Evaluation method for metal powders

Abstract

To provide a metal powder evaluation method that enables effective evaluation of aggregation of metal powder.SOLUTION: A metal powder evaluation method of the present invention is for evaluating the presence or absence of aggregation in magnetic metal powder, the method comprising analyzing the metal powder by electron spectroscopy and determining the presence or absence of magnetism in the metal powder on the basis of a result of he analysis.SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a method for evaluating whether or not aggregation of metal powder has occurred.

Background Art

[0002] Metal powders typified by nickel powder are sometimes used as electrode materials for multilayer ceramic chip capacitors (MLCCs) for computers including multifunctional mobile phones, and materials for nickel-metal hydride batteries and lithium-ion batteries because of their excellent heat dissipation characteristics and electrical characteristics.

[0003] Among these, a multilayer ceramic chip capacitor has a structure in which dielectric layers and internal electrode layers are alternately laminated, and external electrodes are provided at both ends thereof. Here, a material mainly composed of a ceramic with a high dielectric constant such as barium titanate is used for the dielectric layer. On the other hand, powders of various metals or alloys can be used for the internal electrode layer. In particular, in recent years, the development of multilayer ceramic chip capacitors using fine nickel powder for the internal electrode layer has been promoted.

[0004] The internal electrode layer of a multilayer ceramic chip capacitor is formed by heating a metal powder paste provided between green sheets that will become dielectric layers, removing the organic components of the paste, and sintering the metal powder. At this time, if aggregation is included in the metal powder, such aggregation may cause a short circuit between electrodes by piercing through the dielectric layer. Particularly in such applications, it is required to minimize the aggregation of metal powder as much as possible.

[0005] In relation to this, in Patent Document 1, it is inferred that "due to the polarity of the OH groups of nickel hydroxide (for example, Na(OH)2) contained in the oxide film of metal nickel powder, the powders may aggregate and the dispersibility may be impaired." And "metal nickel powder having an oxygen content of 0.1 to 2.0% by weight and having no absorption peak at a wave number of 3600 to 3700 cm -1 is proposed.

[0006] Furthermore, Patent Document 2, based on the finding that "in addition to hydroxides on the surface of metallic nickel powder, the presence of trace amounts of silica causes nickel powder to aggregate and generate coarse particles," states that "the average particle size is 10 nm to 1000 nm, and the measurement is taken at 1200 cm in a Fourier transform infrared spectrophotometer equipped with an MCT detector." -1 From 900cm -1 The S / N ratio (X) of the absorption spectral signal and 3700 cm⁻¹ -1 From 3600cm -1 The disclosure describes a metallic nickel powder characterized in that the signal-to-noise ratio (Y) of the absorption spectral signal is Y ≤ -1.0X + 23.0. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2000-045002 [Patent Document 2] International Publication No. 2013 / 151172 [Overview of the project] [Problems that the invention aims to solve]

[0008] While methods such as those described in Patent Documents 1 and 2, which use infrared absorption spectroscopy to evaluate the aggregation of metal powders based on the presence of OH groups and silicic acid, are somewhat useful, they are not sufficient to determine the presence or absence of further minute aggregations.

[0009] Furthermore, elemental analysis using characteristic X-rays with electron probe microanalyzers (EPMA) and scanning electron microscopes (SEM) may not effectively evaluate aggregation if the constituent elements between aggregated and unaggregated metal particles are the same. In addition, since the characteristic X-rays excited by the electron beam in these elemental analyses have no charge, it is difficult to confirm the presence or absence of an electromagnetic field using characteristic X-rays, which are unaffected by disturbances in electric or magnetic fields.

[0010] This invention aims to solve these problems, and its objective is to provide a method for evaluating metal powders that can effectively evaluate the aggregation of metal powders. [Means for solving the problem]

[0011] After diligent research, the inventor discovered that a certain metal powder is magnetized, and that this magnetism affects the aggregation of the metal powder.

