Metallic tin for producing tin spheres

Abstract

Provided is a high-yield means for producing highly spherical tin spheres having a diameter larger than about 1 millimeter, through the use of a metallic tin that has a surface tension, as measured by electromagnetic levitation, of at least 490 x 10-3Nm-1 at a temperature of 1,000 K and at least 390 x 10-3Nm-1 at a temperature of 1,300 K.

Description

[Technical Field]

[0001] This invention relates to metallic tin for producing tin spheres.[Background Art]

[0002] The production of metal spheres on an industrial scale is an extremely important basic technique. Therefore, techniques for producing metal spheres on an industrial scale have been conventionally developed.

[0003] A common method for producing metal spheres include a method for producing spheres by a mechanical process such as pressing and grinding. However, since this involves machining, the method is suitable for hard metal materials such as high-carbon chromium bearing steels and stainless steels. On the other hand, soft metal materials such as solders that are tin, lead, and their alloys are not suitable for machining such as grinding, and so a casting method is used to produce metal spheres.

[0004] Known as a traditional example of metal sphere production using soft metal materials is the method for producing shotgun shells. This is the method of dropping a molten lead from a height (e.g., 50 m or more) and collecting it in a water tank, and is the large-scale method of building towers for production. Of course, the variation in the resulting lead spheres is large, and that method is not intended to control purity or sphericity.

[0005] Patent Literature 1 (Japanese Patent Application Publication No. H11-221662 A) discloses a technique for producing solder spheres by dropping a molten solder into a soybean oil. However, Patent Literature 1 does not describe the size, sphericity, and purity of the resulting solder spheres, and it discloses the traditional technique that may simply obtain solder having a ball shape.

[0006] Patent Literature 2 (Japanese Patent Application Publication No. S54-085171 A) discloses that metal spheres are obtained by jetting a molten solder alloy metal through a nozzle into a silicone oil while rotating a rotating plate with cutting holes. However, the size of the resulting metal spheres is 1 mm in diameter, and it does not disclose any technique to obtain metal spheres having a larger size than that.

[0007] Patent Literature 3 (Japanese Patent Application Publication No. S55-158875 A) discloses that iron spheres are obtained by dropping droplets of molten iron into water. However, with this technique, the cracking percentage increases rapidly when the diameter of the iron spheres exceeds 1 mm, and for example, when the diameter is 8 mm, the cracking percentage reaches about 70%. There is no disclosure for the sphericity and purity of the resulting iron spheres.

[0008] Patent Literature 4 (Japanese Patent Application Publication No. 2001-226705 A) discloses a technique for producing fine metal spheres having a diameter of about 400 µm by jetting molten solder into a chamber filled with a nitrogen gas mixed with a hydrogen gas while applying vibration with a piezoelectric element. The fine metal spheres obtained by this technique have a smaller diameter of 400 µm and also have large variations in diameter and sphericity.

[0009] Patent Literature 5 (Japanese Patent Application Publication No. S50-17363 A) discloses a technique for producing copper grains by passing molten copper through a stainless steel wire mesh and dropping it into an OF oil. However, Patent Literature 5 does not disclose the purity or sphericity of the resulting copper grains, and the magnified photographs in Patent Literature 5 show extremely large variations in size and sphericity.

[0010] Patent Literature 6 (Japanese Patent Application Publication No. S60-114508 A) discloses a technique for obtaining alloy grains by dropping droplets of molten metals of Co-W alloy, Ni-B alloy, and Cu-B alloy through a nozzle into a cooling oil. However, Patent Literature 6 is silent to describe the purity, size, or sphericity of the resulting alloy grains, but it only evaluates them as "good" based on weight and its distribution.

[0011] Patent Literature 7 (Japanese Patent Application Publication No. 2000-8104 A) discloses a technique for producing spherical metal grains by dropping a molten solder metal through a nozzle into an engine oil or a cooking oil while vibrating it with a stainless steel shaft. However, the average grain size of the grains obtained in Patent Literature 7 is about 0.30 mm to 0.76 mm, which can be a technique resulting in an average grain size of 1 mm or less.

[0012] Thus, in melting soft metals such as tin to form grains, there has been no suitable technique to obtain grains having an average grain diameter larger than 1 mm and having excellent spherical accuracy (sphericity), and there is a need for such a technique.

[0013] Non-Patent Literature 1 and 2 disclose Rayleigh's equation that is useful for calculating a surface tension from a frequency applied to droplets of a molten metal sample and a sample mass (see Non-Patent Literature 1), and Cummings & Blackburn's correction equation (see Non-Patent Literature 2).[Citation List][Patent Literature]

[0014] [PTL 1] Japanese Patent Application Publication No. H11-221662 A [PTL 2] Japanese Patent Application Publication No. S54-085171 A [PTL 3] Japanese Patent Application Publication No. S55-158875 A [PTL 4] Japanese Patent Application Publication No. 2001-226705 A [PTL 5] Japanese Patent Application Publication No. S50-17363 A [PTL 6] Japanese Patent Application Publication No. S60-114508 A [PTL 7] Japanese Patent Application Publication No. 2000-8104 A [Non-Patent Literature]

[0015] [Non-PTL 1] Lord Rayleigh, "On the Capillary Phenomena of Jets", Proceedings of the Royal Society of London, pp. 71-97, 1879. [Non-PTL 2] D. L. Cummings and D. A. Blackburn, "Oscillations of magnetically levutated aspherical droplets", J. Fluid Mech, vol. 224, pp. 395-416, 1991. [Summary of Invention][Technical Problem]

[0016] Thus, an object of this invention is to provide a means for producing tin spheres having a diameter larger than about 1 mm and sphericity with a high yield.[Solution to Problem]

[0017] As a result of intensive studies, the inventors have found that the above object can be achieved by the means as described below and arrived at this invention.

