Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C19/00—Other disintegrating devices or methods
  • B02C19/18—Use of auxiliary physical effects, e.g. ultrasonics, irradiation, for disintegrating
  • B02C19/186—Use of cold or heat for disintegrating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
  • B02C17/10—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls with one or a few disintegrating members arranged in the container
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
  • B02C17/18—Details
  • B02C17/183—Feeding or discharging devices
  • B02C17/186—Adding fluid, other than for crushing by fluid energy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
  • B02C17/18—Details
  • B02C17/20—Disintegrating members
  • B02C17/205—Adding disintegrating members to the tumbling mill

Definitions

• the present invention relates to a method for grinding by cryogenic fluid one or more powders and, in particular, a metal powder.
• the invention also relates to metallic particles characterized by a particular three-dimensional structure, such particles being capable of being obtained by the grinding process mentioned above.
• the invention also relates to the use of such metallic particles.
• the invention relates to a process for coating a material using these metal particles, in particular to form a protective or facing metal coating for all or part of the material, and to the use of such a coated material.
• a metallic coating can be obtained by the application, for example by means of brushes, rollers or even spray guns, of metallic paints on the surface of a part intended to be coated.
• the formulations of these paints resort to the use of additives to disperse, stabilize and/or provide the viscosity and/or the wettability required for a satisfactory application of these paints.
• these formulations use solvents, some of which may be toxic, as well as volatile organic compounds (VOCs) whose negative effects on health and the environment are well known.
• VOCs volatile organic compounds
• these formulations use metal compounds in quantities which are not optimized.
• a metallic coating can also be obtained by the application of inks.
• inks There are numerous ink formulations, each being more particularly suited to the nature of the material to be coated and/or to the intended use. However, some ink formulations are complex, toxic and/or unstable, in particular due to chemical interactions that may occur with the fine metallic powders they contain. In particular, because of their small size, these metal powders oxidize easily.
• a metallic coating can also be obtained by a chemical vapor deposition (CVD) or physical vapor deposition (PVD) process.
• CVD chemical vapor deposition
• PVD physical vapor deposition
• CVD process chemical precursors in gas form are brought to suitable temperatures and pressures to allow the desired deposits.
• CVD process is relatively common, it has the disadvantage of requiring precursors which are not always available and/or which may be difficult to implement.
• the material to be deposited is sputtered by ion or electron beams under controlled temperature and pressure conditions.
• Powder deposition by co-grinding is a process that also makes it possible to form a metallic coating.
• This method consists in depositing a first material in powder form on a second material also in powder form. This process is conventionally carried out in a ball mill using powders having controlled particle sizes. However, by definition, such a method is not suitable for forming a metal deposit on a flat surface and even less so if this flat surface is large.
• the cold metallization process also called the "cold spray” process, is another process allowing the formation of a metallic coating.
• heated metal powder is projected at very high speed by pressurized gas onto the surface of a part to be coated. It is the impact force of the powder particles on the surface that ensures the quality of the deposit. If, depending on this impact force, the cold metallization process can make it possible to produce relatively uniform deposits, it nevertheless requires the implementation of heavy industrial installations with heating devices at high temperatures, potentially higher than 1100°C and high pressures and relatively expensive projection. In addition, this process generates relatively high powder losses.
• This process is gold leaf deposition, a deposit which consists in depositing relatively thin gold leaves (of the order of 0.1 ⁇ m to 0.2 ⁇ m) on a surface. These gold sheets, which are obtained by a thorough prior hammering, are conventionally deposited manually on the surface to be covered. Such a process thus remains relatively artisanal and, consequently, not very suitable for industrial implementation.
• the object of the present invention is to overcome the drawbacks of these coating processes of the prior art and, consequently, to propose a coating process which can be implemented industrially and which makes it possible to produce a homogeneous metallic deposit or coating. on a part, whatever the shape of the latter, by limiting as much as possible the loss of metallic material to be deposited, in particular with a view to controlling industrial costs.
