Direct drying method is an operation method that the products prepared by liquid phase method are directly (or simply washed and filtered) dried or calcined at high temperature to obtain nano-material products. There are many direct drying methods for nanomaterials, as shown in Table 1. Although the direct drying method is simple to operate. The production cost is low and the equipment investment is low, but it is generally difficult to obtain high-quality nano-material products. Because the critical temperature of water is as high as 375℃. And the critical pressure is as high as 22MPa, hydrogel is easy to dissolve in supercritical state, and hydrogel is generally not suitable for direct supercritical drying.

vacuum drying method

1. principle: dry at low temperature and under reduced pressure to remove water, and the reduced amount in the sample is the water content of the sample.

This method is suitable for foods that are easy to deteriorate and contain bound water that is difficult to remove when heated above 100℃. The determination result is close to the real moisture.

2, the operation method

Accurately weigh 2.00 ~ 5.00 g of sample → dry in a weighing pan with constant weight → vacuum furnace with vacuum degree of 93.3 ~ 98.6 kPa (700 ~ 740 mmHg) → dry for 5 hours → cool in the drying pan → weigh to constant weight.

Calculation: Moisture = g/weight

G —— weight loss of the sample after drying (g)

W —— sample weight (g)

Vacuum drying method is generally used to measure the moisture in samples that are easily deteriorated, destroyed or difficult to remove bound water above 100℃, such as syrup, monosodium glutamate, sugar, candy, honey, jam, dehydrated vegetables and so on.