T/SSESB 3-2022 Sample preparation technique specification for freeze-drying of soil and sediment

Scope

Main Technical Content: 7. Sample Preparation 7.1 Pre-freezing the samples: Place the samples to be dried evenly on the sample tray (6.4) without over-compacting them. The sample thickness should not exceed 2 cm. For freeze-dryers with pre-freezing function, place the sample tray containing the samples in the pre-freezing chamber of the freeze-dryer. Insert the temperature probe into the samples so that they can completely surround the probe, avoiding the probe being exposed or contacting the bottom of the tray. Close the chamber door, set the pre-freezing temperature to no higher than -18°C, and pre-freeze the samples for at least 3 hours. Start the freeze-dryer's pre-freezing program to fully freeze the samples. For freeze-dryers without pre-freezing function, transfer the sample tray containing the samples to the pre-freezing refrigerator (6.3), and pre-freeze the samples at a temperature no higher than -18°C for at least 3 hours to ensure they are fully frozen. 7.2 Sublimation drying with heat supplementation in freeze-dryers (6.1): - Reference operating conditions: Set the sample heating temperature to 30°C–40°C. After the pre-frozen samples (7.1) reach a fully frozen state, turn on the condenser for cooling. When the condenser temperature drops below -40°C, start the vacuum pump and the system begins to evacuate. When the drying chamber pressure drops below 60 Pa, start the heating program and the samples begin sublimation drying. - Non-heating freeze-dryers (6.2): Turn on the condenser for cooling. When the condenser temperature drops below -40°C, start the vacuum pump and the system begins to evacuate. The samples then begin sublimation drying. - For freeze-dryers without pre-freezing function, quickly transfer the sample tray (6.4) containing the fully frozen samples to the freeze-dryer's drying chamber, install the temperature probe, and then follow the above-mentioned procedures (7.2). Note: During sublimation, the drying chamber pressure is

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