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Krypton

Krypton (Kr) is a colourless, odourless, nonflammable, inert gas.

Applications
Used in the production of incandescent bulbs and fluorescent light tubes, lasers, and thermally efficient windows.

Materials Compatibility
Metals: Brass; Stainless Steel; Carbon Steel; Aluminum; Zinc; Copper; Monel.
Plastics: Kel-F; PTFE, FEP, and PFA Fluoropolymers resins; Tefzel; Kynar; PVC; Polycxarbonate.
Elastomers: Kalrez; Viton; Buna-N; Neoprene; Polyurethane.

Technical Properties
Molecular Weight: 83.80
Specific Gravity (Air = 1): 2.899
Odour: Odourless
CAS Registry No.: 7439-90-9
Critical Temperature: 209.35 K / -63.8 °C
Critical Pressure: 54.9 bar
Boiling Point: 120.25 K / -152.9 °C
Melting Point: 116.55 K /-156.6 °C

It is estimated that 30 percent of the energy efficient windows sold in England and Germany are filled with krypton. The use of krypton in thermally efficient windows (as a replacement for either air or argon) helps provide the increase in "R" value required to meet new energy efficiency goals. Depending upon the application, argon is sometimes mixed with the krypton, and there are special systems that also require about 10 percent oxygen be added to the krypton.

Lasers use krypton to provide a desired optic wavelength depending upon the application for the laser. Krypton is always mixed with a halogen, typically fluorine, to produce the desired characteristics. Lasers of this nature are called "excimer" lasers.

Some companies involved in the space exploration industry are experimenting with krypton as a fuel source for ion propulsion engines, although xenon provides greater performance. Selection of propulsion fuel for electric engines is often a tradeoff of cost versus efficiency, since the price of xenon is typically 10 times that of krypton.

Krypton is sometimes used within halogen sealed beam headlights, which produce up to double the light output of standard incandescent headlamps.

Halogen sealed beams increase light output on "high beams" to as much as 150,000 candlepower. Specifications on low beams remain the same, at between 8,000 and 20,000 candlepower per lamp. The advantage of halogen is that it gives substantially more light for the same amount of electricity, and actually reduces energy consumption when you maintain the same light output as a non-halogen lamp.
Halogen bulbs are really incandescent lamps with a couple of minor differences which enable their filaments to burn at a higher temperature and thus to provide a brighter light.
The halogen lamp's filament burns hotter because it is very slightly thinner, increasing its efficiency to produce a more intense and "whiter" light than the "yellow" incandescent beam.
The tungsten filaments of both kinds of lamps are in an inert gas atmosphere: argon or nitrogen, or a mixture of both. Newer lamps, however, contain about 1% of a halogen gas (bromine, chlorine, fluorine, iodine, or astatine) and a substantial amount of krypton.
Krypton usually increases the pressure in the bulb, helping to retard filament evaporation, and the halogen material in the bulb atmosphere initiates a "scrubbing" cycle by combining with vaporised tungsten and redepositing it on the filament. Unfortunately, this cycle is not perpetual.
The tungsten is not redeposited in exactly the same spot from which it flaked away, so, eventually some spots in the filament do get thinner and eventually fail. The application and concept is the same for residential light bulbs such as GE's "Watt Miser" series.
Typical mixture components, apart from argon, krypton, and nitrogen, might include methyl bromide, methylene bromide, hydrogen bromide, and methyl iodide, to supply the necessary halogen component.