Method for grinding powders, method for coating a material, metal particles, coated material and uses of these

Abstract

A method for the cryogenic grinding of at least one powder comprising the following steps: (a) introducing a cryogenic fluid into an attrition mill comprising attrition means, (b) introducing the powder or powders into the attrition mill, and (c) setting the attrition mill in rotational motion, and whereinthe ratio V.sub.MA/(V.sub.MA+V.sub.FC) of the volume of the attrition means V.sub.MA to the sum of the volume of the attrition means V.sub.MA and the volume of the cryogenic fluid VFC is comprised between 0.2 and 0.8, and the rotational speed of the attrition mill during step (c) is between 100 rpm and 20,000 rpm. Further, particles of metal or metal alloy, to the use thereof, to a coating method employing them and to the use of such a coated material.

Claims

1. A method for cryogenic-fluid grinding at least one powder, said method comprising the following steps: (a) introducing a cryogenic fluid into an attrition grinder comprising attrition means, (b) introducing the powder(s) into the attrition grinder, (c) rotatably moving the attrition grinder, whereby cryogenic grinding of the powder(s) into particles is carried out, and (d) optionally collecting the particles, and wherein each powder is advantageously selected from a metal powder, a metal alloy powder, a powder of one or more metal oxides, a ceramic powder, an organic powder and a graphite powder, characterised in that the ratio V.sub.MA/(V.sub.MA+V.sub.FC) of the attrition means volume V.sub.MA to the sum of the attrition means volume V.sub.MA and the cryogenic fluid volume V.sub.FC is between 0.2 and 0.8 and, advantageously, between 0.3 and 0.7, and the rotational speed of the attrition grinder, during step (c), is between 100 rpm and 20,000 rpm.

2. The grinding method according to claim 1, wherein, the powder being a metal powder or a metal alloy powder: the metal(s) in the powder are selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni, and the ratio V.sub.MA/(V.sub.MA+V.sub.FL) is such that 0.2V.sub.MA/(V.sub.MA+V.sub.FL)0.7.

3. The grinding method according to claim 2, wherein the metal(s) of the powder are selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Zn and Fe, advantageously from Ag, Sn and Cu, the metal or one of the metals preferably being Cu.

4. The grinding method according to claim 1, wherein the attrition means are formed by beads, bars or rollers, preferably of steel or ceramic, for example of zirconium carbide or zirconia.

5. The grinding method according to claim 1, wherein the cryogenic fluid is selected from nitrogen, argon and krypton and is, preferably, nitrogen.

6. The grinding method according to claim 1, wherein steps (a) and (b) are implemented successively.

7. The grinding method according to claim 1, which method further comprises, after step (c), at least one complementary step (c) of rotatably moving the attrition grinder, where appropriate, with attrition means distinct from those of step (c).

8. The grinding method according to claim 7, wherein the one or more complementary steps (c) are carried out before step (d).

9. Metal or metal alloy particles obtained by a method for cryogenic-fluid grinding a metal or metal alloy powder according to claim 2, the particles being in the form of sheets having three dimensions denoted as e, I and L, e and L being respectively the smallest dimension and the largest dimension of the particles, and the metal(s) of the particles being selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni, wherein the particles have the following morphological characteristics: e such that e1 m, advantageously such that e200 nm and, preferably, such that 10 nme100 nm, a ratio L/e such that 10L/e100, a specific surface area (measured using the BET method) greater than or equal to 1 m.sup.2/g, advantageously greater than or equal to 10 m.sup.2/g and preferably between 25 m.sup.2/g and 200 m.sup.2/g.

10. The metal or metal alloy particles according to claim 9, wherein the particles have the following characteristics: a static angle of repose, denoted as and measured in accordance with ISO 9045:1990(fr), of between 30 and 60 , and/or a secondary dynamic angle of repose, denoted as s, of between 80 and 130.

11. The metal or metal alloy particles according to claim 9, wherein the particles have the following morphological characteristics: a sheet flatness tolerance of less than or equal to 200 nm, and/or a sheet convexity deviation of less than or equal to 10%.

12. The metal or metal alloy particles according to claim 9, wherein the metal(s) are selected from Au, Ag, Cu, Al, Sn, Pt, Pd, Zn and Fe, advantageously from Ag, Sn and Cu, the metal or one of the metals preferably being Cu.

