WO2015092652A1 - Method for manufacturing a ctf product - Google Patents

Abstract

The present invention relates to a molten product comprising iron-doped calcium titanate, optionally doped by an element B', with perovskite structure ABO₃, in which the A site is occupied by calcium and the B site is occupied by titanium and iron, the B site optionally being doped with an element B', such that the product complies with the formula Ca_(1-z)Ti_1-(x+y)Fe_xB'_yO₃, wherein 0< x ≤ 0.4, 0 ≤ y ≤ 0.3, x + y ≤ 0.6 and -0.1 ≤ z ≤ 0.1, the element B' being selected among chromium, niobium and the mixtures thereof.

Description

 Method of manufacturing a CTF product

Technical area

 The invention relates to a novel product comprising an iron-doped calcium titanate perovskite phase and a novel process for producing such a product.

State of the art

Iron-doped calcium titanate perovskite, or "CTF" is conventionally referred to as a perovskite structure material AB0 ₃ , where site A is occupied by calcium, site B by titanium and iron, site B capable of being doped with an element B 'so that the product satisfies the formula Ca ^ Ti ^ _{x + yj} Fe _x B' _y Os with 0 <x≤0.4, 0≤y≤0.3, x + y≤ 0.6 and -0, 1 ≤ z 0 0, 1, the element B 'being chosen from chromium, niobium and their mixtures. The electroneutrality of said perovskite structural product of formula

is ensured by the oxygen content. CaTi ₀ , 85Fe _0, i5O ₃ is a particular example of CTF.

No. 4,117,209 discloses a plasma spraying method in which the projected material may be iron-doped calcium titanate. This document does not describe the dopant content. Moreover, a plasma projection does not necessarily lead to a total melting of all the projected particles.

 The CTF is particularly used in applications requiring the presence of a mixed conductor, in other words an ionic and electronic conductor. It is generally manufactured by the following methods:

 co-precipitation / sol-gel,

 - synthesis by solid-state sintering, or

 - synthesis from precursors and pyrolysis.

 These complex processes lead to a high cost. There is therefore a need for a new process for manufacturing CTF at reduced cost and in industrial quantities. The object of the invention is to satisfy this need.

Summary of the invention

According to the invention, this goal is achieved by means of a product comprising or even consisting of CTF, called "CTF product", which is remarkable in that it is melted, that is to say that it is obtained by melting then solidification. Although the manufacture of fusion-solidification products is well known, it is the merit of the inventors to have discovered that, contrary to a prejudice, this technique makes it possible to manufacture CTF.

Advantageously, the product according to the invention can therefore be manufactured at reduced costs and in industrial quantities.

 A CTF according to the invention may have a composition identical to that of the CTFs manufactured according to the methods of the prior art. However, it has a particular microstructure, which distinguishes it from these latter CTFs, and which therefore constitutes a signature of the fusion-solidification process for CTFs.

 More specifically, the inventors have observed that a melting-solidification process leads to a distribution of iron that is not homogeneous. In fact, there are characteristic local overconcentrations in the grain boundaries.

 If the product is ground very finely, this characteristic is reflected in the resulting powder, by a high variability of the iron concentration in the various particles.

 An analysis of a CTF according to the invention thus makes it easy to distinguish it from a product of the same structure synthesized by solid-state sintering, as described in particular in the articles:

"Influcence of Microstructure on the Electrical Properties of Iron-Substituted Calcium Titanate Ceramics", F. FIGU EI REDO et al. J. Am.Soc., 87, 2252-2261,

, 0.2, 0.3)" de S. MARION et al., lonic 5 (1999), "lonic and electronic conductivity in

, 0.2, 0.3) "from S. MARION et al., Lonic 5 (1999),

 "Oxygen vacancy ordering in iron-doped calcium titanate", by VAN DEN BOSSCH E, M. Se. Thesis, University of TWENTE (2005),

 "Electrical conductivity of iron-doped calcium titanate", L. A. DUNYUSHKI NA et al., Solid State Electronics, 116 (1999), 85-88.

 The content and the nature of a molten CTF depend in particular on the composition of the feedstock. A product according to the invention is however still polycrystalline.

In one embodiment of the invention, the melted product has a CTF level of greater than 50%, said CTF having calcium, calcium, titanium, iron and doping element B ', respectively, such that, by setting x = f / (t + f + b'), y = b '/ (t + f + b') and z = 1 - ( c / (t + f + b ')),

 preferably x ≥ 0.05, preferably x ≥ 0.06, preferably x ≥ 0.07, preferably x ≥ 0.08, or even x≥0.085 and preferably x≤0.35, preferably x≤ 0.3, or even x≤0.25, or even x≤0.2, and

 preferably y≤ 0.2, preferably y 0 0, 1, and

 preferably x + y 0,5 0.5, preferably x + y 0,4 0.4, preferably x + y 0,3 0.35, preferably x + y 0,3 0.3, or even x + y 0,2 0.25 and x + y≥0.05, preferably x + y≥0.07, or even x + y≥0.1, or even x + y≥0.15, and

 preferably z≥0.07, preferably z≥0.04 and preferably z≤0.07, preferably z≤0.04.

du CTF, éventuellement dopé du produit selon l'invention. The variables x and y correspond to the atomic proportions x and y of the structure Ca _{(1 z)}

CTF, possibly doped with the product according to the invention.

