EP2337771A2

EP2337771A2 - Fused ceramic product

Info

Publication number: EP2337771A2
Application number: EP09741436A
Authority: EP
Inventors: Emmanuel Pierre Marcel Nonnet; Yves Marcel Léon BOUSSANT ROUX; Charlotte Catteau; Sophie Papin; Gilles Querel
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2008-10-17
Filing date: 2009-10-16
Publication date: 2011-06-29
Also published as: FR2937320B1; FR2937320A1; CN102186794A; WO2010044079A2; US20110212827A1; WO2010044079A3

Abstract

Process for manufacturing a product, comprising the following successive steps: a) mixing raw materials to form a starting feedstock, b) melting the starting feedstock so as to form a molten liquid, c) solidifying the molten liquid so as to obtain a fused product comprising crystals linked by a glassy phase, and d) crystallization heat treatment of the glassy phase of said fused product, in which the composition of the starting feedstock is adapted in order to manufacture a product having the following chemical composition, as weight percentages based on the oxides, and for a total of 100%: 40% ≤ (ZrO₂ + HfO₂) ≤ 94%, 6% < CeO₂ < 31%, 0% ≤ Y₂O₃, 0% ≤ Al₂O₃, 2% ≤ SiO₂, 0% ≤ MgO, 0% ≤ TiO₂, and other oxides ≤ 1%. Use of the product obtained as a grinding agent, an agent for dispersing in a wet medium, a surface treatment agent, a supporting agent or a heat-exchange agent.

Description

Melted ceramic product Technical area

The present invention relates to a method of manufacturing products made of ceramic material obtained by melting, or "molten products", and in particular melted particles that can be used in particular in apparatus and processes for micromilling, wet microdispersion and surface treatment.

It also relates to products obtained or likely to have been obtained by this process,

State of the art

Apparatuses and processes for micromilling, wet microdispersion and surface treatment are well known, and are particularly developed in industries such as:

- the mineral industry, which implements particles for the fine grinding of dry-milled materials by traditional processes, in particular for the grinding of calcium carbonate, titanium oxide, gypsum, kaolin, mineral ore iron, ores of precious metals and, in general, all ores undergoing chemical or physicochemical treatment;

- the paints, inks, dyes, magnetic lakes and agrochemical compounds industries, which use particles for the dispersion and homogenisation of the various liquid and solid constituents;

- the surface treatment industry, which uses particles in particular for cleaning metal molds (for the manufacture of bottles, for example), deburring parts, descaling, preparing a support for the appearance of a coating, the binding of pre-stressing grenais (called "shot peening" in English), or the forming of pieces (called "peen forming" in English).

The particles conventionally used for these markets are generally substantially spherical in shape and between 0.005 and 4 mm in size. Depending on the target markets, they may have one or more of the following properties:

a chemical and colorant inertness with respect to the products treated,

- a mechanical resistance to shocks, - resistance to wear,

a low abrasiveness for the equipment, in particular the stirring members and the tanks, or the projection members, and

- low open porosity for easy cleaning. In the field of grinding, there are different types of particles, including sand with rounded grains, glass beads, especially glass ceramic glass beads, or metal balls.

Rounded grain sand, such as OTTAWA sand for example, is a natural and inexpensive product, but unsuitable for modern, pressurized and high flow mills. Indeed, the sand is not very resistant, of low density, variable in quality and abrasive for the material.

Glass beads, widely used, have better strength, lower abrasiveness and availability in a wider range of sizes.

The glass-ceramic glass beads, such as those described in JP-S61-168552 or JP-S59-174540, are more resistant than glass beads.

Metal balls, in particular made of steel, have also been known for a long time for the abovementioned applications, but their use remains marginal because they often have insufficient chemical inertia with respect to the products treated, notably resulting in pollution of the mineral charges. and a gray paint, and too high density requiring special grinders involving in particular a high energy consumption, a significant heating and a high mechanical stress of the equipment.

Also known ceramic particles, which have the advantage of having a better mechanical strength than glass beads, a high density and excellent chemical inertness. Among these particles, we can distinguish:

sintered ceramic particles, obtained by cold forming of a ceramic powder followed by consolidation by baking at high temperature, and

- The melted ceramic particles, generally obtained by melting a feed of raw materials, converting the molten liquid into droplets, and solidifying them.

The vast majority of fused ceramic particles used in the aforementioned applications have a zirconia-silica (ZrO ₂ -SiO ₂ ) type composition where the zirconia is crystallized in monoclinic and / or partially stabilized form (by suitable additions), and in which the silica, as well as some of the optional additives, form a matrix binding the zirconia crystals.

These fused ceramic particles provide excellent grinding properties, ie, good mechanical strength, high density, and low chemical inertness and abrasiveness to the grinding material.

Melted ceramic particles based on zirconia and their use for grinding and dispersion are for example described in FR 2 320 276, EP 0 662 461 and FR

These documents describe the influence of SiO ₂ , Al ₂ O ₃ , MgO, CaO, Y ₂ O ₃ , CeO ₂ , and Na ₂ O on the main properties of the resulting particles, in particular on the resistance properties. to crush and abrasion resistance.

Although the melted ceramic particles of the prior art are of good quality, the industry still needs higher quality products. Indeed, the grinding conditions are always more demanding. An object of the invention is to satisfy this need.

Summary of the invention

According to the invention, this object is achieved by means of a method of manufacturing a product, comprising the following successive steps: a) mixing of raw materials to form a feedstock, b) melting of the feedstock of in order to form a molten liquid, c) solidification of the molten liquid so as to obtain a molten product comprising crystals linked by a glassy phase, and d) crystallization heat treatment of the glassy phase of said molten product.

This process is remarkable in that the composition of the feedstock is suitable for producing a product having the following chemical composition, in percentages by mass on the basis of the oxides and for a total of 100%:

40% <(ZrO ₂ + HfO ₂ ) <94%, 4% <CeO ₂ <31%,

0% <Y ₂ O ₃ , 0% <Al ₂ O ₃ , 2% <SiO ₂ , 0% <MgO, 0% <TiO ₂ , and other oxides <1%.

As will be seen below, the melted product manufactured, hereinafter "product according to the invention", has an excellent wear resistance.

This result is amazing. Indeed, the formation of crystallites within a vitreous phase, resulting from the heat treatment of step d), is accompanied by a decrease in the overall volume and generally leads to the creation of porosities, or even cracks. However, these porosities and cracks are detrimental to the mechanical strength.

Without being bound by this theory, the inventors explain the results obtained by the very specific microstructure of the product according to the invention. Indeed, in a product according to the invention, crystallites based on cerium oxide and / or zirconia and / or titanium oxide and / or alumina and / or yttrium oxide and / or or silica, are distributed in the vitreous phase, including in the immediate vicinity of zirconia-based dendritic crystals, whereas in products made by other methods, the possible crystallites are on the contrary substantially absent at the interface between the vitreous phase and the dendritic crystals. This distribution of crystallites throughout the glassy phase could be explained by the presence of crystallites which, given the composition of the feedstock, would be predominantly of a different chemical nature of the dendritic crystals.

With this distribution of crystallites throughout the glassy phase, the inventors have observed a reduction, or even a suppression, of cracks or pores detrimental to the application. Crystallization in step d) is a new way to improve the wear resistance: up to the present invention, in fact, especially to improve the grinding efficiency, the research was aimed exclusively at increasing the density of the products, generally in the form of beads, or to modify their chemical composition.

