PRODUCT CONTAINING CHROMIUM OXIDE 3

Abstract

Product containing, on its surface and / or in its core, an additive selected 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 metallic form, aluminum in metallic form, silicon in metallic form, and mixtures thereof, silicon carbide, - boron carbide, silicon nitride, boron nitride, - glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum, - glass-ceramics containing phosphorus and / or iron and / or tungsten and / or molybdenum, - and mixtures thereof, and having, excluding the additive, the following chemical analysis, in mass percentages based on oxides: - Cr2O3 - 2%, and - Cr2O3 + Al2O3 + CaO + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 ≥ 90%, and - Cr2O3 + Al2O3 + MgO ≥ 60%.

Description

The detailed description of step A) that follows relates to concrete, but the invention extends to any product containing chromium oxide 3. In step A), the starting charge for manufacturing concrete is made up of a mixture of a particulate mixture according to the invention and water, to obtain, at the end of step B) and / or C), an additive product according to the invention. In addition to the particulate mixture and water, it may also contain a liquid shaping agent. Particulate mixture The manufacture of a particulate mixture classically results from a mixture of powders of raw materials having compositions and particle size distributions adapted to the desired additive product. For concrete, the particulate mixture preferably comprises, by mass percentage, 0.9% to 8%, and more preferably 2% to 6%, of hydraulic cement particles. The hydraulic cement may be an aluminous cement or a mixture of different cements, such as CA25 or CA14 cements from Almatis. Preferably, the hydraulic cement contains, as its principal constituents (constituents with the highest concentrations), alumina and calcium aluminates. Preferably, the particulate mixture has a total Cr2O3 + Al2O3 content greater than 47%, preferably greater than 51%, preferably greater than 56%, preferably greater than 60%, preferably greater than 70%, preferably greater than 75%, or even greater than 80%, or even greater than 85%, or even greater than 89%, by mass percentage. In one embodiment, the particulate mixture has a total content of Cr2O3 + Al2O3 + MgO greater than 80%, preferably greater than 85%, preferably greater than 90%, preferably greater than 95%, as a mass percentage. In one embodiment, the particulate mixture has a Cr2O3 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%, by mass percentage. In another embodiment, the Cr2O3 content is greater than 48%, or even greater than 52%. In one embodiment, the particulate mixture comprises a Cr2O3 content greater than 3%, preferably greater than 4%, preferably greater than 5%, and preference less than 15%, preferably less than 12%, preferably less than 9%, as a mass percentage. In one embodiment, the particulate mixture comprises an Al₂O₃ content, preferably as alumina, greater than 2.5%, greater than 4.5%, greater than 9%, greater than 13%, greater than 17%, greater than 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%, by mass percentage. In another embodiment, the particulate mixture comprises an Al₂O₃ content greater than 33%, greater than 35%, or even greater than 39%. In one embodiment, the particulate mixture has an Al2O3 content greater than 70%, preferably greater than 75%, preferably greater than 80%, or even greater than 85%, or even greater than 90%. The SiO2 content, preferably in 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%, as a mass percentage. The ZrO2 content, preferably zirconia, 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 mass percentage. The content of constituents other than Cr2O3, Al2O3, CaO, ZrO2, MgO, Fe2O3, SiO2 and TiO2 of the particulate mixture is less than 20%, preferably less than 15%, preferably less than 12%, preferably less than 8%, or even less than 5%, by mass percentage. 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 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, or even less than 0.1%, by mass percentage. 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 Fe2O3 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 Fe2O3 content of the particulate mixture is less than 30% and greater than 1%, preferably greater than 3%, by mass percentage. The TiO2 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%, as a mass percentage. In one embodiment, the TiO2 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%, as a mass percentage. In one embodiment, the CaO content of the particulate mixture is less than 0.5%, preferably less than 0.3%, by mass percentage. Preferably, the total content of Cr2O3, Al2O3, ZrO2, SiO2, CaO and TiO2 in the particulate mixture is greater than 77%, greater than 83%, greater than 87%, greater than 90%, or greater than 93%, by mass percentage. Preferably, constituents other than 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. In particular, it can be adapted to the apparent density of the product one wishes to obtain. The particulate mixture for concrete comprises a matrix fraction and an aggregate. 