 Preferably, a product according to the invention also comprises one, and preferably several, of the following optional characteristics:

 The level of CTF is greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 90%, preferably greater than 95%, preferably greater than 99%, more preferably greater than 99.9% or 100

%

 - x≥0.05, preferably x≥0.06, preferably x≥0.07, preferably x≥0.08, or even x≥0.085 and x≤0.35, preferably x≤0.3, even x≤0.25, or even x≤0.2;

 y≤ 0.2, preferably y≤ 0.1;

 - x + y 0,5 0.5, preferably x + y 0,4 0.4, preferably x + y 0,3 0.35, preferably x + y 0,3 0.3, or even x + y 0,2 0.25 and x + y≥0.05, preferably x + y≥0.07, or even x + y≥0.1, or even x + y≥0.15;

 - z≥ -0.07, preferably z≥ -0.04 and z 0,0 0.07, preferably z 0,0 0.04;

 Element B 'is chromium. Chromium improves the ionic conductivity of the product according to the invention;

 Preferably, the product has the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

 37.9% <calcium expressed as CaO <43.6%,

- 33.1% <titanium expressed as Ti0 ₂ <57.6%,

2.7% <iron expressed as Fe ₂ O ₃ <24.5%, - other elements (classically expressed as the most stable oxide) <2%.

 Preferably, the product has the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

 - 40% <calcium expressed as CaO <43.6%

- 33.1% <titanium expressed as Ti0 ₂ <55.8%

2.7% <iron expressed as Fe ₂ O ₃ <23.5%

 - other elements <2%.

 Preferably, the product has the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

 - 40% <calcium expressed as CaO <42.7%

- 38.7% <titanium expressed as Ti0 ₂ <54, 1%

- 4.4% <iron expressed as Fe ₂ O ₃ <17.6%

 - other elements <2%.

Preferably, the total mass content of impurities (elements other than calcium, titanium, iron, niobium and chromium), expressed as oxides, is less than 2%, preferably less than 1.5% by weight. %, preferably less than 1%, preferably less than 0.6%;

 - Preferably,

Na ₂ 0 <0.1%, preferably Na ₂ 0 <0.07%, preferably

Na ₂ 0 <0.05%, and / or

 MgO <0.5%, preferably MgO <0.3%, preferably MgO <0.15%,

SiO ₂ <0.5%, preferably SiO ₂ <0.3%, preferably SiO ₂ <0.1%. Advantageously, these optional features improve the conductivity properties.

In a particular embodiment, the CTF is not doped with an element B ', and has the formula

A product according to the invention may in particular be in the form of a particle. The particle size may in particular be greater than 0.01 μηι, or even greater than 0, 1 μηι, or even greater than 0.5 μηι, or even greater than 1 μηι, or even greater than 10 μηι, or even greater than 50 μηι, or even greater at 100 μηι, or even greater than 0.2 mm, or even greater than 0.25 mm and / or less than 5 mm, or even less than 4 mm, or even less than 3 mm. The invention also relates to a powder comprising more than 90% by weight, or even more than 95%, or even substantially 100% of particles according to the invention.

 A product according to the invention may also be present, without this being preferred, in the form of a block of which all the dimensions are preferably greater than 1 mm, preferably greater than 2 mm, preferably greater than 5 cm, more preferably greater than 15 cm. Preferably a block according to the invention has a mass greater than 200 g.

 In one embodiment, the median size of a powder according to the invention is preferably greater than 0.4 μηι, preferably greater than 1 μηι and / or less than 5 μηι, preferably less than 4 μηι, preferably less than 3 μηι. Such a powder may in particular be obtained by grinding a block according to the invention, in particular by grinding a set of balls.

 The invention also relates to a manufacturing method comprising the following steps:

 a) mixing raw materials so as to form a suitable starting charge to obtain, at the end of step c), a product having a composition of a CTF,

 b) melting of the feedstock until a liquid mass is obtained, c) cooling to complete solidification of said liquid mass, so as to obtain a molten product,

 d) optionally grinding said molten product.

 By simple adaptation of the composition of the feedstock, fusion-solidification processes thus make it possible to manufacture CTF products according to the invention of different sizes and having a CTF content of greater than 50%, preferably greater than 70%, preferably greater than 90%, preferably greater than 95%, more preferably greater than 99%, preferably still greater than 99.9%, or even substantially 100%.

