Study On Thermoelectric Properties And Ice Melting Technology Of Modified MWCNTs Reinforced Cement-based Composites

Thermoelectric cement-based composite material,a new type of intelligent building material,which can not only monitor the health of the building structure,but also can convert heat and electricity to each other to meet a variety of needs:In summer,while reducing the city heat island effect,the converted electricity can be used for low power consumption such as lighting to reduce energy consumption.In winter,under the load of the power source,the Joule heat generated inside the composite material will migrate from one side to the other and the high temperature side has a higher ice melting efficiency due to the Peltier effect.In this paper,the capillary force of carbon nanotubes is used to fill the cavity with lithium carbonate,which affects the migration of carriers in carbon nanotubes and achieves the purpose of modifying carbon nanotubes.XRD was used to characterize the crystal phase and internal uniformity of aerogel samples which was treated at different temperatures,and the optimal heat treatment conditions were obtained.Modified MWCNTs reinforced cement-based composites were prepared by mixing modified carbon nanotubes with sulphoaluminate cement in a certain ratio.The thermoelectric properties of different modified MWCNTs reinforced cement-based composites were tested by a self-made experimental device.Finally,based on the modified MWCNTs reinforced cement-based composite material with the best thermoelectric properties,a 10.0×85.0×85.0 mm³ flat cement-based composite material was successfully prepared through a combination of press molding and pouring molding processes.A device consisting of a data logger and a DC power supply was used to test the temperature distribution of the surface of the flat cement-based composite material under different currents and calculate the Joule heat generated over a period of time.It is predicted whether 100 g of ice can be completely melted into water within a specified time.The"pavement melting ice"experiment was simulated in a refrigerator at 0 ^oC,and the obtained melting time was consistent with the predicted result.The main research contents and results are as follows:Lithium acetate was filled into the cavity of carbon nanotubes by capillary force,and polyvinyl alcohol 124?PVA124?was added to the mixed solution,and chemically cross-linked by boric acid.The aerogel samples were heat-treated at 1200 ^oC,800 ^oC,600 ^oC,400 ^oC,280 ^oC,and 270 ^oC,and the best heat treatment conditions?heat treatment at 280 ^oC for 5 hours under air atmosphere?were obtained by XRD characterization.After heat treatment under this condition,lithium acetate will be completely converted into lithium carbonate,the conductivity of modified carbon nanotube?3.43 S/cm,30.0 MPa?between 2.0 and 30.0 MPa is significantly lower than that of pure carbon nanotubes?49.8 S/cm,30.0 MPa?.TEM morphology and electron diffraction results show that lithium acetate enter the lumen of carbon nanotubes,and is converted into lithium carbonate after heat treatment.Modified MWCNTs reinforced cement-based composites were prepared according to the mass mixing ratios of modified carbon nanotubes and sulphoaluminate cement of 0.0500,0.1000 and 0.1500.Based on the measured resistance and temperature,the conductivity,Seebeck coefficient,and thermoelectric power factor between room temperature and 80 ^oC are calculated.When the mass mixing ratio is0.1000,the absolute value of the Seebeck coefficient reaches a maximum of 73.40?V/K,the conductivity is 0.07 S/cm,and the measured thermoelectric power factor reaches a maximum of 0.039?Wm^-1k^-2.The filling of lithium carbonate affects the migration of the electron carriers in the c-axis direction of the carbon nanotubes to a certain extent,and the hole carriers become the majority carriers.Compared with the cement-based composites?N-type semiconductor?mixed with pure carbon nanotubes?after 500 ^oC pretreatment?,the Seebeck coefficient of the modified MWCNTs reinforced cement-based composites?Mixing ratio 0.0500,P-type semiconductor?is improved,and the conductivity is only reduced by 6 times.When the enhanced phases are all modified carbon nanotubes and with the increasing content of modified carbon nanotubes in the cement matrix?Mixing ratio of 0.1000 and 0.1500?,the increase in the electron carrier concentration compensates for the decrease in mobility,and the semiconductor type changes again?0.0500,P Type;0.1000,N type;0.1500,N type?.By monitoring the temperature and voltage changes of the 20.0×40.0mm² two surfaces of the small cement-based composite material?10.0×20.0×40.0 mm³?under the constant current source?0.1-1.0 A?.Compared with the comparative sample?R=0.43??mixed with expanded graphite,the temperature difference between the positive and negative sides of the sample mixed with the modified carbon nanotubes was greater,reaching a maximum of 10 ^oC,and the resistance was greater?R=8?,the highest temperature that can be reached on one side is higher,up to 78 ^oC?.Combining compression molding and pouring molding,a flat cement-based composite material of10×85×85 mm³ was successfully prepared,and the data on both sides of the flat plate under constant current source loading?1.0-3.0 A?was monitored by a data logger.Based on the obtained voltage data,Joule heat generated in one hour was calculated,and it was evaluated whether 100 g of ice could be completely melted in 1 hour.Finally,the winter road deicing was simulated in a refrigerator freezer.By monitoring the time for the ice to completely melt at a mass of 100 g and a temperature of 0 ^oC,the measured ice melting efficiency of the flat sample under different currents was consistent with the predicted results.