Physical properties of glass

Glass is a valued base material for many products, ranging from optical fibres to light bulbs. The reason for this universal usage can be found in its outstanding physical-chemical properties. Philips Materials Analysis supports glass development, production and recycling with a wide variety of analytical tools and a substantial expertise in glass.

Viscosity

is one of the most important parameters for glass processing. Therefore, it is important to know the viscosity-temperature relation and its characteristic viscosity points (e.g. strain point, working point, melting point).

Thermal expansion behaviour and stress

Often glass parts have to be joined with other glasses or even completely different materials to form the final product. It is of great importance that the thermal expansion behaviour of the materials involved are well matched. Thermal expansion coefficients can be accurately measured using a double quartz dilatometer. This set-up measures the elongation of a sample as a function of temperature. In addition, stress in glass can be measured using the so-called strain slab method; the sample and a standard glass are sealed. A difference in thermal expansion between the two glasses will yield stress in the seal region. The stress can be quantified by measuring an optical birefringe effect with a polarisation microscope.

Electrical resistance

In some applications the specific electrical resistance of the glass below the transformation temperature is important. In high voltage applications, for example, a high electric resistivity is required to realize low leakage currents. The relation between the specific resistance (r) and the temperature (T, °C) can be described with the Rasch-Hinrichsen equation:

Log(r) = A + B/(T + 273.15) where A and B are the fitting constants.