 Preferably, a manufacturing method according to the invention also comprises one, and preferably several, of the following optional characteristics:

At least one or all of the elements calcium, titanium, iron and B 'are introduced in oxide form;

The compounds providing the elements calcium, titanium, iron and B 'together represent more than 90%, preferably more than 99%, in percentages by weight, of constituents of the starting load. Preferably, these compounds, together with the impurities, represent 100% of the constituents of the feedstock;

The compounds providing the elements calcium, titanium, iron and B 'are chosen from CaO, CaCO ₃ , TiO ₂ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , the carbonates of the element B', the hydroxides of the element B ', and the oxides of element B';

 In a particular embodiment, oxide powders are used to provide the titanium, iron and B 'elements, and a carbonate powder to provide the calcium element;

 - In step b), we do not use a plasma torch nor a heat gun. In particular, an arc furnace or induction furnace is preferably used. Advantageously, the productivity is improved. In addition, processes using a plasma torch or a heat gun generally do not make it possible to manufacture fused CTF particles, in particular larger than 200 microns, and at least greater than 500 microns.

In step b), melting is carried out in a crucible in a heat treatment furnace, preferably in an electric furnace, preferably in an oxygenated environment, for example in air.

 In step b), the melting is carried out in an oxygenated, neutral or reducing environment, preferably in an oxygenated environment, for example under air.

In a first preferred embodiment, step c) comprises the following steps:

 Ci) dispersion of the liquid mass in the form of liquid droplets,

c ₂ ) solidification of these liquid droplets by contact with an oxygenated fluid, so as to obtain molten particles.

By simple adaptation of the composition of the feedstock, conventional dispersion processes, in particular by blowing or atomization, thus make it possible to manufacture, from a molten liquid mass, particles having a CTF content of greater than 50%. preferably greater than 60%, preferably greater than 70%, more preferably greater than 90%, more preferably greater than 95%, more preferably greater than 99%, more preferably greater than 99.9%, even more than substantially 100%.

In the first embodiment, preferably, the manufacturing method further comprises one, and preferably more than one, of the optional features listed above and / or the following particular features: In step Ci) and / or in step c ₂ ), said liquid mass is brought into contact with an oxygenated fluid, preferably identical;

 The oxygenated fluid is preferably a gas;

 The oxygenated fluid preferably has an oxygen content of greater than 20% by volume;

 - The stages of dispersion and solidification are simultaneous;

 - It maintains a contact between the droplets and an oxygenated fluid until complete solidification of said droplets. In a second embodiment, step c) comprises the following steps:

 Ci ') pouring the liquid mass into a mold;

c ₂ ') cooling solidification of the liquid mass cast in the mold until a block at least partially solidified;

c ₃ ') demolding the block.

In the second embodiment, preferably, the manufacturing method according to the invention also comprises one, and preferably several, of the optional characteristics listed above and / or the following particular characteristics:

In the step Ci ') and / or in the step c ₂ ') and / or after the step c ₃ '), the said liquid mass being solidified is brought into contact, directly or indirectly, with a fluid oxygenated, preferably having at least 20% oxygen, preferably a gas;

- One starts said contact immediately after demolding the block;

 - The said contact is maintained until complete solidification of the block.

The melted product according to the invention may be at the end of step c) in the form of a block or particles larger than 100 μηι. The molten product is then preferably milled, so as to obtain a powder having a maximum size D ₉₉ , lower than 10 μηι, preferably less than 100 μηι, preferably less than 80 μηι, preferably less than 53 μηι, preferably less than 30 μηι, preferably less than 10 μηι.

 In optional step d), the melt is ground.

Whatever the embodiment considered, other phases than the CTF may be present, as well as impurities from the raw materials.

The invention also relates to a product that may have been obtained by a process according to the invention. The invention also relates to the use of a melted product according to the invention or manufactured or likely to have been manufactured by a method according to the invention in the manufacture of a layer. Advantageously, this layer, porous or dense, has a mixed conduction. The invention also relates to such a layer.

The invention also relates to a layer comprising a product according to the invention or a product manufactured or likely to have been manufactured by a process according to the invention.

 A layer according to the invention preferably has a thickness greater than 1 μηι and less than 3 mm, and a porosity preferably less than 70%.

 In one embodiment, a layer according to the invention preferably has a thickness greater than 200 μηι and / or less than 3 mm, preferably less than 2 mm, and a porosity preferably greater than 10% and / or less than 70%.

 In one embodiment, a layer according to the invention preferably has a thickness greater than 1 μηι and / or less than 1 mm, preferably less than 500 μηι, preferably less than 300 μηι, preferably less than 100 μηι, and a porosity of preferably less than 10%, preferably less than 5%, preferably less than 3%, or even less than 1%.

