PROCESS FOR MANUFACTURING GLASS FIBERS FROM MINERAL MATERIALS INCLUDING ANHYDROUS SODIUM HYDROXIDE

Abstract

The invention relates to a raw material mixture for the preparation of molten glass for the manufacture of glass fibers having a target composition, comprising melting a raw material mixture, in which sodium hydroxide in anhydrous form and preferably in the form of a set of particles having an apparent density of less than 1.2 g / cm3, more preferably an apparent density of less than 1 g / cm3 is used as the sodium source.

Description

Title of the invention: PROCESS FOR MANUFACTURING GLASS FIBERS FROM MINERAL MATERIALS INCLUDING ANHYDROUS SODIUM HYDROXIDE

[0001] The invention relates to the field of melting a mixture of raw materials, in particular for the manufacture of glass wool as used in particular in the field of thermal and / or acoustic insulation of buildings or others. According to another aspect, the invention also relates to the manufacture of C glass used in particular in the field of textile fibers and composite materials.

[0002] The manufacture, in particular by the applicant company, of glass wool by melting and fiberizing natural and abundant raw materials (sand or volcanic rock) is a process known and mastered for a long time. The insulating products thus obtained are in the form of a glass wool "mattress" composed of a structure varying from flexible to rigid and trapping air in a stable and immobile manner in the tangle of fibers.

[0003] Glass wool has excellent thermal and acoustic properties which have given it a prominent place in the insulation of residential and non-residential buildings (tertiary, commercial, industrial) for over 80 years. The forms in which glass wool is marketed are varied: rolls, flexible or semi-rigid panels to be unrolled, rigid panels, shells, sheets or flakes.

[0004] Thanks to its tangled structure generating a multitude of small cavities, glass wool is a porous material that traps air. The still air trapped in these pores gives glass wool a strong insulating power with a minimum of material.

[0005] The basis for the manufacture of glass wool or C glass is quarry sand (naturally abundant) to which fluxes such as sodium carbonate and at least one alkaline earth metal are added (to give the glass resistance to hydrolysis) such as limestone (calcium carbonate) and dolomite (CaMg(CO3)2). In some embodiments, boron may also be introduced to give it better chemical and hydrolytic resistance (particularly for C glass) or to improve its thermal properties, particularly for the glass plate. The fiberization is carried out under conditions such that it is complete (no residues such as unmelted material). The fiberization is carried out by centrifugation through perforated plates. The molten material passes into a die and then into continuous fiberization plates from which it emerges in the form of glass threads which are sprayed with polymer (the binder). to form a mattress. After adding binders and other elements specific to each use, the wool mattress is polymerized and calendered.

[0006] In addition to the criteria of quality and industrial and economic feasibility, which have been added in recent years to that of the biodegradable nature of glass wool, namely its capacity to dissolve rapidly in a physiological environment, with a view to preventing any potential pathogenic risk linked to the possible accumulation of the finest fibres in the body by inhalation, a glass wool composition adapted accordingly has been proposed in application EP 399320, to which reference will be made for more details on this technique.

[0007] At the same time, a process is also known for the manufacture of glass fibers, in particular C glass fibers.

[0008] C glass is a glass specially designed for its better chemical resistance to solvents and water. The raw materials are melted and the resulting glass passes through orifices called bushings. The bushings are generally made of Pt. The glass strands, after leaving the bushing, are cooled in air or steam to form a mattress.

[0009] It can be used in the form of a fiber about 5 microns thick and 10 to 4000 microns long, or even up to a few centimeters long.

[0010] The good chemical resistance of borosilicate C glass makes it ideal for use in various applications such as in vinylester paints, acrylic epoxies and acrylic coatings as a barrier against corrosive attack from chemicals and moisture.

[0011] Usually, C glass is also obtained by melting a bath of raw material comprising silica, limestone, feldspar, borax, sodium carbonate and possibly dolomite, the basic components being judiciously chosen to provide a glass composition producing fibers combining flexibility and robustness to mechanical traction as well as to acidic or basic chemical agents.

[0012] The molten mixture (fibreglass for insulation or C glass) is thus usually prepared by melting in a furnace raw materials comprising silica, a source of sodium, most often sodium carbonate Na2CO3, at least one source of alkaline earth (magnesium and / or calcium) in the form of limestone (calcium carbonate) and / or dolomite (CaMg(CO3)2).

[0013] During the melting of the initial mixture for the manufacture of glass wool or C glass, the carbonates release carbon dioxide, the bubbles of which contribute to the mixing of the mass during melting. Furthermore, certain carbonates such as dolomite, even before releasing their CO2, divide into finer particles according to the phenomenon known as decrepitation, which can be quite violent and generate dust which clogs and even corrodes the various conduits equipping the furnaces (chimneys, regenerators, etc.). In a conventional glass wool or C-glass manufacturing process, CO2 emissions due to the melting of raw materials are generally in the order of 10 to 25% of the total mass of raw materials used.

