Study on Properties of Magnesia-Hercynite Brick

Using magnesia and hercynite as materials, we researched the magnesia hercynite brick in order to solve the problem of chrome free brick used in the burning zone of cement rotary kiln. Effect of different firing temperature and different content of hercynite on properties of the brick were studied. The results show that the magnesia hercynite specimen fired at 1600℃ was densified and when the hercynite content is 7%, the cold crushing strength and the adhesive strength of rupture of the specimen have the highest value.

Characteristics of Hercynite and Its Application in Refractories

The characteristics of hercynite including corystal structure, chemical compositions and physical properties, R ＆ D background of hercynite, synthesis problems of heronite, amt roles of hercynite in refractories were re-riewed. The application of hercynite in refractories was introduced with emphasis. The practical applications in cement rotary kiln showed the prepared magnesia her-cynite brick had better performance than the original magnesia chrome brick obviously.

Present Synthesizing Situation and Application Mechanism of Hercynite in Cement Kilns

The magnesia -hercynite bricks offer a new lining to rotary cement kiln. They are well adopted and widely used in the high temperature zone of cement kiln, and have obtained good performance at rigorous and severe working conditions. The synthesis of hercynite requires a suitable atmosphere with proper O2 partial pressures which makes sure FeO can stably exist at the synthesizing temperature. Current industrial production of hercynite mainly adopts fused method. The other method, sinte- ring method, is not mature and needs further research. The magnesia - hercynite brick shows high hot toughhess, high adhesion strength to kiln crust, and good corrosion resistance to alkali salt in cement kilns. The mismatching of thermal expansion between magnesia and hercynite can improve the thermal shock resistance of the bricks, but the oxidation of partial Fe^2＋ , the high temperature solution, and low temperature exsolution of transgranular secondary spinel lead to cubical expansion, .formation of more cracks, and poor thermal shock resistance of the bricks.

Morphology characterization of periclase–hercynite refractories by reaction sintering

A periclase？hercynite brick was prepared via reaction sintering at 1600℃for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe^2＋, Fe^3＋ and Al^3＋ ions in hercynite crystals migrate and react with periclase to form（Mg1-xFex）（Fe2-yAly）O4 spinel with a high Fe/Al ratio. Meanwhile, Mg^2＋ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg^2＋ migration leads to the formation of（Mg1-uFeu）（Fe2-vAlv）O4 spinel with a lower Fe/Al ratio and results in Al3＋ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.

Study on Sintered Synthetic Hercynite Clinker

Special grade bauxite and roll scale were used as raw materials to investigate the influences of reducing atmosphere and firing temperature on sintering clinker. The results showed that: 1) The mixture of the materials could be sintered enough to synthesise hercynite under reducing atmosphere by adding reducing reagent; 2) The hercynite clinker could be sintered to high density and the content of FeAl 2O 4 may attain 80～90% under the firing temperature of 1550℃.

Reaction behavior of ferric oxide in system Fe_2O_3-SiO_2-Al_2O_3 during reductive sintering process

Pure compounds and kaolin were employed to investigate the reaction behavior of ferric oxide in thetrinarysystem Fe2O3?SiO2?Al2O3 during reductive sintering process. The thermodynamic analyses and reductive sintering experimental results show that ferrous oxide generated from the reduction of ferric oxide by carbon can react with silicon dioxide and aluminum oxide to form ferrous silicate and hercynite at 1173 K, respectively. In the trinary system Fe2O3?SiO2?Al2O3, ferrous oxide obtained from ferric oxide reduction preferentially reacts with aluminum oxide to form hercynite, and the reaction of ferrous oxide with silicon dioxide occurs only when there is surplus ferrous oxide after the exhaustion of aluminum oxide. When sintering temperature rises to 1473 K, hercynite further reacts with silicon dioxide to form mullite and ferrous oxide. Results presented in this work may throw a new light upon the separation of alumina and silica present in Al/Fe-bearing materials with low mass ratio of alumina to silica in alumina production.

