KCl
KCl is an alkali halide crystal transmitting 0.2–20 µm, offered as standard single crystal, RAP (reactive-atmosphere-processed) and hot-forged material.
Reference datasheet — KCl is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the SC condition
KCl tempers and conditions
KCl is supplied in 3 conditions, soft to hard. SC is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SCDefault Single crystal, Bridgman/Czochralski grown, optical grade | Standard optical-grade single crystal for IR windows, prisms and FTIR cells where cost and broad transmission matter more than strength. | 2 | 2 | 9 HV | 7 W/m·K | |
Reactive-atmosphere-processed low-absorption single crystal | Grown/purified under HCl reactive atmosphere to strip OH⁻ and metal impurities; pick for high-average-power 10.6 µm CO₂ laser windows. | 2 | 2 | 9 HV | 7 W/m·K | |
Hot-forged / press-forged polycrystalline KCl | Grain-refined by hot forging (~400–600 °C) to raise yield and flexural strength several-fold; used for large high-power CO₂ laser windows that cannot be supported as fragile single crystals. | 12 | 3 | 15 HV | 6 W/m·K |
What is KCl?
KCl is an alkali halide crystal transmitting 0.2–20 µm, offered as standard single crystal, RAP (reactive-atmosphere-processed) and hot-forged material. Very low absorption made it the historic choice for high-power CO2 laser windows, and it remains a low-cost substrate for IR spectroscopy optics and prisms. It is hygroscopic and mechanically weak — tensile strength about 2.4 MPa, thermal conductivity 6.5 W/m·K, maximum service temperature 500 °C — so dry purge and compliant mounting are required. ZnSe is the usual replacement in modern CO2 laser systems. KCl has a density of 1.98 g/cm³ (0.0717 lb/in³), lighter than 100% of glass grades. It melts at 771°C (1,420 °F). KCl has a tensile strength of 2 MPa (0.348 ksi), weaker than 100% of glass grades. Elongation at break is 2% and the elastic modulus is 29.7 GPa (4.31 Msi).
What is KCl used for?
- CO2 laser windows
- IR spectroscopy optics
- IR prisms
Advantages
- Lightweight — 1.98 g/cm³ (0.0717 lb/in³), better than 100% of glass grades
- Easy to machine — 60/100, better than 97% of glass grades
- Ductile — tolerates forming and impact — 2%, better than 84% of glass grades
Limitations
- Needs corrosion protection — 5/100, worse than 98% of glass grades
- Hard to polish — 45/100, worse than 92% of glass grades
- Low stiffness — 29.7 GPa (4.31 Msi), worse than 88% of glass grades
- Low fracture toughness — 0.3 MPa·√m (0.273 ksi·√in), worse than 85% of glass grades
KCl properties
Typical room-temperature values for KCl-SC; bars are the position among glass grades.
Physical5
KCl has a density of 1.98 g/cm³ (0.0717 lb/in³), lighter than 100% of glass grades. It melts at 771°C (1,420 °F).
Mechanical13
KCl has a tensile strength of 2 MPa (0.348 ksi), weaker than 100% of glass grades. Elongation at break is 2% and the elastic modulus is 29.7 GPa (4.31 Msi).
Thermal5
KCl is rated for continuous service to 500°C (932 °F). It conducts heat at 6.5 W/m·K (3.76 BTU/hr·ft·°F), better than 74% of glass grades. Thermal expansion is 36 µm/m·K (20 µin/in·°F).
Electrical3
KCl has an electrical resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental2
Corrosion resistance is not recommended (5/100), worse than 98% of glass grades.
Sustainability3
Producing a kilogram of KCl takes about 40 MJ of energy and emits 3 kg of CO₂ — less than 69% of glass grades. Typical recycled content is 20%.
Manufacturability2
KCl's machinability is good (60/100, better than 97% of glass grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the glass family
Yield strength against density for every glass grade FabDigit runs. KCl is highlighted; hover a dot for its name, or open the interactive family chart.
Working with KCl
Is KCl easy to machine?
Cuts easily with dry diamond saws or single-point diamond turning at light depth of cut; never use water-based coolant — cleave planes {100} make it prone to chipping.
Can KCl be welded?
Not weldable; parts are cemented or mechanically clamped with compliant (indium/PTFE) seats to avoid stress-induced fracture.
Can KCl be formed, bent or molded?
Bulk blanks are Bridgman/Czochralski grown; large windows can be hot press-forged at 400–600 °C to refine grains and raise strength.
KCl 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 |
|---|---|---|
| Kstoichiometric KCl | 52.3 – 52.6 | 52.45 |
| total metallic impuritiesoptical grade, typically ≤20–50 ppm; OH⁻ minimized in RAP material | ≤ 0.01 | 0 |
| Cl | balance |
What surface finishes work on KCl?
Polish with dry or anhydrous (alcohol/kerosene) slurries in a low-humidity room; AR or moisture-barrier coatings (e.g. ThF₄/ZnSe, parylene) are standard for field use.
How much does KCl cost?
KCl is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
KCl — frequently asked
What is KCl used for?
KCl is typically used for CO2 laser windows, IR spectroscopy optics and IR prisms. In short: low-absorption CO2 laser window; lower cost than KBr; hygroscopic, purge required.
What is the tensile strength of KCl?
KCl has a typical tensile strength of 2 MPa (0.348 ksi) — weaker than 100% of glass grades. Strength varies by condition: see the 3 listed tempers.
Is KCl easy to machine?
Reasonably — machinability is rated good (60/100, better than 97% of glass grades). Cuts easily with dry diamond saws or single-point diamond turning at light depth of cut; never use water-based coolant — cleave planes {100} make it prone to chipping.
Can KCl be welded?
Not weldable; parts are cemented or mechanically clamped with compliant (indium/PTFE) seats to avoid stress-induced fracture.
What surface finishes work on KCl?
Polish with dry or anhydrous (alcohol/kerosene) slurries in a low-humidity room; AR or moisture-barrier coatings (e.g. ThF₄/ZnSe, parylene) are standard for field use.
Can KCl be formed, bent or molded?
Bulk blanks are Bridgman/Czochralski grown; large windows can be hot press-forged at 400–600 °C to refine grains and raise strength.
What is the maximum service temperature of KCl?
KCl is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does KCl cost?
KCl is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- Potassium Chloride (KCl) optical material data — Crystran Ltd (2023)
- KCl Kristalle — Kenndaten — Korth Kristalle GmbH (2022)
- Handbook of Optical Constants of Solids — Academic Press (Palik, ed.) (1998)
- Engineered Materials Handbook Vol.4: Ceramics and Glasses — ASM International (1991)
- CRC Handbook of Chemistry and Physics, 102nd ed. — CRC Press (2021)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.