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% matrix particles, by mass percentage. The median size of the matrix fraction may be less than 30 pm, less than 25 pm, less than 15 pm, less than 10 pm, or even less than 7 pm. Preferably, at least 90% by mass of the matrix particles have a size less than 40 pm, preferably less than 30 pm, preferably less than 20 pm, or even less than 10 pm. Preferably, the matrix fraction has a chemical composition such that, in mass percentages and for a total of 100%: - Cr2O3 + AI2O3 + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 + CaO > 82%, preferably Cr2O3 + AI2O3 + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 + CaO s 87%, and - Cr2O3 + AI2O3 + MgO > 45%, and - preferably Cr2O3 > 6%, and - preferably 15% > SiO2 > 0.1%. Preferably, the composition of the matrix fraction is such that: - the total content of Cr2O3 + Al2O3 + MgO is greater than 60%, preferably greater than 65%, preferably greater than 70%, preferably greater than 80%, or even greater than 85%, by mass percentage; and / or - the SiO2 content 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 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%, as a mass percentage; and / or - in one embodiment, the Fe2O3 content is less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%, by mass percentage; and / or - in one embodiment, the Fe2O3 content is less than 30% and greater than 1%, preferably greater than 3%, by mass percentage; and / or - the TiO2 content is less than 7%, or even less than 4%, or even less than 3%, or even less than 2%; and / or - the complement to Cr2O3, Al2O3, CaO, ZrO2, MgO, Fe2O3, SiO2 and TiO2 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 TiO2 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 eskolaite particles on the one hand and, on the other hand, alumina particles and / or zirconia particles and / or titanium oxide particles and / or silica particles and / or cement particles and / or additive particles. Preferably, the matrix fraction comprises eskolaite particles on the one hand and, on the other hand, alumina and / or zirconia and / or titanium oxide and / or cement and / or additive particles. In one embodiment, the particulate mixture does not contain zirconia particles, in particular zirconia matrix particles. In one embodiment, the matrix fraction preferably comprises alumina particles on the one hand and, preferably, on the other hand, eskolaite particles and / or magnesia particles and / or additive particles. Granule The particulate mixture preferably comprises less than 90%, preferably less than 85%, preferably less than 80%, of grains, by mass percentage. Preferably, at least 90% by mass of the grains have a size greater than 100 pm, preferably greater than 200 pm, preferably greater than 300 pm, preferably greater than 400 pm. Preferably always, more than 80%, preferably more than 90%, preferably more than 95%, preferably more than 99% by mass of the aggregate grains have a size greater than 200 pm, preferably greater than 300 pm, preferably greater than 400 pm, or even greater than 0.5 mm and / or less than 10 mm, preferably less than 5 mm. Preferably, the particulate mixture should always contain at least 10% of grains larger than 2 mm, by mass percentage. In one embodiment, the aggregate consists of more than 90%, more than 95% of its mass, of sintered particles. Preferably, the aggregate has an apparent 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 mass theoretical volumetric, or even greater than 93%, or even greater than 94%, or even greater than 95%, or even greater than 96% of the theoretical volumetric mass. Preferably, the aggregate 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 aggregate has a median circularity greater than 0.87, preferably greater than 0.88, preferably greater than 0.90, preferably greater than 0.91. Advantageously, resistance to thermal shock and resistance to corrosion, particularly in an application where the product is in contact with molten glass, are improved. Granules are particles with a circularity of 0.8 or more. Preferably, granules are agglomerated particles, particularly sintered particles. Agglomeration can also be achieved using a binder, for example a polymer binder, notably by atomization or spray-drying and / or the use of a granulator or pelletizing device. 