Provided is a transparent spinel sintered body which is formed from an Mg—Al spinel powder having an Al/Mg ratio of from 1.97 to 2.03 or a mixed powder of an Mg oxide and an Al oxide, and wherein the total content of metal impurities excluding Al and Mg is less than 100 ppm. A sample of this transparent spinel sintered body having a thickness of 3 mm has a total light transmittance of 80% or more in the thickness direction for the wavelength range of from 190 nm to 400 nm; and this transparent spinel sintered body is usable as a medium that transmits light from an ultraviolet light emitting element.

The present invention provides a method for making a high strength, small grain size ceramic having a trans-granular fracture mode by rapid densification of a green body and subsequent cooling of the densified ceramic. The ceramic may include dislocations, defects, dopants, and/or secondary phases that are formed as a result of the process and resulting in stress fields capable of redirecting or arresting cracks within the material. This ceramic can maintain transparency from ultraviolet to mid-wave infrared.

The present invention provides a method for making a high strength, small grain size ceramic having a trans-granular fracture mode by rapid densification of a green body and subsequent cooling of the densified ceramic. The ceramic may include dislocations, defects, dopants, and/or secondary phases that are formed as a result of the process and resulting in stress fields capable of redirecting or arresting cracks within the material. This ceramic can maintain transparency from ultraviolet to mid-wave infrared.

A refractory object can include at least 10 wt % Al.sub.2O.sub.3. Further, the refractory object may contain less than approximately 6 wt % SiO.sub.2 or may include a dopant that includes an oxide of Ti, Mg, Ta, Nb, or any combination thereof. In an embodiment, at least approximately 1% of the Al.sub.2O.sub.3 in the refractory object can be provided as reactive Al.sub.2O.sub.3. In another embodiment, the refractory object may have a density of at least approximately 3.55 g/cc, a corrosion rate of no greater than approximately 2.69 mm/year, or any combination of the foregoing. In a particular embodiment, the refractory object can be used to form an Al—Si—Mg glass sheet. In an embodiment, the refractory object may be formed by a process using a compound of Ti, Mg, Ta, Nb, or any combination thereof.

A refractory object can include at least 10 wt % Al.sub.2O.sub.3. Further, the refractory object may contain less than approximately 6 wt % SiO.sub.2 or may include a dopant that includes an oxide of Ti, Mg, Ta, Nb, or any combination thereof. In an embodiment, at least approximately 1% of the Al.sub.2O.sub.3 in the refractory object can be provided as reactive Al.sub.2O.sub.3. In another embodiment, the refractory object may have a density of at least approximately 3.55 g/cc, a corrosion rate of no greater than approximately 2.69 mm/year, or any combination of the foregoing. In a particular embodiment, the refractory object can be used to form an Al—Si—Mg glass sheet. In an embodiment, the refractory object may be formed by a process using a compound of Ti, Mg, Ta, Nb, or any combination thereof.

A gas nozzle according to an embodiment of the present invention includes a columnar main body including a ceramic sintered body having a through hole through which gas flows. An outlet of the through hole for the gas is formed on one end face of the main body. An inner wall of the through hole has a first region located in a vicinity of the outlet, and a second region located further inward of the main body than the first region. The first region and the second region each include a sintered surface of the ceramic sintered body. Average crystal grain size in the first region is larger than average crystal grain size in the second region.

One aspect of the heat insulator of the present invention includes a porous sintered body having a porosity of 70 vol % or more and less than 91 vol %, and pores having a pore size of 0.8 μm or more and less than 10 μm occupy 10 vol % or more and 70 vol % or less of the total pore volume, while pores having a pore size of 0.01 μm or more and less than 0.8 μm occupy 5 vol % or more and 30 vol % or less of the total pore volume. The porous sintered body is formed from an MgAl.sub.2O.sub.4 (spinel) raw material and fibers formed of an inorganic material, the heat conductivity of the heat insulator at 1000° C. or more and 1500° C. or less is 0.40 W/(m.Math.K) or less, and the weight ratio of Si relative to Mg in the porous sintered body is 0.15 or less.

One aspect of the heat insulator of the present invention includes a porous sintered body having a porosity of 70 vol % or more and less than 91 vol %, and pores having a pore size of 0.8 μm or more and less than 10 μm occupy 10 vol % or more and 70 vol % or less of the total pore volume, while pores having a pore size of 0.01 μm or more and less than 0.8 μm occupy 5 vol % or more and 30 vol % or less of the total pore volume. The porous sintered body is formed from an MgAl.sub.2O.sub.4 (spinel) raw material and fibers formed of an inorganic material, the heat conductivity of the heat insulator at 1000° C. or more and 1500° C. or less is 0.40 W/(m.Math.K) or less, and the weight ratio of Si relative to Mg in the porous sintered body is 0.15 or less.

One aspect of the heat insulator of the present invention includes a porous sintered body having a porosity of 70 vol % or more and less than 91 vol %, and pores having a pore size of 0.8 μm or more and less than 10 μm occupy 10 vol % or more and 70 vol % or less of the total pore volume, while pores having a pore size of 0.01 μm or more and less than 0.8 μm occupy 5 vol % or more and 30 vol % or less of the total pore volume. The porous sintered body is formed from an MgAl.sub.2O.sub.4 (spinel) raw material and fibers formed of an inorganic material, the heat conductivity of the heat insulator at 1000° C. or more and 1500° C. or less is 0.40 W/(m.Math.K) or less, and the weight ratio of Si relative to Mg in the porous sintered body is 0.15 or less.

A ceramic substrate is formed of a polycrystalline ceramic and has a supporting main surface. The supporting main surface has a roughness of 0.01 nm or more and 3.0 nm or less in terms of Sa. The number of projections and depressions with a height of 1 nm or more in a square region with 50 μm sides on the supporting main surface is less than 5 on average, and the number of projections and depressions with a height of 2 nm or more in the square region is less than 1 on average.