RUI: Collaborative Research: Redox Ratios by Fe-XANES

RUI：合作研究：Fe-XANES 的氧化还原比

• 批准号: 0809459
• 负责人: Melinda Dyar
• 金额: $ 10.49万
• 依托单位: Mount Holyoke College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809459&HistoricalAwards=false
• 关键词: RUI; Collaborative; Research; Redox; Ratios

Of all the common elements in the Earth's crust, iron is the only element that occurs in multiple valence states; it can be found as a pure Fe(0) metal, as Fe(II), or as Fe(III). The valence state of iron thus reflects the amount of oxygen that was present in the environment at the time the mineral crystallized. The amount of oxygen in turn affects how a magma may crystallize: which minerals will form, and in what order. For this reason, measuring the oxidation state of Fe is extremely important in all rock types in which the minerals occur in equilibrium. The valence state of Fe thus serves as a recorder of the evolution of oxygen in the Earth's interior and on its surface. It is also useful in identifying geological formations of economic interest (for example, garnets in diamond-bearing deposits are usually oxidized). The ability to measure Fe valence state is also useful in understanding chemical reactions that control industrial processing of minerals, chemical and metallurgical engineering, recycling of materials, and even the study of health effects and mineralogy.Historically, it has been very difficult to measure the valence state of Fe in minerals quantitatively. Traditional wet chemistry methods have been used for a half-century, but they require large masses of sample (1 g) and these are difficult to prepare from rocks that may contain intimate mixtures of fine-grained minerals. Mössbauer spectroscopy is another bulk technique that has more recently been used for measurements of Fe, but it also requires 20 mg of sample. Microfocused X-ray Absorption Near-Edge Spectroscopy (XANES) presents a promising technology for making Fe3+/total Fe measurements on small spots (8-30 microns) on mineral grains. This technique utilizes the observation that the energy of the Fe K absorption edge and the absorption pre-edge feature found ~15-20 eV below the edge are very sensitive to the oxidation state of Fe. Past measurements of Fe3+/total Fe by this technique have been only semi-quantitative, but recent upgrades at the hard x-ray microprobe beamline x26a at the National Synchrotron Light Source (higher beam intensity and improved energy resolution available from a Si(311) monochromator) have remedied these issues. Thus, the ambitious goal of this proposal is to develop the XANES technique for use as a quantitative microprobe method for analysis of Fe(II) and Fe(III) in minerals.

在地壳的所有常见元素中，铁是唯一以多种价态存在的元素；它可以以纯铁(0)、铁（II）或铁（III）的形式存在。因此，铁的价态反映了矿物结晶时环境中存在的氧的数量。氧气的含量反过来又影响岩浆的结晶方式：哪些矿物质会形成，以及以何种顺序形成。因此，在矿物处于平衡状态的所有岩石类型中，测量铁的氧化态是极其重要的。因此，铁的价态可以作为地球内部和表面氧演化的记录器。它在确定具有经济价值的地质构造方面也很有用（例如，含金刚石矿床中的石榴石通常是氧化的）。测量铁价态的能力在理解控制矿物工业加工、化学和冶金工程、材料回收、甚至健康影响和矿物学研究的化学反应方面也很有用。在历史上，定量测量矿物中铁的价态是非常困难的。传统的湿化学方法已经使用了半个世纪，但是它们需要大量的样品（1克），而且这些样品很难从可能含有细颗粒矿物的密切混合物的岩石中制备。Mössbauer光谱学是最近用于测量铁的另一种批量技术，但它也需要20毫克的样品。微聚焦x射线吸收近边光谱（XANES）是一种很有前途的技术，可以在矿物颗粒上的小斑点（8-30微米）上测量Fe3+/total Fe。该技术利用了Fe - K吸收边的能量和边缘以下~15 ~ 20 eV的吸收前边特征对Fe的氧化态非常敏感的观察结果。过去用这种技术对Fe3+/总Fe的测量只是半定量的，但最近在国家同步加速器光源的硬x射线微探针光束线x26a上的升级（更高的光束强度和提高的Si（311）单色器的能量分辨率）已经解决了这些问题。因此，本提案的雄心勃勃的目标是开发XANES技术，作为定量微探针方法，用于分析矿物中的铁（II）和铁（III）。