Process for manufacturing granulated metal oxide powder and corresponding granulated metal oxide powder

Abstract

Process for manufacturing granulated metal oxide powder and corresponding granulated metal oxide powder. The manufacturing process comprises the following steps: obtaining an initial metal oxide powder, composed of particles of an oxide of a metal, by hydrolysis of a chloride of said metal; forming a suspension containing the initial metal oxide powder and an organic binder in suspension in a suspension medium; drying the suspension to obtain granulated metal oxide powder, composed of grains formed from agglomerates of particles of the initial metal oxide powder. Figure for the abstract: Figure 1

Description

Title of the invention: Method for manufacturing a granulated metal oxide powder and corresponding granulated metal oxide powder

[0001] The present invention relates to the field of manufacturing a metal oxide powder.

[0002] The metal oxide powder is for example a zirconium dioxide powder, a hafnium dioxide powder, a titanium oxide powder, a niobium oxide powder or an aluminum oxide powder.

[0003] Such metal oxide powders can be used, for example, for the manufacture of ceramics obtained by isostatic compression and sintering.

[0004] Such metal oxide powders can be used in all types of applications, for example in nuclear or medical applications, in particular for medical prostheses, targets for the production of thin layers by cathode sputtering or for the manufacture of parts by additive manufacturing.

[0005] Zirconium dioxide powder and hafnium dioxide powder are used, for example, in the nuclear field, for the manufacture of mechanical parts.

[0006] One of the aims of the invention is to propose a method for manufacturing a metal oxide powder making it possible to obtain a powder having properties facilitating its use for the manufacture of metal parts.

[0007] To this end, the invention proposes the manufacture of a granulated metal oxide powder, in particular a granulated zirconium oxide powder or a granulated hafnium oxide powder, the manufacturing method comprising the following steps: - obtaining an initial metal oxide powder, composed of particles of an oxide of a metal, by hydrolysis of a chloride of said metal; - formation of a suspension containing the initial metal oxide powder and an organic binder suspended in a suspension medium; - drying the suspension so as to obtain granulated metal oxide powder, composed of grains formed from agglomerates of particles of the initial metal oxide powder.

[0008] The initial metal oxide powder obtained by hydrolysis of a metal chloride has particles with a small median diameter, with desired properties, for example a particular crystalline structure of the metal oxide.

[0009] The formation of the suspension and the drying, preferably by atomization, make it possible to obtain a granulated metal oxide powder formed from grains having a median diameter strictly greater than that of the particles of the initial metal oxide powder, while preserving other characteristics of the particles of the granulated metal oxide powder, such as the crystalline structure of the metal oxide, the chemical purity of the metal oxide or the specific surface area of ​​the granulated metal oxide powder.

[0010] The granulated metal oxide powder thus has flow characteristics different from those of the initial metal oxide powder, which allows the use of the granulated metal oxide powder in different manufacturing processes.

[0011] According to particular embodiments, the manufacturing method comprises one or more of the following optional characteristics, taken individually or in all technically possible combinations:

[0012] - the hydrolysis of the metal chloride is carried out from the metal chloride in vapor phase and / or water vapor phase;

[0013] - the drying step is carried out by atomization of the suspension;

[0014] - the suspension medium is water;

[0015] - the organic binder is chosen from polyethylene glycol (PEG), poly- alcohol vinyl (PVA), starch and stearic acid;

[0016] - the manufacturing process comprises a step of calcining the oxide powder granulated metallic;

[0017] - the median diameter of the particles of the initial metal oxide powder is equal or less than 1 pm;

[0018] - the median diameter of the grains of the granulated metal oxide powder is equal to or greater than 5 pm, in particular equal to or greater than 10 pm, even more in particular equal to or greater than 15 pm;

[0019] - the granulated metal oxide powder has a compressibility equal to or less than 25%, in particular a compressibility equal to or less than 20%;

[0020] - the metal is zirconium, the granulated metal oxide powder obtained being a granulated zirconium dioxide powder;

[0021] - the metal is hafnium, the metal oxide powder obtained being a powder of granulated hafnium dioxide.

