WO2018234417A1

WO2018234417A1 - Sintered material made from alumina and zirconia

Info

Publication number: WO2018234417A1
Application number: PCT/EP2018/066491
Authority: WO
Inventors: Thomas PERIE; Eric LINTINGRE
Original assignee: Saint-Gobain Centre De Recherches Et D'etudes Europeen
Priority date: 2017-06-22
Filing date: 2018-06-20
Publication date: 2018-12-27
Also published as: FR3068035A1

Abstract

A sintered product having a chemical analysis such that, as percentages by weight on the basis of the oxides: - ZrO2 partially stabilised with CeO2 and Y2O3: the remainder to 100%, where CeO2: 2.5-5.5 mol% and Y2O3: 0.5-2 mol%, in molar percentages based on the sum of ZrO2, CeO2 and Y2O3, - Al2O3: 3%-19%, - CaO: >0.1%, - Manganese oxide(s): >0.1%, - CaO + manganese oxide(s): <6%, - Iron oxide(s): >0.15%, - Cobalt oxide(s): >0.2%, - Iron oxide(s) + cobalt oxide(s) + chromium oxide(s): <2.5% - Other oxides: <3%, the manganese, iron, cobalt and chromium oxides being expressed in the form of MnO, Fe2O3, Co3O4 and Cr2O3, respectively.

Description

FRITTE PRODUCT BASED ON ALUMINA AND ZIRCONIA

Technical area

The invention relates to a sintered product based on alumina and zirconia, a particulate mixture making it possible to obtain such a product, and a process for manufacturing said product.

Background of the invention

Refractory products include melted and cast products and sintered products.

Unlike sintered products, melted and cast products usually comprise a very abundant intergranular glassy phase which fills a network of crystallized grains. The problems encountered in their respective applications by the sintered products and the cast and cast products, and the technical solutions adopted to solve them, are therefore generally different. Moreover, because of the important differences between the manufacturing processes, a composition developed to manufacture a melted and cast product is not a priori usable as such to manufacture a sintered product, and vice versa.

The sintered products are obtained by mixing appropriate raw materials and then shaping the mixture and baking the resulting preform at a temperature and for a time sufficient to obtain the sintering of this preform. Sintered products, according to their chemical composition, have different properties and are therefore intended for a wide variety of industries.

Of the ceramic sintered products, quadratic yttria products, typically having a molar amount of Y 2 C ≥ 3 of 3%, exhibit high tensile strength and high toughness.

Cerium zirconia products, typically having a molar amount of CeO 2 equal to 12%, have a very high toughness, higher than yttria products, but a lower tensile strength and toughness.

The alumina-zirconia products, in particular those having an alumina content of between 10 and 50%, are known to have good mechanical properties, in particular hardness and mechanical strength. However, a product of yttria, zirconia or alumina-zirconia has a low resistance to falling, especially when it is in the form of a plate. A fall can in particular cause cracks or even breakage of the product.

There is therefore a need for a sintered product having a high resistance to falling.

An object of the invention is to respond, at least partially, to this need.

Summary of the invention

The invention proposes a sintered product presenting

a chemical analysis, in percentages by weight on the basis of the oxides, such that:

Zr0 ₂ partially stabilized with CeO ₂ and Y ₂ O 3: 100% complement,

with Ce0 ₂ : 2.5 - 5.5 mol% and Y ₂ 0 ₃ : 0.5 - 2 mol%, in

molar percentages based on the sum of

Zr0 ₂ , Ce0 ₂ and Y ₂ 0 ₃ ,

- Al ₂ 0 ₃ : 3%

19%

- CaO:> 0,1%, - Oxide (s) of manganese:> 0,1%,

- CaO + manganese oxide (s): <6%,

- Iron oxide (s):> 0,15%,

- cobalt oxide (s):> 0,2%,

- Iron oxide (s) + cobalt oxide (s) + chromium oxide (s): <2,5% - Other oxides: <3%, oxides of manganese, iron, cobalt and chromium being expressed in the form of MnO, Fe ₂ C 3, CO 3 O 4 and Cr ₂ C 3, respectively.

Without being able to explain it theoretically, the inventors have discovered that a sintered product according to the invention advantageously has a high resistance to falling.

Preferably, the microstructure of the sintered product is such that: the sintered product consists of agglomerated grains and the average size of the grains having a form factor of less than 2.5, or "collected grains", is less than 3 μηη,

the average length of the aluminous elongated nodules is less than 50 μηη, an elongated aluminous nodule being a structure having a form factor greater than or equal to 2.5 and consisting of an aluminous grain or of several adjacent aluminous grains, an aluminous grain being a grain containing more than 40% of Al 2 O 3, in weight percentage based on the oxides.

A sintered product according to the invention may in particular be manufactured according to a method according to the invention described below.

