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Sodium Fluoride NaF
Sodium Fluoride has the lowest refractive index of all common optical materials which makes it of interest as a Cerenkov radiator in Particle Physics research. Crystran Ltd. has supplied Sodium Fluoride material which has been made into large arrays at CERN and it is used in Ring Imaging Cerenkov Counters (RICH).
| Transmission Range | 0.14 to 11 μm |
| Refractive Index | 1.3255 at 0.6 μm |
| Reflection Loss | 3.9% at 0.6 μm (2 surfaces) |
| Absorption Coefficient | 1 x 10-3 cm-1 @ 7 μm (1) |
| Reststrahlen Peak | 35.8 μm |
| dn/dT | -13 x 10-6 K-1 @ 293 K |
| dn/dμ | 1.7 μm |
| Density | 2.79 g/cc @ 20°C |
| Melting Point | 980°C |
| Thermal Conductivity | 3.746 W m-1 K-1 @ 273 K |
| Thermal Expansion | 36 x 10-6 K-1 @ 300 K |
| Hardness | Knoop 60 in |
| Specific Heat Capacity | 1088 J Kg-1 K-1 |
| Dielectric Constant | 6 at 1 MHz |
| Young's Modulus (E) | 79.01 GPa |
| Shear Modulus (G) | 12.7 GPa |
| Bulk Modulus (K) | 47.9 GPa |
| Elastic Coefficients | C11 = 79.01; C12 = 12.7; C44 = 47.9 |
| Apparent Elastic Limit | 3.2 MPa (estimated) |
| Poisson Ratio | 0.326 |
| Solubility | 4.22 g/100 g water @ 18°C |
| Molecular Weight | 42.0 |
| Class/Structure | Cubic FCC, NaCl, Fm3m, (100) cleavage |
| μm | No | μm | No | μm | No |
|---|---|---|---|---|---|
| 0.140 | 1.550 | 0.546 | 1.3264 | 6.1 | 1.292 |
| 0.145 | 1.499 | 0.589 | 1.32549 | 7.1 | 1.282 |
| 0.161 | 1.438 | 0.707 | 1.32372 | 8.1 | 1.269 |
| 0.175 | 1.410 | 0.811 | 1.32272 | 9.1 | 1.252 |
| 0.186 | 1.393 | 0.912 | 1.32198 | 10.3 | 1.233 |
| 0.199 | 1.3805 | 1.014 | 1.3215 | 11.3 | 1.209 |
| 0.203 | 1.3772 | 2.00 | 1.3170 | 12.5 | 1.180 |
| 0.302 | 1.34232 | 3.1 | 1.313 | 13.8 | 1.142 |
| 0.405 | 1.33194 | 4.1 | 1.308 | 15.1 | 1.093 |
| 0.486 | 1.32818 | 5.1 | 1.301 | 16.7 | 1.029 |
Sodium Fluoride is produced by vacuum Stockbarger techniques. The Sodium Fluoride is very difficult to anneal and cleaves readily limiting the useful size of pieces to about 80mm. Sodium Fluoride polishes well but must be kept in dry air to maintain the quality of the surfaces and retain the deep UV transmission needed for Cerenkov radiation from this material.
REFERENCES:
(1) H.H.Li, Absorption Coefficients, Int.J.Therm, V1, No. I, 1980