Collaborative Research: A New Mechanism for Metal Isotope Fractionation Induced by Natural Solid-State Ion Conduction

合作研究：天然固态离子传导诱导金属同位素分馏的新机制

• 批准号: 2025320
• 负责人: Ryan Mathur
• 金额: $ 5.97万
• 依托单位: Juniata College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-01 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2025320&HistoricalAwards=false
• 关键词: Collaborative; Research; New; Mechanism; Metal

Naturally occurring metallic silver is sometimes found with a wire-, string- or rope-like morphology, commonly called “wire silver”. Until recently, very little was known about the structural characteristics of wire silver and even less about how it forms. Surprisingly, this morphology can be created in the laboratory under simple conditions very different from those found in nature, yet their structural characteristics are very similar to natural samples. From the study of natural and synthetic specimens, it has been found that wire silver formation occurs by a solid-state process called “ion conduction”, where metal ions can move directly through a crystal structure, and in this case, silver(I) ions move through the mineral argentite. Even more surprising, this ion transport during wire growth causes an enrichment of the heavy stable isotope 109Ag in the wire. This is opposite of that predicted by mechanisms of isotope enrichment known to occur in nature. Thus, further study of wire silver growth may elucidate a previously unrecognized mechanism for isotope separation in nature. Understanding this mechanism and the degree of possible isotope enrichment is significant for our basic understanding of physical and chemical phenomena. These in turn have direct application to the study of geochemical and geological processes such as metal transport and the isotopic signatures found in ore deposits. Broader impacts include possible technological applications where the isotope chemistry of materials can affect their physical properties. This study involves scientists from multiple academic departments and different disciplines, and will include student training and participation at multiple levels, from undergraduates through doctoral candidates. This project integrates experimental mineralogy, analytical geochemistry and computational methods in the study of wire silver formation under highly controlled conditions as a means to elucidate the fundamental mechanism of the observed isotope effect. Isotope fractionation is hypothesized to result from the process of predissociation during superionic conduction, occurring preferentially for 109Ag+ ions as they move through the silver sulfide structure. The study will also test whether this isotope effect extends to other transition metals such as copper, zinc and nickel. Understanding the mechanisms, magnitude and direction of isotope fractionation is essential for the use and accurate interpretation of isotope data in geological studies, and allows for the engineered development of materials with “tuned” isotope chemistries. Finally, this unexploited physical phenomenon might be leveraged to improve the characteristics of technological devices that utilize fast ion conduction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

天然存在的金属银有时具有线状、绳状或绳状形态，通常称为“线银”。直到最近，人们对银丝的结构特征知之甚少，对其形成方式更是知之甚少。令人惊讶的是，这种形态可以在实验室中在与自然界中发现的条件非常不同的简单条件下产生，但它们的结构特征与天然样品非常相似。通过对天然和合成标本的研究，发现银线的形成是通过称为“离子传导”的固态过程发生的，其中金属离子可以直接穿过晶体结构，在这种情况下，银（I）离子穿过矿物银矿。更令人惊讶的是，线生长过程中的离子传输导致线中重稳定同位素 109Ag 的富集。这与已知自然界中发生的同位素富集机制所预测的相反。因此，对银丝生长的进一步研究可能会阐明以前未被认识的自然界同位素分离机制。了解这种机制以及可能的同位素富集程度对于我们对物理和化学现象的基本理解具有重要意义。这些反过来又直接应用于地球化学和地质过程的研究，例如金属迁移和矿床中发现的同位素特征。更广泛的影响包括可能的技术应用，其中材料的同位素化学会影响其物理特性。这项研究涉及来自多个学术部门和不同学科的科学家，并将包括从本科生到博士生的多个级别的学生培训和参与。 该项目将实验矿物学、分析地球化学和计算方法整合到高度受控条件下的线银形成研究中，作为阐明所观察到的同位素效应的基本机制的手段。假设同位素分馏是由超离子传导过程中的预解离过程引起的，当 109Ag+ 离子穿过硫化银结构时，优先发生这种现象。该研究还将测试这种同位素效应是否延伸到其他过渡金属，如铜、锌和镍。了解同位素分馏的机制、大小和方向对于地质研究中同位素数据的使用和准确解释至关重要，并且可以对具有“调整”同位素化学性质的材料进行工程开发。最后，这种未开发的物理现象可用于改善利用快离子传导的技术设备的特性。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。