Lead glass is a glass variant which has had its calcium component replaced by lead. It contains between 18 to 40% of lead (II) oxide by weight. The nomenclature of lead glass is regulated such that any glass that contains a minimum of 24% PbO by weight is referred to as “lead crystal”, and any glass that contains less than 24% PbO by weight is referred to as crystal glass . Lead glass has a chemical composition of SiO2 and PbO along with other impurities or additives added to achieve certain properties.
Lead glass is also known as X-ray glass or radiation shielding glass as one of its major applications is in the absorbance of high energy radiation while maintaining optical transparency. The presence and quantity of PbO are what determines some of lead glass’ most important optical and physical properties
In this article, you will learn about:
Figure 1. Lead glass is used in microscope lenses due to its high refractive index.
Lead glass, when compared to ordinary glass (also referred to as soda-glass or soda-lime silica-glass), is a dense and heavy material as lead is more than five times as heavy as calcium. Soda glass has a density of 2.4 g/cm3 and lead glass has a density of 3.1 - 5.9 g/cm3. Lead glass also has higher electrical resistance, higher refractive index (up to 1.8 compared to 1.5 for lead-free glass), lower working temperature and lower viscosity .
Lead glass is thus more fluid and easier to work with and fabricate than soda glass because it can be worked on at a wider temperature range while still being more malleable and less brittle than ordinary glass. Table 1 below shows a comparison of different lead glass materials in optical, mechanical, thermal, and electrical properties.
Table 1. Properties of selected types of commercial lead glasses
|SCHOTT 8095||SCHOTT 8531||SCHOTT 8532||SCHOTT 8650||SCHOTT 8651|
|Stress optical coefficient||3.1*10-6 mm²/N||2.2*10-6 mm²/N||1.7*10-6 mm²/N||2.8*10-6 mm²/N||3.6*10-6 mm²/N|
|Elastic modulus||60 GPa at 20 °C||52 GPa at 20 °C||56 GPa at 20 °C||62 GPa at 20 °C||59 GPa at 20 °C|
|Poisson's ratio||0.22 at 20 °C||0.24 at 20 °C||0.24 at 20 °C||0.23 at 20 °C||0.24 at 20 °C|
|Loss tangent||1.1*10-3 at 20 °C||9*10-4 at 20 °C||9*10-4 at 20 °C||3.3*10-3 at 20 °C||3.1*10-3 at 20 °C|
|Dielectric constant||6.6 at 20 °C||9.5 at 20 °C||10.2 at 20 °C||7.6 at 20 °C||6 at 20 °C|
|Electrical resistivity||3.98*107 Ω·m at 250 °C||1.00*109 Ω·m at 250 °C||1.00*109 Ω·m at 250 °C||-||1.58*109 Ω·m at 250 °C|
|Coefficient of thermal expansion||9.1*10-6 1/K at 20 °C||9.1*10-6 1/K at 20 °C||8.7*10-6 1/K at 20 °C||5.1*10-6 1/K at 20 °C||4.4*10-6 1/K at 20 °C|
|Specific electrical resistance temperature||330 °C||450 °C||440 °C||-||-|
|Annealing temperature||435 °C||430 °C||430 °C||475 °C||540 °C|
|Working temperature||982 °C||820 °C||760 °C||885 °C||1034 °C|
|Glass transition temperature||430 °C||435 °C||435 °C||475 °C||549 °C|
|Softening temperature||630 °C||585 °C||560 °C||625 °C||736 °C|
|Thermal conductivity||0.9 W/(m·K) at 90 °C||0.7 W/(m·K) at 90 °C||0.7 W/(m·K) at 90 °C||0.5 W/(m·K) at 90 °C||0.9 W/(m·K) at 90 °C|
|Corrosion properties||Hydrolytic resistance Class HGB3 (ISO 719), Acid resistance Class S2 (DIN 12116), Alkali resistance Class A3 (ISO695)|
|Application areas||General electro-technical application and electro-technology (Signal intensifier, Detector and (fibre-) optics), Endoscopy.||Encapsulation of semiconductor components at low temperature (Micro-diodes), Electronics, Sensors||Encapsulation of semiconductor components at low temperature (Micro-diodes), Electronics, Sensors.||Implosion diodes, Electronics and Sensors||For power and pin diodes as well as micro-diodes, Signal intensifier, detector (other Electro-technology / Electronics), Sensors|
The production of lead glass generally proceeds as follows :
The properties of lead glass make it useful for many applications. The majority of them, however, make use of its optical properties, in particular. Here are a few examples :
Figure 2. Lead glass is used as viewing windows in X-ray rooms as they can achieve high radiation attenuation while maintaining visibility.
 Davison, S. and Newton, R.G., 2008. Conservation and restoration of glass. Routledge.
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