Barrons SAT Subject Test Chemistry, 13th Edition

until the proper proportions of additives are established for that “heat” so that the
steel will have the particular properties needed by the customer. The tapping of
one of these furnaces holding 50 to 400 tons of steel is a truly beautiful sight.
The final method of making steel involves the electric arc furnace. This
method uses enormous amounts of electricity through graphite cathodes that are
lowered into the molten iron to purify it and produce a high grade of steel.

Alloys

An alloy is a mixture of two or more metals. In a mixture certain properties of the
metals involved are affected. Three of these are:

1.

Melting

point

The melting point of an alloy is lower than that of its components.

2.

Hardness

An alloy is usually harder than the metals that compose it.

3. Crystal
   structure

The size of the crystalline particles in the alloy determines many of the physical

properties. The size of these particles can be controlled by heat treatment. If the

alloy cools slowly, the crystalline particles tend to be larger. Thus, by heating and

cooling an alloy, its properties can be altered considerably.

Common alloys are:

1. Brass, which is made up of copper and zinc.


2. Bronze, which is made up of copper and tin.


3. Steel, which has controlled amounts of carbon, manganese, sulfur,
   phosphorus, and silicon, is alloyed with nickel and chromium.


4. Sterling silver, which is alloyed with copper.

Metalloids

In the preceding sections, representative metals and nonmetals have been
reviewed, along with the properties of each. Some elements, however, are
difficult to classify as one or the other. One example is carbon. The diamond form
of carbon is a poor conductor, yet the graphite form conducts fairly well. Neither
form looks metallic, so carbon is classified as a nonmetal.
Silicon looks like a metal. However, its conductivity properties are closer to
those of carbon.
Since some elements are neither distinctly metallic nor clearly nonmetallic, a
third class, called the metalloids, is recognized.
The properties of metalloids are intermediate between those of metals and