Use of a powder of sintered beads made of metal carbide(s)

Abstract

Use, in an application for grinding, dispersion in a wet medium or surface treatment, of a powder of sintered beads, said powder having: - a chemical composition such that, as percentages by mass based on the mass of the bead powder: - (77 - C4)% ≤ W + Mo ≤ (97.5 - C3)%, with Mo ≤ 10%; - C1% ≤ C ≤ C2%; - 2.5% < additive ≤ 20.0%, the additive denoting Ti + Ta + Nb + V + Zr + Hf; - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf, or "other elements": ≤ 3%; with: - C1 = 100*(C3 / C5), - C2 = 100*(C4 / C6), - C3 = k*C7, with k selected from 0.5, 0.6, 0.7, 0.8 and 0.9, - C4 = k'*C7, with k' selected from 1.2 and 1.1, - C5 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C3], - C6 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C4], - C7 = M(C)*[(m(W) / M(W)) + (m(Mo) / M(Mo)) + (m(Ti) / M(Ti)) + (m(Ta) / M(Ta)) + (m(Nb) / M(Nb)) + (m(V) / M(V)) + (m(Zr) / M(Zr)) + (m(Hf) / M(Hf))], m(W), m(Mo), m(Ti), m(Ta), m(Nb), m(V), m(Zr) and m(Hf) being the mass, in grams, of the elements W, Mo, Ti, Ta, Nb, V, Zr and Hf, respectively, and M(W), M(Mo), M(Ti), M(Ta), M(Nb), M(V), M(Zr), M(Hf) and M(C) being the molar mass, in g / mol, of the elements W, Mo, Ti, Ta, Nb, V, Zr, Hf and C, respectively; - a crystallographic composition such that more than 60% of the crystalline phases present in said bead powder are in the form of metal carbide(s), as percentage by mass based on the mass of the crystalline phases, said crystalline phases including at least one carbide of at least one element from among Ti, Ta, Nb, V, Zr and Hf.

Description

[0001] USE OF A POWDER OF SINTERED METALLIC CARBIDE(S) BALLS

[0002] technical field

[0003] The present invention relates to a powder of sintered metal carbide(s) beads, to a method of manufacturing this powder, to a method involving the use of this powder, in particular in an application of grinding, dispersion in a wet environment or surface treatment, and to a suspension comprising said powder.

[0004] Previous art

[0005] The mineral or mining industry uses grinding balls for the fine grinding of materials possibly pre-ground dry by traditional processes, in particular for the fine grinding of calcium carbonate, titanium oxide, gypsum, kaolin and ore containing metals in generally combined forms (oxides, sulfides, silicates...), processes which may also involve prior purification methods, for example by flotation.

[0006] All these balls typically have a size of 0.03 to several mm, and they must in particular have good resistance to wear.

[0007] To further improve grinding efficiency, the use of sintered balls made of a high-density material, such as tungsten carbide, can be considered. The higher density also facilitates the separation of particles from the suspension being ground.

[0008] Tungsten carbide-based grinding balls are specifically described in WO / 2020 / 074609.

[0009] During a grinding operation, grinding media can break into pieces. These pieces disrupt the grinding process, not only because they are not in a ball shape and have sharp edges, but also because they alter the particle size distribution of the grinding media. These pieces can also accumulate over time in the system that separates the media from the slurry to be ground, potentially leading to a mill shutdown.

[0010] There is a need for new sintered metal carbide balls, particularly suitable for use as grinding balls, which have improved break resistance.

[0011] There is also a need for a simple and economical process for manufacturing such beads. One aim of the invention is to meet, at least partially, these needs.

[0012] Summary of the invention

[0013] The invention proposes a method comprising using, in a grinding, wet dispersion, or surface treatment application, a powder of sintered beads, referred to as "metal carbide beads," said bead powder having:

[0014] - a chemical composition such that, in mass percentages based on the mass of the powder of beads:

[0015] - (77 - C4)% < W + Mo < (97.5 - C3)%, with Mo < 10%;

[0016] - C1% < C < C2%;

[0017] - 2.5% < additive < 20.0%, the additive denoting Ti + Ta + Nb + V + Zr + Hf;

[0018] - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf, or "other elements": < 3%; with:

[0019] - C1 = 100*(C3 / C5),

[0020] - C2 = 100*(C4 / C6),

[0021] - C3 = k*C7, with k chosen from 0.5, 0.6, 0.7, 0.8 and 0.9, preferably C3 = 0.5*C7,

[0022] - C4 = k'*C7, with k' chosen from 1, 2 and 1, 1, preferably C4 = 1, 2*C7, C5 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C3],

[0023] - C6 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C4],

[0024] - C7 = M(C)*[(m(W) / M(W)) + (m(Mo) / M(Mo)) + (m(Ti) / M(Ti)) + (m(Ta) / M(Ta)) + (m(Nb) / M(Nb)) + (m(V) / M(V)) + (m(Zr) / M(Zr)) + (m(Hf) / M(Hf))], m(W), m(Mo), m(Ti), m(Ta), m(Nb), m(V), m(Zr) and m(Hf) being the mass, in grams, of the elements W, Mo, Ti, Ta, Nb, V, Zr and Hf, respectively, and

[0025] M(W), M(Mo), M(Ti), M(Ta), M(Nb), M(V), M(Zr), M(Hf) and M(C) being the molar mass, in g / mol, of the elements W, Mo, Ti, Ta, Nb, V, Zr, Hf and C, respectively;

[0026] - a crystallographic composition such that more than 60% of the crystallized phases present in said powder of beads are in the form of metallic carbide(s), as a percentage by mass based on the mass of the crystallized phases, said crystallized phases including at least one carbide of at least one element among Ti, Ta, Nb, V, Zr and Hf.

[0027] As will be explained in more detail later in the description, the inventors unexpectedly discovered that the presence of more than 2.5% of an additive, at least partially, preferably completely, in the form of carbide(s), significantly reduces breakage of the metallic carbide balls. The inventors are unable to theoretically explain this surprising result.

[0028] This process may also include one or more of the following optional and preferred features:

[0029] - the content of the crystallized phases present in the form of metallic carbide(s) is greater than 80%, as a percentage by mass based on the mass of the crystallized phases;

[0030] - said crystallographic composition is such that more than 50%, by mass, of at least one of the elements Ti, Ta, Nb, V, Zr and Hf, is in the form of carbide(s);

[0031] - said chemical composition is such that 3.0% < Ti + Ta + Nb + V + Zr + Hf < 15.0%, preferably 5.0% < Ti + Ta + Nb + V + Zr + Hf < 10%;

[0032] - said chemical composition is such that the additive is Nb and Nb > 3.0% and Nb < 9.7%;

[0033] - C3 = 0.8*C7 and / or C4 = 1.1*C7;

[0034] - the oxygen O content in said powder of beads is less than or equal to 0.85%, preferably less than or equal to 0.1%;

[0035] - the average grain size of the sintered balls is greater than or equal to 0.1 pm and less than or equal to 4 pm;

[0036] - said powder of beads has an apparent density greater than or equal to 14.3 g / cm³ 3 ;

[0037] - said chemical composition is such that:

[0038] - W > 64% and W < 92%, and / or

[0039] - C > 3% and C < 13.5%, and / or

[0040] - Co < 0.3%, and / or

[0041] - Ni < 0.3%, and / or

[0042] - Fe < 0.3%, and / or

[0043] - Co + Ni + Fe < 0.3%, and / or

[0044] - Mo > 3% and Mo < 9%, and / or

[0045] - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf < 2.5%;

[0046] - said chemical composition is such that:

[0047] - W > 73% and W < 90%, and / or

[0048] - C < 9%, and / or

[0049] - Co + Ni + Fe < 0.05%, and / or

[0050] - Mo > 5% and Mo < 7%, and / or

[0051] - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf < 1%;

[0052] - said powder of beads has a ratio (D9o - D ) / D5o less than 0.5,

[0053] D5O, DIO, and D9O designating the bead sizes corresponding to the percentages equal to 50%, 10%, and 90% by mass respectively, on the cumulative particle size distribution curve of the powder bead sizes, said bead sizes being classified in ascending order;

[0054] - said powder of beads has a median size D50 less than 1.8 mm and greater than 10 pm.

