A glass tube element having a hollow cylindrical section with a shell having an outer diameter is provided. A first ratio is a difference value to a mean value. The difference value is a difference of a minimal and maximal value of the outer diameter. The mean value is a mean of the minimal and maximal values. A sub-section having a start, an end, and a distance of 1 meter measured along a straight line from the start to the end and intersecting with a center axis of the sub-section at the start and the end. The sub-section having, for every point of the center axis, a shortest distance to the straight line. A second ratio of a specific distance to 1 meter, the specific distance being defined as a largest of all shortest distances. A product of the first and second ratio is smaller than 4×10.sup.−6.

A compositional range of fusion-formable, high strain point sodium free, silicate, aluminosilicate and boroaluminosilicate glasses are described herein. The glasses can be used as substrates for photovoltaic devices, for example, thin film photovoltaic devices such as CIGS photovoltaic devices. These glasses can be characterized as having strain points ≧540° C., thermal expansion coefficient of from 6.5 to 10.5 ppm/° C., as well as liquidus viscosities in excess of 50,000 poise. As such they are ideally suited for being formed into sheet by the fusion process.

A compositional range of fusion-formable, high strain point sodium free, silicate, aluminosilicate and boroaluminosilicate glasses are described herein. The glasses can be used as substrates for photovoltaic devices, for example, thin film photovoltaic devices such as CIGS photovoltaic devices. These glasses can be characterized as having strain points ≧540° C., thermal expansion coefficient of from 6.5 to 10.5 ppm/° C., as well as liquidus viscosities in excess of 50,000 poise. As such they are ideally suited for being formed into sheet by the fusion process.

A vitrified bond grindstone includes abrasive grains and a bonding material for fixing the abrasive grains, the bonding material includes a parent material containing SiO.sub.2 as a main constituent, a sintering assistant oxide, and ZnO, and the content of ZnO is 11 to 15 wt % in weight ratio based on the bonding material. Preferably, the content of the sintering assistant oxide is 20 to 29 wt % in weight ratio based on the bonding material.

A method of producing glass using submerged combustion melting is disclosed. The method includes introducing a vitrifiable feed material into a glass melt contained within a submerged combustion melter. The glass melt contained in the melter has a redox ratio defined as a ratio of Fe.sup.2+ to total iron in the glass melt. The method further includes combusting a combustible gas mixture supplied to each of the submerged burners to produce combustion products, and discharging the combustion products directly into the glass melt. Still further, the method includes adjusting the redox ratio of the glass melt by controlling one or more operating conditions of the submerged combustion melter selected from (1) an oxygen-to-fuel ratio of the combustible gas mixture supplied to each of the submerged burners, (2) a residence time of the glass melt, and (3) a gas flux through the glass melt.

A method of producing glass using submerged combustion melting is disclosed. The method includes introducing a vitrifiable feed material into a glass melt contained within a submerged combustion melter. The glass melt contained in the melter has a redox ratio defined as a ratio of Fe.sup.2+ to total iron in the glass melt. The method further includes combusting a combustible gas mixture supplied to each of the submerged burners to produce combustion products, and discharging the combustion products directly into the glass melt. Still further, the method includes adjusting the redox ratio of the glass melt by controlling one or more operating conditions of the submerged combustion melter selected from (1) an oxygen-to-fuel ratio of the combustible gas mixture supplied to each of the submerged burners, (2) a residence time of the glass melt, and (3) a gas flux through the glass melt.

A laminate sheet article including: a core including an electrical semi-conductor or an electrical conductor; and a continuous glass clad layer on at least four of six sides the core of the sheet article. Also disclosed is an apparatus for making a sheet laminate article as defined herein. Also disclosed is a method of making and using the article.

A laminate sheet article including: a core including an electrical semi-conductor or an electrical conductor; and a continuous glass clad layer on at least four of six sides the core of the sheet article. Also disclosed is an apparatus for making a sheet laminate article as defined herein. Also disclosed is a method of making and using the article.

A ceramic filter is provided with a porous substrate 3 “made of ceramic and having partition walls 1 separating and forming a plurality of cells 2 extending from one end face 11 to the other end face 12”, a separation membrane 21 “made of ceramic and disposed on wall surfaces of the cells 2”, and glass seals 31 disposed on the one end face 11 and on the other end face 12 “so as not to cover openings of the cells 2”. Ceramic particles having a thermal expansion coefficient of 90 to 110% of that of glass contained in the glass seals 31 are dispersed in the glass seals 31. There is provided a ceramic filter usable for a long period of time in high temperature conditions.

A ceramic filter is provided with a porous substrate 3 “made of ceramic and having partition walls 1 separating and forming a plurality of cells 2 extending from one end face 11 to the other end face 12”, a separation membrane 21 “made of ceramic and disposed on wall surfaces of the cells 2”, and glass seals 31 disposed on the one end face 11 and on the other end face 12 “so as not to cover openings of the cells 2”. Ceramic particles having a thermal expansion coefficient of 90 to 110% of that of glass contained in the glass seals 31 are dispersed in the glass seals 31. There is provided a ceramic filter usable for a long period of time in high temperature conditions.