The invention relates to a method to derive a medical form body of lithium silicate glass ceramic. To increase its strength it is proposed that in the form body comprising lithium silicate glass or containing lithium silicate glass the lithium ions are replaced by alkali ions of greater diameter to generate a surface compressive stress. To this end the form body is covered with a melt containing an alkali metal for which an aliquoted quantity of salt containing the alkali metal is used.

A pre-sintered porcelain block for dental restoration; the pre-sintered porcelain block does not contain crystal phases and has a Vickers hardness of 0.5-2 GPa. Due to a hardness which is significantly lower than that of the porcelain block containing a lithium metasilicate crystal phase, the pre-sintered porcelain block may be processed by using dry machining and can simultaneously be processed by using wet machining when being mechanically processed into a dental restoration shape.

Included is a step of exposing a glass blank at a temperature lower than the temperature at which crystals of lithium metasilicate are generated, to an atmosphere at a temperature equal to or higher than the temperature at which crystals of lithium disilicate are generated and lower than the melting point of the crystals of lithium disilicate, to heat the glass blank so that the main crystalline phase of the glass blank is of lithium disilicate.

A block for dental prostheses is in the form of a column or a board, a main crystalline phase of the block being of lithium disilicate, and when the block is observed in a field of view of a partially enlarged cross section of the block, the proportion of the total area of crystals having a length of at least 0.5 μm, the crystals appearing in the field of view, to an area of the field of view is at most 21%.

A black β-spodumene glass ceramic is provided. The glass ceramic includes β-spodumene as a primary crystal phase and gahnite as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 20.0 to 40.0, a*: −1.0 to 0.5, and b*: −5.0 to 1.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

The present application provides transparent glass-ceramics of β-quartz of composition containing a small content of lithium, articles constituted at least in part of said glass-ceramics, glasses precursors of said glass-ceramics, and also a method of preparing said articles. Said glass-ceramics have a composition, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, containing: 62% to 68% of SiO.sub.2; 17% to 21% of AI.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO<6%; optionally up to 2% of at least one fining agent comprising SnO.sub.2; and optionally up to 2% of at least one coloring agent.

A black β-spodumene lithium disilicate glass ceramic is provided. The glass ceramic includes at least one of magnetite, β-quartz, cristobalite, and lithium phosphate as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 15.0 to 35.0, a*: −3.0 to 3.0, and b*: −5.0 to 5.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

A transparent β-quartz glass ceramic is provided. The glass ceramic includes a primary crystal phase including a β-quartz solid solution, a secondary crystal phase including tetragonal ZrO.sub.2, and a lithium aluminosilicate amorphous phase. The glass ceramic may be ion exchanged utilizing molten nitrate salt baths. Methods for producing the glass ceramic are also provided.

A solid electrolyte material comprises Li, T, X and A wherein T is at least one of P, As, Si, Ge, Al, and B; X is one or more halogens or N; A is one or more of S and Se. The solid electrolyte material has peaks at 17.8°±0.75° and 19.2°±0.75° in X-ray diffraction measurement with Cu-Kα(1,2)=1.5418 Å and may include glass ceramic and/or mixed crystalline phases.

The present invention relates to a chemically strengthened glass, satisfying in comparison of an estimated stress profile with an effective stress profile, an absolute value of a difference between tensile stress values at a center in a thickness direction is 30 MPa or smaller, and a value obtained by subtracting, at a depth of 15 μm from a chemically strengthened surface of the glass, a compressive stress value of the effective stress profile from a compressive stress value of the estimated stress profile is 50 MPa or larger.