Environment, chemistry composition

Singh, H. B. (1995) Halogens in the atmospheric environment, in Composition, Chemistry, and Climate of the Atmosphere, edited by H. B. Singh, Van Nostrand Reinhoid, New York, pp. 216-250. 

In this work, the potential for application of Mossbauer spectrometry to corrosion studies was demonstrated for three accelerated corrosion tests in chloride environments. This technique allowed retrieving maximum information from the inherent properties of the rust layers. With VT-MS, it was possible to identify and determine the relative iron phase abundances from which three parameters could be calculated (i) a, (ii) (A + S)/(A + L + S), and (iii) PAI. Moreover, with the physical properties retrieved from the analysis of the hyperfine parameters, it was possible to discuss prospective mechanisms of formation and therefore to contribute to the understanding of the deterioration progress. These studies showed that some corrosion product is lost and/or the conversion of metallic ions into iron oxides may be incomplete, and that the relative iron phase abundances pointed out to a nonprotective and active type of rusts. More work is required on other types and chemistry (composition and abundance of alloying elements) of steels, other environmental conditions, and different exposure times. More efforts are needed to improve the fitting models for nonstoichiometric and substituted iron oxides in rust layers. 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

It is a fundamental principle of quantum mechanics that electrons bound in an atom can have only discrete energy values. Thus, when an electron strikes an atom its electrons can absorb energy from the incident electron in specific, discrete amounts. As a result the scattered incident electron can lose energy only in specific amounts. In EELS an incident electron beam of energy Eq bombards an atom or collection of atoms. After the interaction the energy loss E of the scattered electron beam is measured. Since the electronic energy states of different elements, and of a single element in different chemical environments, are unique, the emitted beam will contain information about the composition and chemistry of the specimen. 

P. Cloud and A. Gibor, The oxygen cycle. Article 4 in Chemistry in the Environment, pp. 31-41, Readings from Scientific American, W. H. Freeman, San Francisco, 1973. P. Brimblecombe, Air Composition and Chemistry, Cambridge Univ. Press, Cambridge, 1986, 224 pp. 

F. J. Stevenson, Humus Chemistry, Genesis, Composition, Reactions, Wiley-Interscience, New York (1982). M. Schnitzer and S. U. Khan, Humic Substances in the Environment., Marcel Dekker, Inc., New York (1972). 

The combined influences of runoff generation mechanisms, runoff flowpaths, and soil properties together control runoff chemistry. In spite of the wide range of interactions that characterize terrestrial environments, a few broad generalities can be offered, as the chemical composition of streamflow typically contains... 

There are some advantages of the temporal models of cloud chemistry associated with the concentrations of molecules at different times. Can we learn about the age of the cloud by its chemical composition or the age of an embedded star by the chemistry observed towards the object Can the molecular environment be understood from the inventory of chemicals Are there chemical diagnostics for planetary formation, star formation or even black holes All of these questions are at the frontier of Astrochemistry. 

Heat of vaporisation. Water has a very large heat capacity (a large amount of energy has to be removed to lower the temperature by 1°C) and a large heat of vaporisation. This means that the temperature in solution is stabilised by the thermochemical properties of the water as a solvent. All life forms on Earth stabilise their internal environments with respect to temperature and composition so that the internal chemistry or metabolism is kept constant - a process called homeostasis. It would, however, be possible to learn to live in an environment that was fluctuating more wildly and develop a unique evolutionary niche. 

The reader will recognize these terms as having of the same form as the correction terms in the two-environment model discussed earlier. With N — 1, 6 j = 0 and the model reduces to the laminar-chemistry approximation. With N —2, additional information is obtained concerning the second-order moments of the composition vector. Likewise, by using a larger N, the Mh-order moments are controlled by the DQMOM correction terms found from Eq. (89). 

As noted earlier, the sum of the mass fractions is unity and thus Eq. (86) will be consistent with Eq. (85) only if the sum of the correction term b m over all chemical species a = 1,..., K is null. In general, this will not be the case if Eq. (89) is used. Another difficulty that can arise is that the mass fractions in two environments may be equal, e.g., i = a2, and thus the coefficient matrix in Eq. (89) will be singular. This can occur, for example, in the equilibrium-chemistry limit where the compositions depend only on the mixture fraction, i.e., (j) — co(0- F°r chemical species that are not present in the feed streams, the equilibrium values for = 0 and = 1 are zero, but for intermediate values of the mixture fraction, the equilibrium values are positive. This implies that the equilibrium values will be the same for at least two values of the mixture fraction in the range 0< < 1. Thus, in the equilibrium limit it is inevitable that two environments will have equal mass fractions for certain species at some point in the flow field. Since singularity implies an underlying correlation between... 

Shape selectivity and orbital confinement effects are direct results of the physical dimensions of the available space in microscopic vessels and are independent of the chemical composition of nano-vessels. However, the chemical composition in many cases cannot be ignored because in contrast to traditional solution chemistry where reactions occur primarily in a dynamic solvent cage, the majority of reactions in nano-vessels occur in close proximity to a rigid surface of the container (vessel) and can be influenced by the chemical and physical properties of the vessel walls. Consequently, we begin this review with a brief examination of both the shape (structure) and chemical compositions of a unique set of nano-vessels, the zeolites, and then we will move on to examine how the outcome of photochemical reactions can be influenced and controlled in these nanospace environments. 

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