Aluminosilicate Glass

A small, but important type of glass, aluminosilicate, contains 20% aluminium oxide (alumina-Al2O3) often including calcium oxide, magnesium oxide and boric oxide in relatively small amounts, but with only very small amounts of soda or potash. It is able to withstand high temperatures and thermal shock and is typically used in combustion tubes, gauge glasses for high-pressure steam boilers, and in halogen-tungsten lamps capable of operating at temperature as high as 750 degrees celsius.

Aluminosilicate glass has in its composition alumina (Al2O3), and boron oxide (B2O3). It has properties similar to borosilicate glass, but has better chemical resistance and a higher operating temperature of up to 600 degrees celsius. Compared to the borosilicate glass aluminosilicate glass is more difficult to manufacture.

Aluminosilicate Glass

Aluminosilicate glass products have a high resistance to thermal shock, do not contain alkaline compounds. Their thermal expansion characteristics are similar to characteristics of the products of molybdenum which allows the use of glass in conjunction with materials such molybdenum wires, for example in the manufacture of halogen lamps and other electronic applications.

Composition

SiO2

60%

Al2O3

16%

CaO

7%

MgO

6%

BaO

6%

B2O3

4%
others
(SrO, Na2O)
1%

Possible content of heavy metals (ie. lead, cadmium, mercury, chromium) = 100 ppm.

Properties:

Density  (@ 18 degrees celsius ) 2 630 kg/m3

Modulus of elasticity (Young’s) 81 GPa

Poisson’s ratio 0,24

Thermal conductivity 1,1 W/(m K)

Coefficient of linear expansion 4,6 * 10 -6  degrees celsius

Index of refraction (@ 380 – 780 nm) 1.5

UV transmittance (@ 330 nm)  less than or equal to 58%

Softening point 910  degrees celsius

Annealing point 688  degrees celsius

Max. working temperature: 660  degrees celsius

Thermal shock  300  degrees celsius

Electrical properties:

Volume resistance:                     1012

Dielectric constant (@ 1 Mhz):  6,1

Chemical properties:

Hydrolytic resistance (ISO 719): class 1

Acid resistance (DIN 12116):      class 2

Alkali resistance (DIN 695):        class 3

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