Foreign matter contamination evaluation method

Abstract

To provide a technique for safely, as well as quickly and easily evaluating a noble metal element content such as gold, silver, platinum and palladium, assuming the risk of foreign matter inclusion from a manufacturing facility in manufacturing a powder material.SOLUTION: Provided is a foreign matter inclusion evaluation method which, while using a selenium-containing substance for a coprecipitant, sequentially feeds a sample that contains noble metal elements to a decomposition step, a white smoke processing step, a dissolving step, a first preliminary reduction step, a second preliminary reduction step, a reducing coprecipitation step, an aging step, a filtration step, a drying step, and a measurement step, thereby obtaining the contents of noble metal elements included in the sample.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the presence of foreign matter in a powder material. [Background technology]

[0002] Powder materials are currently widely used in a variety of fields, including electronic devices. For example, metal fillers such as nickel powder and copper powder are used in the production of wiring and electrodes in electronic devices, such as resin-type conductive pastes and sintered-type conductive pastes. Thermally conductive greases that fill the contact surfaces between electronic components and cooling heat sinks are made from metal powders such as aluminum powder and copper powder, metal oxide powders such as zinc oxide powder and aluminum oxide powder, and inorganic nitride powders such as boron nitride powder, silicon nitride powder, and aluminum nitride powder.

[0003] The properties of these powder materials are influenced by the types of main constituent elements, the types and amounts of additive and impurity elements, the crystal structure, the size of the crystal grains, and the size and distribution of precipitates. Recently, there has been active development of high-purity materials, not only to improve properties but also to realize new properties, and the content of impurity elements at the development level has been significantly reduced. In addition to the development of high-purity materials, efforts are also being made to reduce the impurity elements in mass-produced products. Therefore, evaluating the impurity elements contained in powder materials is essential for advancing research into their properties.

[0004] The manufacturing process of powder materials is always at risk of contamination from manufacturing equipment, etc. Needless to say, it is important to quickly and easily assess whether or not foreign matter has been introduced into intermediate products during manufacturing or finished products, and what type and amount of foreign matter has been introduced. Lubricating oil, packing fragments, adhesive residue, and solder waste are particularly at risk. In particular, the main component of solder, lead, is harmful to humans and the environment. There has been a global shift from SnAgCu-based solder (made of tin, silver, and copper) and SnAgInBi-based solder (made of tin, silver, indium, and bismuth) to lead-free solder and adhesives containing gold and silver. However, it has been difficult to imagine the possibility of precious metals such as gold and silver being introduced as impurities. Therefore, neither investigations into the potential drawbacks of this scenario nor methods for evaluating foreign matter contamination have been adequately studied.

[0005] Patent Document 1 discloses a method for separating and recovering precious metal elements for quantitative analysis, which addresses the drawbacks of the Te coprecipitation method, such as a low recovery rate of platinum group elements and the deterioration of filterability due to the production of hydrous silicate, and is intended for the analysis of precious metal-containing samples, such as catalysts for purifying automobile exhaust gases, petrochemical catalysts, recycled materials, ores, hydrometallurgical residues, and sludge. The method describes a process in which Te and As are added in combination as coprecipitants to a hydrochloric acid solution in which a precious metal-containing sample containing platinum group elements such as Pt, Pd, and Rh, or Au and Ag, is dissolved. A reducing agent such as SnCl2 is then applied to the solution, causing the precious metal elements to precipitate in association with Te and As, and the resulting precipitate is then recovered by filtration.

[0006] Patent Document 2 describes a method for analyzing each of the precious metal elements in a sample containing multiple precious metal elements, which includes the steps of: separating each of the precious metal elements from an acidic solution containing the dissolved sample by coprecipitation reduction using a metal carrier and a reducing agent; dissolving each of the precious metal elements that have been coprecipitated, reduced, and separated to obtain a solution; and analyzing each of the precious metal elements in the solution, as well as related technologies.

[0007] Non-Patent Document 1 discloses the details of a study on the analysis of gold, silver, platinum, palladium, and rhodium in ores using graphite furnace AAS, and describes that after a sample is thermally decomposed in a Teflon sealed container, the precious metals are separated from coexisting elements by tellurium coprecipitation, and then completely separated using cation exchange separation, and that silver cannot be completely collected by tellurium coprecipitation, so it is separated from coexisting elements using only cation exchange separation.

[0008] However, first, the technique of Patent Document 1 uses highly toxic As2O3 to prepare the coprecipitant for Te+As, and therefore is not considered a clean analytical method, and has the drawback of compromising safety. Next, the technology of Patent Document 2 employs a bismuth coprecipitation separation / aqua regia decomposition-ICPMS method, but requires the operation of dissolving the coprecipitated reduced metals and the operation of adjusting the volume of the resulting solution and diluting it, which makes the analysis insufficient in speed. In addition, the evaluation results in the examples only include the platinum content, palladium content, and rhodium content, and do not include the gold content or silver content at all, making it unclear whether gold and silver can actually be analyzed. Furthermore, the technology of Non-Patent Document 1 employs a combined tellurium coprecipitation / ion exchange separation method, but this requires two separation procedures and a separate procedure for silver analysis, which results in complicated procedures and a long analysis time.