A method according to the invention may also have one or more of the following optional features: - In step a), the composition of the feedstock is suitable for producing a product having a chemical composition such that the weight ratio SiO ₂ ZAl ₂ O ₃ is less than or equal to 1, preferably less than or equal to 0.75 and / or greater than 0.3.

- Between step b) and step c), the molten liquid is dispersed to form droplets.

- At the end of step c), the product has a shape of which at least one dimension is less than 30 mm. In particular, it may have the shape of a ball or a thin plate.

- The heat treatment in step d) comprises a step at a temperature of between 800 ^° C. and 1100 ^° C.

- The heat treatment in step d) comprises a bearing at a temperature of between 800 ° C. and 950 ^° C., preferably at a temperature of between 820 ° C. and 880 ^° C., and more preferably at 850 ^° C.

The heat treatment in step d) comprises a step at a temperature of between 950 ° C. and 1100 ^° C., preferably at a temperature of between 970 ° C. and

1070 ^° C., and more preferably at 1000 ^° C.

- The duration of maintenance in stage, whatever the temperature of bearing, is greater than or equal to 1 hour, preferably greater than or equal to 2 hours, preferably greater than or equal to 3 hours, preferably greater than or equal to 5 hours more preferably from 5 to 10 hours, or even 10 hours.

The heat treatment in step d) comprises only a nucleation operation of the vitreous phase at a first temperature higher than the glass transition temperature Tg of the glassy phase of the product resulting from stage c), or comprises a single operation of growth of crystallization seeds at a second temperature, greater than the glass transition temperature Tg of the glass phase of the product from step c. In the latter case, the crystallization seeds can in particular come from the rise in temperature towards the second temperature.

The heat treatment in step d) comprises a nucleation operation of the vitreous phase of the product at a first temperature higher than the glass transition temperature Tg of the glassy phase of the product resulting from step c), and then an operation of growth of the nucleation seeds, or "nuclei", created during the nucleation operation, at a second temperature higher than the first temperature, of preferably greater than at least 50 ^° C., of at least 80 ^° C., of at least 100 ^° C., or even of at least 150 ^° C. at the second temperature.

- The heat treatment in step d) comprises a step at a temperature of between 820 ^° C. and 880 ^° C., and preferably at about 850 ^° C., followed by a plateau at a temperature of between 970 ° C. and 1070 ° C. ⁰ C, and preferably at about 1000 ⁰ C.

- The heat treatment cycle in step d) comprises firstly a 10 hour stage at 850 ⁰ C, followed by a 10 hour stage at 1000 ⁰ C.

In step d), the rates of rise and fall in temperature are between 15 ° C / h and 500 ° C / h, preferably between 20 ° C / h and 200 ° C / h. A speed of 120 ° C / h is well suited.

Preferably, the method is adapted so that the product according to the invention has one or more of the optionally optional characteristics described below.

The invention also relates to a product obtained or obtainable by means of a process according to the invention. To the knowledge of the inventors, such a product differs from known products in particular by the microstructure described above.

According to embodiments of the invention, the product may still have one or more of the following optional features:

The crystallites are distributed within the vitreous phase of the matrix in a substantially homogeneous manner. - The diameter "D" of the largest circle that can be placed on a view of a section at the heart of the product, taken by means of a transmission electron microscope (TEM), without any crystallite being included, even partially, in this circle is preferably less than 3.5 μm, preferably less than 2 μm, more preferably less than 1 μm. - More than 95% by number, or even more than 97% by number, or even more than 99% by number, or even substantially 100% in number of the crystallites distributed in the matrix have a form factor F greater than 0.40, or greater at 0.45, or greater than 0.50, or greater than 0.55, or greater than 0.60, or even greater than 0.70.

The statistical distribution, which represents the number of grains according to their size, is multimodal, and in particular bimodal, a first mode corresponding to the sizes of the crystallites resulting from step d) and a second mode corresponding to the sizes of the dendritic crystals. obtained at the end of step c). A bimodal distribution corresponds to a distribution with two main peaks or "first and second modes". Preferably, the sizes T1 and T2 corresponding to said first and second modes are such that the T2 / T1 ratio is greater than 50, preferably greater than 100, preferably greater than 150 or even greater than 200. Preferably, T1 is greater at 5 nm, preferably greater than 10 nm, or even greater than 0.05 μm and less than 0.15 μm. Preferably, T2 is greater than 15 μm and less than 100 μm.

At least 80%, or at least 90%, or even substantially 100% by number, of the dendritic crystals are greater than or equal to 2 μm, or greater than or equal to 3 μm, or greater than or equal to 5 μm, or greater or equal to 10 microns, or greater than or equal to 15 microns and / or less than or equal to 100 microns.

At least 80%, or at least 90%, or even substantially 100% by number, of the crystallites distributed in the glassy phase are of size less than or equal to 400 nm, or less than or equal to 300 nm, or less than or equal to 250 nm , or less than or equal to 200 nm, even less than or equal to 150 nm and / or of size greater than or equal to 5 nm, greater than or equal to 10 nm, or greater than or equal to 15 nm, or greater than or equal to

20 nm, or greater than or equal to 30 nm, or greater than or equal to 40 nm, or even greater than 50 nm.

Crystallites distributed in the vitreous phase are not of dendritic form.

- The mass ratio SiO ₂ ZAl ₂ O ₃ is less than or equal to 1, preferably less than or equal to 0.75 and / or greater than 0.3.

- The product is in the form of a ball of a size less than or equal to 4 mm and / or greater than or equal to 5 microns.

- The product is in the form of a powder, the maximum size _{of 5} D ₉₉ is preferably less than 5 mm. The invention also relates to the use of a product according to one embodiment of the invention, for example obtained according to a process according to the invention, as a grinding agent, a dispersion agent in a humid medium or for surface treatment.

It relates in particular to the use of a product according to one embodiment of the invention, for example obtained according to a process according to the invention, as a grinding agent for suspensions having a pH> 8, for example CaCO ₃ calcium carbonate suspensions. Definitions

"Particle" means a solid product individualized in a powder.

- "ball" means a particle having a sphericity, that is to say a ratio between its smallest diameter and its largest diameter, greater than or equal to 0.6, regardless of the way in which this sphericity was obtained. Preferably, the balls according to the invention have a sphericity greater than or equal to 0.7, preferably greater than 0.8, more preferably greater than 0.9.

"Crystal" means a domain of matter obtained by translation of the elementary cell of a crystalline structure in the three directions of space and of size greater than or equal to 1 micron.

By "twin" is meant an oriented association of two or more identical crystals. In the remainder of this description and for the sake of simplification, a crystal or a twin is called "crystal". - Classically called "dendrite" is a crystal obtained after growth of a seed and having a fractal or pseudo-fractal geometry. Processes for obtaining dendritic crystals are well known to those skilled in the art. The following tests provide examples of methods for obtaining dendritic crystals.

"Crystallite" means a domain of matter having the same structure as a crystal but having a size of less than 1 micron.

- Here we call "grains" all the crystals and crystallites.

"Matrix" means a binder phase ensuring a continuous structure between the crystals. In a product of the invention, the matrix comprises a glassy phase in which crystallites are distributed. Potential pores are not part of the matrix. The "crystallization" or "degree of crystallization" of the matrix refers to these crystallites.