[0055] The powdered beads can also be used in suspension form after grinding and dispersion in a moist medium. The invention also relates to such a suspension.

[0056] In one embodiment, only a powder of beads is used. In another embodiment, a particulate mixture is used comprising a powder of beads mixed with other particles, said other particles representing preferably less than 10%, preferably less than 5%, preferably less than 2% by mass of the sum of the mass of said beads and said other particles.

[0057] The invention also relates to a device selected from:

[0058] - a crusher comprising a crushing chamber containing a suspension according to the invention and preferably a material to be crushed;

[0059] - a dispersion device comprising a dispersion chamber containing a suspension according to the invention and preferably a material to be dispersed, for example a pigment powder, for example to make a paint.

[0060] The invention also relates to a said powder of beads, and a particulate mixture comprising at least 90%, preferably at least 95%, preferably at least 98% by mass of a powder of beads according to the invention.

[0061] Preferably, the apparent density of the powdered beads should always be greater than or equal to 14.0 g / cm³ 3 , preferably greater than or equal to 14.3 g / cm² 3 , preferably greater than or equal to 14.5 g / cm² 3 Advantageously, using such a powder reduces grinding time.

[0062] In a preferred embodiment, the powdered beads has:

[0063] - a chemical composition such that, in mass percentages based on the mass of the powder of beads:

[0064] - (77 - C4)% < W + Mo < (95.5 - C3)%, with Mo < 10%;

[0065] - C1% < C < C2%;

[0066] - Ti, Ta, Nb, V, Zr, Hf such that

[0067] Ti + Nb + V + Zr > 4.5% and / or Ta + Hf > 5%, and

[0068] Ti + Ta + Nb + V + Zr + Hf < 20.0%;

[0069] - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf or "other elements": < 3%, with:

[0070] - C1 = 100*(C3 / C5),

[0071] - C2 = 100*(C4 / C6),

[0072] - C3 = 0.5*C7,

[0073] - C4 = 1.2*C7,

[0074] - C5 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C3],

[0075] - C6 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C4],

[0076] - C7 = M(C)*[(m(W) / M(W)) + (m(Mo) / M(Mo)) + (m(Ti) / M(Ti)) + (m(Ta) / M(Ta)) + Hf) / M(Hf))], f) being the mass in grams of the elements W, Mo, Ti, Ta, Nb, V, Zr and Hf, respectively, and

[0077] M(W), M(Mo), M(Ti), M(Ta), M(Nb), M(V), M(Zr), M(Hf) and M(C) being the molar mass in g / mol of the elements W, Mo, Ti, Ta, Nb, V, Zr, Hf and C, respectively;

[0078] - a crystallographic composition such that more than 60% of the crystallized phases present in said powder of beads are in the form of metallic carbide(s), as a percentage by mass based on the mass of the crystallized phases, said crystallized phases including at least one carbide of at least one element among Ti, Ta, Nb, V, Zr and Hf.

[0079] In a preferred embodiment, the additive content by mass exceeds 5.0%. Remarkably, the inventors found that such an additive content not only reduces breakage but also provides good wear resistance. An additive content above 5.0% thus offers the best compromise between breakage resistance and wear resistance, particularly in the applications mentioned above.

[0080] Preferably, the Nb content is greater than 5.0%.

[0081] The invention also relates to a method for manufacturing a powder of metallic carbide(s) beads according to the invention, said method comprising the following steps: a) preparation of a starting charge so that the powder of metallic carbide(s) beads obtained at the end of step c) conforms to the invention, b) shaping of the starting charge in the form of a powder of raw beads, c) sintering so as to obtain a powder of metallic carbide(s) beads.

[0082] Preferably, in step a), the additive is supplied, at least partially, preferably entirely, in the form of a powder of additive carbide(s). The additive remains in a carbide form during manufacturing and is therefore advantageously found in a carbide form, particularly a multiple carbide form, within the ball.

[0083] A method according to the invention may further include one or more of the following optional features:

[0084] - in step a), the starting load comprises a particulate mixture of inorganic powders, preferably consisting of

[0085] - of a toilet powder and

[0086] - of one or more powders of titanium carbide, tantalum carbide, niobium carbide, vanadium carbide, zirconium carbide, hafnium carbide, and

[0087] - optionally of a carbon powder and / or a powder containing molybdenum, preferably a molybdenum carbide powder and / or a tungsten oxide powder, said powders being able to be replaced, at least partially, by precursor powders, introduced in equivalent quantities, the median size of all the particles of said powders, preferably the median size of each said powder being less than 2 pm, preferably less than 1 pm, preferably less than 0.5 pm;

[0088] - preferably, in the starting charge, more than 90%, more than 95%, preferably approximately 100% of the additive is supplied in the form of carbide;

[0089] - preferably, in the starting load, the additive content is greater than or equal to 2.7%, preferably greater than or equal to 3.5%, preferably greater than or equal to 4.5%, preferably greater than or equal to 5.0%, and preferably less than or equal to 15.0%, preferably less than or equal to 12.0%, preferably less than or equal to 10.0%;

[0090] - preferably, in the starting charge, Co < 0.5%, preferably Co < 0.3%, preferably Co < 0.2%, preferably Co < 0.1%, preferably Co < 0.05%, preferably the Co content is substantially zero, in mass percentages on the basis of said starting charge;

[0091] - preferably, in the starting charge, Ni < 0.5%, preferably Ni < 0.3%, preferably Ni < 0.2%, preferably Ni < 0.1%, preferably Ni < 0.05%, preferably the Ni content is substantially zero, in mass percentages on the basis of said starting charge;

[0092] - preferably in the starting charge, Fe < 0.5%, preferably Fe < 0.3%, preferably Fe < 0.2%, preferably Fe < 0.1%, preferably Fe < 0.05%, in mass percentages on the basis of said starting charge;

[0093] - preferably, in the starting charge, Co + Ni + Fe < 0.3%, preferably Co + Ni + Fe < 0.2%, preferably Co + Ni + Fe < 0.1%, preferably Co + Ni + Fe < 0.05%, preferably the content of Co + Ni + Fe is substantially zero, in mass percentages on the basis of said starting charge;

[0094] - preferably, the shaping in step b) is carried out at less than 2 bar, less than 1.5 bar, less than 1.1 bar, preferably at a pressure of 1 bar, preferably at atmospheric pressure;

[0095] - preferably, the sintering temperature in step c) is above 1700°C, preferably above 1800°C, preferably above 1900°C and preferably below 2300°C;

[0096] - preferably, the sintering in step c) is carried out at less than 2 bar, less than 1.5 bar, less than 1.1 bar, preferably at a pressure of 1 bar, preferably at atmospheric pressure;

[0097] - preferably, the duration of the sintering rest in step c) is greater than 0.5 hours and less than 10 hours;

[0098] - preferably, in step c), sintering is carried out in an inert or reducing atmosphere.

[0099] Remarkably, a median particle size for the initial feed of less than 2 pm allows for the production of sintered metal carbide beads with an apparent density greater than or equal to 14.0 g / cm³. 3 , preferably greater than or equal to 14.3 g / cm² 3 , preferably greater than or equal to 14.5 g / cm² 3 preferably with very low or even zero nickel and / or cobalt content,

[0100] - without needing to strongly compress the starting load in step b) and

[0101] - without needing to resort to high-pressure heat treatment, such as hot isostatic pressing (or "Hot Isostatic Pressing" in English or HIP) or hot pressing (or "Hot Pressing" in English or HP), during step c) of sintering.

