How to use a freeze-drying machine correctly

Below, we will briefly explain the usage of the glass cover freeze-drying machine

1. Before using a freeze-drying machine, place the sample in a low-temperature refrigerator or liquid nitrogen to pre freeze it into ice. This step must completely freeze the sample into ice, because freeze-drying is sublimation drying, where the moisture contained in the sample is directly sublimated from the solid state to the gaseous state, without any liquefaction process. If the sample is not pre frozen thoroughly, sublimation cannot be completed, and drying will fail.

2. Before placing the sample in the freeze-drying machine, the refrigeration function of the freeze-drying machine should be turned on in advance, usually about 30 minutes in advance. The purpose of doing so is to ensure that the cold trap of the freeze-drying machine is lowered to the lowest temperature for capturing moisture in advance, so that sublimated moisture is not pumped into the vacuum pump.

3. The thickness of the sample preparation stage should not be too thick. If it is a liquid sample, it is recommended that the thickness should not exceed 1 centimeter. If it is a block sample, it is best to cut it thin. The principle to follow is that the thinner the sample, the better the drying effect. If the sample is stacked too thick, it will cause the surface layer of the sample to have already dried, while the deep layer of the sample will delay drying.

4. Drying time: Generally, a drying cycle takes about 24 hours, but this time is not fixed, and the length of drying time also depends on factors such as sample thickness and environmental temperature. The thinner the glass under the same conditions, the faster it dries. Under the same conditions, the higher the ambient temperature, the faster it dries. Sublimation absorbs heat, and the glass cover solves the absolute vacuum state after vacuuming. The thermal conductivity inside is poor, and a slightly higher ambient temperature can supplement the heat required for sublimation.

5. After the drying is completed, first open the intake valve of the freeze-drying machine, slowly enter the gas, and then turn off the vacuum pump. Then, turn off the refrigeration machine, and after the internal pressure returns to normal, open the glass cover to take out the sample. It should be noted that the vacuum pump must be turned off after entering the gas. If the vacuum pump is turned off first, due to the internal vacuum state, the pump oil in the vacuum pump may be sucked back into the freeze-drying machine due to air pressure issues.