Effect of SiO₂ addition on the synthesis of hercynite with high purity

Abstract

Hercynite as a kind of chrome-free and environmental friendly material is widely investigated. In this work, hercynite with high purity was synthesized using Fe 2 O 3 and Al 2 O 3 as raw material with SiO 2 addition under controlled temperature and atmosphere system. The phase and microstructure of the obtained product were investigated using XRD, SEM and TEM techniques. The effect of SiO 2 on the synthesis of hercynite with high purity was discussed from both theoretical and experimental aspects. The results show that SiO 2 addition lowers the formation temperature of the liquid phase, which promotes Al 2 O 3 to melt into the liquid phase and makes the formation of hercynite possible during the heating stage. During the process of crystallization, SiO 2 further facilitates the formation of hercynite by the peritectic reaction. During the fast cooling stage, SiO 2 in the form of amorphous silicate exists between hercynite crystals. Therefore hercynite with high purity and dense structure is successfully synthesized. It also shows that 1 mass % SiO 2 addition can effectively promote the crystal growth of hercynite and thus lead to dense structure.

Magnesium Doped Hercynite: Preparation and Formation Mechanism

“…Majzlan et al suggested that, although all optimized FeAlO3 structures are higher in energy than a mechanical mixture of hematite and corundum, but the slow diffusion of ions through the structure prohibits the structure to achieve any lower-energy, ordered state, even at 1500 °K and at low temperatures, when the driving force for ordering might increase [17]. Meanwhile, MgAl2O4 can be formed from aluminum and magnesium oxides as shown in the following reaction [21]:…”

Application of Molten Salt Method in Hercynite Composite Powder Synthesis at Elevated Temperature

“…Because of their excellent performance, magnesite-chrome refractories are widely used in the burning zone of dry-method cement rotary kilns in the past. However, magnesia chrome bricks are prohibited worldwide, which show a deeply negative impact for Human health and Environment, due to the formation of carcinogenic Cr(VI) species during cement production, so chrome-free refractories have made rapid progress [1][2][3]. Currently, chrome-free refractories are primarily composed of magnesite dolomite bricks, magnesia alumina spinel bricks, magnesia-calcia-zirconia bricks, and Magnesite-hercynite bricks.…”

Çimento Döner Fırınlarında Kullanılan Bazik Refrakter Tuğlaların Özelliklerinin Karşılaştırılması

“…Fakat bu tuğlalar bünyelerindeki krom bileşiklerinden dolayı toksik özelliklere sahiptir. Cr +6 iyonlarının deride alerji, ülser ve kansorejen etkisinden dolayı endişe yaratması krom içeren refrakter atıklarının Avrupa Birliği kurallarına göre düzenlenmesini gerektirmiş ve dolayısıyla Cr2O3 içermeyen alternatif refrakter ihtiyacı gündeme gelmiştir [6][7][8]. Bu anlamda yapılan araştırma çalışmaları genel olarak, magnezya-spinel (MgO-MgAl2O4), dolomit ve magnezya-zirkonya tuğlalarının geliştirilmesi üzerinedir.…”