Alumina-zirconia-silica refractory product

Abstract

The invention relates to a cast refractory product comprising, in mass percent on the basis of the oxides and for a total of 100%, ZrO2 + HfO2: 39.0% to 55.0%, SiO2: 10.5% to 14.0%, Al2O3: make up to 100%, Na2O + K2O: 0.80% to 3.00%, Na2O: lt; 0.60%, B2O3: 1t; 1.0% of Fe2O3 + TiO2: lt; 0.60%, and other types: lt; 1.0%, where HfO2lt; 5%, and wherein the ratio (K2O / 1.52) / (Na2O + K2O / 1.52) is greater than 0.30.

Description

Technical Field

[0001] The present invention relates to an AZS (aluminum oxide - zirconium oxide - silicon dioxide) fused refractory product and also to a glass furnace incorporating such a product. Background Art

[0002] Glass furnaces generally contain a very large number of refractory products, which are arranged in different positions according to their properties. For each part of the furnace, the product selected will be one that does not cause any defects that make the glass unusable (which would reduce the production yield) and has a sufficient tolerance to give the furnace a satisfactory service life.

[0003] Among refractory blocks, there is a distinction between fused blocks and sintered blocks.

[0004] Unlike sintered blocks, fused blocks generally contain an intergranular glassy phase that connects the crystalline grains. Thus, the problems encountered with sintered blocks and fused blocks, and the technical solutions adopted to solve these problems, are generally different. Therefore, the compositions developed for manufacturing sintered blocks cannot in principle be used as such for manufacturing fused blocks, and vice versa.

[0005] Fused blocks, which are commonly referred to as "electrically fused blocks" or "cast blocks", are obtained by melting a mixture of suitable starting materials in an electric arc furnace or by any other suitable technique. The molten material is then usually cast into a mold and then solidified. Typically, the product obtained then undergoes a controlled cooling cycle to reach ambient temperature without cracking. This operation is known to those skilled in the art as "annealing".

[0006] Aluminum oxide - zirconium oxide - silicon dioxide (AZS) fused products are known and mainly contain aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), and silicon dioxide (SiO 2 ). In particular, AZS products generally contain less than 80% by mass of zirconium oxide. AZS products also contain an amount of corundum (free or in the form of a corundum / zirconium oxide eutectic) that is usually greater than 10% or even greater than 30%.

[0007] AZS products generally contain sodium oxide Na 2 O to impart suitable physical and chemical properties to the glassy phase. Generally, K 2 O and Na 2 O are considered to have equivalent effects.

[0008] US2 438 552 proposes adding sodium oxide (1.0% to 2.2%) and a total content of MgO + CaO between 0.2% and 0.8% to address the feasibility issues associated with AZS products containing 9% to 12% of SiO 2 and 0.4% to 1.7% of iron oxide.

[0009] EP 939 065 proposes reducing the exudation degree of AZS products containing 20% to 59% of ZrO 2 O 3 ,P 2 O 5 ,and at least one oxide in the group of SnO 2 、ZnO、CuO and MnO 2 by adding at least one oxide in the group of SnO 2 and 5% to 12% of SiO 2 .

[0010] WO 2011 / 161 588 proposes an anti-exudation AZS product containing, in addition to Al 2 O 3 , 30% to 50% of ZrO 2 , 8% to 16% of SiO 2 , Y 2 O 3 , and more than 0.2% of Na 2 O + K 2 O + B 2 O 3 .

[0011] CN107555971 proposes an AZS product containing 31% to 45% of ZrO 2 , 9% to 14% of SiO 2 , 44% to 56% of Al 2 O 3 , 0.6% to 1.4% of Na 2 O, and at least one oxide in the group of B 2 O 3 , Y 2 O 3 , Li 2 O, Ta 2 O 5 , Nb 2 O 5 , P 2 O 5 and K 2 O.

[0012] With the development of the electrification of glass furnaces, refractory blocks, especially those close to the electrodes, must have the highest possible resistivity to avoid the risk of current deflection in the refractory.

[0013] In particular, the deflection of the current generates local heating through the Joule effect, which promotes the corrosion of the blocks. Inside and around the blocks carrying the electrodes, the intensification of the glass convection movement may also accelerate the corrosion. The glass convection movement has the property of destabilizing the glass-refractory interface and may bring hotter glass into contact with the refractory product.

