Iron, zone-refined

Before this treatment, the cassiterite content of the ore is increased by removing impurities such as clay, by washing and by roasting which drives off oxides of arsenic and sulphur. The crude tin obtained is often contaminated with iron and other metals. It is, therefore, remelted on an inclined hearth the easily fusible tin melts away, leaving behind the less fusible impurities. The molten tin is finally stirred to bring it into intimate contact with air. Any remaining metal impurities are thereby oxidised to form a scum tin dross ) on the surface and this can be skimmed off Very pure tin can be obtained by zone refining. 

During this zone refining, the primary (igneous) rocks are transformed into secondary minerals. These include (1) clay minerals, such as phillipsite, chlorite, montmo-rillonite (smectite), saponite, celadonite, and zeolite (2) iron oxyhydroxides (3) pyrite (4) various carbonates and (5) quartz. These minerals form rapidly, within 0.015 and 0.12 million years after creation of the oceanic crust at the MOR. During these alteration... 

For the production of superpurity aluminum on a large scale, the Hoopes cell is used. This cell involves three layers of material. Impure (99.35 to 99.9% aluminum) metal from conventional electrolytic cells is alloyed with 33% copper (cutcctic composition) which serves as the anode of the cell A middle, fused-salt layer consists of 60% barium chloride and 40% AlF 1.5NaF (chiolite), mp 72(TC. This layer floats above the aluminum-copper alloy. The top layer consists of superpurity aluminum (99.995%). The final product usually is cast in graphite equipment because iron and other container metals readily dissolve in aluminum. For extreme-purity aluminum, zone refining is used. This process is similar to that used for the production of semiconductor chemicals and yields a product that is 99.9996% aluminum and is available in commercial quantities. 

Figure 8.1. Effect of heat treatment of cold-worked 0.076% C steel (85% reduction of thickness) and zone-refined iron (50% reduction of thickness) on corrosion in deaerated 0.1A/ HCI, 25 C [1]. (Reproduced with permission. Copyright 1964, The Electrochemical Society.)...

R. L. Smith and J. L. Rutherford. "Tensile Properties of Zone Refined Iron in the Temperature Range from 298 to 4.2 K, Trans. AIME, (July, 1957). 

The influence of internal stresses on the corrosion current is also not clear. Thus, Foroulis observed that the corrosion rate of zone-refined iron was the same whether it had been cold-worked or annealed. 

Figure 19. Steady-state polarization curves for zone-refined iron in 0.5M SO4 recorded after at least 1 day of immersion. (From Ref. 137, by the courtesy of the authors.)...

Despite this, owing to the sluggish nature of phenomena taking place at the interface, changes in the waiting time from 15 min to 24 h lead to various steady-state polarization curves. For example, Akiyama et al. found that the anodic Tafel slope of zone-refined iron in acidic sulfate solutions decreased with the waiting time, —from 55 mV dec" after 2 min to 42 mV dec" after 10 h, considered to be the time necessary to reach a steady-state value. 

Refined tellurium contains traces of lead, copper, iron, selenium, and other impurities. Highly pure tellurium can be obtained either by distilling refined tellurium in vacuum or by the zone melting process. The last traces of selenium can be removed as hydride by treating molten tellurium with hydrogen. 

Overall, this refined use of hydrogen concentrations supported the results of the bioassays and the complex system of redox zones inferred from the distribution of dissolved redox-sensitive species. The Grindsted Landfill (DK) plume is host to all of the proposed redox reactions, but also to secondary oxidation-reduction reactions involving ammonium, methane, manganese oxides, ferrous iron, and sulfides. 

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