Experimental technique

The experimental realization generally uses short-pulse lasers, such as pulsed dye lasers (Vol. 1, Sect. 5.7), or mode-locked lasers (Sect. 6.1). The time response of the detection system has to be fast enough to resolve the time intervals At h/ ( 2 - 1). Fast transient digitizers or boxcar detection systems (Vol. 1, Sect. 4.5) meet this requirement. 

When atoms, ions, or molecules in a fast beam are excited and the fluorescence intensity is monitored as a function of the distance z downstream of the excitation 

The excitation can even be performed with cw lasers since the bandwidth necessary for coherent excitation of the two levels is assured by the short interaction time At = djv of a molecule with velocity v passing through a laser beam with the diameter fil. 

Because of sub-Doppler resolution, quantum-beat spectroscopy has been used to measure fine or hyperflne structure and Lamb shifts of excited states of neutral atoms and ions [870]. 

Quantum beats can be observed not only in emission but also in the transmitted intensity of a laser beam passing through a coherently prepared absorbing sample. This has first been demonstrated by Lange et al. [872, 873]. The method is based on time-resolved polarization spectroscopy (Sect. 2.4) and uses the pump-and-probe technique discussed in Sect. 6.4. A polarized pump pulse orientates atoms in a cell placed between two crossed polarizers (Fig. 7.12) and generates a coherent superposition of levels involved in the pump transition. This results in an oscillatory time dependence of the transition dipole moment with an oscillation period AF = 1/Av 

When atoms, ions, or molecules in a fast beam are excited and the fluorescence intensity is monitored as a function of the distance z downstream of the excitation point, the time resolution At = Az/v is determined by the particle velocity v and the resolvable spatial interval Az from which the fluorescence is collected [12.37]. In this case, detection systems can be used that integrate over the intensity and measure the quantity 

If the Zeeman sublevels /, M = dzl) of an atomic level with J =l are coherently excited by a pulsed laser, the fluorescence amplitudes are equal for the transitions (7 = l,M = -fl- / = 0) and (/ = 1, M = — 1 7 = 0). One therefore observes Zeeman quantum beats with a 100% modulation of the fluorescence decay (Fig. 12.10  

Older experimental arrangements used Earaday cups with small apertures mounted on goniometers, which could be moved around the sample to collect the back-scattered electron current directly, or spot photometers, which were directed at one dif- 

Data collection is mostly performed at normal incidence of the primary electron beam. Under these conditions usually several equivalent LEED spots exist because of the surface symmetry. By taking care that the I-V curves of equivalent spots are identical, normal incidence conditions can be adjusted to within a few tenths of a degree. 

Experimental Techniques. The values of kxc kisc kD and kTEV can t e determined, if the absolute values of the quantum yield ( t ) for the particular process i can be measured either directly or indirectly, 

Although these values are extremely important quantities, there is no established, general method for measuring them on an absolute basis. Experimental difficulty arises because the species of interest is often a transient, and hence the precise values of its desired physical properties, such as (1) the T-T absorption coefficient and (2) the phosphorescence quantum yield for the specified excitation energy and the specified eigenstate, are not available for the desired spectroscopic analysis. However, some limited methods may be used with adequate caution. These methods involve either luminescence measurement or product analysis  

Sensitized cis-trans isomerization of 2-butenes or other olefins for triplet yield (59,62). 

Triplet-benzene-photosensitized decomposition for triplet yield (70,134). 

Wavelength and pressure dependence of photolytic and thermal unimolecular decomposition for the internal conversion yield (51,52,137,160). 

Experimental techniques used in the assessment of kinetics of precipitation and sizing of precipitate must address the specificity of this process. In particular, they need to be concerned with rapid chemical reactions, high initial supersaturation, high-order nucleation kinetics, very short time-scale of concurrently occurring component-phenomena, and small size of the crystals. 

The experimencal techniques discussed below Include AES, LEED, TPD, XPS, HREELS and cyclic voltammetry. Except for cyclic voltammetry, which is an electrochemical technique, all the others are surface science techniques which require UHV conditions. The surface science techniques were used in this work to characterize geometric structure (LEED), chemical composition 

Broadly speaking, experimental information about the nature of polymer surfaces and interfaces is available in three broad classes, composition, structure and morphology and properties. Let us discuss each in turn. 

Perhaps the most obvious question we can ask about a polymer surface is what it is composed of Compositional information may be restricted to an elemental analysis, or we may be able to obtain more specific information about the chemical species that are present. Alternatively, it may be possible only to detect the presence of a restricted set of elements or compounds. Such a technique is obviously much less helpful if we are faced with a completely unknown sample (such as an industrial material with some unknown contaminant at the surface), but, on the other hand, if we are doing a closely controlled experiment in which we are able to introduce an element to which we are sensitive as a label (for example by using a deuterium label on a polymer component believed surface active), the technique may be much more appropriate. 

The ability of the technique to discriminate between different depths below the surface is also important. We can distinguish between truly surface- 

Several properties of surfaces have origins that are very sensitive to the surface, but are essentially macroscopic in character. Examples include adhesion, surface tension and the contact angle. Techniques to measure these properties are not discussed in this chapter, but rather are mentioned in connection with discussions of the property involved elsewhere in this book. However, surface properties can also be probed at a microscopic level for example the forces between surfaces at microscopic separations may be probed using the surface forces apparatus (SFA). The scanning force microscope 

With these general considerations in mind, we now go on to discuss the techniques in more detail. First we discuss techniques involving reflection of waves of one form or another, then we go on to methods in which the probe consists of fast moving ions. The very important spectroscopic methods are discussed next, before we finish with a look at surface force measurements and the scanning force microscope. 

A wide variety of techniques has been developed to measure radiofrequency intervals of Rydberg states. Some of these techniques are not truly radiofrequency techniques, but since they yield the same information we mention them here, although not in the same detail as the radiofrequency techniques. 

Many of the various techniques associated with metal film preparation have recently been reviewed by Klemperer (76). Much of the catalytic work with thick continuous films has used a cylindrical reaction vessel (Fig. 7a). This cylindrical geometry permits a cylindrical sleeve of mica sheet to be inserved and used as the film substrate for epitaxial film growth 

As will be apparent from the subsequent discussion, a very thin discontinuous film such as occurs in the fringe region of a film formed in a 

(a) Conventional reaction vessel for preparation and use of thick evaporated metal film catalysts (b) reaction vessel for preparation and use of thick, fringe-free evaporated metal film catalysts. 

Recently, ultrathin evaporated films have been used as models for dispersed supported metal catalysts, the main object being the preparation of a catalyst where surface cleanliness and crystallite size and structure could be better controlled than in conventional supported catalysts. In ultrathin films of this type, an average metal density on the substrate equivalent to 0.02 monolayers has been used. The apparatus for this technique is shown schematically in Fig. 8 (27). It was designed to permit use under UHV conditions, and to avoid depositing the working film on top of an outgassing film.  

Evaporated film catalysts are virtually always used with a static gas phase, and with reactant gas pressures less than about 100 Torr. One thus relies upon gaseous diffusion and convection for transport to the catalyst surface. However, provided one is dealing with reaction times of the order of minutes to tens of minutes, gas phase transport has but a negligible effect on the reaction, provided none of the reaction volume is separated from the film by small bore tubulation. Beeck et al. (77) in fact originally used an all-glass magnetically coupled turbine for gas circulation, but this is only 

Several experimental techniques are used to investigate the carrier injection and transport in organic solids. TOP technique, current-voltage (JV) measurement, AS measurement, and DISCLC measurement are used and cross-compared. Table 3.2 shows a summary of fhese fechniques. 

In practice, several very elaborate experimental devices exist for studying orientation. There are also some very simple procedures that can be applied but usually with far less quantitative accuracy. Because of their simplicity we will consider the latter methods first. 