[0014] There is a need for AZS refractory products with increased resistivity. Summary of the Invention

[0015] Overview of the present invention

[0016] The present invention proposes a cast refractory product, based on the mass percentages of oxides and totaling 100%, which comprises:

[0017]

[0018]

[0019] Ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is greater than 0.30.

[0020] As will be seen in more detail later in the specification, the product according to the present invention has increased resistivity. The inventors unexpectedly found that Na 2 O and K 2 O have different effects on the resistivity. In addition, the inventors found that within the content ranges determined by several criteria, in particular by the ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) and with a total Na 2 O + K 2 O content between 0.80% and 3.00%, Na 2 O and K 2 O not only increase the resistivity but also maintain feasibility.

[0021] The product according to the present invention may also include one or more of the following optional features, including when it conforms to the specific embodiments described below and when these optional features are compatible with the specific embodiments:

[0022] - The total porosity of the product is less than 10%, or even less than 5%;

[0023] - Preferably, the oxide accounts for more than 90%, more than 95%, more than 99%, or even substantially 100% of the product quality;

[0024] - ZrO 2 + HfO 2 The mass content 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%;

[0025] - SiO 2 The mass content 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%;

[0026] - Al 2 O 3 The mass content 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%;

[0027] - Sodium oxide Na 2 O and potassium oxide K 2 The total mass content of O is preferably greater than 0.85%, greater than 0.90%, greater than 0.95%, greater than 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%;

[0028] -Na 2 The mass content of O 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, Na 2 O exists as an impurity;

[0029] -K 2 The mass content of O 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 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%;

[0030] -Ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 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;

[0031] -B 2 O 3 exists as an impurity, and / or boron oxide B 2 O 3 has a mass content 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%;

[0032] -Y 2 O 3 has a mass content 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%;

[0033] -Iron oxide and titanium oxide Fe 2 O 3 +TiO 2 The total mass content of is less than 0.40%, preferably less than 0.30%, more preferably less than 0.20%;

[0034] - The total mass content of "other substances" 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%;

[0035] - "Other substances", namely, different from ZrO 2 , HfO 2 , SiO 2 , Al 2 O 3 , Na 2 O, K 2 , B 2 O 3 , Fe 2 O 3 and TiO 2 , consist only of impurities;

[0036] - The mass content of any "other substances", especially Ta 2 O 5 and / or Nb 2 O 5 is less than 0.4%, or even less than 0.3%, or even less than 0.2%, or less than 0.1%;

[0037] - 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%;

[0038] - The mass content of CaO is less than 0.4%, or even less than 0.3%;

[0039] - The mass content of BaO is less than 0.4%, or even less than 0.3%;

[0040] - The mass content of SrO is less than 0.4%, or even less than 0.3%;

[0041] - The mass content of MgO is less than 0.4%, or even less than 0.3%;

[0042] - The product is in the form of a block.

[0043] According to a specific embodiment, the cast refractory product according to the present invention contains, based on the mass percentage of oxides:

[0044]

[0045] The ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is greater than 0.50, or even greater than 0.60, or even greater than 0.65.

[0046] According to a particularly advantageous embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0047]

[0048]

[0049] The ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is greater than 0.65, or even greater than 0.70.

[0050] According to a particularly advantageous embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0051]

[0052] The ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is greater than 0.62, preferably greater than 0.65, preferably greater than 0.70.

[0053] According to a specific embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0054]

[0055] The ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is greater than 0.60, or even greater than 0.65, 0.70 or 0.75.

[0056] According to a specific embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0057]

[0058] According to a specific embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0059]

[0060] According to a specific embodiment, the cast refractory product according to the invention comprises, by mass percentage based on oxides:

[0061]

[0062] If the above optional features are not technically incompatible with each other, they can be combined together.

[0063] The present invention also relates to a method for manufacturing a refractory product according to the present invention, comprising the following steps carried out in sequence:

[0064] a) Mixing starting materials to form a feedstock,

[0065] b) Melting the feedstock until a molten material is obtained,

[0066] c) Casting the molten material and solidifying the molten material by cooling to obtain a refractory product,

[0067] Notably, the starting materials are selected such that the refractory product complies with the present invention.

[0068] Preferably, the lowest content of oxides or precursors of these oxides is systematically and methodically added. Preferably, the content of these oxides in the sources of other oxides in which they are present as impurities is considered.

[0069] Preferably, the cooling is controlled, preferably at a rate of less than 20 °C per hour, preferably at a rate of about 10 °C per hour.

