Chem PR
Chem PR
Chem PR
1. Introduction
2. Some common alloys
3. Characteristics of alloys
4. Uses of alloys
5. Preparation of alloys
6. Analysis of alloy
7. Exp.1
INTRODUCTION:
An Alloy is a homogenous mixture of two or more metals
or a non-metal. An alloy of mercury with another metal is
called amalgam. Alloys are usually harder than their
components but very often less ductile and less
malleable. Thus the hardness of gold is increased by
addition of copper to it. The melting point of an alloy is
always lower than the melting points of the constituent
metals. Other properties such as reactivity towards
atmospheric oxygen and moisture, mechanical strength,
ductility, colour etc., also under goes a change when an
alloy is made from its constituents (metals). This change
of properties is very useful and makes an alloy beneficial.
The composition of alloys may differ slightly depending
upon the quality of the alloy though the main components
remain the same. An alloy(through the Fr. Aloyer, from
Lat. Alligare, to combine), is a partial or complete solid
solution of one or more elements in a metallic matrix.
Complete solid solution alloys give single solid phase
microstructure, while partial solutions give two or more
phases that maybe homogeneous in distribution depending
on thermal (heat treatment) history. Alloys usually have
different properties from those of the component
elements. Alloying one metal with other metal or non
metal often enhances its properties. For instance, steel is
stronger than iron, its primary element. The physical
properties, such as density, reactivity, Young’s modulus,
and electrical and thermal conductivity, of an alloy may
not differ greatly from those of its elements, but
engineering properties, such as tensile strength and shear
strength may be substantially different From those of the
constituent materials. This is sometimes due to the sizes
of the atoms in the alloy, since larger atoms exert a
compressive force on neighbouring atoms, and smaller
atoms exert a tensile force on their neighbours, helping
the alloy resist deformation. Alloys may exhibit marked
differences in behaviour even when small amounts of one
element occur. For example, impurities in semiconducting
ferromagnetic alloys lead to different properties, as first
predicted by White, Hogan, Suhl. Tian Aubrie and
Nakamura. Some alloys are made by melting and mixing
two or more metals. Brass is an alloy made from Copper
and zinc. Bronze, used for bearings, statues, ornaments
and church bells, is an alloy of Copper and tin. Unlike
pure metals, most alloys do not have a single melting
point. Instead, they have a melting range in which the
material is a mixture of solid and liquid phases.
Brass:
A decorative brass paperweight (left), along with zinc and
copper samples. Brass is the term used for alloys of
copper and zinc in a solid solution. It has a yellow colour,
somewhat similar to gold. It was produced in prehistoric
times, long before zinc was discovered, by melting copper
with calamine, a zinc one. The amount of zinc in brass
varies from 5 to 45 percent, creating a range of brasses,
each with unique properties. By comparison, bronze is
principally an alloy of copper and tin. Despite this
distinction, some types of brasses are called bronzes.
Brass is relatively resistant to tarnishing and is often
used for decorative purposes. Its malleability and acoustic
properties have made it the metal of choice for musical
instruments such as the Trombone, tuba, trumpet, and
euphonium. Although saxophones And harmonicas are
made out of brass, the saxophone is a woodwind
instrument, and the harmonica, a free reed aero phone. In
organ pipes designed as “reed” pipes, brass strips are
used as the “reed.” Aluminium makes brass stronger and
more corrosionresistant. It forms a transparent,
selfhealing, protective layer of aluminium oxide (A203) on
the surface. Tin has a similar effect and finds its use
especially in seawater applications (naval brasses).
Combinations of iron, aluminium, silicon, and manganese
make brass resistant to wear and tear.
