Melting point of the metal

Values of the average work function (<(), electronvolts) for the commonly used filament metals. The melting points of the metals are also shown to give some guidance as to the maximum temperature at which they can be used. Normally, the practical maximum would lie a few hundred degrees below the melting point to prevent sagging of the filament. 

S. J. Schneider, Compilation of the Melting Points of the Metal Oxides, National Bureau of Standards Monograph 68, Washiagton, D.C., 1963. 

Fig. 4. Fquilihrium vapor pressure of materials, where x indicates the melting point of the metal. The melting points for In and Sn ate off the graph at 156...

Eiimination. The welding technique must he such that the melting points of the metals to be joined are reached and maintained until a... 

Observe also that increased thermal energy is all that is required for the shift to take place. Such change occurs well below the melting point of the metal. 

The calciothermic reduction of an oxide is naturally designed for the obtainment of the reduced metal in the powder form because of the high melting point of the other product, namely, calcia. The formation of the metal in the form of a powder is favored by some other controllable factors also. One of these factors is that the temperature should not exceed the melting point of the metal during reduction. A second factor is that it is preferable to have the reaction temperature as low as possible, without adversely affecting the rate of the reaction. 

In the iodide refining process described above, several conditions are implicit. Van Arkel has listed them as (i) the metals form volatile iodides (ii) the melting points of the metals are higher than the dissociation temperatures of the corresponding iodides (iii) the volatile iodides are formed at manageable temperatures (iv) the iodides easily decompose at elevated temperatures and (v) the vapor pressures of the metals are very low at the decomposition temperatures of the iodides. 

The outlined sketch is rather rough, but it correctly shows the tendencies, as can be exemplified by the melting points of the metals (values in °C) ... 

FIGURE 34 Melting point of the metals and alloys of antiquity. Heating techniques to attain temperatures higher than about 1500°C were developed as recently as the late nineteenth century. Only metals and alloys melting below 1500°C were, therefore, smelted in antiquity. 

The sporadic use of iron can be traced back as far back as nearly 6000 years ago, but its widespread application came at a much later date, later than that of copper. This is probably due to a number of factors, mainly the high melting point of the metal (1535°C) and, accordingly, the high temperatures required for smelting it. Temperatures above 1200-1300°C were hardly accessible in early antiquity. A rudimentary form of iron known as... 

Since considerable quantities of heat are given out when the sodium is attacked by the water, much of which heat is communicated to the metal, it frequently melts while being attacked, the melting point of the metal being 95 6° C. 

Sintering, The process of agglomerating metal powders to increase strength, conductivity, or density using heat and pressure but at temperatures below the melting point of the metal. 

Another main use is as an alloy with other metals when it will lower the melting point of the metals with which it is alloyed. Alloys of indium and silver and indium and lead have the ability to carry electricity better than pure silver and lead. 

There is a corresponding paucity of experimental determinations of the surface tension of solids, probably because no direct experimental method has been developed. A review of the work on the surface tension of solid metals has been given by Shaler 27). These values were obtained, in most cases, near the melting point of the metals and thermodynamic equilibrium was achieved. These experiments are thus quite different from those where the nonequilibrium state persists, with incomplete relief of surface stress. As this review is mainly concerned with high surface area adsorbents in a state of considerable surface stress in vacuo at least), the above results with metals will not concern us further. 

Efficient refining of the more volatile actinide metals (Pu, Am, Cm, Bk, and Cf) is achieved by selective vaporization for those (Pu, Am, Cm) available in macro quantities. The metal is sublimed at the lowest possible temperature to avoid co-evaporation of the less volatile impurities and then deposited at the highest possible temperature to allow vaporization of the more volatile impurities. Deposition occurs below the melting point of the metal to avoid potential corrosion of the condenser by the liquid metal. Very good decontamination factors can be obtained for most metallic impurities. However, Ag, Ca, Be, Sn, Dy, and Ho are not separated from Am metal nor are Co, Fe, Cr, Ni, Si, Ge, Gd, Pr, Nd, Sc, Tb, and Lu from Cm and Pu metals. 

Table 5. 4 shows that a variety of magnesium-containing compositions have ignition temperatures close to the 649°C melting point of the metal. 

Einally, it should be noted that phase changes can be accommodated in the Ellingham diagram. When the temperature moves above the melting point of the metal or metal oxide, their corresponding standard states must change. For example, above 1100°C, copper metal is no longer solid, and the oxidation reaction of interest is ... 

The melting points of the metals, reported by different investigators, vary somewhat owing probably to differences in the purity of the specimens used for the determination.10 The best representative values are indicated in Table III. According to P. W. Bridgman, the effect of press, in kgrm. per sq. cm. (1 atm. =1 033 kgrm. per sq. cm.) on the m.p. 6 of potassium and sodium is as follows —... 

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