Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
  • C03B32/02—Thermal crystallisation, e.g. for crystallising glass bodies into glass-ceramic articles
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0018—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing SiO2, Al2O3 and monovalent metal oxide as main constituents
  • C03C10/0027—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing SiO2, Al2O3 and monovalent metal oxide as main constituents containing SiO2, Al2O3, Li2O as main constituents
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
  • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
  • C03C4/02—Compositions for glass with special properties for coloured glass
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
  • H05B3/74—Non-metallic plates, e.g. vitroceramic, ceramic or glassceramic hobs, also including power or control circuits
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2204/00—Glasses, glazes or enamels with special properties
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24C—DOMESTIC STOVES OR RANGES ; DETAILS OF DOMESTIC STOVES OR RANGES, OF GENERAL APPLICATION
  • F24C15/00—Details
  • F24C15/10—Tops, e.g. hot plates; Rings

Definitions

• the present invention relates to the field of glass-ceramics. It relates more particularly to a glass-ceramic exhibiting a specific appearance in reflection and also a controlled transmittance curve, and also to articles made of such a glass-ceramic, in particular cooktops, and to the precursor glasses of such glass-ceramics.
• the cooktop In an application as cooktop, in particular for heating devices of the radiant type, it is necessary for the cooktop to meet certain requirements with regard to its optical properties, both in the visible region and in the infrared region. It is in particular important for the heating elements to be able to be concealed when not operating but for them to be clearly visible when they are operating. The energy efficiency of the devices is also important, in order to reduce as much as possible the time for cooking the foodstuffs.
• the esthetic appearance of the cooktop is also a parameter to be taken into account, in particular for the cooktop to be fully integrated in kitchens.
• 5,070,045 are glass-ceramics of the lithium aluminosilicate type comprising a crystal phase essentially composed of a solid solution of p-quartz; they are transparent but have a very low light transmittance and exhibit a black appearance which fits into the majority of kitchens. It can be advantageous, in order to further improve this incorporation, to have available cooktops exhibiting other appearances. In particular, cooktops having a grey color would be particularly nice.
• transparent glass-ceramics comprising a solid solution of ⁇ -quartz as main crystal phase
• transparent glass-ceramics comprising a solid solution of ⁇ -quartz as main crystal phase
• the subject matter of the invention is first of all a glass-ceramic of the lithium aluminosilicate type comprising a solid solution of ⁇ -spodumene and exhibiting, for a thickness of 4 mm;
• Said glass-ceramic is in addition such that its chemical composition comprises the following constituents, varying within the limits by weight defined below:
• the content of V 2 O 5 is preferably at most 0.060%.
• the solid solution of ⁇ -spodumene preferably represents at least 20% by weight, in particular 30% by weight or 40% by weight, of the total crystalline fraction.
• the glass-ceramic according to the invention comprises a solid solution of ⁇ -spodumene as main crystal phase.
• the solid solution of ⁇ -spodumene can represent more than 50% by weight, in particular 60% by weight and even 70% by weight or 80% by weight of the total crystalline fraction.
• the glass-ceramic according to the invention can even sometimes comprise a solid solution of ⁇ -spodumene as sole crystal phase.
• the glass-ceramic can comprise a solid solution of ⁇ -quartz.
• the crystalline fraction can thus advantageously comprise a mixture of solid solution of ⁇ -spodumene and of solid solution of ⁇ -quartz, in proportions by weight of at least 20:80, in particular 40:60, indeed even 50:50 and even 60:40 or 70:30. In some cases, this proportion can even be at least 80:20, 90:10 or 95:5.
• the amounts of a given crystal phase can be determined in x-ray diffraction by the Rietveld method.
• the crystal fraction normally represents at least 60% by weight, in particular 70% by weight and even 75% by weight of the glass-ceramic.
• the light transmittance (within the meaning of the standard EN 410) for a thickness of 4 mm is within a range extending from 0.3 to 2%, in particular from 0.6 to 1.7% and even from 1.0 to 1.7%, more particularly from 1.1 to 1.6%.
• the heating elements in particular of the radiant type
• the heating elements are not visible when they are in use, which presents safety problems.
• the light transmittance is too high, the heating elements are visible even when not in use, which presents an esthetic problem.
