Applying prestress to flat glass by creating a gradient in the surface composition

Abstract

The invention relates to a glass product, in particular a flat glass; wherein the surface material has a gradient material property due to a targeted process control, which in turn leads to a compressive prestress of the surface. The invention also relates to a method for producing a glass product and to the use thereof.

Description

Technical Field

[0001] This invention relates to glass articles, such as flat glass. The surface material exhibits gradient material properties due to targeted process control, which in turn results in compressive prestress on the surface. The invention also relates to a method for producing glass articles and its use. Background Technology

[0002] Many applications require glass with compressive prestressing on its surface, especially in the field of safety glass, or often for glass that is more resistant to mechanical effects than unstressed glass. There are various methods for compressive prestressing the surface of glass products.

[0003] For so-called chemical prestressing, see Arun K. Varshneya, Chemical Strengthening of Glass: Lessons Learned and Yet To Be Learned, International Journal of Applied Glass Science 1[2] 131-142 (2010), smaller ions on the glass surface are replaced by larger ions, such as sodium ions being replaced by potassium ions. This results in a greater space requirement for the surface relative to the core material. Due to its connection with the core material, the surface does not expand in this way, but is instead compressed to its original size, thus generating corresponding compressive stress. The chemical prestressing process is usually carried out at high temperatures, but still significantly below the annealing point.

[0004] For the so-called thermal prestressing, see IaWerner Kiefer, Thermisches Vorspannen von niedriger Glastechnische Berichte 57 (1984), No. 9, pp. 221-228, Glass products, such as flat glass, are heated to a temperature, for example, 100 K above the annealing point, and then cooled by a shock-like process, such as blowing air. The compressive prestress on the surface (thermal prestressing) is generated by the interaction of locally different cooling processes (cooling occurs rapidly on the surface but slowly in the core due to the low thermal conductivity of glass), resulting in locally different thermal expansion, which in turn leads to stress accumulation and subsequent stress relaxation, and this stress relaxation is highly temperature-dependent.

[0005] According to Technical Information Exchange No. 32 (TIE-32), Thermal loads on optical glass, Schott AG, Mainz, Germany, October 2018, the surface compressive stress σ of thermally prestressed glass is...

[0006]

[0007] E is the elastic modulus, μ is Poisson's ratio, and ΔT is the difference between the surface temperature and the core temperature of the sheet when the core temperature passes the annealing point in the impact cooling process. CTE is the coefficient of thermal expansion of the glass. "f" is a factor reflecting the relationship between the difference between the surface temperature and the average sheet temperature and the difference between the surface temperature and the core temperature. "f" is always less than "1"; if a "steady state" with a parabolic temperature distribution has been formed until the glass transition range is reached, f = 2 / 3.

[0008] According to Kiefer,loc, the following applies to ΔT. (Source: [Original Source Name])

[0009]

[0010] Here, h is the heat transfer coefficient between the plate and the cooling medium, such as blower air, d represents the plate thickness, к represents the thermal conductivity of the glass, and T 环境 This represents the temperature of the cooling medium or the ambient temperature.

[0011] T G These are discrete values ​​representing the glass transition range, i.e., stress at T. G Relax above, and no longer below T. G More precisely, this temperature depends on the cooling rate. The most suitable estimate, independent of the cooling rate, is the annealing point. In the literature, the glass transition temperature is also frequently used at this point, meaning that since the annealing point and the glass transition temperature are almost identical, the error is small.

[0012] Both processes, thermal prestressing and chemical prestressing, can be used for sheets and other glass products; the above considerations always apply when the thickness is relatively small relative to the lateral dimension of a piece of such glass. This is especially true for glass sheets. However, both methods require additional process steps, including the reheating of the glass and significant chemical or technical engineering costs. Summary of the Invention

[0013] The existing technology lacks a method for applying compressive prestress to the surface of glass products, which is an improvement on the “industry” production method.

[0014] This objective is achieved through the subject matter of the claims.

[0015] If the composition of the surface layer is successfully altered during the production process to produce a lower CTE than the interior, a viable alternative to the two methods described above in the prior art can be formed. This is precisely what the present invention achieves compared to the two methods described above. This does not preclude the optional chemical or thermal prestressing of the glass articles according to the invention in additional steps after production. However, in contrast, the present invention addresses compressive prestressing on the surface, which can be achieved by introducing a CTE difference between the surface and the core during production.

[0016] Assume that, firstly, the temperature is cooled to the annealing point T. G In the cooling process, all stresses originating from different thermal expansions are completely relaxed, but no longer at a lower temperature. Secondly, compared to the thickness of the glass plate under consideration, the surface layer is thinner, and the two-dimensional stress state of the compressive prestress at the surface follows Hooke's Law:

[0017]

[0018] Here, ΔCTE is the coefficient of thermal expansion of the core, CTE. K With the surface thermal expansion coefficient CTE O The difference between them.

[0019] According to the present invention, the term "surface" refers to the glass portion near the glass / air boundary. Here, the glass forming the surface is referred to as "surface glass," while the remaining glass located further inward is referred to as "body glass" or "core glass." It is difficult to precisely define the surface from the body; therefore, the present invention defines the depth of the surface glass as <20 nm. Surface composition analysis can be performed, in particular, by Cs-TOF-SIMS at 1000 eV. In different cases, the average of measurements close to a surface depth of <20 nm is used as the surface value, and the composition of the constituent phase is determined using the inverse matrix of the oxide composition.

[0020] Preferably, three or more individual measurements are performed, ranging from a depth of approximately 5 nm to <20 nm. The individual measurements are preferably equidistant. For example, individual measurements can be performed at depths of 6 nm, 9 nm, 12 nm, 15 nm, and 18 nm, or at depths of 5 nm, 7.5 nm, 10 nm, 12.5 nm, 15 nm, and 17.5 nm. The precise depth of the individual measurements is not crucial here. The properties of the surface glass are determined by calculation based on the formulas explained herein and the determined composition of the surface glass.

[0021] Since the glass composition does not change at deeper levels during production, the composition of the core glass can be determined through routine chemical analysis of the glass composition. In all cases, the core glass is located at a depth of 500 nm. During glass production, specific measures can be taken to have a beneficial effect on the glass surface.

[0022] Preferably, the TOF-SIMS measurements are standardized using chemical analysis values ​​of the core glass. Specifically, the TOF-SIMS results can be continued along the surface direction (the same signal intensity implies the same mass flow rate). Therefore, preferably, the concentration corresponding precisely in percentage (%) to the concentration obtained from the glass chemical analysis is designated as the specific TOF-SIMS signal intensity of the core glass (e.g., measured or averaged at depths of 500 nm, 600 nm, or 700 nm). These values ​​are continued towards the surface; that is, if a signal intensity x corresponding to a 20% concentration has been generated, and x is also measured at the surface, the surface concentration is initially set to equal 20%. If a value of 2x is measured at the surface instead of x, the surface concentration is set to equal 40%. The surface concentrations determined in this way are then standardized so that their sum is 100%.

[0023] This objective is achieved through a targeted combination of production methods and suitable glass. The core of this production method is to alter the surface composition compared to the core composition by selectively removing individual components. Therefore, the resulting glass articles comprise surface glass with a composition altered compared to the core glass, resulting in a difference in the coefficients of thermal expansion between the surface and the core.

[0024] In the following text, suitable glass is described as a combination of stoichiometric glasses, i.e., glasses existing in the same stoichiometry also exist as crystals, and due to the identical topological structure of the components, as tested in numerous examples in the literature based on NMR measurements, it can be assumed that the properties of both glass and crystal are very similar under different conditions. For this purpose, such stoichiometric glasses are chosen, and mixtures thereof make it possible to achieve the properties in the sense of a solution according to the purpose of the invention. In this application, these stoichiometric glasses are also referred to as “base glass” or “constitutive phase”.

[0025] Describing glass based on its constituent phases is not a new concept. Conclusions about the chemical structure of glass can be drawn from the indicator base glass (see Conradt R: "Chemical structure, medium range order, and crystalline reference state of multicomponent oxide liquids and glasses", in Journal of Non-Crystalline Solids, Vol. 345-346, October 15, 2004, pp. 16-23).

[0026] The fundamental principle of this concept is that, as Conradt stated in the above quotation, one can describe a glass formed by a combination of various base glasses as a good approximation of an ideal mixture, and thus assume that the properties of the mixture can be described as a linear superposition of the properties of the base glasses. This is not the case with simple oxides. Various reactions occur between these substances during mixing; for example, an acid-base reaction occurs when components such as Na₂O (the anhydride of sodium hydroxide) and SiO₂ (the anhydride of silicic acid) meet. Therefore, mixtures of simple oxides can never be considered good approximations of ideal mixtures. The opposite is true in the case of mixtures of “finished” base glasses, especially when an acid-base reaction has already occurred.

[0027] This invention relates to a glass article, particularly a borosilicate glass article, comprising three parts (forming transitions between each other):

[0028] Top surface glass;

[0029] Core glass; and

[0030] Lower surface glass;

[0031] Wherein, the depth of the upper surface glass and the lower surface glass is <20nm in each case, and the core glass is at a depth of 500nm in any case;

[0032] Wherein, the sum of the proportions of tin oxide and bismuth oxide in the lower surface glass is greater than the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass;

[0033] Among them, the CTE of the core glass calculated according to formulas (13, 14) K The range is 2.5–5.0 ppm / K;

[0034] Among them, the CTE of the upper surface glass calculated according to formulas (14, 15, 16) OThe CTE of the core glass calculated according to formulas (13, 14) K At least 0.6 ppm / K lower; and

[0035] Where, if E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O According to formula (10), a compressive prestress of at least 50 MPa σ is generated on the upper surface. O .

[0036] The glass article according to the invention comprises three parts (forming transitions between each other): an upper surface glass, a core glass, and a lower surface glass. These three parts are integral components of the glass article. The division into three parts does not imply that the glass article represents a laminate or similar multilayer composite material, in which case three different glass articles are laminated together to form a novel glass article, or connected to each other in a positive-locking manner. The glass article according to the invention does not include such a laminate or the like, although glass articles can naturally be used as part of a laminate. The distinction of the three parts in the glass article more precisely stems from the fact, particularly in terms of the method of producing the glass article, that is, the glass composition on its surface can be altered, by which advantageous technical effects can be achieved, especially by applying the desired compressive prestress to the upper surface.

[0037] The glass article may be, for example, flat glass, particularly a glass sheet. The dimensions of the glass article can be specifically described as length, width, and thickness. Flat glass, in particular, is glass articles whose width and length are significantly greater than their thickness.

[0038] The thickness of the glass article according to the invention can be in the range of, for example, 0.1 mm to 30 mm, particularly 0.2 mm to 25 mm, 0.5 mm to 20 mm, 1.0 mm to 15 mm, 1.5 mm to 12 mm, 2.0 mm to 10 mm, 3.0 mm to 9.0 mm, or 4.0 mm to 8.0 mm. The thickness of the glass article can be, for example, at least 0.1 mm, at least 0.2 mm, at least 0.5 mm, at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, at least 3.0 mm, or at least 4.0 mm. The thickness of the glass article can be, for example, at most 30 mm, at most 25 mm, at most 20 mm, at most 15 mm, at most 12 mm, at most 10 mm, at most 9.0 mm, or at most 8.0 mm.

[0039] The width of the glass article can range from, for example, 1 cm to 1000 cm, particularly within the ranges of 2 cm to 500 cm, 5 cm to 200 cm, 10 cm to 150 cm, 20 cm to 100 cm, or 40 cm to 60 cm. The width of the glass article can be, for example, at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, at least 20 cm, or at least 40 cm. The width of the glass article can be, for example, at most 1000 cm, at most 500 cm, at most 200 cm, at most 150 cm, at most 100 cm, or at most 60 cm.

[0040] The length of the glass article can be, for example, from 1 cm to 1000 cm, particularly from 2 cm to 500 cm, 5 cm to 200 cm, 10 cm to 150 cm, 20 cm to 100 cm, or 50 cm to 70 cm. The length of the glass article can be, for example, at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, at least 20 cm, or at least 50 cm. For example, the length of the glass article can be, for example, at most 1000 cm, at most 500 cm, at most 200 cm, at most 150 cm, at most 100 cm, or at most 70 cm.

[0041] If E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O Then, according to formula (10), the compressive prestress σ generated on the upper surface O Preferably, it is at least 50 MPa, at least 60 MPa, at least 70 MPa, at least 80 MPa, at least 90 MPa, at least 100 MPa, at least 105 MPa, or at least 110 MPa. In some embodiments, if E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O Then, according to formula (10), the compressive prestress σ generated on the upper surface O The maximum pressure is 250 MPa, 225 MPa, 200 MPa, 175 MPa, 150 MPa, 140 MPa, 130 MPa, or 120 MPa. In some embodiments, if E / (1-μ) and T GThe core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O Then, according to formula (10), the compressive prestress σ generated on the upper surface O Between 50MPa and 250MPa, 60MPa and 225MPa, 70MPa and 200MPa, 80MPa and 175MPa, 90MPa and 150MPa, 100MPa and 140MPa, 105MPa and 130MPa, or 110MPa and 120MPa.

