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，陶器以工艺和艺术品的形式在日常和文化生活中发挥着重要作用。陶器是通过在高达1400°C的温度下烧制粘土和各种矿物添加剂而生产的，其中陶瓷绿色体中的矿物通过不同的颗粒间和颗粒内转化反应转化为新的相组合。了解反应顺序以及微观结构、相组合和块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陶瓷材料至关重要。考古学也需要这样的知识，例如，重建古代陶器生产技术。现代最先进的共焦拉曼光谱仪系统主要允许原位（即，当它们进行时）矿物反应和纹理的二维成像，并且因此允许研究各种热烧结反应的机制。此外，热力学和动力学信息的生长和不同的阶段，包括亚稳相的崩溃，可以得到一个高的温度和时间分辨率。据申请人所知，共焦高光谱拉曼光谱（CHRS）的成像能力尚未用于研究高温固-固或固-熔反应。在本申请中，通过第一实验的结果给出了这种研究的概念证明，该第一实验被设计成在~750 ° C和1150°C之间的温度下对高岭石-长石-石英-方解石基绿色坯体中的烧结反应进行成像。CHRS成像允许可视化随着温度的升高，钙铝黄长石，硅灰石，钙长石和假硅灰石之间的纹理关系的演变。CHRS的烧结反应原位调查的巨大潜力进一步扩大的可能性，图像中的18-O的分布，并在不同的阶段，在微米级时，使用18-O标记的前体反应物。通过振动光谱分析凝聚态物质中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。在本项目中，它的目的是系统地研究，为第一次，在原位高温烧结反应的两相系统，以及在合成混合高岭土为基础的绿色机构的CHRS成像使用18-O-标记的方解石或石英作为同位素示踪反应物。

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.