[0070] The present invention also relates to a glass furnace comprising a refractory product according to the present invention, or a refractory product manufactured or capable of being manufactured by the method according to the present invention, especially in the area intended to be in contact with molten glass, especially in the vessel of the glass furnace, especially constituting an electrode support block, for example in the furnace bottom of such a vessel.

[0071] Thus, the present invention relates to a glass furnace comprising a vessel for containing molten glass or a vessel containing molten glass, the vessel comprising a block made of a product according to the present invention.

[0072] Definition

[0073] Generally, when a product is obtained by a method of melting a feedstock until a molten material is obtained and then solidifying the material by cooling, the product is said to be "melted".

[0074] A block is an object all of whose dimensions are greater than 10 mm. All dimensions of the block according to the present invention are preferably greater than 50 mm, preferably greater than 100 mm. The block according to the present invention can, for example, have a generally parallelepiped shape or a specific shape suitable for its use. Different from a layer, a block made of a cast refractory product is generally obtained by a method including operations of molding and demolding.

[0075] The bulk of the product according to the invention may have one, or even two or three external 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, before or after trimming / machining.

[0076] Unless otherwise stated, the content of all oxides in the product according to the invention is based on the mass percentage of the oxide. According to standard industrial practice, the mass content of the oxide of a metallic element refers to the total content of the element expressed in the form of the most stable oxide.

[0077] HfO 2 cannot be chemically separated from ZrO 2 However, according to the invention, HfO 2 is not intentionally added to the feed. Thus, HfO 2 represents only trace amounts of hafnium oxide, which are always present naturally in zirconium oxide sources in amounts usually less than 5%, more usually less than 2%. In the bulk according to the invention, the mass content of HfO 2 is less than 5%, preferably less than 3%, more preferably less than 2%. For clarity, it may be denoted by "ZrO 2 " or "ZrO 2 +HfO 2 " to represent the total content of zirconium oxide and trace hafnium oxide. Thus, HfO 2 is not included in "other substances".

[0078] The term "impurity" refers to an inevitable component introduced together with the starting materials or produced by reaction with these components. Impurities are not essential components but merely acceptable components. For example, compounds of the group consisting of oxides, nitrides, oxynitrides, carbides, carbon oxides, carbonitrides and metallic substances of iron, titanium, vanadium and chromium are impurities.

[0079] The total porosity is expressed as a percentage and is generally equal to 100×(1 - the ratio of the geometric density to the absolute density).

[0080] The geometric density is measured according to standard ISO 5016:1997 or EN 1094-4 and is expressed in g / cm 3 . Generally, it is equal to the ratio of the mass of the specimen to the bulk volume.

[0081] The value of the absolute density is expressed in g / cm 3 and can be measured by dividing the mass of the specimen by the volume of the specimen, which has been ground to substantially eliminate porosity. Detailed implementation mode

[0082] In the cast product according to the present invention, the content of ZrO 2 +HfO 2 is allowed to meet the requirements of high corrosion resistance. On the other hand, an excessive content is not conducive to the industrial feasibility of the bulk.

[0083] The hafnium oxide HfO present in the product according to the present invention 2 is preferably the hafnium oxide naturally present in the ZrO 2 source. Therefore, its content in the product according to the present invention is less than 4%, usually less than 2%, or even less than 1%.

[0084] The presence of SiO 2 especially enables the formation of an intergranular glass phase that contributes to the feasibility of the product due to its ability to effectively adapt to temperature deformation. Preferably, the mass content of SiO 2 is limited to limit the amount of the glass phase.

[0085] The presence of Na 2 O + K 2 O contributes to the feasibility of the product. Preferably, the mass content of Na 2 O + K 2 O is limited to limit the amount of the glass phase and especially to maintain good corrosion resistance to molten glass and good resistivity.

[0086] In order to have a ratio 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, (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52), and in order to increase the resistivity, the presence of K 2 O is necessary.

[0087] Na 2 O has an adverse effect on the resistivity. Therefore, the mass content of sodium oxide Na 2 O must be kept limited.

[0088] B 2 O 3 has an adverse effect on the feasibility. Therefore, the mass content of boron oxide B 2 O 3 must be kept limited.

[0089] Y 2 O 3 has an adverse effect on the feasibility and resistivity. Therefore, Y 2 O 3The mass content thereof must be kept limited.