Bronze:
Bronze refers to a broad range of copper alloys, usually
with tin as the main additive, but sometimes with other
elements such as phosphorus, manganese, aluminium, or
silicon. Typically, bronze is about 60 percent copper and
40 percent tin. The use of bronze was particularly
significant for early civilizations, leading to the name
“Bronze Age.” Tools, weapons, armour, and building
materials such as decorative tiles were made of bronze,
as they were found to be harder and more durable than
their stone and copper predecessors. In early use, the
natural impurity arsenic sometimes created a superior
natural alloy, called “arsenical bronze.” Though not as
strong as steel, bronze is superior to iron in nearly every
application. Bronze develops a patina (a green coating on
the exposed surface), but it does not oxidize beyond the
surface. It is considerably less brittle than iron and has a
lower casting temperature. Several bronze alloys resist
corrosion (especially by seawater) and metal fatigue
better than steel; they also conduct Heat and electricity
better than most steels. Bronze has myriad uses in
industry. It is widely used today for springs, bearings,
bushings, and similar fittings, and is particularly common
in the bearings of small electric motors. It is also widely
used for cast metal sculpture and is the most popular
metal for top-quality bells and cymbals. Commercial
bronze, otherwise known as brass, is 90 percent copper
and 10 percent zinc. It contains no tin Pewter:
It is traditionally composed of 85 to 99 percent tin, with
the remainder consisting of copper, which acts as a
hardener. Lead is added to lower grades of pewter, giving
a bluish tint. Traditionally, there were three grades of
pewter: fine, for eating ware, with 96 to 99 percent tin
and 1 to 4 percent copper; trifle, also for eating and
drinking utensils but duller in appearance, with 92 percent
tin, 1 to 4 percent copper, and up to 4 percent lead; and
lay or ley metal, not for eating or drinking utensils, which
could contain up to 15 percent lead. Modern pewter mixes
the tin with copper, antimony, and/or bismuth rather than
lead. Physically, pewter is a bright, shiny metal that is
similar in appearance to silver. Like silver, it oxidizes to a
dull grey over time if left untreated. It is a very malleable
alloy, being soft enough to carve with hand tools. It also
takes good impressions from punches or presses. Given
this inherent softness and malleability, pewter cannot be
used to make tools. Some types of pewter pieces, such as
candlesticks, were turned on a metal lathe. And these
items are sometimes referred to as
“hollowware.” Pewter has a low melting point (around
225 to 240°C), depending on the exact mixture of metals.
Duplication by casting gives excellent results. The use of
pewter was common from the Middle Ages up until the
various developments in glass-making during the
eighteenth and nineteenth centuries. Pewter was the chief
tableware until the making of china. With the mass
production of glass products, glass has universally
replaced pewter in daily life. Today, pewter is mainly
used for decorative objects such as collectible statuettes
and figurines, replica coins, and pendants.
CHARACTERISTICS OF ALLOY:
Alloys are Stronger
One of the primary advantages of alloys over pure metals
is that they are stronger. This is because alloys contain
multiple metals that are bonded together, making them
more resistant to breakage and wear than pure metals.
USES OF ALLOYS:
Alloys have wide-ranging applications in our everyday
life. Some of the most common uses of alloys are as
follows:
PREPARATION OF ALLOYS:
Alloys are prepared from the techniques of fusion,
compression or simultaneous electro – deposition.
Generally the components are mixed together in proper
properties in a fuse clay crucible, melted and stirred with
a piece of charcoal to avoid oxidation. The molten
mixture is now allowed to cool. When an alloy is obtained
e.g. brass is prepared by above melted.
EXPERIMENT-1
Aim: To estimate the percentage of copper in the given
sample of brass.
Starch indicator is added near the end point and not in the
beginning for the following reasons.
Procedure:
Weigh brass sample and transfer it in to a clean conical
flask. Dissolve it in minimum amount of nitric acid. Add 1g
(1 spatula) of urea and add 1 t.t. of distilled water. Boil
the solution and cool and then add NH4OH drop wise until
a blue colour persists. Add 1tt of acetic acid followed by
10 ml of 10 % KI.Titrate the liberated iodine against
sodium thiosulphate solution taken in the burette until the
colour of the solution changes to pale yellow. Then add
starch solution till solution becomes blue in colour, and
continue the titration till the blue colour changes to milky
white. Repeat the titration for concordant values.