered with the metal particles corresponding to the particle region B. The same can be said about the relationship between the particle regions A and C. By performing the expansion treatment in this way, the hierarchical relationship between the metal particles in the SEM image can be grasped more accurately, so that the simple substance particles and the connected particles can be discriminated more accurately.

(4) Convex hull deformation process (S8)
This process can be performed to determine whether the metal particles determined to be connected particles because they are covered with other metal particles are actually connected particles or are actually simple substance particles. .. This treatment can also be performed on any particle region, but may be selectively performed on the particle region corresponding to the metal particle determined to overlap with other metal particles. Therefore, preferably, the expansion treatment (S7) is performed on the particle region corresponding to the metal particles determined to be covered with other metal particles.

In the convex hull deformation process, a known convex hull deformation algorithm can be used. For example, the quick full method, the gift wrapping method, the Jarvis update method, the divide-and-conquer method, the Graham scan method, and the like can be mentioned as convex hull deformation algorithms. When using the quick full method, the minimum coordinate point on the x-axis or y-axis (for example, x _min on the x-axis) and the maximum coordinate point (for example, x min) for the data points that make up the boundary of the particle region of interest. x _max on the x-axis) is extracted, and a dividing line LN is drawn between them (see FIG. 7). Two farthest points are searched from this dividing line LN, and the minimum point, the maximum point, and the edge connecting the two farthest points are created.

Next, the same operation is performed focusing on the data points of the remaining boundary existing outside the edge, and the edge is further created. The creation of the dividing line LN, the search for the farthest point, and the creation of the edge are repeated until there are no data points outside the edge. After that, all the created edges are overlapped, and the obtained shape is made into a convex hull. The shape of this convex hull is evaluated, and whether it is a connected particle or a simple substance particle is evaluated. By performing the convex hull deformation, it is possible to estimate the actual shape of the metal particles whose exact shape cannot be grasped on the SEM image because it is covered with other metal particles. It is possible to make an accurate determination.

7. Evaluation Method A method of performing any or a plurality of the above-mentioned processes S2 to S8 to determine whether the particles are single particles or linked particles will be described below.

(1) Judgment based on aspect ratio and circularity In one of the methods for judging the shape of metal particles, parameters related to the particle shape are used. As shown in FIG. 8, the parameters related to the particle shape include the aspect ratio and the circularity (C). In the shape determination by this method, after performing particle boundary detection (S2) by the threshold method, exclusion of the particle region at the end of the SEM image (S3), exclusion of the particle region at the depth of the SEM image (S4), and primary It can be performed on the particle region obtained by performing at least one or a plurality of processings of the particle region division (S5) by the differential filter. The execution order of the processes S3 to S5 may be arbitrarily determined, and is not limited to the order shown in FIG.

Specifically, after the treatment S2, one or a plurality of the treatments S3 to S5 are performed to obtain the aspect ratio and the circularity of the particle region. The aspect ratio is the ratio of the long side to the short side of the virtual rectangle circumscribing the particle region. The virtual rectangle is created so that all four sides of it touch the particle area. Circularity is a parameter expressed by the following equation, and in the equation, S and L are the area and the perimeter of the particle region, respectively.
C = 4πS / L ²

In this evaluation method, when the aspect ratio is equal to or less than a certain threshold value and the circularity is also equal to or more than a certain threshold value, it is determined that the metal particles corresponding to the particle region are simple substance particles. On the other hand, when the aspect ratio is less than a certain threshold value or the circularity is less than a certain threshold value, it is determined that the metal particles corresponding to the particle region are connected particles. The aspect ratio threshold may be selected from, for example, 1.2 or more and 2.0 or less, or 1.3 or more and 1.7 or less, and is typically 1.5. Is. As the threshold value of circularity, for example, it may be selected from the range of 0.5 or more and 0.9 or less, or it may be selected from the range of 0.6 or more and 0.8 or less, typically 0.7. Is. However, even if the metal particles are determined to be linked particles, they can be determined to be single particles by further performing the evaluation method described later as candidates for linked particles. It is not necessary to determine the shape of the metal particles determined to be single particles by this evaluation method again.