[0102] In one embodiment, the process according to the invention does not involve any pressing operation in step b) or in step c), preferably in both steps b) and c).

[0103] The manufacturing process is considerably simplified.

[0104] Definitions

[0105] By "ball" we mean a particle exhibiting sphericity, that is to say a ratio between its smallest Ferret diameter and its largest Ferret diameter, greater than or equal to 0.75, regardless of how this sphericity was obtained.

[0106] By "bead powder" we mean a powder containing more than 90% by mass of beads.

[0107] A "sintered bead" is a bead obtained by mixing suitable raw materials, then shaping this mixture in its raw state and firing the resulting raw bead at a temperature and for a sufficient time to achieve sintering. A sintered bead consists of "grains" bonded together during the sintering process.

[0108] The "size" of a powder particle is classically its dimension measured using a laser particle size analyzer.

[0109] The 50th percentile (denoted D50), the 10th percentile (denoted D10), and the 90th percentile (denoted D10) are called "percentiles." 90) and 99.5 (denoted D99.5), the particle sizes, for example of beads, corresponding to the percentages equal to 50%, 10%, 90% and 99.5%, respectively, by mass, on the cumulative particle size distribution curve of the particle sizes, respectively of beads in the powder, said particle sizes, respectively of beads being ranked in ascending order. According to this definition, 99.5% by mass of the particles or beads in the powder thus have a size less than D 99 0.5% and 0.5% of the particles or beads, by mass, have a size greater than or equal to D 99 5.

[0110] The "median size" of a powder of particles or beads is called the 50th percentile. The median size therefore divides the particles, beads respectively, of the powder into first and second populations equal in mass, these first and second populations consisting only of particles, beads respectively, having a size greater than or equal to, or less than respectively, the median size.

[0111] The 99.5 percentile is called the "maximum size" of a powder of particles or beads.

[0112] The "median sphericity" of a powder divides the particles of that powder into first and second populations equal in mass, these first and second populations consisting only of particles exhibiting a sphericity greater than or equal to, or less than respectively, the median sphericity.

[0113] A total content of several carbides, for example WC + W2C, or of one or more elements, for example W + Mo, or Ti + Ta + Nb + V + Zr + Hf, does not imply that each of said carbides or each of said elements, respectively, is present, even if, in one embodiment, each of said carbides or said elements is present.

[0114] The additive consists of one or more metals from among Ti, Ta, Nb, V, Zr and Hf.

[0115] A multiple carbide is a carbide containing one of the elements Ti, Ta, Nb, V, Zr and Hf, and another element, preferably W, or a combination of several of the elements Ti, Ta, Nb, V, Zr and Hf, preferably also combined with W.

[0116] A multiple metal carbide is considered to be a carbide of each of the metals it contains. For example, a W and Ti carbide is a W carbide and a Ti carbide. The "apparent density" of a powder refers to the ratio of the powder mass to the cumulative volume of the powder particles, thus including the closed porosity located within these particles.

[0117] A “precursor” of a compound is a constituent which is transformed into said compound during the manufacture of a powder of metallic carbide(s) beads according to the invention.

[0118] The "average grain size" of a metallic carbide ball is defined as the dimension measured using a Mean Linear Intercept (MLI) method. Such a measurement method is described in ASTM E1382. The measurement can be performed on a polished surface of a cross-section of the ball, as described in the examples.

[0119] In general, the properties of beads and powders can be measured using the methods described for the examples below.

[0120] “Contain”, “include” or “present” should not be interpreted in a restrictive manner unless otherwise indicated.

[0121] Unless otherwise stated, the percentages used to characterize a composition always refer to mass percentages based on said composition.

[0122] The mass contents of the phases (WC, W2C, ...) are measured on the basis of the total mass of the crystallized phases.

[0123] Detailed description

[0124] Method for manufacturing a powder of beads according to the invention

[0125] To manufacture a powder of beads according to the invention, one can proceed according to a process comprising the steps a) to c) described above and detailed below.

[0126] In step a), a starting charge suitable for the shaping process of step b) is prepared, preferably at room temperature, as is well known to those skilled in the art. The charge is adapted so that the powder of beads obtained at the end of step c) conforms to the invention. To this end, it comprises a particulate mixture of inorganic powders, or "starting powders", preferably consisting of WC powder and one or more powders of an additive source, preferably an additive carbide powder, and optionally a carbon powder and / or a powder containing molybdenum, preferably a molybdenum carbide powder and / or a tungsten oxide powder.

[0127] The additive source preferably contains less than 10%, preferably less than 5%, preferably less than 2%, preferably substantially no additive in oxide form. The additive source preferably contains more than 90%, preferably more than 95%, preferably more than 98%, preferably substantially 100% additive in carbide form, preferably a carbide selected from titanium carbide, tantalum carbide, niobium carbide, vanadium carbide, zirconium carbide, hafnium carbide and mixtures thereof.

[0128] These starting powders can also be replaced, at least partially, by precursor powders, introduced in equivalent quantities.

[0129] Impurities consist of elements not intentionally introduced into the starting feed. Starting powders are preferably selected so that the total impurity content, excluding oxygen, is less than 0.5%, preferably less than 0.3%, and preferably less than 0.1%, as a mass percentage based on the particulate mixture of the starting feed. Tungsten, which may be present in additive powders, preferably in additive carbide powders, is not considered an impurity.

[0130] When a powder of metallic carbide(s) is present in the starting charge, its oxygen content is preferably less than 3%, preferably less than 2%, preferably less than 1%, as a percentage by mass based on the mass of the powder.

[0131] The starting powders are preferably chosen so that their median size is less than 2 µm, preferably less than 1 µm, preferably less than 0.5 µm. The starting powders may be ground or co-ground prior to step a) for this purpose, for example by impact and / or friction grinding.

[0132] Preferably, the ratio of the median size of all said titanium carbide, tantalum carbide, niobium carbide, vanadium carbide, zirconium carbide, hafnium carbide, molybdenum carbide powders, and said precursor powders of these compounds, preferably of the median size of each of said powders, to the median size of the tungsten carbide powder is less than 5, preferably less than 4, preferably less than 3, preferably less than 2, preferably less than 1, preferably less than 0.9, preferably less than 0.8, preferably less than 0.7, preferably less than 0.6, preferably less than 0.5.

[0133] In one embodiment, WC is the only tungsten carbide introduced into the starting charge.

[0134] Preferably, the starting charge has a mass ratio of the W content to the additive content greater than or equal to 3.5, preferably greater than or equal to 5, preferably greater than or equal to 8.1, and preferably less than or equal to 36.2, preferably less than or equal to 34, preferably less than or equal to 30, preferably less than or equal to 25, preferably less than or equal to 21, preferably less than or equal to 18. In one embodiment, in particular where WC is the only tungsten carbide introduced in the starting charge, and where the additive is introduced into the starting charge substantially exclusively in the form of titanium carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of titanium carbide powder greater than or equal to 5, and preferably less than or equal to 30, preferably less than or equal to 23, preferably less than or equal to 17.

[0135] In one embodiment, particularly when WC is the only tungsten carbide introduced into the starting charge, and when the additive is introduced into the starting charge substantially exclusively in the form of tantalum carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of tantalum carbide powder greater than or equal to 3.5, and preferably less than or equal to 11.5.

[0136] In one embodiment, particularly when WC is the only tungsten carbide introduced into the starting charge, and when the additive is introduced into the starting charge substantially exclusively in the form of niobium carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of niobium carbide powder greater than or equal to 8.1, and preferably less than or equal to 33, preferably less than or equal to 27.6, preferably less than or equal to 18.1.