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 aggregate preferably consists of particles of additives and particles containing Cr2O3 on the one hand and, on the other hand, containing Al2O3 and / or ZrO2 and / or MgO and / or Fe2O3 and / or TiO2 and / or SiO2. Preferably, the aggregate consists of particles containing Cr2O3 on the one hand and, on the other hand, containing Al2O3 and / or ZrO2 and / or TiO2 and / or SiO2. In one embodiment, the aggregate consists of additive particles and particles containing Al₂O₃ and / or particles containing Cr₂O₃ and / or particles containing MgO and / or particles containing a mixture of at least two oxides selected from Al₂O₃, Cr₂O₃, and MgO. In another embodiment, the aggregate consists of particles containing Al₂O₃ and Cr₂O₃ on the one hand, and particles containing Al₂O₃ and / or particles containing MgO on the other. Preferably, the aggregate has a chemical composition such that, in mass percentages and totaling 100%: - Cr2O3 + Al2O3 + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 > 90%, preferably Cr2O3 + Al2O3 + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 > 95%, and Cr2O3 + Al2O3 + MgO s 60%, and - preferably Cr2O3 > 9%, and - preferably 20% > SiO2 > 0.5%. Preferably, the composition of the aggregate is such that - the total content of Cr2O3 + 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%, by mass percentage; and / or - the SiO2 content 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, this improves densification without reducing corrosion resistance); 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%, as a 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 Fe2O3 content is less than 5%, preferably less than 3%, preferably less than 1%, preferably less than 0.5%, as a mass percentage based on the oxides; and / or - in one embodiment, the Fe2O3 content is less than 30% and greater than 1%, preferably greater than 3%, by mass percentage; and / or - in one embodiment, the TiO2 content 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 Cr2O3, Al2O3, CaO, ZrO2, MgO, Fe2O3, SiO2 and TiO2 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 Cr2O3 + Al2O3 > 80%, Cr2O3 + Al2O3 > 90%, or even Cr2O3 + Al2O3 > 95%. Preferably, the sum of the oxide contents in the grains, preferably the granules of the aggregate, represents more than 90%, more than 95%, or even approximately 100% of the mass of said grains or granules. Formatting agent The particulate mixture may contain at least 0.1% and / or less than 6% by mass of particles of a shaping agent, as a mass percentage on the basis of the particulate mixture. The optional shaping agent may be introduced in liquid form in equivalent quantities. The formatting agent can be chosen from the following group: - clays; - plasticizers, such as polyethylene glycol (or "PEG" >>) or polyvinyl alcohol (or "PAV" >>); - binders including temporary organic 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 chosen from the group consisting of deflocculants, clays, lignosulfonates, APV and their mixtures. Additive The median size of the additive powder in the particulate mixture is preferably less than 150 pm, preferably less than 100 pm, preferably less than 80 pm, 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 additive content in the particulate mixture is adjusted so as to be greater than 0.3% in the additive product, based on the mass of the additive product. In a first preferred embodiment, the amount of additive in the particulate mixture is adjusted so that, in the additive-treated product (preform or sintered product), it 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 7%, preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3%, based on the mass of the additive-treated product. Preferably, in this embodiment, the additive is selected 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 containing the element iron, boron nitride, and their derivatives. mixtures. Preferably the additive is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, boron nitride and mixtures thereof, preferably the additive is chosen from FePO4, MgPO4, ZnPO4, CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides and mixtures thereof, preferably the additive is chosen from PePO4, MgPO4, phosphoric acid and mixtures thereof. This first embodiment is particularly well suited when the additive-treated product is intended to be subjected to a temperature between 100°C and 400°C. In a second preferred embodiment, the quantity of additive incorporated into the particulate mixture is adjusted so as to be, in 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 less than 8%, preferably less than 7%, preferably less than 