Coatings selection factors

Aromatic solvents or polycyclic aromatic hydrocarbons (PAFI) in water, e.g. can be detected by QCM coated with bulk-imprinted polymer layers. Flere, the interaction sites are not confined to the surface of the sensitive material but are distributed within the entire bulk leading to very appreciable sensor responses. Additionally, these materials show high selectivity aromatic solvents e.g. can be distinguished both by the number of methyl groups on the ring (toluene vs. xylene, etc.) and by their respective position. Selectivity factors in this case reach values of up to 100. 

Cass et al. [66] used a polysaccharide-based column on multimodal elution for the separation of the enantiomers of omeprazole in human plasma. Amylose tris (3,5-dimethylphenylcarbamate) coated onto APS-Hypersil (5 /im particle size and 120 A pore size) was used under normal, reversed-phase, and polar-organic conditions for the enantioseparation of six racemates of different classes. The chiral stationary phase was not altered when going from one mobile phase to another. All compounds were enantioresolved within the elution modes with excellent selectivity factor. The separation of the enantiomers of omeprazole in human plasma in the polar-organic mode of elution is described. 

Progress continues to be made toward the development of practical vapor detection instruments using coated SAW sensors. This paper reviews some of the characteristics of these versatile devices and their current capabilities. Factors affecting sensor performance, such as temperature and coating selection, are considered in terms of the sensitivity and selectivity of the SAW device. Special attention is given to a 4-SAW array instrument that is able to "fingerprint" and identify a variety of chemical vapors. 

The importance of the stationary phase in GC can, once again, be deduced from the resolution equation (Eq. 3,4). In Figure 8, the influence of the plate number N. the separation or selectivity factor a. and the retention factor k on peak resolution is represented graphically. The peak resolution of two solutes (k = 5) with a = 1.05 on a column with a plate number of 20000 (e.g., lOmxO.Smm coated with 0.2 pm methylsilicone) is 1.4. This value, the crossing point of the curves, is taken as reference. The curves are obtained by changing... 

The purpose of a coating is to extend the time required before corrosion attacks the substrate. Properties of the coating material and the severity of the corrosive atmosphere will determine the service life of the coating. These factors must be taken into account when selecting the coating material. 

Figure 5 shows the typical thickness/penetration capabilities of various coating and surface treatments. As indicated in the figure, some surfaceengineering treatments penetrate into the surface and there is no intentional buildup on the surface. These are the surface-engineering processes described in Chapters 4 and 5. Other surface treatments coat or intentionally build up the surface. This is a selection factor. Can a part tolerate a buildup on the surface If not, the selection process is narrowed to the... 

Hydrodynamic principles for gas bearings are similar to those involved with Hquid lubricants except that gas compressibility usually is a significant factor (8,69). With gas employed as a lubricant at high speeds, start—stop wear is minimized by selection of wear-resistant materials for the journal and bearing. This may involve hard coatings such as tungsten carbide or chromium oxide flame plate, or soHd lubricants, eg, PTFE and M0S2. 

Top Goats. The selection of a top coat depends on cost, method of appHcation, and product use and performance requirements, among other factors. As a result of increasingly stringent air quaHty standards and increased solvent costs, approaches to reduction of solvent emissions are being sought. 

Theie aie several additional factors that must be considered in selecting pigments for a specific coating application (40). These factors include processing stabihty requirements, pigment uniformity and reproducibiUty, particle size distribution, dispersibiUty, and compatibiUty of all materials to be used. 

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