Alkali free glass and method for producing alkali free glass
View Patent ↗The present invention relates to an alkali-free glass having a strain point of 725° C. or higher, an average thermal expansion coefficient at from 50 to 300° C. of from 30×10 −7 to 40×10 −7 /° C., a temperature T 2 at which a glass viscosity is 10 2 dPa·s of 1,710° C. or lower, and a temperature T 4 at which a glass viscosity is 10 4 dPa·s of 1,320° C. or lower, the alkali-free glass including, in terms of mol % on the basis of oxides, SiO 2 : 66 to 70, Al 2 O 3 : 12 to 15, B 2 O 3 : 0 to 1.5, MgO: more than 9.5 and 13 or less, CaO: 4 to 9, SrO: 0.5 to 4.5, BaO: 0 to 1, and ZrO 2 : 0 to 2, in which MgO+CaO+SrO+BaO is from 17 to 21, MgO/(MgO+CaO+SrO+BaO) is 0.4 or more, MgO/(MgO+CaO) is 0.4 or more, MgO/(MgO+SrO) is 0.6 or more, and the alkali-free glass does not substantially contain an alkali metal oxide.
1. An alkali-free glass having a strain point of 725° C. or higher, an average thermal expansion coefficient at from 50 to 300° C. of from 30×10 −7 to 40×10 −7 /° C., a temperature T 2 at which a glass viscosity is 10 2 dPa·s of 1,710° C. or lower, a temperature T 4 at which a glass viscosity is 10 4 dPa·s of 1,320° C. or lower, and a devitrification temperature of 1,350° C. or lower, the alkali-free glass comprising, in terms of mol % on the basis of oxides:
SiO 2
66 to 70,
Al 2 O 3
12 to 14.5,
B 2 O 3
0 to 1.5,
MgO
more than 9.5 and 11.5 or less,
CaO
4 to 9,
SrO
0.5 to 4.5,
BaO
0 to 1, and
ZrO 2
0 to 2,
wherein MgO+CaO+SrO+BaO is from 17 to 21,
MgO/(MgO+CaO+SrO+BaO) is 0.4 or more,
MgO/(MgO+CaO) is 0.4 or more,
MgO/(MgO+SrO) is 0.6 or more, and
the alkali-free glass does not substantially contain an alkali metal oxide.
2. The method for producing the alkali-free glass according to claim 1 , wherein a silica sand, in which a median diameter D 50 is from 20 to 27 μm, a proportion of particles having a particle size of 2 μm or less is 0.3 vol % or less, and a proportion of particles having a particle size of 100 μm or more is 2.5 vol % or less, is used as a silicon source of SiO 2 .
3. The method for producing the alkali-free glass according to claim 1 , wherein an alkaline earth metal source containing a hydroxide of an alkaline earth metal in an amount of from 15 to 100 mol % (in terms of MO, provided that M is an alkaline earth metal element, and hereinafter the same) of 100 mol % of the alkaline earth metal source is used as the alkaline earth metal source of MgO, CaO, SrO and BaO.
4. The method for producing the alkali-free glass according to claim 1 , wherein a silica sand, in which a median diameter D 50 is from 20 to 27 μm, a proportion of particles having a particle size of 2 μm or less is 0.3 vol % or less, and a proportion of particles having a particle size of 100 μm or more is 2.5 vol % or less, is used as a silicon source of SiO 2 ; and an alkaline earth metal source containing a hydroxide of an alkaline earth metal in an amount of from 15 to 100 mol % (in terms of MO, provided that M is an alkaline earth metal element, and hereinafter the same) of 100 mol % of the alkaline earth metal source is used as the alkaline earth metal source of MgO, CaO, SrO and BaO.
5. The alkali-free glass according to claim 1 , wherein SrO is included in an amount of 2 to 4.5 mol % on the basis of oxides.
6. The alkali-free glass according to claim 1 having a glass transition point of 760° C. or higher, a specific gravity of 2.65 or less, a Young's modulus of 84 GPa or more, the devitrification temperature of 1,340° C. or lower, a photoelastic constant of 31 nm/MPa/cm or less, and a dielectric constant of 5.6 or more.