Processes for the production of metal powder, as well as metal powder and its use

Abstract

The present invention relates to a process for producing metal powder, in which a mixture comprising at least one metal material and at least one solvent is provided, the mixture is subjected to at least one grinding process, and the at least one solvent is separated from the mixture by evaporation. The at least one metal material is selected from the group consisting of alkali metals, indium, and mixtures and alloys thereof. The at least one solvent has a vapor pressure of at least 0.002 bar at 20 °C and is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof. The at least one grinding process is carried out at a temperature that is at least 10 °C below the melting point of the at least one solvent. The present invention further relates to a metal powder and its use.

Description

[0001] The present invention relates to a process for producing metal powder, in which a mixture comprising at least one metal material and at least one solvent is provided, the mixture is subjected to at least one grinding process, and the at least one solvent is separated from the mixture by evaporation. The at least one metal material is selected from the group consisting of alkali metals, indium, and mixtures and alloys thereof. The at least one solvent has a vapor pressure of at least 0.002 bar at 20 °C and is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof. The at least one grinding process is carried out at a temperature that is at least 10 °C below the melting point of the at least one solvent. The present invention further relates to a metal powder and its use.

[0002] The challenge in grinding down soft metals, such as lithium, into metal powder is that, due to its softness, the metal is not suitable for classic grinding processes, such as grinding with impact or ball mills.

[0003] The focus of previous publications on the comminution of lithium metal has been the so-called "droplet emulsion technique" (DET method), in which the metal is heated to temperatures of 200–210 °C in high-boiling liquids, such as organic solvents or silicone oil, to melt the lithium (melting point: 180.5 °C). Vigorous stirring at speeds of 3,000–25,000 rpm breaks the molten metal down into small droplets (micrometer scale), which solidify upon cooling of the dispersion and can be separated as a solid (see, for example, Song et al., Journal of the Korean Physical Society, Vol. 54, No. 3, March 2009, 1136–1140; and WO 2012 / 052265 A2). This DET method can be used on a small laboratory scale. B. in an open container on a heating plate with a separate stirring element, e.g. in a glovebox or in a drying room.A disadvantage of this approach is the open handling of the hot molten lithium in organic solvents, which poses a significant safety risk. It should also be noted that the stirring element heats up considerably when operating in a glovebox due to the lower thermal conductivity of argon, potentially leading to premature failure. To scale the process, a (stainless steel) reactor system with a temperature control unit can be used, which must be pressure-stable depending on the solvent chosen. Inerting this system can be achieved by operating it in a glovebox or a dry room; both solutions require considerable space and infrastructure. Furthermore, achieving the necessary shear forces requires a high energy input; however, the selection of a suitable stirring element is limited by compatibility with the reactor system, so stirring speeds are generally limited to approximately 3000 rpm.

[0004] Based on this, the object of the present invention was to provide a simple method for producing metal powder of soft metals (or metal materials).

[0005] This problem is solved with respect to a method for producing metal powder with the features of claim 1 and with respect to a metal powder with the features of claim 11. Claim 14 specifies possible uses of the metal powder according to the invention. The dependent claims relate to preferred embodiments.

[0006] According to the invention, a process for the production of metal powder is thus provided, in which a) a mixture comprising at least one metal material and at least one solvent is provided, wherein the at least one metal material is selected from the group consisting of alkali metals, indium and mixtures and alloys thereof, and wherein the at least one solvent has a vapor pressure at 20 °C of at least 0.002 bar and is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons and mixtures thereof, b) the mixture is subjected to at least one milling process carried out at a temperature at least 10 °C below the melting point of the at least one solvent, and c) that at least one solvent is separated from the mixture by evaporation.

[0007] In step a), a mixture is first provided that comprises or consists of at least one metal material and at least one solvent. The at least one metal material is selected from the group consisting of alkali metals, indium, and mixtures and alloys thereof. It is therefore a soft metal material or a metal material made of soft metals. The at least one solvent has a vapor pressure of at least 0.002 bar at 20 °C. Furthermore, the at least one solvent is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof.