[0014] Furthermore, carbon dioxide is a greenhouse gas and it is desirable to develop mineral wool manufacturing processes that generate as little CO2 as possible for environmental reasons, while leading to a good quality product at an acceptable cost.

[0015] In addition to the release of CO2 directly during the melting process of the raw material bath, it is therefore important to consider the glass manufacturing process as a whole, taking into account other factors such as the cost of the raw materials, their transport, the energy cost of making said raw materials available or even the overall energy expenditure enabling the melting of the mixture.

[0016] As previously indicated, glass is usually prepared by melting in a furnace raw materials comprising a significant portion of carbonates.

[0017] During melting, carbonates release carbon dioxide, the bubbles of which contribute to the stirring of the mass being melted. It is desirable to develop glass manufacturing processes that generate as little CO2 as possible for environmental reasons, while leading to good quality glass at an acceptable cost, particularly from the point of view of the energy expenditure required for glass manufacturing.

[0018] Sodium hydroxide has been proposed as an alternative to sodium carbonate and has the effect of reducing the CO2 generated during glass manufacturing, as for example in publications US3753743A or BE761040A. Sodium hydroxide is used in the form of sodium hydroxide solution, with a sodium hydroxide concentration of between 30 and 75% by weight.

[0019] Nevertheless, as described in the remainder of this description, it has appeared that using a sodium hydroxide solution at such a concentration has the consequence of greatly deteriorating the flow of the vitrifiable mixture because it becomes very pasty due to the large quantity of water added and of greatly increasing the energy expenditure necessary for the manufacture of the glass. Also, the chemical homogeneity of the glass has appeared insufficient with such a solution.

[0020] Patent application WO2022 / 229571 also describes the use of sodium hydroxide for the formation of a glass.

[0021] The object of the present invention is to propose a mixture intended for the production of glass comprising boron, in particular for the manufacture of glass fibers, making it possible to solve the preceding problems and in particular to obtain a homogeneous distribution of sodium oxide and silicon oxide in the glass. final, while maintaining good flow of the vitrifiable mixture and reducing the energy consumption required for said production.

[0022] To this end, the experiments carried out by the applicant company have shown the advantages of using sodium hydroxide in anhydrous form as a source of sodium in the initial raw material mixture, in particular if its density and preferably its morphology are specifically adapted to such use. Anhydrous form means any source of sodium hydroxide exhibiting a mass loss of less than 5% after heat treatment at 150°C for 1 hour.

[0023] More specifically, the invention relates in particular to a mixture of raw materials for the preparation of a molten glass suitable for the formation of fibers, the target composition of which corresponds to the formulation below, in weight percentage: - SiO2: between 50 and 75%, preferably between 60 and 70% - Na2O: between 10 and 25%, preferably between 10 and 20% - CaO: between 5 and 15%, preferably between 5 and 10% - MgO: between 1 and 10%, preferably between 2 and 5% - CaO and MgO together preferably representing between 5 and 20% - B2O3: between 1 and 10%, preferably between 2 and 8% - A12O3: between 0 and 8%, preferably between 1 and 6% - K2O: between 0 and 5%, preferably between 0.5 and 2% - Na2O and K2O together preferably representing between 12 and 20% - Iron oxide: between 0 and 3%, preferably less than 2%, preferably even less than 1%, - other oxide(s): between 0 and 5% by weight in total, preferably less than 3% in total,

[0024] the remainder being made up of unavoidable impurities.

[0025] Said mixture comprises: - at least one source of silicon chosen in particular from silica, glass cullet, recycled mineral fibres, in particular recycled glass wool, in particular a mixture of silica and glass cullet or a mixture of silica and recycled mineral fibres, or a mixture of silica, glass cullet and recycled mineral fibres, - at least one source of sodium in the form of sodium hydroxide, - at least one source of calcium, preferably chosen from limestone, quicklime or slaked lime or a mixed oxide of calcium with at least one element chosen from the group consisting of Si, Mg, in particular a calcium silicate, said source of calcium being able to be at least partly cullet, - at least one boron carrier, preferably chosen from a boron oxide such as pentaborax or a mixed oxide of boron with at least one element chosen from the group consisting of Si, Mg, Ca, in particular an oxide chosen from the group consisting of colemanite, ulexite, tincalconite or kemite, - optionally at least one source of magnesium preferably chosen from dolomite, possibly calcined, magnesite (MgCO3), brucite (Mg(OH)2) or a mixed oxide of magnesium with at least one element chosen from the group consisting of Si, Ca, in particular a magnesium silicate, - optionally at least one compound chosen from the group consisting of feldspar, in particular of formula (K,Na)AlSi3O8, nepheline or phonolite, - optionally recycled glass cullet, - optionally a milkman

[0026] wherein sodium hydroxide is in anhydrous form, in particular in the form of anhydrous particles.

