Patent Application
20250091885
The invention relates to a new method for manufacturing or synthesizing diboride of group 4 elements of the periodic table, in particular of titanium diboride.
Diborides of group 4 elements of the periodic table, in particular titanium diboride, zirconium diboride or hafnium diboride, have many advantages, including high refractoriness, high toughness, and excellent chemical inertia.
Titanium diboride in particular is a ceramic material having a low density (about 4.5 g/cm3), a high hardness, a high thermal conductivity and a low electrical resistivity. This makes it a potentially interesting material for several applications, such as refractory applications where the thermal conduction and the high electrical conduction are an asset, in particular heat exchangers, the coating or even the composition of anodes or of cathodes of electrolysis reactors, or even membranes in certain temperature applications or in very aggressive chemical media, as well as the cutting tools of metals, in particular for non-ferrous metals, or cutting tools or shielding or anti-abrasion coating.
All these applications explain that the demand for this material is very high and currently increasing.
Diborides do not exist in the natural state. Titanium diboride can particularly be obtained for example by direct reaction of titanium (or its oxides or hydrides) with elemental boron at 1,000° C. or by carbothermic reduction of titanium oxide and boron oxide. In the latter case, the reaction consists of reacting a mixture of powders according to the following simplified reaction at a temperature above 1500° C.:
TiO2(s)+B2O3(s)+5C(s)→TiB2(s)+5CO(g) (1)
However, this method has a theoretical material efficiency of about 30%.
Another less known method consists in particular in replacing the boron oxide powder with boron carbide, as shown by the following balance reaction:
2TiO2+B4C+3C→2TiB2+4CO (2)
The advantage of such a reaction is its higher theoretical material efficiency (55.4%) and therefore lesser release of carbon monoxide but it has the disadvantage of requiring a reaction temperature greater than 1600° C. and generates a non-negligible amount of CO in gaseous form, which poses problems of hygiene, safety and environment.
Furthermore, methods for manufacturing this material are all the more expensive and energy-consuming as the desired final powder of titanium diboride becomes finer (typically with a median diameter between 5 and 50 micrometers) or ultra-fine (median diameter less than 5 micrometers).
Another known solution consists of metallothermic reduction using, in place of the carbon, an element in metal form such as Al, Si, Mg, Ca. The exothermic reactions associated with the use of these reagents produce diborides by self-propagating high temperature synthesis (SHS) but lead to the incomplete conversion of reagents, which conventionally requires a second reaction typically with boric acid H3BO3 to obtain a better rate of conversion to diboride.
Another solution also consists of synthesis in a mixture of salts that are molten or in solution. The published patent application under WO2020073767A1 from the Wuhan University of Science and Technology thus proposes a method for preparing a layer of TiB2 or (Zr, Hf)B2 that is less expensive and more environmentally sound, from a mixture comprising a source of titanium (or zirconium or hafnium), a source of boron, a reducing agent (Si or Al in metallic form), and an alkali salt. The alkali salt may be chosen from a hydrate, a silicate or a carbonate of sodium, of lithium or of potassium in order to form a liquid phase at low temperature. The addition of silicate, however, leads to reaction products that are difficult to separate. Adding carbonate(s) poses the problem of C02 release due to the decomposition of the carbonate during the synthesis reaction.
The purpose of the invention is thus to improve the synthesis methods described above in order to obtain a diboride powder of a group 4 element of the periodic table, in particular of TiB2, that is:
In particular, according to a first aspect, the present invention relates to an alternative method for manufacturing a diboride powder of a group 4 element of the periodic table, in particular titanium diboride TiB2, at a temperature of less than 1500° C., preferably less than 1400° C., preferably less than 1300° C., or even 1200° C., for this purpose by virtue of an appropriate choice of starting powders, without the use of solvent or surfactant.
More specifically, the present invention relates to a method for manufacturing a diboride powder MB2, where M is a chemical element belonging to group 4 of the periodic table, by reducing an oxide MO2 of said element M, said method comprising the following steps:
MO2+B2O3+yR+xA2O→MB2+A2xRyO5+x (3)
According to preferred but non-limiting embodiments of the present invention, which can, if appropriate, be combined with one another:
According to one possible embodiment, the mixture of raw materials comprises an oxide powder MO2 of a first chemical element M belonging to group 4b of the periodic table and a second oxide powder MO2 of a second chemical element M belonging to group 4b of the periodic table different from the first element, M being chosen from Ti, Zr, or HfO2.
