Nucleation and Growth of Iron Whiskers during Gaseous Reduction of Hematite Iron Ore Fines

Abstract

A high-temperature confocal scanning laser microscope and an online reduction–water quenching experiment system were used to systematically study the generation of iron whiskers during the reduction of hematite ore particles with CO/CO2 gas. The "blooming" phenomenon of the surface during the reduction of iron ore particles was found in this experiment. The orientation of the grain on the longitudinal section of an iron whisker was measured to be uniform by applying the electron back-scattered diffraction technique, which proved that the iron whiskers are most likely to exist in single crystal form. According to the in-situ online experimental video, the average diffusion flux of iron atoms when the layered iron completely covers the surface of the ore particle is about 0.0072 mol/(m2·s). While the iron atom diffusion flux at the root of the iron whisker during the pre-growth process is much larger than the flux when the layered iron is produced, which are defined to be 0.081 mol/(m2·s), 0.045 mol/(m2·s), 0.013 mol/(m2· s), and 0.0046 mol/(m2·s), respectively during the four stages of the growth of an iron whisker. The quantitative relationship between the chemical driving force and the whisker growth is established as Δ G θ + R T ln p CO 2 p CO + 2 n 0.056 r ρ E s T = 0 .

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

“…In the reduced sample after the experiment, iron formed an outer layer of the particles; this migration of iron from the particle core to the outside layer has been reported previously . A single titanium-free iron oxide and pure silicon oxide particle were detected; see the green and orange circles.…”

“…In the reduced sample after the experiment, iron formed an outer layer of the particles; this migration of iron from the particle core to the outside layer has been reported previously. 36 A single titanium-free iron oxide and pure silicon oxide particle were detected; see the green and orange circles. The area within the violet circle, which is attached to the oxygen carrier particle, showed high intensities of sodium, aluminum, silicon, and calcium and an even higher intensity of oxygen compared to that in the other particles.…”

An Unbiased Approach to Low Rank Recovery

“…The elements detected in the ash were mainly silicon and calcium. Iron seemed to form a layer on the iron sand particle's surface, which suggested that iron would migrate to the outer layer during highly reducing environments where it most likely formed wüstite [45]. A similar outward migration of iron was also seen in a sample investigated with gaseous…”

Effect of the Conversion Degree on the Apparent Kinetics of Iron-Based Oxygen Carriers

“… 38 At lower mass conversion degrees, another reaction may take place, and this implies a different reaction mechanism. For instance, the outward migration of iron phases to the particle surface during reduction 49 creates a chemically distinct iron layer, 50 which implies formation of the Fe/FeO interface. 15 , 51 As a result, the diffusion rate of fuel into the particle becomes much slower, so the reaction is likely controlled by diffusion at this stage.…”