Metal melting point

Liquid metal selection is usually limited to the lower melting point metals in Table 15. Figure 17 shows that Hquid metal viscosity generally is similar to water at room temperature and approaches the viscosities of gases at high temperature. Hydrodynamic load capacity with both Hquid metals and water in a bearing is about 1/10 of that with oil, as indicated in Table 2. 

Aluminum is the liighest melting point metal (660°C) applied by hot dipping. Aluminized steel can be used at temperatures up to SSO C without appreciable oxidation. Tliis steel has very good resistance to gases and vapors containing small quantities of sulfur dioxide and hydrogen sulfide [41,42,43]. 

Steels and austenitic stainless steels are susceptible to molten zinc, copper, lead and other metals. Molten mercury, zinc and lead attack aluminum and copper alloys. Mercury, zinc, silver and others attack nickel alloys. Other low-melting-point metals that can attack common constructional materials include tin, cadmium, lithium, indium, sodium and gallium. 

Alloys with rhenium, another high melting point metal (3180°C) exhibit outstanding high temperature properties insofar as they have a higher recrystallisation temperature than pure tungsten and are still ductile in the recrystallised condition. Common alloys with rhenium contain 3%, 5% or 26% rhenium. The 3% and 5% alloys combine ductility with reasonable... 

Consideration will also be given to attack arising from contact with solids such as refractories, and with molten materials such as salts, glasses, and lower-melting-point metals and alloys. On a fundamental basis, the distinction between some of these latter reactions and normal-temperature aqueous corrosion is not always clear, since galvanic effects may be of significance in both cases, but for practical purposes a distinction can be made on the basis of the temperature involved. 

Nickel and nickel-rich alloys must be considered as having generally poor resistance to molten metals. Eldred has made a systematic investigation of the attack of liquid metals on solid metals and alloys, and his results for nickel, and nickel-chromium and nickel-copper alloys, are summarised in Table 7.35. These are for tests at up to 500 C and apart from potassium and sodium all the low-melting-point metals investigated produced moderate to severe attack on the nickel-rich materials. Furthermore, the values for many of the combinations given in the table indicate a marked tendency to preferential intergranular attack. 

So far, few of the commercially operated diffusion processes have been applied to the lower-melting-point metals. While they are being used to an increasing extent for protection of nickel, cobalt and refractory alloys, the bulk of present-day applications is still concerned with the treatment of ferrous materials. 

The advantages of the modern form of this method are that many alloys that cannot be conveniently drawn into wire form can be used in the process, that the hand tool contains no moving parts, and that high outputs can be obtained. The disadvantage of the powder system is that it is not very suitable for high-melting-point metals, and the losses are higher than with wire, because not all the particles are melted. 

Porous refractory (tungsten) infiltrated with a low melting point metal (silver) Hot-pressed refractory metal containing an oxide filler... 

Evaporation is used extensively for the deposition of aluminum and other low melting-point metals as well as hard coatings such as TiN for cutting tools, decorative coatings (jewelry), and for the metallization of paper and fibers. It is also a major coating... 

In earlier work with pure metals, it was generally accepted that the area of films deposited at, say, 0°C was proportional to their weight (with the exception of group IB and low melting-point metals). Information was available on the surface areas of films of Ni, Pt, Pd, Rh, etc. (71), and hence absolute reaction rates could be calculated. It would be a considerable undertaking to establish similar data for alloy systems, bearing in mind that various compositions would have to be examined and also a method for preparing exact compositions would be required. However, for sintered alloy films, approximate methods can be proposed. 

Pressure Atomization 50-500 Standard deviation 1.4 Sn, Pb, Sb, Bi, In, Mg, Al, Zn — -17 — Narrow size distribution High EE Limited to low melting point metals... 

For low melting-point metals (for example, solder materials), the liquid metal and the atomization gas may be mixed internally inside the atomizer for both low and high melting point materials, the two fluids can be mixed externally outside the atomizer in the nearnozzle region. 

How do we make a contact with an optically transparent electrode or a low-melting-point metal such as lead ... 

Electrical contact between the electrode and connecting wires can be made with solder if the electrode is a refractory metal, while lower-melting-point metals such as lead, and reactive metals such as magnesium, should be joined to a connection lead with commercially available conductive silver paint . Contact to ITO-coated electrodes will similarly require this conductive paint. 

If the solid product sinters together under the conditions of the reacion, as for instance low melting point metals produced by the reduction of much higher melting point oxides, then the possibility must be considered of the product choking the reaction, even though the volume ratio if satisfactory. 

A practical application coming out of field ion emission is the liquid metal ion source. Ion sources of a wide variety of chemical elements, most of them low melting point metals, can be produced by using either liquid metals131,132 or liquid alloys.133 The idea of extracting charged droplets out of liquid by application of an electrostatic field is perhaps older than field ion microscopy. But the development of liquid metal ion sources from liquid capillaries, from slit shaped emitter modules and from wetted field emission tips, etc., as well as the understanding of the mechanisms of ion formation in terms of field evaporation and field ionization theories,... 

Process temperature is usually 25-75% of the melting point of the lower ( )-melting-point metal in the intended weld or bond. It is to be understood that the purpose of attaining elevated temperature is to promote or accelerate interdiffusion of the atoms at the joint interface and also to provide some metal softening, which, in turn, aids in surface deformation. The purpose of pressure application is to establish a firm, robust mechanical contact of the surfaces to be joined and further to break up surface oxides (hence the frequent use of silver, as mentioned above). This will provide a rather clean surface for bonding. Dwell time required at the elevated temperature is determined according to metallurgical and sometimes other considerations. 

In low melting point metal dispersed systems, the Al203/Ni system has been studied to obtain the desired microstructure and improvement of mechanical properties by modification of the microstructure. Moreover, considering the magnetic properties of the composites, it was expected to improve both mechanical and magnetic properties by incorporating merely nanometer-sized Ni, Co, and Fe into an A1203 matrix. 

---