JP2019101002A - Electrolytic solution for extracting metallic compound particles and electrolyte extraction method using the same - Google Patents

Abstract

To provide an electrolytic solution and an extraction method for obtaining the accurate data of a precipitate or an inclusion that is stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol.SOLUTION: Provided is an electrolytic solution 9 used when etching a metal material 4 in the electrolytic solution 9 and extracting metal compound particles in the metal material 4, the electrolytic solution 9 being formed by including ions of a metal M' that satisfies Δ=pK[M'A]-pK[MA]≥10, where K[MA] represents the solubility product of a metal compound MAto be extracted that exists in the metal material 4 and K[M'A] represents the solubility product of a metal compound M'A. Here, M and M' are different metal elements; A is a unit atom or an atom group that forms a compound with M or M'; x, x', y, y' represent the composition ratio of a compound that is determined in accordance with the valences of M, M' and A; the solubility product Kis a value in a 25°C aqueous solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolytic solution used when etching a metal material in an electrolytic solution to extract metal compound particles in the metallic material, and an electrolytic extraction method using the electrolytic solution.

Metallic materials, in particular steel materials, are required for steel materials by controlling the types of inclusions and precipitated phases present in the material matrix and the shape, size, etc. of aspect ratio, etc. by minor additive elements and various heat treatments. Control of strength and characteristics is widely practiced.
Therefore, the observation of inclusions and / or precipitated phases, and the measurement of the components and quantities thereof have important meaning in conducting quality control of steel materials and analysis of manufacturing processes.

  In order to observe inclusions and precipitation phases by SEM etc., it is necessary to expose inclusions and precipitation phases in a state of being buried in a matrix on the observation surface, and conventionally, electrolysis is carried out in various electrolyte solutions. The inclusions and the precipitate phase are exposed on the surface of the sample to allow observation.

  In recent years, with the advancement of manufacturing technology for steel materials, the types of inclusions and precipitation phases are diversified, and fine dispersion is also progressing. In observation, only the matrix (Fe) is selectively dissolved and the intervention is performed. With regard to substances and precipitation phases, even if they are fine particles, an electrolytic solution that can be reliably held on the observation surface and does not dissolve is required.

  In addition, when identifying and quantitatively analyzing these inclusions and precipitation phases, similarly, the matrix of the steel sample is dissolved in the electrolyte solution, and the inclusions and precipitation phases are recovered as electrolytic residues, and this is identified Quantitative analysis has been conducted.

  In the case of this quantitative analysis, only the matrix portion of the steel material is efficiently electrolyzed, and the Fe content is reliably dissolved and held in the electrolytic solution, and the portion corresponding to the other inclusions and the precipitation phase is electrolyzed. It is required to be able to be reliably recovered as a residue.

  Non-Patent Document 1 examines the problem that it can not be evaluated because CaO is mainly contained and chemically unstable as in slag-based inclusions and powder-based inclusions, and it can not be evaluated in the extraction process. In the case of constant current electrolysis using an electrolyte solution of the above, it is described that powder inclusions are difficult to dissolve and can be quantitatively extracted.

  Patent Document 1 relates to a method for extracting Ca (calcium) -based inclusions in steel and a method for separately determining the amount of inclusions, and it is difficult to extract CaO and to examine the problem that it is difficult to accurately determine CaO, CaO reacts with the water in the atmosphere in the decomposition and extraction process and changes to another form, which is considered to be easy to dissolve in the solvent, and it is thought that the operation from decomposition of the steel matrix to collection of residue is a dry atmosphere Suggest to do in the box).

Japanese Patent Application Laid-Open No. 06-174716

Chino, Y. et al., Development of extraction and determination method of Ca-rich oxides in steel by constant current electrolysis, iron and steel vol. 93 (2007) No. 2, p105-110

  Even if it is stable in steel, precipitates and inclusions that are easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol may be dissolved in the electrolytic solution and electrolytic extraction may be difficult. An example of such precipitates and inclusions is MgS. MgS is a finely dispersed particle having a high γ grain pinning ability, and is considered to be useful for improvement of toughness and the like. However, MgS is easily decomposed only by etching with an electrolytic solution, so that accurate data on the size distribution and number density of MgS can not be obtained, which is a major limitation in material development. Thus, there is a need for an electrolytic extraction method for obtaining accurate data of easily soluble precipitates and inclusions.

  The inventors of the present invention have been working on improving the measurement accuracy of steel analysis, and in the previous research, inclusions in metal compound analysis in steel due to electrolytic corrosion or the like in nonaqueous solvent-based electrolytes. It is observed that CuS of higher concentration than that measured by means other than electrolytic operation is observed in the surface layer of fine particles of precipitation phase, especially fine particles of various metal compounds, especially MnS. For this reason, it has been found that MnS particles may be detected as CuS (Artifact CuS).

The inventors of the present invention examined the cause of the artifact in detail, and as a result, when a metal ion (Cu ²⁺ ) having a small solubility product K _sp is generated in the electrolytic solution by electrolytic operation, metal sulfide (MnS) It has been found that, on the surface of the above), a metal ion with a high solubility product Ksp (Mn ²⁺ ) is exchanged with a metal ion with a low solubility product Ksp (Cu ²⁺ ). In addition, it was found that such metal ion substitution on the surface of sulfide easily proceeds at ordinary temperature and pressure, and also in an aqueous solution or non-aqueous solvent.

