EP3728161A1

EP3728161A1 - Glass furnace comprising a product containing chromium (iii) oxide

Info

Publication number: EP3728161A1
Application number: EP18822093.3A
Authority: EP
Inventors: Thibault Champion; Pierrick VESPA; Lionel Moitrier; Olivier Citti; Julien Pierre César FOURCADE; Nabil Nahas
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2017-12-22
Filing date: 2018-12-20
Publication date: 2020-10-28
Also published as: CN111511701B; US20210078893A1; FR3075786A1; CN111511701A; FR3075786B1; FR3075785A1; US11905198B2

Abstract

Glass furnace comprising an additivated product comprising, on the surface and/or at the core, an additive chosen from: - phosphorus compounds other than glasses and glass-ceramics, - tungsten compounds other than glasses and glass-ceramics, - molybdenum compounds other than glasses and glass-ceramics, - iron in metal form, aluminum in metal form, silicon in metal form, and mixtures thereof, - silicon carbide, - boron carbide, - silicon nitride, - boron nitride, - glasses comprising the element phosphorus and/or iron and/or tungsten and/or molybdenum, - glass-ceramics comprising the element phosphorus and/or iron and/or tungsten and/or molybdenum, - and mixtures thereof, and having, excluding the additive, the following chemical analysis, in weight percentages, on the basis of the oxides: - Cr2O3 ≥ 2%, and - Cr2O3 + Al2O3 + CaO + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 ≥ 90%, and - Cr2O3 + Al2O3 + MgO ≥ 60%, the weight content of additive being between 0.01% and 6% on the basis of the additivated product.

Description

GLASS FURNACE HAVING A LOXYDE-CONTAINING PRODUCT

CHROME 3

Technical area

The invention relates to a method of manufacturing a product comprising chromium oxide 3, as well as such a product. The invention also relates to a glassware furnace comprising such a product, as well as a method of manufacturing such a furnace.

State of the art

Chromium is an element that exists under several degrees of oxidation: 0, +2, +3, +4, +6.

The +3 form is the most common, as in chromium oxide 3 (or chromium oxide III) or Cr2C> 3.

The products comprising chromium oxide 3 are conventionally obtained by mixing raw materials and shaping to obtain a preform, the raw material mixture comprising a cement when the preform is a hardened concrete. Depending on the intended use, the preform can be fired at a temperature and for a time sufficient to obtain sintering. Sintering can also be performed in situ, when using the preform at high temperatures.

Products comprising chromium oxide 3 are conventionally used in applications where they are subjected to extreme chemical aggression, and in particular in glass furnaces, in particular as furnace tank blocks.

FR 2 918 659 describes in particular a sintered product based on alumina and chromium oxide for use as an electrode holder block. This product has good resistance to corrosion by molten glass and high electrical resistivity, especially at temperatures of about 1500 ° C. FR 2 918 659 does not, however, concern the problem resulting from the formation of hexavalent chromium, which is the form +6 of chromium, or "chromium 6", as in CrC> 3. Chromium 6 is indeed a recognized carcinogenic, mutagenic and reprotoxic substance for humans. It can result from a transformation of chromium oxide 3.

US 6,447,596 discloses a binder which can be used in concrete, and mentions the application to a vessel containing molten glass. High amounts of phosphoric acid H ₃ PO ₄ are thus introduced into the concrete.

The environment of glass furnaces is specific. In particular, in a glassware furnace, the blocks are subjected to mechanical and chemical stresses different from those encountered in metallurgical furnaces in which they are in contact with a dairy. A block of a metallurgical furnace is therefore not suitable for a glass furnace, and vice versa.

There is therefore a constant need to limit the formation of chromium 6, both during manufacture and when using a product, in particular a concrete containing chromium oxide 3.

The present invention aims to at least partially satisfy this need.

Summary of the invention

The invention relates to an additive product comprising, at the heart and / or at the surface, an additive chosen from

- phosphorus compounds other than glass and glass ceramics,

- tungsten compounds other than glass and glass ceramics,

- molybdenum compounds other than glass and glass ceramics,

iron in metal form, aluminum in metal form, silicon in metal form, and mixtures thereof, for example FeSi or AISi,

silicon carbide,

boron carbide,

silicon nitride,

boron nitride,

glasses containing the element phosphorus and / or iron and / or tungsten and / or molybdenum,

vitroceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element,

- and their mixtures,

the additive product having the following chemical analysis, excluding additives, in percentages by weight on the basis of the oxides:

- O2O3 ³ 2%, preferably O2O3 ³ 9% and preferably O2O3 <98%,

preferably CaO <3%, and preferably CaO> 0.1%,

Cr2O3 ⁺ Al2O3 ⁺ CaO + ZrO2 ⁺ MgO + Fe2O3 ⁺ S1O2 ⁺ T1O2 ³ 90%, and

Cr2O3 ⁺ AI2O3 ⁺ MgO ³ 60%.

As will be seen in more detail in the following description, such an additive product generates much less chromium 6 than products without additive. The additive also allows the preform to have sufficient mechanical strength for handling when the preform is made of hardened concrete. The inventors have also discovered that, in a glassmaking furnace, it is advantageous for the mass content of additive to be between 0.01% and 6%, based on the mass of the additive product. In particular, when the mass content of additive is greater than 6%, on the basis of the mass of the additive product, the corrosion of the additive product by the molten glass is too important and / or the amount of defects generated by said additive product in the molten glass is too large and / or the mechanical properties, especially hot, of said additive product are too low to allow use in glass furnace.

The additive product may further comprise one or more of the following optional features:

the additive product has a mass greater than 1 kg or is a particulate mixture;

the additive product is a hardened concrete or is a sintered concrete or is a rammed earth;

the additive is distributed substantially homogeneously at the core and / or at the surface, preferably in a substantially homogeneous manner at the core and at the surface, preferably on a surface which is not intended to be brought into contact with a glass in fusion ;

in one embodiment, the additive at the core of the additive product is different from the additive at the surface of said additive product;

the additive is preferably chosen from FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, WO ₃ , WC, MoO ₃ , Si, Al, Fe, SiAl, FeSi, SiC, B ₄ C, Si ₃ N _4, a glass comprising iron and mixtures thereof;

preferably, the additive is selected from FePO ₄ , MgPO ₄ , phosphoric acid, WO 3, MoO 3, SiAl, Fe Si, SiC, a glass comprising iron, preferably a glass having an iron content, expressed as form Fe ₂ C> 3 of between 1 and 15%, preferably between 4 and 15% and mixtures thereof;

preferably, the additive is chosen from FePO ₄ , MgPO ₄ , WO ₃ , MoO 3, SiAl, Fe Si, SiC, a glass comprising iron, preferably a glass comprising an iron content, expressed as Fe ₂ C> 3 between 1 and 15%, preferably between 4 and 15% and mixtures thereof;

in one embodiment, the additive is chosen FePO ₄ , MgPO ₄ , CuPO ₄ and their mixtures, preferably from FePO ₄ , MgPO ₄ , and mixtures thereof;

in one embodiment, the additive does not comprise phosphorus, in particular when the additive product to be manufactured does not comprise a hydraulic binder, and in particular is not a concrete; the additive product, excluding additive, in percentages by weight on the basis of the oxides:

a chromium content 6 of less than 0.1%, preferably less than 0.08%, preferably less than 0.05%, preferably less than 0.03%, in weight percent;

in one embodiment, a Cr 2 O 3 content greater than 3%, preferably greater than 4%, preferably greater than 6%, preferably greater than or equal to 9%, preferably greater than 15%, preferably greater than 20%. preferably greater than 25%, preferably greater than 30%, preferably greater than 35%; and or

in one embodiment, a Cr 2 O 3 content greater than 4%, preferably greater than 5% and preferably less than 15%, preferably less than 12%, preferably less than 9%; and / or in one embodiment, an Al ₂ O _{3 content} greater than 70%, preferably greater than 75%, preferably greater than 80%, even greater than 85%, or even greater than 90%; and or

in one embodiment, a CaO content greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4% and / or less than 2.5%, preferably less than 2%. preferably less than 1, 5%, preferably less than 1%, preferably less than 0.8%; and or

in one embodiment, a CaO content of less than 0.5%, preferably less than 0.3%; and or

a Cr 2 O 3 + Al 2 O 3 content greater than 55%, preferably greater than 60%, preferably greater than 65%, preferably greater than 70%, preferably greater than 80%, even greater than 90%, or even greater than 92%; or even greater than 94%, as a percentage by weight; and / or an SiO 2 content greater than 0.5%, preferably greater than 1%, and less than 12%, preferably less than 8%, by mass percentage; and or

a ZrO2 content of greater than 1%, preferably greater than 3%, preferably greater than 4% and less than 19%, preferably less than 15%, by mass percentage; and or