It is considered that the crystallites are "distributed" within the vitreous phase when they are present throughout the vitreous phase, and especially near the crystals. To the inventors' knowledge, the crystallization heat treatment of step d) is necessary to obtain distributed crystallites.

- By "glass transition temperature" of a vitreous phase means the middle of the temperature range in which said glassy phase becomes progressively more viscous and goes from the liquid state to the solid state. It is commonly accepted that this temperature corresponds to the temperature for which the viscosity of the vitreous phase is 10 ¹³ Poise. The glass transition temperature of the glassy phases can be determined by differential scanning calorimetry (DSC). - The homogeneity of the distribution of crystallites in the vitreous phase can be evaluated by the diameter "D" of the largest circle which can be placed on a view of a section at the heart of the product, taken by means of a transmission electron microscope (TEM), without any crystallite being included, even partially, in this circle. This diameter thus represents the largest possible circular space between the crystallized crystals observed. A high diameter "D" means that there is a large discoidal zone devoid of crystallites, which corresponds, for the same crystallite coverage rate of the matrix, to a lower homogeneity of the spatial distribution of the crystallites.

- The "coverage rate" CT of the matrix by the crystallites is measured, on an image of a cut at the heart of the product taken by means of a scanning electron microscope (SEM), by the ratio of the area occupied by the crystallites "Sc" on the total surface of the matrix (glassy phase + crystallites) "S _T ". Thus TC = S (VS _T) Preferably, the dimensions are measured using an image processing software, for example ELLIX sold by the company MICROVISION.-The percentiles or "percentiles" 99.5 ( Dc ^) and 50 (D50) are the particle sizes of a powder corresponding to the percentage of 99.5% and 50%, respectively, in mass on the cumulative particle size distribution curve of the particle sizes of the powder, the sizes For example, 99.5% by weight of the particles of the powder have a size less than D ₉ ^ ₅ and 0.5% of the particles by mass have a size greater than Percentiles can be determined using a particle size distribution using a sedigraph, using a laser granulometer, or by sieving through a series of sieves.

- The "size" of a particle, especially a ball, is the average of its largest dimension dM and its smallest dimension dm: (dM + dm) / 2. - The "size" of a crystal, for example in the form of a dendrite, and the size of a crystallite are defined by the mean of the length of the smallest axis "Pa", respectively "Pa" and the length of the largest "Ga" axis, respectively "Ga '" of the minimum area ellipse in which said crystal and said crystallite may be inscribed on a section of the product: (Pa + Ga) / 2, (Pa' + Ga ') / 2, respectively. Classically, the size of a crystal is measured on photographic snapshots taken by means of a scanning electron microscope (SEM), on a polished cut of the product, and the size of a crystallite is measured on photographic snapshots taken at transmission electron microscope (TEM) on a polished section of the product. Preferably, the dimensions are measured using an image processing software, such as for example VISILOG marketed by the company NOESIS.

- By form factor "F" of a crystallite, is meant the ratio between the length of the smallest axis "Pa" and the length of the largest axis "Ga" of the ellipse of minimum area in which may the shape of the crystallite observed on a section of the product. Conventionally, these lengths are measured on photographic plates taken on a polished cut of the product: F = PaVGa '.

"Extended form" here means a form having a form factor F of less than 0.4.

"Globular form" here means a form having a form factor F greater than or equal to 0.4.

- "Melted product" means a product obtained by solidification by cooling of molten liquid. - A "molten liquid" is a liquid mass that may contain some solid particles, but in insufficient quantity so that they can structure said mass. A material undergoing liquid phase sintering can not be considered a molten liquid.

- "Impurities" means the inevitable constituents necessarily introduced with the raw materials. In particular, the compounds forming part of the group of oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides and metallic species of sodium and other alkalis, iron, vanadium and chromium are impurities. By way of examples, mention may be made of CaO, Ee ₂ O ₃ or Na ₂ O. The residual carbon is one of the impurities of the composition of the products according to the invention. Zirconium oxide ZrO ₂ is called zirconia. When reference is made to ZrO ₂ or (ZrO ₂ + Hf0 ₂ ), it is necessary to include zirconia and traces of hafnium oxide. Indeed, a little HfO ₂ , chemically indissociable from ZrO ₂ in a process of fusion and having similar properties, is still naturally present in zirconia sources at levels generally less than 2%. Hafnium oxide is not considered an impurity.

"Precursor" of an oxide means any product which, upon melting, will decompose to give at least said oxide. MgCO ₃ is for example a precursor of MgO oxide. Indeed, during the merger MgCO ₃ will decompose into MgO and CO ₂ .

A material is said to be "based" on a constituent when this constituent is the main constituent, by weight, of said material.

All percentages of the present description are percentages by weight based on the oxides, unless otherwise indicated.

Brief description of the figures

Other characteristics and advantages will become apparent on reading the following description and on examining the appended figures in which: FIG. 1 is a photograph taken under a scanning electron microscope (SEM) of a particle of Example 23;

FIG. 2 is a photograph taken with the transmission electron microscope (TEM) of the matrix of a particle of Example 6; and

FIG. 3 is a photograph taken with the transmission electron microscope (TEM) of the matrix of a particle of Example 5.

detailed description

Process

To manufacture a product according to one embodiment of the invention, it is possible to proceed according to the steps a) to d) mentioned above.

A preferred embodiment of this method is now described. In step a), the feedstock is formed of the desired oxides in the product or precursors thereof. Preferably, to manufacture a zirconia product, ZrSiO ₄ natural zircon sand containing about 66% ZrO 2 and 33% SiO ₂ , plus impurities, is used. The contribution of ZrO ₂ through zircon is indeed much more economical than an addition of ZrO ₂ . The compositions may be adjusted by the addition of pure oxides, mixtures of oxides or mixtures of precursors of these oxides, especially ZrO ₂ + HfO ₂ SiO ₂ , CeO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , and MgO.

Those skilled in the art adjust the composition of the feedstock so as to obtain, after step c), a product having the desired chemical analysis.

The chemical analysis of a molten ceramic product is generally substantially identical to that of the feedstock. In addition, if appropriate, for example to take into account the presence of volatile oxides, or to account for the loss of SiO ₂ when the fusion is operated under reducing conditions, the skilled person knows how to adapt the composition the starting charge accordingly.

Preferably, no oxide other than ZrO ₂ + HfO ₂ , SiO ₂ , CeO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ and MgO is intentionally introduced, in the form of oxide or oxide precursor. in the feedstock, the other oxides present being impurities.

Preferably, the feedstock is prepared so that, in the product manufactured, the mass ratio MgO / SiO ₂ is less than or equal to 1, preferably less than or equal to 0.77 and the weight ratio SiO ₂ ZAl ₂ O ₃ is less than or equal to 1, preferably less than or equal to 0.75 and / or greater than 0.3.

In step b), the feedstock is melted, preferably in an electric arc furnace. Electrofusion makes it possible to manufacture large quantities of particles with interesting yields. But all known furnaces are conceivable, such as an induction furnace or a plasma furnace, provided they allow to melt the feedstock to form a bath of molten liquid.

