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^melting Techniques Make: The physical and chemical properties of metal are characteristic of transition element general. Its melting point of 3,440 ± 50° I exceeded by that of only one other metal, tung« element number 74; its density of 21.04 grams cubic centimeter is surpassed only by that of mium, element number 76. It is susceptible chemical attack by oxidizing agents and displai variety of oxidation states ranging from (-1)VII), the latter being the most stable and im-srtant. Due to its high melting point and its sus-iptibility to air oxidation at elevated tempera-res, powder metallurgy techniques in a nonoxi-zing environment are employed in fabricating e metal.
Pyrrhotite occurs in basic igneous rocks, and sometimes with other sulfide minerals in high-temperature ore veins, where it is one of the first sulfide minerals to form. It is a common mineral in the nickel deposits at Sudbury, Ontario, Canada, where it is associated with the nickel mineral pentlandite. Not only is the nickel recovered, but improved ^melting techniques make it possible to use the pyrrhotite as an iron ore. It is also found in Norway. Sweden, Finland, Bavaria, Brazil, Mexico, Tennessee, and many of the Western states.
Plate Glass.—To melt a mixture for plate glass, the heat enters the melting area from the sides and flows over the surface of the mixture. Although there is no actual line of demarcation, there are three zones in the melting tank: the melting zone, the fining zone, and the working zone. Each is distinct, and under proper conditions is readily discernible. |
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