Alkali-free glass
To provide an alkali-free glass having a high specific elastic modulus, a suitable strain point, a low density, a not too low thermal expansion coefficient, a good clarity and a good solubility. An alkali-free glass, which comprises, as represented by mol % based on oxides, SiO 2 : 62 to 70%, Al 2 O 3 : 11 to 14%, B 2 O 3 : 3 to 6%, MgO: 7 to 10%, CaO: 3 to 9%, SrO: 1 to 5% and BaO: 0 to 1%, wherein [SiO 2 ]+0.7[Al 2 O 3 ]+1.2[B 2 O 3 ]+0.5[MgO]+0.4[CaO]−0.25[SrO]−0.88[BaO] is at least 85, [SiO 2 ]+0.45[Al 2 O 3 ]+0.21[B 2 O 3 ]−0.042[MgO]+0.042[CaO]+0.15[SrO]+0.38[BaO] is from 72 to 75, 0.4[SiO 2 ]+0.4[Al 2 O 3 ]+0.25[B 2 O 3 ]−0.7[MgO]−0.88[CaO]−1.4[SrO]−1.7[BaO] is at most 19, the specific modulus is at least 32 MN·m/kg, the strain point is from 690 to 710° C., the density is at most 2.54 g/cm 3 , the average thermal expansion coefficient at from 50 to 350° C. is at least 35×10 −7 /° C., and the temperature T 2 at which the glass viscosity reaches 10 2 dPa·s is from 1,610 to 1,680° C.
1. An alkali-free glass, which comprises, as represented by mol % based on oxides,
SiO 2 65.5 to 70%,
Al 2 O 3 11 to 14%,
B 2 O 3 3 to 5.5%,
MgO 7 to 10%,
CaO 3 to 9%,
SrO 1 to 5% and
BaO 0 to 1%,
wherein
the mol % content of the alkaline earth metals is related according to [MgO]>[CaO]>[SrO]>[BaO],
[SiO 2 ]+0.7[Al 2 O 3 ]+1.2[B 2 O 3 ]+0.5[MgO]0.4[CaO]−0.25[SrO]−0.88[BaO]is at least 85,
[SiO 2 ]+0.45[Al 2 O 3 ]+0.21[B 2 O 3 ]−0.042[MgO]+0.042[CaO]+0.15[SrO]+0.38[BaO] is from 72 to 75,
0.4[SiO 2 ]0.4[Al 2 O 3 ]0.25[B 2 O 3 ]−0.7[MgO]−0.88[CaO]−1.4[SrO]−1.7[BaO]is at most 19,
the specific modulus is at least 32 MN·m/kg,
the strain point is from 690 to 710° C.,
the density is at most 2.54 g/cm 3 ,
the average thermal expansion coefficient at from 50 to 350° C. is at least 35×10 −7 /° C., and
the temperature T 2 at which the glass viscosity reaches 10 2 dPa·s is from 1,610 to 1,680° C.
2. The alkali-free glass according to claim 1 , wherein the mol % of MgO/(MgO+CaO+SrO+BaO is from 15 to 21%.
3. The alkali-free glass according to claim 1 , wherein the mol % ratio MgO/(MgO+CaO+SrO+BaO) is from 0.35 to 0.70.
4. The alkali-free glass according to claim 1 , wherein the temperature T 4 at which the glass viscosity reaches 10 4 dPa·s is at most 1,320° C.
5. The alkali-free glass according to claim 1 , wherein the devitrification viscosity is at least 10 3.6 d·Pas.
6. The alkali-free glass according to claim 1 , wherein the Young's modulus is at least 81 GPa.
7. The alkali-free glass according to claim 1 , wherein a T 2 -strain point is from 920 to 1,000° C.
8. The alkali-free glass according to claim 1 , wherein the glass transition temperature is from 730 to 770° C.
9. The alkali-free glass according to claim 1 , which is a glass plate having a thickness of from 0.1 to 2.0 mm.
10. The alkali-free glass according to claim 1 , which is produced by a float method or a fusion method.