According to another embodiment, which can be combined with the preceding one, the mixture of raw materials comprises at least one oxide powder MO2 wherein M is a mixture of at least two, preferably two, chemical elements belonging to group 4b of the periodic table.
As will be described in more detail below, such a combination of parameters advantageously makes it possible to obtain a fine powder of MB2 diboride of high purity with a satisfactory material efficiency, using a method that releases little or no CO or CO2 and allows for easy ability to extract said diboride powder without using an excessively industrially complex powder synthesis method.
The respective proportions leading to the reduction of the oxide of element M into diboride of element M are the substantially stoichiometric amounts of the various reagents mentioned in the preceding points a) to d) leading to the balance reaction (3).
For example, in the case of the use of a lithium oxide precursor of the type Na2B4O7, one mole of B2O3 in the reaction (3) corresponds to an addition of a half-mole of the reagent Na2B4O7.
Thus, the balance reaction (3) is written, in the case of the use of boron oxide B2O3:
MO2+B2O3+R+xA2O→MB2+A2xRO5+x
The balance reaction (3) is written, in the case of the use of a boron oxide precursor Na2B4O7:
MO2+B2O3+yR+xA2O→MB2+A2xRyO5+x
where M=Ti A=Na R=Al x=5/3 and y=10/3
In particular, unlike the synthesis methods using molten salts or placing in a solution of a solvent, in particular water, the method according to the invention by dry route and in particular by the use of an oxide powder of a weakly or non-hydroxylated alkaline element A rather than the use of an alkali salt in solution as is described, for example, by WO2020073767A1, advantageously allows an optimal reaction, that is to say with a maximum material balance, while allowing easy separation of the diboride powder of element M after synthesis in the enclosure.
According to other preferred embodiments of the present invention, which can, if appropriate, be combined with one another:
After reaction, the finely divided raw diboride powder of group 4 element of the periodic table can be easily extracted from the crude mixture resulting from the enclosure after the heating step.
According to one possible embodiment, a sieving operation, typically to a diameter of 100 micrometers, preferably of 50 micrometers, or even of light crushing or of vibration, makes it possible to eliminate the agglomerates and to separate out the raw powder of diboride of element M. A suspension is carried out by adding to the previously ground crude mixture a solvent, preferably deionized water, in a mass ratio of 1 part crude mixture to at least 20, preferably 50 parts of solvent. Said suspension is filtered to an optimal size typically less than 30 micrometers, preferably less than 20 micrometers in order to allow through the liquid comprising the very fine residues of the other products of the reaction (3). The filtration retentate, consisting of the diboride powder of element M, is then calcined or dried, preferably in air, at a temperature above 80° C., preferably above 100° C. and/or preferably below 300° C., preferably below 200° C., preferably below 150° C.
According to one possible embodiment, said liquid resulting from the filtration of the suspension described above comprising products of the reaction (3) apart from the diboride powder of element M is heat-treated in the presence of water and a basic solution in order to form a hydrate of element R and an alkali hydroxide. This embodiment makes it possible to upgrade the reaction product (3) of formula A2xRyO5+x. Preferably, this possible embodiment is particularly advantageous in the case where the element R is Al and the alkali A is sodium.
The invention also relates to a diboride powder of element M of group 4 of the periodic table, in particular a powder of titanium diboride TiB2, obtained according to the preceding method.
Said powder comprises more than 95% by mass of the compound MB2, M being selected from Ti, Zr and Hf. The median particle diameter of this powder is between 0.5 and 50 microns, and it further comprises the following mass percents:
Preferably, the sum of elemental oxygen (O)+nitrogen (N)+carbon (C) in the diboride powder of element M is less than 1.5%, or even less than or equal to 1.2%.
Preferably, the mass content of silicon (Si) in metal form in the diboride powder of element M is less than 0.1%.
Preferably, the mass content of aluminum (Al) in metal form of the diboride powder of element M is less than 2%, preferably less than 1%, preferably less than 0.5%.