[0009] As such, until now, a method for safely, quickly, and easily evaluating the content of precious metal elements such as gold and silver in powder materials, taking into account the risk of foreign matter contamination from manufacturing equipment, etc., has unfortunately not been developed. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-308705 [Patent Document 2] Japanese Patent Publication No. 2021-135297 [Non-patent literature]

[0011] [Non-Patent Document 1] BUNSEKI_KAGAKU_Vol.39(1990)_T5~9 Summary of the Invention [Problem to be solved by the invention]

[0012] In view of the problems of the above-mentioned conventional techniques, in one aspect of the present invention, the present inventors have conducted extensive research to develop a new method for safely, quickly, and simply evaluating the content of precious metal elements, taking into account the risk of contamination from manufacturing equipment, etc. As a result, a clean analytical method is provided that uses a selenium-containing substance as a coprecipitant and sequentially performs the following steps: decomposition step, white smoke treatment step, dissolution step, first preliminary reduction step, second preliminary reduction step, reduction coprecipitation step, aging step, filtration step, drying step, and measurement step, thereby enabling safe, quick, and simple evaluation of the content of precious metal elements such as gold, silver, platinum, and palladium, using only coprecipitation separation as a separation procedure. [Means for solving the problem]

[0013] As a result of the above-described intensive research, the inventors have completed one aspect of the present invention, which comprises a decomposition step of thermally decomposing a mixture of a sample containing a precious metal element and an inorganic acid X to obtain a decomposition solution, a white smoke treatment step of heating and concentrating the decomposition solution to generate white smoke, and then evaporating the decomposition solution to dryness to obtain a white smoke-treated product, a dissolution step of heating and dissolving a mixture of the white smoke-treated product and an inorganic acid Y to obtain a solution, a first preliminary reduction step of heating a mixture of the solution and a selenium-containing substance as a coprecipitant to obtain a first preliminary reduction solution, and a second preliminary reduction step of heating a mixture of the first preliminary reduction solution and water to obtain a first preliminary reduction solution. The method for evaluating foreign matter contamination comprises: a second pre-reduction step for obtaining a second pre-reduction solution; a reduction co-precipitation step for obtaining a reduction co-precipitation solution containing a precipitate in which a precious metal element is associated with selenium from a mixture of the second pre-reduction solution and a reducing agent; an aging step for heating the reduction co-precipitation solution to age the precipitate; a filtration step for filtering the reduction co-precipitation solution to obtain an aged precipitate; a drying step for drying the aged precipitate to obtain a dried precipitate; and a measurement step for measuring the concentration of the precious metal element in the dried precipitate by X-ray fluorescence analysis, thereby obtaining the content of the precious metal element contained in the sample.

[0014] A second aspect of the present invention is the method for evaluating foreign matter contamination according to the first aspect, wherein the inorganic acid X includes at least one selected from hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, hydrofluoric acid, and hydrogen peroxide.

[0015] A third aspect of the present invention is the method for evaluating foreign matter contamination, wherein the inorganic acid Y in the first or second aspect includes hydrochloric acid.

[0016] A fourth aspect of the present invention is a method for evaluating foreign matter contamination, wherein the selenium-containing material according to the first or second aspect contains selenium (VI).

[0017] A fifth aspect of the present invention is a method for evaluating foreign matter contamination, characterized in that the reducing agent in the first or second aspect includes one or more selected from stannous chloride, sodium sulfite, hydrazine sulfate, oxalic acid, ascorbic acid, sodium hypophosphite, and sodium borohydride.

[0018] A sixth aspect of the present invention is the method for evaluating contamination, characterized in that in the aging step in the first or second aspect, the heating temperature is 60 to 120° C. and the heating time is 0.5 to 2 hours.

[0019] A seventh aspect of the present invention is the foreign matter contamination evaluation method according to the first or second aspect, characterized in that the precious metal element is one or more selected from gold, silver, platinum, and palladium.

[0020] An eighth aspect of the present invention is the method for evaluating foreign matter contamination, characterized in that the filtration in the first or second aspect is suction filtration using quantitative filter paper.

[0021] A ninth aspect of the present invention is a method for evaluating foreign matter contamination according to the first or second aspect, characterized in that the aged precipitate is dried by microwaves and introduced into a fluorescent X-ray analyzer.

[0022] A tenth aspect of the present invention is a method for evaluating foreign matter contamination in the first or second aspect, characterized in that after measuring the dried precipitate by X-ray fluorescence spectrometry, a sample solution obtained from the dried precipitate is measured using one or more methods selected from ICP atomic emission spectrometry, ICP mass spectrometry, microwave plasma atomic emission spectrometry, flame atomic absorption spectrometry, and flameless atomic absorption spectrometry, and a check analysis is performed against the X-ray fluorescence spectrometry. [Effects of the Invention]

