Synthesis, Characterization, and Modeling of the Mn+1AXn Layered Ternary Carbides and Nitrides

Mn 1AXn 层状三元碳化物和氮化物的合成、表征和建模

• 批准号: 0072067
• 负责人: Michel Barsoum
• 金额: --
• 依托单位: Drexel University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0072067&HistoricalAwards=false
• 关键词: Synthesis; Characterization; Modeling; Mn+1AXn; Layered

In recent years, the PI has identified a new class of ceramic material best described as polycrystalline nanolaminates. These solids are ternary layered hexagonal carbides and nitrides with the general formula, M n+1 AX n , where n = 1 to 3, M is an early transition metal, A is an A-group element and X is either carbon and/or nitrogen. To date 15 of the roughly 50 phases known to exist have been synthesized and characterized. These phases share many of the advantageous attributes of their respective stoichiometric binary metal carbides or nitrides: they are elastically stiff, electrically and thermally conductive. Mechanically, however, they cannot be more different: they are readily machinable, relatively soft, resistant to thermal shock and unusually damage tolerant. They combine ease of machinability with good mechanical properties, especially at T 1000 degrees C. Furthermore, they couple thermal isotropy with mechanical anisotropy. This unusual combination of properties is traceable to their layered structure, the metallic-covalent nature of the MX bonds that are exceptionally strong, together with M-A bonds that are relatively weak, especially in shear. The best-characterized ternary to date is Ti3 SiC2. Despite clear progress in understanding these solids several fundamental issues remain unresolved. Primary amongst them are: i) the physical origin of the brittle-to-plastic transition that occurs at approximately 1100 degrees C in many of these systems; ii) the nature of a solid-solution softening effect observed at higher temperatures in Ti 2 AlN0.5C0.5 ; iii) the relationship between the bonding and the single crystal elastic constants and the electrical and thermal properties. This research project will synthesize and characterize most of the 35 or so ternaries that have never been synthesized before in an attempt to understand their structure-properties-bonding relationships. The fabrication and characterization will take place in the PI's laboratory at Drexel. To carry out the theoretical modeling of the structure, the PI has teamed with the Russian team headed by Dr. Nadia Medvedeva who recently published an excellent paper on the full potential linear-muffin-tin orbital calculations of Ti3 SiC2 and its solid solutions. The ultimate goal is to refine the theoretical model to allow for the prediction of the elastic, thermal and electrical properties. A new class of ceramic material that can be classified as nano-laminates has been explored by the PI. These materials combine some of the better thermal, chemical, electrical and elastic characteristics of ceramics, with few of their drawbacks, such as brittleness. Because of these unusual properties, these ceramic materials are likely to have a broad technological impact.

近年来，PI确定了一类新的陶瓷材料，最能将其描述为多晶纳米胺。 这些固体是三元层的六边形碳化物和氮化物，具有通用公式，m n+1 ax n，其中n = 1至3，m是早期过渡金属，A是A组元素，X是碳和/或氮。 迄今为止，已知存在的大约50个阶段中的15个已经合成和表征。 这些阶段具有其各自的化学计量二进制金属碳化物或硝酸盐的许多有利属性：它们具有弹性僵硬，电气和热传导性。 然而，机械上，它们不能更加不同：它们很容易发动，相对较软，对热冲击和异常损害的耐受性。 它们将可加工性的易于性与良好的机械性能相结合，尤其是在T 1000度的C.此外，它们将热在各向同性与机械各向异性融为一体。 这种不寻常的性质组合可以追溯到其分层结构，即MX键的金属共价性质，它们与相对较弱的M-A键一起，尤其是在剪切中。 迄今为止，特征最佳的三元是TI3 SIC2。 尽管在理解这些固体方面取得了明显进展，但几个基本问​​题仍未解决。 其中的主要是：i）在许多此类系统中，脆性到塑料过渡的物理起源大约在1100度C上发生； ii）在Ti 2 Aln0.5C0.5中观察到的固定溶液软化效应的性质； iii）粘结与单晶体弹性常数以及电和热性能之间的关系。 该研究项目将综合并表征从未合成的35个左右的三元，以了解其结构 - 构成关系的关系。 制造和表征将在Drexel的PI实验室中进行。 为了进行结构的理论建模，PI与Nadia Medvedeva博士领导的俄罗斯团队合作，该团队最近发表了一篇出色的论文，内容涉及TI3 SIC2及其固体解决方案的全部潜在线性 - 无纤维纤维锡轨道计算。 最终目标是完善理论模型，以预测弹性，热和电性能。 PI探索了一类新的可以将其归类为纳米层的陶瓷材料。这些材料结合了陶瓷的一些更好的热，化学，电气和弹性特征，以及它们的弊端很少，例如脆性。 由于这些异常的特性，这些陶瓷材料可能会产生广泛的技术影响。