Presciutti Federica, Capitani Donatella, Sgamellotti Antonio, Brunetti Brunetto Giovanni, Costantino Ferdinando, Viel Stéphane, Segre Annalaura
Chemistry Department and Center SMAArt, University of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy.
J Phys Chem B. 2005 Dec 1;109(47):22147-58. doi: 10.1021/jp0536091.
The aim of this study is to clarify the structure of an iron-rich clay and the structural changes involved in the firing process as a preliminary step to get information on ancient ceramic technology. To this purpose, illite-rich clay samples fired at different temperatures were characterized using a multitechnique approach, i.e., by electron paramagnetic resonance, scanning electron microscopy with electron dispersion X-ray spectrometry, X-ray powder diffraction, magic angle spinning and multiple quantum magic angle spinning NMR. During firing, four main reaction processes occur: dehydration, dehydroxylation, structural breakdown, and recrystallization. When the results are combined from all characterization methods, the following conclusions could be obtained. Interlayer H2O is located close to aluminum in octahedral sites and is driven off at temperatures lower than 600 degrees C. Between 600 and 700 degrees C dehydroxylation occurs whereas, between 800 and 900 degrees C, the aluminum in octahedral sites disappears, due to the breakdown of the illite structure, and all iron present is oxidized to Fe3+. In samples fired at 1000 and 1100 degrees C iron clustering was observed as well as large single crystals of iron with the occurrence of ferro- or ferrimagnetic effects. Below 900 degrees C the aluminum in octahedral sites presents a continuous distribution of chemical shift, suggesting the presence of slightly distorted sites. Finally, over the whole temperature range, the presence of at least two tetrahedral aluminum sites was revealed, characterized by different values of the quadrupolar coupling constant.
本研究的目的是阐明富铁粘土的结构以及烧制过程中发生的结构变化，作为获取古代陶瓷技术信息的初步步骤。为此，采用多技术方法对在不同温度下烧制的富含伊利石的粘土样品进行了表征，即通过电子顺磁共振、带有能量色散X射线光谱仪的扫描电子显微镜、X射线粉末衍射、魔角旋转和多量子魔角旋转核磁共振。在烧制过程中，会发生四个主要反应过程：脱水、脱羟基、结构破坏和重结晶。当综合所有表征方法的结果时，可以得出以下结论。层间H2O位于八面体位置中靠近铝的位置，并在低于600摄氏度的温度下被驱除。在600至700摄氏度之间发生脱羟基反应，而在800至900摄氏度之间，由于伊利石结构的破坏，八面体位置中的铝消失，并且所有存在的铁都被氧化为Fe3+。在1000和1100摄氏度下烧制的样品中观察到铁聚集以及具有铁磁或亚铁磁效应的大铁单晶。在900摄氏度以下，八面体位置中的铝呈现出化学位移的连续分布，表明存在轻微扭曲的位置。最后，在整个温度范围内，揭示了至少两个四面体铝位置的存在，其特征在于四极耦合常数的不同值。