When a crystalline polymer is oriented, the random circular film pattern (random orientation) transforms to a collection of defined reflection arcs that are correlated with particular (hkl) planes that can be identified based on the crystal structure and Bragg relationship (see Fig. 12a-b). It follows that the magnitude of the azimuthal spread (x/2) of these reflections is indicative of the degree of orientation. (The breadth, k, of the reflection is related to crystal size and imperfection—see Ref. 32.) Also, the location of the reflection with respect to the sample axes indicates the orientation of the crystallographic planes. For example Fig. 5(a) and (b) show two X-ray photographs of polyethylene that had been cold rolled. From the (200) reflection in sample (a) one sees that the a-axis is aligned preferentially normal to Z whereas in (b) there are two distinct orientations of the a-axis—one along Z and one normal to this. 

While photographic techniques may allow one to obtain some average orientation values for a deformed crystalline polymer there is need for a quantitative measure of this distribution. In general, the distribution in orientation is determined for a single (hkl) plane—usually a (/lOO), (OkO) or (OOO plane if sufficient diffraction exists. The data are then presented either in a pole figure or may be used to determine the Herman s orientation function defined as 

Although/is a convenient index to characterise orientation, one must note that it is only an average value—specifically the second moment of the whole orientation distribution for the specific set of (hkl) planes utilised. Hence, two different orientation distributions could exist having 

Two different hypothetical uniaxial orientation distributions (a) all chains lie at an angle 0 with respect to the Z-axis (h) a more realistic ellipsoidal distribution. 

A short survey of the most important experimental aspects will be outlined briefly although very complete descriptions of experimental methods in organic photochemical syntheses are available 120,121 701-703 . 

Once the UV-absorption spectrum of the compound to be irradiated — and whenever possible of the reaction product as well — is known, the main parameter to be selected is the excitation wavelength. In unsensitized — i.e. direct — irradiations the reaction product should not absorb any light as to avoid secondary photoreactions. The wavelength of the light used can be influenced by three factors the light source, filters and the solvent. 

The conventional photolysis apparatus consists of a concentrically arranged immersion well for the lamp, which is surrounded by a cooling jacket, which is itself surrounded by the reaction vessel. If this last compartment is used for the filter solution an additional external flask for the reaction mixture has to be used. There are also photochemical reactors wherein the lamps are arranged externally around the reaction flask. 

As for the temperature, preparative photochemical reactions are usually run around room temperature with water as coolant for the lamp, although higher or lower temperatures can be achieved in using a thermostate or a cryostate to circulate the coolant, which obviously should be transparent for the light used. Only very few reactions in a matrix at low temperatures are used for preparative purposes 704). 

Photochemical reactions are usually run in homogeneous solutions notwithstanding it is also possible to irradiate solid compounds directly. Examples of such reactions on a preparative scale 705) as well as a discussion on crystal lattice control on photoreactions 706) are found in the literature. Finally, specific effects of a micellar environement is also being used in photochemical reactions of preparative purposes707). 

Ion exchange experimental techniques have been described in monographs [1-6] and reviews [7-14]. Information on high-speed ion exchange chromatography techniques can be found in books [21-26] and assays [27,29,32,34,57,73-75]. For instrumentation of LC see also chapters 4.1-4.4 of this volume. 

In this section we consider some of the techniques which are used to obtain data relevant to the operation of a nuclear reactor. Some of the methods described are employed in the measurement of basic data, such as 

In this chapter we shall consider the various techniques which have been used for observation of the Mbssbauer effect, together with methods of source and absorber preparation and computer techniques for data analysis. Some of the advantages and limitations of Mossbauer spectroscopy will become apparent during the discussion of these problems. References to more recent development will be found in the review by J. R. De Voe and J. J. Spijkerman in Analytical Chemistry, 1970, 42, 366R, and in Spectroscopic Properties of Inorganic and Organometallic Compounds published annually by the Chemical Society (London). 

The method of velocity modulation of the y-ray energy by means of the Doppler effect was described by Mossbauer in 1958 [2] and provides the basis for all modern spectrometers. 

In this section, experimental techniques for the characterization of zeolites and adsorbate/zeolite samples via IR spectroscopy, Raman scattering and inelastic neutron scattering will be briefly discussed. For more detailed information, the reader is referred to Refs. [145-150]. 

Two techniques are principally responsible for the experimental development of dynamics in surface chemistry. These are the application of molecular beams and laser state-to-state techniques to gas-surface interactions. This roughly parallels their application to gas phase chemistry, although there are certainly some different technical requirements. More detailed discussion of some of these experimental techniques are in Refs. [104] and [105]. 

Laser state-to-state techniques include both the application of highly sensitive laser spectroscopy for internal state-resolved detection of molecules in the gas phase, e.g., desorbing or scattering from a surface, and second, for laser pumping an initial state prior to interaction with a surface. To date, laser detection of internal states has been widely applied in gas-surface dynamics experiments, while those involving optical state preparation techniques have only been applied in a limited fashion. 

Tunable laser spectroscopic techniques such as laser-induced fluorescence (LIF) or resonantly enhanced multi-photon ionization (REMPI) are well-established mature fields in gas-phase spectroscopy and dynamics, and their application to gas-surface dynamics parallels their use elsewhere. The advantage of these techniques is that they can provide exceedingly sensitive detection, perhaps more so than mass spectrometers. In addition, they are detectors of individual quantum states and hence can measure nascent internal state population distributions produced via the gas-surface dynamics. The disadvantage of these techniques is that they are not completely general. Only some interesting molecules have spectroscopy amenable to be detected sensitively in this fashion, e.g., H2, N2, NO, CO, etc. Other interesting molecules, e.g. 02, CH4, etc., do not have suitable spectroscopy. However, when applicable, the laser spectroscopic techniques are very powerful. 

A typical application is the use of the (2 + 1) REMPI scheme for measuring the (v,./) distribution of H2 produced in associative desorption from a surface. When the laser is tuned to a spectroscopic transition between individual quantum states in the X - E electronic band, resonant two-photon absorption populates the E state and this is subsequently ionized by absorption of another photon. The ion current is proportional to the number in the specific (v,./) quantum state in the ground electronic state that is involved in the spectroscopic transition. Tuning the laser to another spectroscopic feature probes another (v, J) state. Therefore, recording the ion current as the laser is scanned over the electronic band maps out the population distribution of H2(v, J) produced in the associative desorption. Ef of the (v, J) state can also often be simultaneously measured using field - free ion TOF or laser pump - probe TOF detection techniques. The (2 +1) REMPI scheme for detecting H2 is almost independent of the rotational alignment and orientation f(M) of molecules so that only relative populations of the internal states 

Elaborate irradiation procedures, vessels and analyzing techniques are also requisite for specific irradiation and measurements. 

In this section, some useful experimental techniques for the analysis of the reaction kinetics of thermosetting polymers are discussed. 

A set of differential equations for the generation and consumption of the different species may be stated. For example, by assuming that the catalytic mechanism predominates over the noncatalytic mechanism in most of the conversion range, the following kinetic scheme may be written  

The set of differential equations was analytically solved by assuming R21 = k2 / ki = constant. A very good fit with experimental results was obtained for R21 = 0.4, as shown in Fig. 5.12. 

For chainwise polymerizations, the analysis of model systems implies consideration of the homopolymerization or copolymerization of bifunctional monomers. Kinetic results cannot be directly extrapolated to the case of networks, because very important features such as intramolecular cycliza-tion reactions are not present in the case of linear polymers. However, the nature of initiation and termination reactions may be assessed. For example, using electron spin resonance (ESR), Brown and Sandreczki (1990) identified different types of radicals produced during the homopolymerization of a monomaleimide (a model compound of bismaleimides). 

