Evaporation Rate 05
Evaporation Rate 05 : MSDS sheets: The rate at which a material will vaporize (evaporate, change from liquid to?vapor) compared to the rate of?vaporization?of a specific known material. This quantity is a ratio, therefore it is unitless. General usage: The mass of material that evaporates from a surface per unit time (examples: 3?grams?per?square meter?per hour, 1?inch?per?acre?per month). MSDS Relevance: Evaporation rate can be useful in evaluating the health and fire hazards of a material. For example, a substance with a high evaporation rate will readily form a vapor which can be?inhaled?or?explode. Evaporation rates generally have an inverse relationship toboiling points; i.e. the higher the boiling point, the lower the rate of evaporation. The general reference material for evaporation rates is?n-butyl acetate (commonly abbreviated BuAc) which has the chemical?structure?shown below. Whenever a relative evaporation rate is given, the reference material must be stated. The relative evaporation rate of butyl acetate is 1.0. Other materials are then classified as: Speed: Fast, Evaporation Rate (BuAc = 1.0): > 3.0, Examples: Methyl Ethyl?Ketone?= 3.8, Acetone = 5.6, Hexane?= 8.3; Speed: Medium, Evaporation Rate (BuAc = 1.0): 0.8 to 3.0, Examples: 95%?Ethyl Alcohol?= 1.4, Naphtha = 1.4; Speed: Slow, Evaporation Rate (BuAc = 1.0): < 0.8, Examples: Xylene = 0.6, Isobutyl Alcohol = 0.6, Water = 0.3, Mineral Spirits = 0.1. We are not aware of a specific number for the absolute evaporation rate (i.e. in mass/time units) of butyl acetate. Presumably, such a number would depend on myriad variables such as temperature, atmospheric pressure, humidity,?air?flow, viscosity?etc. The?ASTM?has developed a standard test method,?D3539-87(2004) Standard Test Methods for Evaporation Rates of Volatile Liquids by Shell Thin-Film Evaporometer. We don't own a copy so we can't give you a synopsis of the variables involved. In the absence of evaporation rate data, you can roughly assess the volatility using the?vapor pressure?of the material. See also: Alcohol,?Boiling Point, Vapor Pressure,?Volatility
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