Method for producing float glass from mixture of mineral materials comprising calcium silicate

Abstract

The invention relates to a method for producing sheet glass, comprising melting a raw material mixture forming a molten bath, said raw material mixture comprising calcium silicate comprising, in weight percent, more than 30% SiO2 and more than 20% CaO, preferably at least 25% CaO, CaO and SiO2 together making up more than 60%, or even more than 70%, of the total weight of the silicate, or actually more than 80%, and the silicate is introduced into the mixture in the form of a powder having a median particle size of less than or equal to 400 microns.

Description

[0001] The present invention relates to the field of glass melting, in particular for the production of float glass as is prominently used in construction or even in the automotive industry.

[0002] Glass is typically made by melting raw materials in a furnace that include silica and at least one silica flux (e.g., sodium carbonate), and at least one alkaline earth metal (to impart hydrolysis resistance to the glass), such as limestone (calcium carbonate) and dolomite (CaMg(CO 3 ) 2 During melting, the carbonates release carbon dioxide, which bubbles help stir the molten material. In addition, some carbonates (such as dolomite) even release carbon dioxide during their melting process. 2 Before that, it breaks up into smaller particles according to a phenomenon called popping, which can be very violent and produces dust, which blocks and even corrodes the various pipes used in the furnace (chimneys, regenerators, etc.). Eliminating bubbles in the glass usually requires the addition of a refining agent (such as sodium sulfate), which releases sulfur oxides that attract residual carbon dioxide and water bubbles to the surface of the glass. However, sulfur oxides are a particularly corrosive gas. It is desirable to develop a glass production method that, for environmental reasons, produces as little CO as possible. 2 , while at the same time producing high-quality glass at an acceptable cost (especially in terms of the energy required to produce the glass).

[0003] In addition to the direct release of CO during the melting of the raw material pool 2 Furthermore, it is therefore important to consider the process for producing glass as a whole, taking into account other factors such as the cost of raw materials, the transportation of raw materials, or even the energy costs for supplying and melting said raw materials.

[0004] The present invention relates to a raw material mixture for preparing molten glass, wherein the target composition thereof has the following formula in terms of weight percentage:

[0005] -SiO 2 : 65 to 80%, preferably 70 to 75%,

[0006] -Na 2 O: 8 to 20%, preferably 10 to 20%,

[0007] -CaO: 5 to 20%, preferably 5 to 15%,

[0008] -MgO: 0 to 10%, preferably 0 to 7%,

[0009] -Al 2 O 3 : 0 to 10%, preferably 0.5 to 3%,

[0010] -K 2 O: 0 to 10%, preferably 0 to 2%,

[0011] - Iron oxide: 0 to 15%, preferably 0 to 10%,

[0012] Other (one or more) oxides: 0 to 5% in total, of which less than 2% is preferred. 2 O 3 , and very preferably less than 1% B 2 O 3 .

[0013] The remainder thereof consists of unavoidable impurities.

[0014] The raw material mixture is intended to be heated to a certain temperature and under conditions to melt it, so as to obtain glass having the target composition.

[0015] The originality of the invention lies in the choice of raw materials. In fact, contrary to the prejudice generally held in the field and indicated by the previously cited publications, it has been found that in a process for producing flat glass, silicates can be used as raw materials in order to limit the energy consumption of its production process while maintaining good homogeneity of the final glass.

[0016] According to the present invention, the Applicant Company has discovered that the particle size of such mineral raw materials should also be taken into account when making the initial mixture in order to limit the energy consumption of such a process for producing flat glass.

[0017] Thus, according to the first aspect, for soda-lime-silica glass, among the various oxides constituting the glass, calcium oxide has the greatest influence on the homogeneity of the glass because its optical index is different from that of silicon dioxide (the main component of the glass lattice). However, CaO is essential in the composition of flat glass: it is cheap and easily found in nature, it enhances hydrolysis resistance, and helps control the viscosity and liquidus temperature of the molten pool of the raw materials.