[0137] In one embodiment, particularly when WC is the only tungsten carbide introduced into the starting charge, and when the additive is introduced into the starting charge substantially exclusively in the form of vanadium carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of vanadium carbide powder greater than or equal to 11.5, and preferably less than or equal to 30.4, preferably less than or equal to 24, preferably less than or equal to 16.4.

[0138] In one embodiment, particularly when WC is the only tungsten carbide introduced into the starting charge, and when the additive is introduced into the starting charge substantially exclusively in the form of zirconium carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of zirconium carbide powder greater than or equal to 10, and preferably less than or equal to 30.7, preferably less than or equal to 24, preferably less than or equal to 18.7.

[0139] In one embodiment, particularly when WC is the only tungsten carbide introduced in the starting charge, and when the additive is introduced in the starting charge substantially exclusively in the form of hafnium carbide powder, the starting charge has a mass ratio of the amount of WC powder to the amount of hafnium carbide powder greater than or equal to 7.4, and preferably less than or equal to 23.6, preferably less than or equal to 20, preferably less than or equal to 17.2. The WC content in the metal carbide bead(s) can be adjusted using the carbon content in the starting charge.To increase the WC content in the metal carbide(s) beads, the carbon content in the starting charge can be increased, for example by adding a carbon source, in particular carbon black powder, an organic compound in powder or liquid form, preferably with little or no oxygen, in particular sucrose.

[0140] To increase the W2C content and / or to decrease the free carbon content in the metal carbide(s) beads, one can add to the starting charge a metallic tungsten powder and / or a tungsten carbide powder with a higher oxygen content and / or a tungsten oxide powder.

[0141] The starting charge may include, in addition to the particulate mixture, a solvent, preferably water, the quantity of which is adapted to the shaping method of step b). The starting charge may also include a dispersant, a plasticizer, a surface tension modifier, a gelling agent, and / or an antifoaming agent. These additives, well known to those skilled in the art, are suitable for the shaping method used in step b).

[0142] In step b), any conventional shaping process known for the manufacture of sintered balls can be implemented.

[0143] Among these processes, we can mention:

[0144] - granulation processes, for example using granulators, fluidized bed granulators, or granulation discs,

[0145] - the atomization-drying processes of a slip,

[0146] - gelling processes,

[0147] - injection or extrusion molding processes, and

[0148] - pressing processes.

[0149] In one embodiment, steps a) and b) are at least partially coincident, particularly when a solvent is added progressively during shaping.

[0150] In a preferred embodiment, step b) does not involve pressing.

[0151] In step c), the raw beads are sintered in an inert atmosphere, for example in argon or nitrogen, or a reducing atmosphere, for example in an atmosphere of hydrogen and / or carbon monoxide, or under vacuum.

[0152] Preferably, sintering is carried out in an electric furnace, ideally at atmospheric pressure. As is well known, the duration and temperature of sintering allow adjustment of the apparent density of the resulting beads. It is also well known that applying pressure during sintering increases the apparent density of the resulting beads. As the examples below show, a small median size, however, allows the desired apparent density to be obtained by shaping and sintering at ambient pressure.

[0153] Preferably, the sintering time is greater than 0.5 hours and less than 10 hours.

[0154] In step c), sintering is carried out at a temperature above 1700°C, preferably above 1800°C, preferably above 1900°C and preferably below 2300°C.

[0155] After step c) of sintering, the resulting bead powder can undergo an optional particle size sorting step, for example by sieving and / or air separation, configured to obtain a particle size distribution suitable for the intended use. The bead powder can also undergo morphological sorting, notably using a spiral separator.

[0156] Powder of marbles

[0157] A powder of beads according to the invention is made up of beads of metallic carbide(s).

[0158] A said metallic carbide ball(s), preferably each metallic carbide ball(s), may in particular include one or more of the following optional characteristics:

[0159] - preferably C3 = 0.6*C7, preferably C3 = 0.7*C7, preferably C3 = 0.8*C7, preferably C3 = 0.9*C7;

[0160] - preferably C4 = 1.1 * C7;

[0161] - preferably, the oxygen O content is less than or equal to 0.85%, preferably less than or equal to 0.7%, preferably less than or equal to 0.5%, preferably less than or equal to 0.4%, preferably less than or equal to 0.2%, preferably less than or equal to 0.1%, as a percentage by mass based on the mass of the ball;

[0162] - preferably more than 70%, preferably more than 80%, preferably more than 85%, preferably more than 90%, preferably more than 95% of the crystallized phases are in the form of metallic carbide(s), as a percentage by mass based on the mass of the crystallized phases;

[0163] - in one embodiment, all the crystalline phases present are in the form of metallic carbide(s);

[0164] - in one embodiment, at least one metal carbide is a multiple metal carbide;

[0165] - at least a part of Ti, Ta, Nb, V, Zr and Hf is present in the form of a metallic carbide, said metallic carbide being a multiple metallic carbide;

[0166] - preferably more than 50%, preferably more than 60%, preferably more than 70%, preferably more than 80%, preferably more than 90%, preferably more than 95%, by mass of the additive, preferably of at least one of the elements Ti, Ta, Nb, V, Zr and Hf, preferably of each of the elements Ti, Ta, Nb, V, Zr and Hf, are in the form of carbide(s);

[0167] - preferably W > 64%, preferably W > 66%, preferably W > 68%, preferably W > 70%, preferably W > 71%, preferably W > 73%, preferably W > 77%, and preferably W < 92%, preferably W < 91%, preferably W < 90%, as percentages by mass based on the mass of the ball;

[0168] - preferably, C > 3%, and preferably C < 13.5%, preferably C < 11%, preferably C < 10%, preferably C < 9%, preferably C < 8%, as a percentage by mass based on the mass of the ball;

[0169] - preferably, Ti + Ta + Nb + V + Zr + Hf > 2.7%, preferably Ti + Ta + Nb + V + Zr + Hf > 3.0%, preferably Ti + Ta + Nb + V + Zr + Hf > 3.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 4.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 5.0%, and preferably Ti + Ta + Nb + V + Zr + Hf < 15.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 12.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 10.0%, as a percentage by mass based on the mass of the ball;

[0170] - preferably, W > 64%, preferably W > 66%, preferably W > 68%, preferably W > 70%, preferably W > 71%, preferably W > 73%, preferably W > 77%, and preferably W < 92%, preferably W < 91%, preferably W < 90% and C > 3%, and preferably C < 13.5%, preferably C < 11%, preferably C < 10%, preferably

[0171] C < 9%, preferably C < 8%, and Ti + Ta + Nb + V + Zr + Hf > 2.7%, preferably Ti + Ta + Nb + V + Zr + Hf > 3.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 4.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 5.0%, and preferably Ti + Ta + Nb + V + Zr + Hf < 15.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 12.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 10.0%, as percentages by mass based on the mass of the ball;

[0172] - in one embodiment, Nb > 1.5%, preferably Nb > 2.0%, as percentages by mass based on the mass of the ball;

[0173] - in one embodiment, Ta < 5.0%, preferably Ta < 4.0%, preferably

[0174] Ta < 3.0%, preferably Ta < 2.0%, preferably Ta < 1.0%, as percentages by mass based on the mass of the ball. Advantageously, this reduces the cost of the ball;

[0175] - in a preferred embodiment, the additive is Nb and Nb > 3.0%, preferably Nb > 4.5%, preferably Nb > 5.0%, and preferably Nb < 9.7%, preferably

[0176] Nb < 8.0%, as a percentage by mass based on the mass of the ball. Advantageously, the manufacture of the ball is facilitated, in particular when the niobium is supplied by a niobium carbide powder and the starting powders are ground or co-ground, a niobium carbide powder being easier to grind than carbide powders of other additives;

[0177] - the metallic carbide ball(s) has a sphericity greater than 0.90;

[0178] - in one embodiment, WC and W2C together represent more than 80% of the mass of all the crystallized phases of the ball.