In step c), a stream of the molten liquid is dispersed in small liquid droplets which, as a result of the surface tension, take, for the majority of them, a substantially spherical shape. This dispersion can be performed by blowing, in particular with air and / or steam, or by any other method of atomizing a molten liquid known to those skilled in the art. A melted ceramic particle with a size of 5 μm to 4 mm can thus be produced.

The cooling resulting from the dispersion leads to the solidification of the liquid droplets. Particles, in particular beads, are then melted. Any conventional method for producing melted particles, especially melted beads, can be implemented. These melted particles can be milled to change their particle size.

At the end of step c), the particles comprise dendritic crystals bonded by a substantially non-crystallized matrix, especially in the immediate vicinity of the dendritic crystals.

In step d), the particles obtained in step c) are heat treated. In one embodiment, this heat treatment is applied, after step c), to particles cooled to a temperature below the nucleation temperature, for example up to room temperature. The heat treatment then involves a rise in temperature. But it is also possible, according to another embodiment, to apply the heat treatment during the cooling of the particles, that is to say to temporarily stabilize the temperature to perform one or more stages of nucleation or growth, and therefore to group steps c) and d). The rates of rise and fall in temperature can be, for example, between 10 ° C / h and 1200 ° C / h, preferably between 15 ° C / h and 500 ° C / h, preferably between 20 ° C / h and ° C / h and 200 ° C / h. A speed of 120 ° C / h is well suited. The heat treatment may comprise a single temperature step. In one embodiment, the heat treatment comprises a bearing at a temperature of between 800 ^° C. and 950 ^° C., preferably at a temperature of between 820 ° C. and 880 ^° C., and more preferably at 850 ^° C., while a duration greater than or equal to 1 hour, preferably greater than or equal to 2 hours, preferably greater than or equal to 3 hours, more preferably greater than or equal to 5 hours. A duration of maintenance level ranging from 5 to 10 hours, or even equal to 10 hours, is well suited. In one embodiment, the heat treatment comprises a bearing at a temperature of between 950 ^° C. and 1100 ^° C., preferably at a temperature of between 970 ^° C. and 1070 ° C., and more preferably at 1000 ^° C., while a duration greater than or equal to 1 hour, preferably greater than or equal to 2 hours, preferably greater than or equal to 3 hours, more preferably greater than or equal to 5 hours. A duration of maintenance level ranging from 5 to 10 hours, or even equal to 10 hours, is well suited. Preferably, the heat treatment cycle comprises two stages. Preferably, the first step is determined to generate seed crystals in the vitreous phase and the second step is determined to grow these seeds. The temperature of the second stage is greater than that of the first stage, preferably greater than at least 50 ^° C., of at least 80 ^° C., of at least 100 ^° C., or even of at least 150 ^° C. at the temperature. of the first landing.

In one embodiment, the first stage is at a temperature of between 800 ^° C. and 950 ^° C., preferably at a temperature of between 820 ° C. and 880 ° C., and more preferably at 850 ^° C., and the second bearing is at a temperature between 950 ⁰ C and 1100 ⁰ C, preferably at a temperature between 970 ⁰ C and 1070 ⁰ C ₅ and more preferably at 1000 ⁰ C.

Preferably, the temperature keeping time of at least one of the first and second bearings, preferably of each of these two stages, is greater than or equal to 1 hour, preferably greater than or equal to 2 hours, preferably greater than or equal to equal to 3 hours, more preferably greater than or equal to 5 hours. For each of the two levels, a duration of maintenance ranging from 5 to 10 hours, or even equal to 10 hours, is well suited. However, it is possible to maintain a level of 10 hours or more.

In a most preferred embodiment, the heat treatment comprises a first stage at 850 ^° C. for a period ranging from 5 to 10 hours, or even equal to 10 hours, followed by a plateau at 1000 ^° C. for a period of time ranging from from 5 to 10 hours, or even 10 hours.

The implementation of a heat treatment after solidification makes it possible to control the crystallites generation, and in particular to determine the degree of crystallization and / or to adjust the size of the crystallites: Thus, the inventors have found that the majority of crystallites are created during the first stage or, when the heat treatment comprises a single stage, during the rise in temperature. The duration of these phases therefore determines the number of crystallites, a longer duration corresponding to a greater amount of crystallites. This observation has also led the inventors to recommend the implementation of two levels, the control of the creation of crystallites being improved.

The inventors have also found that the size of the crystallites increases with the temperature of the second stage. Other methods of manufacturing a product according to the invention can be envisaged. For example, it is possible to manufacture a melted and cast product in the form of a plate, preferably with rapid cooling, as described for example in FR 2,290,266, incorporated by reference, then to grind it and, where appropriate , to make a granulometric selection, and then to subject the powder obtained crystallization heat treatment as described in step d) described above. Alternatively, said heat treatment may be carried out before grinding.

The form of the molten product is preferably adapted to facilitate crystallization in step d). Indeed, if the shape of the product is too massive, for example if the product is in the form of a brick of several kilograms, crystallization can be effective, according to current techniques, only on the surface of the product. Preferably, the melted product has at least one of its dimensions less than 30 mm, preferably less than 20 mm, preferably less than 10 mm, more preferably less than 5 mm, preferably less than 2 mm. Preferably, the product is in the form of a thin plate with a thickness of less than 30 mm, preferably less than 20 mm, preferably less than 10 mm, more preferably less than 5 mm, preferably less than 2 mm.

Products A product according to the invention is preferably in the form of a particle, or even a ball, or a set of particles or beads. These beads and particles may have a size less than or equal to 4 mm and / or greater than or equal to 5 μm.

The content of oxides in the composition of a product according to the invention may represent more than 99.5% or even more than 99.9%, and even substantially 100% of the total mass of the product.

The ZrO ₂ content, in weight percentage on the oxide basis, may be greater than or equal to 45% and / or less than or equal to 90%.

According to one embodiment, the ZrO ₂ content, as a percentage by weight on the oxide basis, may be greater than or equal to 50%, or greater than or equal to 55%, or greater than or equal to 60% and / or less than or equal to 85%, or less than or equal to 80% or less than or equal to 75%, or less than or equal to 70%. As indicated above, the CeO ₂ content of a molten product according to the invention is less than 31%, as a percentage by weight based on the oxides. The CeO ₂ content, as a percentage by weight on the oxide basis, may be greater than or equal to 5%. According to one embodiment, the content of CeO ₂ , as a percentage by weight on the basis of the oxides, may be greater than or equal to 6%, or greater than or equal to 8%, or greater than or equal to 10%, or greater or equal to 12%, or greater than or equal to 15%, greater than or equal to 17%, even greater than or equal to 19% and / or less than or equal to 30%, or less than or equal to 28%, or even less than or equal to at 26%. The Y ₂ O _{3 content} , as a percentage by weight based on the oxides, may be greater than or equal to 0.1% and / or less than or equal to 10%.

According to one embodiment, the content of Y ₂ O ₃ , as a percentage by weight on the oxide basis, may be greater than or equal to 0.5%, or greater than or equal to 1%, or greater than or equal to 1, 5%, or greater than or equal to 2%, or greater than or equal to 2.5%, even greater than or equal to 3% and / or less than or equal to 8%, or less than or equal to 6%, or less or equal to 5.5%, or less than or equal to 5%.

The SiO ₂ content, in weight percent based on the oxides, may be greater than or equal to 2% or greater than or equal to 3% and / or less than or equal to 40%.