[0018] In other words, in the conventional art, it has been attempted to produce tin spheres having a diameter larger than about 1 mm and high sphericity (accuracy of spherical shape) with a high yield by devising steps of the production, while this invention achieves the above object by using specific tin for producing tin spheres.

[0019] Thus, the present invention includes the following aspect (1): (1) A metallic tin, wherein a surface tension as measured by an electromagnetic levitation method is: equal to or more than 490 × 10 -3< Nm -1< at a temperature of 1,000 K, and equal to or more than 390 × 10 -3< Nm -1< at a temperature of 1,300 K. [Advantageous Effects of Invention]

[0020] According to this invention, high-purity tin spheres having a diameter larger than about 1 mm and high sphericity can be produced with a high yield.[Brief Description of Drawings]

[0021] [FIG. 1] FIG. 1 is a schematic view of a device for measuring a surface tension of molten metallic tin. [FIG. 2] FIG. 2 is a graph illustrating results of measuring a surface tension of molten metallic tin which is high purity tin (Sample 1) (Example) and high purity tin (Sample 2) (Comparative Example). [FIG. 3] FIG. 3 is a schematic view of a device for producing tin sphere. [FIG. 4] FIG. 4 is a method for determining pass / fail for tin spheres. [FIG. 5] FIG. 5 is results of the pass / fail determination for tin spheres. [FIG. 6A] FIG. 6A is a photograph illustrating the appearance of tin spheres produced in Example. [FIG. 6B] FIG. 6B is a photograph illustrating the appearance of tin spheres produced in Comparative Example. [FIG. 7] FIG. 7 is a photograph illustrating the appearance of a group of tin spheres, which are spherical products remaining after visual classification and rolling classification in Example 1. [Description of Embodiments]

[0022] This invention is described below in detail with specific embodiments. This invention is not limited to the specific embodiments disclosed below.[Tin for Producing Tin Spheres]

[0023] The metallic tin according to this invention is a tin for producing tin spheres, wherein a surface tension as measured by an electromagnetic levitation method is equal to or more than 490 × 10 -3< Nm -1< at a temperature of 1,000 K and equal to or more than 390 × 10 -3< Nm -1< at a temperature of 1,300 K.

[0024] The metallic tin for producing tin spheres can be used to produce high-purity tin spheres having a diameter larger than about 1 mm and high sphericity with a high yield.

[0025] When obtaining spherical grains by solidifying molten metallic tin, the principle force acting to form the grains includes the surface tension.

[0026] However, prior to this invention, the relationship between the surface tension of the molten metallic tin and grain formation was not disclosed as a specific technique. In other words, it is not clear what kind of grain formation occurs when a specific value of the surface tension of the molten metallic tin is given.

[0027] Its reason is unknown, but one possible reason would be that measuring the surface tension of molten metallic tin itself is extremely difficult.

[0028] In other words, if the surface tension of molten metallic tin is to be measured, the molten tin is generally placed on any substrate and measured thereon, but the contact with the substrate will affect the surface tension of the molten metallic tin itself, resulting in non-negligible differences in measured values.

[0029] However, this invention was able to measure the surface tension of molten metallic tin by suspending the molten metallic tin in midair without any contact with any substrate material, as shown in Examples described below. Then, by examining the relationship between the surface tension measured in this manner and grains formed, the inventors have found that tin with a specific surface tension is particularly excellent for obtaining grains having an average grain diameter larger than 1 mm and having good spherical shape accuracy (sphericity), and have arrived at the invention of this application.[Surface Tension as Measured by Electromagnetic Levitation Method]

[0030] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be, at a temperature of 1,000 K, for example, 490 × 10 -3< Nm -1< or more, preferably 495 × 10 -3< Nm -1< or more, more preferably 500 × 10 -3< Nm -1< or more, or 505 × 10 -3< Nm -1< or more, preferably 510 × 10 -3< Nm -1< or more, and at a temperature of 1,300 K, for example, 390 × 10 -3< Nm -1< or more, preferably 395 × 10 -3< Nm -1< or more, more preferably 400 × 10 -3< Nm -1< or more, or 405 × 10 -3< Nm -1< or more, preferably 410 × 10 -3< Nm -1< or more.

[0031] The measurement of the surface tension by the electromagnetic levitation method can be performed by the means as described below in Examples.

[0032] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be, at a temperature of 1,000 K, for example, in the range of 490×10 -3< Nm -1< to 510×10 -3< Nm -1< , preferably in the range of 495×10 -3< Nm -1< to 510×10 -3< Nm -1< , more preferably in the range of 500×10 -3< Nm -1< to 510×10 -3< Nm -1< , or in the range of 500×10 -3< Nm -1< to 505 × 10 -3< Nm -1< , or in the range of 490 × 10 -3< Nm -1< to 505 × 10 -3< Nm -1< , preferably in the range of 490 × 10 -3< Nm -1< to 500 × 10 -3< Nm -1< , more preferably in the range of 495 × 10 -3< Nm -1< to 500 × 10 -3< Nm -1< , or in the range of 490 × 10 -3< Nm -1< to 495 × 10 -3< Nm -1< .

