Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
  • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
  • C03C4/10—Compositions for glass with special properties for infrared transmitting glass

Definitions

• the present invention relates to a glass sheet having high transmission properties of visible and infrared radiation.
• the glasses used In applications where the glass is used in the form of a glass sheet covering photovoltaic cells or solar cells, it is essential that the glasses used have an extremely high transmission of visible and / or infrared radiation, especially greater than 90 %, because the quantum efficiency of the cell can be strongly affected by even a very small decrease in the transmission by the glass of visible or infrared radiation.
• Transmission in the visible or infrared range is generally expressed as a transmission factor integrating the transmission for each wavelength over a certain part of the spectrum, taking into account a determined spectral distribution and possibly of the sensitivity of the human eye.
• a light transmission factor called light transmission, often abbreviated "T L ", calculated between 380 and 780 mm and reduced to a glass thickness of 3.2 mm, is thus defined.
• T L light transmission factor
• T E energy transmission factor
• Iron oxide present as impurity in most natural raw materials used in glassworks (sand, feldspar, limestone, dolomite 7), absorbs both in the field of the visible and near ultraviolet (absorption due to the ferric ion Fe 3+ ) and especially in the visible and near infrared domain (absorption due to Fe 2+ ferrous ion).
• the total weight content of iron oxide is of the order of 0.1% (1000 ppm).
• transmissions of more than 90% require lowering the iron oxide content to less than 0.02% or 200 ppm, or even less than 0.01% (100 ppm), which requires the selection of particularly valuable raw materials. pure and increases the cost of the final product.
• Cerium oxide is likely to be at the origin of the so-called “solarisation” process, in which the transmission of the glass decreases sharply after absorption of ultraviolet radiation. It is also known to add to the glass of antimony oxide (Sb2 ⁇ 3) or arsenic (AS2O3), oxides traditionally used as refining glass and which have the particularity of oxidizing iron. The use of Sb2 ⁇ 3 is for example described in application US 2006/249199. These oxides, however, proved to be incompatible with the process of floating glass. It would seem that under the reducing conditions necessary for non-oxidation of the tin bath, some of these oxides volatilize and then condense on the forming glass sheet, generating an undesirable veil.
• Sb2 ⁇ 3 antimony oxide
• AS2O3 arsenic
• the present invention therefore aims to obviate the aforementioned drawbacks and to propose new sheets of glass whose transmission luminous and energetic is very high, allowing their use in photovoltaic cells.
• the subject of the invention is a glass sheet whose chemical composition is of the soda-lime-silica type and comprises the following constituents in a content varying within the weight limits defined below:
• Fe 2 O 3 total iron 0 to 0.02%, WO 3 0.1 to 2%.
• Fe 2 O 3 and WO 3 respectively represent the total contents of iron and tungsten oxides in the glass, irrespective of the degree of oxidation of their respective ions.
• the glass sheet is particularly likely to have been obtained by a method of floating on a molten tin bath
• silica-lime composition is intended to mean a composition comprising silica (SiO 2 ) as forming oxide and oxides of sodium (sodium Na 2 O) and calcium (lime CaO). This composition preferably comprises the following constituents in a content varying within the weight limits defined below:
• the presence of iron in a glass composition may result from raw materials, as impurities, or from a deliberate addition to color the glass. It is known that iron exists in the glass structure in the form of ferric ions (Fe 3+ ) and ferrous ions (Fe 2+ ). The presence of Fe 3+ ions gives the glass a very slight yellow color and can absorb ultraviolet radiation. The presence of Fe 2+ ions gives the glass a more pronounced blue-green color and induces an absorption of infrared radiation. The increase in the content of iron in its two forms accentuates the absorption of radiation at the ends of the visible spectrum, this effect being to the detriment of light transmission.
• the content of Fe2O3 (total iron) is preferably less than or equal to 0.015%, especially 0.01%, in order to limit the light and energy transmission.
• Tungsten oxide was found to be able to oxidize iron, decreasing the Fe 2+ ion content. This effect had, to the knowledge of the inventors, never been demonstrated, and would seem to exist only in the case of glasses very poor in iron oxide. In addition, the compatibility of this oxide with the glass float process is perfect and the glass thus produced has no solarization.
• the content of WO 3 is preferably greater than or equal to 0.2%, even 0.3% and even 0.4% or 0.5%. It would seem, however, that the oxidation effect saturates beyond a certain value. Given the cost of this oxide, its content is preferably less than or equal to 0.9%, or even 0.8% and even 0.7%. A content of the order of 0.5% is preferred. Beyond 2% of WO 3 , a phase separation is observed.
• the content of WO 3 is preferably between 0.2 and 1%, especially between 0.3 and 0.7% or between 0.3 and 0.5%. A content of the order of 0.35% is preferred.
• Redox which is an indicator of the redox state of glass, is preferably less than or equal to 0.1, even 0.07 and even 0.05, to maximize the transmission of glass.
• the glass sheet according to the invention preferably has, for a thickness of 3.2 mm, a light transmission T L of at least 91%, especially 91.1%, or even 91.2% or 91.3%, and even 91, 4% or 91, 5%.
• an energy transmission T E of at least 91%, in particular 91.5%, or even 91.2% or 91.3% and even 91.4% or 91.5%.
• a particularly preferred composition comprises the following constituents in a content varying within the weight limits defined below:
• Fe 2 O 3 total iron 0.010 to 0.015%, WO 3 0.3 to 0.5%
• Such a composition makes it possible to obtain very low redox glasses (0.07 or less), or even lower when the K 2 O content of the matrix is greater than or equal to 1.5%, especially 2%, or even 3% and even 4%, as explained below.
