JP2018130670A - Dispersant, dispersant for field flow fractionation, fractionation method of fine particle in steel material and analysis method of fine particle in steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersant capable of dispersing fine particles containing Ti and V in steel material.SOLUTION: A dispersant which contains any one kind or more of cholates, cholate ester, deoxycholates, chenodeoxycholates, ursodeoxycholates, hyodeoxycholates, hyodeoxycholate ester, lithocholates, dehydrocholates, oxochenodeoxycholates, glycocholates, glycodeoxycholates. glycochenodeoxycholates, glicoursodeoxycholates or glicolithocholates is adopted.SELECTED DRAWING: None

Description

  The present invention relates to a dispersant, a dispersant for field flow fractionation, a method for fractionating fine particles in a steel material, and a method for analyzing fine particles in a steel material.

  In recent years, there has been an increasing demand for higher quality metal materials. Relatively large inclusions generated during the deoxidation process of steel and the like are the causes of significant deterioration in the quality of steel materials. For example, alumina-based oxides cause many adverse effects such as surface defects in thin steel plates for automobiles, cracks when making cans of beverage cans, and causes of disconnection when drawing wire products. Thus, many efforts have been made to reduce the amount and size of such inclusions.

  On the other hand, many efforts have been made to artificially increase or decrease the amount and size of fine precipitates to further improve the quality of steel materials. For example, in many heat treatment processes such as hot rolling, cold rolling, continuous annealing, strain relief annealing, and welding, many significant fine precipitates are precipitated in the steel, or the crystal grain size of the steel material is made finer. Strength and weld zone toughness are improved. In addition, the amount of fine precipitates is reduced, the crystal grain size is increased, and the iron loss is improved.

  Therefore, in order to industrially mass-produce these high-quality steels with high reproducibility, accurate analysis is insufficient only with the analysis values of conventional components, and the amount and size of fine particles contained in the steel material. It is important to develop a particle size distribution measurement method that can accurately and accurately evaluate the particle size.

  As conventional inspection methods for fine particles in steel, there are known microscopic test methods such as the ASTM method, the JIS method, and the MICHELIN method developed by MICHELIN. For example, in the microscope test method defined in Non-Patent Document 1, after polishing a metal sample, the magnification of the microscope is set to 400 times, and at least the number of fields of view is 60 or more. It determines the cleanliness of steel. In any of these conventional methods, the inspection speed is slow because visual inspection is performed using an optical microscope. There is also a problem in that it is difficult to perform measurement with high accuracy because a certain scale for distinguishing inclusions from misidentification factors such as dust, abrasive flaws, and rust is not clear.

  Patent Document 1 describes a method aiming to compensate for such a low number density in microscopic observation. In this conventional method, first, steel is electrolyzed, and the extracted residue is dropped and dried on a support film to prepare a sample having an extremely large number of residue particles. Next, this sample is subjected to optical microscope analysis, scanning electron microscope (SEM) analysis, transmission electron microscope (TEM) analysis, and the like. Patent Document 1 describes that, as an effect of such a method, highly representative particle size distribution data including a large number of particles can be obtained.

  However, in this method, in order to measure the particle size distribution of all sizes from each photograph at the time of microscopic analysis, a large number of photographs and image processing are required, and a number count by a human is also required. For this reason, the inspection speed cannot be improved, and individual differences are likely to occur and it is difficult to obtain high reproducibility.

  Therefore, recently, as described in Patent Document 2, using a field flow fractionation device, fine particles in a metal material are separated for each predetermined size, and the number density of each fine particle divided for each size is determined. A method of measuring and further analyzing the composition of each fine particle by ICP mass spectrometry is disclosed.

JP 2004-317203 A Japanese Patent No. 4572001

JIS G 0555 (2003), JIS Handbook (Steel I), Japanese Standards Association

In Patent Document 2, sodium dodecyl sulfate (hereinafter referred to as SDS) is used as a dispersant for field flow fractionation (hereinafter referred to as FFF), and a developing solution containing SDS is separated by size by FFF. It is introduced into the ICP mass spectrometer together with the fine particles. SDS generates polyatomic molecular ions such as ³² S ¹⁶ O ⁺ and ³⁴ S ¹⁶ O ¹ H ⁺ in ICP mass spectrometry. ³² S ¹⁶ O ⁺ shows an ion peak at m / z = 48 in the mass spectrum, and ³⁴ S ¹⁶ O ¹ H ⁺ shows an ion peak at m / z = 51. That is, in the analysis method of Patent Document 2, the ion peak of m / z = 48, 51 is always detected as the background.

By the way, the carbide | carbonized_material, nitride, etc. of Ti and V may exist in the microparticles | fine-particles in the steel material containing Ti and V. Ti mainly shows an ion peak at m / z = 48 in mass spectrometry, and V mainly shows an ion peak at m / z = 51, but the ion peaks at m / z = 48, 51 of Ti and V are Overlapping the ion peaks of polyatomic molecular ions due to SDS as background, causing mass spectral interference. Thus, in the method of Patent Document 2, since a developing solution in which sodium dodecyl sulfate (SDS) is added as a dispersant is used, mass spectrum interference occurs due to sulfur polyatomic molecular ions, and trace amounts of Ti and V can be detected. It was difficult.
In addition, fine particles separated from steel materials by techniques such as electrolytic extraction may be directly introduced into various analyzers such as ICP mass spectrometry for analysis. In this case as well, the fine particles are dispersed and the mass spectrum is dispersed. A dispersion that did not cause interference was required.

