Solid-state techniques

The most widely studied slice-selection technique uses spin-locking in a magnetic field gradient (Fig. 5.3.14) [Haf2]. It is applicable not only to solids, but also to liquids [Rom2, Winl] (cf. Section 9.1.1). The spin-lock induced slice excitation (SLISE) consists of a hard 90° pulse followed by a period where the transverse magnetization is locked in the 

With this technique, the spatial resolution is not limited by the requirement that B must be larger than the largest frequency offset. In fact, selective excitation can improve 

A solid-state variant of the DANTE sequence (Fig. 5.3.15) is obtained by replacing the rf pulses and the free precession periods of the original sequence by line-narrowing multi-pulse sequences [Carl, Corl, Flepl, Hep2J. Such DANTE sequences can be used for selective excitation in solid-state spectroscopy (cf Fig. 7.2.8) and for slice selection in solid-state imaging (Fig. 5.3.16). 

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No experimental technique exists for determining I-structures in either the liquid or the solid state. Techniques do exist for obtaining information on both the V- and D-structures of liquid water the results of applying these techniques are considered next. 

In molecular DFT calculations, it is natural to include all electrons in the calculations and hence no further subtleties than the ones described arise in the calculation of the isomer shift. However, there are situations where other approaches are advantageous. The most prominent situation is met in the case of solids. Here, it is difficult to capture the effects of an infinite system with a finite size cluster model and one should resort to dedicated solid state techniques. It appears that very efficient solid state DFT implementations are possible on the basis of plane wave basis sets. However, it is difficult to describe the core region with plane wave basis sets. Hence, the core electrons need to be replaced by pseudopotentials, which precludes a direct calculation of the electron density at the Mossbauer absorber atom. However, there are workarounds and the subtleties involved in this subject are discussed in a complementary chapter by Blaha (see CD-ROM, Part HI). 

The main drawbacks of solid-state techniques are that (i) the distribution of the dopant in the host lattice may not be even since the precursors are not mixed on the atomic scale, and (ii) particle growth cannot be easily controlled and so milling and sieving is necessary. 

A.K. Cheetham and P. Day, Solid State Techniques, Oxford University Press, New York, 1987. 

Spectroscopic analyses of solid-state reactions must first use solid-state techniques (IR, UV/Vis, Raman, luminescence, NMR, ESR, CD, X-ray powder diffraction, DSC, etc.) in order to secure the solid-state conversion, before the solution techniques (detection of minor side products, specific rotation, etc.) are applied. 

Azo couplings of diazonium salts with primary or secondary amines give triazenes which are normally hard to get in pure form. It is, however, quite easy to get triazenes with aliphatic or aromatic amines if solid-state techniques are applied that give rise to pure products in quantitative yield [98-100]. The di-methyltriazenes 309 have been quantitatively obtained by very cautious addition of gaseous dimethylamine (exothermic ) [98] (Scheme 47). Extreme care has to be taken for safety reasons ... 

Later, Kariv-Miller et al. have studied the properties of tetraalkylammonium amalgams both in situ, applying electrochemical techniques [218], and ex situ, applying solid-state techniques [219, 220]. It has been concluded that the solid products, which belong to R4N metals, are formed in chemically and electrochemi-cally reversible process ... 

Many of the high Tc ceramic superconductors can be prepared by similar solid state techniques. In the Bi-Sr-Ca-Cu-O system Bi2Os, SrCOs, CaCOs or Ca(OH)2, and CuO are often used... 

Along similar lines, carbon-13 magnetic resonance has been applied to coal and to the elucidation of the character of soluble coal fractions and other coal-derived materials (Bartuska et ah, 1978 Ladner and Snape, 1978 Miknis, 1988). In fact, it is the advances in carbon-13 magnetic resonance that have brought new thoughts to the chemical nature of, and structural types in, coal. The technique brought with it the innovative solid-state techniques that allowed coal to be viewed in its natural solid state without invoking the criterion of sample solubility. This removed the need for dissolution of coal fractions and the often... 

The main purpose of quantum-chemical modeling in materials simulation is to obtain necessary input data for the subsequent calculations of thermodynamic and kinetic parameters required for the next steps of multiscale techniques. Quantum-chemical calculations can also be used to predict various physical and chemical properties of the material in hand (the growing film in our case). Under quantum-chemical, we mean here both molecular and solid-state techniques, which are now implemented in numerous computer codes (such as Gaussian [25], GAMESS [26], or NWCHEM [27] for molecular applications and VASP [28], CASTEP [29], or ABINIT [30] for solid-state applications). 

In the following pages, an attempt will be made to describe many of the properties of the solid state that come into play and need to be considered when formulating low-dose pharmaceuticals. The solid forms may be broadly classified as crystalline and amorphous and then describe the solid-state techniques used in their characterization. Many of the quantitative aspects and their respective advantages and disadvantages will be described. Finally, a few approaches will be described that may be used to investigate the effect of formulation on the low-dose active ingredient in the tablet. 

TABLE 12.2 Common Solid-State Techniques and Approximate Sensitivities to Physical Forms... 

Spectroscopic methods are nondestructive and can be used in conjunction with other solid-state techniques (TGA, microscopy, DSC, XRD) for the quantitative analysis of... 

The present contribution does not include solid state techniques to measure electrochemical parameters, nor does it consider applications of solid state electrochemistry. Such topics will be dealt with in a second part which will appear separately.1... 

The kinetics of solid state chemical reactions are ordinarily limited by the rate at which reactant species are able to diffuse across phase boundaries and through intervening product layers. As a result, conventional solid state techniques for manufacturing ceramic materials invariably require the use of high processing temperatures to ensure that diffusion rates are maintained at a high level, thus allowing chemical reaction to proceed without undue kinetic constraint. ... 

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