JP2014021060A - Measuring method for particle size distribution of fine particle in metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure a particle size distribution of fine particles even when a distribution width of particle sizes of the fine particles is wide.SOLUTION: The measuring method for a particle size distribution of fine particles in metal includes an extraction step of extracting fine particles in a metallic material, a dispersion step of preparing a fine particle dispersion solution by dispersing the fine particles extracted in the extraction step in a liquid; a classification step of classifying the fine particles in the fine particle dispersion solution by particle sizes by applying centrifugal force to the fine particle dispersion solution prepared in the dispersion step; and a calculation step of calculating volume fractions of the fine particles by the particle sizes classified in the classification step. Consequently, even when a distribution width of the particle sizes of the fine particles is wide, the particle size distribution of the fine particles can be precisely measured.

Description

  The present invention relates to a method for measuring the particle size distribution of fine particles in a metal, which measures the particle size distribution of fine particles in a metal material.

  In recent years, in various technical fields, development of products and technologies using unique functions of fine particles has been actively performed. This is because even if the material is the same, the particle size becomes small, so that the activity of the particle surface is remarkably changed and a new function can be expected. The performance of products and technologies that utilize the unique function of fine particles is closely related to the particle size of the fine particles. For this reason, development of techniques for measuring the particle size distribution of fine particles has been actively conducted along with the development of fine particle materials. Patent Document 1 discloses a method for measuring the particle size distribution of fine particles. Patent Document 2 discloses a method for evaluating fine particles having a large particle size and fine particles having a small particle size by using independent optical systems.

Japanese Patent Laid-Open No. 02-96636 JP-A-63-265139

  By the way, in the steel field, material development that actively utilizes the function of fine precipitates existing in steel is being actively conducted. This includes steel sheets for automobiles in which strength and tension are improved by dispersing fine precipitates in steel, grain-oriented electrical steel sheets that utilize fine precipitates in steel as inhibitor precipitates, and the like. In such a steel material, since the amount and particle size of the precipitates directly affect the quality of the steel material, it is necessary to measure the particle size distribution of the precipitates. In any steel material, the particle diameter of the precipitate that is present most frequently is about several nanometers to several tens of nanometers. Therefore, it can be sufficiently measured by using, for example, the method disclosed in Patent Document 1.

  However, according to the study of the inventor of the present invention, the particle size distribution of the precipitates measured using the method described in Patent Document 1 and observed using an electron microscope such as SEM (Scanning Electron Microscope). There was a gap between the particle size distribution of the precipitates. Therefore, the inventor of the present invention considered that this separation is caused by the wide distribution width of the particle size of the precipitate. That is, the particle size distribution of the precipitate observed with an electron microscope is a distribution state of the number of particles, that is, a number distribution, whereas the method described in Patent Document 1 is used to measure light as a probe. The particle size distribution of the resulting precipitate is a distribution of light scattering intensity.

  In general, the light scattering intensity is proportional to the sixth power of the particle size of the precipitate. For this reason, especially when the distribution range of the particle size is large or when the distribution state is not a normal distribution but a complicated distribution such as a plurality of peaks, the contribution of particles having a large particle size to the scattering intensity distribution is The difference between the number distribution and the scattered intensity distribution becomes significant. As a result, the distribution state of the scattering intensity shifts to the larger particle size as compared with the number distribution, and in some cases, the difference in the average particle size in the number distribution may not be detected. In particular, since the distribution range of the size of the precipitates in the steel material is wide, it is difficult to accurately measure the particle size distribution state of the precipitates.

  The present invention has been made in view of the above problems, and its object is to make fine particles in metal capable of accurately measuring the particle size distribution of fine particles even when the particle size distribution range of the fine particles is wide. It is to provide a diameter distribution measuring method.

  In order to solve the above problems and achieve the object, a method for measuring the particle size distribution of fine particles in a metal according to the present invention includes an extraction step for extracting fine particles in a metal material, and the fine particles extracted by the extraction step as a liquid. Dispersion step of preparing a fine particle dispersion solution by dispersing in, and a classification step of classifying the fine particles in the fine particle dispersion solution for each particle size by applying centrifugal force to the fine particle dispersion solution prepared by the dispersion step And a calculating step of calculating a volume fraction of fine particles for each particle size classified by the classification step.

  In the method for measuring the particle size distribution of fine particles in metal according to the present invention, in the above invention, the classification step continuously classifies the fine particles in the fine particle dispersion solution for each particle size using a field flow fractionation method. The calculation step includes introducing fine particles continuously classified by the field flow fractionation method into an inductively coupled plasma emission spectrometer or an inductively coupled plasma mass spectrometer, thereby forming fine particles for each particle size. The step of calculating the volume fraction of is included.

