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Definitions

• the present invention relates to the field of the manufacture of a metal oxide powder.
• 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.
• Such metal oxide powders can be used, for example, for the manufacture of ceramics obtained by isostatic compression and sintering.
• Such metal oxide powders can be used in all types of application, for example in nuclear or medical applications, in particular for medical prostheses, targets for the production of thin layers by sputtering or for the manufacture of parts by additive manufacturing
• Zirconium dioxide powder and hafnium dioxide powder are used, for example, in the nuclear field, for the manufacture of mechanical parts.
• One of the aims of the invention is to propose a process for the manufacture of a metal oxide powder making it possible to obtain a powder having properties facilitating its use for the manufacture of metal parts.
• the invention proposes a process for manufacturing a granulated metal oxide powder, in particular a granulated zirconium oxide powder or a granulated hafnium oxide powder, the manufacturing process comprising the steps following:
• 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.
• the formation of the suspension and the drying make it possible to obtain a granulated metal oxide powder formed of 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.
• the granulated metal oxide powder thus has different flow characteristics from those of the initial metal oxide powder, which allows the use of the granulated metal oxide powder in different manufacturing processes.
• the manufacturing process includes one or more of the following optional characteristics, taken individually or according to all the technically possible combinations:
• the hydrolysis of the metal chloride is carried out using metal chloride in the vapor phase and/or water in the vapor phase;
• the drying step is carried out by atomization of the suspension
• the suspending medium is water
• the organic binder is chosen from polyethylene glycol (PEG), polyvinyl alcohol (PVA), starch and stearic acid;
• the manufacturing process includes a step of calcining the granulated metal oxide powder
• the median particle diameter of the initial metal oxide powder is equal to or less than 1 ⁇ m
• the median diameter of the grains of the granulated metal oxide powder is equal to or greater than 5 ⁇ m, in particular equal to or greater than 10 ⁇ m, even more in particular equal to or greater than 15 ⁇ m;
• the granulated metal oxide powder has a compressibility equal to or less than 25%, in particular a compressibility equal to or less than 20%;
• the metal is zirconium, the granulated metal oxide powder obtained being a granulated zirconium dioxide powder;
• the metal is hafnium, the metal oxide powder obtained being a granulated hafnium dioxide powder.
• 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. .
• 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 ⁇ m, in particular equal to or greater than 10 ⁇ m, the median diameter of the grains being equal to or less than 70 ⁇ m, in particular equal to or less than 60 ⁇ m and/or 90% of the grains having an equal diameter or less than 115 pm.
• the metal is zirconium or hafnium.
• FIG. 1 is a diagram illustrating the steps of a process for manufacturing granulated metal oxide powder
• FIG. 2 is a block diagram illustrating an installation for the implementation of the process for manufacturing granulated metal powder.
• the manufacturing process includes:
• step E2 for forming a suspension containing the initial metal oxide powder and an organic binder in suspension in a suspension medium
• step E4 of calcining the granulated metal oxide powder optionally, a step E4 of calcining the granulated metal oxide powder.
• 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. .
• the hydrolysis of the 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).
• the hydrolysis of the metal chloride is preferably carried out by bringing the metal chloride vapor into contact with water vapour.
• the initial metal oxide powder is obtained, which is formed of particles of the metal oxide.
• 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 ⁇ m.
• the median diameter of the particles of a powder is measured for example by gravity settling technique in water and measurement of concentration over time by attenuation of a beam of light (for example using a device of SEDIGRAPH brand measurement) or by sedimentation under a centrifugal field with concentration measurement over time of a blue or red light laser beam (for example using a LUMISIZER brand measuring device).
• the hydrolysis is carried out at a temperature of 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.
• the metal oxide of the metal oxide powder preferably has a monoclinic and tetragonal (or quadratic) crystalline morphology, the ratio between these two crystalline structures being able to vary according to the parameters used for the implementation of the process.
• the metal is in particular zirconium, in which case the initial metal oxide powder is a powder of zirconium oxide, in particular a powder of zirconium dioxide (or zirconia), or hafnium, in which case the powder of The initial metal oxide is a powder of hafnium oxide, in particular a powder of hafnium dioxide (or hafnone).
• step E2 a suspension containing the initial metal oxide powder and an organic binder suspended in a suspension medium is formed.
• the suspension medium is for example water.
• the organic binder is for example chosen from polyethylene glycol (PEG), polyvinyl alcohol (PVA), starch and stearic acid. Such organic binders can be eliminated subsequently, for example by calcination.
• 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%.
• the suspension is formed, for example, by mixing the metal oxide powder with a solution containing the organic binder and the suspension medium.
• the suspending 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 in suspension in the solution.
• step E3 the suspension obtained at the end of step E2 is dried so as to obtain the granulated metal oxide powder.