• the optical transmittance for a wavelength of 625 nm is greater than 2.0%, in particular greater than 3.0% or 4.0%, preferably greater than 4.5% or even 5.0%. It is normally at most 50%. In that way, red indicators, commonly used for cooktops, are fully visible through the glass-ceramic.
• the optical transmittance for a wavelength of 950 nm is within a range extending from 50 to 75%, in particular from 55 to 70%, which makes possible use of conventional electronic control keys, emitting and receiving at this wavelength.
• the optical transmittance of a wavelength of 1600 nm is at least 50%, in particular within a range extending from 55% to 80% and even from 60% to 75%. This transmittance affects the thermal performances of the cooktop, which are too low if the transmittance is itself too low and, when the transmittance is too high, can bring about excessive and dangerous heating.
• the color in reflection obtained is such that the L*, a*, b* colorimetric coordinates in diffuse reflection for an illuminant D65 and a reference observer at 2° comply with the following inequalities: 15.0 ⁇ L* ⁇ 40.0, ⁇ 3.0 ⁇ a* ⁇ 3.0 and ⁇ 10.0 ⁇ b* ⁇ 3.0.
• the colorimetric coordinates preferably observe at least one of the following inequalities, indeed even two or three of these inequalities:
• the colorimetric coordinates are calculated from a diffuse reflection spectrum, obtained using a spectrophotometer equipped with an integrating sphere, under perpendicular incidence and after subtraction of the specular reflection and of a baseline obtained by the same measurement carried out on Spectralon®.
• the inventors have been able to demonstrate, after lengthy studies, that the desired transmittance curve and the desired color in single reflection could, surprisingly, be achieved by virtue of the presence of a solid solution of ⁇ -spodumene in combination with a specific choice of colorants and refining agents, in very precise contents.
• the high values of L* testify to the importance of the diffuse reflection, due to the presence of crystals of ⁇ -spodumene.
• the composition includes SnO 2 as refining agent.
• the refining becomes easier to carry out and becomes more effective in proportion as the amount of SnO 2 present increases. However, it is advisable to minimize, indeed even to avoid, any phenomenon of devitrification and to control the influence of said SnO 2 on the optical transmittance and the optical reflection. This is because the tin oxide is capable of reducing the vanadium and the iron present, during the ceramization.
• An SnO 2 content of 0.2 to 0.6% by weight is required, in particular of 0.25 to 0.5%, indeed even of at most 0.4%.
• the glass-ceramics according to the invention include neither As 2 O 3 nor Sb 2 O 3 or include only traces of at least one of these toxic compounds, SnO 2 being present instead of these conventional refining agents. If traces of at least one of these compounds are present, it is as contaminating product; it is a priori due to the presence, in the charge of vitrifiable starting materials, of recycled materials of cullet type (resulting from previous glass-ceramics refined with these compounds). In any case, only traces of these toxic compounds are capable of being present: As 2 O 3 +Sb 2 O 3 ⁇ 1000 ppm, indeed even 500 ppm.
• V 2 O 5 is a main colorant of the glass-ceramics according to the invention. This is because V 2 O 5 , in the presence of SnO 2 , significantly darkens the glass during its ceramization (see above). V 2 O 5 is responsible for the absorption, mainly below 700 nm, and it is possible, in its presence, to retain a sufficiently high transmittance at 950 nm and in the infrared. An amount of V 2 O 5 within a range extending from 0.015 to 0.070%, in particular from 0.015 to 0.060%, more particularly from 0.015 to 0.050%, indeed even from 0.015 to 0.035%, has proved to be adequate.
• the invention employs the combination of V 2 O 5 with at least one other main colorant chosen from Cr 2 O 3 , Bi 2 O 3 and their mixture.
• the glass-ceramic comprises V 2 O 5 and Cr 2 O 3 (in the abovementioned contents and those explained below) but not Bi 2 O 3 .
• the content by weight of Cr 2 O 3 is within a range extending from 0.01 to 0.04%, in particular from 0.015 to 0.035%, indeed even from 0.02% to 0.03%, and the Bi 2 O 3 content is zero.
• the glass-ceramic comprises V 2 O 5 and Bi 2 O 3 (in the abovementioned contents and those explained below) but not Cr 2 O 3 .
