Alumina-zirconia-silica refractory product

Abstract

The present invention relates to a molten cast refractory product comprising, in mass percent on the basis of oxides, and for a total of 100%: ZrO2 + HfO2: 39.0% to 55.0%, SiO2: 10.5% to 14.0%, Al2O3: complement to 100%, Na2O + K2O: 0.80% to 3.00%, Na2O: < 0.60%, B2O3: < 1.0%, Fe2O3 + TiO2: < 0.60%, other types: < 1.0% with HfO2 < 5% and with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) of greater than 0.30.

Description

[0001] Description

[0002] Title: ALUMINA-ZIRCONIA-SILICA REFRACTORY PRODUCT

[0003] Domain

[0004] The invention relates to a fused refractory product AZS (Alumina-Zirconia-Silica) and to a glass melting furnace comprising such a product.

[0005] Glass melting furnaces generally include a very large number of refractory products, arranged in different locations according to their properties. For each part of the furnace, the product chosen will be one that does not cause defects that render the glass unusable (which would reduce production yields) and that is resistant enough for a satisfactory lifespan for the furnace.

[0006] Among the refractory blocks, we distinguish between cast blocks and sintered blocks.

[0007] Unlike sintered blocks, fused blocks most often contain an intergranular glassy phase connecting crystallized grains. The problems posed by sintered blocks and by fused blocks, and the technical solutions adopted to resolve them, are therefore generally different. A composition developed to manufacture a sintered block is therefore not a priori usable as is to manufacture a fused block, and vice versa.

[0008] Fused blocks, often referred to as "electrocast" or "melted and cast," are obtained by melting a mixture of suitable raw materials in an electric arc furnace or by any other suitable technique. The molten material is then conventionally poured into a mold and then solidified. Typically, the resulting product then undergoes a controlled cooling cycle to bring it to room temperature without fracturing. This operation is called "annealing" by those skilled in the art.

[0009] Fused Alumina-Zirconia-Silica products, known as "AZS", are known, comprising mainly alumina (AI2O3), zirconia (ZrO2) and silica (SiO2). In particular, AZS products typically comprise less than 80% by mass of zirconia. AZS products also contain corundum (free, or in the form of a corundum / zirconia eutectic) in an amount generally greater than 10%, or even greater than 30%. AZS products typically contain sodium oxide Na2O to give the glassy phase suitable physical and chemical properties. Generally, K2O and Na2O are considered to have equivalent effects.

[0010] US 2,438,552 recommends the addition of sodium oxide (1.0 to 2.2%) and a total MgO+CaO content of between 0.2% and 0.8%, to address feasibility issues concerning AZS products containing 9% to 12% SiO2 and 0.4% to 1.7% iron oxide.

[0011] EP939065 proposes to reduce the exudation rate of AZS products containing 20% ​​to 59% ZrO2 and 5% to 12% SiO2 by adding B2Os, P2Os and at least one of the oxides of the group SnO2, ZnO, CuO and MnO2.

[0012] WO201 1161588 offers AZS products resistant to exudation having, in addition to AI2Os, from 30% to 50% of ZrO2, from 8% to 16% of SiO2, Y2Os and more than 0.2% of Na2O+K2O+B2O3.

[0013] CN107555971 offers AZS products with 31% to 45% ZrO2, 9% to 14% SiO2, 44% to 56% AI2C>3, 0.6% to 1.4% Na2O and at least one of the oxides of the group B2C>3, Y2Os, Li2O, Ta2Os, Nb2Os, P2Os, K2O.

[0014] With the development of electrification of glass melting furnaces, refractory blocks, particularly those located near the electrodes, must have the greatest possible electrical resistivity to avoid the risk of electric current being diverted into the refractory.

[0015] In particular, a deviation of the electric current produces local heating, by Joule effect, which promotes corrosion of the block. At and near the electrode holder blocks, corrosion can also be accelerated by the intensification of convection movements of the glass, likely to destabilize the glass-refractory interface and potentially bring hotter glass into contact with the refractory product.

[0016] There is a need for AZS refractory products with improved electrical resistivity.

[0017] Statement of the invention

[0018] Summary of the invention

[0019] The invention provides a molten and cast refractory product comprising, in mass percentages based on the oxides and for a total of 100%:

[0020] ZrO2+ HfO2: 39.0% to 55.0%, with HfO2< 5%

[0021] SiO2: 10.5% to 14.0% AI2O3: complement to 100%

[0022] Na2O + K2O: 0.80% to 3.00%, with Na2O < 0.60%

[0023] B2O3: < 1.0%

[0024] Fe2O3+ TiO2: < 0.60% other species: < 1.0% with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.30.

[0025] As will be seen in more detail in the remainder of the description, a product according to the invention has improved resistivity. Surprisingly, the inventors discovered that Na2O and K2O have a different effect on resistivity. Furthermore, they discovered that, within a content range determined by several criteria, and in particular by the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) and by a total Na2O + K2O content of between 0.80% and 3.00%, Na2O and K2O not only improve resistivity, but also preserve feasibility.

[0026] A product according to the invention may also include one or more of the following optional characteristics, including when it conforms to the particular embodiments described below and when these optional characteristics are not incompatible with said particular embodiments:

[0027] - the total porosity of the product is less than 10%, or even less than 5%;

[0028] - preferably, the oxides represent more than 90%, more than 95%, more than 99%, or even substantially 100% of the mass of the product;

[0029] - the mass content of ZrO2+ HfO2 is less than 54.0%, or even less than 53.0%, or even less than 52.5%, or even less than 52.0%, or even less than 51.0%, or even less than 50.5%, or even less than 50.0%, or even less than 49.5%, or even less than 49.0%, or even less than 48.5%, or even less than 48.0%, or even less than 47.0%, or even less than 46.0%, and / or greater than 40.0%, or even greater than 41.0%, or even greater than 42.0%, or even greater than 42.5%, or even greater than 43.0%, or even greater than 43.5%, or even greater than 44.0%, or even greater than 44.5%, or even greater than 45.0%, or even greater than 45.5%;

[0030] - the mass content of SiO2 is less than 13.8%, or even less than 13.6%, or even less than 13.5%, or even less than 13.4%, or even less than 13.3%, or even less than 13.2%, or even less than 13.0%, or even less than 12.7%, or even less than 12.5% ​​and / or preferably greater than 10.6%, or even greater than 10.7%, or even greater than 10.8%, or even greater than 10.9%, or even greater than 11.0%, or even greater than 11.3%, or even greater than 11.5%;

[0031] - the mass content of AI2O3 is less than 46.0%, or even less than 45.5%, or even less than 45.0%, or even less than 44.0%, or even less than 43.5%, or even less than 43.0%, or even less than 42.0% and / or greater than 29.0%, or even greater than 30.0%, or even greater than 32.0%, or even greater than 34.0%, or even greater than 36.0%;

[0032] - the sum of the mass contents of sodium oxide Na2O and potassium oxide K2O is preferably greater than 0.85%, greater than 0.90%, greater than 0.95%, greater than

[0033] 1.00% and / or preferably less than 2.90%, preferably less than 2.80%, preferably less than 2.70%, preferably less than 2.60%, less than 2.50%, or even less than 2.30%, or even less than 2.20%, or even less than 2.10%, or even less than 2.00%, or even less than 1.90%;

[0034] - the mass content of Na2O is preferably less than 0.55%, or even less than 0.50%, or even less than 0.40%, less than 0.30%, less than 0.20%, or less than 0.10%; in one embodiment, Na2O is present as an impurity;

[0035] - the mass content of K2O is preferably less than 2.50%, or even less than 2.00%, or even less than 1.90%, or even less than 1.80%, or even less than 1.70%, or even less than

[0036] 1.60%, or even less than 1.50% and / or greater than 0.60%, greater than 0.65%, or even greater than 0.70%, or even greater than 0.75%, or even greater than 0.80%, or even greater than 1.00%;

[0037] - the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.40, or even greater than 0.45, or even greater than 0.50, or even greater than 0.60, or even greater than 0.65, or even greater than 0.70, or even greater than 0.75, or even greater than 0.80, and / or less than 0.95, or even less than 0.90;

[0038] - B2O3 is present as an impurity and / or the mass content of boron oxide B2Os is less than 0.90%, preferably less than 0.80%, preferably less than 0.70%, preferably less than 0.60%, preferably less than 0.50%, less than 0.40%, %, or even less than 0.30%, or even less than 0.20%, or even less than 0.10%;

[0039] - the mass content of Y2Os is less than 0.80%, or even less than 0.60%, or even less than 0.50%, or even less than 0.40%, or even less than 0.30%, or even less than 0.20%;

[0040] - the sum of the mass contents of iron oxide and titanium oxide, Fe2Os + TiO2, is less than 0.40%, preferably less than 0.30%, preferably less than 0.20%;

