INHIBITION MECHANISM OF Na_2MoO_4 FOR CARBON STEEL IN 55% LiBr SOLUTION

Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na2MoO4 for carbon steel,which is studied in 55%LiBr＋0.07mol/L LiOH solution at high temperature.Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe3O4,and Mo is involved in the process of film forming,in a form of MoO3 and MoO2.The parametric analysis of the evolving potential and the blend potential of MoO2 shows that Mo mainly exists as MoO2 in passive film when the concentration of Na2MoO4 is lower than 150 mg/L.While its concentration is greater than 150mg/L,it mainly exists as MoO3 inside the film and exists as MoO2 outside the film.MoO4^2- is deoxidized as MoO2 on the surface of carbon steel,which may impede the corrosion of active-site and raise the blend potential of carbon steel,and then MoO4^2- adsorbs onto the defects of the passive film and decompounds as MoO3 during the process of film forming.The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution.As a result,heavy concentrated Na2MoO4 solution（greater than 150mg/L）has excellent inhibition effect on carbon steel in LiBr solution.

Mass transfer enhancement for LiBr solution using ultrasonic wave

The methods were studied to improve the cooling performance of the absorption refrigeration system(ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boiling mass transfer in LiB r solution was also analyzed with experiment. The experimental results indicate that, under the driving heat source of 60–100 oC and the ultrasonic power of 20–60 W, the mass flux of cryogen water in Li Br solution is higher after the application of ultrasonic wave than auxiliary heating with electric rod of the same power, so the ultrasonic application effectively enhances the heat utilization efficiency. The distance H from ultrasonic transducer to vapor/liquid interface significantly affects mass transfer enhancement, so an optimal Hopt corresponding to certain ultrasonic power is beneficial to reaching the best strengthening effect for ultrasonic mass transfer. When the ultrasonic power increases, the mass transfer obviously speeds up in the cryogen water; however, as the power increases to a certain extent, the flux reaches a plateau without obvious increment. Moreover, the ultrasound-enhanced mass transfer technology can reduce the minimum temperature of driving heat source required by ARS and promote the application of solar energy during absorption refrigeration.