  The particle size distribution measuring method for fine particles in metal according to the present invention is characterized in that, in the above invention, the calculating step includes a step of calculating a number distribution of fine particles from a volume fraction of fine particles for each particle size. .

  The particle size distribution measuring method for fine particles in metal according to the present invention is characterized in that, in the above invention, the particle size of the fine particles to be measured is 1 μm or less.

  According to the method for measuring the particle size distribution of fine particles in metal according to the present invention, the particle size distribution of the fine particles can be accurately measured even when the particle size distribution range of the fine particles is wide.

FIG. 1 is a diagram showing the results of measuring the distribution state of fine particles in a mixed solution using a dynamic light scattering particle size distribution meter. FIG. 2 is a diagram showing the results of measuring the particle size of the suspended component and the sedimented component with a dynamic light scattering type particle size distribution meter after separating the mixed solution using a centrifuge. FIG. 3 is a schematic diagram illustrating a configuration example of the electrolysis apparatus. FIG. 4 is a diagram showing the number distribution of Ti precipitates measured by the particle size distribution measuring method for fine particles in metal according to an embodiment of the present invention.

  Hereinafter, a method for measuring the particle size distribution of fine particles in metal, which is an embodiment of the present invention, will be described with reference to the drawings.

  The inventors of the present invention, as a result of earnest research, after classifying the fine particles extracted and stably dispersed from the metal material for each particle size, by measuring the volume fraction of the fine particles for each particle size, It was found that the particle size distribution of fine particles can be measured with high accuracy. The inventors of the present invention have also found that a classification method using centrifugal force is extremely effective when classifying fine particles. Specifically, in the method for measuring the particle size distribution of fine particles in metal according to an embodiment of the present invention, centrifugal force is applied to a container containing a suspension solution in which fine particles are stably dispersed in accordance with the particle size. The particle size distribution of the fine particles is measured by distributing the fine particles at positions that balance the diffusion, and measuring the concentration at each position by the amount of transmitted light.

  If there is only one kind of fine particles, the fine particles are distributed in the container according to the particle size. Therefore, the particle size distribution of the fine particles can be known by using the light intensity at each position as an index. When this method is used, nothing is detected when fine particles are not present, so the particle size is compared with a general particle size distribution apparatus that evaluates the entire particle size distribution state from the particle size center and distribution width. The distribution can be measured accurately. However, it is preferable to use an index other than light intensity when measuring the amount of fine particles. This is because, as described above, the light intensity is different from the absolute amount of particles, and it is appropriate to use a means such as quantification for the measurement of the amount of fine particles.

  For example, as described above, a centrifugal force is applied to the fine particles placed in the container to create a distribution state in the container, and then the fine particles present at each position are collected, decomposed with acid, etc., and then subjected to elemental analysis. A method of performing is considered. Since the information obtained by elemental analysis is a numerical value that reflects the volume of fine particles, it is possible to know the volume fraction of fine particles by particle size by conducting elemental analysis of the solution classified and sorted by particle size. . For example, when the dispersion state of precipitates greatly affects the performance of steel sheets, it is important to know the number distribution of precipitates in the evaluation of the distribution state of precipitates, and in that respect, it is compared with the scattering intensity distribution. Thus, the accuracy is improved by obtaining the number distribution from the volume distribution.

  In recent years, a field flow fractionation (FFF) method using centrifugal force has been proposed as a method for continuously classifying fine particles in a liquid. This FFF method is a technique in which centrifugal force is applied to the fine particles in the liquid, and the fine particles are continuously classified based on the difference in resistance to the applied load. In this FFF method, the smaller the particle size, the higher the moving speed in the liquid, that is, the resistance to the applied load, so the particles are discharged in order from the smaller particle size by gradually decreasing the rotational speed. Is done. If the solution classified according to the particle size after discharging the column using this FFF method is collected, decomposed, and quantified, the volume distribution of the fine particles for each particle size can be known. Furthermore, if the target particle size is small, the discharged particle dispersion solution is directly introduced into the inductively coupled plasma emission spectrometer (ICP emission spectrometer) or inductively coupled plasma mass spectrometer (ICP mass spectrometer). By doing so, the volume distribution for each element can be evaluated. However, when the particles are large, care must be taken because the particles may not be sufficiently decomposed in the plasma.

  Here, the FFF method also includes a method in which another solution flow is created from a direction orthogonal to the flow of the fine particles, and a load is applied to the fine particles. As a result of investigation, depending on the type of solution and fine particles, adsorption to the membrane filter arranged in the column may be remarkable, and quantitative evaluation is difficult, so a method of applying a load by centrifugal force is more appropriate It was judged. Note that when the load applied to the fine particles is centrifugal force, the volume distribution actually obtained by this method varies depending on the type of particles because the load is also affected by the particle density. Therefore, when several types of particles are mixed, calibration with a size on the horizontal axis may be performed according to the particle density.