Definitions

Regardless of the CTF considered, ICDD sheet 00-042-0423 of perovskite CaTi0 ₃ is considered to be the ICDD sheet (International Center for Diffraction Data) of said CTF. This ICDD sheet makes it possible to identify the angular domains of the diffraction peaks corresponding to said CTF.

 The level of CTF in% is defined in a product according to formula (1) below:

T = 100 * (ACTF) / (AcTF ⁺ Secondary Aphases) (1)

OR

ACTF is the area of the CTF phase, measured on an X-ray diffraction diagram of said product, for example obtained from a BRUKER D5000 diffractometer type apparatus provided with a copper anode tube, without treatment. of deconvolution. The area of the CTF phase is defined as the average of the areas of the 3 peaks of higher intensity, each of these areas having previously been normalized with respect to the relative intensity of the corresponding peak of the ICDD record.

The so-called 3 peaks of higher intensity are in the following angular domains: the peak corresponding to the combination of the reflections 101 and 020 is situated between 22.9 ° and 23.5 °, and has a relative intensity equal to 15% on the ICDD file 00-042-0423; the peak corresponding to the combination of the reflections 200, 121 and 002 is between 32 ° and 34 °, and has a relative intensity equal to 150% on said ICDD sheet; and the peak corresponding to the combination of the reflections 202 and 040 is between 47 ° and 48.2 ° and has a relative intensity of 67% on said ICDD sheet;

Secondary Apuases is the sum of the areas of the secondary phases, measured on the same diagram, without deconvolution treatment. The area of a secondary phase is defined as that of its higher intensity diffraction peak or its diffraction multiplet of higher intensity, not superimposed, normalized with respect to the relative intensity of the corresponding peak of the ICDD record. . The secondary phases are the phases detectable by X-ray diffraction other than the CTF phase. Among others, FeO, Ca ₄ Ti ₃ O 10, Ca ₃ Ti ₂ O ₇ , CaO, may be secondary phases identified on the X-ray diffraction pattern, in particular when the CTF is not doped, i.e. say when it does not contain element B '.

"Particle" means a solid object whose size is less than 10 mm, preferably between 0.01 μηι and 5 mm. The "size" of a particle is the average of its largest dimension dM and its smallest dimension dm: (dM + dm) / 2. The size of a particle can be evaluated classically by a particle size distribution characterization performed with a laser granulometer. The laser granulometer may be, for example, a Partica LA-950 from the company HORIBA.

 By "block" is meant a solid object that is not a particle.

The percentiles or "percentiles" 50 (D ₅₀ ), 99.5 (D995) are the particle sizes corresponding to the percentages, by mass, of 50% and 99.5%, respectively, on the cumulative particle size distribution curve. particles of the powder, the particle sizes being ranked in ascending order. For example, 99.5%, by weight, of the particles of the powder have a size less than or equal to D995 and 0.5% of the particles by mass have a size greater than D995. Percentiles can be determined using a particle size distribution using a laser granulometer.

The "50th percentile" (D ₅₀ ) of said powder is called the "median size of a powder".

 The "maximum size of a powder" is the 99.5 percentile (D99 5) of said powder.

"Impurities" means the inevitable constituents introduced involuntarily and necessarily with the raw materials or resulting from reactions with these substances. components. Impurities are not necessary constituents, but only tolerated.

 Unless otherwise indicated, all the oxide contents of the products according to the invention are mass percentages expressed on the basis of the oxides. The oxides preferably represent more than 90%, more than 95%, more than 97%, more than 99%, or even substantially 100% of the mass of the product.

 "Containing a", "comprising a" or "containing a" means "having at least one", unless otherwise indicated.

detailed description

A molten product according to the invention is preferably obtained by melting a starting charge, casting the liquid mass, preferably in a mold or in the form of a net, then solidification.

 An exemplary method according to the invention is now described in detail.

In step a), a feedstock for making a molten product according to the invention is formed from compounds of calcium, titanium, iron and optionally element B ', especially in the form of oxides or of carbonates or hydroxides. The composition of the feedstock may be adjusted by the addition of pure oxides or mixtures of oxides and / or precursors, in particular CaO, CaCO ₃ , TiO ₂ , Fe ₂ O ₃ , FeO, Fe ₃ 0 ₄ , oxide (s) of the element B ', carbonate (s) of the element B', hydroxide (s) of the element B '.

 The amounts of calcium, titanium, iron and element B 'of the feedstock are found essentially in the melted product manufactured. Some of the constituents, for example chromium, which varies according to the melting conditions, can volatilize during the melting step. By his general knowledge, or by simple routine tests, a person skilled in the art knows how to adapt the quantity of these constituents in the starting charge according to the content he wishes to find in the melted products and the melting conditions. implemented.

 The granulometries of the powders used can be those commonly encountered in the melting processes.