[0042] The terms "upper side" and "lower side" should not be construed as meaning that, when using glass articles, the upper side must be spatially positioned at the top and the lower side at the bottom. Rather, these terms are used only to clearly distinguish the two sides of a glass article and the corresponding surface glass. According to the invention, for example, the terms "first side" and "second side" can also be used instead of "upper side" and "lower side." In embodiments using float glass production, the terms "upper side" and "lower side" indicate orientation during the float process. The lower side faces the float tank, and the upper side faces away from the float tank. However, the term "core glass" refers to the composition of the core of the glass article, the composition of which is not changed by the production method compared to the composition of the upper and lower surface glass.

[0043] Preferably, the core glass is characterized by a constituent phase system comprising 10-50 mol% of sodium borosilicate, 0-30 mol% of potassium borosilicate, 0-15 mol% of anorthite, 0-20 mol% of boron trioxide, and 20-75 mol% of silicon dioxide.

[0044] The core glass is characterized by a constituent phase system comprising 10–50 mol% of sodium borosilicate, 0–30 mol% of potassium borosilicate, 0–20 mol% of anorthite, 0–20 mol% of boron trioxide, and 20–75 mol% of silicon dioxide. This constituent phase system is particularly suitable for CTE testing of the core glass. K CTE with the upper surface glass O The difference between the two values ​​yields the required compressive prestress.

[0045] Constituent phase Minimum value (mol%) Maximum value (mol%) Sodium borosilicate 10 50 Potassium silicate borosilicate 0 30 Iolite 0 20 calcium feldspar 0 20 Diopside 0 20 Boron trioxide 0 20 silicon dioxide 20 75

[0046] Constituent phase Minimum value (mol%) Maximum value (mol%) Sodium borosilicate 10 50 Potassium silicate borosilicate 0 30 Sodium feldspar 0 50 calcium feldspar 0 20 Boron trioxide 0 20 silicon dioxide 20 75

[0047] Preferably, the glass according to the invention should further satisfy other conditions, which are formulaically related to the composition of the constituent phases, and their relationship will be further emphasized below.

[0048] We will first point out the transformation matrix used to convert the compositional details of the constituent phases into simple oxides.

[0049] The composition of the constituent phase is converted into the composition of a simple oxide, and vice versa.

[0050] For ease of conversion, the composition of the constituent phases of the particularly preferred glass is expressed in the following standardized form:

[0051] Constituent phase Molecular formula (normalized to simple oxides) Sodium borosilicate <![CDATA[(Na2O·B2O3·6SiO2) / 8]]> Potassium silicate borosilicate <![CDATA[(K2O·B2O3·6SiO2) / 8]]> Iolite <![CDATA[(2MgO·2Al2O3·5SiO2) / 9 <!-- 5 -->]]> calcium feldspar <![CDATA[(CaO·Al2O3·2SiO2) / 4]]> Diopside <![CDATA[(MgO·CaO·2SiO2) / 4]]> Boron trioxide <![CDATA[B2O3]]> silicon dioxide <![CDATA[SiO2]]>

[0052] # oxides 1 <![CDATA[SiO2]]> 2 <![CDATA[B2O3]]> 3 <![CDATA[Al2O3]]> 4 MgO 5 CaO 6 <![CDATA[Na2O]]> 7 <![CDATA[K2O]]>

[0053] matrix

[0054]

[0055] The glass composition, expressed as a mole percentage, can be obtained by multiplying a column vector by a matrix. Conversely, the mole percentage composition can be easily converted into the base glass composition using the corresponding inverse matrix. Of course, only those base glass compositions that do not provide any negative values ​​to the base glass during the conversion are considered to be the base glass compositions according to the present invention.

[0056] For ease of conversion, the composition of the constituent phases of the further particularly preferred glass is expressed in the following standardized form:

[0057] Constituent phase Molecular formula (normalized to simple oxides) Sodium borosilicate <![CDATA[(Na2O·B2O3·6SiO2) / 8]]> Potassium silicate borosilicate <![CDATA[(K2O·B2O3·6SiO2) / 8]]> Sodium feldspar <![CDATA[(Na2O·Al2O3·6SiO2) / 8]]> calcium feldspar <![CDATA[(CaO·Al2O3·2SiO2) / 4]]> Boron trioxide <![CDATA[B2O3]]> silicon dioxide <![CDATA[SiO2]]>

[0058] # oxides 1 <![CDATA[SiO2]]> 2 <![CDATA[B2O3]]> 3 <![CDATA[Al2O3]]> 4 CaO 5 <![CDATA[Na2O]]> 6 <![CDATA[K2O]]>

[0059] matrix

[0060]

[0061]

[0062] As a result of multiplying a column vector by a matrix, the glass composition expressed as a mole percentage can be obtained. Conversely, the mole percentage composition can be easily converted into the base glass composition using the corresponding inverse matrix. Of course, only those base glass compositions that do not provide any negative values ​​to the base glass during the conversion are considered to be according to the invention.

[0063] Other conditions that the glass according to the invention should satisfy, which are formulaically related to the constituent phases, particularly specific surface properties, will be explained below.

[0064] In order to accurately describe these surface properties, the derivation of formula (3) must first be reported, including the assumptions made.

[0065] In the derivation of (3), it is first assumed that during the cooling process to the annealing point, all stresses are instantaneously relaxed, and that relaxation ceases from the annealing point onwards, corresponding to Franz Simon's similar work " den Zustand derunterkühlten Flüssigkeiten und Zeitschrift für anorganische undallgemeine Chemie 203, No.1 (1931), pp.219-227. Relative deformation of surface and core materials (T) G – T 环境 ΔCTE is determined by room temperature (here referred to as T). 环境 This is caused by the difference in the coefficients of thermal expansion between the lower surface and the core material. Assume 25°C is room temperature. Under equilibrium conditions, the surface is primarily under compressive prestress σ. O The core is mainly composed of tensile prestressed σ K Due to the equilibrium condition,

[0066]

[0067] They must satisfy the following relationship:

[0068]

[0069] Here, the integral in formula (4) is performed along the normal direction of plate thickness a, d O This refers to the surface thickness.

[0070] Under plane stress, the following relationship applies to the deformation ε and stress σ:

[0071]

[0072] So that it can be used in the following situations:

[0073]

[0074] Where, ε O It is surface deformation, ε K It's a deformation of the core.

[0075] As mentioned above, the relationship is:

[0076] ε O -ε K =-(T) G -T环境 )·ΔCTE (8)

[0077] Applicable to the relative deformation between the surface and the core, i.e., ε O -ε K If we still assume that the surface layer altered by CTE is much thinner than the glass core, we can ignore ε. K And written as:

[0078] ε O ≈-(T G -T 环境 )·ΔCTE (9)

[0079] or

[0080]

[0081] Once this point is ignored, it becomes irrelevant whether the prestress is symmetrical with respect to the center plane of the glass product or whether there is an asymmetrical stress distribution.

[0082] In the transition from (9) to (10), it is approximately assumed that the elastic modulus E and Poisson's ratio μ depend on the composition only to a very small extent, which can be ignored in this case, while CTE is highly dependent on the composition. This assumption is consistent with the properties of ordinary technical glasses, see Schott, Technical Glasses, Physical and Technical Properties, Mainz, 2014, at: https: / / www.us.schott.com / d / epackaging / 0ad24277-2ace-4d9a-999d-736ed389f6cc / 1.3 / 18.11.15_final_schott_technical_glasses_us.pdf.

[0083] Formula (10) and all subsequent considerations are also applied by design to the case described as being limited to one side of the glass article.

[0084] Equation (10) can be immediately extended to the case where the CTE near the surface has a depth-dependent distribution, provided that the thickness of the surface layer, whose CTE differs from that of the core region, is less than the total thickness of the substrate. Thus, we obtain:

[0085]

[0086] According to the present invention, glass articles, particularly sheets, wherein a stepped or continuous stress distribution is formed near the surface by means of the change of CTE with depth z, having a tensile stress zone in the core of the glass article and a compressive stress (distribution) zone on the surface.

[0087] If we insert typical values ​​of technical glass E = 72 GPa, μ = 0.2, T into (10), G =575℃, and set T 环境 =25℃, then we get:

[0088] σ O =49500 GPa·K·ΔCTE (12)

[0089] Therefore, a ΔCTE of 0.5 ppm / K results in σ O ≈25MPa, 1ppm / K ΔCTE makes σ O ≈ 50MPa, etc.

[0090] This value, 50 MPa, falls on the order of magnitude of the compressive prestress measured directly at the surface of what is known as partially prestressed glass (i.e., glass with a compressive prestress of 40 MPa to 60 MPa) (see S. Tasche, Glasbau; in: Wendehorst Bautechnische Zahlentafeln, Ed.: OWWetzell, 32). nd Edition, 2007; cited in K.-Ch. Thienel, Scriptum zur Vorlesung "Werkstoffe des Bauwesens / Glas", Institutfür Werkstoffe des Bauwesens, für Bauingenieur- und Vermessungswesen, der Bundeswehr München, Frühjahrstrimester 2018, www.unibw.de>lehre>skripte-werkstoffe>glas-2018.pdf).

[0091] The objective of this invention is to achieve a compressive prestress value of this order of magnitude. This compressive prestress increases strength by compressing cracks, the depth of which is on the same order of magnitude as the thickness of the compressive stress zone. For example, for a compressive prestress zone with a thickness in the double-digit nanometer range, cracks typically 1 nm to 10 nm deep in newly drawn glass can be compressed; for a compressive prestress zone with a thickness in the triple-digit nanometer range, cracks typically 100 nm deep in newly drawn glass that has subsequently undergone heat treatment (e.g., for stress relaxation) can be compressed. See REMould, The Strength of Inorganic Glasses, in: Fundamental Phenomena in the Materials Sciences, Publisher L.J. Bonis, JJ Duga and JJ Gilman, 119-149 (1967), cited by Hong Li in his invited presentation “Strength of Glass and Glass Fiber” at the 76th Conference on Glass Problems, GMIC, Alfred University, Am. Ceram. Soc. (Columbus, OH, Nov. 2-5, 2015), URL: https: / / www.researchgate.net / publication / 303099608_Strength_of_Glass_and_Glass_Fibers.

[0092] If the components according to the invention, for example, particularly glass plates, are successfully treated, the cracks of that magnitude should not be ignored in particular, so as not to cause deeper (literal) damage to the glass.

[0093] Therefore, according to the invention, the glass articles, especially those having the aforementioned composition in the core, have a CTE K -CTE O The difference is at least 0.6 ppm / K, preferably at least 0.8 ppm / K, particularly preferably at least 1 ppm / K, very particularly preferably at least 1.2 ppm / K, even more preferably at least 1.4 ppm / K, and most preferably at least 1.6 ppm / K.

[0094] This difference is determined by the composition of the core and surface regions, from which the corresponding coefficient of expansion is derived. This difference is also determined by the combination of composition and manufacturing method, which in turn leads to the difference between the core and surface compositions.

[0095] Since the coefficient of thermal expansion can be well approximated by the average bond strength of the composition, the value calculated in this way is used here. The CTE is calculated from the composition of the core glass or the surface glass according to formulas (13, 14, 15, 16). K and CTE O Formulas (13, 14) are used to calculate CTE. K CTE O The calculation can be performed using formulas (13, 14) or (14, 15, 16), but formula (14, 15, 16) is preferred. This is because, with regard to the production method, the composition of the surface glass may change such that its composition can no longer be described using the phase system according to the invention, especially if one or more phases exhibit negative proportions. Therefore, the phase-independent formulas (14, 15, 16) are more suitable for CTE. O The calculation.

[0096] In the above sample calculations, typical values ​​have been used to calculate the quotient of elastic modulus and variable (1-μ).

[0097] According to the invention, glass articles, particularly glass articles having the aforementioned composition in the core, preferably have an elastic modulus quotient of at least 80 GPa to a variable (1-μ).

[0098] Since the elastic modulus can be well approximated by the average bond strength of the composition, and Poisson's ratio can also be well approximated by the filler density and the number of crosslinks, the values ​​calculated in this way are used as follows (Formulas (29) and (27)).

[0099] The quotient of the elastic modulus calculated from the composition of the core glass using formulas (31) and (29) and the variable (1-μ) is preferably in the range of 80 GPa to 100 GPa, particularly in the range of 85 GPa to 95 GPa. The quotient of the elastic modulus calculated from the composition of the core glass using formulas (31) and (29) and the variable (1-μ) is, for example, at least 80 GPa or at least 85 GPa. The quotient of the elastic modulus calculated from the composition of the core glass using formulas (31) and (29) and the variable (1-μ) is preferably at most 100 GPa, particularly at most 95 GPa.