[0027] Preferably the mixture is made up, for more than 90% by weight or even more than 95% by weight, more preferably for more than 99% by weight, of the constituents mentioned above.

[0028] In said mixture according to the invention, the sodium hydroxide is preferably in the form of a set of particles with an apparent density of less than 1.2 g / cm3, more preferably an apparent density of less than 1.0 g / cm3, or even less than 0.8 g / cm3.

[0029] In the present description, the term "particle" describes an individualized entity of anhydrous sodium hydroxide.

[0030] Apparent density, or apparent volumetric mass, is a quantity usually used essentially with substances in the form of particles (or grains), in order to account for the mass of material contained in a given volume, including the volume of interstitial air.

[0031] Apparent density (also called bulk density) is measured as follows:

[0032] According to an easily reproducible operating protocol for measuring the apparent density of the granular mixture, the latter is first poured into a container, for example a bucket, of known mass and volume. The container must be at least 1 liter to have sufficient precision and respect an aspect ratio making it possible to limit the settling of the mixture, by verifying the formula: Lmax — VF In which Lmax is the maximum extent of the container in a given direction, by analogy with the Feret diameter of a particle, and V is the volume of said container.

[0033] It is also important to ensure that the mixture is poured gently, without any movement of the bucket or mechanical compression of the mixture, in order to limit the settling of the mixture as much as possible. The filled bucket is then weighed in order to determine the mass of the poured mixture. The apparent density is the ratio between the measured mass of the mixture and the volume of the bucket.

[0034] In the present description, the term "particle" describes an individualized entity of anhydrous hydroxide.

[0035] By the expression "for the preparation of a molten glass of target composition", it is meant that the various raw materials previously cited are present in said mixture in proportions suitable for the final production, after melting according to the techniques of the art, of the glass of the target composition described above.

[0036] This mixture of raw materials is therefore intended to be heated to a temperature and under conditions allowing its melting to obtain a glass corresponding to said target composition and its drawing in the form of the fibers described above.

[0037] According to particular and advantageous embodiments of the present invention which can of course be combined with each other if necessary: - Said anhydrous sodium hydroxide is in the form of a set of particles having an average circularity of less than 0.85, preferably less than 0.80 or even greater than 0.75. - Said anhydrous sodium hydroxide is in the form of a set of particles having an average aspect ratio greater than 1.15, preferably greater than 1.20. - Said anhydrous sodium hydroxide is in the form of a set of particles whose average Feret diameter is greater than 5 millimeters, greater than 10 millimeters. - Anhydrous sodium hydroxide comprises a total water proportion of less than 30% by weight, preferably less than 25% by weight. - Sodium hydroxide is the only source of sodium (apart from possible additions of cullet or feldspar, nepheline or phonolite). - Alternatively, the sodium is provided in the form of a mixture of sodium hydroxide and sodium carbonate Na2CO3, the anhydrous sodium hydroxide according to the invention preferably representing more than 20% by weight of said mixture, or even more than 50% by weight of said mixture. - A source of calcium is a mineral calcium silicate, preferably natural. - A source of calcium is calcium oxide. - A source of calcium is calcium hydroxide. - A source of magnesium is a mineral magnesium silicate, natural preference. - A source of calcium is a mineral calcium silicate, preferably natural, comprising, in weight percentage, more than 30% of SiO2 and more than 10% of CaO, preferably more than 15% of CaO, CaO and SiO2 together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said source. - A source of magnesium is a mineral magnesium silicate, preferably natural, comprising, in weight percentage, more than 30% of SiO2 and more than 10% of MgO, preferably more than 15% of MgO, MgO and SiO2 together representing more than 60%, or even more than 70% or even more than 75% of the total weight of said source. - A source of magnesium is brucite Mg(OH)2. - The raw materials of said molten bath comprise a source of calcium as previously described and a source of magnesium as previously described. - A source of potassium is potassium hydroxide.

[0038] According to the invention, said raw materials, in particular the mineral oxides such as the silicates mentioned above, are natural. In particular, according to the invention, natural silicates can be used, that is to say in their initial geological composition after their extraction from their deposit, in particular without chemical alteration aimed at modifying the initial composition, that is to say mineral materials not chemically transformed. In particular, according to the method of the present invention, the initial basis is the exact composition of these untransformed geological mineral materials, as precisely determined by any suitable technique (for example chemical analysis, X-ray diffraction, etc.) to determine the composition of the initial bath. However, they can of course undergo steps prior to their use as raw material for fusion but without chemical transformation of the crystalline grains constituting them.Such steps may be crushing, screening, washing or even flotation, magnetic separation or any other physical separation of impurities present between said grains of the natural mineral matter.