Preferably, the final powder of MB2 according to the invention does not comprise any crystallized phases such as M2O3, M3B4 as measured (detectable) by X-ray diffraction. Preferably, said powder comprises only a crystalline phase of MB2, as measured (detectable) by X-ray diffraction.
Preferably, the ratio (D90−D10)/D50 of equivalent diameter of the particles of the raw powder, i.e. the powder after extraction of the crude mixture from the enclosure after the heating step, in particular after separating the reaction product (3) of formula A2xRyO5+x, is less than 2, preferably less than 1.5, more preferably less than 1.2 or even less than 1. The percentiles D10, D50 and D50 being the diameters corresponding respectively to the percentages of 10%, 50% and 90% on the cumulative curve of grain diameter distribution by volume classified in increasing order of said powder.
If M=Ti, the elemental Ti mass content is preferably greater than 68% and/or less than 72% and the elemental boron mass content is preferably greater than 29% and/or less than 33%. Preferably, the elemental phosphorus mass content is less than 0.3%, preferably less than 0.2% or even less than 0.1%.
Such a diboride powder of element M of group 4 of the periodic table, in particular a TiB2 powder of high purity and of fine, regular particle size makes it possible to obtain by sintering a sintered ceramic body having a total porosity of less than 7% by volume without the use of the addition of transition metals such as Ni, Fe or Co which are capable of resulting in the formation of secondary metal borides from these metals which are not desired.
Such a powder makes it possible to obtain a sintered ceramic body in the form of a part, at least one dimension of which, preferably all of the overall dimensions, is greater than 5 cm, or even greater than 10 cm, and having a total porosity also less than 7%, a very narrow pore size distribution, without deformation on sintering and without shrinkage cracking.
Preferably, M is Ti.
Said diboride powder of element M of group 4 of the periodic table is then a powder of compound TiB2 which further comprises one or more of the following mass percents:
Said diboride powder of element M of group 4 of the periodic table is then a powder TiB2 whose chemical composition comprises the following elemental mass percents:
The ratio D90−D10)/D50 of equivalent diameter of the particles of the MB2 powder is advantageously less than 1.5, more preferably less than 1.2 or even less than or equal to 1.0.
The invention also relates to a mixture comprising between 90 and 99.9% by weight of diboride of element M of group 4 of the periodic table or even consisting of a powder of diboride of element M of group 4 of the periodic table, preferably titanium diboride (TiB2), according to the invention and between 0.1 and 10% by weight of one or more sintering powders selected from powders of aluminum diboride, magnesium diboride, zirconium diboride, tungsten pentaboride, calcium hexaboride, preferably silicon hexaboride, optionally zirconium diboride if M=Ti or Hf, the purity of which is greater than 95% by mass, preferably greater than 98% by mass. A purity greater than 95% by mass is that of said phase or of the most stable main compound: for example, in the case of a powder of aluminum diboride, more than 95% by mass of AlB2 or for a tungsten pentaboride powder, containing more than 95% by mass of W2B5.
The invention likewise relates to a method for manufacturing a sintered ceramic body, comprising the following steps:
The invention also relates to the sintered ceramic body thus obtained and the use of the sintered ceramic body obtained by the preceding method as all or part of a membrane, in particular for the filtration of liquids or gases, a shielding or an anti-abrasion coating, a covering or a refractory block, an anode coating or block or a cathode coating or block, in particular an electrolysis reactor, a heat exchanger, a metal melting crucible, in particular for non-ferrous metal, a cutting tool.
The following indications and definitions are given in connection with the preceding description of the present invention:
In particular, the following mass contents of:
Unless otherwise specified, all percentages in this description are mass percentages.
The invention and its advantages will be better understood on reading the detailed description given below. Of course, the present invention is not limited to such a mode, in any of the aspects described below.