[0023] According to the present invention, the content of precious metal elements such as gold, silver, platinum, and palladium can be safely, quickly, and simply evaluated in the production of powder materials, taking into account the risk of contamination from production equipment, etc. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is an operational flow diagram showing an overview of a method for evaluating foreign matter contamination according to one embodiment of the present invention. FIG. [Figure 2]1A and 1B are diagrams showing an example of an X-ray tube and a sample holder of an X-ray fluorescence spectrometer according to one embodiment of the present invention, in which FIG. 1A is a schematic cross-sectional view, and FIG. 1B is an exploded perspective view of the sample holder. [Figure 3] FIG. 1 is a diagram showing an example of a calibration curve for gold by fluorescent X-ray analysis in a method for evaluating foreign matter contamination according to one embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing an example of a calibration curve for silver by fluorescent X-ray analysis in a foreign matter contamination evaluation method according to an embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing an example of a calibration curve for platinum by fluorescent X-ray analysis in a foreign matter contamination evaluation method according to an embodiment of the present invention. [Figure 6] FIG. 1 is a diagram showing an example of a calibration curve for palladium by fluorescent X-ray analysis in a foreign matter contamination evaluation method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] [One embodiment of the present invention] The following is an outline of a method for evaluating foreign matter contamination according to one embodiment of the present invention. The present embodiment described below does not unduly limit the content of the present invention as defined in the claims, and modifications are possible without departing from the spirit of the present invention. It should be noted that not all of the configurations described in this embodiment are necessarily essential as a means for solving the problem of the present invention.

[0026] 1. Overview When evaluating powder materials using instrumental analysis, such as inductively coupled plasma atomic emission spectrometry (ICP-AES, ICP-OES), ICP-mass spectrometry (ICP-MS), microwave plasma atomic emission spectrometry (MP-AES), flame atomic absorption spectrometry (AAS), and flameless atomic absorption spectrometry (FLAAS), the sample is first dissolved by pretreatment such as acid decomposition or alkali fusion. However, when analyzing ultratrace elements in the sample, further separation and concentration of the target elements is required.

[0027] The coprecipitation method is one such technique, a separation and concentration operation that utilizes a coprecipitation reaction. The sample solution is mixed with a coprecipitant (carrier) containing coprecipitating elements that behave similarly to the target element, and reaction reagents such as neutralizing agents, reducing agents, and complexing agents, causing the target element to precipitate as an insoluble substance along with the coprecipitating element. This prevents the main component (matrix) elements of the sample from adversely affecting the evaluation results or contaminating the analytical equipment, while concentrating the sample solution and increasing detection sensitivity.

[0028] The characteristics of the coprecipitation separation method are as follows: first, by adding an appropriate coprecipitant or reaction reagent depending on the characteristics of the target element, it is possible to selectively precipitate only the target element or to precipitate many elements simultaneously; second, it is safe, quick, and simple to operate without using environmentally undesirable organic solvents or ion exchange resins, which take time to operate; and third, it is possible to precipitate elements as simple substances in addition to hydroxides, sulfates, and sulfides, and the resulting precipitates can be recovered by means of filtration, centrifugation, flotation, etc.

[0029] Incidentally, X-ray fluorescence spectrometry (XRF) is widely known as a means of directly performing qualitative and quantitative analysis on solid samples such as powdered materials without the need to dissolve them in water. Generally, with the above-mentioned instrumental analysis methods, there is daily variation, so a calibration curve must be created using a standard solution each time a measurement is made. However, with X-ray fluorescence spectrometry, once a calibration curve is created using a standard sample, it can be used repeatedly, and this offers many advantages.

[0030] However, the X-ray fluorescence analysis method does not have sufficient sensitivity for detecting ultratrace elements, and the present inventors have considered whether the above-mentioned coprecipitation separation method could be applied as a countermeasure to this problem. That is, if a sample contains 0.1 ppm (μg / g) of element M, and 1 g of this sample is used, once the sample has been dissolved, all of the element M will be captured in 10 mg of coprecipitated elements, resulting in a precipitate containing 10 ppm of element M. One of the major features of the present invention is that the precipitate from which element M has been separated and concentrated can be quickly and easily evaluated by X-ray fluorescence analysis without dissolving it again.

[0031] In addition, in the present invention, a selenium-containing substance is used as a coprecipitant, and a precipitate in which a noble metal element such as gold, silver, platinum, or palladium is associated with selenium is obtained by reduction reaction. For example, when a powder material containing iron (III) as the main component is dissolved in hydrochloric acid and silver present in the sample solution is co-precipitated using tin (II) as a reducing agent, the reactions shown in the following equations (1) to (4) are thought to proceed simultaneously in the solution.

[0032] [ka]

[0033] From the above reaction equation, iron(III) ions are reduced to iron(II) ions, but remain dissolved, and only silver and selenium precipitate. By recovering this precipitate, silver can be separated from the main component element, iron(III). Tin(II) ions are oxidized to tin(IV) ions, and in a hydrochloric acid solution, many ions can be reduced to their metallic state.

[0034] Furthermore, in the case of liquefying a sample, pretreatment such as acid decomposition or alkali fusion can be performed. When alkali fusion is used as a pretreatment, it is necessary to use an excess amount of flux relative to the amount of sample. For example, if sodium peroxide (Na2O2), a common flux also described in Patent Document 1, remains, the reaction shown in formula (5) below will proceed during leaching with water after alkali fusion, producing hydrogen peroxide (H2O2).

[0035] [ka]

[0036] This hydrogen peroxide has a very strong oxidizing power and may have a negative effect on the reduction reaction, so particular care must be taken to avoid its adverse effect on the reduction reaction of silver. In this respect, when acid decomposition is performed as a pretreatment, even if oxidizing acids such as nitric acid and perchloric acid are used, these can be completely vaporized by white fume treatment using sulfuric acid, which is an advantage over alkali fusion. Note that for samples that can be dissolved solely with hydrochloric acid, a reducing acid, white fume treatment using sulfuric acid may be omitted.

