Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • 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
  • 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
• • 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
• • 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
  • C03C3/078—Glass compositions containing silica with 40% to 90% silica, by weight containing an oxide of a divalent metal, e.g. an oxide of zinc
• • 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
• • 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
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
  • C03C3/093—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium containing zinc or zirconium
• • 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

Definitions

• the present invention relates to glass-ceramic materials in general, precursor glasses therefore, articles comprising a glass-ceramic material, and process for making a glass-ceramic material.
• the present invention relates to glass-ceramic materials comprising /2-quartz as the predominant crystalline phase that are essentially transparent and colorless in the visible spectrum, as well as precursor glass materials thereof, articles comprising the same and processes for making the same.
• Transparent glass-ceramic materials with a low thermal expansion coefficient (CTE), which contain a solid solution of ⁇ -quartz as the principal crystalline phase, have been described in a number of publications, in particular by W. Hoeland and G. Beall, in "Glass-ceramic technology", Am. Ceram. Soc, Westerville (2002), pages 88-96.
• Said glass-ceramic materials are generally obtained by heat treating a precursor glass (more conventionally a mixture of the constituents of said glass: a mineral charge, a precursor of such glass), the composition of which is of the Li ⁇ 2 -Al 2 ⁇ 3 -Si ⁇ 2 (LAS) type.
• Said heat treatment includes a nucleation stage followed by a crystal growth stage.
• the manufacture of articles made of ⁇ -quartz glass-ceramic conventionally includes the three principal successive steps: a first step of melting a batch, such as a mixture of raw starting materials and/or glass cullet, usually carried out between 1550 0 C to 175O 0 C; a second step of cooling and forming the molten glass obtained into desired shape; and a third step of crystallizing or ceramming the shaped cooled glass by a suitable heat treatment (including the phases of nucleation and crystal growth mentioned above).
• a suitable heat treatment including the phases of nucleation and crystal growth mentioned above.
• a first aspect of the present invention relates to a transparent, essentially colorless glass-ceramic material, comprising a /?-quartz solid solution as the predominant crystalline phase, having a composition, expressed in terms of weight percentages on the basis of oxides, consisting essentially of:
• Fe 2 O 3 ⁇ 0.03; and and being free of arsenic oxide and antimony oxide, with the exception of unavoidable traces thereof.
• the glass-ceramic material of the first aspect of the present invention has a composition, expressed in terms of weight percentages on an oxide basis, consisting essentially of:
• SnO 2 0.3 - 0.8
• the composition of the glass-ceramic material is further free of halides, with the exception of unavoidable traces thereof.
• the composition of the glass-ceramic material is further free of phosphates, with the exception of unavoidable traces thereof.
• a second aspect of the present invention relates to an article made of a glass-ceramic material according to the first aspect of the present invention (including but not limited to the specific embodiments of the first aspect of the present invention described above), such as a cook plate, a cooking utensil, a plate of microwave oven, a fireplace window, a fire door or window, a viewing window for pyrolysis or catalysis furnaces, a lens item, an item of tableware, an architectural element or part of a ballistic protection.
• a third aspect of the present invention relates to a lithium aluminosilicate glass, which is a precursor glass of a glass-ceramic material according to the first aspect of the present invention described above (including but not limited to those of the specific embodiments of the first aspect of the present invention described above).
• the composition of the glass material of the third aspect of the present invention corresponds to the composition of a glass-ceramic material of the first aspect of the present invention.
• a fourth aspect of the present invention relates to a method for preparing a glass-ceramic material of the first aspect of the present invention, comprising the heat treatment of a lithium aluminosilicate glass, a precursor of said glass-ceramic material, or of a mineral charge, itself a precursor of such a lithium aluminosilicate glass, under conditions ensuring its ceramming, characterized in that said glass or said mineral charge has a composition which corresponds to that of a glass-ceramic material of the first aspect of the present invention.
• the method comprises the following steps in sequence: (i) melting a lithium aluminosilicate glass, or a mineral charge, a precursor of such a glass, said glass or said charge containing an efficient, non-excessive quantity of at least one fining agent; followed by fining the molten glass obtained; (ii) cooling the fined, molten glass obtained and, simultaneously, forming it into desired shape for the intended article; (iii) ceramming said formed glass; characterized in that said glass or said mineral charge has a composition which corresponds to that of a glass-ceramic material according to the first aspect of the present invention (including but not limited to the specific embodiments of the first aspect of the present invention described above).
