Chemical tracers inert

Some attempts have been made to use reactive hydrocarbons in conjunction with inert chemical tracers to deduce HO concentrations in urban plumes (139,140,141). Difficulties in deducing [HO ] from these experiments have been studied by McKeen et al (142), who conclude that such experiments can underpredict HO concentrations by a factor of 2 when more reactive hydrocarbons are used and parameterization of transport processes is not properly accounted for. 

Concurrent with the injection of iron is the injection of the inert chemical tracer sulfur hexafluoride (SFg). By presaturating a tank of sea water with SFg and employing an expandable displacement bladder, a constant molar injection ratio of Fe SFg can be achieved (Figure 6). In this way, both conservative and nonconservative removal of iron can be quantified. Sulfur hexafluoride traces the physical properties of the enriched patch the relatively rapid shipboard detection of SFg can be used to track and... 

The time that a molecule spends in a reactive system will affect its probability of reacting and the measurement, interpretation, and modeling of residence time distributions are important aspects of chemical reaction engineering. Part of the inspiration for residence time theory came from the black box analysis techniques used by electrical engineers to study circuits. These are stimulus-response or input-output methods where a system is disturbed and its response to the disturbance is measured. The measured response, when properly interpreted, is used to predict the response of the system to other inputs. For residence time measurements, an inert tracer is injected at the inlet to the reactor, and the tracer concentration is measured at the outlet. The injection is carried out in a standardized way to allow easy interpretation of the results, which can then be used to make predictions. Predictions include the dynamic response of the system to arbitrary tracer inputs. More important, however, are the predictions of the steady-state yield of reactions in continuous-flow systems. All this can be done without opening the black box. 

The detection of a test gas using mass spectrometers is far and away the most sensitive leak detection method and the one most widely used in industry. The MS leak detectors developed for this purpose make possible quantitative measurement of leak rates in a range extending aaoss many powers of ten (see Section 5.2) whereby the lower limit = 10 mbar l/s, thus making it possible to demonstrate the inherent gas permeability of solids where helium is used as the test gas. It is actually possible in principle to detect all gases using mass spectrometry. Of all the available options, the use of helium as a tracer gas has proved to be especially practical. The detection of helium using the mass spectrometer is absolutely ( ) unequivocal. Helium is chemically inert, non-explosive, non-toxic, is present in normal air in a concentration of only 5 ppm and is quite economical. Two types of mass spectrometer are used in commercially available MSLD s ... 

In Section 3.1.1, self-diffusion was analyzed by studying the diffusion of radioactive tracer atoms, which were isotopes of the inert host atoms, thereby eliminating any chemical differences. Possible effects of a small difference between the masses of the two species were not considered. However, this difference has been found to have a small effect, which is known as the isotope effect. Differences in atomic masses result in differences of atomic vibrational frequencies, and as a result, the heavier isotope generally diffuses more slowly than the lighter. This effect can—if migration is approximated as a single-particle process—be predicted from the mass differences and Eq. 7.14. If mi and m2 are the atomic masses of two isotopes of the same component, Eqs. 7.13 and 7.52 predict the jump-rate ratio,... 

A model for the tracer self-diffusivity of the interstitials is now developed for a system in which the total concentration of inert interstitials and chemically similar radioactive-tracer interstitials is constant throughout the specimen but there is a gradient in both concentrations. Since the inert and tracer interstitials are randomly intermixed in each local region,... 

However, in this system, the ideal free energy of mixing of the inert and tracer interstitials is the only component that varies with x. By taking the derivative of the free energy to obtain the chemical potential, the -dependent component of the chemical potential of the tracer interstitials is simply kTln( p/p), and therefore, because p is constant, (d p/dx) = (kT/ p)(d p/dx). Putting this result into Eq. 10.30,... 

One must be aware of the possible occurrence of certain problems in isotope dilution analysis. One of these is incomplete isotopic exchange, in which the active and inactive atoms do not mix. This lack of exchange can be due to differing physical and chemical states of tracer and inactive materials. Steps must be taken to ensure complete exchange. One must also be sure that the labeled position in any compound is relatively inert. If the atom in question is very labile, one can get a reduction in specific activity without any dilution having taken place. To compare specific activities, all samples must be counted under identical conditions with proper corrections for self-absorption in samples of varying mass. 

The Airborne Submillimeter SIS Radiometer (ASUR), operated on-board the German research aircraft FALCON, measures thermal emission lines of stratospheric trace gases at submillimeter wavelength. Measurement campaigns with respect to ozone depletion in the Arctic winter stratosphere were carried out in yearly intervals from 1992-97 to investigate the distributions of the radical chlorine monoxide (CIO), the reservoir species hydrochloric acid (HC1), the chemically inert tracer nitrous oxide (N20), and ozone (O3). The high sensitivity of the receiver allowed to take spatially well resolved measurements inside, at the edge, and outside of the Arctic polar vortex. This paper focuses on the results obtained for CIO from... 