The mixture of starting raw materials comprises:
If necessary, the certain raw materials such as borates or alkaline element oxide powder can be dried or calcined in order to reduce their H2O or hydroxyl content. In the case of starting materials such as the natural borax of formula Na2B4O7·10H2O (also expressed in the form Na2B4O5(OH)4·8H—O), the tinicalite of formula Na2B4O7·5H2O (also expressed in the form Na2B4O5(OH)4·3H2O) the kernite of formula Na2B4O7·4H2O (also expressed in the form Na2B4O6(OH)2·3H2O), the ulexite of formula NaCaB5O9·8H2O (also expressed in the form of NaCaB5O6(OH)6·5H2O), the probertite NaCaB5O9·5H2O (also expressed in the form of NaCaB5O7(OH)4·3H2O), this treatment reduces the presence of hydrogen present in the form of water H2O adsorbed on the surface of the OH powder or hydroxyls. It makes it possible to improve the conversion rate into the diboride of element M, which also results in a raw powder of MB2 having after synthesis a very low content of reducing metal at element R.
Preferably, in order to maximize the conversion rate into diboride MB2, the content of hydroxyl (OH) provided by the raw materials in the reaction (3) is minimized. In particular, the borates may be calcined in order to dehydroxylate them. Even more preferably, the oxide powder of alkali element A has a hydroxyl content, calculated by dividing its mass of OH by the mass of alkali metal A2O, is less than 40%, preferably less than 30%, more preferably less than 20%, or even less than 10%, or even less than 5% or even substantially zero.
The median size or median diameter of the oxide particles of element M is respectively between 1 and 100 microns, preferably between 7 and 80 microns. That of the particles comprising boron oxide, that of the metal particles of reducing element R and that of the oxide particles of alkali element A is preferably between 30 and 100 micrometers, preferably between 30 and 80 micrometers.
Preferably, the median size ratio of the particles comprising boron oxide to those of oxide of element M is between 1 and 10.
Preferably, in a mixture according to the invention comprises in mass proportion respectively 20 to 25% oxide of element M, 25 to 40% powder comprising a boron oxide or a boron oxide precursor, 20 to 30% metal powder of reducing element of element R and 15 to 25% an oxide powder of an alkali element A. In particular, in the case where the element M is Ti and A is Na, the mixture according to the invention respectively comprises, in mass proportion, 20 to 25% titanium oxide, 25 to 35% powder comprising a boron oxide or a boron oxide precursor, preferably sodium borate, 20 to 30% metallic powder of reducing element R, preferably Al and/or Si, and 15 to 25% sodium oxide powder.
The total content of alkali oxide calculated in form A2O in said mixture of raw materials is greater than or equal to the stoichiometric amount required for said reaction (3), preferably less than 10%, or even less than 5%;
The mixture is preferably dried in air, preferably at a temperature above 40° C., more preferably at a temperature above 100° C., in order to obtain a mixture whose residual moisture content, that is to say the residual mass content of H2O as measured by a moisture meter well known to a person skilled in the art, said mixture of raw materials is less than 5%, preferably less than 2%, or even more preferably less than 1%.
The mixture is placed in an inert crucible, preferably by diboride of element M or even of alumina, preferably of alumina coated with diboride of element M, for example in an induction furnace. The loose density of the mixture before heat treatment measured according to the ASTM D7481-18 standard is preferably greater than 0.1 times the density of MB2, or greater than 0.2 and/or preferably less than 0.5, less than 0.3 times the density of MB2.
A temperature rise is carried out to at least one temperature preferably higher than the melting point of the metal of element R selected from Al, Si, Ti, Zr, Hf, Y, Sc, and the lanthanides, their mixture or their alloy, the content of other elements Al, Si, Ti, Zr, Hf, Y, Sc, and the lanthanides, preferably greater than 600° C., preferably greater than 700° C., preferably greater than 800° C., and less than 1500° C., preferably less than 1300° C., in a non-oxidizing atmosphere, preferably under a flow of rare gas, in particular Argon in order to prevent oxidizing the powder of metal reducer R.
Preferably, the non-oxidizing gas sweeping is carried out at a normal flow rate of 0.5 and 5 L/min per m3 of enclosure, preferably between 0.5 and 3 L/min/m3, preferably between 0.5 and 2 L/min/m3 of enclosure.
Preferably, the temperature rise is less than 20° C./minute, preferably less than 10° C./minute, preferably less than 5° C./minute, or even less than 3° C./minute. This temperature rise ramp, like the duration of the plateau, can be adjusted as a function of the mixing volume and the power of the reactor. In particular, such a temperature rise range promotes better control of the exothermic effect due to the synthesis reaction of the powder according to the invention.