  As a result, inclusions and precipitates originally present as MnS in the steel sample will be observed as CuS as long as the surface is observed, and Cu ions in the electrolytic solution on the surface of MnS will also be observed. Even if mass analysis is carried out from the residue by exchanging CuS due to a thickness of several tens of nm (1 to 100 nm), CuS occupies a considerable portion of the volume in the case of fine particles. Therefore, accurate quantification was impossible.

  In our previous studies, as a method for suppressing the above-mentioned artifact (Artifact), a metal (attack metal) that forms an artifact (pseudomorphic) metal sulfide is selectively selected in the solvent-based electrolyte. By adding a drug (such as a chelating agent) to be captured, it was conceived that free attack metal in the electrolyte was reduced and that no artifact metal sulfide was formed.

  However, in the case of precipitates and inclusions that are more easily hydrolyzed than MnS such as MgS, since they are dissolved in the electrolytic solution, it has been conventionally considered that electrolytic extraction is impossible. As a matter of course, even if a drug (chelate or the like) that supplements an attack metal causing an artifact (Artifact) is added, the dissolution of easily soluble precipitates or inclusions can not be suppressed.

  The inventors of the present application intensively studied about this problem, and as a result, conceived that it was possible to form a waterproof barrier sheet such as Ag or AgS on the surface of precipitates and inclusions such as MgS easily soluble using ion exchange reaction. . That is, although precipitates and inclusions such as MgS are easily dissolved with a large solubility product Ksp, the inclusion of a compound or the like having a small solubility product Ksp (for example, AgS or Ag) in the electrolytic solution leads to a large solubility product Ksp. It was predicted that the surface of the (easy to dissolve) precipitates and inclusions would be covered and difficult to dissolve by a compound having a small solubility product Ksp (which is difficult to dissolve). In fact, the inventors of the present invention attached the mirror-polished MgS-containing steel material to an electrolytic solution to which Ag was added, and conducted an electrolytic extraction experiment. As a result, ion exchange reaction between Mg and Ag occurred in the MgS surface layer and waterproofed. It confirmed that it could form a quality barrier sheet.

In the above, (the ion exchange reaction between Mg atoms and Ag atoms on the MgS surface occurs, and a waterproof barrier sheet of Ag is formed on the MgS surface, but the same phenomenon occurs in combinations other than Mg and Ag. It can be estimated that the metal ion substitution on the metal compound surface proceeds easily when the solubility product K _sp has a considerable difference (greater than 10 digits (10 ¹⁰ )). to it can be estimated more detail., when the difference between the pK _sp of two compounds having different solubility product K _sp (sometimes hereinafter referred to as delta) is about 10 or more, the pK _sp large (solubility product K _sp It can be inferred that the substitution of the (small) compound with the small (large solubility product) compound of pK _sp easily proceeds.
The above conditions can be expressed by the following equation.
Δ = pK _sp [compound (small one of K _sp )]-pK _sp [compound (large one of K _sp )]
= (-Log ₁₀ K _sp [compound (small one of K _sp )])-(-log ₁₀ K _sp [large one (compound of K _sp )])
10 10
Here, the solubility product K _sp of a compound is represented as K _sp [compound], and pK _sp [compound] = − log ₁₀ K _sp [compound].

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) An electrolytic solution which etches a metallic material in an electrolytic solution to extract metal compound particles in the metallic material,
_Let the solubility product of the extraction target metal compound M _x A _y contained in the metal material be K _sp [M _x A _y ],
Assuming that the solubility product of the metal compound M '_x' A _{y '} is K _sp [M' _{x '} A _y' ]
An electrolytic solution characterized by comprising an ion of metal M 'in which Δ defined by the following formula is 10 or more.

Δ = pK _sp [M '_x' A _{y '} ]-pK _sp [M _x A _y ]
= (-Log ₁₀ K _sp [M '_x' A _{y '} ])-(-log ₁₀ K _sp [M _x A _y ])

Here, M and M ′ are different metal elements, A is a single atom or atomic group forming a compound with M or M ′, x, x ′, y, y ′ are M, M ′, A It represents the composition ratio of the compound determined depending on the valence, and the solubility product K _sp is a value at 25 ° C. in an aqueous solution.

(2) The electrolyte according to the above (1), which is a non-aqueous solvent-based electrolyte.

(3) The electrolytic solution as described in (1) or (2) above, wherein the metal compound to be extracted M _x A _y is MgS.

(4) The metal M ′ is at least one of Hg, Ag, Cu, Pb, Cd, Co, Zn, and Ni, and any one of the above (1) to (3) Electrolyte solution.

(5) The electrolytic solution according to any one of (1) to (4), wherein the concentration of the metal M 'is 0.0002 to 0.2 mass%.

(6) The electrolytic solution according to any one of the above (1) to (5), wherein the metal material is a steel material.

  (7) The electrolytic solution according to any one of claims 2 to 5, wherein the non-aqueous solvent comprises at least one of methanol and ethanol.

