Methods for grinding powders, methods for coating materials, metal particles, coated materials, and their uses

Abstract

The present invention relates to a method for cryogenically grinding at least one powder, comprising the following steps: (a) introducing a cryogenic fluid into an attrition mill comprising attrition means; (b) introducing one or more powders into an attritor mill; and (c) setting the grinding mill in rotary operation; Where: - volume V of the grinding means MA and the volume of the cryogenic fluid V FC The volume of the grinding means V for the sum of MA Ratio of V MA / (V MA +V FC ) is between 0.2 and 0.8, and The rotation speed of the attritor mill during step (c) is between 100 rpm and 20,000 rpm. The present invention also relates to metal or metal alloy particles, their uses, coating methods employing them, and uses of the coated materials.

Description

Technical Field

[0001] The present invention relates to a method for cryogenic liquid milling of one or more powders, particularly metal powders.

[0002] The present invention also relates to metal particles characterized by a specific three-dimensional structure, which particles are likely to be obtained by the milling method described above.

[0003] The present invention also relates to the use of such metal particles.

[0004] Finally, the present invention relates to a method for coating a material employing these metal particles, particularly a method for forming a protective metal coating or a surface metal coating on all or part of the material, and to the use of such coated materials.

Background Art

[0005] Currently, there are many methods for forming a metal coating or film on a material or component, and these methods can be grouped particularly according to the technique implemented for applying the coating and / or according to the formulation being coated.

[0006] A metal coating can be obtained, for example, by applying a metallized paint to the surface of the component to be coated using a brush, roller or spray gun. However, the formulation of these paints relies on additives to disperse, stabilize and / or provide the viscosity and / or wettability necessary to apply these paints adequately. In particular, these formulations use not only volatile organic compounds (VOCs), which are well known to have an adverse effect on health and the environment, but also solvents that can be toxic. Furthermore, these formulations use non-optimized amounts of metal compounds.

[0007] Metal coatings can also be obtained by applying ink. Numerous ink formulations exist, each particularly suited to the properties of the material being coated and / or its intended application. However, some ink formulations are complexes, toxic, and unstable, especially due to potential chemical interactions with the fine metal powders they contain. These metal powders are particularly susceptible to oxidation due to their small size.

[0008] Metal coatings can also be obtained by chemical vapor deposition (CVD) or physical vapor deposition (PVD). In the CVD method, the desired deposition is made possible by setting a gaseous chemical precursor to the appropriate temperature and pressure. Although the CVD method is relatively common, it has the disadvantage that the necessary precursors are not always available and / or it may not be easy to implement. In the PVD method, the material to be deposited is sprayed by an ion beam or electron beam under controlled temperature and pressure conditions. However, both these CVD and PVD methods rely on heavy industrial equipment, particularly reactors that can control and manage the temperature and pressure required for deposition.

[0009] Co-grinding for powder coating is a method that can also form metal coatings. This method involves coating a second material, also in powder form, with a first material in powder form. Conventionally, this method has been performed using a ball grinder with powders of controlled particle size. However, naturally, such a method is not suitable for forming metal coatings on flat surfaces, and is even less suitable when the flat surface is large.

[0010] Cold metallization, also known as the "cold spray" method, is another method for forming metal coatings. In this method, heated metal powder is sprayed at extremely high speed onto the surface of the part to be coated using a pressurized gas. The quality of the coating is guaranteed by the impact force that the powder particles exert on the surface. As a result of this impact force, cold metallization can produce a relatively uniform coating, but it requires heavy industrial equipment with relatively expensive heating and spraying devices that operate at high temperatures (potentially exceeding 1100°C) and high pressures. Furthermore, this method results in relatively large powder losses.

[0011] For completeness, another method for producing metal coatings will also be mentioned. This method involves covering the surface with relatively fine gold foil (approximately 0.1 μm to 0.2 μm). These gold foils are obtained by thoroughly hammering them beforehand, and traditionally, they were applied to surfaces by hand. Therefore, such methods are relatively small-scale and not suitable for industrial implementation.

[0012] As mentioned above, while the coating methods described here can actually apply a metal coating to the parts, each has one or more drawbacks.

[0013] The object of the present invention is to overcome the shortcomings of these prior art coating methods and, as a result, to provide a coating method that can be industrially implemented and, in particular from the viewpoint of suppressing industrial costs, enables homogeneous metallic coating or plating on parts of any form while minimizing the loss of the metallic material to be coated. Furthermore, this coating method should not use compounds that pose health and / or environmental risks, nor should it use heavy and expensive industrial equipment of the type associated with CVD, PVD, and cold spray methods. Moreover, this method should be able to apply metallic coating to all or part of the surface of a part, as well as to material in segmented forms such as powder.

