Gold powder and method for producing the same

Abstract

To provide a gold powder excellent in dispersibility in gold paste.SOLUTION: In a gold powder, a sulfur content is present on a surface, a sulfur amount per unit surface area obtained by dividing a surface sulfur amount per unit mass obtained by quantitatively analyzing a treatment solution obtained by nitric acid extraction treatment by a specific surface area is 250 μg / m2 or more and 1,500 μg / m2 or less, and an average particle diameter measured on an SEM image is preferably 0.7 μm or more and 1.5 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to gold powder and a method for producing the same, and more particularly to gold powder that is a main component of gold paste used as a raw material for producing conductive films such as wiring layers and electrodes of electronic devices, and a method for producing the same. [Background technology]

[0002] Gold (Au) is chemically stable, has excellent corrosion resistance, and has excellent electrical and thermal conductivity, making it an industrially useful metal used in a variety of fields. For example, in the field of electronic devices, gold is used in the form of gold paste as a raw material for producing conductive films such as wiring layers and electrodes. This gold paste consists of components such as gold powder, resin, hardener, and solvent, and is generally prepared by kneading these components using a three-roll mill.

[0003] For example, Patent Document 1 discloses a technique for producing gold paste by weighing out gold powder as a conductive metal powder, a binder resin such as epoxy resin, a curing agent such as a phenolic compound, and a diluent such as alkylacetalized polyvinyl alcohol or ethylene glycol in a predetermined mixing ratio and kneading them in a three-roll mill. The gold paste produced in this way is printed in a predetermined pattern and then heated and baked to form a conductive film having the predetermined pattern. The gold powder particles in the formed conductive film are connected to form electrically connected current paths, allowing the film to function as a wiring layer, electrode, or the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-111525 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, since the conductive film is formed by firing the gold paste, in order to form a conductive film with the desired properties, it is preferable not only to mix the components constituting the gold paste in appropriate proportions but also to use gold powder, which is the main constituent, having predetermined properties. These predetermined properties of the gold powder include powder properties that affect the properties of the conductive film, such as particle size, particle size distribution, specific surface area, tap density, and dispersibility. Among these, the dispersibility of the gold powder in the gold paste is particularly important.

[0006] Dispersibility is particularly important because uniform dispersion of gold powder in the gold paste allows for the formation of wiring layers of uniform thickness and electrodes of uniform thickness after firing the gold paste. Conversely, poor dispersion of gold powder in the gold paste tends to cause the gold powder to aggregate and form aggregates, which may be crushed between, for example, three rolls during the gold paste kneading process and become flaky. Furthermore, if aggregates or flakes larger than the thickness of the conductive film are formed, these may cause protrusions in the conductive film, resulting in uneven film thickness or uneven distribution of the gold particles constituting the conductive film. This may result in problems such as locally high or low resistance values ​​in the conductive film or weakened mechanical strength of the conductive film.

[0007] The dispersibility of gold powder in the gold paste can be evaluated based on two criteria: whether the gold particles constituting the gold powder are individually dispersed throughout the paste, with almost no agglomerates present, and whether the surfaces of the gold particles are compatible with the other components of the gold paste. An indicator for evaluating the former is tap density, and a high tap density is desirable. On the other hand, an indicator for evaluating the latter is a surface texture evaluation method, typified by the SP value (Solubility Parameter). However, because the SP value is a material-specific physical property defined as the square root of the cohesive energy density, it varies depending on the components constituting the gold paste, making it difficult to identify a single preferred range.

[0008] In addition, since gold powder is the main component of gold paste and accounts for a large proportion of the price of gold paste, low manufacturing costs are also required for gold powder for gold paste. In order to reduce the manufacturing costs of gold powder, it is necessary not only to reduce the unit prices of the raw materials and ingredients used, but also to stably manufacture gold powder with the properties required for gold paste at a high yield.

[0009] A known method for producing gold powder for use in gold paste is to produce a chloroauric acid solution containing chloroauric acid (HAuCl4) obtained by leaching waste electronic devices and other materials with a solution capable of dissolving gold, such as aqua regia, and then adding an aqueous solution of a reducing agent, such as a sulfite (sodium sulfite or potassium sulfite), to reduce the gold ions and precipitate gold. The resulting gold powder slurry containing fine gold particles is then subjected to solid-liquid separation, washed, and dried by heating.