The state of mixing in a given reactor can be evaluated by RTD experiments by means of inert tracers, by temperature measurements, by flow visualization and, finally, by studying in the reactor under consideration the kinetics of an otherwise well-known reaction (because its mechanism has been carefully elucidated from experiments carried out in an ideal reactor, the batch reactor being generally chosen as a reference for this purpose). From these experimental results, a reactor model may be deduced. Very often, in the laboratory but also even in industrial practice, the real reactor is not far from ideal or can be modelled successfully by simple combinations of ideal reactors this last approach is of frequent use in chemical reaction engineering. But... 

A radioactive tracer technique was ultimately chosen as a mapping tool. The isotope Kr-85 was selected because it can represent the gaseous, vaporous and solid materials in the reactor. Being an inert gas it does not interact chemically with any of the species present. It is readily dispersible... 

The experiments with the inert tracer may only show that the time, necessary for the fluid in the reactor to be well mixed, is much smaller than the average residence time. When a chemical reaction takes place, an additional time-scale, the time constant of the chemical reaction, appears. This time characterizes the reaction rate and can be defined as the time in which the reaction proceeds to a certain conversion, say 50%. For many practical heterogeneous catalytic reactions, the reaction time is so short that reactants entering the reactor may be converted without being mixed, for example, during the first cycle. For such fast reactions, of course, the reactor cannot be considered as gradient-free, whatever the recirculation ratio is. 

Noble gases have been widely exploited as geochemical tracers. They have three attributes that make them particularly sensitive as tracers of mantle processes. Specifically, noble gases are (i) composed of different components each having diagnostic isotope characteristics, (ii) incompatible, and hence depleted in the solid Earth, and (iii) chemically inert. Each of these feamres of the noble gas family is discussed in mrn. 

The escape of Rn from soils is the source of 99% of the Rn in the atmosphere. Typical radon escape rates are on the order of 1 atomcm s from the land surface, which result in a radon inventory of the global atmosphere of 1.5Xl0 Bq. Atmospheric radon itself is a chemically inert and unscavenged, i.e., not removed from the atmosphere by physical or chemical means. Because its half-life is much less than the mixing time of the atmosphere, it is a tracer of atmospheric transport and can be used in a synoptic approach to identify air masses derived from continental boundary layers or in a climatological manner to verify the predictions of numerical models of transport. 

The RTD is determined experimentally by injeeting an inert chemical, molecule, or atom, called a tracer, into the reactor at some time t = 0 and then measuring the tracer concentration, C, in the effluent stream as a function of time. In addition to being a nomeaetive species that is easily detectable, the tracer should have physical properties similar to those of the reacting mixture and be completely soluble in the mixture. It also should not adsorb on the walls or other smfaces in the reaetor. The latter requirements are needed so that the tracer s behavior will honestly refleet that of the material flowing... 

The conclusions presented above can be applied in designing experiments on chemical identification and studies of element 112. There is little doubt that the element is a congener of mercury, at least equally volatile and chemically inert. Then proper chemical environment can be even simpler than in the case of HSO4. However, the experimental technique must allow for the possibility that element 112 is much more volatile and chemically inert than mercury. The problem is to guarantee the registration of the element (not to lose it) even if it resembles Rn, rather than Hg, in volatility and inertness. Atomic mercury in tracer quantities can be transported by inert gas at ambient temperature through tubes made of various materials. However, it adsorbs onto some metals, in particular, on gold. 

Carrier gas here usually consists of a major component, chemically inert towards tracer(s) and of minor (still macroscopic) quantities of reactive gases or vapors (see below). 

In order to reconstruct the process of chemical weathering, it is necessary to select a substance in the source rock and resultant soil that can be considered relatively inert to weathering, with which concentrations of other soil constitutents can be compared. AI2O3 and Ti02 have been used for such purposes. Once an inert "tracer has been selected, how is such an analysis of weathering performed ... 

In practice, especially in large-scale reactors, plug-flow or complete mixing are rarely achieved, and it is desirable to quantify the deviation from those idealized flow conditions. Also, when a chemical reactor does not perform at the expected level, it is necessary to identify the reason. A diagnostic method that is applied in such situations is based on measuring the residence time distribution (RTD) in the reactor. An inert tracer is injected at the reactor inlet, and its concentration at the reactor outlet is measured with time. By comparing the outlet concentration curve to the inlet concentration curve, the RTD curve of the reacting fluid in the reactor can be constructed [1,7,10,43]. 

In this context, Griffiths reported in 1911 the interactions of an aqueous plug with a chemically inert carrier stream flowing through a narrow, straight tube [53]. He carried out the first experimental work demonstrating the essence of the dispersion process and concluded (without a mathematical treatment) that "a tracer injected into a water stream spreads out in a symmetrical manner about a plane in the cross section that moves with the mean flow velocity" [54], He also pointed out the establishment of a fully developed laminar flow regime. 

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