EP2155612A2

EP2155612A2 - Method for producing carbon coated nanoparticles of a transition metal oxide

Info

Publication number: EP2155612A2
Application number: EP08805653A
Authority: EP
Inventors: Christine Bogicevic; Fabienne Karolak; Gianguido Baldinozzi; Mickael DOLLÉ; Dominique Gosset; David Simeone
Original assignee: Centre National de la Recherche Scientifique CNRS; Commissariat a lEnergie Atomique CEA; Ecole Centrale de Paris ECP; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Centre National de la Recherche Scientifique CNRS; Ecole Centrale de Paris ECP; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2007-06-06
Filing date: 2008-06-06
Publication date: 2010-02-24
Also published as: KR101427247B1; RU2009148871A; BRPI0811962A2; US8337799B2; RU2485052C2; FR2917080A1; WO2009004187A2; WO2009004187A3; JP2010528967A; FR2917080B1; KR20100062989A; CN101743201B; CA2690121A1; CN101743201A; CA2690121C; US20100202956A1

Abstract

The invention relates to a method for producing nanoparticles of at least one oxide of a transition metal selected from Ti, Zr, Hf, V, Nb and Ta, which are coated with amorphous carbon, wherein said method includes the following successive steps: (i) a liquid mixture containing as precursors at least one alkoxyde of the transition metal, an alcohol, and an acetic acid relative to the transition metal is prepared and diluted in water in order to form an aqueous solution, the precursors being present in the solution according to a molar ratio such that it prevents or sufficiently limits the formation of a sol so that the aqueous solution can be freeze-dried, and such that the transition metal, the carbon and the oxygen are present in a stoichiometric ratio according to which they are included in the nanoparticles; (ii) the aqueous solution is freeze-dried; (ii) the freeze-dried product obtained during the preceding step is submitted to pyrolysis under vacuum or in an inert atmosphere in order to obtain the nanoparticles. The invention also relates to the application of the method for producing transition metal carbide.

Description

PROCESS FOR MANUFACTURING TRANSITION METAL OXIDE NANOPARTICLES COATED WITH CARBON.

DESCRIPTION

TECHNICAL AREA

The present invention relates to the field of nanomaterials based on transition metal can be included in the composition of nuclear reactor elements. It relates in particular to a process for manufacturing nanoparticles of at least one carbon-coated transition metal oxide.

STATE OF THE ART

Transition metal carbides are particularly suitable materials for manufacturing some of the elements of next-generation nuclear reactors (particularly so-called Generation reactors).

IV) because they are highly refractory, have good thermal conductivity, low neutron absorption, a small absorption cross section and good resistance under irradiation.

On the contrary, they have a fragility detrimental to such applications.

It has been proposed to reduce this fragility by reducing the size of the crystallites of these carbides to an average size typically between a few nanometers and a few hundred nanometers to form nanocrystallites.

These can be obtained by carbothermic reduction of transition metal oxide particles coated with amorphous carbon of medium size. ranging from a few nanometers to a few hundred nanometers (called "oxide nanoparticles" in the following description). This reduction must be as complete as possible so that the nanocrystallites of transition metal carbides are as free as possible from any impurity.

For this purpose, the carbothermic reduction is most often carried out at a high temperature, which temperature must be higher as the crystallites of the nanoparticles of oxides are of medium size and / or initially contain a large quantity of impurities.

However, even if the use of a very high temperature makes it possible to obtain crystallites of transition metal carbides having a good degree of purity, it has the disadvantage of greatly increasing the average size, or even leading to form a coarse powder.

It is therefore often necessary in a last step to grind this powder in an attempt to reduce the average size of the crystallites that compose it. This grinding must be carried out under an inert atmosphere (usually in glove boxes) in order to avoid the oxidation of carbides. However, it has the disadvantage of inducing pollution by the mill materials and at best only lead to crystallites of transition metal carbides of average micron size.

