Method for producing fused mayenite product

Abstract

The present invention relates to a method for producing mayenite in the form of an electride, comprising: a) producing a feedstock suitable for obtaining, at the end of the following step c), a product containing more than 90% mayenite, comprising calcium and / or strontium, aluminum and oxygen atoms, as a mass percentage based on the mass of the crystalline phase; b) melting the feedstock until a molten material is obtained; and c) cooling the molten material to solidify it and obtain a polycrystalline molten product, wherein the melting is carried out using an electric arc furnace and in a reducing medium.

Description

[Technical Field]

[0001] The present invention relates to a melt product of mayenite electride and to a method for producing such a product. Finally, the present invention relates to a device comprising a melt product according to the invention or a melt product produced by a method according to the invention. [Background technology]

[0002] European Patent No. EP1717217 discloses mayenite in the form of an electride containing calcium and / or strontium, aluminum and oxygen atoms, i.e., "mayenite electride", in particular ((Ca 24 Al 28 O 64 ) 4+ )(4e - ) and ((Sr 24 Al 28 O 64 ) 4+ )(4e - These mayenites are produced by melting feedstocks, maintaining the molten material in an atmosphere with an oxygen partial pressure of 10 Pa or less, and then cooling.

[0003] Weber Sebastian et al., "Ayenite-based electride C12A7e - ": an innovative synthetic method via plasma arc melting," Materials Chemistry Frontiers, 2021, pages 1301-1314, describes a method for producing mayenite-based electrides by melting them using a plasma furnace.

[0004] Mayenite in the form of an electride can also be obtained by replacing the oxygen ions present in the nanocages with electrons after solid-state calcination, which replacement occurs, for example, by exposure to reducing metal vapors.

[0005] It is also known that the electrons of mayenite in the form of electride can be partially or totally replaced by anions arranged in the nanocages of the mayenite. When the replacement is partial, the electrons keep the mayenite conductive, i.e., in the form of electride. Otherwise, the mayenite becomes electrically insulating and is no longer an electride.

[0006] Methods for producing mayenite containing calcium and / or strontium, aluminum, and oxygen atoms in the form of electride are complicated and expensive. They can only produce small amounts of mayenite. Therefore, there is a continuous need for a simpler production method for producing mayenite, particularly mayenite in the form of electride, in large quantities. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to at least partially meet this need. [Means for solving the problem]

[0008] According to the invention, the object is a method for producing mayenite in the form of an electride, said method comprising: a) Preparing the feedstock; b) melting said feedstock until a molten material is obtained; c) cooling the molten material to solidify it and obtain a polycrystalline melt product, wherein in step a) the feedstock comprises: calcium and / or strontium, Aluminum and Oxygen atoms and at the end of step c), a product containing more than 90% mayenite, as a percentage by mass based on the mass of the crystalline phase; d) optionally grinding the molten product into powder form; e) optionally, particle size screening of the powder; f) Optionally, only a portion of the free electrons of the mayenite of the melt product is replaced by anions arranged in the nanocages of the mayenite, preferably F - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - and combinations thereof, wherein the anions in the nanocage can be different depending on the nanocage considered, or preferably are the same regardless of the nanocage considered; The method includes the sequential steps of The melting is carried out using an electric arc furnace and in a reducing medium; This is achieved by the method described above.

[0009] In other words, the melting is performed using heat generated by an electric arc passing through the feedstock.

[0010] As will be seen in more detail in the remainder of this specification, the inventors have discovered that the above method is simple and inexpensive since it involves only a single melting step, and is capable of producing a melt product containing a very large amount of mayenite electride at the end of step c).

[0011] The manufacturing method according to the invention may also exhibit one or more of the following optional characteristics: In step b), the electrodes of the electric arc furnace are immersed in the molten material; In step a), the feedstock comprises more than 0.5% of a reducing agent, as a mass percentage based on the mass of the feedstock; In step a), the feedstock comprises less than 7% of a reducing agent, as a mass percentage based on the mass of the feedstock; the reducing agent is selected from a carbon source, a metal, and combinations thereof; In step a), the feedstock is with calcium and / or strontium Aluminum and Oxygen atoms and containing less than 50% mayenite; In step c), the cooling is adapted to completely solidify the molten material in less than 3 minutes.

[0012] In one embodiment, step f) is carried out by converting substantially all of the free electrons of the mayenite of the melt product into anions, preferably F, arranged in the nanocages of the mayenite. - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - and combinations thereof, wherein the anions in the nanocages may be different depending on the nanocages considered, or preferably are the same regardless of the nanocages considered. Thus, step f') makes the mayenite electrically insulating.

[0013] The present invention also provides a polycrystalline melt product containing more than 90% mayenite in the form of an electride, as a mass percentage based on the crystalline phase, The mayenite is calcium and / or strontium, Aluminum and Oxygen atoms and Including, wherein the molten product comprises carbon atoms in an amount of 15 ppm or more and 5% or less by weight based on the weight of the molten product; The mayenite is Preferably in the form of an electride, or Electrical insulation That is, With respect to the polycrystalline melt product described above.