[0022] The invention also relates to a granulated metal oxide powder, in particular a granulated zirconium oxide powder or a granulated hafnium oxide powder, obtained or capable of being obtained by a process as defined above.

[0023] In one embodiment, the granulated metal oxide powder comprises grains formed from agglomerates of oxide particles of a metal, the median diameter of the grains being equal to or greater than 5 μm, in particular equal to or greater than 10 μm, the median diameter of the grains being equal to or less than 70 pm, in particular equal to or less than 60 pm and / or 90% of the grains having a diameter equal to or less than 115 pm.

[0024] In one embodiment, the metal is zirconium or hafnium.

[0025] The invention and its advantages will be better understood upon reading the description which will follow, given solely as a non-limiting example, and made with reference to the attached drawings, in which:

[0026] - [Fig.l] [Fig.l] is a diagram illustrating steps of a manufacturing process granulated metal oxide powder;

[0027] - [Fig.2] [Fig.2] is a block diagram illustrating an installation for the implementation implementation of the granulated metal powder manufacturing process.

[0028] As illustrated in [Fig.l], the manufacturing method comprises:

[0029] - a step E1 of obtaining an initial metal oxide powder, composed of particles of an oxide of a metal, by hydrolysis of a chloride of said metal,

[0030] - a step E2 of forming a suspension containing the oxide powder me initial metal and an organic binder suspended in a suspension medium,

[0031] - a step E3 of drying the suspension so as to obtain powder granulated metal oxide, and,

[0032] - optionally, a step E4 of calcination of the metal oxide powder granulated.

[0033] During step E1, the metal chloride is placed in the presence of water with which it reacts chemically to give, on the one hand, the oxide of said metal and, on the other hand, hydrochloric acid.

[0034] Hydrolysis of metal chloride is carried out with metal chloride in the vapor phase (in the vapor state) and with water in the vapor phase (in the vapor state).

[0035] Thus, in a particular implementation example, the hydrolysis of the metal chloride is preferably carried out by bringing the metal chloride vapor into contact with water vapor.

[0036] At the end of the hydrolysis, the initial metal oxide powder is obtained which is formed from particles of the metal oxide.

[0037] Advantageously, the hydrolysis is carried out so as to obtain an initial “submicronic” metal oxide powder, i.e. the particles of which have a median diameter equal to or less than 1 μm.

[0038] The median diameter of the particles of a powder is measured for example by gravity decantation technique in water and measurement of concentration over time by attenuation of a light beam (for example using a measuring device of the SEDIGRAPH brand) or by sedimentation under centrifugal field with measurement of concentration over time of a blue light laser beam or red (for example using a measuring device from the LUMISIZER brand).

[0039] Preferably, the hydrolysis is carried out at a temperature between 300°C and 700°C, with a ratio between the water flow rate and the metal chloride flow rate at least equal to the stoichiometric ratio and / or a residence time in the hydrolysis reactor which is between 5 seconds and 60 seconds, preferably between 10 seconds and 30 seconds.

[0040] The metal oxide of the metal oxide powder preferably has a monoclinic and tetragonal crystalline morphology, the ratio between these two crystalline structures being able to vary depending on the parameters used for implementing the method.

[0041] The metal is in particular zirconium, in which case the initial metal oxide powder is a zirconium oxide powder, in particular a zirconium dioxide (or zirconia) powder, or hafnium, in which case the initial metal oxide powder is a hafnium oxide powder, in particular a hafnium dioxide (or hafnone) powder.

[0042] During step E2, a suspension containing the initial metal oxide powder and an organic binder suspended in a suspension medium is formed.

[0043] The suspension medium is for example water.