[0033] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be, at a temperature of 1,300 K, for example, in the range of 390×10 -3< Nm -1< to 410×10 -3< Nm -1< , preferably in the range of 395×10 -3< Nm -1< to 410×10 -3< Nm -1< , more preferably in the range of 400×10 -3< Nm -1< to 410×10 -3< Nm -1< , or in the range of 400×10 -3< Nm -1< to 405 × 10 -3< Nm -1< , or in the range of 390 × 10 -3< Nm -1< to 405 × 10 -3< Nm -1< , preferably in the range of 390 × 10 -3< Nm -1< to 400 × 10 -3< Nm -1< , more preferably in the range of 395 × 10 -3< Nm -1< to 400 × 10 -3< Nm -1< , or in the range of 390 × 10 -3< Nm -1< to 395 × 10 -3< Nm -1< .

[0034] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 490×10 -3< Nm -1< to 510×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 390×10 -3< Nm -1< to 410×10 -3< Nm -1< at a temperature of 1,300 K.

[0035] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 495×10 -3< Nm -1< to 510×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 395×10 -3< Nm -1< to 410×10 -3< Nm -1< at a temperature of 1,300 K.

[0036] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 500×10 -3< Nm -1< to 510×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 400×10 -3< Nm -1< to 410×10 -3< Nm -1< at a temperature of 1,300 K.

[0037] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 490×10 -3< Nm -1< to 505×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 390×10 -3< Nm -1< to 405×10 -3< Nm -1< at a temperature of 1,300 K.

[0038] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 490×10 -3< Nm -1< to 500×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 390×10 -3< Nm -1< to 400×10 -3< Nm -1< at a temperature of 1,300 K.

[0039] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 495×10 -3< Nm -1< to 500×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 395×10 -3< Nm -1< to 400×10 -3< Nm -1< at a temperature of 1,300 K.

[0040] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 490×10 -3< Nm -1< to 495×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 390×10 -3< Nm -1< to 395×10 -3< Nm -1< at a temperature of 1,300 K.

[0041] In a preferred embodiment, the surface tension of the metallic tin according to this invention, as measured by an electromagnetic levitation method, can be in the range of 500×10 -3< Nm -1< to 505×10 -3< Nm -1< at a temperature of 1,000 K, and in the range of 400×10 -3< Nm -1< to 405×10 -3< Nm -1< at a temperature of 1,300 K.[Production of Tin Spheres]

[0042] The metallic tin can be heated and melted to form a molten metal of the metallic tin, which can then be used to produce tin spheres.

[0043] Known means for heating and melting metallic tin to form the molten metal of the metallic tin can be used, for example, radiation heating and induction heating can be used to prepare the molten metal of the metallic tin.

[0044] In a suitable embodiment, the tin spheres can be suitably produced by a method including the following steps: dropping a molten metal of the metallic tin according to this invention into a cooling liquid medium; cooling droplets of the metallic tin while falling through the cooling liquid medium to form solid tin spheres.

[0045] In a preferable embodiment, the cooling liquid medium that can be used to drip the molten metal of the metallic tin can suitably be used if it is stable at a temperature higher than the melting point of the metallic tin. Examples of such a cooling liquid medium that can be used herein includes animal and vegetable oils, mineral oils, and synthetic oils, preferably lubricating oils and silicone oils, and more preferably silicone oils.

[0046] In a preferable embodiment, as a means for feeding the molten metal of the metallic tin into the cooling liquid medium, any known means can be used with no limitation as long as it is by dripping, and examples include gravity dripping and power dripping, preferably, natural dripping and discharging by a pump.

[0047] In a preferable embodiment, after the molten metal of the metallic tin according to this invention is dropped into the cooling liquid medium, it is cooled while falling through the cooling liquid medium to form solid tin spheres. The falling is due to gravity, and the height of the cooling liquid medium is preferably set so that it can fall over a distance sufficient to form solid tin spheres.[Tin Spheres]

[0048] The tin spheres produced using the molten metal of the metallic tin according to this invention have the above surface tension as measured by the electromagnetic levitation method, resulting in high-purity tin spheres having a diameter larger than about 1 mm and high sphericity, which are produced with a high yield.

[0049] As used herein, the high sphericity possessed by the produced tin spheres means that a group of the produced tin spheres has both a high percentage of spherical products, as described below, and a high percentage of spherical products having a ratio of variation of ball diameter of less than 0.04.[Percentage of Spherical Products]

[0050] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention can have a percentage of spherical products (%), calculated by the following equation, of 80% or more, preferably 90% or more, more preferably 95% or more, in the group of solid tin spheres formed, for example:

[0051] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention have no limitation for the upper limit of the percentage of sphere products (%) calculated by the above equation in the group of solid tin spheres formed, but for example, the percentage can be 100% or less, 99.5% or less, 99% or less, 98.5% or less, 98% or less.

[0052] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention have a percentage of spherical products (%) calculated by the above equation in the group of solid tin spheres formed, for example, in the range of 80% to 100%, preferably in the range of 80% to 99.5%, more preferably in the range of 80% to 99%, more preferably in the range of 80% to 98.5%, even more preferably in the range of 80% to 98%, for example in the range of 90% to 100%, preferably in the range of 90% to 99.5%, more preferably in the range of 90% to 99%, even more preferably in the range of 90% to 98.5%, still more preferably in the range of 90% to 98%, for example in the range of 95% to 100%, preferably in the range of 95% to 99.5%, more preferably in the range of 95% to 99%, even more preferably in the range of 95% to 98.5%, and even more preferably in the range of 95% to 98%.

