HIGH ZIRCONIA REFRACTORY PRODUCT

Abstract

Cast and molten refractory product comprising, in mass percentages based on oxides and totaling 100%: ZrO2: to 100%; Hf2O: < 5%; SiO2: 8.0% to 11.0%; Al2O3: 4.0% to 6.5%; Na2O + K2O + B2O3: 0.40% to 1.00%; B2O3: < 0.60%; Y2O3: < 1.0%; Fe2O3 + TiO2: < 0.60%; other species: < 1.0%; with a SiO2 / (Na2O + K2O + B2O3) ratio between 10 and 19. No abbreviated figure.

Description

Title of the invention: HIGH ZIRCONIA REFRACTORY PRODUCT technical field

[0001] The invention relates to a molten refractory product with a high zirconia content and to a glass melting furnace comprising such a product. Previous technique

[0002] Glass melting furnaces generally comprise 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 rendering the glass unusable (which would reduce production yields) and is sufficiently durable to ensure a satisfactory furnace lifespan.

[0003] Among refractory blocks, a distinction is made between molten blocks and sintered blocks.

[0004] Unlike sintered blocks, fused blocks most often include a An intergranular glassy phase connects crystallized grains. The problems posed by sintered and fused blocks, and the technical solutions adopted to solve them, are therefore generally different. A composition developed to manufacture a sintered block is thus not, a priori, directly usable for manufacturing a fused block, and vice versa.

[0005] Cast blocks, often called "electro-fused" or "cast and melted," are obtained by melting a mixture of suitable raw materials in an electric arc furnace or by any other appropriate technique. The molten material is then conventionally poured into a mold and solidified. Generally, 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.

[0006] Very high zirconia (VHZ) fused blocks are known, generally containing more than 80%, or even more than 85%, zirconia by mass. They are known for their very high corrosion resistance and their ability not to color the glass produced and not to generate defects in the latter.

[0007] EP 403 387 describes high zirconia molten and cast products which contain, by mass percentages, 4 to 5% SiO2, about 1% Al2O3, 0.3% sodium oxide and less than 0.05% P2O5.

[0008] FR 2 932 475 describes high zirconia molten and cast products which contain, by mass percentages, 3.5 to 6.0% SiO2, 0.7 to 1.5% Al2O3, 0.05 to 0.80% boron oxide B2O3, 0.10 to 0.43% Na2O + K2O and less than 0.55% Fe2O3 + TiO2.

[0009] High zirconia fused blocks, such as ER 1195 produced and marketed by SEFPRO, are now widely used in glass furnaces. However, the need for ever-improving glass quality and longer furnace lifespans is driving the search for increasingly resistant refractory products that withstand molten glass, even under increasingly severe conditions.

[0010] There is a need for refractory products with a very high zirconia content exhibiting high resistance to molten glass while maintaining good feasibility.

[0011] , Description of the invention Summary of the invention

[0012] The invention provides a molten and cast refractory product comprising, in mass percentages based on oxides and totaling 100%:

[0013] ZrO2: 100% complement Hf2O: < 5% SiO2: 8.0% to 11.0% A12O3: 4.0% to 6.5% Na2O + K2O + B2O3: 0.40% to 1.00% B2O3: < 0.60% Y2O3: < 1.0% Fe2O3 + TiO2: < 0.60% other species: < 1.0% with a SiO2 / (Na2O + K2O + B2O3) ratio between 10.0 and 19.0.

[0014] As will be seen in more detail later in the description, such a composition gives a molten and poured product remarkable inertness with respect to molten glass. Tests have also shown good feasibility. A product according to the invention is therefore perfectly suited for use in a glass melting furnace or furnace throat.