(2) Evaluation method using the minimum gradation in the diversion ridge and the gradation of the marker in the water shed treatment As described above, in the water shed treatment, the metal particles appearing as connected particles in which a plurality of fragment particles are connected in the SEM image. However, by confirming the presence or absence of the low gradation region due to the groove, it is possible to determine whether the metal particle is a truly connected particle or a single particle having a somewhat distorted shape. .. Therefore, when applying the watershed process, the gradation of the watershed and the gradation of the marker with the lower gradation among the two markers that are the base points of the watershed are compared, and the gradation difference is a constant threshold value. If it is the following, it is judged to be a single particle. On the other hand, when the gradation difference is equal to or more than a certain threshold value, it is determined that the particles are connected particles (FIG. 9A). The threshold value can be selected from, for example, a gradation difference of 35 or more and 45 or less, and is typically a gradation difference of 40. However, even a metal particle determined to be a connected particle by this evaluation method can be determined to be a single particle by further combining the above-mentioned evaluation method and the evaluation method described later. Also in this evaluation method, it is not necessary to determine the shape of the metal particles determined to be single particles again.

(3) Evaluation method using circularity in the convex hull deformation process As described above, the actual shape of the metal particles covered with other metal particles can be estimated by performing the convex hull deformation process. Therefore, this evaluation method is preferably applied to the particle region determined to overlap with other metal particles by performing the expansion treatment. In this convex hull deformation process, the above-mentioned circularity can be used as an evaluation parameter, and when the circularity is equal to or higher than a certain threshold value, it is determined that the metal particles corresponding to the particle region are simple substance particles. On the contrary, when the circularity is less than this threshold value, it is determined that the particles are connected particles (FIG. 9B). The threshold value may be selected from the range of 0.50 or more and 0.90 or less, or may be selected from the range of 0.55 or more and 0.80 or less, and is typically 0.60. However, even metal particles determined to be linked particles by this evaluation method can be determined to be single particles by further combining the above-mentioned evaluation methods.

As described above, the distinction between the connected particles and the single particles contained in the metal powder may be performed by visual observation of the SEM image. For this reason, the evaluator is required to have a certain level of technical proficiency, and the evaluation requires a long time. For example, when evaluating nickel or copper powder, although it depends on the technical proficiency of the evaluator, it usually takes several minutes to several tens of minutes, and the burden on the evaluator is large.

However, since the evaluation can be completed in about 30 seconds by performing the above-mentioned processing on a computer, the processing speed is significantly increased (specifically, about 6 to 70 times). Can be made to. Further, not only the burden on the evaluator is reduced, but also the connected particles and the simple substance particles can be discriminated while eliminating the influence of the evaluator's technical proficiency on the evaluation result.

8. Evaluation program and evaluation system The evaluation method described above can be carried out by an evaluation system having a calculation function and an evaluation program mounted on the evaluation system. Therefore, one of the embodiments according to the present invention is an evaluation program for causing the evaluation system to perform one or more of the above processes for discriminating between the single particles and the connected particles in the metal powder, and the other. One of the embodiments is an evaluation system that operates according to the instructions of this evaluation program. A computer-readable recording medium on which an evaluation program is recorded is also one of the embodiments according to the present invention.

FIG. 10 shows an example of the configuration of an evaluation system for evaluating metal particles by this evaluation method. In the example shown in FIG. 10, the evaluation system includes an SEM 100 and an evaluation server 110, which are connected by a network 102 so as to be able to communicate with each other. The network 102 may be an external network such as the Internet, or an internal network such as a LAN (Local Area Network). The evaluation server 110 is a computer having a communication function, and may be a notebook type or a stationary type personal computer, or a portable communication terminal such as a tablet computer.

The evaluation server 110 is provided with an application programming interface (API) 112, and the evaluation server 110 is connected to the network 102 through the API 112. This establishes communication between the evaluation server 110 and the SEM100.

The evaluation server 110 is further provided with an input unit 116, an output unit 118, a transmission / reception unit 120, a storage unit 122, and the like, in addition to the control unit 114 that controls the operation of the evaluation server 110. The storage unit 122 stores an evaluation program for executing the evaluation system together with a basic application program for operating the evaluation server 110. The control unit 114 includes a processor such as a central processing unit (CPU), operates a basic application program and an evaluation program stored in the storage unit 122, and controls various processes executed on the evaluation server 110. The input unit 116 is a user interface used when inputting commands and information to the evaluation server 110, and typically includes a keyboard, a touch panel, or a combination thereof. The output unit 118 provides various data stored in the storage unit 122 as an image or a printed matter, and is a display such as a liquid crystal display or an organic electroluminescent display, or an output device such as a printer. The transmission / reception unit 120 has a function of communicating with other communication devices including the SEM 100 via the network 102. For example, the transmission / reception unit 120 receives the SEM image acquired by the SEM 100.

