Real Coatings

The models for film formation described above are based on latex-only systems. Real waterborne latex coatings contain much more pigments of different kinds (see chapter 2) coalescing agents to soften the outer part of the polymer particles and surfactants, anulsifiers, and thickeners to control wetting and viscosity and to maintain dispersion. 

Whether or not a waterborne paint will succeed in forming a continuous film depends on a number of factors, including  

To work in a coating formulation, whether solvent-borne or waterborne, a pigment must be well dispersed, coated by a binder during cure, and in the proper ratio to the binder. The last point is the same for solvent-borne and waterborne formulations however, the first two require consideration in waterborne coatings. 

FIGURE 3.2 Pigment and binder particle combinations. The polymer particles are black, and 

The chemistry of real latex formations is complex and currently defies predictive modeling. A reported problem for waterborne modelers is that an increase in curing temperature can affect various coating components differently. Snuparek and colleagues added a nonionic emulsifier to a dispersion of copolymer butyl meth-acrylate/butyl acrylate/acrylic acid. When cure took place at room temperature, the water resistance of the films increased with the amount of emulsifier added. When cure happened at 60°C, however, the water resistance of the films decreased with the amount of emulsifier added [4]. 

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Fig. 11.1 Electrical equivalent circuits for an organic coating (a) ideal coating, (b) real coating without corrosion, (c) adhering coating with the onset of corrosion in pinholes, (d) coating with disbonding, (e) coating with disbonding and small...

The real coating process in the studied Wurster coater apparatus with the bed mass of 3 kg contains about 21.8x10 particles with the size of 550 im. Unfortunately, the numerical effort for the calculation of the DPM model increases with increasing the number of simulated particles. The DPM model is unable to represent this number of particles, at least with the actually available computing power. However, the number of particles can be reduced by conservation of the particle and fluid dynamics in the simulated apparatus and its real geometry. In this work a scaling approach proposed by Link et al. (2009) and extended by Sutkar et al. (2013) has been used, in which the scahng of the particle size was carried out. Due to the size increase, the adequate properties of sohd and gas phase have been adapted to keep the dimensionless numbers Archimedes At) and Reynolds Re) and the velocities of minimal fluidization and elutriation constant. 

The required resolution for the powder coating thickness measurement problem is about 5 microns. Therefore a processing time unit of 0.08 ps (12.5 MHz) seemed to be ok (compare line 2 in table 1). First results based on real measurement are documented in Fig. 7. and are very promising result. Today corresponding patent is pending [7]. 

When considering how the evolution of life could have come about, the seeding of terrestrial life by extraterrestrial bacterial spores traveling through space (panspermia) deserves mention. Much is said about the possibility of some form of life on other planets, including Mars or more distant celestial bodies. Is it possible for some remnants of bacterial life, enclosed in a protective coat of rock dust, to have traveled enormous distances, staying dormant at the extremely low temperature of space and even surviving deadly radiation The spore may be neither alive nor completely dead, and even after billions of years it could have an infinitesimal chance to reach a planet where liquid water could restart its life. Is this science fiction or a real possibility We don t know. Around the turn of the twentieth century Svante Arrhenius (Nobel Prize in chemistry 1903) developed this theory in more detail. There was much recent excitement about claimed fossil bacterial remains in a Martian meteorite recovered from Antarctica (not since... 

The enthalpy hberated on the VDP of parylene is real and in an adiabatic situation causes a rise in temperature of the coated substrate. For Parylene C, 229.1 kj/mol (54.7 cal/mol) corresponds to 1654 J/g (395 cal/g) whereas its specific heat at 25°C is only 1.00 J/(g-K) [0.239 cal/(g-K)] (33). In most practical situations, however, the mass of parylene deposited is dwarfed by the substrate mass, and the heat of polymeriza tion is dissipated within the coated substrate over the time required to deposit the coating with minimal actual temperature rise. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Inhibitors are often iacluded ia formulations to iacrease the pot life and cute temperature so that coatings or mol dings can be convenientiy prepared. An ideal sUicone addition cure may combine iastant cure at elevated temperature with infinite pot life at ambient conditions. Unfortunately, real systems always deviate from this ideal situation. A proposed mechanism for inhibitor (I) function is an equUibtium involving the inhibitor, catalyst ligands (L), the sUicone—hydride groups, and the sUicone vinyl groups (177). 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

Grund-sebicht, /. primary layer, fundamental layer ground course, -stein, m. foundation stone, cornerstone lower (mill) stone, -stock, m. matrix, -stoff, m. element raw material base Paper) ground pulp, -stofflndustrie, /. basic industry, -stoff-wechsel, m. basal metabolism, -stricb, m. first coat, priming down stroke, -stuck, m. premises, (real) property. -substanz, /. element basic substance Anat.) ground substance, matrix, -teil, m. element, principle basic part, -teilcben, n. fundamental particle, -ton, m. fundamental tone, primary tone, -umsatz, m. Biol.) basal metabolism. 

As a kind of specialty solutions for the real hard cases where fouling is intense and unavoidable, IMM first proposed ideas to develop special micro mixers for fouling-intense reactions and conducted feasibility tests, among them very fast organic reactions with spontaneous precipitation such as the amidation of acetyl chloride in THF [134]. The Forschimgszentrum Karlsruhe developed special anti-foul-ing coatings in cooperation with partners [135]. 

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