6%, preferably less than 5%, preferably less than 4%, preferably less than 3% on the basis of the mass of the additive product.Preferably, in this embodiment, the additive 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 metallic form, aluminum in metallic form, silicon in metallic form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics containing phosphorus and / or iron and / or tungsten and / or molybdenum, and mixtures thereof.Preferably, in this embodiment, the additive is chosen from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, and mixtures thereof, preferably from FePO4, MgPO4, ZnPO4, CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides, and mixtures thereof. Preferably, the additive is chosen from FePO4, MgPO4, phosphoric acid, and mixtures thereof. This second embodiment is particularly well suited when the additive-enhanced product is intended to be subjected to a temperature between 500°C and 1200°C. Introducing the additive in step A) advantageously allows for a substantially homogeneous distribution of the additive. Preferably, the mixing time is determined for this purpose. Additive particles are counted, according to their size, in the aggregate or matrix fraction. The particulate mix can be delivered ready-to-use. For a particular type of concrete, it simply needs to be mixed with water to prepare the starting charge. Water The amount of water depends on step B). In the case of pouring, an addition of a quantity of water between 3 and 7%, as a mass percentage based on the particulate mixture, optionally with additives, is preferred. Unlike the starting material for concrete, the starting material for rammed earth does not contain a hydraulic binder and is therefore not activated by wetting. It may, however, contain a chemical, ceramic, and / or organic binder. The activation methods are determined accordingly. In step B), all conventional methods used to manufacture preforms, particularly in hardened concrete, can be considered. The starting load can in particular be shaped in situ, so that the preform is positioned in its service position. Particularly for rammed earth, shaping typically results from a vibration or compaction process. The resulting preform therefore has low mechanical strength and is thus preferably created in situ. Typically, after formwork removal, the preform "holds its shape," but lacks the physical integrity to allow it to be transported, for example. In one embodiment, the additive is applied to the surface of the preform. Any known technique for depositing a composition onto a block can be used, in particular trowel or brush application, or wet or dry spraying, such as glazing, so as to form a thin or thick layer. Preferably, the additive is mixed with a liquid, such as water and / or oil, before being applied to the surface. The amount of liquid varies depending on the particle size of the additive to ensure good adhesion to the surface. In a third preferred embodiment, the quantity of additive deposited in step B) on the preform or in step C) on the sintered product is adjusted so as to be, in the additive-treated product, 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 additive-treated product. Preferably, in this embodiment of In production, the additive 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 metallic form, aluminum in metallic form, silicon in metallic form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses containing the element phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics containing the element phosphorus and / or iron and / or tungsten and / or molybdenum, and mixtures thereof.Preferably, the additive is selected from phosphorus compounds other than glasses and glass-ceramics, tungsten oxides, molybdenum oxides, glasses containing iron and mixtures thereof, preferably selected from FePO4, MgPO4, ZnPO4, CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides, boron nitride, glasses containing iron and mixtures thereof. Preferably, the additive is selected from PePO4, MgPO4, phosphoric acid, tungsten oxides, molybdenum oxides, glasses containing iron, preferably glasses with an iron content, expressed as Fe2O3, of 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 between 100°C and 1000°C, or even to a temperature between 100°C and 850°C, and when a reduction in the quantity of chromium 6 is desired on at least one of the faces of the product. In one embodiment, a bonding agent is mixed with the additive to promote its deposition on the surface of the product. Bonding additives can be selected from clays, plasticizers, celluloses and their mixtures, polyvinyl alcohols or "PVAs", polyethylene glycols or "PEGs". In optional step C), the sintering