A sintered product according to the invention may also have one or more of the following optional features:

the molar content of Y 2 O 3 is preferably less than 1, 9%, preferably less than 1.7%, preferably less than 1.5%, and / or preferably greater than 0.6%, preferably greater than 0%; , 8%, preferably greater than 1%, in mole percent based on the sum of ZrO 2, CeO 2 and Y 2 O 3;

the molar content of CeO 2 is preferably less than 5%, preferably less than 4.5%, or even less than 4.2%, and / or greater than 3%, in molar percentage on the basis of the sum of ZrO 2, CeO2 and Y2O3;

the content of Al 2 O 3 is preferably less than 18%, preferably less than 17%, and / or preferably greater than 5%, preferably greater than 6%, preferably greater than 7%, preferably greater than 9%, preferably greater than 10%, or even greater than 1 1%, or even greater than 12%, or even greater than 13%, as a weight percentage based on the oxides;

the total content CaO + manganese oxide (s), the content of manganese oxide (s) being expressed in the form MnO, is preferably greater than 0.4%, or even greater than 0.5%, or even greater than 0 , 6%, and / or preferably less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2.5%, preferably less than 2%, preferably less than 1%, 5%, preferably less than 1%, in weight percent based on the oxides;

the CaO content is preferably greater than 0.2%, and / or less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.8%, preferably less than 0.6%, or even less than 0.5%, as a percentage by weight based on the oxides;

the content of manganese oxide (s) expressed as MnO is preferably greater than 0.2%, preferably greater than 0.3%, and / or less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.8%, preferably less than 0.6%, as a percentage by weight based on the oxides;

the CaO content is preferably greater than 0.2% and less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.8%, preferably less than 0.6%, or even less than 0.5%, as a percentage by weight based on the oxides, and

the content of manganese oxide (s) expressed in the MnO form is preferably greater than 0.2%, preferably greater than 0.3% and less than 4%, preferably less than 3%, preferably less than 2%; %, preferably less than 1%, preferably less than 0.8%, preferably less than 0.6%, as a percentage by weight based on the oxides;

the content of iron oxide (s), expressed as Fe 2 O 3, is preferably greater than 0.2%, preferably greater than 0.3% and / or preferably less than 2%, preferably less than 1%, 5%, preferably less than 1%, preferably less than 0.8%, as a percentage by weight based on the oxides;

the content of cobalt oxide (s), expressed in the form of CO 3 O 4, is preferably greater than 0.3% and / or preferably less than 2%, preferably less than 1.5%, preferably less than 1% preferably less than 0.8%, as a percentage by weight based on the oxides;

in one embodiment, the content of chromium oxide (s), expressed as Ο2Ο3, is less than 0.1%, preferably less than 0.05%, or even substantially zero, as a mass percentage based on oxides;

in one embodiment, the content of chromium oxide (s), expressed as Ο2Ο3, is greater than 0.2% and / or preferably less than 2%, preferably less than 1.5%, preferably less than 1%, preferably less than 0.8%, as a percentage by weight based on the oxides;

the total content of iron oxide (s), cobalt oxide (s) and chromium oxide (s) is greater than 0.4%, preferably greater than 0.5%, preferably greater than 0.6%, preferably greater than 0.8%, and / or less than 2%, preferably less than 1, 8%, preferably less than 1, 5%, as a percentage by weight based on the oxides;

preferably, the content of iron oxide (s), expressed as Fe2C> 3, is greater than 0.2%, preferably greater than 0.3% and / or preferably less than 2%, preferably less than at 1, 5%, preferably less than 1%, preferably less than 0.8%, and

the content of cobalt oxide (s), expressed in the form of CO 3 O 4, is greater than 0.3% and / or preferably less than 2%, preferably less than 1.5%, preferably less than 1%, of preferably less than 0.8%, and

the content of chromium oxide (s), expressed in the form of Ο2Ο3, is greater than 0.2% and preferably less than 2%, preferably less than 1.5%, preferably less than 1%, preferably less than 1%, 0.8%, in percentages by mass on the basis of the oxides;

preferably, the Al 2 O 3 content is less than 18%, preferably less than 17%, and greater than 9%, preferably greater than 10%, even greater than 11%, even greater than 12%, or even greater than 13%. %, as a weight percentage based on the oxides, and

the total content of iron oxide (s), cobalt oxide (s) and chromium oxide (s) is greater than 0.4%, preferably greater than 0.5%, preferably greater than 0.6%, preferably greater than 0.8%, and less than 1.8%, preferably less than 1.5%, in weight percent based on the oxides, and

preferably, the CaO content is greater than 0.2% and less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.8%; preferably less than 0.6%, or even less than 0.5%, as a percentage by weight based on the oxides, and

preferably, the content of manganese oxide (s) expressed in the MnO form is greater than 0.2%, preferably greater than 0.3% and less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.8%, preferably less than 0.6%, as a percentage by weight based on the oxides;

in one embodiment, the content of chromium oxide (s), expressed as C Os, is less than 0.1%, preferably less than 0.05%, or even substantially zero, and the weight ratio of the iron oxide content and cobalt oxide (s) content, expressed as Fe2O3 / Co3C> 4, is greater than 0.5, preferably greater than 1, preferably greater than 1.5, and / or preferably less than 2.5;

in one embodiment, the mass ratio of the chromium oxide (s) content and the sum of the iron oxide (s) content and the cobalt oxide (s) content, expressed as Cr203 / (Fe 2 O 3 + Co 3 C> 4) is less than 0.6, preferably less than 0.5;