in one embodiment, a total content of Cr 2 O 3 + Al 2 O 3 + MgO greater than 80%, preferably greater than 85%, preferably greater than 90%, preferably greater than 95%; and or a total content in addition to O 2 O 3, Al 2 O 3, CaO, ZrC 2, MgO, Fe 2 C 3, SiO 2 and TiO 2 preferably less than 8%, preferably less than 6%, preferably less than 5%, preferably less than 5%; 4%, preferably less than 3% of the mass of the additive product, excluding additive; and or

in one embodiment, an MgO content of less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, or even less than 0.1%; and or

in one embodiment, an MgO content of greater than 5%, preferably greater than 7%, preferably greater than 10% and less than 15%; and or

in one embodiment, a Fe 2 O 3 content of less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%; and or

in one embodiment, a Fe2O3 content of less than 30% and greater than 1%, preferably greater than 3%; and or

a TiO 2 content greater than 0.3%, preferably greater than 0.5%, preferably greater than 0.7%, preferably greater than 1% and less than 5%, preferably less than 4.5%; preferably less than 4%, preferably less than 3.5%, preferably less than 3%;

in a preferred embodiment, the additive product has, in addition to the additive, in percentages by weight based on the oxides:

a MgO content of less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%; preferably less than 1%, preferably less than 0.5%, or even less than 0.1%; and

a Fe 2 O 3 content of less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%;

the mass content of additive is preferably greater than 0.015%, preferably greater than 0.02%, or even, in particular when the additive is core of the additive product, greater than 0.1%, preferably greater than 0; , 2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%; the mass content of additive is preferably less than 5%, preferably less than 4%, preferably less than 3%, based on the additive product;

the content of the additive, based on the mass of the additive product, preferably at least at the core of the product, is preferably greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%; in particular in this embodiment, the additive is preferably chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses and glass-ceramics, glasses comprising the iron element, boron nitride and their mixtures; preferably, such an additive product is intended to be used at a temperature between 100 and 400 ° C; preferably, in this embodiment, the additive is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, boron nitride and their mixtures, preferably from FePO _4. , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides, and mixtures thereof. Preferably the additive is selected from FePO ₄ , MgPO ₄ , phosphoric acid and mixtures thereof, preferably from FePO ₄ , MgPO ₄ and mixtures thereof;

the content of the additive, based on the mass of the additive product, preferably at least at the core of the product, is greater than 0.1%, preferably greater than 0.2%, preferably greater than 0, 3%, preferably greater than 0.4%, preferably greater than 0.5%, and less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%; in particular in this embodiment, the additive is preferably chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses and vitroceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, and mixtures thereof; preferably such an additive product is intended to be used at a temperature between 500 and 1200 ° C; Preferably, in this embodiment, the additive is chosen from the compounds of phosphorus other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, and mixtures thereof, preferably among FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, oxides molybdenum, and mixtures thereof. Preferably the additive is selected from FePO ₄ , MgPO ₄ , phosphoric acid and mixtures thereof, preferably from FePO ₄ , MgPO ₄ and mixtures thereof;

the content of the additive, on the basis of the mass of the additive product, preferably at least at the surface of the product or exclusively at the surface of the product, is greater than 0.01%, preferably greater than 0.015%, preferably greater than 0.02% and less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.5%, preferably less than 1%; in particular in this embodiment, the additive is preferably chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses and vitroceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, and mixtures thereof; preferably such an additive product is intended to be used at a temperature between 100 and 1000 ° C, or even at a temperature between 100 and 850 ° C; Preferably, the additive is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, a glass comprising the iron element and their mixtures, preferably the additive is chosen from FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides, boron nitride, a glass comprising the iron element, and mixtures thereof. The additive is preferably selected from FePO ₄ , MgPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides, a glass comprising the iron element, preferably a glass having an iron content, expressed as Fe ₂ C 3 form between 1 and 15%, preferably between 4 and 15%, and mixtures thereof, preferably among FePO ₄ , MgPO ₄ , tungsten oxides, molybdenum oxides, a glass comprising the element iron, preferably a glass having an iron content, expressed as Fe ₂ C> 3 of between 1 and 15%, preferably between 4 and 15%, and mixtures thereof; the additive product, excluding additive, consists of more than 90%, preferably more than 95%, preferably more than 99%, preferably substantially 100% of oxides.

In one embodiment, the additive product is a rammed earth and has:

- excluding additive, in percentages by mass on the basis of the oxides:

an O2O3 content greater than 2%, preferably greater than 3%, preferably greater than 4% and preferably less than 25%, preferably less than 20%, preferably less than 15%, preferably less than 12%; %, preferably less than 9%, and

a CaO content of less than 2%, preferably less than 1%, preferably less than 0.7%, preferably less than 0.5%, preferably less than 0.3%, and

an AI2O3 content greater than 60%, preferably greater than 65%, preferably greater than 70%, preferably greater than 75%, preferably greater than 80%, even greater than 85%, or even greater than 90%, and o a total content of O 2 O 3 + Al 2 O 3 + MgO greater than 80%, preferably greater than 85%, preferably greater than 90%, preferably greater than 95%, and

an MgO content greater than 4%, preferably greater than 6% and less than 18%, preferably less than 15%, and

a mass content of the additive, based on the mass of rammed earth, greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%; % and less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%, the additive being preferably selected from phosphorus compounds other than glasses and glass-ceramics, the compounds tungsten other than glass and glass-ceramics, molybdenum compounds other than glass and glass-ceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, glasses comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, and their mixtures; preferably, among the phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, and mixtures thereof, preferably among FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, the tungsten oxides, molybdenum oxides, and mixtures thereof, the additive being preferably selected from FePO ₄ , MgPO ₄ and mixtures thereof, and

a granulate preferably comprising particles comprising Al 2 O 3 and / or particles comprising Cr 2 O 3 and / or particles comprising MgO and / or particles comprising a mixture of at least two oxides chosen from Al 2 O 3, O 2 O 3 and MgO and / or particles of additive, the granulate preferably consisting of particles comprising Al 2 O 3 and O 2 O 3 on the one hand, and particles comprising Al 2 O 3 and / or particles containing MgO on the other hand, the quantity of said granulate, in percentage by mass on the basis of rammer being preferably less than 90%, preferably less than 85%, and more than 99% by weight of the grains of the granulate having a size preferably of less than 20 mm, and

a matrix fraction preferably comprising particles comprising Al 2 O ₃ and / or particles comprising O 2 O ₃ and / or particles comprising MgO and / or particles comprising a mixture of at least two oxides chosen from Al 2 O 3, Cr 2 O 3 and MgO and and / or additive particles, the amount of matrix fraction being preferably greater than 10%, preferably greater than 15% and preferably less than 25%, as a percentage by weight based on rammed earth.

The invention also relates to a method for manufacturing an additive product, in particular a hardened concrete and / or a sintered concrete and / or a rammed earth, said method comprising the following successive steps:

A) preparing a feedstock;

B) shaping said feedstock so as to form a preform;

C) optionally, sintering said preform so as to obtain a sintered product, a precursor of said additive being added to the feedstock and / or applied to the surface of the preform and / or applied to the surface of the sintered product ,

the starting charge being determined so that the preform and the sintered product have, apart from additive, the following chemical analysis, in percentages by weight on the basis of the oxides:

- O2O3 ³ 2%, preferably O2O3 ³ 9% and preferably O2O3 <98%,

preferably CaO <3%, and preferably CaO> 0.1%,

Cr2O3 ⁺ Al2O3 ⁺ CaO + ZrO2 ⁺ MgO + Fe2O3 ⁺ S1O2 ⁺ T1O2 ³ 90%, and

Cr2O3 ⁺ AI2O3 ⁺ MgO ³ 60%.

An additive precursor is a compound which, during the implementation of the process, is converted into an additive in the additive product. In particular, in the absence of step C), an additive precursor added to the feedstock can be found substantially integrally in the preform. In some embodiments, an additive may thus be a particular example of an additive precursor.

A preform, when it comprises an additive, and a sintered product manufactured according to a process according to the invention are additive products according to the invention. The feedstock may be adjusted so that these additive products have one or more of the optional characteristics relating to an additive product according to the invention.