In order to carry out a carbothermic reduction at temperatures lower than those of the existing processes, the document "Dollé et al., Journal of the

European Ceramic Society, Vol. 27, No. 4, 2007, p. 2061-2067 "proposes a new route of synthesis of nanoparticles of zirconium oxides. The first step of this synthesis is a sol-gel reaction in which sucrose is dissolved in acetic acid and then add zirconium n-propoxide to form a viscous gel. The drying and pyrolysis of the gel thus obtained then leads to oxide nanoparticles with an average size of 15 nm grouped in the form of agglomerates with an average size of 2 to 3 μm. After a carbothermic reduction at 1400 ^° C. of these oxide nanoparticles, nanocrystallites of zirconium carbide are obtained which, while being of a relatively small average size (of the order of 93 nm), nevertheless contain impurities. For the purposes of the description which follows, these impurities are considered to consist in particular of free carbon, dissolved oxygen and oxycarbides.

In an attempt to increase the degree of purity, these nanocrystallites of zirconium carbide are in turn heated to a high temperature of 1600 ^° C., which has the detrimental consequence of increasing their average size to 150 nm without however having managed to totally eliminate impurities.

SUMMARY OF THE INVENTION

One of the aims of the invention is therefore to provide a process for manufacturing oxide nanoparticles of the smallest possible average size, such nanoparticles making it possible, after moderate carbothermic reduction, to obtain nanocrystallites of transition metal carbide. of a higher degree of purity and / or a smaller average size than the nanoparticles obtained by the best current processes, in particular of the sol-gel type. The subject of the invention is therefore a process for producing nanoparticles of at least one transition metal oxide selected from Ti, Zr, Hf, V, Nb and Ta coated with amorphous carbon, the process comprising the following successive steps: (i) a liquid mixture containing as precursors at least one transition metal alkoxide, an alcohol, excess acetic acid with respect to the transition metal is prepared, and then diluted in water to to form an aqueous solution, the precursors being present in the aqueous solution in a molar ratio such that it prevents or sufficiently limits the formation of a sol so that the aqueous solution is lyophilizable and such as the transition metal, carbon and oxygen are present according to the stoichiometric ratio in which they are found in the nanoparticles,

(ii) the aqueous solution is subjected to lyophilization,

(iii) the lyophilizate obtained in the preceding step is pyrolyzed under vacuum or under an inert atmosphere in order to obtain the nanoparticles.

For the purposes of the invention, the transition metal oxide nanoparticles are said to be "coated" with amorphous carbon in the sense that their surface is partially or totally covered with amorphous carbon. Carbon is said to be "amorphous" because, essentially or mainly, it does not occur in the form of crystallites, although a short-range atomic order can exist locally. Preferably, the freeze-drying comprises spraying the aqueous solution in a liquid nitrogen bath in order to obtain frozen particles having the homogeneous composition of this solution, and then putting these particles under vacuum in order to remove the water therefrom. sublimation, whereby a powder is obtained which leads to the lyophilisate following its secondary desiccation. For the purposes of the invention, the term "homogeneous composition" means a composition which is the same or essentially the same for any volume of micron size, preferably of nanometric size. The spraying can be carried out with a wide variety of sprayers, for example with a nozzle sprayer or an ultrasonic sprayer.

To obtain oxide nanoparticles having the highest degree of purity possible, it is preferable that the lyophilisate contain no element other than the transition metal, carbon, hydrogen or oxygen. For this purpose, the alkoxide is advantageously chosen from isopropoxide and n-propoxide. Alkoxides comprising different transition metals may also be mixed to form nanoparticles containing a mixture of the corresponding oxides, for example a mixture of Ti oxides and Zr oxides. In particular, the alcohol acts as a diluting agent for the alkoxide. It may be chosen from isopropanol (or 2-propanol) and propanol-1, these alcohols having carbon chains derived from the same family as those of the abovementioned preferred alkoxides. Acetic acid is a chemical modifier that allows, within the metal alkoxide, the substitution of alkoxy groups with acetate groups. Advantageously, it therefore provides a modified alkoxide which, compared to the starting alkoxide, has a lower reactivity with respect to water, which has the effect of preventing or limiting the spontaneous reaction of condensation (sol-gel reaction) of the alkoxide, a reaction that can lead to the formation of precipitates. When this reaction is only limited, a sol can then begin to form by initiating the sol-gel reaction, this sol being within the meaning of the invention as it comprises oligomers and / or colloids suspended in the water.

