Surface characteristics crystallinity

Fig. 6 displays the X-ray powder diffraction patterns of rhenium oxide. While the as-prepared sample is amorphous to X-ray, the sample soaked in acetone and dried at 100"C clearly exhibits sharp reflections corresponding to Re03. The large difference between the two X-ray patterns suggests that the processing conditions play a key role in the crystallinity and surface characteristics. As shown in the TGA plot of the as-prepared sample (Fig. 7), the weight loss of about 10% below 100 C results from the loss of water. 

Saleh, A.M. Jones A.A. (1984) The crystallinity and surface characteristics of synthetic ferrihydrite and its relationship to kaolinite surfaces. Clay Min. 19 745-755 Salfity, J.A., Regazzoni, A.E. Blesa, M.A. 

One can drastically alter the properties of polymers by suitable reactor design during forming of the polymer into its final shape. As examples, crystallinity, anisotropy, and surface characteristics can be tailored by ... 

Layer or layers of minerals (especially calcium carbonate) deposited, by the throwing down, or precipitation, onto a heat-transfer surface, reducing its U value. Scales are often hard and dense and difficult to remove. The scale can be crystalline in nature (a solid body having a characteristic internal structure, with symmetrically arranged plane surfaces and definite angles), or amorphous (lacking any characteristic crystalline shape). 

Silica exists in several crystalline and amorphous forms which greatly differ in their surface characteristics, namely topography (down to a nanometric level), hydrophobicity, silanol distribution and presence of contaminants. 

Considering the importance of the structural characteristics (crystalline phase, crystalline size, and geometrical surface area) in the control of band structure and in the concentration and mobility of photocatalyst charges, studies have been conducted on the influence of preparation methods on the photophysical properties of CdS (Arora et al., 1998 Jing and Guo, 2006). Improvement in CdS photoactivity is observed from preparation methods that lead to CdS phases with good crystallinity and few crystal defects. 

Depending on conditions during processing and storage, a crystalline microstructure develops in many foods that can significantly impact food propaties. Some important characteristics of the crystalline dispersion include the crystalline phase volume, mean size and size distribution of crystals, shape and surface characteristics of the particles, polymorphic characteristics, and any network structure that forms between... 

A high degree of hydrophobic character is an almost unique characteristic of silicon-rich or pure-silica-type microporous crystals. In contrast to the surface of crystalline or amorphous oxides decorated with coordinatively unsaturated atoms (in activated form), the silicon-rich zeolites offer a well-defined, coordinatively saturated sur ce. Such surfrces, based on the strong covalent character of the silicon-oxygen bond and the absence of hydrophilic centers, display a strong hydrophobic character unmatched by the coordinativeiy unsaturated, imperfect surfaces. Also, hydrophobic zeolite crystals have been reported to suppress the water affinity of transition metal cations contained in the zeolite pores. This property permits the adsorption of reactants such as carbon monoxide or hydrocarbons in the presence of water. 

Some empirical observations can help to understand how the feedstock physical state (i.e., suspension, emulsion, solution) and the physicochemical properties of the formulation components relate to the morphology and surface characteristics of the spray dried particles. As mentioned above shell formation will occur when one of the formulation components reaches its solubility and precipitates leading to the formation of a solid shell that may be either amorphous or crystalline. Low aqueous solubility components tend to precipitate early in the drying process and lend to form corrugated... 

The phase angle shift can be used to obtain contrast due to local differences in energy dissipation as a consequence of different surface characteristics related to materials properties. These different properties allow one to differentiate materials with different adhesion [110] or widely different Young s moduli, if these differences are related to differences in energy dissipation [111-115]. Hence the amorphous and crystalline phases in semicrystalline polymers can be clearly differentiated, as discussed in Sect. 3.2, as well as different phases in polymer blends or filled systems (see below). As an example, we show in Fig. 3.52 an intermittent contact AFM phase image of a block copolymer thin film on silicon [116]. 

Decomposition of copper(II) malonate Examination of fracture sections of cooled, solidified particles of partly reacted salt, by electron microscopy, revealed the intraparticular generation of a frothlike material composed of bubbles with rounded surfaces (30). This texture was ascribed to the evolution of gaseous products within a fluid matrix. The predominantly curved surfaces were ascribed to surface tension control, and no regularly aligned features or flat surfaces, characteristic of crystalline materials, were found. 

The salt-free crystalline polysaccharides reviewed by Bluhm et al. [15] are stabilized in characteristic crystalline unit cells by specific amounts of water. Two kinds of locations have been proposed for the water molecules one is unique, i.e., the water lies clustered in an existing interstitial cavity between double helices of B-starch. The other has water bound at specific sites within each unit cell. Additional water in this second type expands one or more unit cell dimension. This almost continuous expansion of the unit cell with increasing content of water may represent a more ordered aspect of the same interaction that occurs between water and accessible, disordered surfaces of celluloses crystallites (and other imperfectly crystalline polysaccharides). 

Un-cross-linked semicrystalline poly vinyl alcohol) hydrogels were prepared by solvolysis of the corresponding vinyl trifluoroacetate polymers and copolymers. The relationships between polymer crystallinity, hydrogel structure, and mechanical properties in the subject hydrogels were examined. Evidence was presented that comonomers acted to disrupt crystal structure and increase water content. The effects of copolymer structure on surface characteristics important to biomedical applications were examined, and the importance of hydrogel nonionic character was demonstrated through protein binding studies. 

From a practical standpoint, the plastic nature of our modern existence carries with it important questions concerning the surface characteristics and interactions of primarily amorphous (i.e., noncrystalHne) polymeric surfaces. Because of the molecular size, polydispersity, and generally random nature of polymeric solids (and their surfaces), many of the principles applied to studying and modeling ordered crystalline surfaces are no longer valid. Like... 

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