Zirconium, Hafnium Alkoxide Electrochemical Synthesis And Characterization

As a result of a series of problems in the current method of preparation of zirconium and hafnium alkoxides by metal halides, such as the long process flow, poor efficiency, heavy pollution, difficulty to obtain reactant, and so on. In this paper, coarse Me(OR)4 products of zirconium and hafnium were synthesized by electrochemical reactions of corresponding alcohol at sacrificial metal anode in the presence of tetraethylammonium chloride as a conductive additive. The surplus alcohol was removed from the electrolyte. Then the pure Me(OR)4 products used for electronic material were obtained by reduced pressure distillation. Another way can also separate the Me(OR)4 from the coarse products, which is redissolving in n-hexane and then filtrating to eliminate the impurity.The electrochemical behaviors of zirconium in ethanol solutions containing Et₄NCl were investigated using cyclic voltammetry, linear polarization potentiostatic current-time transient and Tafel curve techniques. The results revealed that, zirconium suffered from classical pitting corrosion in ethanol solution. It was more difficult to start pitting for zirconium owing to the increase of the scanning rate. The pitting potential descended with the increase of the concentration of Cl" by enhancing the content of conductive additive. The increase of solution temperature could improve the activity of reactive ion and accelerate the pitting of zirconium in ethanol. The corrosion current density was recorded from Tafel curves under various temperatures, and then the apparent activation energy of zirconium in Et₄NCl ethanol solution (13.97kJ/mol) was calculated by Arrhenius formula.Comprehensive electrolytic synthetic experiment indicated that the cell voltage magnified with increasing of the polar distance, current density and the concentration of the supporting electrolyte. The current efficiency reduced as a result of the increase current density. In view of energy consumption and product quality, the optimum conditions of electrosynthesis is as follows, the polar distance 15mm, Et₄NCl concentration 0.05mol/L and current density 145A/m² The current efficiency can reach more than 99%, when electrochemical synthesis of Me(OR)4 (R=Et, Prn, Bun) was performed in stable condition.The structures of the purified products were characterized by Fourier Transform Infrared spectra (FT-IR) and 1H nuclear magnetic resonance spectra ('H NMR), the concentrations of impurity elements in the sample were detected by ICP, thermal properties and volatility of these metal alkoxides were analysed by TG-DSC. The results suggested that impurity concentration was not more than 0.02% in all, volatility of metals normal alkoxides decreased as increased number of C in the alcohol groups. Compared with M(OPrn)4 and M(OBun)4, M(OEt)4 was suited for chemical vapor deposition of zirconium and hafnium oxides films, because of better volatility and the temperature window between volatilization and thermal pyrolysis.