[0014] Another object of the present invention is to overcome the shortcomings of conventional coating methods by providing not only metal particles that can be produced by the above-described coating method, but also a method for grinding metal powder to obtain those metal particles.

[0015] Finally, more generally, another object of the present invention is to provide a grinding method that is not limited to grinding metal powders but can also be applied to grinding other types of powders, such as ceramic powders or organic materials, and even graphite powders.

[0016] Patent document 1 is known, which describes a method for grinding actinide powders, particularly actinide oxide powders such as UO2, PuO2, and / or CeO2. This grinding method is carried out, in particular, by a cryogenic grinding apparatus containing a solidified cryogenic gaseous grinding medium. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] French Patent Application Publication No. 3072308 [Overview of the project]

[0018] [Disclosure of the Invention] The above and other objectives are achieved, firstly, by a method of cryogenically pulverizing at least one powder.

[0019] According to the present invention, this method includes the following steps: (a) A step of introducing a low-temperature fluid into a grinder equipped with grinding means; (b) The process of introducing the powder into the grinder; (c) A process of operating a grinder so that it can rotate freely, thereby grinding the powder at low temperature to form particles; and (d) A step of recovering particles as needed; - Each powder is advantageously selected from metal powders, metal alloy powders, powders of one or more metal oxides, ceramic powders, organic powders, and graphite powders. - Volume V of the grinding means MA and the volume V of the low-temperature fluid FC Volume V of the grinding means relative to the total volume V MA Ratio V MA / (V MA +V FC ) is between 0.2 and 0.8, preferably between 0.3 and 0.7, and - The rotational speed of the grinder during process (c) is between 100 rpm and 20,000 rpm.

[0020] Therefore, the method according to the present invention consists of grinding one or more powders using a low-temperature fluid, and by this grinding, one or more pulverized powders formed of particles having a uniform particle size can be obtained. This uniformity is characterized by a relatively dense and narrow particle size distribution, and may be particularly fine, and can be characterized by a relatively large particle size value of less than 100 nm. Such a uniform, and in appropriate cases particularly fine particle size, cannot be achieved by conventional grinding methods.

[0021] As used herein, the above expression "between... and..." should be understood to define not only the values ​​of the interval, but also the values ​​of the boundary of this interval.

[0022] The method according to the present invention is carried out by a grinder equipped with a grinding means, also called a grinding medium or mobile, within its housing.

[0023] These grinding means are formed by spherical or substantially spherical movable elements. That is, the grinding medium can take the form of beads, but it can also take the form of rods or rollers.

[0024] Regardless of the form of the grinding means, it shall be made of a material that has sufficient mechanical strength and hardness and is suitable for the properties of the powder being ground.

[0025] Therefore, in an advantageous version of the grinding method according to the present invention, the grinding means is made of steel or ceramic, and the ceramic is in particular zirconium carbide ZrC, tungsten carbide WC, or zirconium dioxide ZrO2, also known as zirconia.

[0026] In advantageous modifications, the grinding means are identical in terms of form, size, and constituent material. However, this does not preclude the implementation of grinding means that differ in form, size, and / or constituent material.

[0027] During step (a) of the grinding method according to the present invention, a low-temperature fluid is introduced into a grinder equipped with a grinding means.

[0028] A low-temperature fluid refers to a liquefied gas that is kept in a liquid state at a low temperature, usually below 0°C. This liquefied gas is chemically inert to the powder being pulverized under the conditions of the method according to the present invention.

[0029] This cryogenic fluid can be selected from nitrogen, argon, and krypton in particular. Preferably, the cryogenic fluid is nitrogen.

[0030] During step (b) of the pulverization method according to the present invention, the powder to be pulverized is introduced into a grinder equipped with a grinding means.

[0031] This powder or these powders are advantageously selected from metal powders, metal alloy powders, powders of one or more metal oxides, ceramic powders, organic powders, and graphite powders.

[0032] In other words, a single powder, or conversely, a mixture of two, three, or more different powders, can be introduced into the grinder.

[0033] Metal powder refers to powdered metal with an oxidation level of 0. The metal can be selected from the metallic elements of the periodic table, particularly alkali metals, alkaline earth metals, transition metals, lanthanides, and poor metals such as aluminum.

[0034] Metal alloy powder refers to a powder formed by combining at least two metallic elements from the periodic table.

[0035] Metal oxide powder refers to an oxide powder of one metal element from the periodic table. If it is a powder of several metal oxides, it may be a powder formed from two or more different oxides of the same metal element, or a powder formed from one or more oxides of two or more different metal elements.

[0036] If this powder is a ceramic powder, it can be selected from alumina, zirconia, and mullite in particular.

[0037] If the powder is an organic powder, it may be a medicinal powder in particular.