13. A use of metal or metal alloy particles according to claim 9 for making a piece comprising a metal coating on all or part of one of its surfaces, this metal coating can be intended to protect, treat or decorate all or part of said surface of the piece.

14. The use according to claim 13 in the mechanical industry, in the electronics or microelectronics industry, in the optics field, in the construction field, in the packaging field, in the design field, in the cosmetics field or in the medical or paramedical field.

15. A method for coating a material comprising the following steps: (1) preparing metal or metal alloy particles by implementing a method according to claim 2, and then (2) depositing the metal or metal alloy particles prepared in step (1) onto all or part of the material, whereby a coated material is obtained.

16. The coating method according to claim 15, the method further comprises a step (3) of applying energy or complementary coating to consolidate the coating on all or part of the material.

17. The coating method according to claim 15, wherein the deposition step (2) is carried out by electrostatic attraction or by applying a potential difference between the particles and the surface(s) of the material onto which the deposition is to be carried out.

18. The coating method according to claim 15, wherein the material is in divided form or in the form of one piece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0133] FIG. A schematically illustrates the static angle of repose and secondary dynamic angle of repose characteristics.

[0134] FIG. B schematically illustrates the flatness tolerance characteristic of a sheet.

[0135] FIG. C schematically illustrates the convexity deviation characteristic of a sheet.

[0136] FIGS. 1A, 1B and 1C correspond respectively to pictures taken by means of a scanning electron microscope (SEM) of the Fe.sub.3O.sub.4 powder P.sub.1 used in example 1 to prepare the metal oxide particles according to the invention, of the powder P.sub.2 resulting from a first grinding and then of the powder P.sub.3 resulting from the second grinding.

[0137] FIG. 2 illustrates the time course of the grain size of the powder P.sub.1 of FIG. 1A (curve denoted as P.sub.1), of the powder P.sub.1 obtained after 30 min of implementation of the first grinding step (curve denoted as P.sub.1) and of the powder P.sub.2 obtained at the end of the first grinding step (curve denoted as P.sub.2), this time course being evaluated by the percent by volume (denoted as V and expressed in %) as a function of the mean diameter of the particles (denoted as d and expressed in m).

[0138] FIG. 3 illustrates the time course of the grain size of the powder P.sub.1 of FIG. 1A (curve denoted as P.sub.1) and of the powder P.sub.3 obtained at the end of the second grinding step (curve denoted as P.sub.3), this time course being evaluated by the percent by volume (denoted as V and expressed in %) as a function of the mean diameter of the particles (denoted as d and expressed in m).

[0139] FIG. 4 illustrates the time course of the grain size of the silica powder P.sub.4 before grinding (curve denoted as P.sub.4), of the powder P.sub.5 obtained at the end of the first grinding step (curve denoted as P.sub.5) and of the powder P.sub.6 obtained at the end of the second grinding step (curve denoted as P.sub.6), this time course being evaluated by the percent by volume (denoted as V and expressed in %) as a function of the mean diameter of the particles (denoted as d and expressed in m).

[0140] FIG. 5 corresponds to a picture taken by means of a scanning electron microscope (SEM) of the copper powder used to prepare the metal particles according to the invention.

[0141] FIG. 6 corresponds to a picture taken by means of a scanning electron microscope (SEM) of the copper particles as prepared by implementing the method according to the invention.

[0142] FIGS. 7A and 7B correspond to an enlargement of two parts of the picture in FIG. 6, including the part with the 100 m scale (FIG. 7A).

[0143] FIG. 8 illustrates the time course of the grain size of the copper particles forming the powder in FIG. 5, of the copper particles forming the powder as obtained after the first grinding step and of the copper particles forming the powder as obtained after the second grinding step, this time course being evaluated by the percent by volume (denoted as V and expressed in %) as a function of the mean diameter of the particles (denoted as d and expressed in m).

[0144] FIG. 9 shows two photographic pictures illustrating the angle of repose and the dynamic secondary angle of repose s of the powder P.sub.9 according to the present invention.

[0145] FIG. 10A is a photographic picture of a metal coating made by the method according to the invention on a cylindrical polycarbonate support.

[0146] FIG. 10B is a photographic picture of a metal coating made by the method according to the invention on a square polycarbonate support.

[0147] FIG. 11 is a photographic picture of a metal coating made by the method according to the invention on a square glass support.

[0148] FIG. 12 is a schematic representation of the device used to determine the concealment rate provided by the metal coating in FIG. 11.

