Metal degassing

In the vacuum region, pressures down to 0.00133 bar (0.0193 psia) are of interest to process engineers for process operations such as distillation, drying and evaporation. Some applications below 0.00132 bar (0.193 psia) are molten metal degassing, molecular distillation, and freeze drying. 

Some applications of cryogenic-fluid transfer require optimization of many aspects of transfer-system design. This study examines methods of transfer-line insulation, the problems of metal degassing, and line storage life. 

An effective and economical method for elimination or reduction of metal degassing is not known. However, the detrimental effects of the gas which has entered the vacuum space can be overcome by chemical combination with a getter or by adsorption with some material—in this case the solidified condensable substance. It is reasonable to expect that CO2 at 20 K would adsorb some gaseous hydrogen. Any oxygen or nitrogen present would, of course, be adsorbed or frozen out at 20°K. 

Data were taken on a cylindrical, guarded calorimetric apparatus (see Fig. 1). Associated equipment permits the introduction of known amounts of CO2 and H2 gas into the calorimeter vacuum space, the former for the condensing-vacuum study and the latter for the simulated metal degassing study. A wet test meter is used to measure boil-off gas from the calorimeter test chamber, thus permitting heat transfer calculations. 

Metal degassing may not be a problem in the service life of large vacuum-insulated lines. 

HBI is an effective trim coolant for molten steel in ladle metallurgy faciUties, ladle refiners, ladle furnaces, and vacuum degassers. It provides cold iron units in an ideal size and density for penetrating the ladle slag and cooling the metal. 

Lithium is used in metallurgical operations for degassing and impurity removal (see Metallurgy). In copper (qv) refining, lithium metal reacts with hydrogen to form lithium hydride which subsequendy reacts, along with further lithium metal, with cuprous oxide to form copper and lithium hydroxide and lithium oxide. The lithium salts are then removed from the surface of the molten copper. 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

Dispersed mixtures of boron and another metal are used as deoxidizing and degassing agents to harden steel (qv) (5,6), to increase the conductivity of copper (qv) in turbojet engines, and in the making of brass and bronze (see Copper alloys). Two examples are alloys of ferroboron and manganese boron. 

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

Similar relationships can be written for the dissolution of hydrogen and oxygen. These relationships are expressions of Sievert s law which can be stated thus the solubility of a diatomic gas in a liquid metal is proportional to the square root of its partial pressure in the gas in equilibrium with the metal. The Sievert s law behaviour of nitrogen in niobium is illustrated in Figure 3.8. The law predicts that the amount of a gas dissolved in a metal can be reduced merely by reducing the partial pressure of that gas, as for example, by evacuation. In practice, however, degassing is not as simple as this. Usually, Sievert s law is obeyed in pure liquid metals only when the solute gas is present in very low concentrations. At higher concentrations deviations from the law occur. 

The first condition must be satisfied for purification to occur. The second condition ensures that degassing occurs at a reasonably fast rate. Hydrogen, nitrogen, and oxygen behave differently with respect to the above requirements in different metals. 

Many metals take up considerable amounts of nitrogen in solid solution. The engassing and degassing of nitrogen in respect of metals is represented by the equilibrium... 

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