(8) In a method of etching a metal material in an electrolytic solution and electrolytically extracting metal compound particles in the metal material,
Using the electrolytic solution according to any one of (1) to (7), extracting particles of the metal compound to be extracted M _x A _y in a form in which at least the surface is covered with the metal M ′ or the compound thereof , A method of extracting metal compound particles.

-According to the present invention, it is possible to suppress the dissolution in the electrolytic solution of precipitates and inclusions which are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol. As a result, it is possible to provide an electrolytic solution capable of obtaining accurate data on the precipitates, the size distribution of inclusions, and the number density, and an electrolytic extraction method.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an example of a sketch of an electrolytic device using an electrolytic solution according to the present invention. It is a chart which shows the SEM photograph and the element concentration of the microparticles | fine-particles on the surface of the steel sample etched using the electrolyte solution which concerns on this invention. It is a schematic sectional drawing of the microparticles | fine-particles obtained by an etching using the electrolyte solution which concerns on this invention.

According to the present invention, it is an electrolytic solution which etches a metallic material in an electrolytic solution to extract metal compound particles in the metallic material,
_Let the solubility product of the extraction target metal compound M _x A _y contained in the metal material be K _sp [M _x A _y ],
Assuming that the solubility product of the metal compound M '_x' A _{y '} is K _sp [M' _{x '} A _y' ]
An electrolytic solution comprising ions of a metal M ′ having a Δ defined in the following formula of 10 or more, and a method of extracting metal compound particles using the electrolytic solution are provided.

Δ = pK _sp [M '_x' A _{y '} ]-pK _sp [M _x A _y ]
= (-Log ₁₀ K _sp [M '_x' A _{y '} ])-(-log ₁₀ K _sp [M _x A _y ])
Here, M and M ′ are different metal elements, A is a single atom or atomic group forming a compound with M or M ′, x, x ′, y, y ′ are M, M ′, A It represents the composition ratio of the compound determined depending on the valence, and the solubility product K _sp is a value at 25 ° C. in an aqueous solution.

The present invention relates to the extraction of metal compound particles in metal materials. More specifically, by etching the metal material in the electrolyte solution, the matrix (Fe or the like) is selectively dissolved to expose metal compound particles such as inclusions and precipitation phase contained in the metal material on the sample surface. . Thereby, the metal compound particles can be brought into an observable state.
As a method of extracting fine particles in the metal sample, for example, acid decomposition method which dissolves iron matrix of steel sample in acid solution, halogen dissolution which dissolves iron matrix of steel sample in iodine methanol mixed solution or bromine methanol mixed solution A non-aqueous solvent-based constant current electrolysis method or a non-aqueous solvent-based constant potential electrolysis (SPEED: Selective Potentiostatic Etching by Electrolytic Dissolution Method) method can be used. Among these, the SPEED method using a non-aqueous solvent is preferable because when the fine particles are dispersed in the solvent, the change in the composition or the size does not easily occur, and even the unstable fine particles can be extracted relatively stably. In the present embodiment, an evaluation method of fine particles in steel material by non-aqueous solvent based constant potential electrolysis method (SPEED method) will be described as an example with reference to FIG. 1, but the extraction method in the present invention is It is not limited to the SPEED method, and the metal material is not limited to the steel material.

  First, the metal sample 4 is processed into a size of, for example, 20 mm × 40 mm × 2 mm, and oxide films and the like such as scale on the surface layer are removed by chemical polishing or mechanical polishing to release the metal layer. . On the contrary, when analyzing the fine particles contained in the oxide film layer, it is left as it is.

  The metal sample is then electrolyzed using the SPEED method. Specifically, the electrolytic cell 10 is filled with the electrolytic solution 9, and the metal sample 4 is immersed in the electrolytic solution 9 to bring the reference electrode 7 into contact with the metal sample 4. The platinum electrode 6 and the metal sample 4 are connected to the electrolytic device 8. In general, when the above-mentioned electrolysis method is used, the electrolysis potential of fine particles in steel such as precipitates has a high electrolysis potential as compared with the electrolysis potential of the metal portion which becomes the matrix of the metal sample 4. Therefore, it is possible to selectively dissolve only the matrix by setting the voltage between the electrolysis potentials for dissolving the matrix of the metal sample 4 using the electrolytic device 8 and not dissolving the fine particles such as precipitates. It becomes. Inclusions or precipitation phase 5 floats on the surface of the sample on which Fe in the surface matrix portion is electrolytically eluted, and is in a state suitable for observation by SEM or the like. Further, the electrolysis can be continued to separate the inclusions and the precipitation phase from the surface of the sample, to be collected as an electrolysis residue 11 (not shown), and separated from the electrolyte by filtration for identification / quantitative analysis.

The electrolytic solution for metal materials according to the present invention, that is, the electrolysis of the Fe matrix on the surface to observe inclusions and precipitated phases, and the Fe matrix to quantitatively analyze inclusions and precipitated phases, The electrolytic solution used for electrolysis to recover the residue is preferably
(1) complexing agents for Fe ions,
(2) An electrolyte for securing conductivity to the electrolyte,
(3) A solvent for holding the formed complex such as Fe in a liquid,
including.