  The present invention relates to a dispersant capable of dispersing fine particles containing Ti and V in a steel material, a dispersant for field flow fractionation, a method for fractionating fine particles in a steel material, and the fine particles in a steel material. The issue is to provide an analysis method.

Field flow fractionation is a method for separating fine particles by size using the diffusion phenomenon of fine particles in a developing solution. A dispersing agent is added to the developing solution used to suppress aggregation of fine particles. ing. Since the conventional dispersant (SDS) containing sulfur causes mass spectrum interference when identifying fine particles containing Ti and V as described above, a dispersant containing no sulfur was searched. As a result, cholic acids, which are a type of bile acid, can disperse fine particles containing Ti and V in steel materials, and these fine particles can be separated by particle size in field flow fractionation. It has been found that mass spectrum interference does not occur between Ti and V in mass spectrometry because sulfur does not contain sulfur. Furthermore, it has been found that cholic acids can prevent the aggregation of fine particles even in the electrolytic extraction method.
The dispersant containing cholic acids can also be applied to the case where fine particles separated by a technique such as electrolytic extraction are introduced into various analyzers such as ICP mass spectrometry.
The gist of the present invention based on such knowledge is as follows.

(1) Cholate, cholate, deoxycholate, kenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholate, lithocholic acid, dehydrocholate, oxokenodeoxy Dispersant containing any one or more of cholate, glycocholate, glycodeoxycholate, glycochenodeoxylate, glycoursodeoxycholate or glycolitocholate.
(2) Cholate, cholate, deoxycholate, kenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholate, lithocholic acid, dehydrocholate, oxokenodeoxy Field flow fraction containing one or more of cholate, glycocholate, glycodeoxycholate, glycochenodeoxylate, glycoursodeoxycholate or glycolitocholate Nation dispersant.
(3) A fine particle extracted and separated from a steel material is a method for fractionating each particle size by a field flow fractionation method, and as a developing solution for the field flow fractionation method, the dispersing agent according to (2) above A method for fractionating fine particles in steel materials using field flow fractionation using a developing solution obtained by adding water to water.
(4) After performing electrolytic extraction on the steel material in an electrolytic solution containing the dispersant described in (2) above, the steel material is added to the extract containing the dispersant described in (2) above. A first step of immersing and dispersing the fine particles in the extract;
A developing solution in which the dispersant described in (2) above is added to water as a developing solution for the field flow fractionation method, and the extract containing the fine particles obtained in the first step is used as a sample solution. A second step of performing a field flow fractionation method and separating the fine particles by particle size;
A third step of analyzing a component of the fine particles by ICP mass spectrometry; and a method of analyzing the fine particles in the steel material.
(5) Between the second step and the third step, the fine particles separated for each particle size are irradiated with laser light, and the absolute value of the particle size of the fine particles is measured from the angle dependency of the reflection intensity. In addition, the method for analyzing fine particles in the steel material according to (4), wherein a measurement step of measuring the number density from the strength of the reflection intensity is performed.
(6) After performing electrolytic extraction on the steel material in an electrolytic solution containing the dispersant described in (1) above, the steel material is added to the extract containing the dispersant described in (1) above. Immersing and dispersing the fine particles in the extract;
Analyzing the components of the fine particles by ICP mass spectrometry, and analyzing the fine particles in the steel material.

  ADVANTAGE OF THE INVENTION According to this invention, the dispersing agent which can disperse | distribute the microparticles | fine-particles containing Ti and V in steel materials, the dispersing agent for field flow fractionation, the separation method of the microparticles | fine-particles in steel materials, and in steel materials A method for analyzing fine particles can be provided. In addition, according to the present invention, it is possible to classify the fine particles by size in the field flow fractionation after the fine particles are dispersed, and to prevent the occurrence of mass spectral interference in ICP mass spectrometry. it can.

FIG. 1 is a flowchart for explaining an example of a method for analyzing fine particles in a steel material according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining another example of a method for analyzing fine particles in a steel material according to an embodiment of the present invention. FIG. 3 is a schematic diagram for explaining the electrolytic extraction method in the first step. FIG. 4 is a schematic diagram for explaining the field flow fractionation method in the second step. FIG. 5 is a view showing a result of performing separation of gold nanocolloid particles by a field flow fractionation method using various dispersants. FIG. 6 is a diagram showing a result of performing fine particle separation in a steel material by a field flow fractionation method using sodium dodecyl sulfate as a dispersant. FIG. 7 is a diagram showing the result of the separation of fine particles in a steel material by a field flow fractionation method using sodium cholate as a dispersant. FIG. 8 is a view showing the result of the fine particle separation in the steel material before and after heat treatment by the field flow fractionation method using sodium cholate as a dispersant.

