SPI Supplies® Brand Pyrolytic Graphite Planchets
Other information about this extraordinarily interesting material
We have listed below a general description of the processing and a summary
of the main properties of the SPI Supplies® Brand of pyrolytic graphite.
The product offered for some number of years by SPI Supplies as pyrolitic
graphite planchetts was of what is now referred to as "substrate nucleated"
or SN Grade of the material. The properties of the "continuously nucleated"
or CN Grade are not terribly different, but they are different enough that
for some applications, the one grade is clearly preferred over the other.
Other useful information:
- Both forms of the SPI Supplies Brand of pyrolytic graphite are
markedly different from polycrystalline graphite and is in a specialty
category, such as HOPG, if for no reason
other than it much higher cost. The absence of granular components and
the unique structures of CVD deposited pyrolytic graphite, yields components
that achieve drop out rates at or below 10 per wafer - far below commercial
graphite, and approaching that of silicon. In addition to having a very
low erosion rate, the size of the particulates generated is <0.1 µm and
the drop out distribution is uniform.
- The low ion sputtering rate in plasma applications results in enhanced
lifetime, approaching several hundred hours in RF driven plasma devices, and
is therefore, economically beneficial in spite of its high unit cost. It is
used widely in ion guns, due to its combination of high conductivity (in the
a-b plane) and the very low sputtering rate offered by carbon in general.
- Having been synthesized from purified hydrocarbon gases, total metallic
impurities are exceptionally low, on the order of <5 ppm. This is well
below the sensitivity of commerically available EDS detectors.
- The SPI Supplies Brand of pyrolytic graphite performs well at
exceptionally high temperatures and is stable up to 2200 °C.
- Due to the nature of the deposition process by CVD, the SPI Supplies
Brand of pyrolytic graphite approaches the theoretical density = 2.25, and
hence is essentially non-porous. Therefore, one does not observe the
off-gassing problems normally associated with graphite generally.
- Pyrolytic graphite is very stable in the more chemically active etching
plasma applications employing chlorofluoro carbons and nitrogen trifluoride,
which attack silicon.
- The anisotropic conductivity of the SPI Supplies Brand of pyrolytic
graphite has excellent conductivity, approaching copper in the a-b
direction, whereas it acts almost as a ceramic on the 'c' direction,
requiring special fixturing to take maximum advantage of its directional
conductivity. In this regard it is an excellent material in special thermal
management applications, including heat sinks.
Physical Properties:
The following two tables compare and contrast the two forms of pyrolytic
graphite, remembering that the standard product offered by SPI Supplies is
the SN Grade but CN Grade could be offered on special order for those
requiring this special form of the product.
Price Differentials:
In general, the pricing for the CN Grade is about 30-35% higher than for the
SN Grade, that being due to the longer production process since the growth
rate of the material, as it is being formed, is much slower.
Custom Machinging Capabilities:
We can produce fully machined parts according to any customer supplied
drawings, such as etching cathodes or grids. A proprietary surface
treatment can be applied upon request after the SPI Supplies supplied parts
are machined to minimize or virtually eliminate particulate debris from the
production process.
Physical Properties for SPI Supplies Brand SN Grade Pyrolytic Graphite
|
Property | Direction* | Metric Units | English Units |
|
Density | --- | 2.22 g/cc | 137 lb/ft3 |
|
Flexural Strength | | | |
|
Room Temperature | a | 840 kg/cm2 | 12,000 psi |
|
2750°C | a | 3,500 kg/cm2 | 50,000 psi |
|
Compressive Strength | | | |
|
Room Temperature | a | 1,050 kg/cm2 | 15,000 psi |
|
| c | 1,750 kg/cm2 | 25,000 psi |
|
Shear Strength | | | |
|
Room Temperature | a | 70 kg/cm2 | 1,000 psi |
|
Coefficient Thermal Expansion | | | |
|
Room Temperature | a | 0.6x10-6 cm/cm°C | 1.0x10-6 in/in°F |
|
2200°C | a | 0.68x10-6 cm/cm°C | 1.2x10-6 in/in°F |
|
Room Temperature | c | 6.8x10-6 cm/cm°C | 12.0x10-6 in/in°F |
|
2200°C | c | 8.0x10-6 cm/cm°C | 14.7x10-6 in/in°F |
|
Thermal Conductivity | | | |
|
Room Temperature | a | 345 W/m°K | 200 BTU/(hr ft2)(°F/ft) |
|
1650°C | a | 114 W/m°K | 66 BTU/(hr ft2)(°F/ft) |
|
Room Temperature | c | 1.73 W/m°K | 1.00 BTU/(hr ft2)(°F/ft) |
|
3000°F | c | 1.30 W/m°K | 0.75 BTU/(hr ft2)(°F/ft) |
|
Electric Resistivity | | | |
|
Room Temperature | a | 500 µWcm | |
|
1650°C | a | 200 µWcm | |
|
Room Temperature | c | 0.6 Wcm | |
|
1650°C | c | 0.22 Wcm | |
|
Scleroscope Hardness | a | 103 | 103 |
|
| c | 68 | 68 |
|
Oxidation Threshold | | 650°C | 1200°F |
|
Permeability | | Helium Leak Tight at 10-6 mmHg |
Physical Properties for SPI Supplies Brand CN Grade Pyrolytic Graphite
|
Property | Direction* | Metric Units | English Units |
|
Density | --- | 2.19 g/cc | 136 lb/ft3 |
|
Flexural Strength | | | |
|
Room Temperature | a | 840 kg/cm2 | 12,000 psi |
|
2750°C | a | 3,500 kg/cm2 | 50,000 psi |
|
Compressive Strength | | | |
|
Room Temperature | a | 1,200 kg/cm2 | 17,500 psi |
|
| c | 2,500 kg/cm2 | 38,011 psi |
|
Shear Strength | | | |
|
Room Temperature | a | 140 kg/cm2 | 2,000 psi |
|
Coefficient Thermal Expansion | | | |
|
Room Temperature | a | 0.6x10-6 cm/cm°C | 1.0x10-6 in/in°F |
|
2200°C | a | 0.68x10-6 cm/cm°C | 1.3x10-6 in/in°F |
|
Room Temperature | c | 6.8x10-6 cm/cm°C | 12.0x10-6 in/in°F |
|
2200°C | c | 8.0x10-6 cm/cm°C | 14x10-6 in/in°F |
|
Thermal Conductivity | | | |
|
Room Temperature | a | 304 W/m°K | 176 BTU/(hr ft2)(°F/ft) |
|
1650°C | a | 114 W/m°K | 66 BTU/(hr ft2)(°F/ft) |
|
Room Temperature | c | 1.73 W/m°K | 1.00 BTU/(hr ft2)(°F/ft) |
|
3000°F | c | 1.30 W/m°K | 0.75 BTU/(hr ft2)(°F/ft) |
|
Electric Resistivity | | | |
|
Room Temperature | a | 500 µWcm | |
|
1650°C | a | 200 µWcm | |
|
Room Temperature | c | 0.6 Wcm | |
|
1650°C | c | 0.22 Wcm | |
|
Scleroscope Hardness | a | 101 | 101 |
|
| c | 83 | 83 |
|
Oxidation Threshold | | 650°C | 1200°F |
|
Permeability | | Helium Leak Tight at 10-6 mmHg |
*a: Along basal planes (across surface)
c: Through basal planes (through thickness)
|
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Monday March 22, 2010
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