Surface area and crystallinity

Of the many physical and chemical procedures thus far applied to enhance lignocellulose reactivity (1), fine grinding appears to offer the most direct response to both lignin and crystallinity. When the grinding is done in a vibratory ball mill, particle size can be reduced to micron dimensions, with attendant expansion of external surface area, and crystallinity can be essentially eliminated (2). This combination of events markedly influences carbohydrate accessibility and, hence, the degree of response of a milled lignocellulosic material to chemical, enzymatic, and microbiological attack. 

Fig. 4. Changes in specific surface area and crystallinity index by enzymatic hydrolysis (reproduced from [18]). Specific surface area (SSA) and crystallinity index (CrI) change quickly as enzymatic hydrolysis proceeds until leveling out at a constant level. Initial enzymatic action breaks cellulose into smaller particles (increased SSA) and attacks amorphous regions (increased CrI)... 

A. G. Shastri, A. K. Datye, J. Schwank, Gold-titania interactions Temperature-dependence of surface-area and crystallinity of TiQz and gold dispersion, /. Catal. 87(1) (1984) 265. 

Cation and anion adsorption by hydrous metal oxides influence several processes of environmental concern including contaminant transport, nutrient availability, and mineral dissolution rates (i,2). Various factors influence the amount of a particular ion adsorbed including solution pH, type of oxide and its surface area and crystallinity, time, ionic strength, properties and concentration of the adsorbing species, and competing species. These factors have received various degrees of scrutiny in previous studies. Temperature is another potentially important variable but has not to date received as much... 

S Molecular Weight, Conductivity, Surface Area, and Crystallinity... 

Hermanek, M., Zboril, R., Medrik, N., Pechousek, J., Gregor, C. Catalytic efficiency of iron (III) oxides in decomposition of hydrogen peroxide competition between the surface area and crystallinity of nanoparticles. J. Am. Chem. Soc. 129, 10929 (2007)... 

No significant changes are observed in the dielectric properties of magnetic nanocomposites before the percolation concentration, which usually is near to 30% v/v. Analysing the evolution of the dielectric permittivity of magnetic nanocomposites as a function of concentration, one can say that there is a similarity with the evolution of Tg. For low concentrations the phenomenon of stress-induced crystallization predominates, since a crystallized polymer chain, and consequently more ordered, presents ease on filler separation. For higher concentrations, the values of the dielectric constant are practically constant. The same parameters that previously influenced Tg are responsible for the greater capacity of filler separation in the nanocomposites, with emphasis on the surface area and crystalline character of the NZF nanoparticles. 

Table 2 gives the surface areas and crystalline state of binary oxide aerogels prepared by co-hydrolysis or by the two-step procedure. 

The whiskers with high stiffness, surface area, and crystallinity are suitable for application in polymeric matrices, acting as reinforcing element (Gardner et al., 2008). Also, it can be used as a rheology modifier in foods, paints, cosmetics, and pharmaceutical products (Turbak et al., 1983). 

Raman spectroscopy essentially does not provide any surface information about bulk metal oxide catalysts because of their modest surface areas and crystalline nature. In other words, the Raman scattering is dominated by the bulk crystalline phase of these catalytic materials. Coexisting amorphous metal oxide phases also cannot be detected because of their much weaker Raman scattering relative to the crystalline bulk metal oxide phases. Consequently, Raman studies of bulk metal oxide catalysts can provide insights about the following ... 

Each metal phosphate has different crystal structures depending on the preparation and activation conditions. Acid — base properties and catalytic activities usually vary with the crystal structure. By changing the metals and preparetion conditions, it is possible to obtain wide varieties of catalysts of different acid —base properties, surface areas and, crystalline structure. This flexibility enables metal phosphates to be used in many types of reactions. Selected reactions catalyzed by phosphorous metal oxides are listed in Table 3.40. In this section, the acid —base properties and catalytic activities of aluminum phosphorous oxide, boron phosphorous oxide, zirconium phosphorous oxide, and calcium phosphorous oxide are described. 

The thermal techniques are routinely used for quality control purposes. A typical TG/DTA analysis is shown in Fig. 13 for a Thessalian brick clay.t None of these clays contains kaolin and the characteristic mullite peak is absent. The endothermic peak between lOOand 160°Cisdue to the removal of adsorbed water, and its size is dependent on the surface area and crystallinity of the clay. The peak (400-700°C) is attributed to the dehydration of the combined water (dehydroxylation of the silicate lattice) and decomposition of the clay. The third peak (800°C) indicates decomposition of the carbonates and other salts present in the clays. 

---