Space fillers

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

An enormous variety of solvates associated with many different kinds of compounds is reported in the literature. In most cases this aspect of the structure deserved little attention as it had no effect on other properties of the compound under investigation. Suitable examples include a dihydrate of a diphosphabieyclo[3.3.1]nonane derivative 29), benzene and chloroform solvates of crown ether complexes with alkyl-ammonium ions 30 54>, and acetonitrile (Fig. 4) and toluene (Fig. 5) solvates of organo-metallic derivatives of cyclotetraphosphazene 31. In most of these structures the solvent entities are rather loosely held in the lattice (as is reflected in relatively high thermal parameters of the corresponding atoms), and are classified as solvent of crystallization or a space filler 31a). However, if the geometric definition set at the outset is used to describe clathrates as crystalline solids in which guest molecules... 

Solvent molecules may play a variety of roles in liquid phase reactions. In some cases they merely provide a physical environment in which encounters between reactant molecules take place much as they do in gas phase reactions. Thus they may act merely as space fillers and have negligible influence on the observed reaction rate. At the other extreme, the solvent molecules may act as reactants in the sequence of elementary reactions constituting the mechanism. Although a thorough discussion of these effects would be beyond the scope of this textbook, the paragraphs that follow indicate some important aspects with which the budding ki-neticist should be familiar. 

All of our observations lead us to believe that the crystallization of VPI-5 involves a solid phase reordering process. This solid phase transformation does not involve TBA as either a template or a space-filler. TBA may be present in the solid phase in very low concentrations that are below detection limits by IR and NMR and may still play some role in the crystallization mechanism. Also, it may serve to moderate the pH of the reaction mixture during its formulation and heating such that certain aluminophosphate precursor species are present in the solid phase. Here we will explore these two possibilities in order to further understand the crystallization process for forming VPI-5. 

In our previous papers (refs. 4,5) we described syntheses of VPI-5 using DPA and TBA. Since that time we have been able to crystallize VPI-5 using many other organics such as diisopropylamine, dipentylamine (DPentA), triethanolamine (TEOA), triisopropanolamine (TIPOA), cyclopentyl amine, and cyclohexyl amine at synthesis temperatures from 120 to 150 C. The wide variety of organics able to crystallize VPI-5 suggests further that the organic does not act as a template and from chemical analyses it is clear that it does not act as a space-filler. 

Bloactive Glass-Ceramic Bone Space Fillers... 

Protection from excessive transmission of reactive gases (atmospheric oxygen, inert head-space filler gas, or other organic vapors) into or out of the packaging system... 

The A/A values have been found to correlate extremely well with aromatic molecules van der Waals volumes, suggesting that the liquid cavity model in which the aromatic is a space filler is an accurate one. The constancy of the A/A value suggests that the cation-anion association produces fairly well-defined solution voids with a volume that is invariant with change of solvent. 

Figure 19 Concept of Space Filler Determination of molecular length...

Fig. 25 The 13C NMR signal in CDC13 of C60, in the absence and presence of the nanotubes (left). Looking down the axis of a space filler model of the nanotube (centre). Looking laterally at a ball and stick model of the helix, as found in the molecular modelling studies (right). AMI semi-empirical level using Hyperchem package the starting geometries for the nanotube and fullerenes were obtained from X-ray data for the free nanotube and the free fullerene and convergence criterion was 0.01 kcal A 1 mol-1...

The TEA does not appear to act as a template or space filler. TEA is quickly expelled into solution and is not detected in any of the heated samples. (It is not detected during the rapid VPI-5 crystallization that occurs between 45 and 60 minutes). The possible role of TEA as a catalyst for the formation of the VPI-5 structure in concentrations below the detection limit can not be ruled out, however TEA seems to mainly serve as an effective pH moderator. 

Many years ago, expansion joints in concrete floors were frequently filled with hot asphalt, and it was sometimes used as a space filler in void areas to prevent fluid penetration. Neither of these applications is recommended. If extruded by the two sides of a closing joint, when the structure expands in hot weather, it stays extruded when the weather cools off, and the structure shrinks back to its old size, leaving a void to be filled with rainwater, etc. (which can freeze causing expansion damage) or with chemicals which can attack the concrete. 

Thus, the U V ratio plays a key role in the type of polymerization and on the obtained 2-D or 3-D structural architectures. However, the role of the counter ion is not obvious. It can be suggested that, as already observed for other uranyl oxoanion compounds, the counter ions have no template effects but rather act as space fillers within the uranium vanadate substructure. 

The fetal circulation contains high levels of HA, as do fetal tissues, and amniotic fluid [48]. Some of the immune suppression of the fetus is provided by HA, which, as a space filler, sequesters immune cell receptors and prevents interactions with ligands. 

Zeolites are a subclass of microporous materials in which the crystalline inorganic framework is composed of four-coordinated species interconnected by two-coordinated species. Traditionally these materials are aluminosilicates however, many different compositions have been synthesized. The templates used in the synthesis of microporous materials are typically small ionic or neutral molecular species. The function of the template in the synthesis of microporous materials is little understood, and there are at least four different modes by which an additive can operate in a zeolite synthesis a) It may act as a space filler occupying the voids in the structure, thereby energetically stabilizing less dense inorganic framework b) the additive may control the equilibria in the synthesis mixture, such as solution pH or complexation equilibria c) it may preorganize the solution species to favor the nucleation of a specific structure d) it may act as a true template determining the size and the shape of the voids in the structure. 

A variety of porous 3-dimensional (3-D) 4-connected AIPO4 nets have been synthesised, some of which have the same topologies as their zeolite counterparts while others have novel topologies [13, 14]. As with porosils and silica-rich zeolites, basic organic species are involved in their synthesis, to occupy channels and cavities as space fillers and stabilisers. AlPO s have... 

With a moisture sensitive product, moisture pick by this means can be quite rapid. Alternative materials to wool are either plastic shapes or plugs of expanded polystyrene, polyethylene or polyurethane foams. Closures can also be obtained which incorporate spring extensions. Such closures may have chambers which hold desiccants. Transit tests (vibration/drops) would be advised to check whether space fillers are necessary. 

Fig. 2. Ball and stick representation of BuSi(OSiMe20H)3-toluaie as result of an X-ray single crystal structure analysis. The methyl substituents on the carbon and silicon atoms are drawn as sticks. The Si-O distances in the Si-OH parts of the molecule (Si-0 ea = 1.622(6) A) are distinctly larger than those in the Si-O-Si bridges (Si-Omean = 1.570(5) A). In the crystal the molecules form dimers through hydrogen bridging with a crystallographic inversion center in the middle of the aggr ate. The toluene molecule serves as space filler in the crystal lattice [18],...

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