• This coating process must not, moreover, use compounds presenting health and/or environmental risks or resort to heavy and costly industrial installations of the type of those involved in the CVD, PVD and “cold spray” processes.
• this process must also make it possible to produce a metallic coating both on all or part of the surface of a part and on a material which is in a divided form, such as a powder.
• Another object of the present invention is to provide not only metal particles which can be implemented in the coating process mentioned above to remedy the drawbacks of the coating processes of the prior art but also a process for grinding a metallic powder making it possible to obtain such metallic particles.
• another object of the present invention is to provide a grinding process which is not limited solely to the grinding of a metal powder but which also applies to the grinding of other types of powders, such as as ceramic powders or even organic materials or even graphite powders.
• Document FR 3 072 308 A1 describes a process for grinding actinide powders, in particular actinide oxide powders such as UÜ2, PuÜ2 and/or CeÜ2.
• This grinding process is implemented by means of a cryogenic grinding device comprising, among other things, grinding media in the form of solidified cryogenic gas.
• this method comprises the following steps:
• each powder being advantageously chosen 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, - the VMA / (VMA + VFC) ratio of the volume of the VMA attrition means to the sum of the volume of the VMA attrition means and the volume of the VFC cryogenic fluid is between 0.2 and 0.8 and, advantageously, between 0.3 and 0.7, and
• step (c) the speed of rotation of the attrition mill, during step (c), being between 100 rpm and 20,000 rpm.
• the method according to the invention therefore consists in carrying out the grinding of one or more powders by means of a cryogenic fluid, this grinding leading to the production of one or more ground powders formed by particles having a particle size which is homogeneous, this homogeneity being characterized by a relatively tight and narrow particle size distribution, and which may, moreover, be particularly fine and be characterized by values of larger particle size which may be less than 100 nm, such a homogeneous and , if necessary, particularly fine which cannot be achieved with conventional grinding methods.
• the method according to the invention is carried out by means of an attrition mill which comprises, within its enclosure, attrition means, also called media or attrition mobiles.
• attrition means also called media or attrition mobiles.
• Attrition means are formed by moving elements which may have a spherical or substantially spherical shape. If the attrition means can thus be in the form of balls, they can also be constituted by bars or even by rollers.
• the attrition means are formed from a material having sufficient mechanical strength and hardness and adapted to the nature of the powders to be ground.
• the attrition means are formed of steel or else of ceramic, the ceramic possibly being in particular zirconium carbide ZrC, tungsten carbide WC or carbon dioxide. zirconium ZrO2, also called zirconia.
• the attrition means are identical in terms of shape, size and constituent material. However, nothing prohibits resorting to the implementation of attrition means which are different in terms of shape, size and/or constituent material.
• a cryogenic fluid is introduced into the attrition mill equipped with attrition means.
• cryogenic fluid is meant a liquefied gas stored in the liquid state at low temperature, typically at a temperature below 0°C.
• This liquefied gas is chemically inert with respect to the powder or powders intended to be ground under the conditions of implementation of the process according to the invention.
• This cryogenic fluid can in particular be chosen from nitrogen, argon and krypton.
• the cryogenic fluid is nitrogen.
• step (b) of the grinding process according to the invention the powder or powders intended to be ground are introduced into the attrition mill equipped with attrition means.
• This or these powders are advantageously chosen 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.
• a single powder or, on the contrary, a mixture of two, three, or even more different powders can be introduced into the attrition mill.
• metal powder means a powder of a metal in its oxidation state 0. transition, lanthanides and poor metals such as aluminum.
• Metal alloy powder is understood to mean a powder formed by the combination of at least two of the metallic elements of the Periodic Table of the Elements.
• Powder of a metal oxide is understood to mean an oxide powder of one of the metal elements of the Periodic Table of the Elements. When it is a powder of several metal oxides, it may just as well be a powder formed of two or more distinct oxides of the same metallic element as a powder formed of a or more oxides of two or more different metallic elements.
• this powder is a ceramic powder, it can in particular be chosen from alumina, zirconia and mullite.