  As a complexing agent for the Fe ion, one or more may be selected from acetylacetone, maleic anhydride, maleic acid, triethanolamine, salicylic acid and methyl salicylate.

  As the electrolyte, one or more types can be selected from tetramethyl ammonium chloride (TMAC), sodium chloride (NaCl), and lithium chloride (LiCl).

  The solvent needs to be capable of holding various complex-forming agents or complexes of these with Fe in a dissolved state, and may be a non-aqueous solvent. In the case of aqueous electrolytes, various precipitates are decomposed even at relatively low electrolysis voltage (for example, -300 mV or less), while in non-aqueous electrolytes the stable electrolysis area is wide and superalloys, high alloys, stainless steel It can be applied to almost all steel materials from carbon steel to carbon steel. In the case of using a non-aqueous solvent-based electrolytic solution, only dissolution of the matrix and (complexation) reaction between the dissolved Fe ions and the chelating agent mainly occur, and the inclusion or precipitated phase 5 is not dissolved, Three-dimensional observation and analysis in the "in situ" state can be performed on the base material. As the non-aqueous solvent, a compound which facilitates electrolysis and dissolves a complexable organic compound and a supporting electrolyte is suitable. For example, lower alcohol such as methanol, ethanol or isopropyl alcohol is used. Can. Methanol, or ethanol, or mixtures thereof can be selected. Further, any solvent having polarity (dipolar moment etc.) equal to or higher than these alcohols can be used.

  In the conventional constant potential electrolysis method, as an electrolytic solution, 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% by weight TMAC-methanol solution is used. In these electrolytic solutions, the electrolytically eluted Fe forms a complex, and the generated Fe complex is preferably used from the viewpoint of dissolving in the electrolytic solution, and therefore, it is widely used.

  However, in the conventional electrolytic solution, precipitates and inclusions which are more easily hydrolyzed than MnS such as MgS are dissolved in the electrolytic solution, and it has been considered that electrolytic extraction is impossible. In fact, even if the steel containing MgS was electrolytically extracted using a conventional electrolytic solution, MgS could not be confirmed in the extract or inclusions.

In general, the solubility of the metal compound in the electrolyte can be ordered by the magnitude of the solubility product K _sp . That is, the larger the solubility product K _sp (in other words, the smaller pK _sp (= −log ₁₀ K _sp )), the easier it is to dissolve. Electrolytic solution of the present invention, in order to suppress the dissolution of the (large solubility product K _sp) metal compounds such easily soluble, sparingly soluble (solubility product K _sp is smaller) in the electrolyte the metal of the metal compound Comprising ions. Soluble metal compound (large solubility product K _sp ) is easy to dissolve (solubility product) by causing ion exchange reaction with metal ion of metal compound difficult to dissolve (small solubility product K _sp ) in electrolytic solution The surface of the large K _sp ) metal compound is coated with a poorly soluble (low solubility product K _sp ) metal compound. That is, on the surface of the easily soluble metal compound, a waterproof barrier sheet is formed of the hardly soluble metal compound. Thereby, the dissolution of the easily soluble metal compound in the electrolytic solution is suppressed, and the extraction of the easily soluble metal compound becomes possible.

Solubility product difference between soluble (high solubility product K _sp ) metal compound M _x A _y and poorly soluble (low solubility product K _sp ) metal compound M ′ _{x ′} A _{y ′} to be extracted More specifically, when Δ is 10 digits (10 ¹⁰ ) or more, by setting Δ defined in the following formula to 10 or more, the dissolution of the easily soluble metal compound in the electrolytic solution is suppressed. It is possible to extract the soluble metal compound.

Δ = pK _sp [M '_x' A _{y '} ]-pK _sp [M _x A _y ]
= (-Log ₁₀ K _sp [M '_x' A _{y '} ])-(-log ₁₀ K _sp [M _x A _y ])
Here, M and M ′ are different metal elements, A is a single atom or atomic group forming a compound with M or M ′, x, x ′, y, y ′ are M, M ′, A It represents the composition ratio of the compound determined depending on the valence, and the solubility product K _sp is a value at 25 ° C. in an aqueous solution.
Note that the metal compound M _x A _y is a metal compound that is easily soluble (large solubility product K _sp ), and the metal compound M ′ _{x ′} A _{y ′} is not easily soluble (small solubility product K _sp ) metal compound It is.

If the difference Δ in solubility product is 10 or more, the ion exchange reaction is considered to proceed between M and M ′. As the difference Δ in solubility product is larger, the ion exchange reaction rate is considered to be faster, ie, it is considered that the formation of the barrier sheet by the ion exchange reaction is considered to be faster. In particular, when the solubility product K _{sp of} the metal compound M _x A _y to be extracted is very large, the dissolution rate in the electrolytic solution is very fast, but the dissolution is achieved by accelerating the formation of the barrier sheet. Dissolution of the easy-to-use metal compound M _x A _y can be suppressed (in other words, a barrier sheet is formed before dissolution of the extraction target, and dissolution of the extraction target can be suppressed).