[0012] Based on the above findings, the present invention provides a method for evaluating metal powder, which evaluates whether or not aggregation of metal powder has occurred, wherein the metal powder is a magnetic metal powder. The particle size of the aforementioned metal powder is 10 nm to 1000 nm. The metal powder is analyzed by Auger electron spectroscopy, and the presence or absence of magnetism is determined from the analysis results. death , In analyzing the metal powder, a sample stage is used in which the orientation of the metal powder relative to an electron detector that detects electrons emitted from the metal powder can be changed. Multiple analysis steps are performed in which the orientation of the metal powder on the sample stage is changed relative to the electron detector. The analysis steps include a first analysis step and a second analysis step. When the orientation of the metal powder on the sample stage relative to the electron detector in the first analysis step is set to 0°, the orientation of the metal powder on the sample stage relative to the electron detector in the second analysis step is set to 90°. The first spectrum obtained as an analysis result in the first analysis step and the second analysis step are used to obtain the The process includes a spectrum comparison step in which the first spectrum and the second spectrum obtained as an analysis result are compared, and in the spectrum comparison step, the comparison of the first spectrum and the second spectrum is performed in the energy region where the kinetic energy value is 50 eV or less, and in the spectrum comparison step, it is confirmed whether the difference between the kinetic energy value at the rising position of the electron detection intensity in the first spectrum and the kinetic energy value at the rising position of the electron detection intensity in the second spectrum is 1.0 eV or more, and if the difference in the kinetic energy values ​​at the rising position is 1.0 eV or more, it is determined that the metal powder is magnetized. That is the case.

[0020] The aforementioned metal powder can be, for example, nickel powder. [Effects of the Invention]

[0021] According to the metal powder evaluation method of this invention, the aggregation of metal powder can be effectively evaluated. [Brief explanation of the drawing]

[0022] [Figure 1] This is an SEM image of nickel powder A in the example. [Figure 2] This is an SEM image of nickel powder B in the example. [Figure 3] This is an SEM image of nickel powder C in the example. [Figure 4] This is a schematic diagram showing how the orientation of the sample relative to the electron detector (analyzer) was changed during the AES evaluation in the example. [Figure 5] This graph shows the spectrum of the AES evaluation analysis results for the copper plate in the example. [Figure 6] This is a magnified view of a portion of Figure 5. [Figure 7] It is a graph showing the spectrum of the analysis result of AES evaluation for nickel powder B of the example. [Figure 8] It is a graph obtained by enlarging a part of FIG. 7. [Figure 9] It is a graph showing the rising position in each spectrum of FIG. 8. [Figure 10] It is a graph showing the spectrum of the analysis result of AES evaluation for nickel powder C of the example. [Figure 11] It is a graph showing the spectrum of the analysis result of AES evaluation for demagnetized nickel powder C2 by heating in the example. [Figure 12] It is a graph showing a method for obtaining the rising position of the electron detection intensity in the spectrum of the analysis result of AES evaluation.

Mode for Carrying Out the Invention

[0023] Hereinafter, embodiments of this invention will be described in detail. The method for evaluating metal powder according to one embodiment of this invention is a method for evaluating whether or not aggregation of metal powder has occurred. Here, the metal powder is a magnetic metal powder, and the metal powder is analyzed by electron spectroscopy analysis, and from the analysis result obtained thereby, the presence or absence of magnetism of the metal powder is determined. Thereby, even for fine metal powders having a relatively small particle size, it is possible to effectively evaluate whether or not aggregation is included therein.

[0024] (Metal powder) The metal powder to be evaluated is a magnetic metal powder. Specifically, the metal powder is at least one selected from the group consisting of nickel powder, iron powder, cobalt powder, nickel powder, and gadolinium powder as single metals. In the applications of electrode materials for multilayer ceramic chip capacitors (MLCCs) and materials for nickel-metal hydride batteries and lithium-ion batteries as described above, the evaluation target may be nickel powder.

[0025] Metal powder may contain sulfur, for example, to suppress activation during the manufacturing of multilayer ceramic chip capacitors. The sulfur content in the metal powder is preferably 5000 ppm by mass or less, more preferably 3000 ppm by mass or less, and particularly preferably 2000 ppm by mass or less. The lower limit of the sulfur content is not particularly limited, but it may be the detection limit of the component analyzer or a value smaller than the detection limit.