• the powder is an organic powder, it may in particular be a drug powder.
• Steps (a) and (b) can be implemented in any order.
• the attrition mill is set in rotational motion, for example by means of a stirring shaft. Due to the presence of the attrition means and the cryogenic fluid, which is very cold and very low in viscosity and with a low surface tension (compared to water), the powder(s) present in the enclosure of the attrition are then subjected to concomitant impaction and shear forces generated by the moving attrition means, which allows thorough grinding of the powder or powders. Indeed, the powder or powders will be weakened by the temperature and the liquid phase formed by the cryogenic fluid will be able to insinuate itself in depth into the microcracks generated as the grinding progresses to promote the separation of the particles between them once crushed.
• step (c) particles are therefore obtained which are in the form of a cryogenic suspension of particles. Kept in suspension, these particles are preserved from any risk of oxidation.
• the grinding process according to the invention can, in addition, comprise a step (d) of collecting the particles, this step (d) of collecting being implemented after the step (c) of grinding itself .
• the particles can be stored, advantageously under inerting by means of an inert gas, for example under nitrogen.
• the grinding method according to the invention further comprises, after step (c), at least one additional step (c′) of setting the attrition mill into rotational motion.
• step (c') makes it possible to reduce, if it were still necessary, the size of the particles resulting from the cryogenic grinding of the powder from step (c) until reaching the desired grain size.
• this or these additional steps (c′) can be carried out with attrition means distinct from those implemented during step (c).
• these attrition means can be of different shape, size and/or constituent material.
• the mean diameter of these complementary attrition means is smaller than the mean diameter of the attrition means implemented in step (c).
• the ratio VMA / (VMA + VFC) always verifies the inequality 0.2 ⁇ VMA / ( MA + FC) ⁇ 0 ,8 and, advantageously,
• step (c′) it is preferable for this or these additional step(s) (c′) to be carried out before step (d) of collecting the particles.
• This monitoring of the particle size can in particular be ensured in situ by means of a laser diffractometer, it being specified that the measurement of the particle size is facilitated by the transparent nature of the cryogenic fluid
• the powder is a metal powder or a metal alloy powder, the metal or metals of the powder being chosen from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni, and the VMA / (VMA + VFL) ratio is such that 0.2 ⁇ VMA / (VMA + VFL) ⁇ 0.7.
• the grinding process according to the invention makes it possible to prepare metal and metal alloy particles having very specific morphological characteristics. which will be detailed below.
• the metal or metals of the powder are chosen from Au, Ag, Cu, Al, Sn, Pt, Pd, Zn and Fe, advantageously from Ag, Sn and Cu, the metal or one metals preferably being Cu.
• the invention relates, secondly, to metal or metal alloy particles in the form of three-dimensional sheets denoted e, I and L, e and L being respectively the smallest dimension and the largest dimension. of the particles, and the metal or metals of the particles being chosen from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni.
• these metal or metal alloy particles have the following morphological characteristics:
• an L/e ratio such that 10 ⁇ L/e ⁇ 100, a specific surface (measured according to the BET method) greater than or equal to 1 m 2 /g, advantageously greater than or equal to 10 m 2 /g and, preferably, comprised between 25 m 2 /g and 200 m 2 /g.
• metal or metal alloy particles have very specific morphological characteristics. Indeed, these particles are formed by very fine sheets, with an average aspect factor or L/e ratio which is between 10 and 100, and whose smallest dimension e, such that e ⁇ 1 ⁇ m, is negligible. in front of the two other dimensions L and I.
• L/e ratio average aspect factor
• TEM transmission electron microscope
• the measurement can be carried out by an indirect measurement, by application of the following formula, the sheets being considered flat cylindrical and of thickness and low:
• these metal or metal alloy particles are capable of being obtained by the cryogenic fluid grinding process of a metal or metal alloy powder which has just been defined previously. More particularly, these metal or metal alloy particles can be obtained by a process for preparing particles from a metal or metal alloy powder comprising the following steps:
• the metal or metals of the powder are chosen from Au, Ag, Cu, Al, Sn, Pt, Pd, Pb, Zn, Fe and Ni,
• VMA / (VMA + VFC) of the volume of the attrition means VMA to the sum of the volume of the attrition means VMA and the volume of the cryogenic fluid VFC is such that 0.2 ⁇ VMA / (VMA + VFC) ⁇ 0.7
• step (c) the speed of rotation of the attrition mill, during step (c), is between 100 rpm and 20,000 rpm.