[0038] There are no obstacles to considering the pulverization of metalloid powders, such as boron powder.

[0039] Steps (a) and (b) can be performed in any order.

[0040] However, in an advantageous modification of the method according to the present invention, steps (a) and (b) are carried out sequentially.

[0041] During process (c), the grinder is rotatably operated, for example, by a stirring shaft. Due to the presence of the grinding means and the low-temperature fluid (which is much colder, has lower viscosity, and lower surface tension compared to water), the powder inside the grinder housing is simultaneously subjected to impact and shear forces generated by the operating grinding means, thereby allowing the powder to be thoroughly ground. In fact, the powder becomes brittle with temperature, and the liquid phase formed by the low-temperature fluid penetrates deeply into the microcracks that develop as grinding progresses, promoting the separation of the ground particles. For this reason, the grinding energy is used more effectively than in most conventional grinders where it is limited to the de-agglomeration of the powder.

[0042] At the end of step (c), particles in the form of a low-temperature suspension of the particles are thus obtained. These particles held in the suspension are protected from the risk of oxidation.

[0043] Optionally, the grinding method according to the invention can further include a step (d) of recovering the particles, and this recovery step (d) is carried out after the actual grinding step (c).

[0044] After recovery, the particles can advantageously be stored under inert conditions with an inert gas, for example under nitrogen.

[0045] In a particular embodiment, the grinding method according to the invention further includes at least one additional step (c') of operating the grinder rotatably after step (c).

[0046] By carrying out one or more additional steps (c'), it is possible, if necessary, to reduce the size of the particles resulting from the cryogenic grinding of the powder in step (c) to a desired particle size.

[0047] This additional step or these additional steps (c') can be carried out using grinding means different from those used during step (c). In particular, these grinding means can be of various forms, sizes and / or constituent materials. Advantageously, the average diameter of these additional grinding means is smaller than the average diameter of the grinding means used in step (c). However, whatever the grinding means used in the additional step (c'), the ratio V MA / (V MA +V FC ) always satisfies the inequality 0.2 ≦ V MA / (V MA +V FC ) ≦ 0.8, and preferably 0.3 ≦ V MA / (V MA +V FC ) ≦ 0.7.

[0048] This additional step or these additional steps (c') can be carried out either before or after the particle recovery step (d).

[0049] However, from a time-saving perspective, it is preferable that this supplementary step or these supplementary steps (c') be performed before the particle recovery step (d).

[0050] An advantageous modification of the grinding method according to the present invention allows for in-line control or monitoring of the low-temperature grinding of the powder, thereby making it possible to determine when to interrupt step (c) and / or whether to perform one or more additional steps (c') as a function of the progression of the particle size of the ground powder.

[0051] This particle size monitoring can be reliably performed in situ, particularly using a laser diffractometer, and it has been demonstrated that the transparency of low-temperature fluids facilitates particle size measurement.

[0052] In a more particularly preferred variation of the grinding method according to the present invention, the powder is a metal powder or a metal alloy powder, and the metal of the powder is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni, in a ratio V MA / (V MA +V FL ) is 0.2 ≤ V MA / (V MA +V FL ) ≤ 0.7.

[0053] By selecting such specific operating conditions and metals, all of them possess specific ductility combined with specific malleability, and the grinding method according to the present invention makes it possible to prepare metal and metal alloy particles having the highly unique morphological properties detailed below.

[0054] According to a particular embodiment, the metal in the powder is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Zn, and Fe, and is advantageously selected from Ag, Sn, and Cu, with the metal or one of the metals being preferably Cu.

[0055] Secondly, the present invention relates to sheet-like metal or metal alloy particles having three dimensions denoted as e, l, and L. e and L are the minimum and maximum dimensions of the particle, respectively, and the metal of the particle is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe, and Ni.

[0056] According to the present invention, these metal or metal alloy particles have the following morphological characteristics: - e is e ≤ 1 μm, advantageously e ≤ 200 nm, and preferably 10 nm ≤ e ≤ 100 nm; - The ratio L / e is such that 10 ≤ L / e ≤ 100; - Specific surface area (measured by BET method) is 1m 2 / g or more, 10m is advantageous. 2 / g or more, preferably 25m 2 / g and 200m 2 It is between / g.

[0057] These metal or metal alloy particles possess highly unique morphological characteristics. In fact, these particles are formed in extremely thin sheets with an average aspect ratio L / e between 10 and 100, and the smallest dimension e is, for example, e ≤ 1 μm, which is negligible compared to the other two dimensions L and l. Therefore, they can be called two-dimensional metal or two-dimensional metal alloy particles, or 2D metal or 2D metal alloy particles.