According to one embodiment, the content of SiO ₂ , as a percentage by weight on the basis of the oxides, may be greater than or equal to 4%, or even greater than or equal to 5% and / or less than or equal to 35%, or less or equal to 30%, or less than or equal to 20%, or less than or equal to 18%, or less than or equal to 16%, or less than or equal to 14%, or less than or equal to 12%, or less than or equal to 10%, or less than or equal to

8%. The content of Al ₂ O ₃ , as a percentage by weight on the oxide basis, may be greater than or equal to 0.5% and / or less or equal to 25%.

According to one embodiment, the content of Al ₂ O ₃ , as a percentage by weight on the basis of the oxides, may be greater than or equal to 1%, or greater than or equal to 2%, or greater than or equal to 4% and / or less than or equal to 20%, or less than or equal to 15%, or less than or equal to 12%.

The TiO ₂ content, as a percentage by mass on the oxide basis, may be greater than or equal to 0.5% and / or less than or equal to 8.5%. The presence of TiO ₂ can advantageously favor the homogeneity of the crystallite distribution in the matrix.

According to one embodiment, the content of TiOj, in percentage by weight on the basis of the oxides, may be greater than or equal to 1%, or greater than or equal to 1, 25%, or even greater than or equal to 1.5% and / or less than or equal to 5%, or less than or equal to 3%, or even less than or equal to 2%,

The mass ratio MgO / SiO ₂ is preferably less than or equal to 1, more preferably less than or equal to 0.77.

According to one embodiment, the MgO content, as a percentage by weight on the oxide basis, may be greater than or equal to 0.5%, or greater than or equal to 1%, or greater than or equal to 1.25% or even greater than or equal to 1, 5%, and / or less than or equal to 4%, or less than or equal to 3.2%.

Preferably, the mass ratio (ZrO ₂ + HfO ₂ ) / SiO ₂ is greater than or equal to 1, or greater than or equal to 1.5, or greater than or equal to 2, or greater than or equal to 2.5 and or less than or equal to 25, or less than or equal to 20, or even less than or equal to 15, or even less than or equal to 10.

According to one embodiment, the mass ratio SiO ₂ / Al ₂ O ₃ is less than or equal to 1, preferably less than or equal to 0.75 and / or greater than 0.3.

The content of "other oxides", that is to say the oxides other than the abovementioned oxides, is preferably less than 1%, or even less than or equal to 0.6% of the total mass of oxides. Indeed, it is considered that a total content of "other oxides" of less than 1% does not substantially modify the results obtained.

The other oxides are in particular oxides such as CaO, Na ₂ O, P ₂ Os or Fe ₂ O ₃ . Preferably, the "other oxides" are present only in the form of impurities.

As shown in FIG. 1, a product according to an embodiment of invention, for example obtained according to a method according to the invention, comprises dendritic crystals 10 bonded by a matrix 11. The dendritic crystals 10 shown are isolated from each other. other. They can, however, also be in contact, or even nested within each other. They then advantageously form a skeleton that is difficult to deform. IS

The dendritic crystals are based on zirconia. Their composition may especially comprise at least 60 mol%, or at least 70 mol%, or at least 80 mol%, of zirconia.

Measuring the length of the smallest axis "Pa" and the length of the largest axis "Ga" of the ellipse "E" of minimum area in which a dendritic crystal 10 can be inscribed gives access to its size L , equal to (Pa + Ga) / 2.

At least 80%, or 90%, or even substantially 100% by number of the dendritic crystals may be larger than or equal to 2 microns.

According to one embodiment, at least 80%, or 90%, or even substantially 100% by number of the dendritic crystals are greater than or equal to 3 microns, or greater than or equal to 5 microns, or greater than or equal to 10 microns, or even greater than or equal to 15 microns and / or less than or equal to 100 microns.

As represented in FIGS. 2 and 3, the matrix 11 comprises a glassy phase 12 in which crystallites 13 and 14 are distributed. Depending on the crystallization conditions, the crystallites may have various, and in particular elongated, forms (crystallite 13) or globular (crystallite 14).

According to one embodiment, the crystallites are not of dendritic form.

As indicated in FIG. 2, the shape factor F and the size of a crystallite can be determined by inserting the shape of this crystallite in an ellipse E 'of minimum area, and then measuring the length of the smallest axis Pa 'and that of the largest axis Ga'. The size L 'is equal to (Pa' + Ga ') / 2. The form factor F is equal to PaVGa '.

According to one embodiment, more than 95% by number, or even more than 97% by number, or even substantially 100% by number, of the crystallites distributed in the matrix have a form factor F greater than 0.40, or greater than 0, 45, or greater than 0.50, or greater than 0.55, or greater than 0.60, or even greater than 0.70.

At least 80%, or 90%, or even substantially 100% by number of the crystallites distributed in the matrix may be less than or equal to 400 nm in size.

According to one embodiment, at least 80%, or 90%, or even substantially 100% by number of the crystallites distributed in the matrix are less than or equal to 300 nm, or less than or equal to 250 nm, or less than or equal to at 200 nm, even less than or equal to 150 nm and / or of size greater than or equal to 5 nm, or greater or equal to 10 nm, or greater than or equal to 15 nm, or greater than or equal to 20 nm, greater than or equal to 30 nm, or greater than or equal to 40 nm, or even greater than 50 nm.

As indicated above, a melted product according to the invention comprises dendritic crystals linked by a matrix in which crystallites are distributed.

The crystallites can be distributed within the vitreous phase of the matrix in a substantially homogeneous manner. Preferably, the "D" diameter defined above is less than 3.5 μm, preferably less than 2 μm, more preferably less than 1 μm.

The crystallites may contain one or more crystalline phases, for example crystalline phases based on cerium oxide and / or zirconia and / or on titanium oxide and / or on alumina and / or on yttrium oxide. and / or silica.

They may also contain crystalline phases of compounds comprising several metal oxides, for example ceria - zirconia compounds or cerium oxide - yttria - zirconia compounds. Crystallites can represent, in a view of a section in the heart of a product of the invention, more than 15%, even more than 30%, even more than 40%, even more than 60%, or even more than 70%. % or even more than 80% of the surface of the matrix (vitreous phase + crystallites). In other words, the coverage rate of the matrix by the crystallites can be greater than 15%, or even greater than 30%, or even greater than 40%, or even greater than 60%, or even greater than 70%, or even greater than 80%.

In one embodiment of the invention, a molten product may have the following chemical composition, in percentages by weight based on the oxides and for a total of 100%:

40% <(ZrO ₂ + HfO ₂ ) <94%, 4% <CeO ₂ <31%,

0% <Y ₂ O ₃

0% <Al ₂ O ₃

2% <SiO ₂ ,

0% <MgO, 0% <TiO ₂ , and other oxides <1%, and comprise dendritic crystals bonded by a matrix in which crystallites are distributed.

According to a first particular embodiment, particularly adapted to obtain a high planetary wear resistance, the composition of a product according to the invention is such that, for a total of 100%:

45% <(ZrO ₂ + HfO ₂ ) <85%,

6% <CeO ₂ <31%,

0.8% <Y ₂ O ₃ <8.5%,

0% <Al ₂ O ₃ <30%, 2% <SiO ₂ <37%,

0 <MgO <6%,

0 <TiO ₂ <8.5%, and other oxides <1%. ^"

Preferably, denoting by "C" the mass ratio CeO ₂ Z (ZrO ₂ + HfO ₂ ) and by "Y" the mass ratio Y ₂ O ₃ Z (ZrO ₂ + HfO ₂ ),

0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (63.095.Y ² - 11.214.Y + 0.4962; 0.25) <C and C <250.Y ² - 49 , lY + 2,6.

