Chemistry Reference
In-Depth Information
temperature by the interaction of the atoms in the space between them.
The rate at which heat is transferred is determined by the
thermal con-
ductivity
of the solid, an intrinsic property of every material that describes
the rate at which heat flows within a body of the material at a given tem-
perature difference. Most metals and alloys have
high thermal conductiv-
ity
and are said, therefore, to be
good conductors
of heat. The nonmetals,
whether inorganic or organic, on the other hand, generally have
low
thermal conductivity
and are
bad conductors
(but
good insulators
) of heat.
Stone, brick, pottery, glass, and all forms of living matter, such as wood
and textile fibers, for example, are good insulators of heat, shielding from
either heat or cold. It is because of their low heat-conducting properties
that these materials are used for in building constructions and making
clothes. Table 101a lists the thermal conductivities of solids frequently
found in archaeological sites.
Temperature changes also cause dimensional changes in materials.
When a material is heated or cooled, its length changes by an amount pro-
TABLE 101a Thermal Properties of Some
Archaeological Materials
Thermal Conductivity (at 25°C)
Material
Thermal conductivity
a
Metals and Alloys
Silver
4.3
Copper
4.0
Gold
3.2
Brass
0.8
Iron
3.2
Steel
0.5
Lead
0.4
Nonmetals
Obsidian (at 0°C)
1.35
Pottery
1.2
Sodalime glass
0.9
Mortar cement
0.5
Wood (at 20°C)
0.03-0.3
a
Expressed as the amount of heat (measured in watts) that
passes, per second, through one cubic meter of the material
when the temperature at opposite sides of the cube is kept at
a difference of one degree centigrade, at the temperature
stated.
