JP4970355B2 - Standard sample for quantification in glow discharge emission analysis and glow discharge emission analysis method using the same - Google Patents

Description

  The present invention relates to a glow discharge emission analysis method for accurately and quickly and easily quantitatively analyzing an internal oxide layer on a metal surface formed in a heat treatment step or the like in a depth direction.

  The glow discharge emission analysis method (hereinafter referred to as GD-OES) is a method for examining the distribution of elements in the depth direction from a relatively smooth material surface. Industrially, the range of application of this analysis method to the evaluation of thin metallic plates and foils, such as the distribution of elements in the depth direction of the alloy surface layer of various steel plates and the like, is extremely wide.

  GD-OES introduces a rare gas such as Ar gas into a discharge tube, causes abnormal glow discharge using the sample as a cathode, and sputters the surface of the sample continuously and at high speed with ions of the generated rare gas element. This is a technique for analyzing a plating layer, an oxide layer, and the like on a sample surface in the depth direction by spectroscopic analysis of an emission spectrum when a constituent element emits light in a negative glow region.

  As a quantification method by GD-OES, for example, a light intensity integration method described in Patent Document 1 is known. This method is based on both the apparent luminescence yield of each element and the density of each element obtained from a standard sample whose composition is known, and the change in luminescence intensity in the depth direction of the oxide layer of the measurement sample is measured by sputtering. This is a quantitative analysis method in which the concentration of each element and the sputter depth are obtained by converting into the mass of the oxidized layer. Patent Document 2 describes a quantitative analysis method for a surface oxide layer.

  In GD-OES, a pure metal or an alloy is used as a standard sample for quantification. In order to quantify high concentration oxygen such as an oxide film, an oxide sintered body or a pure metal oxide film may be used as a standard sample. By using these standard samples, it is possible to create a calibration curve and quantitatively analyze the element distribution in the alloy or oxide film.

On the other hand, in the steel manufacturing process, in the metal Fe matrix, for example, an affinity for oxygen such as Si or Al is larger than the oxygen affinity for Fe, and an internal oxide layer in which Si, Al or the like is selectively oxidized may be formed. The internal oxidation phenomenon is caused by the difference in affinity between the matrix element and the oxygen of the alloy element. That is, even when annealed in an atmosphere that is reducible to the matrix element, the alloy has a higher affinity for oxygen. This is a phenomenon in which elements are oxidized inside the alloy. For example, in a high-tensile steel sheet having a large Si content, an internal oxide layer mainly composed of SiO ₂ having a thickness of several μm is formed after continuous annealing in an atmosphere that is reducible to Fe. Moreover, an internal oxide layer is formed also after the decarburization annealing process of a grain-oriented electrical steel sheet.

In the method of forming an internal oxide layer in the pre-plating process, the amount of internal oxide affects the plating performance improvement effect as a purpose of improving the plating performance in the production of hot-dip galvanized material of high-tensile steel plates. In the grain-oriented electrical steel sheet, an annealing separator mainly composed of MgO is applied to the steel sheet surface after decarburization annealing, and in the subsequent finish annealing process, SiO ₂ and MgO as internal oxides react to form Mg _2. An insulating coating of SiO ₄ is formed. The internal oxide layer formed by decarburization annealing has a great influence on the quality of the insulating coating. In any steel sheet, it is important to optimize the amount and distribution of the internal oxide, and for that purpose, it is necessary to quantitatively and accurately analyze the internal oxide layer.

Japanese Patent Laid-Open No. 7-103898 JP-A-9-273992

  However, when the internal oxide layer in which a fine oxide is present in the metal matrix as described above is measured by GD-OES and quantified using the methods described in Patent Documents 1 and 2, particularly the oxygen concentration There is a problem that cannot be obtained with good quantitativeness.

  Therefore, in view of the above-mentioned problems of the prior art, the present invention measures the internal oxide layer on the surface of the material by GD-OES, and quantifies the composition of the measurement element by creating a calibration curve using a standard sample. In order to improve the quantitative characteristics, a standard sample and a glow discharge emission analysis method using the same are provided.