[0039] Silica is generally introduced into the raw material mixture in the form of sand.

[0040] If necessary, as indicated previously, the mixture of raw materials can also advantageously comprise an Al carrier, a precursor of alumina in the glass, such as a feldspar or alternatively a blast furnace slag for example.

[0041] The mixture of raw materials may also comprise in small proportions a colorant such as an iron oxide, a cobalt oxide, a chromium oxide.

[0042] According to the invention, as little carbonate as possible, or even no carbonate, is introduced into the mixture of raw materials. Preferably, the sum of the weight of alkali carbonate and alkaline earth carbonate is less than 30%, and preferably less than 10%, and preferably less than 5%, and preferably less than 1% by weight, or is even zero in the mixture of raw materials. According to a possible advantageous embodiment, the mixture of raw materials may be substantially free of any carbonate. It is advantageously capable of releasing only a minimal portion of carbon oxide during its heating and melting into glass due, for example, to the addition of coke to the initial mixture.

[0043] To produce the glass, the Si carrier is introduced into the mixture of raw materials in the form of sand, the alkali carriers are advantageously introduced into the mixture of raw materials in the form of hydroxides, in particular in the form of anhydrous NaOH and preferably of density and morphology adapted according to the invention. The possible aluminum carrier can be introduced into the mixture of raw materials in the form of feldspar powder.

[0044] Each raw material is introduced into the raw material mixture in such an amount that the molar percentage of its cation (such as Si, Na, Mg, Ca, B, K Al, etc.) relative to the sum of the moles of all cations is the same as in the final glass. As previously indicated, the raw materials in the mixture are chosen to lead to a glass whose target composition falls within the framework (the percentage ranges for the different oxides) described previously.

[0045] The mixture of raw materials is heated until a molten glass is obtained, generally in a furnace. The heating is carried out at a higher or lower temperature and for a longer or shorter time depending on the quality of the glass required, in particular depending on the degree of tolerance for unmelted particles (called "unmelted") and bubbles. Generally, the maximum heating temperature of the molten glass is between 1200 and 1700°C. For the transformation of the mixture of raw materials into glass, glass melting techniques well known to those skilled in the art can be used. This transformation can be carried out in any type of furnace such as an electric electrode furnace, an overhead burner furnace such as a transverse burner furnace or a loop furnace, or a submerged burner furnace.

[0046] For heating and melting into glass, the mixture of raw materials may be introduced into a furnace in a powdered state, which implies that each raw material it contains is in a powdered state. For heating and melting into glass, the mixture of raw materials may be introduced into a furnace in a compositional state comprising cullet and said mixture of raw materials, the latter being, where appropriate, powdered.

[0047] The invention also relates to a method for manufacturing a glass having this same target composition, comprising the melting of a mixture of raw materials as described above, said mixture constituting a melt bath, said method comprising the following steps:

[0048] a) the necessary quantities of said raw materials are selected to obtain, after melting, a glass of said target composition, said raw materials being chosen from at least: - at least one source of silicon chosen in particular from silica, glass cullet, recycled mineral fibres, in particular recycled glass wool, in particular a mixture of silica and glass cullet or a mixture of silica and recycled mineral fibres, or a mixture of silica, glass cullet and recycled mineral fibres, - at least one source of sodium in the form of sodium hydroxide, - at least one source of calcium, preferably chosen from limestone, quicklime or slaked lime or a mixed oxide of calcium with at least one element chosen from the group consisting of Si, Mg, in particular a calcium silicate, said source of calcium being able to be at least partly cullet, - at least one boron carrier, preferably chosen from a boron oxide such as pentaborax or a mixed oxide of boron with at least one element chosen from the group consisting of Si, Mg, Ca, in particular an oxide chosen from the group consisting of colemanite, ulexite, tincalconite or kemite, - optionally at least one source of magnesium preferably chosen from dolomite, possibly calcined, magnesite (MgCO3), brucite (Mg(OH)2) or a mixed oxide of magnesium with at least one element chosen from the group consisting of Si, Ca, in particular a magnesium silicate, - optionally at least one compound chosen from the group consisting of feldspar, in particular of formula (K,Na)AlSi3O8, nepheline or phonolite, - optionally recycled glass cullet, - optionally a milkman,

[0049] b) said mixing of said raw materials is carried out according to said quantities,

[0050] c) the said mixture is melted and cooled under conditions allowing the said glass to be obtained,

[0051] wherein said sodium hydroxide of said mixture is in anhydrous form, in particular in anhydrous particles.