Preferably, 0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (70.238.Y ² - 12.393.Y + 0.544; 0.25) <C.

More preferably, 0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.089, Min (- 38.095.Y ² + 0.3571.Y + 0.2738; 0.25) <C.

Preferably 0 <C <0.6 and 0.02 <Y <0.098 and C <150. Y ² - 30.7. Y + 1.72, more preferably C <- 51.1905.Y ² + 0.25.Y + 0.4826. More preferably, the mass ratio CeO ₂ Z (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.2, preferably greater than or equal to 0.3 and Zou less than or equal to 0.5.

Preferably still, the mass ratio Y ₂ O ₃ Z (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.03, preferably greater than or equal to 0.03, preferably greater than or equal to 0.045 and / or lower. or equal to 0.09, preferably less than or equal to 0.06. The characteristics described above in the general scope of the invention are applicable to this first particular embodiment, insofar as they are not incompatible with it. According to a second particular embodiment, the composition of a product according to the invention is such that for a total of 100%:

55% <ZrO ₂ + HfO ₂ <75%, 10% <CeO ₂ <30%,

1.5% <Y ₂ O ₃ <5%,

0% <Al ₂ O ₃ <15%, preferably 4% <Al ₂ O ₃ <12% 3% <SiO ₂ <12%, preferably SiO ₂ > 5%, O% <MgO <2%, 0% <TiO ₂ <5%, preferably TiO ₂ > 1.5%, other oxides <1%.

In this embodiment, it is particularly advantageous, especially in an application in a basic medium, that the diameter "D" as defined above is less than 3.5 microns. Preferably, a product according to this second particular embodiment has one or more of the following optional features:

- The mass ratio 810 ₂ / Al ₂ O ₃ is less than or equal to I ₃ , preferably less than or equal to 0.75 and / or greater than 0.3: The glassy phase is then rich in alumina.

- The mass ratio SiO ₂ ZAl ₂ O ₃ is less than or equal to 1, preferably less than or equal to 0.75 and / or greater than 0.3, and SiO ₂ > 5%: The glassy phase is then abundant and rich in alumina.

More than 95% by number, preferably more than 97% by number, preferably more than 99% by number, and more preferably substantially 100% by number of the crystallites have a form factor F greater than 0.45, or greater than 0.50, or greater than 0.55, or greater than 0.60, or even greater than 0.70.

- The diameter "D" is less than 2 microns, preferably less than 1 micron.

- denoting by "C" the mass ratio CeO ₂ / (ZrO ₂ + HfO ₂ ) and by "Y" the mass ratio Y ₂ O ₃ / (ZrO ₂ + HfO ₂ ),

0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (63.095.Y ² - 11.214, Y + 0.4962, 0.25) <C, and

C ≤ 250.Y ² - 49, Y + 2.6. More preferably, 0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (70.238.Y ² - 12.393.Y + 0.544; 0.25) <C, preferably when Y <0.089, Min (- 38.095.Y ² + 0.3571.Y + 0.2738, 0.25) <C

- More preferably, 0 <C <0.6 and 0.02 <Y <0.098 and C <150. Y ² - 30.7. Y + 1, 72, preferably always C <- 51, 1905.Y ² + 0.25.Y + 0.4826.

- The mass ratio CeO ₂ Z (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.2, preferably greater than or equal to 0.3 and / or less than or equal to 0.5.

The mass ratio Y ₂ O ₃ Z (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.03, preferably greater than or equal to 0.045 and / or less than or equal to 0.09, preferably less than or equal to 0.06.

The characteristics described above in the general scope of the invention are applicable to this second particular embodiment, insofar as they are not incompatible with it.

The inventors have discovered that a product according to the second particular embodiment has, in a highly basic medium, a particularly high resistance to corrosion.

Without being able to explain it, the inventors have found that these performances correspond, in a transmission electron microscope view, to a percentage of less than 5% in number of crystallites having a form factor of less than 0.4 (this is elongated form).

A subset of the products according to this second particular embodiment has the following chemical composition, for a total of 100%, 55% <ZrO ₂ + HfO ₂ <75%, 10% <CeO ₂ <30%, 1.5 % <Y ₂ O ₃ <5%,

5% ≤ SiO ₂ <12%, 4% <A1 ₂ O ₃ <12% 0% <MgO <2%, the _s 5% <TiO ₂ <3% other oxides <1%.

Preferably, the matrix has a diameter "D" of less than 1 μm. Preferably, a product according to this subset of this second particular embodiment has one or more of the following optional features:

- More than 99% by number, and more preferably substantially 100% by number of the crystallites have a form factor F greater than 0.50, preferably greater than 0.55, preferably greater than 0.60, preferably greater than at 0.70.

- denoting by "C" the mass ratio Ce ⁽ V (ZrO ₂ + HfO ₂ ) and by "Y" the mass ratio Y ₂ O ₃ / (ZrO ₂ + HfO ₂ ),

0 <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (63.095.Y ² - 11.214, Y + 0.4962, 0.25) <C, and C ≤ 250.Y ² - 49, lY + 2.6

Preferably 0 <C <0.6 and 0.02 <Y <0.098 and when Y 0.082, Min (70.238.Y ² - 12.393.Y + 0.544; 0.25) <C, preferably when Y <0.089, Min (- 38.095.Y ² + 0.3571, Y + 0.2738, 0.25) <C.

Preferably 0 <C <0.6 and 0.02 <Y <0.098 and C <150.Y ² - 30.7.Y + 1.72, preferably C <- 51, 1905. Y ² + 0, 25. Y + 0.4826.

- The mass ratio CeO ₂ / (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.2, preferably greater than or equal to 0.3 and / or less than or equal to 0.5.

The mass ratio Y ₂ O ₃ / (ZrO ₂ + HfO ₂ ) is greater than or equal to 0.03, preferably greater than or equal to 0.03, preferably greater than or equal to 0.045 and / or less than or equal to 0.09, preferably less than or equal to 0.06.

In the case of stress in a strongly basic medium, that is to say for pH> 8, for example for grinding suspensions of calcium carbonate, such products are particularly suitable because they have a wear resistance high coupled with good resistance to chemical attack of the medium in which the grinding is carried out.

Whatever the embodiment, a product according to the invention preferably has a density greater than or equal to 4, or greater than or equal to 4.5, or greater than or equal to 4.7, or greater than or equal to 5 or even greater than or equal to 5.2. It is considered that the higher the density, the better the grinding efficiency. Planetary wear and wear in basic conditions are defined below. The product may have a basic wear of less than or equal to 2.2 g / h, or less than or equal to 2 g / h, or less than or equal to 1.8 g / h, or less than or equal to 1.5 g / h.

Preferably, the product has a wear in basic medium of less than or equal to 1.8 g / h and a density greater than or equal to 5.2.

The product may also have a planetary wear less than or equal to 3.5%, or less than or equal to 2.9%, or less than or equal to 2.5%, or less than or equal to 2.3%, or less or equal to 2.1%, or even lower than or equal to 1.8%.

