A black lithium silicate glass ceramic is provided. The glass ceramic includes lithium silicate as a primary crystal phase and at least one of petalite, -quartz, -spodumene, cristobalite, and lithium phosphate as a secondary crystal phase. The glass ceramic is characterized by the color coordinates: L*: 20.0 to 40.0, a*: 1.0 to 1.0, and b*: 5.0 to 2.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

The present invention discloses a glass-ceramic article and a glass-ceramic for an electric device cover plate, the glass-ceramic comprises, as a predominant crystalline phase, lithium silicate and the quartz crystalline phase, and has a composition expressed in weight percent including: SiO.sub.2: 65-85%, Al.sub.2O.sub.3: 1-15%, Li.sub.2O: 5-15%, ZrO.sub.2: 0.1-10%, P.sub.2O.sub.5: 0.1-10%, K.sub.2O: 0-10%, MgO: 0-10%, ZnO: 0-10%, and Na.sub.2O: 0-5%, wherein (SiO.sub.2+Al.sub.2O.sub.3+Li.sub.2O+ZrO.sub.2)/P.sub.2O.sub.5 is 40-90, the falling ball test height is 700 mm or more. By reasonable component design, the present invention achieves excellent mechanical properties of the glass-ceramic and the glass-ceramic article of the present invention and obtains the glass-ceramic or the glass-ceramic article suitable for electronic devices at a lower cost.

Ceramics and glass-ceramics have low and/or negative coefficients of thermal expansion. Crystalline phases of the formula AM.sub.2Si.sub.2-yGe.sub.yO.sub.7 (A=Sr and Ba and M=Zn, Mg, Ni, Co, Fe, Cu, Mn, with Sr, Ba and Zn necessarily having to be present) can be produced by conventional ceramic processes or by crystallization from glasses. The compositions form solid solutions, where the elements indicated as component M can be replaced by one another in virtually any concentration but the concentration of Zn must always be at least 50% of the sum of all components indicated under M. The stoichiometry of these silicates and also their structure can differ to a greater or lesser extent.

The invention relates to glass ceramics based on the lithium metasilicate system (Li.sub.2O.SiO.sub.2(Li.sub.2SiO.sub.3)), which are mechanically processible in a simple manner in an intermediate stage of the crystallization and, after complete crystallization, represent a high-strength, highly translucent and chemically stable glass ceramic.

To provide a dental lithium silicate glass composition capable of providing a dental lithium silicate glass ceramic capable of efficiently precipitating the main crystals (lithium disilicate and/or lithium metasilicate) even after heat treatment. To provide a Al.sub.2O.sub.3-free dental lithium silicate glass composition including the following components: SiO.sub.2: 60.0 to 80.0% by weight, Li.sub.2O: 10.0 to 17.0% by weight, K.sub.2O: 0.5 to 10.0% by weight, ZrO.sub.2: 0.0 to 5.0% by weight, a nucleating agent: 1.0 to 6.0% by weight, a glass stabilizer: 0.0 to 8.0% by weight and a colorant: 0.0 to 10.0% by weight.

The invention relates to glass-ceramics based on the lithium disilicate system which can be mechanically machined easily in an intermediate step of crystallisation and, after complete crystallisation, represent a very strong, highly-translucent and chemically-stable glass-ceramic. Likewise, the invention relates to a method for the production of these glass-ceramics. The glass-ceramics according to the invention are used as dental material.

Glass and glass ceramic compositions having a combination of lithium silicate and petalite crystalline phases along with methods of making the glass and glass ceramic compositions are described. The compositions are compatible with conventional rolling and float processes, are transparent or translucent, and have high mechanical strength and fracture resistance. Further, the compositions are able to be chemically tempered to even higher strength glass ceramics that are useful as large substrates in multiple applications.

The invention relates to glass-ceramics based on the lithium silicate system which can be mechanically machined easily in an intermediate step of crystallization and, after complete crystallization, represent a very strong, highly-translucent and chemically-stable glass-ceramic. Likewise, the invention relates to a method for the production of these glass-ceramics. The glass-ceramics according to the invention are used as dental material.

Glass and glass ceramic compositions having a combination of lithium disilicate and -spodumene crystalline phases along with methods of making the glass and glass ceramic compositions are described. The compositions are compatible with conventional rolling and float processes and have high mechanical strength and fracture resistance. Further, the compositions are able to be chemically tempered to even higher strength glass ceramics that are useful as large substrates in multiple applications.

A glass composition SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3, and RO, where RO represents one kind or two or more kinds selected from MgO, CaO, SrO, and BaO, and allows two or more kinds of crystals selected from a SiO.sub.2Al.sub.2O.sub.3RO-based crystal, a SiO.sub.2-based crystal, and a SiO.sub.2Al.sub.2O.sub.3-based crystal to precipitate in a temperature range of from a liquidus line temperature to (the liquidus line temperature50? C.)