[0053] The selection of the spherical products and the irregularly shaped products for the tin spheres in this invention can be carried out by the means disclosed in Examples below.

[0054] When a large number of spheres are produced, it is useful to measure their weights against a group of tin spheres for quality control, and the above percentage of the spherical products is a suitable indicator for such quality control.[Ratio of Variation of Ball Diameter]

[0055] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention can be such that in a group of spheres obtained from a group of solid tin spheres formed, a percentage of sphere products having a ratio of variation of ball diameter of less than 0.04, calculated by the following equation, is 50% or more, preferably 55% or more, and more preferably 60% or more:

[0056] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention have no limitation for the upper limit of the percentage (%) of the spherical products in the group of solid tin spheres formed in which the ratio of the variation of the ball diameter calculated by the above equation is less than 0.04, but the percentage can be 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less.

[0057] In a preferable embodiment, the tin spheres produced using the molten metal of the metallic tin according to this invention can be such that in the group of the sphere products obtained from the group of the solid tin spheres formed, a percentage of spherical products having a ratio of variation of ball diameter of less than 0.04 is, for example, in the range of 50% to 100%, preferably in the range of 50% to 99%, preferably in the range of 50% to 95%, preferably in the range of 50% to 90%, preferably in the range of 50% to 85%, preferably in the range of 50% to 80%, preferably in the range of 50% to 75%, for example, in the range of 55% to 100%, preferably in the range of 55% to 99%, preferably in the range of 55% to 95%, preferably in the range of 55% to 90%, preferably in the range of 55% to 85%, preferably in the range of 55% to 80%, preferably in the range of 55% to 75%, for example, in the range of 60% to 100%, preferably in the range of 60% to 99%, preferably in the range of 60% to 95%, preferably in the range of 60% to 90%, preferably in the range of 60% to 85%, preferably in the range of 60% to 80%, preferably in the range of 60% to 75%.

[0058] The measurement of the variation of ball diameter (mm) in accordance with JIS B1509: 2009 and the diameter average value (mm) for the tin spheres according to this invention can be performed by the means disclosed in Examples below.[Diameter]

[0059] In a preferable, the diameter of the tin spheres produced using the molten metal of the metallic tin according to this invention can be larger than about 1 mm. The diameter of the tin spheres can be determined by calculating a diameter average value of each tin sphere entity for 10 tin spheres taken from a group of tin spheres, and averaging the diameter average values of the respective entities, and the resulting value, i.e., the average value of the diameter average values, can be in the range of 1 mm to 5 mm, preferably 1.5 mm to 4.5 mm, preferably 2 mm to 4 mm.[Preferable Aspects of Invention]

[0060] As preferable aspects, this invention includes the following aspects (1) to (8): (1) A metallic tin, wherein a surface tension as measured by an electromagnetic levitation method is: equal to or more than 490 × 10 -3< Nm -1< at a temperature of 1,000 K, and equal to or more than 390 × 10 -3< Nm -1< at a temperature of 1,300 K. (2) The metallic tin according to (1), wherein a surface tension as measured by an electromagnetic levitation method is: in a range of 490 × 10 -3< Nm -1< to 510 × 10 -3< Nm -1< at a temperature of 1,000 K, and in a range of 390 × 10 -3< Nm -1< to 410 × 10 -3< Nm -1< at a temperature of 1,300 K. (3) The metallic tin according to (1), wherein the metallic tin is for producing tin spheres. (4) A method for producing tin spheres using a molten metal of the metallic tin according to (1). (5) A method for producing tin spheres, the method comprising the steps of: dropping the molten metal of the metallic tin according to (1) into a cooling liquid medium; and cooling droplets of the metallic tin while falling through the cooling liquid medium to form solid tin spheres. (6) The method according to (5), wherein in a group of the solid tin spheres formed, a percentage of sphere products (%) calculated by the following equation is 80% or more: (7) The method according to (5), wherein in a group of spherical products obtained from a group of the solid tin spheres formed, a percentage of spherical products having a ratio of variation of ball diameter calculated by the following equation of less than 0.04 is 50% or more: (8) The method according to (5), wherein the tin spheres have a diameter in a range of 1 mm to 5 mm. [EXAMPLES]

[0061] This invention will be described below in detail with reference to Examples. This invention is not limited to Example illustrated below.[Example 1: Production of High-Purity Tin (Sample 1)][Casting]

[0062] 1.7 kg of raw material tin (purity of 99.999 wt%) was heated in a graphite crucible at 300°C or more and melted. After removing slags that surfaced, it was poured into a graphite mold to obtain two plates each having a thickness of about 10 mm, a width of 70 mm and a height of 150 mm.[Electrolytic Dissolution]

[0063] One raw material tin in the form of the plate was used as an anode and placed in an electrolytic bath so as to face a titanium plate (a width of 70 mm and a height of 150 mm) as a cathode. The cathode plate was placed in a cathode box with an anion exchange membrane attached to the surface facing the anode. The cathode box was filled with an aqueous sulfuric acid solution having a normal concentration of 9, which was connected to an outer container with a tube pump so that the aqueous sulfuric acid solution was circulated. Outside the cathode box and inside the electrolytic bath, dilute sulfuric acid with a normal concentration of 0.5 was placed. Subsequently, the raw tin cast in the form of the plate was connected to a positive pole of a rectifier, and the titanium plate was connected to a negative pole of a rectifier by electrical wirings.