[0037] The present invention was made based on the above findings. A method for evaluating foreign matter contamination according to one embodiment of the present invention includes a decomposition step, a white smoke treatment step, a dissolution step, a first preliminary reduction step, a second preliminary reduction step, a reduction co-precipitation step, an aging step, a filtration step, a drying step, and a measurement step. The method for evaluating foreign matter contamination according to one embodiment of the present invention assumes contamination with lubricating oil, packing pieces, adhesive residue, solder shavings, etc., and indicates contamination containing organic matter, silicon, tin, etc., and takes as an example a case where the content of precious metal elements such as gold, silver, platinum, and palladium in the sample is evaluated. Hereinafter, each step in the foreign matter contamination evaluation method according to one embodiment of the present invention will be specifically described.

[0038] 2.Each process FIG. 1 is an operational flow diagram showing an overall picture of a method for evaluating contamination by foreign matter according to one embodiment of the present invention, and will be described in the order of the operational flow diagram.

[0039] <Disassembly process> This is a process in which a sample weighed on an electronic balance is transferred to a container, mixed with inorganic acid X, and then thermally decomposed to obtain a decomposition solution. Examples of containers include glass beakers and Teflon (registered trademark) beakers (hereinafter, the "(registered trademark)" that should follow "Teflon" will be omitted). For samples containing silicon, hydrofluoric acid is required to decompose and volatilize the silicon, so a Teflon beaker that is not corroded by hydrofluoric acid is preferably used. The sample amount depends on the content of the target precious metal element, such as gold or silver, but is preferably 10 g or less, more preferably 5 g or less, and particularly preferably 0.1 to 2 g.

[0040] The inorganic acid X includes one or more selected from hydrochloric acid (HCl), nitric acid (HNO), sulfuric acid (HSO), perchloric acid (HClO), hydrofluoric acid (HF), and hydrogen peroxide (HO). Hydrochloric acid, nitric acid, and sulfuric acid are preferred for dissolving the sample and decomposing and volatilizing organic matter. Hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid are more preferred for decomposing and volatilizing silicon. Hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and hydrofluoric acid are particularly preferred for efficient decomposition and volatilization. If the sample contains a large amount of organic matter, perchloric acid is preferably used toward the end of the decomposition process to finish the process. If a portion of the sample remains undissolved (undissolved residue), hydrogen peroxide may be used as needed to dissolve the undissolved residue. The thermal decomposition temperature is preferably 200°C or higher.

[0041] <White smoke treatment process> Following the decomposition step, the decomposition liquid is heated and concentrated to generate white smoke, which is then evaporated to dryness to obtain a white smoke-treated product. The white smoke derived from the nitric acid, sulfuric acid, perchloric acid, and hydrofluoric acid contained in inorganic acid X completely volatilizes organic matter and silicon. Furthermore, excess oxidizing nitric acid and perchloric acid, which may adversely affect the reduction reaction in the subsequent first preliminary reduction step, second preliminary reduction step, reduction co-precipitation step, and aging step, are also completely volatilized by evaporation to dryness after the white smoke is generated. The temperature for heating and concentration and evaporation to dryness is preferably 200°C or higher.

[0042] <Dissolution process> Following the white smoke treatment step, the white smoke-treated product is mixed with inorganic acid Y, and then heated and dissolved to obtain a solution. The inorganic acid Y contains hydrochloric acid, and is preferably hydrochloric acid alone in order to sufficiently pre-reduce the target elements, such as precious metal elements like gold, silver, platinum, and palladium, and the coprecipitated element selenium, in the subsequent first and second pre-reduction steps. The heating and dissolution temperature is preferably 80 to 150°C.

[0043] <First preliminary reduction step> Following the dissolution step, the dissolution solution is mixed with a selenium-containing substance as a coprecipitant, and then heated to obtain a first preliminary reduction solution. If a Teflon beaker was used as the container up to the previous step, it is advisable to transfer the solution to a glass beaker in consideration of workability from this step onwards. Furthermore, selenium-containing coprecipitants containing selenium(IV), such as selenium dioxide (SeO2) and sodium selenite (Na2SeO3), are not as toxic as arsenic trioxide (As2O3), but are still subject to the "skull and crossbones" label (a pictogram indicating acute toxicity) under the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Therefore, from a safety perspective, it is preferable to use selenium(VI)-containing compounds such as sodium selenate (Na2SeO4). The heating temperature is preferably 80–120°C, and the heating time is preferably 10 minutes or longer.

[0044] <Second preliminary reduction step> Following the first preliminary reduction step, this is a step in which the first preliminary reduction solution is mixed with water and then heated to obtain a second preliminary reduction solution. In the subsequent reduction coprecipitation step, in order to sufficiently reduce the target elements, such as precious metal elements like gold, silver, platinum, and palladium, and the coprecipitating element selenium, it is preferable to mix the first preliminary reduction solution with water so that the acid concentration of the hydrochloric acid contained therein is 1.0 to 6.0 mol. The heating temperature is preferably 80 to 120°C, and the heating time is preferably 30 minutes or longer.