in one embodiment, the mass ratio of the iron oxide (s) content and the cobalt oxide (s) content, expressed as Fe 2 O 3 / Co 3 C 4, is greater than 0.4, preferably greater than 0.5, preferably greater than 0.8 and / or preferably less than 3, preferably less than 2.5, preferably less than 2, preferably less than 1.5, and the weight ratio of the iron oxide content (s) and the content of chromium oxide (s) expressed as Fe 2 O 3 / Cr 2 C 3> is greater than 0.5, preferably greater than 1 and / or preferably less than 3, preferably less than 2.5, preferably less than 2;

the content of other oxides, that is to say of other oxides ZrO 2, CeO 2, Y 2 O 3, Al 2 O 3, CaO, and the oxide (s) of manganese, iron, cobalt and chromium, is preferably less than 2%, preferably less than 1.5%, preferably less than 1.0%, preferably less than 0.8%, preferably less than 0.5%, or even less than 0.3%, in weight percent on the basis of oxides;

in a preferred embodiment, the other oxides are impurities;

the sintered product comprises more than 90%, preferably more than 95%, preferably more than 97%, preferably more than 98%, preferably more than 99%, preferably more than 99.5%, preferably more than 99.9% of oxides, as a percentage by weight, based on the mass of the product;

the average size of the collected grains is less than 2.5 μηη, preferably less than 2 μηη, preferably less than 1.5 μηη, preferably less than 1 μηι, preferably less than or equal to 0.5 μηη, and or preferably greater than 0, 1 μηι, preferably greater than 0.2 μηη;

in a preferred embodiment, more than 90%, preferably more than 93%, preferably more than 95%, preferably more than 97%, preferably more than 99% by number of the picked grains are partially zirconia grains stabilized, and / or grains constituted for more than 40% of their mass of A C, and / or grains constituted for more than 95% of their mass of iron oxide and / or cobalt oxide and / or chromium oxide; the average length of the aluminous elongated nodules is preferably less than 40 μηι, preferably less than 30 μηη and / or preferably greater than 2 μηι, preferably greater than 5 μηη;

the form factor of more than 95% by number of the elongated aluminous nodules is preferably greater than 3, preferably greater than 4 and / or preferably less than 20, preferably less than 15, preferably less than 10;

the bulk density of the sintered product is preferably greater than 5.4 g / cm ³ , or even greater than 5.5 g / cm ³ , or even greater than 5.6 g / cm ³ and / or preferably less than 6, 1 g / cm ³ , or even less than 6.0 g / cm ³ ;

the relative density of the sintered product is preferably greater than 95%, preferably greater than 97%, or even greater than 98%;

the sintered product has a Vickers HVo hardness, 3 / is greater than 1000 HV, preferably greater than 1100 HV, preferably greater than 1200 HV, or even greater than or equal to 1250 HV;

the sintered product has a modulus of rupture in three-point bending, measured according to the ISO 6872 standard, greater than 900 MPa, preferably greater than 950 MPa, preferably greater than 980 MPa, or even greater than or equal to 990 MPa;

the sintered product is in the form of a plate, the thickness of the plate being less than 5 times, preferably 10 times its width.

The invention also relates to a method of manufacturing a sintered product according to the invention, comprising the following steps:

a) preparing a feedstock comprising a particulate mixture having a median size of less than 2.0 μηη, and whose composition is adapted so as to obtain, after step c), a sintered product according to the invention,

b) shaping the feedstock so as to obtain a preform, c) sintering the preform at a sintering temperature above 1300 ° C so as to obtain a sintered product according to the invention.

A method according to the invention may also comprise one or more of the following optional features:

in step a), the particulate mixture has a median size of preferably less than 1 μηη, preferably less than 0.8 μηη, preferably less than 0.6 μηι, preferably less than 0.5 μηι, or even less at 0.3 μηη; in step a), a grinding step is carried out, preferably by co-grinding;

the process preferably comprises, in step b), a shaping by casting, preferably by slip casting, strip casting, or by extrusion or by injection or by pressing, preferably by axial pressing, by pressing hot or by isostatic pressing;

in step c), the sintering temperature is preferably less than 1600 ° C, preferably less than 1550 ° C, preferably less than 1500 ° C, and / or greater than 1350 ° C, preferably greater than 1400 ° C ° C. The invention also relates to a particulate mixture comprising:

ZrO 2 particles and / or ZrO 2 precursor particles,

particles of CeO 2 and / or particles of CeO 2 precursor,

particles of Y2C> 3 and / or precursor particles of Y2C> 3,

particles of A C and / or particles of precursor of A C,

particles of CaO and / or particles of CaO precursor,

particles of manganese oxide (s) and / or particles of precursor of manganese oxide (s),

iron oxide particles and / or iron oxide precursor particles,

particles of cobalt oxide (s) and / or particles of cobalt oxide precursor (s),

optionally, particles of chromium oxide (s) and / or chromium oxide precursor particles,

and / or particles of several of these oxides and / or precursors of these oxides, the particulate mixture having a chemical composition suitable for the manufacture of a sintered product according to the invention by sintering said particulate mixture.

Preferably, such a particulate mixture is ready for use.

A particulate mixture according to the invention can in particular be packaged in a bag.

