TEXT 1. METALLURGY
SOME WORDS ABOUT METALLURGY
Metallurgy is one of the oldest of arts but one of the youngest of sciences. Many of our metals were known in ancient times, but it is only within the last century or two that the knowledge of the properties of the metals has made it possible to apply them in any extended way for industrial purposes.
With the development of physics of metals, metallography, theory of heat treatment, and other phases of the science of metals, the field of metallurgy has broadened.
Metallurgy in this broader sense falls into three divisions: chemical or extractive, physical and mechanical. Chemical metallurgy includes the metallurgical processes involving chemical change and the methods of production and refining.
Physical metallurgy deals with the nature, structure, and physical properties of metals and alloys.
Mechanical metallurgy includes the processes of working and shaping metals — processes which do not involve chemical changes.
TEXT 2
PHYSICAL PROPERTIES OF METALS AND ALLOYS
The word constitution used with reference to metallic substances does not have the same meaning as composition. Constitution denotes the manner of arrangement of the metal atoms as to geometric form in solid crystals, and the regular or ordered arrangement of different kinds of metal atoms and their relation to each other in such a crystal.
The pattern formed by this orderly arrangement of the atoms is known as the space lattice.
Most metals crystallize with one of the three following lattice structures:
Close-packed cubic: copper, nickel, lead, aluminium, cobalt, silver, gold, platinum.
Body-centred cubic: iron, molybdenum, tungsten, chromium.
Hexagonal close-packed: zink, cadmium, magnesium, beryllium, titanium.
This union of atoms into a geometric array is the physical difference between liquid and solid metal.
The formation of metal crystals within a melt begins at each cooling surface of the liquid mass and extends from the exterior to the interior as heat is lost from the mass. Every change in the conditions of cooling, such as increasing or decreasing the rate at which heat is conducted away from the freezing mass, will have an influence on the size and shape of the crystals and, therefore, on the constitution and properties of the solidified mass.
Melting and Boiling Points. - The temperature at which a metal melts, is called the melting point, the metals of lower melting points are generally the soft metals and those of high melting the hard metals.
The boiling point of a substance depends on the surrounding-pressure. The term "boiling point" refers to the temperature at which the metal boils under normal atmospheric pressure.
Electrical Conductivity. - The electrical conductivity of a substance is the electrical conducting power of a unit length per unit of cross-sectional area. The electrical resistance of metals or alloys is increased by decreasing the size of the crystals and, therefore, increasing the number of crystal boundaries. In general, all metals increase in resistivity with increase in impurities. The resistivity of metals is also increased in most cases by an increase in temperature.
Heat Conductivity. - Heat conductivity is measured as the heatconducting ability of a unit length or thickness of a substance per unit of cross-sectional area.
Magnetism. - Magnetism is measured as the magnetic force exerted by a unit volume of a substance under standard magnetizing force. Iron, cobalt and nickel are the only metals possessing considerable magnetism at room temperature, and they become non-magnetic when heated to a certain temperature. Strong permanent magnets have been made chiefly of one of several compositions of steel, but in recent years a number of magnet alloys of much greater magnetism, able to exert forces many times their own weights, have been developed.
Density and Porosity. - Porosity, the quality of containing pores is lack of denseness. Density, on the other hand, denotes weight per unit of volume. The distinction will be manifest from the fact that some heavy metals, like grey cast ironware porous enough to leak under heavy hydraulic pressures, whereas some lightweight metals, like aluminium, are dense and compact.
Most metals expand on heating and contract on cooling.
Colour. - Most of the metals are silvery white or grey in colour. Copper is the only red metal, and gold the only yellow one, although a number of copper-base alloys are also yellow. All solid metals have metallic lustre, although the true colour and lustre of many metals are often obscured by a coating of oxide — which may be white, grey, red, brown, bluish, or black.
NOTES AND COMMENTARY
| with reference to – по отношению к the same meaning– то же значение the manner or arrangement– способ расположения as to – что касается to each other– друг к другу is known, as the space lattice - известен как пространственная решетка close-packed cubic – кубическая с плотно упакованными атомами body-centred cubic –кубическая объемно-центрированная структура hexagonal close-packed –гексагональная с плотно упакованными атомами union of atoms into a geometric array –объединение атомов в геометрическом порядке within a melt –в расплавленном металле as the heat is lost from the mass –по мере того, как масса теряет тепло every change –каждое изменение the rate at which heat is conducted away from –скорость, с какой тепло отдается из an influence on –влияние на melting point –точка плавления depends on– зависит от the metal boils under –металл кипит при the electrical conducting power of a unit length per unit of cross sectional area –электрическая проводимость | the number of crystal boundaries –число границ кристаллов in most cases –в большинстве случаев the only -единственный at room temperature –при комнатной температуре when heated to a certain temperature –при нагревании до определенной температуры able to exert forces many times their own weights –могут обладать подъемной силой во много раз большей своего собственного веса is lack of– зд. лишена on the other hand –с другой стороны weight per unit of volume –вес на единицу объема like grey cast iron –подобно серому чугуну under heavy hydraulic pressure –под большим гидравлическим давлением whereas –в то время, как most metals expand on heating –большинство металлов расширяются при нагревании silvery white or grey in colour –серебристо-белого или серого цвета the only yellow one –единственный желтый металл copper-base alloys –сплавы с медной основой the true colour and lustre –истинный цвет и блеск by a coating of oxide– покрытием окисла |