LIMITATIONS ON ACHIEVING NEGATIVE PRESSURES FOR WATER IN A BERTHELOT TUBE AS A RESULT OF METALLIC CORROSION

We inserted pieces of metal foils (Al and Au) into a metal Berthelot t ube together with water or xylene to investigate whether corrosion of metals limits the achievement of negative pressure. For the test using Al foil with water, the negative pressure rose to -30 bar but diminis hed almost to zero after 250 cycles, whereas those for all the others increased with the number of temperature cycles. Corrosive reaction of Al with water yielded Hp gas and the resulting increase in the gas co ncentration in the water enhanced the nucleation probability of cavita tion, not on the metal surface but in the solution. In order to attain high negative pressures for water in a metal tube, we should take int o account a possible restriction of this achievement of negative press ure by corrosion of metals in contact with water, even though the meta ls used were well de-gassed beforehand.