[0064] Electrolysis was performed at a current density of 2 A / dm 2< to obtain 3 L of a tin sulfate solution having a tin concentration of 90 g / L.

[0065] To the resulting tin sulfate solution was added 5 g / L of strontium carbonate and stirred for 1 hour, and deposited solids were then filtered and removed. To the resulting filtrate was added 5 g / L of hydroquinone and 5 g / L of BLAUNON N-514 from AOKI OIL INDUSTRIAL CO., LTD., as a surfactant, and dissolved with stirring to obtain 2.8 L of a tin sulfate electrolyte.[Electrowinning]

[0066] The tin sulfate electrolyte obtained above was diluted with pure water to a tin concentration of 20 g / L and placed on the anode side of the electrolytic bath to make an anode side electrolyte (anolyte). The above tin sulfate electrolyte was added to the cathode side of the electrolytic bath without dilution to make a cathode side electrolyte (catholyte). The raw material tin cast in the form of the plate described above was placed as the anode in the electrolytic bath, and a titanium plate having the same size was placed as the cathode.

[0067] The positive pole of the rectifier was connected to the raw material tin and the negative pole of the rectifier was connected to the titanium plate, and electrolysis was performed at a current density of 1.5 A / dm 2< . The above operation was repeated while replacing the anolyte and the catholyte to obtain about 600 g of electrodeposited tin in the form of the plate.[Vacuum Casting]

[0068] After the resulting electrodeposited tin was thoroughly washed and dried, it was placed in a graphite crucible, heated in air to remove slag, and then cooled and solidified as it was. It was then placed in a vacuum melting furnace, heated to 1,000°C, held for 16 hours, and then cooled and solidified to obtain a high-purity tin ingot.[Cutting and Washing]

[0069] The surface of the high-purity tin ingot was cut and removed, leaving only the internal sound portion.

[0070] Small pieces were cut out by machining from high-purity tin consisting of only the sound portion, and washed with an acid and deionized water.

[0071] Thus, high-purity tin (Sample 1) was obtained. The resulting high-purity tin (Sample 1) was analyzed for impurities using GD-MS. Results of the impurity analysis are shown in Table 1. Unless otherwise specified in Table 1, values are reported in wt. ppm. [Table 1]Li<0.005As<0.005Sm<0.005Be<0.005Se<0.01Eu<0.01B<0.005Br<0.05Gd<0.005F<0.05Rb<0.005Tb<0.005Na<0.01Sr<0.005Dy<0.005Mg<0.01Y<0.005Ho<0.005Al<0.01Zr<0.005Er<0.005Si<0.01Nb<0.005Tm<0.005P<0.01Mo<0.01Yb<0.005S<0.01Ru<0.01Lu<0.005Cl<0.01Rh<0.005Hf<0.01K<0.01Pd<0.005Ta<5Ca<0.01Ag<0.005W<0.01Sc<0.001Cd<0.05Re<0.01Ti<0.005In<1Os<0.01V<0.001SnMatrixIr<0.01Cr<0.005Sb<0.5Pt<0.01Mn<0.005Te<0.1Au<0.05Fe<0.005I<0.05Hg<0.05Co<0.01Cs<0.05Tl<0.02Ni<0.01Ba<0.1Pb<0.01Cu<0.005La<0.1Bi<0.005Zn<0.01Ce<0.005Th<0.005Ga<0.005Pr<0.1U<0.005Ge<0.01Nd<0.005 [Example 2: Production of High-Purity Tin (Sample 2)]

[0072] The high-purity tin used in Comparative Example (Sample 2) was produced as follows: Electrodeposited tin in the form of the plate was obtained by electrolysis as with the high-purity tin produced in Example 1 (Sample 1). After the resulting electrodeposited tin was thoroughly washed and dried, it was placed in a graphite crucible, heated in air to remove slag, and then cooled and solidified as it was. The surface of the resulting tin ingot was cut and removed, and only the internal sound portion was used. Small pieces of tin consisting of only the sound portion were cut out by machining, and washed with an acid and purified water, and they were used as high-purity tin (Sample 2).

[0073] The results of the impurity analysis for high-purity tin (Sample 2) are shown in Table 2 below. Unless otherwise specified in Table 2, values are reported in wt. ppm. [Table 2]Li<0.005As<0.005Sm<0.005Be<0.005Se<0.01Eu<0.01B<0.005Br<0.05Gd<0.005F0.07Rb<0.005Tb<0.005Na<0.01Sr<0.005Dy<0.005Mg<0.01Y<0.005Ho<0.005Al0.03Zr<0.005Er<0.005Si0.05Nb<0.005Tm<0.005P<0.01Mo<0.01Yb<0.005S<0.01Ru<0.01Lu<0.005Cl0.02Rh<0.005Hf<0.01K<0.01Pd<0.005Ta<5Ca<0.01Ag0.2W<0.01Sc<0.001Cd<0.05Re<0.01Ti<0.005In<1Os<0.01V<0.001Sn-Ir<0.01Cr<0.005Sb1.5Pt<0.01Mn<0.005Te<0.1Au<0.05Fe0.42I<0.05Hg<0.05Co<0.01Cs<0.05Tl<0.02Ni<0.01Ba<0.1Pb0.12Cu0.15La<0.1Bi<0.005Zn<0.01Ce<0.005Th<0.005Ga<0.005Pr<0. 1U<0.005Ge<0.01Nd<0.005 [Example 3: Measurement of Surface Tension for High-Purity Tin (Sample 1)][Measuring Device for Surface Tension]

[0074] The surface tension of the resulting high-purity tin (Sample 1) was measured.

