Papers by Author: Yu Qin Liu

Abstract: Vacuum aluminothermic reduction of magnesia is multi-phase chemical reaction and the briquette forming condition has a great influence on the extent of the reactions. This paper focused on the effect of briquette forming condition on the extraction of magnesium from calcined magnesite. Briquettes were prepared at different conditions, including two forming pressures, four briquette thicknesses and two briquette diameters. The reduction ratio was calculated from the weight loss of the briquette before and after thermal reduction. The obtained condensed magnesium and briquette residues were mainly characterized via X-ray diffraction analysis and scanning electron microscopy. It was revealed that the briquette preparation condition had a great influence on the reduction ratio of magnesia and the phase constitution of the briquette residues, but had a minor influence on the morphology of condensed magnesium.

Abstract: In this paper, a new process for the production of the primary magnesium is introduced using the dolomite as the raw material. The magnesia and calcium carbonate were prepared from dolomite by acidification. The content of magnesium oxide can reach 98.92% about the magnesia obtained. The magnesia is used to produce primary magnesium by aluminothermic reduction under vacuum condition. The reduction ratio of MgO can be up to 86.14% under the temperature of 1200°C for 5hrs, briquetting pressure of 10MPa and the molar ratio of MgO to Al of 3:2. The content of magnesium is more than 99.90%. The major phases in the briquette residue are corundum and spinel, which can be used as refractory.

Abstract: The structure and composition of carbon materials affect obviously the result of carbothermic reduction of magnesia. Coke, charcoal and graphite were used in reduction experiments under the same conditions. The reactivity ratio of magnesia and XRD pattern of residues were analyzed and compared. The reactivity ratio of magnesia by coke was similar to the one by charcoal. The amorphous carbon in coke graphitized partly in reduction experiments of 1673K. The results show that the effective composition in coke is the amorphous carbon. It also suggests that the temperature of reaction should be control less than 1700K to avoid the amorphous carbon’s graphitization.

Abstract: The aegirine-augite syenite potash ore, taken from Changling, Luonan in Shannxi province, were hydrothermally decomposed over the temperature ranges of 533 K to 563 K using calcium hydroxide as additive. The dissolution ratio of the K2O at different reaction temperature and time was determined. Analysis of the experimental results revealed that the dissolution rate of potash ore satisfies the chemical reaction controlled kinetic equation. The rate constant of hydrothermal reaction at different temperatures was obtained. The activation energy was calculated using the Arrhenius equation. The hydrothermal decomposition mechanism of microcline was proposed.

Abstract: The present paper focuses on the experimental investigation of the aluminothermic reduction of magnesia under vacuum condition with the fixed magnesia to aluminum molar ratio of 11:6. The influences of reaction temperature and time on the reduction ratio of magnesia were studied. The chemical composition, phase constitution and morphology of the condensed magnesium and the briquettes after thermal reduction were investigated by X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectrometry. The reduction ratio of magnesia increases with the increase in the reaction temperature and time. The briquettes after thermal reduction at 1050°C-1150°C are mainly composed of the spinel, unreacted magnesia and aluminum. The briquette after 1 hrs thermal reduction at 1200°C contains corundum, magnesium aluminium oxide, trace amount of spinel, unreacted MgO and aluminium.

Abstract: The Al-substituted 11Å tobermorite was synthesized from aegirine-augite syenite potash ores by alkaline hydrothermal reaction at 300°C. The obtained tobermorite was characterized by chemical analysis, X-ray diffraction and scanning electron microscopy. The effect of reaction time on the tobermorite formation and the dissolution ratio of the K2O in the potash ores were investigated. It was revealed that the dislocation ratio of K₂O increases with increasing reaction time. The main rock constituents were converted into a well-crystallized Al-substituted 11Å tobermorite after 3 hours hydrothermal reaction at 300°C. The obtained Al-substituted tobermorite forms hollow spherical aggregates with the diameter of 40µm-80µm by the crossing of fibrous tobermorite crystal together. The Al³⁺ may substitute isomorphously up to 15 at % of Si ⁴⁺ in the obtained tobermorite.

Abstract: A new high strength and high toughness Ti-alloy, Ti-63, was designed via the CALPHAD approach using a thermodynamic database including elements Ti-Al-Cr-Mo-O-Si-Sn- V-Zr. Good combinations of strength, ductility and fracture toughness, with the values of tensile strength Rm > 1200 MPa, elongation A > 10%, reduction of area Z > 20% and fracture toughness KIC ≈ 80 MPa·m1/2, were achieved for the Ti-63 alloy after optimized heat treatment process.