[0041] - the total mass content of “other species” is less than 0.9%, or even less than 0.8%, or even less than 0.6%, or even less than 0.5%, or even less than 0.4%;

[0042] - the “other species”, i.e. other than ZrO2, HfO2, SiO2, AI2Os, Na2O, K2O, B2Os, Fe2C>3 and TiO2, are made up only of impurities;

[0043] - the mass content of any “other species”, in particular Ta2Os and / or Nb2Os, is less than 0.4%, or even less than 0.3%, or even less than 0.2%, or less than 0.1%;

[0044] - the sum of the mass contents of calcium oxide CaO, barium oxide BaO, strontium oxide SrO and magnesium oxide MgO is less than 0.6%, less than 0.5%, less than 0.4% or even less than 0.3%;

[0045] - the mass content of CaO is less than 0.4%, or even less than 0.3%;

[0046] - the mass content of BaO is less than 0.4%, or even less than 0.3%;

[0047] - the mass content of SrO is less than 0.4%, or even less than 0.3%;

[0048] - the mass content of MgO is less than 0.4%, or even less than 0.3%;

[0049] - the product comes in the form of a block.

[0050] According to a particular embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0051] ZrO2+ HfC>2: 39.0% to 55.0%, or even 39.0% to 49.5%, or even 42.5% to 49.5%

[0052] SiO2: 10.5% to 14.0%

[0053] AI2C>3: 100% complement

[0054] Na2O + K2O: 0.80% to 2.50%, or even 0.80% to 2.00%

[0055] Na2O: < 0.60%

[0056] B2O3: < 1.0%, or even < 0.5%

[0057] Fe2C>3 + TiO2: < 0.60% other species: < 1.0% with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.50, or even greater than 0.60, or even greater than 0.65.

[0058] According to a particularly advantageous embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0059] ZrO2+ HfO2: 39.0% to 51.0%, preferably 39.0% to 49.5%, preferably

[0060] 42.5% to 49.5%

[0061] SiO2: 10.5% to 13.0%

[0062] AI2C>3: 100% complement, preferably < 44.0%

[0063] K2O: 1.00% to 2.00%, preferably 1.10% to 1.80%

[0064] Na2O: < 0.30%

[0065] B2OS: < 1.0%

[0066] Fe2O3+ TiO2: < 0.60% other species: < 1.0% with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.65, or even greater than 0.70.

[0067] According to a particularly advantageous embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0068] ZrO2+ HfO2: 42.5% to 49.5%, preferably 42.5% to 48.0%, SiO2: 10.5% to 13.0%, preferably 11.0% to 13.0%

[0069] AI2C>3: 100% complement,

[0070] K2O: 0.70% to 1.80%, preferably 0.80% to 1.60%,

[0071] Na2O: < 0.60%, preferably < 0.50%, preferably < 0.40%,

[0072] B2OS: < 1.0%

[0073] Fe2Os + TiO2: < 0.60% other species: < 1.0% with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.62, preferably greater than 0.65, preferably greater than 0.70.

[0074] According to a particular embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0075] AI2O3: < 44.0%

[0076] ZrO2+ HfO2: 45.5% to 49.5%

[0077] SiO2: 10.5% to 13.5%

[0078] Na2O + K2O: 1.00% to 2.00%

[0079] Na2O: < 0.60%

[0080] K2O: < 2.00% with a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.60, or even greater than 0.65, 0.70, or 0.75.

[0081] According to a particular embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0082] ZrO2+ HfO2: 39.0% to 52.5%, or even 42.5% to 52.5%

[0083] SiO2: 10.5% to 14.0%

[0084] AI2O3: 100% complement, preferably < 44.0%

[0085] Na2O + K2O: 0.90% to 2.50%

[0086] Na2O: < 0.60%

[0087] K2O: < 2.00%

[0088] B2OS: < 0.5%.

[0089] According to a particular embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0090] ZrO2+ HfO2: 39.0% to 49.0%

[0091] SiO2: 10.5% to 13.0%

[0092] Na2O + K2O: 1.00% to 2.00% Na2O: < 0.60%

[0093] K2O: < 2.00%

[0094] B2O3: < 0.5%.

[0095] According to a particular embodiment, the melted and cast refractory product according to the invention comprises, in mass percentages based on the oxides:

[0096] ZrO2+ HfO2: 39.0% to 49.0%

[0097] SiO2: 10.5% to 13.0%

[0098] Na2O + K2O: 0.85% to 2.00%

[0099] Na2O: < 0.55%

[0100] K2O: 0.80% to 1.80%

[0101] To the extent that the above optional features are not technically incompatible with each other, they can be combined.

