The Electrical Pulse And Its Applications In The Wastewater Treatment And Micro-arc Oxidation

With the development of science and technology, the study based on multiple subjects becomes especially important. Nowadays, wastewater treatment attracts lots of researchers due to the crisis of environment pollution. At the same time, surface modification of materials also becomes research hot point. However, both of them consist of several subjects and are hard to carry out. Water treatment using electrocoagulation and formation of coatings on valve metals by microarc oxidation (MAO) are typical multiple subjects studies. The main theory included in the two fields is electrochemistry and the equipments are pulse power supplies which belong to the field of power electronics technology.The research work in this paper consists of wastewater treatment and MAO using a pulse power. Based on the analysis of the electrolytic bath, the equivalent circuit model is got. Meanwhile, two pulse power supplies are implemented for the experiments of wastewater treatment and MAO. Lots of experiments are carried out and a series of conclusions are obtained.The research contents of this paper include four aspects:1. The design and debugging of the pulse power supply.The model machines are designed based on the experimental demand. The power supplies can output several kinds of pulses and the parameters of the pulse (such as voltage amplitude, frequency and duty cycle) could be set independently. The waveforms and the parameters are set by an accessorial keyboard and displayed by LEDs. The method of the design is discussed in detail.2. Load characterristics of electrobath.On the basis of the electrochemical theory, academic and the equivalent circuit models of electrobath are obtained by the methods of electrochemical impedance spectroscopy (EIS). Quantitative analysis is carried out through measuring and curve fitting. Further more, the existence and effects of the double layer capacitor in the equivalent circuit are analysed. The relationships between the double layer capacitor and the parameters of the voltage pulse are investigated. In the application of wastewater treatment using a pulse power supply, the basic principle is got on how to choose the appropriate power parameters. Based on the equivalent circuit model, the relationships between the equivalent model of electrobath in wastewater treatment and arrangement of the electrodes are disscused. Statistical theory is used to verify the relationships obtained above. At the same time, some reasonable explanations are proposed to describe the mechanism of such relationships.3. The pulse power supply is practically used in the water treatment.Dye wastewater purified by electrocoagulation with pulse power supply is carried out. Some relationships are got between the parameters and the result of the water treatment. The basic principle is discussed on how to choose the appropriate power parameters. Furthermore, based on the equivalent circuit of electrobath, the power consumption is discussed. The relationships between the power consumption and the parameters and between the power consumption and the arrangement of electrodes are investigated at the same time. Some conclusions are got based on the experimental results and analysis.4. The pulse power supply is practically used in the MAO.Ceramic coatings are fabricated on AZ91D magnesium alloy in alkaline borate solution by MAO using pulse and AC power supply. The results show: when the pulse power is selected, the anode dissolving can be restrained effectively, the performance of corrosion resistance may be improved and at the same time, the pulse MAO process is good for forming coating.A series of MAO experiments are carried out using the pulse power with different parameters, such as amplitude, frequency and duty cycle, etc. The relationship between the parameters and the performance of the coatings are discussed and some meaningful conclusions are obtained at last.