The electrochemical behaviors of Ta in tetrabutylammonium hydrogen sulfate（TBAHS） ethanol solutions were studied using potentiodynamic polarization,cyclic voltammetry,potentiostatic current time transient and impedance techniques.The results revealed that no active-passive transition is presented in the cyclic voltammogram,and the anodic current density increases with the increase of solution temperature,TBAHS concentration,potential scan rate and water content.The apparent activation energy is about 43.389 kJ/mol and the dissolution process is diffusion-controlled.Potentiostatic measurements showed that the current density gradually decays to a steady value when the potential is low;however,when the potential is higher than a certain value,the current density initially declines to a minimum value and then increases gradually.The resistance of passive film decreases with increasing potential,and inductive loops are presented when the potential is higher than 2.0 V.
A novel chemical process for producing well-defined copper particles with satisfied anti-oxidation property was described. The resultant particles were characterized by X-ray diffractometry and scanning electron microscopy. The results show that well-dispersed nano-copper particles with 70 nm in diameter are obtained from the water/organic solution containing 0.2 mol/L Cu2+ ion,with ammonia as ligand and ascorbic acid as reductant. In this process,the formation of copper-ligands in aqueous solution causes initial copper ions concentration very low,which is not only good to obtain homogeneous initial reaction solution,but also slower the initially drastic nucleation reaction rate. This makes the process more convenient for delaying the nuclei processes and for controlling the ultimate copper particles size. In addition,oleic acid acts as both a phase-transfer agent and a particle protector coordinating their carboxyl end groups on the new generated copper particles surface,the carbon tails of the oleic acids are pointed outwards from the surface of the synthesized particles. This organic film also seems to play an important role to prevent the new generated copper particles from oxidation.
Niobium(V) ethoxide(Nb(OEt)5) was synthesized by electrochemical reaction of ethanol with niobium plate as the sacrificial anode,stainless steel as the cathode and tetraethylammonium chloride(TEAC) as the conductive additive.The condensates were isolated by vacuum distillation under 5 kPa.The product was characterized by Fourier transform infrared(FT-IR) spectra,Raman spectra and nuclear magnetic resonance(NMR) spectra.The results indicate that the product is niobium ethoxide.Thermal properties of niobium ethoxide were analysed by TG/DTG.Vapour pressure was calculated from the Langmuir equation and the enthalpy of vaporization was calculated from the vapour pressure-temperature data using the Clausius-Clapeyron equation.The concentrations of impurity metallic elements in the sample were detected by ICP-MS.It is shown that the purity can reach 99.997%.The volatility and purity of the niobium ethoxide ensure that it could be a good precursor for chemical vapor deposition and atomic layer deposition of niobium oxide layers.
Effects of reflux ratio,water addition and content of water in ethanol on the purity and yield of tantalum ethoxide during vacuum distillation were investigated under the operational conditions of pressure of 1 kPa,oil bath temperature of 210-230 ℃,and outlet temperature of 190 ℃.The condensate sample was characterized by FTIR,1H-NMR spectroscopy and Raman spectra,respectively.The contents of tantalum,carbon and hydrogen in the sample were also determined with elemental analysis instrument.The obtained results consistently demonstrate that the condensate is tantalum ethoxide.The content of impurity,such as Al,As,Ca,Co,Cr,Cu,Fe,K,Mg,Mn,Mo,Na,Ni,Pb,Sn,Ti,V and Zn,in tantalum ethoxide is less than 0.000 05%,while Nb content is less than 0.000 5%.The content of impurities in tantalum ethoxide sample excels that of Epichem Group's requirement for Ta(OC2H5)5 of 99.999%.
Tantalum(Ⅴ)propoxide(Ta(OPrn)5),isopropoxide(Ta(OPr i )5)and butoxide(Ta(OBu n )5)were synthesized by electro- chemical reactions of corresponding alcohol at sacrificial tantalum anode in the presence of tetraethylammonium chloride as a conductive additive.The pure products were isolated by reduced pressure distillation under 5 kPa.The crystal of Ta(OPri)5 was obtained by recrystallization from hexane at-10℃.These samples were characterized by Fourier transform infrared spectra(FT-IR), Raman spectra,nuclear magnetic resonance spectra(NMR),TG/DTA and ICP-MS.The results show that direct electrochemical synthesis of metal alkoxides has a high current efficiency and electrolysis yield.These alkoxides have a high purity of 99.97%and can be directly used as the precursor of Ta2O5 films.
