Carbon a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is
Ultrasonic thickness gauge gauge measured the velocity of the waves it emitted in particular test samples, it then calculated the thickness in micrometers from this speed measurement by an applied mathematical equation. There are two types of transducers that can be used as an ultrasonic thickness gauge. These sensors are piezoelectric and EMAT sensors. Both transducer types emit sound waves into the material when excited. Typically these transducers use a predetermined frequency, however certain thickness gauges allow for frequency tuning in order to inspect a wider range of material. A standard frequency used by an ultrasonic thickness gauge is 5 MHz. Some ultrasonic