The melting temperature of Z coal ash was reduced by adding calcium–magnesium compound flux(WCaO/WMgO=1). In the process of simulated coal gasification, the coal ash and slag were prepared. The transformation of mine...The melting temperature of Z coal ash was reduced by adding calcium–magnesium compound flux(WCaO/WMgO=1). In the process of simulated coal gasification, the coal ash and slag were prepared. The transformation of minerals in coal ash and slag upon the change of temperature was studied by using X-ray diffraction(XRD). With the increase of temperatures, forsterite in the ash disappears, while the diffraction peak strength of magnesium spinel increases,and the content of the calcium feldspar increases, then the content of the amorphous phase in the ash increases obviously. The species and evolution process of oxygen, silicon, aluminum, calcium, magnesium at different temperatures were analyzed by X-ray photoelectron spectroscopy(XPS). The decrease of the ash melting point mainly affects the structural changes of silicon, aluminum and oxygen. The coordination of aluminum and oxygen in the aluminum element structure, e.g., tetracoordinated aluminum oxide, was changed. Tetrahedral [AlO4] and hexacoordinated aluminoxy octahedral [AlO6] change with the temperature changing. The addition of Ca2+ and Mg2+ destroys silica chain, making bridge oxide silicon change into non-bridge oxysilicon;and bridge oxygen bond was broken and non-bridge oxygen bond was produced in the oxygen element structure. The addition of calcium and magnesium compound flux reacts with aluminum oxide tetrahedron, aluminum oxide octahedron and silicon tetrahedron to promote the breakage of the bridge oxygen bond. Ca2+ and Mg2+ are easily combined with silicon oxide and aluminum oxide tetrahedron and aluminum. Oxygen octahedrons combine with non-oxygen bonds to generate low-melting temperature feldspars and magnesite minerals, thereby reducing the coal ash melting temperatures. The structure of kaolinite and mullite was simulated by quantum chemistry calculation, and kaolinite molecule has a stable structure.展开更多
Based on recently published experimental data, the Riboud model was modified for viscosity estimation of the slags containing calcium fluoride. The estimated values were in good agreement with measured data. Reasonabl...Based on recently published experimental data, the Riboud model was modified for viscosity estimation of the slags containing calcium fluoride. The estimated values were in good agreement with measured data. Reasonable estimation can be achieved using the modified Riboud model for mould fluxes and ESR (eletro slag remelting) slags. Especially for ESR slags, the modified Riboud model can provide much more precise values than the original Riboud model.展开更多
Slagging is a major problem in boilers,especially the low-rank coal applied in boilers.In this study,the influence of heat transfer surface on the slagging characteristics of a pilot-scale furnace was investigated.Ni ...Slagging is a major problem in boilers,especially the low-rank coal applied in boilers.In this study,the influence of heat transfer surface on the slagging characteristics of a pilot-scale furnace was investigated.Ni coatings were applied in modifying the deposition surface to control slagging.The growth characteristics of the slag were studied using an online digital image technique.Scanning electron microscopy linked with energy-dispersive X-ray analysis and X-ray diffraction(XRD)were applied to investigate the microstructure,semi-quantitative chemical composition,and mineralogy of slag samples.Ni coating demonstrated a positive effect on the mitigation of slagging.Results revealed that the thicknesses of the slag initially increased with experimental time and then inclined toward stable values for both cases(Case 1:substrate material;Case 2:modified surface).The stable thicknesses for Cases 1 and 2 were 4.91 mm and 3.95 mm,respectively.The heat transfer efficiency was improved by approximately 18.2%with the application of Ni coating for probe surface modification.The mechanism of the mitigation of slagging was investigated in this study.XRD results revealed that the content of alkali reduced when the surface was coated with Ni.The alkali significantly affected the adhesion behavior of the deposition.Hence,Ni coating showed potential in reducing slagging and increasing the efficiency of boilers.The overall study makes a contribution to a deep understanding of the effect of Ni coating on the growth characteristics of the slag.展开更多
