JP2009008584A - Analysis method of particulate in steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of extracting particulates (mainly, an average particle size is 1 μm or less) existing in steel without aggregation, performing analysis after the extraction, especially accurately analyzing the particle size distribution. <P>SOLUTION: For example, a steel sample is electrolyzed, then the electrolyzed steel sample is dipped in a solution that is different from the electrolyte used for the electrolysis and has dispersibility, and the particulates in the steel sample are extracted. Then, the extracted particulates are analyzed by a dynamic light scattering method. In this analysis method, after the extraction of the particulates, a magnetic separation operation and a classification operation by ultrasonic wave are performed. This analysis method is effective when particulate analysis of a material of much carbon content is performed or when particulates other than analyzing objects are mixed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for analyzing fine particles (including inclusions, precipitates, etc.), and more particularly to a pretreatment method for accurately and quickly measuring the particle size distribution of fine particles.

  It is known that precipitates or inclusions generated in the steel manufacturing process affect the properties of steel, and various studies have been conducted for a long time. In recent years, a technique for strengthening metallic materials by dispersing fine particles (especially precipitates or inclusions having an average particle diameter of 1 μm or less) in steel using aging precipitation has been known. The development of new steels that are used has been actively conducted. As a material strengthening mechanism, the phenomenon that fine particles effectively suppress the growth of crystal grains (pinning effect) is dominant, and investigating the particle size, density, and inter-particle distance of these fine particles is a highly functional steel plate. Is important in developing.

As a technique that analyzes fine particles in steel and is excellent in representativeness and quickness, there is a technique of analyzing the characteristics of the fine particles after iron is dissolved and the fine particles in the steel are collected. For example, Non-Patent Document 1 discloses a method in which a sample is decomposed with an acid (for example, a mixed acid of nitric acid and sulfuric acid) and the residue is measured with a laser diffraction particle size distribution meter as an example of measurement of inclusion particle size distribution. Has been. Patent Document 1 discloses that inclusions in steel are extracted and collected by dissolving the inclusions in steel in a soluble solution (for example, ferrous ammonium sulfate aqueous solution) and performing electrolysis. A method is disclosed.
Japanese Patent Laid-Open No. 54-110896 S. Chino, S. Ishibashi, Naoki Gunji, and Hideo Iwata, “Measuring Method for Particle Size Distribution of Fine Inclusions in Extremely Low Carbon Steel” Materials and Processes, Vol. 4, 1991, p. 387

  However, in the method shown in Non-Patent Document 1, it is difficult to measure the particle size distribution of only the target particles because the steel sample having a high carbon content contains a large amount of decomposition products of cementite in the residue.

  On the other hand, in the method disclosed in Patent Document 1, basically, fine particles are extracted and collected in a soluble solution, and therefore aggregation occurs in the liquid depending on the type and particle size of the particles. In the case of inclusions having an average particle size of 50 μm to 1000 μm, which is the subject of Patent Document 1, there is no particular problem. In most cases, they aggregate and are not suitable for practical use. In Patent Document 1, the particle size is classified (classified) according to the pore size of the sieve. However, since there is no sieve with a pore size on the order of nm, this technique is also transferred to fine particles in steel. It is difficult to do.

  The present invention solves the above problems and provides a method for extracting fine particles (mainly an average particle size of 1 μm or less) existing in steel without agglomerating and analyzing the post-extraction analysis, particularly the particle size distribution with high accuracy. To do.

  The technique of extracting fine particles in steel by dissolving steel using a soluble solution is a very excellent method for extracting fine particles in steel from steel. Therefore, the present inventors first set this method as a base for completing the invention. As a result of intensive studies to solve the above problems, when using the above method, the fine particles are separated from the soluble solution for the aggregation of the fine particles in the extracted solution. The solution is effective by using a solution for extraction, and further by selecting a solution having dispersibility with respect to the fine particles (hereinafter also referred to as a dispersible solution) as the extraction solution. I found out. That is, the present invention has been completed by considering the use of the above-described extraction solution as a main requirement of the present invention and examining and defining a series of operations.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] Electrolytic operation for electrolyzing a steel sample, and the rest of the steel sample after the electrolysis is immersed in a solution that is different from the electrolytic solution used for the electrolysis and has dispersibility, and extracts fine particles in the steel sample And an analysis operation for analyzing the fine particles extracted in the solution after the extraction operation by a dynamic light scattering method.
[2] The method for analyzing fine particles in steel according to [1], wherein the dispersible solution is a sodium hexametaphosphate aqueous solution.
[3] The method for analyzing fine particles in steel according to [1] or [2], wherein in the analysis operation, fine particles having an average particle diameter of 1 μm or less are analyzed.
[4] The method for analyzing fine particles in steel according to any one of [1] to [3], wherein, in the analysis operation, only fine particles adhering to the steel sample are analyzed.
[5] In any one of the above [1] to [4], a filtration operation for filtering the fine particles extracted in the solution to obtain a filtrate containing fine particles on the small diameter side to be analyzed; And an analytical operation for analyzing the filtrate containing the fine particles obtained by dynamic light scattering.