The method of manufacturing an additive product according to the invention may also have one or more of the following optional features:

the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses and glass-ceramics, and iron in the form of metal. , aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses comprising the phosphorus and / or iron element and / or tungsten and / or molybdenum, glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, and mixtures thereof;

- said additive precursor is selected from FeP0 ₄ MgP0 ₄ ZnP0 ₄ CuP0 _4, H ₃ P0 _4, WO3, WC, Mo03, Si, Al, Fe, SiAl, FeSi, SiC, B ₄ C, S NU glass with iron, and mixtures thereof;

said additive precursor is chosen from FePO ₄ , MgPO ₄ , FhPCU, WO 3, MoO 3, SiAl, Fe Si, SiC, a glass comprising iron, preferably a glass comprising an iron content, expressed in the Fe ₂ O form; ₃ between 1 and 15%, preferably between 4 and 15%, and mixtures thereof;

the mass content of the additive precursor, based on the mass of the particulate mixture of the starting charge, excluding the shaping agent, is greater than 0.1%, preferably greater than 0.2%, of preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%;

the additive precursor is deposited on the surface of the preform or on the surface of the sintered product, the mass content of the additive precursor being between 0.01% and 5% based on the mass of the preform after deposition of the additive precursor or the sintered product after deposition of the additive precursor;

preferably, the additive precursor is deposited on the surface of the preform or on the surface of the sintered product, the mass content of additive precursor being greater than 0.01%, preferably greater than 0.015%, preferably greater than 0.02% and less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.5%, preferably less than 1%, based on the mass of the preform after deposition of the additive precursor or the sintered product after deposition of the additive precursor respectively;

the starting charge comprises a granulate having a median circularity greater than 0.87;

the starting charge comprises a matrix fraction consisting of particles having a size of less than or equal to 50 μm which does not comprise a hydraulic binder;

the additive precursor is applied to a surface which is not intended to be in contact with molten glass;

the median size of the additive precursor powder in the starting charge is preferably less than 150 μm, preferably less than 100 μm, preferably less than 80 μm, preferably less than 60 μm, preferably less than 50 μm, preferably less than 40 μm, preferably less than 30 μm, or even less than 20 μm;

the mass content of additive precursor in the feedstock is adjusted so that the additive content in the additive product is preferably greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than at 3%, based on the mass of the additive product;

the mass content of additive precursor is preferably adjusted so that the content of additive in the additive product, on the basis of the additive product, is between 0.01% and 6%, preferably greater than 0.015%; , preferably greater than 0.02%, or even, in particular when the additive is core of the additive product, greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and preferably less than 5%, preferably less than 4%, preferably less than 3%, based on the additive product;

the content of the additive, on the basis of the mass of the additive product, preferably at least at the surface of the product or exclusively at the surface of the product, is greater than 0.01%, preferably greater than 0.015%, preferably greater than 0.02% and less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1.5%, preferably less than 1%;

the matrix fraction of the feedstock does not comprise a hydraulic binder; in step B), the median size of the additive precursor powder applied to the surface of the preform is preferably less than 1 mm, preferably less than 500 μm, preferably less than 400 μm, preferably less than 300 μm, preferably less than 200 μm, preferably less than 100 μm;

the mass content of additive precursor applied to the surface of the preform or to the surface of the sintered product is adjusted so that the additive content in the additive product, on the basis of the additive product, is greater than 0.01; %, preferably greater than 0.015%, preferably greater than 0.02% and less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, 5%, preferably less than 1% based on the weight of the additive product;

the additive precursor is an additive; it is therefore found in the additive product in substantially the same quantities.

The invention also relates to a particulate mixture having a composition adapted to obtain, by simple activation and / or simple shaping and / or simple sintering (that is to say without additional operation substantially modifying the composition), a additive product according to the invention. A particulate mixture according to the invention may advantageously constitute a feedstock for a process according to the invention, after addition of water or not.

In general, the invention relates to the use of the additive or precursor of the additive to limit the amount of chromium 6 generated in a product comprising chromium oxide 3 during its manufacture and / or when using it. The use of the additive or precursor of the additive is particularly advantageous on the surfaces of a product comprising chromium oxide 3 which are not exposed to temperatures above 1000 ° C., in particular on surfaces of a product which do not come into contact with molten glass, and / or when all or part of the product is exposed to temperatures between 100 ° C and 1700 ° C, in particular at temperatures between 100 ° C and 1200 ° C.

The invention furthermore relates to a glassware furnace, comprising an additive product, preferably in the form of a block, in particular a tank block or a veneer vat slab, a glass distribution channel, also called a "channel". feeder ", or a consumable part for a glass distribution channel, also called" expendable "in English, in particular a fore-body bowl, a flow washer, a jacket, a plunger, an agitator, or a rotor . The additive product may in particular be disposed in an area of the oven in which it is likely to come into contact with molten glass.

Preferably, at least one region of the additive product defining a surface which is not intended to be in contact with molten glass comprises additive.

The invention also relates to a method of manufacturing a glassware furnace according to the invention, the additive product being manufactured according to a manufacturing method according to the invention.

Definitions

An "additive" in an additive product is the result of the possible conversion, during the manufacture of the additive product, of an "additive precursor" introduced into the feedstock. The nature of an additive precursor is not always modified during the manufacture of the product. The additive is then identical to the additive precursor and it is possible to qualify as "additive" the additive precursor introduced into the feedstock.

- For the sake of clarity, there is a distinction between "product containing chromium oxide 3" and "additive product" which is the product comprising chromium oxide 3 in which the additive has been incorporated and / or on which the additive has been applied.

- "At heart" means "distributed in the mass".

- Hardened concrete is conventionally constituted of a set of coarse grains having a size greater than 50 pm, typically between 50 pm and 25 mm, bonded by a matrix, said matrix providing a substantially continuous structure between the coarse grains.

For a concrete, "granulate" refers to the particles present in the starting charge at the origin of the grains in the hardened concrete. The hardening or sintering does not substantially change the particle size of the aggregate at the origin of the grains in the additive product. Particles of the granulate having a size greater than 50 μm, typically between 50 μm and 25 mm, are therefore also called "grains".

The matrix is obtained, after activation, by curing the matrix fraction of the starting charge, consisting of "matrix particles" having a size of less than or equal to 50 μm.

The particles of the feedstock that are temporary, that is to say that are not found in the sintered product, therefore do not belong to the aggregate or the matrix fraction. The temporary particles, the granulate and the matrix fraction together constitute the "particulate mixture". Activation is a process of fattening. The activated state conventionally results from humidification of a particulate mixture comprising a hydraulic binder, with water or another liquid. During this process, concrete is conventionally called "fresh concrete". To be shaped, the fresh concrete is preferably cast, vibro-cast or even projected.

The solid mass obtained by caking a fresh concrete is called "hardened concrete". When the hardened concrete is intended to be sintered, it constitutes a "preform". The sintering of the preform leads to a "sintered concrete".

- "Hydraulic binder" means a binder which, upon activation, generates a setting and a hydraulic hardening, generally at room temperature. A cement is a hydraulic binder. An aluminous cement is an example of cement. A calcium aluminate cement is an example of aluminous cement.

- A "rammed earth" is a particulate mixture containing a chemical binder and / or ceramic and / or organic, conventionally shaped after possible humidification, by tamping or compaction, by hand or using appropriate mechanical means. Preferably, the particulate mixture is not moistened.

The "preform" thus obtained has a low mechanical strength, which makes it unmanageable, unlike a hardened concrete.

A rammed earth may not be sintered, or sintered, in whole or in part. In particular, when the rammed earth constitutes a refractory lining, only a part of the thickness of the rammed earth, for example the first third from the hot face, that is to say the face which extends from the inner side of the oven, can be sintered. In an application to a steel melting furnace, particularly in a crucible, a rammed earth is preferably at least partially sintered. The "granulate" of a rammed earth refers to the particles present in the feedstock and having a size greater than 50 pm, typically between 50 pm and 25 mm. The manufacture of rammed earth does not appreciably change the particle size of the aggregate, which can also be called "grains".

The "matrix fraction" of a rammed earth refers to the particles present in the initial charge, constituted by "matrix particles", that is to say having a size of less than or equal to 50 μm.

"Glass" is a non-crystalline material having a glass transition temperature of less than 1100 ° C.

The term "glass transition temperature" of a glass means the temperature at which the material passes from the solid state to the viscous state. The glass transition temperature can be determined by differential thermal analysis (DTA). The glass transition temperature is the temperature at which the glass has a viscosity substantially equal to 10 ¹² Pa.s. "Glass-ceramic" conventionally means a microcrystalline compound obtained by controlled crystallization of a "glass-ceramic precursor glass".

- The controlled crystallization of a glass ceramic precursor glass is conventionally performed in a next step, immediately or not, the step of obtaining said glass-ceramic precursor glass.

A glass-ceramic precursor glass is a solid-state glass which, unlike other glasses, contains "nucleating agents".

A nucleating agent is an agent capable of causing the formation of microcrystallizations or "microcrystallites" during the controlled crystallization thermal treatment, usually called "crystallization heat treatment" or "vitroceramization heat treatment", a microcrystallite being a crystal whose half sum of length and width is less than 10 pm. The length and width of a microcrystallite are conventionally evaluated from sectional views of the glass-ceramic.

The microstructure of a glass ceramic thus consists of microcrystallites bathed in a residual vitreous phase.

The melting temperature of a glass-ceramic material is the equilibrium temperature separating the area where coexist liquid and solid phases of the field where only a liquid phase is present.