In addition, in order to avoid or limit the formation of a soil, leading in particular to an aqueous solution of a viscosity so high that it could not be freeze-dried and / or an aqueous solution of inhomogeneous composition, acetic acid, which also has the function of reducing the viscosity of the solution, is in excess relative to the alkoxide and alcohol. The skilled person may for example consider that an aqueous solution according to the invention that meets these criteria is a clear solution. This is one of the essential points of the process of the invention, since the precursors of the oxide nanoparticles (namely the transition metal alkoxide, acetic acid, alcohol and possibly the carbon compound) are for example in the form of a clear aqueous solution guarantees the homogeneous distribution of these precursors at the molecular level and consequently favors a homogeneous composition of the oxide nanoparticles. As a general rule, it is advisable to use an aqueous solution of the lowest possible concentration, insofar as, all things being equal, a decrease in the concentration of the solution induces a decrease in the average size of the nanoparticles. oxide obtained according to the process of the invention. There is theoretically no lower limit to the concentration of the solution, however, especially for economic reasons, it is generally preferable not to use a concentration too low for the solution, especially to limit costs implementation.

Thus, preferably, the concentration of the transition metal in the aqueous solution is less than or equal to 0.1 moles / liter, even more preferably between 0.001 and 0.1 moles / liter, even more preferably between 0.01 and 0 , 1 moles / liter.

In particular, such concentration values have the advantage of preventing or limiting the aggregation of any particles present in the form of a sol. They also make it possible to have an easily lyophilizable aqueous solution using the usual freeze-dryers, since then the triple point of the solution is not too far from that of pure water.

Still with the aim of minimizing the average size of the oxide nanoparticles, the frozen particles obtained during lyophilization can have an average size of between 0.1 μm and 10 μm, preferably less than 2 μm, and even more preferentially between 0.5 μm and 1 μm.

In the present description, the term "average size" is used to define the average value of the diameter of the considered objects (oxide nanoparticles, transition metal carbide nanocrystallites, etc.) when they are substantially spherical, or the average value. major dimensions of these objects when they are not substantially spherical.

In order to achieve the above purpose, preferably, the aqueous solution can be sprayed in liquid nitrogen contained in a Dewar vessel and / or the spray is carried out using a sprayer having a spray nozzle having a calibrated orifice, for example a calibrated orifice of 0.51 mm, through which the aqueous solution is injected at a pressure of between 0.03 and 0.4 MPa, preferably at a pressure of 0.3 MPa, generally under the effect of a carrier gas which may be compressed air, or else a neutral industrial gas advantageously filtered, such as argon or nitrogen.

According to a preferred embodiment, one can ensure within the spray nozzle, a rotation of the aqueous solution by means of a conical groove insert. Such a conical insert allows, by centrifugal effect, to press the aqueous solution on the inner wall of the nozzle before this solution is injected through the outlet orifice. In this way, a liquid jet is generally obtained in the form of an axial hollow cone with a turbulence effect. Lyophilization can be carried out in all types of conventional lyophilizer. In this step, the conditions used are not critical, the particles are, however, preferably maintained in the frozen state until the elimination of water, in particular to avoid interparticle agglomeration phenomena.