Preferably, the particulate mixture according to the invention has one or more of the following characteristics: in a preferred embodiment, the particulate mixture comprises more than 0.2% of chromium oxide (s) particles, and / or chromium oxide (s) precursor particles;

preferably, the oxide (s) of manganese are selected from MnO, Μηθ2, Μη2θ3, Μη3θ ₄ and mixtures thereof. Preferably, the oxides of manganese are chosen from MnO, Mn3 <D ₄ and mixtures thereof;

preferably, the iron oxides are chosen from FeO, Fe2C3 and mixtures thereof. Preferably, the iron oxide is Fe2O3;

the cobalt oxide is Co3 <D ₄ ;

chromium oxide is Ο2Ο3;

in one embodiment, the iron oxide and the cobalt oxide are combined at least partially, preferably completely, in the form of a cobalt-iron spinel of the formula Co _x Fe 3- _x O ₄ with 0 x <3, x being preferably greater than 0.6 and less than 2, preferably less than 1.5, preferably less than 1.2;

the iron oxide and the chromium oxide are combined at least partially, preferably completely, in the form of an iron-chromium spinel of formula Cr _x Fe3-x0 ₄ with 0 <x '<3, x preferably being greater than 0.8 and less than 2.3, preferably less than 1.8, preferably less than 1.5;

in a preferred embodiment, the iron oxide, the cobalt oxide and the chromium oxide are combined at least partially, preferably completely, in the form of an iron-cobalt-chromium spinel, having preferably a Fe203 Co30 ₄ mass ratio greater than 0.5, preferably greater than 1 and less than 3, preferably less than 2.5, preferably less than 2, preferably less than 1.5, and a Fe203 mass ratio. Cr 2 O 3 greater than 0.5, preferably greater than 1, preferably greater than 1.3, and less than 3, preferably less than 2.5, preferably less than 2;

preferably, the median size of said particulate mixture is less than 2 μηη, preferably less than 1 μηι, preferably less than 0.8 μηι, preferably less than 0.6 μηι, preferably less than 0.5 μηι, or even less than 0.3 μηη; - Preferably, the specific surface of said particulate mixture is less than 20 m ² / g, preferably less than 15 m ² / g, and / or preferably greater than 5 m ² / g. Definitions

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

- A "particulate mixture" is a powder obtained by mixing several powders.

- A "median size" of a powder, generally denoted D ₅ o, the size dividing the particles of this powder into first and second populations equal in mass, these first and second populations comprising only particles having a larger size or equal to, or less than, the median size, respectively. The median size can for example be measured using a laser granulometer.

- Sintering is the consolidation by heat treatment at more than 1100 ° C of an agglomerate of grains, or "preform", possibly with a partial or total melting of certain constituents of the grains (but not all constituents).

- The term "average size" grains of a sintered product, the dimension measured according to the method of "Mean Linear Intercept" described in ASTM E1382.

The oxides of manganese comprise in particular MnO, Μη2θ3, Μηθ2 and Μη3θ ₄ .

Iron oxides include, in particular, FeO, Fe 2 O 3, Fe 3 O ₄ .

- "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, and vanadium are impurities. By way of examples, mention may be made of Na 2 O or MgO.

The only exception is that hafnium oxide is not considered an impurity. Hafnium oxide is not chemically separable from zirconium oxide. In the chemical composition of a product comprising zirconia, ZrO 2 therefore conventionally designates the total content of these two oxides.

According to the present invention, HfO 2 is not voluntarily added to the feedstock. Hf02 therefore only designates traces of hafnium oxide, this oxide always being naturally present in zirconia sources at levels generally below 3%. In a product according to the invention, the content of HfO 2, which is not an "other oxide" and accounted for in ZrO 2, is less than 3%, preferably less than 2%, as a percentage by weight on the basis of oxides. .

Similarly, traces of hafnia are here accounted for in "zirconia". "Precursor" of an oxide means a constituent capable of supplying said oxide during the manufacture of a sintered product according to the invention. For example, calcium carbonate CaCC is a possible precursor of CaO.

- "Form factor of a grain or nodule" means the ratio of the largest dimension of the grain or nodule, or "length", to the largest dimension measured perpendicular to the direction of the larger dimension, or "width". These dimensions are measured in a plane of observation of a polished section of the sintered product, conventionally on electron micrographs of this section.

- An "elongated nodule" is a nodule with a form factor greater than or equal to 2.5.

- By "absolute density" of a sintered product according to the invention is meant the absolute density conventionally calculated using a law of the mixtures, from a chemical analysis of said sintered product according to the invention , considering that all the yttrium and cerium oxides stabilize the zirconia, and without taking into account the "other oxides", or any traces of solvent, organic additive and dispersant. The absolute density of the partially stabilized zirconia at Y 2 O 3 and CeO 2 is calculated according to the teaching of the document Phase transformation and lattice constants of zirconia solid solutions in the system 2 O 3 -CeO 2 -T.rO 2, Urabe and Al., Materials. Science Forum Flights. 34-36 (1988) pp 147-152.

"Relative density" of a sintered product means the ratio equal to the bulk density divided by the absolute density, expressed as a percentage.

- "Thickness" of a plate means its smallest dimension.

- "Width" of a plate means its smallest dimension measured in a plane transverse to the direction of the thickness of said plate.

In a sum of oxide contents, "+" means "and / or". For example, "C03O4 + Ο2Ο3" refers to the total content of cobalt oxide (s) and chromium oxide (s), in percentages by weight based on the oxides, but does not require the presence of at least one oxide cobalt and at least chromium oxide.