The best way to elucidate the reaction path is to follow the evolution of as many independent species and functional groups as possible. For example, analysis of the epoxy-amine reaction following the simultaneous evolution of epoxy and primary amine groups by near infrared spectroscopy (NIR) simultaneous determination of the conversion of double bonds belonging to unsaturated polyester (UP) and styrene (S) using FTIR, as shown in Fig. 5.13 (Yang and Lee, 1988) determination of the evolution of the concentration of free radicals using ESR, as shown in Fig. 5.14 (Tollens and Lee, 1993). 

It is pertinent to first briefly discuss the experimental techniques which have been applied to the study of the individual charged particle reaction processes before proceeding to highlight the most important laboratory measurements and their relevance to environmental plasma chemistry. 

The HPMS technique developed and exploited by Kebarle and co-workers 106,107) is very reminiscent of the SA technique. Ionization is created in a pure gas or gas mixture either by using a radioactive source l08) or a high energy electron beam109). Ions are sampled by a pin-hole orifice in the walls of the chamber and reaction rate coefficients deduced. A great deal of data relating to ternary association reactions (Sect. 3.2.3) has been obtained using this technique. 

The temperature range over which critical data is required for the purpose of environmental chemistry is not large (Sect. 2.1) and the temperature variable SA, 

FA and HPMS have provided much valuable data. However, the maximum temperature accessible to these techniques is limited and so variants of the DT technique have been used to study rate coefficients as a function of ion kinetic energy (up to several electron volts). The temperature dependences of the rate coefficient are then deduced (not without difficulty) from the data. The DT technique of Biondi and his co-workers 121 123) and the FDT technique, developed and carefully exploited by Albritton and others 124,125 which combines the versatility of the FA with the conventional DT technique, have proven to be especially useful (Sect. 3.2.2). The HPMS technique developed by Castleman and his co-workers 126, 27 is also providing valuable data of environmental interest. 

Vibration spectroscopy of fluoride melts 5.4.1. Experimental techniques 

High refractory properties, extremely strong sensitivity to moisture and exceptionally high chemical activity of fluoride melts, especially of those containing ions of polyvalent metals, make spectral measurements of such melts extremely complicated. In order to obtain reliable results, the measurement cell must comply with three main requirements  

Due to the above requirements, typical optical ly-transparent materials, such as oxides (glass, quartz, alumina, zirconium oxide etc.) and halides (sodium chloride, lithium fluoride, calcium fluoride, potassium bromide, cesium bromide etc.) are usually unsuitable for use with fluoride melts. Therefore, no standard procedure exists at present for the spectral investigation of fluoride melts, and an original apparatus must be created especially for each particular case. 

Experimental methods of IR spectroscopy measurements can be divided into three main groups  

Information exists about the use of measuring cells made entirely of diamond or graphite with or without embedded diamond windows. Diamond cells were used, for instance, by Toth and Gilpatrick [333] in the investigation of the Nb(IV) spectrum in a LiF - BeF2 molten system at 550°C. Windowless graphite cells for the IR spectroscopy of melts were developed by Veneraky, Khlebnikov and Deshko [334]. Diamond, and in some cases windowless sapphire or graphite micro-cells, were also applied for Raman spectroscopy measurements of molten fluorides. 

Much of the early work on redistribution reactions of main group complexes was handicapped by the lack of modern instrumental techniques. Determination of the equilibrium position was usually obtained by distillative separation of products. This method obviously suffered due to the small 

Any analytical method used to examine redistribution reactions must allow for rapid, quantitative, and precise determination of all the reaction products present in the mixture (1). In order to measure quantitatively an equilibrium mixture by spectroscopy each component of the equilibrium must contain at least one characteristic signal and the concentration of the component must be obtainable from the spectrum. 

The relationship of the extinction coefficient e to concentration is given by Eq. (20), where A is the absorbance, 70//is the ratio of the intensity of the 

When considering the study of redistribution reactions, one must remember that NMR spectra are extremely sensitive to the rates of the processes that cause the exchanges. For very slow exchange, the lifetime at each site is long with reference to the interaction with the rf field thus the spectrum will consist of two sharp lines as it would in the absence of exchange. For moderate 

although as a quantitative tool for examination of transfer reactions NMR is unsurpassed, one must realize its limitations and understand that the accuracy obtained is not on par with that obtained by standard kinetic techniques. 

Althou the formation of cation-radicals is certainly the first step in the reaction sequences resulting from the use of the initiation techniques enumerated above, the subsequent steps are less well established. Various pathways are available to this first transient coupling to give dications, reaction with the monomer to give the carbenium ion or the dimer radical-cation, etc. Eventually, however the carbenium ions become the real active species, i.e., all these polymerisations involve a composite initiation mechanism where the cation-radicals are playing just a momentary role. 

One of the oldest methods employed for following the course of polymerisations with half life longer than about 15 min is based upon the volume contraction which accompanies these processes. This technique can easily be adapted to hi -vacuum manipulations and is quite reliable, provided accurate calibrations are carried out particularly when oligomers are present among the products. Apart from the limitation imposed by the initial dead time, dilatometry is also confined in scope, since it can only provide empirical kinetic relationships between the polymerisation rate and such variables as the concentrations of reactants, the temperature, the polarity of the solvent, etc. It is therefore more useful when used in conjunction with other tools devised to probe more mechanistic aspects of the process. Hi -vacuum equipment 

This chapter is largely restricted to the study of negative-ion-neutral reactions using the mass spectrometer ion source and double mass spectrometer techniques, and only these methods are discussed in detail in this section. 

The properties of silicon electrodes has been investigated using a wide range of experimental techniques. Specific examples are the determination of  

Steady-state or dynamic potential and current relationships to provide information on the energetic dependence of electrode reaction Current or potential versus time to provide information concerning stability of 

Capacitance-potential relationship to reveal information on the energetic position of semiconductor bands and surface states, especially the flatband 

Impedance-frequency relationship to yield information on the resistive and capacitive elements of the current path  

Current on rotating electrode to give information regarding mass transport in electrolyte and on rotating ring-disk electrode for reaction intermediates  

There are several methods for simplifying, or slightly altering, proton magnetic resonance spectra to facilitate their assignment, but relatively few carbohydrate investigations have thus far utilized these techniques. The 

An interesting and, so far, little-used chemical method for simplifying proton magnetic resonance spectra involves replacing ring-hydrogen atoms 

Although these chemical methods are useful, the most versatile and unambiguous aid is undoubtedly double resonance (or spin decoupling). This method allows the unequivocal identification of protons which are mutually coupled. As an extension, this method can be used for measuring chemical shifts when the signal of a proton is partially or completely obscured by 

—Diagrammatic Representation of a Field-sweep, Double-resonance Experiment. 

—Double-resonance Tickling Experiment on n-Glucal Triacetate The Effect on H-1 of a Weak Decoupling Field Set in the Vicinity of the H-2 Resonance. 

A wide range of materials can be usefully characterized by IS, namely electrical and structural ceramics, magnetic ferrites, semiconductors, membranes, polymeric materials, and protective paint films. The measurement techniques used to characterize materials are generally simpler than those used for electrode processes. Impedance spectra are usually independent of applied potential (both ac amplitude and dc bias) up to potentials of 1V or more. Consequently, it is unnecessary to fix the potential of electrodes, as is the case with potentiostatic experiments, and two-electrode symmetrical cells are commonly used. 

Most of the measurement equipment required for impedance studies can be bought off the shelf. The equipment falls into three categories  

Frequency Response Analyzers. These instruments are designed measure a voltage ratio, rather than impedance, but can be adapted to measure impedance by the addition of auxiliary components—in the simplest case, a standard resistor. A detailed account of the circuitry, which was included in the first edition of this volume, would be out of place today here it will be dealt with in brief, to illustrate the principles involved. 

The main disadvantage of this eonfiguration is that input Y is conneeted in parallel to the sample. The inputs of the FRA have a finite impedanee, Z , typically 1MQ in parallel with 30 to 50 pF and, unless Zj Zi , this leads to an error in Z . The problem can be redueed by plaeing fast unity-gain amplifiers (buffers) at the FRA inputs. The situation ean also be helped by interchanging the standard and the unknown, so that the input impedance of Y appears aeross the standard. If the standard resistance is made small, the effeet of Zi is minimized. This, however, adds complexity and results in a low voltage signal at Y . 

The complex quotient VJVy is computed by the impedance analyzer. Normally, Zj is a pure resistor, in which case, Z, has a simple relationship to this qnotienL In principle, any circuit of well-defined impedance may be nsed (e.g. parallel RC combination), bearing in mind, of course, that the multiplication of VJVy and Zj must be performed in the complex domain. It is good practice to select a standard resistor of magnitude comparable to the real part of the unknown. Obvionsly, a trial measurement is needed in order to select the most snitable standard resistor. 

On the other hand, according to the microscopic nature of the absorption of the IR photons, it occurs also with amorphous, disordered, and defective solids. For this reason, vibrational spectroscopies (in particular IR spectroscopy) represent very useful techniques for the structural characterisation of non-metalUc soUds. 

Insulating or weakly semiconducting materials, like most inorganic compounds, do not absorb the radiation outside the skeletal region, where all light is essentially reflected, transmitted, refracted, or scattered. The skeletal vibrations give rise not only to absorbed radiation in transmission and diffuse reflectance experiments, but also to reflected radiation in the reflection experiments. Thus the specular reflectance for insulating materials, both in the form of monocrystals and sintered pellets, is frequently the basis for the best determination of the skeletal spectrum, as far as the IR-active modes are concerned. 

The most common technique in practice, to obtain a good spectrum of the fundamental vibrations of a powdered insulating material with the transmission/absorption IR technique, is to prepare a layer appropriately diluted and sufficiently thin. To do this the most used technique is that of the KBr pressed discs. KBr in fact is an easily available powdered material which does not absorb in the medium IR region (down to near 400 cm i.e. it cuts out the far IR). It can be easily mixed homogeneously with the powder to be investigated, and pressed, thus obtaiiung diluted self-supporting discs very useful for IR transmission. Other materials (such as e.g. Csl or polyethylene for far IR studies) allow the production of similar pressed discs, with cut-off limits at even lower frequencies. Alternatively, the powders can be 

Skeletal IR characterisation of oxidation catalysts case studies 

IR spectroscopy is largely used for the characterisation of metal oxide-based catalysts in relation to their structural features, with additional possible information on morphology. Several collections of IR, Raman, or both IR and Raman spectra of inorganic materials and minerals have been pubhshed and are available electronically. We have previously reported several investigations on this subject.  

The two components of each of the compound-specific complex functions e or h define the optical properties of a medium completely. The availability of both of the related components renders possible to derive the underlying oscillatory structure as well as to calculate the spectra of the medium to be expected with any well-defined experimental technique. 

The possibility to obtain detailed vibrational spectra of surface structures with increased sensitivity, is utilized to study adsorption, chemical modification, catalytic processes etc. (e.g. Chabal, 1988 Allara, 1993 Chabal et al., 1993). Several authors review and compare the potentials of the different techniques (Leyden and Murthy, 1987 Leyden, 1990 Grosse, 1991 Roberts, 1992 Yarwood, 1993). In what follows, the basic reflection techniques are outlined with particular emphasis on weak absorbers. 

Fundamental parameters in photoconductivity studies of solids are the quantum efficiency of photogeneration 0, the injection efficiency Y (where applicable) and the carrier mobility ju. These parameters are not directly obtainable from steady-state measurements, where 0 and appear as products in the expression for photoconductivity. Independent experiments are therefore required [92]. Transient techniques such as time-of-flight (TOF) and xerographic discharge are best suited. Both 

In the xerographic technique the corona-deposited charge plays the same role as the semitransparent electrode. The potential difference across the specimen is monitored by a capacitively coupled probe. In the absence of charge trapping, the rate of potential decay has the form 

The only commercial field where photoconductive or charge-transporting polymers have been applied successfully is electrophotography. Many 

Application in photovoltaic cells has been suggested many times, but the low conversion efficiency and particularly the high UV instability of the polymers have prevented their commercial utilization. Several other possible applications have been reported in the literature, but none have been exploited commercially. Among them are photothermoplastic imaging [93], holographic recording [94] and optical switching devices [95]. 

and Gurney, R.W. (1948) Electronic Processes in Ionic Crystals, Oxford University Press, London, p. 172. 

A survey of different cameras used for small-angle analysis has been given by Pedersen [69] which provides a practically complete overview of all systems used up to now for SANS and SAXS. Here we shall focus on devices used for SAXS-measurements. In particular, an extended discussion of the Kratky-cam-era [70,71] will be given because this device allows very accurate SAXS-measurements using an ordinary X-ray generator. Most of the experimental investigations on polymeric latexes have been conducted using this type of SAXS-cam-era. Since this device works in slit collimation, the correction of the data will be discussed in detail. 

In addition, we will give a brief overview on other cameras which require X-ray sources with high intensity thus necessitating the use of synchrotron radiation. It is evident that, up to now, such X-ray sources are not available on a routine basis. SAXS, on the other hand, will be shown to be a highly versatile tool for the analysis of latexes and instruments allowing measurements by use of conventional X-ray sources are therefore very useful. 

Besides a description of instruments, the following section will also contain a discussion of the treatment of data. This includes the removal of various contributions to the signal stemming from the suspension medium water and from the density fluctuations of the solid polymer in the latex particles. 

In the following, a description of an improved Kratky-camera [73] will be discussed together with an extended discussion of the treatment of data. This device is capable of measuring latex particles up to a diameter of 200 nm and reaches the q-range provided by SAXS-cameras which work in point collimation and use synchrotron radiation (cf. below [73]). 

The previous section showed that interpretable HRTEM images are not obtained unless quite stringent experimental conditions are fulfilled. The important questions - What instrumentation does one need, and what does one actually do, to obtain an interpretable HRTEM image - have recently been considered by Veblen (1985a) who has described in some detail the experimental techniques that he has found essential for successful high-resolution microscopy. Because descriptions of tricks-of-the-trade are relatively rare in the literature, his main points are summarized in the following subsections. 

1 Instrumentation. For many mineralogical studies, the minimum requirement is a 100-kV microscope with a point-to-point resolution of 0.4 nm, fitted with a double-tilt (or tilt-rotate) specimen holder. 

2 Specimen preparation. Most HRTEM investigations have used specimens in the form of crushed fracture fragments supported on a holey carbon film attached to a standard copper grid. Specimens thinned by ion (or atom) bombardment are also used, but the amorphous film which tends to form on the surfaces of foils prepared in this way is sometimes too thick for successful high-resolution imaging. See also Section 2.7. 

3 Alignment of the electron microscope. It is absolutely essential that the microscope be accurately aligned and that the astigmatism of the objective lens be fully corrected with the same objective aperture as used for the high-resolution imaging. 

4 Specimen orientation. The specimen must be oriented so that the incident electron beam is parallel to the zone axis of interest. This is done by tilting the specimen while observing the selected area (or the convergent beam) diffraction pattern. 

