关键词: 针铁矿, 热处理, 高温相变, 米粒状α-Fe₂O₃

Abstract: The structure and morphology evolution of goethite (α-FeOOH) powder under high temperature heat treatments at 250～650 ℃ and 900 ℃ were studied by X-ray powder diffraction, thermogravimetric/differential thermal analysis, and scanning electron microscopy. The results indicate that no significant phase transformation occurs in goethite when calcined at 250 ℃ for 2~8 h. However, as the holding time increases, its acicular morphology gradually breaks down and stacks into short rod-like structures. When the calcination temperature reaches 350 ℃, α-FeOOH begins to dehydroxylate and transform into hematite (α-Fe₂O₃), and it completely transforms into the α-Fe₂O₃ phase at 450 ℃. When the calcination temperature reaches 450～650 ℃, although the product exhibits the α-Fe₂O₃ phase, it retains the original acicular morphology of α-FeOOH. As the heat treatment temperature and time increase, the average grain size of the product gradually increases. With heat treatment temperatures rising, α-Fe₂O₃ crystals grow larger, the specific surface area decreases progressively, sintering phenomena occur between particles, and when the calcination temperature reaches 900 ℃, the broken rod-like structure turns into rice-grain-like α-Fe₂O₃, which has certain application values in fields such as wastewater treatment, photocatalysis, and industrial pigments.

Key words: goethite, heat treatment, high temperature phase transition, rice-grain-like α-Fe₂O₃