[0044] The organic binder is for example chosen from polyethylene glycol (PEG), polyvinyl alcohol (PVA), starch and stearic acid. Such organic binders can be removed subsequently, for example by calcination.

[0045] Advantageously, the suspension comprises from 20 to 70% by mass of initial metal oxide powder and the ratio of the mass of organic binder to the mass of metal oxide powder is between 1 and 5%.

[0046] The suspension is formed for example by mixing the metal oxide powder with a solution containing the organic binder and the suspending medium.

[0047] In a particular embodiment, the suspension medium is water. The suspension obtained at the end of step E2 is a solution of the organic binder in water containing the metal oxide powder suspended in the solution.

[0048] During step E3, the suspension obtained at the end of step E2 is dried so as to obtain the granulated metal oxide powder.

[0049] Drying is carried out in a drying device or dryer.

[0050] Drying is carried out in such a way as to remove the suspending medium, in particular so as to evaporate the suspending medium. In particular, when the suspending medium is water, the drying is carried out in such a way that the water evaporates.

[0051] The presence of the organic binder in the suspension makes it possible to obtain granulation of the metal oxide powder, i.e. agglomeration of the particles of the initial metal oxide powder to obtain grains larger than the particles.

[0052] Drying is carried out for example by atomization of the suspension.

[0053] Atomizing the suspension comprises spraying the suspension in the form of droplets into a hot gas stream, particularly into a hot air stream.

[0054] This makes it possible to evaporate the suspension medium and to recover the granulated metal oxide powder. The spraying is carried out, for example, in an atomization chamber.

[0055] Atomizing the suspension preferably comprises separating the granulated metal oxide powder from the gas stream formed from the hot air and the evaporated suspension medium.

[0056] This allows the granulated metal oxide powder to be recovered. The separation is carried out in a separator, for example in a cyclone effect separator.

[0057] In an exemplary implementation, the median diameter of the grains of the granulated metal oxide powder is equal to or greater than 5 μm, in particular equal to or greater than 10 μm, the median diameter of the grains of the granulated metal oxide powder is equal to or less than 70 μm, in particular equal to or less than 60 μm and / or at least 90% of the grains of the granulated metal oxide powder have a diameter equal to or less than 115 μm.

[0058] In granulometry, the median diameter is also noted D50 and the diameter of at least 90% of the grains is noted D90.

[0059] The metal oxide powder may possibly contain residues of hydrogen, chlorine and carbon resulting from the various steps carried out previously.

[0060] In the case of spray drying, the spraying is carried out in the dryer using at least one sprayer or spraying member, preferably chosen from a spray nozzle, a two-fluid nozzle or a spray turbine. Preferably, the outlet temperature of the dryer is adjusted to obtain a sufficiently low humidity, preferably between 80°C and 150°C.

[0061] Preferably, the inlet temperature of the dryer is adjusted according to the flow rate of water to be evaporated, preferably between 150°C and 300°C.

[0062] In the case of spray drying, the spraying conditions depend on the rheology of the suspension and the type of sprayer (spray nozzle, bifluid nozzle, spray turbine).

[0063] The optional implementation of calcination step E4 makes it possible to eliminate at least in part, and possibly completely, such residues.

[0064] Calcination consists of bringing the powder to a high temperature in a calcination furnace.

[0065] The calcination step can also change the crystal structure of the metal oxide powder.

[0066] The calcination step also makes it possible to control the morphology of the grains and the particle size distribution, which is narrower (lower dispersion of grain size).

[0067] The calcination step is preferably carried out at a temperature between 600 and 1300°C and / or for a duration between 1 h and 3 h, in particular when the metal considered is hafnium.

[0068] Optionally, the manufacturing method comprises a sieving step carried out after the drying step E3. If a calcination step E4 is provided, the sieving step is carried out before or after the calcination step E4. Such a sieving step makes it possible to eliminate the largest grains.

[0069] Thanks to the manufacturing process, the grains of the granulated metal oxide powder are mainly formed from an agglomerate of particles of the initial metal oxide powder, bound together by the organic binder.