Reaction behavior of kaolinite with ferric oxide during reduction roasting

The pre-separation of silica and alumina in aluminosilicates is of great significance for efficiently treating alumina-/ silica-bearing minerals for alumina production. In this work, the reaction behavior of kaolinite with ferric oxide during reduction roasting was investigated. The results of thermodynamic analyses and reduction roasting experiments show that ferrous oxide obtained from ferric oxide reduction preferentially reacts with alumina in kaolinite to form hercynite, meanwhile the silica in kaolinite is transformed into quartz solid solution and/or cristobalite solid solution. With increasing roasting temperature, fayalite formed by reaction of surplus ferrous oxide with silica at low temperature is reduced to silica and metallic iron in the presence of sufficient carbon dosage. However, increasing roasting temperature and decreasing Fe2O3/Al2O3 molar ratio favor mullite formation. The complete conversion of kaolinte into free silica and hercynite can be obtained by roasting raw meal of kaolin, ferric oxide and coal powder with Fe2O3/Al2O3/C molar ratio of 1.2:2.0:1.2 at 1373 K for 60 min. This work may facilitate the development of a technique for comprehensively utilizing silica and alumina in aluminosilicates.

Efficient separation of alumina and silica in reduction-roasted kaolin by alkali leaching

Alkali leaching was employed to investigate the separation of alumina and silica in roasted kaolin obtained by roasting kaolin alone in air at 1273 K for 60 min and in clinker prepared by roasting the mixed raw meal of kaolin,ferric oxide and coal powder with Fe2O3/Al2O3/C molar ratio of 1.2:2.0:1.2 in reducing atmosphere at 1373 K for 60 min.The thermodynamic analyses and alkali leaching results show that the composition of the Al-Si spinel in roasted kaolin is close to that of 3Al2O3·2SiO2 and the spinel is dissolved with increasing leaching time,resulting in difficulty in deeply separating alumina and silica in kaolin by the traditional roasting-leaching process.On the contrary,the efficient separation of alumina and silica in kaolin can be reached by fully converting kaolinite into insoluble hercynite and soluble free silica,namely quartz solid solution and cristobalite solid solution,during reduction roasting,followed by alkali leaching of the obtained clinker.Furthermore,experimental results from treating high-silica diasporic bauxite indicate that the reduction roasting-alkali leaching process is potential to separate silica and alumina in aluminosilicates.

Thermodynamics of Phase Equilibria in FeO-TiO2-Al_(2)O_(3)System

This scientific paper discusses the information on the structure of the three-component system FeO-TiO_(2)-Al_(2)O_(3),which is necessary for the creation of heat-resistant oxide materials.The structure of binary systems:FeO-Al_(2)O_(3),FeO-TiO_(2),and Al_(2)O_(3)-TiO_(2)is described,and the data on the FeO-TiO_(2)-Al_(2)O_(3)system are presented.The thermodynamic data of all compounds of the system are given,on the basis of which the change in the Gibbs free energy in the temperature range of 800-1900 K for twenty-one exchange reactions was calculated.It has been established that the triangulation of the FeO-TiO_(2)-Al_(2)O_(3)system changes in five temperature ranges:up to 1408 K(TiO_(2)exists in the polymorphic modification-anatase),1408-1537 K(TiO_(2)exists in the polymorphic modification-rutile and pseudobrookite is stable),1537-1630 K(thialite is stable),1630-2076 K(rearrangement cannot occur)and above 2076 K(the presence of the stoichiometric compound Al_(4)TiO_(8)is allowed).Two-phase equilibria up to 1408 K are stable:Al_(2)O_(3)-FeTiO_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1408-1537 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);in the temperature range of 1537-1630 K:FeAl_(2)O_(4)-TiO_(2),FeAl_(2)O_(4)-FeTi_(2)O_(5),FeAl_(2)O_(4)-FeTiO_(3),FeAl_(2)O_(4)-Fe_(2)TiO_(4),and FeAl_(2)O_(4)-Al_(2)TiO_(5);in the temperature range of 1630-2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),Al_(2)TiO_(5)-FeTiO_(3),FeTiO_(3)-Al_(2)O_(3),FeTiO_(3)-FeAl_(2)O_(4),and FeAl_(2)O_(4)-Fe_(2)TiO_(4);over 2076 K:FeTi_(2)O_(5)-Al_(2)TiO_(5),FeTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-FeTiO_(3),Al_(4)TiO_(8)-Fe_(2)TiO_(4),Al_(4)TiO_(8)-FeO,and Al_(4)TiO_(8)-FeAl_(2)O_(4).