Titanium Physical properties
A
metallic element, titanium is recognized for its high strength-to-weight ratio.It is a strong metal with low
density that is quite
ductile (especially in an
oxygen-free environment), lustrous, and metallic-white in
color.The relatively high melting point (more than 1,650 °C or 3,000 °F) makes it useful as a
refractory metal. It is
paramagnetic and has fairly low
electrical and
thermal conductivity.
Commercial (99.2% pure)
grades of titanium have
ultimate tensile strength of about 434
MPa (63,000
psi), equal to that of common, low-grade steel alloys, but are 45% less dense. Titanium is 60% more dense than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g.,
Beta C) achieve tensile strengths of over 1400 MPa (200000 psi).However, titanium loses strength when heated above 430 °C (806 °F).
Titanium is fairly hard (although not as hard as some grades of heat-treated steel), non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, as the material will soften and
gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a
fatigue limit which guarantees longevity in some applications.Titanium alloys have lower specific stiffnesses than in many other structural materials such as aluminium alloys and
carbon fiber.
The metal is a dimorphic
allotrope whose hexagonal alpha form changes into a body-centered cubic (lattice) β form at 882 °C (1,620 °F). The
specific heat of the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the β form regardless of temperature. Similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but is metastable at ambient pressures. This phase is usually hexagonal (ideal) or trigonal (distorted) and can be viewed as being due to a soft longitudinal acoustic
phonon of the β phase causing collapse of
(111) planes of atoms.
Titanium Chemical properties
The
Pourbaix diagram for titanium in pure water, perchloric acid or sodium hydroxide.
Like
aluminium and
magnesium metal surfaces, titanium metal and its alloys
oxidize immediately upon exposure to air. Nitrogen acts similarly to give a coating of the nitride. Titanium readily reacts with oxygen at 1,200 °C (2,190 °F) in air, and at 610 °C (1,130 °F) in pure oxygen, forming
titanium dioxide. It is, however, slow to react with water and air, as it forms a
passive and oxide coating that protects the bulk metal from further oxidation.When it first forms, this protective layer is only 1–2
nm thick but continues to slowly grow; reaching a thickness of 25 nm in four years.
Related to its tendency to form a passivating layer, titanium exhibits excellent resistance to corrosion. It is almost as resistant as
platinum, capable of withstanding attack by dilute
sulfuric and
hydrochloric acids as well as chloride solutions, and most organic acids.However, it is attacked by concentrated acids.As indicated by its negative redox potential, titanium is thermodynamically a very reactive metal. One indication is that the metal burns before its melting point is reached. Melting is only possible in an inert atmosphere or in a vacuum. At 550 °C (1,022 °F), it combines with chlorine.It also reacts with the other halogens and absorbs hydrogen.
Titanium is one of the few elements that burns in pure nitrogen gas, reacting at 800 °C (1,470 °F) to form
titanium nitride, which causes embrittlement.Because of its high reactivity toward oxygen, nitrogen and many other gases,
titanium filaments are applied in
titanium sublimation pumps as scavengers for these gases. Such pumps are inexpensive and reliable devices for producing extremely low pressures in
ultra-high vacuum systems.