[0045] <Reduction coprecipitation process> Following the second preliminary reduction step, the second preliminary reduction solution is mixed with a reducing agent to obtain a reduction coprecipitate solution containing a precipitate in which the precious metal element is associated with selenium. The reducing agent includes one or more selected from stannous chloride (SnCl2), sodium sulfite (Na2SO3), hydrazine sulfate (N2H6SO4), oxalic acid (C2H2O4), ascorbic acid (C6H8O6), sodium hypophosphite (NaH2PO2), and sodium borohydride (NaBH4), and it is preferable to include stannous chloride in view of ease of control of the reducing power.

[0046] <Aging process> Following the reduction coprecipitation step, the reduction coprecipitation liquid containing the precipitate is heated to age the precipitate, thereby obtaining an aged precipitate. The heating temperature is preferably 60 to 120° C., and the heating time is preferably 0.5 to 2 hours. When the target element includes rhodium, the heating time is more preferably 6 hours or more.

[0047] <Filtration process> Following the aging step, the reduced coprecipitate containing the aged precipitate is filtered to recover the aged precipitate. The filtration operation may be carried out by a known means such as suction filtration. Examples of filter paper used for filtration include ordinary quantitative filter paper, as well as membrane filters such as cellulose acetate filter paper and hydrophilic PTFE filter paper. However, quantitative filter paper is preferred because the aged precipitate attached to the membrane filter is easily peeled off after drying. It is also preferable to thoroughly stir the reduction coprecipitate containing the aged precipitate with a glass rod or the like before filtration to break the aged precipitate into fine particles. This makes the surface of the aged precipitate layer adhered to the filter paper smooth, which further reduces measurement variability in X-ray fluorescence analysis.The recovered aged precipitate should be washed, for example, five or six times with water.

[0048] <Drying process> Following the filtration step, the aged precipitate adhering to the filter paper is dried to obtain a dried precipitate. As a drying method, drying using a dryer or a hairdryer is preferred, but from the viewpoint of rapid and uniform drying, drying using microwaves using a microwave oven or the like is also preferred.

[0049] <Measurement process> Following the drying step, the concentration of the precious metal element in the dried precipitate is measured, for example, by X-ray fluorescence analysis in the form shown in Figure 2(a), and the precious metal element content of the sample is obtained based on the concentration of the precious metal element in the dried precipitate. When loading the dried precipitate into an X-ray fluorescence analyzer, for example, as shown in Figure 2(b), a sample holder 20 consisting of a frame 21, a support 22, a hole 23, a mask 24, and a mask hole 25 can be used.

[0050] In the X-ray fluorescence analysis shown in FIG. 2(a), the filter paper 26 with the dried precipitate 27 attached is placed on the mask 24 so that the dried precipitate 27 faces the bottom side (the side where the X-ray tube 10, which irradiates primary X-rays X1, and the X-ray detector 30, which detects the generated element-specific fluorescent X-rays X2, are mounted. A weight 28 is placed on the opposite side to secure the filter paper 26 with the dried precipitate 27 attached. In this manner, the primary X-rays X1 irradiated from the X-ray tube 10 pass through the hole 23 in the sample holder 20 and the mask hole 25, impinge on the filter paper 26 with the dried precipitate 27 attached, and generate element-specific fluorescent X-rays X2 from the elements that make up the dried precipitate 27. The fluorescent X-rays X2 are then detected by the X-ray detector 30, and their intensity is measured to ultimately determine the content of the target element.

[0051] Measurements can be performed using the absolute calibration curve method, standard addition method, internal standard method, etc. Furthermore, if qualitative evaluation is sufficient, the fundamental parameter method (FP method), a theoretical calculation that estimates the composition so that the signal intensity matches the type and amount of the constituent elements, can be used instead of the calibration curve method, which uses a correlation equation between the signal intensity and concentration of the evaluation element. Figures 3, 4, 5, and 6 show examples of calibration curves for gold, silver, platinum, and palladium using X-ray fluorescence analysis. [Example]

[0052] The foreign matter contamination evaluation method according to one embodiment of the present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, unless otherwise specified, all reagents used in these examples were Fujifilm Wako Pure Chemical Industries, Ltd. (special grade reagents) or products prepared from these. Furthermore, all water used in these examples was ultrapure water.

[0053] (Sample preparation) Iron oxide (Fe2O3) powder reagent was designated Product A, copper oxide (CuO) powder reagent was designated Product B, and nickel oxide (NiO) powder reagent was designated Product C. To these, assuming that foreign matter had been mixed from manufacturing equipment, etc., dried and crushed adhesive (1533C manufactured by ThreeBond Co., Ltd.) and crushed lead-free solder (Sn4.5N-Ag-Au manufactured by Sasaki Handa Kogyo Co., Ltd., Mitsubishi Materials high-purity tin 4.5N + 4N pure silver + 24K pure gold lead-free solder for audio use / Sn4.5N-Ag-Au) were randomly added and mixed. Products A, B, and C after the mixing process were designated Samples A, B, and C.