• the content by weight of Bi 2 O 3 is within a range extending from 0.05 to 3.0%, in particular from 0.1 to 2.0%, indeed even from 0.2 or 0.3 to 1.0%, and the Cr 2 O 3 content is zero.
• the glass-ceramic comprises V 2 O 5 , Bi 2 O 3 and Cr 2 O 3 (in the abovementioned contents and those explained below).
• the content by weight of Cr 2 O 3 is preferably within a range extending from 0.01 to 0.03%, in particular from 0.015% to 0.025%
• the content by weight of Bi 2 O 3 is preferably within a range extending from 0.1 to 1%, in particular from 0.2 to 0.5%.
• Cr 2 O 3 is advantageously included in a content by weight within a range extending from 0.015 to 0.035%, in particular from 0.02 to 0.03%.
• Bi 2 O 3 is advantageously included in a content by weight Within a range extending from 0.1 to 2.0%, in particular from 0.2 to 1.5%, indeed even from 0.2 to 1.0%.
• the glass-ceramics according to the invention generally have an optical transmittance for a wavelength of 450 nm of less than 0.1%.
• the iron oxide results in an absorption mainly in the infrared and its content must be at least 500 ppm, advantageously at least 700 ppm, in order to obtain the required transmittance. If its content reaches or exceeds 1500 ppm, the absorption in the infrared is too high in the glass-ceramic but also in the starting glass, which makes it more difficult to melt and to refine.
• the content by weight of iron oxide is between 700 and 1200 ppm (0.07 to 0.12%).
• composition of the glass-ceramics comprise, in a more or less significant amount, in addition to V 2 O 5 , Fe 2 O 3 , Bi 2 O 3 and Cr 2 O 3 , at least one other colorant, such as CoO, CuO, MnO 2 , NiO or CeO 2 .
• the manganese oxide MnO 2 can be used to provide a brownish tint.
• the presence of said at least one other colorant must not significantly influence the targeted optical transmittance curve and the targeted appearance in reflection. It is advisable in particular to watch out for possible interactions which are capable, even with low contents of colorants, of significantly modifying said optical transmittance curve or said appearance in reflection, and the like.
• CoO can a priori be present only in a very low amount in so far as this element strongly absorbs in the infrared and not insignificantly at 625 nm and confers a blue coloring in reflection.
• the chemical composition of the glass-ceramic comprises less than 200 ppm, advantageously 100 ppm, indeed even 50 ppm or 30 ppm of cobalt oxide.
• the NiO content is preferably at most 500 ppm, in particular 200 ppm, indeed even zero, with. the exception of inevitable traces.
• the CeO 2 content is preferably at most 0.5%, in particular 0.1%, indeed even zero, except for inevitable impurities.
• the MnO 2 content is preferably at most 0.5%, in particular 0.1%, indeed even zero, except for inevitable impurities.
• the CuO content is preferably at. most 500 ppm, in particular 200 ppm, indeed even zero, except for inevitable impurities.
• the composition of the glass-ceramics according to the invention does not comprise refining aids, such as F and Br. With the exception of inevitable traces, it does not comprise F and Br. This is particularly advantageous in the light of the price and/or toxicity of these compounds.
• refining aid(s) is a priori superfluous in so far as SnO 2 , present in the amounts indicated.
• the base composition of the glass-ceramics of the invention can vary to a large extent.
• the chemical composition of the glass-ceramic comprises the following constituents, varying within the limits by weight defined below:
• compositions lend themselves perfectly to the melting of glass precursor and then to the ceramization, and in particular to the development of solid solution of ⁇ -spodumene.
• the content by weight of MgO is at most 2%, in particular 1%.
• the content by weight of CaO is advantageously at most 1%.
• the sum of contents by weight of Na 2 O and K 2 O is preferably at most 1%, in particular 0.5%.
• the content by weight of BaO is preferably at Most 3%, in particular 2% and even 1%.
• the sum of the contents of SiO 2 , Al 2 O 3 , Li 2 O, MgO, ZnO, TiO 2 , ZrO 2 , BaO, SrO, CaO, Na 2 O, Li 2 O, K 2 O, P 2 O 5 , B 2 O 3 , SnO 2 , V 2 O 5 , Fe 2 O 3 , Cr 2 O 3 and Bi 2 O 3 is at least 98%, in particular 99%.