Preferably, no compound other than those providing the elements calcium, titanium, iron and B ', or any compound other than CaO, CaCO ₃ , TiO ₂ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , oxide (s) of the element B ', carbonate (s) of the element B', hydroxide (s) of the element B 'and their precursors (that is to say transforming into said compound during the fusion) n' is introduced voluntarily in the starting load, the other elements present being thus impurities. In one embodiment, the sum of CaO, CaCO ₃ , TiO ₂ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , oxide (s) of element B ', carbonate (s) of element B' , hydroxide (s) of the element B 'and their precursors represents more than 99% by weight of the feedstock. To increase the CTF content in the molten product, it is preferable that the molar proportions of the calcium, titanium, iron and B 'elements in the feedstock are close to those of the CTF that it is desired to manufacture.

 Thus, it is preferable, in the feedstock, that the molar contents c, t, f and b 'of the elements calcium, titanium, iron and B', respectively, in molar percentages based on the sum of the contents c, t, f and b 'comply with the following conditions:

• ki. (1-z) / (1-xy) ≤ c / t ≤ k ₂ . (1-z) / (1-xy) (2), and / or

• kL (1-z) / x≤c / f ≤ k ₂ . (1-z) / x (3), and / or

• kL (1-z) / y≤c / b'≤ k ₂ . (1-z) / y (4), and / or

• M / (1-z) ≤ (t + f + b ') / c k k ₂ .1 / (1-z) (5),

or

 x and y may take the values defined above, in particular 0 <x≤0.4, 0≤y≤0.3, x + y≤0.6 and -0, 1≤z≤0.1, and

 ki is 0.8, preferably 0.9, and

k ₂ is 1, 2, preferably 1, 1.

Of course, these values of k ₁ and k ₂ are those to be adopted under established operating conditions, that is to say outside the transition phases between different compositions and outside the start-up phases. Indeed, if the desired product involves a change in the composition of the feedstock relative to that used to manufacture the previous product, it is necessary to take into account the residues of the previous product in the oven. Those skilled in the art, however, know how to adapt the starting load accordingly.

 Intimate mixing of the raw materials can be done in a mixer. This mixture is then poured into a melting furnace.

 In step b), the feedstock is melted, preferably in an electric arc furnace. Electrofusion makes it possible to manufacture large quantities of melted product with interesting yields.

For example, it is possible to use a Héroult type arc furnace comprising two electrodes and whose vessel has a diameter of approximately 0.8 m and can contain approximately 180 kg of liquid. in fusion. Preferably, the energy is between 1400 and 2000 kWh / T. The voltage is for example close to 160 volts and the power of the order of 250 kW.

 But all known furnaces are conceivable, such as an induction furnace, a plasma furnace or other types of Herault furnace, provided they allow to melt substantially completely the starting charge. A melting furnace in electric furnace is also possible.

 The melting can be carried out in an oxygenated, neutral or reducing environment, preferably in an oxygenated environment, for example in air.

 At the end of step b), the feedstock is in the form of a liquid mass, which may optionally contain some solid particles, but in an amount insufficient for them to structure said mass. Typically, the amount of solid particles is less than 10% of the liquid mass. By definition, to maintain its shape, a liquid mass must be contained in a container.

In a first preferred embodiment, step c) consists of the steps Ci) and c ₂ ) described above.

 In step Ci), a stream of molten liquid, at a temperature preferably greater than 1800 ° C., preferably greater than 1900 ° C. and preferably less than 2000 ° C., is dispersed in liquid droplets.

 The dispersion can result from blowing through the net of the liquid mass. But any other method of atomizing a liquid mass, known to those skilled in the art, is possible.

In step c ₂ ), the liquid droplets are converted into solid particles by contact with an oxygenated fluid, preferably a gas, more preferably with air and / or steam. The oxygenated fluid preferably comprises at least 20% by volume of oxygen.

Preferably, the process is adapted so that, as soon as formed, the droplet of molten liquid is in contact with the oxygenated fluid. More preferably, the dispersion (step Ci)) and the solidification (step c ₂ )) are substantially simultaneous, the liquid mass being dispersed by an oxygenated fluid, preferably gaseous, able to cool and solidify this liquid.

Preferably, the contact with the oxygenated fluid is maintained at least until complete solidification of the particles. Air blowing at room temperature is possible.

At the end of step c ₂ ), solid particles are obtained which have a size of between 0.1 μηι and 5 mm, or even between 1 μηι and 5 mm, or even between 10 μηι and 5 mm, depending on the dispersion conditions.

In a second embodiment, step c) consists of the steps Ci '), c ₂ ' and c ₃ ') described above.

 In step Ci '), the liquid mass is cast in a mold capable of withstanding the bath of molten liquid. Preferably, graphite molds, cast iron molds, or as defined in US 3,993,119 are used. In the case of an induction furnace, the coil is considered to constitute a mold. Casting is preferably carried out under air.