[0010] However, gold powder produced by the above method can have variations in particle size and tap density, which are indicators of product quality, depending on the lot of the reducing agent, which can cause quality control problems. One possible cause of this variation in product quality is impurities contained in the reducing agent. For example, when potassium sulfite is used as the reducing agent, various potassium salts such as potassium sulfite hydrate, potassium bisulfite, potassium sulfate, potassium pyrosulfite, potassium thiosulfate, potassium carbonate, and potassium hydroxide may be contained as impurities, which may affect the reduction reaction.

[0011] However, even if any of these elements are present in trace amounts in potassium sulfite, it is generally difficult to analyze them, and therefore inspecting and managing the reducing agent on a lot-by-lot basis is often ineffective for product quality control. In such cases, it is only after changing the reducing agent lot that it is discovered that the quality of the gold powder produced does not meet the standards, and the current situation is that the only effective solution is to determine that the changed reducing agent lot is defective and switch to a different reducing agent lot.

[0012] When a defective reducing agent lot occurs as described above, the gold powder produced using it must be reprocessed, and since this defective reducing agent lot cannot be used as is, it must be discarded or reprocessed, which increases the production cost, which has been a problem. The present invention has been made in consideration of these conventional circumstances, and its object is to provide a gold powder that has excellent dispersibility in gold paste. [Means for solving the problem]

[0013] The gold powder according to each embodiment of the present invention has sulfur on its surface, and the amount of sulfur per unit surface area, calculated by dividing the amount of surface sulfur per unit mass by the specific surface area, obtained by quantitatively analyzing the treatment solution obtained by nitric acid extraction treatment, is 250 μg / m 2 More than 1500μg / m 2 The present invention is characterized by the following:

[0014] Furthermore, the gold powder manufacturing method according to each embodiment of the present invention includes a reduction step in which a chloroauric acid solution is reduced using a reducing agent solution to precipitate gold particles, and a post-treatment step in which the slurry containing the gold particles obtained in the reduction step is subjected to solid-liquid separation, washing, and drying, and is characterized in that the reducing agent solution contains a sulfur compound containing divalent sulfur. [Effects of the Invention]

[0015] According to each embodiment of the present invention, it is possible to provide gold powder that is highly dispersible in gold paste. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a graph showing the relationship between the amount of sulfur per unit surface area of ​​gold powder and the tap density, with the average particle size as a parameter. [Figure 2] 1 is a flowchart of a method for producing gold powder according to an embodiment of the present invention. [Figure 3] 1 is a graph showing the relationship between the concentration of thiosulfate added and the amount of sulfur per unit surface area of ​​gold powder. [Figure 4]1 is a graph showing the relationship between the average particle size and tap density of gold powder produced by a manufacturing method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Specific embodiments of the gold powder and method for producing the gold powder according to the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments and can include various modifications and alternatives without departing from the spirit of the present invention. In other words, the rights of the present invention extend to the scope of the claims and their equivalents.

[0018] The gold powder according to an embodiment of the present invention is a gold powder having sulfur on its surface, and the amount of sulfur per unit surface area of ​​the gold powder is 250 μg / m, which is calculated by dividing the amount of surface sulfur per unit mass of the gold powder by the specific surface area of ​​the gold powder, by quantitative analysis of the treatment solution obtained by subjecting the gold powder to nitric acid extraction. 2 More than 1500μg / m 2 The reason for using nitric acid extraction to determine the amount of surface sulfur per unit mass of the above gold powder is that when gold powder with sulfur content on the surface was irradiated with a beam of primary ions, secondary ions were emitted from the surface and mass-separated using differences in their flight times. This method was used to analyze the surface, and it was found that sulfur existed on the gold powder surface in the form of gold sulfide, modifying the gold powder.

