Most materials expand when they are heated. This expansion is a complicated process that depends on temperature. For example, when ice is heated to the melting point, the volume actually decreases during the phase transition. Even after the ice is melted, water continues to contract until it reaches a minimum volume at about 4°C. Additional heat causes water to expand, but not at a constant rate.

More practical applications of the measurement of this expansion involve various solid-material samples, typically plastics or metal alloys. Instruments for measuring this expansion are known as dilatometers, and different systems can perform the measurements under differing conditions of temperature and atmosphere.

The physical measurement can be carried out in a variety of ways. The sample is insulated in a measurement chamber that can be refrigerated or heated by a furnace. In some dilatometers, the sample’s expansion is measured by a sensor that is in physical contact with the sample. The sensor may be a displacement transducer or capacitance-based sensor that converts the deformation in the sample into an electrical signal. Other methods are non-contact and involve direct imaging of the sample to measure its size or utilizing a laser interferometer.

Most dilatometers are sensitive enough to resolve changes of length on the order of 10 nm. Dilatometry can be carried out in an environment of normal air, but more frequently (and especially for high-temperature measurements), the analysis is carried out in a vacuum or inert gas to avoid any chemical reactions that might occur between the sample and oxygen.

Dilatometry can be directly used to measure the expansion coefficients of various materials, but more interesting applications involve monitoring various processes in polymers, such as phase changes and polymerization reactions, which have effects on the volume of the material. Other sample types include metals, alloys, refractory compounds, glasses, ceramics and other materials, particularly those that are intended for industrial uses at very high or very low temperatures.

Dilatometry is a thermal analysis method. Many vendors of thermal analyzers offer dilatometry, though most of the market leaders provide a more functional technology known as thermomechanical analysis (TMA). TMA provides similar measurements to dilatometry but adds the option of a variable external force or load during the analysis. While TA Instruments (Waters) has long offered TMA instrumentation, it did not compete in the dilatometry market until very recently. The acquisitions of Anter (see IBO 7/31/11) and BÄHR Thermoanalyse (see IBO 2/29/12) added dilatometry to TA Instruments’ portfolio, making Waters a significant competitor in the market. Other suppliers include Linseis, Misura, NETZSCH, Orton Ceramic, Theta Industries, Ulvac-Riko and Xiangtan Huafeng Instrument. The global market demand for dilatometry (excluding TMA) was roughly $10 million in 2011.

Dilatometry at a Glance:

Leading Suppliers

• NETZSCH

• Ulvac-Riko

• TA Instruments (Waters)

Largest Markets

• Polymers/Plastics

• Metals

• Construction Materials

Instrument Cost

• $10,000–$50,000