KTH Industrial Engineering and Management Sulfur and Nitrogen in Ladle Slag
Sweden Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av Teknologie Doktorsexamen, fredagen den 1 april 2016, ABSTRACT The present work deals with some aspects of slags related to secondary metallurgy in the steelmaking process. More specifically the focus is given to sulfur and nitrogen in ladle slags. Even though slags have been fairly well–researched in the past, the available data for these elements in typical ladle slag compositions is rather scarce. In some cases the available data is in discordance. There are also inconsistencies between the literature data and what is commonly observed in the industrial processes. Sulfide capacities were measured at steelmaking temperatures, 1823–1873 K, in ladle slags. The data was found to be in reasonable agreement with the industrial process norms. The sulfide capacity was found to increase with the basic oxides CaO and MgO; and decrease with the acidic components Al 2 O 3 and SiO 2. The sulfide capacity was also found to increase with temperature. The dependence of sulfide capacity on the oxygen partial pressure, for slags containing multivalent elements, was investigated experimentally at 1873 K with a slag containing vanadium oxide. A strong dependence of oxygen partial pressure was observed. The sulfide capacity increase by more than two orders of magnitude when the oxygen partial pressure was increased from 4.6×10-16 atm to 9.7×10-10 atm. The nitrogen solubility and the effect of carbon was investigated in typical ladle slags and the CaO–MgO–SiO 2 system at 1873 K. Carbon increases the nitrogen solubility substantially. In the absence of carbon, the nitrogen solubility is extremely low. Low concentrations of cyanide was detected in the carbon saturated slag. This was much lower than the total nitrogen content and formation of cyanide cannot explain the large increase. The possibility of removing sulfur with oxidation from used ladle slag was investigated experimentally at 1373–1673 K. The sulfur removal of mostly solid slag was found to be a slow process, and would not suitable for industrial practice. At 1673 K the slag was mostly liquid and more than 85% of the sulfur was removed after 60 min of oxidation in pure oxygen atmosphere. ii ACKNOWLEDGEMENTS
Estimation of sulphide capacities of multi-component silicate melts
The present paper presents a mathematical model for the estimation of sulphide capacities. The sulphide capacity, Cs is expressed as C S = exp (- ΔG 0 /RT) exp (- ξ/RT), where ξ is a function of both temperature and composition and ΔG 0 is the standard Gibbs energy change for the reaction, 1/2S 2 (gas)+O -2 (slag)=1/2O 2 (gas)+S -2 (slag). By optimizing ξ, the sulphide capacities could be estimated as functions of temperature and composition. The slag composition is described with a Temkin approach, where complex polymeric ions are considered as dissociated to simple species. Parallel experimentation is being carried out to get reliable data for the calculations. The model has been applied to the binary systems CaO-SiO 2 , CaO- Al 2 O 3 , MnO-SiO 2 as well as the ternary systems CaO-MnO-SiO 2 and CaO-Al 2 O 3 - SiO 2 . The results show that reliable predictions of the sulphide capacities can be made using the above model, and thus offer a powerful tool to the process metallurgists.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.