  By the above method, fine particles such as precipitates and inclusions in the metal material that have a large distribution width of the particle size or a complicated distribution profile such as two peaks of the particle size distribution are shown. The particle size distribution can be accurately evaluated.

[Example 1]
In this example, a gold colloid solution was prepared as a simulated sample of fine particles in metal. This is because it is difficult to accurately evaluate the presence state of fine particles in metal, and as a means for verifying the accuracy of the measurement means using this method, fine particles with known particle diameters and particle densities can be used as standard samples. This is because it was judged appropriate. Among the commercially available gold colloid standard solutions, Au fine particles having an average particle diameter of 20 nm and 100 nm were purchased and mixed at a ratio such that the scattering intensity was approximately 1: 1 to prepare a mixed solution.

  First, the mixed solution was measured with a dynamic light scattering particle size distribution meter (hereinafter referred to as DLS). The measurement results are shown in FIG. FIG. 1 also shows the average particle size calculated when measured by DLS. As shown in FIG. 1, the measurement result by DLS has a broad profile shape over a wide region from about 10 nm to about 300 nm. However, there are almost no Au fine particles having a particle size of, for example, 50 nm or 200 nm in the actual mixed solution. This is a particle size distribution meter such as DLS, which is a device that evaluates the distribution state of particle size from the center particle size and dispersion degree. This suggests that accurate evaluation of a wide sample is difficult.

  Therefore, after separating the mixed solution using a desktop centrifuge, the particle sizes of the suspended component and the sedimented component were measured by DLS. About the centrifugation conditions, the rotation speed and the separation time were set according to the particle diameter of each Au fine particle mixed. After classification using centrifugal separation under each condition, collect supernatant liquid for suspended components with small particle size, and remove components attached to the bottom of the cell with appropriate solvent for sedimented components with large particle size. Each particle size distribution was measured by re-dispersing it. The measurement results are shown in FIG. As shown in FIG. 2, the center particle diameter of each Au fine particle measured after centrifugation is 19.6 nm and 97.5 nm, which are reasonable numerical values according to the standard value (particle diameter) before mixing. However, the scattering intensity ratio (20 nm: 100 nm) obtained when the same operation was repeated was highly variable.

  On the other hand, the standard solution was mixed and centrifuged in exactly the same manner, and then each particle size particle was dissolved with acid, and the concentration of Au element was quantified with an ICP emission spectrometer. Table 1 shows the repeated measurement results. As is apparent from Table 1, the center particle diameter of the Au fine particles can be evaluated with high accuracy, but the scattering intensity ratio varies greatly. On the other hand, the volume fraction calculated from the quantitative value of the Au element concentration has good repeatability. This suggests that it is difficult to accurately evaluate the volume fraction and the like in the particle size distribution measurement method using the light intensity as an index. Therefore, not only the centrifugal separation method and the particle size measurement method but also a combination with another means capable of evaluating the volume fraction makes it possible to evaluate an accurate amount useful for material development.

[Example 2]
After melting and heat-treating steel samples (C: 0.1% by mass, Mn: 0.05% by mass, Ti: 0.2% by mass, S: 0.002% by mass), the purpose is to change the grain size of precipitates in the steel samples. Further, reheating was performed at two levels (900 ° C. and 1000 ° C.) with different temperatures. After the heat-treated steel sample was processed into a size of 20 mm × 50 mm × 1 mm, the surface oxide layer was removed by grinding. After washing the surface of each of the two types of samples (900 ° C treated material, 1000 ° C treated material) with different heat treatment temperatures, 10vol% acetylacetone-10g / L tetramethylammonium chloride-90vol% methanol (hereinafter, 10% AA) (Abbreviated as “system”) The solution was used as an electrolytic solution, and about 0.5 g was electrolyzed by the electrolytic apparatus 1 shown in FIG.

  3 includes an electrolytic solution 3 placed in a container 2, a ring-shaped anode electrode 4 immersed in the electrolytic solution 3, and a sample 5 as a cathode electrode inserted through the anode electrode 4. It is equipped with. The anode electrode 4 is connected to the positive electrode of the constant current power source 6, and the sample 5 is connected to the negative electrode of the constant current power source 6 through a fixing jig 7. In the electrolysis apparatus 1, the sample 5 can be electrolyzed by applying a voltage between the anode electrode 4 and the sample 5 using the constant current power source 6. The electrolyzed sample was immersed in about 20 ml of 0.05% hexametaphosphoric acid aqueous solution in a beaker, and then the particles extracted from the steel by ultrasonic peeling operation were dispersed and held in the liquid.

