Glass seals for sealing beta-alumina in electro-chemical cells or other energy conversion devices, glasses for use in such seals and cells or other energy conversion devices with such seals

DETAILED DESCRIPTION According to the present invention, a glass for sealing to beta-alumina in an electro-chemical cell or other energy conversion device containing sodium, consists essentially of: (a) 40-60 mol % glass former consisting of 28-48 mol % B.
sub.
2 O.
sub.
3 and 0-20 mol % SiO.
sub.
2 (b) 16-28 mol % Al.
sub.
2 O.
sub.
3 (c) 18-33 mol % of at least one alkaline earth oxide selected from the group consisting of BaO, CaO, MgO and SrO, where the proportions of the constituents furthermore are such that: 0.
0517A.
sub.
1 +0.
0354A.
sub.
2 -0.
0063A.
sub.
3 +0.
168A.
sub.
4 +0.
1336A.
sub.
5 +0.
098A.
sub.
6 +0.
1597A.
sub.
7 lies between 5.
7 and 6.
4, where A.
sub.
1, A.
sub.
2, A.
sub.
3, A.
sub.
4, A.
sub.
5, A.
sub.
6 and A.
sub.
7 are the respective molar percentages of B.
sub.
2 O.
sub.
3, SiO.
sub.
2, Al.
sub.
2 O.
sub.
3, BaO, CaO, MgO and SrO.
The coefficients of A.
sub.
1, A.
sub.
2 etc.
quoted above are, as will be explained later, truncated values of regression coefficients relating to effect of the constituent proportions on the mean linear coefficient of thermal expansion.
The proportion of Al.
sub.
2 O.
sub.
3 would usually be between 17 and 28 mol %.
The glass may contain one or more of the alkaline earth oxides; preferably the proportions of these oxides lie in the ranges 0-25 mol % BaO, 0-15 mol % SrO, 0-30 mol % CaO and 0-20 mol % MgO with a minimum total of 18 and a maximum total of 33 mol %.
It will be appreciated by those skilled in the art that some of the compositions defined above lie close to the boundary of the glass-forming region.
These boundaries, such as those discussed with reference to alkali alumina borate glass systems by Hiramaya in the above-mentioned reference, are diffuse.
Care has to be taken in the use of compositions in the boundary region because of the possibility of devitrification.
The invention furthermore includes within its scope a hermetic seal between ana lpha-alumina components and a beta-alumina component in a sodium sulphur cell comprising a glass body fused between surfaces of these components, the glass consisting essentially of 28-48 mol % B