The present invention for solving the above problems is as follows.
(1) A standard sample used for measuring a metal sample by a glow discharge optical emission spectrometry and quantifying the composition of a measurement element in the metal sample by a calibration curve method, wherein the standard sample is contained in a metal matrix. A standard sample for quantification in glow discharge emission analysis, characterized by being a composite material in which oxide particles of one or more elements having an average particle diameter of 5 μm or less are dispersed;
(2) The standard sample for quantification in the glow discharge optical emission analysis according to (1), wherein the standard sample is produced by a discharge plasma sintering method,
(3) The standard sample for quantification in the glow discharge optical emission analysis according to (1) or (2), wherein the metal matrix is iron,
(4) After preparing a calibration curve using the standard sample according to any one of (1) to (3), a glow discharge emission analysis of a metal sample having an internal oxide layer on the surface layer is performed. A glow discharge emission analysis method characterized by quantifying the composition of the measurement element of
(5) The glow discharge emission analysis method according to (4), wherein the metal sample is a steel material,
It is.

  According to the present invention, for example, the internal oxide layer present on the surface of the material is measured by GD-OES, and a calibration curve is created using a standard sample, thereby improving the quantitativeness when quantifying the composition of the measurement element. The industrial significance is enormous.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  The present invention is a standard sample applied when quantitatively analyzing an internal oxide layer existing on a material surface by GD-OES, and a glow discharge emission analysis method using the standard sample.

The internal oxidation phenomenon occurs when the affinity of the matrix metal with the oxygen of the alloy element is larger than the affinity of the matrix metal with oxygen, and the Ni-Cr alloy, Ni-Al alloy, Cu-Ti alloy, Cu-Fe alloy, Cu There are many reports on Co alloys and Ag-In alloys. In general steel materials, alloy elements such as Al, Si, Cr, Mn and the like having a higher affinity for oxygen than Fe are added, and Al ₂ O ₃ , SiO ₂ , Cr ₂ O _3, etc. are respectively obtained during annealing at high temperatures. In some cases, a composite internal oxide such as FeCr ₂ O ₄ , FeAl ₂ O ₄ , Mn ₂ SiO _4, and Fe ₂ SiO ₄ is generated. Embodiments of the present invention will be described below with reference to the drawings, taking as an example the case of forming an internal oxide layer of SiO ₂ in an Fe—Si alloy.

The Fe-3 mass% Si alloy at _P H2O _{/ P H2} ratio in an atmosphere of about 0.5, when 5min oxidation at 850 ° C., in the matrix of the metal Fe, about SiO ₂ are dispersed by selective oxidation of dissolved Si An internal oxide layer having a thickness of 4 μm is formed. In the internal oxide layer, the concentration of Si dissolved in the Fe matrix is very low, and almost all Si exists as SiO ₂ . Here, since the mass number of O is 15.999 and the mass number of Si is 28.086, the mass composition ratio of O and Si in SiO ₂ (hereinafter referred to as C 2 _{O 3} / C _Si ) is 1.14.

However, the GD-OES, using a standard sample of oxides, such as alloy and SiO ₂ composition is known, when quantifying inner oxide layer of the Fe-3 mass% Si alloy, _{C O} in the inner oxide layer / C _Si is less than 1.0. At this time, the Si concentration in the internal oxide layer is quantified as 3 to 4%, which is consistent with the volume fraction of SiO ₂ estimated from the cross-sectional observation of the same sample by a scanning electron microscope. Therefore, the reason why C _O / C _Si in the internal oxide layer is reduced by quantification in GD-OES is that the O concentration is quantified to be smaller than actual.

