Mechanism and Kinetics of Phase Transformation in Two-phase TiAl-based Alloys

The aged and quenched microstructures of both alloys, Ti-42at-%Al and Ti-45at -%Al,homogenized in the disordered single phase field. were investigated And the results show that the quinched microstructure is a supersaturated single phase of ordered 22. When the supersaturated phase is aged in the two phase range at 1273 and 1373 K, it will transform to a lamellar microstructure of γ+α2. with a discontinuous decomposition mechanism in Ti-42at-%Al alloy and a semicontinuous decomposition mechanism in T1-45at-%Al alloy. With the methods of quantitative metallograph examination and X-ray diffraction analysis. the relationship between the amount of γ, phase precipitation and the time of isothermal transformation is agreed

Reduction mechanism of high-chromium vanadium–titanium magnetite pellets by H_2–CO–CO_2 gas mixtures

The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows： Fe2O3 → Fe3O4 → FeO → Fe; Fe9 TiO 15 ＋ Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeT iO 3 → TiO 2;（Cr0.15V0.85）2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeC r2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.

Crystallization behavior of zeolite beta from acid-leached metakaolin

Well-crystallized zeolite beta was synthesized by using acid-leached metakaolin as the silica-alumina source and tetraethylammonium hydroxide structure-directing agent.The influence of the composition of the reaction mixture on product crystallinity was investigated,and the crystallization process was studied by examining solid samples obtained at different synthesis times.Results showed that the acid-leached metakaolin was fully converted into soluble aluminum and silicon species,which is crucial for the formation of well-crystallized zeolite beta.At the beginning of the crystallization process,these soluble aluminum and silicon species formed a aluminum-rich intermediate structure with layer morphology.With the crystallization proceeding,more silicon species were incorporated into the zeolite beta framework and the layered structure was changed into spherical particles of zeolite beta with high SiO 2 /Al 2 O 3 ratio and crystallinity.

Reaction condition optimization and kinetic investigation of roasting zinc oxide ore using (NH_4)_2SO_4

An orthogonal test was used to optimize the reaction conditions of roasting zinc oxide ore using（NH_4）_2SO_4. The optimized reaction conditions are defined as an（NH_4）_2SO_4/zinc molar ratio of 1.4：1, a roasting temperature of 440°C, and a thermostatic time of 60 min. The molar ratio of（NH_4）_2SO_4/zinc is the most predominant factor and the roasting temperature is the second significant factor that governs the zinc extraction. Thermogravimetric-differential thermal analysis was used for（NH_4）_2SO_4 and zinc mixed in a molar ratio of 1.4：1 at the heating rates of 5, 10, 15, and 20 K·min-1. Two strong endothermic peaks indicate that the complex chemical reactions occur at approximately 290°C and 400°C. XRD analysis was employed to examine the transformations of mineral phases during roasting process. Kinetic parameters, including reaction apparent activation energy, reaction order, and frequency factor, were calculated by the Doyle-Ozawa and Kissinger methods. Corresponding to the two endothermic peaks, the kinetic equations were obtained.

Carbothermic Reduction Mechanism of Vanadium-titanium Magnetite

To achieve the high-efficiency utilization of vanadium-titanium magnetite（ VTM）,reduction experiments were conducted to determine the carbothermic reduction mechanism of VTM. Effects of volatile matter,temperature,time,and carbon ratio（ molar ratio of fixed carbon in coal to oxygen in iron oxides of VTM） on reduction degree were investigated.Results show that reduction degree increases with increasing volatile matter in coal,temperature,time,and carbon ratio.Phase transformation,microstructure,and reduction path were analyzed by X-ray diffraction,scanning electron microscopy,energy-dispersive X-ray spectroscopy,and Fact Sage 6. 0. The thermoravimetry-differential scanning calorimetry-quadrupole mass spectrometer method was used for kinetic analysis of the main reduction process. Results indicate that the kinetic mechanism follows the principle of random nucleation and growth（ n = 4）,and the activation energy values at 600-900 and 900-1 350 ℃ are 88. 7 and 295. 5 kJ / mol,respectively.

Microstructure evolution and mechanical properties influenced by austenitizing temperature in aluminum-alloyed TRIP-aided steel

The Fe-0.21C 2.2Mn 0.49Si-1.77A1 transformation induced plasticity （TRIP） aided steel was heat trea- ted at various austenitizing temperatures under both TRiP-aided polygonal ferrite type （TPF） and an- nealed martensite matrix （TAM） processes. The microstructure evolution and their effects on mechanical properties were systematically investigated through the microstructure observation and dilatometric analysis. The microstructure homogeneity is improved in TPF steel heated at a high temperature due to the reduced banded martensite and the increased bainite. Compared with the mechanical properties of the TPF steels, the yield strength and elongation of the TAM steels are much higher, while the tensile strength is lower than that of TPF steels. The stability of intercritical austenite is affected by the heating tempera- ture, and thus the following phase transformation influences the mechanical properties, such as the bain- ite transformation and the precipitation of polygonal ferrite. Obvious dynamic bainite transformation occurs at TAM850, TAM900 and TAM950, More proportion of polygonal ferrite is found in the sample heated at 950 ℃. The bainite transformation beginning at a higher temperature results in the wider bainitic ferrite laths. The more proportion of polygonal ferrite and wide bainitic ferrite laths commonly contribute to the lower strength and better elongation. The uniform microstructure with lath-like morphology and retained austenite with high average carbon content ensures a good mechanical property in TAM850 with the product of strength and elongation of about 28 GPa ·%,