Dilatometry

What is dilatometry used for?

Dilatometry can measure material properties, such as the thermal expansion coefficient and glass transition temperature. The method can also give valuable information about phase changes and chemical reactions within a sample if they are accompanied by a change in density. 

Typical samples for dilatometry include metals, ceramics, polymers, and composites. This wide range of sample variety allows the method to be used in the research and quality control of semiconductors, plastics, and construction materials, among others. 

Presently, the most common application of dilatometry is measuring the coefficient of linear thermal expansion (CTLE, α) of metals and other solid materials (ASTM E228) or plastics (ASTM D696). However, other important information about a material's morphology can also be obtained using dilatometry measurements. These include the densification and sintering behavior of ceramics and temperatures at which phase transitions occur in metal alloys.

Dilatometry has been used in the past to measure the glass transition temperature. Nowadays, glass transitions are usually analyzed using more accurate thermal analysis methods, such as thermomechanical analysis (TMA) and differential scanning calorimetry (DSC), which have become more accessible.

How does dilatometry work?

There are two main types of dilatometry; push-rod dilatometry and optical dilatometry. The measurement technique is different between the two, but they fundamentally operate in the same manner. An external heat source is applied to a sample, and as the temperature increases, the physical changes experienced by the sample (volume, length, density, and phase changes) are recorded.

Push rod dilatometer vs. optical dilatometer

In push-rod dilatometry, the sample is in contact with a rod, which in turn connects to a strain gauge. As the sample is heated, it expands and applies a force to the rod from which the strain is recorded. This method is highly accurate when analyzing hard solids like metals and ceramics, and can measure CTLE values down to 10 nm/m*°C. Softer materials such as plastics can be measured by this method if their CTLE is greater than 1 µm/m*°C.

Optical dilatometry uses a non-contact detection method in which a digital camera captures the microscopic changes in sample dimensions as it is heated. This method is advantageous as it can be used on softer, more ductile materials like polymers, as well as fragile crystals, thin films, and organic matter. It is accurate for materials with a CTLE greater than 1 µm/m*°C. Optical dilatometry can also be applied to the study of molten materials on a given substrate using the Sessile drop technique. These experiments allow for the determination of interfacial properties, such as contact angle or surface tension at extremely high temperatures.

Need thermal analysis services?

Measurlabs offers coefficient of thermal expansion measurements and additional thermal analyses using dilatometry and several additional techniques. Available methods include thermomechanical analysis (TMA), differential scanning calorimetry (DSC), and thermogravimetric analysis, among others. Do not hesitate to contact our experts through the form below to discuss the most suitable testing options for your samples.