[0014] In the polycrystalline product, a carbon content of more than 15 ppm and less than 5%, as a mass percentage based on the crystalline phase, and a mayenite content of more than 90%, are considered to be characteristic of the process of melting in an electric arc furnace and in a reducing medium.Therefore, the product according to the present invention can be produced by the method according to the present invention.In a preferred embodiment, the product is obtained by the method according to the present invention.

[0015] The melt product obtained directly by the method according to the present invention, i.e., the melt product obtained without any additional treatment, has a color representative of its electrical conductivity. The color of insulating mayenite is white. The color of mayenite in the form of electride is between cream yellow and black, preferably between green and black. Preferably, mayenite in the form of electride is dark green or black, preferably black. The closer the color is to black, the higher the electrical conductivity.

[0016] As described in European Patent No. EP3489197, the color between cream yellow and yellow is 1×10 -4 The green color corresponds to electrical conductivity less than 1×10 -4corresponds to an electrical conductivity of 1 S / cm to 1 S / cm, and black corresponds to an electrical conductivity of more than 1 S / cm.

[0017] In one embodiment of mayenite in the form of an electride, the total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, is greater than 97% as a mass percentage based on the mass of the melt product.

[0018] Polycrystalline melt products according to the present invention may also include one or more of the following optional features: the product contains more than 95%, preferably more than 98%, of mayenite in the form of electride, as a mass percentage based on the crystalline phase; the product has a carbon atom content of more than 300 ppm, preferably more than 700 ppm, and / or less than 3%, preferably less than 1.5%; the product has a total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, of ​​more than 97%, preferably more than 98%, as a percentage by mass based on the mass of the molten product; the product has a ratio (CaO+SrO) / Al2O3 of greater than 1.60, preferably greater than 1.68, and / or less than 2, preferably less than 1.80, where CaO, SrO and Al2O3 are molar contents based on the oxides; The mayenite contains at least one element selected from Mg, K, Na, Li, Ba, Ga, Si, Ge, Sn, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, and Zn.

[0019] Finally, the present invention relates to a device comprising a product according to the invention and / or a product produced by a method according to the invention.

[0020] When the product is in the form of an electride, the device Catalytic supports, in particular for the synthesis of NH3 or the decomposition of CO2; solid oxide fuel cells (i.e., SOFCs), particularly electrodes, especially cathodes; organic light-emitting diodes (i.e., OLEDs), particularly the cathodes of such diodes; Hall-effect thrusters, especially the cathodes of such thrusters; gridded ion thrusters (i.e., ion thrusters), in particular the cathodes of such thrusters; proton-conducting ceramic fuel cell (i.e., PCFC) is selected from.

[0021] If the product is electrically insulating, the device may solid oxide fuel cells (i.e., SOFCs), i.e., the electrolyte of such cells; solid oxide electrolysis cell (i.e., SOEC); CO2 capture device is selected from.

[0022] The device may also be a hydrogen storage and / or transport device, where the product is in the form of an electride or is electrically insulating.

[0023] definition

[0024] An "electride" is conventionally an ionic compound in which a trapped electron acts as a negatively charged ion.

[0025] The term "mayenite" is conventionally understood to mean a compound having the chemical formula 12CaO 7Al2O3 or 12SrO 7Al2O3 or 12(Ca,Sr)O 7Al2O3, in which part of Ca and / or Sr and / or Al may optionally be replaced by other elements, in particular by Mg, K, Na, Li, Ba, Ga, Si, Ge, Sn, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, Ir, V, P, Er, Yb, Eu, Au, Tb or Zn. Mayenite crystals have a crystal lattice that forms nanocages. Mayenite is electrically neutral.

[0026] Electrically insulating mayenite is conventionally composed of 12 nanocages per unit cell and 2 O atoms within the nanocages. 2- ions, where O 2- ions are commonly referred to as "free oxygens." The electrically insulating mayenite has the formula ((Ca 24 Al 28 O 64 ) 4+ )(O 2- )2.

[0027] It is known that all or part of the free oxygen can be replaced by electrons, commonly called "free electrons", and can be localized in nanocages. The initially electrically insulating mayenite then becomes conductive, i.e., in the form of an electride. In the specific case where all of the free oxygen has been replaced by free electrons, mayenite is commonly represented by the formula ((Ca 24 Al 28 O 64 ) 4+ )(4e - ) is obtained in the form of an electride.

[0028] All or part of the free oxygen and / or free electrons are converted to anions, e.g., F - , it is also known that (F -The number of anions makes it possible to ensure electrical neutrality).

[0029] To express a composition or content "on an oxide basis," in accordance with normal industry practice, all elements other than carbon are converted to their most stable oxide form. For example, the content of the elements calcium, strontium, and aluminum is expressed after converting these elements to their respective forms: CaO, SrO, and Al2O3. Thus, the content of elements other than converted carbon is expressed based on the content of all elements other than converted carbon.