The melted products, that is to say, produced by melting-cooling, which, during their manufacture, do not pass through a step in which they are in the glass state are therefore not glass-ceramic materials. Molten corundum, fused alumina, molten spinels, molten magnesia, molten mullite, molten mullite-zirconia, molten aluminum titanate, possibly doped, and molten nitrides are not, in particular, materials ceramic.

The "bulk density" of a granulate is conventionally defined as the ratio of the mass of the powder divided by the sum of the apparent volumes of said particles.

- The "circularity" of an observed particle is the ratio P _D / P _{I ·} , P _r designating the perimeter of the particle as observed, and P _D designating the perimeter of the disc having the same surface as that of the particle as observed. Circularity depends on the direction of observation. To evaluate the circularity "Ci" of a particle P, we determine the PD perimeter of the disk D having an area equal to the area A _p of the particle P in a photograph of this particle. The perimeter P _r of this

2 * Æ

particle. Circularity is equal to the ratio of PD / R _G. Thus Ci =. More

Pr particle is elongated, the circularity is weaker. The SYSMEX FPIA 3000 user manual also describes this procedure (see "detailed specification sheets" on www.malvern.co.uk). The percentile or "percentile" (Ciso) of a set of particles is the circularity of particles corresponding to the percentage, in number, of 50%, on the cumulative distribution curve of the particles of this set, the circularities of particles being ranked in ascending order. 50% by number of the particles of this set have a circularity lower than Ciso. The percentile 50 can be evaluated using a device of the Morphologi® G3 type marketed by Malvern. Ciso is still called "median circularity".

For the sake of clarity, the chemical formulas of the oxides are used to designate the contents of these oxides in a composition. For example, "Zr0 ₂ ", "S1O2" or "Al2O3" designate the contents of these oxides and "zirconia", "silica" and "alumina" are used to designate phases of these oxides consisting of Zr0 ₂ , S1O2 and Al2O3 , respectively.

- Unless otherwise indicated, all percentages relating to the composition of the feedstock, the product containing chromium oxide 3, or the additive product are in bulk, based on the oxides.

- Unless otherwise indicated, all percentages of the composition of the particulate mixture or of the matrix fraction or granulate are by mass, based on the particulate mixture or the matrix fraction or granulate, respectively.

- A mass content of an oxide of a metallic element refers to the total content of this element expressed in the form of the most stable oxide, according to the usual convention of the industry.

detailed description

The detailed description of step A) which follows relates to a concrete, but the invention extends to any product comprising chromium oxide 3.

In step A), the feedstock for making a concrete is constituted by mixing a particulate mixture according to the invention and water, to obtain, after step B) and / or C ), an additive product according to the invention.

In addition to the particulate mixture and water, it may still contain a liquid forming agent.

Particulate mixture The manufacture of a particulate mixture conventionally results from a mixture of raw material powders having compositions and particle size distributions adapted to the desired additive product.

For a concrete, the particulate mixture preferably comprises, as a percentage by weight, from 0.9% to 8%, preferably from 2% to 6% of particles of a hydraulic cement. The hydraulic cement may be an aluminous cement or a mixture of different cements, such as CA25 or CA14 cements from Almatis. More preferably, the hydraulic cement contains, as main constituents (constituents whose contents are the highest), alumina and calcium aluminates.

Preferably, the particulate mixture has a total content of O 2 O 3 + Al 2 O 3 greater than 47%, preferably greater than 51%, preferably greater than 56%, preferably greater than 60%, preferably greater than 70%, preferably greater than 70%. at 75%, or even greater than 80%, or even greater than 85%, or even greater than 89%, as a percentage by weight.

In one embodiment, the particulate mixture comprises a total content of O 2 O 3 + Al 2 O 3 + MgO greater than 80%, preferably greater than 85%, preferably greater than 90%, preferably greater than 95%, by mass percentage.

In one embodiment, the particulate mixture has an O2O3 content, greater than 13%, greater than 17%, greater than 21%, greater than 26%, greater than 30%, greater than 35%, and / or less than 71%, less than 66%, or less than 62%, less than 50%, as a percentage by weight. In one embodiment, the O2O3 content is greater than 48%, or even greater than 52%.

In one embodiment, the particulate mixture has an O 2 O 3 content, greater than 3%, preferably greater than 4%, preferably greater than 5% and preferably less than 15%, preferably less than 12%, preferably less than 9%, as a percentage by mass.

In one embodiment, the particulate mixture has a content of Al 2 O 3, preferably alumina, greater than 2.5%, greater than 4.5%, greater than 9%, greater than 13%, greater than 17%, greater than at 21% and / or less than 95%, less than 90%, less than 85%, less than 80%, less than 76%, less than 71%, less than 66%, less than 62%, less than 57% , less than 52%, or even less than 33%, as a percentage by weight. In one embodiment, the particulate mixture has an Al2O3 content greater than 33%, greater than 35%, and even greater than 39%. In one embodiment, the particulate mixture has a higher Al2O3 content at 70%, preferably greater than 75%, preferably greater than 80%, even greater than 85%, or even greater than 90%.

The content of SiO 2, preferably silica, of the particulate mixture may be greater than 0.4%, greater than 0.9%, and / or less than 11.5%, or less than 7.5%, by weight percentage. .

The Zr0 ₂ , preferably zirconia, content of the particulate mixture may be less than 18%, less than 14.5%, and / or greater than 0.9%, or greater than 2.6%, by weight percent.

The content of constituents other than O ₂ O 3, Al ₂ O 3, CaO, ZrO ₂ , MgO, Fe ₂ C 3, SiO 2 and TiO 2 of the particulate mixture is less than 20%, preferably less than 15%, preferably less than 12%, preferably less than 12%. at 8%, or even less than 5%, as a percentage by weight.

In one embodiment, the MgO content of the particulate mixture is less than 19%, preferably less than 14%, preferably less than 10%, preferably less than 5%, preferably less than 4%, preferably less than at 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, or even less than 0.1%, in weight percent.

In one embodiment, the MgO content of the particulate mixture is greater than 5%, preferably greater than 7%, preferably greater than 10% and less than 15%, by mass percentage.

In one embodiment, the Fe ₂ 0 _{3 content} of the particulate mixture is less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%, by mass percentage.

In one embodiment, the Fe ₂ 0 _{3 content} of the particulate mixture is less than 30% and greater than 1%, preferably greater than 3%, by mass percentage.

In a preferred embodiment, the particulate mixture has, in addition to the precursor of additive, in percentages by weight based on the oxides:

a MgO content of less than 20%, preferably less than 19%, preferably less than 15%, preferably less than 14%, preferably less than 10%, preferably less than 5%, preferably less than 4%; preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, or even less than 0.1%; and a content of Fe ₂ C> 3 of less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%.

The TiO ₂ content of the particulate mixture may be greater than 0.3%, greater than 0.5%, greater than 0.7%, greater than 1%, and / or less than 5%, less than 4.5% , less than 4%, less than 3.5%, less than 3%, by weight percentage. In one embodiment, the TiO ₂ content of the particulate mixture is less than 0.2%.

In one embodiment, the CaO content of the particulate mixture is greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4% and / or less than 2.4%, preferably less than 1, 9%, preferably less than 1, 4%, preferably less than 1%, preferably less than 0.8%, in weight percent.

In one embodiment, the CaO content of the particulate mixture is less than 0.5%, preferably less than 0.3%, by weight percent.

Preferably, the total content of Cr ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , SiO ₂ , CaO and TiO ₂ in the particulate mixture is greater than 77%, greater than 83%, greater than 87%, greater than 90 %, or greater than 93%, as a percentage by weight.

Preferably, the constituents other than the oxides represent less than 14%, preferably less than 10%, preferably less than 8%, preferably less than 5% of the mass of the particulate mixture.

The particle size distribution is not limiting. It can in particular be adapted to the bulk density of the product that is desired.

The particulate mixture for a concrete comprises a matrix fraction and a granulate.

Matrix fraction

The particulate mixture preferably comprises more than 10%, more than 15%, more than 20% or even more than 25%, and / or less than 40% or even less than 35% or even less than 30% of particles. matrixes, in percentage by mass.

The median size of the matrix fraction may be less than 30 μm, less than 25 μm, less than 15 μm, less than 10 μm, or even less than 7 μm.

Preferably, at least 90% by weight of the matrix particles have a size of less than 40 μm, preferably less than 30 μm, preferably less than 20 μm or even less than 10 μm.

Preferably, the matrix fraction has a chemical composition such that, in percentages by weight and for a total of 100%: - O2O3 + Al2O3 + MgO + Fe203 + Z1Ό2 S1O2 + + T1O2 + CaO> 82%, preferably Cr2O3 ⁺ Al2O3 ⁺ ZrO2 + Fe2O3 ⁺ MgO ⁺ CaO + S1O2 ⁺ T1O2 ³ 87%, and

Cr2O3 ⁺ Al2O3 ⁺ MgO ³ 45%, and

preferably O2O3 ³ 6%, and

- preferably 15%> S1O2 ³ 0.1%.