The inventors of the present invention have prepared sintered bodies formed by mixing Fe and SiO ₂ powders having various particle sizes, analyzed by GD-OES, and studied. As a result, a high-purity Fe plate and quartz glass were obtained. It has been found that C 2 _{O 3} / C _Si changes depending on the average particle diameter of SiO _{2 in} the sintered body relative to C 2 _{O 3} / C _Si when quantified as a standard sample. That is, as shown in FIG. 1, to an average particle diameter of SiO ₂ is about 5μm _is, C O _{/ C Si} is substantially constant, the _C O _{/ C Si} If the average particle diameter of SiO ₂ is greater than about 5μm It became large and it became close to 1.14 which is a value estimated from the stoichiometric composition of SiO ₂ with the increase in particle size. This indicates that when an O calibration curve is prepared using a standard sample containing quartz glass or SiO ₂ having a large particle diameter, the O concentration is quantified small in a material containing fine SiO ₂ .

In order to use a sintered compact formed by mixing Fe and SiO ₂ powder as a standard sample for quantification in GD-OES, the composition ratio of Fe, Si and O in the analysis region in GD-OES is: It is important that it is constant and known regardless of the measurement location. From the viewpoint of dispersion of SiO ₂ in the GD-OES analysis region, the average particle size of SiO _{2 in} the sintered body is desirably about 1/100 or less of the GD-OES analysis region diameter, and as described above, the quantitative property is also obtained. From this viewpoint, it is desirable that the average particle diameter of SiO ₂ is about 5 μm or less.

Similarly, in the sintered body of the Fe matrix and other oxides such as Al ₂ O ₃ and Cr ₂ O ₃ , similarly, when the average particle size is about 5 μm or less, it is expected from the stoichiometric composition of the oxide. From the composition ratio, it was confirmed that the O concentration became lower at a certain value.

Generally, the size of the internal oxide is several tens of nanometers to several μm, and the size of the internal oxide generated by annealing a high-tensile steel plate or decarburizing annealing of a grain-oriented electrical steel plate is about 0.1. ˜1 μm. Therefore, in order to analyze and quantify the internal oxide layer by GD-OES, for example, a composite material of an oxide and a metal matrix of the same kind as the internal oxide of interest such as SiO ₂ is used, and the oxide The average particle size is preferably 5 μm or less.

  In GD-OES, it has been conventionally known that there is a matrix effect in which the light emission efficiency varies depending on the chemical state of a measurement element. However, in GD-OES, as described above, the reason why the accuracy in quantification of O depends on the particle size of the oxide has not been elucidated at present, but the inventors think as follows. ing. That is, when the particle size of the internal oxide is small, when the O element jumps out of the sample surface by sputtering, the emission efficiency of O atoms decreases due to the interaction with the metal atoms of the matrix, whereas the internal oxide When the particle size of the substrate becomes larger, the distance from the metal atom of the matrix becomes larger, so the above action becomes smaller, and the luminous efficiency is the same as when the oxide is measured. Therefore, it is considered that the above effect strongly depends on the particle size of the oxide, and the difference depending on the oxide species is small.

  In GD-OES, since the inside of the discharge tube is decompressed and analysis is performed while introducing an inert gas such as Ar, the measurement sample is required to be dense and have low gas permeability. Therefore, the standard sample used for GD-OES must be dense.

In order to produce a dense sintered body by a normal sintering method, annealing at a high temperature for a long time is required. Even if the starting material SiO ₂ is fine, it is coarsened during the sintering process, and the average grain size is reduced. It is difficult to make the diameter less than 5 μm. In particular, when the melting point of the matrix metal and the oxide is close or lower than the melting point of the oxide, a sintered body in which the oxide is finely and uniformly dispersed in the metal matrix is prepared by the usual sintering method. It is extremely difficult to do. Furthermore, in the sintering process at a high temperature for a long time, for example, a reaction occurs in which SiO ₂ is dissociated and O and Si are dissolved in metal Fe, respectively. Therefore, a standard sample for quantifying the internal oxide layer is usually used. In some cases, it is not preferable to produce the material by this sintering method.