[0018] However, inhomogeneous glasses can easily exhibit "waviness", areas of localized variation in refractive index due to compositional variations. Sometimes, even if the variation in calcium oxide weight is less than 0.1%, undetectable by conventional analytical methods, these variations can lead to optically observable distortions.

[0019] For soda-lime-silica glass used in the production of flat glass, standard limestone has a PSD (particle size distribution) of: median diameter D 50About or greater than 600 microns, with a maximum particle size of up to 2 mm or even 3 mm. In order to improve the homogeneity of the glass, it may be considered to reduce the particle size distribution of the raw materials, and in particular the PSD of the limestone used in the initial pool of raw materials, as shown in the publication "Influence of limestone grain size on glass homogeneity, Glass Technology, Society of Glass Technology, 2010, 51 (3), page 116".

[0020] In the attached [ Figure 1 ] In the conventional glass melting furnace shown in FIG. 1 , if such a reduction in PSD is considered, another aspect of the raw materials must also be considered.

[0021] Figure 1 A furnace 2 for melting raw materials is schematically shown. The raw materials are fed into the furnace 7 as a mixture in the form of a dense mass 1. The mass 1 initially floats on the molten glass 6. The lower surface of the mass is first melted by convection of the molten glass under the action of a resistor 4 (electric auxiliary heating) located in the lower part of the furnace. Bubblers 8 enhance the convection of the glass and thus mechanically lead to a better homogeneity of the glass. The upper surface of the mass is also heated by radiation by a series of burners 3 located in the side walls of the furnace, as follows Figure 1 Schematically shown. After the block is melted, foaming can be observed due to the clarification of the glass 5.

[0022] Experiments carried out by the applicant company have shown that the heating efficiency of the burner 3 is related to the emissivity of the raw materials used, and in particular the calcium source used. Thus, raw materials with low emissivity create a heat mirror on the surface of the tile, which reduces the melting kinetics and increases the energy consumption of the furnace to achieve the same degree of melting.

[0023] If we thus exert an influence on the particle size distribution (PSD) of the raw materials, and in particular the PSD of the calcium source used, a major disadvantage is that the emissivity of the raw materials decreases. Lower emissivity therefore means lower heat transfer efficiency. Thus, while the use of finer-grained limestone improves on the one hand the chemical and optical homogeneity of the glass, and in particular the distribution of calcium oxide in the final glass, on the other hand it increases the energy consumption of the furnace, since the energy transfer is less favorable.

[0024] Based on these two antagonistic effects, limestone with a median particle size of about 600 microns, or even larger than 600 microns, is usually used as the raw material source of calcium (or CaO in the final glass).

[0025] The object of the present invention is therefore to propose a method for producing glass that provides a homogeneous distribution of calcium oxide in the final glass while reducing the energy consumption required for said production.

[0026] More precisely, the present invention relates to a method for producing glass having a target composition, comprising melting a mixture of raw materials constituting a molten pool, wherein the target composition satisfies the following criteria (in weight percentages):

[0027] SiO 2 : 65 to 80%, preferably 70 to 75%,

[0028] Na 2 O: 8 to 20%, preferably 10 to 20%,

[0029] CaO: 5 to 20%, preferably 5 to 15%,

[0030] MgO: 0 to 10%, preferably 0 to 7%,

[0031] Al 2 O 3 : 0 to 10%, preferably 0.5 to 3%,

[0032] K 2 O: 0 to 10%, preferably 0 to 2%,

[0033] Iron oxide: 0 to 15%, preferably 0 to 10%,

[0034] Other (one or more) oxides: 0 to 5% in total, of which less than 2% is preferred. 2 O 3 , and very preferably less than 1% B 2 O 3 .

[0035] The remainder consists of unavoidable impurities,

[0036] The method is characterized in that the raw material mixture in the molten bath contains calcium silicate, which contains more than 30% by weight of SiO 2 and more than 20% CaO, preferably at least 25% CaO, CaO and SiO 2 Together they represent more than 60%, even more than 70% or indeed even more than 80% of the total weight of the silicates, and the calcium silicates are introduced into the mixture in the form of a powder having a median particle size less than or equal to 400 microns.

