Yan Wu’s research while affiliated with Peking University and other places

In this study, steelmaking slag was utilized as heat carrier and catalyst to perform the coal gasification; meanwhile, CO2 was used as gasifying agent rather than steam from the viewpoint of carbon circulation. An overview on research activities and technology development on the effect of steelmaking slag on coal gasification are provided. The effects of coal type, slag composition, CO2 gas ratio and temperature on the gas producing behavior were discussed through the high temperature experiment. The results showed that coal gasification was remarkably enhanced and the produced CO amount increased considerably with the addition of slag. On the contrary, with the increase of the slag amount, the produced CO amount has the decreasing trend. Coal combined with higher FeO content slag presented higher CO generation rate and less CO generation amount. Moreover, the increase of the CO2 gas ratio and reaction temperature would promote the gasification of coal.

High temperature slags could act as not only heat carrier and catalyst but also reactants in some chemical reactions to produce syngas due to the individual components in slags. A new method is put forward to utilize the thermal energy of converter slags to generate CO gas which could improve the energy utilization efficiency. Thermodynamics of the reactions among coal, FeO–CaO–SiO2 slag and gas was studied by thermodynamic calculation under steady temperature condition or no enthalpy change condition. The effects of FeO amount in initial slag, mass%CaO/mass%SiO2 ratio of slag, and slag temperature on the behavior of the production of H2 and CO gases were clarified.

Purpose This research aims to provide a theoretical method and data supports for a future study on interfacial reaction mechanism and spreading mechanism between molten solder and V-shaped substrate, which also gives guidance for those complicated welding operation objects in brazing technique. Design/methodology/approach Wetting experiments were performed to measure the contact angles at different temperatures of molten Sn-3.0Ag-0.5Cu wetting on the quartz substrate with an included angle of 90°. According to the experimental results, the theoretical spreading morphology of molten solder on V-shaped substrate at corresponding temperature was simulated by Surface Evolver. Findings The theoretical morphology profiles of the molten solder sitting on the V-shaped substrate are simulated using Surface Evolver when the molten solder reaches spreading equilibrium. The spreading mechanisms as well as the impact of surface tension and gravity on interfacial energy of the molten solder wetting on the V-shaped groove substrate are also discussed where theoretical results agree well with experiment results. The contact area between the gas and liquid phases shows a tendency of first increasing and later decreasing. Otherwise, the spreading distance and the height of the molten solder increases as the droplet volume increases as the included angle and the contact angle are given as constants, and both the interfacial energy and the gravitational energy increase as well. This research has a wide influence on predicting the outcomes in commercial impact and also gives guidance for those complicated welding operation objects in brazing technique. Research limitations/implications It is of very important significance in both science and practice to investigate the differences between the flat surface and V-shaped surface. Some necessary parameters including intrinsic contact angle and surface tension need to be directly measured when the droplet spreads on the flat surface. The relevant simulation conclusions on the inherent characteristics can be given based on these intrinsic parameters. Compared with the flat surface, the V-shaped substrate is chosen for further discuss on the effects of gravity on the droplet spreading behavior and the changes of apparent contact angle which can only occurs as the substrate is inclined. Therefore, this research provides theoretical method and data supports for a future study on interfacial reaction mechanism and spreading mechanism between molten solder and substrate. Practical implications The research is developed for verifying the accuracy of the model built in Surface Evolver. Based on this verified model, other researches on the spreading distance along y-axis and the contact area that are especially difficult to be experimentally measured can be directly simulated by Surface Evolver, which can provides a convenient method to discuss the changes of horizontal spreading distance, droplet height and contact area with increasing the included angle of V-shaped substrate or with increasing the droplet volume. Actually, the modeling results are calculated for supplying the theoretical parameters and technical guidance in the welding process. Social implications This research provides theoretical method and data supports for a future study on interfacial reaction mechanism and spreading mechanism between molten solder and substrate, which has a wide influence on prediction the outcomes in commercial impact and also gives guidance for those complicated welding operation objects in brazing technique. Originality/value Surface Evolver, can also be used to discuss the structure and spreading mechanism of droplets on V-shaped substrates, which have not been discussed before.