[0030] In particular, the contents of CaO, SrO and Al2O3 relate to the overall contents of the corresponding chemical elements Ca, Sr and Al, respectively. Therefore, the contents of CaO, SrO and Al2O3 referred to in this specification represent the contents of the elements Ca, Sr and Al not only in the form of CaO, SrO and Al2O3 phases, but also in other forms. This therefore includes the contents of the elements Ca, Sr and Al in particular in the form of suboxides, optionally nitrides, oxynitrides, carbides, oxycarbides, carbonitrides or metals.

[0031] When oxide phases, such as CaO, SrO, or Al2O3 phases, are referred to, these are identified by designating them as CaO, SrO, or Al2O3 "phases."

[0032] The total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, is expressed as a mass percentage based on the mass of the melt product, without converting the metals to their most stable oxide forms.

[0033] The term "impurities" is understood to mean unavoidable components inevitably introduced with the starting materials. In particular, oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides, and compounds belonging to the group of metal species of silicon, sodium and other alkali metals, iron and vanadium are impurities, especially when partial substitution of the elements Ca and / or Sr and / or Al of the mayenite is not sought.

[0034] The term "precursor" of an oxide is understood to mean a component capable of providing said oxide during the manufacture of the molten product according to the invention.

[0035] The term "molten product" is understood to mean a solid product obtained by solidification by cooling of a molten substance.

[0036] A "molten mass" is a mass that has been liquefied by heating the feedstock, and may contain small amounts of solid particles, but the amount is insufficient to constitute the mass. To maintain its shape, the molten mass must be contained in a container.

[0037] Electric arc furnaces are well-known furnaces commonly used for the production of molten products, in particular refractory blocks or abrasive grain. They are equipped with electrodes that generate an electric arc between them. This arc generates a large amount of heat, making it possible to melt the feedstock.

[0038] An electric arc furnace generates an electric arc between electrodes, typically made of graphite, typically in air, which passes through a feedstock to melt it. An electric arc furnace (EAF) is notably different from a plasma arc furnace (PAF), in which a plasma melts the feedstock, where the plasma is generated by excitation of a gas using an electric arc (and therefore is not used to melt the feedstock directly). The heating dynamics are also very different, which can change the phase of the product produced.

[0039] Conventionally, the electrode is said to be immersed "in a bath of molten material" when the electrode is positioned so that its free end is submerged in the liquid bath during melting.

[0040] A "reducing medium" is a medium that causes the extraction of oxygen atoms from the molten material. Melting in a reducing medium is not difficult to perform. In particular, a reducing agent may be added to the feedstock, or in an electric arc furnace, process conditions may be adjusted to ensure reduction, in particular by bringing the electrode close to the bath of molten material or immersing the electrode in the bath.

[0041] When referring to "all of the free electrons" or "substantially all of the free electrons," it is understood that this means all of the free electrons, with a few exceptions that do not change the measurable properties of mayenite. When referring to "a portion of the free electrons," it excludes "substantially all of the free electrons."

[0042] The term "median size" of a powder refers to the size that separates the particles into first and second populations equal in mass, where the first and second populations contain only particles that are equal to or greater than the median size, or only particles that are less than the median size. The median size of a powder can be determined using a laser particle size analyzer.

[0043] The words "including," "comprising," and "having" are to be interpreted broadly and without limitation. DETAILED DESCRIPTION OF THE INVENTION

[0044] The following description is intended to be illustrative and not limiting of the invention.

[0045] Method for producing mayenite in the form of electride

[0046] The method according to the invention may be as described in the examples below, comprising steps a) to f).

[0047] In step a), the starting materials are conventionally weighed, preferably mixed, to obtain a feedstock having the desired composition.

[0048] The skilled person has no difficulty in selecting the starting materials of the feedstock so that the melted product, i.e. the solid mass obtained at the end of step c), has the desired composition, and in particular knows how to adapt the feedstock, in particular in accordance with the fact that part of the starting materials of the feedstock will be dispersed during melting.

[0049] The feedstock is preferably in the form of a particulate mixture, wherein the median diameter of at least one starting material, preferably the median diameter of each starting material, of the particulate mixture is preferably less than 1 mm, more preferably less than 0.5 mm.

[0050] Preferably, the feedstock comprises less than 70%, preferably less than 50%, preferably less than 30%, preferably less than 10%, where mayenite comprises calcium and / or strontium, aluminum and oxygen atoms.

[0051] More preferably, the feedstock does not contain mayenite, which contains calcium and / or strontium, aluminum and oxygen atoms. Advantageously, the method is simplified.

[0052] The elements Ca and / or Sr, and Al are preferably introduced into the feedstock in the form of CaO and / or SrO, and Al2O3 oxides. They may also be conventionally introduced in the form of precursors of these oxides, for example, in the form of CaCO3 and / or SrCO3 phases. The element Al is preferably introduced into the feedstock at least partially in the form of the Al2O3 phase and / or in the form of precursors of this oxide, for example, in the form of aluminum hydroxide and / or boehmite. Preferably, the element Al is introduced into the feedstock partially in the form of the Al2O3 phase and partially in metallic form. In one embodiment, the element Al is introduced into the feedstock entirely in the form of the Al2O3 phase.

