Titanium is lightweight, strong, corrosion resistant and abundant in nature.
Titanium and its alloys possess tensile strengths from 30,000 psi to 200,000 psi
(210-1380 MPa), which are equivalent to those strengths found in most of alloy steels.
The density of titanium is only 56 percent that of steel, and its corrosion resistance
compares well with that of platinum. Of all the elements in the earth’s crust,
titanium is the ninth most plentiful.
Physical Properties
If all the elements are assembled in order of atomic number, it can he noticed that
there is a relationship in properties corresponding to the atomic number.
Titanium is found in column four along with chemically similar zirconium, hafnium,
and thorium. Therefore, it was not unexpected that titanium would possess some
properties similar to those found in these metals.
Titanium has two electrons in the third shell and two electrons in the fourth shell.
When this arrangement of electrons, where outer shells are filled before the inner
shells are completely occupied, occurs in a metal, it is known as a transition metal.
This arrangement of electrons is responsible for the unique physical properties of
titanium. To mention a few, chromium, manganese, iron, cobalt, and nickel are found
in the transition series.
The atomic weight of titanium is 47.88, while aluminum has an atomic weight of 26.97,
and iron 55.84.
A crystal structure may he thought of as a physically homogeneous solid in which the
atoms are arranged in a repeating pattern. This arrangement is instrumental in the
physical behavior of a metal. Most metals have either a body-centered cubic,
face-centered cubic, or a hexagonal-close-packed structure.
Titanium has a high melting point of 3135°F (1725°C). This melting point is
approximately 400°F above the melting point of steel and approximately 2000°F
above that of aluminum.
Thermal Conductivity. The ability of a metal to conduct or transfer
heat is called its thermal conductivity. Thus, a material, to be a good insulator,
would have a low thermal conductivity, whereas a radiator would have a high rate
of conductivity to dissipate the heat. The physicist would define this phenomenon
as the time rate of transfer by conduction, through unit thickness, across unit
area for unit temperature gradient.
Linear Coefficient of Expansion. Heating a metal to temperatures
below its melting point causes it to expand or increase in length. If a bar or rod
is uniformly heated along its length, every unit of length of the bar increases.
This increase per unit length per degree rise in temperature is called the coefficient
of linear expansion. Where a metal will be alternately subjected to beating and
cooling cycles and must maintain a certain tolerance of dimensions, a low coefficient
of thermal expansion is desirable. When in contact with a metal of a different
coefficient, this consideration assumes greater importance.
Titanium has a low coefficient of linear expansion which is equal to
5.0x10-6 inch per inch/°F, whereas that of stainless steel is
7.8x10-6, copper 16.5x10-6, and aluminum 12.9x10-6.
Electrical Conductivity and Resistivity. The flow of electrons
through a metal due to a drop in potential is known as electrical conductivity. The
atomic structure of a metal strongly influences its electrical behavior.
Titanium is not a good conductor of electricity. If the conductivity of copper is
considered to be 100%, titanium would have a conductivity of 3.1%. From this it follows
that titanium would not be used where good conductivity is a prime factor. For
comparison, stainless steel has a conductivity of 3.5% and aluminum has a conductivity
of 30%.
Electrical resistance is the opposition a material presents to the flow of electrons.
Since titanium is a poor conductor, it follows that it is a fair resistor.
Magnetic Properties. If a metal is placed in a magnetic field, a
force is exerted on it. The intensity of the magnetization, called M, can be measured
in terms of the force exerted and its relation to the magnetic field strength, H,
depending upon the susceptibility, K, which is a property of the metal.
Metals have a wide variance in susceptibility and can be classified in three groups:
- The diamagnetic substances in which K is small and negative, and thus are feebly
repelled by a magnetic field; examples are copper, silver, gold and bismuth.
- The paramagnetic substances in which K is small and positive, and thus are
slightly attracted by a magnetic field; the alkali, alkaline and the nonferromagnetic
transition metals fall in this group (it can be seen that titanium is slightly
paramagnetic).
- The ferromagnetic substances, which have a large K value and are positive;
iron, cobalt, nickel, and gallium fall under this heading.
Most of the more important physical properties of titanium have now been indicated.
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