While a knowledge of the vapour pressure curve of any material is of theoretical significance in understanding its basic physical properties, it can also be of practical importance in, for example, the use of the material in high-temperature vacuum applications. Therefore readily
usable equations which accurately predict values of vapour pressure over a wide range of temperatures and pressures can have an important practical use. For the platinum group metals (pgms) the vapour pressures can be immediately assessed from about 10−16 bar to just above
the boiling point by the use of Equation (i), fitted for the solid and liquid metals separately: ln(p, bar) = A + Bln(T) + C/T + DT + ET
, where p is the vapour pressure, T is the temperature in kelvin and A, B, C, D
and E are constants. Although containing five coefficients, this equation can easily be evaluated by computers and scientific calculators. Although it gives values of vapour pressure at fixed temperatures, by a simple and rapid use of iteration values of temperature at fixed vapour pressure,
temperature-dependent values of vapour pressure can also be obtained.
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