[0070] As a result, the grains of the granulated metal oxide powder and the particles of the initial metal oxide powder have in particular the same chemical purity and the same crystalline structure of the metal oxide, the granulated metal oxide powder having a particle size greater than that of the initial metal oxide powder, which modifies the properties of the granulated metal oxide powder compared to the initial metal oxide powder.

[0071] The granulated metal oxide powder has characteristics different from those of the initial (non-granulated) metal oxide powder, in particular due to the grain size of the granulated metal oxide powder being greater than the particle size of the initial metal oxide powder.

[0072] The granulated metal oxide powder has in particular an apparent density and flow properties different from those of the initial metal oxide powder obtained at the end of step E1, i.e. at the end of the hydrolysis.

[0073] In particular, the granulated metal oxide powder has a compressibility (or Carr index) greater than that of the initial non-granulated metal oxide powder resulting from step E1, i.e. at the end of the hydrolysis.

[0074] The compressibility (or Carr index) of a powder is the percentage variation between the packed density of the powder and the unpacked density of the powder relative to the packed density of the powder.

[0075] The unpacked density and the packed density of a powder are measured in a known manner, for example using a device of the DENSITAP brand.

[0076] The lower the compressibility, the higher the flowability.

[0077] Preferably, the granulated metal oxide powder has a compressibility equal to or less than 25%, in particular a compressibility equal to or less than 20%.

[0078] In a first example, a zirconium dioxide powder (or zirconium dioxide powder) zirconia) was obtained according to the manufacturing process, using the parameters indicated below.

[0079] The hydrolysis was carried out in a hydrolysis reactor with an hourly mass flow rate of zirconium chloride (ZrCl4) of 19 kg / h, an hourly mass flow rate of water vapor of 3 kg / h and at a temperature of 500 °C.

[0080] The suspension was made by mixing the zirconia powder obtained from the hydrolysis with an aqueous solution of polyethylene glycol (PEG), such that the suspension contains by mass 60% zirconia powder and 40% aqueous solution.

[0081] In such an aqueous solution, the suspending medium is water and the organic binder is PEG.

[0082] The PEG content of the aqueous solution is chosen such that, in the suspension obtained, the ratio of the mass of PEG to the mass of zirconia powder is 3%.

[0083] Drying was carried out by spray drying in a 17.78 cm diameter (7 in) turbine atomizer and a 2.5 m diameter dryer, with an inlet temperature of 300°C and an outlet temperature of 130°C. The residual moisture content of the granulated zirconium dioxide powder after spray drying was less than 0.1%.

[0084] This process has been implemented on a pilot installation and on an industrial installation, the latter making it possible to achieve higher particle sizes.

[0085] The initial zirconium dioxide powder and the granulated zirconium dioxide powder were analyzed to verify that the initial zirconium dioxide powder particles and the grains of the granulated zirconium dioxide powder have substantially the same chemical purity and the same crystalline structure in the absence of or prior to the calcination step.

[0086] The median diameter, untapped density, and tapped density of each of the initial zirconium dioxide powder and the granulated zirconium dioxide powder were measured, and the compressibilities of the initial zirconium dioxide powder and the granulated zirconium dioxide powder were calculated.

[0087] Table 1 below shows the results.

[0088] [Tableauxl] Zirconia powder Median diameter (pm) Unpacked density Packed density Compressibility (%) Before granulation 0.3 0.43 0.62 30 After granulation on a pilot plant 15 0.96 1.18 19 After granulation on an industrial plant 30 1.06 1.29 18

[0089] It appears that the granulated zirconium dioxide powder has a lower compressibility than that of the initial zirconium dioxide powder, and therefore a higher flowability.

[0090] Furthermore, for a spray-dried granulated zirconia powder, production on an industrial installation makes it possible to obtain a higher particle size than on a pilot installation.