[0075] FIG. 1 illustrate an overview of the measuring device used for measuring the surface tension.

[0076] The measuring device illustrated in FIG. 1 includes a sealed quartz chamber 4, and has a structure in which a gas can be introduced into the interior of the quartz chamber 4 through a gas introduction pipe 7 and can be discharged through a gas discharge pipe 8. The interior of the quartz chamber 4 is provided with a sample holder 5 for holding the sample. The sample holder 5 has a structure that can hold the sample, tin 1, in a position where it can be placed and inductively heated by a coil 2, and at the same time, the sample (tin 1) inductively heated by the coil 2 can be pulled down as soon as it melts and floats. The measuring device is provided with a high-frequency power source that can supply high-frequency current to the coil outside the quartz chamber 4. The top of the quartz chamber 4 is provided with an observation window 6 for observing the interior, through which the interior can be taken at a high speed by a camera 9.[Measuring Procedure for Surface Tension]

[0077] The measuring device illustrated in FIG. 1 was used to measure the surface tension of high-purity tin as follows.

[0078] Tin was cut from high purity tin (Sample 1) to have 420 to 480 mg of a cube (each side having about 5 mm) and collected.

[0079] The surface of the collected cubic tin sample was etched with an aqueous 3 vol.% hydrochloric acid solution using an ultrasonic cleaner, and then washed with acetone.

[0080] The tin sample was placed in a quartz glass holder in an electromagnetic levitation chamber.

[0081] After evacuating the measurement system in a vacuum (at 10 -7< atm), an ambient gas (argon-helium) was introduced from the top at 2 L / min. The oxygen partial pressure of the atmosphere gas (argon-helium) was set to 1 × 10 -7< atm (volume concentration: 0.1 vol. ppm).

[0082] A high-frequency alternating current was applied to the electromagnetic levitation coil, and the sample was heated simultaneously with the electromagnetic levitation. To separate the sample from the holder before melting the sample, the sample holder was pulled down simultaneously with the start of heating.

[0083] Temperatures were measured using two monochromatic radiation thermometers with different wavelengths. Wavelength 1: 1.64 µm; Wavelength 2: 1.4 µm.

[0084] At the inlet of the chamber, the ambient oxygen partial pressure of the introduced gas was measured with a zirconia type oxygen sensor operated at 1,008 K.

[0085] Surface vibration behavior of droplets after melting the sample was recorded from above with a high-speed camera (500 FPS, 8192 pictures (16.384 seconds)).

[0086] Immediately after recording, a helium gas was blown from the top of the sample at 20 L / min for rapid cooling and solidification.

[0087] The mass of the sample was measured on an electronic balance.

[0088] Changes in center-of-gravity shift, radius, and area of the droplets were analyzed from droplet projection images to determine the m = 0, m = ±1, and m = ±2 frequencies in the 1 = 2 mode and the m = 0 and m = ±1 frequencies in the 1 = 1 mode.

[0089] From the determined frequency and sample mass determined, the surface tension was calculated using Rayleigh's equation (see Non-Patent Literature 1) and Cummings & Blackburn's correction equation (see Non-Patent Literature 2).[Measurement Results of Surface Tension]

[0090] The surface tension thus measured is shown in FIG. 2.[Example 4: Measurement of Surface Tension for High-Purity Tin (Sample 2)]

[0091] The surface tension of high purity tin (Sample 2) was measured as with high purity tin (Sample 1) measured in Example 3. The measured surface tension is summarized in FIG. 2.[Evaluation for Measurement Results of Surface Tension]

[0092] From the graph in FIG. 2, the surface tension of Sample 1, an example of this invention, was 500 (490 to 510) × 10 -3< Nm -1< or more at a temperature of 1,000 K and 400 (390 to 410) × 10 -3< Nm -1< or more at a temperature of 1,300 K. In contrast, the surface tension of Sample 2, a comparative example, was measured by the same method, and as a result, the surface tension was 440 to 460 × 10 -3< Nm -1< or more at a temperature of 1,000 K and 330 to 350 × 10 -3< Nm -1< or more at a temperature of 1,300 K. It was found from the results that there was a negative correlation between the temperature and the surface tension in the sample according this invention, and that the surface tension of Sample 1 as an example is higher than that of Sample 2 as a comparative example.[Example 5: Production of Tin Spheres (Examples 1 to 3)][Production Device for Tin Spheres]

[0093] The resulting high-purity tin (Sample 1) was used to produce tin spheres.

[0094] FIG. 3 illustrates an overview of the production device used for producing tin spheres.