[0100] According to the present invention, glass articles, particularly glass articles having the aforementioned composition in their core, are further preferred, wherein T G The temperature must be at least 570°C.

[0101] However, due to the annealing point T GIt can be calculated very well by the average bond strength of the composition and the number of angular degrees of freedom of each atom, so the values ​​calculated in this way are used here (Formulas (35) and (33)).

[0102] Preferably, T is calculated from the composition of the core glass using formula (37). G Within the range of 570°C to 630°C, particularly 580°C to 620°C. T is calculated from the composition of the core glass using formula (37). G For example, at least 570°C or at least 580°C. T is calculated from the composition of the core glass using formula (37). G For example, up to 630°C or up to 620°C.

[0103] Preferably, the operating point VA is calculated from the composition of the core glass constituent phase according to formula (35). K The operating point VA is calculated from the composition of the core glass constituent phase according to formula (35) within the range of 1200°C to 1350°C, preferably 1250°C to 1300°C. K Preferably, the temperature is at least 1200°C or at least 1250°C. The operating point VA is calculated from the composition of the core glass constituent phase according to formula (35). K Preferably, the temperature is at most 1350°C or at most 1300°C.

[0104] Preferably, for float glass with an upper atmospheric side and a lower tin bath side, the surface compressive prestress σ calculated according to formula (10) is... O At least 50 MPa on the upper side and at least 25 MPa on the lower side. If E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O For float glass, especially for float glass with an upper atmospheric side and a lower tin bath side, the surface compressive prestress σ calculated according to formula (10) is... O The pressure on the upper side is preferably at least 60 MPa, at least 70 MPa, at least 80 MPa, at least 90 MPa, at least 100 MPa, at least 105 MPa, or at least 110 MPa. In some embodiments, if E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE OFor float glass, especially for float glass with an upper atmospheric side and a lower tin bath side, the surface compressive prestress σ calculated according to formula (10) is... O The pressure on the upper side is up to 250 MPa, up to 225 MPa, up to 200 MPa, up to 175 MPa, up to 150 MPa, up to 140 MPa, up to 130 MPa, or up to 120 MPa. In some embodiments, if E / (1-μ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O For float glass, especially for float glass with an upper atmospheric side and a lower tin bath side, the surface compressive prestress σ calculated according to formula (10) is... O The upper side is within the range of 50MPa to 250MPa, 60MPa to 225MPa, 70MPa to 200MPa, 80MPa to 175MPa, 90MPa to 150MPa, 100MPa to 140MPa, 105MPa to 130MPa, or 110MPa to 120MPa.

[0105] Coefficient of thermal expansion below the glass transition range

[0106] As can be seen from the literature, the coefficient of thermal expansion (e.g., the coefficient of thermal expansion of metals) is inversely proportional to the bond energy (or the "depth of the interatomic potential well"). See, for example, H. Skript zur Vorlesung "Einführung in dieMaterialwissenschaft I (Introduction to Materials Science I)", Christian Albrechts- Kiel, pp. 79-83.

[0107] In the simplified picture of oxide glasses, in each case, the cation is placed in a potential well formed by the surrounding oxygen atoms, and its depth is assumed to be the sum of the bonding strengths of the various simple bonds with the surrounding oxygen atoms, thus concentrating all the interaction energy in the potential well, which has a cation at the center and oxygen atoms on the periphery. Therefore, the reverse case no longer needs to be considered. Analysis is also more difficult because oxygen atoms can be located between several different types of cations, which cannot be reversed in pure oxide glasses. These values ​​are tabulated, for example, DE102014119594A1:

[0108] cation Potential well depth / (kJ / mol) Si 1864 B 1572.5 Al 1537 Mg 999 Ca 1063 Na 440.5 K 395

[0109] The average potential well depth can be calculated from the composition of the glass constituting the above-mentioned phases, the number of different cations contained in each phase, and the potential well depth of each cation listed above:

[0110]

[0111] Here, m is the number of cation types present, and E pot,j z is the potential well depth for the j-th cation type listed above. i,j This represents the number of cations of type j in the i-th constituent phase. The sums related to j are shown in the table below:

[0112] Table 4 “z-sum” and “z-E” pot sum"

[0113]

[0114] See H. The aforementioned quote states that the average bond strength, for example in the case of metals, is inversely proportional to the coefficient of thermal expansion. An evaluation of a range of different types of silicate glass (soda-lime glass, borosilicate glass, aluminosilicate glass) yields the following formula:

[0115]

[0116] Therefore, the average CTE 玻璃 The accurate prediction is 0.3 ppm / K.

[0117] Due to CTE 玻璃 The calculations only include the properties of oxides, therefore the CTE can also be calculated directly from the composition shown in the simple oxides. 玻璃 Therefore, (13) is amended to:

[0118]

[0119] The molar concentration k of the simple oxide containing the j-th cation j and the number of cations x in this simple oxide j The product of ∑c i ·z i,j :

[0120]

[0121] Since the ability to achieve the required CTE difference between the core and the surface depends on the CTE of the core. K Therefore, certain values ​​are preferred in this regard. The CTE of the core glass is calculated according to formulas (13, 14). KPreferably, it is 2.5 to 5.0 ppm / K, more preferably 3.0 to 4.5 ppm / K. The CTE of the core glass is calculated according to formulas (13, 14). K Preferably at least 2.5 ppm / K, more preferably at least 3.0 ppm / K. The CTE of the core glass is calculated according to formulas (13, 14). K Preferably, it is up to 5.0 ppm / K, and more preferably up to 4.5 ppm / K.

[0122] The CTE of the upper surface glass is calculated according to formulas (14, 15, 16). O Preferably, it is 1.2 to 3.0 ppm / k, more preferably 1.5 to 2.5 ppm / k. The CTE of the upper surface glass is calculated according to formulas (14, 15, 16). O Preferably at least 1.2 ppm / k, more preferably at least 1.5 ppm / k. The CTE calculated according to formulas (14, 15, 16) O Preferably 3.0 ppm / k, more preferably up to 2.5 ppm / k.

[0123] Preferably, the CTE of the surface glass is calculated according to formulas (14, 15, 16). O The CTE of the core glass calculated according to formulas (13, 14) K The concentration is at least 0.6 ppm / K, more preferably at least 0.8 ppm / K, particularly preferably at least 1.0 ppm / K, more preferably at least 1.2 ppm / K, more preferably at least 1.4 ppm / K, more preferably at least 1.6 ppm / K, more preferably at least 1.8 ppm / K, and more preferably at least 2.0 ppm / K. Preferably, ΔCTE = CTE. K -CTE O Within the range of 0.6 ppm / K to 3.6 ppm / K, for example, 0.8 ppm / K to 3.4 ppm / K, 1.0 ppm / K to 3.2 ppm / K, 1.2 ppm / K to 3.0 ppm / K, 1.4 ppm / K to 2.8 ppm / K, 1.6 ppm / K to 2.6 ppm / K, 1.8 ppm / K to 2.4 ppm / K, or 2.0 ppm / K to 2.2 ppm / K. ΔCTE = CTE K -CTE O It can be, for example, up to 3.6 ppm / K, up to 3.4 ppm / K, up to 3.2 ppm / K, up to 3.0 ppm / K, up to 2.8 ppm / K, up to 2.6 ppm / K, up to 2.4 ppm / K, or up to 2.2 ppm / K.

[0124] Density, molar volume and packing density

[0125] Knowing the density, molar volume, and filling density is necessary for calculating the elastic modulus.

[0126] It is worth noting that the molar mass M of each constituent phase can be obtained very easily using the lever rule. i and density ρ i Calculate the density ρ:

[0127]

[0128] In this case, the numerator of (17) is the molar mass, and the denominator is the molar volume V of the glass. mol Therefore, the density of the glass system discussed here can be predicted with an average accuracy of 1%.

[0129] For density values, see OVMazurin, MVStreltsina, TPShvaiko-Shvaikovskaya, Handbook of Glass Data AC, Elsevier, Amsterdam, 1983-1987.

[0130] Based on the molar volume, we also calculate the glass's packing density χ as an intermediate variable for further calculations. For this, we first calculate the (molar) ionic volume of each constitutive phase. This refers to the volume occupied by one mole of constitutive phase (more precisely: one mole of constitutive phase normalized to a simple oxide), if one considers them as spherical ions with Robert Shannon's "crystal radii," see Robert D. Shannon, Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides, ActaCryst. A32 (1976), pp. 751-767. These radii vary depending on the coordination number. For cations, the coordination number required for this has been deduced from the mineralogical literature on the constitutive phases discussed below. Following the above citation by Conradt R., we assume that the coordination number of cations in the glass is equal to the coordination number of the corresponding crystal phase. Oxygen atoms are allocated to cations according to this value, i.e., half an oxygen ion is allocated to a sodium ion, etc. Then it is assumed that a single oxygen ion is coordinated according to this allocation, i.e., one oxygen ion allocated to a silicon ion is coordinated twice, etc. In the above quotation, if Robert D. Shannon's table does not have an explicit radius value for a single coordination number, then interpolation or extrapolation is performed.

[0131] The resulting molar ion volume, along with the molar mass and density values, are listed in the table below.

[0132] Table 5. Molar mass, density, and molar ionic volume of the standardized constituent phases.

[0133]

[0134] The filling density can then be obtained using the following formula:

[0135]

[0136] elastic modulus

[0137] The calculation of the elastic modulus begins with the theory of Makishima and Mackenzie, see "Direct calculation of Young's modulus of glass" and "Calculation of bulk modulus, shear modulus and Poisson's ratio of glass", J. Non-Crystall. Sol., 1973 and 1975. According to this theory, the elastic modulus can be expressed as:

[0138]

[0139] Here, e 离解,i It is the dissociation energy density of the i-th component (with dimensions, for example, kJ / cm²). 3 ), c i It is its molar ratio. χ is the packing density.

[0140] For further calculation, it can be rewritten as:

[0141]

[0142] Makishima and Mackenzie argued that the dissociation energy is the same as the aforementioned bond strength. Above, we attributed the latter to the cation; thus, if we are referring to simple oxides in terms of composition, the average molar dissociation energy can be determined by multiplying the average potential well depth of the cation by the number of cations per mole, z.

[0143]

[0144] therefore:

[0145]

[0146] Using the above theory, very good results can be obtained for glasses without boron oxide rings. The temporary extensions to borates made by Makishima and Mackenzie were not satisfactory.

[0147] Plucinski and Zwanziger’s new theory (“Topological constraints and the Makishima–Mackenzie model”, J. Non-Crystall. Sol., 2015) supplements the expression features with topological pre-factors, but in the published form, it only applies to purely covalently bonded glasses (chalcogenides).

[0148] Therefore, an improved topological prefactor is defined in this example.

[0149] For example, DE102014119594A1 explains in detail that the essence of topological matters is the calculation of constraints imposed on atoms due to bonding with neighboring atoms. These constraints relate partly to the interatomic distances (“distance conditions”) and partly to the bond angles (“angle conditions”). If an atom has r neighbors (r = coordination number), and these distance conditions are evenly distributed between two bond pairs, the distance conditions to be assigned to that atom follow a range from the r distance conditions to the r / 2 distance conditions of those neighbors. Furthermore, the 2r-3 angle conditions to be assigned to that atom follow the bond angles between these neighbors, with the angles considered at their apexes.

[0150] DE102014119594A1 describes a method that, during the calculation of distance and angle conditions, weights all conditions by a single bond strength and then additionally weights the angle conditions (angle conditions only from the oxygen-cation-oxygen angle; conditions belonging to the cation-oxygen-cation angle are ignored) by the covalent degree of the corresponding bond. The weighting factors are normalized because, in each case, the silicon-oxygen bond is separated by a single bond strength or the covalent degree of the silicon-oxygen bond, resulting in multiple (rounded) 1.333333333 (i.e., 4 / 3) distance conditions and (rounded) 1.666666667 (i.e., 5 / 3) angle conditions per atom for quartz glass. As explained in DE102014119594A1, if all distance and angle conditions are simply calculated and the angle condition for the silicon-oxygen-silicon angle is ignored, it corresponds to a direct analysis of the topology of quartz glass.

[0151] Therefore, each atom in quartz glass has "3" constraints, which corresponds exactly to the number of degrees of freedom per atom. Thus, quartz glass should not have any (or in fact: very small) configurational degrees of freedom per atom, which corresponds to the small c-degrees of freedom of quartz glass during the glass transition as measured by differential calorimetry. p For transition, see R. Brüning, "On the glass transition in vitreous silica by differential thermal analysis measurements", Journal of Non-Crystalline Solids 330 (2003) 13–22.