Unless otherwise stated, all percentages relating to the composition of a product or relating to a starting load are mass percentages on the basis of Oxides and all percentages of CeO2 and Y2O3 are molar percentages based on the sum of ZrC> 2, CeO2 and Y2O3.

Unless otherwise stated, all means are arithmetic means.

Brief description of the figures

Other features and advantages of the invention will become apparent on examining the accompanying drawing, provided for illustrative and non-limiting, in which Figure 1 shows schematically the assembly used in the measurement of the resistance to the fall.

detailed description

To manufacture a sintered product according to the invention, it is possible to proceed according to steps a) to c) described above and detailed below.

In step a), a particulate mixture according to the invention is prepared.

Grinding may be necessary to obtain a particulate mixture having a median size of less than 2.0 μηη.

In particular, the raw material powders supplying the oxides can be ground individually or, preferably, coarsened, if they do not respect the desired particle size distribution. The grinding can be carried out in a humid medium, for example in an attritor mill. After grinding in a moist medium, the comminuted particulate mixture is preferably dried.

Preferably, in step a), the powders used, in particular the ZrO 2, A C, Y 2 O 3, CeO 2, CaO, manganese oxide (s), oxide (s) powders, iron, cobalt oxide (s) and optionally chromium oxide (s) each have a median size less than 5 μηη, less than 3 μηη, less than 2 μηη, less than 1 μηη, less than 0,7 μηι, preferably less than 0.6 μηι, preferably less than 0.5 μηι. Advantageously, when each of these powders has a median size of less than 2 μηη, preferably less than 1 μηη, preferably less than 0.8 μηι, preferably less than 0.6 μηι, preferably less than 0.5 μηι. , or less than 0.3 μηι, grinding is optional.

The use of powders having a small median size also advantageously makes it possible to reduce the sintering temperature. These powders may also be replaced, at least partially, by powders of precursors of these oxides, introduced in equivalent amounts.

Preferably, the zirconia powder used has a specific surface area, calculated by the BET method, greater than 5 m ² / g, preferably greater than 6 m ² / g, preferably greater than 7 m ² / g, and less than 20 m ² / g, preferably less than 15 m ² / g. Advantageously, the sintering temperature in step d) is reduced. Grinding, generally in suspension, and suspension are facilitated.

The powders providing the oxides or precursors are preferably chosen so that the total content of impurities is less than 2%, as a weight percentage based on the oxides.

In one embodiment, Y 2 O 3 is introduced at least partly in the form of a zirconia partially stabilized with yttrium oxide.

In one embodiment, CeO 2 is introduced at least partly in the form of a zirconia partially stabilized with cerium oxide or even stabilized with cerium oxide. As is well known to those skilled in the art, the starting charge may comprise, in addition to the particulate mixture, a solvent and / or an organic shaping additive and / or a dispersant, the nature and amounts of which are adapted to the shaping method of step b).

Preferably, the solvent is water.

The organic formulating additive may be chosen in particular from polyethylene glycol (or PEG), polyvinyl alcohols (or PVA), latices, cellulose derivatives and mixtures thereof.

The dispersant may be, for example, a polyacrylate.

The solvent, organic shaping additive and dispersant disappear during the subsequent manufacturing steps, but may leave some traces.

In step b), the feedstock is shaped by any technique known to those skilled in the art, preferably by casting, preferably by slip casting, strip casting, or by extrusion or injection or by pressing, preferably by axial pressing, hot pressing or isostatic pressing. In the case where the initial charge is shaped by pressing, a preliminary drying step, for example by atomization, can be carried out. The size of the atomisates can for example be between 20 μηη and 250 μηη. Optionally, the shaping comprises a drying of the preform.

In step c), the preform is sintered at a temperature greater than 1300 ° C, preferably greater than 1350 ° C, preferably greater than 1400 ° C, so as to obtain a sintered product according to the invention. Preferably, the sintering temperature is below 1600 ° C, preferably below 1550 ° C, preferably below 1500 ° C. The sintering is preferably carried out under air, preferably at atmospheric pressure.

Preferably, the sintering time is greater than 1 hour, greater than 2 hours, and / or less than 10 hours, less than 7 hours, or less than 5 hours. Preferably, the sintering time is between 2 and 5 hours.

The inventors have noted the presence of a particular microstructure in the sintered products according to the invention.

Said microstructure is characterized by the presence of elongated aluminous nodules, which may be in the form of substantially rectilinear rods, and which may also contain inclusion grains, in particular zirconia grains. The average length of elongated aluminous nodules is typically greater than 1 μηη and less than 50 μηη. The microstructure specific to the products according to the invention also comprises picked grains. The collected grains typically have an average size of less than 3 μηη and greater than 0.1 μηη.

An elongated aluminous nodule may consist of a grain or a cluster of adjacent aluminous grains, which have "coalesced" during sintering. An aluminous grain is preferably constituted, for more than 50%, more than 60%, or even more than 70% of its mass, of A C, of CeO 2, of CaO, of manganese oxide, of iron oxide , cobalt oxide and chromium oxide.

Typically, more than 90%, more than 95%, or even more than 98% or 100% of the mass of the zirconia is in the form of picked grains of zirconia.

These O2 and Y2O3 serve to stabilize the zirconia but may also be present outside of it.