• Another subject matter of the invention is an article comprising a glass-ceramic according to the invention.
• Said article is advantageously completely composed of a glass-ceramic according to the invention.
• Said article is in particular a cooktop, a cooking utensil or a microwave oven floor.
• the cooktop is advantageously incorporated in a cooking device, in particular of the radiant type, comprising at least one element which heats by radiation.
• the cooktop can be coated with an enamel decor.
• the linear thermal expansion coefficient between 20 and 700° C. of the glass-ceramic is advantageously at most 10.10 ⁇ 7 /K.
• a further subject matter of the invention is a lithium aluminosilicate glass which is a precursor of the glass-ceramics of the invention as described above.
• Said glass exhibits the bulk composition of said glass-ceramics, as explained above. It may incidentally be noted that said precursor glasses advantageously exhibit an optical transmittance, for any wavelength between. 1000 and 2500 nm, of greater than 60%, for a thickness of 3 mm. The melting and refining thereof are then facilitated.
• a subject matter of the invention is a process for the preparation of a glass-ceramic according to the invention, comprising the heat treatment of a charge of vitrifiable starting materials under conditions which successively provide for the melting, refining and then ceramization, wherein said charge exhibits a composition which makes it possible to obtain a glass-ceramic according to the invention.
• the ceramization is carried out at temperatures which make possible the development of a solid solution of ⁇ -spodumene.
• the appropriate ceramization temperature which can vary as a function of the glass matrix, can be chosen after differential thermal analysis, which makes possible the determination of the crystallization temperature of the ⁇ -quartz phase and then, at a higher temperature, of the temperature at which the transformation (irreversible) of the ⁇ -quartz into ⁇ -spodumene takes place.
• the ceramization temperature is preferably at least 950° C., in particular 970° C. and even 1000° C. or 1020° C.
• Composition C1 (comparative) comprises neither Bi 2 O 3 nor Cr 2 O 3 .
• the other compositions are in accordance with the invention.
• the glass plates were subsequently ceramized according to different cycles, characterized by different ceramization temperatures and stationary-state times at this temperature.
• the ceramization cycle employs rapid heating up to 650° C., then a rise up to 820° C. at a rate of 5° C./min and, finally a rise up to the ceramization temperature at a rate of 15° C./min, followed by maintenance at this temperature.
• Comparative example A while it has advantageous transmittance characteristics in accordance with the requirements, exhibits an appearance in reflection which is not that desired as it appears black. It is crystallized essentially in the ⁇ -quartz form, as a result of a ceramization temperature which is too low to make possible the growth of crystals of ⁇ -spodumene.
• the glass-ceramic having the comparative composition C1 even ceramized so as to bring about the growth of the crystals of ⁇ -spodumene type, on the other hand exhibits a blue color in reflection, characterized in particular by a very negative b* value and an excessively high a* value.
• example E has both a lower light transmittance and a lighter grey color in reflection.
• Examples F to K are other examples according to the invention.

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• 2013
  • 2013-02-28 FR FR1351769A patent/FR3002532B1/fr not_active Expired - Fee Related
• 2014
  • 2014-02-28 DE DE202014010349.6U patent/DE202014010349U1/de not_active Expired - Lifetime
  • 2014-02-28 ES ES14713195.7T patent/ES2685663T3/es active Active
  • 2014-02-28 EP EP14713195.7A patent/EP2961704B1/fr active Active
  • 2014-02-28 US US14/193,868 patent/US9593040B2/en active Active
  • 2014-02-28 TR TR2018/11741T patent/TR201811741T4/tr unknown
  • 2014-02-28 CN CN201480011216.6A patent/CN105209400B/zh active Active
  • 2014-02-28 WO PCT/FR2014/050438 patent/WO2014132005A1/fr active Application Filing
  • 2014-02-28 US US14/770,233 patent/US20160009591A1/en not_active Abandoned
  • 2014-02-28 JP JP2015559550A patent/JP6166389B2/ja active Active
• 2017
  • 2017-01-26 US US15/416,034 patent/US10160685B2/en active Active
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