[0058] The measurements of dimensions L, l, and e are specified to be performed by the direct method: - For dimensions larger than 100 nm, a scanning electron microscope (SEM) was used. - For values ​​between 20 nm and 100 nm, a transmission electron microscope (TEM) is used.

[0059] When determining dimensions less than 20 nm, especially the minimum dimension e, measurement can be performed indirectly by applying the following formula. The sheet is considered to be a flat cylindrical shape with a small thickness e:

[0060]

number

[0061] During the ceremony, ρ: density of powder S BET Specific surface area of ​​powder R: Average radius of the sheet e: Average thickness of the sheet

[0062] According to the present invention, these metal or metal alloy particles can be obtained by the previously defined method of low-temperature liquid pulverization of the metal or metal alloy powder.

[0063] More specifically, these metal or metal alloy particles can be obtained by a method of preparing particles from metal or metal alloy powder, which includes the following steps: (a) A step of introducing a low-temperature fluid into a grinder equipped with grinding means; (b) The process of introducing the powder into the grinder; (c) A process of operating a grinder so that it can rotate freely, thereby grinding the powder at low temperature to form particles; and (d) A step of recovering particles as needed; Here, - The powdered metal is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe, and Ni. - Volume V of the grinding means MA and the volume V of the low-temperature fluid FC Volume V of the grinding means relative to the total volume V MA Ratio V MA / (V MA +V FC ) is 0.2≦V MA / (V MA +V FC ) ≤ 0.7 and - The rotational speed of the grinder during process (c) is between 100 rpm and 20,000 rpm.

[0064] According to a specific modification, the powdered metal is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Zn, and Fe, and is advantageously selected from Ag, Sn, and Cu, with the metal or one of the metals being preferably Cu.

[0065] According to a specific modification, the metal or metal alloy particles according to the present invention have the following supplementary properties: - Denoted as Θ, the static angle of repose measured in accordance with ISO 9045:1990(fr) is between 30° and 60°, and / or - The quadratic dynamic angle of repose, denoted as Θs, is between 80° and 130°.

[0066] As shown in Figure A of the paper "Modelling the energy input by alternative fuels in cement production rotary kilns" by B.-JRMungyeko Bisulandu dated March 6, 2018, the static angle of repose Θ, also called the angle of repose or natural angle of repose, is the angle that the slope of a pile of uncompressed stacked material makes with the horizontal. This static angle of repose Θ is determined according to ISO 9045:1990(fr) "Industrial Screens and Screening".

[0067] As shown in the same Figure A, the second-order dynamic angle of repose Θs is determined by rotating a pile of uncompressed stacked material until the slope formed by the pile collapses, and then determining the angle that the collapsed slope makes with the horizontal. This second-order dynamic angle of inclination Θs can be determined according to the protocol described in S. Courrech du Pont's paper "Granular avalanches in a fluid medium" dated November 14, 2003.

[0068] The unique values ​​of the static angle of repose and the quadratic dynamic angle of repose exhibited by the metal or metal alloy particles according to the present invention reflect the completely original rheological behavior of these particles and can be explained by their very specific form.

[0069] In certain modifications, the metal or metal alloy particles according to the present invention further have at least one of the following supplemental morphological properties: - Flatness tolerance of sheets smaller than 200 nm, and - Sheet convexity deviation of 10% or less.

[0070] Flatness describes the property of a surface in which all its components are inscribed within a plane. Referring to Figure A, the flatness tolerance corresponds to the height (denoted as h) of the zone enclosed by the two parallel planes shown by the dotted line, and the surface in question must lie inside this zone. Within the scope of this invention, the flatness tolerance of this sheet is 200 nm or less.

[0071] The convexity deviation corresponds to the ratio of the total surface area of ​​the sheet shown in gray in Figure C to the sum of the surface areas shown in gray and white in Figure C.

[0072] Thirdly, the present invention relates to various uses of the metal or metal alloy particles described above.

[0073] According to the present invention, these metal or metal alloy particles can be used to manufacture parts that have a metal coating on all or part of their surface.

[0074] Such metal coatings may, in particular, be intended to protect, treat, or decorate all or part of the surface of the component.

[0075] These metal or metal alloy particles, like the components mentioned earlier, can be used in many fields, particularly in the machinery industry, electronics or microelectronics industry, optics, architecture, packaging, design, cosmetics, or medical or medical aid fields.

[0076] Fourthly, the present invention relates to a method for coating a material.

[0077] According to the present invention, this method includes the following steps: (1) The powder is a metal or metal alloy powder, and the metal is selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni, and ratio V MA / (V MA +V FL ) is 0.2 ≤ V M A / (V MA +V FL The process of preparing metal or metal alloy particles by performing the method defined above when ) ≤ 0.7; and, (2) A coating step in which the metal or metal alloy particles prepared in step (1) are coated onto all or part of the material, thereby obtaining a coated material.