• the method is characterized in that ceramming is implemented for a time of 150 min or less at a temperature of less than 1000 0 C, advantageously less than 95O 0 C.
• ceramming is implemented for a time of 150 min or less at a temperature of less than 1000 0 C, advantageously less than 95O 0 C.
• One or more embodiments of the various aspects of the present invention have one or more of the following advantages: an essentially colorless, highly transparent glass-ceramic material comprising ⁇ -quartz solid solution as the predominant crystalline phase can be made.
• FIG. 1 shows the transmission curves of (i) a glass-ceramic material according to one embodiment of the present invention (Example 4 below); and (ii) a comparison example (Keralite , a glass-ceramic material comprising TiO 2 described below).
• Ranges can be expressed herein as from “about” one particular value, and/or to "about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. [0023] As used herein, a “wt%” or “weight percent” or “percent by weight” of a component, unless specifically stated to the contrary, is based on the total weight of the composition or article in which the component is included.
• the present invention relates to the field of transparent, essentially colorless /?-quartz glass-ceramic materials.
• the subject-matter of the invention is more particularly: (i) novel transparent, essentially colorless /?-quartz glass-ceramic materials whose composition is devoid of As 2 O 3 and Sb 2 O 3 , said composition containing a very specific combination of three nucleating agents: TiO 2 , ZrO 2 and SnO 2 ; the TiO 2 content being low; (ii) articles made of said novel glass-ceramic materials; (iii) lithium aluminosilicate glasses, the precursors of said novel glass-ceramic materials, allowing the preparation of said novel, transparent, essentially colorless glass-ceramic materials, with short ceramming times, which is highly advantageous from an economic viewpoint; and (iv) methods for preparing said novel glass-ceramic materials and said articles made of said novel glass-ceramic materials.
• TiO 2 is by far the most frequently used nucleating agent, since ZrO 2 , when used alone, must be used in amounts close to the solubility limit (resulting in a higher melting temperature for the precursor glass, inhomogeneous nucleation, risks of devitrification during processing and/or residual ZrO 2 -rich areas in the glass-ceramic material). Furthermore, ZrO 2 is a much less efficient nucleating agent than TiO 2 . It requires much longer ceramming times. [0026] To obtain transparent, "essentially colorless" glass-ceramic materials, the presence of coloring sites within said glass-ceramic materials, i.e. the presence of ions or ion pairs which on exposure to visible light may undergo electronic transitions, is to be avoided.
• CeO 2 , SnO 2 and other compounds such as halides has also been described. Since As 2 O 3 , the halides and Sb 2 O 3 are advantageously excluded on account of their toxicity, said halides and Sb 2 O 3 also being highly volatile, persons skilled in the art chiefly recommend the use of SnO 2 . On the other hand, CeO 2 is known to generate a strong yellow coloring in the presence of TiO 2 , and the inventors have evidenced the same problem subsequently to SnO 2 (and Nb 2 Os) interaction with TiO 2 .
• the technical problem approached by said inventors was therefore to obtain transparent, essentially colorless /?-quartz glass-ceramic materials and glass-ceramic material articles (with a low thermal expansion coefficient (CTE)), from precursor glasses with low TiO 2 content and free of undesirable fining agents (As 2 O 3 and Sb 2 O3); and with no devitrification problems occurring during fusion and/or forming and with reasonable ceramming times (unexpectedly this proved to be possible within 150 min or even less).
• CTE thermal expansion coefficient
• the present invention therefore relates to a transparent, essentially colorless glass-ceramic material containing a solid ⁇ -quartz solution as main crystalline phase, having a composition, expressed in terms of weight percentages on an oxide basis, consisting essentially of:
• SiO 2 > 65 - 71 Al 2 O 3 : 19 - 23 Li 2 O : 3 - 4 B 2 O 3 : 0 - 1 TiO 2 0.3 - ⁇ 1.6 SnO 2 0.25-1.2
• samples of the glass-ceramic materials according to the invention 3 mm thick, generally have the following values given below for the L* (lightness), a* and b* (color coordinates) parameters in the color space laid down by "CIE 1976 Lab” (International Commission on Illumination, 1976), measured using the standard C illuminator:
• the thermal expansion coefficient (CTE) of the glass-ceramic materials according to the invention (measured from 25°C to 700 0 C) generally lies from -1OxIO "7 K "1 to +15xl0- ? K ' ⁇
• the solid ⁇ -quartz solution is present as main crystalline phase.