[0152] For other oxide glasses, the numerical values ​​of the distance condition and the corner condition per atom are typically less than (rounded) 1.33333333 (4 / 3) or 1.666666667 (5 / 3). However, in the case of the corner condition, it is still possible to distinguish whether the relevant corner condition is related to all in-plane corners (triangular coordination) or not (tetrahedral or higher coordination). The latter is referred to here as the 3D corner condition.

[0153] Therefore, in each case, for each atom (abbreviated as "pA"), "4 / 3 minus the distance condition number" is called the distance degree of freedom, "5 / 3 minus the angle condition number" is called the angle degree of freedom, and "5 / 3 minus the 3D angle condition number" is called the 3D angle degree of freedom.

[0154] The following considerations still apply. The Makishima-Mackenzie model method sums and averages isotropic interactions. However, in the boron-oxygen ring region, the interactions are not isotropic; instead, “powerless” slip may occur on the boron-oxygen ring plane.

[0155] To account for this, the elastic modulus E is considered to consist of shear and compression / expansion ratios. This is expressed by the following formula, see, for example, H. Skript zur Vorlesung "Einführungin die Materialwissenschaft I",Christian Albrechts- Kiel, pp. 79–83:

[0156]

[0157]

[0158]

[0159]

[0160] Here, G is the shear modulus, K is the compression modulus, and μ is Poisson's ratio. E can be calculated from any one of the variable pairs G and K, G and μ, and K and μ according to (23).

[0161] The theory of Makashima and Mackenzie has now been revised because the aforementioned ratio between modulus and dissociation energy density is set for the shear modulus G, not the elastic modulus E:

[0162]

[0163] At this point, no further setting of the ratio of shear modulus to filler density is required. The relationship between filler density and filler density, as indicated by Makashima and Mackenzie, will be discussed further below.

[0164] Due to the aforementioned sliding surface, the presence of the boron-oxygen ring leads to a decrease in shear modulus. This fact is taken into account by the prefactor f, which is defined as the ratio between the numbers. The first number is the number of conditions per atomic angle minus the difference between the number of 3D degrees of freedom per atom and the number of degrees of freedom per atomic angle (2 / 3). The second number is the number of conditions per atomic angle. If the boron-oxygen ring is absent, the prefactor is 1; if the boron-oxygen ring is present, the prefactor is less than 1.

[0165]

[0166]

[0167] The number (2 / 3) is derived from the following considerations regarding shear. It is assumed that the boron-oxygen rings are distributed such that (1 / 3) lies within the plane covered by the shear angle, and (2 / 3) lies within the plane perpendicular to it. Only the latter two contribute to reducing the shear modulus. If not all angular conditions are calculated, but only the 3D angular conditions are calculated, then only (2 / 3) of the additional angular degrees of freedom are calculated accordingly.

[0168] Unlike the shear modulus, the compressive modulus is not expected to change significantly due to the presence of the sliding surface. For consistency reasons, this affects the Poisson's ratio μ. Therefore, (23d) is considered. If G changes due to the introduction of the sliding surface, and K should not change due to other conditions remaining constant, this can and must be achieved by Δμ f The change in μ is used to compensate. To quantify this change in the first approximation, K undergoes a first-order increase after f and μ, and then ΔK = 0 is still required:

[0169]

[0170] Therefore, we can conclude that:

[0171]

[0172] Since the glass according to the present invention is a silicate glass, quartz glass was chosen as the starting point for development. For quartz glass, μ = 0.17, f = 1, and these values ​​are inserted accordingly into the square bracket expression. Therefore, the expression is assumed to have a value of 0.2574. To obtain Δμ for different silicate glasses... f Multiply -0.2574 by Δf = f - 1, where f is the value generated by (25) for different glasses.

[0173] When switching from quartz glass to different silicate glasses, another factor related to μ should also be considered. Other silicate glasses have similar but different filling densities, but there is a positive correlation between μ and filling density; see Greaves, G., Greer, A., Lakes, R., Rouxel, T., Poisson's ratio and modern materials, Nature Mater 10, 823–837 (2011). This takes into account a second term, Δμ, which is referred to as Δμ. χ For the glass according to the invention, this can be assumed to be linear, and therefore applies to the following cases:

[0174]

[0175] Starting again with quartz glass, χ = 0.33367062. Then, using the χ value calculated according to (18) and 0.33367062, Δχ is determined according to Δχ = χ - 0.33367062. In the left denominator, μ = 0.17, and in the right denominator, χ = 0.33367062. Therefore, we calculate μ of the glass according to the present invention by the following formula:

[0176] μ = 0.17 + Δμ f +Δμ χ (29)

[0177] Therefore, E is calculated using (23b):

[0178]

[0179] "a" and "b" are adjustable parameters. An evaluation of a range of different types of silicate glass (soda lime glass, borosilicate glass, aluminosilicate glass) yielded the following formula:

[0180]

[0181] In this case, insert the unit in kJ / Mol. z is dimensionless (molar cations per mole of glass) and expressed in cm 3 V in units mol In each case, the results should be derived from formula (13) and table (4). V mol It is the denominator in formula (18). f is derived from the angle condition according to formula (25) and table (6). Δμ is derived from formula (29). f and Δμ χ Δμ is obtained. Δμ is derived from f according to formula (27). f Δμ is obtained from formula (28). χ The fill density χ must be entered, which is derived from formula (18). Therefore, the average error in the calculation of E is 2.5 GPa.

[0182] Since the glass according to the invention has the combination of the above-described constituent phases, it is advantageous to initially represent these conditions of each constituent phase numerically for calculating the distance condition number, angular condition number, and 3D angular condition number of each atom.

[0183] The following values ​​were originally calculated according to the method indicated in DE102014119594A1, where, in fact, as described in DE102014119594A1 (but only for boron and aluminum), the angular condition number has been calculated for all cations. Furthermore, the degree of ionization of the cation-oxygen compound cannot be calculated according to formula (8) of DE102014119594A1, but rather according to formula (3) of Alberto Garcia, Marvon Cohen, First Principles Ionicity Scales, Phys. Rev. B 1993. The required coordination number for this purpose is taken from the mineralogical literature listed below when discussing the constitutive phases. Based on the above citation by Conradt R., we assume that the coordination number of the cations in the glass is equal to the coordination number of the corresponding crystalline phase.

[0184] Applicable to the following situations:

[0185] Table 6 shows the number of conditions, etc.

[0186]

[0187] Therefore, the angular condition b used to determine each atom in the finished glass W The calculation rules are as follows:

[0188]

[0189] Among them, c i y is the molar proportion of the i-th constituent phase in the glass composition under consideration.i b is the number of atoms in each structural unit of the i-th constituent phase. W,i It is the angular condition number of each atom in the i-th constitutive phase. "n" is the number of constitutive phases.

[0190] The 3D angular condition b for each atom in the finished glass is determined in a similar manner. 3D-W The calculation rules are:

[0191]

[0192] Among them, b 3D-W,i It is the 3D angular condition number of each atom in the i-th constituent phase.

[0193] The distance condition b for each atom in the finished glass is determined in a similar manner. A The calculation rules are:

[0194]

[0195] Among them, b A,i It is the distance condition number for each atom in the i-th constituent phase.

[0196] work point

[0197] Calculate the annealing point T G First, the operating point VA needs to be calculated.

[0198] The operating point VA can be calculated using the average bond strength in a manner similar to thermal expansion, at which the viscosity is 10. 4 dPa·s. As can be seen from the literature, melting point (e.g., the melting point of a metal) is inversely proportional to bond energy (or "depth of the interatomic potential well"), see, for example, H. Skript zur Vorlesung "Einführung in die MaterialwissenschaftI",Christian Albrechts- Kiel, pp. 79-83. Here, the melting point is determined based on the operating temperature.

[0199] Therefore, adopt The method involves evaluating a range of different types of silicate glass (soda-lime glass, borosilicate glass, aluminosilicate glass) and deriving the following formula:

[0200]

[0201] Therefore, the average error when calculating VA is 28K.

[0202] The difference between the working point and the annealing point, annealing point

[0203] Based on the aforementioned meanings of "short" or "long" for glass, that is, a steep or flat profile of the viscosity curve above the annealing point, when the viscosity is 10... 13 At dPa·s, the operating point VA and the annealing point T G The differences between them become particularly important.

[0204] Surprisingly, it is clear that this difference is related to the number of angular degrees of freedom. This makes the VA-T... G To express directly, and through relation T G =VA-(VA-T) G Indirectly determine the annealing point.

[0205] The starting point is this. (T) G The distance between the thermogravimetric (VA) and the viscosity is related to the temperature distribution of viscosity in the supercooled melt region. This can be described by a narrow temperature range using a thermally activated model from Arrhenius. More complex models are needed to describe the entire temperature range. The most widely used is the model by Adam and Gibbs, see G. Adam, JH Gibbs, On the Temperature Dependence of Cooperative Relaxation Properties in Glass-Forming Liquids, J. Chem. Phys. 43 (1965) pp. 139-145. It combines Arrhenius's thermally activated method for the motion of individual atoms and takes into account how many atomic interactions are necessary for partial motion of the viscous flow to be possible. The result is a relationship between viscosity and configurational entropy.

[0206] This relationship helps explain why there are "short" and "long" glasses, and how they depend on composition. A rule of thumb is: "The higher the degree of configurational freedom, the 'shorter' the glass." As mentioned above, the degree of configurational freedom, in turn, depends on composition. In glasses primarily composed of covalent bonds (e.g., the covalent bond between silicon and oxygen), this number is small. In glasses with a large number of ionic bonds (e.g., the ionic bond between sodium and oxygen), this number is large.

[0207] Based on deeper physicochemical considerations, quantitative measurement of glass “shortness” has outstanding applicability, which can be traced back to Austen Angell’s concept of “brittleness”, see Charles Austen Angell, Thermodynamic aspects of the glass transition in liquids and plastic crystals, Pure & Appl. Chem. 63, No. 10 (1991), pp. 1387-1392.

[0208] In this context, it is recommended to test the variable VA-T. G The relationship between angular and configurational degrees of freedom. Since actual reconstruction always involves the utilization of angular degrees of freedom, we will focus on the latter here. The angular degrees of freedom f for each atom are calculated from the number of constraints related to angles. W See below, see (15).

[0209]

[0210] By evaluating a range of different types of silicate glass (soda-lime glass, borosilicate glass, aluminosilicate glass), the following formula was derived:

[0211]

[0212] By VA and VA-T G T can be calculated G Therefore, T G The average error is 22K.

[0213] Select appropriate constituent phases

[0214] Sodium borosilicate

[0215] The production of the product according to the invention should be carried out by specifically developing the varying trends of evaporation of different glass components from an open, hot glass surface. This trend is particularly pronounced in the case of boron and alkali metals, thus alkali metal borates typically evaporate from the open surface of hot borosilicate glass (here, "hot" refers to the environment around the operating point, i.e., when the glass viscosity is 10). 4temperature of dPa·s), see Johannes Alphonsius Christianus van Limpt, Modeling of evaporation processes in glass melting furnaces, Dissertation, Technische Universiteit Eindhoven, 2007, ISBN: 978-90-386- 1147-1.

[0216] Therefore, according to the present invention, sodium borosilicate is a fundamental component of glass. At high temperatures, typically at VA, sodium borosilicate partially dissociates into evaporated sodium borate and SiO2 remaining in the melt. At low temperatures, typically at T... G Sodium borosilicate exists in a non-dissociated form, composed of SiO4- and BO4 tetrahedra, i.e., a framework silicate. The sodium ions filling the framework are coordinated five times, see Appleman, DE, Clark, JR: Crystal structure of sodium borosilicate, a boron albite, and its relation to feldspar crystal chemistry. Am. J. Sci. 50, 1827–1850 (1965). This is advantageous for the equally desired high elastic modulus.

[0217] With respect to the CTE required in this article 玻璃 Compared to the maximum value, the CTE of sodium borosilicate glass is... 玻璃 The value is high, with the proportion of sodium borosilicate at most 50 mol%. One mole of sodium borosilicate is understood as one mole of (Na2O·B2O3·6SiO2) / 8.

[0218] The proportion of sodium borosilicate in each core glass according to the present invention is preferably 10 to 40 mol%, more preferably in the range of 12 to 36 mol%.

[0219] The proportion of sodium borosilicate in the core glass according to the present invention is 10-50 mol%, preferably 11-40 mol%, more preferably 12-36 mol%, more preferably 13-34 mol%, more preferably 14-32 mol%, more preferably 15-30 mol%, more preferably 16-28 mol%, more preferably 17-26 mol%. The proportion of sodium borosilicate in the core glass according to the present invention is at least 10 mol%, preferably at least 11 mol%, more preferably at least 12 mol%, more preferably at least 13 mol%, more preferably at least 14 mol%, more preferably at least 15 mol%, more preferably at least 16 mol%, more preferably at least 17 mol%. The proportion of sodium borosilicate in the core glass according to the present invention is at most 50 mol%, more preferably at most 40 mol%, more preferably at most 36 mol%, more preferably at most 34 mol%, more preferably at most 32 mol%, more preferably at most 30 mol%, more preferably at most 28 mol%, more preferably at most 26 mol%.

