USE OF A GLASS COMPOSITION FOR MAKING A SOLAR COLLECTOR WITH A GLASS-METAL JOINT

摘要

Use of a glass composition to make a tubular glass body that is adapted to form a glass-metal joint in a tubular solar collector. The composition is a borosilicate glass having a dilatometric chart with a hard segment and a soft- segment hysteresis where the soft segment glass transition temperature is less than the hard-segment glass transition temperature for a temperature difference (??) higher than 20°C, in particular higher than 30°C, preferably higher than 40°C. In particular, the composition comprises: - 5% to 8% Na2O, - 0, 1% to 3% K2O, - 0, 1% to 1, 5% CaO, - 5% to 7,5% Al2O3, - 70% to 75% SiO2, - 11,6% to 13,7% ?2O3, and owing to the choice of the B2O3 in the range indicated, in combination with the other components, there is a glass transition temperature lower than other borosilicate glasses, and the remarkable difference between the soft and hard segments glass transition temperatures make it possible to obtain a tubular glass body for a solar collector with minimum thermal stress in the working temperature ranges. To the above described composition an oxide can be added selected from the group consisting of: from 0,01% to 1,0% MgO; from 0,01 % to 1% Li2O; from 0,01% to 2% BaO; or a combination thereof.