The first consideration is the choice of model system, and this may involve an aqueous electrolyte or nonaqueous media such as an organic electrolyte or molten salt. The selection of electrolyte and scavenger will depend on the energetics of the electrolyte reduction (good stability to reduction is needed) and upon the acceptor reactivity. Apparatus and electrochemical cells for metal/ electrolyte and semiconductor/electrolyte systems are similar generally. Some guidelines are presented below to assist with experimental practice (see also Chapter 3 in Ref. 10). Theses, also, are a good source of practical information, e.g., Refs. 20, 21, and 81. 

the scavenger should react rapidly with solvated electrons but be nonelectroactive at the electrode in dark to large negative potentials. The review of the physical properties and chemistry of solvated electrons by Matheson is helpful in the selection of suitable scavengers. It is helpful, too, to choose an acceptor whose kinetic parameters and follow-up chemical reactions are known, unless the interest is in the reaction chemistry of the scavenger per se. Nitrous oxide has proven to be an excellent acceptor for aqueous systems, both at metallic and semiconducting electrodes. This is 

It is not possible to lay down any universal rules since receptivities vary widely and relaxation times may be very long, especially for Li, or extremely short. Where the relaxation times are not too long, data are easy to obtain in the FT mode and the disadvantages of shorter relaxation times and broad lines can often be overcome to a great extent since short acquisition times and rapid pulse repetition rates are permissible, especially if some line-shape distortion can be tolerated. For maximum use to be made of such techniques access to memory sizes less than IK must be possible. 

As mentioned above, the study of the dynamics of adsorption layers at liquid interfaces is mainly restricted to surface and interfacial tension measurements. Only for slow adsorption processes, methods such as radiotracer technique [163, 164], the significantly improved surface ellipsometry [165, 166], or the very recently developed technique of neutron reflectivity [167, 168, 169, 170] can be used to directly follow the change of surface concentration with time. Neutron reflectivity allows even distinguishing between different species adsorbed at a fluid interface [171, 172, 173]. These techniques are reviewed in more detail in the preceding chapter 3 as they yield data most of all for the equilibrium state of adsorption layers. 

The surface activity of surfactants varies over a broad concentration range and hence a broad time interval has to be studied. Therefore, complementary experiments are necessary to cover the extensive time range from less than a millisecond up to minutes, hours and sometime days. The following Table 4.2 summarises the most frequently used surface tension methods, their available time and temperature intervals and suitability for studying the liquid/air and liquid/liquid interface. The given values represent the interval available by standard instruments, while particular modifications certainly allow to go beyond these limits. 

In the following a brief overview will be given of the most frequently used surface and interfacial tension methods, mostly available as commercial set-ups. 

There are a number of techniques available to measure the surface or interfacial tension of liquid systems, which together cover a wide range of time. In many cases, several methods are required in order to receive the complete surface tension time dependence of a surfactant system. One of the important points in this respect is that the data obtained from different experimental techniques have to be recalculated such that a common time scale results, i.e. one has to calculate the effective surface age from the experimental time, which is typically determined by the condition of the methods. For example, the maximum bubble pressure 

Overview of dynamic surface tension and surface relaxation methods 

The incremental capacity of an insertion electrode material used in ambient temperature batteries can be estimated from voltage spectroscopy measurements which can help to the determination of phase diagram of the insertion compotmd [1], In the first section, we examine the various aspects of electrochemical lithium insertion into a number of electrode materials. The experimental techniques of solid-state electrochemistry are presented in the second section. Voltage spectroscopy and phase diagram during Li intercalation into cathode materials are investigated. Finally, the experimental determination of the diffusion coefficient of ions in solid materials is investigated. 

A large class of ambient temperature batteries involves electrode insertion reaction, where a fraction (x) of foreign cations (Li ) together with compensating electrons (c ) are incorporated into the lattice of a host electrode material (H) forming a nonstoichiometric compound  

In case the reaction product bears a close structural relationship to the pristine electrode (unreacted) material (H), this type of reaction is classified as topochemical [2]. A special case of the topochemical process is the intercalation or insertion reaction which proceeds without any breakage of bonds in the host structure. This reaction (Eq. 13.1) is generally reversible. 

For some materials, the measured velocity profiles can be subject to different interpretations. Highly blunted profiles may indicate a complex fluid with a highly 

Once the velocity profile has been obtained, the shear rate is calculated. This is the most difficult step. To ensure that the viscosity is determined without any bias, no assumption is made regarding the constitutive behavior of the material. Every effort is made to obtain smooth, robust values of the shear rate without any bias towards a particular model of the flow behavior. Particularly near the tube center, the velocity profiles are distorted by the discrete nature of the information. The size of a pixel is defined by the velocity and spatial resolutions. These are given by 

Other schemes have been proposed in which data are fit to a lower, even order polynomial [19] or to specific rheological models and the parameters in those models calculated [29]. This second approach can be justified in those cases when the range of behavior expected for the shear viscosity is limited. For example, if it is clear that power-law fluid behavior is expected over the shear rate range of interest, then it would be possible to calculate the power-law parameters directly from the velocity profile and pressure drop measurement using the theoretical velocity profile 

The MRI technique has also been used with systems of more practical importance, such as a polymer melt [19]. Here a low density polyethylene melt was 

Magnetic resonance imaging has enabled the development of a completely novel type of viscometer. This technique is based on the capacity of MRI to accurately measure velocity profiles in opaque liquids. Its potential applications include many systems of industrial relevance, such as polymer melts and slurries. The data presented here clearly show that a wide range of fluid behaviors can be measured. 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43 

Exhausted liquid ion exchangers may be regenerated in an analogous manner to ion exchange resins, e.g. Amberlite LA.l saturated with nitrate ions can be converted to the chloride form by treatment with excess sodium chloride solution. 

The properties and applications of liquid ion exchangers have been reviewed.44 

Ion exchange resins (standard grades) as received from the manufacturers may contain unwanted ionic impurities and sometimes traces of water-soluble intermediates or incompletely polymerised material these must be washed out before use. This is best done by passing 2M hydrochloric acid and 2M sodium 

A 50 mL or 100 mL burette, with Pyrex glass-wool plug or sintered-glass disc at the lower end, can generally be used for the determinations described below alternatively, the column with side arm (Fig. 7.4a) is equally convenient in practice for student use. Reference will be made to the Duolite resins the equivalent Amberlite or other resin (see Table 7.1 in Section 7.1) may of course be used. 

In order to improve the catalytic TON, chemo-, and regioselectivity (in the case of monosubstituted alkynes), the reaction parameters have been systematically optimized for a large number of [YCoL] catalysts. This screening was performed in a continuous-flow reactor connected to a process chromatography set up (84MI12) (Fig. 1). 

Solution of the educts and catalyst are pumped through the system, which is controlled by electronic balances. The actual reaction is performed in 87 ml continuous-flow reactor, from which samples are taken automatically and analyzed by gas chromatography (GC). The analytical data are processed online. 

There are only a few really basic schemes which have been used to determine fluorescent lifetimes. The minor variations upon these, however, are truly astronomical. We therefore consider only a few representatives from this vast group. It should be pointed out, however, that only some of the instruments considered in this section are truly practical and have been consistently applied to rare earths. Some are novel and illustrate new and ingenious ways that might prove useful for future work. 

The measurement of the growth and decay of fluorescence requires essentially two items (a) modulated excitation source and (b) a detector. The modulation of an excitation source may be accomplished in various ways. These range from simple mechanical choppers to highly sophisticated electronic pulsers. Detectors may be phototubes or semiconducting devices, or even the human eye. The detector itself, in some instances, may be modulated. Of course, the detector chosen must depend upon the spectral range to be studied and the response time desired. 

One of the simplest and earliest methods for the measurement of decay times was due to Becquerel (58). His instrument consisted of two disks mounted concentrically on a rotating shaft. Each disk contains a slit, or sector, cut into the circumference, and the sample to be studied is placed between the disks. The slits act as two shutters. The first opens to illuminate the sample, and the second permits the fluorescent light to exit to a detector. 

It is difficult to give a resolving time for this type of instrument, since it depends upon the minimum fluorescent intensity one can tolerate. A representative figure would be about 25 fisec. 