[0149] FIG. 13 is a photographic picture of a metal coating made by the method according to the invention on a graphite lead.

[0150] It is specified that FIGS. A to C have already been discussed in the section Disclosure of the invention above.

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

Example 1: Grinding Fe.SUB.3.O.SUB.4 .Iron Oxide Particles

[0151] An Fe.sub.3O.sub.4 iron oxide powder, denoted as P.sub.1, has been subjected to two successive grinding steps, by implementing liquid nitrogen as the cryogenic fluid and attrition means formed by zirconia beads of different diameters.

[0152] For implementing the first grinding step, 125 ml (V.sub.FL) of liquid nitrogen and then 27.8 g of Fe.sub.3O.sub.4 have been introduced into an attrition grinder of the type represented in FIG. 1 or 3 of document WO2017/076944 A1 and comprising 125 ml (V.sub.MA) of beads having a diameter of 5 mm.

[0153] In this first grinding step, the ratio V.sub.MA/V.sub.MA+V.sub.FL) is therefore equal to 0.50.

[0154] The attrition grinder has then been rotatably moved at a rotational speed of 1250 rpm for a duration of 90 minutes.

[0155] At the end of this first grinding step, the zirconia beads and 24.4 g of ground Fe.sub.3O.sub.4 powder P.sub.2 have been extracted from the attrition grinder.

[0156] A sample of the Fe.sub.3O.sub.4 powder P.sub.2 thus prepared has been analysed. The specific surface area of the Fe.sub.3O.sub.4 powder P.sub.2 obtained at the end of this first grinding step, as measured according to the BET method, by nitrogen adsorption at the boiling temperature of liquid nitrogen (196 C.), is in the order of 10 m.sup.2/g.

[0157] For implementing the second grinding step, 125 ml (V.sub.MA) of zirconia beads having a diameter of 1.25 mm and then 17.5 g of Fe.sub.3O.sub.4 powder P.sub.2 have been introduced into the attrition grinder.

[0158] In this second grinding step, the ratio V.sub.MA/(V.sub.MA+V.sub.FL) is still equal to 0.50, the volume V.sub.FL of liquid nitrogen still being 125 ml.

[0159] The attrition grinder has then been rotatably moved again at a rotational speed of 1250 rpm for a duration of 90 min.

[0160] At the end of this second grinding step, the zirconia beads and 9.2 g of ground Fe.sub.3O.sub.4 powder P.sub.3 have been extracted from the attrition grinder.

[0161] A sample of the Fe.sub.3O.sub.4 powder P.sub.3 thus prepared has been analysed. The specific surface area of the powder P.sub.3 obtained after this second grinding step, as measured according to the BET method, by nitrogen adsorption at the boiling temperature of liquid nitrogen (196 C.), is in the order of 30 m.sup.2/g.

[0162] FIGS. 1A, 1B and 1C correspond to the SEM pictures of Fe.sub.3O.sub.4 powders P.sub.1, P.sub.2 and P.sub.3 respectively.

[0163] The time course of the grain size of the Fe.sub.3O.sub.4 particles before grinding, during and at the end of the first grinding step has been monitored and is represented in FIG. 2. The corresponding curves, which illustrate the percent by volume as a function of the mean diameter of the Fe.sub.3O.sub.4 particles forming the powders P.sub.1, P.sub.1, and P.sub.2, are denoted as [P.sub.1], [P.sub.1] and [P.sub.2] respectively in FIG. 2. It is specified that this mean diameter of the Fe.sub.3O.sub.4 particles of the powders P.sub.1, P.sub.1, and P.sub.2 has been measured by the laser granulometry method (via laser diffraction).

[0164] The time course of the grain size of the Fe.sub.3O.sub.4 particles before grinding and after the second grinding step has been monitored and is represented in FIG. 3. The corresponding curves, which illustrate the percent by volume as a function of the mean diameter of the Fe.sub.3O.sub.4 particles forming the powders P.sub.1and P.sub.3, are denoted as [P.sub.1] and [P.sub.3] respectively in FIG. 3. It is specified that this mean diameter of the Fe.sub.3O.sub.4 particles of the powders P.sub.1 and P.sub.3 has also been measured by the laser granulometry method (via laser diffraction).

Example 2: Grinding SiO2 Silica Particles

[0165] An SiO.sub.2 silica powder, denoted as P.sub.4, has been subjected to two successive grinding steps, by implementing liquid nitrogen as the cryogenic fluid and attrition means formed by zirconia beads of different diameters.