[0037] According to preferred but non-limiting embodiments within the scope of the present invention:

[0038] - The calcium silicate has the following composition (by weight percentage):

[0039] -SiO 2 : 30 to 60%, preferably 40 to 55%,

[0040] -CaO: 25 to 55%, preferably 35 to 50%,

[0041] -Fe 2 O 3 : 0 to 4%, for example 0.1 to 0.5%,

[0042] -Al 2 O 3 : 0 to 8%, for example 0.5 to 2%,

[0043] -CO 2 : 0 to 20%, in particular 0 to 15%,

[0044] - Less than 5% of other oxides, preferably less than 3% of other oxides.

[0045] The calcium silicate is introduced into the mixture in the form of a powder having a median particle size of between 20 and 400 microns, preferably between 30 and 350 microns and very preferably between 40 and 300 microns.

[0046] The calcium silicate is introduced into the mixture in the form of a powder having a maximum diameter of less than 1500 micrometers, preferably less than 1250 micrometers and very preferably less than 1000 micrometers.

[0047] - The raw material mixture contains:

[0048] - the calcium silicate,

[0049] - silicon dioxide, especially in the form of sand,

[0050] - at least one sodium source, preferably selected from sodium hydroxide NaOH, sodium carbonate Na 2 CO 3 or sodium hydroxide NaOH and sodium carbonate Na 2 CO 3 A mixture of

[0051] - optionally at least one magnesium source chosen from mixed oxides of magnesium with at least one element chosen from Si, Ca or magnesium hydroxide,

[0052] -Optionally feldspar (K,Na)AlSi 3 O 8 , or other aluminum sources, such as hydrated alumina or calcined alumina, or phonolite or nepheline or slag,

[0053] -optionally limestone CaCO3 ,

[0054] - optionally dolomite,

[0055] - Optionally recycled glass cullet.

[0056] - The raw material mixture contains sodium hydroxide as a sodium source.

[0057] The raw material mixture contains magnesium silicate as a source of magnesium, the mineral magnesium silicate preferably containing more than 30% by weight of SiO 2 and more than 10% MgO, preferably more than 15% MgO, MgO and SiO 2 Together they represent more than 60%, even more than 70% or indeed even more than 75% of the total weight of the source.

[0058] - The magnesium source is magnesium silicate having the following composition, in weight percentage:

[0059] -SiO 2 : 40 to 55%, preferably 45 to 50%,

[0060] -Al 2 O 3 : 0 to 10%, for example 1 to 10%,

[0061] -MgO: 20 to 40%, preferably 25 to 35%,

[0062] -Fe 2 O 3 : 0 to 4%, for example 1 to 3%,

[0063] - less than 5% of other oxides, preferably less than 3% of other oxides,

[0064] - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

[0065] - The magnesium source is magnesium silicate having the following composition, in weight percentage:

[0066] -SiO 2 : 55 to 70%, preferably 58 to 65%,

[0067] -Al 2 O 3 : 0 to 10%, for example 1 to 10%,

[0068] -MgO: 20 to 40%, preferably 25 to 35%,

[0069] -Fe 2 O3 : 0 to 4%, for example 0.5 to 2%,

[0070] - less than 5% of other oxides, preferably less than 3% of other oxides,

[0071] - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

[0072] - The magnesium source is magnesium silicate having the following composition, in weight percentage:

[0073] -SiO 2 : 30 to 50%, preferably 35 to 45%,

[0074] -Al 2 O 3 : 0 to 10%, for example 1 to 5%,

[0075] -MgO: 25 to 45%, preferably 30 to 40%,

[0076] -Fe 2 O 3 : 0 to 10%, for example 5 to 10%,

[0077] - less than 5% of other oxides, preferably less than 3% of other oxides,

[0078] - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

[0079] - The magnesium source is magnesium hydroxide having the following composition, in weight percentage:

[0080] -MgO: 50 to 75%, preferably 55 to 70%,

[0081] -H 2 O: 10 to 35%, preferably 25 to 35%,

[0082] -SiO 2 : 0 to 10%, for example 0.5 to 5%,

[0083] -CaO: 0 to 5%, for example 0.5 to 2%,

[0084] -Fe 2 O 3 : 0 to 4%, for example 0.5 to 2%,

[0085] Less than 5% other oxides, preferably less than 3% other oxides.