Preferably, the composition of the matrix fraction is such that:

the total content O 2 O 3 + Al 2 O 3 + MgO is greater than 60%, preferably greater than 65%, preferably greater than 70%, preferably greater than 80%, or even greater than 85%, as a percentage by weight; and or

the content of SiO 2 is less than 12%, preferably less than 10%, preferably less than 8%, preferably less than 6%, preferably less than 5%, or even less than 4%, or even less than 3%; ; and or

the content of MgO is less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, by mass percentage; and or

in one embodiment, the Fe 2 O 3 content is less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%, in weight percent; and or

in one embodiment, the Fe 2 O 3 content is less than 30% and greater than 1%, preferably greater than 3%, in weight percent; and or

the content of T1O2 is less than 7%, or even less than 4%, or even less than 3%, or even less than 2%; and or

the complement to Cr 2 O 3, Al 2 O 3, CaO, ZrO 2, MgO, Fe 2 O 3, SiO 2 and TiO 2 preferably represents less than 8%, preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%.

In one embodiment, the composition of the matrix fraction is such that Cr2O3 +

Al2O3> 73%, Cr2O3 + Al2O3> 80%, or even Cr2O3 + Al2O3> 90%.

In one embodiment, the composition of the matrix fraction is such that Cr2O3 +

Al2O3 + MgO> 75%, Cr2O3 + Al2O3 + MgO> 80%, or even Cr2O3 + Al2O3 + MgO> 90%.

In one embodiment, the composition of the matrix fraction is such that Al2O3 +

MgO> 75%, Al2O3 + MgO> 80%, or even Al2O3 + MgO> 90%. In one embodiment, the composition of the matrix fraction is such that the T1O2 content is less than 0.2%.

In one embodiment, the composition of the matrix fraction is such that the Al2O3 content is greater than 4%, greater than 5%, greater than 7.5%, greater than 10%, greater than 15%, and / or is less than 70%, less than 65%, less than 60%, less than 50%.

The matrix fraction preferably comprises eskolite particles on the one hand and, on the other hand, alumina particles and / or particles of zirconia and / or particles of titanium oxide and / or particles of silica and / or cement particles and / or additive particles. Preferably, the matrix fraction comprises particles of eskolite on the one hand and, on the other hand, alumina and / or zirconia and / or titanium oxide and / or cement and / or particles of 'additive.

In one embodiment, the particulate mixture does not contain zirconia particles, especially zirconia matrix particles.

In one embodiment, the matrix fraction preferably comprises particles of alumina on the one hand and, preferably, on the other hand, particles of eskolite and / or magnesia particles and / or particles of additive.

aggregate

The particulate mixture preferably comprises less than 90%, preferably less than 85%, preferably less than 80%, of grains, as a percentage by weight.

Preferably, at least 90% by weight of the grains have a size greater than 100 μm, preferably greater than 200 μm, preferably greater than 300 μm, and preferably greater than 400 μm.

More preferably, more than 80%, preferably more than 90%, preferably more than 95%, preferably more than 99% by weight of the grains of the granulate have a size greater than 200 μm, preferably greater than 300 μm, preferably greater than 400 μm, even greater than 0.5 mm and / or less than 10 mm, preferably less than 5 mm.

Still preferably, the particulate mixture contains at least 10% of grains larger than 2 mm in weight percent.

In one embodiment, more than 90% of the granules comprise more than 95% of their mass, of sintered particles.

Preferably, the granulate has a bulk density greater than 85% of the theoretical density, preferably greater than 88%, preferably greater than 90%, preferably greater than 91%, preferably greater than 92% of the theoretical density, even greater than 93%, even greater than 94%, or even greater than 95%, or even greater than 96% of the mass; theoretical volume.

Preferably, the granulate has an open porosity of less than 10%, preferably less than 6%, preferably less than 5%, preferably less than 3%, preferably less than 2%, preferably less than 1%, or even less than 0.7%, or even less than 0.6%.

Preferably, the granulate has a median circularity greater than 0.87, preferably greater than 0.88, preferably greater than 0.90, preferably greater than 0.91. Advantageously, the thermal shock resistance and the corrosion resistance, in particular in an application in which the product is brought into contact with molten glass, are improved.

Granules are particles having a circularity of 0.8 or more. Preferably, the granules are agglomerated particles, in particular sintered particles. The agglomeration can also be obtained by means of a binder, for example a binder polymer, in particular by spray drying or spray drying, and / or by use of a granulator or a spray apparatus. pelletizing.

In a particular embodiment, at least 80%, preferably at least 90%, preferably at least 95%, preferably at least 99%, or even substantially 100% by number of grains are granules.

The granulate is preferably composed of particles of additives and particles having Cr 2 O 3 on the one hand and, on the other hand, comprising Al 2 O 3 and / or ZrC 2 and / or MgO and / or Fe 2 O 3 and / or TiO 2 and / or S1O2. Preferably, the granulate consists of particles comprising O2O3 on the one hand and, on the other hand, comprising Al2O3 and / or ZrC2 and / or T1O2 and / or S102.

In one embodiment, the granulate is composed of additive particles and particles comprising Al 2 O 3 and / or particles comprising O 2 O 3 and / or particles comprising MgO and / or particles comprising a mixture of at least two oxides chosen from AI2O3, Cr2O3 and MgO. In one embodiment, the granulate consists of particles comprising Al 2 O _{3 and} O ₃ O ₃ on the one hand, and particles comprising Al 2 O ₃ and / or particles containing MgO on the other hand. Preferably, the granulate has a chemical composition such that, in percentages by weight and for a total of 100%:

- 0 ^ 03 + AI2O3 + ZrO2 + MgO + Fe2O3 + S1O2 + T1O2 ³ 90%, preferably 0 ^ 03 + Al2O3 ⁺ ZrO2 ⁺ MgO + Fe2O3 ⁺ S1O2 ⁺ T1O2 ³ 95%, and

Cr2O3 ⁺ Al2O3 ⁺ MgO ³ 60%, and

preferably 0 ^ 03 ³ 9%, and - preferably 20%> S1O2 ³ 0.5%.

Preferably, the composition of the granulate is such that

the total content O2O3 + Al2O3 + MgO is greater than 65%, preferably greater than 70%, preferably greater than 80%, or even greater than 90%, or even greater than 92%, or even greater than 94%, as a percentage by weight; ; and or

the content of SiO 2 is less than 16%, preferably less than 13%, preferably less than 10%, preferably less than 8%, preferably less than 6%, preferably less than 5%, or even less than 4%; or even less than 3% (advantageously, the densification is improved, without the corrosion resistance being reduced); and or

in one embodiment, the MgO content is less than 20%, preferably less than 15%, preferably less than 10%, preferably less than 5%, preferably less than 4%, preferably less than 3%; %, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, by mass percentage; and or

in one embodiment, the MgO content is greater than 1%, preferably greater than 3% and less than 20%, preferably less than 10%; and or

in one embodiment, the MgO content is less than 1%, preferably less than 0.8%; and or

in one embodiment, the Fe 2 O 3 content is less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%, as a weight percentage based on the oxides; and or

in one embodiment, the content of T1O2 is greater than 0.5%, or even greater than 0.7%, and / or less than 4%, preferably less than 3%, less than 2.2%, or even less than 2%; and or

the complement to Cr 2 O 3, Al 2 O 3, CaO, ZrO 2, MgO, Fe 2 O 3, SiO 2 and TiO 2 preferably represents less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%.

In some embodiments, the composition of the aggregate is such that 0 ^ 0 ₃ + AI 2 O ₃

> 80%, 0 ^ 03 + AI2O3> 90%, or even 0 ^ 03 + AI2O3> 95%. Preferably still, the sum of the oxide contents in the grains, preferably the granules of the aggregate, represents more than 90%, more than 95%, or even substantially 100% of the mass of said grains or granules.

Fitness Agent

The particulate mixture may contain at least 0.1% and / or less than 6% by weight of particles of a shaper, in weight percent based on the particulate mixture.

The optional shaping agent may be introduced in liquid form in equivalent amounts.

The shaping agent may in particular be chosen from the group consisting of:

- clays;

plasticizers, such as polyethylene glycol (or "PEG") or polyvinyl alcohol (or "PVA");

binders including organic temporary binders such as resins, lignosulfonates, carboxymethylcellulose or dextrin;

deflocculants, such as alkali metal polyacrylates, polycarboxylates; and

mixtures of these agents.

Preferably, the shaping agent is selected from the group consisting of deflocculants, clays, lignosulfonates, PVA and mixtures thereof.

