Aging chemical change

There is supporting evidence in the literature for the validity of this method two cases in particular substantiate it. In one, tests were made on plastics heated in the pressure of air. Differential infrared spectroscopy was used to determine the chemical changes at three temperatures, in the functional groups of a TP acrylonitrile, and a variety of TS phenolic plastics. The technique uses a film of un-aged plastic in the reference beam and the aged sample in the sample beam. Thus, the difference between the reference and the aged sample is a measure of the chemical changes. 

Over the past decade, particular attention has been focused on the characterization of organic materials occurring, for example, as the residues of food, medicines and balms in archaeology, as adhesives, and as binders in paints. The mixture of many materials in ancient recipes and technologies, and the chemical changes induced by ageing make it even more difficult to study these samples. 

The unique appearance of an infrared spectrum has resulted in the extensive use of infrared spectrometry to characterize such materials as natural products, polymers, detergents, lubricants, fats and resins. It is of particular value to the petroleum and polymer industries, to drug manufacturers and to producers of organic chemicals. Quantitative applications include the quality control of additives in fuel and lubricant blends and to assess the extent of chemical changes in various products due to ageing and use. Non-dispersive infrared analysers are used to monitor gas streams in industrial processes and atmospheric pollution. The instruments are generally portable and robust, consisting only of a radiation source, reference and sample cells and a detector filled with the gas which is to be monitored. 

The plants and animals we have chosen to use as foods naturally contain, as we have already noted, thousands of chemicals that have no nutritional role, and when we eat to acquire the nutritionally essential chemicals we are automatically exposed to this huge, mostly organic, chemical reservoir. Of course, human beings have always manipulated foods to preserve them or to make them more palatable. Processes of food preservation, such as smoking, the numerous ways we have to cook and otherwise prepare food for consumption, and the age-old methods of fermentation used to make bread, alcoholic beverages, cheeses and other foods, cause many complex chemical changes to take place, and so result in the introduction of uncounted numbers of compounds that are not present in the raw agricultural products. 

Note The aging of a gel can involve polymerization, crystallization, aggregation, syneresis, phase changes, formation of branch points and junction points as well as scission and chemical changes to constitutional units of network chains. 

A frequent source of error is poor standards. Besides the obvious error of standards being wrongly made, it should not be forgotten that trace metal standards are unstable. Concentrations of 10 pg cm and less usually need to be prepared daily. Even standards purchased from commercial suppliers will age and this is especially true when chemical changes can be expected in the analyte (e.g. silicon). 

Alchemy fell into disrepute in Europe in the Middle Ages because of its obscure symbolism, introduction of irrelevant religious ideas and superstitions, and preoccupation with perfectibility that led to belief in the possibility of the transmutation of metals (as opposed to chemical change). The prospect of changing base metals such as lead into gold attracted all... 

Is aging primarily an example of a physical or chemical change ... 

The changes that occur as we age involve the chemical re-formation of our biomolecules. These are chemical changes. 

To understand how radioactive substances can be used to determine the age of an object, it is necessary to understand radioactivity, the spontaneous or forced breakdown or rearrangement of the atomic nucleus with a release of radiation. We have discussed chemical changes in atoms in which outer electrons are shared, partially shared, or transferred, but the atomic nucleus remains intact. Here we are considering nuclear changes and the products produced, including radiation. We need a system of symbols to represent these nuclear changes. 

Rikans, L.E., Influence of aging on chemically induced hepatotoxicity Role of age-related changes in metabolism, Drug Metab. Rev., 20, 87,1989. 

One type of aging, frequently leading to complete inactivity, is caused by poisoning. It may consist of a purely chemical change of the catalyst, but also of a decrease of the active surface, caused by the fact that substances formed at the reaction are deadsorbed more slowly than the substrate is adsorbed. 

Some of the most important chemical changes that occur during the biological and /or oxidative aging of sherry wines are reviewed below. 

---