Preparation Of Carbon System Electrothermal Coating With Controllable Temperature And Study On Electrothermal Property

Electrothermal coating, as functional coatings which change directly electric energy into heat energy, is a hot spot in the field of special function coatings at present.However,there are many problems about traditional organic electric heating coating,such as surface heating temperature low, heat-resistant property bad and easy to degradation and drop off.At the same time, the adhesion of common inorganic electric heating coating is poor and it is easily deliquesces and the property of heating is unsteady. These problems restrict the application of the coating in many fields and the electric heating property of the coating and mechanism of self-regulating temperature is lack of intensive study by domestic and foreign researchers. To solve the issues that present electric heating coating is hard to apply to electrothermal heating for its fault of material, maintenance cost is high and prepare self-regulating temperature electrothermal carbon coating which has excellent property of thermostable under safe voltage,the preparation of the coating and the research about property of thermostable and mechanism were developed in this paper.(1) The formulation, preparation technology and electric heating property of electrothermal carbon coating which was obtained with composite carbon powders as main conductive filler, inorganic or organic binder as matrix were investigated. The influence of different carbon conductive fillers and binders on conductivity, heating, thermal resistance and age resistance was systematically studied. The surface topography of the carbon coating was characterized by SEM. The thermal stability was analyzed by TG-DTG, while the electric property and surface temperature were tested respectively by resistivity tester and electrical parameter tester. The results showed that, in the same condition, the conductivity and heating property of the coating with graphite/carbon black mixture as filler was superior to that with single carbon powder as filler. The coating with inorganic binder as matrix had better thermal resistance and age resistance than that with organic resin as matrix. It found that composite inorganic electrothermal carbon coating had fine electric heating property. The surface temperature of coating which was made with water glass as binder could stabilized in about 302℃, while the surface temperature of coating that with modified resin as binder was only 76℃when the mass contents of conductive fillers (graphite/carbon black) reached 40% and conducting 15 minutes under 36V. (2) The formulation, preparation technology and electric heating property of self-regulating temperature electrothermal carbon coating were researched. The coating was prepared through molding with special coating technique followed by twice solidification after embedding ultrathin electric pole in the surface of heat resistance carrier, with inorganic binder as matrix, into which composite carbon powders as main conductive filler were added together with certain amount of metal elements. The influence of different carbon conductive fillers and binders on conductivity, heating, thermal resistance and age resistance was systematically studied. The microstructure and particle size distribution of the carbon coating were characterized and analyzed by SEM, while the electric and thermal properties tested by voltage-current volume resistivity tester and electrical parameter tester. The results showed that the electric coating obtained by using water glass and silica sol as matrix and graphite/carbon black/metal powder mixture as filler had controllable surface temperature, excellent water resistence and electric heating property. It had also found that the surface heating temperature of the coating maintains about 120℃under the condition of heating for 30 minutes at room temperature(23℃) and 36V when the dimensions were 200x 100mm2 and the thickness was 0.5mm.(3) Electron breakdown model of the electrothermal carbon coating was studyed. The result showed that the main factor influencing electric breakdown strength of the coating was density. It was found that the electron breakdown property of the electrothermal carbon coating was chiefly aroused by Joule heating effect which produce huge amounts of energy when conducting. Because the energe transferred out of balance, the matrix expanded and original conductive network was destroyed. Thus electron breakdown phenomenon turned up.(4) The model of self-regulating temperature of electrothermal carbon coating was discussed and the influence factors of temperature controllability was analyzed. The results indicated that the more uniform dense the internal structure of coating was, the better combination property such as strength and conductivity it had. Combineding carbon with coating, composite conductive filler formed compact carbon/mental conductive network among the continuous phase of inorganic binder. Thus the heat through electrical current and thermal radiation of coating reached balanced in the air, that is to say Qabsorb=Qrelease.