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Volatility (also volatility or evaporation number ) is a dimensionless relative number that describes the evaporation of a solvent .

Evaporation rate

By definition , volatility is given as the ratio of the vapor pressure of the substance in question to the vapor pressure of the highly volatile reference substance diethyl ether (this at 20  ° C and 65 ± 5% relative humidity ):

In Germany, the evaporation rate (VD) is determined according to DIN 53170. The time it takes for a substance to completely evaporate (evaporation time = VDZ) is related to the time it takes diethyl ether to evaporate.

A high evaporation rate means relatively slow evaporation, i.e. low volatility. A small evaporation number means faster evaporation, i.e. a relatively high volatility.

Examples of the evaporation rates of solvents (for diethyl ether = 1)
solvent Evaporation rate
Butyl diglycol > 1200
2-butoxyethyl acetate 250
Butyl glycol 163
N -methyl pyrrolidone 095
water 080
Test petrol 145-200 (K30) 035
Xylene 017th
1-butanol 033
1-methoxy-2-propanol 028
Butyl acetate (acetic acid n- butyl ester) 011
Ethanol 008.3
Methyl isobutyl ketone 007th
acetone 002
Hexane 001.4

Evaporation rate

In the USA, the evaporation rate (E) is determined over time and in relation to butyl acetate .

with = time, up to 90% of the sample has evaporated.

Examples of the evaporation rates of solvents (for butyl acetate = 1)
solvent Evaporation rate
Methyl ethyl ketone 3.8
acetone 5.6
Hexane 8.3
Ethanol, 95% 3.8
naphtha 1.4
Xylene 0.6
2-methyl-1-propanol 0.6
water 0.3
White spirit 0.1

Classification of solvents according to volatility

Comparison of different classifications
In Germany In the USA
Classification Evaporation rate Classification evaporation rate
very difficult to volatilize > 50 slow evaporation <0.8
not very volatile 35… 50 medium evaporation 0.8 ... 3.0
medium volatile 10 ... 35 rapid evaporation > 3.0
volatile <10

See also

Individual evidence

  1. a b Brock, Groteklaes, Mischke: Textbook of paint technology . Vincentz, Hannover 2000, ISBN 3-87870-569-7 , p. 100 ( limited preview in Google Book search).
  2. a b MSDS Glossary: ​​Evaporation Rate. Retrieved October 3, 2013 .