conditions, and in particular the sintering temperature, depend on the composition of the particulate mixture. Typically, a sintering temperature between 1400°C and 1700°C, preferably between 1450°C and 1650°C, and preferably between 1500°C and 1600°C, is well-suited. Sintering can be carried out in situ, that is, after the preform has been formed or placed 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 rammed earth. In one embodiment, the additive is applied to the surface of the sintered product. The techniques described for applying the additive in step B) are applicable. Examples To manufacture the particles "Cr2O3, Al2O3, SiO2, TiO2" used in the products of examples 1 to 4, the following raw materials were used: - of pigmentary chromium oxide Cr2O3 with a purity greater than 95%, having a specific surface area of ​​4 m2 / g and a median size of 0.7 pm; - of alumina Al2O3 of a purity greater than 99%, having a specific surface area of ​​7 m2 / g, and a median size of 0.6 pm; - silica fume, with a purity exceeding 92%; and - titanium oxide, in rutile form, with a purity greater than 93% and a median size of 1.5 pm. These raw materials were measured and mixed to obtain a mixture of oxides with the following chemical composition: Chemical analysis: Cr2O3 (%) 40.0, Al2O3 (%) 48.0, SiO2 (%) 3.2, TiO2 (%) 1.70, ZrO2 (%) 6.00, Other (%) 1.10 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 mixture is then kneaded for 1 minute with a vortex rotating at 300 rpm and a tank set at 43 rpm to obtain a homogeneous blend. The vortex speed is then increased to 1050 rpm, and an additional 900 grams of the oxide mixture is gradually added over one minute. Rotation is maintained for 2 minutes after the addition of this extra quantity. The particles are then discharged, air-dried for 24 hours at 110°C, and then sintered at 1550°C for a 3-hour holding time under air, with a heating and cooling rate of 50°C / h. After sintering, the particles exhibit an open porosity of 1.05% and a median circularity greater than 0.85. They are then sieved and three particle size ranges are kept: 0 - 0.5 mm, 0.5 - 2 mm, and 2 - 5 mm. The hardened concretes of examples 2 and 3 were then manufactured following steps A) and B) described above. In step A), the following raw materials were then mixed with the particles "Cr2O3, Al2O3, SiO2, TiO2": - chromium oxide pigment Cr2O3 with a purity greater than 95%, having a specific surface area of ​​4 m2 / g and a median size of 0.7 pm, - alumina (Al2O3) with a purity greater than 99%, having a specific surface area of ​​7 m2 / g, and a median size of 0.6 pm, - an aluminous CA25R cement from the company Almatis. The mass contents of the different raw materials are summarized in the following table 2: Cr2O3, Al2O3, SiO2, TiO2 particles >> 2-5 mm 28.5% Cr2O3, Al2O3, SiO2, TiO2 particles >> 0.5 - 2 mm 26.5% Cr2O3, Al2O3, SiO2, TiO2 particles >> 0 - 0.5 mm 23.5% Pigmentary chromium oxide 15.5% Alumina 5% CA25R aluminous cement 1% Table 2 A modified polycarboxylate ether was then added in an amount equal to 0.17% of the mass of said mixture of raw materials. An additive was then added, according to the invention, to obtain a ready-to-use mixture. The nature and quantity of the additive are summarized in Table 3 below: Example 2 Example 3 Nature of the additive Tungsten oxide WO3 Iron phosphate PePO4 Quantity of the additive, as a percentage based on the mass of the ready-to-use mixture 0.5% 1% Table 3 The tungsten oxide used had a purity greater than 99% and a median size of 35 pm. The iron phosphate used was E53-98 iron phosphate marketed by the Budenheim company. 4.5% water, as a percentage by mass based on the mass of the ready-to-use mixture, was added to create the starting load. The mixing time was 12 minutes. In step B), the starting charge was shaped by a vibro-casting technique into a hardened concrete according to the invention, with dimensions of 230 x 120 x 80 mm3, suitable for the characterizations to be carried out. Example 1, comparative, was carried out in the same way as examples 2 and 3, but no additions were made. 