An analysis has shown that elongated aluminous nodules comprise aluminum and the metal cations of oxides of calcium, manganese, iron, cobalt, optionally added chromium. The said aluminous elongated nodules may also include the element Cerium (Ce). A sintered product can be used in particular in all applications in which it is likely to suffer shocks, and in particular to fall on the ground from a height greater than 50 cm. A sintered product may in particular be used in a consumer good.

The good resistance to falling of a sintered product is particularly useful when the product has a thickness of less than 10 mm, less than 5 mm, less than 3 mm, or less than 2 mm.

The product may in particular be in the form of a plate, the thickness of the plate being less than 5 times, preferably 10 times, even 15 times, or 20 times its width. Examples

The following nonlimiting examples are given for the purpose of illustrating the invention.

Sintered products were prepared from:

a yttria-containing zirconia powder containing a molar content of Y 2 O 3 equal to 3%, having a specific surface area of the order of 10 m ² / g and a median size of less than 0.3 μηη for Example 1,

a yttria-containing zirconia powder containing a molar content of Y 2 O 3 equal to 1%, having a specific surface area of the order of 8 m ² / g and a median size of less than 5 μηη for Examples 2, 3 and 4,

a CeO 2 powder of purity greater than 99% and having a median size of less than 10 μηη for Examples 2, 3 and 4,

an alumina powder of purity greater than 99% and having a median size of less than 0.5 μηη for Examples 1 to 4,

a powder of manganese oxides, mainly in the form Mn30 ₄ and also containing MnO, of purity, expressed as MnO, greater than 88%, and of which more than 90% by mass of the particles have a smaller size; at 44 μηι, for Examples 3 and 4,

a calcium carbonate powder having a median size equal to 5 m for Examples 3 and 4,

- a powder of iron spinel, cobalt and chromium, of median size equal to 1, 4 μηη and having a mass content of iron oxide, expressed in the form

Fe 2 O> 3, equal to 40%, a content by weight of cobalt oxide, expressed as CU30 ₄ form, equal to 31% and a content by mass of chromium oxide, expressed in the form Ο2Ο3, equal to 27%, the mass content of impurities being equal to 2%, for Examples 3 and 4.

These powders were mixed and then co-milled in a humid medium until a particulate mixture having a median particle size of less than 0.3 μηι was obtained. Polyvinyl alcohol was then added in an amount of 2% based on the dry matter of the particulate mixture. The starting charge obtained was then atomized in a spray-dryer, in the form of a powder of atomizers having a median size equal to 60 μηη, a relative density of between 30% and 60% and a sphericity index. greater than 0.85, the relative density of an atomized powder being the ratio of the true density divided by the absolute density, expressed as a percentage; the absolute density of a powder of atomizers being the ratio equal to the mass of dry matter of said powder after grinding to a fineness such that it remains substantially no closed pore, divided by the volume of this mass after grinding , measured by helium pycnometry, and the actual density of a powder of atomisats being the average of the apparent densities of each atomisat of the powder, the apparent density of an atomisate being the ratio equal to the mass of said atomisate divided by the volume occupied by said atomisate.

In step b), each atomized powder was then pressed on a uni-axial press at a pressure equal to 100 MPa.

In step c), the preforms obtained were then transferred to a sintering furnace where they were brought, after a deboning bearing of 2 hours at 500 ° C., to 1450 ° C. at a speed of 100 ° C. h. The temperature of 1450 ° C was maintained for 2 hours. The descent in temperature was carried out by natural cooling.

Measurement protocols

The hardness of the sintered products is measured from Vickers indentations to 0.3 kg, said charge being applied for a time equal to 15 seconds (HVo, 3 / is).

The 3-point bending failure modulus is measured on the sintered products under the conditions of ISO 6872.

The apparent density of the sintered products is measured by hydrostatic weighing. The chemical analysis of sintered products is measured by Inductively Coupled Plasma or ICP for oxides whose quantity does not exceed 0.5%. To determine the content of the other oxides, a pearl of the product to be analyzed is made by melting the product, then the chemical analysis is carried out by X-ray fluorescence.

The specific surface area is measured by the BET method (Brunauer Emmet Teller) as described in Journal of American Chemical Society 60 (1938), pages 309-316.

The drop resistance is measured using the following method: for each example, 13 samples are taken in the form of pellets with a diameter of 22 mm and a thickness of 2 mm (the tolerance on the thickness is equal to +/- 0.02 mm), the large faces of said pellets being surfaced so as to obtain a roughness such that the average arithmetical difference with respect to the average line, Ra, is less than 1 μηη.

Each pellet 4 is clamped between upper 2 and lower 6 parts of a steel assembly as shown in FIG. 1. The upper part 2 of the assembly is perforated so as to allow contact between the pellet 4 and a steel ball. diameter equal to 22 mm and mass equal to 43.5 grams in free fall, without initial speed, to said pellet. The clamping force is substantially identical, regardless of the pellet tested, and is just equal to the value necessary to immobilize the pellet 4 in its housing.

A first pellet makes it possible to determine, by several successive releases of the ball of a height of increasing height, an order of magnitude of the height from which the ball causes the breakage of said pellet. This height is called HR.