• the metal or metals of the powder are chosen 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.
• the metal or metal alloy particles according to the invention have the following additional characteristics: a static angle of slope, denoted O and measured in accordance with standard ISO 9045: 1990 (fr) of between 30° and 60 °, and/or a secondary dynamic slope angle, denoted Os, between 80° and 130°.
• the static slope angle O is the angle that the slope of a heap of unpacked piled material makes with the horizontal.
• This static slope angle O is determined in accordance with the ISO 9045:1990(en) standard entitled “Screens and industrial screening”.
• the secondary dynamic slope angle Os is determined by subjecting a pile of unpacked piled material to a rotation until the break in the slope formed by this pile and corresponds to the angle that makes this slope broken with the horizontal.
• This secondary dynamic slope angle Os can be determined in accordance with the protocol described in the thesis of S. Courrech du Pont held on November 14, 2003 and entitled "Granular avalanches in a fluid medium”.
• the metal or metal alloy particles according to the invention also have at least one of the following additional morphological characteristics: a tolerance to the flatness of the sheets of less than or equal to 200 nm, and a deviation to the convexity of the sheets less than or equal to 10%.
• Flatness expresses the character of a surface having all its elements inscribed in a plane.
• the flatness tolerance corresponds to the height, denoted h, of the zone limited by the two parallel planes marked in dotted lines inside which the surface considered must be located.
• this tolerance to the flatness of the sheets is less than or equal to 200 nm.
• the deviation from convexity corresponds to the ratio of the total surface of a sheet, represented in gray in figure C, to the sum of the surface in gray and the surface represented in white in figure C.
• the invention relates, thirdly, to various uses of the metallic or metallic alloy particles which have just been described.
• these metallic or metallic alloy particles can be used for producing a part comprising a metallic coating on all or part of one of its surfaces.
• Such a metal coating may in particular be intended to protect, treat or decorate all or part of said surface of the part.
• metal or metal alloy particles can be used in many fields, in particular in the mechanical industry, in the electronics or microelectronics industry, in the field of optics, in the field of construction, in the field of packaging (packaging), in the field of design, in the cosmetics field or even in the medical or paramedical field.
• the invention relates, fourthly, to a process for coating a material.
• this method comprises the following steps:
• step (2) depositing the metal or metal alloy particles prepared in step (1) on all or part of the material, whereby a coated material is obtained.
• the coating process according to the invention makes it possible to obtain a material comprising a homogeneous metal coating and this, by limiting the quantity of metal or metal alloy particles necessary for the production of this coating.
• metal or metal alloy coatings characterized by a surface coverage rate of at least 5 g/m 2 , or even at least 10 g/m 2 can be easily obtained.
• this surface mass is of the order of 9 g/m 2 .
• metallic coatings can also make it possible to achieve an occultation rate greater than 400.
• step (1) for preparing the metal or metal alloy particles reference may be made to what has been previously described in connection with the preparation of these particles, the advantageous characteristics of this process being able to be taken alone or in combination.
• Step (2) of the coating process according to the invention consists in depositing the metallic or metallic alloy particles on all or part of the material to obtain a coated material.
• This deposition step (2) can be done by any coating process conventionally used to form, from a powder, a metallic coating on a material, including the processes of the state of the art discussed above ( paints, inks, etc.). Furthermore, the generation of cryogenic suspension of metal particles or of charged metal alloys makes it possible to carry out a deposition by immersion of the surfaces to be coated (deposition by bath).