  Hereinafter, the dispersant, the dispersant for field flow fractionation, the method for fractionating fine particles in the steel material, and the method for analyzing the fine particles in the steel material, which are embodiments of the present invention, will be described.

  1 and 2 are flowcharts showing a method for separating fine particles in a steel material and a method for analyzing fine particles in a steel material. As shown in FIG. 1 and FIG. 2, the method for fractionating fine particles in steel materials is based on the field flow fractionation method using an extract containing fine particles electrolytically extracted from steel materials as a sample solution. A step (second step shown in FIG. 1 and FIG. 2) for sorting each time is provided. The method for analyzing fine particles in a steel material includes a first step in which after the electrolytic extraction is performed on the steel material, the steel material is immersed in the extract and the fine particles are dispersed in the extract. And a third step of analyzing the components of the fine particles separated in the second step by ICP mass spectrometry. Further, in the method for analyzing fine particles in the steel material of this embodiment, as shown in FIG. 2, the absolute value of the particle size of the fine particles and the number density of the fine particles are measured between the second step and the third step. A measurement step may be performed.

  In the method for analyzing fine particles in a steel material according to this embodiment, first, in a first step, the fine particles contained in the steel material are extracted and separated by performing electrolytic extraction on the steel material. In this embodiment, the addition of cholic acids as a dispersant to the electrolytic solution and the extract prevents the fine particles from agglomerating and facilitates the separation of the particle size of the fine particles in the next second step field flow fractionation method. To do. In the second step, which is a method for fractionating fine particles in steel materials, the addition of cholic acids to the developing solution prevents the adhesion of fine particles to the permeable membrane installed in the channel in the field flow fractionation method. In addition, by facilitating the dispersion of the fine particles in the channel, the fine particles are caused to flow out of the system in order from the particles having a large diffusion coefficient. Then, the discharged fine particles are sequentially introduced into the ICP mass spectrometer in the third step to perform the qualitative analysis of the fine particles, and the holding time from the start of the second step to the detection time of the fine particles in the ICP mass analysis is measured. To estimate the particle size. Since cholic acids do not contain sulfur, mass spectrum interference between Ti and V does not occur as in the prior art. Further, the particle size and number density of the fine particles may be separately measured between the second step and the third step.

  The cholic acids in this embodiment are cholic acid ester, deoxycholate, chenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholic acid ester, lithocholic acid salt, dehydrocholate, It refers to any one or two or more of chenodeoxylate, glycocholate, glycodeoxycholate, glycochenodeoxycholate, glycoursodeoxycholate or glycolitocholate.

Cholic acids, a kind of bile acid, have three phenolic hydroxyl groups and one carboxyl group in the molecule, and show a strong surface activity in aqueous solution. Has been. Cholic acids can be extracted and dispersed without agglomerating fine particles in steel. Furthermore, cholic acids are obtained by fractionating nano-carbides containing Ti and V obtained by electrolytic extraction from model steel materials by size by the field flow fractionation method (FFF method), and TiC that could not be detected in the past by ICP mass spectrometry. And V ion peaks can be detected. The inventors have found the above findings and have reached the present invention. Generally, SDS and CTAB, which are ionic surfactants, Triton X-100, Tween 20, which are nonionic surfactants, NaCl, NaN ₃ and NH ₄ NO ₃ which are electrolyte salts are used as a developing solution in the FFF method. Etc. are used. It is known that the type of solvent that can be applied differs depending on the type and size of the fine particles, but it can be applied if it does not impair the presence state of the measurement sample. On the other hand, when a salt such as citric acid or ammonium acetate that does not contain sulfur is used, there is a problem that separation and detection cannot be performed even though the dispersibility of the fine particles is not impaired. In the present invention, by using cholic acids as a dispersing agent, it has succeeded in clearly grasping the coarsening (2.1 nm → 3.8 nm) of fine particles (nanoprecipitates) due to heat treatment of steel materials. From this analysis result, it was found that cholic acids can be suitably used as a dispersant for a developing solution in the FFF method.
It has also been found that a dispersing agent may be added to the electrolytic solution in the electrolytic extraction method and the extract that separates and disperses the fine particles in the steel after the electrolysis.

  Details of each step will be described below.

(First step)
As methods for extracting and separating fine particles contained in steel materials, acid decomposition methods, halogen decomposition methods, and electrolytic extraction separation methods are known. In this embodiment, inclusions and precipitates in steel materials are dissolved as much as possible. Electrolytic extraction separation method is used because it is necessary to perform extraction without the use of an organic solvent. In particular, among the electrolytic extraction separation methods, it is more preferable to apply a nonaqueous solvent-based constant potential electrolysis method (SPEED: Selective Potentiostatic Etching by Electrolytic Dissolution Method). The SPEED method is suitable because the composition and size hardly change when the fine particles are dispersed in a solvent, and even unstable fine particles can be stably extracted. However, the extraction separation method in the present invention is not limited to the SPEED method.