[0102] The invention also relates to a method for manufacturing a refractory product according to the invention, comprising the following successive steps: a) mixing raw materials so as to form a starting charge, b) melting said starting charge until a molten material is obtained, c) casting and solidifying said molten material, by cooling, so as to obtain a refractory product, this method being remarkable in that said raw materials are chosen so that said refractory product conforms to the invention.

[0103] Preferably, the oxides for which a minimum content is required, or precursors of these oxides, are systematically and methodically added. Preferably, the contents of these oxides in the sources of other oxides where they are present as impurities are taken into account.

[0104] Preferably, the cooling is controlled, preferably so as to be carried out at a rate of less than 20°C per hour, preferably at a rate of about 10°C per hour.

[0105] The invention also relates to a glass melting furnace comprising a refractory product according to the invention, or a refractory product manufactured or capable of having been manufactured according to a method according to the invention, in particular in a region intended to be in contact with molten glass, in particular in a glass melting furnace tank, in particular to constitute an electrode holder block, for example in a hearth of such a tank. The invention thus relates to a glass melting furnace comprising a tank intended to contain or containing molten glass, the tank comprising a block made of a product according to the invention.

[0106] Definitions

[0107] A product is classically said to be "molten" when it is obtained by a process involving the melting of a charge until a molten material is obtained, then solidification of this material by cooling.

[0108] A block is an object all of whose dimensions are greater than 10 mm. All the dimensions of a block according to the invention are preferably greater than 50 mm, preferably greater than 100 mm. A block according to the invention may, for example, have a generally parallelepiped shape or a specific shape adapted to its use. Unlike a layer, a block made of a molten and cast refractory product is conventionally obtained by a process comprising molding and demolding operations.

[0109] The block of a product according to the invention, before or after demassing / machining, may have one, or even two or three overall dimensions (thickness, length, or width) of at least 150 mm, preferably at least 250 mm, or even at least 400 mm, or even at least 500 mm, or even at least 600 mm, or even at least 800 mm or even at least 1000 mm, and / or less than 2000 mm,

[0110] Unless otherwise stated, all oxide contents in a product according to the invention are percentages by mass based on the oxides. A mass content of an oxide of a metallic element refers to the total content of that element expressed in the form of the most stable oxide, according to the usual industry convention.

[0111] HfC>2 is not chemically dissociable from ZrCl. However, according to the present invention, HfC>2 is not intentionally added to the feedstock. HfC>2 therefore only designates the traces of hafnium oxide, this oxide always being naturally present in zirconium oxide sources at contents generally less than 5%, generally less than 2%. In a block according to the invention, the mass content of HfC>2 is less than 5%, preferably less than 3%, preferably less than 2%. For the sake of clarity, the total content of zirconium oxide and traces of hafnium oxide can be referred to indifferently as "ZrC>2" or as "ZrC>2 + HfC>2". HfC>2 is therefore not included in the "other species".

[0112] Impurities are unavoidable constituents introduced with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated ones. For example, compounds belonging to the group of oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides and metallic species of iron, titanium, vanadium and chromium are impurities.

[0113] Total porosity, in percentage, is typically equal to 100 x (1 - the ratio of geometric density divided by absolute density).

[0114] Geometric density is measured according to ISO 5016:1997 or EN 1094-4 and expressed in g / cm 3 It is classically equal to the ratio of the mass of the sample divided by the apparent volume.

[0115] The absolute density value, expressed in g / cm 3, can be measured by dividing the mass of a sample by the volume of that sample ground in such a way as to substantially remove porosity.

[0116] Detailed description

[0117] In the fused and cast products according to the invention, the ZrO2 + HfO2 content makes it possible to meet the requirements of high corrosion resistance. On the other hand, excessively high contents are detrimental to the industrial feasibility of blocks.

[0118] The hafnium oxide, HfC>2, present in the product according to the invention is preferably the hafnium oxide naturally present in ZrO2 sources. Its content in a product according to the invention is therefore less than 4%, generally less than 2%, or even less than 1%.

[0119] The presence of SiC>2 allows in particular the formation of an intergranular vitreous phase contributing to the feasibility of the products because it is able to effectively accommodate temperature deformations. The mass content of SiC>2 is preferably limited in order to limit the quantity of vitreous phase.

[0120] The presence of Na2O+K2O contributes to the feasibility of the products. The mass content of Na2O+K2O is preferably limited in order to limit the quantity of glass phase and in particular to maintain good resistance to corrosion by molten glass as well as good electrical resistivity.