Additive and additive precursor

The median size of the additive powder or, more generally, of the additive precursor powder in the particulate mixture is preferably less than 150 μm, preferably less than 100 μm, preferably less than 80 μm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 40 pm, preferably less than 30 pm, or even less than 20 pm.

Preferably, the content of additive or, more generally, of additive precursor in the particulate mixture, based on the mass of the particulate mixture excluding shaping agent, is greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and preferably less than 6%, preferably less than 5%, preferably less than at 4%, preferably below 3%. Preferably, the content of the additive or, more generally, of the additive precursor in the particulate mixture is adjusted so that the amount of additive in the additive product is greater than 0.3%, on the basis of the mass of the additive product.

In a first preferred embodiment, the amount of additive or, more generally, additive precursor in the particulate mixture is adjusted so that the amount of additive in the additive product (preform or sintered product) is greater than 0.1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3% based on the weight of the additive product. Preferably, in this embodiment, the additive or, more generally, the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses and glass-ceramics, glasses comprising the iron element, boron nitride and mixtures thereof. Preferably, the additive or, more generally, the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, boron nitride and their mixtures, preferably the additive or, more generally, the additive precursor is selected from FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides and mixtures thereof, preferably from FePO ₄ , MgPO ₄ , phosphoric acid and mixtures thereof. Preferably the additive or, more generally, the additive precursor is selected from FePO ₄ , MgPO ₄ and mixtures thereof.

This first embodiment is particularly well suited when the additive product is intended to be subjected to a temperature of between 100 ° C. and 400 ° C.

In a second preferred embodiment, the amount of additive or, more generally, the amount of additive precursor incorporated in the particulate mixture is adjusted so that the additive content in the additive product is greater than 0, 1%, preferably greater than 0.2%, preferably greater than 0.3%, preferably greater than 0.4%, preferably greater than 0.5%, and less than 6%, preferably less than 5%; %, preferably less than 4%, preferably less than 3% based on the weight of the additive product. Preferably, in this embodiment, the additive or, more generally, the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glass and glass-ceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, nitride silicon, boron nitride, glasses comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, and mixtures thereof . Preferably, in this embodiment, the additive or, more generally, the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, and mixtures thereof. preferably, among FePO ₄ , MgPCU, ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides, and mixtures thereof. Preferably the additive or, more generally, the additive precursor is selected from FePO ₄ , MgPO ₄ , phosphoric acid and mixtures thereof. Preferably the additive or, more generally, the additive precursor is selected from FePO ₄ , MgPO ₄ and mixtures thereof.

This second embodiment is particularly well suited when the additive product is intended to be subjected to a temperature of between 500 ° C. and 1200 ° C.

The introduction of the additive or, more generally, of the additive precursor in step A) advantageously allows a substantially homogeneous distribution of the additive. Preferably, the mixing time is determined for this purpose.

The additive particles or, more generally, the additive precursor are counted, depending on their size, in the granulate or the matrix fraction.

The particulate mixture can be delivered ready-to-use. For a concrete in particular, it is then sufficient to mix it with water to prepare the starting charge.

Water

The amount of water is a function of step B).

In the case of casting, an addition of a quantity of water of between 3 and 7%, in weight percentage on the basis of the particulate mixture, optionally additive, is preferred.

Unlike the starting load for making a concrete, the starting load for making a rammed earth has no hydraulic binder and is therefore not activated by any humidification. It may, however, comprise a chemical and / or ceramic and / or organic binder. The activation means are determined accordingly.

In step B), all the conventional methods used to make preforms, in particular hardened concrete, can be envisaged.

The starting load can in particular be shaped in situ, so that the preform is arranged in its service position. In particular for a rammed earth, the formatting conventionally results from a vibration operation or damage. The preform obtained therefore has a low mechanical strength and is therefore preferably produced in situ. Classically, after stripping, the preform "stands", but has no physical integrity that would allow it to be transported for example.

In one embodiment, the additive, or more generally the additive precursor, is applied to the surface of the preform. Any known technique for depositing a composition on a block may be used, in particular a trowel or brush deposit, or wet or dry spraying, such as enameling, so as to form a thin or thick layer.

Preferably, the additive, or more generally the additive precursor, is mixed with a liquid, for example water and / or an oil before it is deposited on the surface. The amount of liquid is variable and depends on the particle size of the additive, or more generally the additive precursor, to have a good grip on the surface.

In a third preferred embodiment, the amount of additive, or more generally of additive precursor, deposited in step B) on the preform or in step C) on the sintered product, is adjusted so that the additive content in the additive product is greater than 0.01%, preferably greater than 0.015%, preferably greater than 0.02%, and less than 5%, preferably less than 4%, preferably less than at 3%, preferably less than 2%, preferably less than 1.5%, preferably less than 1%, based on the weight of the additive product. Preferably, in this embodiment, the additive, or more generally the additive precursor, is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glass and glass-ceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, nitride boron, glasses comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics comprising the element phosphorus and / or iron and / or tungsten and / or molybdenum, and mixtures thereof. Preferably, the additive, or more generally the additive precursor, is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, glasses containing the iron element and their mixtures, preferably selected from FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , phosphoric acid, tungsten oxides, molybdenum oxides, boron nitride, glasses containing the iron element and mixtures thereof. Preferably, the additive, or more generally the additive precursor, is selected from FePO ₄ , MgPO ₄ , the acid phosphoric oxide, tungsten oxides, molybdenum oxides, glasses containing the iron element, preferably glasses having an iron content, expressed as Fe2C> 3, of between 1 and 15%, preferably between 4 and 15%, and mixtures thereof, preferably among FePO ₄ , MgPO ₄ , tungsten oxides, molybdenum oxides, glasses containing the iron element, preferably glasses having an iron content, expressed as Fe 2 C> 3, between 1 and 15%, preferably between 4 and 15%, and mixtures thereof.

This third embodiment is particularly well suited when the product is intended to be subjected to a temperature of between 100 ° C. and 1000 ° C., or even to a temperature of between 100 ° C. and 850 ° C., and that a reduction in amount of chromium 6 is desired on at least one side of the product.

In one embodiment, a coupling agent is mixed with the additive, or more generally with the additive precursor, to promote its deposition on the surface of the product. The attachment additives may be chosen from clays, plasticizers, celluloses and mixtures thereof, polyvinyl alcohols or "PVA", polyethylene glycol or "PEG".

In optional step C), the sintering conditions, and in particular the sintering temperature, depend on the composition of the particulate mixture. Usually, a sintering temperature of between 1400 ° C and 1700 ° C, preferably between 1450 ° C and 1650 ° C, preferably between 1500 ° C and 1600 ° C is well suited. The sintering can be carried out in situ, that is to say after the preform has been formed or arranged in its service position.

At the end of step C), a sintered product according to the invention is obtained, in particular a sintered concrete or a sintered mud.

In one embodiment, the additive, or more generally the additive precursor, is applied to the surface of the sintered product. The techniques described for applying the additive to step B) are applicable.

Examples

To manufacture the particles "O2O3, Al2O3, S1O2, ^" PO2 "used in the products of Examples 1 to 4 and 7 to 12, the following raw materials were used:

pigmentary chromium oxide O2O3 with a purity higher than 95%, having a specific surface area equal to 4 m ² / g and a median size of 0.7 μm; alumina Al 2 O 3 with a purity greater than 99%, having a specific surface area equal to 7 m ² / g, and a median size of 0.6 μm;

silica fume with a purity higher than 92%; and

titanium oxide, in the rutile form, with a purity greater than 93% and having a median size of 1.5 .mu.m.

These raw materials were dosed and mixed in order to obtain a mixture of oxides having the following chemical composition:

Table 1

For each example, 3000 g of oxide mixture, 350 g of water and 150 g of polyvinyl alcohol (PVA) are introduced into an Eirich RV02 mixer.

The assembly is then kneaded for 1 minute, with a vortex rotating at 300 rpm and a tank set at 43 rpm to obtain a homogeneous mixture. The rotational speed of the vortex is then increased to 1050 rpm, and an additional 900 grams of the oxide mixture is then gradually added in one minute. Rotation is maintained 2 minutes after the end of introduction of the additional quantity. The particles are then discharged, dried under air for 24 hours at 110 ° C. before being sintered at 1550 ° C. for a hold time of 3 hours, in air, with a temperature rise rate and a temperature descent rate. 50 ° C / h. After sintering, the particles have an open porosity equal to 1.05% and a median circularity greater than 0.85. They are then sieved and three granulometric slices are preserved: 0 - 0.5 mm, 0.5 - 2 mm, and 2 - 5 mm.

The cured concretes of Examples 2 and 3, and 7 to 12 were then manufactured following steps A) and B) described above.

