Thermal behavior analysis of halloysite selected from Inner Mongolia Autonomous Region in China

Thermal behavior of halloysite selected from Erdos, Inner Mongolia Autonomous Region in China, was investigated by thermogravimetry and differential thermal gravity (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscope (SEM). The XRD results indicated that the mineralogical composition of halloysite sample was determined as 7 Å halloysite with the d ₍₀₀₁₎ value of 0.734 nm, a small amount of 10 Å halloysite with the d ₍₀₀₁₎ value of 0.998 nm, quartz, calcite, anhydrite, siderite, and analcite. The crystal chemical formula of halloysite specimen is (Ca_0.007Na_0.039K_0.048)(Al_1.935Fe _0.032 ³⁺ Mn _0.003 ²⁺ Ti _0.002 ⁴⁺ Mg _0.015 ²⁺ Ca _0.021 ²⁺ )₂ (Si_1.935Al _0.065 ³⁺ )₂](OH)₄·2H₂O according to the oxygen atom method. The TG–DTG–DSC data showed that a small amount of water molecule layer in the interlayer and the dehydroxylation was observed at 493.6 °C. The XRD, FT-IR, and SEM data clearly show that the structure changes and dehydroxylation of the halloysite with the temperature increased from 200 to 1200 °C. The dehydration of the halloysite is followed by the loss of intensity and evolution of the OH vibration bands and the change in microstructure. Dehydroxylation is followed by the decrease in the intensity of the bands at 3696 and 3620 cm^?1, which is completely disappeared at 700 °C. The thermal behavior of halloysite was influenced by the mineralogy composition and impurities.