[0019] Furthermore, when gold powder with sulfur adsorbed on its surface is extracted with pure water, the surface sulfur content determined from the sulfur oxide concentration in the extraction solution is smaller than that determined by extraction with nitric acid. This is because gold does not dissolve in nitric acid, but gold compounds such as gold sulfide do. By performing qualitative and quantitative analysis on the extraction solution obtained by the nitric acid extraction, the surface sulfur content per unit mass of gold powder due to the sulfur present in the form of gold sulfide can be determined. Examples of such qualitative and quantitative analysis include ICP atomic emission spectroscopy, in which an atomized solution sample is introduced into a plasma to emit spectra specific to the elements contained in the solution sample, and qualitative and quantitative analysis is performed based on the wavelengths and intensities of these spectra.

[0020] The gold powder of the present invention has a sulfur content per unit surface area of ​​250 μg / m, which is calculated by dividing the surface sulfur content per unit mass by the specific surface area. 2 More than 1500μg / m 2 The sulfur content per unit surface area is 250 μg / m or less. 2 More than 1500μg / m 2 By keeping the value within the range below, aggregation of the gold powder is suppressed and dispersibility is improved, thereby increasing the tap density. On the other hand, if the sulfur content per unit surface area is 250 μg / m 2 If the sulfur content is lower than 1500 μg / m, the active metallic gold portion on the gold powder surface increases, making it easier for the powder to aggregate, resulting in a lower tap density. 2 If the concentration exceeds this value, an excessive amount of sulfur will adhere to the surface of the gold powder, which is undesirable because it may adversely affect the properties of the conductive film after firing the gold paste.

[0021] While there are no particular limitations on the method for measuring the specific surface area, the BET method is preferred, in which a cooled sample is adsorbed with an inert molecule, such as nitrogen, with a known adsorption area, and the amount of adsorption determined from the adsorption amount. The BET single-point method, which is easier to measure, is even more preferred. The specific surface area of ​​a powder is known to vary with particle size; specifically, a smaller particle size increases the specific surface area, and conversely, a larger particle size decreases the specific surface area. Furthermore, gold powder used in gold pastes preferably has an average particle size of 0.7 μm to 1.5 μm, with an average particle size of around 1 μm being more preferable. Note that an average particle size greater than 1.5 μm is undesirable because it requires a higher firing temperature for conductive film formation. Conversely, an average particle size less than 0.7 μm is undesirable because the viscosity of the gold paste becomes too high, making printing difficult.

[0022] Therefore, the amount of sulfur per unit surface area (μg / m) was calculated by dividing the amount of surface sulfur per unit mass by the specific surface area measured by the BET single-point method for samples taken from each of several types of gold powder produced using various reducing agent lots. 2 When the correlation between the tap density (bulk density) and the tapped density (bulk density at which the surface height of the powder sample stops changing) was plotted as a parameter using the particle size of the gold powder, a strong correlation was found, as shown in Figure 1.

[0023] Thus, different reducing agent lots change the amount of sulfur compounds adhering to the surface of the reduced gold powder, thereby affecting the tap density of the gold powder. In other words, changing the reducing agent lot changes the amount of surface sulfur per unit mass of the gold powder, which in turn changes the tap density, ultimately affecting the dispersibility. Even in such cases, it is possible to estimate the tap density by using the amount of sulfur per unit surface area of ​​the gold powder as an indicator. Furthermore, since tap density is a characteristic value dependent on the average particle size, and the amount of surface sulfur determined by quantitative analysis after nitric acid extraction can vary depending on the average particle size, the tap density of gold powder can be estimated with greater accuracy by making the average particle size consistent to a certain extent.

[0024] To ensure good dispersion, the tap density of the gold powder mentioned above must be 5g / cm 3 Therefore, when the gold powder has an average particle size of 0.7 to 0.9 μm, the amount of sulfur per unit surface area is about 700 μg / m 2 It is preferable that the amount of sulfur per unit surface area is about 500 μg / m when the average particle size is 0.9 to 1.1 μm. 2 It is preferable that the amount of sulfur per unit surface area is about 250 μg / m when the average particle size is 1.1 to 1.3 μm. 2 It is preferable that the amount of sulfur per unit surface area is about 220 μg / m when the average particle size is 1.3 to 1.5 μm. 2 It is preferable to set it to more than this.

