Plasma smelting

The focus of this section is the emission of ultraviolet and visible radiation following thermal or electrical excitation of atoms. Atomic emission spectroscopy has a long history. Qualitative applications based on the color of flames were used in the smelting of ores as early as 1550 and were more fully developed around 1830 with the observation of atomic spectra generated by flame emission and spark emission.Quantitative applications based on the atomic emission from electrical sparks were developed by Norman Lockyer (1836-1920) in the early 1870s, and quantitative applications based on flame emission were pioneered by IT. G. Lunde-gardh in 1930. Atomic emission based on emission from a plasma was introduced in 1964. 

Plasma DC arc smelting technology - South Africa Anglo American Corp. Carbothermic smelting of ilmenite in DC arc plasma furnace to yield pig iron and titania slag (A) Namakwa Sands Ltd., South Africa (B) ISCOR, South Africa... 

The graph shows that there are no more solid substances in the universe at temperatures above 3600 °C — only smelts, gases, and plasmas. 

Tetronics A process for treating dusts from electrical arc furnaces for making steel and nonferrous metals. Volatile metals (zinc, lead, cadmium) are recovered, and residual slag is nontoxic and suitable for landfill. The dusts, mixed with coal dust and a flux, are fed to a furnace heated by a plasma gun. The metal oxides present are selectively reduced and the vapors of zinc, lead, and cadmium are condensed in a modified Imperial Smelting furnace. Developed by Tetronics Research Development Company, United Kingdom, and first commercialized for steel dusts at Florida Steel, Jackson, TN, in 1989. Seven plants were operating in several countries in 1992. 

Spherical particles proved to be superior in several applications owing to their favorable properties. Thus, they are used in thermal spraying for their excellent flowabil-ity, in powder metallurgy because of their excellent reproducibility in manufacturing parts with controlled porosity and as a filler material, as well. Metal microspheres can be easily produced by melt atomization. Similar method in the case of ceramics is impractical. Micron-sized ceramic particles, however, can be smelted by thermal plasmas that provide exceptional conditions for spheroidization due to its high temperature. In terms of purity and residence time of the particles in the hot temperature core, RF plasmas provide better conditions as compared to arc plasmas. 

All the alloys studied were smelted on a base of commercial titanium alloy of technical purity BT1-0 (Fe<0.25 Si<0.1 C<0.07 N<0.04 O<0.2 others<0.3. Compositions are provided in wt. %) with plasma-arc method in argon atmosphere. The BT1-0 alloy itself is determined as pseudo a-alloy, which has coefficient of P-phase stabilization kp = 0.05 [4, 5], Temperatures of smelts were between 1620-1660 °C. Liquid metal was decanted into graphite mold inside of melting chamber. Obtained cylindrical ingots of 60 mm diameter and 150-400 mm length were cooled to 600 °C inside of chamber and after that to room temperature in air outside of equipment. 

Despite these warnings of Craddock, which also apply to other mined and smelted metals like silver and iron, there have been serious attempts to glean locational information from analytical data. Berthoud, in his thesis research and in a paper published with several collaborators using plasma emission and spark source mass spectroscopy, analyzed the multivariate compositional data of copper ores from more than 25 copper mines in Iran, that would have been important in early (4th and 3rd millennium) metallurgy. Their feeling was that the Craddock Assumption 1) was satisfied well enough and furthermore that it was possible to trace certain 4th millennium objects from Susa to a native copper source at Talmessi. Of course, with native copper, Craddock Assumptions 2) and 3) were not tested. 

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