• the residual vitreous phase generally represents less than 35 weight %
• the solid /?-quartz solution represents at least 65 weight %, generally from 70 to 85 weight %, of the crystallized fraction.
• said crystalline phase can be specified as follows but in no way limited thereto.
• said crystalline phase chiefly consists of at least 80 wt. % solid / ⁇ -quartz or /?-eucryptite solution.
• Said crystalline phase also generally contains minor quantities of secondary crystalline phases, such as phases of srilankite, cubic ZrO 2 , rutile, possibly in a solid solution with SnO 2 .
• Said crystalline phase may also contain tertiary crystalline phases such as a solid solution of /£-spodumene (less than 3 wt.%) or others (less than 5 wt.%).
• the crystallite size is generally less than 70 nm, preferably 60 nm or less.
• the sum of the listed compounds (oxides) represents at least 95 %, generally at least 98 weight %. It cannot be fully excluded that in said glass-ceramic materials other compounds may be found in low quantities.
• the weight composition of the glass-ceramic materials according to the invention it can be specified as follows, although in no way limited thereto.
• the glass-ceramic materials under consideration are of LAS type. They contain Li 2 O, AI 2 O 3 and SiO 2 as essential constituents of the solid /2-quartz solution, which gives them their transparency and low thermal expansion coefficient (CTE).
• CTE transparency and low thermal expansion coefficient
• the indicated ranges for said essential constituents are narrow. Hence it was determined that: (i) the SiO 2 content is more than 65 % and no more than 71 % to obtain results of interest in terms of characteristics of the end product (high transparency and low thermal expansion coefficient (CTE)) and in terms of the method for obtaining said end product (melting procedure and ceramming time).
• the SiO 2 content advantageously lies from 67 to 70 %; (ii) the AI2O 3 content is limited to from 19 to 23 %, advantageously from 19.5 and less than 22 %. If said Al 2 O 3 content is not high enough ( ⁇ 19 %), the transparency of the end product decreases and ceramming becomes too slow. If said Al 2 O 3 content is too high (> 23 %), melting and ceramming are difficult to implement, and devitrification phenomena can be seen to occur when forming said glass; (iii) the Li 2 O content is limited to from 3 to 4 %, advantageously from 3.2 to 3.8 %. A minimum of 3.2 % Li 2 O is generally necessary to obtain a transparent glass-ceramic material with low thermal expansion coefficient (CTE) and to minimize ceramming time. If the Li 2 O content is too high, devitrification phenomena can be seen to occur.
• CTE thermal expansion coefficient
• the glass-ceramic materials according to the invention may contain borates.
• B 2 O 3 may be beneficially used to dissolve ZrO 2 and to lower viscosity on melting.
• B 2 O 3 is known to facilitate phase separation and may be responsible for opalescence, for the presence of large crystals and /?-spodurnene. Therefore the glass-ceramic materials according to the invention do not contain more than 1 weight % B 2 O 3 .
• the glass-ceramic materials according to the invention contain: TiO 2 (in limited quantities), ZrO 2 and SnO 2 .
• the amount of these three components are typically:
• the values in the composition of the glass-ceramic materials according to the invention are most advantageously: TiO 2 0.6%-0.8 wt% and/or 3.5% ⁇ ZrO 2 + TiO 2 + SnO 2 ⁇ 4.4 %.
• SnO 2 in addition to its function as nucleating agent, also ensures the function of fining agent. It is recalled that the composition of the glass-ceramic materials according to the invention is free of arsenic oxide and antimony oxide. It was seen above that the content of SnO 2 is at least 0.25 % (with reference therefore to its efficiency as nucleating agent and fining agent) and is no more than 1.2%, with:
• TiO 2 + SnO 2 ⁇ 2 advantageously ⁇ 1.8 %, and 3.0 % ⁇ ZrO 2 + TiO 2 + SnO 2 ⁇ 4.8 %
• CeO 2 , WO 3 , MoO 3 and Nb 2 O 5 may be used, either alone or in combination, as fining agent.