Examples of computer-readable recording media include hard disks, flexible discs, and magnetic media such as magnetic tapes, optical media such as CD-ROMs and DVDs, optical magnetic media such as floptic discs, and Includes hardware devices configured to store and execute evaluation program instructions such as ROM, RAM, flash memory, and the like. Examples of evaluation program instructions include machine language code, such as those generated by a compiler, as well as high-level language code executed by the server using an interpreter or the like. The evaluation program is installed in the storage unit 122 from a computer-readable medium. The evaluation program may be downloadable from the network to the storage unit 122.

1. 1. Example 1
In this embodiment, the result of evaluating nickel powder containing nickel particles by using the evaluation method according to one of the embodiments of the present invention will be described. In this example, after obtaining the SEM image of the nickel powder, the treatments S2 to S8 were performed in this order.

(1) Nickel powder Nickel powder was produced by using a vapor phase reduction method. That is, nickel chloride produced by the chloride of nickel metal was reduced with hydrogen gas to obtain nickel powder. The average particle size of the obtained nickel powder was 250 nm.

(2) Evaluation An SEM image of nickel powder was obtained using a scanning electron microscope (model number SU5000) manufactured by Hitachi High-Technologies Corporation. FIG. 11A is a part of the acquired SEM image. In this embodiment, five SEM images were acquired, and the processing described below was performed on each SEM image data.

First, the boundary detection (S2) of particles was performed by the threshold method. In this process, data points arranged in a 7 × 7 matrix centered on the target data points were used. As shown by the aggregate of black dots in FIG. 11B, this operation detected particle boundaries for almost all of the metal particles observed in the SEM image. Subsequently, the particle region in contact with the end of the SEM image was excluded (S3). In FIG. 11C, the particle regions in contact with the lower side and the left side in the enlarged SEM image are filled, and these particle regions are excluded. The same operation was performed on the particle region in contact with the upper side and the right side in the SEM image. After that, the 65th gradation was adopted as the gradation of the threshold value, and the particle region in the deep part of the SEM image was excluded (S4). By this operation, the dark part in the SEM image (the filled area in FIG. 12A, which is an enlarged SEM image) was excluded. After the above series of treatments were completed, the aspect ratio and circularity of each particle region were determined, and the particle region having an aspect ratio of 1.5 or less and a circularity of 0.7 or more was determined to be a single particle.

On the other hand, the candidate particles corresponding to the particle region having an aspect ratio of more than 1.5 or a circularity of less than 0.7 were subjected to particle region division processing (S5) by a first-order differential filter. A Sobel filter was applied as a first-order differential filter, and a portion having a gradation change of 20 or more was adopted as an edge. The figures on the left and right sides of FIG. 12B are SEM images before and after the application of the first derivative filter, respectively. The particle region was divided by the edges detected by this treatment (white lines in the figure on the right side of FIG. 12B), and the aspect ratio and circularity of the divided particle regions were determined. When the aspect ratio of the divided particle region is 1.5 or less and the circularity is 0.7 or more, it is determined that the divided particle region corresponds to a single particle.

On the other hand, the particle region that does not satisfy the above conditions was subjected to water shed treatment (S6) as a candidate for linked particles. That is, for a particle region in which an edge cannot be detected in the particle region and is not divided as a result, and a particle region having an aspect ratio of more than 1.5 or a circularity of less than 0.7 among the divided particle regions. , Water shed treatment was performed. Multiple markers were set in each of these particle regions and the watershed was explored by the method described above. When the difference between the minimum gradation of the obtained watershed and the gradation of the marker was 40 or less, it was determined that these particle regions corresponded to single particles. As a result, in the particle region division processing, at least a part of the particle region corresponding to the metal particle determined to be a candidate for connected particles could be treated as a particle region corresponding to a single particle.

On the other hand, the expansion treatment (S7) was performed on the particle region where the difference between the minimum gradation of the watershed and the gradation of the marker was more than 40. The particle region determined to be not covered by other particle regions by this treatment was determined to be connected particles.

Subsequently, the convex hull deformation treatment (S8) was performed on the particle region determined to be covered with other particle regions by the expansion treatment. Here, the convex hull deformation process was performed using the quick full method. The left and right figures of FIG. 13 show SEM images before and after the expansion treatment, respectively. As shown in FIG. 13, the particle region (particle region surrounded by a circle) corresponding to the metal particles judged to be candidates for connecting particles because they are single particles but covered with other metal particles is By performing the convex package deformation treatment, it was possible to treat it as a particle region corresponding to a single particle. The circularity of the particle region after the convex package deformation was obtained, and it was determined that the particle region having a circularity of 0.6 or more corresponds to a single particle and the particle region having a circularity of less than 0.6 corresponds to a connected particle.

