A window includes a base region and a compressive stress region disposed on the base region. The compressive stress region includes Li.sup.+, Na.sup.+, and K.sup.+ ions. The compressive stress region includes a first compressive stress portion in which a concentration of the K.sup.+ ions decreases, a concentration of Na.sup.+ ions increases, and a concentration of the Li.sup.+ ions increases, from a surface of the window toward the base region. A second compressive stress portion is adjacent to the first compressive stress portion. In the second compressive stress portion, the concentration of the Na.sup.+ ion decreases and the concentration of the Li.sup.+ ion increases, from the first compressive stress portion toward the base region. The window thereby has a high surface compressive stress value and impact resistance.

The present application discloses a strengthened microcrystalline glass having a high scratch resistance comprising a compressive stress layer and a tensile stress layer. The glass has a main crystalline phase of (Zn, Mg)Al.sub.2O.sub.4 and comprises Na.sub.2O. It has a surface K.sub.2O concentration of 7.00 wt %. Along the thickness direction of the glass, the glass has a depth of 0.07 t, preferably 0.07 t to 0.10 t, which is from any surface of the glass to a location close to that surface and having the same potassium (K) concentration as that at the center of the glass, wherein t is the thickness of the glass. The strengthened microcrystalline glass has an excellent scratch resistance comparable to that of sapphire glass.

A window includes a base region and a compressive stress region disposed on the base region. The compressive stress region includes Li.sup.+, Na.sup.+, and K.sup.+ ions. The compressive stress region includes a first compressive stress portion in which a concentration of the K.sup.+ ions decreases, a concentration of Na.sup.+ ions increases, and a concentration of the Li.sup.+ ions increases, from a surface of the window toward the base region. A second compressive stress portion is adjacent to the first compressive stress portion. In the second compressive stress portion, the concentration of the Na.sup.+ ion decreases and the concentration of the Li.sup.+ ion increases, from the first compressive stress portion toward the base region. The window thereby has a high surface compressive stress value and impact resistance.

A window includes a base region and a compressive stress region disposed on the base region. The compressive stress region includes Li.sup.+, Na.sup.+, and K.sup.+ ions. The compressive stress region includes a first compressive stress portion in which a concentration of the K.sup.+ ions decreases, a concentration of Na.sup.+ ions increases, and a concentration of the Li.sup.+ ions increases, from a surface of the window toward the base region. A second compressive stress portion is adjacent to the first compressive stress portion. In the second compressive stress portion, the concentration of the Na.sup.+ ion decreases and the concentration of the Li.sup.+ ion increases, from the first compressive stress portion toward the base region. The window thereby has a high surface compressive stress value and impact resistance.

A potassium nitrate level detection sensing module M in a strengthening furnace according to the present invention includes a level detection means, which is installed inside a glass strengthening furnace, installed at a height equal to a level line of strengthening liquid to be filled in the strengthening furnace F, and generates an electrical signal having a set threshold or more or an electrical signal having the set threshold or less when it comes into contact with the strengthening liquid and detects that the strengthening liquid filled in the glass strengthening furnace F has reached a set strengthening liquid level line. The potassium nitrate level detection sensing module in the strengthening furnace according to the present invention having such a configuration can automatically identify that potassium nitrate in a liquid state, which is melted in the strengthening furnace, has reached the set level line in the strengthening furnace.

A potassium nitrate level detection sensing module M in a strengthening furnace according to the present invention includes a level detection means, which is installed inside a glass strengthening furnace, installed at a height equal to a level line of strengthening liquid to be filled in the strengthening furnace F, and generates an electrical signal having a set threshold or more or an electrical signal having the set threshold or less when it comes into contact with the strengthening liquid and detects that the strengthening liquid filled in the glass strengthening furnace F has reached a set strengthening liquid level line. The potassium nitrate level detection sensing module in the strengthening furnace according to the present invention having such a configuration can automatically identify that potassium nitrate in a liquid state, which is melted in the strengthening furnace, has reached the set level line in the strengthening furnace.

A refill system includes a tempering furnace, a refill furnace which stores the molten potassium nitrate obtained by melting powdered potassium nitrate, a supply unit which supplies the molten potassium nitrate to the tempering furnace, a tempering furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the tempering furnace, a refill furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the refill furnace, and a central control unit which checks the load amount of the molten potassium nitrate in the tempering furnace and the refill furnace in real time, and controls the supply unit to stop supplying the molten potassium nitrate to the tempering furnace when the load amount of the molten potassium nitrate in the tempering furnace is greater than or equal to a predetermined load amount.

A refill system includes a tempering furnace, a refill furnace which stores the molten potassium nitrate obtained by melting powdered potassium nitrate, a supply unit which supplies the molten potassium nitrate to the tempering furnace, a tempering furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the tempering furnace, a refill furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the refill furnace, and a central control unit which checks the load amount of the molten potassium nitrate in the tempering furnace and the refill furnace in real time, and controls the supply unit to stop supplying the molten potassium nitrate to the tempering furnace when the load amount of the molten potassium nitrate in the tempering furnace is greater than or equal to a predetermined load amount.

A glass article includes lithium aluminosilicate, includes a first surface, a second surface opposed to the first surface, a first compressive region extending from the first surface to a first compression depth, a second compressive region extending from the second surface to a second compression depth, and, a tensile region disposed between the first compression depth and the second compression depth, where a stress profile of the first compressive region has a first local minimum point at which the stress profile is convex downward and a first local maximum point at which the stress profile is convex upward, where a depth of the first local maximum point is greater than a depth of the first local minimum point, and where a stress of the first local maximum point is greater than a compressive stress of the first local minimum point.

A glass article includes lithium aluminosilicate, includes a first surface, a second surface opposed to the first surface, a first compressive region extending from the first surface to a first compression depth, a second compressive region extending from the second surface to a second compression depth, and, a tensile region disposed between the first compression depth and the second compression depth, where a stress profile of the first compressive region has a first local minimum point at which the stress profile is convex downward and a first local maximum point at which the stress profile is convex upward, where a depth of the first local maximum point is greater than a depth of the first local minimum point, and where a stress of the first local maximum point is greater than a compressive stress of the first local minimum point.