Each of the remaining 12 pellets then undergoes several successive releases of the ball at higher and higher heights, until the breakage of the pellet, the successive heights being determined from HR as follows:

The drop resistance of the product of the example is the average of the heights that caused the breakage of each of the other 12 pellets. This resistance to falling is expressed in centimeters. The form factor of the grains and nodules, and the average length of the elongated elongated nodules of the sintered products of the examples are measured on images obtained by electron scanning electron microscopy backscattered samples of sintered products, said sections having previously been polished to a mirror quality and thermally etched to reveal the grain boundaries. The thermal attack is carried out according to a cycle having a rise in temperature at a speed equal to 100 ° C / h, a bearing at a temperature below 50 ° C to the sintering temperature, for 30 minutes, and a temperature decrease in natural cooling. The magnification used for taking the images is chosen so as to visualize between 2 and 4 elongated aluminous nodules on an image. 20 images for example have been made.

The average size of the picked grains was measured by the Mean Linear Intercept method. A method of this type is described in ASTM E1382. According to this standard, lines of analysis are drawn on images of the sintered products, then, along each line of analysis, the lengths, called "intercepts", are measured between two consecutive collected grain boundaries intersecting said line of sintered products. 'analysis. The lines of analysis are determined so as not to cut elongated aluminous nodule.

The average length "Γ" of the "I" intercepts is then determined.

For the tests below, the intercepts were measured on images, obtained by scanning electron microscopy, of samples of sintered products, said sections having previously been polished to obtain a mirror quality and then thermally etched, to a temperature of 50 ° C lower than the sintering temperature, to reveal the grain boundaries. The magnification used for taking the images is chosen so as to display about 100 grains picked up on an image. 5 images per sintered product were made.

The average size "d" of grains of a sintered product is given by the relation: d = 1, 56.1 '. This formula is derived from the formula (13) of "Average Grain Size in Polycrystalline Ceramics" M. I. Mendelson, J. Am. Cerm. Soc. Flight. 52, No.8, pp443-446.

The following Tables 1, 2 and 3 summarize the composition of the particulate mixtures implemented in step a), the chemical analyzes of the products obtained and the physical characteristics measured on these products, respectively. A product is considered acceptable when the resistance to falling is greater than 45 cm, preferably greater than 50 cm, preferably greater than 54 cm, preferably greater than 59 cm, preferably greater than 60 cm, preferably greater than 60 cm. at 62 cm.

( ^* ): Example outside the invention Table 2

( ^* ): Exempe without invention Table 3

Examples 1 and 2 are representative of the state of the art.

Example 3 illustrates the invention.

A comparison of Examples 1, 2, 3 and 4 shows that the resistance to the drop is higher for the product of Example 3 according to the invention, the Al 2 O 3 content of Examples 2 to 4 being substantially identical.

Example 4, outside the invention, shows that a product having a total content of iron oxide, cobalt oxide and chromium oxide, Fe 2 O 3 + Co 3 O 4 + Cr 2 O 3, equal to 3%, has a drop resistance equal to 43 cm, lower than the desired goal.

As is now clear, the inventors have discovered that the simultaneous presence of a low alumina content, a low yttrium oxide content, a low cerium oxide content, manganese oxide, of calcium oxide, iron oxide, cobalt oxide and optionally chromium oxide, advantageously makes it possible to obtain a sintered product based on alumina and zirconia having a resistance to falling greater than 45 cm.

Of course, the invention is not limited to the examples and embodiments described above.

Claims

1. Sintered product having a chemical analysis such that, in percentages by mass on the oxide basis, the manganese, iron, cobalt and chromium oxide (s) being expressed as MnO, Fe2C> 3, CO3O4 and Ο2Ο3, respectively :

ZrO 2 partially stabilized with CeO ₂ and Y ₂ O ₃ : 100% complement, with CeO ₂ : 2.5 - 5.5 mol% and Y ₂ O ₃ : 0.5 - 2 mol%,

molar percentages based on the sum of ZrO2,

- CaO:> 0.1%,

- Manganese oxide (s):> 0,1%,

- CaO + manganese oxide (s): <6%,

- Iron oxide (s):> 0,15%, - Oxide (s) of cobalt:> 0,2%,

- Iron oxide (s) + cobalt oxide (s) + chromium oxide (s): <2.5%

- Other oxides: <3%.

2. Sintered product according to the preceding claim, wherein said molar content of CeO 2 is less than 5% and greater than 3%.

The sintered product according to any one of the preceding claims, wherein said molar content of Y 2 O 3 is less than 1.7% and greater than 0.8%.

4. Sintered product according to any one of the preceding claims, wherein the Al2O3 content is greater than 5%, in weight percent based on the oxides.

5. Sintered product according to the immediately preceding claim, wherein the Al2O3 content is greater than 7%, in weight percent based on the oxides.

The sintered product according to any one of the preceding claims, wherein the CaO content is greater than 0.2% and less than 2%, in weight percent based on the oxides.

7. Sintered product according to the immediately preceding claim, wherein the CaO content is less than 0.6%, in percentages by weight based on the oxides.

Sintered product according to any one of the preceding claims, wherein the content of manganese oxide (s) expressed as MnO is greater than 0.2% and less than 2%, in percentages by weight on the basis of oxides.

Sintered product according to the immediately preceding claim, wherein the content of manganese oxide (s) expressed as MnO is less than 0.6%, in weight percent based on the oxides.

