Railway Science (Chemistry-Metals , Non-Metals and Alloys) (Part-II)

Non-metals are (usually) poor conductors of heat and electricity, and are not malleable or ductile; many of the elemental nonmetals are gases at room temperature, while others are liquids and others are solids. Metals are good conductors of heat and electricity, and are malleable (they can be hammered into sheets) and ductile (they can be drawn into wire). Most of the metals are solids at room temperature, with a characteristic silvery shine (except for mercury, which is a liquid).

Electrical resistivity is the measure of the ability of a material to oppose the flow of current. It is the reciprocal of electrical conductivity. SI Unit - Ohm-metre (Ω-m). Elements and their resistivity : Silver (1.60 × 10⁻⁸), Tungsten (5.20 × 10⁻⁸), Nickel (6.84 × 10⁻⁸), Mercury (94 × 10⁻⁸) .

It is the property of metals by which they can be beaten into thin sheets. Ductility - Property of metal associated with the ability to be stretched into wire without breaking. Conductivity - Capability of water to pass electrical flow. Sonority - The ability of a material to produce a ringing sound when struck.

Constantan (Eureka): It has high ductility, high specific heat resistance and low temperature coefficient of resistance. Uses - Bridge wire, standard resistance coils. Other Alloys - Brass (Copper + Zinc), Bronze ( Copper + Tin), Solder (Lead + Tin), Amalgam (Mercury + Metal).

Metals are good conductors of heat and electricity, and are malleable (they can be hammered into sheets) and ductile (they can be drawn into wire). Most of the metals are solids at room temperature, with a characteristic silvery shine (except for mercury, which is a liquid). Nonmetals are (usually) poor conductors of heat and electricity, and are not malleable or ductile.

All metals except mercury exist as solids at room temperature. Metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if we keep them on our palm. Iodine is non-metal but it is lustrous. Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

Tungsten is used almost exclusively for filaments of electric bulbs, whereas copper and aluminum are generally used for electrical transmission lines. Melting points of some other metals : Silicon (1414°C), mild steel (1400°C), copper (1084°C), aluminum (660°C), Brass (930°C), Iron (1535°C), gold (1064°C), silver (961°C).

Alloys do not oxidize readily at high temperatures. Alloy is a homogenous mixture of two or more metals; or a metal and a non-metal. Therefore, conductors of electric heating devices, such as toasters and electric irons, are made of an alloy rather than pure metal.

Solder has a low melting point and is used for welding electrical wires together. Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the join.

Solder is an alloy of Lead and Tin. Tin-Lead solders are the largest single group and the most widely used of the soldering alloys. Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint.