Real-time Imaging of High-Temperature Sintering and Associated Oxygen Isotope Exchange Reactions by Confocal Hyperspectral Raman Spectroscopy

自人类最早的历史以来，陶器就以工艺和艺术品的形式在日常和文化生活中发挥了重要作用。陶器是由粘土和各种矿物添加剂在高达1400°C的温度下烧制而成，陶瓷绿体中的矿物质通过不同的颗粒间和颗粒内转变反应转变成新的相组合。了解反应顺序以及微观结构、相组合和本体材料性能之间的相互作用，对于优化生产技术和设计具有特定物理性能的新型陶瓷材料至关重要。考古学也需要这些知识，例如重建古代陶器的生产技术。现代最先进的共聚焦拉曼光谱仪系统主要允许对矿物反应和结构进行原位二维成像，即当它们进行时，从而研究各种热烧结反应的机制。此外，还可以获得不同相（包括亚稳相）生长和分解的热力学和动力学信息，具有较高的温度和时间分辨率。据申请人所知，共聚焦高光谱拉曼光谱（CHRS）的成像能力尚未用于研究高温固-固或固-熔反应。第一个实验的结果证明了这种研究的概念，该实验旨在成像高岭石-长石-石英-方解石基绿体在~750至1150°C之间的烧结反应。CHRS成像可以直观地显示辉长石、硅灰石、钙长石和伪硅灰石之间的结构关系随温度升高的演变。当使用18-O标记的前驱物时，可以在微米尺度上对不同相内和不同相间的18-O分布进行成像，这进一步扩大了CHRS在烧结反应原位研究方面的巨大潜力。用振动光谱学分析凝聚态物质中18-O含量的原理是，与振动运动相关的能量或频率取决于振动原子的质量。本项目拟首次以18- o标记方解石或石英作为同位素示踪剂，采用CHRS成像技术系统研究两相体系和合成混合高岭土绿体的原位高温烧结反应。

Since humankind's earliest history pottery has played an important role in daily and cultural life in the form of craft and art objects. Pottery is produced by firing clay with various mineral additives at temperatures of up to 1400°C, whereby the minerals in a ceramic green body transform via different inter- and intra-grain transformation reactions to a new phase assemblage. Understanding the reaction sequence and the interplay between the microstructure, the phase assemblage, and the bulk material properties is essential to optimize production technologies and design new ceramic materials with specific physical properties. Such knowledge is also needed in archaeology to, e.g., reconstruct ancient pottery production technologies. Modern state-of-the-art confocal Raman spectrometer systems principally permit two-dimensional imaging of mineral reactions and textures in situ, i.e. while they are proceeding, and thus the study of the mechanisms underlying the various thermal sintering reactions. In addition, thermodynamic and kinetic information about the growth and breakdown of distinct phases, including metastable phases, can be gained with a high temperature and time resolution. To the best of the applicants' knowledge, the imaging capability of confocal hyperspectral Raman spectroscopy (CHRS) has not yet been used to study high temperature solid-solid or solid-melt reactions. A prove of concept for such investigations is given in this application by the results of a first experiment that was designed to image sintering reactions in a kaolinite-feldspar-quartz-calcite-based green body at temperatures between ~750 and 1150°C. CHRS imaging allowed visualizing the evolution of the textural relationship between gehlenite, wollastonite, anorthite, and pseudowollastonite with increasing temperature. The great potential of CHRS for in situ investigation of sintering reactions is further expanded by the possibility to image the distribution of 18-O within and among different phases at the micrometer scale when using 18-O-labeled precursor reactants. The principle behind analyzing the 18-O content in condensed matter by vibrational spectroscopy is that the energies or frequencies associated with vibrational motions are dependent on the masses of the vibrating atoms. In the present project, it is intended to systematically study, for the first time, in situ high-temperature sintering reactions in two-phase systems as well as in synthetically blended kaolin-based green bodies by CHRS imaging using either 18-O-labeled calcite or quartz as isotope tracer reactant.