[0015] A product according to the invention may also include one or more of the following optional features, including when it conforms to the particular embodiments described below and when these optional features are not incompatible with said particular embodiments:

[0016] - the total porosity of the product is less than 10%, or even less than 5%; - preferably, oxides represent more than 90%, more than 95%, more than 99%, or even approximately 100% of the product's mass; - the mass content of ZrO2 + HfO2 is less than 88.0%, or even less than 87.5%, or even less than 87.0%, or even less than 86.5%, or even less than 86.0% and / or greater than 82.0%, or even greater than 83.0%, or even greater than 83.5%, or even greater than 84.0%; the mass content of SiO2 is less than 10.8%, or less than 10.6%, or less than 10.5%, or less than 10.4%, or less than 10.3%, or less than 10.2%, or less than 10.1%, or less than 10.0% and / or greater than 8.1%, preferably greater than 8.2%, preferably greater than 8.3%, preferably greater than 8.4%, preferably greater than or equal to 8.5%, or greater than 8.6%, or greater than 8.7%, or greater than 8.8%, or greater than 8.9%; the mass content of A12O3 is less than 6.2%, or even less than 6.1%, or even less than 6.0%, or even less than 5.9%, or even less than 5.8%, or even less than 5.7%, or even less than 5.6% or less than 5.5%, or even less than 5.4%, or even less than 5.3%, or even less than 5.2%, or even less than 5.1% or less than 5.0% and / or greater than 4.1%, or even greater than 4.2%, or even greater than 4.3%, or even greater than 4.4%, or even greater than 4.5%; the sum of the mass contents of boron oxide B2O3, sodium oxide Na2O and potassium oxide K2O is preferably greater than 0.45%, preferably greater than 0.50%, preferably greater than 0.55%, preferably greater than 0.60%, or even greater than 0.65%, or even greater than 0.70%, or even greater than 0.75% and / or less than 0.95%, or even less than 0.90%, or even less than 0.85%, or even less than 0.80%; the sum of the mass contents of sodium oxide Na2O and potassium oxide K2O is preferably greater than 0.45%, preferably greater than 0.50%, preferably greater than 0.55%, preferably greater than 0.60%, or even greater than 0.65%, or even greater than 0.70% and / or less than 1.00%, or even less than 0.95%, less than 0.90%, less than 0.85%, less than 0.80%; the mass content of Na2O is greater than 0.45%, or even greater than 0.50%, or even greater than 0.55%, or even greater than 0.60%, or even greater than 0.65%, or even greater than 0.70% and / or less than 0.90%, or even less than 0.85%, or even less than 0.80%; K2O is present as an impurity or partially substitutes for Na2O, and the mass content of K2O is less than 0.70%, or even less than 0.60%, or even less than 0.50%, or even less than 0.40%, or even less than 0.30%; B2O3 is present as an impurity or partially substitutes for Na2O, and the mass content of boron oxide B2O3 is less than 0.55%, less than 0.50%, or even less than 0.40%, or even less than 0.30%; - the mass content of Y2O3 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%; - the sum of the mass contents of iron oxide and titanium oxide, Fe2O3 + TiO2, is less than 0.40%, preferably less than 0.30%, preferably less than 0.20%; - 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%; - the "other species" are made up only of impurities; - the mass content of any "other species" is less than 0.4%, or even less than 0.3%, or even less than 0.2%; - 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%; - the mass content of CaO is less than 0.4%, or even less than 0.3%; - the mass content of BaO is less than 0.4%, or even less than 0.3%; - the mass content of SrO is less than 0.4%, or even less than 0.3%; - the mass content of MgO is less than 0.4%, or even less than 0.3%; - the ratio of mass contents SiO2 / (Na2O + K2O + B2O3) is greater than 10.5, or even greater than 11.0, or even greater than 11.5, or even greater than 12.0 and / or less than 18.5, or even less than 18.0; - the ratio of the mass contents SiO2 / Al2O3 is greater than 1.20, or even greater than 1.30, or even greater than 1.40, or even greater than 1.50, or even greater than 1.60 and / or less than 2.60, or even less than 2.50; - the ratio of mass contents A12O3 / (Na2O + K2O) is less than 8.5 and / or greater than 5.5, or even greater than 6.0.