• the drying is carried out in a drying device or drier.
• the drying is carried out in such a way as to remove the suspension medium, in particular in such a way as to evaporate the suspension medium.
• the suspension medium is water
• the drying is carried out in such a way that the water evaporates.
• the presence of the organic binder in the suspension makes it possible to obtain a granulation of the metal oxide powder, i.e. an agglomeration of the particles of the initial metal oxide powder to obtain grains larger than the particles.
• the drying is carried out for example by atomization of the suspension.
• Slurry atomization includes spraying the slurry as droplets into a hot gas stream, especially a hot air stream.
• the spraying is carried out for example in an atomization enclosure.
• the slurry atomization preferably includes the separation of the granulated metal oxide powder and the gas stream formed from the hot air and the evaporated slurry medium.
• the separation is carried out in a separator, for example in a cyclone effect separator.
• the median diameter of the grains of the granulated metal oxide powder is equal to or greater than 5 ⁇ m, in particular equal to or greater than 10 ⁇ m, the median diameter of the grains of the metal oxide powder granulated is equal to or less than 70 ⁇ m, in particular equal to or less than 60 ⁇ m and/or at least 90% of the grains of the granulated metal oxide powder have a diameter equal to or less than 115 ⁇ m.
• DXX designates the diameter such that at least XX% of the grains of the powder have a diameter equal to or less than DXX. It is common to measure the D10 diameter, the D50 diameter, also called the median diameter, and the D90 diameter.
• the metal oxide powder may possibly contain residues of hydrogen, chlorine and carbon resulting from the various steps carried out previously.
• 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.
• the outlet temperature of the dryer is adjusted to obtain a sufficiently low humidity, preferably between 80°C and 150°C.
• the inlet temperature of the dryer is adjusted according to the flow of water to be evaporated, preferably between 150°C and 300°C.
• the spraying conditions depend on the rheology of the suspension and the type of sprayer (spray nozzle, bifluid nozzle, spray turbine).
• Calcining consists of bringing the powder to a high temperature in a calcining oven.
• the calcination step can also change the crystal structure of the metal oxide powder.
• the calcination step also makes it possible to control the morphology of the grains and the particle size distribution, which is tighter (lower grain size dispersion).
• the calcination step is preferably carried out at a temperature of between 600 and 1300° C. and/or for a period of between 1 h and 3 h, in particular when the metal considered is hafnium.
• the manufacturing process includes a sieving step carried out after the drying step E3. If a calcination step E4 is planned, the sieving step is carried out before or after the calcination step E4. Such a sieving step eliminates the largest grains.
• 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.
• 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 with respect to the initial metal oxide powder.
• the granulated metal oxide powder has characteristics different from those of the initial (non-granulated) metal oxide powder, in particular due to the size of the grains of the granulated metal oxide powder greater than the size of the particles of the initial metal oxide powder.
• the granulated metal oxide powder has in particular a bulk density and flow properties different from those of the initial metal oxide powder obtained at the end of step E1, ie at the end of the hydrolysis .
• the granulated metal oxide powder has a compressibility (or Carr's index) greater than that of the initial non-granulated metal oxide powder resulting from step E1, i.e. at the end of the hydrolysis.
• the compressibility (or Carr's index) of a powder is the percentage variation between the packed density of the powder and the unpacked density of the powder compared to the packed density of the powder.
• the unpacked density and the packed density of a powder is measured in a known manner, for example using a DENSITAP brand device.
• the granulated metal oxide powder has a compressibility equal to or less than 25%, in particular a compressibility equal to or less than 20%.
• a powder of zirconium dioxide (or zirconia powder) was obtained according to the manufacturing process, using the parameters indicated below.
• the hydrolysis was carried out in a hydrolysis reactor with an hourly mass flow rate of zirconium chloride (ZrCL) of 19 kg/h, an hourly mass flow rate of water vapor of 3 kg/h and at a temperature of 500 °C.
• ZrCL zirconium chloride
• the suspension was produced by mixing the zirconia powder obtained at the end of the hydrolysis with an aqueous solution of polyethylene glycol (PEG), in such a way that the suspension contains by mass 60% zirconia powder and 40% aqueous solution.
• PEG polyethylene glycol
• the suspension medium is water and the organic binder is PEG.
• 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%.
• Drying was carried out by atomization in a 17.78 cm diameter (7 inch) 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%.
• 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 structure. crystalline in the absence of or prior to the calcination step.
• the median diameter, the untapped density and the 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 powder of granulated zirconium dioxide were calculated.
• the granulated zirconium dioxide powder has a lower compressibility than that of the initial zirconium dioxide powder, and therefore a higher flowability.