[0220] In some embodiments, the composition of the upper surface glass changes compared to the core glass, particularly due to changes in the manufacturing method, such that the composition of the upper surface glass can no longer be described using the phase system according to the invention, especially because one or more phases exhibit negative proportions. However, this is not the case in all embodiments. The invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the core glass, without any negative phase proportions.

[0221] The proportion of sodium borosilicate in the upper surface glass according to the present invention is, for example, 0–20.0 mol%, 0.1–15.0 mol%, 0.2–10.0 mol%, 0.5–9.0 mol%, or 1.0–8.0 mol%. The proportion of sodium borosilicate in the upper surface glass according to the present invention can be, for example, at least 0.1 mol%, at least 0.2 mol%, at least 0.5 mol%, or at least 1.0 mol%. The proportion of sodium borosilicate in the upper surface glass according to the present invention can be, for example, at most 20.0 mol%, at most 15.0 mol%, at most 10.0 mol%, at most 9.0 mol%, or at most 8.0 mol%.

[0222] The ratio of sodium borosilicate in the core glass to that in the upper surface glass is preferably in the range of 1.4:1 to 150:1, more preferably 1.5:1 to 100:1, more preferably 1.6:1 to 75:1, and more preferably 1.7:1 to 50:1, for example, 2.0:1 to 40:1, 2.2:1 to 30:1, 2.4:1 to 20:1, or 2.5:1 to 10.0:1. The ratio of sodium borosilicate in the core glass to that in the upper surface glass is preferably at least 1.4:1, more preferably at least 1.5:1, more preferably at least 1.6:1, and more preferably at least 1.7:1, for example, at least 2.0:1, at least 2.2:1, at least 2.4:1, or at least 2.5:1. The ratio of sodium borosilicate in the core glass to that in the upper surface glass is preferably at most 150:1, 100:1, 75:1, 50:1, 40:1, 30:1, 20:1, or 10:1. Some difference in the sodium borosilicate ratio between the core glass and the upper surface glass is advantageous because it contributes to the desired CTE difference between them to a certain extent. However, limiting the difference in the sodium borosilicate ratio is advantageous to avoid a very large CTE difference.

[0223] silicon dioxide

[0224] Due to CTE 玻璃 The expected maximum value is relatively low, making it convenient to combine sodium borosilicate glass with pure SiO2 as another constituent phase. Furthermore, a high SiO2 ratio is known to benefit the glass's high chemical resistance. For this reason, a high proportion of SiO2 is also required as a constituent phase.

[0225] However, this ratio is limited for various reasons. First, SiO2 does not possess the effects described above, nor does it have the effect required to generate the CTE gradient of sodium borosilicate. Furthermore, silica glass is composed of unfilled SiO4 tetrahedra, which is detrimental to the desired high elastic modulus. Finally, from a processing perspective, an excessively high proportion of SiO2 will lead to an excessively high operating point for the glass.

[0226] The proportion of silicon dioxide in the core glass according to the present invention is preferably 20-75 mol%, for example 25-70 mol%, 30-65 mol%, 35-62 mol%, or 40-60 mol%. The proportion of silicon dioxide as the constituent phase in the core glass can be, for example, at least 20 mol%, at least 25 mol%, at least 30 mol%, at least 35 mol%, or at least 40 mol%. The proportion of silicon dioxide as the constituent phase in the core glass can be, for example, at most 75 mol%, at most 70 mol%, at most 65 mol%, at most 62 mol%, or at most 60 mol%.

[0227] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described by the same phase system as the composition of the core glass, without any negative phase proportions in any phase.

[0228] The proportion of silica in the upper surface glass is preferably 50–90 mol%, for example 60–88 mol%, 70–86 mol%, or 72–84 mol%. The proportion of silica as the constituent phase in the upper surface glass can be, for example, at least 50 mol%, at least 60 mol%, at least 70 mol%, or at least 72 mol%. The proportion of silica as the constituent phase in the upper surface glass can be, for example, at most 90 mol%, at most 88 mol%, at most 86 mol%, or at most 84 mol%.

[0229] The ratio of silicon dioxide in the upper surface glass to that in the core glass is preferably in the range of 1.1:1 to 2.0:1, more preferably 1.2:1 to 1.9:1, more preferably 1.3:1 to 1.8:1, and more preferably 1.4:1 to 1.7:1. The ratio of silicon dioxide in the upper surface glass to that in the core glass is preferably at least 1.1:1, more preferably at least 1.2:1, more preferably at least 1.3:1, and more preferably at least 1.4:1. The ratio of silicon dioxide in the upper surface glass to that in the core glass is preferably at most 2.0:1, more preferably at most 1.9:1, more preferably at most 1.8:1, and more preferably at most 1.7:1.

[0230] Potassium silicate borosilicate

[0231] To improve devitrification stability, potassium analogs of sodium borosilicate can still be added to the glass. With this addition, the finished glass contains not only sodium but also potassium as an alkali, thus improving its devitrification stability.

[0232] The corresponding constituent phase is referred to below as “potassium borosilicate” because it can be considered as a potassium analog of borosilicate with a dambury structure, see Mineralogical Magazine 57 (1993) 157-164.

[0233] One mole of potassium borate is understood as the number of moles of (K2O·B2O3·6SiO2) / 8.

[0234] The proportion of potassium borate in the core glass according to the present invention is 0-30 mol%, for example, 1.0-25.0 mol%, 2.0-20.0 mol%, or 2.5-15.0 mol%. The proportion of potassium borate in the core glass according to the present invention can be, for example, at least 1.0 mol%, at least 2.0 mol%, or at least 2.5 mol%. The proportion of potassium borate in the core glass can be, for example, up to 30.0 mol%, up to 25.0 mol%, up to 20.0 mol%, or up to 15.0 mol%.

[0235] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0236] The proportion of potassium borate in the upper surface glass is 0–20.0 mol%, for example, 0.5–15.0 mol%, 1.0–12.5 mol%, or 2.0–10.0 mol%. The proportion of potassium borate in the upper surface glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, or at least 2.0 mol%. The proportion of potassium borate in the upper surface glass can be, for example, at most 20.0 mol%, at most 15.0 mol%, at most 12.5 mol%, or at most 10.0 mol%.

[0237] The ratio of potassium borate in the core glass to that in the upper surface glass is preferably 1.05:1 to 2.00:1, more preferably 1.10:1 to 1.75:1, and even more preferably 1.15:1 to 1.50:1. The ratio of potassium borate in the core glass to that in the upper surface glass is preferably at least 1.05:1, more preferably at least 1.10:1, and even more preferably at least 1.15:1. The ratio of potassium borate in the core glass to that in the upper surface glass is preferably at most 2.00:1, at most 1.75:1, or at most 1.50:1.

[0238] Boron trioxide

[0239] Boron trioxide, a constituent phase, also evaporates, and the presence of B2O3 amplifies this evaporation effect. The degree of evaporation can be controlled by relative air humidity; in the presence of H2O, B2O3 evaporates as metaboric acid (HBO2). However, an excessively high proportion of B2O3 still reduces the elastic modulus.

[0240] The proportion of boron trioxide, the constituent phase, in the core glass of the present invention is 0-20 mol%, preferably 0-15 mol%, more preferably 0-10 mol%, more preferably 0.5-8 mol%, more preferably 0.8-7 mol%, more preferably 1-6 mol%, more preferably 1.5-5.5 mol%, more preferably 2-5 mol%, more preferably 2.5-4.5 mol%, and more preferably 3-4 mol%. The proportion of boron trioxide, the constituent phase, in the core glass can be, for example, at least 0.5 mol%, at least 0.8 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 2.5 mol%, or at least 3.0 mol%. The proportion of boron trioxide, a constituent phase, in the core glass can be, for example, up to 20 mol%, up to 15 mol%, up to 10.0 mol%, up to 8.0 mol%, up to 7.0 mol%, up to 6.0 mol%, up to 5.5 mol%, up to 5.0 mol%, up to 4.5 mol%, or up to 4.0 mol%.

[0241] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0242] The proportion of boron trioxide, the constituent phase, in such an upper surface glass is, for example, 0–15 mol%, 0–10 mol%, 0.5–8 mol%, 0.8–7 mol%, 1–6 mol%, 1.5–5.5 mol%, 2–5 mol%, 2.5–4.5 mol%, or 3–4 mol%. The proportion of boron trioxide, the constituent phase, in the upper surface glass can, for example, be at least 0.5 mol%, at least 0.8 mol%, at least 1.0 mol%, at least 1.5 mol%, or at least 2.0 mol%. The proportion of boron trioxide, the constituent phase, in the upper surface glass can, for example, be at most 15 mol%, at most 12.5 mol%, at most 10.0 mol%, at most 9.0 mol%, at most 8.0 mol%, at most 7.0 mol%, at most 6.0 mol%, at most 5.5 mol%, at most 5.0 mol%, at most 4.5 mol%, or at most 4.0 mol%.

[0243] The ratio of boron trioxide in the core glass to that in the upper surface glass is preferably 1.1:1 to 3.5:1, more preferably 1.2:1 to 3.0:1, more preferably 1.4:1 to 2.5:1, more preferably 1.6:1 to 2.2:1, and more preferably 1.7:1 to 2.0:1. The ratio of boron trioxide in the core glass to that in the upper surface glass is preferably at least 1.1:1, more preferably at least 1.2:1, more preferably at least 1.4:1, at least 1.6:1, or at least 1.7:1. The ratio of boron trioxide in the core glass to that in the upper surface glass is preferably at most 3.5:1, at most 3.0:1, at most 2.5:1, at most 2.2:1, or at most 2.0:1.

[0244] calcium feldspar

[0245] Sodium borosilicate and its potassium analogues are alkaline. As mentioned above, alkaline glasses have a high coefficient of thermal expansion. To set the coefficient of thermal expansion to the desired value, SiO2 and B2O3 can be added, but their use is limited in terms of VA and elastic modulus.

[0246] Another possible phase is alkaline earth metal-aluminum-silicate calcium feldspar, the addition of which shifts the expansion coefficient toward the average value without the drawbacks of SiO2 and B2O3 mentioned above. One mole of calcium feldspar is understood as one mole of (CaO·Al2O3·2SiO2) / 4.

[0247] In the case of the glass according to the invention, the advantage of this composition is that aluminum has a very low evaporation tendency, and (even though some degree of calcium consumption can be observed on the surface in the above examples) the evaporation tendency of alkaline earth metals is also lower than that of alkali metals, see van Limpt, loc.cit., thus the presence of these phases can prevent the formation of pure quartz glass due to evaporation on the surface, and due to its extreme properties (very high T... G (etc.) do not want this to happen.

[0248] In the case of the glass according to the invention, the proportion of anorthite in the core glass is preferably 0 to 20 mol%, or 0 to 15 mol%, for example 0 mol% to 10.0 mol%, 0.5 mol% to 9.0 mol%, 1.0 mol% to 8.0 mol%, 1.5 mol% to 7.0 mol%, 2.0 mol% to 6.0 mol%, 2.5 mol% to 5.0 mol%, or 3.0 mol% to 4.5 mol%. The proportion of anorthite in the core glass can be, for example, up to 0.5 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 2.5 mol%, or at least 3.0 mol%. The proportion of anorthite in the core glass can be, for example, up to 20 mol%, up to 15 mol%, up to 10.0 mol%, up to 9.0 mol%, up to 8.0 mol%, up to 7.0 mol%, up to 6.0 mol%, up to 5.0 mol%, or up to 4.5 mol%. In some embodiments, the proportion of anorthite in the core glass is at most 0.2 mol% or at most 0.1 mol%, or the core glass may not even contain anorthite.

[0249] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0250] The proportion of anorthite in such an upper surface glass can range from, for example, 0 mol% to 10.0 mol%, specifically, these proportions can range from 0 mol% to 7.5 mol%, 0 mol% to 5.0 mol%, 0.1 mol% to 4.0 mol%, 0.2 mol% to 3.0 mol%, 0.5 mol% to 2.5 mol%, or 1.0 mol% to 2.0 mol%. The proportion of anorthite in the upper surface glass can, for example, be at least 0.1 mol%, at least 0.2 mol%, at least 0.5 mol%, or at least 1.0 mol%. The proportion of anorthite in the upper surface glass can, for example, be at most 10.0 mol%, at most 7.5 mol%, at most 5.0 mol%, at most 4.0 mol%, at most 3.0 mol%, at most 2.5 mol%, or at most 2.0 mol%. In some embodiments, the proportion of anorthite in the upper surface glass is at most 0.2 mol% or at most 0.1 mol%, or the upper surface glass may not even contain anorthite.

