Gas Mixtures refer to compressed gases that have been combined
or blended into a single container.
The uses for gas mixtures in today's
technologically advanced society are virtually limitless.
Following is a brief list of applications of some
routinely used mixtures.
- Analytical Mixtures: In addition to pure gases,
gas mixtures are used for the operation and/or
calibration of analytical instruments. Zero gases (which
are usually pure materials certified to contain
negligible or known amounts concentrations of a component
of interest) are used for flame ionization detector
instruments that require gases of low hydrocarbon content
to achieve maximum sensitivity. "Zero air" may
be used both to zero the instrument (calibrate the
instrument to the low end of a concentration range) and
to provide oxidant of low hydrocarbon content for the
operation of the analyzer.
- Span gases, which usually contain a minor component of
interest at a known concentration level, permit the
analytical device to be calibrated at a value
corresponding to that concentration. Fuel gas is used in
instruments such as those with flame ionization detectors
which require that the supply of fuel be enhanced by
certain physical properties of diluent. A mixture of 40%
hydrogen in nitrogen is common.
- Pollution Control: Small amounts of nitric
oxide, nitrogen dioxide, sulfur dioxide, carbon monoxide,
vinyl chloride, various hydrocarbons, and other airborne
pollutants are added to air or other gases to calibrate
analytical instruments for emission measurements.These
are sometimes referred to as EPA Protocol Mixes.
- X-Ray Fluorescence Spectroscopy: Mixtures
containing small amounts of butane in a mixture of helium
and neon are used in X-ray fluorescence spectroscopy.
- Electron Capture: A Mixture of 5% methane in
argon is used in electron capture.
- Special Carrier Gases: These include mixtures
such as 8.5 percent hydrogen helium.
- Sterilizing: Mixtures of ethylene oxide, such as
12 percent with hydrocarbon-12 or 10 to 20 percent
ethylene oxide with carbon dioxide, are commonly used in
sterilization. Such mixtures require registration with
the U.S. Environmental Protection Agency.
- Medical Applications: A low concentration of
carbon monoxide in air is used for diagnosing lung
efficiency. Various percentage mixtures of carbon dioxide
in oxygen are used for blood gas analysis. Cyclopropane,
nitrous oxide, and certain other chemically active gases
are used separately and as mixtures for anesthesia.
Additionally, carbon dioxide in combination with other
gases is used to produce atmospheres for biological
study.
- Nuclear Counter Gases: Gas mixtures of 0.95
percent isobutane in helium and 1.3 percent butane in
helium are used as quenching gases in Geiger counters.
Mixtures of 4 percent isobutane in helium and 10 percent
methane in argon are used on proportional counters.
- Electronic Component Manufacture: Gases which
include low levels of dopants such as arsine, phosphine,
diborane, and others in hydrogen, helium, argon or
nitrogen are used for forming insulated nitride barriers
in integrated circuits. Silane, either pure or in
mixtures, is used for silicon deposition. Gas mixtures
similar to the ones above but with higher percentage
levels of arsine and phosphine are common in the
manufacture of compound semiconductors.
- Welding: Mixtures of oxygen or other gases with
argon, carbon dioxide, helium and nitrogen are used for
welding.
- Metallurgical Applications: Hydrogen-nitrogen
mixtures (forming gases) are used to produce reducing
atmospheres in heat treating applications.
- Leak Detection: A low percentage of halocarbons,
such as halocarbon-12, or helium in air or nitrogen, is
used for leak detection.
Illumination: Mixtures of rare gases with
helium, nitrogen or argon are used in lamps, signs,
electronic tubes, and other devices.
- Radioactive Gas Mixtures: Tritium and carbon-14,
usually mixed with inert gases, are commonly used as
tracer gases. Krypton-85 mixed with air is used for
diagnosing heart and brain disorders.
- Spark Chamber Gases: Generally, a mixture of
70-95 percent neon in helium is used in spark chambers.
- Laser Mixtures: Mixtures of rare gases with
nitrogen, and carbon dioxide with helium, are used for
lasers. Excimer lasers use the rare gases mixed with
fluorine or hydrogen chloride.
- Diving Mixtures or oxygen with helium and
possibly other diluents are used for deep diving
applications.
- Propellants: Various mixtures of liquefied gases
are commonly used in aerosol formulations as propellants.
Grades Available Gas mixtures are
available in several grades, namely: primary standard,
certified standard, and unanalyzed mixtures each having
its own preparation tolerance and certification accuracy
depending upon the minor component concentration.
When choosing a particular grade of gas mixture, the
application must be considered in order to achieve the
desired result with a minimum of cost. For example, gas
mixtures used for welding, sterilizing, propellants,
curing agents, leak detection, and certain process
atmospheres need not be blended to costly high tolerance
of primary standard mixtures. However, other
applications, such as mixtures used as standard reference
materials (SRM's) and certified reference materials
(CRM's) used for emission control testing, certain
medical mixtures, and some standard blends used for
calibration of monitoring instrumentation, require the
highest accuracy available.
- Containers Gas mixtures can be
supplied in many different types of containers. These
containers can range in size from .25-L glass flasks to
jumbo tube trailers. The overriding considerations in
choosing a particular container for a given mixture are
material compatibility, volume required, and minimum or
maximum desired pressure.
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