[0095] The production device illustrated in FIG. 3 is provided with a melting vessel 14 for melting and storing tin, which is a raw material for use in the production of tin spheres. The tin in the melting vessel 14 is heated by a heater 15 into a molten state. The melting vessel 14 is sealed, and when a silicone oil contained in a silicone oil container 17 is introduced by a pump 19 through a silicone oil feed pipe 18, the pressure allows the molten tin in the melting vessel 14 to be dropped through a tin feed vessel pipe 16 into the silicone oil filled in a granulation vessel 12. The top of the granulation vessel 12 is provided with a heater 13, and the molten tin is maintained in a molten state at the top of the granulation vessel 12. The space in the production devise is filled with an argon gas, rather than air, thereby suppressing oxidation of the molten tin. Droplets of the molten tin introduced by the tin feed pipe 16 and dropped into the silicone oil filled in the granulating vessel 12 are first formed into spheres, then cooled and solidified to form tin spheres 11, which will be deposited at the bottom of the granulating vessel 12 while free falling in the silicone oil filled in the granulating vessel 12.[Production Procedure for Tin Spheres]

[0096] The high-purity tin (Sample 1) was used to produce tin spheres as follows.

[0097] 2,000 g of small pieces of the high-purity tin (Sample 1) washed with an acid and water were placed in the melting vessel made of quartz for a tin sphere production device. On the other hand, the granulation vessel was filled with a silicone oil. The lids of the melting vessel and the granulation vessel were closed, and a high-purity argon gas flowed continuously at a flow rate of 1 L / min until the oxygen concentration inside the granulation vessel was 0.1 vol% or less.

[0098] The melting vessel and the upper portion of the granulation vessel were heated with an external heater.

[0099] When the high-purity tin in the melting vessel was melted, the pump was started and the molten tin was discharged from the molten vessel into the granulation vessel and allowed to drop and free fall. During the process of the free falling, the surface tension caused the molten tin to form spheres. Since the lower portion of the granulation vessel was not heated, the molten tin was solidified and deposited in a spherical form.

[0100] When the discharging was finished, the discharging pump and the heater were turned off, and cooled, and the flow of the argon gas was then stopped, and the tin spheres were removed.

[0101] The removed tin spheres were washed with toluene to remove the silicone oil, and then with dilute hydrochloric acid.

[0102] The tin spheres were classified according to the shape and size.

[0103] The above procedure was repeated three times to produce tin spheres, which were determined to be Examples 1 to 3.[Example 6: Production of Tin Spheres (Comparative Examples 1 to 3)]

[0104] For the production of tin spheres according to Comparative Example, the high-purity tin (Sample 2) described above was used as the raw material in place of the high-purity tin (Sample 1). The same device and procedure as in Example 5 were used to repeat the production of tin spheres three times to produce tin spheres according to Comparative Examples 1 to 3.[Example 7: Evaluation of Tin Spheres][Procedure for Evaluation of Tin Spheres]

[0105] Six groups of tin spheres obtained by Examples 1 to 3 and Comparative Examples 1 to 3 each had a diameter of tin spheres in the range of 3.2 to 3.6 mm.

[0106] These tin spheres were evaluated by the following procedure. FIG. 4 illustrates the flow of the tin sphere evaluation procedure.[Visual Classification]

[0107] Spheres having an extremely large size, extremely small size, or distorted shape were visually excluded.[Rolling Classification]

[0108] Next, the spheres were rolled on a metal angle bent at 90°, and those that were not rolled were excluded.[Selection of Spherical Products from Irregularly Shaped Products]

[0109] After visual classification and rolling classification, the remaining products were considered to be spherical products. After visual classification and rolling classification, the excluded products were considered to be irregularly shaped products.[Percentage of Spherical Products]

[0110] The percentage of spherical products (%) was calculated from the weight of spherical products and the weight of irregularly shaped products using the following equation: [Ratio of Variation of Ball Diameter]

[0111] Ten spheres were taken at random from the spherical products, and 10 measurements were performed for each sphere using a micrometer in place of a measuring plane and a measuring element perpendicular to it, while changing the measuring points, with reference to the provisions of JIS B1509: 2009, and the variation of ball diameter was calculated using the 10 measured values. In this invention, an arithmetic mean value of the values measured 10 times for each sphere was determined to be the diameter average value for each sphere, and a ratio of variation of ball diameter to the diameter average value was calculated.[Results of Evaluation for Tin Spheres]

[0112] The results of the calculated percentage of spherical products obtained for the tin sphere groups according to Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in FIG. 5.

[0113] As illustrated in FIG. 5, all the percentages of the spherical products according to Examples 1 to 3 were more than 80%, while all the percentages of the spherical products according to Comparative Examples 1 to 3 were less than 80%. This indicates that the samples according to Examples can be more suitable for the production of the spherical products.

[0114] The appearances of the spherical products and the irregularly shaped products obtained from the tin sphere groups according to Examples 1 to 3 are illustrated in FIG. 6A. The appearances of the spherical products and the irregularly shaped products obtained from the tin sphere groups according to Comparative Examples 1 to 3 are illustrated in FIG. 6B.

[0115] As illustrated in FIGS. 6A and 6B, the spherical products had shapes that were very close to a sphere. As illustrated in FIGS. 6A and 6B, the irregularly shaped products were observed as products that looked as if multiple spheres had been joined together or deformed from the shape of a sphere. Although quantification was not shown as data, the majority of the irregularly shaped products with multiple spheres joined consisted of two spheres joined for Examples 1 to 3, while a large number of irregularly shaped products with more than two spheres joined were observed for Comparative Examples 1 to 3.