In step c ₂ '), the liquid mass cast in the mold is cooled until an at least partially solidified block is obtained.

 Preferably, during solidification, the liquid mass is brought into contact with an oxygenated fluid, preferably gaseous, preferably with air. This contacting can be performed as soon as casting. However, it is preferable to start this contacting only after casting. For practical reasons, the contact with the oxygenated fluid preferably begins after demolding, preferably as soon as possible after demolding.

 The oxygenated fluid preferably comprises at least 20% by volume of oxygen.

Preferably, the contact with the oxygenated fluid is maintained until complete solidification of the block.

In step c ₃ '), the block is demolded. To facilitate contacting the liquid mass with an oxygenated fluid, it is preferable to unmold the block as quickly as possible, if possible before complete solidification. The solidification then continues at step <¾ ').

 Preferably, the block is demolded as soon as it has sufficient rigidity to substantially retain its shape. Preferably, the block is removed as quickly as possible and the contact with the oxygenated fluid is then immediately begun.

Preferably, the demolding is carried out less than 20 minutes after the beginning of the solidification.

After complete solidification, a block is obtained capable of giving after step d) a particle powder according to the invention. In the optional step d), the melted product obtained is crushed and / or ground according to the intended application. If necessary, a granulometric selection is then carried out, depending on the intended application. The powder of melted particles obtained at the end of step d) preferably has a maximum size D ₉₉ , lower than 10 μηι, preferably less than 100 μηι, preferably less than 80 μηι, preferably less than 53 μηι, preferably less than 30 μηι, preferably less than 10 μηι, preferably less than 5 μηι.

All types of crushers and grinders can be used to reduce the size of pieces. Preferably, an air jet mill or a ball mill and / or a microbrush, preferably in a wet environment is used. When wet micromill is used, hydrates may be formed, for example Ca ₃ Fe 2 (OH) ₁₂ or Ca ₃ Fe ₂ Ti0 ₄ (OH) 8. The amount of these hydrates can be reduced by drying the powder, for example at a temperature of 500 ° C. Preferably, drying is carried out when grinding the powder in a humid medium is carried out.

The melted product particles according to the invention may advantageously have various dimensions, the manufacturing process is not limited to obtaining submicron CTF powders. It is therefore perfectly suited to industrial manufacturing. In addition, the particles obtained can advantageously be used to produce layers having a mixed, porous or dense conduction.

The work that led to this invention received funding from the European Union under the Seventh Framework Program (FP7 / 2007-2013) under the project number 268165.

Examples

 The following examples are provided for illustrative purposes and do not limit the invention. The melted products were manufactured in the following manner.

 The following starting raw materials were first intimately mixed in a blender:

- CaC0 ₃ calcium carbonate powder, whose purity is greater than 99% by weight and whose median size is equal to 2 μηι;

TiO ₂ powder, the purity of which is greater than 99% by mass and the median size of which is equal to 2.5 μm;

- Powder Fe ₂ 0 ₃ , the purity is greater than 99% by weight and the median size is equal to 0.4 μηι.

For Examples 1 to 8, each of the starting charges obtained was poured into a Herault-type arc melting furnace. It was then melted following a fusion with a voltage of 160 volts, a power of 240 kW, and a substantially applied energy. equal to 2000 kWh / T for Examples 2 to 5, and a voltage of 1 10 volts, a power of 187 kW, and an applied energy substantially equal to 1600 kWh / T for Examples 1 and 6 to 8, in order to melt all the mixture in a complete and homogeneous way.

The fusions were carried out in an air environment.

For the products according to Examples 1 to 4, and 6, when the melting is complete, the molten liquid is cast so as to form a net.

 A compressed dry air blast, at room temperature and at a pressure of 8 bar, breaks the net and disperses the molten liquid into droplets.

 Blowing cools these droplets and freezes them in the form of melted particles. Depending on the blowing conditions, the melted particles may be spherical or not, hollow or solid. They have a size between 0.005 mm and 5 mm.

For the products of Examples 5, 7 and 8, when the melting was complete, the molten liquid was cast under air in a graphite mold. The block was demolded after complete cooling.

The chemical and CTF phase determination analyzes were performed on samples which, after dry milling, had a median size of less than 40 μηι.

Chemical analysis was performed by X-ray fluorescence.

 The determination of the CTF content is carried out on the basis of the X-ray diffraction diagrams, acquired with a BRUKER D5000 diffractometer provided with a copper anode tube and a 0.6 mm receiving slot. The acquisition of the diffraction pattern is carried out from this equipment, on an angular range 2Θ of between 5 ° and 80 °, with a pitch of 0.02 °, and a counting time of 2s / step. The rotation of the sample holder is engaged in order to limit the effects of preferential orientations.