  According to the present invention, since the fine particles are extracted in a solution having dispersibility with respect to fine particles in steel (especially those having an average particle size of 1 μm or less), aggregation of the fine particles in the extracted solution is prevented, Fine particles can be extracted as they are in steel. In addition, since a dispersible solution for extraction different from the soluble solution can be arbitrarily selected, a dispersible solution suitable for fine particles can be used. As a result, analysis after extraction, especially particle size distribution, can be analyzed with high accuracy, and knowledge on various properties of steel materials can be obtained based on the obtained measurement results. Useful information for development.

  The present invention can be applied to the analysis of various types of fine particles in steel (including precipitates and inclusions), and is particularly suitable for steel materials containing many fine particles having an average particle size of 1 μm or less. Can be applied.

  Hereinafter, the present invention will be described in detail by taking as an example a case where fine particles in steel are extracted by an electrolytic method using an electrolytic solution (corresponding to the soluble solution of the present invention) and the particle size distribution of the fine particles in steel is measured. To do. The order of operations is the order from (1) to (7). The analysis flow is shown in FIG.

  (1) First, a steel material is processed into an appropriate size to obtain a sample for electrolysis (sometimes referred to as a steel sample).

  (2) On the other hand, as a solution for extracting fine particles in steel, a solution having dispersibility is prepared separately from the electrolytic solution used for electrolysis (preparation operation 100).

  Here, in order to disperse the fine particles exposed on the surface of the sample for electrolysis in the dispersible solution, the amount of liquid less than half of the electrolytic solution is sufficient. In addition, about the kind and density | concentration of a dispersible solution, the clear correlation is not acquired between the composition and particle size of microparticles | fine-particles, and the particle density in a liquid. For example, an aqueous solution of sodium hexametaphosphate has been reported to have an effect of improving dispersibility with respect to many inorganic fine particles, and is suitable as an acidic solution. The concentration is generally around 2000 mg / l. Excessive addition rather hinders the dispersion effect. That is, it is necessary to optimize the type and concentration of the dispersion according to the properties and density of the particles. In particular, when the solvent of the dispersion solution is water, there is a close correlation between the surface charge and dispersibility of the particles. It is preferable to establish the conditions.

  As for the type of dispersible solution, in addition to the aqueous solution of sodium hexametaphosphate, the effect has been confirmed even for pure water that can be expected to work stronger than the repulsive force between the fine particles in the liquid than methanol. For the effect in water, refer to the particle size distribution of fine particles in steel when pure water (invention example) or methanol (comparative example) is used as a dispersible solution, as shown in Fig. 10. The extraction method and the particle size distribution measurement method are based on the analysis flow shown in FIG.

  (3) Then, the electrolysis sample of (1) is electrolyzed with the apparatus configuration schematically shown in FIG. 2 (electrolysis operation 101). It should be noted that the waste electrolysis for removing the contamination of the surface layer may be performed immediately before the electrolysis operation 101 in accordance with the degree of cleaning of the electrolysis sample and the analysis accuracy.

  FIG. 2 is an example of an electrolysis apparatus used in the electrolysis method. The electrolysis apparatus 7 includes an electrolysis sample fixing jig 2, an electrode 3, an electrolytic solution 6, a beaker 4 for containing the electrolytic solution 6, and a constant current electrolysis device 5 for supplying current. The fixing jig 2 is connected to the anode of the constant current electrolysis apparatus, and the electrode 3 is connected to the cathode of the DC constant current source. The electrolytic sample 1 is connected to the fixing jig 2 and held in the electrolytic solution 6. The electrode 3 is immersed in the electrolytic solution 6 and disposed so as to cover the surface of the sample for electrolysis (mainly the portion immersed in the electrolytic solution 6). It is most convenient to use a permanent magnet for the fixing jig 2. However, since it dissolves in contact with the electrolytic solution 6 as it is, even if a platinum plate is used in a portion that is easily in contact with the electrolytic solution 6, 2a between the sample 1 for electrolysis in the case of FIG. good. Similarly, the electrode 3 uses a platinum plate in order to prevent dissolution by the electrolytic solution 6.

  Electrolysis of the sample 1 for electrolysis is performed by supplying a charge from the constant current electrolysis apparatus 5 to the electrode 3. Since the amount of electrolysis of steel is proportional to the amount of charge, the amount of electrolysis can be determined by time if the amount of current is determined.

Here, the current density during electrolysis is preferably 10 mA / cm ² or less, more preferably ² mA / cm ² or less. Usually, the current density condition in the electrolysis method is 20 mA / cm ² or more in many cases, but by performing electrolysis at a current density smaller than this normal condition, the uniformity of the electrolysis with respect to the position of the sample surface for electrolysis is improved. There is a further effect on suppressing the aggregation of particles during electrolysis. In addition, the possibility of dissolving particularly fine particles can be reduced, and more accurate extraction of fine particles can be expected.

  Further, the amount of electrolysis in the electrolysis operation 101 is set to be not less than 1 and not more than 50 times the approximate average particle diameter of the fine particles in the electrolysis sample 1 obtained in advance in terms of the thickness of the electrolysis sample 1. Is preferred. More preferably, it is 1 to 10 times. This amount of electrolysis is particularly suitable when measuring the particle size distribution of the extracted fine particles. This is because in the case of ordinary steel, even if the iron matrix around the fine particles to be extracted is dissolved, most of the fine particles do not immediately fall into the electrolyte 6 solution, but adhere to the surface of the sample 1 for electrolysis. is doing. For this reason, when the electrolysis of steel further progresses and the fine particles adhering to the surface of the electrolysis sample 1 come into contact with another microparticle that appears next, there is a possibility that the surface of the electrolysis sample 1 is aggregated. By setting the amount of electrolysis in the above-described range, it is considered that aggregation on the sample surface during electrolysis can be avoided.

