Study On The Mechanism Of Multi-type Interface Scattering Enhancement Of Seebeck Effect Of EGCFRC

Expanded Graphite/Carbon Fiber Reinforced Cement-based Composites?EGCFRC?is a new type of intelligent structural material which can realize the thermoelectric conversion.It can be used widely in the field of urban waste heat utilization,structural health monitoring and deicing and snow melting with low power consumption.It is one of the most important areas of smart cement-based compositions.Nevertheless,the lower Seebeck coefficient of EGCFRC has become the key factor that restricts its large-scale application.In this paper,EGCFRC was prepared by compression moulding.The effects of different molding pressure on Seebeck effect of EGCFRC and conductivity were analyzed.The interfaces between carbon fiber/expanded graphite and cement matrix,gas/solid interface produced by micro/nano pores and microcracks were quantitatively characterized by stereology method.The influence of water content,different types of gas/solid interface,interface between metal oxide,ionic liquid and cement matrix on EGCFRC-Seebeck coefficient and conductivity was carried out.The scattering enhancement mechanism of multiple type interfaces of EGCFRC was obtained.The main contents and results are listed as follows:?1?2D microstructure information of interfaces between carbon fiber/expanded graphite and cement matrix,gas/solid interface produced by micro/nano pores and microcracks were obtained by image analysis method.According with stereological principle,3D microstructure informations were derived quantitatively.The mathematic relationship between interface parameters and Seebeck coefficient of EGCFRC and electrical conductivity was established.Results shown that the conductivity of EGCFRC increases with the increasing of molding pressures.But the gas/solid interface content was opposite.The higher the forming pressure,the lower the gas/solid interface content.The higher defect density in lower forming pressure could hinder the transportion of carriers and enhance the Seebeck effect.Overall,the best molding pressure that could improve the thermoelectric properties of EGCFRC was 60 MPa.?2?The effect of porosity on the thermoelectric properties of EGCFRC was discussed.In order to study the influence of gas solid interface on the thermoelectric properties of EGCFRC,different angles between gas/solid interface and the heat flow were constructed through slicing.It was found that the conductivity of EGCFRC prepared by compression moulding could reach to 0.063 S·cm^-1,which has increased by three orders compared with the conventional method.The largest conductivity 0.063 S·cm^-1,power factor 7.26×10^-4 ?Wm-1K-2 and ZT value 2.22×10-7 were got as pressing in 60 MPa.The Seebeck effect of EGCFRC was enhanced as the angle between gas/solid interface and heat flow was 90 o.Especially,the most significant enhancement was obtained by molding in 20 MPa.?3?The water content of EGCFRC samples were measured.Simultaneously,the effect of water content on the thermoelectric properties of EGCFRC was investigated.Results shown that higher water content results in an increasing in the absolute Seebeck coefficient but a decreasing in conductivity.The maximum absolute Seebeck coefficient 11.59 ?V/oC was obtained with moisture of 14.98% at 33 oC.Simultaneously,the maximum of electrical conductivity 0.78 S·cm^-1 was got with moisture of 11.44%.The largest power factor 7.85×10^-4 ?Wm-1K-2 was obtained at 33 oC with moisture of 11.44%.The carrier scattering,polarization effects and high density defects interface of EGCFRC were attributed to the enhancement of thermoelectric properties in the case of higher moisture.?4?The effect of Fe₂O₃ content on the thermoelectric properties of EGCFRC was studied.We found that the conductivity and Seebeck effect of EGCFRC were improved together as the amount of Fe₂O₃ powder was 5.0 wt%.The maximum absolute Seebeck coefficient 16.80 ?V/oC and conductivity 0.084 S·cm^-1 were obtained.When mixed with the amount of 10.0 wt% Fe₂O₃ powder,the absolute value of Seebeck coefficient was up to 20.85 ?V/oC,but the conductivity was only 0.036 S·cm^-1.?5?The effect and mechanism of curing methods and the amount of ionic liquid [Bmim]Br on thermoelectric properties of EGCFRC were investigated.The results shown that the absolute value of Seebeck coefficient increases with the increasing of [Bmim]Br content.However,the higher the [Bmim]Br content,the lower the electrical conductivity.Because of the common influence of mechanical and thermal motion,the [Bmim]Br could be dispersed more evenly in EGCFRC as curing after pretreatment.Though Seebeck effect was promoted by the migration and rearrangement of cations and anions in ions liquid,the electrical conductivity was decreased.The maximum of absolute Seebeck coefficient 115.39 ?V/oC and the maximum power factor of 8.56×10-3 mWm-1K-2 was got with [Bmim]Br of 3.0 wt% at 72 oC as EGCFRC curing immediately.The largest absolute Seebeck coefficient 580.10 ?V/oC and the largest power factor 9.97×10-2 mWm-1K-2 was obtained at 72 oC with ionic liquid of 3.00 wt% as EGCFRC curing after pretreatment.