Using Differential Scanning Calorimetry to Measure Changes in Enthalpy

1. Baseline Measurement

1. Controller, Measuring unit, Computer system, Thermostat approximately 60 min. before starting the measurement. Purge gases must be connected to the system.
2. Place two empty crucibles (with lid) into the sample carrier. The crucible material may be chosen based on the temperature range to be measured.
3. Move the furnace to measuring position.
4. Adjust the measuring conditions (gas, vacuum).
5. Start the measurement program.
6. Proceed to create a baseline measurement using Sample Mass = 0.
7. Open Temperature Recalibration, Open Sensitivity programs.
8. Set Temperature Program, initial temperature, heating rate.
9. Set the initial conditions and the temperature threshold values. After purging the system with Argon/nitrogen gas a few times, allow the gas to continuously flow through the system, adjusting the flow rate to a steady rate (e.g. 50 mL/min).
10. Start the measurement.
11. The DSC measurements are started at room temperature after an initial stabilization at the starting temperature. The temperature stabilization is important step to avoid any offset due to a difference in the thermal capacities of the sample pan and the reference pan and contents. A steady heating rate of 20 °C /min, under Argon gas atmosphere is generally used. The range of temperature is determined according to the sample and the temperature range of interest.

2. Standard Sample Measurement to Ensure Accuracy of the System

1. Open the measuring unit after the furnace has cooled down.
2. Remove the empty crucible that is designated as the sample pan.
3. Choose the standard depending on the temperature range to be measured.
4. Weigh the standard. A finely polished synthetic sapphire (carborundum, aluminium oxide) disk is used as heat capacity and transformation enthalpy standard. Sapphire is stable over a wide range of temperature, and its heat capacity has been accurately determined over a wide range of temperature.
5. Insert standard sample carefully in the sample crucible using tweezers.
6. Move the furnace to measuring position.
7. Adjust the measuring conditions (gas, vacuum).
8. Proceed as follows to combine the standard measurement with the correction measurement:
9. Use sample mass = x mg (mass of standard sample).
10. Open Temperature Recalibration, Open sensitivity
11. Use the same Temperature program (temperature program remains the same as the baseline temperature program)
12. Start the measurement.
13. Set the initial conditions and the temperature threshold values. After purging the system a few times, allow the purging gas to continuously flow through the system, adjusting the flow rate.
14. Measurement conditions (e.g. heating rate, gases, type of crucible) for the baseline and the subsequent standard measurement must be the same.
15. Using the same sensitivity and temperature calibration files, the start program to measure the standard sample.

3. Sample Measurement

1. Polish the sample surfaces. Place the flattest sample surface facing the bottom of the pan. Use an optimal sample size that fits the pan, without touching the lid. The sample is finely polished to obtain good thermal contact with the sample pan, so the temperature can be accurately determined and the data is less noisy.
2. Measure the sample mass accurately.
3. Open the measuring unit after the furnace has cooled down.
4. Remove the standard sample from the crucible.
5. Clean the crucible using alcohol. Insert the sample to be measured in the crucible replacing the standard.
6. Follow step 3 to measure the sample. The measurement conditions (e.g. heating rate, gases, type of crucible) for the baseline measurement and the subsequent standard and sample measurement must be the same.
7. Follow step 3 to complete the measurement.