  In this respect, Δ is preferably 11 or more, more preferably 12 or more, still more preferably 13 or more, still more preferably 14 or more, even more preferably 15 or more, more preferably 16 or more. Is more preferably 17 or more, still more preferably 18 or more, still more preferably 19 or more, still more preferably 20 or more, still more preferably 21 or more, still more preferably 22 or more The size is preferably 23 or more, more preferably 24 or more, still more preferably 25 or more, still more preferably 26 or more, still more preferably 27 or more, still more preferably 28 or more, Larger than 29 Is more preferably 30 or more, more preferably 31 or more, still more preferably 32 or more, still more preferably 33 or more, still more preferably 34 or more, even more preferably 35 or more The size is preferably 36 or more, more preferably 37 or more, still more preferably 38 or more, still more preferably 39 or more, and still more preferably 40 or more.

Table 1 shows the solubility product K _sp of sulfide at 25 ° C. in an aqueous solution and the difference Δ between pK _sp (= −log ₁₀ K _sp ) between sulfides. In the table, the double line frame (or the dark gray frame) is a combination of sulfides having a pK _sp difference Δ of 22 or more, and their combination facilitates the ion exchange reaction and the barrier sheet formation thereby. Or expected to progress in seconds. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as ◎. The bold frame (or light gray frame) is a combination of sulfides with a pK _sp difference Δ of 10 or more and less than 22. It may take from several minutes to several hours, but ion exchange reaction and the resulting barriers Sheet formation is expected to proceed. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as 〜 to △. A thin line frame (or a white frame) is a combination of sulfides having a pK _sp difference Δ of less than 10, and it is expected that the combination of ion exchange reaction and thereby the barrier sheet formation is unlikely to progress. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as Δ △ ×.
With regard to the solubility product of sulfides, some sulfides of the same element may exhibit different solubility products depending on the crystal form and the like. Table 1 lists sulfides having crystal forms and the like in which the difference Δ of pK _sp decreases. This may be in the form of the difference between the pK _sp delta increases, the difference between the pK _sp of the sulfide to be delta becomes 10 or more, it is considered that exchange reaction proceeds.

Moreover, in Table 1, although the sulfide with the largest solubility product K _sp is MnS, in fact, there are compounds that are more soluble than MnS, such as MgS. However, the solubility of MgS etc. is very large, and there is no accurate measurement value. However, empirically, the presence of easily soluble compounds than MnS as MgS is known, the solubility product K _sp is considered to be greater than the solubility product K _sp of MnS. Therefore, Δ when the compound more soluble than MnS, such as MgS, is the extraction target compound M _x A _y can be considered to be larger than Δ when it is assumed that the extraction target compound is MnS.

The extraction object M _x A _y may be a metal compound having a solubility product K _sp larger than MnS, that is, the solubility product K _sp may be a metal compound larger than 3 × 10 ^-14 . Therefore, the extraction target M _x A _y may be MgS.
Effect that the metal compound having such a large solubility product K _sp (e.g. MgS) is readily soluble in common electrolyte, dissolved by the present invention is suppressed to obtain data that can not be obtained accurately heretofore Can be enjoyed notably.

The above-mentioned solubility product K _sp is a value in an aqueous solution, but it is presumed that the same tendency is also observed in non-aqueous solvents such as methanol which is the same polar solvent. From this, the electrolyte solution of the present invention may be a non-aqueous solvent system.

The inventors conducted a test and as shown in Table 2, even when using a non-aqueous solvent (lower alcohol), the difference Δ of pK _sp (−log ₁₀ K _sp ) determined from K _sp is 10 or more, It has been confirmed that a reaction is observed. Specifically, the following confirmation tests were conducted.
· Two steels containing MgS (having a particle diameter of 1 μm or more and a particle diameter of 100 to 150 nm) containing MgS were prepared as samples containing an extraction target, and mirror polishing was performed on their surfaces. .
· Six kinds of standard solutions for atomic absorption analysis (M '+ solution), in which metal ion concentrations of Ag, Cu, Pb, Co, Zn, and Ni are 1000 μg / ml, respectively, as metal M' + ions to be subjected to ion exchange Prepared. 0.1 ml of M 'solution was mixed with 0.3 ml of methanol which is a non-aqueous solvent.
-The mixed solution was applied to the surface of the steel material, and changes in the surface of the steel material were confirmed.
In the case where the mixture containing Ag and Cu was applied, the surface of the steel material turned black within 5 minutes from the application. In the case where the mixed solution containing Pb was applied, the surface of the steel material turned black in about 10 minutes from the application. In the case where the mixed solution containing Co, Zn and Ni was applied, the surface of the steel material turned black in about 20 minutes from the application.
Further, when SEM and EDS observation was performed on the discolored steel material, it was confirmed that ion exchange (ie, barrier code formation) between Mg and metal M 'occurred on the surface of the MgS particles in each case. .
From this, in the scope of the present invention, although the solubility product K _sp is an index in an aqueous solution, it can be applied to a non-aqueous solution, and the solubility product K _sp there tends to be the same as in an aqueous solution. Is estimated.
・ Moreover, it was also confirmed that the larger the difference Δ in pK _sp, the faster the ion exchange reaction. On the other hand, it was also confirmed that although the reaction rate is relatively slow even if the difference Δ of pK _sp is small, the ion exchange reaction proceeds steadily.