Preferably, the plateau at the maximum temperature is at least one hour, preferably at least two hours.
Preferably, an intermediate plateau is carried out between 60° and 1000° C., and/or a lower ramp, typically at least twice as low, is carried out after 600° C. in order to prevent the removal of the mixture and promote the reaction between the particles.
The cooling can be free or forced, preferably according to a negative ramp less than 20° C./min.
The raw mixture obtained has a particle size of typically between 10 and 100 micrometers.
A sieving operation, typically to a diameter of 100 micrometers, preferably to a diameter of 80 micrometers, preferably to a diameter of 50 micrometers, or even of light crushing or of vibration makes it possible to eliminate the agglomerations and to separate the raw powder of diboride of element M.
According to one possible embodiment, a sieving operation, or even of light crushing or of vibration, makes it possible to eliminate the agglomerates and to separate out the powder of diboride of element M. A suspension is carried out by adding to the previously ground crude mixture a solvent, preferably deionized water, in a mass ratio of 1 part crude mixture to at least 20, preferably 50 parts of solvent. Said suspension is filtered at an optimal size typically at 30 micrometers, preferably 20 micrometers, or 15 micrometers or less in order to allow through the liquid comprising the very fine residues of the other products of the reaction (3). The filtration retentate, consisting of the diboride powder of element M, is then calcined or dried, preferably in air, at a temperature above 80° C., preferably above 100° C. and/or preferably below 300° C., preferably below 200° C., preferably below 150° C.
According to one possible embodiment, said liquid resulting from the filtration of the suspension described above comprising products of the reaction (3) apart from the diboride powder of element M is heat-treated in the presence of water and a basic solution in order to form a hydrate of element R and an alkali hydroxide. This embodiment makes it possible to upgrade the reaction product (3) of formula A2xRyO5+x. Preferably, this possible embodiment is particularly advantageous in the case where the element R is Al and the alkali A is sodium.
After grinding the raw powder, it is possible to obtain a final diboride powder of finely divided element M whose median diameter is between 0.5 and 50 micrometers of large purity, of micron size, the size dispersion of which is very small.
The final powder of diboride of element M makes it possible to obtain by sintering a sintered ceramic body having a total porosity of less than 7% by volume without adding transition metals such as Ni, Fe or Co while exhibiting a very low electrical resistivity.
The final powder obtained according to the method of the invention also makes it possible to obtain a sintered ceramic body in the form of a part, all of the dimensions of which are at least one dimension greater than 5 cm without deformation upon sintering and without shrinkage cracking.
The material of the powder according to the invention has an electrical resistivity, measured at 25° C. and at atmospheric pressure, of less than 0.2 microOhm·m.
The electrical resistivity can be measured according to the Van der Pauw method at 4 points on a sample with a diameter of 20-30 mm and a thickness of 2.5 mm. The sample being obtained by pressing a mixture consisting of said powder with 0.25% of a pressing additive (PVA) and 4.75% of deionized water by mass relative to the mass of M diboride powder in order to be cold-pressed under a pressure of 100 bar and to form a cylinder with a diameter of 30 mm and a thickness of 10 mm. After demolding, each cylinder was dried at 110° C. for 24 hours and then fired without pressure at a temperature of 1850° C. for 12 h in Argon.
A method for manufacturing a sintered ceramic body using the powder according to the invention in particular comprises the following steps:
Any shaping technique known to the person skilled in the art can be applied as a function of the dimensions of the part to be made as soon as all the precautions are taken to avoid contamination of the preform. Thus, the casting in a plaster mold can be adapted by using graphite media between the mold and the preform or oils avoiding excessive contact and abrasion of the mold by mixing and finally contamination of the preform. These controlled precautions for use by a person skilled in the art are also applicable to other steps of the method. Thus, during sintering, the mold or the matrix used containing the preform will preferably be made of graphite.
A sintered ceramic body obtained from the powder according to the invention advantageously has an electrical resistivity, measured at 25° C. and at atmospheric pressure, of less than 0.2 microOhm·m.
