碱-热环境下MX80膨润土导热性能试验研究

Experimental study on thermal conductivity of MX80 bentonite under alkali-thermal environment

以美国怀俄明州钠基(MX80)膨润土为研究对象,采用热探针法测定碱-热环境下MX80膨润土的导热系数,探讨了温度、碱液强度和干密度对试样导热系数λ的影响规律,并选择部分试样进行了X射线衍射(X-raydiffraction,简称XRD)和扫描电镜(scanning electron microscope,简称SEM)试验,揭示了碱-热环境下MX80膨润土导热性能演变的微观机制。试验结果表明:MX80膨润土的导热系数λ随碱液含量和干密度的递增而增大;在不同碱液含量条件下,膨润土的导热系数均随温度升高而增大,且碱液含量越高,导热系数的温度效应越显著;干密度较小时,膨润土导热系数λ随温度升高而增大的影响越明显,主要原因是温度促进了试样内部的水汽潜热传输;同一温度和干密度条件下,热传导系数λ随着碱液pH值的升高而降低,且pH值越高,则λ降幅越明显,主要原因是强碱溶液腐蚀了膨润土的蒙脱石成分,减少了试样内石英含量,增大了膨润土试样的孔隙率,进而降低了膨润土导热系数,这与测试试样的XRD和SEM结果相吻合。

To analyze the effect of various factors such as temperature, strength of alkali solution and dry density on the thermal conductivity of bentonite, thermal conductivity of MX80 bentonite in alkali-thermal environment was measured by a thermal probe method. Meanwhile, the X-ray diffraction(XRD) and scanning electron microscopy(SEM) tests were carried out on selected samples to reveal the micro-mechanism of thermal conductivity evolution of MX80 bentonite under alkaline and thermal environment. The results show that the thermal conductivity of MX80 bentonite increases with the increase of alkali solution content and dry density.The thermal conductivity of bentonite increases with the increase of temperature under different content conditions, and the higher alkali solution content is, the more significant the temperature effect of thermal conductivity is. When the dry density is small, the influence of thermal conductivity λ of bentonite increases with the increase of temperature. The main reason is that temperature facilitates the latent heat transfer of water vapor inside the sample. At the same dry density and temperature, the thermal conductivity decreases with the increase of pH value, the higher the pH value is, the greater the decrease range of λ is. The main reason is that the strong alkali solution erodes the montmorillonite and quartz of bentonite, increases the porosity of bentonite, thereby reduces the thermal conductivity of bentonite, which is consistent with the XRD and SEM image results of the tested samples.