Probe gases and liquids

Probe gases and liquids are often used in a variety of leak detection techniques. Probe gases and liquids are materials not normally found within the vacuum system, or at least not in the quantity created when they enter through a leak. Turnbull72 defines four characteristics of the probe gas, vacuum system, and leak detector that affect the speed and effectiveness of leak detection  

The viscosity of the search gas, which governs the rate at which gas enters the leak 

The speed at which the search gas is removed from the system by the pumping system 

The sensitivity of the leak-detecting element to the particular search gas used 

Although each of these factors can be considered individually, their effects on the speed of effective leak detection are cumulative. Materials that are less viscous will enter a given leak faster than those with greater viscosity. Materials that can be removed from the system faster will allow for faster verification. Materials that are easy for the detector to notice require less hesitation during detection. Finally, the smaller a system is, the less time that is needed for the probe gas to fill all areas. 

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Do not use liquids for leak detection if you are considering using in a mass spectrometer further on in your experimentation. Liquids tend to have slow cleanup times and can severely slow down, or confound, future experimentation. Thus some rules for the use of probe gases and liquids are as follows ... 

Self-healing materials should have many applications. The U.S. Air Force, which partially funded the research at UIUC, is interested in using the materials in tanks that hold gases and liquids under pressure. The current materials used for these tanks are subject to microcracks that eventually grow, causing the tanks to leak. Self-healing materials would also be valuable in situations where repair is impossible or impractical, such as electronic circuit boards, components of deep space probes, and implanted medical devices. ... 

The QJT is compatible for use with the full range of methods for introducing solids, liquids, and gases — solids probe, GC, and LC — and with all the ionization methods described above including MALDI. 

The theories of the viscosity of ordinary liquids are mainly scaling relationships there is no first-principles theory for their viscosities. An important scaling relationship is that the viscosity is related to the ratio of the occupied volume to the free volume. The usefulness of variable-pressure studies lies in their ability to probe this directly. Such studies of low-density fluids (gases and supercritical fluids), interpreted through extensions to the kinetic gas theory, have provided a quantitative understanding of their viscosities. How-... 

Galvanic cells with solid electrolytes can be used for direct measurement of partial pressures in gases and concentrations in liquids and melts. An important example is cell I, which contains doped zirconium dioxide as solid electrolyte. By using cells of this type a wide range of oxygen partial pressures in gases (down to 10 atm) can be determined. The zirconium dioxide probe for such work is used at temperatures between about 500 and 1000°C. 

Samples of gases and volatile liquids can be introduced directly into the ionization chamber. Because the interior of a mass spectrometer is kept at a high vacuum, volatile liquids and even some solids are vaporized. For less volatile liquids and solids, the sample may be placed on the tip of a heated probe that is then inserted directly into the ionization chamber. Another extremely useful method for introducing a sample into the ionization chamber is to link a gas chromatograph (GC) or liquid chromatograph (LC) directly to the mass spectrometer. These machines can separate complex mixtures of molecules into pure firactions. Each firaction eluted firom the chromatograph enters directly into the ionization chamber of the mass spectrometer, enabling mass determination of the individual components. 

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