Method for realizing low temperature in laboratory
In the experiment, we not only use the high temperature environment frequently, but also must use the low temperature environment in some highly active materials. Therefore, it is very important to make a low temperature environment.
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1. Using a frozen mixture of ice during the dissolution process (ice salt refrigerant) to produce low temperatures
(1) Crushed ice: 0 to -5 °C.
(2) 3 parts of ice +1 part salt: -15 to -18 °C.
(3) 3 parts ice + 3 parts of crystalline calcium chloride (CaCl2•6H2O): -40 °C.
(4) 4 parts of ice + 5 parts of crystalline calcium chloride: -40 ° C ~ -50 ° C. (5) 2 parts ice +1 part concentrated HNO3: -56 °C.
Regardless of which of the above frozen mixtures is used, it is a prerequisite that the ice and the salt are well comminuted and uniformly mixed. When using two frozen mixtures, they must be cooled in the refrigerator to reach the above temperature.
2. Use the sublimation process to produce low temperatures:
(1) solid carbon dioxide (dry ice): -78.9 ° C;
(2) solid carbon dioxide + ethanol: -72 ° C;
(3) Solid carbon dioxide + diethyl ether, chloroform or acetone: -77 ° C.
Since solid carbon dioxide has poor thermal conductivity, it should be mixed in a suitable liquid such as acetone or alcohol. Trichloroethylene is particularly suitable because the solid carbon dioxide floats on the surface of the trichloroethylene so that the mixture does not foam and overflow.
3 Use the evaporation process to produce low temperatures:
In practical applications, liquid nitrogen has certain advantages. It is a colorless, odorless, tasteless liquid, slightly soluble in water, poorly conductive to heat and electricity, slightly lighter than water, and does not produce toxic or irritating gases. At the same time, it does not burn or self-explode, and combines with sodium, calcium or magnesium to form nitride (Nitrides), and the cold point of zui is -196 °C. Therefore, the use of liquid nitrogen has many advantages: (1) a lower boiling point at atmospheric pressure (-196 ° C), and any temperature between minus 37 and 196 ° C can be obtained with an appropriate adjustment control system. (2) The production cost is low and the source is easy. (3) Safe and reliable.
