Ultra high purity carbon rods are used for carbon evaporation in EM applications. Either to coat non-conductive samples with a thin layer of carbon or to produce support films for TEM samples. The structure of the carbon rods is in reality high purity graphite which is formed during the purification process of the rods. The maximum level of impurity for the high-purity carbon rods is 2ppm with none of the elements exceeding 1ppm. See typical statements of purity.

The typical level of impurity is 1ppm or less. This makes the ultra-high purity carbon rods ideal for SEM/EDS, EBSD, WDS and EPMA applications. Currently two grades of ultra-high purity carbon rods are offered:

• Grade F-S which is the high-purity standard grade. This is the most common grade of carbon rods. The rods tend to be stronger and more brittle. Stepped points of this grade are best made with an electrical carbon rod shaper. Available in Ø3.05mm (Ø0.120”) and Ø6.15mm (Ø0.242”) with a length of 305mm (12”). Compatible with carbon coaters from Cressington, AGAR, JEOL, Quorum, Leica, Edwards , Anatech (Hummer) and Denton.
• Grade F-A which is a high purity softer grade. This is a softer grade and stepped points are somewhat easier to make from this grade, when using a hand carbon rod shaper. Compatible with coaters from Cressington (50Hz), AGAR (50Hz), JEOL (50Hz), Edwards and Denton.

Specifications of the ultra-high purity carbon rod grades.

Parameter	Grade F-S	Grade F-A
Density (g/cm3)	1.80	1.61
Electrical resistivity (µOhm.cm)	939.7	635
Hardness (shore)	42	32
Porosity (%)	16.5	28.5
Tensile strength (MPa)	41.4	22.1
Flexural strength (MPa)	51.8	24.2
Compressive strength (MPa)	65.6	48.2
Thermal expansion rate (x10-6/K)	2.9	1.9
Purity	Ultra-high	Ultra-high
Impurities (ppm)	Max. 1/element	Max. 1/element
Structure	Graphite	Graphite
Appearance	Hard, brittle	Softer