Metals vacuum melting

Two other factors are noteworthy the deleterious effects on chemical and mechanical properties of small amounts of impurities residual from extraction of the metal, and its toxicity. The first of these factors is obviated by vacuum melting the raw metal (for purification) as an essential prerequisite to further processing. The toxicity of beryllium is essentially a pulmonary problem and great care must be taken in handling the finely divided metal or its compounds. In practice, this type of activity is usually carried out under well-ventilated conditions. Certain tolerance levels for atmospheric beryllium are now internationally accepted and merit careful study before work on beryllium is embarked upon. 

Reduction of the fluoride Generally, Ca with RF3 is heated up to 1450°C in a Ta crucible. After cooling, the slag and the reduced metal are easily separated. The metal obtained contains Ca, some fluoride and Ta, which can be removed by vacuum melting (for La, Ce, Pr, Nd) or by vacuum melting plus distillation (Gd, Tb, Dy, Ho, Er, Lu, Sc, Y). Especially pure Ca must be used, such as triple-distilled Ca further re-distilled under low He pressure and handled in He-filled glove boxes. 

Potential hazards associated with electron beam vacuum melting of metals include the possibility of ignition of metal aerosols or condensate films in the event of sudden loss of vacuum at elevated temperatures. 

Vacuum Melting without Distillation of the Product Metal... 

Thorium metal also can he prepared hy thermal reduction of its hahdes with calcium, magnesium, sodium, or potassium at elevated temperatures (950°C), first in an inert atmosphere and then in vacuum. Fluoride and chloride thorium salts are commonly employed. Berzehus first prepared thorium by heating tetrachloride, ThCh, with potassium. Magnesium and calcium are the most common reductant. These metals are added to thorium halides in excess to ensure complete reduction. Excess magnesium or calcium is removed by heating at elevated temperatures in vacuum. One such thermal reduction of hahdes produces thorium sponge, which can be converted into the massive metal by melting in an electron beam or arc furnace. 

Post reduction treatment Vacuum melting (i) Vacuum distillation of excess reductant and reduc-tant halides (ii) Purification with respect to contamination from container (a) Holding above the melting point to get rid of Ta picked up during reduction (for Ce, La, Pr and Nd) (b) Vacuum distillation of metals and their collection on the condensers (Y, Gd, Tb, Lu, Dy, Ho, Er) ... 

Industrially, the operation is carried out on 20-30 kg of metal at a time. The metal is melted under vacuum then the Hj is progressively introduced. The heat given off by ... 

When a metal contains impurities more volatile than the metal, such as a volatile reductant metal or its halide, heating the metal well above its melting point in vacuum serves as a useful purification step. The lighter rare earth and actinoid metals, especially those prepared by the iodine vapor process, are efficiently refined by vacuum melting . Vacuum melting is not often employed industrially because of the expenses associated with heating and corrosion of crucibles. 

W-lOTi alloy targets are produced by blending ultrapure tungsten (see also Section 5.7.6) and titanium powders (obtained by vacuum melting and subsequent pulverizing), followed by pressure sintering. The impurity level has to be very low, in particular, with respect to radioactive elements (U, Th) and mobile alkaline metals (Na, K). 

The preparation of the alloys can proceed by two essentially different methods. Vacuum melting in an induction furnace is the more common method. First, Fe and B are melted in alumina crucibles under purified argon gas. Subsequently, the reaction vessel is degassed under vacuum and Nd metal is added to the melt after the latter has reached a temperature only slightly above the Fe-B liquidus temper-... 

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