[0053] In a preferred embodiment, the feedstock comprises a reducing agent, i.e., an agent that generates a reducing medium during melting, preferably selected from a carbon source, a metal, and combinations thereof. Preferably, the reducing agent consists of a carbon source, preferably selected from carbon, petroleum coke, pitch, coal, and combinations thereof, preferably petroleum coke, and preferably the metal is aluminum.

[0054] Those skilled in the art know how to determine a suitable amount of reducing agent. Preferably, the amount of reducing agent in the feedstock is, as a percentage by mass based on the feedstock, more than 0.5%, preferably more than 1%, preferably more than 1.5%, and preferably less than 7%, preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3.5%.

[0055] In step b), an electric arc furnace is used, preferably an electric arc furnace of the Heroult type equipped with graphite electrodes, but all known electric arc furnaces can be envisaged, provided that they are capable of melting the feedstock in a reducing medium.

[0056] Melting in a reducing medium is preferably obtained by the presence of a reducing agent in the feedstock and / or by the proximity of a graphite electrode to a bath of molten material.

[0057] Melting the feedstock is carried out with an electrode placed away from the feedstock suitable for achieving melting in a reducing medium, preferably in skimming mode (where the distance between the electrode and the feedstock is preferably less than 2 cm), or in a mode in which the electrode is immersed in a bath of molten material.

[0058] Preferably, the electrodes are in skimming mode or immersed in a bath of molten material, preferably immersed in a bath of molten material. Preferably, the feedstock comprises a reducing agent. Preferably, the electrodes are immersed in a bath of molten material and the feedstock comprises a reducing agent.

[0059] Preferably, the starting materials are melted at atmospheric pressure.

[0060] Preferably, the starting materials are melted in an uncontrolled gaseous environment, preferably under air.

[0061] Preferably, an electric arc furnace with a capacity of more than 200 kW is used, equipped with a 160 liter tank and with a melting energy before casting of more than 1 kWh / kg of starting material, preferably less than 6 kWh / kg of starting material, or an electric arc furnace of a different capacity used under equivalent conditions is used, the skilled person knowing how to determine such equivalent conditions.

[0062] In step c), the molten material is cooled to solidify it and obtain the molten product.

[0063] Preferably, the cooling is rapid, preferably so rapid that the molten material is completely solidified in less than 3 minutes, preferably less than 2 minutes, preferably less than 1 minute, preferably less than 40 seconds, preferably less than 30 seconds, and preferably more than 1 second. Rapid cooling can in particular result by pouring into a mold as described in U.S. Pat. No. 3,993,119.

[0064] Steps a) to c) make it possible to produce a melt product containing in particular a large amount of mayenite electride, which contains free electrons housed in nanocages and possibly free oxygen.

[0065] In an optional step d), the molten product is ground to obtain a powder, which can be carried out by any conventional technique.

[0066] In optional step e), particle size selection is carried out to adapt the particle size of the powder to the intended application. Particle size selection, such as sieving or cyclone particle size selection, can be used.

[0067] In an optional step f), only a portion of the free electrons (and any free oxygen) of the mayenite of the melt product is converted into at least anions, preferably F, arranged in the nanocages of the mayenite, optionally in the form of a powder. - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - and combinations thereof, wherein the anions in the nanocage can be different depending on the nanocage considered, or preferably are the same regardless of the nanocage considered.

[0068] Methods for replacing the free electrons (and any free oxygen) present in the mayenite of the melt product with anions are well known to those skilled in the art. For example, H - Anions can replace at least a portion of the free electrons present in the mayenite of the melt product by heat treatment at 1250°C for 2 hours in a 100% H2 atmosphere.

[0069] Method for producing insulating mayenite

[0070] In a non-preferred embodiment, the method comprises, instead of step f), an optional step f'), during which substantially all free electrons (and any free oxygen) of the mayenite of the melt product, optionally in the form of a powder, are replaced by anions arranged in the nanocages of the mayenite, wherein the electroneutrality of the mayenite is maintained. The anions are preferably F - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - and combinations thereof. The anion may be different depending on the nanocage under consideration, or preferably is the same regardless of the nanocage under consideration.

[0071] Thus, before step f'), the mayenite in the form of electride becomes electrically insulating.

