We Claim:
1. A glass composition with improved mechanical strength and reduced brittleness
comprising a following composition essentially in terms of weight percent on the
oxide basis as calculated from the batch of, 60 – 80% SiO2, 1.5 – 8% R’O, 0 – 5%
5 Al2O3, 8 – 17% R2O, 5 – 13% R”O provided that R’ is at least one member
selected from alkaline earth metals whose size is smaller that of R’’, which is at
least another one member selected from alkaline earth metals, and R is at least one
member selected from Li, Na and K; and wherein,
a ratio for Resistance to Crack Initiation Factor (RCIF) = (R’O × R2O) / (R”O) =
10 4.5 indicating that the crack initiation load of the resulting glass will be = 1000 gf
(grams-force) , wherein
R’O = 2% by weight , R’’O = 9.5% by weight and R2O is at least 10% by weight.
2. A glass composition set forth in claim 1, characterized in that it consists
15 essentially of the following components in terms of weight percent on the oxide
basis as calculated from the batch of, 60 – 78% SiO2, 2 – 6% R’O, 0 – 3%
Al2O3, 10 – 15% R2O, 6.5 – 11.5% R”O provided that R’ is at least one member
selected from alkaline earth metals whose size is smaller that of R’’, which is at
least another one member selected from alkaline earth metals, and R is at least one
20 member selected from Li, Na and K; and wherein a ratio for Resistance to Crack
Initiation Factor (RCIF) = (R’O × R2O) / (R”O) = 4.5 indicating that the crack
initiation load of the resulting glass will be = 1000 gf (grams-force) , wherein R’O
= 2% by weight, R’’O = 9.5% by weight and R2O is at least 10% by weight.
3. A glass composition set forth in claim 1, wherein the glass has a Vickers Crack
25 Initiation threshold of at least about 1000 gram force (gf).
4. A glass composition set forth in claim 1, characterized in that R’ is essentially Mg.
5. A glass composition set forth in claim 1, characterized in that R is essentially Na