Development Of Electrolytic Capacitor Anode Of Niobium Suboxide And Study On The Correlative Mechanisms

Compared with tantalum, niobium is richer in resources and less expensive in price. The electrolytic capacitor has a huge market, with the total amount of imports reaching 28946.8 ten thousand US dollars in the first six months of last year. In the recent years, its consumption has shown a tendency towards a high-grade market. Compared with the worse properties and lower price of aluminum electrolytic capacitor, tantalum electrolytic capacitor has better properties and higher price, therefore niobium electrolytic capacitor with better properties and lower price will have much room for development. However, niobium electrolytic capacitor must solve such problems as instability before it can meet the market requirements. Niobium suboxide anode for electrolytic capacitor in the present study has such features as high specific capacity, small leakage current, steady capability and high reliability.The technology for preparing suboxide anode for electrolytic capacitor with excellent electrical properties is adopted for the first time, including preparation of niobium suboxide powder by solid-solid reaction between Nb and Nb2O5, pressing to the mould, sintering and oxidation of the niobium anode. The present research makes a detailed study on the effects of technological conditions on electrical properties of anode by orthogonal experiments and analysis of variance and the technological conditions are further optimized. The specific capacity of niobium suboxide anode prepared by this technique is 72950uF V g-1, the loss is 16.3%, leakage current (value of K) is 4.27x10-5 uA F-1 V-1, and the electrical properties are better than the national standard (GB/T 3136-1995) of FTal6-300 tantalum powder for capacitor.The preparation of niobium suboxide powder by solid-solid reaction between Nb and Nb2O5 is a perfect technique to prepare niobium suboxide for electrolytic capacitor anode. The advantages involve that the products are free from pollution and the oxygen content can be easily controlled. The X-ray diffraction analysis indicates that primary phase in prepared niobium suboxide powder is NbO. Kinetic analysis shows that the reaction between Nb and Nb2O5is controlled by the diffusion of oxide in different phases, so milling and mixing and roasting in high temperature can speed up the reaction.Based on the theories of quantum chemistry and structural chemistry, the research makes a detailed analysis of the structure, stability, and conductive mechanism of NbO for the first time. It can be proved that NbO is more stable due to the out shell electron structure, ionization potential, characteristics of orbit separating of the niobium and free energy of disproportionation reaction between NbO and NbO2. Theoretical calculation of structural chemistry indicates that NbO possesses structure of NaCl type of cubic crystal shape. The band theory in quantum chemistry illustrates that NbO crystal has excellent electrical properties and it can meet with the demand of electrolytic capacitor on conductivities of anode.The reasons for the high specific capacity of the niobium suboxide powder and the changes of microscopic appearance in the process of anode sintering and forming are investigated by SEM in detail for the first time.The researcher also conducts a detailed study on the agglomeration state of niobium suboxide powder by SEM and the diagram of pressing density and logarithm of pressure (i.e., D-lgP) for the first time. In addition, effects of state of agglomeration on electrical properties of anode are studied.The relation between oxygen content of niobium suboxide and its electrical properties is studied by experimentation for the first time. The results indicate that oxygen content of niobium suboxide has great influence on the electrical properties of anode.The study on formation voltage from 20V to 50V shows that niobium suboxide is similar to tantalum and niobium. The product between formation voltage of niobium suboxide anode and the absolute temperature of forming solution is a constant. The product betwe...