ZnMgO/ZnO Interface Structure And Thermoelectric Properties Of Cement-based Composites

Thermoelectric properties of Expanded Graphite/Carbon Fiber Reinforced Cement-based Composites?EGCFRC?are used primarily to alleviate urban heat island effects,reduce building energy consumption,and decrease road heat and snow removal.In the future,EGCFRC has the greatest extensive development prospects.Whereas owing to the low thermoelectric conversion efficiency of cement-based composites caused by the coupling relationship between the Seebeck effect and conductivity of EGCFRC,the applications of cement-based composites are restricted by the low thermoelectric figure of merit?ZT?.However,in this paper,the ZnMgO/ZnO thin film with excellent surface structure on the surface of carbon fiber?CF@ZnO@ZnMgO?was firstly prepared by sol-gel method.Then,CF@ZnO@ZnMgO and expanded graphite were mixed into the cement matrix to investigate analyse consider deliberate the effects of ZnMgO/ZnO heterogeneous interface structures and dosages of CF@ZnO@ZnMgO on the thermoelectric properties of EGCFRC.The strengthening mechanism of ZnMgO/ZnO heterostructure on the thermoelectric properties of cement-based composites was investigated.The main research contents are presented as following:?1?The effect of sol concentration?0.05,0.1,0.15,0.3,0.5 mol/L?,annealing temperature?400,500,600°C?,impregnation conditions?impregnation once or twice?and Mg/Zn molar ratio?Mg/Zn=0.20,0.40,0.60?on the microstructure of ZnMgO/ZnO two-dimensional electron gas films was discussed.Those results show that ZnO film and the ZnMgO film were hexagonal wurtzite structure.The ZnMgO film had a preferred orientation at?002?.The surface particles of the ZnMgO/ZnO heterogeneous film were uniform and dense,and the film thickness was measured to be about 2?m.As a result,the morphology of ZnMgO/ZnO film formed on carbon fiber was uniform and compact,and it has excellent electrical conductivity when ZnO and Zn_0.83Mg_0.17O sol concentration is 0.1 mol/L and heat treatment temperature is 500°C.The double impregnation can make up for the pores of the particles formed by once impregnation,and the film performance was more excellent.In summary,0.1 mol/L concentration of the ZnO and Zn_0.83Mg_0.17O sol can be anneal at 500°C after secondary impregnation to form the best ZnMgO/ZnO two-dimensional electron gas heterogeneous film on the carbon fiber surface.?2?The effect of ZnMgO/ZnO heterogeneous interface structures on the thermoelectric properties of EGCFRC was studied,and investigating the effect of high alkaline environment for the microstructure of ZnMgO/ZnO thin film on carbon fibers.The results show that compared with CF@ZnO@ZnMgO with sol concentration of 0.05mol/L and 0.15 mol/L,when the sol concentration is 0.1 mol/L,the ZnMgO/ZnO film on the surface of carbon fiber is smooth and compact,and the thermoelectric performance is the best.The Seebeck coefficient of EGCFRC decreases with increasing temperature,achieving a maximum of 43 mV/^oC at 40 ^oC,and the conductivity of0.1×10^-4S/cm,The maximum power factor 0.8?Wm^-1K^-22 and ZT value 1.3×10^-4were obtained,which is 2-3 orders of magnitude higher than the EGCFRC power factor and ZT value of 0.05 mol/L and 0.15 mol/L.After simulating the hydration conditions,it was found that the high alkaline environment had little effect on the microstructure of the ZnMgO/ZnO film on the carbon fiber in EGCFRC,which was negligible.?3?The effect of CF@ZnO@ZnMgO in the matrix?0.5,0.8,1.2 and 1.5 wt.%?on the thermoelectric properties of EGCFRC was investigated.The results show that when the amount of CF@ZnO@ZnMgO is 0.5-1.5 wt.%,the Seebeck coefficient is negative and belongs to n-type semiconductor.When the content of CF@ZnO@ZnMgO is 1.5wt.%,EGCFRC has the best thermoelectric performance.The Seebeck coefficient decreases with temperature from 35 to 50 ^oC and then stabilizes with the increase of temperature,reaching-32.5?V/^oC,the conductivity is 0.663 S/cm,and the carrier mobility is maximized?8.32 cm²/V·s?.The power factor and ZT value of EGCFRC were decreased with increasing temperature.The power factor was decreased from 0.13?Wm^-1K^-22 to 0.067?Wm^-1K^-22 and the ZT value was reduced from 2.1×10^-55 to 1.12×10^-5.However,both the power factor and the ZT value were larger than the EGCFRC with0.5,0.8,and 1.2 wt.%.