• the soda-lime-silica glass composition may comprise, in addition to the unavoidable impurities contained in particular in the raw materials, a small proportion (up to 1%) of other constituents, for example agents which assist in melting. or the refining of the glass (SO 3 , CI ...), or else the elements resulting from the dissolution of the refractories used for the construction of the furnaces (for example ZrO 2 ).
• the composition according to the invention preferably does not include oxides such as Sb 2 O 3 , As 2 O 3 or CeO 2 .
• the MoO 3 content is zero.
• the composition of the glass sheet according to the invention preferably comprises no agent absorbing visible or infrared radiation (especially for a wavelength between 380 and 1000 nm) other than those already mentioned.
• the composition according to the invention preferably does not contain agents selected from the following agents, or any of the following agents: transition element oxides such as CoO, CuO, Cr 2 O 3 , MnO 2 , rare earth oxides such as CeO 2 , La 2 O 3 , Nd 2 O 3 , or elemental coloring agents such as Se, Ag, Cu.
• transition element oxides such as CoO, CuO, Cr 2 O 3 , MnO 2 , rare earth oxides such as CeO 2 , La 2 O 3 , Nd 2 O 3 , or elemental coloring agents such as Se, Ag, Cu.
• the silica is generally kept within narrow limits for the following reasons. Above 75%, the viscosity of the glass and its ability to devitrify strongly increase, making it more difficult to melt and pour on the molten tin bath.
• Al2O3 alumina plays a particularly important role in the hydrolytic resistance of glass.
• the alumina content is preferably greater than or equal to 1%.
• the alkali metal oxides Na 2 O and K 2 O facilitates melting of the glass and used to adjust its viscosity at high temperatures in order to keep close to that of a standard glass.
• K 2 O can be used up to 10% because beyond this arises the problem of the high cost of the composition.
• the increase in the percentage of K 2 O can be done, for the most part, only to the detriment of Na 2 O, which contributes to increasing the viscosity.
• the sum of the contents of Na 2 O and K 2 O, expressed in weight percentages, is preferably equal to or greater than 10% and advantageously less than 20%. If the sum of these contents is greater than 20% or if the Na 2 O content is greater than 18%, the hydrolytic resistance is greatly reduced.
• the glasses according to the invention are preferably free of lithium oxide Li 2 O because of its high cost.
• the K 2 O content is preferably greater than or equal to 1.5% or even 2%, especially 3%, and even 4% or 5%.
• the K 2 O content is preferably less than or equal to 8%, or even
• the alkaline earth oxides make it possible to adapt the viscosity of the glass to the conditions of preparation.
• MgO can be used up to about 10% and its removal can be offset, at least in part, by an increase in the content of Na2 ⁇ and / or SiO2.
• the MgO content is less than 5%.
• MgO also make it possible to reduce the number of raw materials necessary for melting the glass.
• the glasses according to the invention are free of BaO and also of strontium oxide (SrO), these elements having a high cost.
• the glass composition according to the invention is capable of being melted under the conditions of production of glass intended for forming flat glass by stretching, rolling or, preferably, floating techniques.
• the melting generally takes place in flame furnaces, possibly provided with electrodes for heating the glass in the mass by passing the electric current between the two electrodes.
• the glass sheet according to the invention may be coated on at least one of its faces with an antireflection coating.
• This coating may comprise a layer (for example based on porous silica with a low refractive index) or several layers: in the latter case a stack of layers based on dielectric material alternating layers with low and high refractive indexes and ending with a low refractive index layer is preferred. It may especially be a stack described in WO 01/94989 or WO 2007/077373.
• the surface of the glass sheet may be textured, for example present patterns (in particular pyramid), as described in WO 03/046617, WO 2006/134300, WO 2006/134301 or WO 2007/015017.
• the invention also relates to the use of the glass sheet according to the invention in photovoltaic cells, solar cells, flat or parabolic mirrors for the concentration of solar energy, or diffusers for backlighting screens display type LCD (liquid crystal displays).
• the glass sheet according to the invention can also be used for interior applications (partitions, furniture ...) or in household appliances
• the subject of the invention is also a photovoltaic cell, a solar cell, a plane or parabolic mirror for the concentration of solar energy, or a diffuser for backlighting of LCD-type display screens.
• a photovoltaic cell comprising at least one glass sheet whose light transmission T L is at least 91% or even 91.5% and / or whose energy transmission T E is at least 91%, or even 91.4% (in both cases in the absence of any antireflection treatment) for a thickness of 3.2 mm, regardless of the composition of the glass.
• the glass sheet is preferably capable of being obtained by a float process on a molten tin bath. It seems that the invention has made it possible, for the first time, to obtain such performances.
• T E energy transmission
• T L overall light transmittance
• Table 1 also shows the weight contents of oxides of potassium, iron and tungsten, measured by chemical analysis.
• compositions appearing in Table 1 are made from a matrix which comprises the following oxides, the contents of which are expressed in percentages by weight:
• Composition C1 is a comparative example, not including tungsten oxide.
• the introduction of this oxide makes it possible to substantially increase the light and energy transmissions of the glass, up to values greater than or equal to 91%.
• Example 5 is particularly advantageous because it has very high transmission values for a moderate content of WO 3 and K 2 O. None of the glasses obtained had solarization after an accelerated test of 100 hours under ultraviolet radiation.

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• Chemical & Material Sciences (AREA)
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• Engineering & Computer Science (AREA)
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• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Glass Compositions (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
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• 2007
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