Slag-metal interface

For any chemical species there are probably many ways in which the U ansfer across the metal-slag interface can be effected under the constraint of the... 

Can one explain this importance of the slag Measurements of conductance as a function of temperature and of transport number indicate that the slag is an ionic conductor (liquid electrolyte). In the metal-slag interface, one has the classic situation (Fig. 5.81) of a metal (i.e., iron) in contact with an electrolyte (i.e., the molten oxide electrolyte, slag), with all the attendant possibilities of corrosion of the metal. Corrosion of metals is usually a wasteful process, but here the current-balancing partial electrodic reactions that make up a corrosion situation are indeed the very factors that control the equilibrium of various components (e.g., S ) between slag and metal and hence the properties of the metal, which depend greatly on its trace impurities. For example,... 

The cost of refractories on a global scale is around 2 billion US per annum. Frequently, erosion of refractories occurs around the metal/slag interface or the gas/slag interface, which is known as slag line attack (Figure 45). This has frequently been attributed to Marangoni convection [69]. 

The quality of the metal in a blast furnace is thus determined largely by electrochemical reactions at the slag-metal interface. Making good steel and varying its properties at... 

The corrosion product, a mixture of oxide, sulphide at the metal interface and sulphate outside, has a weak adhesive bond to the metal surface and cannot support large deposit masses. It is therefore unusual to find excessive amounts of sintered ash deposits and fused slag in the exact localities where severe high temperature corrosion occurs. Conversely, a strongly adhering matrix of sintered ash deposit in the absence of sulphate, sulphide or chloride phases is not markedly corrosive. 

Slag Line. The normal level of the slag/ metal interface in the working chamber... 

Electrocapillarity curves have been obtained for interfaces between molten metals, and either molten salts or molten slags, which are ionic in nature [6]. It has been established that the metal side of the interface has a net positive charge and the slag a net negative charge. In this case there are no solvent molecules to separate the ions from one another. It is believed that there is an excess charge at the interface (+ for metal and - for the slag) and this excess falls to zero over 3-4 ionic, or metal, molecule layers. 

Consider an inclusion at the slag/metal interface. For an inclusion to be removed it is necessary for it to travel through the slag/metal interface and on into the slag phase. The spreading coefficient, S, is a measure of the ability of a liquid (denoted M but could be metal or slag phase) to spread across the solid and is defined by Equation 8. 

When an electric field is applied to a system consisting of droplets of liquid phase B present in liquid A, electrocapillary forces can bring about the movement of these droplets. These forces can be used to recover trace metals and metal mattes from waste pyrometallurgical slags [47]. The driving force in thermocapillary flows is (dy/dT) i.e. the temperature dependence of the surface tension. Whereas in electrocapillarity the driving force is (dy/dE) where E is the electrical potential at constant chemical potential X, and (dy/dE) is equal [47] to the surface excess charge density (qi) at the droplet interface (Equation 18). 

Figure 48 Schematic representation of the manner in which local corrosion of the immersion nozzle at the slag-metal interface proceeds [69].

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