Download Alloys and elements

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Question No19
Electromotor, portable generator
Alloys and elements
An alloy is a mixture of two or more elements in solid solution in which the major
component is a metal. Most pure metals are either too soft, brittle or chemically reactive for
practical use. Combining different ratios of metals as alloys modifies the properties of pure
metals to produce desirable characteristics. The aim of making alloys is generally to make
them less brittle, harder, resistant to corrosion, or have a more desirable color and luster.
Among significant metallic alloys, there are those of aluminium, titanium, copper and
magnesium. Copper alloys have been known since prehistory—bronze gave the Bronze Age
its name—and have many applications today, most importantly in electrical wiring. The
alloys of the other three metals have been developed relatively recently; due to their chemical
reactivity they require electrolytic extraction processes. The alloys of aluminium, titanium and
magnesium are valued for their high strength-to-weight ratios; magnesium can also provide
electromagnetic shielding.
Alloy properties are checked again at regular intervals throughout the production
process in coordination with our established ISO-9001:2008 quality control system. Highly
engineered components must be produced from billet production through the extrusion and
cold working processes as well as finish machining and electroplating as required
A semiconductor is a material with electrical conductivity due to electron flow (as
opposed toionic conductivity) intermediate in magnitude between that of a conductor and an
insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per
centimeter. Semiconductor materials are the foundation of modern electronics, including
radio, computers, telephones, and many other devices. Such devices include transistors, solar
cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier,
and digital and analog integrated circuits. Similarly, semiconductor solar photovoltaic panels
directly convert light energy into electrical energy. In a metallic conductor, current is carried
by the flow of electrons. In semiconductors, current is often schematized as being carried
either by the flow of electrons or by the flow of positively charged "holes" in the electron
structure of the material.
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Actually, however, in both cases only electron movements are involved. Common
semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are
known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and
tellurium in a variety of proportions. Such compounds share with better known
semiconductors intermediate conductivity and a rapid variation of conductivity with
temperature, as well as occasional negative resistance. Organic semiconductors, that is,
organic materials with properties resembling conventional semiconductors, are also known.
Piezoelectric materials They produce an electric field when exposed to
a change in dimension caused by an imposed mechanical force (piezoelectric
or generator effect). Conversely, an applied electric field will produce a
mechanical stress (electrostrictive or motor effect).
They transform energy from mechanical to electrical and vice-versa. The stress is very
small, 0.1-0.3%. They are used for sensing purposes (e.g. microphone, transducer), and for
actuating applications.
Optoelectronic Devices
OPTOELECTRONIC devices either produce light or use light in their operation. The
first of these, the light-emitting diode (LED), was developed to replace the fragile, short-life
incandescent light bulbs used to indicate on/off conditions on panels. A LIGHT-EMITTING
DIODE is a diode which, when forward biased, produces visible light. The light may be red,
green, or amber, depending upon the material used to make the diode.
Figure 3-27 shows an LED and its schematic symbol. The LED is designated by a
standard diode symbol with two arrows pointing away from the cathode. The arrows indicate
light leaving the diode. The circuit symbols for all optoelectronic devices have arrows
pointing either toward them, if they use light, or away from them, if they produce light. The
LED operating voltage is small, about 1.6 volts forward bias and generally about 10
milliamperes. The life expectancy of the LED is very long, over 100,000 hours of operation.
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Question No 24
Conductors, insulators, semiconductors
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