Textured kaolinite and halloysite-based materials were shaped by tape casting in order to promote the alignment of clay particles along the tape casting direction and to investigate the structure evolution of these phyllosilicates during the dehydroxylation process. The crystallinity indexes HI and R2 of the starting kaolins (KRG and KCS) were determined and appeared close to values found for the well-ordered reference kaolin KGa-1b. The halloysite clay exhibited trimodal grain size distribution and tended to be less textured than KRG and KCS according to the (002) pole figures performed on green tapes. The constant heating rate derived kinetic parameters matched the expected range. We followed the dehydroxylation of kaolinite and halloysite through in situ high-temperature X-ray diffraction measurements at the ESRF synchrotron radiation source on the D2AM beamline. The dehydroxylation of these kaolinite and halloysite occurred between 425 °C and 675 °C for KRG and KCS and from 500 °C to 650 °C for halloysite. In addition, the evolution of the basal distance of kaolinite regarding the heat treatment temperature confirmed that the dehydroxylation process occurred in three steps: delamination, dehydroxylation, and formation of metakaolinite. The calculated coefficient of thermal expansion (CTE) along the c axe values were close to 17 × 10⁻⁶ °C⁻¹ for kaolinite (KCS and KRG) and 14 × 10⁻⁶ °C⁻¹ for halloysite.

中文翻译：

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通过原位高温X射线衍射探测高岭石和埃洛石的脱羟基

通过流延成型使带纹理的高岭石和基于埃洛石的材料成形，以促进粘土颗粒沿流延方向排列，并研究这些页硅酸盐在脱羟基过程中的结构演变。测定了起始高岭土（KRG和KCS）的结晶度指数H 1和R 2，它们的结晶度指数接近于整理良好的参比高岭土KGa-1b的值。根据在生胶布上进行的（002）极图，埃洛石粘土表现出三峰粒度分布，并且往往比KRG和KCS的织构少。恒定加热速率得出的动力学参数与预期范围相匹配。我们通过在D2AM光束线上的ESRF同步加速器辐射源进行原位高温X射线衍射测量，跟踪了高岭石和埃洛石的脱羟基反应。对于KRG和KCS，这些高岭石和埃洛石的脱羟基发生在425°C至675°C之间，对于埃洛石，这些脱钙作用发生在500°C至650°C之间。另外，关于热处理温度的高岭石基距的变化证实了脱羟基过程发生在三个步骤中：脱层，脱羟基和偏高岭石的形成。计算出的沿c ax值的热膨胀系数（CTE）接近17×10 高岭石基本距离随热处理温度的变化证实了脱羟基过程发生在三个步骤中：脱层，脱羟基和偏高岭石的形成。计算出的沿c ax值的热膨胀系数（CTE）接近17×10 高岭石基本距离随热处理温度的变化证实了脱羟基过程发生在三个步骤中：分层，脱羟基和偏高岭石的形成。计算出的沿c ax值的热膨胀系数（CTE）接近17×10^-6 ℃， ^-1为高岭石（KCS和KRG）和14×10 ^-6 ℃， ^-1为多水高岭石。