[0121] The presence of K2O is necessary to have a ratio (K2O / 1.52) / (Na2O + K2O / 1.52) greater than 0.30, or even greater than 0.40, or even greater than 0.50, or even greater than 0.60, or even greater than 0.62, or even greater than 0.65, and to improve the electrical resistivity. Na2O has an adverse effect on the electrical resistivity. The mass content of sodium oxide Na2O must therefore remain limited.

[0122] B2O3 can have an adverse effect on feasibility. The mass content of boron oxide B20s must therefore remain limited.

[0123] Y20s can have an adverse effect on feasibility and electrical resistivity. The mass content of Y20s must therefore remain limited.

[0124] According to the invention, the mass content of Fe2O3 + TiC>2 is less than 0.60%, preferably less than 0.50%, preferably less than 0.30%. Preferably, the mass content of P2O5 is less than 0.05%. Indeed, these oxides are harmful, in particular for the exudation of refractory products or the coloring of glass and their content must be limited to traces introduced as impurities with the raw materials.

[0125] “Other species” are oxide species not listed above, namely species other than ZrO2, HfC>2, SiC>2, AI2O3, Na2O, K2O, B2O3, Y2O3, TiC>2 and Fe2O3. In one embodiment, “other species” are limited to species whose presence is not particularly desired and which are generally present as impurities in the raw materials.

[0126] Preferably, the product according to the invention is in the form of a block, preferably a block of which at least one, preferably at least two, or even all of the overall dimensions are greater than 150 mm.

[0127] The total porosity of the product according to the invention is less than 15%, or even less than 10%, or even less than 5%, or even less than 2%, or even less than 1%.

[0128] A product according to the invention can be conventionally manufactured according to steps a) to c) described below: a) mixing of raw materials so as to form a starting charge, b) melting of said starting charge until a molten material is obtained, c) solidification of said molten material, by cooling, so as to obtain a refractory product according to the invention.

[0129] In step a), the raw materials are chosen so as to guarantee the oxide contents in the finished product obtained at the end of step c). A person skilled in the art knows perfectly well how to choose the raw materials for this purpose. In step b), the melting is preferably carried out thanks to the combined action of a fairly long electric arc, not producing reduction, and stirring promoting the reoxidation of the products.

[0130] It is preferable to carry out fusion under oxidizing conditions for the intended applications.

[0131] Preferably, the long arc fusion process described in French patent No. 1,208,577 and its additions No. 75893 and 82310 is used.

[0132] This process consists of using an electric arc furnace whose arc strikes between the charge and at least one electrode spaced from this charge and of adjusting the length of the arc so that its reducing action is reduced to a minimum, while maintaining an oxidizing atmosphere above the molten bath and stirring said bath, for example by the action of the arc itself.

[0133] In step c), the cooling is preferably carried out at a rate of less than 20°C per hour, preferably at a rate of approximately 10°C per hour, preferably in a mold of the desired dimensions, taking into account the feeder and possible machining after step c).

[0134] Any conventional process for manufacturing zirconia-based molten products intended for applications in glass melting furnaces may be implemented, provided that the composition of the starting charge makes it possible to obtain products having a composition consistent with that of a product according to the invention.

[0135] Examples

[0136] The following non-limiting examples are given for the purpose of illustrating the invention.

[0137] In these examples, the following raw materials were used:

[0138] - Q1 zirconia containing on average 99% ZrO2 + HfC>2,

[0139] - “Bedouin Sand BE01” silica containing on average 99% SiC>2,

[0140] - AC34 type alumina containing on average 99% AI2C>3,

[0141] - sodium carbonate containing on average 99.5% Na2COs as a source of Na2O,

[0142] - potassium carbonate containing on average 99.5% K2CO3 as a source of K2O.

[0143] The products were prepared using the classic arc furnace melting process, then cast into a mold to obtain blocks with a minimum size of 150 mm x 250 mm x 500 mm after demassaging.

[0144] The average chemical analysis of the products obtained is given in Table 1; this is a chemical analysis of the liquid charge poured into the mold, given in mass percentages. Example 5 contains 0.68% Ta20s.

[0145] Species other than ZrC>2, HfC>2, SiC>2, AI2O3, B2O3, Na2O and K2O, and Ta20s for example 5, in particular Fe2O3, TiC>2 and Y2O3 (possibly present) are impurities, with Y2O3 < 0.2% and Fe2O3 + TiC>2 < 0.3%. In Table 1, the HfC>2 content is always less than 4%. The ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is noted "Ratio".