  In addition, the approximate average particle diameter of the fine particles in the electrolysis sample 1 obtained in advance, which is a measure of the amount of electrolysis, is the following using the same sample as the electrolysis sample 1 before the electrolysis operation 101: It can be obtained by the procedure described in 1. An example of the analysis flow in this case is shown in FIG. Before the electrolysis operation 101 described above, an approximate average particle size pre-calculation operation 306 is provided, which includes a pre-analysis step S3061 of an approximate average particle size of fine particles in steel and an electrolysis amount calculation step S3062. In the mean particle size pre-analysis step S3061, the analysis method for obtaining the average particle size of the fine particles in steel in advance is a high-magnification ratio of a small region of a sample collected from the same steel material separately from the sample 1 for electrolysis. It is desirable to select a method that allows observation and analysis in For example, a method of analyzing using a scanning electron microscope, a transmission electron microscope, an electron beam microprobe analyzer, an Auger analyzer, an X-ray electron spectrometer, and a secondary ion mass spectrometer can be used.

  (4) When a predetermined amount of the electrolysis sample is electrolyzed, the electrolysis sample piece that has not been electrolyzed (dissolved) is removed from the electrolyzer and immersed in a dispersible solution, so that fine particles in steel are contained in the dispersible solution (Extraction operation 102). The extraction operation 102 includes a cleaning step S1021, an extraction step S1022, and a determination step S1023.

  First, the sample piece for electrolysis removed from the electrolyzer is gently immersed in methanol and then removed (cleaning step S1021).

  Next, the taken sample piece for electrolysis is immersed in the dispersible solution prepared in the preparation operation 100 of (2) above.

  Then, by irradiating ultrasonic waves while being immersed in the dispersible solution, the fine particles adhering to the surface are peeled off and extracted into the dispersible solution (extraction step S1022). Then, it is determined whether or not the amount of fine particles extracted into the dispersible solution has reached a measurable amount (determination step S1023). If the measurable amount has not been reached, the process returns to the electrolysis operation 101 in (3) above, and the process from the electrolysis operation 101 to the determination step S1023 is repeated. If the measurable amount is reached, proceed to the next operation.

  The washing step S1021 is a step for preventing the electrolytic solution colored by the iron complex generated during electrolysis from being mixed into the dispersible aqueous solution. This is because if the dispersible aqueous solution is also colored by the colored electrolyte solution, the measurement sensitivity is impaired when a particle size distribution measuring device using light intensity such as laser diffraction method or dynamic light scattering method is used. Therefore, if the analysis content is, for example, elemental analysis of components not included in the electrolytic solution after melting steel, there is no need to provide (except for the constituent elements of the electrolytic solution). Whether or not the cleaning step S1021 is provided may be determined as appropriate in consideration of the analysis content, the amount mixed into the analyzer or the dispersible solution, and the like. The washing solution is preferably washed with the main component of the electrolytic solution so that it can be well blended with the electrolytic solution and drop the electrolytic solution in a small amount.

  It should be noted that almost all the fine particles targeted in the present invention can be recovered by the operation shown in the extraction step S1022.

  In the determination step S1023, whether or not the amount of fine particles extracted in the dispersible solution has reached a measurable amount is determined by whether or not the total mass of the electrolysis amount of the electrolysis sample has reached a predetermined amount. Substitute with. That is, if the total mass of the electrolyzed sample has not reached a predetermined amount, the process returns to the electrolysis operation 101, and if it has reached, the electrolysis operation 101 and the extraction operation 102 are stopped and the operation proceeds to the next operation. At this time, the total mass of the electrolysis amount of the sample for electrolysis is determined from the concentration of fine particles and the particle size in the dispersible solution. This is because, when measuring the particle size distribution of the fine particles, the concentration of the fine particles in the solution is important from the viewpoint of the measurement sensitivity of the apparatus. Usually, the operation from the electrolysis operation 101 to the determination step S1023 is repeated several times for one electrolysis sample. In fact, if the surface area of the sample 1 for electrolysis is reduced, the electrolysis thickness (hereinafter also referred to as electrolysis thickness) is increased in order to perform electrolysis up to an amount capable of obtaining the fine particle concentration required for the analysis technique in the analysis operation 105 It is necessary to take. In this case, the predetermined electrolytic thickness performed in the electrolysis operation 101 is set to be 1 to 50 times the approximate average particle diameter of the fine particles in the electrolysis sample 1 obtained in advance, and from the electrolysis operation 101 If the total mass of the electrolyzed sample to be electrolyzed becomes an amount that gives a measurable fine particle concentration by repeating the extraction operation 102 a plurality of times, it is still a desirable form.

  (5) Next, cementite is removed from the fine particles extracted in the dispersible solution by a magnetic separation method (magnetic separation operation 103). This operation is performed when it is necessary to remove cementite or the like in analyzing fine particles such as a material having a high carbon content.

