Thermal diffusion in kinetic and equilibrium measurements by levitation technique

Abstract

NUMBER OF PAGES: xv,147. SCOPE AND CONTENTS:An experimental investigation of the rmal diffusion .,.,as carried out using a levitated iron sample and , a binary gas mixture of hydrogen and hydro ge n s ulphide . The iron was I iquid and the moving gas stream was at room temperat ure. A range of drop temperatures, gas flow rates and compo sitions was studied.The fluxes due to thermal diffusion were found to be significant in this pa rti cular system. Interpretation of the rate data for the sulphurisation and des u lphurisation of the iron showed a pronounced effect of thermal diffusion upon rate and equilibrium measurements.An overal I rate expression whi ch accounts for thermal diffusion and normal mass transfer in the ga s phase has been developed. It is in agreemen t with expe ri ment. Equi I ibriu m data in the I iterature have been corrected for thermal diffusion error by means of this expression. These corrected equi I ibria are in agreement with measurements ~zde by crucible techniques.i i · ACKNO\'/LEDGMENTS am indebted to Dr, A, ~~clean for his suggestion of this particular r e search project. A special debt is felt for his enthus iastic introduction of t he general field of iron-and steelmaking to the author . ' / I would like to record the deep gratitude which I feel to Dr. A. E.Hamielec and Dr. W-K. Lu. Both supervisors provided extensive advice which a ssisted my progress considerably. The guidance was continuous and always available, In addition, I appreciate particularly the freedom which they so readily permitted, to explore many fringe areas which were subsidiary to the main project.iii ·TABLE OF CONTENTS 38.Values of the Equilibrium Constant Found from Six Independent Experi-/ mental Rate Curves at 1675 and 1750°C.39. Correction of Equi 3.Cross-Section of a Typical Levitation Coi I and the Former on which it was Wound. 4.Apparatus for Calibration of Pyrometer on a Liquid Iron Melt . 5.Galibration Curve for Pyrometer Against Thermocouple. 6.Cross-Section of Device for Taking Samples of the Gas Mixtures for Analysis.7. Sulphur Content of Supercooled Drops for Rapid Quenching. Initial Rates of Sulphurisation of Drops Levitated in Various H 2 -H 2 SGas Ratios. 9.Weight Percent Sulphur in Levitated Drops Against Time (Table 8). DT Thermal diffusion coefficient. E Col lecfive constant defined by equation (7,2), e Interaction para meter for sulphur, s f Activity coe fficient for sulphur. K' log K' = log f + log K. Time of any operation.Velocity of th e gas.Weight of the drop. Driving force vectorMole fraction in a mixture of gasesThe rma l diffusion factor. Subscript o refers to the Fe-H 2 0-H 2 system in Chapter 7Subscript co refers to the bulk state (of gas or liquid).Subscript refers to the gas-I i quid interface.Subscript f refers to some average condition in the gas between state co and state i • This is a concept rather than a physical location. XV CHAPTER I INTRODUCTIONThe history of steelmaking shows that the manufacture of steel for many years, has been by processes which have involved t...

Effect of dissolved oxygen on the surface tension of liquid iron

“…Similar results were observed by others in the studies of iron-sulphur and iron-oxygen systems using the levitation technique with H2 -H2 Sand H2 -H 2 0 mixtures respectively (8).…”

“…The broken line corresponds to the equilibrium value according to Dastur and Chipman (7). The deviation at steady state is due to thermal diffusion (8). No measurements were made with a gas mixture having PH 2 0/PH 2 greater than 1.0 (which corresponds to about 0.272 wt.…”

“…equilibrium with the metal is lower in these species than the bulk composition of the gas. A quantitative treatment of this problem has been presented by Sunderland et ale (8). Since the oxygen contents reported in Figure 3 are the results of chemical analysis of the quenched droplets, thermal diffusion would not cause an error in dissolved oxygen determination.…”

Thermodynamic and Kinetic Aspects of Sulfur Evaporation from Fe–C Alloy Droplets

“…Formation of volatile sulfides during the experiments is thought to have an impact on the reliability of measurements. Also, as pointed out by Sunderland et al, 18) when gas mixtures are passed over molten alloys during gas dissolution experiments, the measured steady-state solubilities may differ from the true equilibrium values due to the presence of thermal diffusion effects. By contrast, thermal diffusion may be less relevant in the case of thermodynamic measurements based on sulfur evaporation in vacuum or inert atmosphere with a levitated droplet.…”

“…22) This relatively wide range of values seems to indicate that, for experiments conducted in a H 2 -H 2 S atmosphere, the measurements are more susceptible to errors that may arise from the effects of thermal diffusion. 18) …”