ULTRASONIC VELOCITY AND ABSORPTION-COEFFICIENT IN MOLTEN ALKALI-METAL NITRATES AND CARBONATES

The ultrasonic velocity and absorption coefficient, alpha in molten alkali metal nitrates and carbonates have been measured by a pulse transmission method. The adiabatic and isothermal compressibilities, internal pressure and bulk viscosity were derived from the ultrasonic velocity and absorption coefficient. The results obtained are summarized as follows. (1) The ultrasonic velocity and the value of alpha/f2 decrease with increasing temperature, but they are not dependent on frequency, f, in the frequency range investigated (5 approximately 75 MHz). (2) The compressibility increases and the internal pressure decreases with increasing cation size in the series of molten alkali carbonates. The compressibility and internal pressure show similar cation size dependence in the series of molten alkali nitrate, except LiNO3. (3) The bulk viscosities of alkali metal carbonates and nitrates have negative temperature dependence, and the value of eta-B/eta-S increases with increasing cation size in the series of molten alkali nitrates and carbonates. (4) The compressibilities calculated on the basis of a hard sphere model agree well with the experimental values, but the bulk viscosities calculated are obviously smaller than the experimental values.