Using the EVA software (marketed by the BRUKER company) and after performing a subtraction of the continuous background (background 0.8), it is possible to measure the area A _C TF (without deconvolution treatment) of the phase CTF and, for each secondary phase, the area A side _Ph ases (without deconvolution treatment) of the peak of highest intensity or byte highest non-superimposed intensity. One can then calculate the total secondary Aphases by the sum of the areas A _Ph ases area secondaires- CTF rate is then calculated according to the formula (1).

Thus, if the CTF phase is the only phase present in the X-ray diffraction pattern, the CTF level is equal to 100%. Thus, the product of Example 5 has an X-ray diffraction pattern showing the 3 peaks of higher CTF intensity in the following angular domains: 22.9 ° -23.5 °, 32 ° -34 ° and 47 °. ° - 48.2 °, as well as a peak of higher intensity not superimposed for the wustite secondary phase (FeO) in the angular range 2Θ between 35.9 ° and 36.6 °.

 On said diffraction diagram X:

the area of the CTF peak corresponding to the combination of the reflections 101 and 020 situated between 22.9 ° and 23.5 ° is equal to 21 blows. degree. s ^"1 before normalization and equal to 21/0, 15, ie 140 shots, degree, s ^{" 1} after normalization,

the area of the CTF peak corresponding to the combination of the reflections 200, 121 and 002 situated between 32 ° and 34 ° is equal to 199 knots. degree. s ^"1 before normalization and equal to 199/1, 5, ie 132.7 strokes, degree, s ^{" 1} after normalization,

the area of the CTF peak corresponding to the combination of the reflections 202 and 040 situated between 47 ° and 48.2 ° is equal to 107 shots. degree. s ^"1 before normalization and equal to 107 / 0.67, ie 159.7 strokes, degree s ^{" 1} after normalization,

ACTF is therefore equal to (140 + 132, 7 + 159.7) / 3, ie 144.1 strokes. degree.s ^"1 .

The area of the peak of non-superimposed intensity for the wustite secondary phase (FeO) in the angular range 2Θ between 35.9 ° and 36.6 °, corresponding to the reflection 11, is 1.69 shots. . degree. s ^"1 before normalization and equal to 1, 69 / 0.8, ie 2, 1 shots, degree, s ^{" 1} after normalization. A secondary _ph ases is equal to 2 1 hits. degree. s ^"1. The rate of CTF, calculated according to formula (1) is equal to 144, 1 / (144, 1 + 2, 1) or 99%.

The following Table 1 summarizes the results obtained:

Chemical analysis obtained

 (in percentages by weight based on the oxides) perovskite obtained

CTF rate Ca (i_ _Z) Ti (i_ _X) Fe _x 03

impurities

 (%)

eg Ti0 ₂ CaO Fe ₂ 0 ₃ Al ₂ 0 ₃ MgO Na _z O z X Si0 ₂ Other

1 39.9 52.3 6.7 0.07 0.04 0.30 0.30 0.28 100 0.035 0.113

2 40.8 54.1 4.4 0.10 0.04 0.10 0.04 0.31 100 0.006 0.076

3 41, 6 52.3 5.7 0.03 0.04 0.09 0.04 0.21 100 -0.019 0.098

4 42.1 52.0 5.5 0.03 0.04 0.09 0.04 0.21 100 -0.044 0.095

5 39.7 52.9 5.9 0.15 0.04 0.30 0.39 0.60 99 - -

6 40.0 52.8 6.0 0.19 0.04 0.32 0.38 0.28 98 - -

7 40.1 53.6 4.8 0.18 0.04 0.31 0.40 0.57 91 - -

8 41, 9 54.0 2.7 0.16 0.04 0.31 0.38 0.46 82 - -

Table 1

avec 0 < x ≤ 0,4, 0≤y≤0,3, x + y≤ 0,6 et -0, 1 ≤ z≤ 0,1 , l'élément B' étant choisi parmi le chrome, le niobium et leurs mélanges. These examples make it possible to demonstrate the effectiveness of the process according to the invention. As it is now clear, the process according to the invention makes it possible to manufacture in a simple and economical manner, in industrial quantities, products comprising large quantities of CTF.

with 0 <x ≤ 0.4, 0 y y 0 0.3, x + y 0 0.6 and -0, 1 ≤ z 0,1 0.1, the element B 'being selected from chromium, niobium and their mixtures.