[0116] The measurement results of the diameter average values obtained from the tin sphere groups according to Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 3. In Table 3, "No." is the number assigned to each entity of the tin spheres taken out for measurement. Unless otherwise specified in Table 3, the unit of measurement is mm. [Table 3]No.Example 1Example 2Example 3Comp. 1Comp. 2Comp. 313.3433.4453.4073.3593.4843.35223.3453.4073.3443.4183.4633.30133.3953.3363.4973.4213.3473.34143.4573.4443.3813.4063.3543.41153.3483.5473.3343.4473.3043.34963.3313.3623.3143.4033.3943.34173.3653.3503.3653.3263.4273.32583.4413.3913.3923.3523.2853.38393.3563.3453.4013.4843.3413.324103.4043.3743.3323.4053.3453.422Average of Diameter Average Values3.3783.4003.3773.4023.3743.355

[0117] As shown in Table 3, each of the resulting tin spheres had a sufficiently large diameter (average of diameter average values), which was between 3 and 4 mm.

[0118] The results of the ratio of variation of ball diameter obtained from the tin sphere groups according to Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 4. In Table 4, "No." is the number assigned to each individual tin sphere taken out for measurement. [Table 4]No.Example 1Example 2Example 3Comp. 1Comp. 2Comp. 310.0240.0280.0350.0390.0240.03120.0440.0320.0570.0480.0580.04630.0330.0440.0240.0610.0400.04740.0610.0240.0520.0390.0430.03750.0210.0420.0220.0420.0460.06760.0380.0230.0350.0440.0270.04570.0410.0400.0300.0260.0320.04680.0400.0200.0370.0440.0530.05190.0210.0230.0220.0130.0620.055100.0170.0440.0470.0420.0290.036Percentage of Those of Less Than 0.0460%60%70%40%40%30%Average0.0350.0320.0360.0400.0410.046

[0119] As shown in Table 4, for Examples 1 to 3, the percentage of those having a ratio of variation of ball diameter of less than 0.04 accounted for 50% or more of the total. On the other hand, for Comparative Examples 1 to 3, the percentage of those having a ratio of variation of ball diameter of less than 0.04 was less than 50% of the total. Based on these results, when compared amount the spherical products, the sphericity of the samples according to Examples is higher than that of the samples according to Comparative Examples, indicating that the samples according Examples are more suitable for the production of the spherical products. The average values of the ratios of variations of ball diameters for the measured samples were less than 0.04 for Examples 1 to 3 and were more than 0.04 for Comparative Examples 1 to 3, indicating that the sphericity of the samples according to Examples is higher than that of Comparative Examples.

[0120] FIG. 7 illustrates a photograph for the appearance of the group of tin spheres, which were spherical products remaining after visual classification and rolling classification in Example 1. According to the high-purity tin of this invention, a large number of tin spheres of high-quality spherical products, as shown in FIG. 7, were able to be produced efficiently and simultaneously.[Relationship between Surface Tension and Evaluation Results of Tin Spheres]

[0121] The tin according to this invention has a surface tension, as measured by the electromagnetic levitation method, of 492×10 -3< Nm -1< at a temperature of 1,000 K, and 397x10 -3< Nm -1< at a temperature of 1,300 K, and the percentage of the spherical products, excluding irregularly shaped products, contained in the tin spheres produced using the tin was 96.9 to 97.5%, which were higher.

[0122] On the other hand, the surface tension of the tin having a lower surface tension than that, as measured by electromagnetic levitation, was 455 × 10 -3< Nm -1< at a temperature of 1,000 K and 365 × 10 -3< Nm -1< at a temperature of 1,300 K, and the percentage of spherical products, excluding irregularly shaped products, contained in tin spheres producing using this tin, was 70.1 to 75.9%, which were lower.[Possibility of Contribution to SDGs]

[0123] According to an embodiment of this invention, the tin spheres having a large diameter and improved sphericity are provided. Since high precision of materials and components is important for the development of IoT and AI technologies, an embodiment of this invention may contribute to the development of IoT and AI technologies, and the like. Thus, an embodiment of this invention may contribute to Goal 9 of the Sustainable development goals led by the United Nations (SDGs), which is to "build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation".[Industrial Applicability]

[0124] According to this invention, tin spheres having a large diameter and high sphericity can be produced with a high yield. This invention is industrially useful.

Claims

1. A metallic tin, wherein a surface tension as measured by an electromagnetic levitation method is: equal to or more than 490 × 10-3 Nm-1 at a temperature of 1,000 K, and equal to or more than 390 × 10-3 Nm-1 at a temperature of 1,300 K.

2. The metallic tin according to claim 1, wherein the surface tension as measured by the electromagnetic levitation method is: in a range of 490 × 10-3 Nm-1 to 510 × 10-3 Nm-1 at a temperature of 1,000 K, and in a range of 390 × 10-3 Nm-1 to 410 × 10-3 Nm-1 at a temperature of 1,300 K.

3. The metallic tin according to claim 1, wherein the metallic tin is for producing tin spheres.

4. A method for producing tin spheres using a molten metal of the metallic tin according to claim 1.

5. A method for producing tin spheres, the method comprising the steps of: dropping the molten metal of the metallic tin according to claim 1 into a cooling liquid medium; and cooling droplets of the metallic tin while falling through the cooling liquid medium to form solid tin spheres.

6. The method according to claim 5, wherein in a group of the solid tin spheres formed, a percentage of sphere products (%) calculated by the following equation is 80% or more:

7. The method according to claim 5, wherein in a group of spherical products obtained from a group of the solid tin spheres formed, a percentage of spherical products having a ratio of variation of ball diameter calculated by the following equation of less than 0.04 is 50% or more:

8. The method according to claim 5, wherein the tin spheres have a diameter in a range of 1 mm to 5 mm.

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