• the sum of oxides of tungsten and/or molybdenum, expressed as WO 3 + MoO 3 is limited to less than 1 wt.% for the following reasons: while both constituents in limited quantity can be used to assist fining of the melt, if their total amount exceeds lwt.%, a large number of small bubbles may form in the glass melt at temperatures between 155O 0 C and 175O 0 C, and those bubbles are very difficult to remove. Thus, used in too large quantities, the effect of WO 3 and MO3 may be rendered negative.
• both constituents and particularly MoO 3 may generate different types of colorations in the final glass-ceramic.
• the use of CeO 2 + WO 3 + MoO 3 is limited to less than 1 %. Beyond this value, the onset of a yellowish tint is observed.
• WO 3 and MoO 3 are not present and the contents of CeO 2 and Nb 2 O 5 are each limited to 0.2 %.
• (6) ZnO and the alkaline-earth oxides of the MgO, SrO and BaO group are used to improve the melting properties, to stabilize the vitreous phase and to influence the microstructure of the glass-ceramic material.
• the glass-ceramic materials according to the invention contain 0 to 2 % MgO, 1 % to 4 % ZnO, O to 2 % SrO and O to 1.8 % BaO.
• Their MgO content advantageously lies from O and 1.5 %; their ZnO content from 1.3 % to 2.4 %; their SrO content from O to 1.2 %; and their BaO content from O to 1.5 %.
• the glass-ceramic materials according to the invention may also contain O to 3% P 2 O 5 . Advantageously they do not contain any phosphates: thereby homogeneity and transparency can so be optimized.
• the glass-ceramic materials according to the invention may also contain 0 to 2.1 %, advantageously 0 to 1.5 %, alkaline oxides other than Li 2 O, e.g., Na 2 O and K 2 O. Preferably Na 2 O is not present. Preferably, K 2 O is present alone (at a content of from O to 1.3 %). After ceramming, the alkaline ions remain in the vitreous phase.
• the glass-ceramic materials according to the invention may also contain up to 4% oxides, such as Gd 2 O 3 , La 2 O 3 , Ta 2 O 5 and Y 2 O 3 (this list not being truly exhaustive). Said oxides can allow increased transparency and optical appearance of the glass-ceramic, by increasing the refractive index of the residual vitreous phase, without coloring said glass-ceramic.
• the glass-ceramic materials according to the invention do not contain more than 2 weight % of such oxides.
• the presence of colorant(s) complementary to the yellow in the glass-ceramic materials according to the invention is not excluded. This aims to improve the desired object: the elimination of any yellowish tinge (by compensation).
• use may be made OfNd 2 O 3 and/or Er 2 O 3 .
• Nd 2 O 3 and Er 2 O 3 must be used in limited quantities, from 0 to 0.08 %, advantageously from 0 to 0.06 %, further advantageously from 0 to 0.04 %. For example, if too much Nd 2 O 3 is used, a bluish tint is observed; if too much Er 2 O 3 is used, a pink tint is observed.
• the Fe 2 O 3 content in the glass-ceramic materials according to the invention was less than 300 ppm. Obviously, Fe 2 O 3 is not voluntarily added as a constitutive glass ingredient. If it is present, this is because it is a common impurity in the raw materials used. Within the context of the invention, Fe 2 O 3 is only likely to interfere with a limited quantity of TiO 2 . Generally, it is obviously preferred to minimize the presence of iron but if, for this purpose, the raw materials used have to be purified, then this would often prove to be too costly. Also in some cases the presence of Fe 2 O 3 can prove to be of interest with respect to melting and fining. Generally, the glass-ceramic materials according to the invention contain 100 to 250 ppm Fe 2 O 3 . Advantageously, the glass-ceramic materials according to the invention contain less than 200 ppm Fe 2 O 3 .
• the glass-ceramic materials according to the invention whose composition has just been described above, are also characteristically free of arsenic oxide and antimony oxide, with the exception of unavoidable traces thereof: in this way the use of these undesirable products is avoided.
• the advantageous ranges indicated above are to be considered independently of each other, and also in combination with each other.
