Twin formation in hematite during dehydration of goethite

Abstract

Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM).When synthetic goethite was heated at different temperatures between 100 and 800 °C, a phase transformation occurred at temperatures above 250 °C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001] G was transformed into hematite with a growth direction of [100] H . Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 °C, the majority of the twin boundaries disappeared; however, some hematite particles remained in the twinned variant. The electron diffraction patterns and high-resolution TEM observations indicated that the twin boundaries consisted of crystallographically equivalent prismatic (100), (010), and (11 � 0) planes. According to the total energy calculations based on spin-polarized density functional theory, the twin boundary of prismatic (100) screw had small interfacial energy (0.24 J/m 2 ). Owing to this low interfacial energy, the prismatic (100) screw interface remained after higher-temperature treatment at 800 °C.

High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean)

“…Secondly, the highest reflection at 4.2 Å also starts to collapse, being replaced by a reflection typical of hematite ( Figure 5A). The same behaviour for thermic treatment of goethite has been found by several authors [64][65][66].…”

Reduction Behaviors and Generated Phases of Iron Ores using Ammonia as Reducing Agent

“…Goethite (FeOOH), the main component of high-CW iron ore, can change to porous hematite (Fe 2 O 3 ) by low-temperature dehydration (i.e., 250-500°C). [22][23][24] This pore generation can be even faster during dehydration under vacuum conditions. 25) The generated pores significantly increase the ore reduction reactivity due to the nano-contact between iron oxides and reducing agents.…”

“…This finding agreed with other reports mentioning that the ore with higher CW could have a higher surface area due to nanopore generation. [22][23][24][25]…”

Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings

“…The influence of the drying temperature T Dry was investigated in order to induce a color change of the coatings. The yellow pigment goethite is known to be completely transformed into red hematite (α-Fe 2 O 3 ) by a dehydration reaction in a temperature range of about 250-280 • C [40][41][42][43][44]. This step was considered in more detail, since the control of the coating color by simple adjustment of the drying temperature provides an easily achievable and highly useful process modification.…”