Textural and structural features

The structural picture of the BIF is emphasized not only by differences in composition and thickness of the layers, but also by textural characteristics. In metamorphosed BIF granoblastic or hornfels textures are very common in the barren quartz and semi-ore siderite-quartz bands equidimensional quartz grains with undulating boundaries constitute their matrix. Alternation of higher-order bands, consisting of grains of different size but of the same texture, within layers is a usual phenomenon in slightly metamorphosed rocks. 

However, a post-sedimentation, metamorphic origin of some of the textures cannot be ruled out, in particular the lenticular and boudinage type of disturbances of the bedding (Tochtuyev, 1967). 

The overall geochemical particulars of the formation indicate processes of deep differentiation of the material in the formation of the iron-formations. 

If the volatile components (H2O and CO2) are not taken into account, it turns out that 99% of the iron-formations, proper, of the BIF consist of Si02, Fc20, FeO, AI2O3, MgO, and CaO and 97-98% of SiOj, FcjOj, FeO, AI2O3, and MgO, the last two components constituting not more than 10-15%. To compare such rocks it is convenient to use ratios (molar ratios) of iron content (F), alumina content A), magnesium content (M), and calcium-alkali content (C) (Semenenko et al., 1956), determined from relationships of the type  

In a number of cases, it can be limited to three coefficients—F, A, and M—for rocks with MgO CaO. 

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Arcos, D., Greenspan, D.C. and Vallet-Regi, M. (2002) Influence of the stabilization temperature on textural and structural features and ion release in Si02-Ca0-P20s sol-gel glasses. Chemistry of Materials, 14, 1515-1522. 

Petrologic and SEM analyses of these clay samples reveal micro-textural and structural features and mineral association suggesting that they deposited directly from the brine in the surface facilities, and are not hydrothermal alteration minerals transported from production wells. 

Textural and structural features of nano/mesoporous LiChrolut EN adsorbent, its predominantly hydrophobic character at low content of oxygen-containing functionalities at the surface, cause the specific behavior of adsorbed water in a mixture with nonpolar or weakly polar organics. WAW (8h=1-2 ppm) appears for these mixtures. Adsorbed water can be divided into several types. There are weakly (frozen at Tclose to 273 K and AG > -0.8 kJ/mol) and strongly (unfrozen at r= 190-250 K and AG <-0.8 kJ/mol) bonnd, and WAW (small clusters or individual molecules at 8g=1-2 ppm) and SAW (nanodomains and droplets at 8h=3-5 ppm). Organic componnds can affect the amounts of different types of water and displace a portion of water from narrow pores of the adsorbent. This behavior of interfacial water and water/organics as well as the stmctnral features of the adsorbent... 

As has already been mentioned, iron-rich rocks characterized by uniform chemical composition and very diverse mineral associations, textures, and structures are of decisive importance in the composition of the Precambrian BIF. A general feature of these rocks is similar silica and total iron contents the other essential components occur in subordinate amounts, although some of them, such as MgO and AI2O3, greatly influenced mineral formation. 

The results that have been obtained with the catalysts after reduction and passivation are the same as those after calcination, i.e. the textural and structural properties of the support material have completely been retained after the treatments (as determined with nitrogen physisorption. X-ray diflfiaction and transmission electron microscopy). Information concerning the metallic nickel particles has been obtained with X-ray diffraction and transmission electron microscopy. Diflractograms of the catalysts after passivation are shown in Fig. 8. The observed features are exactly the same as for the oxidic systems (Fig. 4) only very broad and low diffractions are visible for the catalyst ex citrate, whereas sharp, intense peaks with a broad onset are observed for the catalyst ex nitrate. Consequently the nickel particles of the catalyst ex citrate have resisted sintering during the reduction treatment, thereby conserving the high dispersion of the catalyst. These results were confirmed by transmission electron microscopy measurements (not shown) only very small nickel nanoparticles situated inside the mesopores were found for the catalyst ex citrate. 

The results described in a previous paper [7] and this one indicate that the use of chelated metal precursors for the preparation of heterogeneous catalysts can suitably be extended to mesoporous support materials. The mechanisms underlying the fundamental processes occurring during catalyst preparation appear to be the same for both types of support materials. Therefore no limitations appear to exist to apply a wide variety of other elements into the pores of several types of mesoporous supports, with retention of the unique textural and structural properties of the support materials. Catalysts thus prepared will feature very high dispersions of active phase as well as very small particles with sizes even smaller tlmn on conventional support materials (due to the limiting size of the pores of mesoporous support materials). 

