Measuring Glass CTE, Glass Transition, and Softening Point with a Horizontal Push-Rod Dilatometer

Thermal expansion coefficient (CTE), glass transition temperature, and softening point are key parameters that define the performance of glass materials. A push-rod dilatometer provides a straightforward, rapid method to characterize these properties by tracking dimensional change as a function of temperature or time under near-zero load. The DIL 0809 PC horizontal push-rod dilatometer is designed for ease of operation, broad application coverage, and high measurement repeatability. Its optimized differential sensor design delivers excellent reproducibility even without external isothermal enclosures. The horizontal furnace layout simplifies handling: the tube-style sample carrier allows easy placement, including for non-ideal specimen shapes. A thermocouple positioned close to the specimen ensures consistent temperature measurement. In addition to linear expansion, the instrument’s c-DTA capability captures endothermic and exothermic events during the same run. Test principle: Under a programmed temperature profile and a load approaching zero, the instrument measures specimen length change versus temperature or time. From these data, average CTE values over specified temperature intervals, as well as characteristic temperatures such as Tg (glass transition) and softening point, can be determined. Specimen preparation: Prepare the test sample to either a cylinder of diameter Φ(6–8) × 50 mm or a rectangular prism of (6–8) × (6–8) × 50 mm. Because fabrication may lead to slight deviations from 50 mm, record the actual specimen length for use in calculations. Setup and loading: Switch on the instrument and open the furnace to expose the sample carrier. Place the specimen in the designated cradle so it is parallel to the carrier and in good contact with the push rod face. Close the furnace so the specimen sits at the center of the heated zone. Displacement baseline check: Observe the displacement display. If the reading is not around 2000 (instrument units), adjust using the displacement knob if available; if the reading is acceptable, proceed. Note that some instrument versions do not include this adjustment. Stabilization: Press the Work/Start button to initialize. Allow the system to idle for 5–10 minutes until the displacement reading is fully stable. Temperature program: In the test software, define the control temperature profile under the Temperature Curve settings. Enter the specimen length and the target end temperature. Start the run from the Test Control interface. The system will heat according to the program and automatically record and process data. Data processing: The software computes average linear expansion coefficients at each temperature interval and can identify transitions such as Tg and softening behavior. Example datasets have been generated on commercial glass specimens (e.g., E-glass) to produce analysis reports demonstrating these outputs.

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