[0179] In one embodiment, the metal carbide ball(s) comprises more than 1%, preferably more than 3%, preferably more than 5%, and less than 9%, preferably less than 7% of molybdenum Mo, as a percentage by mass based on the mass of the ball.

[0180] In one embodiment, the metal carbide ball(s) comprises at most 1%, preferably at most 0.5% of molybdenum Mo, as a percentage by mass based on the mass of the ball.

[0181] Cobalt and / or nickel and / or iron are generally used as metallic binders in the manufacture of sintered tungsten carbide balls and allow the sintering temperature to be lowered.

[0182] The wear generated during the use of these tungsten carbide balls results in the release of cobalt, nickel, and / or iron compounds. These compounds can cause pollution of the ground or homogenized material, and may also lead to hygiene and environmental problems. Similarly, hygiene and environmental issues can arise during the manufacturing of these balls.

[0183] Remarkably, the inventors found that very good performance is achieved in the aforementioned applications, even with very low quantities of Co, Ni, and Fe. These low quantities advantageously limit hygiene and environmental problems and / or pollution of the ground material.

[0184] Preferably,

[0185] - Co < 0.5%, preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%;

[0186] - Ni < 0.5%, preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%;

[0187] - Fe < 0.5% preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%;

[0188] - Co + Ni + Fe < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%.

[0189] A metal carbide ball(s), preferably each metal carbide ball(s) has an average grain size greater than or equal to 0.5 pm and / or less than or equal to 4 pm, preferably less than or equal to 3 pm, preferably less than or equal to 2 pm.

[0190] Preferably, a metal carbide ball(s), preferably each metal carbide ball(s) has a sphericity greater than 0.80, preferably greater than 0.85, preferably greater than 0.90, preferably greater than 0.92, preferably greater than 0.94, preferably greater than 0.95.

[0191] The powder beads preferably have a maximum size of less than 2 mm, preferably less than 1.5 mm, preferably less than 1 mm, preferably less than 800 pm.

[0192] The powder beads preferably have a median size D50 of less than 1.8 mm, preferably less than 1.5 mm, preferably less than 1 mm, preferably less than 600 µm, and / or preferably greater than 10 µm, preferably greater than 20 µm, preferably greater than 30 µm. Such median sizes are particularly well suited to dispersion applications in humid environments.

[0193] The powder of beads has a ratio (D 9D - Dw) / D5o preferably less than 0.5, preferably less than 0.4, preferably less than 0.3, preferably less than 0.2, preferably less than 0.1. Advantageously, the separation of the balls and the suspension to be ground is facilitated.

[0194] A powder of beads according to the invention may in particular have one or more of the following optional characteristics:

[0195] - C3 = 0.6*C7, preferably C3 = 0.7*C7, preferably C3 = 0.8*C7, preferably

[0196] C3 = 0.9*C7;

[0197] - C4 = 1.1*C7;

[0198] - the oxygen O content is less than or equal to 0.85%, preferably less than or equal to 0.7%, preferably less than or equal to 0.5%, preferably less than or equal to 0.4%, preferably less than or equal to 0.2%, preferably less than or equal to 0.1%, as a percentage by mass based on the mass of the powder of beads;

[0199] - more than 70%, preferably more than 80%, preferably more than 85%, preferably more than 90%, preferably more than 95% of the crystallized phases present are in the form of metallic carbide(s), as a percentage by mass based on the mass of the crystallized phases;

[0200] - in one embodiment, all the crystalline phases present are in the form of metallic carbide(s);

[0201] - in one embodiment, at least one metal carbide is a multiple metal carbide; - at least a portion of Ti, Ta, Nb, V, Zr and Hf is present in the form of a metal carbide, said metal carbide being a multiple metal carbide;

[0202] - preferably more than 50%, preferably more than 60%, preferably more than 70%, preferably more than 80%, preferably more than 90%, preferably more than 95%, by mass of the additive, preferably of at least one of the elements Ti, Ta, Nb, V, Zr and Hf, preferably of each of the elements Ti, Ta, Nb, V, Zr and Hf, are in the form of carbide(s);

[0203] - preferably W > 64%, preferably W > 66%, preferably W > 68%, preferably W > 70%, preferably W > 71%, preferably W > 73%, preferably W > 77%, and preferably W < 92%, preferably W < 91%, preferably W < 90%, as a percentage by mass based on the mass of the ball powder;

[0204] - preferably, C > 3%, and preferably C < 13.5%, preferably C < 11%, preferably C < 10%, preferably C < 9%, preferably C < 8%, as a percentage by mass based on the mass of the ball powder;

[0205] - preferably, Ti + Ta + Nb + V + Zr + Hf > 2.7%, preferably Ti + Ta + Nb + V + Zr + Hf > 3.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 4.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 5.0%, and preferably Ti + Ta + Nb + V + Zr + Hf < 15.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 12.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 10.0%, as a percentage by mass based on the mass of the ball powder;

[0206] - preferably, W > 64%, preferably W > 66%, preferably W > 68%, preferably W > 70%, preferably W > 71%, preferably W > 73%, preferably W > 77%, and preferably W < 92%, preferably W < 91%, preferably W < 90% and C > 3%, and preferably C < 13.5%, preferably C < 11%, preferably C < 10%, preferably C < 9%, preferably C < 8%, and Ti + Ta + Nb + V + Zr + Hf > 2.7%, preferably Ti + Ta + Nb + V + Zr + Hf > 3.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 4.5%, preferably Ti + Ta + Nb + V + Zr + Hf > 5.0%, and preferably Ti + Ta + Nb + V + Zr + Hf < 15.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 12.0%, preferably Ti + Ta + Nb + V + Zr + Hf < 10.0%, as a percentage by mass based on the mass of the ball powder;

[0207] - in one embodiment, Nb > 1.5%, preferably Nb > 2.0%, as percentages by mass based on the mass of the powder of beads;

[0208] - in one embodiment, Ta < 5.0%, preferably Ta < 4.0%, preferably

[0209] Ta < 3.0%, preferably Ta < 2.0%, preferably Ta < 1.0%, as percentages by mass based on the mass of the ball powder;

[0210] - in a preferred embodiment, the additive is Nb and Nb > 3.0%, preferably Nb > 4.5%, preferably Nb > 5.0%, and preferably Nb < 9.7%, preferably Nb < 8.0%, as a percentage by mass based on the mass of the powder of beads;

[0211] - the powder of metallic carbide(s) beads has a median sphericity greater than 0.80, preferably greater than 0.85, preferably greater than 0.90, preferably greater than 0.92, preferably greater than 0.94, preferably greater than 0.95, preferably greater than 0.97, preferably greater than 0.98. Advantageously, the energy required for grinding is reduced;

[0212] - in one embodiment, WC and W2C together represent more than 80% of the mass of all the crystallized phases;

[0213] - in one embodiment, the metal carbide bead powder comprises more than 1%, preferably more than 3%, preferably more than 5% and less than 9%, preferably less than 7% of molybdenum Mo, as a percentage by mass based on the mass of the bead powder;

[0214] - in one embodiment, the metal carbide bead powder comprises at most 1%, preferably at most 0.5% of molybdenum Mo, as a percentage by mass based on the mass of the bead powder;

[0215] - Co < 0.5%, preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%, as a percentage by mass based on the mass of the ball powder;

[0216] - Ni < 0.5% preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%, as a percentage by mass based on the mass of the ball powder;

[0217] - Fe < 0.5% preferably < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%, as a percentage by mass based on the mass of the powder of the balls;

[0218] - Co + Ni + Fe < 0.3%, preferably < 0.2%, preferably < 0.1%, preferably < 0.05%, as a percentage by mass based on the mass of the powder of the beads;