[0008] The vapor pressure of at least one solvent at 20 °C can be determined, for example, using an isoteniscope (or can be determined isotenisoscopically).

[0009] In step b), the mixture provided in step a) is subjected to at least one grinding process. This grinding process takes place at a temperature that is at least 10 °C below the melting point of the at least one solvent.

[0010] In step c), after the grinding process carried out in step b), the at least one solvent is separated from the mixture by evaporation. Evaporation can be carried out, for example, at room temperature and / or without applying a vacuum.

[0011] The process according to the invention enables the comminution of soft metal material, namely at least one metal material selected from the group consisting of alkali metals, indium, and mixtures and alloys thereof, so that a metal powder of soft metal material is obtained. At least one grinding process is used for comminution, wherein the at least one metal material is subjected to the grinding process together with a mixture and at least one special solvent. This solvent serves to protect the at least one metal material, e.g., from unwanted reactions.It was surprisingly discovered that solvents selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof provide excellent protection for at least one metal material during the grinding process, provided the grinding process is carried out at a temperature at least 10 °C below the melting point of the solvent. In this case, the solvent is in solid form during the grinding process, which surprisingly results in excellent protection for the metal material. Furthermore, selecting the solvent from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof ensures that the solvent itself does not react with the metal material, as these solvents are, for example, nonpolar.Without the use of the solvent, the material being ground could, for example, melt together or deposit on surrounding surfaces (grinding balls, container wall), which can be attributed, for example, to a high energy input.

[0012] A particular advantage of the process according to the invention arises from the fact that the at least one solvent has a vapor pressure of at least 0.002 bar at 20 °C. This allows the at least one solvent to be easily separated from the mixture (or from the metal powder) after the at least one grinding process by evaporation (e.g., at room temperature). Thus, the process according to the invention eliminates the need for complex purification steps to separate the solvent, further simplifying the process. Avoiding such purification steps also increases both the yield and the purity. Furthermore, the process can be scaled up more effectively and is therefore more economical overall.

[0013] A preferred embodiment of the method according to the invention is characterized in that the at least one metal material is selected from the group consisting of lithium, sodium, indium and mixtures and alloys thereof.

[0014] Another preferred embodiment of the method according to the invention is characterized in that the at least one metal material is in the form of granules, at least one film, and / or at least one ingot, wherein the granules preferably consist of granule particles with a mean particle size d50 in the range of 0.5 mm to 10 mm, preferably from 1 mm to 5 mm.

[0015] The mean particle size d50 of the granular particles can be determined, for example, by laser diffraction (or by devices that perform laser diffraction). In this process, the sample is irradiated with a laser beam, and the intensity of the scattered light is then measured. The mean particle size is then determined based on these results.

[0016] Another preferred embodiment of the method according to the invention is characterized in that the at least one solvent - selected from the group consisting of xylene, toluene, hexane, heptane, octane, nonane, cyclohexane, and mixtures thereof, preferably selected from the group consisting of p-xylene, n-heptane, and mixtures thereof, and / or - has a vapor pressure at 20 °C of at least 0.005 bar, preferably at least 0.01 bar, particularly preferably at least 0.05 bar, most preferably in the range of 0.09 bar to 0.14 bar, and / or - has a boiling point of at most 151 °C, preferably at most 140 °C, particularly preferably in the range of 60 °C to 140 °C.

[0017] The vapor pressure of at least one solvent at 20 °C can be determined, for example, using an isoteniscope (or can be determined isotenisoscopically).

[0018] The boiling point of at least one solvent can be determined, for example, by means of differential scanning calorimetry (DSC).

[0019] If the solvent is selected from the group consisting of xylene, toluene, hexane, heptane, octane, nonane, cyclohexane, and mixtures thereof, particularly good protection of the at least one metal material, e.g., against unwanted reaction, can be achieved. Even better protection of the at least one metal material, e.g., against unwanted reaction, can be achieved if the at least one solvent is selected from the group consisting of p-xylene, n-heptane, and mixtures thereof.