  FIG. 3 shows the electrolytic extraction apparatus used in the first step. The electrolytic extraction apparatus shown in FIG. 3 includes an electrolytic cell 10, a cathode 6 disposed in the electrolytic cell 10, an anode 4 disposed in the electrolytic cell 10, a power supply 8 to which the cathode 6 and the anode 4 are connected, It is composed of Further, the electrolytic extraction apparatus shown in FIG. 3 is provided with a reference electrode 7 for measuring the potential of the anode 4. The reference electrode 7 is connected to the power source 8.

An electrolytic solution 9 described later is accommodated in the electrolytic cell 10. The electrolytic cell 10 may have a structure that can be sealed or an inert gas atmosphere in order to suppress oxidation of the electrolyzed iron.
Moreover, the anode 4 is comprised from the steel material 4a which is an electrolysis target object, and the holding means 4b which hold | maintains the steel material 4a. Examples of the holding means 4b include a metal clip that holds the steel material 4a and can ensure energization. In the steel material 4a, the surface to be the electrode surface may be polished in advance to remove the natural oxide film. The steel material 4a is not particularly limited, but the steel material 4a containing inclusions and precipitates containing Ti or V as fine particles is preferable.
Furthermore, as the cathode 6, a platinum electrode can be exemplified.
The power source 8 is preferably one that can precisely control the voltage and current. For example, a constant voltage power source such as an electrochemical potentiostat or a constant current power source such as a galvanostat may be used. .

  Next, a method for extracting and separating fine particles in the steel material using the electrolytic extraction apparatus shown in FIG. 3 will be described. First, the electrolytic bath 9 is filled with the electrolytic solution 9, the steel material 4a is immersed therein, and the reference electrode 7 is disposed near the steel sample 4a. The cathode 6 and the anode 4 are connected to a power source 8. Compared to the electrolytic potential of iron that is a matrix of the steel material 4a, the electrolytic potential of fine particles in steel such as precipitates has a higher electrolytic potential. Therefore, by using the power source 8 to dissolve the matrix of the steel material 4a and to set a voltage between the electrolytic potentials that do not dissolve fine particles such as precipitates, only the matrix is selectively dissolved. The fine particles 5 in the steel material 4 a are exposed on the surface layer portion of the steel material 4 a, and a part thereof is dispersed in the electrolytic solution 9.

  Next, the steel material 4a is gently taken out and immersed in a clean extract. And by irradiating these with ultrasonic waves etc., the fine particles 5 adhering to the surface layer portion of the steel material 4a are detached from the steel material 4a. As a result, an extract containing fine particles 5 extracted from the steel material 4a is obtained.

  The irradiation time of the ultrasonic wave varies depending on the output and the amount of liquid, but if left for more than 10 minutes, it is heated and the content of the extract containing the dispersant is likely to change. On the other hand, if it is less than 1 minute, dispersion may be insufficient.

  In this way, an extract in which the fine particles 5 are dispersed is obtained, but the size of the fine particles 5 contained in the extract may include a wide range of coarse particles. In the next second step, field flow fractionation is performed. There is a possibility that coarse particles in the apparatus (hereinafter sometimes referred to as FFF apparatus) are clogged. For this reason, it is preferable to remove the coarse particles 5 in advance. For example, it may be pre-filtered with a filter of several μm mesh. In addition, it takes several minutes or more in a centrifugal separator to settle coarse particles of 1 μm or more downward, collect the supernatant liquid of the obtained liquid, and introduce it into the FFF apparatus in the second step. Good.

Next, the electrolytic solution and the extract used in the first step will be described.
The basic composition of the electrolytic solution is, for example, 10% by mass acetylacetone (hereinafter referred to as “AA”)-1% by mass tetramethylammonium chloride (hereinafter referred to as “TMAC”)-methanol solution, or 10% by mass maleic anhydride-2. A mass% TMAC-methanol solution can be illustrated. In addition, an electrolyte solution in which a chelating reagent that forms a chelate complex with a metal ion such as methyl salicylate and an electrolyte for passing a current such as tetramethylammonium chloride (TMAC) is dissolved in a methanol solvent that is a non-aqueous solvent is used. May be. In the above basic composition, methanol is exemplified as the solvent, but it may be water or other alcohols such as ethanol. Although water is the most readily available solvent, alcohols such as methanol may be used as a solvent when analyzing fine particles that are soluble in water.

  In addition to the above basic composition, a dispersant composed of cholic acids is further added to the electrolytic solution according to the present embodiment. By using the electrolytic solution 9 to which a dispersing agent is added, electrolytic extraction can be performed without agglomerating the fine particles 5 such as inclusions. When a dispersant composed of cholic acids is added, the dispersant is stably wrapped around the microparticles 5 immediately after being separated from the metal matrix and released into the electrolytic solution 9, so that the microparticles are encapsulated. Presumed to be less likely to aggregate. Further, when the electrolytically extracted fine particles 5 are dispersed in the extract, an effect that the fine particles 5 are easily dispersed quickly into a single particle can be obtained. In addition, the dispersing agent which consists of cholic acids which concerns on this embodiment is added not only to electrolyte solution but to the extract solution used for electrolytic extraction, and the developing solution used for the 2nd step field flow fractionation method. A detailed description of the dispersant will be described later.