  In order to perform this operation most simply, a magnetic rod or the like may be placed in a solution in which fine particles are dispersed and stirred. In addition, when cementite is magnetically attached to a magnetic rod, fine particles may also be involved. Therefore, the cementite and fine particles to be analyzed are separated by, for example, vibrating the dispersible solution with ultrasonic waves. It is preferable. In addition, when the magnet is used repeatedly, in view of ease of cleaning, a glass tube that can be decanted from the outside of the container in which the dispersible solution is placed and the magnet is brought close to the magnet rod is attached to the magnet rod. A method such as performing a stirring operation in a state of being arranged around is conceivable.

  (6) A classification operation is performed on the fine particles dispersed in the dispersible solution by using ultrasonic waves to classify them according to particle diameter (classification operation 104). When the non-analytical particles and the analysis target fine particles coexist in the dispersible solution, it is necessary to separate only the analysis target fine particles by the classification operation 104. This operation can be used when the non-analysis particles and the analysis microparticles have different particle sizes, and the analysis particles are smaller than the non-analysis particles.

  The instrument used for the classification operation 104 may be a commonly used one, but the filter paper needs to be selected according to the characteristics of the dispersible solution to be filtered. When the viscosity of the dispersible solution and the concentration of fine particles in the liquid are high, it may take time for filtration. Therefore, it is preferable to adopt a system that can perform suction filtration as necessary.

  In order to prevent aggregation in the dispersible solution, it is more preferable to classify the dispersible solution while suppressing aggregation of the fine particles by applying ultrasonic vibration. Although there are various ways of applying vibration to the dispersible solution, it is efficient to immerse the ultrasonic oscillator directly in the particle dispersion solution. Depending on the particle size distribution measuring apparatus used after this operation and its principle, the particle size measurement of fine particles is easily affected by large particles. In particular, in the case of a measuring device using the particle scattering intensity as an index, the influence of large-sized particles that are not analyzed (specifically, precipitates or inclusions with an average particle size exceeding 1 μm) is large, so these are removed. It is important to.

  Here, either the magnetic separation operation 103 in (5) or the classification operation 104 in (6) may be performed first. However, when fine particles in steel are classified, a filter having a small pore size is usually used. Therefore, it is better to perform (5) magnetic separation operation 103 first. (6) If the classification operation 104 is performed first, the filter may be clogged by cementite, so that filtration may take a long time.

  Further, the magnetic separation operation 103 in (5) and the classification operation 104 in (6) may be omitted if they are not necessary, for example, when no interference components other than the measurement target are included.

  In particular, when it is desired to accurately measure the particle size distribution on the small diameter side by the dynamic light scattering method, the particle removal on the large diameter side is performed after the above (5) magnetic separation operation 103 or (6) classification operation 104. It is desirable to add operation 407. This is because, in the dynamic light scattering method, since the scattering intensity increases in proportion to the sixth power of the particle size, the number of fine particles having a large particle size tends to increase apparently.

  In the large-diameter side particle removal operation 407, a filtration method or a centrifugal separation method can be used as a method for separating the small-diameter side particles to be analyzed from the large-diameter side particles to be excluded from the analysis target. That is, the large-diameter side particle removal operation 407 includes a filtration step S4071 for performing a filtration method or a centrifugation step S4072 for performing a centrifugation method. FIG. 4 shows an example of the analysis flow when the large-diameter side particle removal operation 407 is added after the classification operation 104 in the analysis flow of FIG.

  In FIG. 4, when the small-diameter side particle size and the large-diameter side particle size are greatly different, the process proceeds to filtration step S4071 to which a filtration method is applied. On the other hand, when the density of the microparticles to be analyzed can be expected to be substantially uniform, it is desirable to select to proceed to the centrifugation step S4702. In the case of the centrifugal separation method, as compared with the filtration method, it is possible to arbitrarily set the separation conditions by fine control of the rotation speed and time. Also, the centrifugal separation method is effective when the amount of the dispersion is small. The filtration method is a preferred method because a method using a filter is the simplest.

  (7) The dispersive solution containing the fine particles obtained after the classification operation 104 (in some cases, after the large-diameter side particle removal operation 407) obtained by the above procedure is applied to the particle size distribution measuring apparatus (analysis operation 105). ). For example, it can be analyzed by a dynamic light scattering method.

  If the procedure of (1) to (7) is performed, the fine particles exposed on the steel surface after electrolysis can be immediately extracted and collected in a suitable solvent having good dispersibility. It can be secured. By this operation, the subsequent magnetic separation operation 103 and classification operation 104 are accurately performed, and a highly accurate particle size distribution measurement result is obtained. If the dispersibility of the fine particles extracted in the dispersible solution is poor, for example, the fine particles to be analyzed are entrained in cementite during magnetic separation, or agglomeration occurs and the classification operation 104 becomes as intended. The problem of not being generated.

  In addition, since a dispersible solution for extraction different from the soluble solution can be arbitrarily selected, a dispersible solution suitable for fine particles can be used. By these, it becomes possible to analyze the analysis after extraction, particularly the particle size distribution with high accuracy. Moreover, a statistically reliable analysis result can be obtained in a simple and extremely short time.