[0091] In a second example, a hafnium dioxide powder (or hafnone powder) was obtained according to the manufacturing process, using the following parameters

[0092] The hydrolysis was carried out in a hydrolysis reactor with an hourly mass flow rate of hafnium chloride (HfCl4) of 26 kg / h, an hourly mass flow rate of water vapor of 3 kg / h and at a temperature of 500 °C.

[0093] The suspension was made by mixing the hafnone powder obtained from the hydrolysis with an aqueous solution of water and polyethylene glycol (PEG) containing by mass 60% hafnone powder and 40% aqueous solution.

[0094] The PEG content of the aqueous solution is chosen such that in the suspension obtained, the ratio of the mass of PEG to the mass of hafnone powder is 3%.

[0095] Drying was carried out by spray drying with an inlet temperature of 300°C and an outlet temperature of 120°C. The residual moisture content of the granulated zirconium dioxide powder after spray drying was less than 0.1%.

[0096] This process was implemented on a pilot installation.

[0097] The initial hafnium dioxide powder and the granulated hafnium dioxide powder were analyzed to verify that the hafnium dioxide grains have substantially the same chemical purity, crystal structure and size.

[0098] The median diameter, untapped density, and tapped density of each of the initial hafnium dioxide powder and the granulated hafnium dioxide powder were measured, and the compressibilities of the initial hafnium dioxide powder and the granulated hafnium dioxide powder were calculated.

[0099] Table 2 below shows the results.

[0100] [Tables2] Hafnone Powder Median Diameter (pm) Untapped Density Tapped Density Compressibility (%) Before Granulation 0.3 0.68 0.97 30 After Granulation 15 1.25 1.57 20

[0101] It appears that the granulated hafnium dioxide powder has a lower compressibility than that of the initial hafnium dioxide powder, and therefore a higher flowability.

[0102] As illustrated in [Fig.2], an installation 2 for implementing the manufacturing method comprises, for example, a hydrolysis reactor 4, a mixing reactor 6, a dryer 8 and, optionally, a calcination furnace 10.

[0103] The hydrolysis step E1 is carried out in the hydrolysis reactor 4. The hydrolysis reactor 4 comprises a hydrolysis chamber 12 which receives the chloride of the metal CM and the water H2O, preferably in the form of water vapor.

[0104] The hydrolysis reactor 4 provides on the one hand the initial metal oxide powder PI and hydrochloric acid HCl.

[0105] The hydrolysis reactor 4 is for example provided, at an outlet of the hydrolysis enclosure 12, with a separator 14, in particular a cyclone effect separator, for separating the initial metal oxide powder from the hydrochloric acid.

[0106] As an alternative or in addition to the separator 14, the hydrolysis reactor is equipped with a bag filter (not shown) to separate the initial metal oxide powder from the hydrochloric acid.

[0107] The suspension step E2 is implemented for example in the mixing reactor 6. The mixing reactor 6 comprises for example a mixing enclosure 16 for receiving the elements to be mixed, namely the suspension medium MS, the organic binder L and the initial metal oxide powder PI, the mixing being carried out in the mixing enclosure 16.

[0108] The mixing reactor 6 provides the suspension S comprising the organic binder L and the initial metal oxide powder PI suspended in the suspension medium MS

[0109] The mixing reactor 6 optionally comprises an agitator device 18 configured to agitate the contents of the mixing chamber 16.

[0110] The drying step E3 is implemented for example in the dryer 8.

[0111] The dryer 8 is for example configured to carry out drying by atomization.

[0112] The dryer 8 comprises an atomization enclosure 20 having a hot gas inlet 22 for injecting a hot gas flow FG into the atomization enclosure 20, in particular a hot air flow, and a spraying member 24 for spraying the suspension S into the hot gas flow.

[0113] The spraying member 24 is for example a spraying nozzle 24. Alternatively, it is a two-fluid nozzle or a spraying turbine.