It is also preferable, more often than not, that the conditions of this step ultimately lead to a substantial elimination of the water, in particular to avoid the creation of a porosity within the oxide nanoparticles during the pyrolysis of the water. lyophilisate. For this purpose, the freeze-drying is advantageously carried out between -200 ^° C. and + 50 ^° C., and more preferably between -20 ^° C. and + 30 ^° C., and at a pressure of between 0.1 Pa and 100 Pa and more preferably less than or equal to 10 Pa. Thus, for lyophilization to take place efficiently and as quickly as possible, it can for example be conducted at a temperature of the order of -2O ⁰ C and under a pressure of 1 order. 0.1 Pa. The freeze-drying step may advantageously comprise an adsorbed water removal step which consists in maintaining the lyophilizate under the pressure of freeze-drying, preferably at 0.1 Pa, and then raising the temperature to a value preferably between 30 ^° C. and 100 ^° C., more preferably equal to 30 ^° C.

The lyophilizate obtained from the aqueous solution makes it possible to dispose the precursors in a form which has several characteristics: the freeze-dried product has a homogeneous composition throughout its volume due in particular to the fact that freeze-drying is a process which makes it possible to to eliminate the water without causing a concentration gradient in the solution, the lyophilisate is finely divided, which increases its reactivity, for example with respect to a heat treatment, and, on the other hand, has the advantage that it can be handled in the open air and makes it possible to obtain oxide nanoparticles of reduced average size.

Thus, the average size of the transition metal oxide crystallites (equivalent to the average size of the oxide nanoparticles) is generally between 10 and 100 nm, preferably between 10 and 50 nm, more preferably between 10 and 20 nm. .

Advantageously, the characteristics of the lyophilizate make, after pyrolysis, obtaining oxide nanoparticles with properties such that they can undergo the most complete carbothermic reduction possible to obtain nanocrystallites of transition metal carbide of medium size. reduced and high degree of purity, without this requiring the use of high temperatures.

It is also essential that the pyrolysis step of the lyophilizate be conducted i) under vacuum or under an inert atmosphere in order to avoid the formation of by-products such as oxycarbides and ii) at a temperature such that it allows crystallization oxide nanoparticles without leading by carbothermic reduction to unwanted carbide nanocrystallites at this stage of the manufacture of oxide nanoparticles. This temperature is most often between 400 ^° C. and 900 ^° C., preferably between 400 ^° C. and 600 ^° C., more preferably still between 400 ^° C. and 450 ^° C. The invention also relates to the application of the manufacturing process. of nanoparticles of oxides for obtaining a transition metal carbide in the form of nanocrystallites by subjecting the nanoparticles to a carbothermic reduction, subsequently or in continuity with said process. This carbothermic reduction can be in continuity with the process for manufacturing oxide nanoparticles in that the lyophilisate undergoes a single heat treatment which comprises both the pyrolysis (in order to form the oxide nanoparticles) followed directly by the reduction. carbothermal. It may also be successive in that the lyophilisate undergoes a first thermal treatment in an inert atmosphere which constitutes pyrolysis, then the oxide nanoparticles thus obtained subsequently undergo a second heat treatment which constitutes the carbothermic reduction.

Advantageously, the carbon, oxygen and transition metal element necessary for the formation of the oxide nanoparticles can be provided solely by the alkoxide, acetic acid and alcohol. These contributions can be determined beforehand by calculation from the precursor chemical formula and / or after ThermoGravimetric Analysis (ATG) precursors or oxide nanoparticles with respect to the carbon and oxygen inputs. However, in a preferred embodiment, the carbon and / or oxygen element may be provided in a complementary manner with a precursor consisting of at least one carbon compound added to the aqueous solution. This compound is within the aqueous solution that is chemically inert with respect to the alkoxide, and in particular it does not comprise an OH group (s) that can cause the hydrolysis of the alkoxide: it can therefore be chosen from a derivative cellulose meeting these criteria.

For example, preferentially it is methyl cellulose.

The process according to the invention is therefore flexible in that it makes it possible to obtain oxide nanoparticles having a large variety in the molar ratio of amorphous carbon to transition metal oxide, and thus to oxide nanoparticles in which the oxide of the metal transition has a wide variety of amorphous carbon coating rates. This ratio is preferably between 1 and 4, even more preferably between 2 and 3. According to a preferred embodiment, the excess of acetic acid in the aqueous solution of the invention is such that the molar ratio between the amount of the amount of alcohol and the amount of alkoxide is between 20: 6: 1 and 3: 1: 1, even more preferably 16: 4: 1. such molar ratio also makes it possible to limit the increase in viscosity after the possible addition of the carbon compound according to the invention.