Depending on the desired properties, a product according to the invention can be used in other applications than grinding in a humid environment. For example, it can be used as a dry grinding, propping and heat exchange agent.

testing

Measurement Protocols The density of the products tested is measured by a method using a helium pycnometer (AccuPyc 1330 from Micromeritics®), according to a method based on the measurement of the volume of gas (in this case Helium) displaced.

The homogeneity of the distribution of crystallites in the vitreous phase is determined _. using observations made in Transmission Electron Microscopy (or TEM) as follows. The preparation of the samples to be observed consists in mechanically thinning a particle by successive polishing to a thickness of about 30 microns. Then the sample preparation is finalized by ion thinning (argon sputtering) via a PIPS ("Precision

Ion Polishing System "). The sample to be observed is then in the form of a blade.

This slide is deposited in the Transmission Electron Microscope (Philips CM 30 - 300KV), on a molybdenum support and a copper washer. The purpose of electronic bombardment is to observe the sample in transmission.

At least 5 photos of the microstructure are made in different areas of the sample chosen randomly. The enlargements of the photos are adapted so as to be able to observe matrix surfaces of between 15 and 150 μm ² and so that that the sum of the surfaces observed is at least 450 μm ² . The magnification is adapted to distinguish the crystallites in the matrix.

A circle of a determined diameter is then moved over the entire matrix surface, looking for a position in which no crystallite is included, even partially, in the circle.

- If we find such a position, we repeat the operation with a circle with a diameter greater than 0.1 microns to the previous circle. This procedure is continued until no position is found that meets the above criterion. The diameter "D" is then equal to the diameter of the circle of the preceding cycle, that is to say to the diameter of the largest circle that it has been possible to place on the observed surface without any crystallite being included, even partially, in this circle.

- Reciprocally, if we can find such a position, we decrease the diameter of the tested circle by 0.1 microns and we repeat the operation until finding a circle meeting the above criterion. The diameter "D" is then equal to the diameter of this last circle.

The photos also measure crystallite size and shape factors.

The following methods provide excellent simulation of actual service behavior in grinding applications. To determine the so-called "planetary" wear resistance, 20 ml (volume measured with a measuring cylinder) of particles to be tested, selected by sieving between 0.8 and 1 mm on square mesh sieves , were weighed (mass mo) and introduced into one of 4 alumina-coated 125 ml capacity bowls and fixed on the tray of a RETSCH type PM400 fast planetary mill. 2.2 g of Presi brand silicon carbide (having a median size D ₅ o of 23 μm) and 40 ml of water are added to the bowl. The bowl is closed and the tray is rotated at 400 rpm with reversal of the direction of rotation every minute for 1h30. The plate is rotated relative to the frame of the mill and the bowl is rotated relative to the plate, imposed by the speed of rotation of the plate. The contents of the bowl are then washed on a 100 μm sieve so as to remove the residual silicon carbide as well as the tearing of material due to wear during grinding. The particles are then dried in an oven at 100 ^° C. for 3 h and then weighed (mass m). Planetary wear, expressed as a percentage, is given by the following formula:

100 (m ₀ -m) / m

In order to determine the so-called "basic" wear, that is to say in media having a pH greater than 8, a charge of particles to be tested is sieved between 0.6 and 0.8 mm on sieves. square stitches. An apparent volume of 1.04 liter of particles is weighed (mass mo). The particles are then introduced into a horizontal mill Netzsch LMEl type (useful volume of 1.2 L) with eccentric steel discs. An aqueous suspension of calcium carbonate CaCO ₃ having a pH equal to 8.2, containing 70% of dry matter and of which 40% of the grains by volume are less than 1 μm, passes continuously through the mill, with a flow rate of 4. liters per hour. The mill is started gradually until reaching a linear speed at the end of 10 m / s disks. The mill is kept in operation for a time t, between 16 and 24 hours, then stopped. The particles are rinsed with water, carefully removed from the mill and then washed and dried. They are then weighed (mass m). The wear speed V in grams / hour is determined as follows:

V = (m _o -m) / t

The particle charge is taken up and supplemented with (mo-m) grams of new particles so as to repeat the grinding operation as many times as necessary (n times) so that the cumulative grinding time is at least 100 hours and that the difference between the wear speed calculated in step n and in step n-1 is less than 15% in relative. Typically, the total grinding time is between 100 hours and 140 hours. The wear in basic medium is the wear speed measured for the last grinding operation n. The percentage improvement compared to Comparative Example 3 is defined by the following formula: 100 * (wear of the product of Comparative Example 3 - wear of the product under consideration) / wear of the product of Comparative Example 3. considers that the results are particularly satisfactory if the products exhibit an improvement in wear resistance of at least 10% compared with that of Comparative Example 3. The results are considered to be particularly satisfactory if the products exhibit improvement of the basic wear resistance of at least 15% compared with that of Comparative Example 2. Manufacturing protocol

A starting charge is prepared from powders of zircon, yttrium oxide, cerium oxide, aluminum oxide and optionally zirconium oxide (zirconia) and titanium oxide. This feedstock is then melted in an electric Heroult arc furnace so as to form a bath of molten liquid. This bath is then cast so as to form a net of liquid which is then dispersed in particles, in the form of balls by blowing compressed air and isolated by casting.

Several melting / casting cycles are carried out by adjusting in the composition the oxides of yttrium, cerium, aluminum and optionally zirconium and titanium.

This technique makes it possible to have several batches of particles of different compositions which can be characterized according to methods well known to those skilled in the art.

Blast cooling, very fast, does not crystallize the matrix, if not marginally. A heat treatment is therefore necessary to generate crystallites distributed within the matrix.

To do this, the particles to be treated are arranged batchwise in nacelles which are charged in a heat treatment furnace. The cycle comprises a rise in temperature at a speed of 120 ^° C., from ambient temperature to a first stage temperature (called "plateau 1") equal to 850 ^° C., for a duration of between 0 and 10 hours, possibly followed by a second stage (called "stage 2") at a temperature of 1000 ⁰ C for a period of between 1 hour and 10 hours.

The rate of rise in temperature between the end of stage 1 at 850 ^° C. and the beginning of stage 2 at 1000 ^° C. is 120 ^° C.Zh. After temperature plateau 2, the temperature is reduced to 200 ° CZh.

Results

The results obtained are summarized in the following table: - "pvc" specifies the presence ("yes") or the absence ("no") of a crystallization distributed throughout the vitreous phase; - "D" specifies the diameter "D" of the largest circle that can be placed on a view of a section at the heart of the product, taken by means of an electron microscope transmission (TEM), without any crystallite being included, even partially, in this circle;

- "crystallite size" specifies that at least 80% of the crystallites have a size within the indicated range; - "F <0.4" indicates the presence ("yes") or absence ("no") of more than 5% in number of crystallites with F <0.4;

- "TC" specifies the coverage rate of the matrix.

K>

(*): example outside the invention

Table 1

Planetary wear

The examples according to the invention have a greater resistance to planetary wear than the examples of the same chemical composition but without crystallites distributed within their matrix, as illustrated by a comparison between Example 4 (non-crystallized matrix) and Examples 5 and 6 (crystallized matrix) or a comparison between Example 7 (uncrystallized matrix) and Examples 8, 9 and 11

(crystallized matrix). Examples 5 and 6 show an improvement of 16% and 11%, respectively, compared to Example 4, while Examples 8, 9, 10 and

11 show an improvement of 11%, 11%, 17% and 17% compared to Example 7. A comparison of Examples 5 and 6 also shows the advantage of a two-stage heat treatment with greater dwell times. at 1 o'clock.

