High-performance chromite by structure stabilization treatment

Cleaner Production of Chromium Oxide from Low Fe(II)-Chromite

“…Moreover, Vaari [39] has proposed that the diffusion coefficient of Fe 2+ are much larger compared with that of other metallic ions in spinel. In the oxidizing atmosphere, Fe 2+ ions tend to migrate from the core of spinel crystals toward the reaction interface and are oxidized into Fe 3+ producing tetrahedral vacancies [41,42]. Hydrogen ions provided by the acid attack the oxygen skeleton of the lattice, destructing the spinel structure and releasing metallic ions.…”

Eco-friendly design of complex refractory aggregates as alternatives to the magnesia-chromite ones

“…Thus, it is well-known that many of the desired properties are mutually exclusive, as is the case of reducing thermal conductivity and enhancing thermal shock damage resistance [9], or high elastic modulus and significant 'flexibility' of the microstructure (which is a term that accounts for the ability to accommodate deformation generating less stress) [10]. Thus, the search for refractory systems capable of leading to a proper balance between these properties is a constant demand of high-temperature industries [11][12][13]. To address such a scenario, refractories containing electrofused magnesia-chromium aggregates (EMCA) have been broadly applied since the 1960s [11,14,15].…”

“…Thus, the search for refractory systems capable of leading to a proper balance between these properties is a constant demand of high-temperature industries [11][12][13]. To address such a scenario, refractories containing electrofused magnesia-chromium aggregates (EMCA) have been broadly applied since the 1960s [11,14,15]. In these systems, which fit into the compositionally complex ceramic classification firstly proposed by Wright and Lou in 2020 [16], the predominant phases are periclase and a solid solution based on a complex spinel [(Fe, Mg)(Fe, Al, Cr)2O4], obtained by combining different types of spinel structures (AB2O4-type phases, in 4 which A represents a divalent cation and B a trivalent one) [17][18][19].…”

“…Additionally, a high number of preferentially oriented microcracks on the EMCA microstructure gives rise to a material with good flexibility and thermal shock damage resistance. Although the literature does not report in detail the phenomena that induce this preferentially-oriented microcracking, it is known that the anisotropy of the phases, their distinct thermal expansion coefficient and sesquioxide exsolution (A2O3-type phases, such as Al2O3 and Fe2O3) may play key roles [11,15,20] Besides its outstanding corrosion and thermal shock damage resistance, EMCA has received little attention from the scientific community in recent decades, which can be attributed to its toxicity (mainly due to the formation of hexavalent chromium [21,22]). Thus, greater efforts have been made to study safer systems, especially based on MgAl2O4, as alternatives to replace EMCA, but equivalent performance in applications such as in RH degassers has not yet been achieved [6].…”

ZnO and MgO as inducers of spinel-like phase formation on alumina-based castables

“…The severe operating conditions in steelmaking equipment, such as high temperatures (close to 1600 ºC), corrosive slags, and constant thermal cycling, led to the use of chromium-containing refractories since the 1990s 2,3 . The chromium in these materials reacts with other oxides (e.g., Al2O3, Fe2O3, MgO, MnO, and NiO) giving rise to a plethora of spinel-like phases, which results in a complex microstructure that merges high corrosion resistance, refractoriness and thermal shock damage resistance 4,5 .…”