2.4 Glass
Properties of glass:
- High light transmission
- Resistant to a wide range of chemicals
- Very low thermal expansion
- Maximum temperature of use: 400 – 750°C
- Sensitive to mechanical loads/stresses
Special feature of glass:
- On contact with aqueous liquids, commonly used window glass forms a gel layer which is no longer firmly attached to the underlying glass, although this is not perceptible to the human eye and touch.
- For effective bonded joints, the gel layer must be either stabilised or removed by suitable surface treatment.
Special note for glass: The gel layer is not firmly attached to the base material, namely it must either be stabilised or removed by suitable surface treatment.
Surface treatment of glass:
- Degreasing with solvents
- Cleaning with aqueous cleaning agents or distilled water
- Warm drying after cleaning or degreasing to prevent formation of a layer of condensation and hence new formation of a gel layer
- Risk of microcrack formation on mechanical pretreatment
- Stabilisation of the gel layer by using primers