[0251] The ratio of the anorthite component in the core glass to that in the upper surface glass is preferably 1.1:1 to 10.0:1, more preferably 1.2:1 to 7.5:1, more preferably 1.3:1 to 5.0:1, more preferably 1.4:1 to 4.0:1, and even more preferably 1.5:1 to 3.5:1. The ratio of the anorthite component in the core glass to that in the upper surface glass is preferably at least 1.1:1, more preferably at least 1.2:1, more preferably at least 1.3:1, for example, at least 1.4:1, or at least 1.5:1. The ratio of the anorthite component in the core glass to that in the upper surface glass is preferably at most 10.0:1, at most 7.5:1, at most 5.0:1, at most 4.0:1, or at most 3.5:1.

[0252] Other constituent phases

[0253] In addition to the aforementioned constituent phases of sodium borosilicate, silicon dioxide, potassium sodium borosilicate, boron trioxide, and anorthite, the glass preferably has a composition characterized by a constituent phase system that includes other constituent phases, particularly albite or cordierite and diopside in the core glass as described above.

[0254] Sodium feldspar

[0255] To suppress the potential segregation tendency of pure borosilicate systems, albite (an aluminum analog of sodium borosilicate) can be added as another phase (American Mineralogist, Volume 81, pp. 1344-1349, 1996). See issue of separation JWGreig, Immuniscibility in silicate melts, Am.J.Sci., 5th ser., Vol.13 (1927), 1-44 and 133-154. According to the present invention, the term one mole of albite refers to one mole of (Na₂O·Al₂O₃·6SiO₂) / 8. At high albite proportions, melting capacity may be impaired.

[0256] A particularly preferred core glass is characterized by the following constituent phases (listed below): sodium borosilicate, potassium sodium borosilicate, sodium feldspar, calcium feldspar, boron trioxide, and silicon dioxide.

[0257] The proportion of albite in the core glass can be, for example, 0–50 mol%, preferably 0.5–45 mol%, more preferably 1–40 mol%, more preferably 1.5–35 mol%, more preferably 2–33 mol%, more preferably 4–30 mol%, more preferably 5–27 mol%, more preferably 7–25 mol%, more preferably 8–22 mol%, more preferably 10–20 mol%, more preferably 11–18 mol%, and more preferably 12–16 mol%. The proportion of albite in the core glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 4.0 mol%, at least 5.0 mol%, at least 7.0 mol%, at least 8.0 mol%, at least 10.0 mol%, at least 11.0 mol%, or at least 12.0 mol%. The proportion of albite in the core glass can be, for example, up to 50 mol%, up to 45 mol%, up to 40 mol%, up to 35 mol%, up to 33 mol%, up to 30 mol%, up to 27 mol%, up to 22 mol%, up to 20 mol%, up to 18 mol%, or up to 16 mol%.

[0258] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0259] The proportion of albite in the upper surface glass can be, for example, 0–50 mol%, preferably 0.5–45 mol%, more preferably 1–40 mol%, more preferably 1.5–35 mol%, more preferably 2–33 mol%, more preferably 4–30 mol%, more preferably 5–27 mol%, more preferably 7–25 mol%, more preferably 8–22 mol%, more preferably 10–20 mol%, more preferably 11–18 mol%, and more preferably 12–16 mol%. The proportion of albite in the upper surface glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 4.0 mol%, at least 5.0 mol%, at least 7.0 mol%, at least 8.0 mol%, at least 10.0 mol%, at least 11.0 mol%, or at least 12.0 mol%. The proportion of albite in the glass on the upper surface can be, for example, up to 50 mol%, up to 45 mol%, up to 40 mol%, up to 35 mol%, up to 33 mol%, up to 30 mol%, up to 27 mol%, up to 22 mol%, up to 20 mol%, up to 18 mol%, or up to 16 mol%.

[0260] The ratio of the constituent phase albite in the core glass to that in the upper surface glass is preferably 0.5:1 to 2.0:1, more preferably 0.6:1 to 1.5:1, and even more preferably 0.7:1 to 1.3:1. The ratio of the constituent phase albite in the core glass to that in the upper surface glass is preferably at least 0.5:1, more preferably at least 0.6:1, and even more preferably at least 0.7:1. The ratio of the constituent phase albite in the core glass to that in the upper surface glass is preferably at most 2.0:1, at most 1.5:1, or at most 1.3:1. In some embodiments, the ratio of the constituent phase albite in the core glass to that in the upper surface glass may be greater than 1:1, for example at least 1.1:1 or at least 1.2:1.

[0261] Iolite, Diopside

[0262] However, other phases can also be added, whose size does not shift the expansion coefficient towards the average value, nor do they have the disadvantages of SiO2 and B2O3 mentioned above. These are alkaline earth metal-aluminum-silicate cordierite and diopside. One mole of cordierite can be understood as one mole of (2MgO·2Al2O3·5SiO2) / 9. One mole of diopside can be understood as one mole of (MgO·CaO·2SiO2) / 4.

[0263] The advantages of these two components are similar to those of anorthite, especially since the presence of these phases prevents the formation of pure quartz glass due to surface evaporation, and also due to their extreme properties (very high T). G (etc.) do not want this to happen.

[0264] A particularly preferred core glass is characterized by the following constituent phases (listed below): sodium borosilicate, potassium sodium borosilicate, cordierite, anorthite, diopside, boron trioxide, and silicon dioxide.

[0265] The proportion of cordierite in the core glass can be, for example, 0–20 mol%, preferably 0–15 mol%, more preferably 0–10.0 mol%, more preferably 0.5–9.0 mol%, more preferably 1.0–8.0 mol%, more preferably 1.5–7.0 mol%, more preferably 2.0–6.0 mol%, more preferably 2.5–5.0 mol%, and more preferably 3.0–4.0 mol%. The proportion of cordierite in the core glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 2.5 mol%, or at least 3.0 mol%. The proportion of cordierite in the core glass can be, for example, up to 20 mol%, up to 15 mol%, up to 10.0 mol%, up to 9.0 mol%, up to 8.0 mol%, up to 7.0 mol%, up to 6.0 mol%, up to 5.0 mol%, or up to 4.0 mol%.

[0266] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0267] The proportion of cordierite in the upper surface glass can be, for example, 0–20 mol%, preferably 0–15 mol%, more preferably 0–10.0 mol%, more preferably 0.5–9.0 mol%, more preferably 1.0–8.0 mol%, more preferably 1.5–7.0 mol%, more preferably 2.0–6.0 mol%, more preferably 2.5–5.0 mol%, and more preferably 3.0–4.0 mol%. The proportion of cordierite in the upper surface glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, at least 1.5 mol%, at least 2.0 mol%, at least 2.5 mol%, and at least 3.0 mol%. The proportion of cordierite in the glass on the upper surface can be, for example, up to 20 mol%, up to 15 mol%, up to 10.0 mol%, up to 9.0 mol%, up to 8.0 mol%, up to 7.0 mol%, up to 6.0 mol%, up to 5.0 mol%, or up to 4.0 mol%.

[0268] The ratio of cordierite in the core glass to that in the upper surface glass is preferably 0.5:1 to 2.0:1, more preferably 0.6:1 to 1.5:1, more preferably 0.7:1 to 1.3:1, for example, 0.8:1 to 1:1. The ratio of cordierite in the core glass to that in the upper surface glass is preferably at least 0.5:1, more preferably at least 0.6:1, more preferably at least 0.7:1, for example, at least 0.81. The ratio of cordierite in the core glass to that in the upper surface glass is preferably at most 2.0:1, at most 1.5:1, or at most 1.3:1, for example, at most 1:1.

[0269] The proportion of diopside in the core glass can be, for example, 0 to 20 mol%, or 0 to 17.5 mol%, preferably 0 to 15.0 mol%, more preferably 0.5 to 14.0 mol%, more preferably 1.0 to 13.0 mol%, more preferably 2.0 to 12.0 mol%, more preferably 3.0 to 11.0 mol%, more preferably 5.0 to 10.0 mol%, more preferably 6.0 to 9.0 mol%, and more preferably 7.0 to 8.0 mol%. The proportion of diopside in the core glass can be, for example, at least 0.5 mol%, at least 1.0 mol%, at least 2.0 mol%, at least 3.0 mol%, at least 5.0 mol%, at least 6.0 mol%, or at least 7.0 mol%. The proportion of diopside in the core glass can be, for example, up to 20 mol%, up to 15.0 mol%, up to 14.0 mol%, up to 13.0 mol%, up to 12.0 mol%, up to 11.0 mol%, up to 10.0 mol%, up to 9.0 mol%, or up to 8.0 mol%.

[0270] As described above, the present invention also includes embodiments in which the composition of the upper surface glass can be described using the same phase system as the composition of the core glass, without any negative phase ratios.

[0271] The proportion of diopside in the upper surface glass can be, for example, 0–10.0 mol%, preferably 0–7.5 mol%, more preferably 0–5.0 mol%, more preferably 0–4.0 mol%, more preferably 0.1–3.0 mol%, more preferably 0.2–2.0 mol%, more preferably 0.5–1.5 mol%, and more preferably 0.7–1.0 mol%. The proportion of diopside in the upper surface glass can be, for example, at least 0.1 mol%, at least 0.2 mol%, at least 0.5 mol%, or at least 0.7 mol%. The proportion of diopside in the upper surface glass can be, for example, at most 10.0 mol%, at most 7.5 mol%, at most 5.0 mol%, at most 4.0 mol%, at most 3.0 mol%, at most 2.0 mol%, at most 1.5 mol%, or at most 1.0 mol%.

[0272] The ratio of diopside in the core glass to that in the upper surface glass is preferably in the range of 1.1:1 to 50:1, more preferably in the range of 1.5:1 to 25:1, and even more preferably in the range of 2.0:1 to 20:1, for example, in the range of 5.0:1 to 15:1 or in the range of 7.5:1 to 12.5:1. The ratio of diopside in the core glass to that in the upper surface glass is preferably at least 1.1:1, more preferably at least 1.5:1, and even more preferably at least 2.0:1, for example, at least 5.0:1 or at least 7.5:1. The ratio of diopside in the core glass to that in the upper surface glass is preferably at most 50:1, at most 25:1, or at most 20:1, for example, at most 15:1 or at most 12.5:1.

[0273] Other components

[0274] In addition to the components already stated, the glass may also contain other components referred to herein as “residues.” The proportion of residues in the glass according to the invention is preferably up to 5 mol% so as not to interfere with the glass properties set by a suitable base glass selected through careful screening. In particularly preferred embodiments, the proportion of residues in the glass is up to 3 mol%, more preferably up to 2 mol%, or up to 1 mol%, or up to 0.5 mol%. The residues particularly contain oxides not present in the base glass described herein. Therefore, the residues are particularly free of any SiO2, Al2O3, B2O3, MgO, CaO, Na2O, or K2O.

[0275] If this specification states that the glass is free of a component or constituent phase, or does not contain a specific component or constituent phase, it means that the component or constituent phase may be present in the glass as a contaminant under any circumstances. This means that it will not be added in large quantities. According to the invention, the insignificant amount is less than 300 ppm (mol), preferably less than 100 ppm (mol), particularly preferably less than 50 ppm (mol), and most preferably less than 10 ppm (mol). In particular, the glass of the present invention is free of zinc, barium, zircon, lead, arsenic, antimony, and / or cadmium.

[0276] The core glass and / or the upper surface glass are preferably also free of bismuth. Conversely, the lower surface glass may particularly contain tin oxide and / or bismuth oxide, preferably in a total proportion of at least 300 ppm (mol), for example, at least 350 ppm (mol), at least 400 ppm (mol), at least 450 ppm (mol), at least 500 ppm (mol), at least 600 ppm (mol), at least 700 ppm (mol), at least 800 ppm (mol), at least 900 ppm (mol), at least 0.1 mol%, at least 0.2 mol%, at least 0.3 mol%, or at least 0.4 mol%. The lower surface glass preferably contains tin oxide and / or bismuth oxide in a total proportion of at most 2.0 mol%, at most 1.5 mol%, at most 1.0 mol%, at most 0.8 mol%, or at most 0.6 mol%. The total proportion of tin oxide and bismuth oxide in the lower surface glass can be, for example, 300 ppm (mol) to 2.0 mol%, 350 ppm (mol) to 2.0 mol%, 400 ppm (mol) to 2.0 mol%, 450 ppm (mol) to 1.5 mol%, 500 ppm (mol) to 1.5 mol%, 600 ppm (mol) to 1.0 mol%, 700 ppm (mol) to 1.0 mol%, 800 ppm (mol) to 1.0 mol%, 900 ppm (mol) to 0.8 mol%, 0.1 mol% to 0.8 mol%, 0.2 mol% to 0.6 mol%, 0.3 mol% to 0.6 mol%, or 0.4 mol% to 0.6 mol%.