[0086] - The raw materials of the molten pool include the calcium silicate and a magnesium source (such as magnesium silicate), as described above.

[0087] - Introducing the recovered glass cullets into the melting bath.

[0088] - The recycled glass cullet accounts for 5 to 70% of the total weight of the molten bath.

[0089] The silicates are natural silicates, ie they are used in their original geological composition after extraction from their deposits, in particular without being chemically altered to modify their original mineralogical composition, ie the silicates have not undergone chemical transformations.

[0090] -The production method comprises the following steps:

[0091] a) selecting raw materials to form a molten pool as described above,

[0092] b) determining the amount of the raw materials required to obtain the glass of the target composition,

[0093] c) mixing the materials according to the amounts,

[0094] d) melting the mixture under conditions to obtain the glass and cooling it.

[0095] The invention also relates to a raw material mixture as described above, and in particular comprises calcium silicate, said calcium silicate comprising more than 30% by weight of SiO 2 and more than 20% CaO, preferably more than 25% CaO, CaO and SiO 2 Together they represent more than 60%, even more than 70%, or indeed even more than 80% of the total weight of the silicates, and wherein the silicates are introduced into the mixture in the form of a powder having a median particle size less than or equal to 400 microns.

[0096] The present invention relates in particular to a raw material mixture comprising and preferably consisting of the following components:

[0097] - the calcium silicate,

[0098] - silicon dioxide, especially in the form of sand,

[0099] - at least one sodium source, preferably selected from sodium hydroxide NaOH, sodium carbonate Na 2 CO 3 or sodium hydroxide NaOH and sodium carbonate Na 2 CO 3 A mixture of

[0100] - optionally at least one magnesium source chosen from mixed oxides of magnesium with at least one element chosen from Si, Ca or magnesium hydroxide,

[0101] -Optionally feldspar (K,Na)AlSi 3 O 8 , or another source of aluminum, such as hydrated or calcined alumina, or phonolite or nepheline or slag,

[0102] -optionally limestone CaCO 3 ,

[0103] - optionally dolomite,

[0104] - Optionally recycled glass cullet.

[0105] Unless otherwise stated, all particle size values ​​(median diameter D50, maximum diameter D max ) are given in mass and are obtained by conventional sieving techniques, in particular for the calcium silicates according to the invention.

[0106] The invention will be better understood by reading the following examples which are intended to illustrate the advantages of the invention without, of course, limiting the invention to any aspect described. Example

[0107] In the following examples, different raw material mixtures have been prepared in order to compare the same final glass composition with the mixtures currently used in glass production, which essentially have the following composition:

[0108] Table 1

[0109] element Weight% <![CDATA[SiO 2 ]]> 73.1 CaO 9.5 MgO 2.0 <![CDATA[Al 2 THE 3 ]]> 1.1 <![CDATA[Fe 2 THE 3 ]]> 0.1 <![CDATA[Na 2 The]]> 13.5 <![CDATA[K 2 The]]> 0.3

[0110] Embodiment 1 (Prior Art)

[0111] According to the first embodiment, glass corresponding to the aforementioned composition is synthesized according to the current technology.

[0112] Table 2 below gives the proportions of various raw materials and the final composition of the glass obtained therefrom:

[0113] Table 2

[0114]

[0115] NM: Not Measured

[0116] The particle size of various raw materials is determined by sieving.

[0117] A representative sample of approximately 100 g was measured (accuracy 10 -2The test sample is placed on the upper sieve of a sieve column (standard NF X 11501). The sieve column is shaken for 5 minutes in a ROTAP sieve analyzer (Retsch AS200 TAP). The retentate in the first sieve containing the particles is weighed (accuracy 10 -2 Proceeding in the same manner, add the retentate from each sieve to the retentate of the previous sieve and record the cumulative mass each time.

[0118] The results are expressed as cumulative % relative to the final total mass MF.