[0026] The particle size of the metal powder is preferably 10 nm to 1000 nm, preferably 1 nm to 1000 nm, preferably 0.5 nm to 1000 nm, and preferably 0.1 nm to 1000 nm. Such fine metal powder can be mixed with an organic solvent, plasticizer, organic binder, etc., to form a metal powder paste, which can be suitably used to form the internal electrode layer of a multilayer ceramic chip capacitor. However, since fine metal powder is prone to aggregation, it is effective to evaluate the presence or absence of aggregation using the evaluation method described here.

[0027] The particle size mentioned above refers to the average diameter of the smallest inclusion circle that encloses each metal particle in a scanning electron microscope (SEM) image obtained by observing the metal powder with an SEM. To determine the particle size, image analysis software can be used on an SEM image containing a relatively large number of metal particles, for example, about 40,000. The image analysis software is not particularly limited as long as it conforms to the JIS standard Z8827-1 and can perform evaluation analysis of the major axis, minor axis, aspect ratio, etc., of the primary particle diameter. One example is Mac View from Mountec. Software that can perform automatic measurement due to the large number of particles is preferable, and in the case of spherical metal particles, it recognizes the three points of the triangle inside and automatically recognizes the circle passing through these three points as the particle. Furthermore, it is even preferable to have software that incorporates a manual analysis function that can directly trace and identify along the outer contour of the metal particle, in preparation for analyzing irregularly shaped metal particles or metal particles that are connected to each other, which are sometimes difficult to distinguish with software that can perform automatic measurement.

[0028] The metal powder, such as nickel powder, used in the evaluation method of this embodiment can be manufactured by known methods such as the gas phase method or the liquid phase method, or it can be a commercially available product.

[0029] (electron spectroscopy) The metal powders described above are subjected to analysis by electron spectroscopy to evaluate whether or not aggregation occurs.

[0030] Electron spectroscopy is a technique that involves irradiating a sample with an electron beam or X-ray and detecting the emitted electrons (secondary electrons) to perform energy analysis. Unlike characteristic X-rays detected by electron probe microanalyzers (EPMA) or scanning electron microscopes (SEM), the electrons detected here have an electric charge. Therefore, the Lorentz force caused by the magnetism of magnetic metal powder significantly alters the spectrum of the analysis result. This makes it possible to determine whether or not the metal powder is magnetic.

[0031] In elemental analysis using electron probe microanalyzers and scanning electron microscopes, the detection target is characteristic X-rays, so the presence of magnetism in the sample does not affect the spectrum. Furthermore, in general, when electron beam techniques are applied to magnetic samples, the irradiated electrons can be deflected by the Lorentz force, making analysis difficult. Especially when magnetism is locally concentrated, even electrons accelerated by high voltage can be deflected by the Lorentz force. This can make focusing difficult and distort the image when observing magnetic samples.

[0032] The inventor focused on the fact that electron spectroscopy allows for the observation of electric charges that cannot be observed with electron probe microanalyzers or scanning electron microscopes. As a result, they gained new insights, finding that if metal powders possess a weak magnetism that does not cause image distortion with electron probe microanalyzers or scanning electron microscopes, this magnetism can cause aggregation of the metal powders. Based on this finding, it becomes possible to evaluate whether or not aggregation is occurring based on the presence or absence of magnetism in metal powders, which can be determined by electron spectroscopy.

[0033] Generally, magnetic force microscopy (MFM) is used to measure magnetic fields in minute regions. In MFM, magnetic attraction and repulsion are detected by the deflection and phase difference of a magnetic probe brought close to the sample. The spatial resolution is comparable to that of electron microscopes, but currently, due to limitations such as the flatness and size of the sample, it cannot be applied to samples with uneven surfaces, such as metal powders. In contrast, with electron spectroscopy, charged electrons emitted from magnetized metal powder are subjected to the Lorentz force, causing a change in the spectrum, so the presence or absence of magnetism can be effectively determined even in metal powders with uneven surfaces.