[0078] By implementing metal or metal alloy particles characterized by the specific morphological properties described in detail above, the coating method according to the present invention makes it possible to obtain a material containing a homogeneous metallic coating while limiting the amount of metal or metal alloy particles required to produce the coating.

[0079] As can be seen from the following example, at least 5 g / m 2 Furthermore, at least 10g / m 2 A metal or metal alloy coating characterized by its surface coverage can be easily obtained.

[0080] It should be noted that such a coating amount is relatively close to that of a single-layer coating. In fact, if the average thickness e is 1 μm, the mass M of a single-layer coating of copper particles per square meter can be expressed as follows:

[0081]

number

[0082] During the ceremony, e: Average thickness of the sheet S: surface area ρ: density of powder

[0083] In the case of copper particles, this surface density is 9 g / m². 2 It is to that extent.

[0084] As can be seen from the following example, it is possible to achieve an opacity of over 400 with metal coating.

[0085] With respect to the step (1) of preparing metal or metal alloy particles, one can refer to the preceding information relating to the preparation of these particles, and the advantageous features of this method can be used alone or in combination.

[0086] Step (2) of the coating method according to the present invention comprises coating all or part of a material with metal or metal alloy particles to obtain a coated material.

[0087] This coating step (2) can be carried out by any conventional coating method used to form a metal coating on a material from powder, including the state-of-the-art methods described above (paints, inks, etc.). Alternatively, by generating a low-temperature suspension of charged metal or metal alloy particles, it becomes possible to carry out immersion coating (bath coating) of the surface to be coated.

[0088] Advantageously, the coating process (2) is carried out by electrostatic attraction or by applying a potential difference between the metal or metal alloy particles according to the present invention and the surface of the material to be coated.

[0089] Two charging techniques can be used for this purpose. The first technique involves applying an electric field along metal or metal alloy particles, thereby charging these metal or metal alloy particles. The second technique involves performing tribological charging, that is, charging by stripping surface electrons by rubbing the metal or metal alloy particles along their surface. Tribological charging is usually more effective and easier to implement, so this second technique is preferred.

[0090] The coating methods described above are relatively easy to implement industrially and have the advantage of not relying on heavy and expensive industrial equipment. Furthermore, in the case of coating by co-grinding, bathing, electrocharging, or lamination, metal or metal alloy particles can be coated in the absence of solvents or other additives that may be harmful to health and / or the environment.

[0091] At the end of the coating process (2), a process (3) aimed at strengthening the coating over the entire material or in part can be performed to improve the strength and / or durability of the coating.

[0092] Therefore, according to certain embodiments, the coating method according to the present invention may further include a step (3) of applying energy, such as thermal energy by heating a coated surface (or, for example, a complementary coating of the lacquer or varnish type).

[0093] The coating method according to the present invention can be applied to materials that can be in a segmented or integrated form.

[0094] If this material is in a segmented form, it may be granular or plate-like, and these segmented forms can then be integrated.

[0095] If this material is in a single, integrated form, this part could easily be a new part, i.e., a part that has never been used, or a part undergoing maintenance, i.e., a part that has already been used and whose properties will be improved by coating.

[0096] Fifth and sixth, the present invention relates to a material including a metal coating and the use thereof, wherein the coated material is obtained by the coating method defined above, and the advantageous features of this method can be used alone or in combination.

[0097] Similar to the metal or metal alloy particles described earlier, this coated material can be used in particular in the machinery industry, electronics or microelectronics industry, optics, architecture, packaging, design, cosmetics, or medical or medical aid fields.

[0098] As a non-limiting example, if the metal particles are copper particles, the coated materials obtained from these particles can be advantageously used in the medical or medical support fields to impart bactericidal and antiviral properties.

[0099] Furthermore, by implementing the coating method according to the present invention using tin particles, silver and copper particles, or silver-copper alloy particles, it is conceivable to manufacture printed circuits or electronic circuits containing tin coatings, silver and copper coatings, or silver-copper alloy coatings, respectively, as an alternative to the currently very expensive silver coatings. Tin and copper have excellent electrical conductivity.

[0100] Other features and advantages of the present invention will become apparent from reading the following description of examples of preparation of Fe3O4 iron oxide particles, silica particles, and copper particles, examples of manufacturing metal coatings using these copper particles on various surfaces (polycarbonate, glass, graphite), and the characterization of these particles and metal coatings.

