Study On Scale Inhibition Mechanism Of Cu-Zn Alloy In Boiler Water

Cu-Zn alloy's scale inhibition mechanism on the boiler inner wall was studied in this paper.The scale was inhibited by Cu-Zn alloy with zinc ions and free electrons which were both generated from Cu-Zn alloy micro battery reaction.The scale inhibition mechanisms of zinc ion,free electron and Cu-Zn electrode galvanic cell reaction were studied respectively with their respective experimental systems.The effect of zinc ions on scale formation in hard water was studied with EDTA titration,X-ray diffraction and scanning electron microscope,and the scale inhibition mechanism of zinc ions was analyzed.The results showed that the scaling kinetics of hard water followed power function rule.The dynamic mechanism of scale formation in hard water was not changed by zinc ions.Zinc ion reacts with carbonate ion and water to basic zinc carbonate,which impeded the crystallization nucleation process of scale and restrained the formation of dense calcite from loose aragonite.But scale inhibition of zinc ion had time effectiveness.In static experiments,zinc ion lost its scale inhibition ability and the process of calcium carbonate's growth got right in 24 hours.As zinc ion's concentration increased,the scale inhibition ability of zinc ion became more and more powerful.Almost all of zinc ions lost scale inhibition ability when the mass concentration of zinc ion was above 10 mg/L because zinc ion,in preference to calcium ion,reacted with carbonate ion to zinc carbonate.The effect of free electrons on scale formation in hard water was studied by EDTA titration and X-ray diffraction,and the scale inhibition mechanism of free electron was analyzed.The results showed that on the one hand,the energy and the phase transformation driving force of calcium carbonate crystal nucleus raised because of free electrons' bombardment.Calcite scale was converted into aragonite and vaterite and the solubility of scale was increased by this change.On the other hand,water polymer could form hydrogen bond.Some free electrons will bombard hydrogen bond.Part of the electrons in water molecules were stimulated by these free electrons and jumped from lower energy state to higher energy state.The electrical potential energy and electrical potential of water molecules and the potential difference between container wall and water molecules decreased.The ions of salt in water couldn't adhere to container wall because of the decrease of electrostatic force.In the meantime,some free electrons could strike off a few hydrogen bond and the solubility of scale increased.The galvanic cell reaction of Cu-Zn electrodes was studied by X-ray diffraction.The results showed that galvanic cell reaction of Cu-Zn electrodes followed power function rule.Cu-Zn alloy micro battery reaction had timeliness and the reaction lasted 36 hours.The proportion of electrodes' surface area was major influence factor for reaction rate.The rate of galvanic cell reaction of Cu-Zn electrodes was increased by cathode with larger surface area ratio in initial stage of the experiment.But the reaction rate decreased heavily in later period as anodizing was faster.The rate of anodizing could be decreased by smaller surface area ratio of cathode in initial stage of the experiment,but the consume of anode was so few in the end that the scale inhibition ability of Cu-Zn alloy decreased.When proportion of electrodes' surface area was 1:1,the scale inhibition ability was the most excellent.In addition,the rate of galvanic cell reaction of Cu-Zn electrodes could be increased by higher hardness of solution,but the consume of anodizing is almost invariant in the end.