[0034] Examples of electron spectroscopy include photoelectron spectroscopy (specifically, X-ray photoelectron spectroscopy (XPS), vacuum ultraviolet photoelectron spectroscopy (UPS), etc.) and Auger electron spectroscopy (AES). X-ray photoelectron spectroscopy involves irradiating a sample with X-rays and capturing the photoelectrons emitted as the sample is ionized. Vacuum ultraviolet photoelectron spectroscopy uses vacuum ultraviolet light instead of X-rays.

[0035] Auger electron spectroscopy involves irradiating or scanning a sample with an electron beam ranging from a few eV to a few keV in an ultra-high vacuum. This causes Auger electrons, each with an energy specific to the element, to be emitted from the extreme surface of the sample. Auger electron spectroscopy uses an electron detector (electrostatic hemispherical analyzer) to precisely detect electrons within a specific energy range with high energy resolution, enabling qualitative and quantitative analysis by accurately measuring the peak intensity of selected Auger electrons.

[0036] Generally, secondary electrons emitted from a sample have relatively low energy and travel slower than the irradiated electrons (primary electrons), making them highly susceptible to the effects of magnetization if the sample is magnetized. In contrast, Auger electron spectroscopy inherently analyzes Auger electrons (secondary electrons) with high energy resolution, allowing for sensitive detection of the effects of the Lorentz force.

[0037] When performing analysis using Auger electron spectroscopy, it is preferable to use an Auger electron spectroscopy analyzer equipped with a field emission electron gun, a high-precision eucentric sample stage that enables the analysis of insulators, and a floating ion gun. This allows for highly versatile analysis of the compositional and chemical information of metal and insulating samples.

[0038] (Analysis process) When analyzing metal powder using the electron spectroscopy method described above, it is preferable to perform multiple analysis steps, changing the orientation of the metal powder in relation to the electron detector that detects electrons emitted from the metal powder.

[0039] In the case of non-magnetic metal powders, secondary electrons emitted from the powder during analysis are not affected by any magnetism. Therefore, even electrons with low kinetic energies of 0 eV to 50 eV can be detected by the electron detector without their trajectories being bent. As a result, even if the intensity differs, the energy spectra obtained will have almost the same or similar shapes. On the other hand, in the case of magnetic metal powders, secondary electrons emitted from the powder during analysis are affected by the Lorentz force originating from the sample's magnetism (magnetic flux density). Therefore, changing the orientation of the metal powder between analysis steps significantly bends the trajectories of electrons, especially those with low kinetic energies of 0 to 50 eV. This causes a change in the amount of electrons captured by the electron detector. As a result, differences in spectral shape and the rise positions of major secondary electron peaks can be observed in each of the multiple analysis steps. From this, it is possible to more accurately determine whether or not the metal powder is magnetic. Based on this, it is possible to evaluate whether or not aggregation is occurring in the metal powder.

[0040] In particular, with Auger electron spectroscopy, it has been found that when using high energy resolution of 0.1% or less, spectra with sharp peaks can be obtained in multiple analysis steps, depending on the environment (chemical state, etc.) of the metal powder.

[0041] More specifically, the analysis process preferably involves at least a first and second analysis step, where the orientation of the metal powder relative to the electron detector in the first analysis step is set to 0°, and the orientation of the metal powder relative to the electron detector in the second analysis step is set to 90°. By rotating the orientation of the metal powder in the second analysis step within this range relative to the orientation of the metal powder in the first analysis step, the magnetism of the metal powder can be determined with even higher accuracy.

[0042] To perform multiple analysis steps with altered metal powder orientations as described above, it is preferable to use an electron spectrometer equipped with an electron detector and a sample stage capable of changing the orientation of the sample relative to the electron detector. The sample stage is preferably one that allows for free rotation and control of the sample orientation within 360°.

