Abstract: Rigid electrical insulator including a soda-lime glass dielectric with an average thickness of 10 to 15 mm, exhibiting a substantially parabolic stress curve, wherein the maximum value of the surface compression stresses at any point in the part falls within the range of 30 to 80 MPa, while the maximum value of the internal tensile stresses at any point in the part falls within the range of 15 to 40 MPa.

Abstract: A tempered glass dielectric material for use as an electrical insulator is thermally tempered to produce surface compression between 200 MPa and 400 MPa. At least part of the material is then chemically tempered under conditions of temperature and duration such that the surface compression due to the thermal tempering is reduced by between 50% and 80%. The chemical tempering is effected by applying to the relevant part of the material, at ambient temperature, a solution containing alkaline salts. This solution is dried and the material then heated for several hours at a temperature between 300.degree. C. and 500.degree. C. The solution has the following composition (in percentage by weight):______________________________________ H.sub.2 O 70% to 90% Starch 2% to 10% KNO.sub.3 4% to 12% K.sub.2 HPO.sub.4 + KCl + K.sub.2 SO.sub.

Abstract: A vitreous material suitable for coating a semiconductor component comprises, by weight:30% to 40% zinc oxide ZnO,15% to 30% lead oxide PbO,20% to 40% boron oxide B.sub.2 O.sub.3,5% to 20% silicon dioxide SiO.sub.2,2% to 10% aluminum titanate Al.sub.2 TiO.sub.5, and0% to 5% bismuth oxide Bi.sub.2 O.sub.3.