[0166] For implementing the first grinding step, 125 ml (V.sub.FL) of liquid nitrogen and then 12.7 g of SiO.sub.2 powder, denoted as P.sub.4, have been introduced into an attrition grinder in accordance to that represented in FIG. 1 or 3 (but comprising only a single stage) of document WO02017/076944 A1 and comprising 125 ml (V.sub.MA) of beads having a diameter of 3 mm.

[0167] In this first grinding step, the ratio V.sub.MA(V.sub.MA+V.sub.FL) is therefore equal to 0.5.

[0168] The attrition grinder has then been rotatably moved at a rotational speed of 1250 rpm for a duration of 10 minutes.

[0169] At the end of this first grinding step, the zirconia beads and 12.2 g of ground SiO.sub.2 powder P.sub.5 have been extracted from the attrition grinder.

[0170] For implementing the second grinding step, 125 ml (V.sub.MA) of zirconia beads having a diameter of 1.25 mm and 5.6 g of the SiO.sub.2 powder P.sub.5 have been introduced into the attrition grinder.

[0171] In this second grinding step, the ratio V.sub.MA/(V.sub.MA+V.sub.FL) is still equal to 0.5, the volume V.sub.FL of liquid nitrogen being 125 ml.

[0172] The attrition grinder has then been rotatably moved again at a rotational speed of 1250 rpm for a duration of 10 min.

[0173] At the end of this second grinding step, the zirconia beads and 4.7 g of ground SiO.sub.2 powder P.sub.6 have been extracted from the attrition grinder.

[0174] The time course of the grain size of the SiO.sub.2 particles before grinding, after the first grinding step and then after the second grinding step has been monitored and is represented in FIG. 4. The corresponding curves, which illustrate the percent by volume as a function of the mean diameter of the SiO.sub.2 particles forming the powders P.sub.4, P.sub.5 and P.sub.6, are denoted as [P.sub.4], [P.sub.5] and [P.sub.6] respectively in FIG. 4. It is specified that this mean diameter of the silica particles of the powders P.sub.4, P.sub.5 and P.sub.6 has been measured by the laser granulometry method (via laser diffraction).

Example 3: Preparing Copper Particles in Accordance With the Invention

[0175] The metal particles in accordance with the invention have been prepared from a so-called millimetric copper powder, hereinafter denoted as P.sub.7.

[0176] With reference to FIG. 5, which corresponds to the SEM picture of this copper powder P.sub.7, it is observed that the latter is formed of three-dimensional particles whose three dimensions e, I and L are of the same order of magnitude, between 300 m and 500 m. The particles of this copper powder are clearly not in the form of sheets.

[0177] This copper powder P.sub.7 has been subjected to two successive grinding steps, by implementing liquid nitrogen as the cryogenic fluid and attrition means formed by zirconia beads of different diameters.

[0178] For implementing the first grinding step, 200 ml (V.sub.FL) of liquid nitrogen and then 5 g of copper powder P.sub.7 have been introduced into a single-stage attrition grinder in accordance to that represented in FIG. 1 or 3 of document WO02017/076944 A1 and comprising 125 ml (V.sub.MA) of beads having a diameter of 5 mm.

[0179] In this first grinding step, the ratio V.sub.MA/(V.sub.MA+V.sub.FL) is therefore equal to 0.38.

[0180] The attrition grinder has then been rotatably moved at a rotational speed of 1200 rpm for a duration of 30 minutes.

[0181] At the end of this first grinding step, all of the 5 mm diameter zirconia beads have been removed from the attrition grinder and a sample of the copper powder, denoted as P.sub.8, thus prepared has been collected and analysed.

[0182] The aspect ratio of the copper particles forming this powder P.sub.8, which corresponds to the ratio L/e of the largest dimension to the smallest dimension, is 50.

[0183] For implementing the second grinding step, 125 ml (V.sub.MA) of zirconia beads having a diameter of 1.25 mm have been introduced into the attrition grinder.

[0184] In this second grinding step, the ratio V.sub.MA/(V.sub.MA+V.sub.FL) is equal to 0.38, the volume V.sub.FL of liquid nitrogen being still 200 ml.

[0185] The attrition grinder has then been rotatably moved again at a rotational speed of 1200 rpm for a duration of 30 min.