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 having the composition shown in the following Table 4: Composition of the additive as a percentage by mass based on the total mass of the additive: Iron-containing glass 77.5%, Silicon carbide 36-70 6.2%, Silicon carbide 80-180 6.2%, Silicon carbide 220F 6.2%, Aluminum triphosphate 2.9%, Phosphoric acid 1% Table 4 The glass powder containing iron had a median particle size of 13 µm, and the following chemical analysis results were obtained: SiO₂ = 56.1%, Fe₂O₃ = 9%, Al₂O₃ = 17.4%, Na₂O = 2.4%, K₂O = 1.7%, CaO = 7.9%, MgO = 3.8%, TiO₂ = 1.2%, Other = 0.5%. The silicon carbide powders had a purity greater than 98%. The aluminum triphosphate powder was Budenheim M13-01. The phosphoric acid (H₃PO₄) was present at a concentration of 85%. The additive components were mixed together, and 29% water, based on the total quantity of additive, was added. The total mixing time was 10 minutes, to form a coating. The samples for 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 applied with a trowel to one of the two faces with a diameter of 150 mm, and the total quantity of additive based on the mass of the coated sample was 4%. The product in Example 5 was manufactured following steps A) and B) described above from the following raw materials: - chromium oxide pigment Cr2O3 with a purity greater than 95%, having a specific surface area of ​​4 m2 / g and a median size of 0.7 pm, - titanium oxide, in rutile form, with a purity greater than 93% and a median particle size of 1.5 pm, - "High chromium oxide 3" particles containing 98% Cr2O3 and exhibiting an open porosity of less than 3%, - zirconia with a purity greater than 99% and a median size of 3.5 pm, - a tungsten oxide WO3, of a purity greater than 99% and having a median size of 35 pm. The mass contents of the different raw materials are summarized in the following table 5: Particles "high chromium oxide content" 2-4 mm 12.1 Particles "high chromium oxide content" 0.5-2 mm 31.9 Particles "high chromium oxide content" 0-0.5 mm 37.4 Pigmentary chromium oxide 10.1 Titanium dioxide 0.4 Zirconia 8.1 Table 5 The order of introduction of the raw materials was as follows: hydroxyethyl methylcellulose Tylose MH 4000 P2, marketed by Shin Etsu, and calcium lignosulfonate BRETAX C, marketed by Brenntag, in quantities of 0.2% and 0.5%, respectively, were added to 2.5% water. These percentages are based on the total mass of the raw materials, including the additive. High-chromium oxide particles were then added, and the mixture was mixed for 10 minutes. Pigmented chromium oxide, zirconia, titanium dioxide, and 1% tungsten oxide WO3 were then added, and a further 10 minutes of mixing was performed to achieve the starting charge.The amount of tungsten oxide used was expressed as a percentage by mass based on the mass of high chromium 3 oxide particles, pigmentary chromium oxide, zirconia, and titanium oxide. In step B), the starting charge was shaped by a pressing technique under a pressure equal to 800 bar, in the form of an additive product with dimensions equal to 230 x 114 x 35 mm3, suitable for the characterizations to be carried out. Comparative example 6 was carried out in the same way as example 5, without tungsten oxide. Measurement protocols The apparent density and open porosity of the products are measured by hydrostatic weighing. The measurements of the apparent density and open porosity of an aggregate are carried out according to the following method: Dry four 35-gram samples, each consisting of particles between 2 and 5 mm in size, at 110 °C for at least 12 hours. The dry mass of each sample is denoted Psi, Ps2, Ps3, and Ps4. Ps = Psi + Ps2 + Ps3 + Ps4. Place each sample in a vial. Using a vacuum pump, create a vacuum of at least 0.07 MPa in each of the flasks and maintain this vacuum for 7 minutes. Then introduce water into the flask so as to cover the particles with at least 2 cm of water, ensuring that the particles remain covered with water during subsequent vacuum cycles. Re-establish a vacuum of 0.08 MPa in each bottle containing the particles and water, and maintain this vacuum for 7 minutes. Break the vacuum. Re-establish a vacuum of 0.08 MPa in each bottle, and maintain this vacuum for 7 minutes. Break the vacuum. Re-establish a vacuum of 0.08 MPa in each bottle, and maintain this vacuum for 7 minutes. Break the vacuum. Determine the submerged weight of each sample, Pi4, Pi2, Pi3 and Pi4. We denote Pi = Pi1+Pi2+Pi3+Pi4. Next, pour the contents of the 4 bottles onto a 2 mm square mesh sieve to remove the water. Then pour the particles onto a dry cotton cloth to remove excess water and wipe the particles until the moisture sheen has disappeared from their surface. Determine the wet weight (Ph) of the entire set of particles. The apparent 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 they do not take into account the gaps between the different particles. The median circularity of a set of aggregate particles is evaluated using the following method: A sample of particles ranging in size from 0.5 to 2 mm is placed on the glass plate of a Morphologi® G3 instrument marketed by Malvern. The magnification is set to 1x. The analysis is initiated. To avoid counting any scratches on the glass plate or dust particles, measurements corresponding to particles with a width of less than 0.4 mm are