[0054] (Precious metal element to be evaluated) (1) In Examples 1 to 3 and Comparative Examples 1 to 4, the evaluation targets were "gold" and "silver" derived from lead-free solder. (2) In Example 4 and Comparative Example 5, "platinum" and "palladium" were also evaluated to confirm that no precious metal elements were contained. [Example]

[0055] (1) Preparation of normal specimens (A1, A2) Two samples of sample A were pretreated in parallel to prepare normal samples (A1, A2). First, 1.0 g of sample was weighed out onto a drug packing paper using an electronic balance and transferred to a 200 ml Teflon beaker. A small amount of water was added to the Teflon beaker, and inorganic acid X (10 ml of hydrochloric acid, 10 ml of nitric acid, 2 ml of sulfuric acid (1+1), 5 ml of perchloric acid, and 10 ml of hydrofluoric acid) was added and mixed. The Teflon beaker was then covered with a watch glass and heated on a hot plate at 200°C or higher to thermally decompose the sample and obtain a decomposition liquid. Subsequently, the Teflon beaker was heated to 200°C or higher, and the decomposition liquid was heated and concentrated until sufficient white smoke originating from the nitric acid, sulfuric acid, perchloric acid, and hydrofluoric acid contained in inorganic acid X was generated in the Teflon beaker. After that, the watch glass was removed, and the Teflon beaker was heated until no more white smoke was generated, and the decomposition liquid was completely evaporated to dryness, thereby obtaining a white smoke-treated product.

[0056] Next, 40 ml of hydrochloric acid was added to the Teflon beaker as inorganic acid Y and mixed, and then the Teflon beaker, covered with a watch glass, was heated on a hot plate at 120°C to heat and dissolve the white smoke-treated material, thereby obtaining a solution. This solution was transferred to a 300 ml glass beaker with a small amount of water, and 1 ml (approximately 5 mg of selenium) of selenium VI solution (1 g of sodium selenate dissolved in 80 ml of water) was added to the glass beaker as a coprecipitant and mixed. After mixing, the glass beaker was covered with a watch glass and heated on a hot plate at 120°C for 10 minutes to obtain a first preliminary reduction solution.

[0057] Next, water was added to the glass beaker so that the liquid volume was 200 ml (acid concentration of hydrochloric acid: 2.4 mol) and mixed, and then the glass beaker, covered with a watch glass, was heated on a hot plate at 120°C for 30 minutes to obtain a second preliminary reduction liquid.

[0058] Then, 20 ml of a stannous chloride solution (20 w / v %, 2.4 mol of hydrochloric acid) was added as a reducing agent to the glass beaker and mixed to obtain a reduced coprecipitate solution containing a precipitate in which the noble metal element was associated with selenium. The glass beaker was then covered with a watch glass and heated on a hot plate at 120° C. for 1 hour to allow the precipitate contained in the reduction coprecipitate to fully mature. The reduced coprecipitate solution after the aging procedure was subjected to suction filtration using quantitative filter paper No. 5C (diameter 50 mm) to separate the aged precipitate, and the recovered aged precipitate was washed 5 to 6 times with water.

[0059] Next, the aged precipitate was placed together with the filter paper in a microwave oven (600W) and heated for 3 minutes to dry, thereby obtaining filter paper with the dried precipitate attached, i.e., normal specimens (A1, A2).

[0060] (2) Preparation of spiked recovery rate sample (A+) In addition to the normal samples (A1, A2), one spiked recovery sample (A+) was prepared to evaluate the spiked recovery rates of gold and silver. 1 ml of gold standard solution (1 mg / L) and 1 ml of silver standard solution (1 mg / L) were added to a 200 ml Teflon beaker, dried at 60°C, and then the Teflon beaker was cooled. Using this Teflon beaker containing dried gold and silver, the same procedure as for the preparation of the normal samples (A1, A2) was carried out to obtain a spiked recovery sample (A+). In other words, if there is no loss of elements during the analytical procedure, the amount of gold and silver added to the spiked recovery sample (A+) is 0.001 mg (1 μg), which is detected at a value 1 ppm higher on a sample basis than the normal samples (A1, A2).

[0061] (3) Preparation of blank test specimen (BL) In addition to the normal samples (A1, A2) and spiked recovery rate sample (A+), one blank test sample (BL) was prepared to check for the presence or absence of gold and silver contamination during the analytical procedure. A blank test sample (BL) was obtained by carrying out the same procedure as in the preparation of the normal samples (A1, A2) described above, except that no sample was weighed into the 200 ml Teflon beaker.

[0062] (4) Preparation of standard samples In addition to the normal samples (A1, A2), spiked recovery rate sample (A+), and blank test sample (BL), six standard samples were prepared as standard samples for creating a calibration curve in X-ray fluorescence analysis. Instead of weighing the sample into a 200-ml Teflon beaker, a 300-ml glass beaker was charged with gold standard solution and silver standard solution at 0, 1, 2, 5, 10, and 20 μg, respectively. 40 ml of hydrochloric acid was added as inorganic acid Y and mixed. The glass beaker was then heated on a hot plate with a watch glass lid on at 120°C to obtain a solution. 1 ml of selenium (VI) solution (1 g of sodium selenate dissolved in 80 ml of water) was added as a coprecipitant and mixed. The glass beaker was then heated on a hot plate with a watch glass lid on at 120°C for 10 minutes to obtain a first preliminary reduction solution. Thereafter, the same procedures as those for preparing the above-mentioned normal specimens (A1, A2) were carried out to obtain standard samples.

