Deterioration mechanisms

Two other broad areas of food preservation have been studied with the objective of developing predictive models. En2yme inactivation by heat has been subjected to mathematical modeling in a manner similar to microbial inactivation. Chemical deterioration mechanisms have been studied to allow the prediction of shelf life, particularly the shelf life of foods susceptible to nonen2ymatic browning and Hpid oxidation. 

For many years hydrogen was considered as a deleterious impurity which deteriorates mechanical properties of materials. This is clearly illustrated by hydrogen embrittlement of ferrous metals and alloys. The main effort of the research was aimed therefore at the study of hydrogen embrittlement and at the ways to avoid it. ... 

Microbial growth, enzymatic reactions, non-enzymatic browning (reaction between carbonyl and amino compounds), and lipid oxidation are the major deterioration mechanisms that limit the stability of low moisture (o intermediate moisture foods (o.6o < <0.85) and biological materials. 

The sensitivity of Magnetic Resonance (MR) to the local concentration, molecular dynamics and molecular environment of these nuclei make it well suited for the study of deterioration processes in concrete materials. Hydrogen (water), lithium, sodium, chlorine and potassium are all MR sensitive nuclei and play an important role in cement chemistry. The ability of MRI to spatially resolve and non-destructively examine test samples as a function of treatment or exposure has the potential to provide new insight to better understand deterioration mechanisms and mass transport properties of concrete materials. 

Although other dairy products have not been studied extensively, reports suggest that titratable acidity as well as hydrogen ion concentration tend to influence the development of oxidative deterioration. A relationship was found between the titratable acidity and the development of an oxidized flavor in milk (Parks 1974). While milks developed an oxidized flavor at a titratable acidity of 0.19%, the deteriorative mechanism was inhibited when the milks were neutralized to acidities of 0.145% or less. An increase in pH of 0.1 was sufficient to inhibit the development of oxidized flavors in fluid milks for 24 hr (Parks 1974). In addition to fluid milk, Dahle and Folkers (1933) attributed the development of oxidized flavors in strawberry ice cream to the presence of copper and the acid content of the fruit. 

The oil deterioration mechanism, various deterioration indicators (viscosity change, total base number (TBN), total acid number (TAN), insolubles concentration, etc.) have been proposed and their respective detecting methods were reported. The oil deterioration component is divided into two general categories deterioration of the base oil and ingression of foreign matter. Ultimately, however, particles are considered to exist in engine oil in the form of insoluble elements. Fig. 6.1 shows the mechanism of the oil deterioration (Tomita et ah, 1995). 

Oxidation and acid hydrolysis are the two principal deterioration mechanisms for paper, and recently chemiluminescence (CL) has been used to follow the oxidation of cellulosic materials at temperatures of 40 °C and below (I). CL is thought to be produced by the termination... 

Kinugasa, H. and Takeo, T. 1990. Deterioration mechanism for tea infusion aroma by retort pasteurization. Agric. Biol. Chem. 54 2537-42. 

There is another key thermally-promoted deterioration mechanism, oxidation. This is driven by free radicals and results in both cross-linking and chain scission, as well as discolouration to yellow/brown. These reactions will occur slowly at normal temperatures, but are accelerated by the presence of pre-existing free radicals, such as those arising from photolysis. Lignin and, to a lesser extent, hemicelluloses are both more susceptible to thermal damage than is cellulose. 

Eennema, O. 1982. Behavior of proteins at low temperatures. In Food Protein Deterioration Mechanisms and Functionality (Cherry, J.P., ed.), p. 109. ACS Symposium Washington, DC. 

J. E. Kinsella. in Food Protein Deterioration, Mechanisms and Func-... 

Freidman, M. Lysinoalanine formation. Soy Proteins Kinetics and Mechanism, in Food Protein Deterioration Mechanisms and Functionality ACS Symposium Series 1982, 206, 231—273. 

Requirements specified in this way are deemed-to-satisfy rules. Such rules cannot be used to quantify the performance of the structure in general, specific effects of additional measures (for instance increasing the cover to the steel), or the consequences of sub-standard practice (for example using a higher w/c). In this respect it is important to note that EN 206 also allows the use of alternative performance-related design methods with respect to durability that consider in a quantitative way each relevant deterioration mechanism, the service life of the element or structure, and the criteria that define the end of the service life. Such methods should draw a picture of the characteristics that the concrete must possess to protect the reinforcement for the service life requested from a predictive model of the corrosion attack. These refined methods (as opposed to standard methods) may be based on long-term experience with local practices in local environments, on data from an established performance test method for the relevant mechanism, or on the use of proven predictive models. 

Thiebaut, B., VUmont, L.-B. and Lavediine, B. (2006). D6.1 Report on video and audio tape deterioration mechanisms and considerations about implementation of a collection condition assess-mentmethod (D6.2) [online] http //www.prestospace.org/prqject/deliverables/D6-l.pdf [Accessed 2 August 2007]. 

The deterioration mechanism for WC-Co (and similar materials) is assumed to be as follows the binder phase of metal around the carbide particles corrodes away so fliat the WC particles are more easily removed by erosion. The transition from the unexposed state to a corroded and eroded state is schematically illustrated in Figure 7.43. It should be noticed that under extremely erosive conditions or if die metal phase is highly corrosion resistant in the actual environment, erosion is dominating and the effect of die shown mechanism may be insignificant. 

Protection and deterioration mechanisms of paints are described by Munger [10.50], Stratmann et al. [10.51], and others. For barrier coatings, the resistance to transport of water, ions and oxygen is of crucial significance for protection of the substrate, and transport and absorption of these substances are also important factors in the deterioration of the coating. The film resistance and the potential determine the... 

Corrosion is not the only deterioration mechanism in reinforced concrete. Alkali-silica reactivity (ASR), sulphate attack, thurmasite attack, delayed ettringite formation, freeze thaw, thermal movement, settlement and other movement can all lead to concrete damage and their assessment must be included in the surveys. 

The deterioration of concrete can be the consequence of the presence of some aggregates components which, for example, as iron sulphide, decompose to give iron(lll) hydroxide and sulphuric acid [71]. This phenomenon will be presented later. Let us discuss now the studies of concrete deterioration mechanism caused by alkali silica reaction, the most important in practice. The two types of reactions can be distinguish ... 

Deterioration. Mechanisms and Functionality Cherry, J. P., Ed. American Chemical Society Washington, DC, 1982 pp 55-66. 

The expression repetition of loading during the pavement s service life implies that the structural condition of the pavement deteriorates with time. In fact, the deterioration mechanism of the pavement is a fatigue phenomenon, related to the number of load repetitions and the magnitude of the exerted strain. 

For intact coatings, the major deterioration mechanism is the transport of electrolyte solutions to the interface between the steel substrate and the coating. This transport results from the equalization of concentration and temperature differences. Water molecules disrupt the bonding and polar interactions that are responsible for a good adhesion at the interface [86]. Underfilm corrosion is possible because of the loss of adhesion. The coatings have been defined as intact when the potential of the steel panel was not measurable at the beginning of the test. 

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