Metallic iron whisker formation and growth during iron oxide reduction: basicity effect

Abstract

The effect of basicity on the metallic iron whisker growth during wü stite reduction was studied in the present investigation. Compacts of pure and CaO/SiO 2 doped wü stite were synthesised. The annealed compacts were isothermally reduced in thermogravimetric apparatus with CO gas at 800-1100uC. The course of reduction was followed by measuring the weight loss as a function of time. X-ray diffraction (XRD), scanning electron microscope (SEM), optical microscope and porosity measurements were used to characterise the annealed and reduced samples. The influence of temperature and basicity (CaO/SiO 2 ) on the reduction behaviour and the morphology of the annealed samples were investigated. The reduction rate increased with temperature but decreased by increasing basicity value. Metallic iron whisker shape structure was detected in the pure wü stite samples after reduction at high temperatures while in basic wü stite samples, whiskers were formed at the surface of the compacts. From the activation energy values, the reduction of pure wü stite is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. The reduction of basic wü stite compacts with 0?2 and 0?5 basicity ratios are most likely controlled by chemical reaction mechanism while for 0?8 basicity ratio, the reduction rate is most likely controlled by solid state reaction mechanism.

Reduction of Iron Oxides with Hydrogen—A Review

“…Abdel Halim et al investigated the formation of metallic iron whiskers during wüstite reduction with CO. Reduction at 800 °C leads to a low reduction rate and 40% conversion.…”

Effects of Reducing Gas on Swelling and Iron Whisker Formation during the Reduction of Iron Oxide Compact

“…Reduction swelling of iron oxide pellets or compacts has been studied by a number of investigators 1–26. The formation and growth of fibrous iron whiskers during the reduction of wustite to iron has been determined to be the major cause for catastrophic swelling.…”

“…The formation and growth of fibrous iron whiskers during the reduction of wustite to iron has been determined to be the major cause for catastrophic swelling. It has been found that other oxides in the pellet6–19 and firing and reduction conditions20–25 have significant effects on iron whisker formation and growth. Industrial ironmaking processes are carried out with various mixtures of CO, CO 2 , H 2 , H 2 O, and N 2 .…”

Upgrading of Blast Furnace Sludge and Recycling of the Low-Zinc Fraction via Cold-bonded Briquettes

“…Furthermore, Seaton et al [36] referred to swelling indices between 20 and 27% as acceptable and normal. Also, Nascimento et al [37] and Abdel Halim et al [38] proposed that swelling indices around 20% are normal, whereas much higher values are considered catastrophic. These much higher indices were exemplified by studies reporting swelling indices exceeding 400% [38].…”

“…Also, Nascimento et al [37] and Abdel Halim et al [38] proposed that swelling indices around 20% are normal, whereas much higher values are considered catastrophic. These much higher indices were exemplified by studies reporting swelling indices exceeding 400% [38]. In contrast to these values, the higher swelling indices during reduction accompanied by the addition of upgraded BF sludge in the present study were modest.…”