[0114] The dryer 8 preferably comprises a separator 26 arranged at an outlet of the atomization enclosure 20 to separate, on the one hand, the granulated metal oxide powder PG resulting from the drying, and on the other hand, the gas flow containing the hot gas flow FG and the evaporated suspension medium MS. The separation 26 is for example a cyclone effect separator or a filter, in particular a bag filter.

[0115] The optional calcination step E4 is carried out in the calcination furnace 10, which receives and heats the granulated metal oxide powder PG obtained at the end of step E3.

[0116] The calcination furnace 10 is for example a rotary furnace or a tunnel furnace.

[0117] When a screening step (optional) is implemented, after drying (if applicable before or after calcination) the installation comprises a screening device (not shown).

[0118] Thanks to the invention, it is possible to obtain a granulated metal oxide powder which preserves certain of the characteristics of the initial non-granulated metal oxide powder obtained by hydrolysis of a chloride of the metal in question, in particular the crystalline structure of the metal oxide, the chemical purity of the metal oxide and the specific surface area of ​​the powder, while modifying other characteristics, in particular by reducing the compressibility of the granulated metal oxide powder compared to the initial (non-granulated) metal oxide powder.

[0119] The preservation of certain characteristics while improving other characteristics, in particular compressibility, makes it possible to use the metal oxide powder for the manufacture of the same parts, but with different manufacturing processes, in particular manufacturing processes requiring good flowability of the metal oxide powder.

[0120] For example, good flowability of the metal oxide powder is favorable to its use for the production of mechanical parts by additive manufacturing.

[0121] Carrying out spray drying is the preferred method because such drying makes it easier to handle the metal oxide powder, which is very fine and has a very low density (typically a density of less than 300 kg / m3) because it is integrated into a liquid suspension.

[0122] Carrying out spray drying makes it possible to generate regular agglomerates (close to spherical grains) and a narrow particle size distribution that is easily adjustable by adjusting spray drying parameters, such as the rotation speed of the turbine, if the spray drying is carried out using a turbine, or the inlet pressure of a spray nozzle, if the spray drying is carried out using a spray nozzle.

[0123] Other granulation processes, such as a granulation process using a fluidized bed or a mixer, would pose problems with non-granulated metal oxide powder, such non-granulated metal oxide powder being difficult to "fluidiz" and / or requiring very large volumes of equipment due to its low density.

[0124] Such granulation processes can generate more irregular agglomerates and a more spread particle size distribution than what is obtained with the spray drying process.

Claims

Claims

1. A method of manufacturing a granulated metal oxide powder, the manufacturing method comprising the following steps: - obtaining an initial metal oxide powder, composed of particles of an oxide of a metal, by hydrolysis of a chloride of said metal; - forming a suspension containing the initial metal oxide powder and an organic binder suspended in a suspension medium; - drying the suspension so as to obtain granulated metal oxide powder, composed of grains formed from agglomerates of particles of the initial metal oxide powder, wherein the hydrolysis of the metal chloride is carried out from the metal chloride in the vapor phase and / or water in the vapor phase.

2. A manufacturing method according to claim 1, wherein the drying step is carried out by atomizing the suspension.

3. A manufacturing method according to claim 1 or claim 2, wherein the suspending medium is water.

4. A manufacturing method according to any preceding claim, wherein the organic binder is selected from polyethylene glycol (PEG), polyvinyl alcohol (PVA), starch and stearic acid.

5. A manufacturing method according to any preceding claim, comprising a step of calcining the granulated metal oxide powder.

6. A manufacturing method according to any preceding claim, wherein the median particle diameter of the initial metal oxide powder is equal to or less than 1 pm.

7. A manufacturing method according to any preceding claim, wherein the metal is zirconium, the resulting granulated metal oxide powder being granulated zirconium dioxide powder.

8. A manufacturing method according to any one of claims 1 to 6, wherein the metal is hafnium, the metal oxide powder obtained as a granulated hafnium dioxide powder.

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