[0090] According to the present invention, the mass content of Fe 2 O 3 + TiO 2 is less than 0.60%, preferably less than 0.50%, more preferably less than 0.30%. Preferably, the mass content of P 2 O 5 is less than 0.05%. Specifically, these oxides are harmful, especially for the exudation of refractory products or the coloring of glass, and their content must be limited to the trace amounts introduced as impurities together with the starting materials.

[0091] "Other substances" are oxide substances not listed above, i.e., substances different from ZrO 2 、HfO 2 、SiO 2 、Al 2 O 3 、Na 2 O、K 2 O、B 2 O 3 、Y 2 O 3 、TiO 2 and Fe 2 O 3 In one embodiment, "other substances" are limited to substances whose presence is not particularly desired and which are usually present as impurities in the starting materials.

[0092] Preferably, the product according to the present invention is in the form of a block, preferably in the form of at least one, preferably at least two, or even all blocks with external dimensions greater than 150 mm.

[0093] The total porosity of the product according to the present 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%.

[0094] The product according to the present invention can be conventionally manufactured according to the following steps a) to c):

[0095] a) Mixing the starting materials to form a feedstock,

[0096] b) Melting the feedstock until a molten material is obtained,

[0097] c) Solidifying the molten material by cooling to obtain a refractory product according to the present invention.

[0098] In step a), starting materials are selected to ensure the oxide content in the final product obtained at the end of step c). A person skilled in the art knows perfectly well how to select the starting materials for this purpose.

[0099] In step b), melting is preferably carried out by the combined action of a relatively long electric arc that does not produce any reduction and stirring that promotes reoxidation of the product.

[0100] For the target application, melting is preferably carried out under oxidizing conditions.

[0101] Preferably, the long-arc melting process described in French Patent No. 1,208,577 and its supplementary patents Nos. 75,893 and 82,310 is used.

[0102] The process consists in using an electric arc furnace in which an electric arc is triggered between the feed and at least one electrode spaced apart from the feed, and in adjusting the arc length such that its reducing action is minimized, while maintaining an oxidizing atmosphere above the molten bath and stirring the bath, for example by the action of the electric arc itself.

[0103] In step c), cooling is preferably carried out at a rate of less than 20 °C / hour, preferably at a rate of about 10 °C / hour, preferably in a mold of the desired size, taking into account the feedstock and any possible processing after step c).

[0104] Any conventional manufacturing method for melting zirconia-based products intended for applications in glass furnaces can be used, provided that the composition of the starting feedstock is such that a product with a composition conforming to that of the product according to the invention can be obtained.

[0105] Examples

[0106] The following non-limiting examples are given for the purpose of illustrating the invention.

[0107] In these examples, the following starting materials were used:

[0108] - Zirconia Q1 containing on average 99% of ZrO 2 + HfO 2 ,

[0109] - "Sable BE01 Bédouin" silica containing on average 99% of SiO 2 ,

[0110] - AC34 alumina containing on average 99% of Al 2 O 3 ,

[0111] - As a Na 2 O source, containing on average 99.5% of Na2 CO 3 sodium carbonate of

[0112] - As a K 2 O source, it contains 99.5% of K 2 CO 3 potassium carbonate.

[0113] The product is prepared by a conventional electric arc furnace melting process and then cast in a mold to obtain a block with a minimum size of 150 mm × 250 mm × 500 mm after trimming.

[0114] Chemical analysis

[0115] The average chemical analysis of the obtained product is given in Table 1; this is the chemical analysis of the liquid feed poured into the mold, given in mass percentage.

[0116] Example 5 contains 0.68% of Ta 2 O 5 .

[0117] For Example 5, different from ZrO 2 , HfO 2 , SiO 2 , Al 2 O 3 , B 2 O 3 , Na 2 O and K 2 O, and substances of Ta 2 O 5 (especially Fe 2 O 3 , TiO 2 and Y 2 O 3 (possibly present)) are impurities, where Y 2 O 3 < 0.2% and Fe 2 O 3 + TiO 2 < 0.3%.

[0118] In Table 1, the content of HfO 2 is always less than 4%. The ratio (K 2 O / 1.52) / (Na 2 O + K 2 O / 1.52) is called "Ratio".

