The Phase Transition of Calcium Sulfide Under High Pressure

We carried out the accurate in situ angle derisive x-ray diffraction experiments and the electrical resistivity in CaS under high pressure. The result shows the pressure-induced phase transition of CaS from Na Cl-type structure (the space group Fm3m, phase I ) to Cs Cl-type structure (the space group Pm3m, phase II ) is reversible and the transition point is around 40.0 GPa; in the meantime, the electrical resistivity and light permeability decrease as the pressure increases and occur obvious discontinuities at the corresponding phase transition point; the result of the first-principles calculations is in concordance with the measurement results.

Optimizing Slag Content to Control Ds-Type Inclusions in 10B21 Cold Heading Steel

Ds-type inclusions during production are an important factor affecting the performance and quality of manufactured 10B21 steel. To minimize Ds-type inclusions in steel and improve the production qualification rate of steelmaking plants, a refining slag system optimization scheme was proposed based on the analysis of current inclusion evolution during the steelmaking process, and industrial tests were conducted to verify improvements resulting from application of the proposed scheme. The results showed that the composition of Ds inclusions in 10B21 steel are mainly CaO–Al2O3–MgO–CaS–TiN, which exists in the form of calcium–magnesium aluminate coated with titanium nitride and calcium sulfide. The main reason for the formation of Ds inclusions is the poor fluidity of the refining slag and its low capability to absorb inclusions. The poor coverage of the refining slag on the molten steel during refining can easily cause secondary oxidation of the molten steel. Thus, the formation and growth of Ds-type inclusions are aggravated after the calcium feeding line and soft blowing operation. Here, we propose to minimize Ds inclusions using our optimized refined slag system. The mass percentage of the optimized slag system is CaO: 55–60%, Al2O3: 20–35%, SiO2: 3–7%, MgO: 4–8%, (MnO + FeO) < 1%, and the basicity is controlled within the range of 7–11. We observed that our optimized refining slag system has a significantly improved ability to remove inclusions, particularly Ds inclusions, which improves the qualification rate of 10B21 steel.

Investigation of the Kinetic Regularities of the Interaction of Petroleum Coke with Phosphogypsum to Calcium Sulfide

This study describes the research results of petroleum coke (carbon) and phosphogypsum reaction and the methods used for the above. Stoichiometric petroleum coke and phosphogypsum mixtures were prepared for the study. The coke was cut and screened with particle size distribution of 0.25-0.315 mm and dried at 110 °С temperature. The phosphogypsum sample was also cut and screened with the same particle size and was pre-heated within the 100-200 °С range up to permanent mass. The weighed samples were heated within 900 till 1000 °С, the range being typical to one of reaction stages between coke and phosphogypsum, i.e. the decomposition reaction with the products of calcium sulfide and carbon dioxide. The extend and rate of samples conversion and their time correlations were obtained for the number of reaction temperatures. Reaction rate constant and activating energy were calculated based on this correlations results.

Research on the variation of the inclusion and sulfur content in Pipeline steel

Pipeline steel is widely used in various industries, and the sulfur content and inclusions in steel have a significant impact on performance, which determines whether the steel quality is qualified. The experiments were carried out to explore the sulfur content and inclusion evolution of pipeline steel which was deoxidized by Si–Mn–Al with “EAF-LF-VD-T-CC”. The samples of molten steel and slag were taken during the process of LF-VD-Tundish after EAF tapping. The kinetics model was established to simulate the desulfuration process of molten steel in actual production, obtaining a result which the error is within 3 ppm. It can be summarized that proper calcium treatment can transform the inclusion into a liquid inclusion, the value of [Ca] ranges from 25 to 45 ppm. Too high and lower calcium treatment can cause the compositions of inclusions to deviate from the liquid phase area, while too low calcium treatment will increase the overall size and density of the inclusions. In addition, the evolution of inclusion in steel at refining temperature and during solidification process was comprehensively calculated, considering all types of inclusions such as calcium oxide, magnesium oxide, aluminum oxide, calcium sulfide, spinel, calcium aluminate and liquid inclusion. The thermodynamic calculations are in good agreement with experimental results, which can predict the formation of the inclusions in Si–Mn–Al deoxidized pipeline steel.

FEATURES OF SYNTHESIS OF INORGANIC LUMINESCENT MATERIAL FROM PHOSPHOGYPSUM

The paper discusses technological methods for obtaining a luminescent material from phosphogypsum. The obtained materials were characterized using X-ray phase analysis, X-ray fluorescence analysis, and electron microscopy. The elemental composition of the samples was determined using a laboratory micro-fluorimeter. In the course of the study, the technological conditions for converting the main part of phosphogypsum into a luminescent material based on calcium sulfide were established. It is shown that the process of obtaining luminescent CaS consists of dehydration stages: the initial stage, carried out at a temperature of 373 K to remove physically bound water, and the final stage, at a temperature of 1073 K – to remove crystallization water, as well as the stage of phosphogypsum reduced at a temperature of 1173 K for 0.5 h. An environmentally friendly material-sucrose-is considered as a reducing agent. It is shown that in the case of changing the technological modes of reduction the luminescent material cannot be obtained. Conducting the reduction process at a temperature of 773 K is accompanied by obtaining a sample contaminated with products of incomplete decomposition of the organic component of the charge. In this case, the sample does not contain calcium sulfide. Under prolonged isothermal exposure at a temperature of 1173 K, repeated oxidation of samples with loss of luminescence ability was observed. Optimal technological modes for obtaining materials with phosphor properties are formulated. According to the results of X-ray phase analysis, samples that do not show luminescence capacity contain calcium sulfate as the main phase. Samples-phosphors consist of a mixture of calcium sulfate and sulfide. Results obtained open up wide opportunities for involving in the re-processing of production waste to obtain cheap products in demand.