In step A), the following raw materials were then mixed with the particles "O2O3, Al2O3, SiO2, TiO2":

pigment of chromium Cr ₂ 0 ₃ with a purity greater than 95%, having a specific surface area equal to 4 m ² / g and a median size of 0.7 μm, alumina Al 2 O 3 with a purity greater than 99%, having a specific surface area equal to 7 m ² / g, and a median size of 0.6 μm,

an aluminous cement CA25R from Almatis.

The mass contents of the various raw materials are summarized in Table 2 below:

Table 2

A modified polycarboxylate ether was then added in an amount equal to 0.17% of the mass of said raw material mixture.

An additive precursor was then added, according to the invention, so as to obtain a ready-to-use mixture. The nature and amount of additive precursor are summarized in Table 3 below:

Table 3 The tungsten oxide used had a purity greater than 99% and a median size equal to 35 μm.

The iron phosphate used was iron phosphate E53-98 marketed by the company Budenheim.

The silicon carbide used was a Sika® Unikiln FCP07 powder marketed by Saint-Gobain Silicon Carbide.

The aluminum and silicon alloy had a silicon mass content equal to 12.3%, an element content other than silicon and aluminum less than 1.5%, and a median size equal to 40 μm.

The iron-containing glass powder had a median size of 13 μm, and the following chemical analysis: S102 = 56.1%, Fe2C3 = 9%, Al2O3 = 17.4% Na2O = 2.4%, K ₂ O = 1. 7%, CaO = 7.9%, MgO = 3.8%, TiO ₂ = 1.2%, Other = 0.5%.

4.5% water, as a percentage by mass based on the mass of the ready-to-use mixture, was added in order to achieve the initial charge. The mixing time was 12 minutes.

In step B), the initial charge was shaped by a vibrocolding technique in the form of a hardened concrete according to the invention, with dimensions equal to 230 × 150 × 80 mm ³ , adapted to the characterizations to be carried out. carry out.

Comparative Example 1 was carried out identically to Examples 2 and 3, and 7 to 12, but no additive precursor was added.

Example 4 is a hardened concrete identical to the hardened concrete of Example 1, except that one of its faces has been coated with the additive precursor having the composition appearing in the following Table 4:

Table 4 The iron-containing glass powder had a median size of 13 μm, and the following chemical analysis: S1O2 = 56.1%, Fe ₂ O3 = 9%, Al2O3 = 17.4% Na ₂ O = 2.4 %, K2O = 1, 7%, CaO = 7.9%, MgO = 3.8%, T1O2 = 1, 2%, Other = 0.5%. The silicon carbide powders had a purity greater than 98%. The aluminum triphosphate powder was a M13-01 powder from Budenheim.

The components of the additive precursor were mixed together, and 29% water based on the total amount of the additive precursor was added. The total mixing time was 10 minutes to form a coating.

The samples of Examples 1 and 4 to be tested were in the form of cylinders with a height of 50 mm and a diameter of 150 mm. For Example 4, the coating was troweled on one of the two faces of diameter equal to 150 mm and the total amount of additive precursor on the basis of the mass of the coated sample was 4 %.

The product of Example 5 was manufactured following the steps A) and B) described above from the following raw materials:

pigment of chromium Cr ₂ 0 ₃ with a purity greater than 95%, having a specific surface area equal to 4 m ² / g and a median size of 0.7 μm,

titanium oxide, in the rutile form, with a purity greater than 93% and having a median size of 1.5 μm,

particles "high content of chromium oxide 3" containing 98% of O 2 O 3 and having an open porosity of less than 3%,

zirconia of purity greater than 99% and having a median size equal to 3.5 μm,

a tungsten oxide WO 3 with a purity greater than 99% and having a median size equal to 35 μm.

The mass contents of the different raw materials are summarized in Table 5 below:

Table 5 The order of introduction of the raw materials was as follows: a hydroxyethyl methyl cellulose Tylose MH 4000 P2 sold by the company Shin Etsu and a calcium lignosulfonate BRETAX C sold by the company Brenntag in an amount equal to 0.2% and 0 , 5%, respectively, were added in 2.5% water, the percentages being percentages on the total mass of raw materials, including additive. Particles with a high content of chromium oxide 3 were then added and kneading was carried out for 10 minutes. Pigmented chromium oxide, zirconia, titania and 1% tungsten oxide WO ₃ were then added, and an additional mixing time of 10 minutes was then applied to achieve the charge. departure. The amount of tungsten oxide used was in percent by weight based on the mass of the high chromium oxide content particles 3, chromium pigment oxide, zirconia and titania.

In step B), the initial charge was shaped by a pressing technique under a pressure equal to 800 bar, in the form of an additive product having dimensions equal to 230 × 114 × 35 mm ³ , adapted to the characterizations to be performed.

Example 6, comparative, was carried out in the same manner as in Example 5, without tungsten oxide.

The samples of Examples 5 and 6 to be tested were in the form of cylinders with a height of 50 mm and a diameter of 150 mm.

The product of Example 13 was manufactured according to step A) and shaped according to step B) described above.

In step A), the following raw materials were mixed:

melted alumina-chromium oxide particles having a Cr 2 O 3 content equal to 13% and an alumina content equal to 82%,

fused alumina with a purity greater than 99%,

magnesia of greater than 96% purity and having a median size of 35 μm,

iron phosphate E53-98 sold by the company Budenheim.

The mass contents of the various raw materials are summarized in Table 6 below:

Table 6

Dextrin was then added in an amount equal to 0.5% of the mass of said raw material mixture.

0.5% iron phosphate E53-98 marketed by the company Budenheim was then added, the amount of iron phosphate being in percentage based on the melted particles of alumina-chromium oxide, fused alumina and magnesia, so as to obtain a mixture ready for use.

3% water, as a percentage by mass based on the mass of the ready-to-use mixture, was added in order to achieve the initial charge. The mixing time was 15 minutes.

In step B), the feedstock was shaped by a uniaxial pressing technique at a pressure of 800 kg / cm ² so as to obtain an additive product according to the invention having dimensions equal to 230 × 150 x 80 mm ³ , adapted to the characterizations to be carried out.

Comparative Example 14 was carried out in the same manner as in Example 13, but no additive was added.

Measurement protocols

Bulk density and open porosity of products are measured by hydrostatic weighing.

The measurements of the apparent density and the open porosity of a granulate are carried out according to the following method:

- Dry at 110 ° C for at least 12 hours, 4 samples of 35 grams each consisting of particles whose size is between 2 and 5 mm. The dry mass of each of the samples is noted Psi, PS2, Ps ₃ and Ps ₄ . We note Ps = Psi + PS2 + PS3 + ₄ Ps.

- Place each sample in a vial.

- Using a vacuum pump, vacuum at least 0.07 MPa in each vial and maintain this vacuum for 7 minutes. Then introduce water into the bottle to cover the particles at least 2 cm of water, which allows the particles to always be covered with water during subsequent evacuation.

- Make a vacuum of 0.08 MPa in each vial containing the particles and water, and maintain this vacuum for 7 minutes. Break the void.

- Make a vacuum of 0.08 MPa in each bottle, and maintain this vacuum for 7 minutes. Break the void.

- Determine the submerged weight of each sample, Pii, Ph, P and Pi ₄ . We denote Pi = Ph + Ph + P + PU.

- Then pour the contents of the 4 bottles on a sieve of square mesh of 2 mm in order to eliminate the water. Then pour the particles on a dry cotton cloth to remove excess water and wipe the particles until the moisture luster has disappeared from their surface.

- Determine the wet weight Ph of all the particles.

The bulk density of the set of particles is equal to Ps / (Ph-Pi).

The open porosity of the set of particles is equal to (Ph-Ps) / (Ph-Pi).

These measurements correspond to average measurements on the material constituting the particles, that is to say do not take into account the interstices between the different particles.

The median circularity of a set of particles in the aggregate is evaluated by the following method:

A sample of particles having sizes between 0.5 and 2 mm is poured onto the glass plate provided for this purpose a device Morphologi G3 ^® sold by the company Malvern. The magnification chosen is 1x. The analysis is launched. In order to avoid the recognition of any scratches of the glass plate and dust, the measurements corresponding to particles having a width ("width") of less than 0.4 mm are eliminated from the count by creating a filter (" width <400 "). The number of particles counted after filtering is greater than 250.

The apparatus provides an evaluation of the circularity distribution ("Circularity"), the particles being counted in number.

For elements other than chromium 6, the chemical analysis of the products is measured by Inductively Coupled Plasma or ICP for the elements whose quantity does not exceed 0.5%. To determine the content of the other elements, a pearl of the product to be analyzed is made by melting the product, then chemical analysis is performed by X-ray fluorescence.

The measurements of chromium 6 contents are carried out by leaching extraction, according to standard NF EN12457-2, the amount of Cr ^{® +} then being measured by an analysis by ionic chromatography in liquid phase.

