The PELCO® Sapphire Discs or Wafers are made from high purity clear sapphire (Al2O3), ground and optically clear polished on both sides. Sapphire has a wide transmission range; from 150 to 6000nm with low absorbance in the 300 to 4500nm range. The discs are ideal as substrates for thin film research and are suitable for optical research. Excellent resistance against a wide range of chemicals. Surface polish to one microinch or better on each face. Tolerances are ±0.001" (0.025mm) in diameter and thickness; flatness to 0.0003" (0.0008mm) or better. Available in 0.5" (12.7mm), 0.75" (19mm) and 1" (25.4mm) diameter with a choice of thickness between 0.010" or 0.125" (0.25 or 3.2mm).
16005-0520 - Sapphire Substrate Disc, Ø12.7mm x 0.5mm (Ø0.5" x 0.020"), polished
16005-0540 - Sapphire Substrate Disc, Ø12.7mm x 1mm (Ø0.5" x 0.040"), polished
16005-0720 - Sapphire Substrate Disc, Ø19.0mm x 0.5mm (Ø0.75" x 0.020"), polished
16005-0740 - Sapphire Substrate Disc, Ø19.0mm x 1.0mm (Ø0.75" x 0.040"), polished
16005-1010 - Sapphire Substrate Disc, Ø25.4mm x 0.3mm (Ø1" x 0.010"), polished
16005-1020 - Sapphire Substrate Disc, Ø25.4mm x 0.5mm (Ø1" x 0.020"), polished
16005-1040 - Sapphire Substrate Disc, Ø25.4mm x 1.0mm (Ø1" x 0.040"), polished
16005-10125 - Sapphire Substrate Disc, Ø25.4mm x 3.2mm (Ø1" x 0.125"), polished
Sapphire is an anistrophic crystal, hexagonal system, composed of unicrystalline alpha aluminum oxide, essentially 100% pure. Various properties are a function of crystallographic direction (related to the optic axis of the crystal). Sapphire discs are made from sapphire rods, the c-axis of the hexagonal unit cell is in the longitudinal direction. In the tables below, if no orientation is shown, this indicates that the property listed does not vary appreciably in relation to orientation or the variation is less than the experimental error of measurement.
Hexagonal Unit Cell of Sapphire
Transmission of synthetic sapphire is shown in the following curve. Data in UV region is approximate, as transmission depends on surface finish, internal quality and purity of individual specimen. The following curve shows transmission of sapphire uncorrected for Fresnel losses.
|Crystaline Structure: Rhombohedral Single Crystal||Young's Modulus: 50 to 55,000,000 PSI|
Hexagonal System: A=4.763Å C=13.003Å
Melting Point: 2040°C
Density: 3.97 g/cm³
Bending Modulus (Minimum):
20° C 60,000 PSI
500° C 40,000 PSI
1000° C 60,000 PSI
Refractive Index: 20° C
12K (-261° C) = 8.0 cal/cm2/sec/C/cm
300K (23° C) = 0.9 cal/cm2/sec/C/cm
50° C = .07 cal/cm2/sec/C/cm
Coefficient of Expansion
(Mean between 20° C and T) per° C
20° C 1014 ohm-cm
500° C 1011 ohm-cm
1000° C 109 ohm-cm
Loss Tangent: < 1 x 10-4 at 1MHz
Hardness: Moh 9, Knoop 1525 to 2000
Sapphire can be wetted by glass, titanium, zirconium or moly-manganese mixtures. It can be matched to titanium, molybdenium, the high nickel-iron allows such as Carpenter 49, Kovar and the Corning glass 7520. With the good technique, bonds can be made directly to Corning 7052.
As can be seen from the list of properties, sapphire is unique when compared to optical materials useful within its transmission range in that it is by far the strongest, toughest, thermal shock and chemically resistant material available, and it can be used at far higher temperatures than most optical materials. Also, its thermal conductivity is relatively high despite its extreme electrical non-conductivity. Moderate refractive index, transparency in visible region, good transmission and relatively low emission at high temperatures plus unusual stability combine to make it valuable as a component on military optics.