Monolithic stoppers play a very important role in continuous casting（ short for CC）. Sometimes,the stopper slag line is seriously eroded and broken,CC has to pause. The research shows that there are three main reaso...Monolithic stoppers play a very important role in continuous casting（ short for CC）. Sometimes,the stopper slag line is seriously eroded and broken,CC has to pause. The research shows that there are three main reasons which bring severe erosion of monolithic stopper slag line. Firstly,much Fe_2O_3 and MnO in slag react with carbon（ C） in the stopper,C is gradually eroded and erosion resistance of the stopper greatly weakens. Secondly,F increase in tundish covering flux will quicken erosion of the stopper slag line. Thirdly, High LOI of tundish covering flux also makes erosion of the stopper slag line speed up. On one hand,CaCO_3 in tundish covering flux decomposes and brings CO_2; on the other hand,minerals with water in tundish covering flux decompose at high temperatures and bring water vapor.Then CO_2 and water vapor react with C in the stopper,C is gradually eroded,aggravating the erosion.展开更多
Prevention of nitrogen porosity in weld metal deposited with self-shielded flux cored wire with CaF2-TiO2-MgO slag system can be accomplished by using a 'killing agent' such as titanium to react with nitrogen ...Prevention of nitrogen porosity in weld metal deposited with self-shielded flux cored wire with CaF2-TiO2-MgO slag system can be accomplished by using a 'killing agent' such as titanium to react with nitrogen dissolved in the weld metal. The amount of titanium needed to prevent porosity is calculated thermodynamically for various dissolved nitrogen levels. Experimental flux cored wires are used to verify the thermodynamic model. It is concluded that approximately 0.11 wt% titanium in the weld deposit is need to prevent nitrogen porosity when welding without externally applied shielding.展开更多
In order to solve the problem of the high surface longitudinal crack ratio of heavy peritectic steel slabs produced by the No. 3 continuous caster at Baosteel,the physical properties of the original mold flux and the ...In order to solve the problem of the high surface longitudinal crack ratio of heavy peritectic steel slabs produced by the No. 3 continuous caster at Baosteel,the physical properties of the original mold flux and the optimized mold flux were compared in a comprehensive way by using analytical measures, such as a slag film heat-flow simulator, a thermowire molten flux crystallization tester and an X-ray diffractometer in the laboratory. The results reveal that one of the major reasons for the cracks is the poor heat transfer ability of the original mold flux. However, the optimized mold flux with a high basicity features a high crystallizing rate,low crystallization temperature and low heat-flow density. Therefore, the optimized mold flux is more suitable for casting peritectic steel by the heavy slab continuous caster. The test results show that the slabs produced by using the optimized mold flux had no surface longitudinal crack in four test casts, while the surface longitudinal crack ratio of the slabs produced by using the original mold flux was 5%. The optimized mold flux can effectively prevent slab surface longitudinal cracks from occurring.展开更多
基金Supported partially by the Major Science and Technology Special Projects Foundation of Anhui Province(15czz02045)the Natural Science Foundation of Anhui Province(1508085MB41)the China Postdoctoral Science Foundation(2015M571915)
文摘The melting temperature of Z coal ash was reduced by adding calcium–magnesium compound flux(WCaO/WMgO=1). In the process of simulated coal gasification, the coal ash and slag were prepared. The transformation of minerals in coal ash and slag upon the change of temperature was studied by using X-ray diffraction(XRD). With the increase of temperatures, forsterite in the ash disappears, while the diffraction peak strength of magnesium spinel increases,and the content of the calcium feldspar increases, then the content of the amorphous phase in the ash increases obviously. The species and evolution process of oxygen, silicon, aluminum, calcium, magnesium at different temperatures were analyzed by X-ray photoelectron spectroscopy(XPS). The decrease of the ash melting point mainly affects the structural changes of silicon, aluminum and oxygen. The coordination of aluminum and oxygen in the aluminum element structure, e.g., tetracoordinated aluminum oxide, was changed. Tetrahedral [AlO4] and hexacoordinated aluminoxy octahedral [AlO6] change with the temperature changing. The addition of Ca2+ and Mg2+ destroys silica chain, making bridge oxide silicon change into non-bridge oxysilicon;and bridge oxygen bond was broken and non-bridge oxygen bond was produced in the oxygen element structure. The addition of calcium and magnesium compound flux reacts with aluminum oxide tetrahedron, aluminum oxide octahedron and silicon tetrahedron to promote the breakage of the bridge oxygen bond. Ca2+ and Mg2+ are easily combined with silicon oxide and aluminum oxide tetrahedron and aluminum. Oxygen octahedrons combine with non-oxygen bonds to generate low-melting temperature feldspars and magnesite minerals, thereby reducing the coal ash melting temperatures. The structure of kaolinite and mullite was simulated by quantum chemistry calculation, and kaolinite molecule has a stable structure.
