Common reasons for inaccurate calorimeters

The inaccurate measurement of the calorimeter is mostly due to the aging of the instrument components, fluctuations in ambient temperature and humidity, insufficient purity of the benzoic acid calibrator, or the decline in the sealing of the oxygen bomb, poor electrode contact, etc. These factors will directly interfere with the heat transfer and signal acquisition, resulting in the deviation of the measurement results. Accurate calibration is the core means to solve this problem.

Key Preparation Before Calibration of Calorimeter

1. Environmental specifications: It is necessary to operate in a laboratory with stable temperature (15-30 ° C) and humidity ≤ 75% to avoid direct sunlight and strong airflow interference, and reduce the additional heat loss of the environment.

2. Instrument inspection: First confirm that the oxygen bomb is free of leakage, the electrode connection is stable, and the agitator operates smoothly to ensure that the core components of the instrument are in normal working condition.

3. Calibrator control: Select benzoic acid with a purity of ≥ 99.99% and dry it in a dryer to a constant weight in advance to ensure the accurate quality of the calibrator and lay the foundation for subsequent calibration.

The specific calibration steps of the calorimeter

1. Weighing operation: Use an analytical balance with an accuracy of 0.0001g to accurately weigh 0.9-1 of dried benzoic acid, press it into thin sheets and put it into an oxygen bomb crucible to avoid sample scattering affecting the combustion effect.

2. Sampling and oxygenation: assemble and seal the oxygen bomb, fill it with 3.0-3 MPa of oxygen and let it stand for 15 seconds to ensure sufficient oxygen, ensure that the sample is fully burned, and check the air tightness of the oxygen bomb.

3. Instrument settings: Turn on the calorimeter, set the calibration mode, enter the quality of benzoic acid, and start the calibration procedure after the temperature of the instrument is stable. Keep the instrument stable during the process to avoid vibration interference.

4. Repeated calibration: Carry out 3-5 consecutive calibrations to eliminate data with large deviations, and take the average value as the final calibration result to improve the accuracy and reliability of the calibration.

Verification and adjustment after calibration

After the calibration is completed, use the reference material with known calorific value for verification. If the deviation between the measured value and the standard value is less than or equal to 0.2%, the calibration is qualified; if the deviation is large, check the sealing of the oxygen bomb, re-dry the calibration object, and repeat the calibration process again until the accuracy requirements are met to ensure the accuracy and reliability of the subsequent detection data of the calorimeter.

Routine maintenance avoids repeated calibration

It is necessary to regularly clean the inner wall of the oxygen bomb and replace the sealing ring to avoid the residue affecting the combustion; check the electrode contact after each use, keep the instrument dry during storage, reduce the loss of the environment to the instrument, reduce the probability of inaccuracy of the calorimeter from the source, reduce the calibration frequency, and ensure the detection efficiency.