Water immersion cycle

The relative aggressiveness of the environments proved to be consistent for all substrates, with the room temperature control the least hostile (virtually no loss of adhesion), and the cycle tests the most aggressive (up to 100% loss of adhesion within 60 days). Humidity cabinet exposure and 60°C water immersion yielded very similar values. As a result, for reasons of clarity, only water immersion data is actually presented here. Joint strength data obtained from either the Ford APG or Fisher Body Cycle Tests were identical, and were therefore also represented by one set of data points. The relative aggressiveness of the host environments toward... 

Humidity cycle Water immersion Humidity cycle1 Water immersion... 

Figure 6 Comparison of absorption cycle for samples with and without post mold curing and exposed to water immersion at 100°C.

Adhesion difficulties due to surface effects and treatments can be present in initial adhesion testing such as lap shear or T-peel. However, it may also be hidden in these tests only to resurface during more demanding adhesion tests, such as hot water immersion (90-100°C) or environmental cycling. When bonding composites in combination with more traditional substrates, it is important to perform a variety of tests to verify results. 

Early accelerated weathering apparatus utilized carbon arc lamps with various filters to generate a spectrum that reproduced some of the harmful effects of sunlight. Improved versions of these are still in use and are specified for certain applications. However, many users and specifiers have turned to xenon arc lamp-based machines as these produce a spectrum that more closely matches that of sunlight (Fig. 6.1). Additionally, they are generally less expensive to purchase and to run than the carbon arc machines. Both types nowadays have facilities for the provision of controlled humidity, water spray, periodic water immersion and/or variable temperature cycles. 

Cycle Testing of Painted Surfaces Water Immersion Test for Painted Parts... 

Remarkably, an apparent mass loss is found for the second immersion cycle (Adv-fdc-2) reflective of a hydrophobic surface (0adv2 = 106°). Now, water-hydrogen bonding interactions are stronger than water-surface interactions and water resists wetting the surface. Contact angles measured by drop profile analysis are close to those observed for DCA. 

Figure 3.3 Deformation cycle to demonstrate the water-sensitive shape memory effect. is the maximum strain applied in the cyclic tensile testing, is the strain in the unloading dry state, and e is the residual strain values of the two successive cycles after shape recovery was triggered by water immersion. Reproduced with permission from [40].

This requirement for hot curing was their major disadvantage as many structures were too delicate to withstand the thermal cycles. However, they were ideal for plywood manufacture, the major advantage being their hot water resistance and their ability to withstand limited periods of boiling water immersion. 

Adhesives for ceramic tiles are specified by the standard EN 12004 2007 (Adhesives for tiles. Requirements, evaluation of conformity, classification, and designation), and includes performance requirements for cementitious, dispersion, and reaction resin adhesive types for all internal and/or external wall, floor and ceiling applications. Annex ZA, of this standard, sets out the requirements, which address the provisions of the Construction Products Directive (see O Sect. 35.4 below), and include assessments of durability. Compliance with these requirements confers a presumption of fitness for purpose for the applications and form part of a CE mark. In these cases durability is assessed by elevated temperature and/or water immersion accelerated ageing or freeze-thaw cycling of test specimens and then determining tensile or shear adhesion strength against minimum requirements. 

To favour reproducibility of results, the cycles of immersion and withdrawal must be kept the same from test to test. It is necessary to control the temperature and humidity of the atmosphere surrounding the test setup as these affect the rate of evaporation of the solution and of drying of the specimens when they are out of the solution. It is also necessary to provide for replenishing losses of water from the test solution resulting from evaporation. 

There are new ideas and experiments on the rTCA cycle. A group from Harvard University studied some reaction steps in the rTCA cycle which were kept going by mineral photochemistry. The authors assumed that solar UV radiation can excite electrons in minerals, and that this energy is sufficient to initiate the corresponding reaction steps. In this photocatalytic process, semiconductor particles were suspended in water in the presence of a zinc sulphide colloid (sphalerite) the experiments were carried out in a 500 mL reaction vessel at 288 K. Irradiation involved a UV immersion lamp (200-410 nm) in the photoreactor. Five reactions out of a total of 11 in the rTCA cycle were chosen to check the hypothesis ... 

Nicholson and Pizzarello.35"40 Collins and Schiffrin s Lu(Pc)2 was initially studied as a film immersed in aqueous electrolyte, but hydroxide ion from water causes gradual film destruction, attacking nitrogens of the Pc ring.33 Acidic solution allows a greater number of stable write-erase cycles, up to 5 x 106 cycles in sulfuric acid 33 Lu(Pc)2 films in ethylene glycol solution were found to be more stable 34... 

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