  Next, the obtained slurry sample was classified by centrifuging with an FFF apparatus manufactured by Postnova. Specifically, 100 μl of the sample is introduced into the disc-shaped column that is rotated at the maximum rotation speed, and the stress applied to the fine particles is released by gradually decreasing the rotation speed as time passes. The small particles were discharged sequentially from the column. It is possible to evaluate the particle size distribution state with a connected particle size measurement device, but the volume fraction is not the scattering intensity distribution but the volume fraction for the purpose of evaluating a more accurate particle size distribution state. Calculated.

  As a procedure, a certain amount of the slurry discharged from the column was sequentially collected. After the separated slurry was dissolved with an acid, the content of each element was quantitatively evaluated with an ICP mass spectrometer. Since the fine particles are discharged in ascending order, the volume fraction for each element can be known by this operation. However, since the time until discharge is affected by the density in addition to the particle size, an appropriate calibration is required to convert the time into the particle size. It is best if standard particle diameters having the same density as the fine particles to be evaluated can be obtained. However, if standard particles having a density as close as possible are used, the particle diameters of the evaluation target particles can be converted by correction by calculation.

  In addition, the more detailed particle size distribution can be obtained for the slurry after classification at a short pitch, but each particle density, that is, the element content is naturally reduced, which is disadvantageous from the viewpoint of analytical sensitivity. Therefore, it is necessary to determine the sorting interval under appropriate conditions according to information to be known. In addition, the smaller the amount, the more the liquid amount will vary even if the same time fraction is taken, so the accuracy can be improved by operations such as measuring a certain amount from the slurry after fractionation. Is desirable.

  The number distribution of Ti precipitates evaluated by this operation is shown in FIG. The number distribution on the vertical axis shown in FIG. 4 was calculated by dividing the volume fraction obtained by decomposing and quantifying the preparative solution by the cube of the particle size. Further, for the purpose of evaluating the reproducibility of the measurement by this operation, the operation after the introduction of the slurry was confirmed by the same procedure for the 900 ° C. treated material. As shown in FIG. 4, in the 1000 ° C. treated material, the diameter of the center particle was increased by about 3.5 nm compared to the 900 ° C. treated material, suggesting that the Ti precipitate was coarsened due to an increase in the heat treatment temperature. .

  This result was almost the same as when the precipitates in the same material were evaluated using transmission electron microscopy (TEM method), whereas the TEM method took about one month. In addition to being able to evaluate in an extremely short time of about half a day, this method was judged to be good from the viewpoint of quantitativeness and reproducibility. In addition, the slurry obtained by the same operation was measured by the FFF method of applying a load to the fine particles by using the solution flow from the direction perpendicular to the fine particle flow in the column, but it was installed in the column. Adsorption to the membrane filter was remarkable, and a reliable result could not be obtained.

  In addition, if it is this size, even if it introduce | transduces the slurry after size separation in a column as it is to an ICP mass spectrometer as it is, it is thought that it can decompose | disassemble. However, if the particle size exceeds 1 μm, depending on the type of particles, decomposition in the plasma may not be sufficient, leading to a decrease in accuracy, so caution and confirmation are required.

DESCRIPTION OF SYMBOLS 1 Electrolyzer 2 Container 3 Electrolyte solution 4 Anode electrode 5 Sample 6 Constant current power supply 7 Fixing jig

Claims (4)

An extraction step for extracting fine particles in the metal material;
A dispersion step of preparing a fine particle dispersion solution by dispersing the fine particles extracted in the extraction step in a liquid;
A classification step of classifying the fine particles in the fine particle dispersion solution for each particle size by applying centrifugal force to the fine particle dispersion solution prepared by the dispersion step;
A calculation step of calculating a volume fraction of fine particles for each particle size classified by the classification step;
A method for measuring the particle size distribution of fine particles in a metal. The classifying step includes a step of continuously classifying the fine particles in the fine particle dispersion solution for each particle size using a field flow fractionation method,
The calculation step includes introducing the fine particles continuously classified by the field flow fractionation method into an inductively coupled plasma emission spectrometer or an inductively coupled plasma mass spectrometer, so that the volume fraction of the fine particles for each particle size is obtained. The method of measuring a particle size distribution of fine particles in metal according to claim 1, further comprising:   The particle size distribution measuring method for fine particles in metal according to claim 1, wherein the calculating step includes a step of calculating a number distribution of fine particles from a volume fraction of fine particles for each particle size.   The particle size distribution measuring method for fine particles in metal according to any one of claims 1 to 3, wherein the particle size of the fine particles to be measured is 1 µm or less.

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