• the glass-ceramic materials according to the invention advantageously have the following weight composition [i.e. their composition expressed in oxide weight percent essentially consists (in the meaning specified above)] of:
• the composition of the glass-ceramic materials according to the invention is also free of halides, with the exception of unavoidable traces. Mention was made above of the problem related to the use of halides (corrosion, pollution). Advantageously therefore, no halide is voluntarily added as a raw material when preparing the glass-ceramic materials according to the invention.
• the composition of the glass-ceramic materials according to the invention is free of phosphates, with the exception of unavoidable traces (see above). The presence of phosphates particularly facilitates opalescence. Therefore, advantageously no phosphate is voluntarily added as a raw material when preparing the glass-ceramic materials according to the invention.
• composition of the glass-ceramic materials according to the invention is also free of halides and phosphates, with the exception of unavoidable traces thereof.
• the present invention relates to articles made of glass-ceramic materials such as described above.
• Said articles may consist for example in cook plates, cooking utensils, plates for microwave ovens, fireplace windows, fire doors or fire windows, viewing windows for pyrolysis or catalysis furnaces, lens items, tableware items, architectural elements or parts of ballistic protections.
• the present invention relates to lithium aluminosilicate glasses, the precursors of the glass-ceramic materials according to the invention such as described above.
• the lithium aluminosilicate glasses with the above-indicated compositions for the glass-ceramic materials according to the invention are effectively novel.
• the present invention relates to a method for preparing a glass-ceramic material according to the invention such as described above.
• said method comprises thermal treatment of a lithium aluminosilicate glass, a precursor of said glass-ceramic material, or of a mineral charge, itself a precursor of such a lithium aluminosilicate glass, under conditions ensuring its ceramming. Said ceramming treatment is known per se.
• the method is carried out with a glass or a mineral charge having a weight composition corresponding to that of a glass-ceramic material according to the invention such as specified above.
• the present invention relates to a method for manufacturing an article made of a glass-ceramic material according to the invention.
• said method comprises the following three successive steps: (a) melting a lithium aluminosilicate glass, or a mineral charge, a precursor of such a glass, said glass or said charge containing an efficient, non-excessive amount of at least one fining agent; followed by fining the molten glass obtained; (b) cooling the fined, molten glass obtained and simultaneously forming it to desired shape for the intended article; and (c) ceramming said formed glass.
• said glass or said mineral charge under consideration is present in a weight composition which corresponds to that of a glass-ceramic material according to the invention, such as specified above.
• the above-mentioned forming (shaping) advantageously consists in rolling between rollers to obtain sheets.
• the glass under consideration can be cerammed in 150 min or less.
• the ceramming of said formed glass is advantageously conducted for a period of 150 min or less at a temperature of less than 1000 0 C, advantageously less than 950 0 C. It quite unexpectedly proved possible to obtain the glass-ceramic material according to the invention with such short ceramming times.
• the ceramming time mentioned above corresponds to the time lapsed from the temperature of 65O 0 C to the maximum ceramming temperature (less than 1000 0 C), advantageously from 65O 0 C to less than 950 0 C; said ceramming time corresponds to the nucleation and crystal growth phases.
• Said ceramming time does not include the time needed to reach the temperature of 650 0 C or the cooling time from the maximum temperature. [0075] It was indicated above that said ceramming time may be 150 min or less. It may even be 120 min or less, even 90 min or less. It most unexpectedly proved possible to obtain the glass-ceramic material according to the invention within these short ceramming times.
• the temperature of 650 0 C is reached in less than one hour (starting from the temperature of the formed product), most advantageously in less than 30 min; and/or the glass-ceramic material obtained is cooled by at least 40 0 C from its maximum ceramming temperature in less than 10 min.
• the mixtures were placed in platinum crucibles for melting.
• the filled crucibles were placed in a pre-heated furnace at 1400 0 C. They underwent the following melting cycle (i) rising temperature up to 165O 0 C at a heating rate of
• the glass plates obtained were generally very transparent.
• the glass-ceramic materials obtained had the properties indicated in the second part of said Table 1.
• the indicated transmissions T were measured on 3 mm thick glass-ceramic material samples.