[0119] X1% = M1 x 100 / MF

[0120] X1 = Cumulative retention on screen 1%

[0121] M1 = the mass of the accumulated material on screen 1

[0122] MF = final product quality.

[0123] This calculation is performed for each nominal mesh size.

[0124] D50 is calculated by interpolating the upper and lower particle sizes closest to 50%.

[0125] Specifically, D 50 Usually determined by the following equation:

[0126] D 50 =[T<50%]+(50%-[X<50%])×([T<50%]-[T>50%]) / ([X<50%]-[X>50%])

[0127] in:

[0128] T<50% = sieve openings with less than 50% retention

[0129] T>50% = sieve openings with more than 50% retention

[0130] X<50% = Cumulative retention % when T<50%

[0131] X>50% = Cumulative retention % when T>50%

[0132] This therefore allows us to infer the particle size distribution by weight as reported in Tables 2 to 4.

[0133] Example 2 (Comparative Example)

[0134] In this example, the same raw materials as in Example 1 are used, but limestone with finer particle size, i.e., D 50 Equal to 114 microns.

[0135] Embodiment 3:

[0136] In this example, the raw material mixture is as shown in Table 3 below.

[0137] In order to replace the limestone in this initial mixture, another mineral material is introduced as reagent, this reagent consisting of a calcium silicate according to the invention, ie with a median diameter D50 equal to 107 micrometers.

[0138] Analysis using conventional techniques showed that the natural mineral material had the composition described in Table 3 below:

[0139] Table 3

[0140]

[0141]

[0142] Embodiment 4:

[0143] In this example, the same raw materials as in Example 3 were used, but calcium silicate with a larger particle size, i.e., a particle size D of 826 microns was used. 50 .

[0144] Table 4 below shows the particle size characteristics of various calcium sources used as raw materials in the previous examples, measured according to the method described above:

[0145] Table 4

[0146]

[0147] Take the following measurements:

[0148] 1) The emissivity of the calcium source used is measured by the reflectance spectrum using the law of conservation of energy for opaque materials: absorbance α(λ,T) + reflectivity ρ(λ,T) = 1. According to Kirchhoff's law, the spectral emissivity can be expressed as total reflectivity,

[0149] ε(λ,T)=α(λ,T)

[0150] in:

[0151]

[0152] Among them B T is the spectral irradiance of a black body at a temperature T of 2000°C, corresponding to the temperature of the air-gas flame of the burner.

[0153] Hemispherical reflectance measurements between 300 and 2500 nm were performed at room temperature using a 150 mm integrating sphere mounted on a Lambda spectrophotometer, using a Spectralon plate as a reflectance reference.

[0154] For ease of operation, the sample was subjected to a 0.4 ton / cm 2 Press with force and moisten with 10% water.

[0155] 2) Based on the following [ Figure 1 The mixture of the above example was melted in a typical soda-lime-silica glass furnace using the flame technique schematically shown in FIG.

[0156] Measuring the energy consumed in melting a mixture in a furnace:

[0157] In the various melting tests corresponding to the above examples, the gas consumption was adjusted in order to maintain a similar temperature profile in the furnace and at all points thereof. From this the gas consumption and therefore the energy required to achieve the same heating point was derived.

[0158] 3) CaO homogeneity in the final glass:

[0159] As previously described, samples of the same mixture derived from the raw materials were melted in a cylindrical platinum crucible. The samples were heated in air at 1480°C for 2 hours. The cooled glass was then cored and cut to obtain a slide containing a cross section of a cylinder. The slide was polished, carbon metallized and analyzed using a 15kV electron microprobe. The analysis included determining the mass percentage of CaO at 100 measurement points over the entire height of the slide (or molten sample), with a step length of 250 microns.

[0160] Therefore, the average CaO concentration and standard deviation can be calculated. The standard for CaO homogeneity in the glass is the standard deviation divided by the average concentration (σ CaO / [CaO]) ratio is provided.

