Study On Preparation Of Geopolymer-carbon Based Electrothermal Coatings And Its Performance

Geopolymer has stable and compact three-dimensional polymeric network structure linked alternatively by the SiO4 and AlO4 tetrahedral sharing all oxygen atoms.They possess many excellent properties including chemical resistance,heat-resisting,good mechanical performance and simple preparation process.Naturally,geopolymer is as an ideal alternative to be used for'building materials,corrosion resistance,fire retardant and other high-strength composite materials.In this thesis,geopolymer based on slag was chosen as the film-forming material,carbon powder,graphite and multi-walled carbon nanotubes were used as conductive fillers,by low-speed stirring technology to prepare water-based environmental-friendly inorganic electrothermal coatings with excellent comprehensive performance.The electrical properties,thermal properties,mechanical properties,adhesion,corrosion resistance and micro-structure of the electrothermal coating are also investigated.During the preparation,the effects of different kinds and contents of conductive fillers,water content of solvents(water-solid ratio),curing temperature and curing time on the composite coatings were carried out through single factor experiments.and the self-regulating temperature performance of the coatings were also investigated.The research results showed that:(1)With the increase of the content of conductive filler,the volume resistivity of slag-based geopolymer composites decreases gradually and seepage appears.When graphite content is 25wt.%,carbon.powder content is 20wt.%,and carbon nanotubes content is 4wt.%,the volume resistivity of the coating decreases to 17.68?·cm,15.88?·cm and 8.96?·cm respectively.The microstructure of samples was characterized by TG-DSC,SEM,and XRD,it was found the carbon conductive filler is only filled in the polymer and does not change the curing mechanism and process of the polymer.(2)The electrical properties of the coatings with different carbon content as conductive fillers at different water-solid ratios were studied.When the water-solid ratio ranged from 0.35 to 0.6,the electrical properties of the coatings increased gradually.The volume resistivity of the C20 decreased from 17.95?·cm to 15.03?·cm,and the heating temperature increased from 28.3? to 40.5?,and the output power increased from 6.9 W to 10.2 W,and the compressive strength of the coatings increased first and then decreased.The water content of the coatings showed good adhesion and acid and alkali corrosion resistance.(3)The comprehensive properties of the composite coating were also investigated,it was found that when the ratio of graphite to carbon powder was 4:3,the volume resistivity of the coating decreased to the minimum and the heating temperature and output power reached the optimum.Compared with graphite as a single component filler,the volume resistivity of the coating decreased to 25.80?·cm,and the heating temperature and out power were respective.The compressive strength of the coatings varies in the range of 23.15MPa-26.67MPa and the temperature rises to 68.8? and 16.4W.Compared with the single component,the coatings retain excellent adhesion and acid-alkali corrosion resistance,and the comprehensive properties of the coatings are improved.(4)The curing time and curing temperature of the coatings were also investigated.When the water-solid ratio was 45wt.%,the coatings were cured for 91 days at 25?and 60?,respectively.With the increase of curing time and curing temperature,the volume resistivity of the coatings increased gradually,the heating temperature and output power decreased and the compressive strength of the coating also shows an increasing trend.When the conductive fillers reached the seepage value of the coatings,their electrothermal properties changed slightly.(5)The self-regulating temperature performance of the coating was also investigated,it was found that geopolymer-carbon based electrothermal coatings can achieve temperature control performance by adjusting the volume resistivity of the coatings,and different applied voltages and the thickness of the coating to achieve the thermal control performance of the coating.