[0017] According to a particular embodiment, the invention provides a molten and cast refractory product comprising, in mass percentages based on oxides:

[0018] - SiO2: 8.5% to 11.0% A12O3: 4.0% to 6.0% Na2O + K2O: 0.50% to 1.00% B2O3: 0.00% to 0.40%.

[0019] According to a particular embodiment, the invention provides a molten and cast refractory product comprising, in mass percentages based on oxides:

[0020] - SiO2: 8.5% to 10.5% A12O3: 4.4% to 5.5% Na2O + K20: 0.55% to 0.95% B2O3: 0.00% to 0.30%.

[0021] The invention also relates to a method for manufacturing a refractory product according to the invention, comprising the following successive steps: a) mixing of raw materials to form a starting charge, b) melting of said starting charge until a molten material is obtained, c) pouring and solidifying said molten material by cooling to obtain a refractory product, This process is remarkable in that the said raw materials are chosen in such a way that the said refractory product conforms to the invention.

[0022] Preferably, the oxides for which a minimum content is required, or precursors of these oxides, are added systematically and methodically. Preferably, the contents of these oxides in the sources of the other oxides where they are present as impurities are taken into account.

[0023] 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.

[0024] 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 process according to the invention, in particular in a region intended to be in contact with molten glass, in particular in a tank or a groove of the glass melting furnace. Definitions

[0025] 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, followed by the solidification of this material by cooling.

[0026] A block is an object whose dimensions are all greater than 10 mm, preferably greater than 50 mm, and preferably greater than 100 mm. A block may, for example, have a general 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 involving molding and demolding operations.

[0027] Unless otherwise stated, all oxide contents in a product according to the invention are mass percentages 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.

[0028] HfO2 is not chemically dissociable from ZrO2. However, according to the present According to the invention, HfO2 is not intentionally added to the feedstock. Therefore, HfO2 refers only to traces of hafnium oxide, this oxide being naturally present in zirconium oxide sources at levels generally less than 5%, and generally less than 2%. In a block according to the invention, the mass content of HfO2 is less than 5%, preferably less than 3%, and preferably less than 2%. For clarity, the total content of zirconium oxide and traces of hafnium oxide can be referred to interchangeably as "ZrO2" or "ZrO2 + HfO2". HfO2 is therefore not included in "other species".

[0029] By "impurities" is meant unavoidable constituents introduced with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but merely tolerated. 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.

[0030] The total porosity, as a percentage, is classically equal to 100 x (1 - the ratio of the geometric density divided by the absolute density).

[0031] The geometric density is measured according to ISO 5016:1997 or EN 1094-4 and expressed in g / cm3. It is classically equal to the ratio of the mass of the sample divided by the apparent volume.

[0032] The absolute density value, expressed in g / cm3, can be measured by dividing the mass of a sample by the volume of that sample ground in such a way as to substantially eliminate porosity. Brief description of the drawings

[0033] Other features and advantages of the invention will become apparent upon reading the detailed description that follows and upon examination of the accompanying drawing, in which:

[0034] • [Fig. 1] represents the photograph of a product outside the scope of the invention (example 1*); and • [Fig.2] represents the photo of a product according to the invention (example 4).

[0035] The photos in figures 1 and 2 have been digitally processed to better show the asperities. Detailed description

[0036] In the molten and cast products according to the invention, the high ZrO2 content makes it possible to meet the requirements of high corrosion resistance without generating defects harmful to the quality of the glass.

[0037] The hafnium oxide, HfO2, present in the product according to the invention is the hafnium oxide naturally present in ZrO2 sources. Its content in a product according to the invention is therefore less than 5%, generally less than 2%.

[0038] The presence of SiO2 notably allows the formation of an intergranular glassy phase capable of efficiently accommodating deformations of the skeleton of zirconia. On the other hand, the addition of SiO2 should not exceed 11% because this addition is at the expense of the zirconia content and can therefore impair corrosion resistance.