[0161] The results obtained are reported in Table 5 below:

[0162] Table 5

[0163]

[0164] According to Example 3 of the invention, in which a calcium source of the calcium silicate composition according to the invention is used as the raw material of the molten bath, it is possible to regulate the energy of the first burner 1 (closest to the charging point, i.e. the entrance of the raw material into the furnace), maintaining a reduction of about 10% in energy consumption. In addition, as mentioned above, in the case of Example 3 of the invention, the homogeneity of the calcium oxide appears to be improved.

[0165] To evaluate the optical quality (or homogeneity) of the glass, the "shadow imaging" technique is used, which reveals variations in the refractive index and / or local variations in thickness. Depending on the type of defect, only defects due to variations in the refractive index or variations in chemical homogeneity can be filtered, as described in publication WO2002012869A1. Periodically, samples are taken from the entire length of the glass ribbon and the intensity of the defect is measured (0 if there is no defect, 1 if the defect is not too obvious, 2 if it is more obvious, etc.), each intensity value being defined using a reference sample.

[0166] An assessment or "rating" is thereby determined which is the average value calculated from the glass strength as defined using the reference sample and a production run at 9.5 mm thick glass.

[0167] The results obtained for the glasses in Example 1 and Example 3 are reported in Table 6 below.

[0168] Table 6

[0169]

[0170] It can be seen that Example 3 according to the present invention has fewer defects than Reference Example 1.

Claims

1. A method for producing glass having a target composition, comprising melting a mixture of raw materials constituting a molten pool, wherein the target composition satisfies the following criteria, in weight percentage: SiO 2 : 65 to 80%, preferably 70 to 75%, Na 2 O: 8 to 20%, preferably 10 to 20%, CaO: 5 to 20%, preferably 5 to 15%, MgO: 0 to 10%, preferably 0 to 7%, Al 2 O 3 : 0 to 10%, preferably 0.5 to 3%, K 2 O: 0 to 10%, preferably 0 to 2%, Iron oxide: 0 to 15%, preferably 0 to 10%, (One or more) other oxides: 0 to 5% in total, The remainder consists of unavoidable impurities, The method is characterized in that the raw material mixture contains calcium silicate, which contains more than 30% by weight of SiO 2 and more than 20% CaO, preferably at least 25% CaO, CaO and SiO 2 Together they represent more than 60%, even more than 70% or indeed even more than 80% of the total weight of said silicates, and are characterised in that said calcium silicate is introduced into the mixture in the form of a powder having a median particle size less than or equal to 400 microns.

2. The production method according to claim 1, wherein the calcium silicate has the following composition, by weight percentage: -SiO 2 : 30 to 60%, preferably 40 to 55%, -CaO: 25 to 55%, preferably 35 to 50%, -Fe 2 O 3 : 0 to 4%, for example 0.1 to 0.5%, -Al 2 O 3 : 0 to 8%, for example 0.5 to 2%, -CO 2 : 0 to 20%, in particular 0 to 15%, - Less than 5% of other oxides, preferably less than 3% of other oxides.

3. The method according to any one of the preceding claims, wherein the calcium silicate is introduced into the mixture in the form of a powder having a median particle size of 20 to 400 microns, preferably 30 to 350 microns and very preferably 40 to 300 microns.

4. The method according to any one of the preceding claims, wherein the calcium silicate is introduced into the mixture in the form of a powder having a maximum diameter of less than 1500 microns, preferably less than 1250 microns and very preferably less than 1000 microns.

5. The method according to any one of the preceding claims, wherein the raw material mixture comprises: - the calcium silicate, - silicon dioxide, especially in the form of sand, - at least one sodium source, which is preferably selected from sodium hydroxide NaOH, sodium carbonate Na 2 CO 3 or sodium hydroxide NaOH and sodium carbonate Na 2 CO 3 A mixture of - optionally at least one magnesium source chosen from mixed oxides of magnesium with at least one element chosen from Si, Ca or magnesium hydroxide, -Optionally feldspar (K,Na)AlSi 3 O 8 , or another source of aluminum, such as hydrated or calcined alumina, or phonolite or nepheline or slag, -optionally limestone CaCO 3 , - optionally dolomite, - Optionally recycled glass cullet.