[0072] Melt products of mayenite in the form of electrides

[0073] The melt product according to the invention, which contains more than 90% mayenite in the form of electride, preferably has one or more of the following optional characteristics: the content of oxide compounds is, as a mass percentage based on the mass of the molten product, greater than 95%, preferably greater than 96%, more preferably greater than 97%, more preferably greater than 98%; carbon atoms and oxide compounds together account for more than 99%, preferably more than 99.5%, more preferably 100% of the mass of the molten product; the carbon content, as a mass percentage based on the mass of the molten product, is more than 15 ppm, preferably more than 20 ppm, preferably more than 100 ppm, preferably more than 300 ppm, preferably more than 500 ppm, preferably more than 700 ppm, and / or preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.5%; the amount of mayenite, as a mass percentage based on crystalline phases, is greater than 92%, preferably greater than 93%, preferably greater than 94%, preferably greater than 95%, preferably greater than 96%, preferably greater than 97%, preferably greater than 98%, preferably greater than 99%; the amount of amorphous phase, measured as described in the examples, is less than 30%, preferably less than 20%, preferably less than 15%, preferably less than 10%, as a percentage by weight based on the weight of the molten product; In a preferred embodiment, preferably in the case of mayenite in the form of an electride, the total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, as a mass percentage based on the mass of the melt product, is greater than 97%, preferably greater than 98%, preferably greater than 99%; the ratio (CaO+SrO) / Al2O3 (wherein CaO, SrO and Al2O3 are molar contents based on oxides) is greater than 1.60, preferably greater than 1.64, preferably greater than 1.68, and preferably less than 2, preferably less than 1.94, preferably less than 1.86, preferably less than 1.80, preferably less than 1.76, preferably less than 1.74; In one embodiment, the mayenite comprises at least one element selected from Mg, K, Na, Li, Ba, Ga, Si, Ge, Sn, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, Zn, preferably substituting Ca and / or Sr and / or Al; The Raman spectrum of the melt product according to the present invention shows a peak at 1870 cm -1 wherein the Raman spectrum is determined using a monochromatic light source having a wavelength equal to 532 nm; A portion of the mayenite nanocages contains anions, preferably F - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - and combinations thereof, wherein the mayenite additionally contains free electrons; A part of the nanocages of the mayenite is O 2- and some of the nanocages of the mayenite are occupied by F - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - wherein the anions may be the same or different depending on the nanocage under consideration, and the mayenite additionally contains free electrons; Different anions may be accommodated in different nanocages of the mayenite, and preferably all of the nanocages occupied by anions are occupied by the same anion, wherein the mayenite additionally contains free electrons.

[0074] In a preferred main embodiment, the melt product according to the invention comprises: a content of oxide compounds, expressed as a percentage by mass based on the mass of the molten product, of more than 95%, preferably more than 96%, preferably more than 97%, preferably more than 98%, and a carbon atom content of more than 15 ppm, preferably more than 20 ppm, preferably more than 100 ppm, preferably more than 300 ppm, preferably more than 500 ppm, preferably more than 700 ppm, as a percentage by mass based on the mass of the molten product, and less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.5%; an amount of mayenite phase of more than 90%, preferably more than 92%, preferably more than 93%, preferably more than 94%, preferably more than 95%, preferably more than 96%, preferably more than 97%, preferably more than 98%, preferably more than 99%, as a mass percentage based on crystalline phases; an amount of amorphous phase, measured as a percentage by mass based on the mass of the molten product, of less than 30%, preferably less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 10%, as described in the examples; and the total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, of ​​more than 97%, preferably more than 98%, preferably more than 99%, as a percentage by mass based on the mass of the molten product; A ratio (CaO+SrO) / Al2O3 (wherein CaO, SrO and Al2O3 are the molar contents on an oxide basis) of more than 1.60, preferably more than 1.64, preferably more than 1.68, and preferably less than 2, preferably less than 1.94, preferably less than 1.86, preferably less than 1.80, preferably less than 1.76, preferably less than 1.74.

[0075] Preferably, the color of the mayenite in the melt product is between green and black, preferably dark green or black, more preferably black.

[0076] In one embodiment, the melt product is in the form of a powder, preferably having a median diameter of more than 0.1 μm and less than 1 mm.

[0077] Melt products of electrically insulating mayenite

[0078] In one non-preferred embodiment, the mayenite is electrically insulating. The mayenite does not contain substantially any free electrons, and some of the nanocages are ionized by anions, preferably F. - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - where the anions within the nanocages may be the same or different depending on the nanocages considered. Preferably, some of the nanocages of the mayenite contain free oxygen O 2- and some of the nanocages of the mayenite are occupied by F - , Cl - , O.H. - , H - , O2 - , O - , O2 (2-) , N 3- , N.H. 2- , NH2 - , C2 (2-) , S - , C.N. - , NO2 - , S2 - where the anions may be the same or different depending on the nanocage under consideration.

[0079] Therefore, the present invention provides a polycrystalline melt product containing electrically insulating mayenite in a mass percentage based on the crystalline phase of more than 90%, The mayenite is calcium and / or strontium, Aluminum and Oxygen atoms and Including, wherein the molten product contains carbon atoms in an amount greater than 15 ppm and less than or equal to 5% by weight based on the weight of the molten product; With respect to the polycrystalline melt product described above.

[0080] The molten product has a white color.

