Material: Difference between Borosilicate and Leadsilicate

 

Borosilicate and lead silicate are both glasses with distinct properties and applications. Borosilicate glass contains silica and boron trioxide as the main glass-forming constituents, while lead silicate glass is a variety of glass in which lead replaces the calcium content of a typical potash glass14. The addition of lead oxide to glass raises its refractive index and lowers its working temperature and viscosity4.

Here's a comparison of the two materials:

Composition:

Borosilicate: Primarily composed of silica and boron trioxide1. Typical composition includes approximately 80% silica, 13% boric oxide, 4% sodium oxide or potassium oxide, and 2–3% aluminum oxide1.

Lead Silicate: Contains lead(II) oxide (PbO), typically 18–40% by mass, replacing the calcium content of potash glass4. Modern lead crystal contains a minimum of 24% PbO4.

Thermal Properties:

Borosilicate: Known for its very low coefficient of thermal expansion (≈3 × 10^-6^ K^-1^ at 20 °C), making it resistant to thermal shock1. Can withstand temperature differentials of about 165 °C (300 °F) without fracturing12.

Lead Silicate: The thermal expansion coefficient increases with the content of lead oxide in the material3.

Density:

Borosilicate: Less dense (about 2.23 g/cm^3^) than typical soda-lime glass due to the low atomic mass of boron1.

Lead Silicate: Higher density compared to soda glass. Typical lead crystal has a density of around 3.1 g/cm^3, and high-lead glass can be over 4.0 g/cm^3 or even up to 5.9 g/cm^34.

Optical Properties:

Borosilicate: Crown glass with low dispersion (Abbe numbers around 65) and relatively low refractive indices (1.51–1.54 across the visible range)1.

Lead Silicate: Higher refractive index compared to ordinary glass, ranging up to 1.7 or 1.84. This heightened refractive index also correlates with increased dispersion, which measures the degree to which a medium separates light into its component wavelengths, thus producing a spectrum4.

Chemical Resistance:

Borosilicate: Exhibits extremely high chemical resistance in corrosive environments1. Resistant to scratches, abrasion, and chemical reactions2.

Lead Silicate: Used as a glaze for ceramics5.

Applications:

Borosilicate: Used for reagent bottles and flasks, lighting, electronics, cookware, glass tubing, glass piping, and glass containers, especially for the chemical industry1. Also used in various optical instruments due to its excellent optical transparency2.

Lead Silicate: Used in decorative hollowware, radiation shielding, glass solders, sealants, and colored enamels and glazes45. Also used in fireproofing fabrics5.

Safety Considerations:

Borosilicate: Generally considered safe for use in contact with food and beverages.

Lead Silicate: Lead is a toxic substance, and lead crystal glassware was formerly used to store and serve drinks, but due to the health risks of lead, this has become rare45. Contact may cause irritation or ulcers, and lead silicate is a carcinogen, teratogen, and suspected mutagen5.

Manufacturing:

Borosilicate: Created by combining and melting boric oxide, silica sand, soda ash, and alumina1.

Lead Silicate: A white, crystalline powder that is made by the reaction of lead acetate and sodium silicate5. The addition of lead oxide to potash glass also reduces its viscosity, rendering it more fluid than ordinary soda glass above softening temperature (about 600 °C or 1,112 °F), with a working point of 800 °C (1,470 °F)4.