  In the present embodiment, steel is melted by an electrolytic method using an electrolytic solution, but the present invention is not limited to this. In addition, in the case of fine particles with low solubility, an acid dissolution method using an acidic aqueous solution as a soluble solution can also be used. In this case, instead of the electrolysis operation 101, the electrolysis method in the electrolysis operation 101 is a dissolution operation in which the acid dissolution method or the like is used. An appropriate melting method may be determined as appropriate depending on the fine particles to be analyzed, the type of steel to be dissolved, and the amount of dissolution.

  An example in which the particle size distribution measurement is performed according to the procedures (1) to (7) of the embodiment and the analysis flow of FIG. 1 will be described as an example of the present invention of Example 1. Specific conditions for each operation are as follows, but the present invention is not limited to the following specific conditions.

  Carbon steel is used as the steel, and its chemical composition is C: 0.10 mass%, Si: 0.2 mass%, Mn: 1.0 mass%, P: 0.024 mass%, S: 0.009 mass%, Cr: 0.03 mass%, Ti : 0.05 mass%. Four pieces of this steel processed into a size of 20 mm × 50 mm × 1 mm were prepared as electrolysis samples.

  The electrolysis operation 101 was carried out with the same apparatus configuration as in FIG. 2, and 500 ml of 10% AA-based electrolyte (10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol) was used as the electrolyte. In addition, 0.1 g of electrolysis was performed for each electrolysis sample. Further, all the electrolysis samples were subjected to discarded electrolysis for removing the surface layer contamination first before the electrolysis operation 101 only once.

  As a dispersible solution used for the extraction operation 102, a sodium hexametaphosphate aqueous solution having a concentration of 500 mg / l was used, and 50 ml of this was prepared in a beaker separate from the electrolyzer.

  In addition, about the optimal sodium hexametaphosphate density | concentration, it determined using the zeta electrometer. An example of the relationship between the sodium hexametaphosphate concentration and the zeta potential or the measured average particle size is shown in FIG. The average particle diameter was determined using another sample having the same structure as the sample of this example. From FIG. 11, it can be seen that when the absolute value of the zeta potential of the dispersible solution is increased, the average particle size is decreased and aggregation tends to be prevented. From this result, it was determined that the optimum sodium hexametaphosphate concentration in this example was 500 mg / l.

  This aqueous sodium hexametaphosphate solution is widely dispersible with respect to inorganic fine particles. The concentration of the aqueous sodium hexametaphosphate solution is preferably 100 mg / l or more and 10000 mg / l or less. This is because if the concentration is too low, the dispersion effect is insufficient, while if the concentration is too high, the effect of aggregation is manifested.

  In addition, during the extraction operation 102, ultrasonic vibration was applied to the dispersible solution.

  Then, the electrolysis operation 101 to the extraction operation 102 were repeated 10 times per electrolysis sample, and then the magnetic separation operation 103 was performed. Here, in order to collect statistically reliable data, all the fine particles obtained by repeating the electrolysis operation 101 to the extraction operation 102 for one electrolysis sample 10 times are extracted into the same dispersive solution. did.

  The magnetic separation operation 103 was performed by putting a magnetic rod in the dispersible solution and stirring. In addition, ultrasonic vibration was applied to the dispersible solution during the magnetic separation operation.

  The classification operation 104 as a means for removing non-analyzed particles was performed by classifying the dispersible solution containing the fine particles after the removal of cementite using an ultrasonic wave using a 0.4 μm filter. Using an ultrasonic generator of the type that immerses the chip in the solution and vibrates, about 20 ml of a sodium hexametaphosphate aqueous solution with a concentration of 500 mg / l is poured onto the filter, and an ultrasonic wave is generated by immersing the oscillator. After being in the state, a dispersible solution containing fine particles was added.

  Thereafter, the particle size distribution of the fine particles in the dispersible solution was measured with a dynamic light scattering type particle size distribution measuring apparatus. The obtained results are shown in FIG.

  As a comparative example, a methanol solution is also obtained in which the washing step S1021 is not performed after the electrolysis operation 101, and the fine particles in steel are extracted into methanol that is not dispersible with respect to the fine particles in the extraction step S1022. Oita. Other than this, the electrolysis operation 101, steps S1022 to S1023, and the magnetic separation operation 103 to the analysis operation 105 are exactly the same as in the embodiment. The result of the obtained particle size distribution is also shown in FIG.

  In FIG. 5, compared with the comparative example, the example of the present invention is distributed on the side where the average particle size is smaller as a whole. This is because in the comparative example, the apparent particle size is increased due to aggregation, so that it is considered that the same steel is distributed to the side having a relatively large average particle size. Therefore, from this result, according to the present invention, it has been clarified that aggregation that tends to occur when fine particles are extracted can be significantly suppressed.

  The result of investigating the relationship between the electrolytic thickness in the electrolytic method (represented by the magnification with respect to the average particle diameter of the fine particles obtained in advance) and the average particle diameter of the extracted fine particles was taken as Example 2. The particle size distribution was measured according to the procedures (1) to (7) of the embodiment and the analysis flow of FIG. 3, and the average particle size was calculated from the results. Specific conditions for each operation are as follows, but the present invention is not limited to the following specific conditions.