[0081] Other features described above for the melt product of mayenite in the form of an electride, in particular those relating to the content of oxide compounds, the content of carbon and oxide compounds, the content of carbon, the amount of mayenite, the amount of amorphous phase, the total amount of the elements Ca, Sr, Al, C and O, the ratio (CaO + SrO) / Al2O3 (CaO, SrO and Al2O3 are molar contents based on the oxides), the elements that may be present in the mayenite (in particular elements substituting Ca and / or Sr and / or Al), and the anions present in the nanocages, are optionally applicable to this embodiment.

[0082] Example

[0083] The following non-limiting examples are given for the purpose of illustrating the present invention.

[0084] Measurement protocol

[0085] To determine the composition of the melt product, beads are produced by melting the powder of the melt product, and the content of elements other than carbon atoms is measured by X-ray fluorescence, where oxygen atoms are considered to make up the remaining mass to 100%.

[0086] The carbon atom content of the melt product is measured using a CS744 model carbon-sulfur analyzer sold by LECO.

[0087] The median diameter of the powder is conventionally measured using an A950V2 model laser particle size analyzer sold by Horiba.

[0088] The amount of the various crystalline phases present in the molten product is measured on samples ground dry in an RS100 mill sold by Retsch equipped with a bowl and a tungsten carbide wheel so that the sample is in the form of a powder with an oversize of less than 5% by mass at 40 μm.

[0089] A Bruker D8 Endeavor was used for data acquisition, with a 2θ angular range of 5° to 80°, a step of 0.01°, and a count time of 0.34 seconds per step. The front lens was equipped with a 0.3° primary slit and a 2.5° Soller slit. The sample was rotated by itself using an automatic knife at a speed equal to 15 rpm. The rear lens was equipped with a 2.5° Soller slit, a 0.0125 mm nickel filter, and a 1D detector with an aperture equal to 4°.

[0090] The diffractograms are then qualitatively analyzed using EVA software version 6.0 and the COD database.

[0091] The mayenite phase can be identified by the COD database (Crystallography Open Database) record COD 4308076. The peaks of the mayenite phase present in the melt product may have a slight offset from the data record used depending on the presence of the element Sr and an element selected from Mg, Ga, Si, Ge, Sn, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, Zn and combinations thereof.

[0092] Once the phases present have been identified, the mass abundance of mayenite and other crystalline phases is assessed by Rietveld refinement using HighScore Plus software.

[0093] The amount of amorphous phase present in the molten product is determined by X-ray diffraction using a D8 Endeavour machine from Bruker according to the following method: Diffractograms are obtained with this equipment in the same way as for the determination of crystalline phases. The samples analyzed are in the form of powders with an oversize at 40 μm of less than 5% by weight.

[0094] After opening the obtained diffractogram in EVA6.0 software, click on the "define background" icon, and the "define background" window will appear on the screen.

[0095] In the "define background" window, select "original measurement" and "add background as scan", then check the "Auto Curvature and Threshold" box.

[0096] In the "Properties" window of the diffractogram, check the "Calculate crystallinity" and "Display amorphous" boxes.

[0097] The value for the amount of amorphous phase is the "% amorphous" value in the "Properties" window of the diffractogram as a mass percentage based on the mass of the sample.

[0098] Manufacturing Protocol

[0099] The examples were prepared from the following starting materials: alumina powder having a purity greater than 99.8% by mass and a median diameter equal to 90 μm; Calcium carbonate powder having a purity of more than 99.3% by mass and a median diameter equal to 1.6 μm. Petroleum coke.

[0100] The fused product of Example 1* was prepared according to the teachings of EP 1717217 as follows: 37.3 g of alumina powder and 62.7 g of calcium carbonate powder were mixed in a jar mixer for 30 minutes, then the mixture was placed in a carbon crucible, and the crucible was closed with a carbon lid. Finally, the crucible thus filled was placed in the quartz tube of a tubular furnace, and an argon atmosphere was maintained in the quartz tube for the entire duration of the following heat treatment: From room temperature to 1650°C, at a rate equal to 400°C / hour, Hold at 1650°C for 9 hours and 30 minutes. From 1650°C to room temperature, it is decreased at a rate equal to 400°C / hour.

[0101] The melt product of Example 2* was prepared in a similar manner to Example 1*, except that the feedstock further contained 3.1 g of petroleum coke (3%).

[0102] The product of Example 3 according to the present invention was prepared according to the following manufacturing process according to the present invention: a) producing by blending a feedstock consisting of 36.2% alumina powder, 60.8% calcium carbonate powder, and 3% petroleum coke, as percentages by mass based on the mass of the feedstock; b) melting the feedstock in a reducing medium in a single-phase electric arc furnace of the Heroult type (furnace vessel with a diameter of 0.8 m, a voltage of 80 V, a current of 2250 A and a supplied specific electric energy of 3 kWh / kg charged) with graphite electrodes, the electrodes being immersed in a bath of molten material; c) Rapid cooling of the molten material by a device for casting between thin metal plates, such as that presented in US Pat. No. 3,993,119, so that the molten material is completely solidified in the form of a plate in less than 3 minutes.