Preferably, the aqueous solution of the invention has a pH of between 3 and 10 and more preferably between 3 and 5 so as not to lower its freezing point and thus promote its lyophilization.

DETAILED DESCRIPTION OF THE INVENTION

Other objects, features and advantages of the invention will appear better on reading the description which follows, given by way of illustration and not limitation. The examples which follow illustrate, according to the invention, the process for manufacturing nanoparticles of dioxide of various transition metals, having different coating levels, then the use of these nanoparticles in order to obtain the corresponding carbides. 1 - Manufacture of coated titanium dioxide nanoparticles (TiO ₂ ) in which the carbon / TiO ₂ molar ratio is about 3.

A volume of 2.27 ml of ¹ titanium isopropoxide (IsopTi) corresponding to 0.59 g of TiO ₂ was added to 2.27 ml isopropanol (2-propanol) and 6.81 ml of glacial acetic acid (100%). The molar ratios 16 (acid) / 4

(alcohol) / 1 (isopropoxide) and volume 3 (acid) / 1

(alcohol) / 1 (isopropoxide) were thus made. This liquid mixture is added to 200 ml of an aqueous solution in which 1.0790 g of methylcellulose has previously been dissolved.

(MC) corresponding to 0.1802 g of carbon (prior verification by ATG).

The solution obtained was clear, thus marking the absence of the significant formation of a soil and a homogeneous composition. It was diluted in water to obtain 600 ml of concentrated aqueous solution.

0.03 moles / liter of Ti.

This aqueous solution was then nebulized (Spraying Systems Emani Co nebulizer, 0.51 mm diameter nozzle) in order to form droplets of an average size of

1 μm projected into liquid nitrogen to obtain corresponding ice particles.

These particles were introduced into a freeze-dryer (commercial freeze-dryer Alpha 2-4 Christ

LSC) at the temperature of the liquid nitrogen. The pressure of the chamber of the lyophilizer was then reduced to 0.1 Pa, and the chamber of the lyophilizer was kept under this reduced pressure and at -20 ^° C. for 48 hours. The enclosure was then heated for 3 hours at + 30 ^° C., keeping the pressure at 0.1 Pa.

This holding under vacuum at -20 ^° C. for 48 hours and at + 30 ^° C. for 3 hours induces elimination of the water by sublimation and then desorption, by which, after this treatment, 16 g of particles in the form of a dry powder.

The dry powder or freeze-dried product obtained in the preceding step was placed in a graphite nacelle and pyrolysed in a tubular furnace made of alumina (Adamel) under an argon flow U (Arcal, flow of 1.2 liters / minutes) by a increasing in temperature at a rate of 5 ° C./minutes until a temperature of 45 ^° C. was reached which was maintained for 0.1 hour and then decreased at a rate of 5 ° C./minutes to room temperature. At the end of this pyrolysis, a black powder is obtained. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis indicate that this powder is composed of TiO ₂ titanium dioxide nanoparticles of tetragonal structure (also called anatase) in the form of nanocrystallites of a average size of 16 nm. The presence of carbon coating these nanoparticles has been quantified by ATG under air. In the proportions of IsopTi, alcohol, acetic acid and MC used, the carbon / TiO ₂ molar ratio produced was thus equal to 3.04; knowing that the molar ratio of carbon / Ti0 ideal ₂ is equal to 3 in order to create the complete reduction of the titanium dioxide according to the carbothermal reduction reaction: TiO ₂ (S) + 3C (s) -> TiC (s) + 2CO ( boy Wut)

2 - Manufacture of nanocrystallites of titanium carbide TiC.

