Lead coatings sprayed

Enclosed agitated filters are useful when volatile solvents are in use or when the solvent gives off toxic vapor or fume. Another significant advantage is that their operation does not require any manual labor. Control can be manual or automatic, usually by timers or by specific measurements of the product. Most filters are made of mild steel, with the exposed surfaces protected by lead, tile, mbber lining, or by coating or spraying with other substances as necessary. Filtration areas up to 10 m are available and the maximum cake thickness is 1 m. Apphcations are mainly in the chemical industry for the recovery of solvents. 

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

In summary, preliminary studies indicate that plasma spray coatings show great potential for improving the bondability of steel. Potential drawbacks include the requirement for relatively expensive plasma spray equipment and the necessity to keep the substfate temperature below that which would lead to undesirable metallurgical changes. 

Flame sprayed molybdenum articles have poor corrosion resistance, no doubt owing to the porosity of the coating. However, modern plasma spraying techniques produce a dense coating and this should lead to more widespread use of clad materials such as molybdenum clad steel where the clad product should have the same corrosion resistance as the solid material. 

The use of roll and coil coating systems leads to pollution prevention over traditional spray application systems due to their higher transfer efficiency (>95%) and lower volatilization of organic solvents. 

The use ofDa plasma synthetic route can lead to materials with advantageous new physical characteristics such as high surface area (eg TiOp), spherodised powders and sprayed-on coatings. 

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