Abstract: The present invention relates to: a glass-ceramic which is opaque which has a low, or zero thermal expansion coefficient, which contains a solid solution of &bgr;-quartz as crystalline phase, which has a specific composition; and, to a process for obtaining said glass-ceramic.

Abstract: The present invention relates to:

Abstract: The invention relates to a decorated glass-ceramic plate, suitable in particular as a cooktop, comprising a glass-ceramic plate having a low coefficient of thermal expansion between ±15×10−7 K−1 (20-700° C.) and a decoration on the surface of said plate. Characteristically, said decoration comprises a vitrified glass frit containing 10 to 35% by weight of pigments and said decorated glass-ceramic cooktop has a modulus of rupture of at least 120 MPa. The invention also relates to a method of decorating glass-ceramic plates and to an enamel which is useful in particular for implementing said method.

Abstract: The object of the present invention is a novel inorganic glass, which is capable of being strengthened by ionic exchange, and which has a refractive index of between 1.67 and 1.72; said novel glass strengthened on the surface thereof; its method of strengthening; and the corresponding ophthalmic lenses. Said novel glass has the following composition, expressed in wt. % of oxides: SiO2 33-37 B2O3 7.5-13  with SiO2 + B2O3 44-48 Li2O 5-8 Na2O >2.5-7.5   K2O 0-2 with Li2O + Na2O + K2O <14 CaO   0-<8 Al2O3 0-6 Nb2O5  8-13 ZrO2 4-6 TiO2  5-10 La2O3 12-19 SrO 2-4 As2O3 and/or Sb2O3   0-0.8 (refining agents).

Abstract: The invention relates to brown glasses which absorb ultraviolet radiation that are used in the production of ophthalmic sun glasses, and that have the following composition, expressed in wt. %:______________________________________ SiO.sub.2 59-78 Al.sub.2 O.sub.3 2-6 B.sub.2 O.sub.3 0-3 Na.sub.2 O 7-16 K.sub.2 O 2-9 CaO 0-7 BaO 0-12 ZnO 0-12 ZrO.sub.2 0-6 TiO.sub.2 0-6 MnO.sub.2 0.25-6 V.sub.2 O.sub.5 1-3 Fe.sub.2 O.sub.3 0-1.5 NiO 0-0.5 CoO 0-0.1 Sb.sub.2 O.sub.3 0-0.7 As.sub.2 O.sub.3 0-0.7 F 0.05-1.0 With MnO.sub.2 + Fe.sub.2 O.sub.3 + V.sub.2 O.sub.5 >1.5 Al.sub.2 O.sub.3 + SiO.sub.2 .gtoreq.65.

Abstract: This invention is directed to the production of glasses essentially free of Nb.sub.2 O.sub.5, and having refractive index close to 1.7, an Abbe number of about 35 and a density close to 3.2. The glasses consist essentially in weight percent on the oxide basis, of______________________________________ SiO.sub.2 38-45 TiO.sub.2 15-<20 ZrO.sub.2 6-10 La.sub.2 O.sub.3 0.5-4 BaO 12-19 CaO 3-8 BaO + CaO + SrO 17-25 Na.sub.2 O 2-6 K.sub.2 O 4-8 Li.sub.2 O + Na.sub.2 O + K.sub.2 O 6-10.

Abstract: The present invention relates to the production of lead-free glasses exhibiting densities of at least 2.9 g/cm.sup.3 and refractive indices of at least 1.545 which consist essentially, in weight percent, of______________________________________ SiO.sub.2 51-63 Al.sub.2 O.sub.3 0-5 Li.sub.2 O 0-3 ZrO.sub.2 0-6 Na.sub.2 O 0-8 SiO.sub.2 + Al.sub.2 O.sub.3 + 55-66 ZrO.sub.2 K.sub.2 O 0-12 TiO.sub.2 0-3 Li.sub.2 O + Na.sub.2 O + 7-15 CaO 0-5 K.sub.2 O SrO 0-<8 MgO 0-3 BaO >13-21 B.sub.2 O.sub.3 0-3 ZnO 5-15 La.sub.2 O.sub.3 0-8.

Abstract: This invention is principally directed to the preparation of transparent glass-ceramic articles which, when very rapidly crystallized in situ from precursor glass articles in plate form, exhibit very minimal distortion. The glass-ceramic articles contain .beta.-quartz solid solution as the predominant crystal phase and consist essentially, in weight percent, of______________________________________ SiO.sub.2 65-70 MgO + BaO + SrO 1.1-2.3 Al.sub.2 O.sub.3 18-19.8 ZrO.sub.2 1.0-2.5 Li.sub.2 O 2.5-3.8 As.sub.2 O.sub.3 0-1.5 MgO 0.55-1.5 Sb.sub.2 O.sub.3 0-1.5 ZnO 1.2-2.8 As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0.5-1.5 TiO.sub.2 1.8-3.2 Na.sub.2 O 0-<1.0 BaO 0-1.4 K.sub.2 O 0-<1.0 SrO 0-1.4 Na.sub.2 O + K.sub.2 O 0-<1.0 BaO + SrO 0.4-1.4 2.8Li.sub.2 O + 1.2ZnO/ >1.8 5.2MgO ______________________________________The preferred glass-ceramics contain 0.1-1.0% V.sub.2 O.sub.5.

Abstract: This invention relates to the preparation of glass-ceramic articles in which potassium fluorrichterite and/or a related fluormica constitutes the predominant crystal phase(s). The precursor glasses can be crystallized in situ very rapidly and exhibit very little thermal deformation during the crystallization heat treatment. The base glasses are essentially free of Li.sub.2 O and consist essentially, expressed in terms of weight percent on the oxide basis, of:______________________________________ SiO.sub.2 61-70 Na.sub.2 O 0.5-3 BaO 0-3.5 Al.sub.2 O.sub.3 2.75-7 K.sub.2 O 2.5-5.5 P.sub.2 O.sub.5 0-2.5 MgO 11-16 Na.sub.2 O + K.sub.2 O <6.8 CaO 4.75-9 F 2-3.