KBr
KBr is a soft, hygroscopic alkali halide crystal transmitting 0.2–25 µm, supplied as single crystal, hot-pressed blanks and FTIR-grade material.
Reference datasheet — KBr 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
KBr tempers and conditions
KBr 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 |
|---|---|---|---|---|---|---|
Spectroscopic-grade powder for pressed pellets | Choose for making 13 mm KBr pellets of solid samples in FTIR analysis; consumable, not an optical component. | 3 | 0.1 | 7 HV | 4 W/m·K | |
SCDefault Single crystal, IR window / prism grade | Choose for IR windows, prisms, beamsplitter substrates and ATR optics needing maximum 0.25–25 µm clarity. | 6 HV | 5 W/m·K | |||
Hot-pressed / forged polycrystalline KBr | Choose when larger, tougher and less cleavage-prone blanks are needed and slight far-IR scatter is acceptable. | 9 HV | 5 W/m·K |
What is KBr?
KBr is a soft, hygroscopic alkali halide crystal transmitting 0.2–25 µm, supplied as single crystal, hot-pressed blanks and FTIR-grade material. It offers the widest usable spectral range among common IR window materials at low cost, which makes it the default for FTIR pellets, gas-cell windows and prisms. The limits are severe: corrosion resistance is rated 5, maximum service temperature is 300 °C, elastic modulus is only 26.8 GPa and thermal conductivity 4.8 W/m·K, so parts need desiccated storage. KCl is a lower-cost substitute; ZnSe is used where humidity cannot be controlled. KBr has a density of 2.75 g/cm³ (0.0994 lb/in³), heavier than 51% of glass grades. It melts at 734°C (1,353 °F). The elastic modulus is 26.8 GPa (3.89 Msi).
What is KBr used for?
- FTIR windows/pellets
- IR spectroscopy cells
- IR prisms
Advantages
- Easy to machine — 55/100, better than 93% of glass grades
Limitations
- Needs corrosion protection — 5/100, worse than 98% of glass grades
- Low fracture toughness — 0.15 MPa·√m (0.137 ksi·√in), worse than 97% of glass grades
- Hard to polish — 45/100, worse than 92% of glass grades
- Low stiffness — 26.8 GPa (3.89 Msi), worse than 90% of glass grades
- Limited service temperature — 300°C (572 °F), worse than 80% of glass grades
KBr properties
Typical room-temperature values for KBr-SC; bars are the position among glass grades.
Physical5
KBr has a density of 2.75 g/cm³ (0.0994 lb/in³), heavier than 51% of glass grades. It melts at 734°C (1,353 °F).
Mechanical10
The elastic modulus is 26.8 GPa (3.89 Msi).
Thermal4
KBr is rated for continuous service to 300°C (572 °F). It conducts heat at 4.8 W/m·K (2.77 BTU/hr·ft·°F), better than 69% of glass grades. Thermal expansion is 43 µm/m·K (23.9 µin/in·°F).
Electrical3
KBr has an electrical resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental2
Corrosion resistance is not recommended (5/100), worse than 98% of glass grades.
Sustainability2
Producing a kilogram of KBr takes about 60 MJ of energy and emits 4 kg of CO₂ — more than 58% of glass grades.
Manufacturability2
KBr's machinability is good (55/100, better than 93% of glass grades).
Common Calculations2
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. KBr is highlighted; hover a dot for its name, or open the interactive family chart.
Working with KBr
Is KBr easy to machine?
Cleaves readily on {100}; saw or single-point diamond turn dry with low forces, never use water-based coolant — use dry air, kerosene or anhydrous alcohol-free oils.
Can KBr be welded?
Not weldable; assemble as a mounted optic with dry elastomer or indium seals and avoid hard clamping on the soft crystal.
Can KBr be formed, bent or molded?
Cold-pressed at ~700–1000 MPa into transparent FTIR pellets; can be hot-forged/hot-pressed near 400 °C into larger polycrystalline blanks.
KBr 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 KBr | 32.5 – 33.1 | 32.85 |
| total impuritiesoptical grade typically ≥99.95 %; main contaminants Cl, SO4, Ca, H2O/OH- | ≤ 0.5 | 0.05 |
| Br | ≥ 66.8 (balance) |
What surface finishes work on KBr?
Polish with anhydrous solvents (dry ethanol/isopropanol-free oil slurries) on pitch; store desiccated, and consider parylene or thin polymer moisture-barrier coatings — conventional AR coatings adhere poorly.
How much does KBr cost?
KBr is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
KBr — frequently asked
What is KBr used for?
KBr is typically used for FTIR windows/pellets, IR spectroscopy cells and IR prisms. In short: widest IR transmission range; standard FTIR pellet material; strongly hygroscopic.
Is KBr easy to machine?
Reasonably — machinability is rated good (55/100, better than 93% of glass grades). Cleaves readily on {100}; saw or single-point diamond turn dry with low forces, never use water-based coolant — use dry air, kerosene or anhydrous alcohol-free oils.
Can KBr be welded?
Not weldable; assemble as a mounted optic with dry elastomer or indium seals and avoid hard clamping on the soft crystal.
What surface finishes work on KBr?
Polish with anhydrous solvents (dry ethanol/isopropanol-free oil slurries) on pitch; store desiccated, and consider parylene or thin polymer moisture-barrier coatings — conventional AR coatings adhere poorly.
Can KBr be formed, bent or molded?
Cold-pressed at ~700–1000 MPa into transparent FTIR pellets; can be hot-forged/hot-pressed near 400 °C into larger polycrystalline blanks.
What is the maximum service temperature of KBr?
KBr is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does KBr cost?
KBr is a high-cost glass ($$$$), 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 Bromide (KBr) optical crystal data — Crystran Ltd (2023)
- KBr IR window and lens specifications — ISP Optics / Thorlabs (2022)
- CRC Handbook of Chemistry and Physics, 102nd ed. — CRC Press (2021)
- Engineered Materials Handbook Vol. 4: Ceramics and Glasses — ASM International (1991)
- Refractive index dispersion of alkali halides (Li, J. Phys. Chem. Ref. Data) — NIST/AIP (1976)
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.