Poor crystallinity

Besides the amorphous red P which is a commercial product, there are perhaps five other crystalline or poorly crystalline red modifications that are not produced commercially. These include a triclinic, an orthorhombic, a high temperature form, and two poorly crystalline forms. Red phosphoms varieties are rather stable in air and are of lower reactivity than white phosphoms. 

At low relative humidities, adsorption is due to interaction of water with accessible hydroxyl groups. These are present on the lignin and on the carbohydrates ia the noncrystalline or poorly crystalline regions. The high differential heat of adsorption by dry wood, - 1.09 kJ/g (469 Btu/lb) water. 

Fluid coking has several characteristics that make it undesirable for most petroleum coke markets. These characteristics are high sulfur content, low volatility, poor crystalline structure, and low grindability index. 

Many studies have been made of the rates of water evolution from layer-type silicate minerals which contain structural hydroxyl groups (clays and micas). Variations in composition of mineral specimens from different sources hinders comparison of the results of different workers. Furthermore, the small crystallite sizes and poor crystallinity that are features of clays limit and sometimes prevent the collection of ancillary observations (e.g. microscopic examination and diffraction measurements). 

A recent approach was based on the DMAc/LiCl and N-methyl-2-pyrrohdone/IiCl solvent systems [252,253] that enabled better dry tensile strengths although they did not provide adequate wet tenacities, due to poor crystallinity and poor consohdation of the fibre. A further problem was the... 

The sharp peak around OV in Fig. 4 may be caused by the insertion of protons into the empty A sites of the poorly crystalline WO3 with a distorted perovskite structure. Amorphous... 

Bonn Poorly crystalline 0.2M Tamm s solution pH 3.25 shake in darkness for 4 h... 

As previously discussed, compound form differs markedly between early discovery and the late discovery/development interface. The early discovery compound is poorly characterized as to its crystalline form - it may be nonsolid, amorphous, or possibly crystalline but uncharacterized as to polymorphic form. The late discovery/development interface compound is crystalline as defined by phase-contract microscopy or powder X-ray diffraction, and its polymorphic and salt form is frequently characterized. This difference has profound implications for the design of a discovery solubility assay. The key question is this Is it better to design an early discovery solubility assay as a separate type of experiment, or is it better to try to automate a traditional thermodynamic solubility assay to handle the very large number of compounds likely to be encountered in early discovery Another way to state this question is this Does it make sense to run a thermodynamic solubility assay on poorly crystalline early discovery compounds This is the type of question about which reasonable people could disagree. However, this author does have a distinct opinion. It is much better to set up a distinctively different solubility assay in early discovery and to maintain a clear distinction between the assay type appropriate in early discovery and the assay type appropriate at the late discovery/ development interface. Two issues are relevant to this opinion One relates to the need for a solubility assay to reflect/predict early discovery stage oral absorption and the other relates to people/chemistry issues. 

In general it has been found that polypyrrolc is extremely poorly crystalline, limiting the information that can be obtained from direct structural techniques such as X-ray crystallography, and hence much of our knowledge has been obtained from indirect measurements and/or experiments on model compounds (e.g. X-ray studies on pyrrole trimers and dimers). It is now generally accepted that the ideal structure of the polymer is a planar (a a>bonded chain in which the orientation of the pyrrole molecules alternates. 

The authors postulated that since it was obvious from X-ray data that polypyrrole is a poorly crystalline material, for which there is no evidence for long conjugation lengths, it does not seem unreasonable to suppose that there is a wide distribution of conjugation lengths, a hypothesis supported by other workers. The cations of shorter conjugated units will be reduced... 

The inkjet-printed (or inkjetted ) TFT operated with a mobility of 6.5cm2/ Vs and an on/off ratio of three digits as shown in Fig. 5.6b. This low mobility is attributed to the poor crystallinity and rough surface, whereas the large off current, which was confirmed to be the current between source and drain rather than a leakage current through the gate insulator, is also attributed to... 

SEM-EDS. All the samples of fresh ochre-precipitates exhibit XRD patterns typical of poorly crystalline material, such as ferrihydrite (Schwertmann Cornell 2000). They present the strongest band centred at 2.56A, corresponding to the (110) reflection of 6-line ferrihydrite, as well as the characteristic poorly resolved reflections at d spacings 1.47 - 1.73 - 1.98 and 2.24k. 

In view of the problems associated with the expanding 2 1 clays, the smectites and vermiculites, it seemed desirable to use a different clay mineral system, one in which the interactions of surface adsorbed water are more easily studied. An obvious candidate is the hydrated form of halloysite, but studies of this mineral have shown that halloysites also suffer from an equally intractable set of difficulties (JO.). These are principally the poor crystallinity, the necessity to maintain the clay in liquid water in order to prevent loss of the surface adsorbed (intercalated) water, and the highly variable morphology of the crystallites. It seemed to us preferable to start with a chemically pure, well-crystallized, and well-known clay mineral (kaolinite) and to increase the normally small surface area by inserting water molecules between the layers through chemical treatment. Thus, the water would be in contact with both surfaces of every clay layer in the crystallites resulting in an effective surface area for water adsorption of approximately 1000 tor g. The synthetic kaolinite hydrates that resulted from this work are nearly ideal materials for studies of water adsorbed on silicate surfaces. 

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