[0052] Preferably, the sodium hydroxide is in the form of a set of particles having an apparent density of less than 1.2 g / cm3, more preferably an apparent density of less than 1.0 g / cm3. Examples

[0053] In the following examples, different mixtures of raw materials were prepared in order to compare a mixture as currently used for the manufacture of glass for an identical final glass composition, which has substantially the following composition:

[0054] [Tables 1] Elements Percentage wt% SiO2 65.0 CaO 6.7 B2O3 5.6 Na2O 15.7 MgO 2.8 A12O3 2.5 Fe2O3 <1 k2o 0.7 Other oxy Impurities

[0055] Table 2 below gives the proportions of the different raw materials for the 5 mixtures prepared:

[0056] [Tables2] Mix A Mix B Mix D Mix C kg / tonne glass kg / tonne glass kg / tonne glass kg / tonne glass Sand 543 543 543 543 Feldspar 151 151 151 151 Sodium carbonate 208 Sodium hydroxide 1 314 Sodium hydroxide 2 157 Sodium hydroxide 3 157 Calcined dolomite 74 74 74 74 Limestone 41 41 41 41 Borax pentahydrate 127 127 127 127

[0057] The mixtures are differentiated by the particle size and the size of the sodium hydroxide source used.

[0058] The particle size and the different geometric characteristics of the different forms of sodium hydroxides used were determined by image analysis using ImageJ® software. The median diameter, the Feret diameter, the circularity and the aspect ratio are thus determined for each of the sodium hydroxides and their values ​​are given in Table 3 below.

[0059] More precisely:

[0060] The circularity of a particle is given by the formula S = 4ir (A / P2), with A area and P the perimeter of said particle.

[0061] The Feret diameter is classically defined as the distance between two parallel tangents to the periphery of the projected surface of the particle in one direction.

[0062] The median diameter d50 of each sodium hydroxide sample is also measured by image analysis using ImageJ® software.

[0063] The equivalent diameter of a particle is defined as the diameter of a circle whose perimeter is equivalent to the perimeter of said particle, as measured on said images.

[0064] The aspect ratio of a particle is the ratio of its greatest length to its least length, such that the entire projection of the particle lies between these two parallels.

[0065] An average circularity, Feret diameter, equivalent diameter and aspect ratio are then defined for all the particles in each sodium hydroxide sample, as reported in Table 3 below.

[0066] The proportions of free water and bound water of these different qualities of sodium hydroxide are also reported there.

[0067] Conventionally, the median diameter is the diameter for which 50% of the particles in number have a diameter less than this diameter and 50% a diameter greater than this diameter.

[0068] [Tables3] Mixture B Mixture D Mixture C Sodium Hydroxide 1 Sodium Hydroxide 3 Sodium Hydroxide 2 Media Diameter nd50 - 5325pm 9484pm Iron Diameter - 5775pm 1231pm Equivalent Diameter - 6210pm 12368pm Roundness - 0.75 0.59 Aspect Ratio - 1.11 1.35 Apparent Density (g / cm3) - 1.08 0.74 Total Water 61.5% 23% 23% Free Water 50% Less than 2% Less than 2% Bound Water 11.5% remainder remainder

[0069] Total water corresponds to the set of free water plus bound water.

[0070] The percentage of bound water is therefore obtained by subtracting the percentage of free water from the percentage of total water (“remainder” in table 3 above).

[0071] Bound water means water chemically bound to the structure via strong bonds, i.e. typically the hydroxyl group -OH in a general formulation NaOH. The temperature for removal of bound water (dehydroxylation) is well above 100°C. In the case of dehydroxylation of anhydrous sodium hydroxide, the water released is essentially bound water according to the formula 2NaOH to Na2O + H2O).

[0072] By anhydrous form is meant in particular any source of sodium hydroxide exhibiting a mass loss of less than 5%, preferably less than 2%, after heat treatment at 150°C for 1 hour.

[0073] By free water, on the contrary, we mean all the water molecules bound by weak interactions. Free water can, for example, correspond to the water of solution in which sodium hydroxide is present as described in application US3753743A but also to the water present between the hydroxide particles. sodium, particularly due to the hygroscopic nature of this compound. Unlike bound water, this water is weakly bound to sodium hydroxide by weak bonds.

[0074] Thus, an “anhydrous” sodium hydroxide comprises less than 5% free water and preferably less than 2% free water, in the sense previously described.

[0075] For the purposes of the present invention, a sodium hydroxide is therefore said to be anhydrous when it comprises less than 5% free water.

[0076] Mixture B is in accordance with the teaching of publication US3753743A. Mixtures C and D are in accordance with the subject of the present invention. Example A is a comparative example in which sodium carbonate is conventionally used as the sodium source.

