The Linear Coefficient of Expansion of Titanium?
by Jim
(United Kingdom)
Q : I am currently working on an A-Level Physics research project on Titanium, it's properties and uses. I read about the fact that Titanium has a low Linear Coefficient of Expansion, but am unable to find an explanation of the reason why Titanium's is low. I have only found a generic piece of information saying the L-C of E is related to bond energies, not information specific to Titanium. Thank-you!
A :
A great question and a not so simple answer. I’ll try to take it gradually, so that everybody can understand what we’re talking about, Jim.
So, the coefficient linear of expansion is about the thermal expansion of different materials, when exposed to an increased temperature. When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature. The linear thermal expansion coefficient relates the change in a material's linear dimensions to a change in temperature. It is the fractional change in length per degree of temperature change. There is also possible to calculate the area and volume coefficients of thermal expansion.
The difference linear coefficient of expansion of materials is determined by the different thermal conductivity of each material, which is subsequently affected by the different specific heats of materials.
To clarify the definition – the thermal conductivity the thermal conductivity can be thought of as the container for the medium-dependent properties which relate the rate of heat loss per unit
area to the rate of change of temperature. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.
It is generally known that metals are better heat conductors than non-metallic solids and gases, and the physics fundaments for this property is the actual heat-transfer in mechanism which involves electrons, similar as in electrical conductivity. . You may have already guessed that this two are closely related. At a given temperature, the thermal and electrical conductivities of metals are proportional. It should also be noted that raising the temperature increases the thermal conductivity while decreasing the electrical conductivity
And now, we return to the matter at hand. Titanium is documented to display both low thermal conductivity and low electrical conductivity properties. The answer to your questions lies in the way electrons are distributed in titanium atoms, as compared to other metals that have better conductivity properties.
More precisely, in physics, the notion is known as Free Electron Density, which should be pretty self – explanatory. This coefficient differs from metals to metal based on atomic mass, density of the material and some other more coefficients related to advanced physics theories (Fermi energies)
In titanium metal, both the atom mass and density of materials are lower than of other, better conductive metals, say, copper.
I think this should be enough for a start in the right direction. You may find further references about titanium’s electrical and thermal conductivity in E.W. Collings books: “A sourcebook of titanium alloy superconductivity” and “Applied Superconductivity, Metallurgy, and Physics of Titanium Alloys”