6. The method according to any one of the preceding claims, wherein the raw material mixture comprises sodium hydroxide as a sodium source.

7. The method according to any one of the preceding claims, wherein the raw material mixture comprises magnesium silicate as a source of magnesium, the mineral magnesium silicate preferably comprising more than 30% by weight of SiO 2 and more than 10% MgO, preferably more than 15% MgO, MgO and SiO 2 Together they represent more than 60%, or even more than 70%, or indeed even more than 75% of the total weight of the source.

8. The process according to the preceding claim, wherein the magnesium source is a magnesium silicate having the following composition, expressed in weight percentages: -SiO 2 : 40 to 55%, preferably 45 to 50%, -Al 2 O 3 : 0 to 10%, for example 1 to 10%, -MgO: 20 to 40%, preferably 25 to 35%, -Fe 2 O 3 : 0 to 4%, for example 1 to 3%, - less than 5% of other oxides, preferably less than 3% of other oxides, - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

9. The method of claim 8, wherein the magnesium source is magnesium silicate having the following composition, in weight percent: -SiO 2 : 55 to 70%, preferably 58 to 65%, -Al 2 O 3 : 0 to 10%, for example 1 to 10%, -MgO: 20 to 40%, preferably 25 to 35%, -Fe 2 O 3 : 0 to 4%, for example 0.5 to 2%, - less than 5% of other oxides, preferably less than 3% of other oxides, - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

10. The method of claim 8, wherein the magnesium source is magnesium silicate having the following composition, in weight percent: -SiO 2 : 30 to 50%, preferably 35 to 45%, -Al 2 O 3 : 0 to 10%, for example 1 to 5%, -MgO: 25 to 45%, preferably 30 to 40%, -Fe 2 O 3 : 0 to 10%, for example 5 to 10%, - less than 5% of other oxides, preferably less than 3% of other oxides, - Optionally water, in particular in the form of hydroxide(s), is present in the source, preferably in an amount of less than 20%, and in particular between 5 and 15%.

11. The method according to any one of claims 1 to 6, wherein the magnesium source is magnesium hydroxide having the following composition, in weight percentage: -MgO: 50 to 75%, preferably 55 to 70%, -H 2 O: 10 to 35%, preferably 25 to 35%, -SiO 2 : 0 to 10%, for example 0.5 to 5%, -CaO: 0 to 5%, for example 0.5 to 2%, -Fe 2 O 3 : 0 to 4%, for example 0.5 to 2%, Less than 5% other oxides, preferably less than 3% other oxides.

12. A method according to any one of the preceding claims, wherein the raw materials of the molten bath comprise the calcium silicate and a source of magnesium, such as magnesium silicate, in particular as described in any one of the preceding claims 8 to 11.

13. The method according to any one of the preceding claims, wherein recycled glass cullet is introduced into the molten bath.

14. The method according to the preceding claim, wherein the recycled glass cullet represents 5 to 70% of the total weight of the molten bath.

15. A raw material mixture as claimed in any one of the preceding claims, comprising calcium silicate containing more than 30% by weight of SiO 2 and more than 20% CaO, preferably more than 25% CaO, CaO and SiO 2 Together they represent more than 60%, even more than 70% or indeed even more than 80% of the total weight of the silicates, and wherein the calcium silicate is introduced into the mixture in the form of a powder having a median particle size less than or equal to 400 microns.

16. The raw material mixture according to the preceding claim, comprising: - the calcium silicate, - silicon dioxide, especially in the form of sand, - at least one sodium source, which is preferably selected from sodium hydroxide NaOH, sodium carbonate Na 2 CO 3 or sodium hydroxide NaOH and sodium carbonate Na 2 CO 3 A mixture of - optionally at least one magnesium source chosen from mixed oxides of magnesium with at least one element chosen from Si, Ca or magnesium hydroxide, -Optionally feldspar (K,Na)AlSi 3 O 8 , or another source of aluminum, such as hydrated or calcined alumina, or phonolite or nepheline or slag, -optionally limestone CaCO 3 , - optionally dolomite, - Optionally recycled glass cullet.

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