[0101] Naturally, these embodiments are provided solely to illustrate the objectives of the present invention and are not intended to limit them in any way. [Brief explanation of the drawing]

[0102] [Figure 1] Figure A schematically shows the static angle of repose characteristics and the second-order dynamic angle of repose characteristics. Figure B schematically shows the flatness tolerance characteristics of the sheet. Figure C schematically shows the convexity deviation characteristics of the sheet. Figures 1A, 1B, and 1C correspond to scanning electron microscope (SEM) images of Fe3O4 powder P1, powder P2 obtained from the first grinding, and powder P3 obtained from the second grinding, respectively, used in Example 1 to prepare metal oxide particles according to the present invention. [Figure 2] Figure 2 shows the change in particle size over time of powder P1 from Figure 1A (the curve labeled P1); the change in particle size over time of powder P1' obtained 30 minutes after the first grinding process (the curve labeled P1'); and the change in particle size over time of powder P2 obtained at the end of the first grinding process (the curve labeled P2). This change over time is evaluated by the volume % (denoted as V, expressed as %) as a function of the average particle diameter (denoted as d, expressed in μm). [Figure 3] Figure 3 shows the change in particle size of powder P1 from Figure 1A over time (the curve labeled P1), and the change in particle size of powder P3 obtained at the end of the second grinding process over time (the curve labeled P3). This change over time is evaluated by the volume % (denoted as V, expressed as a percentage) as a function of the average particle diameter (denoted as d, expressed in μm). [Figure 4]Figure 4 shows the change in particle size over time of silica powder P4 before grinding (curve labeled P4); the change in particle size over time of powder P5 obtained at the end of the first grinding process (curve labeled P5); and the change in particle size over time of powder P6 obtained at the end of the second grinding process (curve labeled P6). This change over time is evaluated by the volume % (denoted as V, expressed as %) as a function of the average particle diameter (denoted as d, expressed in μm). [Figure 5] Figure 5 corresponds to a photograph taken with a scanning electron microscope (SEM) of copper powder used in the preparation of metal particles according to the present invention. [Figure 6] Figure 6 corresponds to a scanning electron microscope (SEM) image of copper particles prepared by the method according to the present invention. [Figure 7] Figures 7A and 7B correspond to enlarged versions of two portions of the photograph in Figure 6, including a portion at the 100 μm scale (Figure 7A). [Figure 8] Figure 8 shows the change over time in the particle size of the copper particles forming the powder in Figure 5, the copper particles forming the powder obtained after the first grinding step, and the copper particles forming the powder obtained after the second grinding step. This change over time is evaluated by the volume % (denoted as V, expressed as %) as a function of the average particle diameter (denoted as d, expressed in μm). [Figure 9] Figure 9 shows two photographs illustrating the angle of repose Θ and the second-order dynamic angle of repose Θs of powder P9 according to the present invention. [Figure 10] Figure 10A is a photograph of a metal coating fabricated on a cylindrical polycarbonate support using the method according to the present invention. Figure 10B is a photograph of a metal coating fabricated on a square polycarbonate support using the method according to the present invention. [Figure 11] Figure 11 is a photograph of a metal coating fabricated on a square glass support by the method according to the present invention. [Figure 12] Figure 12 is a schematic diagram of the apparatus used to determine the opacity provided by the metal coating in Figure 11. [Figure 13]Figure 13 is a photograph of a metal coating fabricated on a graphite lead by the method according to the present invention.

[0103] Figures A through C have already been explained in the "Disclosure of the Invention" section above. [Examples]

[0104] Example 1: Grinding of Fe3O4 iron oxide particles The Fe3O4 iron oxide powder, designated as P1, was subjected to two consecutive grinding processes using liquid nitrogen as the low-temperature fluid and a grinding mechanism formed by zirconia beads of various diameters.

[0105] To carry out the first grinding step, 125 ml (V FL ) liquid nitrogen, then 27.8 g of Fe3O4, in a grinder of the type shown in Figure 1 or 3 of reference WO2017 / 076944 A1 (125 ml (V MA It was introduced into (including a 5mm diameter bead).

[0106] In this first grinding step, therefore ratio V MA / (V MA +V FL ) is equal to 0.50.

[0107] Afterward, the grinder was operated at a rotational speed of 1250 rpm for 90 minutes.

[0108] At the end of this first grinding process, the zirconia beads and 24.4 g of ground Fe3O4 powder P2 were removed from the grinder.

[0109] The Fe3O4 powder P2 sample prepared in this way was analyzed. According to the BET method using nitrogen adsorption at the boiling point of liquid nitrogen (-196°C), the specific surface area of ​​the Fe3O4 powder P2 obtained at the end of this first grinding step was 10 m². 2 It is on the order of / g.

[0110] To carry out the second grinding process, 125 ml (V MA Zirconia beads with a diameter of 1.25 mm and 17.5 g of Fe3O4 powder P2 were introduced into the grinder.

[0111] In this second grinding process, ratio V MA / (V MA +V FL ) is still equal to 0.50, and the volume of liquid nitrogen V FL It is still 125ml.