[0119] Feasibility

[0120] Observe the external state of the obtained products. Their dimensions (three dimensions are greater than 150 mm and at least one dimension is at least 400 mm) enable the assessment of industrial feasibility. If there are through cracks, the feasibility is determined to be unsatisfactory. Then the product is cut in half to observe the filling. If incorrect filling occurs, the feasibility is regarded as unsatisfactory. Otherwise, the feasibility is regarded as satisfactory. All embodiments in the present invention have satisfactory feasibility.

[0121] Measurement of resistivity

[0122] In various embodiments of the produced blocks, cylindrical product rods with a diameter of 30 mm and a height of 30 mm are subjected to a potential difference of 1 volt at a frequency of 60 Hz at 1400 °C for the measurement of the resistivity R.

[0123] [Table 1]

[0124]

[0125] * indicates "outside the present invention".

[0126] It can be seen that when the Na 2 O content is less than 0.60%, a ratio greater than 0.30 allows achieving a resistivity value higher than the reference. When the ratio is greater than 0.60, or even greater than 0.62, or even greater than 0.65, the resistivity value increases significantly.

[0127] Obviously, the present invention thus provides a product that has remarkable properties in the environment of the container of a glass furnace, especially the furnace bottom.

[0128] It is beyond doubt that the present invention is not limited to the embodiments described and shown, which are provided for illustrative purposes only.

Claims

1. A fused-cast refractory product comprising, in percentages by mass based on oxides and totaling 100%, in, Ratio (K 2 O / 1.52) / (Na 2 O+K 2 O / 1.52) is greater than 0.

30.

2. The product according to the preceding claim, in, The ratio (K 2 O / 1.52) / (Na 2 O+K 2 O / 1.52) is greater than 0.

50.

3. A product as claimed in the immediately preceding claim, in, The ratio (K 2 O / 1.52) / (Na 2 O+K 2 O / 1.52) is greater than 0.

60.

4. A product as claimed in the immediately preceding claim, in, The ratio (K 2 O / 1.52) / (Na 2 O+K 2 O / 1.52) is greater than 0.

62.

5. The product according to the immediately preceding claim, in, The ratio (K 2 O / 1.52) / (Na 2 O+K 2 O / 1.52) is greater than 0.

65.

6. A product as claimed in any one of the preceding claims, in, The SiO 2 The mass content is less than 13.5%.

7. The product according to the immediately preceding claim, in, The SiO 2 The mass content is less than 13.0%.

8. A product as claimed in any one of the preceding claims, in, The SiO 2 The mass content is greater than 11.0%.

9. A product as claimed in any one of the preceding claims, in, The K 2 The mass content of O is greater than 0.60% and less than 2.00%.

10. The product according to any one of the preceding claims, in, The K 2 The mass content of O is greater than 0.70%.

11. The product according to the immediately preceding claim, in, The K 2 The mass content of O is greater than 0.80%.

12. The product according to the immediately preceding claim, in, The K 2 The mass content of O is greater than 1.00%.

13. A product as claimed in the immediately preceding claim, in, The K 2 The mass content of O is less than 1.80%.

14. A product as claimed in any one of the preceding claims, in, The ZrO 2 +HfO 2 The mass content is greater than 42.5% and less than 52.5%.

15. A product as claimed in any one of the preceding claims, in, The ZrO 2 +HfO 2 The mass content is greater than 43.5%.

16. A product as claimed in any one of the preceding claims, in, The ZrO 2 +HfO 2 The mass content is less than 51.0%.

17. The product according to the immediately preceding claim, in, The ZrO 2 +HfO 2 The mass content is less than 49.5%.

18. The product according to the immediately preceding claim, in, The ZrO 2 +HfO 2 The mass content is less than 48.0%.

19. A product as claimed in any one of the preceding claims, in, The Al 2 O 3 The mass content is less than 44.0% and greater than 30.0%.

20. The product according to the immediately preceding claim, in, The Al 2 O 3 The mass content is less than 42.0% and greater than 34.0%.

21. A product as claimed in any one of the preceding claims, in, The Na 2 The mass content of O is less than 0.55%.

22. The product according to the immediately preceding claim, in, The Na 2 The mass content of O is less than 0.50%.

23. A product as claimed in any one of the preceding claims, in, The Na 2 O+K 2 The mass content of O is less than 2.50%.

24. The product according to the immediately preceding claim, in, The Na 2 O+K 2 The mass content of O is less than 2.00%.

25. A glass melting furnace comprising a vessel intended to contain molten glass or a vessel containing molten glass, said vessel comprising a block made from a product as claimed in any one of the preceding claims.

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

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