[0077] The performances and qualities of the mixtures of raw materials according to the preceding examples A to D, including the quality of the glass after their melting, are measured according to the following different criteria:

[0078] 1°) Flow measurement by slope angle tests

[0079] The angle of slope is a method for evaluating the flowability of powder, carried out by predicting the flow of vitrifiable mixtures at the outlet of the mixer until they are put into the kiln.

[0080] This technique makes it possible to estimate, with respect to the reference mixture (mixture A), the way in which the other vitrifiable mixtures flow. If the flow is weak or poor, the risks of clogging on the conveyor belts or in the loading hoppers are greater.

[0081] As for the angle of slope, the vitrifiable mixture is introduced into a trapdoor funnel. Then the trapdoor is removed to allow the vitrifiable mixture to flow onto a sheet of graph paper, resulting in a cone. The height of the cone is measured and its circumference is plotted on the graph paper to then deduce its average diameter. Finally, with the height and diameter of the cone, the angle of slope of the vitrifiable mixture is calculated according to the formulas: Angle of slope (degrees) = 180 x Arc Tangent (height of slope / (1 / 2 x diameter of cone)) / jt. The interpretation of the measurement results is made on the basis of the classification present in the Engineering Technique - Forming of Solids. Ref J3380 VL

[0082] The results obtained are grouped in Table 4 below.

[0083] The reference mixture (Mixture A) has a very good flow, as do mixtures C and D, with angles of slope between 25 and 30° (see the Technical classification of the engineer - Forming of solids. Ref J3380 VI). Mixture D has a good flow with an angle of slope of 32°. On the other hand, with its angle of slope greater than 50°, mixture B has a poor flow and suggests the use of suitable devices to assist discharge in the event of passage of the mixture in a hopper for example. In addition, the risks of clogging of the mixer or clogging on the conveyor belts are high in the case of mixture B.

[0084] Mixtures B, C and D were characterized and the results obtained are presented in Table 4 below. Mixtures C and D according to the invention, and more particularly the mixture according to Example C, can be considered as those which flow the most freely. [Table 4] Mixture A Mixture B Mixture D Mixture C Angle of repose 25° >50° 28° 25° Fracture energy (relative to Mixture A) Reference No flow -3% -4%

[0085] 2°) Measurement of emissivity

[0086] A mixture of low-emissivity raw materials produces a thermal mirror on the surface of the composition lump, which reduces the melting kinetics and increases the energy consumption of the furnace to achieve the same degree of melting.

[0087] The emissivity of the different mixtures indicated in Table 5 below was measured from the reflectance spectra using the law of conservation of energy for opaque materials: absorbance a(X, T) + reflectance p(X, T) = 1. By applying Kirchhoff's law, the spectral emittance can be expressed in terms of total reflectance,

[0088] e(X, T) = a(X, T)

[0089] with:

[0090] where Bt is the spectral irradiance of the black body at temperature T of 2000°C, corresponding to the temperature of the air-gas flame of the burner.

[0091] Room temperature hemispherical reflectance measurements are performed with a 150 mm integrating sphere mounted on a Lambda spectrophotometer between 300 and 2500 nm, using a Spectralon plate as a reflectance reference.

[0092] For easy handling, the vitrifiable mixture samples are pressed by applying a force of 0.4 tonnes / cm2 and wetted with 2% water prior to measurement.

[0093] [Tables5] Mix A Mix B Mix D Mix C Emissivity 0.30 nd >0.4 >0.4

[0094] In order to improve the heat transfer between the flame and the glass, the person skilled in the art seeks to maximize the emissivity of the batch as far as possible. Too low an emissivity is a sign of high thermal reflectivity which could result in a screening effect. This will produce an increase in the temperature of the roof and a low temperature of the glass bath. The data in Table 5 show that anhydrous sodium hydroxide according to Examples C and D improves the thermal absorption of the batch compared to the use of sodium carbonate (mixture A).

[0095] 3°) Energy required for fusion

[0096] A reduction in energy consumption logically leads to a reduction in costs (less energy to be used to melt the mixture of raw materials) and in the carbon footprint of glass production (less gas to be used, for example).

[0097] The energy required to melt the different raw material mixtures was determined using FactSage 8.0 software. The energy is calculated over the temperature range 25 and 1400°C.

[0098] The results of the evaluation are reported in Table 6 below:

[0099] [Tableauxô] Mix A Mix B Mix D Mix C Evolution of energy consumption vs. mix A Reference +30% -13% -13%

[0100] Table 6 shows that with mixture B (50% free water), the fusion energy of the vitrifiable mixture is drastically increased: +23% compared to the reference (mixture A). On the contrary, with mixtures C and D according to the invention, the energy consumption is significantly reduced compared to this same reference, by approximately 11%.

