Schott® borosilicate glass 8250 is widely used as a Kovar Sealing glass. In addition to machine drawn sizes available from Schott®, Glass Dynamics LLC has the ability to produce "redrawn" sizes from .010 to .50" diameters in small lots of 10 to 15 pounds. Our current OVER STOCK BARGIN sizes can be viewed below. You can also view Corning® 7052 Kovar Sealing glass, Corning® 7056 Kovar Sealing glass and Corning® 7720 Nonex Tungsten Sealing glass.
| Kovar Sealing Glass: Schott® 8250 | |||||||||
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| Glass Code: Schott® | 8250 | ||||||||
| Glass Type/Application | Borosilicate glass for sealing KOVAR metal and molybdenum, electrically highly insulating |
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| Physical Data | |||||||||
| Coefficient of mean linear thermal expansion α (20 °C; 300 °C) acc. to ISO 7991 |
5,0 |
10-6K-1 |
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| Transformation Temperature Tg | 490 |
°C |
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| Glass Temperature at Viscosity η in dPa · s | 1013 (Annealing Point) | 500 |
°C |
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| 107.6 (Softening Point) | 720 |
°C |
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| 104 (Working Point) | 1055 |
°C |
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| Stress-Optical Coefficient K | 3,6 |
10-6mm2· N-1 |
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| Density ρ at 25°C | 2,28 |
g · cm-3 |
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| Modulus of Elasticity E (Young's Modulus) | 64 |
103N · mm-2 |
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| Poisson's Ratio µ | 0,21 |
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| Thermal Conductivity λw at 90 °C | 1,2 |
W · m-1 · K-1 |
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| Log of the electric volume resistivity (Ω · cm) @ | 250 °C | 10 |
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| 350 °C | 8,3 |
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| tk100 | 375 |
°C |
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| Dielectric Constant ε for 1 MHz at 25 °C | 4,9 |
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| Dielectric Loss Factor tan δ for 1 MHz at 25 °C | 22 |
10-4 |
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| Refractive index nd (λ =587.6nm) | 1,487 |
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| Chemical Resistance | |||||||||
| Hydrolytic Resistance (ISO 719) | Class |
HGB 3 |
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| Acid Resistance (DIN 12116) | Class |
S 4 |
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| Alkali Resistance (ISO 695) | Class |
A 3 |
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| Chemical Compostion: Components in Approx. Weight % | ||||||
|---|---|---|---|---|---|---|
SiO2 |
B2O3 |
AI2O3 |
Na2O |
K2O |
Li2O |
ZnO |
69 |
18,5 |
3 |
1 |
7,5 |
0,5 |
0,5 |
The heavy metal content for the elements lead, cadmium, mercury and hexavalent chromium is below 100 ppm. |
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| Redrawn: Over Stock Bargin Sizes | ||
|---|---|---|
Corning® 9741 |
GE 010 Lead |
Schott® 8337B |
OD 1.145" x ID 1.075" |
OD 5.75mm x ID 4.5mm |
OD 12.30mm x Wall .50mm |
OD 2.55mm x ID 1.22mm |
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OD 2.80mm x ID 2.25mm |
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