Ultrahigh Vacuum Quartz Spring Microbalance for Determination of Evaporation Rate and Vapor Pressure

An ultrahigh vacuum quartz spring mass sorption microbalance was designed and fabricated to measure the evaporation rates of low volatility substances, e.g., lubricants considered for space applications. The balance is accurate to ±7.2×10−4 g. Optimum test temperatures range from room ambient to 120°C. The evaporation rates are used to calculate the vapor pressures by the Langmuir equation. The observed vapor pressures of pure organic compounds were found to agree closely with those calculated and extrapolated according to applicable temperature-vapor-pressure relationships. Typical data are given on the evaluation of a conventional lubricating oil considered for space application.