In this embodiment, it is determined that the particle region is covered with other particle regions by the expansion treatment, and the particle region has a circularity of less than 0.6 by the convex wrapping deformation treatment, and the minimum gradation and marker of the watershed by the watershed treatment. It was determined that the particle region having a difference in gradation of more than 40 and not being covered with other particle regions finally corresponds to the connected particles. The time required for evaluation by the above series of processes was about 30 seconds for each SEM image.

The results are summarized in Table 1. Table 1 also includes the results of visual evaluation of the five SEM images. In the visual evaluation, it took 30 to 60 minutes for each SEM image.

In the footnote of Table 1, the number of linked particles that agrees with the visual result is the number of metal particles that are visually determined to be linked particles among the linked particles detected by this evaluation method. As shown in Table 1, about 55% to 65% of the metal particles determined to be linked particles by this evaluation method are visually determined to be linked particles. Furthermore, from the results of the recovery rate, it was found that about 70% of the metal particles visually judged to be linked particles can be detected as linked particles even in this evaluation method. The above results suggest that by applying this evaluation method, it is possible to discriminate between simple substance particles and linked particles with high reliability in a dramatically shorter time than by visual observation.

2. 2. Example 2
In this embodiment, the results of individually extracting and evaluating some of the effects of the treatments S2 to S8 will be described. Specifically, the effect of the exclusion of the particle region in the deep part of the SEM image (S4), the effect of the expansion treatment (S7) and the convex hull deformation treatment (S8), and the exclusion of the particle region at the end of the SEM image (S3). The effect of was examined. In the second embodiment, the SEM image No. 1 used in the first embodiment. 1 to 5 were used. The results shown in each table are SEM image No. The average value of the results from 1 to 5 was used. In the "Processing" column of the table, "●" indicates the processing performed, and the blank indicates that the processing was not performed (the same applies hereinafter in Example 2). The criteria for determining single particles and linked particles were the same as in Example 1, and those remaining as linked particle candidates at the end of the final treatment were determined to be linked particles.

(1) Effect of Exclusion of Particle Region in Deep SEM Image (S4) Table 2 shows the results of examining the effect of the treatment S4. The conditions of each experiment are as shown in Table 2, but the treatments S2, S5, and S6 were performed in any of the experiments.

From the comparison between Experiments 1 and 2, it was confirmed that the average processing time was shortened by performing the processing S4. It was also found that the correct answer rate improved, although the recovery rate did not change.

(2) Effects of expansion treatment (S7) and convex hull deformation treatment (S8) Table 3 shows the results of examining the effects of the treatments S7 and S8. The conditions of each experiment are as shown in Table 3, but the treatments S2, S5, and S6 were performed in any of the experiments.

From the comparison between Experiments 3 and 4, it was confirmed that the average processing time was increased by performing the treatments S7 and S8, but the correct answer rate was greatly improved. There was no big difference in the recovery rate.

(3) Effect of Exclusion of Particle Region at the End of SEM Image (S3) Table 4 shows the results of examining the effect of the treatment S3. The conditions of each experiment are as shown in Table 4, but the treatments S2, S5, and S6 were performed in any of the experiments.

From the comparison between Experiments 5 and 6, it was found that the average processing time was shortened by performing the processing S3. It was also confirmed that the correct answer rate improved, although the recovery rate did not change.

The above results are not effective for the first time in this evaluation method by performing all of the treatments S1 to S8, and it is possible to efficiently perform powder evaluation even if some treatments are selectively performed. It is shown that.

As an embodiment of the present invention, those skilled in the art have appropriately added, deleted or changed the design of components based on the above-described embodiment, or added, omitted or changed the conditions of the present invention. As long as it has the gist of the above, it is included in the scope of the present invention. Of course, other effects different from those brought about by the embodiments described above, which are obvious from the description of the present specification or which can be easily predicted by those skilled in the art, are described in the present invention. It is understood that it is brought about by the invention.