• hafnium dioxide powder (or hafnone powder) was obtained according to the manufacturing process, using the following parameters
• the hydrolysis was carried out in a hydrolysis reactor with an hourly mass flow rate of hafnium chloride (HfCL) of 26 kg/h, an hourly mass flow rate of water vapor of 3 kg/h and at a temperature of 500 °C.
• HfCL hafnium chloride
• the suspension was produced by mixing the hafnone powder obtained at the end of the hydrolysis with an aqueous solution of water and polyethylene glycol (PEG) containing by mass 60% hafnone powder and 40% solution watery.
• PEG polyethylene glycol
• 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%.
• the drying was carried out by atomization 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%.
• 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.
• 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 of granulated hafnium dioxide powder were calculated.
• the granulated hafnium dioxide powder has a lower compressibility than that of the initial hafnium dioxide powder, and therefore a higher flowability.
• the granulated metal oxide powder has a particle size distribution difference E of between 0.4 and 0.6, for example of the order of 0.5.
• the granulated metal oxide powder and in particular the granulated zirconium dioxide powder or the granulated hafnium oxide powder, has a microstructure defined in particular by the monoclinic crystalline phase ratio, the quadratic crystalline phase ratio, the size of crystallins in monoclinic phase and size of crystallins in quadratic phase.
• Monoclinic crystal phase ratio, quadratic crystal phase ratio, monoclinic phase crystal sizes, and quadratic phase crystalline sizes can be determined by analyzing X-ray diffraction patterns.
• the granulated metal oxide powder and in particular the granulated zirconium dioxide powder or the granulated hafnium oxide powder, has:
• a size of the crystals in the monoclinic crystal phase is between 10 and 20 nm, in particular between 14 and 16 nm and/or
• a size of the crystals in the quadratic crystal phase is between 10 and 20 nm, in particular between 13 and 15 nm.
• an installation 2 for implementing the manufacturing process comprises, for example, a hydrolysis reactor 4, a mixing reactor 6, a dryer 8 and, optionally, a calcining furnace 10.
• the hydrolysis step E1 is implemented in the hydrolysis reactor 4.
• the hydrolysis reactor 4 comprises a hydrolysis chamber 12 which receives the metal chloride CM and the water H2O, preferably in the form of water vapour.
• the hydrolysis reactor 4 supplies on the one hand the initial metal oxide powder PI and hydrochloric acid HCl.
• 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, to separate the initial metal oxide powder from the acid hydrochloric.
• the hydrolysis reactor is equipped with a sleeve filter (not shown) to separate the initial metal oxide powder from the hydrochloric acid.
• the suspension step E2 is implemented for example in the mixing reactor 6.
• the mixing reactor 6 comprises for example a mixing enclosure 16 to receive 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 chamber 16.
• the mixing reactor 6 supplies the suspension S comprising the organic binder L and the initial metal oxide powder PI suspended in the suspension medium MS
• the mixing reactor 6 optionally includes a stirring device 18 configured to stir the contents of the mixing enclosure 16.
• the drying step E3 is implemented for example in the dryer 8.
• the dryer 8 is for example configured to carry out spray drying.
• the dryer 8 comprises an atomization chamber 20 having a hot gas inlet 22 for injecting a flow of hot gas FG into the atomization chamber 20, in particular a stream of hot air, and a spray member 24 for spraying the suspension S in the stream of hot gas.
• the spray member 24 is for example a spray nozzle 24. As a variant, it is a bifluid nozzle or a spray turbine
• the dryer 8 preferably comprises a separator 26 arranged at an outlet of the atomization chamber 20 to separate, on the one hand, the granulated metal oxide powder PG resulting from the drying, and on the other hand, the gas stream containing the hot gas stream 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.
• the optional calcination step E4 is implemented in the calcination furnace 10, which receives and heats the granulated metal oxide powder PG obtained at the end of step E3.
• the calcining furnace 10 is for example a rotary furnace or a tunnel furnace.
• the installation includes a sieving device (not shown).
• a granulated metal oxide powder which preserves some 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 of the powder, while modifying other characteristics, in particular by decreasing the compressibility of the granulated metal oxide powder compared to the powder of initial metal oxide (not granulated).
• a good flowability of the metal oxide powder is favorable to its use for the production of mechanical parts by additive manufacturing.
• the particle size characteristics (in particular median diameter D50, deviation E of particle size distribution, etc.) and crystalline characteristics (in particular, monoclinic crystal phase rate, quadratic crystal phase rate, crystal size, etc.) of the metal oxide powder granulated has an influence on the use of granulated metal oxide powder, especially on the possibility of its use in various manufacturing methods. 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 in a liquid suspension.
• spray drying makes it possible to generate regular agglomerates (close to spherical grains) and a tight and easily adjustable particle size distribution by adjusting the 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.
• Such granulation processes can generate more irregular agglomerates and a more spread out particle size distribution than is obtained with the spray drying process.

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• 2021
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