  Due to the dispersion effect of the fine particles by the dispersant, even if the fine particles 5 are very unstable, for example, to drugs and / or moisture, it is possible to extract stably and efficiently. The concentration of the dispersant to be added is preferably 0.005% by mass to 0.1% by mass, and more preferably 0.01% by mass to 0.05% by mass. If the concentration is less than 0.005% by mass, the dispersion action of the fine particles becomes weak because the film is too thin. Moreover, since it will become easy to produce | generate a bubble when a density | concentration is too deep, it is unpreferable on an operation | work.

  Moreover, what extracted the dispersing agent which consists of cholic acids in the solvent is used for the extract which extracts microparticles | fine-particles from the steel material after electrolytic extraction. As the solvent, alcohols such as methanol and ethanol, or water can be used, but in order to prevent deterioration of the fine particles due to changes in the environment where the fine particles are present, the same solvent as the electrolytic solution used in the electrolytic extraction method is used. It is preferable to use, for example, in the case of using the electrolytic solution having the basic composition described above, methanol may be used as the extraction liquid.

  The concentration of the dispersant in the extract is preferably 0.005% by mass to 0.1% by mass, and 0.01% by mass to 0.05% by mass, as in the case of the electrolytic solution. More preferred. When the concentration is less than 0.005% by mass, the action of dispersing the fine particles becomes weak because the film is too thin. Moreover, since it will become easy to produce | generate a bubble when a density | concentration is too deep, it is unpreferable on an operation | work.

  By adding a dispersant composed of cholic acids to the extract, aggregation of the fine particles 5 such as inclusions in the extract can be prevented, and the fine particles 5 can be dispersed individually. If a dispersant composed of cholic acids is added, it is presumed that the dispersant stably protects and wraps around the fine particles 5, and the fine particles are less likely to aggregate.

(Second step)
Next, in the second step, the extraction liquid containing the fine particles is used as a sample liquid, and the fine particles are separated for each particle size by the field flow fractionation method. In FIG. 4, the cross-sectional schematic diagram of the field flow fractionation apparatus (FFF apparatus) used for a 2nd step is shown. The FFF apparatus shown in FIG. 4 includes a separation cell 16 through which a developing solution flows, a permeable membrane 21 disposed in the separation cell 16, and a crossflow introduction unit (not shown) that introduces the crossflow 14 into the separation cell 16. A sample introduction section (not shown) for introducing the sample liquid 15 into the separation cell 16 and a control means (not shown) for controlling the flow of the developing solution and the cross flow 14 in the separation cell 16 are provided.

The separation cell 16 is configured by arranging an upper housing 16a and a lower housing 16b at a predetermined interval. A space between the upper housing 16a and the lower housing 16b serves as a channel portion 16c through which the developing solution flows.
The lower housing 16b constituting the separation cell 16 is made of a mesh-like member. A permeable membrane 21 is laminated on the surface of the lower housing 16b on the channel part 16c side. The permeable membrane 21 is permeable to liquids such as an extraction solution and a developing solution, but not permeable to fine particles contained in the sample solution.
Further, an ICP mass spectrometer (not shown) is connected to the right side of the separation cell 16 in the drawing.

  Control means (not shown) controls the flow of the developing solution and the cross flow 14 in the channel part 16c of the separation cell 16, and includes a pipe, a control valve, a control part for controlling the operation of the control valve, and the like. The control means can introduce the developing solution from both the left and right sides of the separation cell 16 shown in FIG. 4 and can distribute the developing solution from the left side to the right side in the drawing. Further, the control means can introduce the cross flow 14 from the upper side of the channel portion 16c as shown in FIG. The cross flow 14 is a flow from the top to the bottom of FIG.

  Next, the operation of the FFF device will be described. As a developing solution for the FFF apparatus, an aqueous solution in which a dispersant composed of cholic acids is dissolved is used. First, a flow of a developing solution called a cross flow 14 is generated from the upper side to the lower side of the separation cell 16. Further, the developing solution is also flowed from the left side and the right side of the separation cell 16. Thereby, the flow of the developing solution flowing so as to be opposed from the left and right sides is guided to the flow of the cross flow 14 to form a flow toward the permeable membrane 21.

  After this flow is stabilized, the sample solution 15 containing fine particles is added. Then, the fine particles are locally concentrated in the vicinity of the permeable membrane 21 along the flow of the developing solution. When the flow of the developing solution is maintained for a predetermined time, the fine particles gradually diffuse with Brownian motion. Large sized large particles 20 are pressed against the lower permeable membrane 21 by the flow of the cross flow 14, while the relatively small medium particles 19 and small particles 18 overcome the flow of the cross flow 14. Only the Brownian motion occurs, and the material is floated in the separation cell 16 without being pressed against the permeable membrane 21 located on the lower side of the separation cell 16. Smaller particles 18 are more likely to float upward. This operation is called focusing. In this state, the fine particles are rearranged for each size in the separation cell 16. The holding time for focusing may be set to a time such that the position of the small particles 18 does not exceed the center position in the thickness direction of the channel portion 16c.