[0039] The presence of Al2O3 in the quantities claimed according to the invention is particularly advantageous. Unexpectedly, it reduces, and even prevents, the transfer of zirconia from the refractory product to the molten glass. It also provides good flowability of the molten material in the mold.

[0040] The presence of Na2O+K2O contributes to the feasibility of the products. The mass content of Na2O+K2O is preferably limited in order to maintain good resistance to corrosion by molten glass. In a product according to the invention, the oxides Na2O and K2O are considered to have similar effects.

[0041] The simultaneous presence of B2O3 contributes to the feasibility of the products. However, B2O3 has an adverse effect on zirconia formation in the product, which can result in a detrimental effect on thermal cycling resistance. The mass content of boron oxide B2O3 must therefore remain limited.

[0042] Y2O3 may have an adverse effect on feasibility. The mass content of boron oxide Y2O3 must therefore remain limited.

[0043] In one embodiment, the Y2O3 content is greater than 0.2%.

[0044] According to the invention, the mass content of Fe2O3 + TiO2 is less than 0.5%, preferably less than 0.3%. Preferably, the mass content of P2O5 is less than 0.05%. Indeed, these oxides are detrimental, particularly to 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.

[0045] The "other species" are the oxide species not listed above, namely species other than ZrO2, Hf2O, SiO2, Al2O3, Na2O, K2O, B2O3, Y2O3, TiO2 and Fe2O3. In one embodiment, the "other species" are limited to species whose presence is not particularly desired and which are generally present as impurities in the raw materials.

[0046] Preferably, the product according to the invention is in the form of a block.

[0047] 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%.

[0048] A product according to the invention can conventionally be manufactured following 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.

[0049] In step a), the raw materials are chosen so as to guarantee the oxide content in the finished product obtained at the end of step c). A person skilled in the art knows by- carefully select the raw materials for this purpose.

[0050] In step b), the melting is preferably achieved through the combined action of a sufficiently long electric arc, which does not produce reduction, and stirring which promotes the reoxidation of the products.

[0051] It is preferable to carry out the melting under oxidizing conditions for the intended applications.

[0052] Preferably, the long arc fusion process described in French patent no. 1,208,577 and its additions no. 75893 and 82310 is used.

[0053] This process consists of using an electric arc furnace in which the arc is drawn between the charge and at least one electrode away from this charge and 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.

[0054] In step c), the cooling is preferably carried out at a rate of less than 20°C per hour, preferably at a rate of about 10°C per hour, preferably in a mold of the desired dimensions, taking into account the riser.

[0055] Any conventional process for manufacturing zirconia-based molten products for use in glass melting furnaces can be implemented, provided that the composition of the starting charge allows products to be obtained with a composition consistent with that of a product according to the invention.

[0056] In a product according to the invention, ZrO2 is substantially entirely (typically more than 95% by mass) in the form of zirconia; SiO2 and Al2O3 are found substantially entirely (typically more than 95% by mass) in the intergranular phase linking crystallized zirconia grains. This intergranular phase essentially comprises a glassy phase rich in SiO2 as well as mullite crystals. Examples

[0057] The following non-limiting examples are given for the purpose of illustrating the invention.

[0058] In these examples, the following raw materials were used: - of Q1 zirconia containing on average 99% ZrO2+ HfO2, - silica "BE01 Bedouin Sand" containing on average 99% SiO2, - AC34 type alumina containing on average 99% Al2O3, - sodium carbonate containing on average 99.5% Na2CO3 as a source of Na2O, - boron oxide containing on average 98% B2O3.

[0059] The products were prepared according to the conventional arc furnace melting process, then poured into a mold to obtain blocks measuring 150 mm x 250 mm x 400 mm after unmasking and selotation.

[0060] The chemical analysis of the products obtained is given in Table 1; it is an average chemical analysis, given in mass percentages. In these examples, K2O, Y2O3 and Fe2O3 + TiO2 are possibly present as impurities with K2O < 0.05%, Y2O3 < 0.2% and Fe2O3 + TiO2 < 0.3%.

