Papers by Keyword: Interface Concentration

Abstract: Ammonia absorption process of ammonia vapor into ammonia water solution has been investigated experimentally, by inserting superheated ammonia vapor into a test cell containing a stagnant pool of ammonia water solution of several ammonia mass fractions, Ci. Before commencing the experiment, the pressure in the test cell corresponds to the equilibrium vapor of the ammonia-water system at room temperature. When the valve is opened, mechanical equilibrium is established quickly and the ammonia vapor diffuses into ammonia solution [1]. The difference between the initial pressure in the vapor cylinder and the initial pressure in the test cell ΔPi is found to have a major influence not only on the absorption rate but also on the estimated interface concentration. The interface concentration Cint of the cases ΔPi = 50 and 100 kPa exhibits a similar tendency, Cint decreases rapidly compared to other initial pressures ΔPi = 150 and 200 kPa. On the other hand, the interface concentration Cint of the cases ΔPi = 250 and 300 kPa are increasing within about 50 sec, then are hardly changing with time. They behave almost in a similar way as of Cint = 0.27 kg/kg. A correlation which gives the total absorbed mass of ammonia as a function of the initial concentration, the initial pressure difference and time is derived. In addition, the absorbed mass at no pressure difference could be estimated from the absorbed mass at initial pressure difference.

Abstract: Process of high-temperature (650°С) interaction of Cr(Si)-containing steel EP-823 with stagnant Pb melt containing oxygen (CО[Pb] » 10-5 - 10-6 mass.%) was theoretically and experimentally investigated. The structure and composition of oxide layer formed on the steel surface during exposure to Pb melt was examined. It is determined that thin (£ 1000 Å) Cr(Si) - rich oxide layer is formed on the steel surface in the early stages of oxidation. Oxide layer is being formed intensively over the grain boundaries followed by a lateral diffusion of Cr and spreading of Cr2O3 over alloy surface. Iron diffuses through the Cr(Si) - rich continuous oxide layer in the course of time. The formed oxide layer protects the steel against liquid metal penetration. Kinetics of iron diffusion dissolution in the liquid Pb is analytically described taking into account the chemical interaction between iron and oxygen. It is assumed that oxygen ions serves as a “traps” for iron ions and eliminates them from the diffusion flux. Fe−O complexes are considered as separate slowmoving components of the melt. In order to formulate the diffusion problem equations with additional parameter describing the volume reaction between Fe and O in melt and boundary conditions involved the time dependence of oxygen concentration at the interface of both melt and solid metal sides were used. Result is obtained in analytical form using the Laplace transformation. Analysis of obtained relations allow to assert that in the case of dissolution of iron in the lead melt containing “oxygen traps” the diffusion zone are less than that in the conditions of dissolution (without “traps”). However, the total concentration of iron both on surface of oxide layer and in the contact zone of melt is increased.

Abstract: The phenomenological theory for describing high-temperature interaction between metal and diluted gaseous medium has been developed. The theory is based on the assumption of duplex contact layer existence in the vicinity of interface (with relative thickness 2 d), where chemical reactions and processes of gas component migration occur. The non-stationary conditions of mass transfer at the interface are described involving effective average parameters. These conditions allow considering a wide spectrum of boundary diffusion phenomena (in a short and prolonged time ranges), in order to describe the kinetics of accumulation of diffusing component close to the interface. The description of the kinetic of gaseous saturation of metal (nitriding and borating) in the diluted medium becomes a partial proof of the suggested models. In order to approach the diffusion phenomena, boundary conditions, which contain, besides the coordinate derivative of concentration function, also the time derivative, were suggested. The derived equations describe the time dependence of change of surface concentration of gaseous component, the kinetics of its accumulation owing to chemical reaction, the specimen mass change owing to both, the diffusive addition dissolution in metal and its chemical interaction. The role of temperature is also discussed.