【作者】 黄荣进；

【导师】 李来风；

【作者基本信息】 中国科学院研究生院（理化技术研究所） ， 凝聚态物理， 2009， 博士

【摘要】 针对低温工程和航空航天领域诸方面对材料热膨胀性能的特殊要求,探索了在低温区具有优良负热膨胀性能的掺杂锰铜基氮化物材料,探讨了宽温区负热膨胀行为的机理,并将所发现的在低温区具有优良负热膨胀性能的材料进行了应用初探。以Mn3CuN材料为基础,设计并制备了五种掺杂锰铜基氮化物,包括:Mn3(Cu0.6Ge0.4)N1-xCx , Mn3(Cu0.8-xAgxGe0.2)N , Mn3(Cu0.6-xNixGe0.4)N ,Mn3(Cu0.6SixGe0.4-x)N和Mn3(Cu0.5SixGe0.5-x)N。采用X射线衍射仪和热膨胀测试仪分别测试了样品的物相结构和热膨胀性能,分析了热膨胀性能与掺杂元素种类和含量的关系。研究结果表明Mn3(Cu0.6Ge0.4)N1-xCx材料的负热膨胀温区可以通过C元素含量来调节,而负热膨胀温区宽度和负热膨胀温区内线膨胀率?L/L(300K)变化量基本不受C元素的影响;随Ag元素的增加,Mn3(Cu0.8-xAgxGe0.2)N材料负热膨胀温区向高温区移动,负热膨胀温区内线膨胀率?L/L(300K)变化量减小,对负热膨胀温区的宽度几乎没有影响;同时用Ge和Ni元素部分替代Mn3CuN中的Cu元素后,样品中出现Mn-Ni第二相。Ni元素可以有效地使负热膨胀温区向低温移动,但对负热膨胀温区的宽度几乎没有影响。Mn-Ni第二相导致负热膨胀温区内线膨胀率?L/L(300K)变化量随Ni元素的增加而减小,最终得到“零膨胀”材料;随Si元素的增加,Mn3(Cu0.6SixGe0.4-x)N材料负热膨胀温区宽度增加,在负热膨胀温区内线膨胀率?L/L(300K)变化量受Si元素影响而略微减小。其中,Mn3(Cu0.6Si0.15Ge0.25)N样品的负热膨胀温区为90-190K,负热膨胀温区宽度可达100K,热膨胀系数为-16×10-6K-1;随着Si元素的增加,Mn3(Cu0.5SixGe0.5-x)N(x=0.1, 0.15)材料在室温到液氮温度温区内的平均膨胀系数较小,分别为:1.3×10-6K-1和1.65×10-6K-1。这些在低温区性能优良的负热膨胀、零膨胀和低热膨胀材料的发现为解决低温工程中热膨胀问题和促进低温工程进一步发展奠定了基础。基于对负热膨胀温区较宽样品的变温原位XRD、磁化率和比热等测试结果,分析了宽温区负热膨胀行为的机理。研究结果表明:Mn3(Cu0.6SixGe0.4-x)N材料在负热膨胀温区内会发生磁相变,磁相变类型随Si和Ge含量变化而变化,Mn3(Cu0.6Si0.15Ge0.25)N材料表现出典型的自旋玻璃特征。结合理论分析认为:硅元素分布微观不均匀性导致了自旋玻璃出现,而自旋玻璃是宽温区负热膨胀行为的内在原因。对此机理的认识为进一步研究开发出负热膨胀温区更宽的材料提供理论依据和实验指导。用机械球磨法将Mn3(Cu0.6Si0.15Ge0.25)N材料制备成纳米粉末,经等离子有机表面改性后与环氧树脂复合,调节其膨胀系数和热导率。研究结果表明:Mn3(Cu0.6Si0.15Ge0.25)N负热膨胀材料与环氧树脂复合可以有效地降低热膨胀系数和提高导热能力。其中,Mn3(Cu0.6Si0.15Ge0.25)N体积百分比为32%时,复合材料在Mn3(Cu0.6Si0.15Ge0.25)N材料负热膨胀出现的温区的平均膨胀系数达到了22×10-6K-1,比纯环氧树脂平均膨胀系数(37.9×10-6K-1)减小了42%。复合材料在室温和液氮温度时热导率分别为:0.48 W(m·K)-1和0.28 W(m·K)-1,分别是纯环氧树脂在温室和液氮温度热导率的2.8倍和4倍。此应用研究为解决低温工程中的热膨胀问题提供了新思路。更多还原