[0219] - the apparent density of the powdered beads is greater than or equal to 14.0 g / cm³ 3 , preferably greater than or equal to 14.3 g / cm² 3 , preferably greater than or equal to

[0220] 14.5 g / cm³ 3 ;

[0221] - the content of elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf is less than 2.5%, preferably less than 2%, preferably less than 1.5%, preferably less than 1%, as a percentage by mass based on the mass of the powder of beads;

[0222] - in one embodiment, particularly when a TiC powder is present in the starting charge in step b), the mass content of Ti is greater than 2.6%, preferably greater than 4.5%, preferably greater than 5.0%, and / or less than 15.0%, preferably less than 13.0%, preferably less than 12.0%, as a percentage by mass based on the mass of the bead powder;

[0223] - in one embodiment, particularly when TaC powder is present in the starting charge in step b), the mass content of Ta is greater than 2.6%, preferably greater than 5.0%, preferably greater than 7.5%, as a percentage by mass based on the mass of the powder of beads;

[0224] - in one embodiment, in particular when an NbC powder is present in the starting charge in step b), the mass content of Nb is greater than 2.6%, preferably greater than 3.0%, preferably greater than 4.5%, preferably greater than 5.0%, and / or less than 15.0%, preferably less than 13.0%, preferably less than 10.0%, preferably less than or equal to 9.7%, preferably less than or equal to 8.0%, as a percentage by mass based on the mass of the bead powder;

[0225] - in one embodiment, in particular when a VC powder is present in the starting charge in step b), the mass content of V is greater than 2.6%, preferably greater than 3.0%, preferably greater than 4.5%, preferably greater than 5.0%, and / or less than 15.0%, preferably less than 13.0%, preferably less than 10.0%, preferably less than 6.5%, as a percentage by mass based on the mass of the ball powder;

[0226] - in one embodiment, in particular when a ZrC powder is present in the starting charge in step b), the mass content of Zr is greater than 2.7%, preferably greater than 3.0%, preferably greater than 4.5%, preferably greater than 5.0%, and / or less than 15.0%, preferably less than 13.0%, preferably less than 10.0%, preferably less than 8.0%, as a percentage by mass based on the mass of the bead powder;

[0227] - in one embodiment, in particular when an HfC powder is present in the starting charge in step b), the mass content of Hf is greater than 2.6%, preferably greater than 3.0%, preferably greater than 3.7%, preferably greater than 5.0%, and / or less than 15.0%, preferably less than 13.0%, preferably less than 11.2%, as a percentage by mass based on the mass of the bead powder.

[0228] Applications

[0229] A powder of beads according to the invention is intended for grinding applications (called "microgrinding"), dispersion in wet media and surface treatment.

[0230] In a grinding application, the powdered beads can be suspended in a mixture of a solvent and the material to be ground. In such an application, the powdered beads can also be used in a dry environment.

[0231] The purpose of grinding is to reduce the particle size of a material to be ground, whether liquid or solid. Powdered pellets can be used, in particular, to grind organic matter, especially food.

[0232] In wet dispersion applications, the powder beads are suspended in a mixture of a solvent and the material to be dispersed. The purpose of dispersion is to homogenize a liquid or solid material to be dispersed, particularly a paint, ink, dye, magnetic lacquer, or agrochemical compound.

[0233] Surface treatment aims to modify the appearance and / or nature of a surface. For this purpose, dry powder beads are projected onto the surface, for example, a metallic surface. At the moment of projection, the speed of the beads is typically greater than 10 m / s, preferably greater than 20 m / s, preferably greater than 30 m / s, and preferably greater than 40 m / s.

[0234] Surface treatment can be implemented for cleaning purposes, for example for the removal of rust (descaling), to create compressive prestresses on the surface of a part ("shot-peening") or to modify the surface appearance of a part, including roughness, brightness or gloss ("cosmetic finishing").

[0235] In all these applications, to limit environmental impact and reduce costs, the marbles are typically recovered after use, sorted to remove broken pieces, and then reused.

[0236] Because the pieces of ball bearings are not spherical, they reduce efficiency. In particular, their projection can lead to damage to the part, or even cause it to break.

[0237] Furthermore, in all these applications, the powder must be very fluid. These applications are therefore quite different from those where the powder needs to be shaped, for example to form a part or a preform, as in additive manufacturing, specifically described in US2018 / 023668.

[0238] The following non-limiting examples are given for the purpose of illustrating the invention.

[0239] Measurement protocols

[0240] The following methods were used to determine certain properties of different sintered bead powders.

[0241] To determine the sphericity of a ball, the smallest and largest Feret diameters are measured using Zeiss Zen Core software, on an Axio Imager model microscope marketed by the Zeiss company.

[0242] The quantification of the elements present in the chemical composition of the sintered beads is carried out:

[0243] - for carbon, using a CS744 model carbon-sulfur analyzer marketed by the company LECO;

[0244] - for oxygen, using an ON836 model oxygen-nitrogen analyzer marketed by the company LECO;

[0245] - For boron and lithium, inductively coupled plasma (ICP) spectroscopy of a solution obtained using the following method is performed. The sintered beads to be analyzed are first calcined in air at 650°C for 4 hours. Then, 700 mg of these calcined beads are mixed with 3 g of sodium carbonate, and the mixture is heated to 950°C for 15 minutes. After cooling, the resulting mixture is added to 200 cm 3 of demineralized water and at 10 cm 3 of a 30 vol% hydrochloric acid solution, then the whole is heated to 200°C with stirring. The solution thus obtained is then filtered and made up to 500 ml with demineralized water in order to obtain the solution to be titrated by ICP;

[0246] - for elements other than boron, lithium, oxygen and carbon, by X-ray fluorescence on a bead obtained by melting a mixture of 5 g of lithium tetraborate and 500 mg of sintered beads to be analyzed which have previously undergone calcination under air at 650°C for 24 hours, the determination of element contents being carried out considering that said calcination has oxidized all the elements present in the beads to be analyzed and that said beads no longer contain carbon after said calcination.

[0247] The quantification of the crystallized phases present in the sintered beads of the examples is carried out directly on said beads, said beads being glued onto a self-adhesive carbon pellet, so that the surface of said pellet is covered to the maximum extent by beads.

[0248] The crystalline phases present in the sintered beads are measured by X-ray diffraction, for example, using a Panalytical X'Pert PRO diffractometer equipped with a copper DX tube. The diffraction pattern is acquired with this equipment over an angular range of 5° to 80°, with a step size of 0.017° and a counting time of 150 s / step. The front optics include a fixed 1 / 4° programmable divergence slit, 0.04 rad Soller slits, a 10 mm mask, and a fixed 1 / 2° anti-scattering slit. The sample is rotated to limit preferential orientations. The rear optics include a fixed 1 / 4° programmable anti-scattering slit, a 0.04 rad Soller slit, and a Ni filter.

[0249] The diffraction patterns were then qualitatively analyzed using EVA software and the PDF-5+ 2024 database. Once the phases present were identified, the diffraction patterns were quantitatively analyzed with GSAS-II software using Rietveld refinement according to the following classical protocol, for the example beads:

[0250] The Cl F files (Crystallographic Information Files) of the identified phases are imported to perform the refinement. These Cl F files can, for example, be obtained from the "Crystallography Open Database".

[0251] For each of the following steps, the following options are used for refinements: "Refinement type: analytic Hessian", "Max cycles: 10", "SVD zero tolerance: 1e-06",

[0252] - a refinement of the sample parameters "Histogram scale factor" and "Sample displacement" is carried out, then

[0253] - a refinement of the background signal is performed with the following choices: "background function: chebyschev-1", "Number of coeff" equal to 7, then

[0254] - a refinement of the mesh parameters is performed on the WC phase using the option

[0255] “Refine unit cell”, then

[0256] - a refinement of the roughness parameters "Surface roughness A" and "Surface roughness B" of the sample is carried out, then

[0257] - a refinement of the "microstrain" parameter of the WC phase is carried out.