  Here, the discharge plasma sintering method is a sintering method that uses a high voltage of a discharge plasma generated by a spark discharge phenomenon by applying a pulsed large current at a low voltage to the green compact gap. A dense sintered body can be produced in a short time at a temperature lower by several hundred degrees C. than the sintering method. Further, since rapid temperature rise by self-heating of only the particle surface is possible, it is possible to suppress grain growth of the starting material. Due to these features, the spark plasma sintering method is suitable for preparing a standard sample for quantifying the internal oxide layer.

  However, the preparation method of the standard sample in the present invention is limited to the discharge plasma sintering method as long as a dense composite material in which fine oxides are uniformly dispersed can be produced by a combination of a metal matrix and an oxide. It is not a thing.

Next, a procedure for quantifying a metal sample having an internal oxide layer using the standard sample prepared as described above will be described. First, a standard curve of one composition or a plurality of compositions prepared by sintering Fe and SiO ₂ powder and a high-purity Fe plate are measured, and a calibration curve representing the relationship between the composition of Fe, Si and O and the emission intensity is prepared. . Next, GD-OES analysis of a metal sample having an internal oxide layer in the vicinity of the surface under the same analysis conditions can be performed, and the composition of the measurement element can be determined from the relationship between the emission intensity of the measurement element and the calibration curve described above. .

  Hereinafter, examples of the present invention will be described. However, the conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Fe powder having an average particle size of about 3 μm and SiO ₂ powder having an average particle size of about 20 μm are mixed in the proportions shown in Table 1, and after sufficient stirring, 3 minutes at 1100 ° C. at a molding pressure of 28 MPa by a discharge plasma sintering method. Sintered. Further, 100 or more cross-sections of the sintered body were subjected to SEM observation after mirror polishing, and the secondary electron image was subjected to image processing to determine the number average particle diameter of SiO ₂ .

Fe-3 mass% Si Alloy _P H2O _{/ P H2} ratio at 850 ° C. The performs annealing 5min in an atmosphere of 0.45, was analyzed internal oxide layer using GD-OES with cathode diameter 4 mm. Quantification was performed using a high-purity Fe plate having a purity of 99.99 mass% and a standard sample prepared by the above-described discharge plasma sintering. As a comparative example, the results of quantification using a 99.99% pure Fe plate and 99% pure quartz glass as standard samples are also shown.

When quantified using the standard sample in the present invention, _{CO 2} / C _Si in the internal oxide layer is SiO 2 compared to the case where a high-purity Fe plate and quartz glass similar to the conventional quantification method are used as the standard sample. It was confirmed that C 2 _{O 3} / C _Si, which is a composition ratio expected from the stoichiometric composition of ₂ , was close to 1.14, and the quantitative accuracy was improved. Furthermore, it was confirmed that the quantitative accuracy was high when the average SiO ₂ particle size after sintering was 5 μm or less.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is a diagram showing a relationship between _C O _{/ C Si} the average particle diameter and the quantification of SiO ₂ in the sintered body.

Claims (5)

A standard sample used for measuring a metal sample by glow discharge optical emission spectrometry and quantifying the composition of the measurement element in the metal sample by a calibration curve method,
Quantification in glow discharge emission analysis, characterized in that the standard sample is a composite material in which oxide particles of one or more elements having an average particle diameter of 5 μm or less are dispersed in a metal matrix. Standard sample for crystallization.   The standard sample for quantification in glow discharge optical emission analysis according to claim 1, wherein the standard sample is produced by a discharge plasma sintering method.   The standard sample for quantification in the glow discharge optical emission analysis according to claim 1 or 2, wherein the metal matrix is iron.   After preparing a calibration curve using the standard sample according to any one of claims 1 to 3, a glow discharge emission analysis of a metal sample having an internal oxide layer on the surface layer is performed, and the composition of the measurement element in the metal sample A glow discharge emission analysis method characterized by quantitatively determining the amount. The glow discharge emission analysis method according to claim 4, wherein the metal sample is a steel material.

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