[0025] Next, an embodiment of a gold powder manufacturing method according to the present invention will be described. As shown in Figure 2, this gold powder manufacturing method includes a reducing agent preparation step S1 in which a reducing agent solution of a predetermined concentration is prepared; a reduction step S2 in which a chloroauric acid solution is reduced using the prepared reducing agent solution to precipitate gold particles; a solid-liquid separation step S3 in which the slurry containing the gold particles obtained in the reduction step S2 is separated into solid and liquid phases using a solid-liquid separation device such as a filter (filter paper); a washing step S4 in which the wet gold powder obtained in the solid-liquid separation step S3 is washed; and a drying step S5 in which the washed gold powder is dried. While the solid-liquid separation step S3 uses filtration using a filter, other solid-liquid separation devices such as a filter press or a centrifuge may also be used, adjusting the solid-liquid separation device to prevent deformation or aggregation of the separated gold powder.

[0026] Then, in the reducing agent preparation step S1, a compound containing divalent sulfur is added to the reducing agent solution. This allows the chloroauric acid solution to be reduced in the reduction step S2 using a reducing agent solution containing an increased concentration of the compound containing divalent sulfur. Figure 3 shows the relationship between the concentration of the compound containing divalent sulfur in the reducing agent solution and the sulfur content per unit surface area of ​​the gold powder obtained by reduction using the reducing agent solution. Figure 3 shows that for each reducing agent lot, the sulfur content per unit surface area of ​​the gold powder increases almost linearly with increasing concentration of the compound containing divalent sulfur in the reducing agent solution. In other words, the sulfur content per unit surface area of ​​the gold powder can be controlled by the amount of compound containing divalent sulfur added to the reducing agent solution.

[0027] As described above, by using the gold powder manufacturing method of the present invention, it is possible to stably produce gold powder with high tap density and excellent dispersibility. Furthermore, since the tap density can be indirectly controlled by the amount of thiosulfate added to the reducing agent, the concentration of thiosulfate added can be adjusted appropriately depending on the reducing agent lot, thereby avoiding waste of the reducing agent lot or incurring extra reprocessing costs, thereby reducing manufacturing costs.

[0028] Potassium sulfite or sodium sulfite can be used as the reducing agent for reducing the chloroauric acid solution. Potassium thiosulfate or sodium thiosulfate can be used as the divalent sulfur-containing compound added to the reducing agent solution. Any combination of sulfite as the reducing agent and thiosulfate can be used. The gold powder and method for producing the same of the present invention will now be described in more detail with reference to examples and comparative examples. However, the present invention is not limited in any way to the following examples and comparative examples. [Example]

[0029] Example 1 A 2.4 L volume of chloroauric acid solution diluted with pure water to a gold concentration of 33.3 g / L was placed in a 5 L beaker equipped with a stirrer equipped with a 60 mm diameter flat paddle blade, and the temperature was adjusted to 18 ± 1 ° C. Meanwhile, potassium sulfite (manufactured by Daito Chemical Co., Ltd.: Lot. No. 11002-1) was dissolved in pure water to prepare a reducing agent solution with a concentration of 450 g / L and a volume of 480 mL. This solution was placed in a 2 L beaker and the temperature was adjusted to 18 ± 1 ° C. 0.11 g of potassium thiosulfate n-hydrate (manufactured by Kanto Chemical Co., Ltd., special grade: 87% as anhydrous) was added to this reducing agent solution, resulting in a concentration of 379 ppm relative to the potassium sulfite, and dissolved.

[0030] The 5-L beaker containing the chloroauric acid solution had four 15-mm-wide, rectangular baffles mounted at equal intervals (i.e., every 90°) around the periphery. The reducing agent solution was supplied to the beaker while maintaining a turbulent flow by rotating the agitator at 530 rpm. The reducing agent solution was supplied through a funnel with a fixed bottom outlet located at a random position on the circumference of the 5-L beaker containing the chloroauric acid solution, approximately half the beaker's radius when viewed from above. The funnel had a capacity of approximately 1 L and a valve and a 21-mm inner diameter hose were attached to the bottom outlet. The temperature-adjusted reducing agent solution was temporarily stored in the funnel, and the valve was quickly opened to allow the solution to be supplied to a fixed location at a fixed time each time. The supply time for 480 mL of reducing agent solution was 1.6 seconds.