In particular, this method makes it possible to manufacture particles whose CTF Ca ₍₁ .z _j T -xFexOs with 0 <x ≤ 0.4 and -0.1 ≤ z ≤ 0.1 is higher than 99%, higher 99.9% or even 100% This process allows the manufacture of products containing CTF including:

the mass content of "calcium expressed as CaO" is greater than 37.9%, preferably greater than 38.7%, preferably greater than 40%, or even greater than 40.5% and / or less than 43; 6%, preferably less than 42.7%, and / or

the mass content of "titanium expressed as TiO ₂ " is greater than 33.1%, preferably greater than 35.9%, preferably greater than 37.4%, preferably greater than 38.7%, preferably greater than 40.3%, preferably greater than 41.1%, and / or less than 58.2%, preferably less than 57%, preferably less than 55.8%, preferably less than 54.1%. %, and or

the mass content of "iron expressed as Fe ₂ O ₃ " is greater than 2.7%, preferably greater than 3.5%, preferably greater than 4%, preferably greater than 4.4%, preferably greater than 4.6% or more than 5%, and / or less than 24.5%, preferably less than 23%, preferably less than 20.5%, preferably less than 17.6%, and / or

 the mass content of impurities is less than 2%, preferably less than 1.5%, preferably less than 1%, preferably less than 0.6%.

The dimensions of these products can then be reduced, for example by grinding in the form of powders if their use requires it. These products can also be obtained directly in the form of particles.

 Of course, the present invention is not limited to the described embodiments provided by way of illustrative and non-limiting examples.

In particular, the products according to the invention are not limited to particular shapes or dimensions.

Claims

1. A molten product comprising iron-doped calcium titanate, optionally doped with a B 'element of perovskite structure AB0 ₃ , where site A is occupied by calcium and site B by titanium and iron, site B being doped with an element B ', so that the product respects the formula

with 0 <x≤0.4, 0≤y≤0.3, x + y≤0.6 and -0, 1≤z≤0.1, the element B 'being selected from chromium, niobium and their mixtures. 2. Melted product according to the preceding claim, wherein the element B 'is chromium. A molten product according to any one of the preceding claims, wherein x + y> 0.05 A molten product according to any one of the preceding claims, wherein x ≥ 0.05 and / or x + y> 0.07 and / or z> -0.07. 5. The molten product according to the preceding claim, wherein x≥ 0.08 and / or z> -0.04. A molten product according to any one of the preceding claims, wherein y ≤ 0.2 and / or x <0.35 and / or x + y <0.5 and / or z <0.07. 7. The molten product according to the preceding claim, wherein y ≤ 0, 1 and / or x <0.3 and / or x + y <0.4 and / or z <0.04. A molten product according to any one of the preceding claims, wherein x + y 0,3 0.3. 9. A molten product according to any one of the preceding claims, comprising a level of perovskite of calcium titanate doped with iron, optionally doped with a B 'element, greater than 50%. 10. The molten product according to the preceding claim, wherein the perovskite level of iron-doped calcium titanate, optionally doped with a B 'element, is greater than 90%. 1. Melted product according to the preceding claim, wherein the rate of perovskite iron doped calcium titanate, optionally doped with a B 'element, is greater than 99%. 12. A molten product according to any one of the preceding claims, having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:  37.9% <calcium expressed as CaO <43.6%, - 33.1% <titanium expressed as Ti0 ₂ <57.6%, 2.7% <iron expressed as Fe ₂ O ₃ <24.5%,  - other elements <2%. Melted product according to the immediately preceding claim, having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:  40% <calcium expressed as CaO <43.6%, - 33.1% <titanium expressed as Ti0 ₂ <55.8%, 2.7% <iron expressed as Fe ₂ O ₃ <23.5%,  - other elements <2%. 14. A molten product according to the immediately preceding claim, having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:  40% <calcium expressed as CaO <42.7%, 38.7% <titanium expressed as Ti0 ₂ <54.1%, - 4.4% <iron expressed as Fe ₂ O ₃ <17.6%,  - other elements <2%. 15. A molten product according to any one of the preceding claims, in the form of a powder whose median size is greater than 0.4 μηι and less than 5 μηι. 16. Manufacturing process comprising the following steps:  a) mixing raw materials so as to form a suitable starting feedstock to obtain, at the end of step c), a product according to any one of the preceding claims, b) melting the feedstock to a liquid mass, c) cooling until complete solidification of said liquid mass, so as to obtain a molten product. 17. The method of claim immediately preceding, wherein step c) comprises the following steps:  Ci) dispersion of the liquid mass in the form of liquid droplets, c ₂ ) solidification of these liquid droplets by contact with an oxygenated fluid, so as to obtain molten particles,  or the following steps:  Ci ') pouring the liquid mass into a mold; c ₂ ') cooling solidification of the liquid mass cast in the mold until a block at least partially solidified; c ₃ ') demolding the block. 18. A method according to any one of the two immediately preceding claims, comprising, after step c), a step d) of grinding the molten product. 19. Layer having a thickness of between 1 μηι and 3 mm, and a porosity of less than 70%, obtained from a powder in a product according to any one of claims 1 to 15 or manufactured according to a process according to claim 18. 20. Layer according to the immediately preceding claim, having a thickness of between 200 μηι and 3 mm, and a porosity greater than 10%. 21. Layer according to claim 19, having a thickness of between 1 μηι and 1 mm, and a porosity of less than 10%.