  Carbon steel is used as the steel, and its chemical composition is C: 0.10 mass%, Si: 0.2 mass%, Mn: 1.0 mass%, P: 0.024 mass%, S: 0.009 mass%, Cr: 0.03 mass%, Ti : 0.05 mass%. Four pieces of this steel processed into a size of 20 mm × 50 mm × 1 mm were prepared as electrolysis samples. On the other hand, one sample collected separately from the same steel was prepared as a sample for preliminary analysis.

The average particle size pre-analysis step S3061 in the average particle size pre-calculation operation 306 was performed using a scanning electron microscope. After lightly etching the sample for preliminary analysis, the surface of the sample was photographed at 10 × 3 × 10 ⁴ times with a scanning electron microscope. The photograph taken was subjected to image processing with a computer, and the average diameter of each fine particle was determined as the particle diameter. Then, the median (median) with respect to the particle size distribution of all the fine particles was determined in advance as the approximate average particle size of the fine particles in the sample for electrolysis (hereinafter referred to as the prior average particle size). Four levels of electrolytic thickness were set to 6 times, 12 times, 18 times, and 36 times with respect to the prior average particle diameter. In the next electrolysis amount calculation step S3062, the set electrolysis thickness was converted into the mass of steel of the sample for electrolysis, and further, the converted mass of steel was converted into the supply charge amount that can be electrolyzed. The electrolysis time was calculated from the supplied charge amount and the current density, and the electrolysis amount was controlled by this electrolysis time.

  The electrolysis operation 101 was performed with the same apparatus configuration as in FIG. 2, and 200 ml of 10% AA-based electrolyte was used as the electrolyte. For all the electrolysis samples, the discard electrolysis for removing the surface contamination was first performed just before the electrolysis operation 101 once.

Further, electrolysis was performed for the electrolytic thickness set in the average particle size pre-calculation operation 306 using one electrolysis sample for each level of electrolytic thickness. The current density during electrolysis was 20 mA / cm ^{2 at} all levels.

  As a dispersible solution used for the extraction operation 102, a sodium hexametaphosphate aqueous solution having a concentration of 500 mg / l was used and prepared in another beaker. During the extraction operation 102, ultrasonic vibration was applied to the dispersible solution to disperse the fine particles adhered to the surface of the electrolysis sample in the aqueous solution of sodium hexametaphosphate.

  Then, the electrolysis operation 101 to the extraction operation 102 were repeated 10 times per electrolysis sample, and then the magnetic separation operation 103 was performed. In addition, in order to collect statistically reliable data, all the fine particles obtained by repeating the electrolysis operation 101 to the extraction operation 102 10 times per one electrolysis sample were extracted into the same dispersive solution. .

  The magnetic separation operation 103 was performed by putting a magnetic rod in the dispersible solution and stirring. In addition, during the magnetic separation operation 103, ultrasonic vibration was applied to the dispersible solution.

  The classification operation 104 as a means for removing non-analyzed particles was performed by classifying a dispersible solution containing fine particles after removal of cementite using an ultrasonic wave using a filter having a pore diameter of 0.4 μm. Using an ultrasonic generator of the type that immerses the chip in the solution and vibrates, about 20 ml of a sodium hexametaphosphate aqueous solution with a concentration of 500 mg / l is poured onto the filter, and an ultrasonic wave is generated by immersing the oscillator. After the state was reached, an aqueous solution of sodium hexametaphosphate containing fine particles was added.

  Thereafter, the particle size distribution of the fine particles in the dispersible solution was measured with a dynamic light scattering type particle size distribution measuring apparatus. An example of the particle size distribution when the electrolytic thickness is 6 times and 36 times the prior average particle size is shown in FIG.

  From this particle size distribution result, the median (median) with respect to the particle size distribution of all the fine particles was calculated as the average particle size. In addition, the particle size distribution measurement was performed four times per electrolytic level per the same procedure and conditions as above, and the average value per electrolytic thickness was calculated by further averaging the four average particle sizes obtained. The particle size was taken. The obtained results are shown in FIG. In FIG. 7, white circles (symbols: ◯) indicate the average particle size per level of electrolytic thickness, and error bars indicate the range of four average particle size values.

  In FIG. 7, the average particle diameter of the extracted fine particles tended to decrease as the electrolytic thickness was reduced. That is, when the electrolytic thickness is increased, it is considered that the apparent particle size is increased due to aggregation. Therefore, from this result, in order to suppress the aggregation of fine particles generated during the electrolysis operation 101, it is more desirable that the amount of electrolysis from the electrolysis operation 101 to the extraction operation 102 is thinner in terms of the thickness of the electrolysis sample 1. Became clear. In the case of this sample, when the electrolytic thickness in the electrolysis operation 101 was set to about 6 times or less of the prior average particle diameter, aggregation could be further greatly reduced. Note that since the optimum electrolytic thickness varies depending on the sample, it is necessary to optimize the electrolytic thickness condition according to the sample.

  The result of investigating the relationship between the current density in the electrolysis method and the average particle diameter of the extracted fine particles was taken as Example 3. The particle distribution was measured according to the procedures (1) to (7) of the embodiment and the analysis flow of FIG. Specific conditions for each operation are as follows, but the present invention is not limited to the following specific conditions.