[0043] For example, the analysis process can be performed using an Auger electron spectrometer equipped with a one-sided detection electron detector, with an energy resolution of ΔE / E = 0.5% at 10 kV and 10 nA. There are no particular restrictions on the acceleration voltage or irradiation current, but below 100 V, there is a risk of being affected by the magnetic field of the metal powder sample. It is desirable to use an electron beam of 1 kV or higher.

[0044] (Spectral comparison process) After the analysis process, which includes the first and second analysis steps, a spectrum comparison step can be performed to compare the first spectrum obtained as an analysis result in the first analysis step with the second spectrum obtained as an analysis result in the second analysis step. The spectrum can be represented on a graph with kinetic energy on the horizontal axis and electron detection intensity on the vertical axis.

[0045] As mentioned earlier, in the case of magnetized metal powder, the first and second spectra obtained in the first and second analysis steps, respectively, in which the orientation of the metal powder is changed, will not be similar in shape but will have different shapes. By performing a spectral comparison step that compares these first and second spectra, it is possible to infer whether or not the metal powder is magnetic, and consequently whether or not it is agglomerating.

[0046] In the spectral comparison step, it is preferable to compare the first and second spectra in the energy region where the kinetic energy value is 50 eV or less, and even more so, 30 eV or less. This is because, depending on various conditions, the change in the spectrum due to the presence or absence of magnetism in the metal powder is almost negligible in the energy region where the kinetic energy value is relatively high, but tends to become significant in the energy region below 50 eV.

[0047] Furthermore, in the energy region below 50 eV, the spectrum contains true secondary electron peaks. These peaks are affected by the bending of electron orbits depending on the magnetism of the metal powder, reducing the amount of electrons captured by the electron detector. As a result, differences in kinetic energy values ​​are observed between the first and second spectra, in terms of spectral shape and the rising position of the main secondary electron peaks.

[0048] The rising point of the electron detection intensity in spectra such as the first spectrum and the second spectrum can be determined as shown in Figure 12. In other words, in many cases, spectra composed of numerous measurement points have a shape in which the electron detection intensity increases and rises as the kinetic energy value increases from 0 eV towards the peak. At the rising point of such a spectrum, a rising line is drawn passing through three or more measurement points that are closest to the position of half (Pmax / 2) of the maximum peak intensity (Pmax) of the initial peak that first appears on the side of low kinetic energy values, and these three or more measurement points lie on the same straight line. The intersection of this rising line and the X-axis is defined as the rising point of the spectrum.

[0049] In the spectrum comparison step, it is preferable to check whether the difference in kinetic energy values ​​at the rising point of the electron detection intensity in each spectrum (the difference between the kinetic energy value at the rising point of the first spectrum and the kinetic energy value at the rising point of the second spectrum) is 1.0 eV or more. If the difference in kinetic energy values ​​at these rising points is 1.0 eV or more, it can be considered that the metal powder is magnetized and that agglomeration is present in the metal powder. On the other hand, if it is less than 1.0 eV, it can be determined that the metal powder is substantially not magnetized and that almost no agglomeration has occurred.

[0050] As described above, by analyzing the metal powder and determining the presence or absence of magnetism from the analysis results, it is possible to effectively and easily evaluate whether or not aggregation of the metal powder has occurred. Metal powder that is evaluated as not having aggregated can be suitably used as an electrode material for multilayer ceramic chip capacitors. This is because such metal powder does not contain even minute aggregates, thus suppressing the occurrence of short circuits between electrodes due to aggregation. [Examples]

[0051] Next, we experimentally implemented the metal powder evaluation method of this invention and confirmed its effects, which are described below. However, this explanation is for illustrative purposes only and is not intended to be limiting.

[0052] As a standard, we prepared a non-magnetic copper plate and three types of nickel powders A to C that were presumed to retain magnetism. We then performed the following observations and evaluations on these nickel powders A to C.