[0020] A higher vapor pressure allows at least one solvent to be separated from the mixture (or from the metal powder) even faster and more easily by evaporation (e.g. at room temperature) after at least one grinding process.

[0021] Another preferred embodiment of the method according to the invention is characterized in that the at least one grinding process - over a period of 1 minute to 5 hours, preferably from 10 minutes to 90 minutes, and / or - in a vibrating mill (e.g. cryogenic mill) at a vibration frequency in the range of 1 Hz to 100 Hz, preferably from 5 Hz to 40 Hz.

[0022] Another preferred embodiment of the method according to the invention is characterized in that the at least one grinding process comprises at least one pre-grinding process and at least one main grinding process, which are carried out in a vibrating mill (e.g. cryogenic mill), wherein preferably the at least one pre-grinding process is carried out at a vibration frequency in the range of 1 Hz to 10 Hz and for a duration of 1 min to 30 min and / or the at least one main grinding process is carried out at a vibration frequency in the range of 15 Hz to 100 Hz, preferably from 20 Hz to 40 Hz, and for a duration of 10 min to 5 h, preferably from 20 min to 90 min.

[0023] Another preferred embodiment of the method according to the invention is characterized in that the at least one grinding process is carried out using grinding balls, wherein the grinding balls are preferably - containing or consisting of a material selected from the group consisting of zirconium dioxide, silicon nitride, tungsten carbide, stainless steel, and mixtures thereof, wherein the grinding balls preferably contain or consist of zirconium dioxide, and / or - each have a diameter in the range of 5 mm to 30 mm, preferably from 10 mm to 20 mm.

[0024] The use of zirconium dioxide grinding balls is particularly preferred, as this best minimizes the risk of contamination.

[0025] Another preferred embodiment of the method according to the invention is characterized in that the at least one grinding process takes place at a temperature - which is at least 20 °C, preferably at least 30 °C, particularly preferably at least 40 °C, below the melting point of the at least one solvent, and / or - which is at most -100 °C, preferably at most -150 °C, particularly preferably in the range of -230 °C to -150 °C, most preferably in the range of -210 °C to -175 °C, wherein the at least one grinding process is carried out in particular under cooling with liquid nitrogen.

[0026] By carrying out the at least one grinding process at a temperature that is at least 20 °C, preferably at least 30 °C, particularly preferably at least 40 °C, below the melting point of the at least one solvent, it can be better ensured that the at least one solvent is in solid form and is not partially in liquid form due to energy input from the grinding process.

[0027] Another preferred embodiment of the method according to the invention is characterized in that the evaporation in step c) takes place at a temperature in the range of 5 °C to 50 °C, preferably at a temperature in the range of 10 °C to 40 °C, and particularly preferably at room temperature.

[0028] Furthermore, the present invention relates to a metal powder made from a metal material selected from the group consisting of alkali metals, indium and mixtures and alloys thereof, wherein the metal powder consists of powder particles which are present as aggregates and each have a particle size in the range of 0.6 µm to 20 µm, and wherein the metal powder is (preferably) producible or produced by the method according to the invention.

[0029] By being produced using the inventive method, the powder particles of the inventive method have an irregular shape (e.g. platelet-like shape), and are also present as aggregates (comprising or consisting of several powder particles) and each have a particle size in the range of 0.6 µm to 20 µm.

[0030] The shape of the powder particles and / or their presence as aggregates can be determined, for example, using SEM (or based on SEM images).

[0031] The respective particle size of the powder particles can be determined, for example, using scanning electron microscopy or laser diffraction.

[0032] A preferred embodiment of the metal powder according to the invention is characterized in that the at least one metal material is selected from the group consisting of lithium, sodium, indium and mixtures and alloys thereof.

[0033] Another preferred embodiment of the metal powder according to the invention is characterized in that - the powder particles each have a particle size in the range of 0.8 µm to 10 µm, preferably from 1 µm to 5 µm, and / or - the aggregates each have a particle size in the range of 5 µm to 250 µm, preferably from 1 µm to 100 µm.