[0031] After adding the reducing agent solution as described above, stirring was continued for 5 minutes. During this time, the liquid temperature rose by several degrees and the pH decreased due to the reduction reaction. However, this increase in liquid temperature stopped after about 1 minute, and the decrease in pH stopped after about 5 minutes. Five minutes after adding the reducing agent solution, the gold powder-containing slurry was filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was placed in 1 L of pure water at approximately 50 °C, repulped, and washed by stirring for 20 minutes. The washed gold powder-containing slurry was again filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was placed in 1 L of pure water at room temperature, repulped, and washed again by stirring for 20 minutes. The rewashed gold powder-containing slurry was again filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was then dried in an atmospheric oven at an ambient temperature of 105 °C. The dried gold powder weighed approximately 79 g.

[0032] The particle size of the gold powder obtained after the drying process was measured using a scanning electron microscope (SEM) at a magnification of 5000x. The particle size of 200 or more gold particles selected from 1 to 3 fields of view was measured in a certain direction, and the average particle size was calculated by arithmetically averaging these. In addition, the specific surface area was measured using the BET single-point method, and the treated solution obtained by nitric acid extraction was analyzed by ICP emission spectroscopy to calculate the amount of surface sulfur per unit mass of gold powder. Furthermore, the surface area of ​​10 to 12 cm 3 The tap density was measured by tapping the sample 50 times with a stroke of 10 mm.

[0033] The obtained gold powder had an average particle size of 1.17 μm and a tap density of 5.00 g / cm 3 , specific surface area 0.22m 2 / g, the surface sulfur content per unit mass of gold powder is 57 ppm, and the sulfur content per unit surface area of ​​gold powder is 265 μg / m 2 It was.

[0034] Example 2 Gold powder was produced in the same manner as in Example 1, except that 0.23 g of potassium thiosulfate n-hydrate was added, which was 926 ppm relative to the potassium sulfite.

[0035] The obtained gold powder had an average particle size of 1.05 μm and a tap density of 6.32 g / cm 3 , specific surface area 0.26m 2 / g, the surface sulfur content per unit mass of gold powder is 200 ppm, and the sulfur content per unit surface area of ​​gold powder is 784 μg / m 2 It was.

[0036] Example 3 Gold powder was produced in the same manner as in Example 1, except that the reducing agent solution used was prepared by dissolving potassium sulfite (Lot. No. 01103-2) in pure water to a concentration of 250 g / L and a liquid volume of 0.80 L, and 0.23 g of potassium thiosulfate n-hydrate (1000 ppm relative to the potassium sulfite) was added and dissolved in the reducing agent solution.

[0037] The obtained gold powder had an average particle size of 0.90 μm and a tap density of 5.36 g / cm 3 , specific surface area 0.29m 2 / g, the surface sulfur content per unit mass of gold powder is 210 ppm, and the sulfur content per unit surface area of ​​gold powder is 724 μg / m 2 It was.

[0038] Example 4 Gold powder was produced in the same manner as in Example 3, except that 0.12 g of potassium thiosulfate n-hydrate was added, which was 500 ppm relative to the potassium sulfite.

[0039] The obtained gold powder had an average particle size of 0.96 μm and a tap density of 4.00 g / cm 3 , specific surface area 0.26m 2 / g, the surface sulfur content per unit mass of gold powder is 72 ppm, and the sulfur content per unit surface area of ​​gold powder is 273 μg / m 2 It was.

[0040] Example 5 Gold powder was produced in the same manner as in Example 3, except that a reducing agent lot (Lot. No. 10402-13) was used and sodium thiosulfate pentahydrate was not added.

[0041] The obtained gold powder had an average particle size of 0.95 μm and a tap density of 4.69 g / cm 3 , specific surface area 0.28m 2 / g, the surface sulfur content per unit mass of gold powder is 130 ppm, and the sulfur content per unit surface area of ​​gold powder is 458 μg / m 2 It was.

[0042] Example 6 Gold powder was produced in the same manner as in Example 3, except that the additive was changed from potassium thiosulfate n-hydrate to sodium thiosulfate pentahydrate (99% manufactured by Kanto Chemical Co., Inc.), and 0.06 g of this was added, which was 200 ppm relative to the potassium sulfite.

