Crystalline particle

Figure 14-15 shows three X-ray diffraction patterns obtained from small crystalline particles of metallic copper, aluminum, and sodium. The qualitative similarity of the patterns given by copper and aluminum shows that they have the same crystal packing. Careful measurements of the spacing of the lines indicate that the atoms... 

DeSa, R., Hastings, J. W., and Vatter, A. E. (1963). Luminescent crystalline particles an organized subcellular bioluminescent system. Science 141 1269-1270. 

Progressive growl of crystalline particles of t e product phoir I---------------------------... 

There is no fundamental theory for electro-crystallization, owing in part to the complexity of the process of lattice formation in the presence of solvent, srrrfactants, and ionic solutes. Investigations at the atomic level in parallel with smdies on nonelectrochemical crystallization wotrld be rewarding and may lead to a theory for predicting the evolution of metal morphologies, which range from dertse deposits to crystalline particles and powders. 

As an example, consider the following. Suppose we have a crucible half-filled with a powder. We now fill the crucible with another powder of different composition and then heat the filled crucible. Any solid state reaction which does occur can only do so at the boundary of the two layers of powders. If the reaction is A -t- B = AB, then we find that the reaction product, which is also a solid, forms as a phase boundary between the two layers. The same condition exists in a solid state reaction between two crystalline particles having differing compositions. That is, they can only react at the interface of each particle. This is illustrated in the following diagram, which is a model of how the components react through a phase boundary ... 

Besides electronic effects, structure sensitivity phenomena can be understood on the basis of geometric effects. The shape of (metal) nanoparticles is determined by the minimization of the particles free surface energy. According to Wulffs law, this requirement is met if (on condition of thermodynamic equilibrium) for all surfaces that delimit the (crystalline) particle, the ratio between their corresponding energies cr, and their distance to the particle center hi is constant [153]. In (non-model) catalysts, the particles real structure however is furthermore determined by the interaction with the support [154] and by the formation of defects for which Figure 14 shows an example. 

Figure 7. High resolution TEM image of a single Au nanoparticle observed inside a stem of alfalfa seedlings grown in gold emiched medium. The inset corresponds to the fast Fourier transform of the crystalline particle. (Reprinted from Ref. [28], 2002, with permission from American Chemical Society)...

The homogeneity of the product should be addressed. The adequacy of mixing processes should be shown (and confirmed with appropriate process validation data) and potential segregation discussed (as affected by surface properties, crystallinity, particle size, etc.). The Ph Eur uniformity of content requirements should apply to the dosage forms and uniformity of distribution needs to be shown between batches and within batches. The need for appropriate routine tests as part of the release specification should be discussed. 

Jang, Y.J., Simer, C. and Ohm, T. (2006) Comparison of zinc oxide nanoparticles and its nano-crystalline particles on the photocatalytic degradation of methylene blue. Materials Research Bulletin, 41,67-77. 

Raman and resonance Raman (RR) measurements of fullerene-like particles of MoS2 recently have been carried out (93). By using 488-nm excitation from an Ar ion laser light source, the two strongest Raman features in the Raman spectrum of the crystalline particles, at 383 and 408 cm-1, which correspond to the E g and Aig modes, respectively (see Table I), were found to be dominant also in IF-MoS2... 

Bismuth Molybdates. Bismuth molybdates are used as selective oxidation catalysts. Several phases containing Bi and/or Mo may be mixed together to obtain desired catalytic properties. While selected area electron diffraction patterns can identify individual crystalline particles, diffraction techniques usually require considerable time for developing film and analyzing patterns. X-ray emission spectroscopy in the AEM can identify individual phases containing two detectable elements within a few minutes while the operator is at the microscope. 

Gel. A jelly-like substance formed as solutes (materials in solution) from submicroscopic crystalline particle groups that capture much or all of the solvent in their interstices or structure. Usually, the solutes are a small proportion, maybe 1-2% of the gel. Gels can be used for filters and clarifying agents, textile and paper adhesives, polymerization precursors, and of course, as a component in gelatin the Italian ice cream. 

Liquid crystals are mainly used for decorative purposes in cosmetics. Cholesteric liquid crystals are particularly suitable because of their iridescent color effects, and find applications in nail varnish, eye shadow, and lipsticks. The structure of these thermotropic liquid crystals changes as a result of body temperature, resulting in the desired color effect. In recent times, such thermotropic cholesteric liquid crystals have been included in body care cosmetics, where they are dispersed in a hydrogel. Depending whether this dispersion requires stirring or a special spraying process, the iridescent liquid crystalline particles are distributed statistically in the gel (Estee Lau-... 

Polymeric materials are used as binders to hold sohd particles together so as to formulate composite explosives or composite propellants. The polymeric materials also constitute part of the fuel ingredients when the crystalline particles are oxidizer-rich. Various types of hydrocarbon polymers are used as polymeric binders. 

The physicochemical properties of explosives are fundamentally equivalent to those of propellants. Explosives are also made of energetic materials such as nitropolymers and composite materials composed of crystalline particles and polymeric materials. TNT, RDX, and HMX are typical energetic crystalline materials used as explosives. Furthermore, when ammonium nitrate (AN) particles are mixed with an oil, an energetic explosive named ANFO (ammonium nitrate fuel oil) is formed. AN with water is also an explosive, named slurry explosive, used in industrial and civil engineering. A difference between the materials used as explosives and propellants is not readily evident. Propellants can be detonated when they are subjected to excess heat energy or mechanical shock. Explosives can be deflagrated steadily without a detonation wave when they are gently heated without mechanical shock. 

Crystalline particles that produce gaseous oxidizer fragments are used as oxidizer components and hydrocarbon polymers that produce gaseous fuel fragments are used as fuel components. Mixtures of these crystalline particles and hydrocarbon polymers form energetic materials that are termed composite propellants . The oxidizer and fuel components produced at the burning surface of each component mix together to form a stoichiometrically balanced reactive gas in the gas phase. 

Since the energetics of nitropolymer propellants composed of NC-NG or NC-TMETN are limited due to the limited concentration of oxidizer fragments, some crystalline particles are mixed within these propellants in order to increase the thermodynamic energy or specific impulse. The resulting class of propellants is termed composite-modified double-base (CMDB) propellants . The physicochemical properhes of CMDB propellants are intermediate between those of composite and double-base propellants, and these systems are widely used because of their great potential to produce a high specific impulse and their flexibility of burning rate. 

Since pyrolants are mixtures of various chemicals, such as crystalline particles, metal particles, metal oxide particles, and/or polymeric materials, the physico-... 

Melting-point temperature Decomposition temperature Boiling-point temperature Crystalline particles or polymers Phase transition Shape of crystal Shock sensitivity Friction sensitivity... 

When particles or large molecules make contact with water or an aqueous solution, the polarity of the solvent promotes the formation of an electrically charged interface. The accumulation of charge can result from at least three mechanisms (a) ionization of acid and/or base groups on the particle s surface (b) the adsorption of anions, cations, ampholytes, and/or protons and (c) dissolution of ion-pairs that are discrete subunits of the crystalline particle, such as calcium-oxalate and calcium-phosphate complexes that are building blocks of kidney stone and bone crystal, respectively. The electric charging of the surface also influences how other solutes, ions, and water molecules are attracted to that surface. These interactions and the random thermal motion of ionic and polar solvent molecules establishes a diffuse part of what is termed the electric double layer, with the surface being the other part of this double layer. 

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