Experimental Study On Electrochemical Properties Of Soil Affected By Temperature

In this paper,the distribution of resistivity and electrochemical properties of silty soil and sand samples at different temperatures was studied by laboratory experiments.Analyzed the electrochemical equivalent circuit and variation of the components after fitting,the influence of temperature on soil circuit parameters is revealed.Combined with water content,the influence mechanism of temperature on the electrochemical properties of soil under different water content is studied.The influence of temperature on the electrochemical properties of silty soil and sand are follows:Nyquist curves of the two soils at different temperatures display two arcs of the high frequency area and the middle frequency area,and a spread oblique line in the low frequency area.As the temperature reduce,the radius of both arcs increases,the image moves to the right;the Bode curves display the rapid decline of the low frequency area and the high frequency area,the slow phase of the middle frequency area,and the curves moves upward as the temperature decreases.Comparing silty soil and sand Nyquist curves,at the same temperature,the arc radius of silty soil in high frequency and middle frequency is smaller than sand.The intersection point of high frequency arcs of silty soil and abscissa Z'is less than that of sand;Compare the Bode curves,at the same temperature,the impedance modulus of sand is greater than silty soil.By analyzing the electrochemical impedance spectroscopy image,the equivalent circuit of silty soil and sand at different temperatures contains six electrochemical components,which are solution resistance,charge transfer resistance,the constant phase angle element,resistance of porous layer,capacitance of porous layer and diffusion resistance.The charge transfer resistance is series with the diffusion resistance and parallel with the constant phase angle element.Series with the resistance of porous layer and parallel with the porous layer capacitive,and then series with solution resistance.The equivalent circuit expression is R_e(C_l(R_l(Q(R_tW))))).Analyzed two kind of soils the variation of components parameter after fitting.Found that the solution resistance,resistance of porous layer and charge transfer resistance in equivalent circuit increase with the decrease of temperature.Double layer capacitance of the constant phase angle element increases with the temperature increase.The reason is as the temperature increases,the rate of electrode reacts increases,the transfer of electric charge in soil increases rapidly.Lead to the value of the resistance elements in the equivalent circuit decreases with temperature increase.Double layer capacitance of the constant phase angle element value increases with temperature because in the silty system,as the temperature increases,the ions in soil become more active,so the electric quantity of the electric double layer increases,and the double layer capacitance value becomes larger.Comparing and analyzing the equivalent circuit parameters of the two soils at the same temperature,the solution resistance and double layer capacitance of the silty soil are larger than sand,and the resistance of porous layer and charge transfer resistance are smaller than the sand.The reason is sand saturation is greater than silty soil,so the solution resistance of the sand is smaller than silty soil;silty soil particle size is smaller than sand lead to the bound water film area around silty soil is larger than sand,so the electric double layer electric quantity is more than sand.Because the contact area between sand and electrode is smaller than silty soil,and the insulating film on the contact area is larger than the silty soil,the resistance of porous layer of sand is larger than silty soil.The complexity of charge transfer in two kinds of soil leads to the sand charge transfer resistance is greater than silty soil.Comparing and analyzing the electrochemical impedance spectroscopy of two soils under different water contents,as the water content increases,the two arcs in the Nyquist curves become smaller and the curves moves to the left,the Bode curves moves down.As the water content increases,the solution resistance,resistance of porous layer,and charge transfer resistance in the silty soil and sand are reduced,and the electric double layer capacitance value increase.The reason is that as the water content increases,the internal void solution of the soil increases,the charge resistance decreases,so the solution resistance decreases.The soil water contents increases leads to the contact between electrode and soil particles better.The void between the contact surfaces are reduced,the conductive area is increased,so the resistance of porous layer is reduced.The water content increased so the saturation increased,charge diffusion rate at the solid-liquid interface is increased,and the electric double layer is increased,the capacitance value increases.As the content of free water and bound water in soil increases,the thickness of water film around soil particles increases,makes charge transfer easier,the charge transfer resistance decreases.