Measurements of the influence of sand/dust impact erosion on FLIR ZnS, coated with a range of durable coatings, have been made using spectral transmission. This activity has been carried out as part of a program to identify a sand/dust and rain erosion protective coating, for use on the Martin Marietta LANTIRN E-O system front element ZnS/ZnSe laminate window. Assessments have been carried out against MIL STD 810E sand/dust erosion specification, using the Defence Nuclear Agency sand erosion facility. A range of sand particle diameters (< 38 to 177 micrometers ), and velocities 45 to 206 m/s), has been investigated. Three anti- reflective durable coatings have been tested: thorium fluoride, diamond like carbon (DLC -- supplied from three separate vendors), and boron phosphide (BP) overcoated with DLC. BP/DLC showed no significant erosion damage or change in transmission for the range of test conditions, while DLC and ThF4 exhibited significant erosion damage and consequent transmission reduction. A basic theory of solid particle impact is used to model transmission reduction in relation to coating hardness, velocity, and size of impacting sand particles. The concept of `erosion parameter and threshold velocity' is introduced, which provides a means of predicting transmission reduction for a range of sand erosion conditions.
|Name||Proceedings of SPIE|
|Conference||SPIE's 1994 International Symposium on Optics, Imaging and Instrumentation|
|Period||24/07/94 → 29/07/94|
- Optical coatings
- Forward looking infrared