[0186] At the end of this second grinding step, all of the 1.25 mm diameter zirconia beads have been removed from the attrition grinder and the copper powder thus prepared, denoted as P.sub.9, has been collected and analysed.

[0187] The aspect ratio, or ratio L/e, of the copper particles forming this copper powder from the second grinding step is 10.

[0188] During this second grinding step, the sheets forming the copper powder P.sub.8 are cut and, in doing so, the aspect ratio decreases.

[0189] FIG. 6 corresponds to the SEM picture of the copper powder as obtained at the end of the second grinding step. It is observed that the powder is formed of particles being in the form of sheets whose three dimensions e, I and L are no longer of the same order of magnitude at all.

[0190] In particular, with reference to the picture in FIG. 7B, it is observed that the smallest dimension e of the sheets is in the order of 1 m.

[0191] The specific surface area of the copper powder P.sub.9 obtained at the end of the second grinding step, as measured according to the BET method, by nitrogen adsorption at the boiling temperature of liquid nitrogen (196 C.), is in the order of 28 m.sup.2/g.

[0192] The time course of the grain size of the copper particles before grinding, after the first grinding step and after the second grinding step has been monitored and is represented in FIG. 8. The corresponding curves, which illustrate the percent by volume as a function of the mean diameter of the copper particles forming the powders P.sub.7, P.sub.8 and P.sub.9, are denoted as [P.sub.7], [P.sub.8] and [P.sub.9] respectively in FIG. 8. It is specified that this mean diameter of the copper particles of the powders P.sub.7, P.sub.8 and P.sub.9 has been measured by the laser granulometry method (via laser diffraction).

[0193] FIG. 9 shows the angles of repose as presented by the powder P.sub.9. It is observed that the powder P.sub.9 is characterised by a secondary dynamic angle of repose s negative relative to the vertical or greater than 90 relative to the horizontal. This atypical property is especially related to the particular morphology of the copper particles in the powder P.sub.9.

Example 4: Making Metal Coatings on Polycarbonate Surfaces

[0194] A first deposition of 0.1 g of powder P.sub.9 as prepared in accordance with the protocol in example 3 above, has been performed by electrostatic spraying onto the inner lateral surface of a polycarbonate cylinder 5 cm high and 1 cm in radius.

[0195] As shown in the photographic picture in FIG. 10A, a uniform single-layer coating is obtained, being characterised by a coverage of 31.83 g/m.sup.2.

[0196] A second deposition has been performed, by electrostatic deposition, of 0.02 g of this same powder P.sub.9 onto one of the faces of a square polycarbonate plate with 3.5 cm sides.

[0197] As shown in the photographic picture in FIG. 10B, a uniform single-layer coating is obtained, being characterised by a coverage of 16.33 g/m.sup.2.

Example 5: Making Metal Coatings on a Glass Surface

[0198] A deposition has been performed, by electrostatic deposition, of 0.02 g of the above powder P.sub.9 onto one of the faces of a square glass plate with 3.5 cm sides.

[0199] As shown in the photographic picture in FIG. 11, a uniform coating of 16.32 g/m.sup.2 is obtained on the face of the glass plate.

[0200] The evaluation of the concealment rate of the coating thus deposited onto the glass plate is carried out by measuring the ratio I.sub.a/I.sub.r of the intensity of illuminance applied to the coated glass plate, denoted as I.sub.a, to the intensity of illuminance that the coated glass plate has let through, denoted as I.sub.r.

[0201] To do so, and with reference to FIG. 12, the glass plate 1 comprising the copper coating 2 is disposed vertically. The face of the plate 1 comprising the coating 2 is exposed to a horizontal intensity of illuminance I.sub.a of 55,000 lux. The horizontal intensity of illuminance I.sub.r reflected by the plate 1 is 120 lux.

[0202] The single-layer copper coating made in this example 5 is therefore characterised by a concealment rate I.sub.a/I.sub.r of 458.33.

Example 6: Making Metal Coatings on a Graphite Surface

[0203] A deposition by electrostatic attraction of the powder P.sub.9 of example 3 has been performed onto a graphite lead having a diameter of 1 m.

[0204] This deposition has been carried out by contacting the powder P.sub.9 with the graphite lead of opposite electrical charge to this powder P.sub.9.

[0205] The photographic picture in FIG. 13 illustrates the copper coating thus obtained and shows the propensity of the metal powder according to the invention to deposit uniformly by simple contact, even onto a small surface.