[0258] Then, we fix the parameters resulting from the previous refinements, that is to say, we no longer let them vary freely.

[0259] Then, for each of the identified secondary phases (example 1: WB; examples 2 and 3: Nb and W multiple carbide), said secondary phase is taken into account in the refinement, and, for examples 2 and 3, the lattice parameter is manually adjusted so that the position of the simulated peaks of the Nb and W multiple carbide phase is sufficiently close to the experimental peaks so as not to diverge the refinement.

[0260] Then, we successively perform a refinement of the fraction of phases present, then a refinement of the "microstrain" parameter of the secondary phase, then a refinement of the mesh parameters of the secondary phase using the "Refine unit cell" option.

[0261] Then, we freeze the results from "Refine unit Cell" and "microstrain" and leave "scale factor" free.

[0262] Finally, assuming, for examples 2 and 3, that the element Nb is entirely contained in the multiple carbide of Nb and W, we refine the fraction of phases present by iteratively varying the relative proportion of Nb and W in said multiple carbide, until the mass percentage of Nb in the whole sample, determined from the refinement, corresponds to the mass percentage of Nb measured by chemical analysis, to within 0.1%.

[0263] The apparent density of the beads was determined on a powder of beads using a helium pycnometer (AccuPyc 1330 from Micromeritics®), according to the classical method based on measuring the volume of helium displaced.

[0264] Particle size analyses of the powders used in the starting charges were carried out using an LA-950 laser scattering particle size analyzer marketed by the company Horiba.

[0265] Particle size analysis of the metal carbide bead powders in the examples was performed on a sample of at least 500 beads using Zeiss Zen Core software on an Axio Imager microscope marketed by Zeiss, after converting the surface area of ​​each observed bead into a volume using the following formula: V = with S being the projected surface area of ​​the ball.

[0266] The average grain size of the sintered balls was measured using the Mean Linear Intercept method. A method of this type is described in ASTM E1382. According to this standard, analysis lines are drawn on images of the balls, and then, along each analysis line, the lengths, called "intercepts," are measured between two consecutive grain boundaries intersecting said analysis line.

[0267] We then determine the average length "I'" of the intercepts "I".

[0268] The average size "d" of the grains of the sintered beads of the powder is given by the relation: d = 1.56.1'. This formula is derived from formula (13) of "Average Grain Size in Polycrystalline Ceramics" MI Mendelson, J. Am. Cerm. Soc. Vol. 52, No. 8, pp 443-446.

[0269] To determine the break resistance of the beads, for each example, 300 g of beads (having passed through a square-mesh sieve with an opening of 106 microns, as described below) corresponding to the residue on a square-mesh sieve with an opening of 38 µm were projected, with recirculation, onto a surface to be treated made of XC65 steel, using a Venturi effect gun equipped with an 8 mm diameter projection nozzle, positioned 150 mm from the surface to be treated, with a projection angle of 85° and an overpressure of 2 bar. The projection continued for 10 minutes.

[0270] After processing, the beads, including bead fragments, were recovered and sieved again using a square-mesh sieve with an opening of 38 µm. The mass m1, in grams, of beads corresponding to the residue on the square-mesh sieve with an opening of 38 µm was determined. The break strength, R c , expressed as a mass percentage, is calculated according to the following formula: R c = 100 * m1 / 300.

[0271] To determine wear, a powder of each type of ball was sieved to retain the material retained on a 63 µm square mesh sieve and the material passing through an 80 µm square mesh sieve. It was then polished, in several batches, with a diamond suspension with a median particle size of 1 µm, for 12 hours in a Labstar mill marketed by NETZSCH, in a MiniPur configuration, rotating at 3250 rpm with a 0.2-liter chamber filled to 80% by volume with the balls to be polished. After polishing, the powder was dried and then sorted using a vibrating sorting table to remove non-spherical balls.Then, 365.5 ml (volume measured using a graduated cylinder) of the polished bead powder is weighed (mass mO) and introduced into the chamber of a NETZSCH Alpha® Lab laboratory bead mill equipped with a ceramic grinding chamber (CeramC) and a ceramic stirring shaft (CeramZ), as well as an open, gridless, dynamic selection system with separate drive for separating the ground beads (ZETA RS configuration). A suspension containing 1037 g of Nabalox® 684 alumina powder, marketed by Nabaltec, with a median particle size Dso of 1 µm, and 1555 ml of water is ground in recirculation at 2570 rpm for 2 hours with an average flow rate of 20 l / h.

[0272] The wear of the beads is then evaluated by measuring the amount of tungsten, titanium, tantalum, niobium, vanadium, zirconium, and hafnium, expressed as tungsten carbide WC, titanium carbide TiC, tantalum carbide TaC, niobium carbide NbC, zirconium carbide ZrC, and hafnium carbide HfC, respectively, in the ground alumina powder. These amounts are measured by X-ray fluorescence on a bead obtained by melting a mixture of 5 g of lithium tetraborate and 500 mg of the ground alumina powder, the ground alumina powder having previously undergone calcination in air at 650°C for 24 hours. It is considered that said calcination has resulted in the oxidation of all elements from the wear of the powder of beads of the examples present in the ground alumina powder, and that said ground alumina powder does not contain carbon after said calcination.

[0273] Let P be the total quantity WC + TiC + TaC + NbC + ZrC + HfC, expressed as a mass percentage based on the mass of the ground alumina powder.

[0274] Wear, U, expressed as a percentage, is equal to 100 * {P / [(100-P) * 1037]} / mO.

[0275] Manufacturing protocol The sintered beads in examples 1 to 3 were prepared from:

[0276] - of a tungsten carbide powder comprising more than 99% WC tungsten carbide and having a median size of 0.7 pm for examples 1 to 3,

[0277] - of a boron carbide powder, having an O content of 2.3%, a total carbon content of 21.8%, and a content of elements other than O, B and C of less than 0.4%, and having a median size of 0.4 pm for example 1,

[0278] - of a niobium carbide powder, for examples 2 and 3, obtained after grinding under the following conditions: an aqueous suspension containing 2400 g of niobium carbide powder marketed by the company HC Starck, having a median size Dso equal to 1.4 pm and 1720 ml of water is ground using ULTIMIL tungsten carbide balls marketed by the company Saint-Gobain Zirpro, having a median size equal to 2 pm, in a LabStar laboratory ball mill marketed by the company NETZSCH equipped with a grinding chamber and a NEIast polymer stirring shaft, in recirculation at 4220 rotations per minute for 4 hours with a peristaltic pump speed of 104 rotations per minute.After grinding and drying, the niobium carbide powder has an O content of 1.9%, a total carbon content of 10.2%, a tungsten content of 14%, and a content of elements other than O, Nb, W and C of less than 0.1%, and a median size of 0.4 pm.

[0279] - of a sucrose powder (D+) marketed by the company Sigma-Aldrich.

[0280] For each example, a mixture

[0281] - of carbide powders,

[0282] - of a sucrose powder (D+),

[0283] - demineralized water,

[0284] - of an aqueous solution of acetic acid with a concentration of 12 g / l,

[0285] - of an aqueous solution of poly(ethyleneimine) of average molar mass by weight, Mw, equal to 750,000 and of concentration equal to 29% by mass, in the quantities shown in the following table 1, is stirred in a paddle mixer for 1 hour in order to obtain a suspension.

[0286] [Table 1]

[0287] For each example, the viscosity of the suspension is then adjusted within a range between 10 Pa.s and 25 Pa.s, measured using an Anton Paar ViscoQC-300R viscometer, using an RH5 rotary vane at a rotation speed of 5 rpm, said viscosity being adjusted using an aqueous solution of ammonia NH4OH with a mass concentration of 10%.