[0277] According to the present invention, the sum of the proportions of tin oxide and bismuth oxide in the lower surface glass is greater than the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass. The sum of the proportions of tin oxide and bismuth oxide in the lower surface glass may exceed the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass, for example, exceeding at least 1 ppm (mol), at least 10 ppm (mol), at least 50 ppm (mol), at least 100 ppm (mol), at least 200 ppm (mol), at least 300 ppm (mol), at least 350 ppm (mol), at least 400 ppm (mol), at least 450 ppm (mol), at least 500 ppm (mol), at least 600 ppm (mol), at least 700 ppm (mol), at least 800 ppm (mol), at least 900 ppm (mol), at least 0.1 mol%, at least 0.2 mol%, at least 0.3 mol%, or at least 0.4 mol%. The sum of the proportions of tin oxide and bismuth oxide in the lower surface glass can exceed the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass, for example, by up to 2.0 mol%, up to 1.5 mol%, up to 1.0 mol%, up to 0.8 mol%, or up to 0.6 mol%. The sum of the proportions of tin oxide and bismuth oxide in the lower surface glass can be greater than the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass, for example, 300 ppm (mol) to 2.0 mol%, 350 ppm (mol) to 2.0 mol%, 400 ppm (mol) to 2.0 mol%, 450 ppm (mol) to 1.5 mol%, 500 ppm (mol) to 1.5 mol%, 600 ppm (mol) to 1.0 mol%, 700 ppm (mol) to 1.0 mol%, 800 ppm (mol) to 1.0 mol%, 900 ppm (mol) to 0.8 mol%, 0.1 mol% to 0.8 mol%, 0.2 mol% to 0.6 mol%, 0.3 mol% to 0.6 mol%, or 0.4 mol% to 0.6 mol%. In some embodiments, the sum of the proportions of tin oxide and bismuth oxide in the lower surface glass may be at least 50 ppm (mol), at least 100 ppm (mol), at least 150 ppm (mol), at least 200 ppm (mol), or at least 250 ppm (mol) greater than the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass. For example, 50 ppm (mol) to 2.0 mol%, 100 ppm (mol) to 1.5 mol%, 150 ppm (mol) to 1.0 mol%, 200 ppm (mol) to 0.8 mol%, or 250 ppm (mol) to 0.6 mol%.

[0278] The term "tin oxide" is used herein as a general term for various tin oxides, particularly SnO, SnO2, and Sn2O3. Specifically, the proportion of tin oxide describes the sum of the proportions of SnO, SnO2, and Sn2O3. Similarly, the term "bismuth oxide" is used herein as a general term for various bismuth oxides, particularly Bi2O3 and Bi2O5. Specifically, the proportion of bismuth oxide describes the sum of the proportions of Bi2O3 and Bi2O5.

[0279] All formulas used for calculating properties are configured to calculate values ​​for a glass containing 100% of the constituent phases. Therefore, the presence or absence of residues is irrelevant for calculating its properties from the phase composition. The formulas are configured to obtain the same results with and without residues. With larger residues, the calculations become correspondingly less accurate.

[0280] manufacture

[0281] This invention also relates to a method for producing glass articles, comprising the following steps:

[0282] - Melt the glass raw material;

[0283] - Glass articles, especially flat glass sheets, are formed from molten glass; and

[0284] - Cool the glass product.

[0285] The method preferably includes forming flat glass by float glass.

[0286] The glass is first melted in a molten bath and then “refined” in a bubble-free manner in a refining section. In a channel downstream of the molten bath, the liquid glass can be homogenized, for example, by a stirrer, and the viscosity required for forming can be achieved by adjusting (regulating) a specified glass temperature.

[0287] The formation of flat glass ribbons is preferably carried out in a flotation tank. The regulated glass melt can flow into the flotation tank, particularly through a spout. The float process according to the invention differs significantly from the standard float process described, for example, for the production of soda-lime float glass, especially in terms of temperature control and residence time.

[0288] In the float process, a continuous glass ribbon of desired width and thickness is produced by continuously adding molten glass to the surface of a molten metal bath. The glass, floating on the surface of the molten metal, extends across this surface. Molten tin is preferably used as the molten metal. The temperature in the molten tin, and especially above it, has hotter and colder zones, in which the molten glass is applied in the hot zone and slowly lifted and removed in a solidified state in the colder zone. The float process according to the invention, particularly suitable for borosilicate glass, operates at a relatively low production rate of 20-100 tons / day (typically 500-1000 tons / day for soda-lime float systems).

[0289] The required glass thickness can be precisely adjusted by production volume, total glass ribbon width, and transport speed. The glass ribbon width is adjusted, for example, using top rollers in the forming section of the float facing the molten pool. These either pull the glass outwards (for a balance thickness less than 7 mm) or transport the glass inwards (for a balance thickness greater than 7 mm). For glass thicknesses greater than 12 mm, graphite barriers are also used to prevent outward flow of glass in the float. Precise thickness distribution can be controlled by glass temperature. Glass temperature is regulated, in particular, by segmented SiC heating elements. Preferably, only the surface of the glass ribbon is heated in the float. The glass temperature (ribbon temperature) is measured, for example, along the longitudinal axis of the float using a radiation pyrometer. Tin temperature can also be recorded using thermocouples.

[0290] Due to the heating of the glass surface, in the case of borosilicate glass, the glass components (especially alkali metal borates and / or metaborates) evaporate into the surrounding atmosphere. These evaporation products can be continuously discharged (exhaust) along with the forming gas atmosphere to prevent condensation of these evaporation products in the cold flotation area (outlet end).

[0291] The type and extent of evaporation can be specifically adjusted through temperature control and / or residence time at a particular temperature. Evaporation can also be influenced by the composition of the forming gas atmosphere. Evaporation, in turn, significantly determines the compositional variations of the upper surface glass, thereby creating a CTE difference between the upper surface glass and the core glass, which is itself necessary for the compressive prestress required on the upper surface.

[0292] To avoid oxidation of liquid tin, the flotation tank is preferably operated under a reducing protective gas atmosphere, preferably a forming gas mixture of N2 and H2. Specifically, a small overpressure (e.g., approximately 0.3 mbar) may be present in the flotation tank to avoid or minimize the infiltration of oxygen from the air. The partial pressure of oxygen (pO2) can be continuously measured at multiple points in the flotation tank. If air infiltrates the flotation tank or O2 escapes from the glass melt into the flotation tank atmosphere, O2 will react with H2 to form vapor.

[0293] This manufacturing process utilizes the varying evaporation trends of various glass components (particularly boron and alkali metals) from an open, hot glass surface. The evaporation rate can be adjusted to the desired level by selectively tuning various process parameters. A certain degree of evaporation is beneficial for achieving favorable compressive prestress on the upper surface. On the other hand, limiting evaporation can also be advantageous, particularly in reducing the tendency for brittleness or fragmentation that may be associated with particularly high evaporation rates in some cases.

[0294] In the flowing glass section, the glass temperature (temperature of the glass strip) is preferably between VA and VA + 0.2 (VA - T). G )between.

[0295] In the flowing glass section, the glass temperature is preferably at least VA. This is advantageous for the flow characteristics of the glass. The glass temperature in the flowing glass section is further preferably at least VA + 10°C or higher, more preferably at least VA + 20°C, for example at least VA + 30°C, at least VA + 40°C, at least VA + 50°C, at least VA + 60°C, at least VA + 70°C, at least VA + 80°C, at least VA + 90°C, or at least VA + 100°C. Because the glass temperature in the flowing glass section is selected to be higher than VA, the desired degree of evaporation can be increased. This refers to the VA value calculated based on the composition of the core glass (also referred to herein as VA). K ).

[0296] However, the glass temperature in the flowing glass section is preferably at most VA + 0.2 (VA - TG). The glass temperature in the flowing glass section is preferably at least VA + 140°C, at least VA + 130°C, at least VA + 120°C, or at least VA + 110°C. Limiting the flow temperature helps reduce evaporation to a desired level, thereby allowing for targeted adjustment of the desired compressive prestress on the upper surface. These refer to the VA value calculated based on the composition of the core glass (also referred to herein as VA). K ).

[0297] The glass temperature in the flowing glass section can be particularly within the range of VA+10°C to VA+140°C, especially within the ranges of VA+20°C to VA+140°C, VA+30°C to VA+140°C, VA+40°C to VA+130°C, VA+50°C to VA+130°C, VA+60°C to VA+120°C, VA+70°C to VA+120°C, VA+80°C to VA+110°C, VA+90°C to VA+110°C, or VA+100°C to VA+110°C. These refer to the VA values ​​calculated based on the composition of the core glass (also referred to as VA in this document). KTo achieve the desired evaporation rate, the temperature is VA to VA+6.5mm / d*100℃, preferably VA+6.5mm / d*2℃ to VA+6.5mm / d*80℃, preferably VA+6.5mm / d*5℃ to VA+6.5mm / d*50℃, preferably VA+6.5mm / d*8℃ to VA+6.5mm / d*30℃, and particularly preferably VA+6.5mm / d*10℃ to VA+6.5mm / d*15℃, where d is the thickness of the (cooled) glass article in mm.

[0298] The glass temperature in the outlet region of the flotation tank is preferably at T. G and T G +0.2(VA-T G Between ) . This refers to the composition of the core glass and T . G The calculated VA value (also referred to as VA in this paper) K ).

[0299] Annealing point T G The composition of the phase consisting of the core glass is calculated according to formula (37), and the operating point VA is calculated according to formula (35).

[0300] To achieve the evaporation target, the glass is formed in the flotation tank (viscosity at 10). 3 dPas to 10 8 The preferred range for the dwell time (within the dPa range) is 5 to 60 minutes, for example, 10 to 50 minutes, 15 to 40 minutes or 20 to 30 minutes.

[0301] In particular, the evaporation rate of alkali metal borates from the glass surface in the flotation tank depends on the residence time and temperature, and essentially on the temperature and residence time of the glass in the evaporation zone. With a constant glass production rate (pulling rate), the residence time is determined by the thickness of the glass to be manufactured.

[0302] Given a residence time, the evaporation rate can be adjusted by regulating the glass temperature. Given a thickness, the residence time can also be adjusted by correspondingly adjusting the glass production rate.

[0303] Glass forming area in the flotation tank (viscosity at 10) 3 dPas to 10 8The residence time in the glass (viscosity in the range of 103 dPas) is preferably at least 5 minutes, at least 10 minutes, at least 15 minutes, or at least 20 minutes. At least 10 minutes, at least 15 minutes, or at least 20 minutes are particularly advantageous for further increasing the degree of evaporation. The residence time of the glass in the forming zone of the flotation tank (viscosity in the range of 103 dPas to 108 dPas) is preferably at most 60 minutes, at most 50 minutes, at most 40 minutes, or at most 30 minutes. This is beneficial for reducing evaporation to the desired level.

[0304] Evaporation behavior may be influenced by one or more other factors:

[0305] Preferably, the glass melt should contain 30-60 mmol of water per liter of glass in dissolved form, for example, 40-50 mmol of water. For example, the water content can be determined, preferably, in the cooled core glass, according to "David Pearson, A., Pasteur, GA & Northover, WR Determination of the absorptivity of OH in a sodium borosilicate glass. J Mater Sci 14, 869–872 (1979). https: / / doi.org / 10.1007 / BF00550718". To achieve this, the glass can be melted in a bath in an atmosphere containing gaseous water, at least at its surface. A water-containing atmosphere can be generated, in particular, by burning fossil fuels or hydrogen with pure oxygen. Therefore, the degree of boric acid evaporation can be optimized. Water releases boric acid from the glass and contributes to its evaporation. Therefore, the glass melt preferably contains at least 30 mmol or at least 40 mmol of water per liter of glass. To limit the degree of evaporation, it may be advantageous if the glass melt contains at most 60 mmol or 50 mmol of water per liter of glass in dissolved form.

[0306] The degree of evaporation can also be affected by the amount of forming gas (particularly the inflow and outflow rates). The flotation tank pressure can advantageously be adjusted between 0.05 and 0.3 mbar, for example, between 0.1 and 0.2 mbar, particularly by changing the amount of forming gas and the outflow rate. The flotation tank pressure can be, for example, at least 0.05 mbar or at least 0.1 mbar. The flotation tank pressure can be, for example, at most 0.3 mbar or at most 0.2 mbar.

[0307] It is also advantageous if the hydrogen content in the forming gas atmosphere is between 2 and 15 vol%, for example, between 5 and 10 vol%. For example, the hydrogen content in the forming gas atmosphere is at least 2 vol% or at least 5 vol%. For example, the hydrogen content in the forming gas atmosphere is at most 15 vol% or at most 10 vol%.