filtered out (width < 400). The number of particles counted after filtering is greater than 250. The device provides an assessment of the circularity distribution ("Circularity >>", with particles being counted by number. For elements other than chromium VI, chemical analysis of the products is performed by Inductively Coupled Plasma (ICP) for elements present in quantities not exceeding 0.5%. To determine the content of other elements, a bead of the product to be analyzed is made by melting the product, and then chemical analysis is performed by X-ray fluorescence. Chromium 6 content measurements are carried out by leaching extraction, according to the NF EN12457-2 standard, the quantity of Cr6+ then being measured by liquid phase ion chromatography analysis. To measure the ability of a product to generate chromium 6, two tests are carried out depending on the location of the additive: one test when the additive is located within the product (examples 2, 3 and 5) and one test when the additive is located on the surface of the product (example 4). The test, when the additive is localized in the product, is as follows: samples of the products to be tested are placed in a baking oven. They are then heated to a temperature T, under air, for a holding time at temperature T of 24 hours, with a rate of temperature rise to T of 50 °C / h and a rate of temperature fall of 50 °C / h. After testing, the chromium VI content is determined. The test when the additive is localized on a surface of the product is as follows. The cylinder from Example 4 is placed in a tubular furnace with an internal diameter of 150 mm, so as to substantially block part of the tube, with the coated face oriented towards the side where an alkaline mist of a 0.5 g / l NaOH solution is injected into the furnace. with a flow rate of 32 mg / h per m³ available in the furnace, for 24 hours, the furnace being maintained at a temperature of 800 °C during the injection of the alkaline mist. The same test is performed on a cylinder of the same product whose faces are not coated with additive (example 1). The presence, more or less pronounced, of a yellow color on the larger face of the product facing the direction of the alkaline mist introduction is related to the presence of chromate: the more intense the yellow color, the greater the quantity of chromate. Table 5 below summarizes the results obtained on examples 1 to 3, and 5 to 6. Example V*) 2 3 5 6(*> Chemical analysis of the product containing chromium oxide 3 (excluding additives) (%) Cr2O3 46.5 46.5 46.5 89.3 89.3 Al2O3 44.8 44.8 44.8 0.1 0.1 CaO 0.3 0.3 0.3 0.05 0.05 SiO2 2.1 2.1 2.1 0.05 0.05 MgO 0 0 0 0 0 Fe2O3 0.3 0.3 0.3 0.1 0.1 ZrO2 4.2 4.2 4.2 8 8 TiO2 1.3 1.3 1.3 2.1 2.1 Cr2O3 + Al2O3 + CaO + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 99.5 99.5 99.5 99.7 99.7 Cr2O3 + Al2O3 + MgO 91.3 91.3 91.3 89.4 89.4 Other oxides 0.5 0.5 0.5 0.3 0.3 Other characteristics Apparent density (g / cm3) 3.55 3.55 3.55 4.31 4.32 Open porosity (%) 15.7 16.2 16 15.3 15 Chromium 6 content after test at T = 400°C (ppm) 690 390 210 90 280 Reduction in chromium 6 content compared to example 1 - 43.8% 69.6% - - Reduction in chromium 6 content by Compared to example 6 - - - 67.9% - Chromium 6 content after test at T = 800°C (ppm) 870 460 100 - - Reduction in chromium 6 content compared to example 1 - 47.1% 88.5% - - (*) : comparative examples Table 5 A comparison of the product of Example 1, outside the scope of the invention, with the additive products of Examples 2 and 3, according to the invention, shows that the additive products of Examples 2 and 3 exhibit an ability to generate a much lower quantity of chromium 6 than the product of example 1, after 24 hours of exposure to a temperature of 400 °C or 800 °C. A comparison of the products of examples 1 to 3 shows the effectiveness of the invention when the additive is distributed in a substantially homogeneous way in the product. Furthermore, after testing, the additive product of example 4 does not show yellow coloration on the coated surface placed inside the oven, unlike the product of example 1. A comparison of the products in examples 1 and 4 shows the effectiveness of the invention when the additive is disposed 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 lower quantity of chromium 6 than the product of example 6, after exposure for 24 hours at a temperature of 400°C. As is now clear, the invention makes it possible to reduce the ability of a product, and in particular of concrete, to generate chromium 6 during its manufacture or use, particularly at temperatures between 100°C and 1200°C. Of course, the invention is not limited by the examples, which are provided for illustrative purposes only.