[0112] Afterward, the grinder was operated again at a rotational speed of 1250 rpm for 90 minutes.

[0113] At the end of this second grinding process, the zirconia beads and 9.2 g of ground Fe3O4 powder P3 were removed from the grinder.

[0114] The Fe3O4 powder P3 sample prepared in this way was analyzed. According to the BET method using nitrogen adsorption at the boiling point of liquid nitrogen (-196°C), the specific surface area of ​​the powder P3 obtained after this second grinding step was 30 m². 2 It is on the order of / g.

[0115] Figures 1A, 1B, and 1C correspond to SEM images of Fe3O4 powders P1, P2, and P3, respectively.

[0116] The time-dependent changes in the particle size of Fe3O4 particles were monitored before grinding, during the first grinding process, and at the end of the process, and are shown in Figure 2. Powder P1, P 1’ The corresponding curves representing the volume percentage as a function of the average diameter of the Fe3O4 particles forming P2 are shown in Figure 2 as [P1] and [P2], respectively. 1’ These are denoted as ] and [P2]. ​​Powder P1, P 1’ It should be noted that this average diameter of the Fe3O4 particles in P2 was measured by laser particle size analysis (by laser diffraction).

[0117] The change in particle size of Fe3O4 particles over time was monitored before and after the second grinding process and is shown in Figure 3. The corresponding curves representing the volume percentage as a function of the average diameter of the Fe3O4 particles forming powders P1 and P3 are denoted as [P1] and [P3], respectively, in Figure 3. It should be noted that this average diameter of the Fe3O4 particles in powders P1 and P3 was measured by laser particle size analysis (laser diffraction method).

[0118] Example 2: Grinding of SiO2 silica particles The SiO2 silica powder, designated as P4, was subjected to two consecutive grinding processes using liquid nitrogen as the low-temperature fluid and a grinding mechanism formed of zirconia beads of various diameters.

[0119] To carry out the first grinding step, 125 ml (V FL ) liquid nitrogen, followed by 12.7 g of SiO2 powder, indicated as P4, in 125 ml (V) as shown in Figure 1 or Figure 3 of reference WO2017 / 076944 A1 (including single-stage only). MA It was introduced into a grinder containing 3mm diameter beads.

[0120] In this first grinding step, therefore ratio V MA / (V MA +V FL ) is equal to 0.5.

[0121] Afterward, the grinder was operated at a rotational speed of 1250 rpm for 10 minutes.

[0122] At the end of this first grinding process, the zirconia beads and 12.2 g of ground SiO2 powder P5 were removed from the grinder.

[0123] To carry out the second grinding process, 125 ml of zirconia beads with a diameter of 1.25 mm (V MA ) and 5.6g of SiO2 powder P5 were introduced into the grinder.

[0124] In this second grinding process, ratio VMA / (V MA +V FL ) is still equal to 0.5, and the volume of liquid nitrogen V FL It is 125 ml.

[0125] Afterward, the grinder was allowed to rotate freely again for 10 minutes at a rotational speed of 1250 rpm.

[0126] At the end of this second grinding process, the zirconia beads and 4.7 g of ground SiO2 powder P6 were removed from the grinder.

[0127] The changes in particle size of SiO2 particles over time were monitored before grinding, after the first grinding step, and after the second grinding step, and are shown in Figure 4. The corresponding curves representing the volume percentage as a function of the average diameter of the SiO2 particles forming powders P4, P5, and P6 are denoted as [P4], [P5], and [P6], respectively, in Figure 4. It should be noted that this average diameter of the silica particles in powders P4, P5, and P6 was measured by laser particle size analysis (laser diffraction method).

[0128] Example 3: Preparation of copper particles according to the present invention The metal particles according to the present invention were prepared from so-called "millimeter" copper powder (hereinafter referred to as "P7").

[0129] Referring to Figure 5, which corresponds to the SEM image of copper powder P7, it can be observed that it is composed of three-dimensional particles, and its three-dimensional dimensions e, l, and L are of roughly the same size, between 300 μm and 500 μm. These copper powder particles are clearly not in sheet form.

[0130] This copper powder P7 underwent two consecutive grinding processes using liquid nitrogen as the low-temperature fluid and a grinding mechanism formed from zirconia beads of different diameters.

[0131] To carry out the first grinding process, 200 ml (V FL) liquid nitrogen, followed by 5 g of copper powder P7, in 125 ml (V) as shown in Figure 1 or Figure 3 of reference WO2017 / 076944 A1. MA It was introduced into a single-stage grinder containing 5mm diameter beads.

[0132] In this first grinding step, therefore ratio V MA / (V MA +V FL ) is equal to 0.38.

[0133] Afterward, the grinder was operated at a rotational speed of 1200 rpm for 30 minutes.