文摘Based on recently published experimental data, the Riboud model was modified for viscosity estimation of the slags containing calcium fluoride. The estimated values were in good agreement with measured data. Reasonable estimation can be achieved using the modified Riboud model for mould fluxes and ESR (eletro slag remelting) slags. Especially for ESR slags, the modified Riboud model can provide much more precise values than the original Riboud model.
基金Supported by the National Natural Science Foundation of China(51476137)National Science Fund for Distinguished Young Scholars(51825605)
文摘Slagging is a major problem in boilers,especially the low-rank coal applied in boilers.In this study,the influence of heat transfer surface on the slagging characteristics of a pilot-scale furnace was investigated.Ni coatings were applied in modifying the deposition surface to control slagging.The growth characteristics of the slag were studied using an online digital image technique.Scanning electron microscopy linked with energy-dispersive X-ray analysis and X-ray diffraction(XRD)were applied to investigate the microstructure,semi-quantitative chemical composition,and mineralogy of slag samples.Ni coating demonstrated a positive effect on the mitigation of slagging.Results revealed that the thicknesses of the slag initially increased with experimental time and then inclined toward stable values for both cases(Case 1:substrate material;Case 2:modified surface).The stable thicknesses for Cases 1 and 2 were 4.91 mm and 3.95 mm,respectively.The heat transfer efficiency was improved by approximately 18.2%with the application of Ni coating for probe surface modification.The mechanism of the mitigation of slagging was investigated in this study.XRD results revealed that the content of alkali reduced when the surface was coated with Ni.The alkali significantly affected the adhesion behavior of the deposition.Hence,Ni coating showed potential in reducing slagging and increasing the efficiency of boilers.The overall study makes a contribution to a deep understanding of the effect of Ni coating on the growth characteristics of the slag.
文摘Monolithic stoppers play a very important role in continuous casting（ short for CC）. Sometimes,the stopper slag line is seriously eroded and broken,CC has to pause. The research shows that there are three main reasons which bring severe erosion of monolithic stopper slag line. Firstly,much Fe_2O_3 and MnO in slag react with carbon（ C） in the stopper,C is gradually eroded and erosion resistance of the stopper greatly weakens. Secondly,F increase in tundish covering flux will quicken erosion of the stopper slag line. Thirdly, High LOI of tundish covering flux also makes erosion of the stopper slag line speed up. On one hand,CaCO_3 in tundish covering flux decomposes and brings CO_2; on the other hand,minerals with water in tundish covering flux decompose at high temperatures and bring water vapor.Then CO_2 and water vapor react with C in the stopper,C is gradually eroded,aggravating the erosion.
文摘Prevention of nitrogen porosity in weld metal deposited with self-shielded flux cored wire with CaF2-TiO2-MgO slag system can be accomplished by using a 'killing agent' such as titanium to react with nitrogen dissolved in the weld metal. The amount of titanium needed to prevent porosity is calculated thermodynamically for various dissolved nitrogen levels. Experimental flux cored wires are used to verify the thermodynamic model. It is concluded that approximately 0.11 wt% titanium in the weld deposit is need to prevent nitrogen porosity when welding without externally applied shielding.
文摘In order to solve the problem of the high surface longitudinal crack ratio of heavy peritectic steel slabs produced by the No. 3 continuous caster at Baosteel,the physical properties of the original mold flux and the optimized mold flux were compared in a comprehensive way by using analytical measures, such as a slag film heat-flow simulator, a thermowire molten flux crystallization tester and an X-ray diffractometer in the laboratory. The results reveal that one of the major reasons for the cracks is the poor heat transfer ability of the original mold flux. However, the optimized mold flux with a high basicity features a high crystallizing rate,low crystallization temperature and low heat-flow density. Therefore, the optimized mold flux is more suitable for casting peritectic steel by the heavy slab continuous caster. The test results show that the slabs produced by using the optimized mold flux had no surface longitudinal crack in four test casts, while the surface longitudinal crack ratio of the slabs produced by using the original mold flux was 5%. The optimized mold flux can effectively prevent slab surface longitudinal cracks from occurring.