[0034] The respective particle size of the powder particles can be determined, for example, using scanning electron microscopy or laser diffraction.

[0035] The particle size of the aggregates can be determined, for example, using scanning electron microscopy or laser diffraction.

[0036] Furthermore, the present invention also relates to the use of the metal powder according to the invention for the production of electrodes, preferably electrodes for batteries, as a chemical agent, or as a fuel.

[0037] The following examples are intended to explain the present invention in more detail, without limiting it to the specific embodiments and parameters shown here. Example 1

[0038] 500 mg of lithium metal granules (3-4 mm diameter) and two zirconium dioxide spheres (15 mm diameter) are used as grinding balls in a vibratory mill (e.g., a cryogenic mill). In addition to the granules and grinding balls, 3.5 mL of an organic solvent selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, and mixtures thereof (e.g., p-xylene) is added. This is followed by a 15-minute pre-cooling or pre-grinding process at a vibration frequency of 5 Hz. The actual comminution or main grinding process takes place for 10-90 minutes at 30 Hz. The grinding process is carried out at a temperature at least 10 °C below the melting point of at least one solvent. The product can then be recovered under inert conditions (argon atmosphere) and the solvent evaporated.

[0039] A grey product is obtained. It has irregular, plate-like particles that exist as aggregates and each has a particle size in the range of 0.6 µm to 20 µm, preferably from 0.8 µm to 10 µm, and particularly preferably from 1 µm to 5 µm. Example 2

[0040] Analogous to the procedure described in embodiment 1, the comminution of indium to indium powder is carried out. For this purpose, 1–2.5 g of indium metal granules (< 5 mm diameter) are used (instead of the lithium metal granules used in embodiment 1). Otherwise, the procedure is as described in embodiment 1.

[0041] A grey product is obtained. It has irregular, plate-like particles that exist as aggregates and each has a particle size in the range of 0.6 µm to 20 µm, preferably from 0.8 µm to 10 µm, and particularly preferably from 1 µm to 5 µm. Example 3

[0042] Analogous to the procedure described in embodiment 1, sodium is ground into sodium powder. For this purpose, 500 mg of sodium foil (instead of the lithium metal granules used in embodiment 1) is used. Otherwise, the procedure is as described in embodiment 1.

[0043] A grey product is obtained. It has irregular, plate-like particles that exist as aggregates and each has a particle size in the range of 0.6 µm to 20 µm, preferably from 0.8 µm to 10 µm, and particularly preferably from 1 µm to 5 µm. Example 4

[0044] Analogous to the procedure described in Exemplary Example 1, indium / lithium powder mixtures are produced. For this purpose, a mixture of 60 mg lithium and 2940 mg indium granules (instead of the lithium metal granules used in Exemplary Example 1) is used. Otherwise, the procedure is as described in Exemplary Example 1.

[0045] A grey product is obtained. It has irregular, plate-like particles that exist as aggregates and each has a particle size in the range of 0.6 µm to 20 µm, preferably from 0.8 µm to 10 µm, and particularly preferably from 1 µm to 5 µm. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2012 / 052265 A2

[0003] Cited non-patent literature

[0000] Song et al., Journal of the Korean Physical Society, Vol. 54, No. 3, March 2009, 1136-1140

[0003]