[0103] The product of Example 4 according to the invention was prepared in the same way as the product of Example 3, with the only difference being step c): the molten material was melted into a molten metal tube with dimensions of 220*200*180 mm 3 The melt was then poured into a graphite mold to obtain a molten product. The molten material cooled more slowly than in Example 3.

[0104] The product of Example 5 according to the present invention was prepared according to the following manufacturing process according to the present invention: a) producing by blending a feedstock consisting of 37.3% alumina powder and 62.7% calcium carbonate powder, as percentages by mass based on the mass of the feedstock; b) melting the feedstock in a reducing medium in a single-phase electric arc furnace of the Heroult type (furnace vessel with a diameter of 0.8 m, a voltage of 88 V, a current of 2250 A and a supplied specific electric energy of 6 kWh / kg charged) with graphite electrodes, the electrodes being immersed in a bath of molten material; c) Rapid cooling of the molten material by a device for casting between thin metal plates, such as that presented in US Pat. No. 3,993,119, so that the molten material is completely solidified in the form of a plate in less than 3 minutes.

[0105] Table 1 below summarizes the results obtained.

[0106] [Table 1] nd: not determined *: outside the present invention

[0107] The products of Examples 1 and 2 contain almost no mayenite.

[0108] The products of Examples 3 and 4 are black in color, which is characteristic of mayenite electride having high electrical conductivity.

[0109] The product of Example 5 was yellow in color, which is characteristic of mayenite electride having low electrical conductivity.

[0110] The products of Examples 3-5 exhibit an amount of amorphous phase of less than 10%, as a weight percentage based on the weight of the molten product.

[0111] In Example 1, melting was carried out in a closed carbon crucible placed in a neutral argon atmosphere, and the feedstock did not contain a reducing agent. It was found that the method according to the present invention results in an amount of mayenite electride of more than 90% as a mass percentage based on the mass of the crystalline phase, whereas Example 1 does not contain any mayenite. The substantial absence of mayenite is also contrary to the teaching of European Patent No. EP1717217.

[0112] A comparison of Example 1* and Example 2* shows that under the same production conditions, the addition of 3% petroleum coke as a reducing agent to the feedstock (Example 2*) increases the amount of mayenite, but is insufficient to obtain an amount of mayenite phase electride of more than 90% as a mass percentage based on the mass of the crystalline phase.

[0113] A comparison of Example 2* with Example 3 surprisingly shows that with the same content (3%) of petroleum coke (reducing agent) in the feedstock, where melting is carried out in a reducing medium, it is possible to obtain a melt product containing more than 90% mayenite phase electride as a mass percentage based on the mass of the crystalline phase by using an electric arc furnace.

[0114] The significant 2.9-fold increase in the amount of mayenite is not solely the result of the additional carbon atoms provided by the electrode, although the amount is small. It is also not due to differences in the amount of reducing agent, which are the same in the two examples. Surprisingly, and for reasons that cannot currently be theoretically explained, this increase is due to the use of an electric arc furnace.

[0115] A comparison of Example 3 and Example 4 shows that rapid cooling is advantageous in terms of the amount of mayenite.

[0116] Finally, Example 5 shows that the presence of a reducing agent is not essential to obtain a high mayenite electride content, provided that the melting is carried out in an electric arc furnace that is adjusted to ensure melting in a reducing medium.

[0117] It is noteworthy that the Raman spectrum of Example 3 according to the present invention shows a peak at 1870 cm -1 where the Raman spectrum was determined using a monochromatic light source with a wavelength equal to 532 nm.

[0118] Thus, as the examples show, the method according to the present invention is simple and inexpensive because it involves only one melting step, and it is possible to produce a melt product containing a very large amount of mayenite electride. In other words, it is not necessary to carry out several heating steps before obtaining the desired amount of mayenite phase.

[0119] Of course, the invention is not limited to the described embodiments, which are provided by way of illustrative and non-limiting examples.

[0120] In particular, the melt product according to the present invention is not limited to any particular shape or size.

Claims

1. A method for producing mayenite in the form of an electride, the method comprising: a) preparing feedstock; b) melting said feedstock until a molten material is obtained; c) cooling the molten material to solidify it and obtain a polycrystalline melt product, wherein in step a) the feedstock comprises: calcium and / or strontium, Aluminum and Oxygen atoms and at the end of step c), a product containing more than 90% mayenite, as a percentage by mass based on the mass of the crystalline phase; d) optionally grinding the molten product into powder form; e) optionally, particle size screening of said powder; The method includes the sequential steps of The melting is carried out using an electric arc furnace and in a reducing medium. The method.

2. 2. The method of claim 1, wherein in step b), electrodes of the electric arc furnace are immersed in the molten material.

3. 3. The method of claim 1 or 2, wherein in step a) the feedstock comprises more than 0.5% of reducing agent, as a mass percentage based on the mass of the feedstock.