[0134] At the end of this first grinding process, all 5 mm diameter zirconia beads were removed from the grinder, and a sample of the copper powder thus prepared, designated as P8, was taken and analyzed.

[0135] The aspect ratio of the copper particles forming this powder P8 corresponds to the ratio L / e of the maximum dimension to the minimum dimension, which is 50.

[0136] To carry out the second grinding process, 125 ml of zirconia beads with a diameter of 1.25 mm (V MA ) was introduced into the grinder.

[0137] In this second grinding process, ratio V MA / (V MA +V FL ) is equal to 0.38, and the volume of liquid nitrogen V FL It is still 200ml.

[0138] Afterward, the grinder was operated again at a rotational speed of 1200 rpm for 30 minutes.

[0139] At the end of this second grinding process, all 1.25 mm diameter zirconia beads were removed from the grinder, and the resulting copper powder (denoted as P9) was recovered and analyzed.

[0140] The aspect ratio (or ratio L / e) of the copper particles forming the copper powder obtained in the second grinding process is 10.

[0141] During this second grinding process, the sheet forming the copper powder P8 is cut, and the aspect ratio decreases during this process.

[0142] Figure 6 corresponds to an SEM image of the copper powder obtained at the end of the second grinding process. It can be observed that this powder is composed of sheet-like particles whose three dimensions e, l, and L are no longer of the same order of magnitude.

[0143] In particular, referring to the photograph in Figure 7B, it can be observed that the minimum dimension e of the sheet is approximately 1 μm.

[0144] The specific surface area of ​​copper powder P9 obtained at the end of the second grinding process was measured according to the BET method using nitrogen adsorption at the boiling point of liquid nitrogen (-196°C), and was found to be 28 m². 2 It was approximately / g.

[0145] The changes in copper particle size over time were monitored before grinding, after the first grinding process, and after the second grinding process, and are shown in Figure 8. The corresponding curves representing the volume percentage as a function of the average diameter of the copper particles forming powders P7, P8, and P9 are denoted as [P7], [P8], and [P9], respectively, in Figure 8. It should be noted that this average diameter of copper particles in powders P7, P8, and P9 was measured by laser particle size analysis (laser diffraction method).

[0146] Figure 9 shows the angle of repose exhibited by powder P9. Powder P9 is observed to be characterized by a secondary dynamic angle of repose Θs that is negative in the vertical direction or greater than 90° in the horizontal direction. This atypical property is particularly associated with the specific morphology of copper particles in powder P9.

[0147] Example 4: Preparation of a metal coating on a polycarbonate surface The initial coating of 0.1 g of powder P9, prepared according to the protocol of Example 3 above, was performed by electrostatic spraying onto the inner surface of a polycarbonate cylinder with a height of 5 cm and a radius of 1 cm.

[0148] As shown in the photograph in Figure 10A, 31.83 g / m 2 A uniform single-layer coating characterized by a certain coverage amount can be obtained.

[0149] The second coating was performed by electrostatic coating on one side of a 3.5 cm square polycarbonate plate using 0.02 g of the same powder P9.

[0150] As shown in the photograph in Figure 10B, 16.33 g / m 2 A uniform single-layer coating characterized by a certain amount of coverage was obtained.

[0151] Example 5: Preparation of a metal coating on a glass surface Using an electrostatic coating method, 0.02 g of the above powder P9 was coated onto one side of a square glass plate with sides of 3.5 cm.

[0152] As shown in the photograph in Figure 11, 16.32 g / m² is applied to the surface of the glass plate. 2 A uniform coating can be obtained.

[0153] The opacity of the coating applied to the glass plate in this manner is evaluated by the illuminance (I) irradiated onto the coated glass plate. a (This is written as) and the illuminance transmitted by the coated glass plate (I r The ratio I (which is denoted as) a / I r This is done by measuring [the relevant parameters].

[0154] To that end, referring to Figure 12, the glass plate 1 including the copper coating 2 is positioned vertically. The surface of the plate 1 including the coating 2 is exposed to a horizontal illuminance of 55,000 lux. a It is exposed to horizontal illuminance I reflected by plate 1. r It is 120 lux.

[0155] Therefore, the single-layer copper coating produced in this Example 5 is characterized in that the concealment rate I a / I r is 458.33.

[0156] Example 6: Preparation of a metal coating on a graphite surface The coating by electrostatic attraction of the powder P9 in Example 3 was performed on a graphite lead with a diameter of 1 μm.

[0157] This coating was performed by bringing the powder P9 into contact with a graphite lead having an opposite charge to the powder P9.

[0158] The photograph in Fig. 13 shows the copper coating thus obtained, and the metal powder according to the present invention exhibits the property of uniformly coating even a small surface by simple contact.

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