Sound absorption in titanium at 25 kHz

In the process of studying sound absorption in magnesium sulfate solutions as a function of pressure, a 100 L titanium sphere (a spare ballast tank for the WHOI researc submarine ALVIN) was used up to 300 atm. In calibrating the losses due to the sphere with pure water, Hsu found a resonant mode at 25 kHz (using a HP microHz synthesizer) with a very long decay at 1 atm and 25 °C; a straight line 50 dB decay of 70 s. This means that ultrasonic absorption in the titanium sphere (4 Al, 6 Va alloy) filled with water is 5.5 exp(−7) N/cm. This is four times greater than that of water at 25 kHz. Therefore, subtracting the absorption of water yields an upper limit for absorption in titanium of 4.1 exp(−7) N/cm. The 0.9 m sphere was suspended from two loops of piano wire in a steel vacuum chamber. The resonance (Q=955 000) required considerable attention to insuring pressure, temperature, and frequency control, as well as the usual degassing of the liquid. Discussion of results and details will be presented. [Research supported by ONR.]