Thomas and Colbow (59) have described an elegant method by which one can change the angular position between the slits in a Becquerel phosphoroscope. Their system uses separate mechanical chopping of the 

At plant scale, the diazotization led to a dramatic explosion resulting in 5 fatalities and over 30 injured, as well as a huge damage to the production plant. 

In fact, the simple detection device used in the laboratory was unable to detect the exothermal reaction At laboratory scale, the heat exchange area is larger by about two orders of magnitude (see Section 2.4.1.2), compared to plant scale. Hence the heat of reaction could be removed without detectable temperature difference, whereas at plant scale the same exotherm could not be mastered. This incident enhanced the necessity of a reaction calorimeter and promoted the development of the instrument, which was under development at this time by Regenass [1], Later, it became a commercial device (RC1). 

Thermal Safety of Chemical Processes Risk Assessment and Process Design. Francis Stoessel Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31712-7 

A further positive reaction to this dramatic incident took place in the central research department of the company. A physico-chemist had the idea of using his differential scanning calorimeter (DSC) to look at the energy involved in this reaction. He performed an experiment with the initial concentration and a second with a higher concentration. The thermograms he obtained were different and he realized that he could have predicted the incident (see Exercise 11.1). As a consequence, it was decided to create a laboratory dedicated to this type of experiment. This was the beginning of the scientific approach of safety assessments using thermo-analytic and calorimetric methods. From this time on, many different methods were developed in different chemical companies and became commercially distributed, often by scientific instrument companies. 

In this chapter, some of these instruments are reviewed. A first section is a general introduction to calorimetric principles. In a second part, some methods commonly used in safety laboratories are reviewed. This is not an exhaustive review of such instruments, but based only on the experience of the author. 

In the derivation of Eq. (4) it is assumed that the charge in motion j Fe is small compared to the charge on the electrode CV0. It is also assumed that the charge pulse 

If on the other hand the carriers are lost by bulk trapping, A V(t) becomes, 

The voltage pulse which is a ramp of amplitude —- in the absence of trapping, is an 

If the experiment is carried out with a small series resistance R such that RC Tt (short circuit rase) the current in the absence of trapping is 

A variation of the experimental methods described above is the xerographic discharge technique which is gaining wide acceptance in the study of polymeric systems. The polymer film deposited on a metallic substrate is corona charged and 

The experiments are separated into groups distinguished by the reaction times (lifetimes) with which they are concerned. That the expressions given in Sect. 2 require modifying if the product ions themselves decompose will be taken as being understood. 

Of the six possible hydrogen-exchange reactions, the two most widely used are deuteriodeprotonation (deuteriation) and protiodetritiation (de-tritiation). Nowadays deuterium contents are determined by NMR, 

Early studies of deuteriation (and protiodedeuteriation), used infrared (IR) (which is less convenient) to measure changes in the intensity of the C—H stretching frequencies. This technique was used to study the kinetics of N—H exchange in azoles [75JCS(P2)1316], the decrease in the first overtone band of the N—H stretching mode at 1.48 p-m being followed. 

1 GENERAL INSTRUCTIONS FOR SAFE WORKING IN ORGANIC CHEMICAL LABORATORIES 

Chemistry laboratories need not be dangerous places in which to work, despite the many potential hazards associated with them, provided that certain elementary precautions are taken and that all workers conduct themselves with common sense and alertness. 

There will almost invariably be a senior person assigned to be in charge of a chemical laboratory, irrespective of the nature of the work to be done there. However, it must be emphasised that the exercise of care and the adoption of safe working procedures is the responsibility of each and every person in that laboratory. If there is any doubt as to the safety of a proposed experiment, advice should be sought from an experienced person rather than just hoping for the best. 

All workers must adopt a responsible attitude to their work and avoid any thoughtless, ignorant or hurried behaviour which may lead to an accident and possible harm to themselves or to others. They should always pay attention to what is going on around them and be aware of the possible dangers arising from the work of others as well as from their own experiments. 

Except in an emergency, running, or any over-hurried activity, should be forbidden in and around the laboratories, as should be practical jokes or other irresponsible behaviour. Eating, drinking and smoking in the laboratory should also be forbidden these constitute a further, avoidable, risk of the ingestion of toxic substances, and in the case of smoking an obvious fire hazard. 

The industrial interest in IR spectroscopy in catalysis is demonstrated by the work of Peri and coworkers at Amoco. Peri first published IR studies on the surface properties of alumina in 1960 [12] and performed several studies on alumina, silica and silica-alumina. Peri also published a useful summary of the use of IR spectroscopy in catalysis research in 1984 [13]. 

IR techniques underwent a great improvement with the application of Fourier transform instruments [16], first commercialized at the end of the 1970s. 

If the erq eriment is carrkd out with a miiall series resistance R ich that RC Tt (diort circuit rase) the current in the ab nce of trapping is 

The microscope should be set up using Kohler illumination monochromatic illumination produces a better image if small particles are to be measured. 

The reason that neutron diffraction is so much more effective than x-ray diffraction as a means for locating hydrogen atoms can be seen in the atomic scattering amplitudes given in Table 9-II (taken from reference 94, except for the neutron diffraction scattering factor for deuterons). 

In comparison with carbon and oxygen, hydrogen scatters neutrons much more effectively than x-rays. In fact, there are few x-ray studies of H bonded systems in which H atom positions have been reliably determined (see 403, 1880, 2169, 1933). 

Some workers feel that polarized IR spectra can be interpreted un- 

The most common procedure is to carry out the measurements in the form of a titration. Most commonly a solution containing metal-ion, ligand and acid is titrated with base. Occasionally, when the rate of attaining equilibrium in the system is slow, a batch method is adopted individual solutions of appropriate concentrations are prepared, sealed, placed in a constant-temperature bath and allowed to reach equilibrium, at which time the final pH measurements are made. 

The following provides a brief description of a typical experimental set-up and methods for the determination of metal-ligand binding constants using the pH titration method. 

PROCEDURE. Appropriate volumes of ligand solution, metal-ion solution, acid and distilled water are pipetted into a titration cell, usually a double-walled beaker through which thermostatted water is flowed. The solution is stirred magnetically and blanketed with nitrogen to prevent reaction with carbon dioxide (and occasionally oxygen). Increments of titrant (usually standard base) are added and the pH is recorded after the addition of each increment. 

Bjerrum, Metal Ammine Formation in Aqueous Solution, P. Haase and Son, Copenhagen, 1941. 

The correction factor C may be determined from pH measurements on appropriate acid solutions, or calculated using the Debye-Hiickel equation. For aqueous solutions at 25°C and ionic strength of 0.10, the correction factor is often taken to be -0.10 (calculated from the Debye-Hiickel equation). Experimentally measured values are similar. For the calculation of [OH ], the concentration-product value of Kw must be used at 25°C and I = 0.10, pcf w = 13.75. 

The powder diffraction experiment is the cornerstone of a truly basic materials characterization technique - diffraction analysis - and it has been used for many decades with exceptional success to provide accurate information about the structure of materials. Although powder data usually lack the three-dimensionality of a diffraction image, the fundamental nature of the method is easily appreciated from the fact that each powder diffraction pattern represents a one-dimensional snapshot of the three-dimensional reciprocal lattice of a crystal. The quality of the powder diffraction pattern is usually limited by the nature and the energy of the available radiation, by the resolution of the instrument, and by the physical and chemical conditions of the specimen. Since many materials can only be prepared in a polycrystalline form, the powder diffraction experiment becomes the only realistic option for a reliable determination of the crystal structure of such materials. 

Powder diffraction data are customarily recorded in virtually the simplest possible fashion, where the scattered intensity is measured as a function of a single independent variable - the Bragg angle. What makes the powder diffraction experiment so powerful is that different structural features of a material have different effects on various parameters of its powder diffraction pattern. For example, the presence of a crystalline phase is manifested as a set of discrete intensity maxima - the Bragg reflections - 

Fundamentals of diffraction analysis were considered in Chapter 2. 