[0288] This suspension is then shaped into beads by atomization-drying in a GEA Minor Mobile atomizer, in a hot air stream with an inlet temperature of 300°C and an outlet temperature of 110°C.

[0289] The formed beads are collected and sintered at 2250°C for a holding time of 4 hours under argon, with a heating and cooling rate of 300°C / h. After sintering, the sintered beads are sieved using a square-mesh sieve with an opening of 10⁶ µm, and the particle size fraction passing through the 10⁶ µm sieve is retained. Results

[0290] The results obtained are summarized in the following table 2.

[0291] [Table 2]

[0292] In Examples 2 and 3, at least some of the niobium is present in the form of a carbide, specifically as a niobium-tungsten multiple carbide, in amounts of 7% and 12%, respectively, by mass percentage based on the mass of the crystalline phases. The powder beads of Example 1, outside the scope of this invention, exhibit a wear U of 0.12% and a break resistance of 50%.

[0293] The powder in Example 2 exhibits a wear (U) of 0.31% and a break resistance of 84%, higher than the break resistance of the powder in Example 1 (68%). The powder in Example 3, according to the invention, exhibits a wear (U) of 0.18%, close to that of Example 1, and a break resistance of 83%, higher than the break resistance of the powder in Example 1 (66%). This Example 3 illustrates a good compromise between break resistance and wear.

[0294] As is now clear, the invention provides a powder of metallic carbide(s) beads exhibiting improved break resistance.

[0295] Of course, the present invention is not limited to the embodiments described, which are provided by way of illustrative and non-limiting examples.

Claims

DEMANDS 1. Use, in a grinding, wet dispersion or surface treatment application, of a sintered bead powder, said powder having: - a chemical composition such that, in mass percentages based on the mass of the powder of beads: - (77 - C4)% < W + Mo < (97.5 - C3)%, with Mo < 10%; - C1% < C < C2%; - 2.5% < additive < 20.0%, the additive denoting Ti + Ta + Nb + V + Zr + Hf; - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf, or "other elements": < 3%; with: - C1 = 100*(C3 / C5), - 02 = 100*(C4 / C6), - 03 = k*C7, with k chosen from 0.5, 0.6, 0.7, 0.8 and 0.9, - 04 = k'*C7, with k' chosen from 1.2 and 1.1 , - 05 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C3], - 06 = [m(W) + m(Mo) + m(Ti) + m(Ta) + m(Nb) + m(V) + m(Zr) + m(Hf) + C4], - 07 = M(C)*[(m(W) / M(W)) + (m(Mo) / M(Mo)) + (m(Ti) / M(Ti)) + (m(Ta) / M(Ta)) + (m(Nb) / M(Nb)) + (m(V) / M(V)) + (m(Zr) / M(Zr)) + (m(Hf) / M(Hf))], m(W), m(Mo), m(Ti), m(Ta), m(Nb), m(V), m(Zr) and m(Hf) being the mass, in grams, of the elements W, Mo, Ti, Ta, Nb, V, Zr and Hf, respectively, and M(W), M(Mo), M(Ti), M(Ta), M(Nb), M(V), M(Zr), M(Hf) and M(C) being the molar mass, in g / mol, of the elements W, Mo, Ti, Ta, Nb, V, Zr, Hf and C, respectively; - a crystallographic composition such that more than 60% of the crystallized phases present in said powder of beads are in the form of metallic carbide(s), as a percentage by mass based on the mass of the crystallized phases, said crystallized phases including at least one carbide of at least one element among Ti, Ta, Nb, V, Zr and Hf.

2. Use according to the preceding claim, wherein the content of the crystallized phases present in the form of metallic carbide(s) is greater than 80%, by mass percentage on the basis of the mass of the crystallized phases.

3. Use according to any one of the preceding claims, wherein said crystallographic composition is such that more than 50%, by mass percentage, of at least one of the elements Ti, Ta, Nb, V, Zr and Hf, is in the form of carbide(s).

4. Use according to any one of the preceding claims, wherein said chemical composition is such that 3.0% < Ti + Ta + Nb + V + Zr + Hf < 15.0%.

5. Use according to the immediately preceding claim, wherein said chemical composition is such that the additive is Nb and Nb > 3.0% and Nb < 9.7%.

6. Use according to claim 4, wherein said chemical composition is such that 5.0% < Ti + Ta + Nb + V + Zr + Hf < 10%.

7. Use according to any one of the preceding claims, wherein C3 = 0.5*C7 and C4 = 1.2*C7.

8. Use according to any one of claims 1 to 6, wherein C3 = 0.8*C7 and / or C4 = 1.1*C7.

9. Use according to any one of the preceding claims, wherein the oxygen O content in said bead powder is less than or equal to 0.85%.

10. Use according to the immediately preceding claim, wherein the oxygen O content in said bead powder is less than or equal to 0.1%.

11. Use according to any one of the preceding claims, wherein the average grain size of the sintered balls is greater than or equal to 0.1 pm and less than or equal to 4 pm.

12. Use according to any one of the preceding claims, wherein said powder of beads has an apparent density greater than or equal to 14.3 g / cm³ 3 13. Use according to any one of the preceding claims, wherein said chemical composition is such that: - W > 64% and W < 92%, and / or - C > 3% and C < 13.5%, and / or - Co < 0.3%, and / or - Ni < 0.3%, and / or - Fe < 0.3%, and / or - Co + Ni + Fe < 0.3%, and / or - Mo > 3% and Mo < 9%, and / or - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf < 2.5%.

14. Use according to the immediately preceding claim, wherein said chemical composition is such that: - W > 73% and W < 90%, and / or - C < 9%, and / or - Co + Ni + Fe < 0.05%, and / or - Mo > 5% and Mo < 7%, and / or - elements other than W, Mo, C, Ti, Ta, Nb, V, Zr, Hf < 1%.

15. Use according to any one of claims 1 to 12, wherein said chemical composition is such that the molybdenum content is less than or equal to 1%.

16. Use according to any one of the preceding claims, wherein said bead powder has a ratio (D 90 - Dw) / D5o less than 0.5, D5O, D, and D 90 designating the bead sizes corresponding to the percentages equal to 50%, 10%, and 90% by mass respectively, on the cumulative particle size distribution curve of the powder bead sizes, said bead sizes being classified in ascending order.

17. Use according to any one of the preceding claims, wherein said powder of beads has a median size D5Q less than 1.8 mm and greater than 10 pm.

18. Use according to any one of the preceding claims, wherein a particulate mixture comprising said powder of beads mixed with other particles is used, said other particles representing less than 10% by mass of the sum of the mass of said beads and said other particles.

19. Suspension comprising a powder of beads usable in a use according to any one of the preceding claims.

20. A manufacturing process comprising the following steps: a) preparing a starting charge such that the ball powder obtained at the end of step c) is a ball powder usable in an application according to any one of claims 1 to 18, b) shaping the starting charge into a powder of raw beads, c) sintering at a temperature above 1700°C to obtain a powder of sintered beads.

21. A process according to the immediately preceding claim, wherein the sintering temperature is greater than 1800°C.

22. A method according to any one of the two immediately preceding claims, wherein the sintering is carried out at atmospheric pressure.

23. A method according to any one of the three immediately preceding claims, wherein in step a), the starting charge comprises a particulate mixture consisting of WC powder and one or more powders of titanium carbide, tantalum carbide, niobium carbide, vanadium carbide, zirconium carbide, hafnium carbide, and optionally of carbon powder and / or molybdenum carbide powder and / or tungsten oxide powder, said powders being able to be replaced, at least partially, by precursor powders introduced in equivalent quantities, the median size of all the particles of said powders, preferably the median size of each said powder, being less than 2 pm 24. A method according to the immediately preceding claim, wherein the median size of all the particles of said powders in the starting charge, preferably the median size of each of said powders in the starting charge, is less than 1 pm.

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