Coating material, selection

The material used to produce the part dictates the nature of the substrate that must be coated. Material selection is often entwined in the process-selection decision because not all materials can be used with every process. The ultimate decision may be material-driven, process-driven, or it may represent a compromise based on a variety of factors. In any case, the resulting material snbstrate and its own particular characteristics must be dealt with in terms of coatings performance. 

When selecting a particular paster adhesive, coating material, and coating process for sohd fiber packaging, the fact that sohd fiberboard lacks the open-flute stmcture (to facihtate exit of moisture from internal phes of paperboard) should be considered. It is generally desirable to minimize the amount of process water added with the adhesive or coating with sohd fiber products. Moisture trapped in the filler phes can result in pin holes or bhsters in the coating and/or warp of the sheet (15). 

Scotts technology (17) uses fluid-bed (Wurster column) technology to apply polymeric coatings to a number of fertilizer substrates including urea, potassium nitrate, potassium sulfate, and monoammonium phosphate (MAP). The coating material is appHed as a water-borne latex onto the fluidized substrate. As the substrate is fluidized with warm air (40—50°C), water is driven off and the latex coalesces into a continuous film around the fertilizer particle. The particular latex compositions used have selected glass-transition and blocking temperatures, which enable quick removal of the water before the soluble fertilizer core dissolves. This obviates the need to use precoats prior to the latex appHcation. 

Another type of membrane is the dynamic membrane, formed by dynamically coating a selective membrane layer on a finely porous support. Advantages for these membranes are high water flux, generation and regeneration in situ abiUty to withstand elevated temperatures and corrosive feeds, and relatively low capital and operating costs. Several membrane materials are available, but most of the work has been done with composites of hydrous zirconium oxide and poly(acryhc acid) on porous stainless steel or ceramic tubes. 

Uniform corrosion is the deterioration of a metal surface that occurs uniformly across the material. It occurs primarily when the surface is in contact with an aqueous environment, which results in a chemical reaction between the metal and the service environment. Since this form of corrosion results in a relatively uniform degradation of apparatus material, it can be accounted for most readily at the time the equipment is designed, either by proper material selection, special coatings or linings, or increased wall thicknesses. 

Material selection for the enclosure shell should consider the corrosiveness of the environment. Aluminized sheeting is preferred over zinc-coated material in a steel-production environment. 

All methods of corrosion control such as careful materials selection, including coating and cladding, inhibition and cathodic protection, should be regarded as an integral part of the design process. 

The main criteria for the selection of the current collector material in a central sulfur cell or for the cell case material in a central sodium cell are corrosion resistance to sulfur and sodium polysulfides, good electrical conductivity, and low costs. This cost argument has led to coated materials which have been compared with nickel—chromium alloys (Inconel 600). 

Additional surface modifications on vapor deposited SiC fibers, including WC. TaC, TiN, B4C, Al, Ni and Fe, have been applied with varying degree of success (Wawner and Nutt, 1980 DeBolt, 1982 Wawner, 1988). After exhaustive trial and error, TiB is selected as an additional coating material to further prevent the diffusion-induced reactions between the SCS-6 fibers and matrix materials, including Ti alloys and Ti Al intermetallic alloys (e.g. Ti Al, TiAl and TiAl ) (Donncllan and Frazier, 1991 James et al., 1991). When the coated fiber is subjected to tensile... 

The CORE-SOFC Project was designed to improve the durability of planar SOFC systems to a level acceptable for commercial operation. The work focuses mainly on materials selection for interconnects, contact layers and protective coatings to minimise corrosion between metallic and ceramic parts to achieve reliable and thermally-cyclable SOFCs. In all work packages, cells and stacks will be analysed by advanced chemical and ceramographic methods. 

In adsorption TLC, selectivity is mostly determined by the developing solvent system, whereas in RP-TLC the selectivity is determined primarily by the reversed-phase support and degree of carbon loading on the silica gel base. It should be kept in mind that the coating material of RP-TLC plates will always contain a certain amount of underivatized silanols that will confer to the plates some adsorptive and ionic characteristics that affect selectivity. It is, therefore, erroneous to think that all RP-Q, C8, C18, cyanopropyl, and diphenyl materials will behave similarly and it is strongly suggested that, in an optimization process, an investigator should experiment with plates from different suppliers. 

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