The reaction on the surface of the metal compound to be extracted is described. Here, an example in which the metal compound to be extracted is MgS and the metal ion to be ion-exchanged is Ag ion is used. First, since the sulfide of Ag has a difference Δ of pK _sp with MnS of 36.6, the difference Δ of pK _sp with MgS is larger, and easily causes ion exchange reaction with Mg on the surface of MgS particles.
Ag ions are ion-exchanged with Mg on the surface of MgS particles, and the Mg ions are expelled into the electrolytic solution, and at the same time, they remain as Ag ₂ S on the surface of MgS particles. Ag ₂ S formed on the surface acts as a barrier sheet which has low solubility and suppresses the dissolution of MgS particles coated with the surface layer.

The schematic reaction mechanism is as follows.

MgS + Ag ion → Ag ₂ S + MgS (covered by Ag) Does not decompose into water.

Furthermore, when the electrolytic extraction time becomes long, the ion exchange reaction may further progress on the surface of the MgS particles coated with the Ag ₂ S barrier sheet. That is, it may be infiltrated with Ag ₂ S from the surface to the inside of the MgS particles. In some cases, ion exchange with Ag may be performed up to the central part of MgS particles.

In addition, Ag ₂ S is easily reduced when it reacts with H ions, and can be present as metal Ag, and metal Ag is insoluble in water. Generally, H ions are also contained in the electrolytic solution, so at least a part of the MgS particle surface may be coated with a barrier sheet of metal Ag.

In this way, MgS particles which have been dissolved in the electrolyte up to now can be coated with a barrier sheet of Ag ₂ S or Ag, and can be stably present in precipitates and inclusions. This can be used to estimate the size distribution and number density of MgS particles.
Even if the center part of MgS particles is completely infiltrated with Ag, the size distribution of MgS particles existing in the steel, or the observation of Ag ₂ S particles formed by infiltration or further reduced Ag particles, It can be used to estimate the number density etc.

As metal M 'for forming a barrier sheet which produces an ion exchange reaction, it is considered that it is easier to form a barrier sheet as the pK _sp difference Δ is larger than the metal compound M _x A _y to be extracted. From this point, the metal M ′ of the metal compound M ′ _{x ′} A _{y ′} having a large pK _sp may be at least one of Hg, Ag, Cu, Pb, Cd, Co, Zn, and Ni, These can be metal M 'ions and can be barrier sheets of metal compounds M _x A _y with small pK _sp .

The metal M 'may be added in the form of a compound of the metal M', for example M '_x' A _{y '} , as a method of adding the metal M' to the electrolytic solution, or even in the form of a solution containing the metal M 'ion Alternatively, it may be added in the form of metal M 'and then dissolved in the electrolyte.

  Since metal M 'may be contained in a steel material sample, it is preferable to add the metal which is not contained in a steel material sample to electrolyte solution. This is because the difference between what is contained in the steel material sample and the one which is added to the electrolytic solution is clear, and the subsequent analysis becomes clear. In this respect, Hg and Ag are generally suitable as the metal M ′ to be added to the electrolytic solution, since the content in steel is generally low. Further, compounds of Hg and Ag are also preferable in that they have a low solubility product, that is, they are considered to have a high ability to form a barrier sheet. Therefore, the metal M 'may be at least one of Hg and Ag.

In the electrolytic solution according to the present invention, the concentration of the metal M ′ may be 0.0002 to 0.2% by mass. If the metal M ′ is 0.0002 mass% (2 ppm) or more, a barrier sheet can be sufficiently formed on the surface of the compound M _x A _y to be extracted (easy to be dissolved). It is possible to further increase the concentration of the metal M ′ in the electrolytic solution, and may be appropriately adjusted according to the amount of the extraction object. However, even if the metal M ′ concentration is increased, the ion exchange rate is not improved, and only the cost is increased, so the upper limit of the concentration may be 0.2 mass% (2000 ppm).

A in the metal compounds M _x A _y and M ′ _{x ′} A _{y ′} is a single atom or atomic group forming a compound with M or M ′, and atoms of C, N, H, S, O, P and F And one or more atoms independently selected from the group consisting of

The electrolyte may be agitated in the electrolytic cell. As a result, the surface of the compound M _x A _y to be extracted is easily brought into contact with the metal M ′ ions, and the barrier sheet is easily formed. The means for stirring is not particularly limited, but bubbling with a bubble generator, eddy current with a magnetic stirrer, or the like may be used. Alternatively, droplets of a solution containing metal M ′ ions may be dropped in the vicinity of the steel material containing the extraction target. In the case of bubbling, the lower limit may be 100 cc / min, preferably 200 cc / min, and 100 rpm, preferably 200 rpm, preferably 200 rpm, in order to facilitate contact with metal M ′ ions. When the bubbling amount and the stirrer rotation speed are too high, problems such as peeling of the surface of the object to be electrolyzed and dissolution of the compound M _x A _y to be extracted are caused. Therefore, the upper limit may be 600 cc / min, preferably 500 cc / min for bubbling, and 600 rpm, preferably 500 rpm for a stirrer.
In addition, when stirring an electrolyte solution in general electrolysis operation, stirring operation is performed so that the flow of the electrolyte solution produced by stirring may not contact an electrolysis object. This is based on the idea that the flow of the electrolyte solution generated by stirring does not affect the object to be electrolyzed. In the present invention, from the viewpoint that the metal M 'ions forming the barrier sheet easily come in contact with the surface of the compound M _x A _{y to be} extracted, the flow of the electrolytic solution generated by stirring etc. May be stirred or supplied.
Moreover, as gas for bubbling, inert gas, such as nitrogen gas, helium, and argon, is mentioned. An active gas such as oxygen or hydrogen is not preferable because it may affect the concentration of dissolved oxygen in the electrolyte and may affect the object to be electrolyzed.