• the Tj o and T 60 values (expressed in nm) correspond to the lowest wavelengths in which transmission T respectively exceeds 10 and 60 %; their difference is indicative of opalescence.
• the color points indicated as L*, a* and b* are those mentioned in the introduction hereto (lightness and color coordinates in the "CIE/ 1976 Lab” space, measured using standard illuminator C). They were assessed on 3 mm thick samples. [0086] The thermal expansion coefficient (CTE) was measured by horizontal dilatometry (25°C-700°C).
• the glass-ceramic material in example Cl is slightly opalescent (T 6 o-Tio value is very high). Its TiO 2 content is too low. Its lightness L* is therefore too weak. Its crystal size is not optimized. [0091] The glass-ceramic material in example C2 is also slightly opalescent (Teo-Tio value is still high). Its SnO 2 content is too low. Its crystal size is not optimized.
• the "glass-ceramic material" in example C3 is not cerammed, since the ZrO 2 content is too low, and since, more generally, the nucleating agent content is too low (TiO 2 + ZrO 2 + SO 2 : 2.9 wt. %).
• the glass-ceramic material in example C4 is slightly yellow (which is confirmed by the "a*" color coordinate and Tj o values), in particular due to the cumulated TiO 2 (1.6 %) and SnO 2 (0.4 %) contents : TiO 2 + SnO 2 : 2 %.
• the glass-ceramic material in example C5 is slightly opaque. Its B 2 O 3 content is too high. Consequently large crystals have developed. Their "harmful" presence shows as said slight opalescence.
• the glass-ceramic material in example 1 contains a relatively high quantity Of SnO 2 (0.8 %). Therefore, relatively high T 6 o, T 6 Q-Ti O difference and "a*" color coordinate values are observed. However, the result is acceptable.
• the glass-ceramic materials in examples 2 and 4 are particularly preferred. They show very low Ti 0 values, low Teo-Tio values, low thermal expansion coefficients (CTE) and a crystal size of particular interest. These good results are obtained with a short ceramming time. This - short - ceramming time is the same
• the glass-ceramic material in example 3 has a low TiO 2 content.
• Example 5 illustrates a variant of a glass-ceramic material according to the invention whose composition is devoid of MgO.
• the results in terms of color and transmission are excellent. Regarding said transmission, said excellent results can be explained by the crystal size (very small). However, the absence of MgO has an unfavorable impact on the thermal expansion coefficient (CTE). The overall result remains very acceptable.
• Example 6 illustrates another variant of a glass-ceramic material according to the invention, whose composition is devoid of MgO. Due to the presence of Ta 2 O 5 the thermal expansion coefficient (CTE) is higher. Similarly, the b* color coordinate value is close to the "tolerable" limit (12).
• the glass-ceramic material in example 7 contains a small quantity of
• the glass-ceramic material is highly transparent, colorless and has a thermal expansion coefficient (CTE) such as announced (of interest).
• CTE thermal expansion coefficient
• Examples 8 and 9 illustrate in more detail the roles of BaO and MgO.
• Glass-ceramic materials that satisfy the required specifications can be obtained from precursors glasses that are free of BaO, and also free of MgO.
• K 2 O may be used to replace one or the other or both.
• highly transparent products are derived. However, they possess a somewhat stronger (but acceptable) yellow tint that certain other embodiments of the invention (e.g. examples 1-5).
• the accompanying drawing shows the transmission curves (transmission, expressed as a percentage, as a function of wavelength, expressed in nanometers) of two 3 mm (millimeter) thick glass-ceramic samples.
• the samples were prepared by cutting 32 mm diameter disks from glass-ceramic plates. The disks (4 mm thick) were then polished on both faces to a thickness of 3 mm.
• One sample was the material of Example 4 ("4" in the drawing) and the other was a comparative glass-ceramic material ("C" in the drawing, which is Keralite ® , a TiO 2 -containing glass-ceramic material disclosed in EP 0 437 228).

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• Glass Compositions (AREA)
• Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)

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• 2006
  • 2006-11-30 FR FR0655231A patent/FR2909374B1/fr not_active Expired - Fee Related
• 2007
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  • 2007-11-29 ES ES07847517.5T patent/ES2695049T3/es active Active
  • 2007-11-29 JP JP2009538714A patent/JP2010510951A/ja active Pending
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• 2012
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