[0053] (SEM observation) For each nickel powder A to C, to prepare microscopic observation samples, tap water was filtered through a 0.3 μm filter and activated carbon manufactured by Organo Corporation. The filtered water was then sequentially passed through an Organo Corporation G-10C cartridge pure water purifier and a 0.1 μm filter to obtain a slurry with a concentration of approximately 50% by mass. One spoonful of this nickel powder slurry was added to the upper edge of a Matsunami Glass Industry Co., Ltd. white-green polished No. 2 slide (size 76 mm x 26 mm, thickness 1.0 mm to 1.2 mm) using a micro-spatula. After adding the nickel powder slurry to the slide, the slurry was spread to approximately 5 cm with uniform speed and force using an Eriksen 360 film applicator (4-sided type) with a coating thickness of 30 μm. Finally, the film slurry was air-dried until the water in the coating film was completely dry to obtain the microscopic observation sample.

[0054] Observations were performed on the above-mentioned microscopic samples using a JEOL Ltd. scanning electron microscope (SEM) JSM-6060 under conditions of an acceleration voltage of 20kV and an observation magnification of 500x. SEM images of each nickel powder A to C are shown in Figures 1 to 3. The presence or absence of aggregation, as determined by electron microscopy observation, is shown in Table 1.

[0055] (Filtration evaluation) For each nickel powder A to C, 100g of nickel powder was added to 1900g of pure water to prepare a 5% by mass nickel powder slurry. Next, suction filtration was performed using a 1μm mesh filter. After that, the nickel powder remaining on the filter was dried at 120°C for 30 minutes under an inert gas atmosphere, its weight was measured, and the pass-through rate ((100g - weight of metallic nickel powder on the filter in g) / 100(g)) was calculated to evaluate the aggregation of the metal powder. The results are shown in Table 1. Here, samples with a pass-through rate of 90% or higher are marked with "○", and those with a pass-through rate of less than 90% are marked with "×".

[0056] [Table 1]

[0057] (AES rating) For the AES evaluation, a standard copper plate measuring approximately 1 cm square and 2 mm thick was fixed in place with double-sided tape. For nickel powders A to C, a diamond cutter was used to make incisions in the substrate using SW, and the nickel powder was rubbed into these incisions. After that, any excess nickel powder was blown away with nitrogen gas to create the AES evaluation sample.

[0058] Auger electron spectroscopy was performed on the above AES evaluation samples using a one-sided detection AES (Auger electron spectrometer JAMP-9510F, manufactured by JEOL Ltd.) under two conditions: when the sample was directly facing the electron detector (analyzer) as shown in Figure 4, and when it was rotated 90° from that position. The acceleration voltage was set to 10kV, the irradiation current to 10nA, and the energy resolution to ΔE / E = 0.5%. Analysis was performed in 1eV steps over the energy range of 0 to 2000eV. The dwell time was 20ms, and the number of integrations was 10.

[0059] Figures 5 and 6 show the spectra of a nonmagnetic copper plate when the sample orientation was changed to 0° and 90° using AES. As can be seen in Figures 5 and 6, the peak waveform of the copper plate does not change even when the sample orientation is changed to 0° and 90°.

[0060] Figures 7, 8, and 10 show the spectra of nickel powders B and C when the sample orientation was changed to 0° and 90° using AES, respectively. For reference, Figure 9 shows rising lines drawn on each spectrum of nickel powder B in Figure 8 to indicate the rising point. As can be seen from Figures 7 to 10, for both nickel powders B and C, a characteristic peak in electron intensity was observed in the energy region where the kinetic energy value is 50 eV or less, regardless of whether the sample orientation was 0° or 90°.

[0061] In nickel powder B, as shown in Figures 8 and 9, the rise point (the rise point of the second spectrum) when the sample orientation was changed to 90° was shifted by approximately 2.9 eV toward the lower kinetic energy value compared to the rise point (the rise point of the first spectrum) when the sample orientation was 0°. Furthermore, the spectra of nickel powder B were not similar in shape. Furthermore, as shown in Figure 10, for nickel powder C, the difference in kinetic energy values ​​at the rising position when the sample orientation was 0° and when it was 90° was approximately 3.8 eV. Also, the spectra of nickel powder C were not similar in shape. Considering the filtration evaluation results shown in Table 1, the slope of the secondary electron rise is significantly different in nickel powder B, suggesting that the influence of magnetism, which cannot be confirmed by SEM observation, is significant.