100: SEM ,: 102: Network, 110: Evaluation server, 112: Application programming interface (API), 114: Control unit, 116: Input unit, 118: Output unit, 120: Transmission / reception unit, 122: Storage unit

Claims (11)

It is an evaluation method of a metal powder containing a plurality of metal particles, and the evaluation method is
Capturing a scanning electron microscope image of the metal powder,
Detecting the boundaries of metal particles using the threshold method in the scanning electron microscope image,
To remove the region where the gradation is equal to or less than the first threshold value from the scanning electron microscope image.
The aspect ratio and circularity of the first particle region surrounded by the boundary are calculated, and the metal particles corresponding to the first particle region are single particles based on the aspect ratio and circularity. An evaluation method comprising determining whether at least two fragment particles are linked particles. Processing the scanning electron microscope image with a first-order differential filter,
When the first particle region of the metal particles determined to be connected particles is divided into two or more regions by the first-order differential filtering process, the aspect ratio and circularity of the divided regions are calculated, and The first aspect of claim 1, further comprising determining whether the metal particles corresponding to the divided regions are single particles or linked particles based on the aspect ratio and circularity of the divided regions. Evaluation method. Inverting the gradation of the scanning electron microscope image,
The gradation-inverted scanning electron microscope image is subjected to watershed processing using the local minimum point of gradation as a marker, and in the first particle region corresponding to the metal particles determined to be connected particles. When the difference between the minimum gradation of the diversion ridge obtained by the water shed treatment and the gradation of the marker is equal to or less than the second threshold value, it is determined that the metal particles determined to be connected particles are single particles. The evaluation method according to claim 1, further comprising the above. The first particle region of the metal particles determined to be connected particles is expanded to obtain a first expanded region.
Of the other particle regions that overlap with the first expansion region, the portion that overlaps with the first expansion region is expanded to obtain a second expansion region.
To obtain the maximum gradation G ₁ in the scanning electron microscope image of the portion of the first particle region of the metal particles determined to be connected particles that overlaps with the second expansion region.
When the maximum gradation G ₂ of the other particle region is obtained and the maximum gradation G ₁ is lower than the maximum gradation G ₂ , the metal determined to be a connecting particle in the scanning electron microscope image. The evaluation method according to claim 1, further comprising determining that the particles are partially covered with the metal particles corresponding to the other particle regions. When the maximum gradation G ₁ is lower than the maximum gradation G ₂ , the first particle region of the metal particles determined to be connected particles is convex-hull-deformed, and the convex-hull-deformed first. The evaluation method according to claim 4, further comprising determining that the metal particles corresponding to the first particle region, which are convexally deformed based on the circularity of the particle region, are single particles or linked particles. .. On the computer
Detecting the boundaries of metal particles using the threshold method in a scanning electron microscope image of metal powder,
To remove the region where the gradation is equal to or less than the first threshold value from the scanning electron microscope image.
The aspect ratio and circularity of the first particle region surrounded by the boundary are calculated, and the metal particles corresponding to the first particle region are single particles based on the aspect ratio and circularity. An evaluation program for evaluating metal powders that performs the determination of whether at least two fragment particles are linked particles. Processing the scanning electron microscope image with a first-order differential filter,
When the first particle region of the metal particle determined to be a connecting particle is divided into two or more regions by the first derivative filtering process, the aspect ratio and circularity of the divided regions are calculated, and the circularity is calculated. A claim that further causes the computer to determine whether the metal particles corresponding to the divided regions are single particles or linked particles based on the aspect ratio and circularity of the divided regions. The evaluation program according to 6. Inverting the gradation of the scanning electron microscope image,
The gradation-inverted scanning electron microscope image is subjected to watershed processing using the local minimum point of gradation as a marker, and in the first particle region corresponding to the metal particles determined to be connected particles. When the difference between the minimum gradation of the diversion ridge obtained by the water shed treatment and the gradation of the marker is equal to or less than the second threshold value, it is determined that the metal particles determined to be connected particles are single particles. The evaluation program according to claim 6, further causing the computer to perform the above-mentioned work. The first particle region of the metal particles determined to be connected particles is expanded to obtain a first expanded region.
Of the other particle regions that overlap with the first expansion region, the portion that overlaps with the first expansion region is expanded to obtain a second expansion region.
To obtain the maximum gradation G ₁ in the scanning electron microscope image of the portion of the first particle region of the metal particles determined to be connected particles that overlaps with the second expansion region.
When the maximum gradation G ₂ of the other particle region is obtained and the maximum gradation G ₁ is lower than the maximum gradation G ₂ , the metal determined to be a connecting particle in the scanning electron microscope image. The evaluation program according to claim 6, wherein the computer further performs a determination that the particles are partially covered by the metal particles corresponding to the other particle region. When the maximum gradation G ₁ is lower than the maximum gradation G ₂ , the first particle region of the metal particles determined to be connected particles is convexly packaged and deformed, and the convexly packaged first. 9. The computer further determines that the metal particles corresponding to the first particle region, which are convexally deformed based on the circularity of the particle region, are single particles or connected particles. Described evaluation program. A computer-readable storage medium in which the evaluation program according to claim 6 is recorded.

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