Blocking filters

Corrosion inhibitor/lubricity improvement additives are used panicularly in militai y fuel for the dual puiyiose of passivating metal surfaces and improving the lubricating properties of the fuel in equipment such as fuel pumps. The militai y also specifies the use of a fuel system icing inhibitor as an additive to prevent filter blocking by ice crystal formation, because militai y aircraft tend not to use fuel line filter heaters, which are standard equipment on civil aircraft. 

The reflection calibration method with the specialized filter block has the advantage that it does not require the sample to be moved to recalibrate. As a result it might be particularly useful for long time scale time series data. 

The basic layout of Raman sensors is similar to fluorescence probes. The common sensor form is that of a fibre optic probe, with excitation and collection fibres. As the excitation light comes from a monochromatic source no excitation filter is required, but a spectrally matched emission notch filter blocking the excitation wavelength is almost always part of the sensor head. 

Fluorophores can be visualized in fluorescence microscopy using special filter blocks that are composed of the excitation filter, dichroic mirror and emission filter. The excitation filter must select wavelengths of light from a light source that fall in the maximum absorption region of the fluorophore. The emission filter must pass the fluorescent wavelengths but not the excitation wavelengths. The dichroic mirror... 

Water and sediment usually result from poor fuel handling and storage practices. Water and sediment can enter from atmospheric air, through fuel transportation systems, and from blending operations. Corrosion, filter blocking, injection system wear, and deposit formation can result. A listing of some classes of compounds which can be found in middle distillate fuel is provided in TABLE 3-15. 

Unpolarized light consists of waves vibrating in many different planes (indicated by the arrows). The polarizing filter blocks all waves except those vibrating in a given plane. 

Candle filters Blocked with tar and particulates Removed... 

Fig. 7.1.2 A magnetization filter blocks part of the incoming magnetization from passing through the filter.

Water can contribute to filter blocking and cause corrosion of the injection system components. In addition to clogging of the filters, sediment can cause wear and create deposits both in the injection system and in the engine itself. Thus one of the most important characteristics of a diesel fuel, the water and sediment content (ASTM D-1796, IP 75), is the result of handling and storage practices from the time the fuel leaves the refinery until the time it is delivered to the engine injection system. 

Fig. 7.23. Discrete absorption between 192 and 167 meV of the 203-meV-BAs acceptor spectrum at LHeT in a B-doped GaAs sample annealed at 600° C after an initial annealing at 1200° C. A filter blocking photons with energies above 400 meV has no effect on the absorption coefficient (solid-line spectrum) compared to the dashed-line spectrum obtained without filter (after [166]). Copyright 1994, American Institute of Physics...

It is advisable to use only a feeble vacuum when filtering, otherwise solvent may be lost and filters blocked. The Emich stick should be lowered slowly into the solution, so that the crystals collect at the bottom of the testtube and can be well pressed together. After release of the vacuum, the walls of the testtube and the crystals are washed with a few drops of cold solvent, which is then sucked off. Finally the filter stick is lifted carefully out of the tube, and the crystals adhering to its surface are removed by a micro spatula. 

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