The effects of Bi addition on the properties of Sn-3.0Ag-0.5Cu molten alloy on Cu substrates are discussed using wettability and interface microstructure analysis. The changes of the contact angles between Sn-3.0Ag-0.5Cu-xBi and Cu substrates with the spreading time are described by Dezellus model. It indicates that the spreading process is governed by the interfacial reaction during the dwelling time. The interface microstructure is observed to clarify the effects of reactions on the spreading behavior. It is found that Cu6Sn5 is formed adjacent to the solder and Cu3Sn appears over the substrate with Bi added at 613K, indicating that Bi exists between the intermetallics and the addition of Bi can hinder the diffusion of copper towards the interior of the solder. Therefore the existence of Bi decreases the agglomeration of Cu-Sn grains. The growth of intermetallics is thus limited and the shape of intermetallics transforms from scallop to zigzag consequently. However, the segregation phenomenon appears when the additive amount of Bi is more than 5.5mass %, which could lead to the occurrence of fracture and degrade the performance of Sn-3.0Ag-0.5Cu-xBi alloy. The results of the present study provide basic physical and chemical data for the application of lead-free solder in the future microgravity space environment.

High-temperature steelmaking slags can act as not only heat carrier and catalyst, but also reactants in some chemical reactions to produce syngas due to the individual components in slags. A new method is put forward to utilize the thermal energy of steelmaking slag for coal reforming to generate CO and H2 gases which could be reused as energy. Thermodynamics of the reaction among carbon, FeO-CaO-SiO2 slag, and CO-CO2-H2O gas is studied by FactSage 6.3 under steady temperature condition. In addition, effects of slag composition, slag temperature, and added carbon amount upon the production of H2 and CO gases are clarified.

To investigate interface properties of molten Sn-3.0Ag-0.5Cu solder melting on the inclined Ni substrate at 540 K, wetting experiments are performed and the numerical simulation is carried out by Surface Evolver. Profile curves of the droplets are fitted with empirical equation, which are proposed to obtain preferable contact angles. The spreading behavior of the droplets is analyzed. It is indicated that the contact line hardly moves at the very beginning; the rear point of triple line moves forward along the substrate subsequently, but the front point of triple line is still pinned on the substrate. Correspondingly, the advancing contact angle gradually increases to the peak value, and then declines with the migration of the front point of triple line. The spreading process is simulated to demonstrate the contact angle hysteresis. Interface microstructure is observed to clarify the effect of reactions on the spreading behavior, and the distribution of intermetallic compounds including Ni3Sn4 and (Cu,Ni)6Sn5 are identified.

The reactive spreading processes of Sn–17Bi–0.5Cu melt alloy on Cu substrate were studied by sessile drop method in the temperature range of 523–673 K. Dynamic contact angles between the solder and Cu substrate at different times were recorded with high-resolution CCD digital video. The smallest contact angle was observed at 623 and 673 K. Ultimate spreading radius does not increase monotonously with the temperature increasing. These can be attributed to the strong dissolution of Cu substrate into the liquid solder, which hinders the solder from spreading. Triple line area configuration of the Sn–17Bi–0.5Cu/Cu system was discussed by the description of the equilibrium state. The calculated results based on experiments of the tension balances along each of the three interfaces show good agreement with theoretical analysis. Intermetallic compounds at the Sn–17Bi–0.5Cu/Cu interface are identified as Cu6Sn5 adjacent to the solder and Cu3Sn adjacent to the Cu substrate, respectively. These results are of practical interest for composite lead-free solders’ preparations and joining of Sn–17Bi–0.5Cu to Cu substrate.

The thickness control of lining is vital to the normal operation of converter. Vulnerable parts of the furnace would be found and repaired timely by applying thickness measuring technique by laser. According to the measured results, the load part of the facet of the converter is the weakest location of the lining in the early campaign life, while the section of the trunnion is the weakest in the middle campaign life. When it comes to the later stage of campaign, the erosion of lining is severe. In line with the quantification of erosion parts, the lining thickness range can be divided into three parts, which are safety smelting area, stability control area and dangerous area. The economic life of the furnace life, which is 20 to 23 thousand heats, can be maintained as the thinnest lining is still above the stable range when the campaign reaches mid-late period.

Wetting experiments in two cases have been carried out to measure the wettability between molten slag and MgO-C refractories. Especially, the variations of wettability with time are taken into consideration in this paper. The spread diameter increased significantly and the slag height decreased with the increase of the time from 0 to 237 s at 1 783 K. While the spread diameter changed slowly, and reached the steady state from 300 to 500 s. More specifically, the fitting formulae for diameter, height, area of the slag as a function of time have been determined. Moreover, the interfacial characteristics of the non-melting slag and MgO-C refractories and of the wetting slag and MgO-C refractories were investigated to further explain the wettability in two cases. With the help of the wetting experiment, adhesion and protection mechanism was demonstrated. It could optimize the slag splashing process and give guides to the increase of the converter lining life, which can make the contribution to the promotion of technological transformation and innovation of the steel industry.