Chemistry Reference
In-Depth Information
widely used in antiquity, were sometimes prepared from ores or mixtures
of ores that incorporate two metals in their composition. It seems that in
some regions of the world arsenical copper was derived from ores that
include in their composition copper as well as arsenic. Some ancient bronze
and brass seem to have been produced also by smelting together ores of
copper and tin or of copper and zinc, respectively.
Cast iron
, as a number
of alloys of iron and carbon are known (see Table 33), was formed mostly
when smelting iron, as a result of the combination of hot iron with carbon,
the main component of wood and charcoal used as fuel in the smelting
furnace.
TABLE 33
Ferrous Alloys
Composition (%)
Alloy
Iron
Carbon
Cast iron
Pig iron
96.5-95.8
3.5 -4.2
White iron
98.2-97.0
1.8 -3.0
Malleable iron
98.0-96.4
2.0 -3.6
Gray iron
97.5-96.2
2.5 -3.8
Ductile iron
97.8-95.8
3.2 -4.2
Steel
Mild
above 99.7
0.03-0.3
Medium
99.7-99.2
0.3 -0.8
Hard
99.2-98.0
0.8 -2.0
Many of the so-called metals used in everyday life are actually not
metal but alloys. Pure gold, for example, is too soft a metal for most prac-
tical purposes and is therefore generally alloyed with other metals. When
alloyed with copper or silver, for example, it forms relatively hard and
durable alloys from which most of the so called “gold objects” are made.
In informal, common language, however, the gold alloys are usually, albeit
erroneously, referred to as “gold.” Also, most objects said to be made from
“silver” or “iron” are actually made from silver- or iron alloys and not from
the pure metals (see text below). Making alloys usually entails adding, to
a molten
base metal
, as the main component of an alloy is usually referred
to, other metals or nonmetals, thoroughly mixing the resulting melt, and
then cooling it under controlled conditions to cause the alloy formed to
solidify.
The alloys are often classified according to different criteria. One con-
venient classification is based on the most characteristic method used for
shaping alloy-based objects. Examples are
cast alloys
and
wrought alloys
.
Cast alloys
, such as cast bronze, cast brass, and cast iron, are generally