Claims

[1] Method for the production of metal powder in which a) a mixture comprising at least one metal material and at least one solvent is provided, wherein the at least one metal material is selected from the group consisting of alkali metals, indium and mixtures and alloys thereof, and wherein the at least one solvent has a vapor pressure at 20 °C of at least 0.002 bar and is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons and mixtures thereof, b) the mixture is subjected to at least one milling process carried out at a temperature at least 10 °C below the melting point of the at least one solvent, and c) that at least one solvent is separated from the mixture by evaporation. [2] Method according to the preceding claim, characterized bythat at least one metal material is selected from the group consisting of lithium, sodium, indium, and mixtures and alloys thereof. [3] Method according to any one of the preceding claims, characterized by , that the at least one metal material is in the form of granules, at least one film, and / or at least one ingot, wherein the granules preferably consist of granule particles with a mean particle size d50 in the range of 0.5 mm to 10 mm, preferably from 1 mm to 5 mm. [4] Method according to any one of the preceding claims, characterized by that at least one solvent - selected from the group consisting of xylene, toluene, hexane, heptane, octane, nonane, cyclohexane, and mixtures thereof, preferably selected from the group consisting of p-xylene, n-heptane, and mixtures thereof, and / or - has a vapor pressure at 20 °C of at least 0.005 bar, preferably at least 0.01 bar, particularly preferably at least 0.05 bar, most preferably in the range of 0.09 bar to 0.14 bar, and / or - has a boiling point of at most 151 °C, preferably at most 140 °C, particularly preferably in the range of 60 °C to 140 °C. [5] Method according to any one of the preceding claims, characterized by that at least one grinding process - over a period of 1 minute to 5 hours, preferably from 10 minutes to 90 minutes, and / or - in a vibrating mill at a vibration frequency in the range of 1 Hz to 100 Hz, preferably from 5 Hz to 40 Hz. [6] Method according to any one of the preceding claims, characterized by, that the at least one grinding process comprises at least one pre-grinding process and at least one main grinding process, which are carried out in a vibrating mill, wherein preferably the at least one pre-grinding process takes place at a vibration frequency in the range of 1 Hz to 10 Hz and for a duration of 1 min to 30 min and / or the at least one main grinding process takes place at a vibration frequency in the range of 15 Hz to 100 Hz, preferably from 20 Hz to 40 Hz, and for a duration of 10 min to 5 h, preferably from 20 min to 90 min. [7] Method according to any one of the preceding claims, characterized by that the at least one grinding process is carried out using grinding balls, wherein the grinding balls are preferably - containing or consisting of a material selected from the group consisting of zirconium dioxide, silicon nitride, tungsten carbide, stainless steel, and mixtures thereof, wherein the grinding balls preferably contain or consist of zirconium dioxide, and / or - each have a diameter in the range of 5 mm to 30 mm, preferably from 10 mm to 20 mm. [8] Method according to any one of the preceding claims, characterized by that at least one grinding process takes place at a certain temperature, - which is at least 20 °C, preferably at least 30 °C, particularly preferably at least 40 °C, below the melting point of the at least one solvent, and / or - which is a maximum of -100 °C, preferably a maximum of -150 °C, particularly preferably in the range of -230 °C to -150 °C, most preferably in the range of -210 °C to -175 °C. [9] Method according to any one of the preceding claims, characterized bythat at least one grinding process takes place under cooling with liquid nitrogen. [10] Method according to any one of the preceding claims, characterized by , that the evaporation in step c) takes place at a temperature in the range of 5 °C to 50 °C, preferably at a temperature in the range of 10 °C to 40 °C, particularly preferably at room temperature. [11] Metal powder made from a metal material selected from the group consisting of alkali metals, indium and mixtures and alloys thereof, wherein the metal powder consists of powder particles which are present as aggregates and each have a particle size in the range of 0.6 µm to 20 µm, and wherein the metal powder can be produced or manufactured by a method according to any one of claims 1 to 10. [12] Metal powder according to claim 11, characterized bythat at least one metal material is selected from the group consisting of lithium, sodium, indium, and mixtures and alloys thereof. [13] Metal powder according to claim 11 or 12, characterized by , that - the powder particles each have a particle size in the range of 0.8 µm to 10 µm, preferably from 1 µm to 5 µm, and / or - the aggregates each have a particle size in the range of 1 µm to 250 µm, preferably from 5 µm to 100 µm. [14] Use of a metal powder according to any one of claims 11 to 13 for the manufacture of electrodes, preferably electrodes for batteries, as a chemical agent, or as a fuel.