  Thereafter, while maintaining the cross flow 14, the flow of the developing solution pressed from the left and right of the separation cell 16 is changed to form a channel flow 17 made of the developing solution. Specifically, as shown in FIG. 4, a flow is formed in which the fine particles in the separation cell 16 are pushed to the right side from the left side to the right side. The channel flow 17 is a laminar flow and has a flow velocity distribution as shown in FIG. That is, the flow velocity at the center in the thickness direction of the channel portion 16c is the fastest, and the flow velocity is slowed away from the center. That is, the flow velocity is high in the region where the small particles 18 are present, and the flow velocity is small in the region where the large particles 20 are present.

  At this time, if the pressure of the cross flow 14 that keeps the fine particles in the vicinity of the permeable membrane 21 is gradually reduced, the fine particles held in the vicinity of the separation membrane 21 ride on the laminar flow of the channel flow 17, Gradually, small particles are discharged to the right in order of large particles.

  In addition, although the example which carried out size separation by combining the pressing force by a crossflow liquid and Brownian motion for separation was shown here, as a separation principle of FFF, besides this, gravity, electric field, magnetic field By applying a temperature gradient or the like, the particles can be separated more precisely.

  The microparticles separated for each size are guided by channel flow 17 to an ICP mass spectrometer installed outside the FFF apparatus. Fine particles arrive at the ICP mass spectrometer in ascending order of particle size. The reached fine particles are decomposed to the atomic level by the thermal energy of the plasma, then ionized, and introduced into the mass spectrometer. A mass spectrum that is unique to each microparticle is obtained by the mass spectrometer. In addition, a chart of the time change amount of each ion with the detected amount of each ion as the vertical axis and the detection time as the horizontal axis is also obtained.

  Further, a laser light irradiation detection unit may be disposed between the FFF device and the ICP mass spectrometer. The light intensity scattered by the laser beam is obtained from photodetectors installed at a plurality of angles in the laser beam irradiation detection unit. In the case of a small particle, the angle dependency is very small and an omnidirectional scattering phenomenon is exhibited. On the other hand, since the forward scattering phenomenon becomes stronger as the particles become coarser, the size of the electrolytic extraction particles 5 can be uniquely determined by taking the inclination of the angle dependency.

  The developing solution used in the FFF method is an aqueous solution in which a dispersant is dissolved. The solvent is preferably water. If a solvent other than water is used, the plasma cannot be stably maintained in the ICP mass spectrometer. The dispersant is preferably made of cholic acids as in the case of the electrolytic solution and the extract described above. The concentration of the dispersant in the developing solution is preferably 0.005% by mass to 0.1% by mass, as in the case of the electrolytic solution or the extract. If the concentration is less than 0.005% by mass, the action of dispersing the fine particles becomes too weak, and the fine particles are aggregated in the separation cell 16 so that Brownian motion does not occur, and the fine particles cannot be separated according to particle size. On the other hand, if the concentration is too high, bubbles are likely to be generated, and sensitivity and accuracy are reduced in ICP mass spectrometry.

Next, the dispersant according to this embodiment will be described. The dispersant of the present embodiment is added to the electrolytic solution and the extract used in the first step and the developing solution used in the second step, respectively, to prevent the aggregation of fine particles and improve the dispersibility. Facilitates sorting. Dispersants include cholate, cholate, deoxycholate, chenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholate, lithocholic acid, dehydrocholate, oxocheno It includes any one or more of deoxycholate, glycocholate, glycodeoxycholate, glycochenodeoxylate, glycoursodeoxycholate or glycolitocholate. As a kind of salt, it is preferable that they are alkali metal salts, such as sodium salt and potassium salt, and especially sodium salt is good. The esters are preferably methyl or ethyl.
The specific chemical structural formulas of cholic acids applicable to this embodiment are shown below.

The above cholic acids do not contain a sulfur atom in the molecule. For this reason, even if these cholic acids are introduced into the ICP mass spectrometer, polyatomic molecular ions such as ³² S ¹⁶ O ⁺ (m / z = 48) and ³⁴ S ¹⁶ O ¹ H ⁺ (m / z = 51) are Not generated. Thereby, it is possible to reliably detect Ti and V without causing mass spectrum interference with Ti (m / z = 48) and V (m / z = 51).

  In addition, the above-mentioned cholic acids have a carboxyl group in the molecule and have a negative charge in the developing solution. When the developing solution containing cholic acids is introduced into the separation cell of the FFF apparatus, it collects on the surface of the permeable membrane 21 and the surface of the permeable membrane 21 is negatively charged. On the other hand, it is assumed that the extract liquid, which is a sample liquid of the FFF method, contains fine particles separated and extracted from the steel material together with the dispersant, and the fine particles in the liquid are surrounded by cholic acids as the dispersant. Therefore, the fine particles are negatively charged.

  For this reason, even if the sample liquid is introduced into the FFF device, the negatively charged fine particles are not adsorbed by the negatively charged permeable membrane 21, and the Brownian motion in the channel portion 16c is not inhibited. Thereby, the classification for each particle size is performed smoothly.