[0101] 4°) Homogeneity of the glass obtained after melting

[0102] Non-homogeneous glass exhibits “waves” (optical defects), i.e. areas where the refractive index varies locally due to a variation in chemical composition.

[0103] Glass samples were melted in a cylindrical platinum crucible from the mixtures indicated in Table 2. Each sample was heated in air to 1480°C for 2 hours. The cooled glass was then cored and cut to obtain a slide comprising the cross-section of the cylinder. This slide was polished, carbon-plated and analyzed using an electron microprobe at 15 kV. The analysis consisted of determining the mass percentages of Na2O, CaO and SiO2 on the height of the blade (or melted sample) on 50 measurement points, the measurement step being 500 microns.

[0104] It is thus possible on this basis to calculate the average of the concentration of Na2O, CaO and SiO2 and the standard deviations. A criterion of homogeneity in Na2O, CaO and SiO2 in the glass is provided by the standard deviation ratio divided by the average concentration (oNa2O / [Na2O], oCaO / [CaO] and oSiO2 / [SiO2]).

[0105] The results obtained are reported in Table 7 below.

[0106] [Tables?] Mix. A Mix. B Mix. D Mix. C Glass homogeneity (standard deviation / mean in %) Na2O 1.9 1.5 0.8 0.8 CaO 4.2 4.6 1.9 1.5 SiO2 1.0 1.0 0.5 0.4

[0107] The homogeneity of sodium oxide and silicon oxide appears particularly improved in the case of mixtures C and D according to the invention, in particular in the case of mixture C according to the invention.

[0108] All of the results previously set out and the advantages of the present invention are summarized below, materialized by the superiority of mixtures C and D, in particular C according to the invention:

[0109] - good flow of the mixture of raw materials,

[0110] - an improved emissivity of the vitrifiable mixture, which implies a better transfer thermal effect of flames on the mixture of raw materials during melting

[0111] - A significant decrease in the overall fusion energy of the mixture

[0112] - Better homogeneity of the glass finally obtained.

Claims

Claims

1. Mixture of raw materials for the manufacture of glass, in particular glass fibers, having a target composition, said target composition corresponding to the following formulation: - SiO2: between 50 and 75%, preferably between 60 and 70% - Na2O: between 10 and 25%, preferably between 10 and 20% - CaO: between 5 and 15%, preferably between 5 and 10% - MgO: between 1 and 10%, preferably between 2 and 5% - CaO and MgO together preferably representing between 5 and 20% - B2O3: between 1 and 10%, preferably between 2 and 8% - A12O3: between 0 and 8%, preferably between 1 and 6% - K2O: between 0 and 5%, preferably between 0.5 and 2% - Na2O and K2O together preferably representing between 12 and 20% - Iron oxide: between 0 and 3%, preferably less than 2%, more preferably less than 1%, - other oxide(s): between 0 and 5% by weight in total, preferably less than 3% in total, the remainder being made up of unavoidable impurities, said mixture comprising#: - at least one source of silicon chosen in particular from silica, glass cullet, recycled mineral fibres, in particular recycled glass wool, in particular a mixture of silica and glass cullet or a mixture of silica and recycled mineral fibres, or a mixture of silica, glass cullet and recycled mineral fibres, - at least one source of sodium in the form of sodium hydroxide, - at least one source of calcium, preferably chosen from limestone, quicklime or slaked lime or a mixed oxide of calcium with at least one element chosen from the group consisting of Si, Mg, in particular a calcium silicate, said source of calcium being able to be at least partly cullet, - at least one boron carrier, preferably chosen from a boron oxide such as pentaborax or a mixed boron oxide with at least one element chosen from the group consisting of Si, Mg, Ca, in particular an oxide chosen from the group consisting of colemanite, ulexite, tincalconite or kemite, - optionally at least one magnesium source preferably chosen from dolomite, optionally calcined, magnesite or a mixed magnesium oxide with at least one element chosen from the group consisting of Si, Ca, in particular a magnesium silicate, - optionally at least one compound chosen from the group consisting of feldspar, in particular of formula (K,Na)AlSi3O8, nepheline or phonolite, - optionally slag, - optionally recycled glass cullet, characterized in that the sodium hydroxide is in anhydrous form.

2. A mixture according to claim 1, wherein the anhydrous sodium hydroxide is in the form of a collection of particles having an apparent density of less than 1.2 g / cm3.

3. A mixture according to claim 1 or 2, wherein the anhydrous sodium hydroxide is in the form of a set of particles having an average circularity of less than or equal to 0.85, preferably less than 0.80, or even less than 0.

75.