• step (2) of deposition is carried out by electrostatic attraction or by application of a potential difference between the metallic or metallic alloy particles according to the invention and the surface or surfaces of the material on which the deposition must be carried out.
• the first technique consists in applying an electric field in line with the metal or metal alloy particles for a time during which these metal or metal alloy particles will in fact become electrically charged.
• the second technique consists in carrying out the electrical charging by tribology, that is to say by stripping electrons from the surface by rubbing metal or metal alloy particles in line with a surface.
• the tribological loading being generally more effective and also of easier implementation, it is this second technique which is privileged.
• the deposition processes which have just been mentioned have the advantage of being relatively easy to implement industrially and of not having to resort to heavy and costly industrial installations.
• the metal or metal alloy particles can be deposited in the absence of solvents or any other additive which may present a danger to health and/or the environment.
• the resistance and/or durability properties of the coating can be reinforced by the implementation of a step (3) aimed at consolidating the coating on all or part of the material.
• the coating method according to the invention may further comprise a step (3) of applying energy, such as thermal energy, for example by raising the temperature the coated surface, or with an additional coating, for example of the lacquer or varnish type.
• energy such as thermal energy
• the coating method according to the invention can be implemented on a material which can be in a divided form or else in the form of a piece.
• this material When this material is in a divided form, it may in particular be in the form of granules or else of platelets, this divided form possibly being intended to be subsequently transformed into a part.
• this part may just as well be a new part, that is to say a part which has never been used before, or a part under maintenance, which corresponds to a part already in use and whose properties are to be improved by the application of a coating.
• the present invention relates, fifthly and sixthly, to the material comprising a metallic coating as well as to its uses, this coated material being obtained by the coating process as defined above, the advantageous characteristics of this process being able to be taken alone or in combination.
• this coated material can in particular be used in the mechanical industry, in the electronic or micro-electronics industry, in the field of optics, in the field of construction, in the field of packaging, in the field of design, in the cosmetics field or even in the medical or paramedical field.
• the metal particles are copper particles, they can advantageously be used, like the coated materials obtained from such particles, in the medical or paramedical field to confer bactericidal and virucidal properties.
• Figure A schematically illustrates the static slope angle and secondary dynamic slope angle characteristics.
• Figure B schematically illustrates the flatness tolerance characteristic of a sheet.
• Figure C schematically illustrates the convexity deviation characteristic of a sheet.
• Figures IA, IB and IC correspond respectively to images taken by means of a scanning electron microscope (SEM) of the Pi powder of Fe3O4 used in example 1 to prepare the metal oxide particles according to the invention, of the powder P2 resulting from a first grinding then the powder P3 resulting from the second grinding.
• SEM scanning electron microscope
• FIG. 2 illustrates the evolution of the particle size of the powder Pi of FIG. IA (curve denoted Pi), of the powder Pr obtained after 30 min of implementation of the first grinding step (curve denoted Pr) and of the powder P2 obtained at the end of the first grinding stage (curve denoted P2), this evolution being evaluated by the volume percentage (denoted V and expressed in %) according to the average diameter of the particles (denoted d and expressed in pm) .
• FIG. 3 illustrates the evolution of the particle size of the powder Pi of FIG.
• Figure 4 illustrates the evolution of the particle size of the silica powder P4 before grinding (curve denoted P4), of the P5 powder obtained at the end of the first grinding step (curve denoted P5) and of the Pe powder obtained at the end of the second grinding stage (curve denoted Pe), this evolution being evaluated by the volume percentage (denoted V and expressed in %) as a function of the mean diameter of the particles (denoted d and expressed in pm).
• FIG. 5 corresponds to an image taken by means of a scanning electron microscope (SEM) of the copper powder used to prepare the metal particles according to the invention.
• SEM scanning electron microscope
• FIG. 6 corresponds to an image taken by means of a scanning electron microscope (SEM) of the copper particles as prepared by the implementation of the method according to the invention.
• SEM scanning electron microscope
• FIGS. 7A and 7B correspond to an enlargement of two parts of the image of FIG. 6, including that bearing the scale marking the 100 ⁇ m (FIG. 7A).