[0063] (5) Measurement by X-ray fluorescence analysis The standard samples, normal samples (A1, A2), spiked recovery rate samples (A+), and blank test samples (BL) were measured using an X-ray fluorescence analyzer, Axios (manufactured by Spectris Inc.). The above procedure assumes the application of the calibration curve method, a common analytical method, but it is not limited to this. Analytical samples can also be prepared using the standard addition method. The calibration curve method can be chosen from either the "absolute calibration curve method," which does not use an internal standard, or the "internal standard method," which uses an element with similar physical and chemical properties to the target element as the internal standard.

[0064] The calibration curve method involves preparing multiple standard samples with known concentrations in stages relative to the target element concentration in the analytical sample, measuring the signal specific to the analytical device being used, and determining the relationship between concentration and signal to obtain a calibration curve. It is preferable that the standard sample has a composition as close as possible to the analytical sample, and if the analytical sample contains large amounts of elements other than the target element, these elements are also added to the standard sample to offset the interference caused by their effects.

[0065] The standard addition method involves preparing multiple parallel samples by taking predetermined amounts of a single sample, adding different amounts of a standard substance in stages to each sample, creating multiple analytical samples with different concentrations of the target element, and measuring the signal specific to the analytical equipment being used.

[0066] In other words, the analytical specimen is prepared by "directly adding the standard substance to the sample to be analyzed." This allows the relationship between the concentration of the added standard substance and the signal to be determined, creating a calibration curve, and the concentration of the target element in the sample can be obtained from the intersection of the calibration curve with the X-axis. This method is applicable when the calibration curve shows good linearity and intersects with the X-axis, and since it eliminates the influence of coexisting elements, it is highly suitable for analyzing samples with complex compositions and liquids. However, the standard addition method requires the preparation of multiple analytical samples with different concentrations of the target element from a single sample, which has the disadvantage of significantly increasing the number of analytical samples and therefore the time required for measurement compared to the calibration curve method.The choice between the calibration curve method and the standard addition method should be made based on the coexisting elements contained in the sample, as well as the required analytical accuracy and analysis delivery time.

[0067] (6) Evaluation results The gold and silver content of each analytical sample was calculated from the gold and silver measurement values. Specifically, the gold and silver content was calculated using formula (6) from the "sample measurement values," which were the measurement values ​​of the normal samples (A1, A2), and the "blank value," which was the measurement value of the blank test sample (BL). In addition, the spike recovery rates of gold and silver were calculated from the measurement values ​​of gold and silver in each analytical sample. Specifically, the spike recovery rates of gold and silver were calculated using formula (7) from the "spike measurement values," which were the measurement values ​​of the spike recovery rate sample (A+), and the "sample measurement values," which were the measurement values ​​of the normal samples (A1, A2).

[0068] [ka]

[0069] [ka]

[0070] The evaluation results for gold and silver calculated from the above formulas (6) and (7) are shown in Table 1. [Example]

[0071] The same procedure as in Example 1 was carried out except that Sample B was used instead of Sample A, and the evaluation results of gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1. [Example]

[0072] The same procedure as in Example 1 was carried out except that Sample C was used instead of Sample A, and the evaluation results of gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1. [Example]

[0073] In order to confirm that sample A does not contain any other precious metal elements, the evaluation results for platinum and palladium were obtained by the same procedures as in Example 1, except that the precious metal elements to be evaluated were replaced with platinum and palladium and standard solutions for these elements were prepared. The calculated evaluation results for platinum and palladium are shown in Table 2.

[0074] (Comparative Example 1) The same operations as in Example 1 were carried out, except that in the first preliminary reduction step, a tellurium-containing substance (sodium tellurite) was used as the coprecipitating agent instead of a selenium-containing substance, and the evaluation results of gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1.

[0075] (Comparative Example 2) The same procedure as in Comparative Example 1 was carried out except that Sample B was used instead of Sample A, and the evaluation results for gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1.

[0076] (Comparative Example 3) The same procedure as in Comparative Example 1 was carried out except that Sample C was used instead of Sample A, and the evaluation results for gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1.

[0077] Comparative Example 4 The same operations as in Example 1 were carried out, except that in the first preliminary reduction step, a bismuth-containing substance (bismuth chloride) was used as the coprecipitating agent instead of a selenium-containing substance, and the evaluation results of gold and silver were obtained. The calculated evaluation results for gold and silver are shown in Table 1.

[0078] (Comparative Example 5) In order to confirm that Sample A does not contain any other precious metal elements, the precious metal elements to be evaluated were replaced with platinum and palladium, and a standard solution was prepared. Except for this, the same operations as in Comparative Example 1 were carried out to determine the evaluation results for platinum and palladium. The calculated evaluation results for platinum and palladium are shown in Table 2.

[0079] 3. Conclusion As shown by the evaluation results for gold and silver in Table 1, in Examples 1 to 3 using the present invention, the contents of two parallel normal samples (e.g., A1 and A2) were in good agreement for both elements, and the spike recovery rates of the spike recovery samples (e.g., A+) were also good, ranging from 99.0 to 102% for both elements, which were within very favorable ranges for judging the reliability of the quantitative values ​​of gold and silver obtained.

[0080] In contrast to this, as described in Patent Document 1, Patent Document 2, and Non-Patent Document 1, in Comparative Examples 1 to 4 in which tellurium or bismuth was used as a coprecipitating element, which is a conventional technology, only gold obtained evaluation results similar to those of the Examples, but for silver, good evaluation results comparable to those of Examples 1 to 3 were not obtained.