[0308] The saturation of the atmosphere by evaporating substances could also limit the extent of evaporation. However, there are problems with limiting evaporation in this way. This is because the atmosphere in the floating pool is constantly being replaced, and the evaporation products are constantly being removed, so saturation is never reached.

[0309] According to the present invention, process parameters are selected to produce the desired product characteristics in terms of surface evaporation. Different glass thicknesses may require different settings. For example, for ultrathin glass with a thickness of 1 mm or less, if the preferred residence time of at least 5 minutes for surface evaporation is not achieved, the production rate of the float tank (lifting rate) can be reduced to increase the residence time accordingly.

[0310] Conversely, in terms of the degree of evaporation, different residence times may also be advantageous for different glass thicknesses. A residence time of 1 to 10 minutes per millimeter of glass thickness is particularly advantageous, especially 2 to 8 minutes or 3 to 5 minutes per millimeter of glass thickness. Preferably, the residence time is at least 1 minute, at least 2 minutes, or at least 3 minutes per millimeter of glass thickness. More preferably, the residence time is at most 10 minutes, at most 8 minutes, or at most 5 minutes per millimeter of glass thickness. This refers to the glass thickness of the finished (cooled) glass product and the glass's viscosity in the flotation zone (viscosity at 10). 3 dPas to 10 8 The dwell time within the range of dPas.

[0311] All relevant process parameters for molding can be recorded in the "Settings". This ensures that, in addition to geometric target parameters such as glass thickness, wedge value, warpage, and waviness, the desired effects, especially in evaporation, are achieved.

[0312] use

[0313] The present invention also relates to the use of glass articles, particularly in cooking appliances, preferably in induction cooking appliances; as fire doors; as fireplace viewing panels or as windows. Detailed Implementation

[0314] Example

[0315] Preferred embodiments and manufacturing processes of the present invention are described in more detail below.

[0316] The examples listed below are examples of bulk materials whose surfaces have undergone chemical analysis. In these cases, surface analysis was performed using TOF-SIMS; for targets capable of compressing cracks at a depth of at least 1–10 nm, in each case, the average of measurements near the surface up to a depth less than 20 nm was used as the surface value. This also explains the noise that inevitably arises with this method. In each case, approximately three separate measurements were performed at approximately equidistant depths of approximately 9 nm, approximately 14 nm, and approximately 19 nm.

[0317] The TOF-SIMS signal intensities (for Si, B, Na, etc.) remain constant from a depth of approximately 250 nm. These signal intensities are essentially those obtained from normal chemical analysis and specify a concentration in percent. These values ​​are continuous towards the surface. The surface concentrations determined in this way are then normalized so that their sum is 100%.

[0318] Example 1

[0319] Example 1 is a borosilicate glass that has been produced using the float glass process to a thickness of 6.5 mm as a flat glass. The molten bath is heated with oxygen-enriched fuel, and the bath's production capacity is 53 t / d. The feed channel leads from the molten bath to the "lip nozzle." This channel is covered to prevent the alkaline borate from evaporating there.

[0320] The hot glass first flows through the "lip nozzle" below the gate (TWEEL) at an operating temperature of 1350°C into the float tank area, reaching the hot tin surface. This location is referred to as "Separation Room 0"; the name derives from dividing the float tank into areas called "Separation Rooms". In this example, there are "8" Separation Rooms; each area is 3m long.

[0321] The production capacity of the floating pool is approximately 50 tons per day.

[0322] In section 1, the molten glass spreads out and flows out to a width of approximately 1.50 m under the influence of gravity. As a result, the glass strip further expands to the target width of 2.8 m.

[0323] The higher the temperature, the better the evaporation of alkaline borate from the glass surface. Therefore, the heating power (top) of partition 1 is approximately 50-150 kW. The glass surface temperature is 1200-1300 °C.

[0324] In dividing chambers 2 to 4, the glass ribbon is formed to the desired thickness using an upper rolling mill. The forming zone has advantageous heating power and glass surface temperature.

[0325] • Partition 2: 100-200KW and 1050-1150℃

[0326] • Partition 3: 200-300KW and 1000-1100℃

[0327] • Partition 4: 50-100KW and 950-1050℃

[0328] Divided compartments 1 to 4 form an evaporation zone.

[0329] In dividing chambers 5-8, the glass ribbon is cooled only and lifted at an outlet temperature of 650–700°C and conveyed from the float tank to the annealing furnace. The heating power of dividing chambers 5-8 is approximately 50–150 kW. Evaporation of basic borates no longer occurs in these areas.

[0330] Constituent phase mol% (standardized) <![CDATA[Sodium borosilicate (Na2O·B2O3·6SiO2) / 8]]> 17.8 <![CDATA[(K2O·B2O3·6SiO2) / 8]]> 3.0 <![CDATA[Sodium feldspar (Na2O·Al2O3·6SiO2) / 8]]> 11.4 <![CDATA[Boron Oxide B2O3]]> 9.1 <![CDATA[Silicon dioxide SiO2]]> 58.7

[0331] nature core CTE 3.3ppm / K E / (1-μ) 84.7 GPa <![CDATA[T G ]]> 584℃ VA 1294℃

[0332] nature upper side CTE 1.9ppm / K

[0333] upper side <![CDATA[σ O ]]> 68MPa

[0334] Example 2

[0335] Constituent phase mol% (standardized) <![CDATA[Sodium borosilicate (Na2O·B2O3·6SiO2) / 8]]> 25.4 <![CDATA[(K2O·B2O3·6SiO2) / 8]]> 4.2 <![CDATA[Albite (Na2O·Al2O3·6SiO2) / 8]]> 11.6 <![CDATA[Anorthite (CaO·Al2O3·2SiO2) / 4]]> 4.4 <![CDATA[Boron Oxide B2O3]]> 5.7 <![CDATA[Silicon dioxide SiO2]]> 48.7

[0336] nature Core CTE 3.8ppm / K E / (1-μ) 89.1 GPa <![CDATA[T G ]]> 599℃ VA 1264℃

[0337] nature upper side CTE 1.8ppm / K

[0338] upper side <![CDATA[σ O ]]> 106MPa

[0339] Example 3

[0340] Constituent phase mol% (standardized) <![CDATA[Sodium borosilicate (Na2O·B2O3·6SiO2) / 8]]> 23.0 <![CDATA[(K2O·B2O3·6SiO2) / 8]]> 12.6 <![CDATA[Cordierite (2MgO·2Al2O3·5SiO2) / 9]]> 3.5 <![CDATA[Anorthite (CaO·Al2O3·2SiO2) / 4]]> 3.1 <![CDATA[Diopside (MgO·CaO·2SiO2) / 4]]> 7.5 <![CDATA[Boron Oxide B2O3]]> 4.3 <![CDATA[Silicon dioxide SiO2]]> 46.0

[0341] nature Core CTE 4.0ppm / K E / (1-μ) 92.4 GPa <![CDATA[T G ]]> 612℃ VA 1255℃

[0342] nature upper side CTE 2.2ppm / K

[0343] upper side <![CDATA[σ O ]]> 95.4MPa

Claims

1. A glass article comprising three parts: - Upper surface glass; - Core glass; and - Lower surface glass; in, The depth of the upper surface glass and the lower surface glass is <20nm under different conditions, and the core glass is located at a depth of 500nm in any case; Wherein, the sum of the proportions of tin oxide and bismuth oxide in the lower surface glass is greater than the sum of the proportions of tin oxide and bismuth oxide in the upper surface glass, in mol. The CTE of the core glass calculated according to formulas (13, 14) K The range is 2.5–5.0 ppm / K; Among them, the CTE of the upper surface glass calculated according to formulas (14, 15, 16) O The CTE of the core glass calculated according to formulas (13, 14) K At least 0.6 ppm / K lower; and Where, if E / (1-µ) and T G The core glass is calculated using formulas (31), (29), and (37), and if ΔCTE is the difference between the CTE values ​​calculated for the core glass and the upper surface glass, then ΔCTE is used. K -CTE O According to formula (10), a compressive prestress of at least 50 MPa σ is generated on the upper surface. O ; in Official (10) Where E is the elastic modulus, μ is Poisson's ratio, and T is the elastic modulus. G It is a discrete value of the glass transition range, T 环境 This represents the temperature of the cooling medium or the ambient temperature. Official (13), in, It is the average well depth, m is the number of cation types present, and E is the mean well depth. pot,j It is the potential well depth of the j-th cation type, z i,j It represents the number of cations of the j-th type in the i-th constituent phase; Official (14), Official (15), Official (16), Wherein, the molar concentration k of the simple oxide containing the j-th cation is used. j and the number of cations x in this simple oxide j The product of ∑c i ·z i,j ; Official (29), in, , ; Official (31), Among them, c i χ is the molar proportion of the i-th constituent phase in the glass composition under consideration, χ is the packing density, the prefactor f is defined as the ratio between the numbers, and V mol It is the molar volume of glass; Official (37), Where VA is the operating point, f W These are the angular degrees of freedom of the atom. It is the compressibility modulus.

2. The glass article according to claim 1, wherein, The glass product is a borosilicate glass product.

3. The glass article according to claim 1, wherein, The core glass is characterized by a constituent phase system comprising 10-50 mol% of sodium borosilicate, 0-30 mol% of potassium borosilicate, 0-20 mol% of anorthite, 0-20 mol% of boron trioxide, and 20-75 mol% of silicon dioxide.

4. The glass article according to any one of claims 1 to 3, wherein the composition of the core glass is characterized by the following constituent phases: 。 5. The glass article according to any one of claims 1 to 3, wherein the composition of the core glass is characterized by the following constituent phases: 。 6. The glass article according to any one of claims 1 to 3, wherein, The ratio of the constituent phase silica in the upper surface glass to the constituent phase silica in the core glass is in the range of 1.1:1 to 2.0:

1.

7. The glass article according to any one of claims 1 to 3, wherein, The proportion of silica, the constituent phase, in the upper surface glass is at least 50 mol.

8. The glass article according to any one of claims 1 to 3, wherein, The proportion of the anorthite phase in the upper surface glass is at most 5 mol%.

9. The glass article according to any one of claims 1 to 3, wherein, The proportion of sodium borosilicate in the upper surface glass is at most 10 mol.

10. The glass article according to any one of claims 1 to 3, wherein, The CTE of the upper surface glass is calculated according to formulas (14, 15, 16). O The concentration ranges from 1.2 ppm / K to 3.0 ppm / K.

11. The glass article according to any one of claims 1 to 3, wherein, The operating point VA is calculated from the composition of the core glass phase according to formula (35). K Within the range of 1200℃ to 1350℃, Official (35).

12. The glass article according to any one of claims 1 to 3, wherein, The elastic modulus calculated from the composition of the core glass using formulas (31) and (29) is in the range of 80 GPa to 100 GPa.

13. The glass article according to any one of claims 1 to 3, wherein, The thickness of the glass product is in the range of 0.1 mm to 30 mm.

14. A method for producing a glass article according to any one of claims 1 to 13, comprising the following steps: - Melt the glass raw material; - A flat glass plate is formed from molten glass, wherein the flat glass is formed by float glass forming, wherein the molten glass is added to the surface of a float pool composed of molten metal; -in 10 3 dPa.s to 10 8 At viscosities within the range of dPa.s, the residence time of the glass in the forming zone of the flotation tank is in the range of 5 to 60 minutes; and - Cool the glass product.

15. The method according to claim 14, wherein, The glass raw material is melted in a melting bath.

16. The method according to any one of claims 14 to 15, wherein, The glass melt contains 30 mmol to 60 mmol of water per liter of dissolved glass.

17. The method according to any one of claims 14 to 15, wherein, The molten metal is tin and / or bismuth.

18. The method according to any one of claims 14 to 15, wherein, The molten glass flows onto the surface of the floating pool.

19. The method according to any one of claims 14 to 15, wherein, The dwell time is in the range of 1 to 10 minutes per millimeter of the thickness of the glass article.

20. The method according to any one of claims 14 to 15, wherein, The glass temperature in the flowing glass section is in VA K +10°C to VA K Within the range of +140℃.

21. The method of claim 20, wherein the glass temperature is the glass strip temperature.

22. The method according to any one of claims 14 to 15, wherein, The floating pool is operated in a reducing protective gas atmosphere.

23. The method of claim 22, wherein the reducing protective gas atmosphere is a forming gas mixture consisting of N2 and H2.

24. The method according to any one of claims 14 to 15, wherein, The pressure of the floating pool is between 0.05 mbar and 0.3 mbar and / or the hydrogen content in the forming gas atmosphere is between 2 vol% and 15 vol%.

25. The glass article according to any one of claims 1 to 13, used in cooking appliances as a fire door, fireplace observation panel or window.

26. Use of the glass article according to any one of claims 1 to 13 in an induction cooking appliance.

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