• FIG. 8 illustrates the evolution of the particle size of the copper particles forming the powder of FIG. 5, of the copper particles forming the powder as obtained after the first grinding step and of the copper particles forming the powder such as obtained after the second grinding step, this evolution being evaluated by the volume percentage (denoted V and expressed in %) as a function of the mean diameter of the particles (denoted d and expressed in pm).
• FIG. 9 shows two photographic images illustrating the slope angle O and the dynamic secondary slope angle Os of the powder P9 according to the present invention.
• FIG. 10A is a photographic negative of a metal coating produced by the method according to the invention on a cylindrical polycarbonate support.
• FIG. 10B is a photographic negative of a metal coating produced by the method according to the invention on a square polycarbonate support.
• FIG. 11 is a photographic negative of a metal coating produced by the process according to the invention on a square glass support.
• Figure 12 is a schematic representation of the device used to determine the occultation rate conferred by the metal coating of Figure 11.
• FIG. 13 is a photographic negative of a metal coating produced by the method according to the invention on a graphite mine.
• a FesO/i iron oxide powder, denoted Pi was subjected to two successive grinding stages, by the use of liquid nitrogen as cryogenic fluid and attrition means formed by zirconia balls of different diameters.
• 125 ml (VFL) of liquid nitrogen then 27.8 g of FesO4 were introduced into an attrition mill of the type shown in Figure 1 or 3 of document WO 2017/076944 Al and comprising 125 ml (VMA) of beads having a diameter of 5 mm.
• the VMA/(MA+FL) ratio is therefore equal to 0.50.
• the attrition mill was then set in rotational motion at a rotational speed of 1250 rpm for a period of 90 min.
• the zirconia balls and 24.4 g of ground FesO4 P2 powder were extracted from the attrition mill.
• a sample of the FesO4 P2 powder thus prepared was analyzed.
• the specific surface of the P2 powder of FesO4 obtained at the end of this first step of grinding, as measured according to the BET method, by adsorption of nitrogen at the boiling point of liquid nitrogen (-196° C.), is of the order of 10 m 2 /g.
• VMA zirconia balls having a diameter of 1.25 mm then 17.5 g of the P2 powder of Fe304 were introduced into the attrition mill.
• the VMA/(MA+VFL) ratio is always equal to 0.50, the VFL volume of liquid nitrogen always being 125 mL.
• the attrition mill was then again put into rotational motion at a rotational speed of 1250 rpm for a period of 90 min.
• the zirconia balls and 9.2 g of ground Fe3O4 powder P3 were extracted from the attrition mill.
• Figures IA, IB and IC correspond respectively to the SEM shots of the Fe3O4 powders P1, P2 and P3.
• a SiO2 silica powder, denoted P4 was subjected to two successive grinding steps, by the use of liquid nitrogen as cryogenic fluid and attrition means formed by zirconia balls of different diameters.
• the VMA/(MA+FL) ratio is therefore equal to 0.5.
• the attrition mill was then set in rotational motion at a rotational speed of 1250 rpm for a period of 10 min.
• the zirconia balls and 12.2 g of ground SiO2 Ps powder were extracted from the attrition mill.
• VMA zirconia balls having a diameter of 1.25 mm then 5.6 g of the Ps powder of SiO2 were introduced into the attrition mill.
• the VMA/(VMA+VFL) ratio is always equal to 0.5, the VFL volume of liquid nitrogen being 125 mL.
• the attrition mill was then again set in rotational motion at a rotational speed of 1250 rpm for a period of 10 min.
• the zirconia balls and 4.7 g of ground SiO2 Pe powder were extracted from the attrition mill.
• the metal particles in accordance with the invention were prepared from a so-called “millimetric” copper powder, hereinafter denoted P7.
• This P7 copper powder was subjected to two successive grinding steps, using liquid nitrogen as the cryogenic fluid and attrition means formed by zirconia balls of different diameters.
