Evaluation after Accelerated Aging

After the accelerated aging, samples should be evaluated for changes. By comparing samples before and after aging, one can find  

The coatings scientist uses a combination of techniques for detecting maCTOscopic and submicroscopic changes in the coating-substrate system. The quautitative and qualitative data this provides must theu be interpreted so that a prediction can be made as to whether the coating will faU, and if possible, why. 

Changes that can be seen by the unaided eye or with optical (light) microscopes, such as rust-through and creep from scribe 

Large-scale changes that are found by measuring mechanical properties, of which the most important are adhesion to the substrate and the abiUty 

Changes in both the adhesion values obtained in before-and-after testing and in the failure loci can reveal quite a bit about aging and failure mechanisms. Changes in barrier properties, measured by electrochemical impedance spectroscopy (EIS), are important because the ability to hinder transport of electrolyte in solution is one of the more important corrosion-protection mechanisms of the coating. 

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At room temperature or body temperature, the oxidation of UHMWPE takes years to reach an appreciable level that may result in decay of mechanical performance. Thermal aging techniques were developed to accelerate the rate of oxidation of irradiated UHMWPE. The material behavior after accelerated aging is assumed comparable to naturally aged ones. The standard method [ASTM F2003 - 02(2008)] permits the evaluation of oxidative stability in a relatively short period of time, i.e. weeks. 

For sunlight stability, products can be evaluated after exposure in their packages to direct sunlight for various periods of time. Accelerated aging can also be evaluated in instruments such as the Atlas Weatherometer in which products can be subjected to intense radiation at elevated temperatures. 

ABSTRACT This research project aims to use reactive powder concrete, RPC. as a new repair material and evaluate its bond strength and bond durability to existing concrete. One accelerated aging environment, namely a freeze-thaw cycle acceleration deterioration test, was selected for the evaluation of bond durability of the repair materials. Before and after aging, the samples were evaluated by the compressive strength, bond strength (slant shear test), steel pull out strength, and relative dynamic modulus NDT tests. 

Virlogeux, F. Bianchini, D. Delor-Jestin, F. Baha, M. Lacoste, J., Evaluation of Cross-Linking After Accelerated Photo-Aging of Silicone Ruhher. Polym. Int. 2004,53,163-168. 

The reliability of die attach adhesive has been extensively investigated for the past three decades. A complete survey of these studies has been previously published [4]. The following sections underline the critical factors that have an impact on the electrical, mechanical, and thermal properties of the adhesive bonds. For process engineers, the main concern is the evaluation of die attach integrity in relation with the assembly technologies and after a series of accelerated ageing tests. 

The long-term performance of fibre reinforced cements is of great significance in the development and evaluation of new composites. An important practical tool for this purpose is accelerated testing in the laboratory, where the properties of the composites are determined before and after exposure to the accelerated ageing conditions. In order to develop an efficient test of this kind, it is necessary first to evaluate the physical and chemical processes that may lead to changes in properties in natural exposure, and then devise the means to accelerate them in laboratory-controlled tests. In view of the variety of processes which may lead to ageing, it is difficult to devise a universal test. An illustration of this problem is presented in Table 5.1 and In [33,43], which show that composites which perform well in one type of accelerated test may do poorly in another, and the critical test is different for the different composites. 

In the headache evaluation, diagnostic alarms should be identified. These include acute onset of the first or worst headache ever, accelerating pattern of headache following subacute onset, onset of headache after age 50 years, headache associated with systemic illness (e.g., fever, nausea, vomiting, stiff neck, and rash), headache with focal neurologic symptoms or papilledema, and new-onset headache in a patient with cancer or human immunodeficiency virus infection. 

Chemical and Corrosion Resistance The corrosion resistance of CCCs depends on thickness and coating age. Corrosion resistance has been observed to scale with total chromium content [153]. Some studies have found that corrosion resistance does scale with Cr(VI) content [154], while others have found no such correlation [155]. Corrosion resistance is evaluated by continuous or cyclic accelerated exposure testing and electrochemical methods. On aluminum alloys, heavy CCCs will resist pitting for as long as 400 to 1000 h [156]. CCC-coated surfaces will exhibit total impedances of 1 to 2 Mf2 cm after exposure to aerated 0.5 M NaCl solution for 24 h. Such coatings can be expected to withstand 168 h of salt spray exposure without serious pitting [157]. CCCs usually perform well in mild neutral environments, but do not fare as well under... 

Applications of liposomes in cheese ripening were developed by the 1980s (El Soda, 1986). Enhancement of proteolysis by encapsulated cyprosins was evident 24 h after manufacture of Manchego cheese. Addition of encapsulated cyprosins to milk perceptibly accelerated the development of flavor intensity in experimental cheese through 15 days of age without enhancing bitterness (Picon et al., 1996). The capability of neutral and charged liposomes to entrap the proteolytic enzyme neutrase, and the stability of the preparation, were evaluated in the ripening of Saint-Paulin cheese milk (Alkhalaf et al., 1989). 

EIS is an extremely useful technique in evaluating the ability of a coating to protect the underlying metal. It is frequently used as a before-and-after test because it is used to compare the water content and diffusion coefficient of the coating before and after aging (accelerated or natural exposure). KroUkowska [16] has suggested... 

A range of thiuram secondary accelerators is evaluated in an ENB-based EPDM compound and in a new technology EPDM compound. The recipes used are fairly basic, utilising CV and EV vulcanisation systems. The rheology is tested on an MDR rheometer and the compound viscosity and scorch tested on a Mooney viscometer. Stress-strain properties are established after cure at 160 deg.C and after ageing at 100 deg.C. In addition, tear properties and compression set values at various temperatures are determined. The observed... 

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