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ZnS (Zinc Sulphide Multispectral, CVD)

ZnS Multispectral (water-clear) is used for IR windows and lenses in the thermal band (8 to 14 μm) where maximum transmission and lowest absorption is required. Also selected for use where visible alignment is an advantage.

Physical and optical properties

Transmission Range :	0.37 to 13.5 μm
Refractive Index :	2.20084 at 10 μm
Reflection Loss :	24.7% at 10 μm (2 surfaces)
Absorption Coefficient :	0.0006 cm-1 at 3.8 μm
Reststrahlen Peak :	30.5 μm
dn/dT :	+38.7 x 10-6 /°C at 3.39 μm
dn/dμ = 0 :	n/a
Density :	4.09 g/cc
Melting Point :	1827°C (See notes below)
Thermal Conductivity :	27.2 W m-1 K-1 at 298K
Thermal Expansion :	6.5 x 10-6 /°C at 273K
Hardness :	Knoop 160 with 50g indenter
Specific Heat Capacity :	515 J Kg-1 K-1
Dielectric Constant :	88
Youngs Modulus (E) :	74.5 GPa
Shear Modulus (G) :	n/a
Bulk Modulus (K) :	n/a
Elastic Coefficients :	Not Avalailable
Apparent Elastic Limit :	68.9 MPa (10,000 psi)
Poisson Ratio :	0.28
Solubility :	65 x 10-6 g/100g water
Molecular Weight :	97.43
Class/Structure :	HIP polycrystalline cubic, ZnS, F42m

Refractive Index

No = Ordinary Ray

µm	No	µm	No	µm	No
0.4047	2.54515	0.4358	2.48918	0.4678	2.44915
0.480	2.43691	0.5086	2.41279	0.5461	2.38838
0.5876	2.36789	0.6438	2.34731	0.6678	2.34033
0.7065	2.33073	0.780	2.31669	0.7948	2.31438
0.8521	2.30659	0.8943	2.30183	1.014	2.29165
1.1287	2.28485	1.5296	2.27191	2.0581	2.26442
3.000	2.25772	3.500	2.25498	4.000	2.25231
4.500	2.24955	5.000	2.24661	8.000	2.22334
9.000	2.22334	10.00	2.20084	11.25	2.18317
12.00	2.17101	13.00	2.15252

Product Notes

Zinc Sulphide is produced by synthesis from Zinc vapour and H2S gas, forming as sheets on Graphite susceptors. Zinc Sulphide is microcrystalline in structure, the grain size being controlled to produce maximum strength. Multispectral grade is then Hot Isostatically Pressed (HIP) to improve the mid IR transmission and produce the visibly clear form. Single crystal ZnS is available, but is not common.

Zinc Sulphide oxidizes significantly at 300°C, exhibits plastic deformation at about 500°C and dissociates about 700°C. For safety, Zinc Sulphide windows should not be used above 250°C in normal atmosphere.

Tags: ZnS (Zinc Sulphide Multispectral, CVD)