On the other hand, semifusinite is intermediate between fusinite and vitrinite showing the well-defined structure of wood, but the cell cavities (round, oval, or elongated) vary in size and are smaller and sometimes less well-defined than those of fusinite. Semifusinite has the cell texture and general features of fusinite except that it is of lower reflectance. In fact, semifusinite has the largest range of reflectance of any of the various coal macerals going from the upper end of the pseudovi-trinite range to fusinite. Semifusinite is also the most abundant of the inertinite macerals. 

Combining the POM observations and structural features resulted in the supposition that the droplet texture was polygonal and that the smectic layers were arranged as Duppin cyclides with the cone ellipses oriented on the plane of the droplet wall and the peak to its center. 

The structural features of ceU wall polysaccharides of carrots have been studied by Stevens and Selvendran (1984) and Massiot et al.(1988). Plat et al.(1991), Ben Shalom et al.(1992) and Massiot et al.(1992) investigated the changes in pectic substances of carrots after blanching, dehydration and extended heat treatment. Data on the changes in ceU waU polysaccharides of canned carrots are lacking. This study aims to investigate the effect of preheating time at low temperature and the addition of CaCL on texture and on the composition of various pectin fractions of carrots canned by conventional and by a new process. 

Electrodeposition of metal onto structured objects, such as circuits, is controlled in part by a template. At the same time, the deposit must fill all the recesses uniformly and seamlessly, the texture and crystal structure must fall within tolerances, and the quality of the features must be sustained over a large workpiece. The distribution of material within recesses or onto widely separated portions of the workpiece is subject to a limited number of macroscopic control-parameters such as applied potential and plating bath composition. Success therefore depends on exploitation of the natural pathways of the process. The spontaneous and unconstrained development of structure must be taken into consideration in the production of highly organized and functional patterns. 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

Nowadays it is well established that the interactions between different macromolecular ingredients (i.e., protein + protein, polysaccharide + polysaccharide, and protein + polysaccharide) are of great importance in determining the texture and shelf-life of multicomponent food colloids. These interactions affect the structure-forming properties of biopolymers in the bulk and at interfaces thermodynamic activity, self-assembly, sin-face loading, thermodynamic compatibility/incompatibility, phase separation, complexation and rheological behaviour. Therefore, one may infer that a knowledge of the key physico-chemical features of such biopolymer-biopolymer interactions, and their impact on stability properties of food colloids, is essential in order to be able to understand and predict the functional properties of mixed biopolymers in product formulations. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

Quality of a food product is related to its sensorial (shape, size, color) and mechanical (texture) characteristics. These features are strongly affected by the food structural organization (Stanley, 1987) that, according to Fardet et al. (1998), can be studied at molecular, microscopic, and macroscopic levels. In particular, micro structure and interactions of components, such as protein, starch, and fat, determine the texture of a food that could be defined as the external manifestation of this structure (Allan-Wojtas et al., 2001). 

This influences the structural features of the mesophase which remains more disordered, a point made by Cranmer et al. (43). Stadelhofer (107) found that the presence of QI did not change rates of formation of mesophase. Romovacek et al. (108) consider that pyrolytic particles in pitch (primary QI) retard the development of mesophase and suppress coalescence. Decrease in size of optical texture, as brought about by mechanical modification as distinct from chemical modification of pitch properties can increase both the strength and reactivity to oxidising gases of the resultant coke, as recently put forward by Markovic et al. (109). ... 

As has already been mentioned. Gross (1965, 1973) distinguished two types of iron cherts on the Canadian shield, differing in textural-structural features, paragenetic associations, and also in sources of the material. 

Fedorchenko, V.S., 1969. Mineral composition and textural-structural features of Precambrian iron-formations of low-rank metamorphism (greenschist facies). In Problemy obrazovaniya zhelezistykh porod dokembriya (Problems oS FotmaWow of Precambrian Iron Formations), Izd. Naukova Dumka. Kiev, pp. 168-177 (in Russian),... 

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