Metal pool

The melt is heated by passing a large elecuical cunent between two electrodes, one of which is tire metal rod to be refined, and the otlrer is the liquid metal pool standing in a water-cooled copper hearth, which collects the metal drops as tlrey fall tluough the molten electrolyte. This pool tlrerefore freezes at the bottom, forming the ingot. Under optimum chcumstances tire product billet takes the form of a cylindrical solid separated from the molten salt by... 

Speciation science seeks to characterise the various forms in which PTMs occur or, at least, the main metal pools present in soil. This chapter provides a review of the single and sequential chemical extraction procedures that have been more widely applied to determine the plant and the human bioavailability of PTMs from contaminated soil and their presumed geochemical forms. Examples of complementary use of chemical and instrumental techniques and applications of PTMs speciation for risk and remediation assessment are illustrated. 

Metal bioavailability is the fraction of the total metal occurring in the soil matrix, which can be taken up by an organism and can react with its metabolic system (Campbell, 1995). Metals can be plant-bioavailable, if they come in contact with plants (physical accessibility) and have a form which can be uptaken by plant roots (chemical accessibility). Soil metals become accessible for humans by ingestion, inhalation and dermal contact. Available forms of PTMs are not necessarily associated with one particular chemical species or a specific soil component. Main soil PTMs pools of different mobility, target organisms and routes of transfer are sketched in Fig. 9.2. The most labile fraction, corresponding to the soluble metal pool, occurs as either free ions or soluble complexed ions and is considered the... 

The method of soil suspensions extracts is based on metal desorption/dissolution processes, which primarily depend on the physico-chemical characteristics of the metals, selected soil properties and environmental conditions. Metal adsorption/ desorption and solubility studies are important in the characterization of metal mobility and availability in soils. Metals are, in fact, present within the soil system in different pools and can follow either adsorption and precipitation reactions or desorption and dissolution reactions (Selim and Sparks, 2001). The main factors affecting the relationship between the soluble/mobile and immobile metal pools are soil pH, redox potential, adsorption and exchange capacity, the ionic strength of soil pore water, competing ions and kinetic effects (e.g. contact time) (Evans, 1989 Impelhtteri et al., 2001 McBride, 1994 Sparks, 1995). 

The most used liquid metal pool electrode is the aluminum cathode (m.p. 660°C) in the Hall-Heroult aluminum extraction cell. Alkali metals and alkaline-earth metals are also used as liquid cathodes in their molten salt extraction processes. 

Anode elements are commonly prebaked low ash carbon blocks, since any ash residue ends up in the electrolyte. These are electrically connected to copper or aluminum bus bars (heavy electrical conductors) suspended over the cell, which also provide mechanical support and a means for vertical adjustment of the anode elements. An anode variant is the Soderberg paste option, which uses powdered petroleum coke formed into a paste with hard pitch. Electrical contact is established and mechanical adjustment provided by using specially shaped steel pins (Fig. 12.3). As the baked portion of this anode (Fig. 12.3) is gradually consumed, the paste approaches the molten electrolyte and the volatile components in the paste vaporize to leave a hard baked working anode element. Either type of anode element is consumed at the rate of 1-2 cm/day during normal operation, requiring periodic vertical adjustment to maintain an anode-aluminum metal pool spacing of about 5 cm. 

EVF level the pool temperature field, intensify heat and mass transfer in the metal pool, thus providing the formation of metal with a high chemical and physical homogeneity. Vibration of the melt allows metal structure refining. 

It is shown that superposition of external magnetic field on the melting zone makes it possible to control the depth and shape of the metal pool. Mechanical properties of a new class of titanium alloys with an intermetallic strengthening, produced by MEM method, are given. 

Key words electroslag melting, magnetic field, metal pool, titanium alloys, ingot. 

Figure 1. Scheme of MEM process 1 - consumable electrode, 2 - slag pool, 3 - metal pool, 4 - ingot, 5 -electromagnetic system, 6 - vacuum chamber, 7 - mould. 

EFFECT OF MAGNETIC FIELDS ON PARAMETERS OF METAL POOL... 

Volume and shape of metal pool in ESR is one of the most important characteristics, which define the quality of metal of ingot being melted. With increase in volume and depth of metal pool the length of zone of two-phase state is increased which is the source of all defects of a liquation origin. Therefore, to produce quality ingots, it is necessary to approach shallow shape of the metal pool. 

In traditional scheme of ESR the flows of melt are formed in the slag pool, which are directed from a consumable electrode, along its axis downward to the metal pool [3], These flows of overheated slag promote the... 

This restructuring of melt circulation changes greatly the distribution of hydrodynamic pressure to the metal pool surface. 

Figure 3. Shape of metal pool during melting in longitudinal field a - B=0 T b - B=0,06 T c - B=0,1 T.

MEM in longitudinal magnetic field makes it possible to decrease in depth (volume) of the metal pool and to equalize the front of metal crystallization. 

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