  The metal material in the present invention may be a steel material. The iron and steel material refers to a material containing iron as a main component, and may contain a trace amount of carbon.

  When the electrolytic solution after etching is passed through a filter and metal compound particles are extracted as a collected residue, the filter may be a tetrafluoroethylene resin filter. In order to identify and quantitatively analyze inclusions, precipitation phase 5 and residue 11 (not shown), a filter for filtering inclusions or precipitation phase 5 and residue 11 from an electrolytic solution is a conventionally used nucleopore filter In the case of (manufactured by GE Co.), it is difficult to dissolve and damage the residue.

  According to the present invention, analysis of metal compound particles extracted by the above method may also be provided. For metal compound particles, general composition analysis may be performed by XRF, or fine composition analysis may be performed by ICP. As a surface analysis method, observation by SEM, elemental analysis by EDS, or the like may be used. By analyzing the surface of the sample from which the metal compound is extracted in the middle of the etching, it is also possible to observe the extraction condition of the metal compound in time series.

  According to the present invention, it is possible to suppress the dissolution in the electrolytic solution of precipitates and inclusions which are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol even if they are stable. It is possible to provide an electrolytic solution capable of obtaining accurate data on the precipitates, the size distribution of inclusions, and the number density, and an electrolytic extraction method.

In the above description, metal sulfide is mainly used as the metal compound, but the metal compound is not limited to sulfide. It is believed that the formation of the barrier sheet can occur depending on the difference in solubility product for any compound species. Table 3 shows the difference Δ between pK _sp (= −log ₁₀ K _sp ) between selenides at 25 ° C. in aqueous solution. In Table 3, the double-lined frame (or the dark gray frame) is a combination of selenides having a pK _sp difference Δ of 22 or more, and their combination facilitates the ion exchange reaction and the barrier sheet formation thereby. Or expected to progress in seconds. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as ◎. The bold frame (or light gray frame) is a combination of selenides with a pK _sp difference Δ of 10 or more and less than 22 and may take from several minutes to several hours, but ion exchange reactions and the barriers thereby Sheet formation is expected to proceed. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as 〜 to △. A thin line frame (or a white frame) is a combination of selenides having a pK _sp difference Δ of less than 10, and it is predicted that the exchange reaction and the resulting barrier sheet formation do not progress easily with these combinations. If expressed simply by symbols, the expectation (prediction) of the exchange reaction is expressed as Δ △ ×.

  The invention is also applicable to selenide.

Furthermore, according to the present invention, metal compound particles characterized in that particles of the metal compound to be extracted M _x A _y are extracted using the above-mentioned electrolytic solution in a form in which at least the surface is coated with the metal M ′ or the compound thereof. A method of extraction is also provided.

  The electrolyte solution according to the present invention may contain a particle dispersing agent such as SDS as necessary, as a component other than those described above.

  Hereinafter, the present invention will be described through examples. However, the present invention should not be construed as being limited to the following examples.

The inclusions or precipitated phases in the steel sample were observed by the electrolytic solution and the electrolysis method according to the present invention.
As steel samples, C: 0.07 wt%, Si: 0.05 wt%, Mn: 1.45 wt%, S: 0.005 wt%, Cu: 0.3 wt%, Al: 0.08 wt%, Mg: 0. The steel plate for a heavy plate containing 007 wt% was processed into a size of 20 mm × 40 mm × 2 mm and mirror-polished. The obtained steel material was subjected to about 20 coulombs of electrolytic etching by constant current electrolysis using the apparatus shown in FIG.
The same two types of electrolytic solutions were used to observe inclusions or precipitation phases of the same steel sample.
(1) Electrolyte solution of Comparative Example: Electrolyte solution containing 4% by mass of methyl salicylate + 1% by mass of salicylic acid + 1% by mass of tetramethylammonium chloride (TMAC) capable of recovering sulfide inclusions conventionally known as a residue (4) % MS)
(2) Electrolyte solution according to the present invention: 1 ml of 1000 ppm Ag standard solution for atomic absorption (5% HNO3) was added to 500 ml of the above 4% MS electrolyte solution to make the concentration equivalent to 2 ppm Ag.
The solvent was methanol in any of (1) and (2).
After completion of the electrolytic etching, the film was further immersed for about 40 minutes in each electrolytic solution and left to stand, and after dropping the electrolytic solution with clean methanol, the steel sample was air dried and subjected to SEM observation.

