| In the experiment,the solvent of 0.3 mol/L oxalic acid electrolyte is a mixture solution of ethanol and de-ionized with volume ratios of 1:1,1:2,1:3 and 1:4,respectively.Meanwhile,use magnetic stirrer to dissipate heat during hard anodizing process.Through analyze the evolution of the current as a function of time and the AFM microstructure to study the effect on the high voltage anodization of ethanol content and magnetic stirring.Use the first principle to calculate the adsorption behavior of single particle as water molecule,oxalic acid molecule,hydroxide ion and oxalate ion at seven high symmetry position of ?-Al2O3(0001)surface.And calculate the adsorption behavior of three hydroxide ions,as well as the adsorption behavior of four hydroxide ions and three oxalic acid molecules.By analyzing the adsorption energy value and the relaxation result configuration diagram to find a way which can dissolve the aluminaIn the summary diagram of current curves of first and second oxidation in the solution of ethanol and de-ionized with volume ratios of 1:1,1:2,1:3 and 1:4,the generated current value increases with the increase of volume ratio.In the AFM diagram of AAO template prepared by adding sulfuric acid to 0.3 mol/L oxalic acid electrolytes,the template prepared without magnetic stirring has small pore size and low degree of order,while the template prepared with magnetic stirring has high degree of order.The calculation result of four kinds single particle adsorbed on ?-Al2O3(0001)surface show that,the adsorption energy both of water molecule and oxalic acid molecule are small,the adsorption of water molecule can take place at the top of aluminum and the dissociation of oxalic acid molecule at the top of oxygen,The adsorption energy of hydroxide ion was the highest among the four kinds of particles,and has a maximum value of 2.84643eV at the aluminum top position.Hydroxide ion can absorbed on the system surface at aluminum top position,oxygen bridge position,oxygen facedcentered cubic position and oxygen top position.Oxalate ion can adsorbed on the system surface at the aluminum top position,oxygen bridge position and oxygen facedcentered cubic position.The calculation result of three hydroxide ions adsorbed on ?-Al2O3(0001)surface show that,an Al-O bond breaks when the X and Y coordinates of the absorbed particles are fixed,and the chemical bond direction of the adsorbed particles rotates when the X and Y coordinates of the absorbed particles are not fixed,three hydroxide ions can adsorb on the same aluminum atom in the system surface but fail to drag it away from the system in both cases.The calculation result of four hydroxide ions and three oxalic acid molecules adsorbed on ?-Al2O3(0001)surface show that,the O-H bonds in the three oxalic acid molecules broke and the broken hydrogen atoms are absorbed on the three oxygen atoms around the aluminum atom;Three hydroxide ions are adsorbed on the central aluminum atom and drag it away from the system.The result of experiment indicate that the value of volume ratio of de-ionized water to ethanol almost has no effect on hole diameter and interpore distance.Breakdown can be effectively avoid by change the magnetic stirring speed timely.Highly degree of ordered AAO templates can also be prepared by use variable speed magnetic stirring.According to the above calculation results can conclude that,the adsorption of water molecule,oxalic acid molecule,hydroxide ion and oxalate ion single particle and three hydroxide ions on a-Al2O3(0001)surface can t drag aluminum atom away from system.However,the adsorption of four hydroxide ions and three oxalic acid molecules on ?-Al2O3(0001)surface can drag aluminum atom away from system.Based on this phenomenon,a new chemical reaction equation for dissolution mechanism of alumina is proposed,that is,alumina reacts with hydroxide ions and oxalic acid molecules to produce aluminum hydroxide and oxalate ions. |
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