4. 4. The method according to claim 1, wherein in step a) the feedstock comprises less than 7% of reducing agent, expressed as a mass percentage based on the mass of the feedstock.

5. 5. The method of claim 3 or 4, wherein the reducing agent is selected from a carbon source, a metal, and a combination thereof.

6. 6. The method according to claim 1, wherein in step a), the feedstock contains less than 50% mayenite containing calcium and / or strontium, aluminum and oxygen atoms.

7. 7. The method according to claim 1, wherein the electric arc furnace is equipped with graphite electrodes, and wherein in step b) melting the feedstock is carried out with electrodes positioned away from the feedstock that are suitable for achieving melting in a reducing medium.

8. 8. The method according to any one of claims 1 to 7, wherein in step c) the cooling is adapted so that the molten material completely solidifies in less than 3 minutes.

9. The method according to any one of claims 1 to 8, comprising a step f) after step c) and / or, if the method comprises steps d) and / or e), after step d) and / or step e), in which only a part of the free electrons of the mayenite of the melt product are replaced by anions, wherein the anions are preferably all identical.

10. The anion is F - , Cl - , O.H. - , H - , O 2 - , O - , O 2 (2-) , N 3- , N.H. 2- , N.H. 2 - , C 2 (2-) , S - , C.N. - , NO 2 - , S 2 - 10. The method of claim 9, wherein the hydroxyl group is selected from the group consisting of:

11. A method for producing insulating mayenite, A method according to any one of claims 1 to 8; After step c), and / or if the method according to any one of claims 1 to 8 comprises step d) and / or step e), after step d) and / or step e), a step f') in which substantially all free electrons of the mayenite of the melt product are replaced by anions. The method comprising:

12. The anion is F - , Cl - , O.H. - , H - , O 2 - , O - , O 2 (2-) , N 3- , N.H. 2- , N.H. 2 - , C 2 (2-) , S - , C.N. - , NO 2 - , S 2 - 12. The method of claim 11 , wherein the hydroxyl group is selected from the group consisting of:

13. A polycrystalline melt product containing more than 90% mayenite in the form of an electride as a mass percentage based on the crystalline phase, The mayenite is calcium and / or strontium, Aluminum and Oxygen atoms and Including, wherein the molten product contains carbon atoms in an amount of 15 ppm or more and 5% or less by weight based on the weight of the molten product; The polycrystalline melt product.

14. Contains more than 95% mayenite in the form of electride, as a percentage by mass based on the crystalline phase; and / or having a carbon atom content greater than 300 ppm and less than 3%; and / or having a total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, of ​​greater than 97% by mass percentage based on the mass of the molten product; and / or Ratio (CaO+SrO) / Al greater than 1.60 and less than 2 2 O 3 where CaO, SrO and Al 2 O 3 is the molar content based on the oxide, Here, the mayenite contains at least one element selected from Mg, K, Na, Li, Ba, Ga, Si, Ge, Sn, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The melt product of claim 13.

15. Contains more than 98% mayenite in the form of electride, as a percentage by mass based on the crystalline phase; and / or having a carbon atom content greater than 700 ppm and less than 1.5%; and / or and / or having a total amount of the elements Ca, Sr, Al, C and O, Ca+Sr+Al+O+C, greater than 98% by mass percentage based on the mass of the molten product; and / or Ratio (CaO+SrO) / Al greater than 1.68 and less than 1.80 2 O 3 where CaO, SrO and Al 2 O 3 is the molar content based on the oxide, 15. The melt product of claim 14.

16. 1×10 -4 16. The melt product according to any one of claims 13 to 15, having an electrical conductivity of from 1 S / cm to 1 S / cm, or an electrical conductivity of more than 1 S / cm.

17. 1870cm -1 17. The melt product according to any one of claims 14 to 16, having a Raman spectrum with a band at 0.555° C., wherein the Raman spectrum is determined using a monochromatic light source having a wavelength equal to 532 nm.

18. A melt product according to any one of claims 13 to 17, produced by a method according to any one of claims 1 to 10.

19. Formula ((Ca 24 Al 28 O 64 ) 4+ )(O 2- ) 2 A white polycrystalline melt product containing more than 90% of mayenite as a mass percentage based on the crystalline phase, The mayenite is calcium and / or strontium, Aluminum and Oxygen atoms and Including, wherein the molten product contains carbon atoms in an amount of 15 ppm or more and 5% or less by weight based on the weight of the molten product; The white polycrystalline melt product.

20. 20. The melt product of claim 19, produced by the method of claim 11 or 12.

21. A device, 19. A product according to any one of claims 13 to 18, wherein the device comprises: Catalyst support; solid oxide fuel cell electrodes; organic light-emitting diodes; Hall effect thrusters; lattice ion thrusters; Proton-conducting ceramic fuel cells; Hydrogen storage and / or transport device or 21. The product of claim 19 or 20, wherein the device comprises: solid oxide fuel cell electrolytes; solid oxide electrolysis cells; CO 2 capture devices; Hydrogen storage and / or transport device Selected from: The device comprising:

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