[0062] (Confirmation of the effects of magnetism) Nickel powder C1 and nickel powder C2, obtained by demagnetizing the above-mentioned nickel powder C using the two methods described below, were subjected to the same AES evaluation and filtration evaluation.

[0063] For demagnetization, we employed two methods: one using a demagnetizer, as described below, and another using heating.

[0064] In the method using a demagnetizer, a switch was used as a substrate, and cuts were made with a diamond cutter. Next, nickel powder (nickel powder C) was rubbed into the cuts and placed in a plastic bag. Finally, a demagnetizer manufactured by Hozan Corporation, HC-33 (maximum magnetic flux density 68 mT), was used to gradually move the demagnetizer away from the plastic bag containing the nickel powder, thereby holding it over the bag to obtain demagnetized nickel powder (nickel powder C1).

[0065] In the heating method, a switch was used as a substrate, and cuts were made with a diamond cutter. Next, nickel powder (nickel powder C) was rubbed into the cuts. Then, the stainless steel tray containing the nickel powder was heated in a dryer to 400°C (above the Curie temperature). After reaching 400°C, the temperature was maintained and heating continued for 30 minutes. After heating was completed, the temperature was lowered to room temperature, and finally the stainless steel tray containing the nickel powder was removed from the dryer to obtain demagnetized nickel powder (nickel powder C2). Note that the Curie temperature of nickel is approximately 358°C, and once heated to a temperature above the Curie temperature, it will not return to being magnetic even when returned to room temperature.

[0066] Figure 11 shows the spectrum of the AES evaluation analysis results for nickel powder C2 that has been demagnetized by heating. Compared with the spectrum of nickel powder C before demagnetization, the spectrum of nickel powder C2 after demagnetization shows no change in the number of electrons with energies of 100 eV or more, which remains at 0.0 eV in all cases, and the spectra are similar in shape.

[0067] Furthermore, when the same filtration evaluation as described above was performed on each nickel powder C1 and C2, it was confirmed that all nickel powders C1 and C2 had a pass-through rate of 95% or higher, resulting in a "◎" rating, and that no minute aggregation due to magnetism occurred.

[0068] From the above, it has been found that the metal powder evaluation method of this invention can effectively evaluate the aggregation of metal powder.

Claims

1. A method for evaluating whether or not metal powder aggregation has occurred, The metal powder is a magnetic metal powder, and the particle size of the metal powder is 10 nm to 1000 nm. The metal powder is analyzed by Auger electron spectroscopy, and the presence or absence of magnetism in the metal powder is determined from the analysis results. In analyzing the metal powder, a sample stage capable of changing the orientation of the metal powder relative to an electron detector that detects electrons emitted from the metal powder is used, and multiple analysis steps are performed with respect to the electron detector, changing the orientation of the metal powder on the sample stage. The aforementioned analysis process includes a first analysis process and a second analysis process, When the orientation of the metal powder on the sample stage relative to the electron detector in the first analysis step is set to 0°, the orientation of the metal powder on the sample stage relative to the electron detector in the second analysis step is set to 90°. The process includes a spectrum comparison step of comparing a first spectrum obtained as a result of the analysis in the first analysis step with a second spectrum obtained as a result of the analysis in the second analysis step. In the spectrum comparison step, the first spectrum and the second spectrum are compared in the energy region where the kinetic energy value is 50 eV or less. In the spectrum comparison step, it is confirmed whether the difference between the kinetic energy value at the rising point of the electron detection intensity in the first spectrum and the kinetic energy value at the rising point of the electron detection intensity in the second spectrum is 1.0 eV or greater. A method for evaluating metal powder, in which it is determined that the metal powder is magnetized if the difference in kinetic energy values ​​at the aforementioned rising position is 1.0 eV or more.

2. The method for evaluating metal powder according to claim 1, wherein the metal powder is nickel powder.

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