Hot pressing, hot isostatic pressing, or SPS (Spark Plasma Sintering) techniques are particularly suitable.
The following examples are for illustrative purposes only and do not limit the scope of the present invention in any of the aspects described.
The starting mixture was made with a powder of titanium oxide with a median diameter D50 of 10 μm mainly in a crystallographic form of TiO2 in rutile form provided by Traxys France (95% purity), a powder of boron oxide B2O3 of median diameter D50 equal to 15 μm and a carbon black powder of median diameter D50 of 0.2 μm according to the following respective mass proportions 38.1% TiO2, 33.2% B2O3 and 28.7% C.
A mixture sample was placed in a graphite crucible with dimensions of 6 cm internal diameter, 8 cm external diameter and 8 cm tall. The open crucible is placed in an induction furnace in order to be subjected respectively to a heat treatment at 1600° C. for a plateau duration of 2 hours in an oven in an Argon flow of 1.25 L/min/m3.
The synthesis mixture obtained was ground for 3 minutes in order to obtain a powder with a median size of less than 10 microns.
The starting mixture was made with a powder of titanium oxide with a median diameter D50 of 10 μm mainly in a rutile crystallographic form as in the previous example, a powder of sodium tetraborate (Na2B4O7) of median diameter D50 equal to 50 μm from Sigma Aldrich with purity greater than 99% by mass and a metal aluminum powder with a median diameter D50 of 10 μm from Alfa Aesar with purity greater than 99% by mass, a powder of sodium oxide (Na2Y) of median diameter D50 of 50 μm from Sigma Aldrich with a purity of greater than 99% by mass, in the following respective mass proportions 23.3%, 29.3%, 26.2% and 21.2%. A mixture sample was placed in a graphite crucible of the same size as the previous example. The open crucible is placed in a tubular furnace in order to be subjected respectively to a heat treatment at 800° C. at a temperature rise of 2° C./minute in a tubular furnace followed by a stage of 2 hours in a furnace in an Argon flow of 1.25 L/min/m3 enclosure of the tubular furnace.
The corresponding balance reaction is:
3TiO2+1.5Na2B4O7+10Al+3.5Na2O→TiB2+10NaAlO2
or, expressed according to the reaction (3) as a function of the simple oxides TiO2, B2O3 and Na2O:
TiO2+B2O3+10/3Al+5/3Na2O+TiB2+10/3NaAlO2.
The synthesis mixture obtained was ground for 1 minute in order to obtain a powder with a median size of less than 30 microns. The powder obtained was mixed with deionized water according to the following proportion of 1 g of powder for 50 ml of water. This mixture was filtered through passage through a VWR 185 mm 12-15 μm paper to catch the titanium diboride particles. The retentate was dried at 110° C. to obtain the final dry titanium boride powder.
This example differs from example 2 in that the starting mixture comprises sodium hydroxide granules (NaH content greater than 99%) instead of a sodium oxide powder. The respective proportions by weight of the powders of titanium, sodium tetraborate, and aluminum metal, and the sodium hydroxide granules, were the following 21.9%, 27.6%, 24.7% and 25.8%.
The properties of the final powders obtained are presented in table 2 below. Each powder was mixed with 0.25% of a pressing additive (PVA) and 4.75% of deionized water by mass relative to the mass of powder in order to be cold-pressed under a pressure of 100 bar and to form a cylinder with a diameter of 30 mm and a thickness of 10 mm. After demolding, each cylinder was dried at 11000 for 24 hours and then fired without pressure at a temperature of 1850° C. for 12 h in Argon. The electrical resistivity of each example was measured at room temperature according to the Van der Pauw method at 4 points on an obtained sintered body sample with a diameter of 20-30 mm and a thickness of 2.5 mm.
These results of example 2 by difference with comparative example 1 show that it is possible to obtain, according to the method of the invention, a very pure, fine powder without releasing CO and at a lower synthesis temperature. The comparison of example 2 with examples 1 and 3 shows that the raw powder according to the invention is significantly less dispersed, in particular that produced by the method of example 3 based on a soda solution (see D90−D10)/D50).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2200195 | Jan 2022 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2023/050036 | 1/10/2023 | WO |
