Sodium Fluoride
Sodium fluoride is seldom used for its optical properties, these being inferior to calcium fluoride and lithium fluoride, but it has one of the lowest refractive indexes of all materials in the UV, and is generating considerable interest as a detector material in high energy physics RICH (Ring Imaging Cherenkov) counters. Sodium fluoride may also be used as an a/r coating material.
GENERAL PROPERTIES
Formula: NaF
Molecular Weight: 42.0
Crystal Structure: Cubic, NaCl structure. (100) cleavage
Applications: Cherenkov counters
Optical Properties:
Transmission Range: 0.15 to 14 microns
Refractive Index: 1.327 at 0.5 microns
Reflection Loss: 3.8% at 0.5 microns (2 surfaces)
Restrahlen Peak: 35.8 microns
Physical Properties:
Density: 2.726 gm/cc
Melting Point: 980 oC
Solubility in Water: 4.22gm/100gm at 18 oC
Thermal Conductivity: 3.746 Wm-1 oK-1 at 0 oC
Thermal Expansion: 36 x 10-6/oC
Hardness: Knoop 60
Specific Heat Capacity: 1088 J Kgm-1 oK-1 at 0 oC
Dielectric Constant: 6.0
Young’s Modulus: 79.01 GPa
Shear Modulus: 12.7 GPa
Bulk Modulus: 47.9 GPa
Elastic Coefficients: C11 = 90.9 C12 = 26.4 C44 = 12.7
Poisson Ratio: 0.326