基于实验模拟的月壤热导率空间分布特征研究

The spatial variation of thermal conductivity of lunar s soil and its controlling factors are important contents of lunar surface environment researches. Previous studies have shown that, under vacuum condition like lunar surface, factors including temperature, density and grain size affect significantly the thermal conductivity of powder materials. However, thermal conductivities of the main minerals in lunar soil have neither been studied, nor the coupled effect of density and grain size on thermal conductivity of powder materials is clear, which make it difficult to understand and predict the horizontal and vertical distribution of thermal conductivity of lunar soil. To solve these problems, pyroxene, olivine, plagioclase, ilmenite which are main minerals in lunar soil and simulated lunar soil will be chosen in this proposed study. By measuring the thermal conductivities of powder samples of different densities and grain sizes, the coupled effect of density and grain size on thermal conductivity would be revealed. Then a comprehensive model of thermal conductivity of lunar soil including mineral composition, density and grain size would be proposed when considering the thermal conductivity’s differences among these minerals. Finally, based on this model, the horizontal and vertical distribution of thermal conductivity of lunar soil would be obtained with the published data of mineral composition and temperature on lunar surface. The results of this project will provide experimental reference to some scientific problems on moon such as interpreting thermal infrared and microwave data, inferring the composition and thickness of soil, calculating the temperature and heat flow in surface/subsurface layer.

月壤热导率的空间变化及影响因素分析是月球表面热环境研究的重要内容之一。已有研究表明，月表真空环境下颗粒物质的热导率受到温度、密度、粒径等因素的影响。但尚未有研究针对月壤中的主要单矿物粉末进行分析，另外对热导率与密度和粒径的耦合关系的认识也含混不清，这对于理解和预测月壤热导率在空间上的变化非常不利。针对以上问题，本项目以辉石、橄榄石、斜长石、钛铁矿等月表主要矿物的粉末以及模拟月壤为研究对象，在真空环境下测量不同粉末样品的热导率，揭示密度和粒径对单矿物粉末样品热导率的耦合影响。在此基础上，考虑矿物间热导率的差异，建立以矿物含量、密度和粒径为变量的综合定量模型。最后，结合已有的月壤矿物组成数据和粉末样品热导率与温度的关系，利用该模型得到月壤热导率在空间上的分布规律。本项目的结果将为准确解译热红外和微波数据、反演月壤矿物成分和厚度、计算表层/次表层温度和热流等科学问题提供重要的实验依据。

月壤主要矿物及模拟月壤在真空条件下的热导率测量，可使我们获得较为真实可靠的月表热导率数据，为我们研究月表物质热导率的分布和月表温度，解译月球微波探测数据，开展月球探测载荷设计，建立月球基地奠定重要的研究基础。本研究主要采用改造后的HOT DISK TPS 2500S导热仪对月壤主要组成矿物的热导率进行测量，包括6种不同粒径的辉石、橄榄石、斜长石、钛铁矿的粉末样品，及由中科院地球化学研究所研制的CLRS-1和CLRS-2模拟月壤样品，获取了可靠的热导率实测数据。同时，分析了矿物组分、真空度、温度、粒度、密度等因素对月壤热导率的影响，为研究月表物质热导率的分布及解译微波亮温数据提供了重要的输入参数。通过实验分析发现，月壤中主要矿物的热导率之间存在着一定的差异，且随粒度、密度、温度和真空度的变化而变化，具体表现为：1) 在真空条件下，月壤中三种硅酸盐矿物的热导率差异非常小，钛铁矿的热导率相对硅酸盐矿物的热导率较大，接近0.01 W/(m·K)；2) 热导率随矿物颗粒粒径的增大而增大；3)热导率与密度呈正相关系；4)在温度小于300K时，热导率随着温度的增加呈缓慢上升趋势，温度大于300K以后热导率随温度的增加出现快速上升趋势；5)热导率随着大气压力的下降呈下降趋势，大气压力在500Pa以下时，热导率的变化趋于平缓，其原因是空气传导在热传导过程中的作用几乎可以忽略。由以上热导率随各种影响因素的变化规律，我们提出一个新的热导率关于温度、矿物成分和密度的数学模型，并由此模型给出了月球表面月壤热导率的分布。