To measure the ability of a product to generate chromium 6, two tests are performed depending on the location of the additive: a test when the additive is located within the product (Examples 2, 3, 5 and 7). to 13) and a test when the additive is located on the surface of the product (Example 4). The same test is carried out on a cylinder of the same product containing no additive (Examples 1, 6 and 14).

The test when the additive is located in the product is as follows: samples of the products to be tested are placed in a baking oven. They are then brought to a temperature T, under air, the holding time at the temperature T being equal to 24 hours, the rate of rise to the temperature T being equal to 50 ° C./h and the rate of descent in temperature being equal to 50 ° C / h. After testing, the chromium content 6 is determined.

The test when the additive is located on one surface of the product is as follows. The cylinder of Example 4 is placed in a tubular furnace with an internal diameter of 150 mm, so as to substantially close off part of the tube, the coated face being oriented towards the introduction of an alkaline mist of a solution at 0.5 g / l of NaOH, injected into the oven at a flow rate of 32 mg / h and per m ³ available in the oven, for 24 hours, said oven being maintained at a temperature of 800 ° C. during injection of alkaline fog. The same test is performed on a cylinder of the same product whose faces are not coated with additive (Example 1). The more or less marked presence of a yellow color on the large face of the product oriented towards the introduction of the alkaline fog is related to the presence of chromate: the more the yellow color is supported, the greater the amount of chromate is important .

The following Table 7 summarizes the results obtained in Examples 1 to 3, and 5 to 14. o

o \

h3

O

H

O

( ^* ): comparative examples O o \ *

Table 7

A comparison of the product of Example 1, excluding the invention, with the additives of Examples 2 and 3, and 7 to 12, according to the invention, shows that the additive products of Examples 2 and 3, and 7 to 12 show a ability to generate a much lower amount of chromium 6 than the product of Example 1, after 24 hours exposure at a temperature of 400 ° C or 800 ° C.

A comparison of the products of Examples 1 to 3, and 7 to 12 shows the effectiveness of the invention when the additive is distributed substantially homogeneously in the product.

Furthermore, after testing, the additive product of Example 4 does not show a yellow color on the coated surface disposed inside the oven, unlike the product of Example 1.

A comparison of the products of Examples 1 and 4 shows the effectiveness of the invention when the additive is placed on a surface of the product.

A comparison of the additive product of Example 5, according to the invention, with the product of Example 6, outside the invention, shows that the additive product of Example 5 has an ability to generate a much higher amount of chromium 6. as the product of Example 6, after exposure for 24 hours at a temperature of 400 ° C.

A comparison of the product of Example 14, excluding the invention, with the additive product of Example 13, according to the invention, shows that the additive product of Example 13 has an ability to generate a quantity of chromium 6 much more as the product of Example 14, after exposure for 24 hours at a temperature of 600 ° C.

As now clearly apparent, the invention makes it possible to reduce the ability of a product, and in particular of a concrete, to generate chromium 6 during its manufacture or its use, in particular at temperatures between 100 ° C and 1200 ° C.

Of course, the invention is not limited by the examples, provided for illustrative purposes only.

Claims

1. Glass furnace comprising an additive product comprising, on the surface and / or at the core, an additive chosen from:

phosphorus compounds other than glass and glass-ceramics, tungsten compounds other than glass and glass-ceramics, molybdenum compounds other than glass and glass-ceramics, iron in metal form, aluminum in metal form, silicon in metal form, and mixtures thereof,

silicon carbide,

boron carbide,

silicon nitride,

boron nitride,

glasses comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element,

glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element,

and their mixtures,

and having, in addition to the additive, the following chemical analysis, in percentages by weight, based on the oxides:

Cr ₂ C> 3 ³ 2%, and

Cr ₂ C 3 ⁺ Al ₂ O ₃ ⁺ CaO + ZrO ₂ + MgO + Fe ₂ O 3 ⁺ SiO ₂ + TiO ₂ ³ 90%, and

Cr ₂ C 3 ⁺ Al ₂ O ₃ ⁺ MgO ₃ 60%,

the mass content of additive being between 0.01% and 6% based on the additive product.

2. Glass furnace according to the preceding claim, wherein the additive product is in the form of a block, in particular a tank block or a veneer vat slab, a glass distribution channel, or a consumable part for a glass distribution channel, in particular a fore-body bowl, a flow washer, a jacket, a plunger, an agitator, or a rotor.

3. Glass furnace according to any one of the preceding claims, wherein the additive product is disposed in a zone of the furnace in which it is likely to come into contact with molten glass and / or has at least one region defining a surface which is not intended to be in contact with molten glass and which has additive.

4. Glass furnace according to any one of the preceding claims, wherein the additive product has, in addition to additive, in percentages by weight on the basis of the oxides, a content of Cr2Ü3 ³ 9%.

Glass furnace according to any one of the preceding claims, wherein the additive product has, in addition to the additive, in percentages by weight based on the oxides:

an O2O3 content of greater than 15% and less than 98%; and / or a CaO content greater than 0.1% and less than 3%; and or

an O2O3 + Al2O3 content of greater than 55%; and or

an SiO 2 content greater than 0.5% and less than 12%; and or

a ZrC> 2 content of greater than 1% and less than 19%; and or

a MgO content of less than 20%; and or

a Fe 2 O 3 content of less than 30%; and or

a content of constituents other than Cr 2 O 3, Al 2 O 3, CaO, ZrO 2, MgO, Fe 2 O 3, SiO 2 and TiO 2 less than 5%.

6. Glass furnace according to any one of the preceding claims, wherein the additive product has, in addition to additive, in percentages by weight on the basis of the oxides:

a Cr 2 O 3 content greater than 30%; and or

a CaO content greater than 0.3% and less than 1.5%; and / or a Cr 2 O 3 + Al 2 O 3 content greater than 80%; and or

an SiO 2 content greater than 1% and less than 8%; and or

a ZrO2 content of greater than 3% and less than 15%; and or

a MgO content of less than 5%; and or

a Fe 2 O 3 content of less than 5%; and or

a content of constituents other than Cr 2 O 3, Al 2 O 3, CaO, ZrO 2, MgO, Fe 2 O 3, SiO 2 and TiO 2 less than 3%.

7. Glass furnace according to any one of the preceding claims, wherein the additive product is in the form of a cured concrete or a sintered concrete.

8. A method of manufacturing a glass furnace according to any one of the preceding claims, said manufacture of the additive product comprising the following successive steps:

A) preparing a feedstock comprising a particulate mixture and water;

B) shaping said feedstock so as to form a preform;

C) optionally, sintering said preform so as to obtain a sintered product, a precursor of said additive being added to the feedstock and / or applied to the surface of the preform and / or applied to the surface of the sintered product.

9. Process according to the preceding claim, in which the additive precursor is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten compounds other than glasses and glass-ceramics, molybdenum compounds other than glasses. and glass-ceramics, iron in metal form, aluminum in metal form, silicon in metal form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum element, glass-ceramics comprising the phosphorus and / or iron and / or tungsten and / or molybdenum element, and mixtures thereof.

10. Method according to the preceding claim, wherein said additive precursor is selected from FePO ₄ , MgPO ₄ , ZnPO ₄ , CuPO ₄ , H ₃ PO ₄ , WO ₃ , WC, MoO ₃ , Si, Al, Fe, SiAl. , FeSi, SiC, B ₄ C, S NU, a glass comprising iron, and mixtures thereof.

1. Method according to the preceding claim, wherein said additive precursor is selected from FePO ₄ , MgPO ₄ , FhPCU, WO ₃ , MoO ₃ , SiAl, Fe Si, SiC, a glass comprising iron, preferably a glass having an iron content, expressed as Fe ₂ O 3 of between 1 and 15%, preferably between 4 and 15%, and mixtures thereof.

A process according to any of the four immediately preceding claims, wherein the mass content of the additive precursor, based on the mass of the particulate mixture excluding shaping agent, is greater than 0.1% and lower. at 6%.

The process according to any one of claims 8 to 11, wherein the mass content of the additive precursor, based on the mass of the particulate mixture excluding shaping agent, is greater than 0.5% and lower. at 3%, or in which the additive precursor is deposited on the surface of the preform, the mass content of the additive precursor being between 0.01% and 5% based on the weight of the preform after deposition of the additive precursor , or

wherein the additive precursor is deposited on the surface of the sintered product, the mass content of the additive precursor being between 0.01% and 5% based on the weight of the sintered product after deposition of the additive precursor .

A process according to any one of the six immediately preceding claims, wherein the feedstock comprises a granulate having a median circularity greater than 0.87 and / or a matrix fraction consisting of particles having a size less than or equal to 50 μm. which does not have a hydraulic binder.

15. Use of the additive of a product of a glassmaking furnace according to any one of

Claims 1 to 7 or an additive precursor in a process according to any one of the seven immediately preceding claims for limiting the amount of chromium 6 generated by said product.