Thermomechanical Analysis (TMA) is a technique used to determine the dimensional changes of a sample with respect to temperature, such as the softening temperature, glass transition temperature, and coefficient of linear thermal expansion (CTE). The most common application of TMA is to determine the CTE. CTE is defined as the degree of expansion divided by the change in temperature:
Where ΔL is the change in length, L0 is the initial length, and ΔT is the change in temperature.
Understanding the CTE of a material is essential for proper usage in different environmental conditions. Failure to account for CTE in certain applications can introduce detrimental stress and ultimately lead to failure. A precise understanding of thermal expansion behaviour provides crucial insight into firing processes, the influence of additives, reaction kinetics, and other important aspects of how a material responds to environmental changes.
TAL offers Thermomechanical analysis testing using Rigaku TMA 8311- the first TMA to offer differential methods. This extremely precise system offers a temperature range of -70°C to 1500°C, and multiple attachments are available to conform to specific testing needs. TAL currently offers single rod & differential compression loading (expansion, shrinkage, glass transition) and differential penetration (softening).
Application 1: Comparing Raw vs Fired Ceramic Samples
Comparison of a ceramic’s thermal expansion before and after firing gives insight into its behaviour across a range of temperatures. This data is valuable in refining the firing process, and understanding how materials perform in high temperature applications.
Below: The unfired raw ceramic (white) undergoes a variety of complex irreversible changes (x) such as diffusion, water expulsion, chemical reaction and sintering, as well as reversible overall thermal expansion. In contrast, the fired ceramic (blue) exhibits only thermal expansion and a phase transition (O) at 552°C, demonstrating the overall effects of firing and the resulting fired ceramic’s thermal expansion behavior.
Application 2: Understanding Ceramic Glazes
Glazing is a critical process in the final production of ceramics, from capacitors to cookware. To ensure a properly glazed ceramic, the Coefficient of Thermal Expansion (CTE) must be considered for both the glaze and the base ceramic. Ideally, the glazing exhibits a slightly lower CTE than the ceramic to facilitate a tight lamination. A larger glaze CTE can result in cracking and a weaker finished product, due to a CTE mismatch between the glaze and substrate.
Below: a ceramic glaze (white) was heated through its glass transition point (Tg) at 785°C and to its softening point (894°C). The resulting CTE (blue) is calculated and displayed on the right y-axis.
|Temperature Range||-70°C – 1500°C|
|Maximum Heating Rate||100°C/min (20°C/min for low temperature furnace)|
|Length Change Resolution||0.3nm|
Differential and Non-Differential Compression Loading
L = 10-20mm, D = 5mm (up to 9mm)
L ≤ 4mm, D ≤ 5mm
I was well pleased with the experience. The instructions for the sample configuration was clear. The people responded promptly to questions. The lab double checked results to address any questions. The report was clear, easily understood.
Vice President of Technology