Spray charging

Electrostatic spray Charged particles are sprayed on electronically conductive parts process gives high paint utilization more expensive than conventional spray. Spray gun, high-voltage power supply pumps dryers Pretreating station for parts (coated or preheated to make conductive). 

Conventional electrostatic spray coating pumps a liquid coating formulation through a spray gun, which puts an electrostatic charge on the liquid, and sprays charged droplets toward a grounded metal product. The droplets are attracted to the product, where they discharge and adhere to the metal surface. 

For the type spray-charging device described, pesticide-liquid resistivity is generally limited to the fairly narrow 10 - 10 ohm m region of values. 

All liquids will spray the same, that is they will have the same mean droplet size independent of fluid properties, if they are charged to the same level. For instance, for oils of interest having viscosities less than approximately 200 centlpolse, uniform spray charging to 4 C/m will result in the electrostatic atomization of a 42 2 ym diameter spray."... 

Table I summarizes the experimentally determined resistivity characteristics for the nine formulations investigated. On the basis of Equation 6 and these data, a high degree of spray charge-ability by the electrostatic induction process could be predicted for all the pesticide samples tested. For these particular pesticide formulations, laboratory spray tests confirmed excellent droplet charging to greater than 10 mC/kg. Similar electrical resistivity measurements will serve as a suitable predictor of the chargeability of other formulations of interest in the electrostatic pesticide-spraying process.

Carbon dioxide. This gas is conveniently generated from marble and dilute hydrochloric acid (1 1) in a Kipp s apparatus it should be passed through a wash bottle containing water or sodium bicarbonate solution to remove acid spray and, if required dry, through two further wash bottles charged with concentrated sulphuric acid. 

It is usually better to use a fire extinguisher charged with carbon dioxide under pressure this produces a spray of solid carbon dioxide upon releasing the pressure intermittently and is effective for extinguishing most fires in the laboratory. 

After being formed as a spray, many of the droplets contain some excess positive (or negative) electric charge. Solvent (S) evaporates from the droplets to form smaller ones until, eventually, ions (MH+, SH+) from the sample M and solvent begin to evaporate to leave even smaller drops and clusters (S H n = 1, 2, 3, etc.). Later, collisions between ions and molecules (Cl) leave MH+ ions that proceed into the mass analyzer. Negative ions are formed similarly. 

Evaporation from a spray of charged droplets produced from a stream of liquid yields ions that can be analyzed in a mass spectrometer. Thermally labile and normally nonvolatile substances such as sugars, peptides, and proteins can be examined successfully. 

A solution of an analyte in a solvent can be sprayed (nebulized) from an electrically charged narrow tube to give small electrically charged droplets that desorb solvent molecules to leave ions of the analyte. This atmospheric-pressure ionization is known in various forms, the one most relevant to this section being called electrospray. For additional detail, see Chapters 8, 9, and 11. 

The Z-spray inlet causes ions and neutrals to follow different paths after they have been formed from the electrically charged spray produced from a narrow inlet tube. The ions can be drawn into a mass analyzer after most of the solvent has evaporated away. The inlet derives its name from the Z-shaped trajectory taken by the ions, which ensures that there is little buildup of products on the narrow skimmer entrance into the mass spectrometer analyzer region. Consequently, in contrast to a conventional electrospray source, the skimmer does not need to be cleaned frequently and the sensitivity and performance of the instrument remain constant for long periods of time. 

The electric field and gas flow work together to provide a finely dispersed spray of charged droplets. An electric potential of about 3-5 kV is used for capillaries of about 50-100-pm diameter. 

Some of the droplets cany an excess of positive electric charge and others an excess of negative electric charge. The spray or stream of droplets is passed along a tube that is usually heated. 

Evaporation of solvent from a spray of electrically charged droplets at atmospheric pressure eventually yields ions that can collide with neutral solvent molecules. The assemblage of ions formed by evaporation and collision is injected into the mass spectrometer for mass analysis. 

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