Imaging of the reciprocal lattice in three dimensions is easily doable in a single crystal diffraction experiment. 

The method of Trumit avoids problems that may arise with a spreading solvent. However, a factor that was not studied was the effect of the electric charge carried by the protein and the accompanying electrical potential barrier produced at the interface, as discussed in Section III,C. For this reason, it is preferable, when using the Trurnit method, to have the protein at a pH close to its isoelectric point to ensure complete spreading. 

Adsorption may be followed at fluid/fluid interfaces by measuring changes in interfacial pressure, potential, or viscosity, using spread monolayers for calibration purposes. The most accurate method for measuring rates of adsorption is by the rate of increase of interfacial area at constant interfacial pressure. If (1/A) (dA/dt) is the fractional rate of increase of interfacial area expressed in sec-1 and n is the interfacial concentration in g cm-2 found from measurements on spread monolayers, then the rate of adsorption dn/dt in g cm-2 sec-1 is given by 

The rate may thus be evaluated from a plot of log A vs t. If measurements of the interfacial pressure, n, are made at a fixed interfacial area (i.e., n — t curves are obtained), the rate of adsorption at a given value of n is 

One of the most useful experimental methods to be applied to protein adsorption in recent years is the radiotracer technique (Mura-matsu, 1973). Proteins labeled with, 31I and 125I (Brash et al., 1974) and [14C]acetyl derivatives of proteins (Phillips et al., 1975) have been used as tracers. As well as measuring adsorption directly, this method has the great advantage that it can detect exchange between interface and bulk even when the total amount adsorbed does not vary. A technique that has been used to obtain independent measurements of the amount of protein adsorbed by measuring film thickness is ellipsometry (Trurnit, 1953). 

The application of infrared difference spectrometry to the measurement of protein adsorption at solid/liquid interfaces is potentially 

Three types of transfer between the electrochemical cell and the UHV enclosure have been used. In the first, the electrochemical cell is built on to the stainless steel system and the electrode is transferred directly. In the second, a glove box is used as an intermediate to the transfer which can then be made to a conventional electrochemical cell. In the third type, there is no direct transfer but electrodes prepared under identical conditions are studied in parallel by UHV electrochemical methods. 

In the discussion of transfer, it is necessary to consider the ways in which 

The sample container, suspended in the calorimeter by a small tube, was constructed of copper and had a capacity of about 106 ml. Tinned copper vanes were arranged radially from the central reentrant well, containing a heater and a platinum resistance thermometer, to the outer wall of the 

Tempering ring Leads with heaters Tube thermocouples Shield with heaters Calorimeter heater Thermometer Shield thermocouples 

The resistance of the platinum thermometer was measured by means of a Mueller bridge. The electrical input energy was determined from the measurements of the current and potential across a 100 Q Constantan wire heater and the time interval of heating. The heater current and potential were measured by means of a Wenner potentiometer in conjunction with a resistor and a volt box. The time interval of heating was measured by means of a precise interval timer. 

The calculations involved in the determination of the specific heat of a sample have been described by Stull (19). During a heat input, an electric current of / amperes flowed through the sample heater because of a voltage e impressed on the heater terminals for t seconds. The heat in calories, H, is then 

This heat input caused the temperature of the sample to go from its initial state, Th before the heat was applied, to 7, the final temperature of the sample after the sample had reached a constant temperature. Thus. Tf - T( = AT, the rise in temperature due to H, and %Tf — 77) = 7],. the average temperature of the space heat input. 

Although it is assumed that the reader is familiar with basic laboratory operations such as dissolution, evaporation, crystallization, distillation, precipitation, filtration, decantation, bending of glass tubes, preparation of ignition tubes, boring of corks, etc., a brief discussion of those laboratory operations which are of special importance in qualitative inorganic analysis, will be given here. 

Qualitative analysis may be carried out on various scales. In macro analysis the quantity of the substance employed is 0.1 to 0.5 g and the volume taken for analysis is about 20 ml. In what is usually termed semimicro analysis these quantities are reduced by a factor of 10-20, i.e. about 

05 g material and 1 ml solution are employed. For micro analysis the factor is of the order of 100-200. The special operations needed for semimicro and micro work will be discussed in somewhat more detail, together with the apparatus needed to perform these. 

It must be said that the semimicro scale is most appropriate for the study of qualitative inorganic analysis, some of the special advantages being as follows  

semimicro and micro procedures will be discussed separately in this book to cater for all requirements. The readers should familiarize themselves first with macro operations, even if they adopt the semimicro 

Direct potentiometry (emf measurements) requires the potential of indicator electrode to be determined by the potential of the redox pair under study. Sometimes this is impossible, because of the low exchange current densities and/or concentrations (particularly, at low solubilities or limited 

If voltammetric and related techniques are used, the ohmic drop should be either compensated (now this is usually done by the software or hardware of electrochemical devices [69]), or reduced by using, for example, a Luggin (Lu in-Gaber) capillary (see in Ref. [12]). Another important technical detail is that the components of reference redox systems (such as fer-rocene/ferrocenium) are frequently added immediately into the working compartment when voltammetry-hke techniques are applied. 

Applications of potentiometry are rather widespread, and its efficiency is high enough when operating with relative potential values. A mention should he made, first of all, of the determination of basic thermodynamic quantities, such as the equilibrium constants for coordination 

Other examples of the use of liquid chromatography to study adsorption isotherms and surface properties are the work of Hammers, Kos, Brederode, and De Ligny on the adsorption of a large number of organic compounds from n-hexane and dichloromethane by N-2-cyanoethyI-N-methylamino-silica and Oscik and Chojacka on the adsorption of six aromatic hydrocarbons from some mixed-solvent mobile phases by silica gel. 

There are three types of pulsed-electron generators. 

Optical absorption spectrophotometry is probably the most commonly used technique [4,a]. Reaction cells are similar to those used in flash work. Photomultipliers cover the uv-visible range the initial photoelectric signal is amplified internally, by an amoimt controlled by selection of the number of dynodes. Nanosecond equipment is commercially available. Picosecond time-resolution has been achieved [l,h]. For the infrared and Raman region, semiconductor photodiodes cover the range 400-3000 nm the vibrational spectra yield structural information about transient species much more detailed and precise than that from electronic spectra. Resonance enhancement of Raman spectra increases their intensity by a factor of 10, and makes them attractive for detection and monitoring [4,b]. They can be recorded with time-resolution down to sub-nanoseconds. Fluorescence detection is sensitive, and fast with single-photon counting or a streak camera (Section 4.2.4.2), it has been used for times down to 30 ps after an electron pulse. Conductivity also provides a fast and sensitive technique [4,c,d,l,m], especially in hydrocarbon solutions, where 

Computerisation for control and automation in pulse radiolysis [4,hJ]. The great volume of experimental results obtained by pulse radiolysis may be attributed to several factors. The radiation sources work reliably and continuously over long periods. The detection techniques mostly allow rapid replication. Digitization is routinely available for times down to about one nanosecond. One consequence is that, with a dedicated computer, the raw data can be quickly analysed on-line, and validity checks can be made on each set of data [4,h]. Another is that the operation of pulse-radiation apparatus can be automated [4,j] for example, a series of experiments at different temperatures over different periods of time, with different radiation doses, and with spectrophotometric detection at a series of 

Some of the more common methods for investigations of reaction kinetics are listed in Table 6.1. 

For the characterization of zeolites and of processes running via their internal surface a number of different physical analytical methods have been used e.g. 

When applied to surface studies, vibrational spectroscopy provides primarily structural data such as molecular symmetry, geometry and bonding, when combined with statistical thermodynamics it allows the estimation of thermodynamic properties. In time-resolved experiments it monitors the transient response of surface species, thus giving an idea of possible intermediates involved in transformations on the solid surface and therefore being of high importance for kinetic investigations. 