【Abstract】 Due to the special requirements for thermal expansion properties in cryogenic engineering and space technology, doped manganese nitride materials with excellent negative thermal expansion (NTE) properties at cryogenic temperatures have been explored, and the mechanism of the broadening of the NTE operation-temperature window has been investigated. Moreover, application studies on doped manganese nitride materials with excellent negative thermal expansion properties at cryogenic temperatures have been also carried out.Based on the Mn3CuN, a series of doped manganese nitride materials, including Mn3(Cu0.6Ge0.4)N1-xCx, Mn3(Cu0.8-xAgxGe0.2)N, Mn3(Cu0.6-xNixGe0.4)N, Mn3(Cu0.6SixGe0.4-x)N and Mn3(Cu0.5SixGe0.5-x)N, were designed and prepared. Their crystal structures and thermal expansion properties were investigated, and the relationship between thermal expansion properties and doping element was discussed. The results show that (1) The NTE operation-temperature window of Mn3(Cu0.6Ge0.4)N1-xCx shifts toward lower temperature region with increasing C content, but the width of NTE operation-temperature window (?T) and the change value of ?L/L(300K) in the NTE operation-temperature window are independent of C. (2) The NTE operation-temperature window of Mn3(Cu0.8-xAgxGe0.2)N shifts toward higher temperature region and the change value of ?L/L(300K) in the NTE operation-temperature window decreases with increasing Ag content, ?T is independent of Ag. (3) The second phase of Mn-Ni alloy appears in the Ni and Ge co-doped manganese nitride materials. The NTE operation-temperature window shifts toward lower temperature region with increasing Ni content and ?T is independent of Ni. The change value of ?L/L(300K) in the NTE operation-temperature window decreases and results to zero with increasing Ni content. (4) The ?T of Mn3(Cu0.6SixGe0.4-x)N increases with increasing Si content. Especially for Mn3(Cu0.6Si0.15Ge0.25)N, the temperature range of NTE behavior of is 90-190K (?T=100K), coefficient of thermal expansion (CTE) is -16×10-6K-1. (5) The average CTEs of Mn3(Cu0.5SixGe0.5-x)N(x=0.1, 0.15) in the temperature range of room temperature to liquid nitrogen temperature are very small, which are 1.3×10-6K-1 and 1.65×10-6K-1 , respectively. The discoveries of nearly zero and negative thermal expansion materials prepare the ground for further development of cryogenic engineering.The mechanism of the broadening of the NTE operation-temperature window was investigated though situ X-ray diffraction, magnetic susceptibility and special heat experiments. The results show that magnetic phase transition appears in the NTE operation-temperature window, and the type of magnetic phase transition gradually changes with increasing Si content. Mn3(Cu0.6Si0.15Ge0.25)N shows a typical characteristic of spin-glass systems. After theoretical analysis, it is concluded that spin-glass which results from the hyperdispersion of Si at micro scale is the reason for the broadening of the NTE operation-temperature window. This investigation provides theoretical and experimental foundations for exploring new NTE materials with broader NTE operation-temperature window.The composite materials made from nano-Mn3(Cu0.6Si0.15Ge0.25)N modified by a plasma treatment and epoxy resin were prepared. Their thermal expansion properties and thermal conductivities were investigated. The results show that the addition of Mn3(Cu0.6Si0.15Ge0.25)N can significantly decrease CTE and increase thermal conductivity. The average CTE of composite contains 32vol% Mn3(Cu0.6Si0.15Ge0.25)N is 22×10-6K-1 in the temperature range of 190-77 K, which is 42% lower than that of pure epoxy resin. The thermal conductivities are 0.48 W(m·K)-1 at 298K and 0.28 W(m·K)-1 at 77K, respectively, which are 2.8 and 4 times as large as that of pure epoxy resin, respectively. This application study provides a new method for resolving thermal expansion problem and simultaneously improving thermal conductivity of materials in cryogenic engineering.更多还原