Since the volumetric and linear coefficients are defined only for extremely small temperature and dimensional changes ( that is, when \ Delta T and \ Delta L are small ), the last two terms can be ignored and we get the above relationship between the two coefficients.
12.
FerNiCo I has the same linear coefficient of expansion as certain types of borosilicate ( " hard " glass ), ( c6.5 ?10 " 6 �K " 1, thus serving as an ideal material for the lead-out wires or other seal structures in light bulbs and thermionic valves.
13.
The coefficient " ? " varies with the temperature and some materials have a very high variation; see for example the variation vs . temperature of the volumetric coefficient for a semicrystalline polypropylene ( PP ) at different pressure, and the variation of the linear coefficient vs . temperature for some steel grades ( from bottom to top : ferritic stainless steel, martensitic stainless steel, carbon steel, duplex stainless steel, austenitic steel ).