[0146] Feasibility

[0147] The external condition of the products obtained is observed. Their size, with the three dimensions greater than 150 mm and at least one dimension of at least 400 mm, makes it possible to estimate the industrial feasibility. If a through slit is present, the feasibility is deemed unsatisfactory. The products are then cut in two to observe the filling. If incorrect filling is present, the feasibility is deemed unsatisfactory. Otherwise, the feasibility is deemed satisfactory. All examples of the invention exhibit satisfactory feasibility.

[0148] Measurement of electrical resistivity On the different examples of blocks produced, cylindrical bars of product 30 mm in diameter and 30 mm in height were subjected to a potential difference of 1 Volt at a frequency of 60 Hertz at 1400 °C to carry out measurements of electrical resistivity R.

[0149] [Table 1] means "outside invention"

[0150] It appears that a Ratio greater than 0.30 when the Na2O rate is less than 0.60%, allows to achieve electrical resistivity values ​​higher than that of the reference. When the Ratio is greater than 0.60, or even greater than 0.62, or even greater than 0.65, the electrical resistivity values ​​are significantly improved.

[0151] As is clearly apparent, the invention therefore provides a product which exhibits remarkable performance in the environment of a glass melting furnace tank, particularly in the hearth. Of course, the invention is not limited to the embodiments described and shown, provided for illustrative purposes only.

Claims

Claims 1. Melted and cast refractory product comprising, in mass percentages based on oxides and for a total of 100%: ZrO2+ HfO2: 39.0% to 55.0%, with HfO2< 5% SiO2: 10.5% to 14.0% AI2OS: 100% complement Na2O + K2O: 0.80% to 3.00%, Na2O: < 0.60%, B2OS: < 1.0% Fe2Os + TiO2: < 0.60% other species: < 1.0% with a ratio (K2O / 1.52) / (Na2O K2O / 1.52) greater than 0.

30.

2. Product according to the preceding claim, in which the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.

50.

3. Product according to the immediately preceding claim, in which the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.

60.

4. Product according to the immediately preceding claim, in which the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.

62.

5. Product according to the immediately preceding claim, in which the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.

65.

6. Product according to any one of the preceding claims, in which the mass content of SiO2 is less than 13.5%.

7. Product according to the immediately preceding claim, in which the mass content of SiO2 is less than 13.0%.

8. Product according to any one of the preceding claims, in which the mass content of SiO2 is greater than 11.0%.

9. Product according to any one of the preceding claims, in which the mass content of K2O is greater than 0.60% and less than 2.00%.

10. Product according to any one of the preceding claims, in which the mass content of K2O is greater than 0.70%.

11. Product according to the immediately preceding claim, in which the mass content of K2O is greater than 0.80%.

12. Product according to the immediately preceding claim, in which the mass content of K2O is greater than 1.00%.

13. Product according to the immediately preceding claim, in which the mass content of K2O is less than 1.80%.

14. Product according to any one of the preceding claims, in which the mass content of ZrO2+ HfO2 is greater than 42.5% and less than 52.5%.

15. Product according to any one of the preceding claims, in which the mass content of ZrO2+ HfO2 is greater than 43.5%.

16. Product according to any one of the preceding claims, in which the mass content of ZrO2+ HfO2 is less than 51.0%.

17. Product according to the immediately preceding claim, in which the mass content of ZrO2+ HfO2 is less than 49.5%.

18. Product according to the immediately preceding claim, in which the mass content of ZrO2+ HfO2 is less than 48.0%.

19. Product according to any one of the preceding claims, in which the mass content of AI2Os is less than 44.0% and greater than 30.0%.

20. Product according to the immediately preceding claim, in which the mass content of AI2C>3 is less than 42.0% and greater than 34.0%.

21. Product according to any one of the preceding claims, in which the mass content of Na2O is less than 0.55%.

22. Product according to the immediately preceding claim, in which the mass content of Na2O is less than 0.50%.

23. Product according to any one of the preceding claims, in which the mass content of Na2O + K2O is less than 2.50%.

24. Product according to the immediately preceding claim, in which the mass content of Na2O + K2O is less than 2.00%.

25. Glass melting furnace comprising a tank intended to contain or containing molten glass, the tank comprising a block made of a product according to any one of the preceding claims.

26. Glass melting furnace according to the preceding claim, the tank comprising a floor comprising a block made of a product according to any one of claims 1 to 24.

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