[0081] Furthermore, as shown by the evaluation results for platinum and palladium in Table 2, in Example 4 using the present invention, the quantitative values ​​for two normal samples (A1, A2) run side by side were less than 0.1 ppm for both elements, confirming that no precious metal elements other than gold and silver were contained. In addition, the spike recovery rate for sample (A+) was good, at 99.0% or more for both elements, demonstrating that even if platinum and palladium are actually contained in the sample, these elements can be accurately analyzed. In contrast, in Comparative Example 5, which uses tellurium as a coprecipitating element according to the prior art, good evaluation results comparable to those of Example 4 were not obtained in terms of the spike recovery rate of the spike recovery sample (A+).

[0082] In other words, according to the present invention, the content of precious metal elements such as gold and silver can be safely, quickly, and simply evaluated in the production of powder materials, taking into account the risk of foreign matter contamination from production equipment, etc., and the above evaluation results can be said to be sufficient to support this. In the present invention, for example, an analytical sample after evaluation by X-ray fluorescence analysis can be optionally subjected to a check analysis for X-ray fluorescence analysis by dissolving the dried precipitate adhering to the filter paper using inorganic acid Z characterized by containing one or more selected from hydrochloric acid, nitric acid, and hydrogen peroxide, and the resulting solution can be diluted to a constant volume or as appropriate to prepare a sample solution, and the obtained sample solution can be evaluated by an instrumental analysis method such as ICP atomic emission spectrometry or ICP mass spectrometry.

[0083] Furthermore, the technical scope of the present invention is not limited to the aspects described in the above embodiment, etc. One or more of the requirements described in the above embodiment, etc. may be omitted. The requirements described in the above embodiment, etc. may be combined as appropriate. Furthermore, to the extent permitted by law, the contents of all documents cited in this specification are incorporated by reference and are incorporated by reference into this specification.

[0084] [Table 1]

[0085] [Table 2] [Explanation of symbols]

[0086] 10 X-ray tube 20 Sample holder 21 Frame 22 Support part 23 Hole 24 Mask 25 Mask hole 26 Filter paper 27 Dry sediment 28 Weight 30 X-ray detector X1 Primary X-ray X2 fluorescent X-ray

Claims

1. a decomposition step of thermally decomposing a mixture of a sample containing a precious metal element and an inorganic acid X to obtain a decomposition solution; a white smoke treatment step of heating and concentrating the decomposition liquid to generate white smoke, and then evaporating the white smoke to dryness to obtain a white smoke treated product; a dissolving step of heating and dissolving the mixture of the white smoke-treated product and inorganic acid Y to obtain a solution; a first preliminary reduction step of heating a mixture of the dissolution solution and a selenium-containing substance as a coprecipitant to obtain a first preliminary reduction solution; a second preliminary reduction step of heating a mixture of the first preliminary reduction solution and water to obtain a second preliminary reduction solution; a reduction coprecipitation step of obtaining a reduction coprecipitation solution containing a precipitate in which a noble metal element is associated with selenium from a mixture of the second preliminary reduction solution and a reducing agent; an aging step of heating the reduction coprecipitate to age the precipitate; a filtration step of filtering the reduced coprecipitate to obtain a ripened precipitate; a drying step of drying the aged precipitate to obtain a dried precipitate; a measuring step of measuring the concentration of the precious metal element in the dried precipitate by fluorescent X-ray analysis, A method for evaluating foreign matter contamination, characterized by obtaining the content of precious metal elements contained in the sample.

2. 2. The method for evaluating foreign matter contamination according to claim 1, wherein the inorganic acid X includes at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, hydrofluoric acid, and hydrogen peroxide.

3. 3. The method for evaluating contamination according to claim 1, wherein the inorganic acid Y includes hydrochloric acid.

4. 3. The method for evaluating foreign matter contamination according to claim 1, wherein the selenium-containing material contains selenium (VI).

5. The method for evaluating foreign matter contamination described in claim 1 or 2, characterized in that the reducing agent includes one or more selected from stannous chloride, sodium sulfite, hydrazine sulfate, oxalic acid, ascorbic acid, sodium hypophosphite, and sodium borohydride.

6. 3. The method for evaluating foreign matter contamination according to claim 1, wherein in the aging step, the heating temperature is 60 to 120° C. and the heating time is 0.5 to 2 hours.

7. 3. The method for evaluating foreign matter contamination according to claim 1, wherein the noble metal element is at least one selected from the group consisting of gold, silver, platinum, and palladium.

8. 3. The method for evaluating contamination according to claim 1, wherein the filtration is suction filtration using quantitative filter paper.

9. 3. The method for evaluating contamination according to claim 1, wherein the aged precipitate is dried by microwaves and then introduced into a fluorescent X-ray analyzer.

10. The foreign matter contamination evaluation method according to claim 1 or 2, characterized in that after measuring the dried precipitate by the X-ray fluorescence analysis, the sample solution obtained from the dried precipitate is measured using one or more methods selected from ICP atomic emission spectrometry, ICP mass spectrometry, microwave plasma atomic emission spectrometry, flame atomic absorption spectrometry, and flameless atomic absorption spectrometry, and a check analysis is performed on the X-ray fluorescence analysis.

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