Results of SEM-EDS Analysis EDX analysis of fine particles on the surface of a steel sample obtained by etching with the electrolytic solution of Comparative Example (1) and Example of the Invention (2) was performed.
In Comparative Example (1), although the peak of MnS was observed, the peak of Mg was not observed. This is because MgS was easily dissolved in the electrolytic solution.
In the inventive example (2), unlike the comparative example (1), the peak of Mg and the peak of Ag coated on the surface layer of the fine particles appeared. This is because Ag ions attack the MgS surface layer that is easily dissolved in water, methanol, etc. to cause ion exchange reaction, and Ag ₂ S, which is highly insoluble in water, in the surface layer of (Mn, Mg) S particles It can be understood that because the Ag coating was formed, it did not dissolve even after being left in the electrolyte for 40 minutes.

In FIG. 2, the SEM-EDS image of the microparticles | fine-particles of the steel sample surface obtained by the etching by the electrolyte solution of (2) is shown. In FIG. 2, the upper left image is an SEM observed image of the observed fine particles, and the upper right image is a SEM observed image overlaid with a chart of the Ag concentration measured by EDS, and the lower left image is a chart of Mg concentration The lower right image is a superimposed image of the chart of the S density.
From the chart of each element concentration in FIG. 2, it is confirmed that the surface portion of the MgS particles is replaced with Ag ₂ S or Ag. The height (concentration) of each element in the chart is relative, but the following can be read. Specifically, spherical fine particles with a diameter of about 100 nm can be confirmed, and in the range where the fine particles exist, the values of the graphs of Ag, Mg and S rise in a mountain shape, and the fine particles ) A nucleus was coated with Ag ₂ S or Ag at its periphery. A schematic cross-sectional view of the fine particles created based on this finding is as shown in FIG. The particle diameter of MgS particles electrolytically extracted according to the present invention and barrier-coated with Ag ₂ S or Ag on the surface was confirmed by observing a mirror-polished surface of a steel sample before electrolysis with SEM-EDS. The particle size was almost the same as

From the results described above, when a steel sample is electrolyzed using a conventional electrolytic solution, and observation by SEM or the like and microanalysis by EDS are performed, MgS originally observed in the steel material is dissolved in the electrolytic solution Was confirmed.
On the other hand, when the electrolytic solution according to the present invention is used, MgS is coated with Ag without causing the above-mentioned problems, so that the dissolution is suppressed and the particles of MgS are stabilized in the electrolytic solution. It was possible to make it exist. As a result, it is possible to perform observation by SEM etc. and micro analysis by EDS with respect to easily soluble metal compounds such as MgS that could not be analyzed due to dissolution so far, thus greatly contributing to improvement of analysis accuracy of steel samples Can.

  By electrolysis of a steel sample using the electrolytic solution according to the present invention, precipitates and inclusions which are stable in steel but are easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol are contained in the electrolytic solution. It is possible to provide an electrolytic solution and an electrolytic extraction method that can suppress dissolution in water, and as a result, accurate data on the precipitates, the size distribution of inclusions, and the number density can be obtained.

4 Metal sample 5 Inclusion / Precipitate phase particle 6 Electrode (cathode side)
7 Reference electrode 8 Power supply (potentiostat)
9 Electrolyte 10 Electrolyzer

Claims (8)

An electrolytic solution used for etching metal materials and extracting metal compound particles in the metal materials,
_Let the solubility product of the extraction target metal compound M _x A _y contained in the metal material be K _sp [M _x A _y ],
Assuming that the solubility product of the metal compound M '_x' A _{y '} is K _sp [M' _{x '} A _y' ]
An electrolytic solution characterized by comprising an ion of metal M 'in which Δ defined by the following formula is 10 or more.
Δ = pK _sp [M '_x' A _{y '} ]-pK _sp [M _x A _y ]
= (-Log ₁₀ K _sp [M '_x' A _{y '} ])-(-log ₁₀ K _sp [M _x A _y ])
Here, M and M ′ are different metal elements, A is a single atom or atomic group forming a compound with M or M ′, x, x ′, y, y ′ are M, M ′, A It represents the composition ratio of the compound determined depending on the valence, and the solubility product K _sp is a value at 25 ° C. in an aqueous solution.   The electrolytic solution according to claim 1, which is a non-aqueous solvent system. The electrolytic solution according to claim 1, wherein the metal compound to be extracted M _x A _y is MgS.   The electrolytic solution according to any one of claims 1 to 3, wherein the metal M 'is at least one of Hg, Ag, Cu, Pb, Cd, Co, Zn, and Ni.   The electrolytic solution according to any one of claims 1 to 4, wherein the concentration of the metal M 'is 0.0002 to 0.2% by mass.   The electrolytic solution according to any one of claims 1 to 5, wherein the metal material is a steel material. The electrolytic solution according to any one of claims 2 to 5, wherein the non-aqueous solvent comprises at least one of methanol and ethanol.
In a method of etching a metal material in an electrolyte and extracting metal compound particles in the metal material,
The electrolytic solution according to any one of claims 1 to 7 is used to electrolytically extract particles of the metal compound to be extracted M _x A _y in a form in which at least the surface is coated with the metal M 'or the compound thereof. A method of extracting metal compound particles, characterized in that.