  Carbon steel is used as the steel, and its chemical composition is C: 0.10 mass%, Si: 0.2 mass%, Mn: 1.0 mass%, P: 0.024 mass%, S: 0.009 mass%, Cr: 0.03 mass%, Ti : 0.05 mass%. Five pieces of this steel processed into a size of 20 mm × 50 mm × 1 mm were prepared as electrolysis samples.

  First, the average particle diameter pre-calculation operation 306 was performed under the same conditions as in Example 2, and the prior average particle diameter and the amount of electrolysis in the electrolysis operation 101 were set. In the case of this example, the amount of electrolysis in the electrolysis operation 101 was set to an amount corresponding to an electrolysis thickness of 6 times the prior average particle diameter. This electrolytic thickness was converted to the mass of steel of the sample for electrolysis, and the converted mass of steel was converted to a supply charge amount that could be electrolyzed, and the electrolysis time was calculated from this supply charge amount and current density.

  The electrolysis operation 101 was performed with the same apparatus configuration as in FIG. 2, and 200 ml of 10% AA-based electrolyte was used as the electrolyte. For all the electrolysis samples, the discard electrolysis for removing the surface contamination was first performed just before the electrolysis operation 101 once. The amount of electrolysis was controlled by the electrolysis time calculated in the previous average particle diameter pre-calculation operation 306.

Current density, the five levels of ^{1mA / cm 2, 2mA / cm} 2, 5mA / cm 2, 10mA / cm 2, and 20 mA / cm ^2, for each level, was used one by one electrolysis sample.

  As a dispersible solution used in the extraction operation 102, a sodium hexametaphosphate aqueous solution having a concentration of 500 mg / l was used and prepared in another beaker. During the extraction operation 102, ultrasonic vibration was applied to the dispersible solution to disperse the fine particles adhered to the surface of the electrolysis sample in the aqueous solution of sodium hexametaphosphate.

  Then, the electrolysis operation 101 to the extraction operation 102 were repeated 10 times for one electrolysis sample, and then the magnetic separation operation 103 was performed. In addition, in order to collect statistically reliable data, all the fine particles obtained by repeating the electrolysis operation 101 to the extraction operation 102 10 times per one electrolysis sample were extracted into the same dispersive solution. .

  The magnetic separation operation 103 was performed by putting a magnetic rod in the dispersible solution and stirring. In addition, during the magnetic separation operation 103, ultrasonic vibration was applied to the dispersible solution.

  The classification operation 104 as a means for removing non-analyzed particles was performed by classifying the dispersible solution containing fine particles after the removal of cementite by a filtration method using a filter having a pore size of 0.4 μm and ultrasonic waves. Using an ultrasonic generator of the type that immerses the chip in the solution and vibrates, about 20 ml of a sodium hexametaphosphate aqueous solution with a concentration of 500 mg / l is poured onto the filter, and an ultrasonic wave is generated by immersing the oscillator. After the state was reached, an aqueous solution of sodium hexametaphosphate containing fine particles was added.

  After that, the particle size distribution of the fine particles in the dispersive solution is measured with a dynamic light scattering type particle size distribution measuring device, and the median (median) for the particle size distribution of all the fine particles is averaged from the particle size distribution result. Calculated as particle size. In addition, the particle size distribution measurement was performed four times per current density level using the same procedure and conditions as above, and the average of the four average particle sizes obtained was further averaged and averaged per current density level. The particle size was taken. The obtained result is shown in FIG. In FIG. 8, black circles (symbol: ●) indicate the average particle diameter per level of electrolytic thickness, and error bars indicate the range of four average particle diameter values.

In FIG. 8, the average particle diameter of the extracted fine particles tended to decrease as the current density during electrolysis decreased. This is considered to be because when the current density is increased, the apparent particle size becomes larger due to aggregation due to local progress of electrolysis. From this result, in this sample, when the current density is ² mA / cm ² or less, the aggregation can be relieved greatly. Note that since the optimum current density is considered to depend on the surface state of the sample, it is necessary to optimize the current density condition according to the sample.

  An example in which the particle size distribution measurement is performed according to the procedures (1) to (7) of the embodiment and the analysis flow of FIG. 4 will be described as an example of the present invention of Example 4. In the large diameter side particle removing operation 407, the centrifugal separation step S4072 was selected. Specific conditions for each operation are as follows, but the present invention is not limited to the following specific conditions.

  Carbon steel is used as the steel, and its chemical composition is C: 0.10 mass%, Si: 0.2 mass%, Mn: 1.0 mass%, P: 0.024 mass%, S: 0.009 mass%, Cr: 0.03 mass%, Ti : 0.05 mass%. Four pieces of this steel processed into a size of 20 mm × 50 mm × 1 mm were prepared as electrolysis samples.

  First, the average particle diameter pre-calculation operation 306 was performed under the same conditions as in Example 2, and the prior average particle diameter and the amount of electrolysis in the electrolysis operation 101 were set. In the case of this example, the amount of electrolysis in the electrolysis operation 101 was set to an amount corresponding to an electrolysis thickness of 6 times the prior average particle diameter. This electrolytic thickness was converted to the mass of steel of the sample for electrolysis, and the converted mass of steel was converted to a supply charge amount that could be electrolyzed, and the electrolysis time was calculated from this supply charge amount and current density.

