Modular structures phases

In the previous sections composition variation has been attributed more or less to point defects and extensions of the point defect concept. In this section structures that can be considered to be built from slabs of one or more parent structures are described. They are frequently found in mineral specimens, and the piecemeal way in which early examples were discovered has led to a number of more or less synonymic terms for their description, including intergrowth phases, composite structures, polysynthetic twinned phases, polysomatic phases, and tropochemical cell-twinned phases. In general, they are all considered to be modular structures. 

Modular structures are those that can be considered to be built from slabs of one or more parent structures. Slabs can be sections from just one parent phase, as in many perovskite-related structures and CS phases, or they can come from two or more parent structures, as in the mica-pyroxene intergrowths. Some of these crystals possess enormous unit cells, of some hundreds of nanometers in length. In many materials the slab thicknesses may vary widely, in which case the slab boundaries will not fall on a regular lattice and form planar defects. 

The design can be made for homopolymer, random copolymer or heterophasic impact copolymer. The modular structure of the process is such that a Spherizone process plant can be upscaled in successive stages, starting with a basic setup for monomodal operations and later adding the barrier recovery section and a fluid bed gas-phase reactor for the production of bimodal and impact copolymer, respectively. 

Modular structures can be built from slabs of the same or different compositions, and the slab widths can be disordered, or ordered in a variety of ways. The simplest situation corresponds to a material built from slabs of only a single parent phase and in which the slab thicknesses vary widely. In this case, the slab boundaries will not fall on a regular lattice, and they then form planar defects, (Figure 8.3), which are two-dimensional analogues of the point defects described above. 

A change in chemical composition is not a mandatory prerequisite for the formation of modular structures. A typical example of a structure built from displaced slabs but without change of composition is provided by the ordered alloy phase CuAu II, (Figure 8.7a). This can be regarded as made up of slabs of another ordered alloy, CuAu I, each of which is five unit cells in thickness, (Figure 8.7b). 

The following status applies to the machine s modular structural units during the holding pressure phase ... 

As well as phases with an ABX composition, large numbers of modular structures have been prepared, all of which are built up, at least in part, from fragments, usually slabs, of perovskite-like stmcture. The formulae of these are not easily reconciled with a composition of ABX until the sttuctural building principles have been found and the nature of the interfaces between the various slabs is clarified. 

There are large numbers of these reactions described in the literature. The transformation of Dion-Jacobson phases into the corresponding Ruddlesden-Popper phases is often the first step in making new compounds. Ruddlesden-Popper phases can, in most cases, be made by heating the corresponding Dion-Jacobson solid in the vapour of an alkali metal, lithium being the exception. These Ruddlesden-Popper structures can then be transformed into modular structures separated by A and OH- or A and Cl- (Figure 4.16). 

When the aluminum content exceeds 8 %, the alpha-beta duplex structures appear. The beta phase is a high-temperature phase retained at room temperature on fast cooling from 565°C (1050°F) or above. Slow cooling or long exposure at temperatures from 320 to 565°C (610 to 1050°F) tends to decompose the beta phase into a britde alpha + gamma-2 eutectoid having either a lamellar or modular structure. The beta phase is less resistant to corrosion than the alpha phase, and eutectoid structures are even more susceptible to attack. 

Regarding the applicability of the guideline with its five phases and six CMs, the modular structure of the guideline, as depicted in Fig. 1.15 enables it to scale its contents as applied to a specific company. One opportunity to reduce the number of analyzed customer segments arises by applying all phases depicted in Fig. 1.11, but conducting the analysis for just one customer segment, one product, or one business unit. 

D. Stones, S. Manku, X. Lu, D. G. Hall, Modular solid-phase synthetic approach to optimize structural and electronic properties of oligohoronic acid receptors and sensors for the aqueous recognition of ohgosaccharides. Chemistry 2004,10, 92-100. 

Muller, A., Drese, K., Gnaser, H., Hampe, M., Hessel, V, Lowe, H., Schmitt, S., Zapf, R., Fast preparation and testing methods using a micro-structured modular reactor for parallel gas phase catalyst screening, Catal. Today 81 (2002) 377-391. 

A formal constructability VIP workshop conducted in the conceptual phase (FEL-I) should focus on the overall project construction strategies regarding site layout, construction and turnaround laydown areas, access to the site for large equipment and modules, modularization, sequencing of heavy lifts, limitations regarding procurement, limitations regarding fabrication and transport, area labor limitations, and coordination with any existing or nearby structures or facilities. 

Figure 3.2. The chemical diversity that is characteristic of NPs can be considered to arise in two phases. In the first phase, a few precursors are joined together in a few similar ways (using a modular or iterative processes) to produce families of structures that provide the basic carbon skeletons that characterise the group. In the second phase, enzymes with broad substrate tolerances tailor the skeletons in versatile ways to generate even greater diversity.

As already stated, the spectrum of reaction types, which have been successfully adapted to the solid-phase format, has expanded noticeably over the last few years. The examples listed above illustrate the fact that a remarkable toolbox is now available to the organic chemist, whose challenge is to creatively combine reactions to powerful modular approaches with broad validity for whole sets of building blocks. Achievements in this area will pave the way toward molecular diversity for lead discovery, as well as efficient analoging of target structures. 

Figure 4.13 Structure of a solution-phase primary modular library L12 based on a chalcone core and of several derived libraries L13-L21.

---