Claims

Demands

1. Glass furnace comprising an additive product having, on the surface and / or in the core, an additive selected 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 metallic form, aluminum in metallic form, silicon in metallic form, and mixtures thereof, - silicon carbide, - boron carbide, silicon nitride, - boron nitride, - glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics containing phosphorus and / or iron and / or tungsten and / or molybdenum, - and mixtures thereof, and having, excluding the additive, the following chemical analysis, in mass percentages, based on oxides: — Cr2O3 > 2%, and Cr2O3 + A12O3 + CaO + ZrO2 + MgO + Fe2O3 + SiO2 + TiO2 > 90%,and Cr2O3 + Al2O3 + MgO > 60%, a product in which the mass content of the additive is between 0.01% and 6% based on the additive-containing product.

2. Glass furnace according to the immediately preceding claim, having, excluding additives, in mass percentages on the basis of oxides, a Cr2O3 content > 9%.

3. Glass furnace according to any one of the preceding claims, wherein the additively treated product is in the form of a block, in particular a tank block or a veneer slab of tank.

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

5. Glass furnace according to any one of the preceding claims, wherein the additive-containing product has, excluding the additive, the following mass percentages based on the oxides: - a Cr2O3 content greater than 15% and less than 98%; and / or - a CaO content greater than 0.1% and less than 3%; and / or - a Cr2O3 + Al2O3 content greater than 55%; and / or - a SiO2 content greater than 0.5% and less than 12%; and / or - a ZrO2 content greater than 1% and less than 19%; and / or - a MgO content less than 20%; and / or - a Fe2O3 content less than 30%; and / or - a content of constituents other than Cr2O3, Al2O3, CaO, ZrO2, MgO, Fe2O3, SiO2 and TiO2 of less than 5%.

6. Glass furnace according to the immediately preceding claim, in which the additive-treated product has, excluding additives, the following mass percentages based on oxides: - a Cr2O3 content greater than 30%; and / or a CaO content greater than 0.3% and less than 1.5%; and / or - a Cr2O3 + A12O3 content greater than 80%; and / or - a SiO2 content greater than 1% and less than 8%; and / or - a ZrO2 content greater than 3% and less than 15%; and / or - a MgO content less than 5%; and / or - a Fe2O3 content less than 5%; and / or a content of constituents other than Cr2O3, A12O3, CaO, ZrO2, MgO, Fe2O3, SiO2 and TiO2 less than 3%.

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

8. Glass furnace according to claim 1, in which the additive product has, excluding additive, in mass percentages on the basis of oxides: - a Cr2O3 content greater than 4% and less than 15%; and / or - a CaO content less than 0.5%; and / or - a Cr2O3 + Al2O3 + MgO content greater than 80%; and / or - an MgO content greater than 5% and less than 15%.

9. Glass furnace according to any one of the preceding claims, wherein the content of the additive is greater than 0.1%, the additive being selected 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 containing the element iron, boron nitride and mixtures thereof.

10. Glass furnace according to the immediately preceding claim, wherein the additive is selected from FePO4, MgPO4, ZnPO4, CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides, and mixtures thereof.

11. Glass furnace according to any one of the two immediately preceding claims, wherein the content of the additive is greater than 0.5% and less than 3%.

12. Glass furnace according to any one of claims 1 to 8, wherein the content of the additive is greater than 0.1%, the additive being selected 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 metallic form, aluminum in metallic form, silicon in metallic form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics containing phosphorus and / or iron and / or tungsten and / or molybdenum, and mixtures thereof.

13. Glass furnace according to the immediately preceding claim, wherein the additive is selected from FePO4, MgPO4, ZnPO4, CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides, and mixtures thereof.

14. Glass furnace according to any one of the two immediately preceding claims, wherein the content of the additive is greater than 0.5% and less than 3%.

15. Glass furnace according to any one of claims 1 to 8, wherein the content of the additive is less than 5%, the additive being selected 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 metallic form, aluminum in metallic form, silicon in metallic form and mixtures thereof, silicon carbide, boron carbide, silicon nitride, boron nitride, glasses containing phosphorus and / or iron and / or tungsten and / or molybdenum, glass-ceramics containing phosphorus and / or iron and / or tungsten and / or molybdenum, and mixtures thereof.

16. Glass furnace according to the immediately preceding claim, wherein the additive is selected from FePO4, MgPO4, ZnPO4,

17.

18.

19.

20.

21. CuPO4, phosphoric acid, tungsten oxides, molybdenum oxides, iron-containing glass, and mixtures thereof. Glass furnace according to any one of the two immediately preceding claims, wherein the content of the additive is greater than 0.02% and less than 1.5%. Use of the additive in a product from a glass furnace according to any one of claims 1 to 17 to limit the amount of chromium 6 generated by said product. Use according to the preceding claim at a temperature between 100 and 400°C, the glass furnace conforming to any one of claims 9 to 11. Use according to claim 18 at a temperature between 500 and 1200°C, the glass furnace conforming to any one of claims 12 to 14. Use according to claim 18 at a temperature between 100 and 1000°C, the glass furnace conforming to any one of claims 15 to 17.