The electrolysis operation 101 was performed with the same apparatus configuration as in FIG. 2, and 200 ml of 10% AA-based electrolyte was used as the electrolyte. For all the electrolysis samples, the discard electrolysis for removing the surface contamination was first performed just before the electrolysis operation 101 once. The amount of electrolysis was controlled by the electrolysis time calculated in the previous average particle diameter pre-calculation operation 306. The current density during electrolysis was ² mA / cm ² for all electrolytic samples.

  As a dispersible solution used in the extraction operation 102, a sodium hexametaphosphate aqueous solution having a concentration of 500 mg / l was used and prepared in another beaker. During the extraction operation 102, ultrasonic vibration was applied to the dispersible solution to disperse the fine particles adhered to the surface of the electrolysis sample in the aqueous solution of sodium hexametaphosphate.

  Then, the electrolysis operation 101 to the extraction operation 102 were repeated 10 times for one electrolysis sample, and then the magnetic separation operation 103 was performed. Here, in order to collect statistically reliable data, all the fine particles obtained by repeating the electrolysis operation 101 to the extraction operation 102 for one electrolysis sample 10 times are extracted into the same dispersive solution. did.

  The magnetic separation operation 103 was performed by putting a magnetic rod in the dispersible solution and stirring. In addition, during the magnetic separation operation 103, ultrasonic vibration was applied to the dispersible solution.

  Further, in the centrifugal separation step S4072 for removing the large-diameter side fine particles, the dispersible solution after the magnetic separation operation 103 was filled in the centrifuge cell with the fine particles dispersed. Then, the centrifuge was operated under the conditions where the rotation speed was 9000 rpm and the time was 2 minutes.

  Thereafter, the particle size distribution of the fine particles in the dispersible solution was measured with a dynamic light scattering type particle size distribution measuring apparatus, and the obtained results are shown in FIG. Compared to the inventive example and the comparative example of Example 1 shown in FIG. 5, the median value (median) of the particle size distribution of Example 4 is shifted to a smaller particle size side. From this, it was found that the particle distribution on the smaller diameter side can be measured by adding the large diameter side particle diameter removing operation 407 after the classification operation 104. In addition, since the optimal centrifugation conditions differ with a sample, it is necessary to optimize according to a sample.

The figure which showed the analysis flow of the example of embodiment which concerns on this invention. The figure which showed typically the structure of the electrolyzer used with the analysis method which concerns on this invention. The figure which showed the analysis flow of the example which added the average particle diameter prior calculation operation 306 to FIG. The figure which showed the analysis flow of the example which added the large diameter side particle removal operation 407 to FIG. The figure which showed the result of the particle size distribution measurement in this invention example and a comparative example. The figure which showed the result of the particle size distribution measurement in case the electrolytic thickness is 6 times and 36 times the prior average particle size in terms of steel thickness. The figure which showed the correlation with the electrolytic thickness with respect to a prior average particle diameter, and the average particle diameter of the extracted microparticles | fine-particles. The figure which showed the correlation with the current density in an electrolysis method, and the average particle diameter of the extracted microparticles | fine-particles. The figure which showed the result of the particle size distribution measurement at the time of adding centrifugation step S4071 after the classification operation 104 in an electrolysis method. The figure which showed the particle size distribution of the fine particle in steel when a dispersible solution is made into pure water (invention example) or methanol (comparative example). The figure which showed the example of the relationship between the sodium hexametaphosphate aqueous solution density | concentration and zeta potential, or the sodium hexametaphosphate aqueous solution density | concentration and the measured average particle diameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolysis sample 2 Electrolytic sample fixing jig 3 Electrode 4 Beaker 5 Constant current electrolysis apparatus 6 Electrolytic solution 7 Electrolysis apparatus 100 Preparatory operation 101 Electrolysis operation 102 Extraction operation 103 Magnetic separation operation 104 Classification operation 105 Analytical operation 306 Average particle Diameter pre-calculation operation 407 Large-diameter side particle removal operation S1021 Washing step S1022 Extraction step S1023 Judgment step S3061 Average particle diameter pre-analysis step S3062 Electrolytic amount calculation step S4071 Filtration step S4072 Centrifugation step

Claims (5)

Electrolytic operation for electrolyzing the steel sample, and extraction operation for extracting the fine particles in the steel sample by immersing the remainder of the steel sample after the electrolysis in a solution different from the electrolytic solution used for the electrolysis and having dispersibility When,
An analysis operation for analyzing fine particles extracted in the solution after the extraction operation by a dynamic light scattering method.   The method for analyzing fine particles in steel according to claim 1, wherein the dispersible solution is an aqueous solution of sodium hexametaphosphate.   3. The method for analyzing fine particles in steel according to claim 1, wherein in the analysis operation, fine particles having an average particle size of 1 μm or less are analyzed.   The method for analyzing fine particles in steel according to any one of claims 1 to 3, wherein in the analysis operation, only fine particles adhering to the steel sample are analyzed.   Filtration operation for filtering the fine particles extracted into the solution to obtain a filtrate containing fine particles on the small diameter side to be analyzed, and the filtrate containing the fine particles obtained by the filtration operation in a dynamic light scattering method 5. The method for analyzing fine particles in steel according to claim 1, further comprising:

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