Sintered product according to any one of the preceding claims, wherein the total content CaO + manganese oxide (s), the content of manganese oxide (s) being expressed as MnO, is greater than 0.4%. and less than 5%, in percentages by weight based on the oxides.

1 1. Sintered product according to the immediately preceding claim, wherein the total content of CaO + manganese oxide (s), the manganese oxide (s) content being expressed as MnO is less than 1%, in percentages by mass based on oxides.

Sintered product according to any one of the preceding claims, wherein the total content of iron oxide (s), cobalt oxide (s) and chromium oxide (s) is greater than 0.4% and less than 2%. %.

13. Sintered product according to any one of the preceding claims, wherein the content of Al2O3 is less than 18% and greater than 9%, in weight percentage on the oxide basis, and the total content of iron oxide (s) , cobalt oxide (s) and chromium oxide (s) is greater than 0.4%, and less than 1.8%, in weight percent based on the oxides.

Sintered product according to any one of the preceding claims, wherein the Al 2 O 3 content is greater than 10%, as a weight percentage based on the oxides.

15. Sintered product according to any one of the preceding claims, wherein the Al2O3 content is less than 17%, in weight percent based on the oxides.

16. Sintered product according to any one of the preceding claims, wherein the total content of iron oxide (s), cobalt oxide (s) and chromium oxide (s) is greater than 0.6% and less than 1%. , 5%.

The sintered product according to any of the preceding claims, wherein the iron oxide (s) content, expressed as Fe2C3 is greater than 0.2% and less than 1.5%.

18. Sintered product according to the immediately preceding claim, wherein the content of iron oxide (s), expressed as Fe2C> 3 is greater than 0.3% and less than 0.8%.

19. Sintered product according to any one of the preceding claims, wherein the content of cobalt oxide (s), expressed as CO 3 O 4, is greater than 0.3% and less than 1.5%.

20. Sintered product according to the immediately preceding claim, wherein the content of oxide (s) cobalt, expressed as CO3O4 is less than 0.8%.

21. Sintered product according to any one of the preceding claims, wherein the content of chromium oxide (s), expressed as Ο2Ο3, is greater than 0.2% and less than 1.5%.

22. Sintered product according to the immediately preceding claim, wherein the content of chromium oxide (s), expressed as Ο2Ο3, is less than 0.8%.

23. Sintered product according to any one of claims 1 to 20, wherein the Ο2Ο3 content is less than 0.1%.

24. Sintered product according to any one of the preceding claims, wherein the content of "other oxides" is less than 2%, preferably less than 1%.

25. Sintered product according to any one of the preceding claims, having a microstructure consisting of agglomerated grains, the average grain size having a form factor of less than 2.5, or "picked grains", being less than 3 μηη, and the average length of the aluminous elongated nodules being less than 50 μηη, an elongated aluminous nodule being a structure having a form factor greater than or equal to 2.5 and consisting of one aluminous grain or several adjacent aluminous grains, an aluminous grain being a grain having more than 40% of A C, in weight percent based on the oxides of said grain.

26. Sintered product according to any one of the preceding claims, having the form of a plate, the thickness of the plate being less than 5 times, preferably 10 times its width.

27. Particulate mixture comprising:

ZrO 2 particles and / or ZrO 2 precursor particles,

particles of CeO 2 and / or particles of CeO 2 precursor,

particles of Y2C> 3 and / or precursor particles of Y2C> 3,

particles of A 03 and / or particles of precursor of A Os,

particles of CaO and / or particles of CaO precursor,

iron oxide particles and / or iron oxide precursor particles,

particles of cobalt oxide (s) and / or particles of cobalt oxide precursor (s),

and / or particles of several of these oxides and / or precursors of these oxides, the particulate mixture having a chemical composition suitable for the manufacture of a sintered product according to any one of the preceding claims by sintering said particulate mixture.

28. Particulate mixture according to the immediately preceding claim, comprising:

particles of ZrO 2,

particles of CeO 2,

particles of Y2C> 3,

particles of A C,

particles of CaO,

particles of manganese oxide (s),

particles of iron oxide (s),

particles of cobalt oxide (s),

particles of chromium oxide (s), and / or particles of precursors of these oxides and / or particles of several of these oxides and / or precursors of these oxides.

29. Particulate mixture according to any one of the two immediately preceding claims, having a median size of less than 2 μηη, preferably less than 1 μηη.

30. A particulate mixture according to any one of the three immediately preceding claims, wherein:

the iron oxide is selected from FeO, Fe2C> 3 and mixtures thereof; and or

cobalt oxide is CO 3 O 4; and or

chromium oxide is Ο2Ο3.

31. A particulate mixture according to any one of the four immediately preceding claims, wherein:

the iron oxide and the cobalt oxide are combined, at least partially, in the form of an iron-cobalt spinel of formula Co _x Fe3-xC> 4 with 0 <x <3; and / or the iron oxide and the chromium oxide are combined, at least partially, in the form of an iron-chromium spinel of the formula Cr _X 'Fe3-x0 ₄ with 0 <x'<3; and / or iron oxide, cobalt oxide and chromium oxide are combined, at least partially, in the form of an iron-cobalt-chromium spinel having a weight ratio Fe203 Co30 ₄ greater than 0 , 5 and less than 3, and a mass ratio Fe203 Cr2O3 greater than 0.5 and less than 3.