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TECHNICAL DATA: Part 2

Technical Data: | Care & Maintenance | Joining & Separating Glass Apparatus | Cleaning

 
Technical Data
 

CHEMICAL COMPOSITION

Borosilicate Glass is a low alkali Type 3.3 glass. Its typical chemical composition is given below. It is virtually free of magnesia-lime-zinc group and contains only traces of heavy metals.

  Approx % by weight
SiO2 81
B2O3 13
Na2O / K2O 4
Al2O3 2

THERMAL PROPERTIES
As the co-efficient of thermal expansion of borosilicate glass is low, the thermal stresses under a given temperature gradient are consequently low and the glass can withstand higher temperature gradients and also sudden temperature changes/thermal shocks. Minute scratching of glass surface can however reduce its thermal resistance.

In general, the “Strain point” should be regarded as the maximum safe operating temperature of borosilicate glassware. When heated above 500º C the glass may acquire permanent stresses on cooling.

All borosilicate labware is annealed in modern Lehr ovens under strictly controlled conditions to ensure minimal residual stress in the products.

The typical thermal properties of borosilicate glassware are given below:

Co-efficient of Linear Expansion 32.5 x 10-7/º C
Strain Point 515º C
Annealing Point 565º C
Softening Point 820º C
Specific Heat 0.2
Thermal Conductivity (Cal/cm3º C/sec) 0.0027

CHEMICAL DURABILITY
Borosilicate Glassware is highly resistant to water, neutral and acid solutions, concentrated acids and their mixtures as well as to chlorine, bromine, iodine and organic matters. Even during extended period of reaction and at temperatures above 100º C, its chemical resistance exceeds that of most metals and other materials. It can withstand repeated dry and wet sterilization without surface deterioration and subsequent contamination. Resistance to attack of various chemicals is shown below. Only hydrofluoric acid, very hot phosphoric acid and alkaline solutions increasingly attack the glass surface with rising concentration and temperature.
 
Contact with Chemicals Duration in hrs. Loss in Wt. mg/m2
Water distilled At 100º C 6 10
Water Vapour Steam at 121º C 1 75
Acid HCL 6 100
80% H2SO4 at 130º CO 12 2
Alkali- 1N Solution of Na2CO3 boiling 6 4000
Infusion Fluids Isotonic NaCl (0.85%) 121º C 21/2 70
Glucose (5%) 121º C 21/2 50
 

FABRICATING WITH BOROSILICATE GLASS
Due to low expansion of glass and easy workability, this glass can be shaped, formed, joined into complicated apparatus. It can be done even by an analyst in his own laboratory and keep on changing till he gets what he needs. In case where annealing in a controlled oven is difficult he can do so by flame annealing which is also a great advantage.

OPTICAL PROPERTIES
Laboratory glassware made from borosilicate glass show no noticeable absorption in the visible region of the spectrum. It appears consequently clear and colourless.

 
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