  As described above, the dispersant for field flow fractionation of the present embodiment can be dispersed without agglomerating fine particles by adding to the developing solution in the field flow fractionation method, Fine particles extracted and separated from the steel material can be separated by size. In addition, since the dispersant of the present embodiment does not contain sulfur in the molecule, it does not cause mass spectrum interference with Ti or V when performing ICP mass spectrometry, and does not interfere with qualitative analysis of fine particles. It can be carried out.

  Further, according to the method for fractionating fine particles in the steel material of the present embodiment, by adding cholic acids to the developing solution, the fine particles adhere to the separation membrane installed in the channel in the field flow fractionation method. In addition, it is possible to facilitate the dispersion of the fine particles in the channel and to allow the fine particles to flow out of the system in order from the particles having the largest diffusion coefficient.

  Furthermore, according to the method for analyzing fine particles in the steel material of the present embodiment, the addition of cholic acids as a dispersant to the electrolytic solution and the extract prevents the fine particles from agglomerating, and the field flow fracture of the next second step is performed. In the Shonation method, the particle size of the fine particles can be easily separated. In addition, since cholic acids do not contain sulfur in the molecule, no mass spectral interference occurs between Ti and V when ICP mass spectrometry is performed, and qualitative analysis of fine particles can be performed without hindrance.

  In the present embodiment, the case where the first step, the second step, and the third step are sequentially performed has been described. However, the second step may be omitted. That is, after extracting the fine particles from the steel material in the first step, the extracted fine particles may be analyzed by ICP mass spectrometry. In the first step, the dispersant of this embodiment may be added to the electrolytic solution and the extract. Addition of cholic acids as a dispersant to the electrolyte and extract prevents aggregation of fine particles, and causes mass spectral interference with Ti and V when performing ICP mass spectrometry in the next third step Therefore, qualitative analysis of fine particles can be performed without any trouble.

Examples of the present invention will be described below.
(Experimental example 1)
A sample aqueous solution containing gold nanoparticles having an average particle diameter of 2 nm and gold nanoparticles having an average particle diameter of 5 nm was prepared. SDS, citric acid, NaCl, NH ₄ NO ₃ , sodium cholate and sodium deoxycholate were added to each sample aqueous solution as a dispersant. The concentration of each dispersant was 500 ppm by mass.
In addition, aqueous solutions containing SDS, citric acid, NaCl, CH ₃ COONH ₄ , sodium cholate, and sodium deoxycholate were prepared as developing solutions for the FFF method. The concentration of each dispersant was 500 ppm by mass.

Next, using the FFF apparatus shown in FIG. 4, the gold nanoparticles contained in the sample aqueous solution were separated. Instead of the ICP mass spectrometer, an ultraviolet spectrophotometer was used as the detection device.
The operating condition of the FFF apparatus was that the developing solution and the cross flow were allowed to flow for 1 minute, then 50 μL of the sample aqueous solution was introduced at a rate of 0.2 mL / min, and focusing was performed for 1 minute. After focusing at a flow rate of 0 mL / min, the cross-flow flow rate was gradually reduced.
The developing solution was introduced into an ultraviolet spectrophotometer as a channel flow that flowed out of the FFF apparatus, and the change in absorbance with time was examined. The results are shown in FIG.

  As shown in FIG. 5, when SDS, sodium cholate and sodium deoxycholate were used as the dispersant, the first peak appeared about 6.9 minutes after the start of introduction of the channel flow, and about 10.9 A second peak appeared after minutes. The first peak was a peak of gold nanoparticles having an average particle diameter of 2 nm, and the second peak was a peak of gold nanoparticles having an average particle diameter of 5 nm.

On the other hand, when citric acid, NaCl, or CH ₃ COONH ₄ was used as a dispersant, no peak appeared. The reason why the peak did not appear is presumed that the gold nanoparticles adhered to the permeable membrane of the FFF device and were not discharged even by the channel flow.
In addition, when the sample solution was not added with a dispersant and the developing solution was ultrapure water containing no dispersant, a small peak appeared as shown in FIG. 5, but the average particle size was 2 nm and 5 nm. There was no corresponding peak.

(Experimental example 2)
By mass%: C: 0.093%, Si: 0.06%, Mn: 0.48%, P: 0.001%, S: 0.001%, V: 0.26%, Ti: 0.2 %, Sol-Al: 0.027%, N: 0.0012%, and a model steel material having the balance of iron and impurities was prepared. The model steel material contained Ti carbide and V carbide as fine particles. The average particle diameters of Ti carbide and V carbide were 2.9 nm in the image analysis result by transmission electron microscope observation (TEM observation) and 1.75 nm in the observation result by atom probe tomography (APT).

  The size distribution of these Ti carbides and V carbides was analyzed by applying the FFF method.