[0061] The other species make up the remaining 100%. Feasibility

[0062] The external condition of the products obtained is observed. If a through crack is present, the feasibility (F) is judged unsatisfactory and noted as "0". The products are then cut in half to observe the filling. If the filling is incorrect, the feasibility (F) is judged unsatisfactory and noted as "0". Otherwise, the feasibility is judged satisfactory and noted as "1". Zirconia dissolution

[0063] To study the ability of the products to resist the dissolution of zirconia by molten glass, tests in autocrucibles were carried out at 1400°C and 1500°C to allow the study of the interfaces.

[0064] A sample of the refractory material to be tested is machined to create a cylindrical crucible with an external diameter of 50 millimeters and a height of 50 millimeters, in which a coaxial cylindrical hole with a diameter of 30 millimeters and a height of 30 millimeters is made. Powdered soda-lime glass (the composition of which is zirconia-free) is placed in the hole. The crucible thus filled is heated for 15 hours at the defined temperature. After cooling, the crucible is sliced ​​vertically to observe a midsection. The midsection is polished. The vertical glass-refractory material interface of this polished section is analyzed using microprobe probes to determine the percentage of zirconia in the glass up to 1000 microns from the boundary between the glass and the refractory material. The highest percentage of zirconia (D_Zr) is given in the table. Measurement of corrosion resistance in the groove

[0065] Corrosion resistance (CR) is measured on U-shaped samples obtained from a rectangular prism 75 mm long, 50 mm wide, and 50 mm high, cut from blocks and in which a central groove 45 mm wide and 30 mm high is machined. The samples are immersed (groove down) in a platinum crucible filled with borosilicate glass in a furnace at 1500°C or 1550°C for 200 hours. The loss of thickness of the central part (between the two legs of the U) due to corrosion is measured. The result is given as a percentage.

[0066] [Tables 1] ZrO2 (%) SiO2 (%) aî,o3 (%) Na2O + K2O (%) B2O3 (%) Na2O+ K2O + B2O3(%) SiO2 / (B2O3+Na2O+ K2O) SiO2 / AI2O3 AI2O3 / (Na2O + K2O) F RC (%) r 93.5 4.3 1.2 0.2 0.2 0.4 10.7 3.58 6.0 1 15.7 2.6 2* 93 5.2 1.5 0.2 0 0.2 26 3.47 7.5 0 10.8 NT 3* 84.8 9.7 3.9 0.63 0 0.63 15.5 2.52 6.2 1 11.0 NT 4 84 10.4 4.3 0.61 0 0.61 17 2.42 7.0 1 2.3 1.4 5 84 9.6 5.1 0.62 0 0.62 15.5 1.88 8.2 1 1.7 NT 6 84.4 9.3 5.4 0.77 0 0.77 12.1 1.73 7.0 1 2.9 0 7 84.5 8.8 5.6 0.49 0 0.49 18 1.57 11.4 1 NT NT S* 83.9 8.7 5.9 0.33 0 0.33 26.3 1.47 17.9 0 NT NT 9* 80.3 11.8 6.3 0.72 0 0.72 16.4 1.87 8.8 1 NM NT 10* 83.8 8.3 6.7 0.73 0 0.73 11.4 1.24 9.2 0 NT NT

[0067] * means "outside the invention", NT means "Not Tested" and NM means "Not Measurable »

[0068] Tests show that - an excessive alumina content leads to a degradation of feasibility (example 10*); - too high a silica content leads to poor corrosion resistance: indeed, D_Zr could not be measured on example 9* because the glass / refractory product interface was very irregular, indicating poor resistance of the refractory product to corrosion by molten glass; - the B2O3+Na2O+ K2O content must be sufficient and / or the SiO2 / (B2O3+Na2 O+ K2O) ratio limited to ensure the feasibility of the products (comparison of examples 7 and 8*); - compared to the conventional product, the products according to the invention lead to less zirconia dissolution in the molten glass while exhibiting good feasibility.

