Bound aggregate

Molecular clusters are weakly bound aggregates of stable molecules. Such clusters can be produced easily using supersonic expansion, and have been extensively studied by both electronic and vibrational spectroscopy [146,... 

Molecular crystals are loosely bound aggregates of molecules which possess a large amount of internal stability, such as crystals of highly stable organic molecules. Since the constituent molecules are almost completely saturated, crystals of this type usually exert little catalytic activity they do not interact strongly with adsorbed molecules. 

Figure 8.4 Nano-Ti02 in fafade run-off (a, b) and in an urban stream (c). Single nanopartides or small matrix-bound aggregates have been found. Reprinted from [7], (2008), with permission from Elsevier.

In the melted state elementary sulfur is an excellent binder for aggregates such as sand, gravel, crushed stone, and similar materials. When a hot sulfur aggregate mixture is left to set, a material of concretelike hardness is obtained. This property leads to the term sulfur concrete or sulfur mortar, which is wrong strictly speaking, since the word concrete is used to refer to a product in which aggregates are bound with hydraulic products such as cement or with limestone. However, since polymer-bound aggregates recently developed to industrial maturity have been called polymer or synthetic resin concrete, the term sulfur concrete is maintained in this chapter. 

The most important compound is lithium aluminum hydride, LiAlHt, a nonvolatile crystalline solid, stable below 120°C, that is explosively hydrolyzed by water. In the crystal there are tetrahedral AlHf ions with an average A1H distance of 1.55 A. The Li+ ions each have four near hydrogen neighbors (1.88 - 2.00 A) and a fifth that is more remote (2.16 A). Lithium aluminum hydride is soluble in diethyl and other ethers and can be solubilized in benzene by crown ethers. In ethers, the Li+, Na+, and R4N+ salts of A1H and GaH4 tend to form three types of species depending on the concentration and on the solvent, namely, either loosely or tightly bound aggregates or ion pairs. Thus LiAlHt is extensively associated in diethyl ether, but at low concentrations in THF there are ion pairs. Sodium aluminum hydride (NaAlH) is insoluble in diethyl ether. 

Loosely bound aggregates (chemical effects) are formed with the hydrocarbons acting as electron donors (Lewis base) and the solvents acting as electron acceptors (Lewis acid). The hydrocarbon that forms the most stable complex with the solvent experiences a decrease in volatility. Electron donors are rated by ionization potential, and electron acceptors are rated by their electron affinities. The selectivity will be higher, the larger the difference in ionization potential between the hydrocarbons and the larger the electron affinity of the solvent (9). While data on ionization potentials of hydrocarbons can be found (15, 16), electron affinities data are rare because of difficulties in their experimental determination. Prausnitz and Anderson (8) recommend that the sigma scale, proposed by Hammett (17), be used to determine approximately the solvents relative ability to form complexes with the two hydrocarbons. Attempts by this author, however, to use this scale were not conclusive. Prausnitz and Anderson (8) should be consulted to understand better the physical and chemical effects. 

Togkalidou, T. Tung, H.-H. Sun, Y. Andrews, A.T. Braatz, R.D. Parameter estimation and optimization of a loosely bound aggregating pharmaceutical crystallization using in situ infrared and laser backscattering measurements. Ind. Eng. Chem. Res. 2004, 43 (19), 6168-6181. 

We prepared effective LSX type adsorbents on a laboratory scale as essentially pure self-bound aggregates. At 50°C under continual circulation 1n a highly alkaline solution of mixed... 

THEORETICAL TOOLS FOR THE STUDY OF THE NATURE OF WEAKLY BOUND AGGREGATES... 

Theoretical Tools for the Study of the Nature of Weakly Bound Aggregates 69... 

Bound aggregate is an aggregate which is coated and bound with a cementitious, or bituminous binder, as in bituminous macadam, or concrete. 

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