[0043] The obtained gold powder had an average particle size of 0.82 μm and a tap density of 4.93 g / cm 3 , specific surface area 0.28m 2 / g, the surface sulfur content per unit mass of gold powder is 170 ppm, and the sulfur content per unit surface area of ​​gold powder is 599 μg / m 2 It was.

[0044] Example 7 Gold powder was produced in the same manner as in Example 6, except that 0.39 g of sodium thiosulfate pentahydrate was added, which was 1250 ppm relative to the potassium sulfite.

[0045] The obtained gold powder had an average particle size of 0.76 μm and a tap density of 5.68 g / cm 3 , specific surface area 0.37m 2 / g, the surface sulfur content per unit mass of gold powder is 550 ppm, and the sulfur content per unit surface area of ​​gold powder is 1495 μg / m 2 It was.

[0046] (Comparative Example 1) Gold powder was produced in the same manner as in Example 1, except that potassium thiosulfate n-hydrate was not added.

[0047] The obtained gold powder had an average particle size of 1.61 μm and a tap density of 4.21 g / cm 3 , specific surface area 0.17m 2 / g, the surface sulfur content per unit mass of gold powder is 13 ppm, and the sulfur content per unit surface area of ​​gold powder is 76 μg / m 2 It was.

[0048] (Comparative Example 2) Gold powder was produced in the same manner as in Example 3, except that potassium thiosulfate n-hydrate was not added.

[0049] The obtained gold powder had an average particle size of 1.29 μm and a tap density of 3.38 g / cm 3 , specific surface area 0.20m 2 / g, the surface sulfur content per unit mass of gold powder is 15 ppm, and the sulfur content per unit surface area of ​​gold powder is 75 μg / m 2 It was.

[0050] (evaluation) The conditions used in the examples and comparative examples, as well as the evaluation results of the gold powders produced, are shown in Table 1 below. The results in Table 1 demonstrate that the properties of the gold powders produced differ even when they are reduced under the same conditions except for the amount of thiosulfate added. This means that when the reducing agent batch is changed, the properties of the gold powder can be changed by appropriately adjusting the amount of thiosulfate added. As a result, the amount of sulfur per unit surface area of ​​the gold powder can be increased as needed, thereby increasing the tap density to a level suitable for use in gold paste.

[0051] [Table 1]

[0052] Figure 4 shows a graph plotting the changes in the average particle size and tap density of gold powders produced in the comparative examples and examples, with the amount of thiosulfate added as a parameter. While a general powder characteristic is that the tap density increases with increasing average particle size, the addition of thiosulfate clearly increases the tap density with decreasing average particle size. In the reduction process, the reduction conditions after the addition of thiosulfate are sometimes adjusted appropriately so that the average particle size of the gold powder falls within the range of 0.7 μm to 1.5 μm. Adjusting the amount of thiosulfate added also ensures stable production of gold powder suitable for use in gold paste, even when the reducing agent batch is changed. In other words, each embodiment allows for stable production of gold powder with excellent dispersibility in gold paste at a high yield.

Claims

1. Sulfur is present on the surface, and the amount of sulfur per unit surface area, calculated by dividing the amount of surface sulfur per unit mass by the specific surface area, is 250 μg / m2 by quantitative analysis of the treated solution obtained by nitric acid extraction. ２ 1500 μg / m or more ２ Gold powder characterized by the following:

2. 2. The gold powder according to claim 1, characterized in that the average particle size measured on an SEM image is 0.7 μm or more and 1.5 μm or less.

3. A method for producing gold powder, comprising a reduction step in which a chloroauric acid solution is reduced using a reducing agent solution to precipitate gold particles, and a post-treatment step in which the slurry containing the gold particles obtained in the reduction step is subjected to solid-liquid separation, washing, and drying, wherein the reducing agent solution contains a sulfur compound containing divalent sulfur.

4. 4. The method for producing gold powder according to claim 3, wherein the reducing agent used in the reducing agent solution is potassium sulfite or sodium sulfite, and the sulfur compound containing divalent sulfur is potassium thiosulfate or sodium thiosulfate.

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