A comparison of Examples 8 and 9 shows that a step time of greater than 3 hours does not necessarily improve the planetary wear resistance.

However a comparison of Examples 10 and 11 shows that a bearing time 1 greater than 3 hours improves the wear resistance in basic medium. These examples also confirm the interest of a two-stage heat treatment.

Examples 11 to 23 illustrate, under identical heat treatment conditions, the influence of the chemical composition on the planetary wear resistance. In particular, they make it possible to observe a sudden deterioration in planetary wear resistance when the CeO ₂ content exceeds 31% (Examples 20 and 21).

Examples 5, 22 and 24 are most preferred for the planetary wear test.

Wear in basic medium

A comparison of Examples 4 and 5 to 6, or 7 and 9 to 11, shows the advantage of a heat treatment, and more generally, the presence of crystallites distributed within the matrix, to increase the resistance to the wear in basic medium.

A comparison of Examples 5 and 6 shows, however, that it is preferable that the matrix does not contain elongate crystallites when the product according to the invention is intended to serve in a basic medium. A comparison of Examples 9 to 11, and in particular of Example 9 with Examples 10 and 11, shows that a decrease in the area of matrix surfaces not containing crystallite lite is also useful in an application in a basic medium .

A SiO ₂ Al ₂ O ₃ ratio <1, or even less than 0.8 is preferable. A comparison of Examples 10 and 11 finally shows that a bearing time 1 greater than 3 hours improves the planetary wear resistance in basic medium. These examples also confirm the interest of a two-stage heat treatment.

To optimize the behavior in a basic medium, in particular for a microbrilling application in a basic medium, Example 5 is considered to be the best product because it combines a density greater than or equal to 5.3, a planetary wear resistance. of 1.6 and a basic wear resistance of 1.8 or less.

In all the examples according to the invention, the inventors have found an absence of cracks and pores. As now clearly apparent, the invention provides a product with remarkable planetary wear resistance, and in some embodiments even a very good wear resistance in a basic medium.

Of course, the present invention is not limited to the described embodiments, provided by way of illustrative and non-limiting examples. In particular, the invention is not limited to molten particles, but extends to any type of molten product, and in particular to thin plates. The field of application of the products according to the invention is not limited to micro-grinding, but extends to all applications where the qualities described above would be likely to be useful, and in particular to wet microdispersion and surface treatment.

Claims

A method of manufacturing a product, comprising the following successive steps: a) mixing raw materials to form a feedstock, b) melting the feedstock to form a molten liquid, c) solidifying the feedstock. molten liquid so as to obtain a molten product having crystals bonded by a glassy phase, and d) crystallization heat treatment of the glassy phase of said molten product, wherein the composition of the feedstock is adapted to manufacture a product having the following chemical composition, in percentages by mass on the basis of the oxides and for a total of 100%:

40% <(ZrO ₂ + HfO ₂ ) <94%,

6% <CeO ₂ <31%, 0% ≤ Y ₂ O ₃

0% <Al ₂ O ₃

2% <SiO ₂ ,

0% <MgO,

0% <TiO ₂ , and other oxides <1%.

2. Method according to the preceding claim, wherein said heat treatment in step d) comprises a nucleation operation at a first temperature above the glass transition temperature Tg of the vitreous phase of the product resulting from step c) and or a growth operation at a second temperature higher than the glass transition temperature Tg of the glass phase of the product resulting from stage c), the second temperature being, when the growth operation follows a nucleation operation, greater than at least 50 ⁰ C at said first temperature.

3. Method according to the preceding claim, wherein the heat treatment in step d) comprises a bearing at a temperature between 800 ⁰ C and 1100 ° C.

4. Method according to the preceding claim, wherein the heat treatment in step d) comprises a first step at a temperature between 820 ° C and 880 ⁰ C followed by a second step at a temperature between 970 ⁰ C and 1070 ^° C.

5. Method according to any one of the two immediately preceding claims, wherein said bearing at a temperature between 800 ⁰ C and 1100 ⁰ C and / or said first bearing and / or said second bearing lasts at least 1 hour.

6. Method according to the preceding claim, wherein said bearing at a temperature between 800 ⁰ C and HOO ⁰ C and / or said first bearing and / or said second bearing lasts at least 5 hours.

7. A process according to any one of the preceding claims, wherein the composition of the feedstock is adapted to manufacture a product having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%: 45% <(ZrO ₂ + HfO ₂ ) <85%,

6% <CeO ₂ <31%,

0.8% <Y ₂ O ₃ <8.5%,

0% <Al ₂ O ₃ <30%,

2% <SiO ₂ <37%, 0 <MgO <6%,

0 <TiO ₂ <8.5%, and other oxides <1%.

8. Method according to the preceding claim, wherein the composition of the feedstock is suitable for producing a product having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

55% <ZrO ₂ + HfO ₂ ≤ 75%, ^' 1.5% <Y ₂ O ₃ <5%, 0% <Al ₂ O ₃ <15%, 3% <SiO ₂ <12%, 0% <MgO <2%, 0% <TiO ₂ <5%, other oxides <1%.

9. Method according to the preceding claim, wherein the composition of the feedstock is suitable for producing a product having the following chemical composition, in percentages by mass on the basis of the oxides and for a total of 100%: 55% <ZrO ₂ + HfO ₂ <75%,

10% <CeO ₂ <30%, 1.5% <Y ₂ O ₃ ≤ 5%,

4% <Al ₂ O ₃ <12%, 5% <SiO ₂ <12%, 0% <MgO <2%, 1.5% ≤TiO ₂ <3%, other oxides <1%, 10.Method according to any one of the preceding claims, wherein the composition of the feedstock is adapted to manufacture a product such that, denoting by "C" the mass ratio CeO ₂ / (ZrO ₂ + HfO ₂ ) and "Y" the mass ratio Y ₂ O ₃ / (ZrO ₂ + HfO ₂ ), O <C <0.6 and 0.02 <Y <0.098 and when Y <0.082, Min (63.095.Y ² - 11.214.Y + 0, 4962; 0.25) <C and

C≤250.Y ² -49, lY + 2.6.

11. A method according to any one of the preceding claims, wherein the composition of the feedstock is adapted to produce a product such that the weight ratio SiO ₂ ZAl ₂ O ₃ is less than or equal to 1.

12.Procédé according to the preceding claim, wherein the composition of the feedstock is adapted to produce a product such that the weight ratio SiO ₂ / Al ₂ O ₃ is between 0.3 and 0.75.

13. Method according to any one of the preceding claims, adapted so that at the end of step c), the product has a shape of which at least one dimension is less than 30 mm.

14.Procédé according to the preceding claim, wherein said product obtained at the end of step c) has the shape of a ball having a size less than or equal to

4 mm.

15. Product obtained or likely to have been obtained by means of a process according to any one of the preceding claims. The use of a product according to the preceding claim, as a grinding agent, a wet dispersion agent, a surface treatment agent, a proppant or a heat exchange agent. π.Utilisatîon according to the preceding claim, as grinding agent suspensions having a pH> 8.