  Preparation of the sample solution used for FFF method extracted and isolate | separated microparticles | fine-particles by the constant current electrolytic extraction method using the electrolytic extraction apparatus shown in FIG. After performing preliminary electrolysis for 15 minutes, main electrolysis was performed at 500 mA for 2 hours to electrolyze a steel material equivalent to 1 g. The electrolytic solution has a basic composition of 10% AA-1% TMAC-MeOH solution, and sodium cholate is used as a developing solvent for FFF analysis (eluent) for the purpose of preventing aggregation of fine particles extracted during electrolytic extraction operation. ) And 500 ppm added at the same concentration. The residue extracted on the surface of the steel plate sample was immersed in a 500 ppm sodium cholate-MeOH solution (extraction solution) together with the steel plate sample without filtration, and the fine particles were collected in the solution by ultrasonic cleaning. In this way, a sample solution was prepared.

  The operating conditions of the FFF apparatus were the same as in Experimental Example 1. The developing solution of the FFF method was an aqueous solution containing 500 ppm of sodium cholate. The fine particles separated by the FFF apparatus were analyzed by an ICP mass spectrometer. ICP mass spectrometry was performed under the conditions of Hot plasma (RF 1400W). Further, in order to improve sensitivity, a solvent removal sample introduction method was used, and the sample was introduced under conditions of heating 140 ° C. and cooling 2 ° C.

  Further, as a comparative example, fine particles in the model steel were analyzed in the same manner as described above except that SDS was used instead of sodium cholate.

The results of using a model steel material without heat treatment as a sample are shown in FIGS. As shown in FIG. 6, when conventional SDS was used as a dispersant, 500 ppm of sulfur was contained in the FFF development solution, so Ti in the measurement sample was a natural isotope to avoid mass spectral interference. In the measurement sample, ⁴⁷ Ti was subjected to abundance interference due to ³² S ¹⁶ O ⁺ in the FFF developing solution, and similarly ⁵¹ V in the measurement sample was ³⁴ S ¹⁶ in the FFF developing solvent. Due to mass spectrum interference due to O ¹ H ⁺ , a trace peak was not detected by ICP mass spectrometry. ⁴⁸ Ti was not measured because of the influence of mass spectrum interference.

  On the other hand, when sodium cholate was used as the dispersing agent, it became clear that both peaks of Ti and V could be detected as shown in FIG. 7, and the average size was about 2.1 nm. This value almost coincided with the particle size observed by TEM and APT (TEM: 2.9 nm, APT: 1.75 nm).

  From the above, the effect of SDS substitution by sodium cholate, which is a novel dispersant containing no sulfur, was demonstrated.

  Next, FIG. 8 shows the result of analyzing a measurement sample obtained by subjecting the model steel material to an additional heat treatment at 780 ° C. in the same manner as described above and the result without heat treatment. From FIG. 8, it was clarified that the size distribution of carbides was coarsened as a whole by the heat treatment. Thus, it is considered that the FFF method using a sulfur-free dispersant can quantitatively evaluate the size distribution of Ti and V precipitates in steel.

  4 ... anode, 4a ... steel material, 5 ... fine particles, 6 ... cathode, 9 ... electrolyte, 14 ... cross flow (developing solution), 15 ... sample solution, 16 ... separation cell, 17 ... channel flow (developing solution).

Claims (6)

  Cholate, cholate, deoxycholate, kenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholate, lithocholic acid, dehydrocholate, oxochenodeoxylate A dispersant comprising any one or more of glycocholate, glycodeoxycholate, glycochenodeoxylate, glycoursodeoxycholate, or glycolithocholic acid.   Cholate, cholate, deoxycholate, kenodeoxycholate, ursodeoxycholate, hyodeoxycholate, hyodeoxycholate, lithocholic acid, dehydrocholate, oxochenodeoxylate , Glycocholate, glycodeoxycholate, glycochenodeoxycholate, glycoursodeoxycholate, or one or more of glycolithocholic acid, for field flow fractionation Dispersant.   The fine particles extracted and separated from the steel material are separated by particle size by the field flow fractionation method, and the dispersant according to claim 2 is added to water as a developing solution for the field flow fractionation method. A method for fractionating fine particles in a steel material using field flow fractionation using the developed solution. After performing electrolytic extraction on the steel material in an electrolytic solution containing the dispersant according to claim 2, the extraction is performed by immersing the steel material in an extract containing the dispersant according to claim 2. A first step of dispersing the fine particles in a liquid;
A developing solution in which the dispersant according to claim 2 is added to water as a developing solution for a field flow fractionation method, and the extract containing the fine particles obtained in the first step is used as a sample solution. A second step of performing a field flow fractionation method to separate the fine particles by particle size;
A third step of analyzing a component of the fine particles by ICP mass spectrometry; and a method of analyzing the fine particles in the steel material.   Between the second step and the third step, the fine particles separated for each particle size are irradiated with laser light, and the absolute value of the particle size of the fine particles is measured from the angle dependency of the reflection intensity, The method for analyzing fine particles in a steel material according to claim 4, wherein a measurement step of measuring the number density from the intensity of reflection intensity is performed. After performing electrolytic extraction on the steel material in an electrolytic solution containing the dispersant according to claim 1, the extraction is performed by immersing the steel material in an extract containing the dispersant according to claim 1. Dispersing the fine particles in a liquid;
Analyzing the components of the fine particles by ICP mass spectrometry, and analyzing the fine particles in the steel material.

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