• VFL liquid nitrogen
• P7 copper powder were introduced into a single-stage attrition mill conforming to that shown in Figure 1 or 3 of document WO 2017/076944 Al and comprising 125 ml (VMA) of beads having a diameter of 5 mm.
• the VMA/(MA+FL) ratio is therefore equal to 0.38.
• the attrition mill was then set in rotational motion at a rotational speed of 1200 rpm for a period of 30 min.
• VMA zirconia balls having a diameter of 1.25 mm were introduced into the attrition mill.
• the VMA/(MA+VFL) ratio is equal to 0.38, the VFL volume of liquid nitrogen still being 200 mL.
• the attrition mill was then again set in rotational motion at a rotational speed of 1200 rpm and this for a period of 30 min.
• the aspect factor, or L/e ratio, of the copper particles forming this copper powder resulting from the second grinding stage is 10.
• the sheets forming the copper powder Ps are cut and, in doing so, the aspect factor decreases.
• FIG. 6 corresponds to the SEM photograph of the copper powder as obtained at the end of the second grinding step. It is observed that the latter is formed of particles in the form of sheets whose three dimensions e, I and L are no longer of the same order of magnitude.
• the smallest dimension e of the sheets is of the order of 1 ⁇ m.
• the specific surface of the P9 copper powder obtained at the end of the second grinding stage, as measured according to the BET method, by nitrogen adsorption at the boiling point of liquid nitrogen (-196°C ), is of the order of 28 m 2 /g.
• Figure 9 shows the slope angles as presented by powder P9. It is observed that the P9 powder is characterized by a secondary dynamic slope angle Os negative with respect to the vertical or greater than 90° with respect to the horizontal. This atypical property is notably linked to the particular morphology of the copper particles of the P9 powder.
• a first deposition was carried out, by electrostatic spraying, of 0.1 g of P9 powder as prepared in accordance with the protocol of example 3 above on the internal lateral surface of a polycarbonate cylinder 5 cm high. and 1 cm in radius.
• a uniform monolayer coating is obtained which is characterized by a coverage rate of 31.83 g/m 2 .
• a second deposition was carried out, by electrostatic deposition, of 0.02 g of this same P9 powder on one of the faces of a square polycarbonate plate with a side of 3.5 cm.
• Example 5 Production of metallic coatings on a glass surface
• a uniform coating of 16.32 g/m 2 is obtained on the face of the glass plate.
• the evaluation of the occultation rate of the coating thus deposited on the glass plate is carried out by measuring the ratio l a / l r of the intensity of illumination applied to the coated glass plate, denoted l a , on l intensity of illumination that the coated glass plate let through, noted l r .
• the glass plate 1 comprising the coating 2 of copper is arranged vertically.
• the face of the plate 1 comprising the coating 2 is exposed to a horizontal illumination intensity of 55,000 lux.
• the measurement of the horizontal illumination intensity l r which is restored by the plate 1 is 120 lux.
• the single-layer copper coating produced in the present example 5 is therefore characterized by an occultation rate l a / l r of 458.33.
• Example 6 Production of metallic coatings on a graphite surface
• the P9 powder of Example 3 was deposited by electrostatic attraction on a graphite lead having a diameter of 1 ⁇ m.
• This deposition was carried out by bringing the P9 powder into contact with the electrically charged graphite lead opposite to this P9 powder.
• the photographic negative in FIG. 13 illustrates the copper coating thus obtained and shows the propensity of the metal powder according to the invention to be deposited uniformly by simple contact, even on a surface of small size.

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Family Cites Families (4)

• 2020
  • 2020-12-10 FR FR2013001A patent/FR3117485B1/fr active Active
• 2021
  • 2021-12-08 WO PCT/FR2021/052244 patent/WO2022123178A1/fr active Application Filing
  • 2021-12-08 US US18/256,795 patent/US20240042453A1/en active Pending
  • 2021-12-08 EP EP21847992.1A patent/EP4259335A1/de active Pending
  • 2021-12-08 JP JP2023535435A patent/JP2024500092A/ja active Pending

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