[0069] Corrosion resistance was measured at 1500°C on a sample of example 4 ([Fig.2]) and on a sample of example 1 ([Fig.1]): the corroded volume (RC) is 1.4% on example 4 according to the invention while it is 2.6% on the product of example 1.

[0070] As illustrated in Figures 1 and 2, the example outside the invention has a surface bearing a multitude of small craters 10, whereas the example according to the invention is essentially devoid of them. The product according to the invention thus has the advantage of resulting in a very regular corrosion profile.

[0071] It appears that enriching the products with alumina makes it possible to stabilize the composition of the glass at the interface with the glass, thus limiting the renewal of the glass at this interface, and therefore limiting the erosion phenomena of the refractory products.

[0072] Corrosion resistance was measured at 1550°C on a sample from Example 6 and on a sample of ER1711 marketed by SEFPRO (typically containing 41% ZrO2, 12% SiO2, 45% Al2O3 and 1% Na2O) as a reference product: the corroded volume is 0% on example 6 according to the invention whereas it is 17.4% on the reference product.

[0073] As is clear, the invention therefore provides a product which exhibits remarkable performance in the environment of a glass melting furnace tank or throat.

[0074] Of course, the invention is not limited to the embodiments described and represented, which are provided for illustrative purposes only.

Claims

Demands

1. Cast and molten refractory product comprising, in mass percentages on the basis of oxides and for a total of 100%: ZrO2: complement to 100% Hf2O: < 5% SiO2: 8.0% to 11.0% Al2O3: 4.0% to 6.5% Na2O + K2O + B2O3: 0.40% to 1.00% B2O3: < 0.60% Y2O3: < 1.0% Fe2O3 + TiO2: < 0.60% other species: < 1.0% with a SiO2 / (Na2O + K2O + B2O3) ratio between 10.0 and 19.

0.

2. Refractory product according to claim 1, wherein: - 83.0% < ZrO2 + HfO2 < 88.0%; and / or - 8.4% < SiO2 < 10.6%; and / or - 4.2% < Al2O3 < 6.1%; and / or - 0.45% < Na2O + K2O; and / or - B2O3 < 0.50%; and / or - Y2O3 < 0.40%; and / or - Fe2O3 + TiO2 < 0.40%; and / or - the ratio SiO2 / (Na2O + K2O + B2O3) is between 11.0 and 19.

0.

3. Refractory product according to claim 2, wherein: - 83.5% < ZrO2 + HfO2 < 87.0%; and / or - 8.5% < SiO2 < 10.5%; and / or - 4.4% < Al2O3 < 6.0%; and / or - 0.50% < Na2O + K2O; and / or - B2O3 < 0.40%; and / or - the ratio SiO2 / (Na2O + K2O + B2O3) is between 12.0 and 18.

0.

4. Refractory product according to any one of the preceding claims, wherein 8.5% < SiO2.

5. Refractory product according to any one of the preceding claims, comprising, in mass percentages based on the oxides: - SiO2: 8.5% to 11.0% - Al2O3: 4.0% to 6.0% - Na2O + K2O: 0.50% to 1.00% - B2O3: 0.00% to 0.40%.

6. Refractory product according to the immediately preceding claim, comprising, in mass percentages on the basis of the oxides: - SiO2: 8.5% to 10.5% - Al2O3: 4.4% to 5.5% - Na2O + K2O: 0.55% to 0.95% - B2O3: 0.00% to 0.30%.

7. Refractory product according to any one of the preceding claims, wherein the SiO2 / A12O3 ratio is greater than 1.2 and less than 2.6, and / or the A12O3 / (Na2O + K2O) ratio is less than 8.

5.

8. Refractory product according to any one of the preceding claims, having the form of a block in which all dimensions are greater than 10 mm.

9. Glass melting furnace comprising a block in a refractory product according to any one of the preceding claims.

10. Glass melting furnace according to the immediately preceding claim, in which the block is arranged in a vat or in a groove.

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