4. Mixture according to one of the preceding claims, in which said anhydrous sodium hydroxide is in the form of a set of particles having an average aspect ratio greater than 1.15, preferably greater than 1.

20.

5. Mixture according to one of the preceding claims, in which said anhydrous sodium hydroxide is in the form of a set of particles whose average Feret diameter is greater than 5 millimeters, greater than 10 millimeters.

6. Mixture according to one of the preceding claims, in which the anhydrous sodium hydroxide comprises a total water proportion of less than 30% by weight, preferably less than 25% by weight.

7. A mixture according to any preceding claim, wherein said anhydrous sodium hydroxide is the sole source of sodium, other than any additions of cullet or feldspar, nepheline or phonolite.

8. Mixture according to one of the preceding claims, in which the sodium is provided in the form of a mixture of anhydrous sodium hydroxide and sodium carbonate Na2CO3, the anhydrous sodium hydroxide preferably representing more than 20% by weight of said mixture, or even more than 50% by weight of said mixture.

9. Mixture according to one of the preceding claims, in which a source of calcium is a mineral calcium silicate comprising, in weight percentage, more than 30% of SiO2 and more than 10% of CaO, preferably more than 15% of CaO, CaO and SiO2 together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said source.

10. Mixture according to one of the preceding claims, in which a source of magnesium is a mineral magnesium silicate comprising, in weight percentage, more than 30% of SiO2 and more than 10% of MgO, preferably more than 15% of MgO, MgO and SiO2 together representing more than 60%, or even more than 70% or even more than 75% of the total weight of said source.

11. A mixture according to any preceding claim, wherein a source of potassium is potassium hydroxide.

12. A mixture according to any preceding claim, wherein a source of calcium is calcium hydroxide.

13. A mixture according to any preceding claim, wherein a source of magnesium is magnesium hydroxide.

14. Mixture according to one of the preceding claims in which the anhydrous sodium hydroxide has an apparent density of less than 1.0 g / cm3, preferably less than 0.8 g / cm3.

15. A method of manufacturing a glass having a target composition, comprising melting a mixture of raw materials according to one of the preceding claims, said mixture constituting a melt bath, said target composition meeting the following criteria, in weight percentages: - SiO2: between 50 and 75%, preferably between 60 and 70% - Na2O: between 10 and 25%, preferably between 10 and 20% - CaO: between 5 and 15%, preferably between 5 and 10% - MgO: between 1 and 10%, preferably between 2 and 5% - CaO and MgO together preferably representing between 5 and 20% - B2O3: between 1 and 10%, preferably between 2 and 8% - A12O3: between 0 and 8%, preferably between 1 and 6% - K2O: between 0 and 5%, preferably between 0.5 and 2% - Na2O and K2O together preferably representing between 12 and 20% - Iron oxide: between 0 and 3%, preferably less than 2%, more preferably less than 1%, - other oxide(s): between 0 and 5% by weight in total, preferably less than 3% in total, said method being characterized in that it comprises the following steps: a) the necessary quantities of said raw materials are selected to obtain, after melting, a glass of said target composition, the raw materials of said melt, said raw materials being chosen from at least: - at least one source of silicon chosen in particular from silica, glass cullet, recycled mineral fibres, in particular recycled glass wool, in particular a mixture of silica and glass cullet or a mixture of silica and recycled mineral fibres, or a mixture of silica, glass cullet and recycled mineral fibres, - at least one source of sodium in the form of sodium hydroxide, - at least one source of calcium, preferably chosen from limestone, quicklime or slaked lime or a mixed oxide of calcium with at least one element chosen from the group consisting of Si, Mg, in particular a calcium silicate, said source of calcium being able to be at least partly cullet, - at least one boron carrier, preferably chosen from a boron oxide such as pentaborax or a mixed oxide of boron with at least one element chosen from the group consisting of Si, Mg, Ca, in particular an oxide chosen from the group consisting of colemanite, ulexite, tincalconite or kemite,

16. - optionally at least one source of magnesium preferably chosen from dolomite, possibly calcined, magnesite or a mixed oxide of magnesium with at least one element chosen from the group consisting of Si, Ca, in particular a magnesium silicate, - optionally at least one compound chosen from the group consisting of feldspar, in particular of formula (K,Na)AlSi3O8, nepheline or phonolite, - optionally slag, - optionally recycled glass cullet, b) said mixing of said raw materials is carried out according to said quantities, c) the said mixture is melted and cooled under conditions allowing the said glass to be obtained, wherein the sodium hydroxide in said mixture is anhydrous. Manufacturing method according to the preceding claim, wherein the anhydrous sodium hydroxide is in the form of a set of particles having an apparent density of less than 1.2 g / cm3, preferably an apparent density of less than 1.0 g / cm3, more preferably less than 0.8 g / cm3.