The lyophilizate obtained at the end of the freeze-drying step placed in a graphite boat was heat-treated in the above-mentioned alumina (Adamel) tubular furnace under argon flow with an increase in temperature at a rate of 5 °. C / minutes until reaching a temperature of 1300 ⁰ C which was maintained for 2 hours, and then decreased at a rate of 5 ° C / minute to room temperature. The carbothermic reduction is in this case in the continuity of the pyrolysis which led to the formation of oxide nanoparticles: the lyophilisate has therefore undergone a single heat treatment. This results in the formation of nanometric titanium carbide TiC of face-centered cubic structure having a mesh parameter of 4.326 Å. (very close to the theoretical value of 4.327 Å), and an average crystallite size of 65 nm determined by XRD and SEM analyzes.

A measurement by ATG made it possible to determine the stoichiometric composition of the TiC and showed a residual oxygen content of less than 1% by mass as well as the presence of an excess of carbon (revealed by a mass gain of 30.4% instead of a theoretical value of 33.40%). The knowledge of the value of this excess of carbon which constitutes an impurity can make it possible to readjust, possibly by successive tests, the quantity of carbon provided by the methylcellulose in order to reduce or render null the carbon content of the transition metal carbide.

3 - Manufacture of coated nanoparticles of titanium dioxide (TiO ₂ ) in which the carbon / TiO ₂ molar ratio is 0.05.

Titanium dioxide nanoparticles (TiO ₂₎ coated in which the molar ratio of carbon / Ti0 ₂ is from 0.05 were manufactured according to a procedure similar to that of Example 1, except that intakes carbon element have been adapted. In particular, such nanoparticles are used as constituent materials for the electrodes of lithium batteries. They then generally have a coating rate such that the carbon / TiO ₂ molar ratio is between 0.01 and 0.06, preferably between 0.02 and 0.05.

4 - Manufacture of coated nanoparticles of zirconium dioxide (ZrO ₂ ) or hafnium dioxide (HfO ₂ ) and zirconium and hafnium carbides.

Zirconium dioxide (ZrO ₂ ) nanoparticles and hafnium dioxide nanoparticles (HfO ₂ ) both coated with amorphous carbon was conducted under conditions similar to those of the previous examples.

It was the same for the carbothermic reduction proper: a lyophilisate obtained under conditions similar to those of the previous examples was subjected to heat treatment at 1400 ⁰ C for respectively 3 hours and 5 hours in order to produce these crystallites of ZrC and HfC an average size of 40 nm and 30 nm respectively. The conditions for obtaining the transition metal carbide from the oxide nanoparticles that form at about 450 ^° C. during the increase in temperature that will lead to the carbothermal reduction may nevertheless vary somewhat depending on the transition metal in question. They generally include increasing the temperature at a rate between 5 ° C / minute and 10 ° C / min, preferably 5 ° C / minute in order to reach a temperature between 1000 and 1600 ⁰ C ⁰ C preferably at 1300 ^° C. or 1400 ^° C., which temperature is maintained for a period of between 2 and 6 hours, preferably 2 hours for TiC, 3 hours for ZrC and 5 hours for HfC.

Those skilled in the art can refine these conditions by successive tests in order to obtain the most complete carbothermic reduction possible and an average size of nanocrystallites as small as possible which can be within the scope of the invention of between 30 and 100 nm, preferably between 30 and 70 nm, more preferably between 30 and 40 nm. Advantageously, the carbothermic reduction is carried out with a carrier gas comprising argon and more advantageously U or Arcal argon.

The foregoing examples relate to the manufacture of oxide and carbide nanoparticles comprising titanium, zirconium and hafnium. With the help of his General knowledge, they can easily be transposed by those skilled in the art to achieve the invention for the other transition metals that are vanadium, niobium and tantalum.

It is clear from the description above that the process of the invention makes it possible to manufacture oxide nanoparticles of a reduced average size which make it possible to obtain nanocrystallites of transition metal carbide after moderate carbothermal reduction. a higher degree of purity and / or a smaller average size than the nanoparticles currently obtained by the sol-gel type processes. It is also simple to implement and in particular makes it easy to obtain oxide nanoparticles in which the transition metal oxide has a wide variety of amorphous carbon coating rates.

