Glass-ceramic materials, precursor glass thereof and process for making the same
The invention relates to: a method of preparing glass-ceramics of β-quartz and/or of β-spodumene; a method of preparing articles made from said glass-ceramics; novel glass-ceramics of β-quartz and/or of β-spodumene; articles made from said novel glass-ceramics; and lithium aluminosilicate glasses, which are precursors of such novel glass-ceramics. The present invention relates to the use, as agent for fining the glass-ceramic glass precursor, of fluorine and at least one oxide of a multivalent element.
1. A glass-ceramic containing a solid solution of β-quartz or of β-spodumene or solid solutions of β-quartz and β-spodumene, as main crystalline phase(s), the composition of which, expressed as percentages by weight of oxides, essentially consists of:
SiO 2
60-72
Al 2 O 3
18-23
Li 2 O
2.5-4
MgO
0.5-2
ZnO
1-3
TiO 2
1.5-3.5
ZrO 2
0-2.5
BaO
<2
SrO
0-2
CaO
0-2
Na 2 O
0-1.5
K 2 O
0-1.5
P 2 O 5
0-5
B 2 O 3
0-3
F
0.05-1,
advantageously 0.05-0.3;
and at least one oxide of a multivalent element selected from the group consisting of SnO 2 , V 2 O 5 , CeO 2 , MnO 2 and Fe 2 O 3 , wherein each respective one of said at least one multivalent element oxide comprises at least 0.15% of the glass-ceramic, such that the sum of said multivalent element oxide(s) comprises 0.2-2% of the glass ceramic, wherein SnO 2 , if included, comprises 0.15-0.7% of the glass-ceramic, and barium oxide is present in an amount up to 2%.
2. The glass-ceramic according to claim 1 , the composition of which contains one or more of the following oxides such that, if included, the oxide is present in the following amounts:
SnO 2
0.2-0.7
CeO 2
0.2-2
MnO 2
0.2-2
Fe 2 O 3
0.2-2
V 2 O 5
0.2-1.
3. The glass-ceramic according to claim 1 , the composition of which further contains an effective amount of at least one colorant, selected from the group consisting of CoO, Cr 2 O 3 , Fe 2 O 3 , MnO 2 , NiO, V 2 O 5 , and CeO 2 .
4. The glass-ceramic according to claim 1 , the composition of which contains, with the exception of inevitable traces, neither arsenic, nor antimony.
5. An article made from a glass-ceramic according to claim 1 , said article selected from the group consisting of a cook-top, a cooking utensil, a microwave oven plate, a fireplace window, a fire-door or fire-window, and a pyrolysis- or catalysis-oven window.
6. A method of preparing a glass-ceramic containing a solid solution of β-quartz or of β-spodumene or solid solutions of β-quartz and β-spodumene, as main crystalline phase(s) as set forth in claim 1 , comprising heat-treating a lithium aluminosilicate glass, which is a precursor of said glass-ceramic, under conditions which ensure its ceramming, wherein said glass jointly contains, as fining agent, fluorine and at least one oxide of a multivalent element which is different from arsenic oxide and from antimony oxide.
7. A method of preparing an article made from a glass-ceramic containing a solid solution of β-quartz or of β-spodumene or solid solutions of β-quartz and β-spodumene, as main crystalline phase(s) as set forth in claim 1 , said method comprising:
melting a lithium aluminosilicate glass or a filler, which is a precursor of said glass ceramic; said glass or said filler containing an effective and non-excess amount of at least one fining agent; followed by fining the molten glass obtained;
cooling the molten fined glass obtained, and, simultaneously, shaping it into the shape desired for the article sought after; and
ceramming said shaped glass;
wherein said glass or said filler contains, as fining agent, fluorine and at least one oxide of a multivalent element which is different from arsenic oxide and from antimony oxide.
8. The method according to claim 6 , wherein said glass or said filler contains, with the exception of inevitable traces, neither arsenic, nor antimony.
9. A glass-ceramic containing a solid solution of β-quartz or of β-spodumene or solid solutions of β-quartz and β-spodumene, as main crystalline phase(s), the composition of which, expressed as percentages by weight of oxides, essentially consists of:
SiO 2
65-70
Al 2 O 3
18-19.8
Li 2 O
2.5-3.8
MgO
0.55-1.5
ZnO
1.2-2.8
TiO 2
1.8-3.2
BaO
0-1.4
SrO
0-1.4
with BaO + SrO
0.4-1.4
with MgO + BaO + SrO
1.1-2.3
ZrO 2
1.0-2.5
Na 2 O
0-<1.0
K 2 O
0-<1.0
with Na 2 O + K 2 O
0-<1.0
with 2.8Li 2 O + 1.2ZnO/5.2MgO
>1.8
F
0.05-1,
advantageously 0.05-0.3;
and at least one oxide of a multivalent element selected from the group consisting of SnO 2 , V 2 O 5 , CeO 2 , MnO 2 and Fe 2 O 3 , wherein each respective one of said at least one multivalent element oxide comprises at least 0.15% of the glass-ceramic, such that the sum of said multivalent element oxide(s) comprises 0.2-2% of the glass ceramic, and SnO 2 , if included, comprises 0.15-0.7% of the glass-ceramic.
10. A glass-ceramic containing a solid solution of β-quartz or of β-spodumene or solid solutions of β-quartz and β-spodumene, as main crystalline phase(s), the composition of which, expressed as percentages by weight of oxides, essentially consists of:
SiO 2
65-70
Al 2 O 3
18-20.5
Li 2 O
2.5-3.8
MgO
0.55-1.5
ZnO
1.2-2.8
BaO
0-1.4
SrO
0-1.4
with BaO + SrO
0.4-1.4
with MgO + BaO + SrO
1.1-2.3
Na 2 O
0-<1
K 2 O
0-<1
with Na 2 O + K 2 O
0-<1
with (2.8 Li 2 O + 1.2 ZnO)/5.2 MgO
>1.8
TiO 2
1.8-3.5
ZrO 2
0.8-1.6
with
TiO
2
ZrO
2
>2.2
F
0.05-1,
advantageously 0.05-0.3;
and at least one oxide of a multivalent element selected from the group consisting of SnO 2 , V 2 O 5 , CeO 2 , MnO 2 and Fe 2 O 3 , wherein each respective one of said at least one multivalent element oxide comprises at least 0.15% of the glass-ceramic, such that the sum of said multivalent element oxide(s) comprises 0.2-2% of the glass ceramic, and SnO 2 , if included, comprises 0.15-0.7% of the glass-ceramic.