KRS-5 POLY-EXT
Grade
Use the hot-extruded fine-grained polycrystal for flexible infrared transmitting fibre and high aspect-ratio light guides; strength beats single crystal but grain-boundary scatter lowers transmission.
Values for the POLY-EXT condition
Other KRS-5 tempers and conditions
KRS-5 is listed in 2 conditions; see the grade overview at KRS-5.
- SC-OPT
- POLY-EXT
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SC-OPTDefault Bridgman-grown single crystal, optical window grade | Choose the Bridgman-grown single crystal for infrared windows, lenses and spectroscopic windows where the highest transmission and scatter-free optics are required. | — | 26 | 2 | 40 HV | 0.54 W/m·K |
POLY-EXTThis page hot-extruded polycrystalline (IR fibre / light-guide stock) | Use the hot-extruded fine-grained polycrystal for flexible infrared transmitting fibre and high aspect-ratio light guides; strength beats single crystal but grain-boundary scatter lowers transmission. | — | 35 | 3 | 45 HV | 0.5 W/m·K |
What is KRS-5 POLY-EXT?
KRS-5 POLY-EXT is KRS-5 in the POLY-EXT grade — use the hot-extruded fine-grained polycrystal for flexible infrared transmitting fibre and high aspect-ratio light guides; strength beats single crystal but grain-boundary scatter lowers transmission. KRS-5 POLY-EXT has a tensile strength of 35 MPa (5.08 ksi), weaker than 75% of glass grades. Elongation at break is 3% and the elastic modulus is 15.5 GPa (2.25 Msi). KRS-5 POLY-EXT has a density of 7.37 g/cm³ (0.266 lb/in³), heavier than 100% of glass grades. It melts at 415°C (778 °F). SC-OPT is the default condition FabDigit quotes; POLY-EXT is available on request or by drawing note.
Advantages
- Easy to machine — 50/100, better than 92% of glass grades
- Ductile — tolerates forming and impact — 3%, better than 90% of glass grades
Limitations
- Heavy — 7.37 g/cm³ (0.266 lb/in³), worse than 100% of glass grades
- Hard to polish — 35/100, worse than 100% of glass grades
- Low stiffness — 15.5 GPa (2.25 Msi), worse than 98% of glass grades
- Limited service temperature — 100°C (212 °F), worse than 98% of glass grades
- Poor heat conductor — 0.5 W/m·K (0.289 BTU/hr·ft·°F), worse than 98% of glass grades
KRS-5 POLY-EXT properties
Typical room-temperature values for KRS-5 POLY-EXT; 16 are specific to this condition. Other listed values are KRS-5 reference data and may not represent this condition. Bars are the position among glass grades.
Physical5
KRS-5 POLY-EXT has a density of 7.37 g/cm³ (0.266 lb/in³), heavier than 100% of glass grades. It melts at 415°C (778 °F).
Mechanical13
KRS-5 POLY-EXT has a tensile strength of 35 MPa (5.08 ksi), weaker than 75% of glass grades. Elongation at break is 3% and the elastic modulus is 15.5 GPa (2.25 Msi).
Thermal4
KRS-5 POLY-EXT is rated for continuous service to 100°C (212 °F). It conducts heat at 0.5 W/m·K (0.289 BTU/hr·ft·°F), worse than 98% of glass grades. Thermal expansion is 58 µm/m·K (32.2 µin/in·°F).
Electrical2
KRS-5 POLY-EXT has an electrical resistivity of 5×10⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is fair (50/100), worse than 80% of glass grades.
Manufacturability2
KRS-5 POLY-EXT's machinability is fair (50/100, better than 92% of glass grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with KRS-5 POLY-EXT
Is KRS-5 easy to machine?
Very soft and highly plastic: single-point diamond turn or cut with a fine-grit wire saw, keeping cutting forces very low so the material does not cold-flow. Run dry or with kerosene lubrication, and enclose the operation with sealed extraction because the debris contains thallium.
Can KRS-5 be welded?
Not weldable — an ionic crystal. Assemble by mechanical clamping or low-stress optical adhesive, and avoid direct contact with silver, copper or nickel.
Can KRS-5 be formed, bent or molded?
Hot extruded or hot forged at roughly 250–350 °C into polycrystalline rod or IR fibre. Single crystals are grown by the Bridgman–Stockbarger method and must be cooled slowly to avoid residual stress and slip bands.
What surface finishes work on KRS-5?
Polish at light pressure with soft felt and fine alumina or diamond in anhydrous (alcohol) media; the surface scratches very easily. AR stacks such as ZnSe/BaF2 are applied to offset the ~30 % reflection loss from n≈2.37, and clamping faces must be supported to prevent plastic deformation.
KRS-5 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Tlas TlBr 42 mol% + TlI 58 mol% solid solution | 64.5 – 66.5 | 65.6 |
| ITlI about 61.7 wt% | 22.5 – 24.5 | 23.6 |
| BrTlBr about 38.3 wt% | 10 – 11.5 | 10.8 |
| (metallic impurities)total metal impurities, optical grade | ≤ 0.01 | 0.01 |
KRS-5 POLY-EXT — frequently asked
What is KRS-5 POLY-EXT used for?
KRS-5 POLY-EXT is typically used for ATR spectroscopy prisms, IR fiber optics and IR windows. In short: widest IR range, to 40 µm; water-insoluble ATR crystal; soft, ductile, thallium-toxic.
What is the tensile strength of KRS-5 POLY-EXT?
KRS-5 POLY-EXT has a typical tensile strength of 35 MPa (5.08 ksi) — weaker than 75% of glass grades. Strength varies by condition: see the 2 listed tempers.
Is KRS-5 POLY-EXT easy to machine?
Reasonably — machinability is rated fair (50/100, better than 92% of glass grades). Very soft and highly plastic: single-point diamond turn or cut with a fine-grit wire saw, keeping cutting forces very low so the material does not cold-flow. Run dry or with kerosene lubrication, and enclose the operation with sealed extraction because the debris contains thallium.
Can KRS-5 POLY-EXT be welded?
Not weldable — an ionic crystal. Assemble by mechanical clamping or low-stress optical adhesive, and avoid direct contact with silver, copper or nickel.
What surface finishes work on KRS-5 POLY-EXT?
Polish at light pressure with soft felt and fine alumina or diamond in anhydrous (alcohol) media; the surface scratches very easily. AR stacks such as ZnSe/BaF2 are applied to offset the ~30 % reflection loss from n≈2.37, and clamping faces must be supported to prevent plastic deformation.
Can KRS-5 POLY-EXT be formed, bent or molded?
Hot extruded or hot forged at roughly 250–350 °C into polycrystalline rod or IR fibre. Single crystals are grown by the Bridgman–Stockbarger method and must be cooled slowly to avoid residual stress and slip bands.
What is the maximum service temperature of KRS-5 POLY-EXT?
KRS-5 POLY-EXT is rated for continuous use to about 100°C (212 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- KRS-5 (Thallium Bromo-Iodide) Optical Material Data — Crystran Ltd. (2023)
- KRS-5 Crystal Properties — Korth Kristalle GmbH (2022)
- Handbook of Optical Constants of Solids — Academic Press (Palik ed.) (1998)
- Handbook of Optical Materials — CRC Press (Weber) (2003)
- KRS-5 ATR Crystals and IR Windows — ISP Optics / Crystaltechno (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.