Claims

1) A process for producing nanoparticles of at least one transition metal oxide selected from Ti, Zr, Hf, V, Nb and Ta coated with amorphous carbon, said process comprising the following successive steps:

(i) a liquid mixture containing as precursors at least one alkoxide of said transition metal, an alcohol, excess acetic acid with respect to said transition metal is prepared, and then diluted in water to to form an aqueous solution, said precursors being present in said aqueous solution in a molar ratio such that it prevents or sufficiently limits the formation of a sol so that said aqueous solution is lyophilizable and such that said transition metal, carbon and oxygen are present according to the stoichiometric ratio in which they are found in said nanoparticles,

(ii) said aqueous solution is subjected to lyophilization,

(iii) the lyophilizate obtained in the preceding step is pyrolyzed under vacuum or under an inert atmosphere in order to obtain said nanoparticles.

2) A method of manufacturing nanoparticles according to claim 1, wherein said molar ratio is adjusted by adding to the aqueous solution of at least one carbonaceous compound chemically inert with respect to the alkoxide.

3) A method of manufacturing nanoparticles according to claim 2, wherein said carbon compound is selected from a cellulose derivative such as methyl cellulose.

4) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein said alkoxide is selected from isopropoxide and n-propoxide.

5) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein said alcohol is selected from propanol-1 and propanol-2.

6) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein the concentration of the transition metal in the aqueous solution is less than or equal to 0.1 moles / liter, more preferably between 0.001 and 0.1 moles / liter, even more preferably between 0.01 and 0.1 moles / liter.

7) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein the molar ratio between the amount of acetic acid, the amount of alcohol and the amount of alkoxide is between 20: 6: 1 and 3 : 1: 1, even more preferably equal to 16: 4: 1.

8) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein said lyophilization is conducted between -200 ⁰ C and +50 ⁰ C, and more preferably between -20 ⁰ C and +30 ⁰ C, and at pressure between 0.1 Pa and 100 Pa and more preferably less than or equal to 10 Pa. 9) A method of manufacturing nanoparticles according to claim 8, wherein said lyophilization comprises an adsorbed water removal step which consists in maintaining the lyophilizate under the pressure of freeze-drying, preferably at 0.1 Pa, then raising the temperature up to a value preferably between 30 ^° C. and 100 ^° C., more preferably equal to 30 ^° C.

10) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein during step (iii), the lyophilizate is pyrolyzed at a temperature between 400 ⁰ C and 900 ⁰ C, preferably between 400 ⁰ C and 600 ^° C., even more preferentially between 400 ^° C. and 450 ^° C.

11) A method of manufacturing nanoparticles according to any one of the preceding claims, wherein the average size of said nanoparticles is between 10 and 100 nm, preferably between 10 and 50 nm, more preferably between 10 and 20 nm.

12) Application of the manufacturing method according to any one of the preceding claims, for obtaining a carbide of said transition metal in the form of nanocrystallites by subjecting, subsequently or in the continuity of said process, said nanoparticles to a carbothermal reduction.

13) Application according to claim 12, wherein said nanocrystallites are of an average size between 30 and 100 nm, preferably between 30 and 70 nm, more preferably between 30 and 40 nm. 14) Application according to claim 12 or 13, wherein said carbothermal reduction comprises increasing the temperature at a speed of between 5 and 10 ° C / min, preferably 5 ° C / min, in order to achieve a temperature between 1000 ⁰ C and 1600 ⁰ C, preferably equal to 1300 ⁰ C or 1400 ⁰ C depending on the desired carbide, which temperature is maintained for a period of between 2 and 6 hours, preferably equal to 2 hours for TiC, 3 hours for the ZrC and 5 hours for the HfC.

15) Application according to any one of claims 12 to 14, wherein said carbothermal reduction is carried out in the presence of a carrier gas comprising argon.