Whether the probing particle is a photon, an electron, an atom or a neutron, vibrational spectroscopy may be divided into the following groups (see e.g. [16]) 

While all of them have been successfully applied to flat surfaces, in the case of zeolites only (i) and (iv) are of essential interest. Due to its significance. Chapter 4 has been devoted to neutron scattering studies. In the following we shall therefore deal essentially with experiments obtained by interaction of infrared radiation with vibrationally changing dipole moments. 

There are several kinds of techniques applied to the study of zeolites  

The current focus is on improving the stability of materials while maintaining faster responses and high diffraction efficiencies at lower electric fields. 

In any given material, the relaxation modulus will reflect the response of the material on different timescales. To make a measurement, materials are deformed under a periodic load with frequency w. Then, G and G are measured across a wide range of frequencies (typically three to four decades). Measurements of G and G can be used to characterize the mechanical properties of soft materials, including polymer networks and colloidal systems. The technique is also known as mechanical spectroscopy. In a viscoelastic material, the elastic modulus will cross over the viscous modulus at the transition point from viscous to elastic bulk behavior and indicates a possible sol-gel transition or the onset of rubbery behavior in a polymer network. 

Jakobsen, Chemical Reactor Modeling, DOI 10.1007/978-3-319-05092-8 13, Springer International Publishing Switzerland 2014 

A critical review of some of the currently used measurement techniques for characterizing multiphase flow systems is presented, describing the working principles of the individual techniques and identifying the averaging procedures that have been applied interpreting the data for each technique. 

The available commercial equipment can be divided into three types. These may be characterized as static, volumetric units, static gravimetric units and flow, thermal conductivity units these are all available as single point or multipoint, manual or automatic. 

Electrons of various energies, as well as photons in the x-ray or ultraviolet energy ranges, are used to probe the electronic structure. The spectroscopic 

Electron energy loss experiments give information about the gap states, the position and shape of the deep level absorption thresholds and the collective plasmon excitations. The gap widths of simple oxides typically range from 3 to 10 eV  

Photon spectroscopies include photoemission in the x- and ultraviolet photon ranges (XPS and UPS, respectively) and x-ray absorption. In 

We can also resort to a diametric compression test, also known as the Brazilian test, for evaluating the tensile stress [CLA 70]. This test, which is particularly suitable for raw materials or for bars (non-sintered products), consists of compressing a pellet monoaxially (diameter D , thickness t) following a diametric direction. The breaking stress is then deduced from the mpture load using the following relationship  

The surface of a test specimen is polished to obtain mirror finish and then is indented, generally with a Vickers probe. Knowing Young s modulus E (Pa) and the load on the probe P (N), hardness measurements H (in Pa), and length of cracks 2c (m), which radiate from the edges of the indentation, we can calculate Kj. (Pa.Vm). Other works are Ml of equations, and the following are the most frequently used ones  

This method is not self-consistent and the prefactor on the RHS is a result of an ejqterimental cahbration on test specimens with known toughness values. 

An indented test specimen is subjected to a bend test, with the indentation located at the centre of the face in tension. The stress measured at fracture enables the calculation of toughness from the indentation load P, Young s modulus E and hardness H [CHA 81]  

This method helps to avoid the often inaccurate measurement, of the length of cracks resulting from the indentation. 

One cannot overemphasize the importance of using a high-purity molten salt solvent for electroanalytical measurements. The method of purification differs from one molten salt solvent system to another and will be discussed briefly for each melt system however, removal of water without hydrolysis is commonly an important consideration. Clearly the exposure of the melt to the atmosphere must be avoided in this respect the use of sealed cells is safer than the use of cells containing ball or standard taper joints, gaskets, or flanges. If a cover gas (commonly argon or helium) is to be used, it should be of the highest purity available. 

The subject of reference electrodes in molten salts has been treated extensively by Laityand Alabyshev et The applicability of a 

Quite frequently a large noble metal electrode is used as a quasireference electrode (QRE) in electroanalytical work. Such an electrode is equivalent to the mercury pool electrode in conventional polarography. Since the QRE is normally used in a three-electrode system, the current passing through the reference electrode is extremely small ( 10 A). Therefore, the potential of the QRE remains quite constant ( 10 mV for prolonged periods of time) provided oxidants or reductants are not added to the melt. In that case the potential shifts in the direction expected from the Nernst equation. 

---

The application of IP can facilitate or even make feasible some experimental techniques in NR, where the neutron source intensity poses a problem for imaging with radiographic films. 

An interesting experimental technique is heat development of nuclei. The liquid is held at the desired temperature for a prescribed time, while nuclei accumulate they are then made visible as crystallites by quickly warming the solution to a temperature just below Tq, where no new nuclei form but existing ones grow rapidly. 

The remainder of the chapter is concerned with increasingly specialized developments in the study of gas adsorption, and before proceeding to this material, it seems desirable to consider briefly some of the experimental techniques that are important in obtaining gas adsorption data. See Ref. 22 for a review of traditional methods, and Ref 23 for lUPAC (International Union of Pure and Applied Chemistry) recommendations for symbols and definitions. 

The liquid-solid interface, which is the interface that is involved in many chemical and enviromnental applications, is described m section A 1.7.6. This interface is more complex than the solid-vacuum interface, and can only be probed by a limited number of experimental techniques. Thus, obtaining a fiindamental understanding of its properties represents a challenging frontier for surface science. 

Tanaka K and Tokuda K 1996 In vivo electrochemistry with microelectrodes Experimental Techniques in Bioelectrochemistry ed V Brabec, D Walz and G Milazzo (Basel Birkhauser)... 

Many experimental techniques now provide details of dynamical events on short timescales. Time-dependent theory, such as END, offer the capabilities to obtain information about the details of the transition from initial-to-final states in reactive processes. The assumptions of time-dependent perturbation theory coupled with Fermi s Golden Rule, namely, that there are well-defined (unperturbed) initial and final states and that these are occupied for times, which are long compared to the transition time, no longer necessarily apply. Therefore, truly dynamical methods become very appealing and the results from such theoretical methods can be shown as movies or time lapse photography. 

Experimental techniques based on the application of mechanical forces to single molecules in small assemblies have been applied to study the binding properties of biomolecules and their response to external mechanical manipulations. Among such techniques are atomic force microscopy (AFM), optical tweezers, biomembrane force probe, and surface force apparatus experiments (Binning et al., 1986 Block and Svoboda, 1994 Evans et ah, 1995 Israelachvili, 1992). These techniques have inspired us and others (see also the chapters by Eichinger et al. and by Hermans et al. in this volume) to adopt a similar approach for the study of biomolecules by means of computer simulations. 

The input to a minimisation program consists of a set of initial coordinates for the system. The initial coordinates may come from a variety of sources. They may be obtained from an experimental technique, such as X-ray crystallography or NMR. In other cases a theoretical method is employed, such as a conformational search algorithm. A combination of experimenfal and theoretical approaches may also be used. For example, to study the behaviour of a protein in water one may take an X-ray structure of the protein and immerse it in a solvent bath, where the coordinates of the solvent molecules have been obtained from a Monte Carlo or molecular dynamics simulation. 

With all-atom simulations the locations of the hydrogen atoms are known and so the order parameters can be calculated directly. Another structural property of interest is the ratio of trans conformations to gauche conformations for the CH2—CH2 bonds in the hydrocarbon tail. The trans gauche ratio can be estimated using a variety of experimental techniques such as Raman, infrared and NMR spectroscopy. 

Ihe rule-based approach to protein structure prediction is obviously very reliant on th quality of the initial secondary structure prediction, which may not be particularly accurate The method tends to work best if it is known to which structural class the protein belongs this can sometimes be deduced from experimental techniques such as circular dichroism... 

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